Structural basis of DNA folding and recognition in an AMP-DNA aptamer complex: distinct architectures but common recognition motifs for DNA and RNA aptamers complexed to AMP.

PubMed

Lin, C H; Patel, D J

1997-11-01

Structural studies by nuclear magnetic resonance (NMR) of RNA and DNA aptamer complexes identified through in vitro selection and amplification have provided a wealth of information on RNA and DNA tertiary structure and molecular recognition in solution. The RNA and DNA aptamers that target ATP (and AMP) with micromolar affinity exhibit distinct binding site sequences and secondary structures. We report below on the tertiary structure of the AMP-DNA aptamer complex in solution and compare it with the previously reported tertiary structure of the AMP-RNA aptamer complex in solution. The solution structure of the AMP-DNA aptamer complex shows, surprisingly, that two AMP molecules are intercalated at adjacent sites within a rectangular widened minor groove. Complex formation involves adaptive binding where the asymmetric internal bubble of the free DNA aptamer zippers up through formation of a continuous six-base mismatch segment which includes a pair of adjacent three-base platforms. The AMP molecules pair through their Watson-Crick edges with the minor groove edges of guanine residues. These recognition G.A mismatches are flanked by sheared G.A and reversed Hoogsteen G.G mismatch pairs. The AMP-DNA aptamer and AMP-RNA aptamer complexes have distinct tertiary structures and binding stoichiometries. Nevertheless, both complexes have similar structural features and recognition alignments in their binding pockets. Specifically, AMP targets both DNA and RNA aptamers by intercalating between purine bases and through identical G.A mismatch formation. The recognition G.A mismatch stacks with a reversed Hoogsteen G.G mismatch in one direction and with an adenine base in the other direction in both complexes. It is striking that DNA and RNA aptamers selected independently from libraries of 10(14) molecules in each case utilize identical mismatch alignments for molecular recognition with micromolar affinity within binding-site pockets containing common structural elements.

Magnetic behavior control in niccolite structural metal formate frameworks [NH2(CH3)2][Fe(III)M(II)(HCOO)6] (M = Fe, Mn, and Co) by varying the divalent metal ions.

PubMed

Zhao, Jiong-Peng; Hu, Bo-Wen; Lloret, Francesc; Tao, Jun; Yang, Qian; Zhang, Xiao-Feng; Bu, Xian-He

2010-11-15

By changing template cation but introducing trivalent iron ions in the known niccolite structural metal formate frameworks, three complexes formulated [NH(2)(CH(3))(2)][Fe(III)M(II)(HCOO)(6)] (M = Fe for 1, Mn for 2, and Co for 3) were synthesized and magnetically characterized. The variation in the compositions of the complexes leads to three different complexes: mixed-valent complex 1, heterometallic but with the same spin state complex 2, and heterometallic heterospin complex 3. The magnetic behaviors are closely related to the divalent metal ions used. Complex 1 exhibits negative magnetization assigned as Néel N-Type ferrimagnet, with an asymmetric magnetization reversal in the hysteresis loop, and complex 2 is an antiferromagnet with small spin canting (α(canting) ≈ 0.06° and T(canting) = 35 K), while complex 3 is a ferrimagnet with T(N) = 32 K.

Spectro- and electrochemical studies of some ruthenium and osmium complexes of 2-(2'-pyridyl)benzimidazole; complexes with intra-molecular charge transfer.

PubMed

Khalil, M M; Ali, S A; Ramadan, R M

2001-04-01

Reaction of Ru3(CO)12, with 2-(2'-pyridyl)benzimidazole (HPBI) resulted in the formation of Ru(CO)3(HPBI) (I) complex. In presence of pyridine or dipyridine, the two derivatives [Ru(CO)3(HPBI)].Py (II) and [Ru(CO)3(HPBI)].dpy (III) were isolated. The corresponding reactions of Os3(CO)12 yielded only one single product; Os(CO)2(HPBI)2 (IV). Spectroscopic studies of these complexes revealed intramolecular metal to ligand CT interactions. Reactions of RuCl3 with HPBI gave three distinct products; [Ru(HPBI)2Cl2]Cl (V), [Ru(HPBI)(dipy)Cl2]C1 (VI) and [Ru(PBI)2(py)2]Cl (VII). The UV-vis studies indicated the presence of intramolecular ligand to metal CT interactions. Electrochemical investigation of the complexes showed some irreversible, reversible and quasi-reversible redox reactions due to tautomeric interconversions through electron transfer.

The Chemistry of Photographic Color Dye Formation

ERIC Educational Resources Information Center

Kahn, Bruce E.

2004-01-01

A laboratory activity that can be used at a number of levels from high school to college is discussed. This activity can be used to teach chemical concepts such as oxidation and reduction, stoichiometry, acids and bases, pH, nucleophilic reactions, conjugation, leaving groups, complexation, solubility, and reversibility.

Dynamic Coordination of Eu-Iminodiacetate to Control Fluorochromic Response of Polymer Hydrogels to Multistimuli.

PubMed

Weng, Gengsheng; Thanneeru, Srinivas; He, Jie

2018-03-01

New fluorochromic materials that reversibly change their emission properties in response to their environment are of interest for the development of sensors and light-emitting materials. A new design of Eu-containing polymer hydrogels showing fast self-healing and tunable fluorochromic properties in response to five different stimuli, including pH, temperature, metal ions, sonication, and force, is reported. The polymer hydrogels are fabricated using Eu-iminodiacetate (IDA) coordination in a hydrophilic poly(N,N-dimethylacrylamide) matrix. Dynamic metal-ligand coordination allows reversible formation and disruption of hydrogel networks under various stimuli which makes hydrogels self-healable and injectable. Such hydrogels show interesting switchable ON/OFF luminescence along with the sol-gel transition through the reversible formation and dissociation of Eu-IDA complexes upon various stimuli. It is demonstrated that Eu-containing hydrogels display fast and reversible mechanochromic response as well in hydrogels having interpenetrating polymer network. Those multistimuli responsive fluorochromic hydrogels illustrate a new pathway to make smart optical materials, particularly for biological sensors where multistimuli response is required. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Pentachlorophenol radical cations generated on Fe(III)-montmorillonite initiate octachlorodibenzo-p-dioxin formation in clays: DFT and FTIR studies

PubMed Central

Gu, Cheng; Liu, Cun; Johnston, Cliff T.; Teppen, Brian J.; Li, Hui; Boyd, Stephen A.

2011-01-01

Octachlorodibenzodioxin (OCDD) forms spontaneously from pentachlorophenol (PCP) on the surfaces of Fe(III)-saturated smectite clay (1). Here, we used in situ FTIR methods and quantum mechanical calculations to determine the mechanism by which this reaction is initiated. As the clay was dehydrated, vibrational spectra showed new peaks that grew and then reversibly disappeared as the clay rehydrated. First principle DFT calculations of hydrated Fe-PCP clusters reproduced these transient FTIR peaks when inner-sphere complexation and concomitant electron transfer produced Fe(II) and PCP radical cations. Thus, our experimental (FTIR) and theoretical (quantum mechanical) results mutually support the hypothesis that OCDD formation on Fe-smectite surfaces is initiated by the reversible formation of metastable PCP radical cations via single electron transfer from PCP to Fe(III). The negatively charged clay surface apparently selects for this reaction mechanism by stabilizing PCP radical cations. PMID:21254769

Mixed system of Eudragit s-100 with a designed amphipathic peptide: control of interfacial elasticity by solution composition.

PubMed

Dexter, Annette F; Malcolm, Andrew S; Zeng, Biyun; Kennedy, Debora; Middelberg, Anton P J

2008-04-01

We report an interfacially active system based on an informational peptide surfactant mixed with an oppositely charged polyelectrolyte. The 21-residue cationic peptide, AM1, has previously been shown to respond reversibly to pH and metal ions at fluid interfaces, forming elastic films that can be rapidly switched to collapse foams or emulsions on demand. Here we report the reversible association of AM1 with the methacrylate-based anionic polymer Eudragit S-100. The strength of the association, in bulk aqueous solution, is modulated by added metal ions and by ionic strength. Addition of zinc ions to the peptide-polymer system promotes complex formation and phase separation, while addition of a chelating agent reverses the association. The addition of salt weakens peptide-polymer interactions in the presence or absence of zinc. At the air-water interface, Eudragit S-100 forms an elastic mixed film with AM1 in the absence of metal, under conditions where the peptide alone does not show interfacial elasticity. When zinc is present, the elasticity of the mixed film is increased, but the rate of interfacial adsorption slows due to formation of peptide-polymer complexes in bulk solution. An understanding of these interactions can be used to identify favorable foam-forming conditions in the mixed system.

Dioxygen Activation and O–O Bond Formation Reactions by Manganese Corroles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Guo, Mian; Lee, Yong-Min; Gupta, Ranjana

Activation of dioxygen (O 2) in enzymatic and biomimetic reactions has been intensively investigated over the past several decades. More recently, O–O bond formation, which is the reverse of the O 2-activation reaction, has been the focus of current research. Herein, we report the O 2-activation and O–O bond formation reactions by manganese corrole complexes. In the O 2-activation reaction, Mn(V)-oxo and Mn(IV)-peroxo intermediates were formed when Mn(III) corroles were exposed to O 2 in the presence of base (e.g., OH –) and hydrogen atom (H atom) donor (e.g., THF or cyclic olefins); the O 2-activation reaction did not occurmore » in the absence of base and H atom donor. Moreover, formation of the Mn(V)-oxo and Mn(IV)-peroxo species was dependent on the amounts of base present in the reaction solution. The role of the base was proposed to lower the oxidation potential of the Mn(III) corroles, thereby facilitating the binding of O 2 and forming a Mn(IV)-superoxo species. The putative Mn(IV)-superoxo species was then converted to the corresponding Mn(IV)-hydroperoxo species by abstracting a H atom from H atom donor, followed by the O–O bond cleavage of the putative Mn(IV)-hydroperoxo species to form a Mn(V)-oxo species. We have also shown that addition of hydroxide ion to the Mn(V)-oxo species afforded the Mn(IV)-peroxo species via O–O bond formation and the resulting Mn(IV)-peroxo species reverted to the Mn(V)-oxo species upon addition of proton, indicating that the O–O bond formation and cleavage reactions between the Mn(V)-oxo and Mn(IV)-peroxo complexes are reversible. The present paper reports the first example of using the same manganese complex in both O 2-activation and O–O bond formation reactions.« less

Dioxygen Activation and O–O Bond Formation Reactions by Manganese Corroles

DOE PAGES

Guo, Mian; Lee, Yong-Min; Gupta, Ranjana; ...

2017-10-22

Activation of dioxygen (O 2) in enzymatic and biomimetic reactions has been intensively investigated over the past several decades. More recently, O–O bond formation, which is the reverse of the O 2-activation reaction, has been the focus of current research. Herein, we report the O 2-activation and O–O bond formation reactions by manganese corrole complexes. In the O 2-activation reaction, Mn(V)-oxo and Mn(IV)-peroxo intermediates were formed when Mn(III) corroles were exposed to O 2 in the presence of base (e.g., OH –) and hydrogen atom (H atom) donor (e.g., THF or cyclic olefins); the O 2-activation reaction did not occurmore » in the absence of base and H atom donor. Moreover, formation of the Mn(V)-oxo and Mn(IV)-peroxo species was dependent on the amounts of base present in the reaction solution. The role of the base was proposed to lower the oxidation potential of the Mn(III) corroles, thereby facilitating the binding of O 2 and forming a Mn(IV)-superoxo species. The putative Mn(IV)-superoxo species was then converted to the corresponding Mn(IV)-hydroperoxo species by abstracting a H atom from H atom donor, followed by the O–O bond cleavage of the putative Mn(IV)-hydroperoxo species to form a Mn(V)-oxo species. We have also shown that addition of hydroxide ion to the Mn(V)-oxo species afforded the Mn(IV)-peroxo species via O–O bond formation and the resulting Mn(IV)-peroxo species reverted to the Mn(V)-oxo species upon addition of proton, indicating that the O–O bond formation and cleavage reactions between the Mn(V)-oxo and Mn(IV)-peroxo complexes are reversible. The present paper reports the first example of using the same manganese complex in both O 2-activation and O–O bond formation reactions.« less

Folding and Stabilization of Native-Sequence-Reversed Proteins

PubMed Central

Zhang, Yuanzhao; Weber, Jeffrey K; Zhou, Ruhong

2016-01-01

Though the problem of sequence-reversed protein folding is largely unexplored, one might speculate that reversed native protein sequences should be significantly more foldable than purely random heteropolymer sequences. In this article, we investigate how the reverse-sequences of native proteins might fold by examining a series of small proteins of increasing structural complexity (α-helix, β-hairpin, α-helix bundle, and α/β-protein). Employing a tandem protein structure prediction algorithmic and molecular dynamics simulation approach, we find that the ability of reverse sequences to adopt native-like folds is strongly influenced by protein size and the flexibility of the native hydrophobic core. For β-hairpins with reverse-sequences that fail to fold, we employ a simple mutational strategy for guiding stable hairpin formation that involves the insertion of amino acids into the β-turn region. This systematic look at reverse sequence duality sheds new light on the problem of protein sequence-structure mapping and may serve to inspire new protein design and protein structure prediction protocols. PMID:27113844

Folding and Stabilization of Native-Sequence-Reversed Proteins

NASA Astrophysics Data System (ADS)

Zhang, Yuanzhao; Weber, Jeffrey K.; Zhou, Ruhong

2016-04-01

Though the problem of sequence-reversed protein folding is largely unexplored, one might speculate that reversed native protein sequences should be significantly more foldable than purely random heteropolymer sequences. In this article, we investigate how the reverse-sequences of native proteins might fold by examining a series of small proteins of increasing structural complexity (α-helix, β-hairpin, α-helix bundle, and α/β-protein). Employing a tandem protein structure prediction algorithmic and molecular dynamics simulation approach, we find that the ability of reverse sequences to adopt native-like folds is strongly influenced by protein size and the flexibility of the native hydrophobic core. For β-hairpins with reverse-sequences that fail to fold, we employ a simple mutational strategy for guiding stable hairpin formation that involves the insertion of amino acids into the β-turn region. This systematic look at reverse sequence duality sheds new light on the problem of protein sequence-structure mapping and may serve to inspire new protein design and protein structure prediction protocols.

Viral RNAi suppressor reversibly binds siRNA to outcompete Dicer and RISC via multiple-turnover

PubMed Central

Rawlings, Renata A.; Krishnan, Vishalakshi; Walter, Nils G.

2011-01-01

RNA interference (RNAi) is a conserved gene regulatory mechanism employed by most eukaryotes as a key component of their innate immune response against viruses and retrotransposons. During viral infection, the RNase III-type endonuclease Dicer cleaves viral double-stranded RNA into small interfering RNAs (siRNAs), 21–24 nucleotides in length, and helps load them into the RNA-induced silencing complex (RISC) to guide cleavage of complementary viral RNA. As a countermeasure, many viruses have evolved viral RNA silencing suppressor (RSS) proteins that tightly, and presumably quantitatively, bind siRNAs to thwart RNAi-mediated degradation. Viral RSS proteins also act across kingdoms as potential immunosuppressors in gene therapeutic applications. Here we report fluorescence quenching and electrophoretic mobility shift assays that probe siRNA binding by the dimeric RSS p19 from Carnation Italian Ringspot Virus (CIRV), as well as by human Dicer and RISC assembly complexes. We find that the siRNA:p19 interaction is readily reversible, characterized by rapid binding ((1.69 ± 0.07)×108 M−1s−1) and marked dissociation (koff = 0.062 ± 0.002 s−1). We also observe that p19 efficiently competes with recombinant Dicer and inhibits formation of RISC-related assembly complexes found in human cell extract. Computational modeling based on these results provides evidence for the transient formation of a ternary complex between siRNA, human Dicer, and p19. An expanded model of RNA silencing indicates that multiple-turnover by reversible binding of siRNAs potentiates the efficiency of the suppressor protein. Our predictive model is expected to be applicable to the dosing of p19 as a silencing suppressor in viral gene therapy. PMID:21354178

Viral RNAi suppressor reversibly binds siRNA to outcompete Dicer and RISC via multiple turnover.

PubMed

Rawlings, Renata A; Krishnan, Vishalakshi; Walter, Nils G

2011-04-29

RNA interference is a conserved gene regulatory mechanism employed by most eukaryotes as a key component of their innate immune response to viruses and retrotransposons. During viral infection, the RNase-III-type endonuclease Dicer cleaves viral double-stranded RNA into small interfering RNAs (siRNAs) 21-24 nucleotides in length and helps load them into the RNA-induced silencing complex (RISC) to guide the cleavage of complementary viral RNA. As a countermeasure, many viruses have evolved viral RNA silencing suppressors (RSS) that tightly, and presumably quantitatively, bind siRNAs to thwart RNA-interference-mediated degradation. Viral RSS proteins also act across kingdoms as potential immunosuppressors in gene therapeutic applications. Here we report fluorescence quenching and electrophoretic mobility shift assays that probe siRNA binding by the dimeric RSS p19 from Carnation Italian Ringspot Virus, as well as by human Dicer and RISC assembly complexes. We find that the siRNA:p19 interaction is readily reversible, characterized by rapid binding [(1.69 ± 0.07) × 10(8) M(-)(1) s(-1)] and marked dissociation (k(off)=0.062 ± 0.002 s(-1)). We also observe that p19 efficiently competes with recombinant Dicer and inhibits the formation of RISC-related assembly complexes found in human cell extract. Computational modeling based on these results provides evidence for the transient formation of a ternary complex between siRNA, human Dicer, and p19. An expanded model of RNA silencing indicates that multiple turnover by reversible binding of siRNAs potentiates the efficiency of the suppressor protein. Our predictive model is expected to be applicable to the dosing of p19 as a silencing suppressor in viral gene therapy. Copyright © 2011 Elsevier Ltd. All rights reserved.

Low temperature and high field regimes of connected kagome artificial spin ice: the role of domain wall topology.

PubMed

Zeissler, Katharina; Chadha, Megha; Lovell, Edmund; Cohen, Lesley F; Branford, Will R

2016-07-22

Artificial spin ices are frustrated magnetic nanostructures where single domain nanobars act as macrosized spins. In connected kagome artificial spin ice arrays, reversal occurs along one-dimensional chains by propagation of ferromagnetic domain walls through Y-shaped vertices. Both the vertices and the walls are complex chiral objects with well-defined topological edge-charges. At room temperature, it is established that the topological edge-charges determine the exact switching reversal path taken. However, magnetic reversal at low temperatures has received much less attention and how these chiral objects interact at reduced temperature is unknown. In this study we use magnetic force microscopy to image the magnetic reversal process at low temperatures revealing the formation of quite remarkable high energy remanence states and a change in the dynamics of the reversal process. The implication is the breakdown of the artificial spin ice regime in these connected structures at low temperatures.

Structural evaluation of crystalline ternary γ-cyclodextrin complex.

PubMed

Higashi, Kenjirou; Ideura, Saori; Waraya, Haruka; Moribe, Kunikazu; Yamamoto, Keiji

2011-01-01

The structure of a crystalline γ-cyclodextrin (γ-CD) ternary complex containing salicylic acid (SA) and flurbiprofen (FBP) prepared by sealed heating was investigated. FBP/γ-CD inclusion complex was prepared by coprecipitation; its molar ratio was determined as 1/1. Powder X-ray diffraction measurements showed that the molecular packing of γ-CD changed from hexagonal to monoclinic columnar form by sealed heating of SA with dried FBP/γ-CD inclusion complex, indicating ternary complex formation. The stoichiometry of SA/FBP/γ-CD was estimated as 2/1/1. Solid-state transformation of γ-CD molecular packing upon water vapor adsorption and desorption was irreversible for this ternary complex, in contrast to the reversible transition for the FBP/γ-CD inclusion complex. The ternary complex contained one FBP molecule in the cavity of γ-CD and two SA molecules in the intermolecular space between neighboring γ-CD column stacks. Infrared and (13) C solid-state NMR spectroscopies revealed that the molecular states of SA and FBP changed upon ternary complex formation. In the complex, dimer FBP molecules were sandwiched between two γ-CD molecules whereas each monomer SA molecule was present in the intermolecular space of γ-CD. Ternary complex formation was also observed for other drug-guest systems using naproxen and ketoprofen. Thus, the complex can be used to formulate variety of drugs. Copyright © 2010 Wiley-Liss, Inc. and the American Pharmacists Association

Demonstrating Encapsulation and Release: A New Take on Alginate Complexation and the Nylon Rope Trick

ERIC Educational Resources Information Center

Friedli, Andrienne C.; Schlager, Inge R.; Wright, Stephen W.

2005-01-01

Three variations on a classroom demonstration of the encapsulation of droplets and evidence for release of the interior solution are described. The first two demonstrations mimic biocompatible applications of encapsulation. Reversible formation of capsules from aqueous solutions of sodium alginate, a negatively charged polysaccharide derived from…

Electric-Field Control of Oxygen Vacancies and Magnetic Phase Transition in a Cobaltite/Manganite Bilayer

NASA Astrophysics Data System (ADS)

Cui, B.; Song, C.; Li, F.; Zhong, X. Y.; Wang, Z. C.; Werner, P.; Gu, Y. D.; Wu, H. Q.; Saleem, M. S.; Parkin, S. S. P.; Pan, F.

2017-10-01

Manipulation of oxygen vacancies (VO ) in single oxide layers by varying the electric field can result in significant modulation of the ground state. However, in many oxide multilayers with strong application potentials, e.g., ferroelectric tunnel junctions and solid-oxide fuel cells, understanding VO behavior in various layers under an applied electric field remains a challenge, owing to complex VO transport between different layers. By sweeping the external voltage, a reversible manipulation of VO and a corresponding fixed magnetic phase transition sequence in cobaltite/manganite (SrCoO3 -x/La0.45Sr0.55MnO3 -y ) heterostructures are reported. The magnetic phase transition sequence confirms that the priority of electric-field-induced VO formation or annihilation in the complex bilayer system is mainly determined by the VO formation energies and Gibbs free-energy differences, which is supported by theoretical analysis. We not only realize a reversible manipulation of the magnetic phase transition in an oxide bilayer but also provide insight into the electric-field control of VO engineering in heterostructures.

Actomyosin-dependent formation of the mechanosensitive talin–vinculin complex reinforces actin anchoring

PubMed Central

Ciobanasu, Corina; Faivre, Bruno; Le Clainche, Christophe

2014-01-01

The force generated by the actomyosin cytoskeleton controls focal adhesion dynamics during cell migration. This process is thought to involve the mechanical unfolding of talin to expose cryptic vinculin-binding sites. However, the ability of the actomyosin cytoskeleton to directly control the formation of a talin–vinculin complex and the resulting activity of the complex are not known. Here we develop a microscopy assay with pure proteins in which the self-assembly of actomyosin cables controls the association of vinculin to a talin-micropatterned surface in a reversible manner. Quantifications indicate that talin refolding is limited by vinculin dissociation and modulated by the actomyosin network stability. Finally, we show that the activation of vinculin by stretched talin induces a positive feedback that reinforces the actin–talin–vinculin association. This in vitro reconstitution reveals the mechanism by which a key molecular switch senses and controls the connection between adhesion complexes and the actomyosin cytoskeleton. PMID:24452080

Characterization of active reverse transcriptase and nucleoprotein complexes of the yeast retrotransposon Ty3 in vitro.

PubMed

Cristofari, G; Gabus, C; Ficheux, D; Bona, M; Le Grice, S F; Darlix, J L

1999-12-17

Human immunodeficiency virus (HIV) and the distantly related yeast Ty3 retrotransposon encode reverse transcriptase (RT) and a nucleic acid-binding protein designated nucleocapsid protein (NCp) with either one or two zinc fingers, required for HIV-1 replication and Ty3 transposition, respectively. In vitro binding of HIV-1 NCp7 to viral 5' RNA and primer tRNA(3)(Lys) catalyzes formation of nucleoprotein complexes resembling the virion nucleocapsid. Nucleocapsid complex formation functions in viral RNA dimerization and tRNA annealing to the primer binding site (PBS). RT is recruited in these nucleoprotein complexes and synthesizes minus-strand cDNA initiated at the PBS. Recent results on yeast Ty3 have shown that the homologous NCp9 promotes annealing of primer tRNA(i)(Met) to a 5'-3' bipartite PBS, allowing RNA:tRNA dimer formation and initiation of cDNA synthesis at the 5' PBS (). To compare specific cDNA synthesis in a retrotransposon and HIV-1, we have established a Ty3 model system comprising Ty3 RNA with the 5'-3' PBS, primer tRNA(i)(Met), NCp9, and for the first time, highly purified Ty3 RT. Here we report that Ty3 RT is as active as retroviral HIV-1 or murine leukemia virus RT using a synthetic template-primer system. Moreover, and in contrast to what was found with retroviral RTs, retrotransposon Ty3 RT was unable to direct cDNA synthesis by self-priming. We also show that Ty3 nucleoprotein complexes were formed in vitro and that the N terminus of NCp9, but not the zinc finger, is required for complex formation, tRNA annealing to the PBS, RNA dimerization, and primer tRNA-directed cDNA synthesis by Ty3 RT. These results indicate that NCp9 chaperones bona fide cDNA synthesis by RT in the yeast Ty3 retrotransposon, as illustrated for NCp7 in HIV-1, reinforcing the notion that Ty3 NCp9 is an ancestor of HIV-1 NCp7.

Probing the dynamic reversibility and generation of dynamic combinatorial libraries in the presence of bacterial model oligopeptides as templating guests of tetra-carbohydrazide macrocycles using electrospray mass spectrometry.

PubMed

Nour, Hany F; Islam, Tuhidul; Fernández-Lahore, Marcelo; Kuhnert, Nikolai

2012-12-30

Over the past few decades, bacterial resistance to antibiotics has emerged as a real threat to human health. Accordingly, there is an urgent demand for the development of innovative strategies for discovering new antibiotics. We present the first use of tetra-carbohydrazide cyclophane macrocycles in dynamic combinatorial chemistry (DCC) and molecular recognition as chiral hosts binding oligopeptides, which mimic bacterial cell wall. This study introduces an innovative application of electrospray ionisation time-of-flight mass spectrometry (ESI-TOF MS) to oligopeptides recognition using DCC. A small dynamic library composed of eight functionalised macrocycles has been generated in solution and all members were characterised by ESI-TOF MS. We also probed the dynamic reversibility and mechanism of formation of tetra-carbohydrazide cyclophanes in real-time using ESI-TOF MS. Dynamic reversibility of tetra-carbohydrazide cyclophanes is favored under thermodynamic control. The mechanism of formation of tetra-carbohydrazide cyclophanes involves key dialdehyde intermediates, which have been detected and assigned according to their high-resolution m/z values. Three members of the dynamic library bind efficiently in the gas phase to a selection of oligopeptides, unique to bacteria, allowing observation of host/guest complex ions in the gas phase. We probed the mechanism of the [2+2]-cyclocondensation reaction forming library members, proved dynamic reversibility of tetra-carbohydrazide cyclophanes and showed that complex ions formed between library members and hosts can be observed in the gas phase, allowing the solution of an important problem of biological interest. Copyright © 2012 John Wiley & Sons, Ltd.

Leishmania amazonensis exhibits phosphatidylserine-dependent procoagulant activity, a process that is counteracted by sandfly saliva

PubMed Central

Rochael, Natalia Cadaxo; Lima, Luize Gonçalves; de Oliveira, Sandra Maria Pereira; Barcinski, Marcello André; Saraiva, Elvira Maria; Monteiro, Robson Queiroz; Pinto-da-Silva, Lucia Helena

2013-01-01

Leishmania parasites expose phosphatidylserine (PS) on their surface, a process that has been associated with regulation of host's immune responses. In this study we demonstrate that PS exposure by metacyclic promastigotes of Leishmania amazonensis favours blood coagulation. L. amazonensis accelerates in vitro coagulation of human plasma. In addition, L. amazonensis supports the assembly of the prothrombinase complex, thus promoting thrombin formation. This process was reversed by annexin V which blocks PS binding sites. During blood meal, Lutzomyia longipalpis sandfly inject saliva in the bite site, which has a series of pharmacologically active compounds that inhibit blood coagulation. Since saliva and parasites are co-injected in the host during natural transmission, we evaluated the anticoagulant properties of sandfly saliva in counteracting the procoagulant activity of L. amazonensis . Lu. longipalpis saliva reverses plasma clotting promoted by promastigotes. It also inhibits thrombin formation by the prothrombinase complex assembled either in phosphatidylcholine (PC)/PS vesicles or in L. amazonensis . Sandfly saliva inhibits factor X activation by the intrinsic tenase complex assembled on PC/PS vesicles and blocks factor Xa catalytic activity. Altogether our results show that metacyclic promastigotes of L. amazonensis are procoagulant due to PS exposure. Notably, this effect is efficiently counteracted by sandfly saliva. PMID:24037188

A quantum dynamical study of the He++2He-->He2++He reaction

NASA Astrophysics Data System (ADS)

Xie, Junkai; Poirier, Bill; Gellene, Gregory I.

2003-11-01

The temperature dependent rate of the He++2He→He2++He three-body association reaction is studied using two complementary quantum dynamical models. Model I presumes a two-step, reverse Lindemann mechanism, where the intermediate energized complex, He2+*, is interpreted as the rotational resonance states of He2+. The energy and width of these resonances are determined via "exact" quantum calculation using highly accurate potential-energy curves. Model II uses an alternate quantum rate expression as the thermal average of the cumulative recombination probability, N(E). This microcanonical quantity is computed approximately, over the He2+ space only, with the third-body interaction modeled using a special type of absorbing potential. Because Model II implicitly incorporates both the two-step reverse Lindemann mechanism, and a one-step, reverse collision induced dissociation mechanism, the relative importance of the two formation mechanisms can be estimated by a comparison of the Model I and Model II results. For T<300 K, the reaction is found to be dominated by the two-step mechanism, and a formation rate in good agreement with the available experimental results is obtained with essentially no adjustable parameters in the theory. Interestingly, a nonmonotonic He2+ formation rate is observed, with a maximum identified near 25 K. This maximum is associated with just two reaction intermediate resonance states, the lowest energy states that can contribute significantly to the formation kinetics.

Reversible photocapture of a [2]rotaxane harnessing a barbiturate template.

PubMed

Tron, Arnaud; Thornton, Peter J; Lincheneau, Christophe; Desvergne, Jean-Pierre; Spencer, Neil; Tucker, James H R; McClenaghan, Nathan D

2015-01-16

Photoirradiation of a hydrogen-bonded molecular complex comprising acyclic components, namely, a stoppered thread (1) with a central barbiturate motif and an optimized doubly anthracene-terminated acyclic Hamilton-like receptor (2b), leads to an interlocked architecture, which was isolated and fully characterized. The sole isolated interlocked photoproduct (Φ = 0.06) is a [2]rotaxane, with the dimerized anthracenes assuming a head-to-tail geometry, as evidenced by NMR spectroscopy and consistent with molecular modeling (PM6). A different behavior was observed on irradiating homologous molecular complexes 1⊂2a, 1⊂2b, and 1⊂2c, where the spacers of 2a, 2b, and 2c incorporated 3, 6, and 9 methylene units, respectively. While no evidence of interlocked structure formation was observed following irradiation of 1⊂2a, a kinetically labile rotaxane was obtained on irradiating the complex 1⊂2c, and ring slippage was revealed. A more stable [2]rotaxane was formed on irradiating 1⊂2b, whose capture is found to be fully reversible upon heating, thereby resetting the system, with some fatigue (38%) after four irradiation–thermal reversion cycles.

Reversibility of red blood cell deformation

NASA Astrophysics Data System (ADS)

Zeitz, Maria; Sens, P.

2012-05-01

The ability of cells to undergo reversible shape changes is often crucial to their survival. For red blood cells (RBCs), irreversible alteration of the cell shape and flexibility often causes anemia. Here we show theoretically that RBCs may react irreversibly to mechanical perturbations because of tensile stress in their cytoskeleton. The transient polymerization of protein fibers inside the cell seen in sickle cell anemia or a transient external force can trigger the formation of a cytoskeleton-free membrane protrusion of μm dimensions. The complex relaxation kinetics of the cell shape is shown to be responsible for selecting the final state once the perturbation is removed, thereby controlling the reversibility of the deformation. In some case, tubular protrusion are expected to relax via a peculiar “pearling instability.”

Reversibility of red blood cell deformation.

PubMed

Zeitz, Maria; Sens, P

2012-05-01

The ability of cells to undergo reversible shape changes is often crucial to their survival. For red blood cells (RBCs), irreversible alteration of the cell shape and flexibility often causes anemia. Here we show theoretically that RBCs may react irreversibly to mechanical perturbations because of tensile stress in their cytoskeleton. The transient polymerization of protein fibers inside the cell seen in sickle cell anemia or a transient external force can trigger the formation of a cytoskeleton-free membrane protrusion of μm dimensions. The complex relaxation kinetics of the cell shape is shown to be responsible for selecting the final state once the perturbation is removed, thereby controlling the reversibility of the deformation. In some case, tubular protrusion are expected to relax via a peculiar "pearling instability."

Nocturnal Reversed Flows Above Parallel Ridges in Perdigão, Portugal

NASA Astrophysics Data System (ADS)

Krishnamurthy, R.; Fernando, H. J.; Leo, L. S.; Vassallo, D.; Hocut, C. M.; Creegan, E.; Rodriguez, C. V.; Palma, J. L.

2017-12-01

Prediction of topographically forced or induced wind events is extremely important for dispersion modeling and wind energy studies in complex terrain. To improve the current understanding of micro-scale processes over complex terrain, a large-scale field experiment was conducted in Perdigão, Portugal from May 1st, 2017 to June 15th, 2017. Measurements over a periodic valley were performed using 52 meteorological met-masts, 30 Doppler Lidars (scanning & vertical profilers), 2 tethered lifting systems and other remote sensing instruments (Sodar-rass, wind profilers & radiometer), and radiosondes were released every 6 hours over the period of study. The observations showed several cases of flow reversals confined to a thin layer of 70 - 100 m above the ridge under stably stratified conditions. These flow reversals were mostly observed during the lee wave formation over the periodic valley. It was observed that the flow reversal occurs predominantly under two atmospheric conditions: a) presence of large recirculation zones on the lee side of the hill causing a pressure gradient between the lee-side floor and the mountain ridge, and b) local change in the horizontal pressure gradient due to differential heating rates of the neighboring valley atmospheres. Microscale flow simulations could capture these observed flow reversals. Based on the network of tower instruments and remote sensing devices, the development, structure and occurrences of the flow reversals are being analyzed and quantified. Since these flow reversals are observed within the rotor swept area of modern wind turbines, they would drastically increase the fatigue loads on wind turbine blades. This presentation will include reversed flow observations from several synchronized scanning Doppler Lidars and meteorological towers and a theoretical framework for reverse flow over parallel valleys.

Formation and Repair of Tobacco Carcinogen-Derived Bulky DNA Adducts

DOE PAGES

Hang, Bo

2010-01-01

DNA adducts play a central role in chemical carcinogenesis. The analysis of formation and repair of smoking-related DNA adducts remains particularly challenging as both smokers and nonsmokers exposed to smoke are repetitively under attack from complex mixtures of carcinogens such as polycyclic aromatic hydrocarbons and N -nitrosamines. The bulky DNA adducts, which usually have complex structure, are particularly important because of their biological relevance. Several known cellular DNA repair pathways have been known to operate in human cells on specific types of bulky DNA adducts, for example, nucleotide excision repair, base excision repair, and direct reversal involving O 6 -alkylguaninemore » DNA alkyltransferase or AlkB homologs. Understanding the mechanisms of adduct formation and repair processes is critical for the assessment of cancer risk resulting from exposure to cigarette smoke, and ultimately for developing strategies of cancer prevention. This paper highlights the recent progress made in the areas concerning formation and repair of bulky DNA adducts in the context of tobacco carcinogen-associated genotoxic and carcinogenic effects.« less

The role of a combined coagulation and disk filtration process as a pre-treatment to microfiltration and reverse osmosis membranes in a municipal wastewater pilot plant.

PubMed

Chon, Kangmin; Cho, Jaeweon; Kim, Seung Joon; Jang, Am

2014-12-01

A pilot study was conducted to assess the performance of a municipal wastewater reclamation plant consisting of a combined coagulation-disk filtration (CC-DF) process, microfiltration (MF) and reverse osmosis (RO) membranes, in terms of the removal of water contaminants and changes in characteristics of effluent organic matter (EfOM). The CC-DF and MF membranes were not effective for the removal of dissolved water contaminants. However, they could partially reduce the turbidity associated with the cake layer formation by particulate materials on the membrane surfaces. Furthermore, most of water contaminants were completely removed by the RO membranes. Although the CC-DF process could remove approximately 20% of turbidity, the aluminium concentrations considerably increased after the CC-DF process due to the residual coagulants complexed with both carboxylic acid and alcohol functional groups of EfOM. Those aluminium-EfOM complexes had a lower negative charge and higher molecular weight (>0.1 μm pore size of the MF membranes) compared to non-complexed EfOM. These results indicate that the control of the formation of the aluminium-EfOM complexes should be considered as a key step to use the CC-DF process as a pre-treatment of the MF and RO membranes for mitigation of membrane fouling in the tested pilot plant. Copyright © 2014 Elsevier Ltd. All rights reserved.

Pattern formation and collective effects in populations of magnetic microswimmers

NASA Astrophysics Data System (ADS)

Vach, Peter J.; Walker, Debora; Fischer, Peer; Fratzl, Peter; Faivre, Damien

2017-03-01

Self-propelled particles are one prototype of synthetic active matter used to understand complex biological processes, such as the coordination of movement in bacterial colonies or schools of fishes. Collective patterns such as clusters were observed for such systems, reproducing features of biological organization. However, one limitation of this model is that the synthetic assemblies are made of identical individuals. Here we introduce an active system based on magnetic particles at colloidal scales. We use identical but also randomly-shaped magnetic micropropellers and show that they exhibit dynamic and reversible pattern formation.

Studies on the mechanism of action of 6-mercaptopurine. Interaction with copper and xanthine oxidase.

PubMed

Kela, U; Vijayvargiya, R

1981-03-01

Interaction between 6-mercaptopurine, Cu2+ and the enzyme xanthine oxidase (EC 1.2.3.2.) was examined. Whereas Cu2+ was found to inhibit the enzyme, 6-mercaptopurine could protect as well as reverse the enzyme inhibition produced by the metal ion. The formation of a complex between 6-mercaptopurine and Cu2+ seems to be responsible for the observed effect. Job's [(1928) Ann. Chem. 9, 113] method has shown the composition of the complex to be 1:1. The apparent stability constant (log K value), as determined by Subhrama Rao & Raghav Rao's [(1955) J. Sci. Chem. Ind. Res. 143, 278], method is found to be 6.74. It is suggested that the formation of a stable complex between 6-mercaptopurine molecules and Cu2+ may be an additional mechanism of action of 6-mercaptopurine, particularly with reference to its anti-inflammatory properties.

Studies on the mechanism of action of 6-mercaptopurine. Interaction with copper and xanthine oxidase.

PubMed Central

Kela, U; Vijayvargiya, R

1981-01-01

Interaction between 6-mercaptopurine, Cu2+ and the enzyme xanthine oxidase (EC 1.2.3.2.) was examined. Whereas Cu2+ was found to inhibit the enzyme, 6-mercaptopurine could protect as well as reverse the enzyme inhibition produced by the metal ion. The formation of a complex between 6-mercaptopurine and Cu2+ seems to be responsible for the observed effect. Job's [(1928) Ann. Chem. 9, 113] method has shown the composition of the complex to be 1:1. The apparent stability constant (log K value), as determined by Subhrama Rao & Raghav Rao's [(1955) J. Sci. Chem. Ind. Res. 143, 278], method is found to be 6.74. It is suggested that the formation of a stable complex between 6-mercaptopurine molecules and Cu2+ may be an additional mechanism of action of 6-mercaptopurine, particularly with reference to its anti-inflammatory properties. PMID:6895465

High Fidelity Modeling of Field Reversed Configuration (FRC) Thrusters

DTIC Science & Technology

2017-04-22

signatures which can be used for direct, non -invasive, comparison with experimental diagnostics can be produced. This research will be directly... experimental campaign is critical to developing general design philosophies for low-power plasmoid formation, the complexity of non -linear plasma processes...advanced space propulsion. The work consists of numerical method development, physical model development, and systematic studies of the non -linear

Study on the crystallographic orientation relationship and formation mechanism of reversed austenite in economical Cr12 super martensitic stainless steel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ye, Dong; Li, Shaohong; Li, Jun

Effect of carbides and crystallographic orientation relationship on the formation mechanism of reversed austenite of economical Cr12 super martensitic stainless steel (SMSS) has been investigated mainly by transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD). The results indicate that the M{sub 23}C{sub 6} precipitation and the formation of the reversed austenite have the interaction effect during tempering process in SMSS. The reversed austenite forms intensively at the sub-block boundary and the lath boundary within a misorientation range of 0–60°. M{sub 23}C{sub 6} has the same crystallographic orientation relationship with reversed austenite. There are two different kinds of formation modesmore » for reversed austenite. One is a nondiffusional shear reversion; the other is a diffusion transformation. Both are strictly limited by crystallographic orientation relationship. The austenite variants are limited to two kinds within one packet and five kinds within one prior austenite grain. - Highlights: • Reversed austenite forms at martensite boundaries with misorientation of 0–60° • M{sub 23}C{sub 6} precipitation and reversed austenite formation have the interaction effect. • Two austenite variants with different orientations can be formed inside a packet. • Two reversed austenite formation modes: shear reversion; diffusion transformation.« less

Disruption of integrin-fibronectin complexes by allosteric but not ligand-mimetic inhibitors.

PubMed

Mould, A Paul; Craig, Susan E; Byron, Sarah K; Humphries, Martin J; Jowitt, Thomas A

2014-12-15

Failure of Arg-Gly-Asp (RGD)-based inhibitors to reverse integrin-ligand binding has been reported, but the prevalence of this phenomenon among integrin heterodimers is currently unknown. In the present study we have investigated the interaction of four different RGD-binding integrins (α5β1, αVβ1, αVβ3 and αVβ6) with fibronectin (FN) using surface plasmon resonance. The ability of inhibitors to reverse ligand binding was assessed by their capacity to increase the dissociation rate of pre-formed integrin-FN complexes. For all four receptors we showed that RGD-based inhibitors (such as cilengitide) were completely unable to increase the dissociation rate. Formation of the non-reversible state occurred very rapidly and did not rely on the time-dependent formation of a high-affinity state of the integrin, or the integrin leg regions. In contrast with RGD-based inhibitors, Ca2+ (but not Mg2+) was able to greatly increase the dissociation rate of integrin-FN complexes, with a half-maximal response at ~0.4 mM Ca2+ for αVβ3-FN. The effect of Ca2+ was overcome by co-addition of Mn2+, but not Mg2+. A stimulatory anti-β1 monoclonal antibody (mAb) abrogated the effect of Ca2+ on α5β1-FN complexes; conversely, a function-blocking mAb mimicked the effect of Ca2+. These results imply that Ca2+ acts allosterically, probably through binding to the adjacent metal-ion-dependent adhesion site (ADMIDAS), and that the α1 helix in the β subunit I domain is the key element affected by allosteric modulators. The data suggest an explanation for the limited clinical efficacy of RGD-based integrin antagonists, and we propose that allosteric antagonists could prove to be of greater therapeutic benefit.

Dynamic regulation of a metabolic multi-enzyme complex by protein kinase CK2.

PubMed

An, Songon; Kyoung, Minjoung; Allen, Jasmina J; Shokat, Kevan M; Benkovic, Stephen J

2010-04-09

The reversible association and dissociation of a metabolic multi-enzyme complex participating in de novo purine biosynthesis, the purinosome, was demonstrated in live cells to respond to the levels of purine nucleotides in the culture media. We also took advantage of in vitro proteomic scale studies of cellular substrates of human protein kinases (e.g. casein kinase II (CK2) and Akt), that implicated several de novo purine biosynthetic enzymes as kinase substrates. Here, we successfully identified that purinosome formation in vivo was significantly promoted in HeLa cells by the addition of small-molecule CK2-specific inhibitors (i.e. 4,5,6,7-tetrabromo-1H-benzimidazole, 2-dimethylamino-4,5,6,7-tetrabromo-1H-benzimidazole, tetrabromocinammic acid, 4,4',5,5',6,6'-hexahydroxydiphenic acid 2,2',6,6'-dilactone (ellagic acid) as well as by silencing the endogenous human CK2alpha catalytic subunit with small interfering RNA. However, 4,5,6,7-tetrabromobenzotriazole, another CK2-specific inhibitor, triggered the dissociation of purinosome clusters in HeLa cells. Although the mechanism by which 4,5,6,7-tetrabromobenzotriazole affects purinosome clustering is not clear, we were capable of chemically reversing purinosome formation in cells by the sequential addition of two CK2 inhibitors. Collectively, we provide compelling cellular evidence that CK2-mediated pathways reversibly regulate purinosome assembly, and thus the purinosome may be one of the ultimate targets of kinase inhibitors.

Antibodies associated with heparin-induced thrombocytopenia (HIT) inhibit activated protein C generation: new insights into the prothrombotic nature of HIT.

PubMed

Kowalska, M Anna; Krishnaswamy, Sriram; Rauova, Lubica; Zhai, Li; Hayes, Vincent; Amirikian, Karine; Esko, Jeffrey D; Bougie, Daniel W; Aster, Richard H; Cines, Douglas B; Poncz, Mortimer

2011-09-08

Heparin-induced thrombocytopenia (HIT) is caused by antibodies that recognize complexes between platelet factor 4 (PF4) and heparin or glycosaminoglycan side chains. These antibodies can lead to a limb- and life-threatening prothrombotic state. We now show that HIT antibodies are able to inhibit generation of activated protein C (aPC) by thrombin/thrombomodulin (IIa/TM) in the presence of PF4. Tetrameric PF4 potentiates aPC generation by formation of complexes with chondroitin sulfate (CS) on TM. Formation of these complexes occurs at a specific molar ratio of PF4 to glycosaminoglycan. This observation and the finding that the effect of heparin on aPC generation depends on the concentration of PF4 suggest similarity between PF4/CS complexes and those that bind HIT antibodies. HIT antibodies reduced the ability of PF4 to augment aPC formation. Cationic protamine sulfate, which forms similar complexes with heparin, also enhanced aPC generation, but its activity was not blocked by HIT antibodies. Our studies provide evidence that complexes formed between PF4 and TM's CS may play a physiologic role in potentiating aPC generation. Recognition of these complexes by HIT antibodies reverses the PF4-dependent enhancement in aPC generation and may contribute to the prothrombotic nature of HIT.

Aspect-ratio dependence of magnetization reversal in cylindrical ferromagnetic nanowires

NASA Astrophysics Data System (ADS)

Sultan, Musaab S.; Atkinson, Del

2016-05-01

The magnetization reversal behavior in isolated cylindrical and square cross-section Ni81Fe19 nanowires was systematically studied as a function of nanowire cross-section dimensions from 10 up to 200 nm using micromagnetic simulations. This approach provides access to the switching field, remanence ratio and most significantly the magnetization structures during reversal, which allows the evolution of magnetization processes to be studied with scaling of the cross-sectional dimensions. The dimensional trends in reversal behavior for both square and circular cross-section were comparable throughout the range of dimensions studied. The thinnest nanowires showed simple square switching and 100% remanence. With increasing diameter the switching field reduces and above 40 nm the reversal behavior shows an increasing rotational component prior to sharp switching of the magnetization. The magnitude of the reversible component increases with increasing dimensions up to 150 nm, above which the magnetization reversal process is more complicated and the hysteresis loops are no longer bistable. The micromagnetic structures evolve from simple uniform parallel single domain states in the thinnest wires through the formation of vortex-like end states in thicker wires to complex multidomain structures during the reversal of the thickest wires. In the later cases the reversal is not simple curling-like behavior, although the angular switching field dependence was comparable with curling.

Protein associations and analytical ultracentrifugation

NASA Astrophysics Data System (ADS)

Laue, Tom

2010-03-01

Analytical ultracentrifugation (AUC) is a first principle method for characterizing the thermodynamics of macromolecules in solution. Since AUC directly assesses mass, it is particularly useful for characterizing both reversible and irreversible binding interactions between macromolecules. The principle measurement in AUC is the concentration as a function of radial position, which may be provided by either absorbance, interference or fluorescence detection. Each of these three different detectors may be used to characterize protein associations using either sedimentation equilibrium or sedimentation velocity analysis. Examples will be shown for characterizing irreversible (aggregate) formation, high-accuracy reversible association analysis, and the detection of protein interactions in complex and concentrated fluids (e.g. serum, cell cytosol).

Formation of stable and functional HIV-1 nucleoprotein complexes in vitro.

PubMed

Tanchou, V; Gabus, C; Rogemond, V; Darlix, J L

1995-10-06

HIV genomic RNA resides within the nucleocapsid, in the interior of the virus, which serves to protect the RNA against nuclease degradation and to promote its reverse transcription. To investigate the role of nucleocapsid protein (NCp7) in the stability and replication of genomic RNA within the nucleocapsid, we used NCp7, reverse transcriptase (RT) and RNAs representing the 5' and 3' regions of the genome to reconstitute functional HIV-1 nucleocapsids. The nucleoprotein complexes generated in vitro were found to be stable, which, according to biochemical and genetic data, probably results from the tight binding of NCp7 molecules to the RNA and strong NCp7/NCp7 interactions. The nucleoprotein complexes efficiently protected viral RNA against RNase degradation and, at the same time, promoted viral DNA synthesis by RT. DNA strand transfer from the 5' to the 3' RNA template was very efficient in nucleoprotein complexes formed in the presence of both RNAs, but not when the RNAs were in separate complexes. These results indicate that the in vitro reconstituted HIV-1 nucleoprotein complexes function like virion nucleocapsids and thus provide a way to study at the molecular level this viral substructure and the synthesis of proviral DNA, and to search for new anti-HIV agents.

Complexation of Contaminants and Aqueous-Phase Ozone with Cyclodextrin for Emerging Contaminant Oxidative Degradation

NASA Astrophysics Data System (ADS)

Khan, N. A.; Carroll, K. C.

2016-12-01

Recalcitrant emerging contaminants in groundwater, such as 1,4-dioxane, require strong oxidants for complete mineralization, whereas strong oxidant efficacy for in-situ chemical oxidation (ISCO) is limited by oxidant decay, reactivity, and non-specificity. Hydroxypropyl-β-cyclodextrin (HPβCD) was examined for its ability to stabilize aqueous phase ozone (O3) and prolong oxidation potential through inclusion complex formation. Partial transformation of HPβCD by O3 was observed but HPβCD proved to be sufficiently resilient and only partially degraded in the presence of O3. The formation of a HPβCD:O3 inclusion clathrate complex was observed, and multiple methods for binding constant measurements carried out and compared for HPβCD complexes with O3 and multiple contaminants. The presence of HPβCD increased the O3 half-life linearly with increasing HPβCD:O3 molar ratio. The O3 half-life in solutions increased by as much as 40-fold relative to HPβCD-free O3 solutions, and complexation reversibility was confirmed. Decay rate coefficients increased for 1,4-dioxane, trichloroethene, and trichloroethane likely due to the formation of HPβCD-O3-contaminant ternary complexes. These results suggest that the use of clathrate stabilizers, such as HPβCD, can support the development of a facilitated-transport enabled ISCO for the O3 treatment of groundwater impacted by recalcitrant emerging contaminants.

Novel One-Tube-One-Step Real-Time Methodology for Rapid Transcriptomic Biomarker Detection: Signal Amplification by Ternary Initiation Complexes.

PubMed

Fujita, Hiroto; Kataoka, Yuka; Tobita, Seiji; Kuwahara, Masayasu; Sugimoto, Naoki

2016-07-19

We have developed a novel RNA detection method, termed signal amplification by ternary initiation complexes (SATIC), in which an analyte sample is simply mixed with the relevant reagents and allowed to stand for a short time under isothermal conditions (37 °C). The advantage of the technique is that there is no requirement for (i) heat annealing, (ii) thermal cycling during the reaction, (iii) a reverse transcription step, or (iv) enzymatic or mechanical fragmentation of the target RNA. SATIC involves the formation of a ternary initiation complex between the target RNA, a circular DNA template, and a DNA primer, followed by rolling circle amplification (RCA) to generate multiple copies of G-quadruplex (G4) on a long DNA strand like beads on a string. The G4s can be specifically fluorescence-stained with N(3)-hydroxyethyl thioflavin T (ThT-HE), which emits weakly with single- and double-stranded RNA/DNA but strongly with parallel G4s. An improved dual SATIC system, which involves the formation of two different ternary initiation complexes in the RCA process, exhibited a wide quantitative detection range of 1-5000 pM. Furthermore, this enabled visual observation-based RNA detection, which is more rapid and convenient than conventional isothermal methods, such as reverse transcription-loop-mediated isothermal amplification, signal mediated amplification of RNA technology, and RNA-primed rolling circle amplification. Thus, SATIC methodology may serve as an on-site and real-time measurement technique for transcriptomic biomarkers for various diseases.

The physiological and pathological biophysics of phase separation and gelation of RNA binding proteins in amyotrophic lateral sclerosis and fronto-temporal lobar degeneration.

PubMed

St George-Hyslop, Peter; Lin, Julie Qiaojin; Miyashita, Akinori; Phillips, Emma C; Qamar, Seema; Randle, Suzanne J; Wang, GuoZhen

2018-04-30

Many RNA binding proteins, including FUS, contain moderately repetitive, low complexity, intrinsically disordered domains. These sequence motifs have recently been found to underpin reversible liquid: liquid phase separation and gelation of these proteins, permitting them to reversibly transition from a monodispersed state to liquid droplet- or hydrogel-like states. This function allows the proteins to serve as scaffolds for the formation of reversible membraneless intracellular organelles such as nucleoli, stress granules and neuronal transport granules. Using FUS as an example, this review examines the biophysics of this physiological process, and reports on how mutations and changes in post-translational state alter phase behaviour, and lead to neurodegenerative diseases such as amyotrophic lateral sclerosis and frontotemporal lobar degeneration. Copyright © 2018. Published by Elsevier B.V.

Paleomagnetic Results From the Mid-Tertiary Cripple Creek Diatreme Complex

NASA Astrophysics Data System (ADS)

Rampe, J. S.; Geissman, J. W.; Melker, M.

2001-12-01

The Cripple Creek diatreme complex, located about 30 km southwest of Pikes Peak, Colorado, is host to gold and high grade telluride deposits associated with mid-Tertiary alkaline magmatism. Formation of the diatreme took place between about 32.5 and 28.7 Ma, based on previously reported ArAr age determinations. The complex consists of breccia (the primary rock type), that was subsequently intruded by aphanitic phonolite, porphyritic phonolite, phonotephrite, and finally lamprophyre. Rocks presently at the surface were emplaced within a few kilometers of the paleosurface, followed by hydrothermal activity resulting in pervasive K metasomatism and gold mineralization. Mineralized deposits within the diatreme are currently being mined in an open pit fashion allowing for fresh three dimensional exposures of all representative rock types in the district. The Front Fange of Colorado, since cessation of northeast-directed Laramide compression, is characterized by east-west Rio Grande rift extension. Determining Laramide and younger deformation in the Front Range of Colorado is diffucult due to the dominance of Laramide structures and exposed Precambrian rocks with complex structural histories. Structures that affect the Cripple Creek diatreme complex and host Precambrian crystalline rocks clearly were active after intrusive activity and therefore reflect tectonism in the Front Range since early diatreme formation. Over 100 sites have been collected from all representative rock types in the district, with eight to ten oriented samples per site. Results indicate that the materials are capable of carrying geologically stable magnetizations and generally reveal excellent magnetization behavior using both AF and thermal methods. Many sites are associated with contact and breccia tests. Site mean directions are of both normal (D = 5.0° , I = 67.5° , α 95 = 6.4, κ = 89.2), N = 7 and reverse polarity (D = 162.2° , I = -67.3° , α 95 = 4.2, κ = 61.1) N =13; with site mean directions steeper than the expected mid-Tertiary polarity direction. Also, some sites exhibit multiple component behavior with both normal and reverse polarity magnetizations that are well defined (D = 29.7° , I = 72.5° , α 95 = 9.2, κ = 28.4) N = 10 and (D = 173.6° , I = -64.1° , α 95 = 3.1, κ = 594.8) N = 5, in aphanitic phonolite site CC89. We interpret these results to indicate that diatreme formation took place over at least one magnetic reversal and that the diatreme was modestly deformed resulting in north-side down tilting.

O2-Promoted Allylic Acetoxylation of Alkenes: Assessment of "Push" vs. "Pull" Mechanisms and Comparison between O2 and Benzoquinone.

PubMed

Diao, Tianning; Stahl, Shannon S

2014-12-14

Palladium-catalyzed acetoxylation of allylic C-H bonds has been the subject of extensive study. These reactions proceed via allyl-palladium(II) intermediates that react with acetate to afford the allyl acetate product. Benzoquinone and molecular oxygen are two common oxidants for these reactions. Benzoquinone has been shown to promote allyl acetate formation from well-defined π-allyl palladium(II) complexes. Here, we assess the ability of O 2 to promote similar reactions with a series of "unligated" π-allyl palladium(II) complexes (i.e., in the absence of ancillary phosphorus, nitrogen or related donor ligands). Stoichiometric and catalytic allyl acetate formation is observed under aerobic conditions with several different alkenes. Mechanistic studies are most consistent with a "pull" mechanism in which O 2 traps the Pd 0 intermediate following reversible C-O bond-formation from an allyl-palladium(II) species. A "push" mechanism, involving oxidatively induced C-O bond formation, does not appear to participate. These results and conclusions are compared with benzoquinone-promoted allylic acetoxylation, in which a "push" mechanism seems to be operative.

Is the gas-particle partitioning in alpha-pinene secondary organic aerosol reversible?

NASA Astrophysics Data System (ADS)

Grieshop, Andrew P.; Donahue, Neil M.; Robinson, Allen L.

2007-07-01

This paper discusses the reversibility of gas-particle partitioning in secondary organic aerosol (SOA) formed from α-pinene ozonolysis in a smog chamber. Previously, phase partitioning has been studied quantitatively via SOA production experiments and qualitatively by perturbing temperature and observing particle evaporation. In this work, two methods were used to isothermally dilute the SOA: an external dilution sampler and an in-chamber technique. Dilution caused some evaporation of SOA, but repartitioning took place on a time scale of tens of minutes to hours-consistent with an uptake coefficient on the order of 0.001-0.01. However, given sufficient time, α-pinene SOA repartitions reversibly based on comparisons with data from conventional SOA yield experiments. Further, aerosol mass spectrometer (AMS) data indicate that the composition of SOA varies with partitioning. These results suggest that oligomerization observed in high-concentration laboratory experiments may be a reversible process and underscore the complexity of the kinetics of formation and evaporation of SOA.

RPPAML/RIMS: A metadata format and an information management system for reverse phase protein arrays

PubMed Central

Stanislaus, Romesh; Carey, Mark; Deus, Helena F; Coombes, Kevin; Hennessy, Bryan T; Mills, Gordon B; Almeida, Jonas S

2008-01-01

Background Reverse Phase Protein Arrays (RPPA) are convenient assay platforms to investigate the presence of biomarkers in tissue lysates. As with other high-throughput technologies, substantial amounts of analytical data are generated. Over 1000 samples may be printed on a single nitrocellulose slide. Up to 100 different proteins may be assessed using immunoperoxidase or immunoflorescence techniques in order to determine relative amounts of protein expression in the samples of interest. Results In this report an RPPA Information Management System (RIMS) is described and made available with open source software. In order to implement the proposed system, we propose a metadata format known as reverse phase protein array markup language (RPPAML). RPPAML would enable researchers to describe, document and disseminate RPPA data. The complexity of the data structure needed to describe the results and the graphic tools necessary to visualize them require a software deployment distributed between a client and a server application. This was achieved without sacrificing interoperability between individual deployments through the use of an open source semantic database, S3DB. This data service backbone is available to multiple client side applications that can also access other server side deployments. The RIMS platform was designed to interoperate with other data analysis and data visualization tools such as Cytoscape. Conclusion The proposed RPPAML data format hopes to standardize RPPA data. Standardization of data would result in diverse client applications being able to operate on the same set of data. Additionally, having data in a standard format would enable data dissemination and data analysis. PMID:19102773

Selective inhibition of deactivated mitochondrial complex I by biguanides.

PubMed

Matsuzaki, Satoshi; Humphries, Kenneth M

2015-03-24

Biguanides are widely used antihyperglycemic agents for diabetes mellitus and prediabetes treatment. Complex I is the rate-limiting step of the mitochondrial electron transport chain (ETC), a major source of mitochondrial free radical production, and a known target of biguanides. Complex I has two reversible conformational states, active and de-active. The deactivated state is promoted in the absence of substrates but is rapidly and fully reversed to the active state in the presence of NADH. The objective of this study was to determine the relative sensitivity of active/de-active complex I to biguanide-mediated inhibition and resulting superoxide radical (O₂(•⁻)) production. Using isolated rat heart mitochondria, we show that deactivation of complex I sensitizes it to metformin and phenformin (4- and 3-fold, respectively), but not to other known complex I inhibitors, such as rotenone. Mitochondrial O₂(•⁻) production by deactivated complex I was measured fluorescently by NADH-dependent 2-hydroxyethidium formation at alkaline pH to impede reactivation. Superoxide production was 260.4% higher than in active complex I at pH 9.4. However, phenformin treatment of de-active complex I decreased O₂(•⁻) production by 14.9%, while rotenone increased production by 42.9%. Mitochondria isolated from rat hearts subjected to cardiac ischemia, a condition known to induce complex I deactivation, were sensitized to phenformin-mediated complex I inhibition. This supports the idea that the effects of biguanides are likely to be influenced by the complex I state in vivo. These results demonstrate that the complex I active and de-active states are a determinant in biguanide-mediated inhibition.

Kinetic mechanism of the dimeric ATP sulfurylase from plants

PubMed Central

Ravilious, Geoffrey E.; Herrmann, Jonathan; Goo Lee, Soon; Westfall, Corey S.; Jez, Joseph M.

2013-01-01

In plants, sulfur must be obtained from the environment and assimilated into usable forms for metabolism. ATP sulfurylase catalyses the thermodynamically unfavourable formation of a mixed phosphosulfate anhydride in APS (adenosine 5′-phosphosulfate) from ATP and sulfate as the first committed step of sulfur assimilation in plants. In contrast to the multi-functional, allosterically regulated ATP sulfurylases from bacteria, fungi and mammals, the plant enzyme functions as a mono-functional, non-allosteric homodimer. Owing to these differences, here we examine the kinetic mechanism of soybean ATP sulfurylase [GmATPS1 (Glycine max (soybean) ATP sulfurylase isoform 1)]. For the forward reaction (APS synthesis), initial velocity methods indicate a single-displacement mechanism. Dead-end inhibition studies with chlorate showed competitive inhibition versus sulfate and non-competitive inhibition versus APS. Initial velocity studies of the reverse reaction (ATP synthesis) demonstrate a sequential mechanism with global fitting analysis suggesting an ordered binding of substrates. ITC (isothermal titration calorimetry) showed tight binding of APS to GmATPS1. In contrast, binding of PPi (pyrophosphate) to GmATPS1 was not detected, although titration of the E•APS complex with PPi in the absence of magnesium displayed ternary complex formation. These results suggest a kinetic mechanism in which ATP and APS are the first substrates bound in the forward and reverse reactions, respectively. PMID:23789618

Reversible Association of the Hemagglutinin Subcomplex, HA-33/HA-17 Trimer, with the Botulinum Toxin Complex.

PubMed

Sagane, Yoshimasa; Mutoh, Shingo; Koizumi, Ryosuke; Suzuki, Tomonori; Miyashita, Shin-Ichiro; Miyata, Keita; Ohyama, Tohru; Niwa, Koichi; Watanabe, Toshihiro

2017-10-01

Botulinum neurotoxin (BoNT) associates with nontoxic proteins, either a nontoxic nonhemagglutinin (NTNHA) or the complex of NTNHA and hemagglutinin (HA), to form M- or L-toxin complexes (TCs). Single BoNT and NTNHA molecules are associated and form M-TC. A trimer of the 70-kDa HA protein (HA-70) attaches to the M-TC to form M-TC/HA-70. Further, 1-3 arm-like 33- and 17-kDa HA molecules (HA-33/HA-17 trimer), consisting of 1 HA-17 protein and 2 HA-33 proteins, can attach to the M-TC/HA-70 complex, yielding 1-, 2-, and 3-arm L-TC. In this study, the purified 1- and 2-arm L-TCs spontaneously converted into another L-TC species after acquiring the HA-33/HA-17 trimer from other TCs during long-term storage and freezing/thawing. Transmission electron microscopy analysis provided evidence of the formation of detached HA-33/HA-17 trimers in the purified TC preparation. These findings provide evidence of reversible association/dissociation of the M-TC/HA-70 complex with the HA-33/HA-17 trimers, as well as dynamic conversion of the quaternary structure of botulinum TC in culture.

DNA (Cytosine-C5) methyltransferase inhibition by oligodeoxyribonucleotides containing 2-(1H)-pyrimidinone (zebularine aglycon) at the enzymatic target site.

PubMed

van Bemmel, Dana M; Brank, Adam S; Eritja, Ramon; Marquez, Victor E; Christman, Judith K

2009-09-15

Aberrant cytosine methylation in promoter regions leads to gene silencing associated with cancer progression. A number of DNA methyltransferase inhibitors are known to reactivate silenced genes; including 5-azacytidine and 2-(1H)-pyrimidinone riboside (zebularine). Zebularine is a more stable, less cytotoxic inhibitor compared to 5-azacytidine. To determine the mechanistic basis for this difference, we carried out a detailed comparisons of the interaction between purified DNA methyltransferases and oligodeoxyribonucleotides (ODNs) containing either 5-azacytosine or 2-(1H)-pyrimidinone in place of the cytosine targeted for methylation. When incorporated into small ODNs, the rate of C5 DNA methyltransferase inhibition by both nucleosides is essentially identical. However, the stability and reversibility of the enzyme complex in the absence and presence of cofactor differs. 5-Azacytosine ODNs form complexes with C5 DNA methyltransferases that are irreversible when the 5-azacytosine ring is intact. ODNs containing 2-(1H)-pyrimidinone at the enzymatic target site are competitive inhibitors of both prokaryotic and mammalian DNA C5 methyltransferases. We determined that the ternary complexes between the enzymes, 2-(1H)-pyrimidinone inhibitor, and the cofactor S-adenosyl methionine are maintained through the formation of a reversible covalent interaction. The differing stability and reversibility of the covalent bonds may partially account for the observed differences in cytotoxicity between zebularine and 5-azacytidine inhibitors.

DNA (Cytosine-C5) Methyltransferase Inhibition by Oligodeoxyribonucleotides Containing 2-(1H)-Pyrimidinone (Zebularine Aglycon) at the Enzymatic Target Site

PubMed Central

van Bemmel, Dana M.; Brank, Adam S.; Eritja, Ramon; Marquez, Victor E.; Christman, Judith K.

2009-01-01

Aberrant cytosine methylation in promoter regions leads to gene silencing associated with cancer progression. A number of DNA methyltransferase inhibitors are known to reactivate silenced genes; including 5-azacytidine and 2-(1H)-pyrimidinone riboside (zebularine). Zebularine is a more stable, less cytotoxic inhibitor compared to 5-azacytidine. To determine the mechanistic basis for this difference, we carried out a detailed comparisons of the interaction between purified DNA methyltransferases and oligodeoxyribonucleotides (ODNs) containing either 5-azacytosine or 2-(1H)-pyrimidinone in place of the cytosine targeted for methylation. When incorporated into small ODNs, the rate of C5 DNA methyltransferase inhibition by both nucleosides is essentially identical. However, the stability and reversibility of the enzyme complex in the absence and presence of cofactor differs. 5-Azacytosine ODNs form complexes with C5 DNA methyltransferases that are irreversible when the 5-azacytosine ring is intact. ODNs containing 2-(1H)-pyrimidinone at the enzymatic target site are competitive inhibitors of both prokaryotic and mammalian DNA C5 methyltransferases. We determined that the ternary complexes between the enzymes, 2-(1H)-pyrimidinone inhibitor, and the cofactor S-adenosyl methionine are maintained through the formation of a reversible covalent interaction. The differing stability and reversibility of the covalent bonds may partially account for the observed differences in cytotoxicity between zebularine and 5-azacytidine inhibitors. PMID:19467223

Poly(allyl methacrylate) functionalized hydroxyapatite nanocrystals via the combination of surface-initiated RAFT polymerization and thiol-ene protocol: a potential anticancer drug nanocarrier.

PubMed

Bach, Long Giang; Islam, Md Rafiqul; Vo, Thanh-Sang; Kim, Se-Kwon; Lim, Kwon Taek

2013-03-15

Hydroxyapatite nanocrystals (HAP NCs) were encapsulated by poly(allyl methacrylate) (PolyAMA) employing controlled surface-initiated reversible addition-fragmentation chain transfer (SI-RAFT) polymerization of allyl methacrylate to afford HAP-PolyAMA nanohybrids. The subsequent thiol-ene coupling of nanohybrids with 2-mercaptosuccinic acid resulted HAP-Poly(AMA-COOH) possessing multicarboxyl group. The formation of the nanohybrids was confirmed by FT-IR and EDS analyses. The TGA and FE-SEM investigation were further suggested the grafting of PolyAMA onto HAP NCs. The utility of the HAP-PolyAMA nanohybrid as drug carrier was also explored. The pendant carboxyl groups on the external layers of nanohybrids were conjugated with anticancer drug cisplatin to afford HAP-Poly(AMA-COOH)/Pt complex. The formation of the complex was confirmed by FT-IR, XPS, and FE-SEM. In vitro evaluation of the synthesized complex as nanomedicine revealed its potential chemotherapeutic efficacy against cancer cell lines. Copyright © 2012 Elsevier Inc. All rights reserved.

Directional reversals enable Myxococcus xanthus cells to produce collective one-dimensional streams during fruiting-body formation

PubMed Central

Thutupalli, Shashi; Sun, Mingzhai; Bunyak, Filiz; Palaniappan, Kannappan; Shaevitz, Joshua W.

2015-01-01

The formation of a collectively moving group benefits individuals within a population in a variety of ways. The surface-dwelling bacterium Myxococcus xanthus forms dynamic collective groups both to feed on prey and to aggregate during times of starvation. The latter behaviour, termed fruiting-body formation, involves a complex, coordinated series of density changes that ultimately lead to three-dimensional aggregates comprising hundreds of thousands of cells and spores. How a loose, two-dimensional sheet of motile cells produces a fixed aggregate has remained a mystery as current models of aggregation are either inconsistent with experimental data or ultimately predict unstable structures that do not remain fixed in space. Here, we use high-resolution microscopy and computer vision software to spatio-temporally track the motion of thousands of individuals during the initial stages of fruiting-body formation. We find that cells undergo a phase transition from exploratory flocking, in which unstable cell groups move rapidly and coherently over long distances, to a reversal-mediated localization into one-dimensional growing streams that are inherently stable in space. These observations identify a new phase of active collective behaviour and answer a long-standing open question in Myxococcus development by describing how motile cell groups can remain statistically fixed in a spatial location. PMID:26246416

Synthesis, characterization, photoluminescence, and electrochemical studies of novel mononuclear Cu(II) and Zn(II) complexes with the 1-benzylimidazolium ligand

NASA Astrophysics Data System (ADS)

Bibi, Sherino; Mohammad, Sharifah; Manan, Ninie Suhana Abdul; Ahmad, Jimmy; Kamboh, Muhammad Afzal; Khor, Sook Mei; Yamin, Bohari M.; Abdul Halim, Siti Nadiah

2017-08-01

Two new mononuclear coordination complexes [Cu(bim)4Cl2]ṡ2H2O (1) and [Zn(bim)2Cl2] (2) containing the 1-benzylimidazole (bim) ligand were successfully synthesized. Both complexes were characterized by IR, UV-vis, and fluorescence spectroscopies, single crystal and powder X-ray diffraction measurements, and thermogravimetric analysis. Self-assembly during the recrystallization process resulted in the formation of octahedral and tetrahedral Cu(II) and Zn(II) complexes, respectively. The single crystals obtained are representative of the bulk material, as shown by the powder X-ray diffraction patterns. Cyclic voltammetry measurements showed that complex 1 undergoes a quasi-reversible redox reaction, while complex 2 undergoes reduction alone, and no oxidation peak was observed; this is due to the stability of the reduced form of complex 2.

Deletion of nfnAB in Thermoanaerobacterium saccharolyticum and Its Effect on Metabolism

DOE PAGES

Lo, Jonathan; Zheng, Tianyong; Olson, Daniel G.; ...

2015-06-29

NfnAB catalyzes the reversible transfer of electrons from reduced ferredoxin and NADH to 2 NADP +. The NfnAB complex has been hypothesized to be the main enzyme for ferredoxin oxidization in strains of Thermoanaerobacterium saccharolyticum engineered for increased ethanol production. NfnAB complex activity was detectable in crude cell extracts of T. saccharolyticum. In this paper, activity was also detected using activity staining of native PAGE gels. The nfnAB gene was deleted in different strains of T. saccharolyticum to determine its effect on end product formation. In wild-type T. saccharolyticum, deletion of nfnAB resulted in a 46% increase in H 2more » formation but otherwise little change in other fermentation products. In two engineered strains with 80% theoretical ethanol yield, loss of nfnAB caused two different responses: in one strain, ethanol yield decreased to about 30% of the theoretical value, while another strain had no change in ethanol yield. Biochemical analysis of cell extracts showed that the ΔnfnAB strain with decreased ethanol yield had NADPH-linked alcohol dehydrogenase (ADH) activity, while the ΔnfnAB strain with unchanged ethanol yield had NADH-linked ADH activity. Deletion of nfnAB caused loss of NADPH-linked ferredoxin oxidoreductase activity in all cell extracts. Significant NADH-linked ferredoxin oxidoreductase activity was seen in all cell extracts, including those that had lost nfnAB. This suggests that there is an unidentified NADH:ferredoxin oxidoreductase (distinct from nfnAB) playing a role in ethanol formation. The NfnAB complex plays a key role in generating NADPH in a strain that had become reliant on NADPH-ADH activity. Importance: Thermophilic anaerobes that can convert biomass-derived sugars into ethanol have been investigated as candidates for biofuel formation. Many anaerobes have been genetically engineered to increase biofuel formation; however, key aspects of metabolism remain unknown and poorly understood. One example is the mechanism for ferredoxin oxidation and transfer of electrons to NAD(P) +. The electron-bifurcating enzyme complex NfnAB is known to catalyze the reversible transfer of electrons from reduced ferredoxin and NADH to 2 NADP + and is thought to play key roles linking NAD(P)(H) metabolism with ferredoxin metabolism. Finally, we report the first deletion of nfnAB and demonstrate a role for NfnAB in metabolism and ethanol formation in Thermoanaerobacterium saccharolyticum and show that this may be an important feature among other thermophilic ethanologenic anaerobes.« less

H3K9me3 demethylase Kdm4d facilitates the formation of pre-initiative complex and regulates DNA replication

PubMed Central

Wu, Rentian; Wang, Zhiquan; Zhang, Honglian; Gan, Haiyun; Zhang, Zhiguo

2017-01-01

DNA replication is tightly regulated to occur once and only once per cell cycle. How chromatin, the physiological substrate of DNA replication machinery, regulates DNA replication remains largely unknown. Here we show that histone H3 lysine 9 demethylase Kdm4d regulates DNA replication in eukaryotic cells. Depletion of Kdm4d results in defects in DNA replication, which can be rescued by the expression of H3K9M, a histone H3 mutant transgene that reverses the effect of Kdm4d on H3K9 methylation. Kdm4d interacts with replication proteins, and its recruitment to DNA replication origins depends on the two pre-replicative complex components (origin recognition complex [ORC] and minichromosome maintenance [MCM] complex). Depletion of Kdm4d impairs the recruitment of Cdc45, proliferating cell nuclear antigen (PCNA), and polymerase δ, but not ORC and MCM proteins. These results demonstrate a novel mechanism by which Kdm4d regulates DNA replication by reducing the H3K9me3 level to facilitate formation of pre-initiative complex. PMID:27679476

Characteristics of alpha-glycerophosphate-evoked H2O2 generation in brain mitochondria.

PubMed

Tretter, Laszlo; Takacs, Katalin; Hegedus, Vera; Adam-Vizi, Vera

2007-02-01

Characteristics of reactive oxygen species (ROS) production in isolated guinea-pig brain mitochondria respiring on alpha-glycerophosphate (alpha-GP) were investigated and compared with those supported by succinate. Mitochondria established a membrane potential (DeltaPsi(m)) and released H(2)O(2) in parallel with an increase in NAD(P)H fluorescence in the presence of alpha-GP (5-40 mm). H(2)O(2) formation and the increase in NAD(P)H level were inhibited by rotenone, ADP or FCCP, respectively, being consistent with a reverse electron transfer (RET). The residual H(2)O(2) formation in the presence of FCCP was stimulated by myxothiazol in mitochondria supported by alpha-GP, but not by succinate. ROS under these conditions are most likely to be derived from alpha-GP-dehydrogenase. In addition, huge ROS formation could be provoked by antimycin in alpha-GP-supported mitochondria, which was prevented by myxothiazol, pointing to the generation of ROS at the quinol-oxidizing center (Q(o)) site of complex III. FCCP further stimulated the production of ROS to the highest rate that we observed in this study. We suggest that the metabolism of alpha-GP leads to ROS generation primarily by complex I in RET, and in addition a significant ROS formation could be ascribed to alpha-GP-dehydrogenase in mammalian brain mitochondria. ROS generation by alpha-GP at complex III is evident only when this complex is inhibited by antimycin.

Involvement of DPP-IV catalytic residues in enzyme–saxagliptin complex formation

PubMed Central

Metzler, William J.; Yanchunas, Joseph; Weigelt, Carolyn; Kish, Kevin; Klei, Herbert E.; Xie, Dianlin; Zhang, Yaqun; Corbett, Martin; Tamura, James K.; He, Bin; Hamann, Lawrence G.; Kirby, Mark S.; Marcinkeviciene, Jovita

2008-01-01

The inhibition of DPP-IV by saxagliptin has been proposed to occur through formation of a covalent but reversible complex. To evaluate further the mechanism of inhibition, we determined the X-ray crystal structure of the DPP-IV:saxagliptin complex. This structure reveals covalent attachment between S630 and the inhibitor nitrile carbon (C–O distance <1.3 Å). To investigate whether this serine addition is assisted by the catalytic His-Asp dyad, we generated two mutants of DPP-IV, S630A and H740Q, and assayed them for ability to bind inhibitor. DPP-IVH740Q bound saxagliptin with an ∼1000-fold reduction in affinity relative to DPP-IVWT, while DPP-IVS630A showed no evidence for binding inhibitor. An analog of saxagliptin lacking the nitrile group showed unchanged binding properties to the both mutant proteins, highlighting the essential role S630 and H740 play in covalent bond formation between S630 and saxagliptin. Further supporting mechanism-based inhibition by saxagliptin, NMR spectra of enzyme–saxagliptin complexes revealed the presence of three downfield resonances with low fractionation factors characteristic of short and strong hydrogen bonds (SSHB). Comparison of the NMR spectra of various wild-type and mutant DPP-IV:ligand complexes enabled assignment of a resonance at ∼14 ppm to H740. Two additional DPP-IV mutants, Y547F and Y547Q, generated to probe potential stabilization of the enzyme–inhibitor complex by this residue, did not show any differences in inhibitor binding either by ITC or NMR. Together with the previously published enzymatic data, the structural and binding data presented here strongly support a histidine-assisted covalent bond formation between S630 hydroxyl oxygen and the nitrile group of saxagliptin. PMID:18227430

Involvement of DPP-IV Catalytic Residues in Enzyme-Saxagliptin Complex Formation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Metzler,W.; Yanchunas, J.; Weigelt, C.

The inhibition of DPP-IV by saxagliptin has been proposed to occur through formation of a covalent but reversible complex. To evaluate further the mechanism of inhibition, we determined the X-ray crystal structure of the DPP-IV:saxagliptin complex. This structure reveals covalent attachment between S630 and the inhibitor nitrile carbon (C-O distance <1.3 Angstroms). To investigate whether this serine addition is assisted by the catalytic His-Asp dyad, we generated two mutants of DPP-IV, S630A and H740Q, and assayed them for ability to bind inhibitor. DPP-IVH740Q bound saxagliptin with an {approx}1000-fold reduction in affinity relative to DPP-IVWT, while DPP-IVS630A showed no evidence formore » binding inhibitor. An analog of saxagliptin lacking the nitrile group showed unchanged binding properties to the both mutant proteins, highlighting the essential role S630 and H740 play in covalent bond formation between S630 and saxagliptin. Further supporting mechanism-based inhibition by saxagliptin, NMR spectra of enzyme-saxagliptin complexes revealed the presence of three downfield resonances with low fractionation factors characteristic of short and strong hydrogen bonds (SSHB). Comparison of the NMR spectra of various wild-type and mutant DPP-IV:ligand complexes enabled assignment of a resonance at {approx}14 ppm to H740. Two additional DPP-IV mutants, Y547F and Y547Q, generated to probe potential stabilization of the enzyme-inhibitor complex by this residue, did not show any differences in inhibitor binding either by ITC or NMR. Together with the previously published enzymatic data, the structural and binding data presented here strongly support a histidine-assisted covalent bond formation between S630 hydroxyl oxygen and the nitrile group of saxagliptin.« less

Synthesis, spectroscopic and thermal studies of transition metal complexes derived from benzil and diethylenetriamine

NASA Astrophysics Data System (ADS)

Khan, Sadaf; Nami, Shahab A. A.; Siddiqi, K. S.

2007-10-01

A macrocyclic ligand, bdta (where bdta = 3,6,9,12,15,18-hexaaza-1,2,10,11-tetraphenyl-2,9,11,18-tetraenecyclododecane) has been prepared by cyclocondensation of benzil with diethylenetriamine which efficiently encapsulates transition as well as pseudo-transition metal ions leading to the formation of M(bdta)Cl 2 type complexes [where M = Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II)]. The analytical, spectroscopic and magnetic moment data suggests an octahedral geometry for all the complexes. EPR spectra of Mn(II) and Cu(II) show considerable exchange interaction in the complex. They are non-conducting in DMSO. The TGA profile of the ligand and its complexes are identical and consists of two discreet stages. The voltammogram of Cu-complex exhibits a quasi-reversible one-electron transfer wave for Cu(II)/Cu(I) couple.

Synthesis, spectroscopic and thermal studies of transition metal complexes derived from benzil and diethylenetriamine.

PubMed

Khan, Sadaf; Nami, Shahab A A; Siddiqi, K S

2007-10-01

A macrocyclic ligand, bdta (where bdta=3,6,9,12,15,18-hexaaza-1,2,10,11-tetraphenyl-2,9,11,18-tetraenecyclododecane) has been prepared by cyclocondensation of benzil with diethylenetriamine which efficiently encapsulates transition as well as pseudo-transition metal ions leading to the formation of M(bdta)Cl2 type complexes [where M=Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II)]. The analytical, spectroscopic and magnetic moment data suggests an octahedral geometry for all the complexes. EPR spectra of Mn(II) and Cu(II) show considerable exchange interaction in the complex. They are non-conducting in DMSO. The TGA profile of the ligand and its complexes are identical and consists of two discreet stages. The voltammogram of Cu-complex exhibits a quasi-reversible one-electron transfer wave for Cu(II)/Cu(I) couple.

Synthesis and characterization of carbazolide-based iridium PNP pincer complexes. Mechanistic and computational investigation of alkene hydrogenation: evidence for an Ir(III)/Ir(V)/Ir(III) catalytic cycle.

PubMed

Cheng, Chen; Kim, Bong Gon; Guironnet, Damien; Brookhart, Maurice; Guan, Changjian; Wang, David Y; Krogh-Jespersen, Karsten; Goldman, Alan S

2014-05-07

New carbazolide-based iridium pincer complexes ((carb)PNP)Ir(C2H4), 3a, and ((carb)PNP)Ir(H)2, 3b, have been prepared and characterized. The dihydride, 3b, reacts with ethylene to yield the cis-dihydride ethylene complex cis-((carb)PNP)Ir(C2H4)(H)2. Under ethylene this complex reacts slowly at 70 °C to yield ethane and the ethylene complex, 3a. Kinetic analysis establishes that the reaction rate is dependent on ethylene concentration and labeling studies show reversible migratory insertion to form an ethyl hydride complex prior to formation of 3a. Exposure of cis-((carb)PNP)Ir(C2H4)(H)2 to hydrogen results in very rapid formation of ethane and dihydride, 3b. DFT analysis suggests that ethane elimination from the ethyl hydride complex is assisted by ethylene through formation of ((carb)PNP)Ir(H)(Et)(C2H4) and by H2 through formation of ((carb)PNP)Ir(H)(Et)(H2). Elimination of ethane from Ir(III) complex ((carb)PNP)Ir(H)(Et)(H2) is calculated to proceed through an Ir(V) complex ((carb)PNP)Ir(H)3(Et) which reductively eliminates ethane with a very low barrier to return to the Ir(III) dihydride, 3b. Under catalytic hydrogenation conditions (C2H4/H2), cis-((carb)PNP)Ir(C2H4)(H)2 is the catalyst resting state, and the catalysis proceeds via an Ir(III)/Ir(V)/Ir(III) cycle. This is in sharp contrast to isoelectronic (PCP)Ir systems in which hydrogenation proceeds through an Ir(III)/Ir(I)/Ir(III) cycle. The basis for this remarkable difference is discussed.

Maturation and function of human embryonic stem cell-derived pancreatic progenitors in macroencapsulation devices following transplant into mice.

PubMed

Bruin, Jennifer E; Rezania, Alireza; Xu, Jean; Narayan, Kavitha; Fox, Jessica K; O'Neil, John J; Kieffer, Timothy J

2013-09-01

Islet transplantation is a promising cell therapy for patients with diabetes, but it is currently limited by the reliance upon cadaveric donor tissue. We previously demonstrated that human embryonic stem cell (hESC)-derived pancreatic progenitor cells matured under the kidney capsule in a mouse model of diabetes into glucose-responsive insulin-secreting cells capable of reversing diabetes. However, the formation of cells resembling bone and cartilage was a major limitation of that study. Therefore, we developed an improved differentiation protocol that aimed to prevent the formation of off-target mesoderm tissue following transplantation. We also examined how variation within the complex host environment influenced the development of pancreatic progenitors in vivo. The hESCs were differentiated for 14 days into pancreatic progenitor cells and transplanted either under the kidney capsule or within Theracyte (TheraCyte, Laguna Hills, CA, USA) devices into diabetic mice. Our revised differentiation protocol successfully eliminated the formation of non-endodermal cell populations in 99% of transplanted mice and generated grafts containing >80% endocrine cells. Progenitor cells developed efficiently into pancreatic endocrine tissue within macroencapsulation devices, despite lacking direct contact with the host environment, and reversed diabetes within 3 months. The preparation of cell aggregates pre-transplant was critical for the formation of insulin-producing cells in vivo and endocrine cell development was accelerated within a diabetic host environment compared with healthy mice. Neither insulin nor exendin-4 therapy post-transplant affected the maturation of macroencapsulated cells. Efficient differentiation of hESC-derived pancreatic endocrine cells can occur in a macroencapsulation device, yielding glucose-responsive insulin-producing cells capable of reversing diabetes.

SAD-3, a Putative Helicase Required for Meiotic Silencing by Unpaired DNA, Interacts with Other Components of the Silencing Machinery

PubMed Central

Hammond, Thomas M.; Xiao, Hua; Boone, Erin C.; Perdue, Tony D.; Pukkila, Patricia J.; Shiu, Patrick K. T.

2011-01-01

In Neurospora crassa, genes lacking a pairing partner during meiosis are suppressed by a process known as meiotic silencing by unpaired DNA (MSUD). To identify novel MSUD components, we have developed a high-throughput reverse-genetic screen for use with the N. crassa knockout library. Here we describe the screening method and the characterization of a gene (sad-3) subsequently discovered. SAD-3 is a putative helicase required for MSUD and sexual spore production. It exists in a complex with other known MSUD proteins in the perinuclear region, a center for meiotic silencing activity. Orthologs of SAD-3 include Schizosaccharomyces pombe Hrr1, a helicase required for RNAi-induced heterochromatin formation. Both SAD-3 and Hrr1 interact with an RNA-directed RNA polymerase and an Argonaute, suggesting that certain aspects of silencing complex formation may be conserved between the two fungal species. PMID:22384347

Selective Inhibition of Deactivated Mitochondrial Complex I by Biguanides †

PubMed Central

Matsuzaki, Satoshi; Humphries, Kenneth M.

2015-01-01

Biguanides are widely used antihyperglycemic agents for diabetes mellitus and prediabetes treatment. Complex I is the rate limiting step of the mitochondrial electron transport chain (ETC), a major source of mitochondrial free radical production, and a known target of biguanides. Complex I has two reversible conformational states, active and de-active. The deactivated state is promoted in the absence of substrates, but is rapidly and fully reversed to the active state in the presence of NADH. The objective of this study was to determine the relative sensitivity of active/de-active complex I to biguanide-mediated inhibition and resulting superoxide radical (O2•−) production. Using isolated rat heart mitochondria, we show that deactivation of complex I sensitizes it to metformin and phenformin (4- and 3-fold, respectively), but not to other known complex I inhibitors, such as rotenone. Mitochondrial O2•− production by deactivated complex I was measured fluorescently by the NADH-dependent 2-hydroxyethidium formation at alkaline pH to impede reactivation. Superoxide production was 260.4% higher than in active complex I at pH 9.4. However, phenformin treatment of de-active complex I decreased O2•− production by 14.9% while rotenone increased production by 42.9%. Mitochondria isolated from rat hearts subjected to cardiac ischemia, a condition known to induce complex I deactivation, were sensitized to phenformin:mediated complex I inhibition. This supports that the effects of biguanides are likely to be influenced by the complex I state in vivo. These results demonstrate that the complex I active/de-active states are a determinant in biguanide-mediated inhibition. PMID:25719498

The Reciprocal Principle of Selectand-Selector-Systems in Supramolecular Chromatography †.

PubMed

Schurig, Volker

2016-11-15

In selective chromatography and electromigration methods, supramolecular recognition of selectands and selectors is due to the fast and reversible formation of association complexes governed by thermodynamics. Whereas the selectand molecules to be separated are always present in the mobile phase, the selector employed for the separation of the selectands is either part of the stationary phase or is added to the mobile phase. By the reciprocal principle, the roles of selector and selectand can be reversed. In this contribution in honor of Professor Stig Allenmark, the evolution of the reciprocal principle in chromatography is reviewed and its advantages and limitations are outlined. Various reciprocal scenarios, including library approaches, are discussed in efforts to optimize selectivity in separation science.

A reversible fluorescence "off-on-off" sensor for sequential detection of aluminum and acetate/fluoride ions.

PubMed

Gupta, Vinod Kumar; Mergu, Naveen; Kumawat, Lokesh Kumar; Singh, Ashok Kumar

2015-11-01

A new rhodamine functionalized fluorogenic Schiff base CS was synthesized and its colorimetric and fluorescence responses toward various metal ions were explored. The sensor exhibited highly selective and sensitive colorimetric and "off-on" fluorescence response towards Al(3+) in the presence of other competing metal ions. These spectral changes are large enough in the visible region of the spectrum and thus enable naked-eye detection. Studies proved that the formation of CS-Al(3+) complex is fully reversible and can sense to AcO(-)/F(-) via dissociation. The results revealed that the sensor provides fluorescence "off-on-off" strategy for the sequential detection of Al(3+) and AcO(-)/F(-). Copyright © 2015 Elsevier B.V. All rights reserved.

Formate-induced inhibition of the water-oxidizing complex of photosystem II studied by EPR.

PubMed

Feyziev, Y M; Yoneda, D; Yoshii, T; Katsuta, N; Kawamori, A; Watanabe, Y

2000-04-04

The effects of various formate concentrations on both the donor and the acceptor sides in oxygen-evolving PS II membranes (BBY particles) were examined. EPR, oxygen evolution and variable chlorophyll fluorescence have been observed. It was found that formate inhibits the formation of the S(2) state multiline signal concomitant with stimulation of the Q(A)(-)Fe(2+) signal at g = 1.82. The decrease and the increase in intensities of the multiline and Q(A)(-)Fe(2+) signals, respectively, had a linear relation for formate concentrations between 5 and 500 mM. The g = 4.1 signal formation measured in the absence of methanol was not inhibited by formate up to 250 mM in the buffer. In the presence of 3% methanol the g = 4.1 signal evolved as formate concentration increased. The evolved signal could be ascribed to the inhibited centers. Oxygen evolution measured in the presence of an electron acceptor, phenyl-p-benzoquinone, was also inhibited by formate proportionally to the decrease in the multiline signal intensity. The inhibition seemed to be due to a retarded electron transfer from the water-oxidizing complex to Y(Z)(+), which was observed in the decay kinetics of the Y(Z)(+) signal induced by illumination above 250 K. These results show that formate induces inhibition of water oxidation reactions as well as electron transfer on the PS II acceptor side. The inhibition effects of formate in PS II were found to be reversible, indicating no destructive effect on the reaction center induced by formate.

Preparation, characterization and in vitro evaluation of a new nucleotide analogue prodrug cyclodextrin inclusion complexes.

PubMed

Diab, Roudayna; Jordheim, Lars P; Degobert, Ghania; Peyrottes, Suzanne; Périgaud, Christian; Dumontet, Charles; Fessi, Hatem

2009-01-01

Bis(tbutyl-S-acyl-2-thioethyl)-cytidine monophosophate is a new cytotoxic mononucleotide prodrug which have been developed to reverse the cellular resistance to nucleoside analogues. Unfortunately, its in vivo utilisation was hampered by its poor water solubility, raising the need of a molecular vector capable to mask its physicochemical characteristics although without affecting its cytotoxic activity. Hydroxypropyl-beta-cyclodextrin was used to prepare the prodrug inclusion complexes, allowing it to be solubilized in water and hence to be used for in vitro and in vivo experiments. A molar ratio of the cyclodextrin: prodrug of 3 was sufficient to obtain complete solubilization of the prodrug. The inclusion complex was characterized by differential scanning calorimetry, which revealed the disappearance of the melting peak of the prodrug suggesting the formation of inclusion complex. Proton Nuclear Magnetic Resonance spectroscopy provided a definitive proof of the inclusion complex formation, which was evidenced by the large chemical shift displacements observed for protons located in the interior of the hydrophobic cyclodextrin cavity. The complex retained its cytotoxic activity as shown by in vitro cell survival assays on murine leukemia cells. These results provided a basis for potential therapeutic applications of co-formulation of this new nucleotide analogue with hydroxypropyl-beta-CD in cancer therapy.

Structural and kinetic study of reversible CO2 fixation by dicopper macrocyclic complexes. From intramolecular binding to self-assembly of molecular boxes.

PubMed

Company, Anna; Jee, Joo-Eun; Ribas, Xavi; Lopez-Valbuena, Josep Maria; Gómez, Laura; Corbella, Montserrat; Llobet, Antoni; Mahía, José; Benet-Buchholz, Jordi; Costas, Miquel; van Eldik, Rudi

2007-10-29

A study of the reversible CO2 fixation by a series of macrocyclic dicopper complexes is described. The dicopper macrocyclic complexes [Cu2(OH)2(Me2p)](CF3SO3)2, 1(CF3SO3)2, and [Cu2(mu-OH)2(Me2m)](CF3SO3)2, 2(CF3SO3)2, (Scheme 1) containing terminally bound and bridging hydroxide ligands, respectively, promote reversible inter- and intramolecular CO2 fixation that results in the formation of the carbonate complexes [{Cu2(Me2p)}2(mu-CO3)2](CF3SO3)4, 4(CF3SO3)4, and [Cu2(mu-CO3)(Me2m)](CF3SO3)2, 5(CF3SO3)2. Under a N2 atmosphere the complexes evolve CO2 and revert to the starting hydroxo complexes 1(CF3SO3)2 and 2(CF3SO3)2, a reaction the rate of which linearly depends on [H2O]. In the presence of water, attempts to crystallize 5(CF3SO3)2 afford [{Cu2(Me2m)(H2O)}2(mu-CO3)2](CF3SO3)4, 6(CF3SO3)4, which appears to rapidly convert to 5(CF3SO3)2 in acetonitrile solution. [Cu2(OH)2(H3m)]2+, 7, which contains a larger macrocyclic ligand, irreversibly reacts with atmospheric CO2 to generate cagelike [{Cu2(H3m)}2(mu-CO3)2](ClO4)4, 8(ClO4)4. However, addition of 1 equiv of HClO4 per Cu generates [Cu2(H3m)(CH3CN)4]4+ (3), and subsequent addition of Et3N under air reassembles 8. The carbonate complexes 4(CF3SO3)4, 5(CF3SO3)2, 6(CF3SO3)4, and 8(ClO4)4 have been characterized in the solid state by X-ray crystallography. This analysis reveals that 4(CF3SO3)4, 6(CF3SO3)4, and 8(ClO4)4 consist of self-assembled molecular boxes containing two macrocyclic dicopper complexes, bridged by CO32- ligands. The bridging mode of the carbonate ligand is anti-anti-mu-eta1:eta1 in 4(CF3SO3)4, anti-anti-mu-eta2:eta1 in 6(CF3SO3)4 and anti-anti-mu-eta2:eta2 in 5(CF3SO3)2 and 8(ClO4)4. Magnetic susceptibility measurements on 4(CF3SO3)4, 6(CF3SO3)4, and 8(ClO4)4 indicate that the carbonate ligands mediate antiferromagnetic coupling between each pair of bridged CuII ions (J = -23.1, -108.3, and -163.4 cm-1, respectively, H = -JS1S2). Detailed kinetic analyses of the reaction between carbon dioxide and the macrocyclic complexes 1(CF3SO3)2 and 2(CF3SO3)2 suggest that it is actually hydrogen carbonate formed in aqueous solution on dissolving CO2 that is responsible for the observed formation of the different carbonate complexes controlled by the binding mode of the hydroxy ligands. This study shows that CO2 fixation can be used as an on/off switch for the reversible self-assembly of supramolecular structures based on macrocyclic dicopper complexes.

O2-Promoted Allylic Acetoxylation of Alkenes: Assessment of “Push” vs. “Pull” Mechanisms and Comparison between O2 and Benzoquinone

PubMed Central

Diao, Tianning

2014-01-01

Palladium-catalyzed acetoxylation of allylic C–H bonds has been the subject of extensive study. These reactions proceed via allyl-palladium(II) intermediates that react with acetate to afford the allyl acetate product. Benzoquinone and molecular oxygen are two common oxidants for these reactions. Benzoquinone has been shown to promote allyl acetate formation from well-defined π-allyl palladium(II) complexes. Here, we assess the ability of O2 to promote similar reactions with a series of “unligated” π-allyl palladium(II) complexes (i.e., in the absence of ancillary phosphorus, nitrogen or related donor ligands). Stoichiometric and catalytic allyl acetate formation is observed under aerobic conditions with several different alkenes. Mechanistic studies are most consistent with a “pull” mechanism in which O2 traps the Pd0 intermediate following reversible C–O bond-formation from an allyl-palladium(II) species. A “push” mechanism, involving oxidatively induced C–O bond formation, does not appear to participate. These results and conclusions are compared with benzoquinone-promoted allylic acetoxylation, in which a “push” mechanism seems to be operative. PMID:25435646

Process of forming compounds using reverse micelle or reverse microemulsion systems

DOEpatents

Linehan, John C.; Fulton, John L.; Bean, Roger M.

1998-01-01

The present invention is directed to a process for producing a nanometer-sized metal compound. The process comprises forming a reverse micelle or reverse microemulsion system comprising a polar fluid in a non-polar or low-polarity fluid. A first reactant comprising a multi-component, water-soluble metal compound is introduced into the polar fluid in a non-polar or low-polarity fluid. This first reactant can be introduced into the reverse micelle or reverse microemulsion system during formation thereof or subsequent to the formation of the reverse micelle or microemulsion system. The water-soluble metal compound is then reacted in the reverse micelle or reverse microemulsion system to form the nanometer-sized metal compound. The nanometer-sized metal compound is then precipitated from the reverse micelle or reverse microemulsion system.

Hrs regulates early endosome fusion by inhibiting formation of an endosomal SNARE complex

PubMed Central

Sun, Wei; Yan, Qing; Vida, Thomas A.; Bean, Andrew J.

2003-01-01

Movement through the endocytic pathway occurs principally via a series of membrane fusion and fission reactions that allow sorting of molecules to be recycled from those to be degraded. Endosome fusion is dependent on SNARE proteins, although the nature of the proteins involved and their regulation has not been fully elucidated. We found that the endosome-associated hepatocyte responsive serum phosphoprotein (Hrs) inhibited the homotypic fusion of early endosomes. A region of Hrs predicted to form a coiled coil required for binding the Q-SNARE, SNAP-25, mimicked the inhibition of endosome fusion produced by full-length Hrs, and was sufficient for endosome binding. SNAP-25, syntaxin 13, and VAMP2 were bound from rat brain membranes to the Hrs coiled-coil domain. Syntaxin 13 inhibited early endosomal fusion and botulinum toxin/E inhibition of early endosomal fusion was reversed by addition of SNAP-25(150–206), confirming a role for syntaxin 13, and establishing a role for SNAP-25 in endosomal fusion. Hrs inhibited formation of the syntaxin 13–SNAP-25–VAMP2 complex by displacing VAMP2 from the complex. These data suggest that SNAP-25 is a receptor for Hrs on early endosomal membranes and that the binding of Hrs to SNAP-25 on endosomal membranes inhibits formation of a SNARE complex required for homotypic endosome fusion. PMID:12847087

Stabilization and prolonged reactivity of aqueous-phase ozone with cyclodextrin

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dettmer, Adam; Ball, Raymond; Boving, Thomas B.

Recalcitrant organic groundwater contaminants, such as 1,4-dioxane, may require strong oxidants for complete mineralization. However, their efficacy for in-situ chemical oxidation (ISCO) is limited by oxidant decay and reactivity. Hydroxypropyl-β-cyclodextrin (HPβCD) was examined for its ability to stabilize aqueous-phase ozone (O3) and prolong oxidation potential through inclusion complex formation. Partial transformation of HPβCD by O3 was observed. However, HPβCD proved to be sufficiently recalcitrant, because it was only partially degraded in the presence of O3. The formation of a HPβCD:O3 clathrate complex was observed, which stabilized decay of O3. The presence of HPβCD increased the O3 half-life linearly with increasingmore » HPβCD:O3 molar ratio. The O3 half-life in solutions increased by as much as 40-fold relative to HPβCD-free O3 solutions. Observed O3 release from HPβCD and indigo oxidation confirmed that the formation of the inclusion complex is reversible. This proof-of-concept study demonstrates that HPβCD can complex O3 while preserving its reactivity. These results suggest that the use of clathrate stabilizers, such as HPβCD, can support the development of a facilitated-transport enabled ISCO for the O3treatment of groundwater contaminated with recalcitrant compounds.« less

Core-Shell Coating Silicon Anode Interfaces with Coordination Complex for Stable Lithium-Ion Batteries.

PubMed

Zhou, Jinqiu; Qian, Tao; Wang, Mengfan; Xu, Na; Zhang, Qi; Li, Qun; Yan, Chenglin

2016-03-02

In situ core-shell coating was used to improve the electrochemical performance of Si-based anodes with polypyrrole-Fe coordination complex. The vast functional groups in the organometallic coordination complex easily formed hydrogen bonds when in situ modifying commercial Si nanoparticles. The incorporation of polypyrrole-Fe resulted in the conformal conductive coating surrounding each Si nanoparticle, not only providing good electrical connection to the particles but also promoting the formation of a stable solid-electrolyte-interface layer on the Si electrode surface, enhancing the cycling properties. As an anode material for Li-ion batteries, modified silicon powders exhibited high reversible capacity (3567 mAh/g at 0.3 A/g), good rate property (549.12 mAh/g at 12 A/g), and excellent cycling performance (reversible capacity of 1500 mAh/g after 800 cycles at 1.2 A/g). The constructed novel concept of core-shell coating Si particles presented a promising route for facile and large-scale production of Si-based anodes for extremely durable Li-ion batteries, which provided a wide range of applications in the field of energy storage of the renewable energy derived from the solar energy, hydropower, tidal energy, and geothermal heat.

Bromamine Decomposition Revisited: A Holistic Approach for Analyzing Acid and Base Catalysis Kinetics.

PubMed

Wahman, David G; Speitel, Gerald E; Katz, Lynn E

2017-11-21

Chloramine chemistry is complex, with a variety of reactions occurring in series and parallel and many that are acid or base catalyzed, resulting in numerous rate constants. Bromide presence increases system complexity even further with possible bromamine and bromochloramine formation. Therefore, techniques for parameter estimation must address this complexity through thoughtful experimental design and robust data analysis approaches. The current research outlines a rational basis for constrained data fitting using Brønsted theory, application of the microscopic reversibility principle to reversible acid or base catalyzed reactions, and characterization of the relative significance of parallel reactions using fictive product tracking. This holistic approach was used on a comprehensive and well-documented data set for bromamine decomposition, allowing new interpretations of existing data by revealing that a previously published reaction scheme was not robust; it was not able to describe monobromamine or dibromamine decay outside of the conditions for which it was calibrated. The current research's simplified model (3 reactions, 17 constants) represented the experimental data better than the previously published model (4 reactions, 28 constants). A final model evaluation was conducted based on representative drinking water conditions to determine a minimal model (3 reactions, 8 constants) applicable for drinking water conditions.

Interactions between HIV-1 Reverse Transcriptase and the Downstream Template Strand in Stable Complexes with Primer-Template

PubMed Central

Rutvisuttinunt, Wiriya; Meyer, Peter R.; Scott, Walter A.

2008-01-01

Background Human immunodeficiency virus type 1 reverse transcriptase (HIV-1 RT) forms stable ternary complexes in which RT is bound tightly at fixed positions on the primer-template (P/T). We have probed downstream interactions between RT and the template strand in the complex containing the incoming dNTP (+1 dNTP•RT•P/T complex) and in the complex containing the pyrophosphate analog, foscarnet (foscarnet•RT•P/T complex). Methods and Results UV-induced cross-linking between RT and the DNA template strand was most efficient when a bromodeoxyuridine residue was placed in the +2 position (the first template position downstream from the incoming dNTP). Furthermore, formation of the +1 dNTP•RT•P/T complex on a biotin-containing template inhibited binding of streptavidin when biotin was in the +2 position on the template but not when the biotin was in the +3 position. Streptavidin pre-bound to a biotin residue in the template caused RT to stall two to three nucleotides upstream from the biotin residue. The downstream border of the complex formed by the stalled RT was mapped by digestion with exonuclease RecJF. UV-induced cross-linking of the complex formed by the pyrophosphate analog, foscarnet, with RT and P/T occurred preferentially with bromodeoxyuridine in the +1 position on the template in keeping with the location of RT one base upstream in the foscarnet•RT•P/T complex (i.e., in the pre-translocation position). Conclusions For +1 dNTP•RT•P/T and foscarnet•RT•P/T stable complexes, tight interactions were observed between RT and the first unpaired template nucleotide following the bound dNTP or the primer terminus, respectively. PMID:18974785

Exploring the directionality of Escherichia coli formate hydrogenlyase: a membrane-bound enzyme capable of fixing carbon dioxide to organic acid.

PubMed

Pinske, Constanze; Sargent, Frank

2016-10-01

During mixed-acid fermentation Escherichia coli produces formate, which is initially excreted out the cell. Accumulation of formate, and dropping extracellular pH, leads to biosynthesis of the formate hydrogenlyase (FHL) complex. FHL consists of membrane and soluble domains anchored within the inner membrane. The soluble domain comprises a [NiFe] hydrogenase and a formate dehydrogenase that link formate oxidation directly to proton reduction with the release of CO 2 and H 2 . Thus, the function of FHL is to oxidize excess formate at low pH. FHL subunits share identity with subunits of the respiratory Complex I. In particular, the FHL membrane domain contains subunits (HycC and HycD) that are homologs of NuoL/M/N and NuoH, respectively, which have been implicated in proton translocation. In this work, strain engineering and new assays demonstrate unequivocally the nonphysiological reverse activity of FHL in vivo and in vitro. Harnessing FHL to reduce CO 2 to formate is biotechnologically important. Moreover, assays for both possible FHL reactions provide opportunities to explore the bioenergetics using biochemical and genetic approaches. Comprehensive mutagenesis of hycC did not identify any single amino acid residues essential for FHL operation. However, the HycD E199, E201, and E203 residues were found to be critically important for FHL function. © 2016 The Authors. MicrobiologyOpen published by John Wiley & Sons Ltd.

Reversible 1,2-Addition of Water To Form a Nucleophilic Mn(I) Hydroxide Complex: A Thermodynamic and Reactivity Study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tondreau, Aaron M.; Michalczyk, Ryszard; Boncella, James M.

( iPrPN HP)Mn(CO) 2(OH) (2; iPrPN HP = HN{CH 2CH 2(P iPr 2)} 2) was formed from the reversible 1,2-addition of water to ( iPrPNP)Mn(CO) 2 (1; iPrPNP = the deprotonated, amide form of the ligand, –N{CH 2CH 2(P iPr 2)} 2). This reversible reaction was probed via variable-temperature NMR experiments, and the energetics of the 1,2-addition/elimination was found to be slightly exothermic (-0.8 kcal/mol). The corresponding manganese hydroxide was found to react with aldehydes, yielding the corresponding manganese carboxylate complexes ( iPrPN HP)Mn(CO) 2(CO 2R), where R = H, methyl, phenyl. While no reaction between 1 and neat benzaldehydemore » was observed, in the presence of water, conversion to the corresponding manganese-bound benzoate with formation of H 2 was observed. The catalytic oxidation of benzaldehyde by water without additives was unsuccessful due to strong product inhibition, with the manganese benzoate formed under a variety of reaction conditions. Upon addition of base, a catalytic cycle for the conversion of aldehyde to carboxylate and hydrogen can be devised.« less

Reversible 1,2-Addition of Water To Form a Nucleophilic Mn(I) Hydroxide Complex: A Thermodynamic and Reactivity Study

DOE PAGES

Tondreau, Aaron M.; Michalczyk, Ryszard; Boncella, James M.

2017-09-20

( iPrPN HP)Mn(CO) 2(OH) (2; iPrPN HP = HN{CH 2CH 2(P iPr 2)} 2) was formed from the reversible 1,2-addition of water to ( iPrPNP)Mn(CO) 2 (1; iPrPNP = the deprotonated, amide form of the ligand, –N{CH 2CH 2(P iPr 2)} 2). This reversible reaction was probed via variable-temperature NMR experiments, and the energetics of the 1,2-addition/elimination was found to be slightly exothermic (-0.8 kcal/mol). The corresponding manganese hydroxide was found to react with aldehydes, yielding the corresponding manganese carboxylate complexes ( iPrPN HP)Mn(CO) 2(CO 2R), where R = H, methyl, phenyl. While no reaction between 1 and neat benzaldehydemore » was observed, in the presence of water, conversion to the corresponding manganese-bound benzoate with formation of H 2 was observed. The catalytic oxidation of benzaldehyde by water without additives was unsuccessful due to strong product inhibition, with the manganese benzoate formed under a variety of reaction conditions. Upon addition of base, a catalytic cycle for the conversion of aldehyde to carboxylate and hydrogen can be devised.« less

Nitrite therapy after cardiac arrest reduces ROS generation, improves cardiac and neurological function and enhances survival via reversible inhibition of mitochondrial complex I

PubMed Central

Dezfulian, Cameron; Shiva, Sruti; Alekseyenko, Aleksey; Pendyal, Akshay; Beiser, DG; Munasinghe, Jeeva P.; Anderson, Stasia A.; Chesley, Christopher F.; Hoek, TL Vanden; Gladwin, Mark T.

2009-01-01

Background Three-fourths of cardiac arrest survivors die prior to hospital discharge or suffer significant neurological injury. Excepting therapeutic hypothermia and revascularization, no novel therapies have been developed that improve survival or cardiac and neurological function after resuscitation. Nitrite (NO2−) increases cellular resilience to focal ischemia-reperfusion injury in multiple organs. We hypothesized that nitrite therapy may improve outcomes after the unique global ischemia-reperfusion insult of cardiopulmonary arrest. Methods and Results We developed a mouse model of cardiac arrest characterized by 12-minutes of normothermic asystole and a high cardiopulmonary resuscitation (CPR) rate. In this model, global ischemia and CPR was associated with blood and organ nitrite depletion, reversible myocardial dysfunction, impaired alveolar gas exchange, neurological injury and an approximate 50% mortality. A single low dose of intravenous nitrite (50 nmol=1.85 μmol/kg=0.13 mg/kg) compared to blinded saline placebo given at CPR initiation with epinephrine improved cardiac function, survival and neurological outcomes. From a mechanistic standpoint, nitrite treatment restored intracardiac nitrite and increased S-nitrosothiol levels, decreased pathological cardiac mitochondrial oxygen consumption due to reactive oxygen species formation and prevented oxidative enzymatic injury via reversible specific inhibition of respiratory chain complex I. Conclusion Nitrite therapy after resuscitation from 12-minutes of asystole rapidly and reversibly modulated mitochondrial reactive oxygen species generation during early reperfusion, limiting acute cardiac dysfunction and death, as well as neurological impairment in survivors. PMID:19704094

Plasma wall sheath contributions to flux retention during the formation of field-reversed configurations

NASA Astrophysics Data System (ADS)

Milroy, R. D.; Slough, J. T.; Hoffman, A. L.

1984-06-01

Flux loss during field reversal on the TRX-1 field-reversed θ pinch is found to be much less than predicted by the inertial model of Green and Newton. This can be explained by a pressure bearing, conducting sheath which naturally forms at the wall and limits the flux loss. A one-dimensional (r-t) magnetohydrodynamic (MHD) numerical model has been used to study the formation and effectiveness of the sheath. The calculations are in excellent agreement with experimental measurements over a wide range of operating parameters. The results indicate that good flux trapping can be achieved through the field reversal phase of FRC formation with much slower external field reversal rates than in current experiments.

Contrasting Secondary Organic Aerosol Formation in Aerosol Liquid Water During Summer and Winter

NASA Astrophysics Data System (ADS)

El-Sayed, M.; Hennigan, C. J.

2017-12-01

In this study, we characterize the formation of aqueous secondary organic aerosols (aqSOA) in the eastern United States during summer and winter. The aim was to identify the main factors affecting the reversible and irreversible uptake of water-soluble organic gases to aerosol liquid water under variable influence from biogenic and anthropogenic sources. The reversible and irreversible uptake of water-soluble organic gases to aerosol water was measured in Baltimore, MD using a recently developed on-line method. The formation of aqSOA was observed during the summer and the winter; however, the amount of aqSOA varied significantly between the two seasons, as did the reversible and irreversible nature of the uptake. While the availability of aerosol liquid water (ALW) predominantly controlled aqSOA formation in the summer, wintertime aqSOA formation was limited by precursor VOCs as well. During the summer, aqSOA formation was tightly linked with isoprene oxidation, while the aqSOA formed in the winter was associated with biomass burning. Irreversible aqSOA was formed in both seasons; however, reversible aqSOA was only observed in the summer. Overall, these results demonstrate the importance of multi-phase chemistry in aerosol formation and underscore the significance of soluble organic gases partitioning to aerosol water both reversibly and irreversibly.

Posttranslational modifications of Sindbis virus glycoproteins: electrophoretic analysis of pulse-chase-labeled infected cells.

PubMed

Bonatti, S; Cancedda, F D

1982-04-01

Cytoplasmic extracts prepared from Sindbis virus-infected chicken embryo fibroblasts pulse-chase-labeled with [35S]methionine 6 h postinfection were analyzed on a highly resolving sodium dodecyl sulfate-gel either directly or after various treatments. The results we obtained suggest that (i) the proteolytic cleavage which converts PE2 to E2 glycoprotein takes place intracellularly, before or at least during the formation of complex-type oligosaccharide side chains; and (ii) E1 glycoprotein undergoes a complex maturation pattern. Newly synthesized E1 has a molecular weight of 53,000: shortly thereafter, this 53,000 (53K) form was converted to a 50K form. Subsequently, the 50K form decreased its apparent molecular weight progressively and eventually comigrated with E1 glycoprotein present in the extracellular virus, which displays a molecular weight of 51,000 to 52,000. The conversion of the 53K to the 50K form was not the result of a proteolytic processing and did not depend on glycosylation or disulfide bridge formation and exchange. The possible mechanisms of this conversion are discussed. The second conversion step (from the 50K to the 51-52K form) was due to the formation of complex-type oligosaccharide and was reversed by incubating the cellular extracts with neuraminidase before electrophoretic analysis.

A Design Principle for an Autonomous Post-translational Pattern Formation.

PubMed

Sugai, Shuhei S; Ode, Koji L; Ueda, Hiroki R

2017-04-25

Previous autonomous pattern-formation models often assumed complex molecular and cellular networks. This theoretical study, however, shows that a system composed of one substrate with multisite phosphorylation and a pair of kinase and phosphatase can generate autonomous spatial information, including complex stripe patterns. All (de-)phosphorylation reactions are described with a generic Michaelis-Menten scheme, and all species freely diffuse without pre-existing gradients. Computational simulation upon >23,000,000 randomly generated parameter sets revealed the design motifs of cyclic reaction and enzyme sequestration by slow-diffusing substrates. These motifs constitute short-range positive and long-range negative feedback loops to induce Turing instability. The width and height of spatial patterns can be controlled independently by distinct reaction-diffusion processes. Therefore, multisite reversible post-translational modification can be a ubiquitous source for various patterns without requiring other complex regulations such as autocatalytic regulation of enzymes and is applicable to molecular mechanisms for inducing subcellular localization of proteins driven by post-translational modifications. Copyright © 2017 The Author(s). Published by Elsevier Inc. All rights reserved.

Probing Aspergillus niger glucose oxidase with pentacyanoferrate(III) aza- and thia-complexes.

PubMed

Kulys, J; Tetianec, L; Ziemys, A

2006-10-01

Complexes of pentacyanoferrate(III) and biologically relevant ligands, such as pyridine, pyrazole, imidazole, histidine, and other aza- and thia-heterocycles, were synthesized. Their spectral, electrochemical properties, electron exchange constants, electronic structure parameters, and reactivity with glucose oxidase from Aspergillus niger were determined. The formation of the complexes following ammonia replacement by the ligands was associated with the appearance of a new band of absorbance in the visible spectrum. The constants of the complexes formation calculated at a ligand-pentacyanoferrate(III) concentrations ratio of 10:1, were 7.5 x 10(-5), 7.7 x 10(-5), and 1.8 x 10(-3) s(-1) for benzotriazole, benzimidazole, and aminothiazole ligands, respectively. The complexes showed quasi-reversible redox conversion at a glassy carbon electrode. The redox potential of the complexes spanned the potential range from 70 to 240 mV vs. saturated calomel electrode (SCE) at pH7.2. For most of the complexes self-exchange constants (k(11)) were similar to or larger than that of hexacyanoferrate(III) (ferricyanide). The complexes containing pyridine derivatives and thia-heterocyclic ligands held a lower value of k(11) than that of ferricyanide. All complexes reacted with reduced glucose oxidase at pH7.2. The reactivity of the complex containing pyrazole was the largest in comparison to the rest of the complexes. Correlations between the complexes' reactivity and both the free energy of reaction and k(11) shows that the reactivity of pentacyanoferrates obeys the principles of Marcus's electron transfer theory. The obtained data suggest that large negative charges of the complexes decrease their reactivity.

H3K9me3 demethylase Kdm4d facilitates the formation of pre-initiative complex and regulates DNA replication.

PubMed

Wu, Rentian; Wang, Zhiquan; Zhang, Honglian; Gan, Haiyun; Zhang, Zhiguo

2017-01-09

DNA replication is tightly regulated to occur once and only once per cell cycle. How chromatin, the physiological substrate of DNA replication machinery, regulates DNA replication remains largely unknown. Here we show that histone H3 lysine 9 demethylase Kdm4d regulates DNA replication in eukaryotic cells. Depletion of Kdm4d results in defects in DNA replication, which can be rescued by the expression of H3K9M, a histone H3 mutant transgene that reverses the effect of Kdm4d on H3K9 methylation. Kdm4d interacts with replication proteins, and its recruitment to DNA replication origins depends on the two pre-replicative complex components (origin recognition complex [ORC] and minichromosome maintenance [MCM] complex). Depletion of Kdm4d impairs the recruitment of Cdc45, proliferating cell nuclear antigen (PCNA), and polymerase δ, but not ORC and MCM proteins. These results demonstrate a novel mechanism by which Kdm4d regulates DNA replication by reducing the H3K9me3 level to facilitate formation of pre-initiative complex. © The Author(s) 2016. Published by Oxford University Press on behalf of Nucleic Acids Research.

The Regulation of Sox9 Gene Expression by the GATA4/FOG2 Transcriptional Complex in Dominant XX Sex Reversal Mouse Models.

PubMed Central

Manuylov, Nikolay L.; Fujiwara, Yuko; Adameyko, Igor I.; Poulat, Francis

2007-01-01

We have previously established an in vivo requirement for GATA4 and FOG2 transcription factors in sexual differentiation. Fog2 null mouse fetuses or fetuses homozygous for a targeted mutation in Gata4 (Gata4ki), which cripples the GATA4-FOG2 interaction, exhibit a profound and early block in testis differentiation in both sexes. Others have shown that XX mice with the Ods transgenic insertion or the Wt1-Sox9 YAC transgene overexpress the testis differentiation gene, Sox9. Thus, these XX animals undergo dominant sex-reversal by developing into phenotypically normal, but sterile, males. Now we have determined that Fog2 haploinsufficiency prevents (suppresses) this dominant sex-reversal and Fog2+/− Wt1-Sox9 or Ods XX animals develop normally - as fertile females. The suppression of sex-reversal in Fog2 heterozygous females results from approximately 50% downregulation of the expression from the transgene-associated allele of Sox9. The GATA4/FOG2-dependent sex reversal observed in the transgenic XX gonads has to rely on gene targets other than the Y chromosome-linked Sry gene. Importantly, Fog2 null or Gata4ki/ki embryos (either XX or XY) fail to express detectable levels of Sox9 despite carrying the Ods mutation or Wt1-Sox9 transgene. Fog2 haploinsufficiency leads to a decreased amount of SOX9-positive cells in XY gonads. We conclude that FOG2 is a limiting factor in the formation of a functional GATA4/FOG2 transcription complex that is required for Sox9 expression during gonadogenesis. PMID:17540364

Topological-charge-driven reversal of ferromagnetic rings via 360∘ domain-wall formation

NASA Astrophysics Data System (ADS)

Oyarce, A. L. Gonzalez; Trypiniotis, T.; Roy, P. E.; Barnes, C. H. W.

2013-05-01

We study the reversal mechanism between opposite closed flux states of ferromagnetic nanorings driven by an azimuthal magnetic field. The reversal proceeds via the formation of 360∘ domain walls, and we show that the role of interacting nucleation sites is essential for the process to take place. Such nucleation is seen to create domain walls with the right topological charge conditions for 360∘ domain-wall formation. Given the symmetry of the system, we utilize an energetic description as a function of the azimuthal field magnitude, which clearly reveals the different stages of this reversal process. The annihilation of the 360∘ domain walls that is necessary for the reversal process to complete is controlling the field value at the final stage of the process. Such a fundamental mechanism for ring reversal has several implications and will guide the design of the various data-storage-device proposals based on nanorings.

Closing the data gap: Creating an open data environment

NASA Astrophysics Data System (ADS)

Hester, J. R.

2014-02-01

Poor data management brought on by increasing volumes of complex data undermines both the integrity of the scientific process and the usefulness of datasets. Researchers should endeavour both to make their data citeable and to cite data whenever possible. The reusability of datasets is improved by community adoption of comprehensive metadata standards and public availability of reversibly reduced data. Where standards are not yet defined, as much information as possible about the experiment and samples should be preserved in datafiles written in a standard format.

A theoretical investigation into the strength of N-NO2 bonds, ring strain and electrostatic potential upon formation of intermolecular H-bonds between HF and the nitro group in nitrogen heterocyclic rings C n H2n N-NO2 (n = 2-5), RDX and HMX.

PubMed

Wang, Bao-Guo; Ren, Fu-de; Shi, Wen-Jing

2015-11-01

Changes in N-NO2 bond strength, ring strain energy and electrostatic potential upon formation of intermolecular H-bonds between HF and the nitro group in nitrogen heterocyclic rings C n H2n N-NO2 (n = 2-5), RDX and HMX were investigated using DFT-B3LYP and MP2(full) methods with the 6-311++G(2df,2p) and aug-cc-pVTZ basis sets. Analysis of electron density shifts was also carried out. The results indicate that H-bonding energy correlates well with the increment of ring strain energy. Upon complex formation, the strength of the N-NO2 trigger-bond is enhanced, suggesting reduced sensitivity, while judged by the increased ring strain energy, sensitivity is increased. However, some features of the molecular surface electrostatic potential, such as a local maximum above the N-NO2 bond and ring, σ + (2) and electrostatic balance parameter ν, remain essentially unchanged upon complex formation, and only a small change in the impact sensitivity h 50 is suggested. It is not sufficient to determine sensitivity solely on the basis of trigger bond or ring strain; as a global feature of a molecule, the molecular surface electrostatic potential is available to help judge the change of sensitivity in H-bonded complexes. Graphical Abstract The strengthened N-NO2 bond suggests reduced sensitivity, while it is reverse by theincreased ring strain energy upon the complex formation. However, the molecular surfaceelectrostatic potential (V S) shows the little change of h 50. The V S should be taken into accountin the analysis of explosive sensitivity in the H-bonded complex.

A New Synthetic Route to N-Benzyl Carboxamides through the Reverse Reaction of N-Substituted Formamide Deformylase

PubMed Central

Hashimoto, Yoshiteru; Sakashita, Toshihide; Fukatsu, Hiroshi; Sato, Hiroyoshi

2014-01-01

Previously, we isolated a new enzyme, N-substituted formamide deformylase, that catalyzes the hydrolysis of N-substituted formamide to the corresponding amine and formate (H. Fukatsu, Y. Hashimoto, M. Goda, H. Higashibata, and M. Kobayashi, Proc. Natl. Acad. Sci. U. S. A. 101:13726–13731, 2004, doi:10.1073/pnas.0405082101). Here, we discovered that this enzyme catalyzed the reverse reaction, synthesizing N-benzylformamide (NBFA) from benzylamine and formate. The reverse reaction proceeded only in the presence of high substrate concentrations. The effects of pH and inhibitors on the reverse reaction were almost the same as those on the forward reaction, suggesting that the forward and reverse reactions are both catalyzed at the same catalytic site. Bisubstrate kinetic analysis using formate and benzylamine and dead-end inhibition studies using a benzylamine analogue, aniline, revealed that the reverse reaction of this enzyme proceeds via an ordered two-substrate, two-product (bi-bi) mechanism in which formate binds first to the enzyme active site, followed by benzylamine binding and the subsequent release of NBFA. To our knowledge, this is the first report of the reverse reaction of an amine-forming deformylase. Surprisingly, analysis of the substrate specificity for acids demonstrated that not only formate, but also acetate and propionate (namely, acids with numbers of carbon atoms ranging from C1 to C3), were active as acid substrates for the reverse reaction. Through this reaction, N-substituted carboxamides, such as NBFA, N-benzylacetamide, and N-benzylpropionamide, were synthesized from benzylamine and the corresponding acid substrates. PMID:24123742

Multi-functional bis(alkynyl)gold(iii) N⁁C complexes with distinct mechanochromic luminescence and electroluminescence properties† †Electronic supplementary information (ESI) available: CCDC 1552808. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c7sc02410j

PubMed Central

Wong, Ben Yiu-Wing; Wong, Hok-Lai; Wong, Yi-Chun; Au, Vonika Ka-Man

2017-01-01

A new class of donor–acceptor type luminescent bis(alkynyl)gold(iii) N⁁C complexes has been synthesized and characterized. These gold(iii) complexes not only exhibit high photoluminescence quantum yields of up to 0.81, but also interesting mechanochromic luminescence behaviors that are reversible. Upon grinding, a dramatic luminescence color change from green to red can be observed in solid samples of the gold(iii) complexes, and the mechanochromic luminescence can be readily tuned via a judicious selection of substituents on the pyridine ring. In addition, solution-processable OLEDs based on this class of complexes with EQE values of up to 4.0% have been realized, representing the first demonstration of bis(alkynyl)gold(iii) N⁁C complexes as emissive materials in solution-processable OLEDs. PMID:29147519

Directed formation of micro- and nanoscale patterns of functional light-harvesting LH2 complexes.

PubMed

Reynolds, Nicholas P; Janusz, Stefan; Escalante-Marun, Maryana; Timney, John; Ducker, Robert E; Olsen, John D; Otto, Cees; Subramaniam, Vinod; Leggett, Graham J; Hunter, C Neil

2007-11-28

The precision placement of the desired protein components on a suitable substrate is an essential prelude to any hybrid "biochip" device, but a second and equally important condition must also be met: the retention of full biological activity. Here we demonstrate the selective binding of an optically active membrane protein, the light-harvesting LH2 complex from Rhodobacter sphaeroides, to patterned self-assembled monolayers at the micron scale and the fabrication of nanometer-scale patterns of these molecules using near-field photolithographic methods. In contrast to plasma proteins, which are reversibly adsorbed on many surfaces, the LH2 complex is readily patterned simply by spatial control of surface polarity. Near-field photolithography has yielded rows of light-harvesting complexes only 98 nm wide. Retention of the native optical properties of patterned LH2 molecules was demonstrated using in situ fluorescence emission spectroscopy.

SKLB060 Reversibly Binds to Colchicine Site of Tubulin and Possesses Efficacy in Multidrug-Resistant Cell Lines.

PubMed

Yan, Wei; Yang, Tao; Yang, Jianhong; Wang, Taijin; Yu, Yamei; Wang, Yuxi; Chen, Qiang; Bai, Peng; Li, Dan; Ye, Haoyu; Qiu, Qiang; Zhou, Yongzhao; Hu, Yiguo; Yang, Shengyong; Wei, Yuquan; Li, Weimin; Chen, Lijuan

2018-05-22

Many tubulin inhibitors are in clinical use as anti-cancer drugs. In our previous study, a novel series of 4-substituted coumarins derivatives were identified as novel tubulin inhibitors. Here, we report the anti-cancer activity and underlying mechanism of one of the 4-substituted coumarins derivatives (SKLB060). The anti-cancer activity of SKLB060 was tested on 13 different cancer cell lines and four xenograft cancer models. Immunofluorescence staining, cell cycle analysis, and tubulin polymerization assay were employed to study the inhibition of tubulin. N, N '-Ethylenebis(iodoacetamide) assay was used to measure binding to the colchicine site. Wound-healing migration and tube formation assays were performed on human umbilical vascular endothelial cells to study anti-vascular activity (the ability to inhibit blood vessel growth). Mitotic block reversibility and structural biology assays were used to investigate the SKLB060-tubulin bound model. SKLB060 inhibited tubulin polymerization and subsequently induced G2/M cell cycle arrest and apoptosis in cancer cells. SKLB060 bound to the colchicine site of β-tubulin and showed antivascular activity in vitro. Moreover, SKLB060 induced reversible cell cycle arrest and reversible inhibition of tubulin polymerization. A mitotic block reversibility assay showed that the effects of SKLB060 have greater reversibility than those of colcemid (a reversible tubulin inhibitor), indicating that SKLB060 binds to tubulin in a totally reversible manner. The crystal structures of SKLB060-tubulin complexes confirmed that SKLB060 binds to the colchicine site, and the natural coumarin ring in SKLB060 enables reversible binding. These results reveal that SKLB060 is a powerful and reversible microtubule inhibitor that binds to the colchicine site and is effective in multidrug-resistant cell lines. © 2018 The Author(s). Published by S. Karger AG, Basel.

Speciation of chromium using reversed phase-high performance liquid chromatography coupled to different spectrometric detection methods

NASA Astrophysics Data System (ADS)

Andrle, C. M.; Jakubowski, N.; Broekaert, J. A. C.

1997-02-01

Speciation of Cr(III) and Cr(VI) based on the formation of different complexes with ammonium-pyrrolidinedithioate (APDC) in a continuous flow technique and their preconcentration using solid phase extraction (SPE) have been elaborated and applied to the analysis of waste waters from the galvanic industry. The Cr complexes were separated and determined using reversed phase-high performance liquid chromatography (RP-HPLC) coupled to different detection methods, namely UV-detection, graphite furnace-atomic absorption spectrometry (GF-AAS) and inductively coupled plasma mass spectrometry with hydraulic high pressure nebulization (HHPN/ICP-MS). After optimization the detection limits for Cr(III) and Cr(VI) of all methods are at the μg 1 -1 level and the precision in terms of RSD is 5% ( cCr = 100 μg 1 -1, N = 10). The procedure was applied to the determination of Cr(III) and Cr(VI) at the μg 1 -1 level in galvanic waste waters, and its accuracy was approved by comparing the results with those of independent methods.

Electrochemical biosensor based on enzyme substrate as a linker: Application for aldolase activity with pectin-thionine complex as recognization element and signal amplification probe.

PubMed

Wang, Xiaonan; Wang, Meiwen; Zhang, Yuanyuan; Miao, Xiaocao; Huang, Yuanyuan; Zhang, Juan; Sun, Lizhou

2016-09-15

A new strategy to fabricate electrochemical biosensor is reported based on the linkage of enzyme substrate, thereby an electrochemical method to detect aldolase activity is established using pectin-thionine complex (PTC) as recognization element and signal probe. The linkage effect of fructose-1,6-bisphosphate (FBP), the substrate of aldolase, can be achieved via its strong binding to magnetic nanoparticles (MNPs)/aminophenylboronic acid (APBA) and the formation of phosphoramidate bond derived from its reaction with p-phenylenediamine (PDA) on the surface of electrode. Aldolase can reversibly catalyze the substrates into the products which have no binding capacity with MNPs/APBA, resulting in the exposure of the corresponding binding sites and its subsequent recognization on signal probe. Meanwhile, signal amplification can be accomplished by using the firstly prepared PTC which can bind with MNPs/APBA, and accuracy can be strengthened through magnetic separation. With good precision and accuracy, the established sensor may be extended to other proteins with reversible catalyzed ability. Copyright © 2016 Elsevier B.V. All rights reserved.

Activation of Latent Dihydroorotase from Aquifex aeolicus by Pressure*

PubMed Central

Hervé, Guy; Evans, Hedeel Guy; Fernado, Roshini; Patel, Chandni; Hachem, Fatme; Evans, David R.

2017-01-01

Elevated hydrostatic pressure was used to probe conformational changes of Aquifex aeolicus dihydroorotase (DHO), which catalyzes the third step in de novo pyrimidine biosynthesis. The isolated protein, a 45-kDa monomer, lacks catalytic activity but becomes active upon formation of a dodecameric complex with aspartate transcarbamoylase (ATC). X-ray crystallographic studies of the isolated DHO and of the complex showed that association induces several major conformational changes in the DHO structure. In the isolated DHO, a flexible loop occludes the active site blocking the access of substrates. The loop is mostly disordered but is tethered to the active site region by several electrostatic and hydrogen bonds. This loop becomes ordered and is displaced from the active site upon formation of DHO-ATC complex. The application of pressure to the complex causes its time-dependent dissociation and the loss of both DHO and ATC activities. Pressure induced irreversible dissociation of the obligate ATC trimer, and as a consequence the DHO is also inactivated. However, moderate hydrostatic pressure applied to the isolated DHO subunit mimics the complex formation and reversibly activates the isolated subunit in the absence of ATC, suggesting that the loop has been displaced from the active site. This effect of pressure is explained by the negative volume change associated with the disruption of ionic interactions and exposure of ionized amino acids to the solvent (electrostriction). The interpretation that the loop is relocated by pressure was validated by site-directed mutagenesis and by inhibition by small peptides that mimic the loop residues. PMID:27746403

Geomagnetic Reversals of the Late Jurassic and Early Cretaceous Captured in a North China Core

NASA Astrophysics Data System (ADS)

Kuhn, T.; Fu, R. R.; Kent, D. V.; Olsen, P. E.

2016-12-01

The Tuchengzi formation in North China nominally spans nearly 20 million years of the Late Jurassic and Early Cretaceous, an interval during which age calibration of the Geomagnetic Polarity Time Scale (GPTS) based on seafloor magnetic anomalies is poorly known. The overlying Yixian formation is of special paleontological interest due to an abundance of spectacularly preserved macrofossils of feathered non-avian dinosaurs, birds, mammals, and insects. Scarce fossils in the Tuchengzi, sparse accurate radiometric dates on both the Tuchengzi and overlying Yixian formation, and scant previous paleomagnetic studies on these formations motivated our application of magnetostratigraphy as a geochronological tool. We constructed a geomagnetic reversal sequence from the upper 142m of a 200m core extracted in Liaoning Province at Huangbanjigou spanning the lower Yixian Formation and the unconformably underlying Tuchengzi Formation. Thermal demagnetization up to 680°C in steps of 25-50°C revealed predominantly normal overprints consistent with the modern day field with unblocking temperatures between 125°C and as high as 550°C, as well as normal and reverse characteristic components with unblocking temperatures between 500°C and 680°C. Going up from the base of the core, there is a reverse polarity magnetozone >6m thick, followed by a 5m normal magnetozone, a 10m reverse magnetozone, a 25m normal magnetozone, and a 6m reverse magnetozone truncated by the Yixian-Tuchengzi unconformity. Above the unconformity, all 81m of core were normal. These results indicate that a meaningful polarity stratigraphy can be recovered from the Tuchengzi and Yixian formations that will be invaluable for correlations across the Tuchengzi and potentially the Yixian formations, which span thousands of square kilometers and vary in thickness by many hundreds of meters. The results also demonstrate that, in combination with accurate and precise radiometric dates, the Tuchengzi Formation has the potential to provide tight constraints on presently poorly constrained Late Jurassic and Early Cretaceous parts of the GPTS and provide an independent reversal time scale by which seafloor-anomaly based time scales can be refined.

Carbinolamine Formation and Dehydration in a DNA Repair Enzyme Active Site

PubMed Central

Dodson, M. L.; Walker, Ross C.; Lloyd, R. Stephen

2012-01-01

In order to suggest detailed mechanistic hypotheses for the formation and dehydration of a key carbinolamine intermediate in the T4 pyrimidine dimer glycosylase (T4PDG) reaction, we have investigated these reactions using steered molecular dynamics with a coupled quantum mechanics–molecular mechanics potential (QM/MM). We carried out simulations of DNA abasic site carbinolamine formation with and without a water molecule restrained to remain within the active site quantum region. We recovered potentials of mean force (PMF) from thirty replicate reaction trajectories using Jarzynski averaging. We demonstrated feasible pathways involving water, as well as those independent of water participation. The water–independent enzyme–catalyzed reaction had a bias–corrected Jarzynski–average barrier height of approximately for the carbinolamine formation reaction and ) for the reverse reaction at this level of representation. When the proton transfer was facilitated with an intrinsic quantum water, the barrier height was approximately in the forward (formation) reaction and for the reverse. In addition, two modes of unsteered (free dynamics) carbinolamine dehydration were observed: in one, the quantum water participated as an intermediate proton transfer species, and in the other, the active site protonated glutamate hydrogen was directly transferred to the carbinolamine oxygen. Water–independent unforced proton transfer from the protonated active site glutamate carboxyl to the unprotonated N–terminal amine was also observed. In summary, complex proton transfer events, some involving water intermediates, were studied in QM/MM simulations of T4PDG bound to a DNA abasic site. Imine carbinolamine formation was characterized using steered QM/MM molecular dynamics. Dehydration of the carbinolamine intermediate to form the final imine product was observed in free, unsteered, QM/MM dynamics simulations, as was unforced acid-base transfer between the active site carboxylate and the N–terminal amine. PMID:22384015

A complex structure in the mRNA of Tf1 is recognized and cleaved to generate the primer of reverse transcription.

PubMed

Lin, J H; Levin, H L

1997-01-15

All retroviruses and LTR-containing retrotransposons are thought to require specific tRNA molecules to serve as primers of reverse transcription. An exception is the LTR-containing retrotransposon Tf1, isolated from Schizosaccharomyces pombe. Instead of requiring a tRNA, the reverse transcriptase of Tf1 uses the first 11 bases of the Tf1 transcript as the primer for reverse transcription. The primer is generated by a cleavage that occurs between bases 11 and 12 of the Tf1 mRNA. Sequence analysis of the 5' untranslated region of the Tf1 mRNA resulted in the identification of a region with the potential to form an RNA structure of 89 bases that included the primer binding site and the first 11 bases of the Tf1 mRNA. Systematic mutagenesis of this region revealed 34 single-point mutants in the structure that resulted in reduced transposition activity. The defects in transposition correlated with reduced level of Tf1 reverse transcripts as determined by DNA blot analysis. Evidence that the RNA structure did form in vivo included the result that strains with second site mutations that restored complementarity resulted in increased levels of reverse transcripts and Tf1 transposition. The majority of the mutants defective for reverse transcription were unable to cleave the Tf1 mRNA between bases 11 and 12. These data indicate that formation of an extensive RNA structure was required for the cleavage reaction that generated the primer for Tf1 reverse transcription.

Reversible inhibition of PSD-95 mRNA translation by miR-125a, FMRP phosphorylation and mGluR signaling

PubMed Central

Muddashetty, Ravi S.; Nalavadi, Vijayalaxmi C.; Gross, Christina; Yao, Xiaodi; Xing, Lei; Laur, Oskar; Warren, Stephen T.; Bassell, Gary J.

2011-01-01

Summary The molecular mechanism how RISC and microRNAs selectively and reversibly regulate mRNA translation in response to receptor signaling is unknown but could provide a means for temporal and spatial control of translation. Here we show that miR-125a targeting PSD-95 mRNA allows reversible inhibition of translation and regulation by mGluR signaling. Inhibition of miR-125a increased PSD-95 levels in dendrites and altered dendritic spine morphology. Bidirectional control of PSD-95 expression depends on miR-125a and FMRP phosphorylation status. miR-125a levels at synapses and its association with AGO2 is reduced in Fmr1 KO. FMRP phosphorylation promotes the formation of an AGO2-miR-125a inhibitory complex on PSD-95 mRNA, whereas mGluR signaling of translation requires FMRP dephosphorylation and release of AGO2 from the mRNA. These findings reveal a novel mechanism whereby FMRP phosphorylation provides a reversible switch for AGO2 and microRNA to selectively regulate mRNA translation at synapses in response to receptor activation. PMID:21658607

Hydrogen evolution in [NiFe] hydrogenases and related biomimetic systems: similarities and differences.

PubMed

Das, Ranjita; Neese, Frank; van Gastel, Maurice

2016-09-21

In this work, a detailed quantum chemical study of the mechanism of [Ni(bdt)(dppf)] (Ni(II)L) catalyzed hydrogen formation [A. Gan, T. L. Groy, P. Tarakeshwar, S. K. S. Mazinani, J. Shearer, V. Mujica and A. K. Jones, J. Am. Chem. Soc., 2015, 137, 1109-1115] following an electro-chemical-electro-chemical (ECEC) pathway is reported. The complex exclusively catalyzes the reduction of protons to molecular hydrogen. The calculations suggest that the first one-electron reduction of the [Ni(II)L] catalyst is the rate limiting step of the catalytic cycle and hence, the buildup of detectable reaction intermediates is not expected. The catalytic activity of the [Ni(II)L] complex is facilitated by the flexibility of the ligand system, which allows the ligand framework to adapt to changes in the Ni oxidation state over the course of the reaction. Additionally, a comparison is made with the catalytic activity of [NiFe] hydrogenase. It is argued that the directionality of the reversible hydrogen formation reaction is controlled by the ligand field of the nickel ion and the possibility for side-on (η(2)) binding of H2: if the ligand framework does not allow for η(2) binding of H2, as is the case for [Ni(II)L], the catalyst irreversibly reduces protons. If the ligand field allows η(2) binding of H2, the catalyst can in principle work reversibly. The conditions for η(2) binding are discussed.

Molecular modeling studies of HIV-1 reverse transcriptase nonnucleoside inhibitors: total energy of complexation as a predictor of drug placement and activity.

PubMed Central

Kroeger Smith, M. B.; Rouzer, C. A.; Taneyhill, L. A.; Smith, N. A.; Hughes, S. H.; Boyer, P. L.; Janssen, P. A.; Moereels, H.; Koymans, L.; Arnold, E.

1995-01-01

Computer modeling studies have been carried out on three nonnucleoside inhibitors complexed with human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT), using crystal coordinate data from a subset of the protein surrounding the binding pocket region. Results from the minimizations of solvated complexes of 2-cyclopropyl-4-methyl-5,11-dihydro-5H-dipyrido[3,2-b :2',3'-e][1,4] diazepin-6-one (nevirapine), alpha-anilino-2, 6-dibromophenylacetamide (alpha-APA), and 8-chloro-tetrahydro-imidazo(4,5,1-jk)(1,4)-benzodiazepin-2(1H)-thi one (TIBO) show that all three inhibitors maintain a very similar conformational shape, roughly overlay each other in the binding pocket, and appear to function as pi-electron donors to aromatic side-chain residues surrounding the pocket. However, side-chain residues adapt to each bound inhibitor in a highly specific manner, closing down around the surface of the drug to make tight van der Waals contacts. Consequently, the results from the calculated minimizations reveal that only when the inhibitors are modeled in a site constructed from coordinate data obtained from their particular RT complex can the calculated binding energies be relied upon to predict the correct orientation of the drug in the pocket. In the correct site, these binding energies correlate with EC50 values determined for all three inhibitors in our laboratory. Analysis of the components of the binding energy reveals that, for all three inhibitors, solvation of the drug is endothermic, but solvation of the protein is exothermic, and the sum favors complex formation. In general, the protein is energetically more stable and the drug less stable in their complexes as compared to the reactant conformations. For all three inhibitors, interaction with the protein in the complex is highly favorable. Interactions of the inhibitors with individual residues correlate with crystallographic and site-specific mutational data. pi-Stacking interactions are important in binding and correlate with drug HOMO RHF/6-31G* energies. Modeling results are discussed with respect to the mechanism of complex formation and the design of nonnucleoside inhibitors that will be more effective against mutants of HIV-1 RT that are resistant to the currently available drugs. PMID:8535257

Reversible solvatomagnetic switching in a single-ion magnet from an entatic state† †Electronic supplementary information (ESI) available: Preparation methods and physical characterization data. Crystallographic refinement and computational details. Additional figures (Fig. S1–S12) and tables (Tables S1–S5). CCDC 952077 and 938463. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c6sc05188j Click here for additional data file. Click here for additional data file.

PubMed Central

Vallejo, J.; Viciano-Chumillas, M.; Castro, I.; Amorós, P.; Déniz, M.; Ruiz-Pérez, C.; Yuste-Vivas, C.; Krzystek, J.; Julve, M.; Lloret, F.

2017-01-01

A vast impact on molecular nanoscience can be achieved using simple transition metal complexes as dynamic chemical systems to perform specific and selective tasks under the control of an external stimulus that switches “ON” and “OFF” their electronic properties. While the interest in single-ion magnets (SIMs) lies in their potential applications in information storage and quantum computing, the switching of their slow magnetic relaxation associated with host–guest processes is insufficiently explored. Herein, we report a unique example of a mononuclear cobalt(ii) complex in which geometrical constraints are the cause of easy and reversible water coordination and its release. As a result, a reversible and selective colour and SIM behaviour switch occurs between a “slow-relaxing” deep red anhydrous material (compound 1) and its “fast-relaxing” orange hydrated form (compound 2). The combination of this optical and magnetic switching in this new class of vapochromic and thermochromic SIMs offers fascinating possibilities for designing multifunctional molecular materials. PMID:28580105

The influence of a reverse-reactivated normal fault on natural fracture geometries and relative chronologies at Castle Cove, Otway Basin

NASA Astrophysics Data System (ADS)

Debenham, Natalie; King, Rosalind C.; Holford, Simon P.

2018-07-01

Despite the ubiquity of normal faults that have undergone compressional inversion, documentation of the structural history of natural fractures around these structures is limited. In this paper, we investigate the geometries and relative chronologies of natural fractures adjacent to a reverse-reactivated normal fault, the Castle Cove Fault in the Otway Basin, southeast Australia. Local variations in strain resulted in greater deformation within the fault damage zone closer to the fault. Structural mapping within the damage zone reveals a complex tectonic history recording both regional and local perturbations in stress and a total of 11 fracture sets were identified, with three sets geometrically related to the Castle Cove Fault. The remaining fracture sets formed in response to local stresses at Castle Cove. Rifting in the late Cretaceous resulted in normal movement of the Castle Cove Fault and associated rollover folding, and the formation of the largest fracture set. Reverse-reactivation of the fault and associated anticlinal folding occurred during late Miocene to Pliocene compression. Rollover folding may have provided structural traps if seals were not breached by fractures, however anticlinal folding likely post-dated the main episodes of hydrocarbon generation and migration in the region. This study highlights the need to conduct careful reconstruction of the structural histories of fault zones that experienced complex reactivation histories when attempting to define off-fault fluid flow properties.

Modeling generic aspects of ideal fibril formation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Michel, D., E-mail: denis.michel@live.fr

Many different proteins self-aggregate into insoluble fibrils growing apically by reversible addition of elementary building blocks. But beyond this common principle, the modalities of fibril formation are very disparate, with various intermediate forms which can be reshuffled by minor modifications of physico-chemical conditions or amino-acid sequences. To bypass this complexity, the multifaceted phenomenon of fibril formation is reduced here to its most elementary principles defined for a linear prototype of fibril. Selected generic features, including nucleation, elongation, and conformational recruitment, are modeled using minimalist hypotheses and tools, by separating equilibrium from kinetic aspects and in vitro from in vivo conditions.more » These reductionist approaches allow to bring out known and new rudiments, including the kinetic and equilibrium effects of nucleation, the dual influence of elongation on nucleation, the kinetic limitations on nucleation and fibril numbers, and the accumulation of complexes in vivo by rescue from degradation. Overlooked aspects of these processes are also pointed: the exponential distribution of fibril lengths can be recovered using various models because it is attributable to randomness only. It is also suggested that the same term “critical concentration” is used for different things, involved in either nucleation or elongation.« less

Modeling generic aspects of ideal fibril formation

NASA Astrophysics Data System (ADS)

Michel, D.

2016-01-01

Many different proteins self-aggregate into insoluble fibrils growing apically by reversible addition of elementary building blocks. But beyond this common principle, the modalities of fibril formation are very disparate, with various intermediate forms which can be reshuffled by minor modifications of physico-chemical conditions or amino-acid sequences. To bypass this complexity, the multifaceted phenomenon of fibril formation is reduced here to its most elementary principles defined for a linear prototype of fibril. Selected generic features, including nucleation, elongation, and conformational recruitment, are modeled using minimalist hypotheses and tools, by separating equilibrium from kinetic aspects and in vitro from in vivo conditions. These reductionist approaches allow to bring out known and new rudiments, including the kinetic and equilibrium effects of nucleation, the dual influence of elongation on nucleation, the kinetic limitations on nucleation and fibril numbers, and the accumulation of complexes in vivo by rescue from degradation. Overlooked aspects of these processes are also pointed: the exponential distribution of fibril lengths can be recovered using various models because it is attributable to randomness only. It is also suggested that the same term "critical concentration" is used for different things, involved in either nucleation or elongation.

The role of Proteus mirabilis cell wall features in biofilm formation.

PubMed

Czerwonka, Grzegorz; Guzy, Anna; Kałuża, Klaudia; Grosicka, Michalina; Dańczuk, Magdalena; Lechowicz, Łukasz; Gmiter, Dawid; Kowalczyk, Paweł; Kaca, Wiesław

2016-11-01

Biofilms formed by Proteus mirabilis strains are a serious medical problem, especially in the case of urinary tract infections. Early stages of biofilm formation, such as reversible and irreversible adhesion, are essential for bacteria to form biofilm and avoid eradication by antibiotic therapy. Adhesion to solid surfaces is a complex process where numerous factors play a role, where hydrophobic and electrostatic interactions with solid surface seem to be substantial. Cell surface hydrophobicity and electrokinetic potential of bacterial cells depend on their surface composition and structure, where lipopolysaccharide, in Gram-negative bacteria, is prevailing. Our studies focused on clinical and laboratory P. mirabilis strains, where laboratory strains have determined LPS structures. Adherence and biofilm formation tests revealed significant differences between strains adhered in early stages of biofilm formation. Amounts of formed biofilm were expressed by the absorption of crystal violet. Higher biofilm amounts were formed by the strains with more negative values of zeta potential. In contrast, high cell surface hydrophobicity correlated with low biofilm amount.

An inhibitor of eIF2 activity in the sRNA pool of eukaryotic cells.

PubMed

Centrella, Michael; Porter, David L; McCarthy, Thomas L

2011-08-15

Eukaryotic protein synthesis is a multi-step and highly controlled process that includes an early initiation complex containing eukaryotic initiation factor 2 (eIF2), GTP, and methionine-charged initiator methionyl-tRNA (met-tRNAi). During studies to reconstruct formation of the ternary complex containing these molecules, we detected a potent inhibitor in low molecular mass RNA (sRNA) preparations of eukaryotic tRNA. The ternary complex inhibitor (TCI) was retained in the total sRNA pool after met-tRNAi was charged by aminoacyl tRNA synthetase, co-eluted with sRNA by size exclusion chromatography, but resolved from met-tRNAi by ion exchange chromatography. The adverse effect of TCI was not overcome by high GTP or magnesium omission and was independent of GTP regeneration. Rather, TCI suppressed the rate of ternary complex formation, and disrupted protein synthesis and the accumulation of heavy polymeric ribosomes in reticulocyte lysates in vitro. Lastly, a component or components in ribosome depleted cell lysate significantly reversed TCI activity. Since assembly of the met-tRNAi/eIF2/GTP ternary complex is integral to protein synthesis, awareness of TCI is important to avoid confusion in studies of translation initiation. A clear definition of TCI may also allow a better appreciation of physiologic or pathologic situations, factors, and events that control protein synthesis in vivo. Copyright © 2011 Elsevier B.V. All rights reserved.

Galaxy and Mass Assembly (GAMA): halo formation times and halo assembly bias on the cosmic web

NASA Astrophysics Data System (ADS)

Tojeiro, Rita; Eardley, Elizabeth; Peacock, John A.; Norberg, Peder; Alpaslan, Mehmet; Driver, Simon P.; Henriques, Bruno; Hopkins, Andrew M.; Kafle, Prajwal R.; Robotham, Aaron S. G.; Thomas, Peter; Tonini, Chiara; Wild, Vivienne

2017-09-01

We present evidence for halo assembly bias as a function of geometric environment (GE). By classifying Galaxy and Mass Assembly (GAMA) galaxy groups as residing in voids, sheets, filaments or knots using a tidal tensor method, we find that low-mass haloes that reside in knots are older than haloes of the same mass that reside in voids. This result provides direct support to theories that link strong halo tidal interactions with halo assembly times. The trend with GE is reversed at large halo mass, with haloes in knots being younger than haloes of the same mass in voids. We find a clear signal of halo downsizing - more massive haloes host galaxies that assembled their stars earlier. This overall trend holds independently of GE. We support our analysis with an in-depth exploration of the L-Galaxies semi-analytic model, used here to correlate several galaxy properties with three different definitions of halo formation time. We find a complex relationship between halo formation time and galaxy properties, with significant scatter. We confirm that stellar mass to halo mass ratio, specific star formation rate (SFR) and mass-weighed age are reasonable proxies of halo formation time, especially at low halo masses. Instantaneous SFR is a poor indicator at all halo masses. Using the same semi-analytic model, we create mock spectral observations using complex star formation and chemical enrichment histories, which approximately mimic GAMA's typical signal-to-noise ratio and wavelength range. We use these mocks to assert how well potential proxies of halo formation time may be recovered from GAMA-like spectroscopic data.

Magnetic anomaly study and geologic implications for Gilbert and Tokelau seamounts, Pacific Ocean

NASA Astrophysics Data System (ADS)

Sager, W. W.; Koppers, A. A.; Staudigel, H.

2006-12-01

The Gilbert and Tokelau seamounts are linear chains in the central Pacific with trends similar to the Emperor seamounts, implying the two poorly-known chains were formed by the same mechanism, widely regarded as hotspot volcanism. Multibeam bathymetry and magnetic data were collected over many Gilbert and Tokelau seamounts and have been used to make magnetic models to help understand the geologic evolution of the two chains. Magnetic models were done for 10 Gilbert and 10 Tokelau seamounts. Gilbert seamounts gave about equal number of reversed and normal polarity models and several have complex magnetizations that may indicate a mixture of opposing polarity rocks. Both observations imply formation during a time that included multiple geomagnetic reversals, consistent with radiometric dates from dredged rocks (65-72 Ma) [Koppers, A., and H. Staudigel, Science, 307, p. 905, 2005]. In the Tokelau chain, large volcanic edifices with summit islands (Howland, Baker, Fakaofu) also appear to have complex anomalies, making interpretation difficult. These volcanoes may also have formed over periods of time including magnetic reversals. The rest of the modeled central Tokelau seamounts have simpler magnetic anomalies and all but one is reversely polarized (6 reversed, 1 normal). Although this bias seems unusual if the geomagnetic field spent equal time in both polarities, it is consistent with radiometric ages of 59-66 Ma [Koppers and Staudigel, 2005], a period of dominantly reversed polarity. Paleomagnetic poles calculated from both seamount groups fall along the N-S trend of the Late Cretaceous to Cenozoic Pacific apparent polar wander path, consistent with Latest Cretaceous or early Cenozoic radiometric ages. More than half of the poles lie >30° east of the accepted polar wander path, perhaps indicating that the early Cenozoic polar wander path should be farther east. Ten (55%) of the paleomagnetic poles have lower latitudes than expected for Late Cretaceous or Cenozoic seamounts and all but one of these seamounts is reversely polarized. This situation implies a present-field overprint that steepens the calculated magnetization vectors for these seamounts and also renders the calculated seamount paleolatitudes unsuitable for interpretation.

Reversible catalytic dehydrogenation of alcohols for energy storage

PubMed Central

Bonitatibus, Peter J.; Chakraborty, Sumit; Doherty, Mark D.; Siclovan, Oltea; Jones, William D.; Soloveichik, Grigorii L.

2015-01-01

Reversibility of a dehydrogenation/hydrogenation catalytic reaction has been an elusive target for homogeneous catalysis. In this report, reversible acceptorless dehydrogenation of secondary alcohols and diols on iron pincer complexes and reversible oxidative dehydrogenation of primary alcohols/reduction of aldehydes with separate transfer of protons and electrons on iridium complexes are shown. This reactivity suggests a strategy for the development of reversible fuel cell electrocatalysts for partial oxidation (dehydrogenation) of hydroxyl-containing fuels. PMID:25588879

Reversible catalytic dehydrogenation of alcohols for energy storage

DOE PAGES

Bonitatibus, Jr., Peter J.; Chakraborty, Sumit; Doherty, Mark D.; ...

2015-01-14

Reversibility of a dehydrogenation/hydrogenation catalytic reaction has been an elusive target for homogeneous catalysis. In this paper, reversible acceptorless dehydrogenation of secondary alcohols and diols on iron pincer complexes and reversible oxidative dehydrogenation of primary alcohols/reduction of aldehydes with separate transfer of protons and electrons on iridium complexes are shown. Finally, this reactivity suggests a strategy for the development of reversible fuel cell electrocatalysts for partial oxidation (dehydrogenation) of hydroxyl-containing fuels.

Complexes between methyltestosterone and β-cyclodextrin for application in aquaculture production.

PubMed

Carvalho, Lucas Bragança de; Burusco, Kepa Koldo; Jaime, Carlos; Venâncio, Tiago; Carvalho, Aline Ferreira Souza de; Murgas, Luis David Solis; Pinto, Luciana de Matos Alves

2018-01-01

The inclusion complexes between 17-α-methyltestosterone (MT) and β-cyclodextrin (bCD) were prepared and characterized in dissolution and solid phase. The complex promoted a sixfold increment in solubility of the hormone. It has a limited solubility and stoichiometry of 2:1 (bCD:MT) determined by DSC, NMR and solubility experiments, the association constant Ka=2846Lmol -1 and complex fraction of 76% (assessed by DOSY-NMR, in (1:3) DMSO/D 2 O). The association constant obtained in water by the solubility isotherms is 7540Lmol -1 . 2D-ROESY experiments indicate the intermolecular orientation (complete inclusion of the hormone in the cavity). Simulations by molecular dynamics agreed with the formation of the inclusion complex 2:1. Release tests showed the slower release for the complexes, with 50% for lyophilization and 56% for malaxation. These results clearly demonstrate the complexation of MT in bCD, which formulations are promising for further applications involving this steroid in aquaculture, both for sexual reversal and in technologies of hormone in water sequestration. Copyright © 2017 Elsevier Ltd. All rights reserved.

Structure and magnetic properties of an unprecedented syn-anti μ-nitrito-1κO:2κO' bridged Mn(III)-salen complex and its isoelectronic and isostructural formate analogue.

PubMed

Kar, Paramita; Biswas, Rituparna; Drew, Michael G B; Ida, Yumi; Ishida, Takayuki; Ghosh, Ashutosh

2011-04-07

The preparation, crystal structures and magnetic properties of two new isoelectronic and isomorphous formate- and nitrite-bridged 1D chains of Mn(III)-salen complexes, [Mn(salen)(HCOO)](n) (1) and [Mn(salen)(NO(2))](n) (2), where salen is the dianion of N,N'-bis(salicylidene)-1,2-diaminoethane, are presented. The structures show that the salen ligand coordinates to the four equatorial sites of the metal ion and the formate or nitrite ions coordinate to the axial positions to bridge the Mn(III)-salen units through a syn-antiμ-1κO:2κO' coordination mode. Such a bridging mode is unprecedented in Mn(III) for formate and in any transition metal ion for nitrite. Variable-temperature magnetic susceptibility measurements of complexes 1 and 2 indicate the presence of ferromagnetic exchange interactions with J values of 0.0607 cm(-1) (for 1) and 0.0883 cm(-1) (for 2). The ac measurements indicate negligible frequency dependence for 1 whereas compound 2 exhibits a decrease of χ(ac)' and a concomitant increase of χ(ac)'' on elevating frequency around 2 K. This finding is an indication of slow magnetization reversal characteristic of single-chain magnets or spin-glasses. The μ-nitrito-1κO:2κO' bridge seems to be a potentially superior magnetic coupler to the formate bridge for the construction of single-molecule/-chain magnets as its coupling constant is greater and the χ(ac)' and χ(ac)'' show frequency dependence. © The Royal Society of Chemistry 2011

Myricetin arrests human telomeric G-quadruplex structure: a new mechanistic approach as an anticancer agent.

PubMed

Mondal, Soma; Jana, Jagannath; Sengupta, Pallabi; Jana, Samarjit; Chatterjee, Subhrangsu

2016-07-19

The use of small molecules to arrest G-quadruplex structure has become a potential strategy for the development and design of a new class of anticancer therapeutics. We have studied the interaction of myricetin, a plant flavonoid and a putative anticancer agent, with human telomeric G-quadruplex TTAGGG(TTAGGG)3 DNA. Reverse transcription PCR data revealed significant repression in hTERT expression in MCF-7 breast cancer cells upon increasing the concentration of myricetin. Further, we conducted a telomeric repeat amplification protocol assay to confirm the inhibition of telomerase by myricetin. Optical spectroscopic techniques like circular dichroism, UV spectroscopy and fluorescence spectroscopy revealed the formation of a stable myricetin-G-quadruplex complex. The thermodynamic parameters of myricetin-G-quadruplex complex formation, presented through isothermal titration calorimetry studies, indicate the binding process to be thermodynamically favorable. In addition, high resolution NMR spectroscopy in conjunction with molecular dynamics simulation is employed to provide detailed mechanistic insights into the binding in the myricetin-G-quadruplex complex at the atomic level. Our results thus propose a new mode of action of myricetin as an anticancer agent via arresting telomeric G-quadruplex structure.

1H NMR studies of molecular interaction of D-glucosamine and N-acetyl-D-glucosamine with capsaicin in aqueous and non-aqueous media.

PubMed

Higuera-Ciapara, Inocencio; Virués, Claudia; Jiménez-Chávez, Marcela; Martínez-Benavidez, Evelin; Hernández, Javier; Domínguez, Zaira; López-Rendón, Roberto; Velázquez, Enrique F; Inoue, Motomichi

2017-11-27

Complex formation of D-glucosamine (Gl) and N-acetyl-D-glucosamine (AGl) with capsaicin (Cp) were studied by 1 H NMR titrations in H 2 O-d 2 and DMSO-d 6 ; capsaicin is the major bioactive component of chili peppers. Every titration curve has been interpreted by formulating a suitable model for the reaction equilibrium, to elucidate intermolecular interactions. In DMSO, glucosamine cations associate with each other to yield linear aggregates, and undergo pseudo-1:1-complexation with capsaicin, the formation constant being ca. 30 M -1 . N-Acetylglucosamine, without self-association, forms a 2:1-complex AGl 2 Cp with the stability of ca. 70 M -2 . These complexations are achieved by intermolecular hydrogen bonds. In D 2 O, glucosamine undergoes reversible protonation equilibrium between Gl 0 and GlH + with the logarithmic protonation constants log K D  = 8.63 for α-glucosamine and 8.20 for β-isomer. Both anomeric isomers of deprotonated glucosamine form Gl 0 Cp-type complexes of capsaicin, in a competitive manner, with a formation constant of 1040 M -1 for the α-glucosamine complex and 830 M -1 for the β-complex; the anomeric carbons result in the difference in thermodynamic stability. The reactant molecules are closed up by the solvent-exclusion effect and/or the van der Waals interaction; the resulting pair is stabilized by intermolecular hydrogen bonding within a local water-free space between the component molecules. By contrast, neither protonated glucosamine (GlH + ) nor N-acetylglucosamine yields a capsaicin complex with the definite stoichiometry. The monosaccharides recognize capsaicin under only a controlled condition; the same phenomena are predicted for biological systems and nanocarriers based on polysaccharides such as chitosan. Copyright © 2017 Elsevier Ltd. All rights reserved.

Microemulsions and Aggregation Formation in Extraction Processes for Used Nuclear Fuel: Thermodynamic and Structural Studies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nilsson, Mikael

Advanced nuclear fuel cycles rely on successful chemical separation of various elements in the used fuel. Numerous solvent extraction (SX) processes have been developed for the recovery and purification of metal ions from this used material. However, the predictability of process operations has been challenged by the lack of a fundamental understanding of the chemical interactions in several of these separation systems. For example, gaps in the thermodynamic description of the mechanism and the complexes formed will make predictions very challenging. Recent studies of certain extraction systems under development and a number of more established SX processes have suggested thatmore » aggregate formation in the organic phase results in a transformation of its selectivity and efficiency. Aggregation phenomena have consistently been interfering in SX process development, and have, over the years, become synonymous with an undesirable effect that must be prevented. This multiyear, multicollaborative research effort was carried out to study solvation and self-organization in non-aqueous solutions at conditions promoting aggregation phenomena. Our approach to this challenging topic was to investigate extraction systems comprising more than one extraction reagent where synergy of the metal ion could be observed. These systems were probed for the existence of stable microemulsions in the organic phase, and a number of high-end characterization tools were employed to elucidate the role of the aggregates in metal ion extraction. The ultimate goal was to find connections between synergy of metal ion extraction and reverse micellar formation. Our main accomplishment for this project was the expansion of the understanding of metal ion complexation in the extraction system combining tributyl phosphate (TBP) and dibutyl phosphoric acid (HDBP). We have found that for this system no direct correlation exists for the metal ion extraction and the formation of aggregates, meaning that the metal ion is not solubilized in a reverse micelle core. Rather we have found solid evidence that the metal ions are extracted and coordinated by the organic ligands as suggested by classic SX theories. However, we have challenged the existence of mixed complexes that have been suggested to exist in this particular extraction system. Most importantly we have generated a wealth of information and trained students on important lab techniques and strengthened the collaboration between the DOE national laboratories and US educational institution involved in this work.« less

Reversible formation of aminals: a new strategy to control the release of bioactive volatiles from dynamic mixtures.

PubMed

Godin, Guillaume; Levrand, Barbara; Trachsel, Alain; Lehn, Jean-Marie; Herrmann, Andreas

2010-05-14

Dynamic mixtures generated by reversible aminal formation of fragrance aldehydes with N,N-dibenzyl alkyldiamines in aqueous systems were found to be suitable delivery systems for the controlled release of bioactive volatiles.

Reversible Oxygenation of 2,4-Diaminobutanoic Acid-Co(II) Complexes

PubMed Central

Li, Hui; Yue, Fan; Wen, Hongmei

2016-01-01

This paper introduces the structural characterization and studies on reversible oxygenation behavior of a new oxygen carrier Co(II)-2,4-diaminobutanoic acid (DABA) complex in aqueous solution. The composition of the oxygenated complex was determined by gas volumetric method, molar ratio method, and mass spectrometry, and the formula of the oxygenated complex was determined to be [Co(DABA)2O2]. In aqueous solution, the complex can continuously uptake and release dioxygen and exhibit excellent reversibility of oxygenation and deoxygenation ability. This complex can maintain 50% of its original oxygenation capacity after 30 cycles in 24 h and retain 5% of the original oxygenation capacity after more than 260 cycles after 72 h. When a ligand analogue was linked to histidine (His), the new complex exhibited as excellent reversible oxygenation property as His-Co(II) complex. Insight into the relationship between structural detail and oxygenation properties will provide valuable suggestion for a new family of oxygen carriers. PMID:27648004

Sleep-dependent directional coupling between human neocortex and hippocampus.

PubMed

Wagner, Tobias; Axmacher, Nikolai; Lehnertz, Klaus; Elger, Christian E; Fell, Jürgen

2010-02-01

Complex interactions between neocortex and hippocampus are the neural basis of memory formation. Two-step theories of memory formation suggest that initial encoding of novel information depends on the induction of rapid plasticity within the hippocampus, and is followed by a second sleep-dependent step of memory consolidation. These theories predict information flow from the neocortex into the hippocampus during waking state and in the reverse direction during sleep. However, experimental evidence that interactions between hippocampus and neocortex have a predominant direction which reverses during sleep rely on cross-correlation analysis of data from animal experiments and yielded inconsistent results. Here, we investigated directional coupling in intracranial EEG data from human subjects using a phase-modeling approach which is well suited to reveal functional interdependencies in oscillatory data. In general, we observed that the anterior hippocampus predominantly drives nearby and remote brain regions. Surprisingly, however, the influence of neocortical regions on the hippocampus significantly increased during sleep as compared to waking state. These results question the standard model of hippocampal-neocortical interactions and suggest that sleep-dependent consolidation is accomplished by an active retrieval of hippocampal information by the neocortex. Copyright 2009 Elsevier Srl. All rights reserved.

Decanuclear Ln10 Wheels and Vertex-Shared Spirocyclic Ln5 Cores: Synthesis, Structure, SMM Behavior, and MCE Properties.

PubMed

Das, Sourav; Dey, Atanu; Kundu, Subrata; Biswas, Sourav; Narayanan, Ramakirushnan Suriya; Titos-Padilla, Silvia; Lorusso, Giulia; Evangelisti, Marco; Colacio, Enrique; Chandrasekhar, Vadapalli

2015-11-16

The reaction of a Schiff base ligand (LH3) with lanthanide salts, pivalic acid and triethylamine in 1:1:1:3 and 4:5:8:20 stoichiometric ratios results in the formation of decanuclear Ln10 (Ln = Dy (1), Tb (2), and Gd (3)) and pentanuclear Ln5 complexes (Ln = Gd (4), Tb (5), and Dy (6)), respectively. The formation of Ln10 and Ln5 complexes are fully governed by the stoichiometry of the reagents used. Detailed magnetic studies on these complexes (1-6) have been carried out. Complex 1 shows a SMM behavior with an effective energy barrier for the reversal of the magnetization (Ueff) = 16.12(8) K and relaxation time (τo) = 3.3×10(-5) s under 4000 Oe direct current (dc) field. Complex 6 shows the frequency dependent maxima in the out-of-phase signal under zero dc field, without achieving maxima above 2 K. Complexes 3 and 4 show a large magnetocaloric effect with the following characteristic values: -ΔSm = 26.6 J kg(-1) K(-1) at T = 2.2 K for 3 and -ΔSm = 27.1 J kg(-1) K(-1) at T = 2.4 K for 4, both for an applied field change of 7 T. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Plasma-gun-assisted field-reversed configuration formation in a conical θ-pinch

NASA Astrophysics Data System (ADS)

Weber, T. E.; Intrator, T. P.; Smith, R. J.

2015-04-01

Injection of plasma via an annular array of coaxial plasma guns during the pre-ionization phase of field-reversed configuration (FRC) formation is shown to catalyze the bulk ionization of a neutral gas prefill in the presence of a strong axial magnetic field and change the character of outward flux flow during field-reversal from a convective process to a much slower resistive diffusion process. This approach has been found to significantly improve FRC formation in a conical θ-pinch, resulting in a ˜350% increase in trapped flux at typical operating conditions, an expansion of accessible formation parameter space to lower densities and higher temperatures, and a reduction or elimination of several deleterious effects associated with the pre-ionization phase.

N-terminal truncations in the FhlA protein result in formate- and MoeA-independent expression of the hyc (formate hydrogenlyase) operon of Escherichia coli.

PubMed

Self, W T; Hasona, A; Shanmugam, K T

2001-11-01

The formate hydrogenlyase complex of Escherichia coli catalyses the cleavage of formate to CO2 and H2 and consists of a molybdoenzyme formate dehydrogenase-H, hydrogenase 3 and intermediate electron carriers. The structural genes of this enzyme complex are activated by the FhlA protein in the presence of both formate and molybdate; ModE-Mo serves as a secondary activator. Mutational analysis of the FhlA protein established that the unique N-terminal region of this protein was responsible for formate- and molybdenum-dependent transcriptional control of the hyc operon. Analysis of the N-terminal sequence of the FhlA protein revealed a unique motif (amino acids 7-37), which is also found in ATPases associated with several members of the ABC-type transporter family. A deletion derivative of FhlA lacking these amino acids (FhlA9-2) failed to activate the hyc operon in vivo, although the FhlA9-2 did bind to hyc promoter DNA in vitro. The ATPase activity of the FhlA9-2-DNA-formate complex was at least three times higher than that of the native protein-DNA-formate complex, and this degree of activity was achieved at a lower formate level. Extending the deletion to amino acid 117 (FhlA167) not only reversed the FhlA(-) phenotype of FhlA9-2, but also led to both molybdenum- and formate-independence. Deleting the entire N-terminal domain (between amino acids 5 and 374 of the 692 amino acid protein) also led to an effector-independent transcriptional activator (FhlA165), which had a twofold higher level of hyc operon expression than the native protein. Both FhlA165 and FhlA167 still required ModE-Mo as a secondary activator for an optimal level of hyc-lac expression. The FhlA165 protein also had a twofold higher affinity to hyc promoter DNA than the native FhlA protein, while the FhlA167 protein had a significantly lower affinity for hyc promoter DNA in vitro. Although the ATPase activity of the native protein was increased by formate, the ATPase activity of neither FhlA165 or FhlA167 responded to formate. Removal of the first 117 amino acids of the FhlA protein appears to result in a constitutive, effector-independent activation of transcription of the genes encoding the components of the formate hydrogenlyase complex. The sequence similarity to ABC-ATPases, combined with the properties of the FhlA deletion proteins, led to the proposal that the N-terminal region of the native FhlA protein interacts with formate transport proteins, both as a formate transport facilitator and as a cytoplasmic acceptor.

Tuning the Reversibility of Mg Anodes via Controlled Surface Passivation by H 2O/Cl – in Organic Electrolytes

DOE PAGES

Connell, Justin G.; Genorio, Bostjan; Lopes, Pietro Papa; ...

2016-10-17

Developing a new generation of battery chemistries is a critical challenge to moving beyond current Li-ion technologies. In this work, we introduce a surface-science-based approach for understanding the complex phenomena controlling the reversibility of Mg anodes for Mg-ion batteries. In addition, we identify the profound impact of trace levels of H 2O (≤3 ppm) on the kinetics of Mg deposition and determine that passive films of MgO and Mg(OH) 2 are formed only after Mg deposition ceases, rather than continuously during Mg reduction. We also find that Cl – inhibits passivation through the formation of adsorbed Cl – (Mg–Cl(ad)) and/ormore » MgCl 2 on the surface, as well as through a dynamic competition with H 2O in the double layer. In conclusion, this surface-science-based approach goes well beyond Mg anodes, highlighting the need for more in-depth understanding of electrolyte chemistries before a new generation of efficient and reversible battery technologies can be realized.« less

cAMP prevents TNF-induced apoptosis through inhibiting DISC complex formation in rat hepatocytes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bhattacharjee, Rajesh; Xiang, Wenpei; Family Planning Research Institute, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030, People's Republic of China

2012-06-22

Highlights: Black-Right-Pointing-Pointer cAMP blocks cell death induced by TNF and actinomycin D in cultured hepatocytes. Black-Right-Pointing-Pointer cAMP blocks NF-{kappa}B activation induced by TNF and actinomycin D. Black-Right-Pointing-Pointer cAMP blocks DISC formation following TNF and actinomycin D exposure. Black-Right-Pointing-Pointer cAMP blocks TNF signaling at a proximal step. -- Abstract: Tumor necrosis factor {alpha} (TNF) is a pleiotropic proinflammatory cytokine that plays a role in immunity and the control of cell proliferation, cell differentiation, and apoptosis. The pleiotropic nature of TNF is due to the formation of different signaling complexes upon the binding of TNF to its receptor, TNF receptor type 1more » (TNFR1). TNF induces apoptosis in various mammalian cells when the cells are co-treated with a transcription inhibitor like actinomycin D (ActD). When TNFR1 is activated, it recruits an adaptor protein, TNF receptor-associated protein with death domain (TRADD), through its cytoplasmic death effector domain (DED). TRADD, in turn, recruits other signaling proteins, including TNF receptor-associated protein 2 (TRAF2) and receptor-associated protein kinase (RIPK) 1, to form a complex. Subsequently, this complex combines with FADD and procaspase-8, converts into a death-inducing signaling complex (DISC) to induce apoptosis. Cyclic AMP (cAMP) is a second messenger that regulates various cellular processes such as cell proliferation, gene expression, and apoptosis. cAMP analogues are reported to act as anti-apoptotic agents in various cell types, including hepatocytes. We found that a cAMP analogue, dibutyryl cAMP (db-cAMP), inhibits TNF + ActD-induced apoptosis in rat hepatocytes. The protein kinase A (PKA) inhibitor KT-5720 reverses this inhibitory effect of cAMP on apoptosis. Cytoprotection by cAMP involves down-regulation of various apoptotic signal regulators like TRADD and FADD and inhibition of caspase-8 and caspase-3 cleavage. We also found that cAMP exerts its affect at the proximal level of TNF signaling by inhibiting the formation of the DISC complex upon the binding of TNF to TNFR1. In conclusion, our study shows that cAMP prevents TNF + ActD-induced apoptosis in rat hepatocytes by inhibiting DISC complex formation.« less

Reactive Oxygen Species Production by Forward and Reverse Electron Fluxes in the Mitochondrial Respiratory Chain

PubMed Central

Selivanov, Vitaly A.; Votyakova, Tatyana V.; Pivtoraiko, Violetta N.; Zeak, Jennifer; Sukhomlin, Tatiana; Trucco, Massimo; Roca, Josep; Cascante, Marta

2011-01-01

Reactive oxygen species (ROS) produced in the mitochondrial respiratory chain (RC) are primary signals that modulate cellular adaptation to environment, and are also destructive factors that damage cells under the conditions of hypoxia/reoxygenation relevant for various systemic diseases or transplantation. The important role of ROS in cell survival requires detailed investigation of mechanism and determinants of ROS production. To perform such an investigation we extended our rule-based model of complex III in order to account for electron transport in the whole RC coupled to proton translocation, transmembrane electrochemical potential generation, TCA cycle reactions, and substrate transport to mitochondria. It fits respiratory electron fluxes measured in rat brain mitochondria fueled by succinate or pyruvate and malate, and the dynamics of NAD+ reduction by reverse electron transport from succinate through complex I. The fitting of measured characteristics gave an insight into the mechanism of underlying processes governing the formation of free radicals that can transfer an unpaired electron to oxygen-producing superoxide and thus can initiate the generation of ROS. Our analysis revealed an association of ROS production with levels of specific radicals of individual electron transporters and their combinations in species of complexes I and III. It was found that the phenomenon of bistability, revealed previously as a property of complex III, remains valid for the whole RC. The conditions for switching to a state with a high content of free radicals in complex III were predicted based on theoretical analysis and were confirmed experimentally. These findings provide a new insight into the mechanisms of ROS production in RC. PMID:21483483

Characterization of Two Classes of Small Molecule Inhibitors of Arp2/3 Complex

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nolen, B.; Tomasevic, N; Russell, A

2009-01-01

Polymerization of actin filaments directed by the actin-related protein (Arp)2/3 complex supports many types of cellular movements. However, questions remain regarding the relative contributions of Arp2/3 complex versus other mechanisms of actin filament nucleation to processes such as path finding by neuronal growth cones; this is because of the lack of simple methods to inhibit Arp2/3 complex reversibly in living cells. Here we describe two classes of small molecules that bind to different sites on the Arp2/3 complex and inhibit its ability to nucleate actin filaments. CK-0944636 binds between Arp2 and Arp3, where it appears to block movement of Arp2more » and Arp3 into their active conformation. CK-0993548 inserts into the hydrophobic core of Arp3 and alters its conformation. Both classes of compounds inhibit formation of actin filament comet tails by Listeria and podosomes by monocytes. Two inhibitors with different mechanisms of action provide a powerful approach for studying the Arp2/3 complex in living cells.« less

Phosphorylation-mediated RNA/peptide complex coacervation as a model for intracellular liquid organelles

NASA Astrophysics Data System (ADS)

Aumiller, William M.; Keating, Christine D.

2016-02-01

Biological cells are highly organized, with numerous subcellular compartments. Phosphorylation has been hypothesized as a means to control the assembly/disassembly of liquid-like RNA- and protein-rich intracellular bodies, or liquid organelles, that lack delimiting membranes. Here, we demonstrate that charge-mediated phase separation, or complex coacervation, of RNAs with cationic peptides can generate simple model liquid organelles capable of reversibly compartmentalizing biomolecules. Formation and dissolution of these liquid bodies was controlled by changes in peptide phosphorylation state using a kinase/phosphatase enzyme pair. The droplet-generating phase transition responded to modification of even a single serine residue. Electrostatic interactions between the short cationic peptides and the much longer polyanionic RNAs drove phase separation. Coacervates were also formed on silica beads, a primitive model for localization at specific intracellular sites. This work supports phosphoregulation of complex coacervation as a viable mechanism for dynamic intracellular compartmentalization in membraneless organelles.

Spectroscopic and phosphorescent modulation in triphosphine-supported PtAg2 heterotrinuclear alkynyl complexes.

PubMed

Zhang, Li-Yi; Xu, Liang-Jin; Zhang, Xu; Wang, Jin-Yun; Li, Jia; Chen, Zhong-Ning

2013-05-06

A series of highly phosphorescent PtAg2 heterotrinuclear alkynyl complexes with bis(diphenylphosphinomethyl)phenylphosphine (dpmp) were prepared and characterized structurally. The solution phosphorescence with various emitting colors is systematically modulated by modifying substituents as well as π-conjugated systems in aromatic acetylides. The crystals, powders, or films exhibit reversible stimuli-responsive phosphorescence changes upon exposure to vapor of MeCN, pyridine, DMF, etc., resulting from perturbation of d(8)-d(10) metallophilic interaction in the excited states as a consequence of the formation/disruption of Ag-solvent bonds. Both experimental and time-dependent density functional theory (TD-DFT) studies demonstrate that d(8)-d(10) metallophilic interaction exerts a crucial role on phosphorescent characteristics due to the PtAg2 cluster-based (3)[d → p] state. This study affords a paradigm for phosphorescence modulation in d(8)-d(10) heteronuclear complexes.

Supramolecular complexation for environmental control.

PubMed

Albelda, M Teresa; Frías, Juan C; García-España, Enrique; Schneider, Hans-Jörg

2012-05-21

Supramolecular complexes offer a new and efficient way for the monitoring and removal of many substances emanating from technical processes, fertilization, plant and animal protection, or e.g. chemotherapy. Such pollutants range from toxic or radioactive metal ions and anions to chemical side products, herbicides, pesticides to drugs including steroids, and include degradation products from natural sources. The applications involve usually fast and reversible complex formation, due to prevailing non-covalent interactions. This is of importance for sensing as well as for separation techniques, where the often expensive host compounds can then be reused almost indefinitely. Immobilization of host compounds, e.g. on exchange resins or on membranes, and their implementation in smart new materials hold particular promise. The review illustrates how the design of suitable host compounds in combination with modern sensing and separation methods can contribute to solve some of the biggest problems facing chemistry, which arise from the everyday increasing pollution of the environment.

Thrombotic safety of prothrombin complex concentrate (Beriplex P/N) for dabigatran reversal in a rabbit model.

PubMed

Herzog, Eva; Kaspereit, Franz J; Krege, Wilfried; Doerr, Baerbel; van Ryn, Joanne; Dickneite, Gerhard; Pragst, Ingo

2014-09-01

In vivo animal data have shown prothrombin complex concentrate (PCC) to be effective in preventing bleeding induced by excessive plasma levels of the direct thrombin inhibitor dabigatran. This animal model study was designed to determine the risk of thrombosis associated with administration of a PCC (Beriplex P/N) to reverse dabigatran-induced bleeding. Anesthetized rabbits were treated with initial 0, 75, 200 or 450 μg kg(-1) dabigatran boluses followed by continuous infusions to maintain elevated plasma dabigatran levels. At 15 min after the start of dabigatran administration, PCC doses of 0, 50 or 300 IU kg(-1) were administered. Thereafter, coagulation in an arteriovenous (AV) shunt was evaluated and histopathologic examination for thrombotic changes performed. Venous thrombosis was also assessed in a modified Wessler model. At the suprapharmacologic dose of 300 IU kg(-1), PCC increased thrombus weight during AV shunting, but this effect could be prevented by dabigatran at all tested doses. AV shunt occlusion after PCC administration was delayed by 75 μg kg(-1) dabigatran and abolished by progressively higher dabigatran doses. High-dose treatment with 300 IU kg(-1) PCC resulted in histologically evident low-grade pulmonary thrombi; however, that effect could be blocked by dabigatran in a dose-dependent manner (p=0.034). In rabbits treated with high-dose PCC, dabigatran inhibited thrombus formation during venous stasis. PCC effectively reversed dabigatran-induced bleeding. In this animal study, thrombosis after PCC administration could be prevented in the presence of dabigatran. PCC reversed dabigatran-induced excessive bleeding while retaining protective anticoagulatory activity of dabigatran. Copyright © 2014. Published by Elsevier Ltd.

The deliberation-without-attention effect: evidence for an artifactual interpretation.

PubMed

Lassiter, G Daniel; Lindberg, Matthew J; González-Vallejo, Claudia; Bellezza, Francis S; Phillips, Nathaniel D

2009-06-01

Proponents of unconscious-thought theory assert that letting the unconscious "mull it over" can enhance decisions. In a series of recent studies, researchers demonstrated that participants whose attention was focused on solving a complex problem (i.e., those using conscious thought) made poorer choices, decisions, and judgments than participants whose attention was distracted from the problem (i.e., those purportedly using unconscious thought). We argue that this finding, rather than establishing the existence of a deliberation-without-attention effect, is explained more compellingly in terms of the well-established distinction between on-line and memory-based judgments. In Experiment 1, we reversed the recent finding by simply changing participants' on-line processing goal from impression formation to memorization. Experiment 2 provided a replication and further established that some cognitive effort appears necessary to produce both the original pattern of results and its reversal, suggesting that such judgments are ultimately a product of conscious, rather than unconscious, thinking.

Abnormal Current–Voltage Hysteresis Induced by Reverse Bias in Organic–Inorganic Hybrid Perovskite Photovoltaics

DOE PAGES

Rajagopal, Adharsh; Williams, Spencer T.; Chueh, Chu-Chen; ...

2016-02-29

In this study, reverse bias (RB)-induced abnormal hysteresis is investigated in perovskite solar cells (PVSCs) with nickel oxide (NiOx)/methylammonium lead iodide (CH 3NH 3PbI 3) interfaces. Through comprehensive current-voltage (I-V) characterization and bias-dependent external quantum efficiency (EQE) measurements, we demonstrate that this phenomenon is caused by the interfacial ion accumulation intrinsic to CH 3NH 3PbI 3. Subsequently, via systematic analysis we discover that the abnormal I-V behavior is remarkably similar to tunnel diode I-V characteristics and is due to the formation of a transient tunnel junction at NiO x/CH 3NH 3PbI 3 interfaces under RB. The detailed analysis navigating themore » complexities of I-V behavior in CH 3NH 3PbI 3-based solar cells provided here ultimately illuminates possibilities in modulating ion motion and hysteresis via interfacial engineering in PVSCs. Moreover, this work shows that RB can alter how CH 3NH 3PbI 3 contributes to the functional nature of devices and provides the first steps toward approaching functional perovskite interfaces in new ways for metrology and analysis of complex transient processes.« less

Evaluation of acceptor selectivity of Lactococcus lactis ssp. lactis trehalose 6-phosphate phosphorylase in the reverse phosphorolysis and synthesis of a new sugar phosphate.

PubMed

Taguchi, Yodai; Saburi, Wataru; Imai, Ryozo; Mori, Haruhide

2017-08-01

Trehalose 6-phosphate phosphorylase (TrePP), a member of glycoside hydrolase family 65, catalyzes the reversible phosphorolysis of trehalose 6-phosphate (Tre6P) with inversion of the anomeric configuration to produce β-d-glucose 1-phosphate (β-Glc1P) and d-glucose 6-phosphate (Glc6P). TrePP in Lactococcus lactis ssp. lactis (LlTrePP) is, alongside the phosphotransferase system, involved in the metabolism of trehalose. In this study, recombinant LlTrePP was produced and characterized. It showed its highest reverse phosphorolytic activity at pH 4.8 and 40°C, and was stable in the pH range 5.0-8.0 and at up to 30°C. Kinetic analyses indicated that reverse phosphorolysis of Tre6P proceeded through a sequential bi bi mechanism involving the formation of a ternary complex of the enzyme, β-Glc1P, and Glc6P. Suitable acceptor substrates were Glc6P, and, at a low level, d-mannose 6-phosphate (Man6P). From β-Glc1P and Man6P, a novel sugar phosphate, α-d-Glcp-(1↔1)-α-d-Manp6P, was synthesized with 51% yield.

Plasma-gun-assisted field-reversed configuration formation in a conical θ-pinch

DOE PAGES

Weber, T. E.; Intrator, T. P.; Smith, R. J.

2015-04-29

We show through injection of plasma via an annular array of coaxial plasma guns, during the pre-ionization phase of field-reversed configuration (FRC) formation how to catalyze the bulk ionization of a neutral gas prefill in the presence of a strong axial magnetic field and change the character of outward flux flow during field-reversal from a convective process to a much slower resistive diffusion process. Our approach has been found to significantly improve FRC formation in a conical θ-pinch, resulting in a ~350% increase in trapped flux at typical operating conditions, an expansion of accessible formation parameter space to lower densitiesmore » and higher temperatures, and a reduction or elimination of several deleterious effects associated with the pre-ionization phase.« less

Plasma-gun-assisted field-reversed configuration formation in a conical θ-pinch

DOE Office of Scientific and Technical Information (OSTI.GOV)

Weber, T. E., E-mail: tweber@lanl.gov; Intrator, T. P.; Smith, R. J.

2015-04-15

Injection of plasma via an annular array of coaxial plasma guns during the pre-ionization phase of field-reversed configuration (FRC) formation is shown to catalyze the bulk ionization of a neutral gas prefill in the presence of a strong axial magnetic field and change the character of outward flux flow during field-reversal from a convective process to a much slower resistive diffusion process. This approach has been found to significantly improve FRC formation in a conical θ-pinch, resulting in a ∼350% increase in trapped flux at typical operating conditions, an expansion of accessible formation parameter space to lower densities and highermore » temperatures, and a reduction or elimination of several deleterious effects associated with the pre-ionization phase.« less

Single-molecule visualization of a formin-capping protein ‘decision complex' at the actin filament barbed end

PubMed Central

Bombardier, Jeffrey P.; Eskin, Julian A.; Jaiswal, Richa; Corrêa, Ivan R.; Xu, Ming-Qun; Goode, Bruce L.; Gelles, Jeff

2015-01-01

Precise control of actin filament length is essential to many cellular processes. Formins processively elongate filaments, whereas capping protein (CP) binds to barbed ends and arrests polymerization. While genetic and biochemical evidence has indicated that these two proteins function antagonistically, the mechanism underlying the antagonism has remained unresolved. Here we use multi-wavelength single-molecule fluorescence microscopy to observe the fully reversible formation of a long-lived ‘decision complex' in which a CP dimer and a dimer of the formin mDia1 simultaneously bind the barbed end. Further, mDia1 displaced from the barbed end by CP can randomly slide along the filament and later return to the barbed end to re-form the complex. Quantitative kinetic analysis reveals that the CP-mDia1 antagonism that we observe in vitro occurs through the decision complex. Our observations suggest new molecular mechanisms for the control of actin filament length and for the capture of filament barbed ends in cells. PMID:26566078

Annexin 2-caveolin 1 complex is a target of ezetimibe and regulates intestinal cholesterol transport.

PubMed

Smart, Eric J; De Rose, Robert A; Farber, Steven A

2004-03-09

Modulation of cholesterol absorption in the intestine, the primary site of dietary cholesterol uptake in humans, can have profound clinical implications. We have undertaken a reverse genetic approach by disrupting putative cholesterol processing genes in zebrafish larvae by using morpholino (MO) antisense oligonucleotides. By using targeted MO injections and immunoprecipitation (IP) experiments coupled with mass spectrometry, we determined that annexin (ANX)2 complexes with caveolin (CAV)1 in the zebrafish and mouse intestine. The complex is heat stable and unaffected by SDS or reducing conditions. MO targeting of anx2b or cav1, which are both strongly expressed in the larval and adult zebrafish intestinal epithelium, prevents formation of the protein heterocomplex. Furthermore, anx2b MO injection prevents processing of a fluorescent cholesterol reporter and results in reduced sterol mass. Pharmacological treatment of mice with ezetimibe disrupts the heterocomplex in only hypercholesterolemic animals. These data suggest that ANX2 and CAV1 are components of an intestinal sterol transport complex.

Hydrogen storage and evolution catalysed by metal hydride complexes.

PubMed

Fukuzumi, Shunichi; Suenobu, Tomoyoshi

2013-01-07

The storage and evolution of hydrogen are catalysed by appropriate metal hydride complexes. Hydrogenation of carbon dioxide by hydrogen is catalysed by a [C,N] cyclometalated organoiridium complex, [Ir(III)(Cp*)(4-(1H-pyrazol-1-yl-κN(2))benzoic acid-κC(3))(OH(2))](2)SO(4) [Ir-OH(2)](2)SO(4), under atmospheric pressure of H(2) and CO(2) in weakly basic water (pH 7.5) at room temperature. The reverse reaction, i.e., hydrogen evolution from formate, is also catalysed by [Ir-OH(2)](+) in acidic water (pH 2.8) at room temperature. Thus, interconversion between hydrogen and formic acid in water at ambient temperature and pressure has been achieved by using [Ir-OH(2)](+) as an efficient catalyst in both directions depending on pH. The Ir complex [Ir-OH(2)](+) also catalyses regioselective hydrogenation of the oxidised form of β-nicotinamide adenine dinucleotide (NAD(+)) to produce the 1,4-reduced form (NADH) under atmospheric pressure of H(2) at room temperature in weakly basic water. In weakly acidic water, the complex [Ir-OH(2)](+) also catalyses the reverse reaction, i.e., hydrogen evolution from NADH to produce NAD(+) at room temperature. Thus, interconversion between NADH (and H(+)) and NAD(+) (and H(2)) has also been achieved by using [Ir-OH(2)](+) as an efficient catalyst and by changing pH. The iridium hydride complex formed by the reduction of [Ir-OH(2)](+) by H(2) and NADH is responsible for the hydrogen evolution. Photoirradiation (λ > 330 nm) of an aqueous solution of the Ir-hydride complex produced by the reduction of [Ir-OH(2)](+) with alcohols resulted in the quantitative conversion to a unique [C,C] cyclometalated Ir-hydride complex, which can catalyse hydrogen evolution from alcohols in a basic aqueous solution (pH 11.9). The catalytic mechanisms of the hydrogen storage and evolution are discussed by focusing on the reactivity of Ir-hydride complexes.

Complexation-induced supramolecular assembly drives metal-ion extraction.

PubMed

Ellis, Ross J; Meridiano, Yannick; Muller, Julie; Berthon, Laurence; Guilbaud, Philippe; Zorz, Nicole; Antonio, Mark R; Demars, Thomas; Zemb, Thomas

2014-09-26

Combining experiment with theory reveals the role of self-assembly and complexation in metal-ion transfer through the water-oil interface. The coordinating metal salt Eu(NO3)3 was extracted from water into oil by a lipophilic neutral amphiphile. Molecular dynamics simulations were coupled to experimental spectroscopic and X-ray scattering techniques to investigate how local coordination interactions between the metal ion and ligands in the organic phase combine with long-range interactions to produce spontaneous changes in the solvent microstructure. Extraction of the Eu(3+)-3(NO3(-)) ion pairs involves incorporation of the "hard" metal complex into the core of "soft" aggregates. This seeds the formation of reverse micelles that draw the water and "free" amphiphile into nanoscale hydrophilic domains. The reverse micelles interact through attractive van der Waals interactions and coalesce into rod-shaped polynuclear Eu(III) -containing aggregates with metal centers bridged by nitrate. These preorganized hydrophilic domains, containing high densities of O-donor ligands and anions, provide improved Eu(III) solvation environments that help drive interfacial transfer, as is reflected by the increasing Eu(III) partitioning ratios (oil/aqueous) despite the organic phase approaching saturation. For the first time, this multiscale approach links metal-ion coordination with nanoscale structure to reveal the free-energy balance that drives the phase transfer of neutral metal salts. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Analysis of reversibility and reaction products of glyoxal uptake onto ammonium sulfate aerosol

NASA Astrophysics Data System (ADS)

Galloway, M. M.; Chhabra, P. S.; Chan, A. W.; Surratt, J. D.; Kwan, A. J.; Wennberg, P. O.; Flagan, R. C.; Seinfeld, J. H.; Keutsch, F. N.

2009-04-01

Glyoxal, the smallest alpha-dicarbonyl, is an oxidation product of both biogenic and anthropogenic volatile organic compounds (Fu et al. JGR 113, D15303, 2008). Despite its low molecular weight, its role in secondary organic aerosol (SOA) formation has gained interest and a recent study suggested that it accounts for more than 15% of SOA in Mexico City (Volkamer et al. GRL 34, L19807, 2007). Despite numerous previous studies, questions remain regarding the processes controlling glyoxal uptake onto aerosol, including the role of acid catalysis, degree of reversibility, and identity of aerosol phase reaction products. We present results of chamber aerosol studies (Galloway et al. ACPD 8, 20799, 2008) and laboratory studies of bulk samples aimed at improving the understanding of these processes, in particular formation of oligomers and organosulfates of glyoxal, as well as the formation of imidazoles (carbon-nitrogen containing heterocyclic aromatic compounds) under dark and irradiated conditions. The relevance of these classes of reaction products extends beyond glyoxal, as evidence of oligomers and organosulfates other than those of glyoxal have been found in ambient aerosol (Surratt et al. JPCA 112, 8345, 2008; Denkenberger et al. Environ. Sci. Technol. 41, 5439, 2007). Experiments in which a chamber air mass was diluted after equilibration of glyoxal uptake onto ammonium sulfate seed aerosol (relative humidity 60% and glyoxal mixing ratios of 25-200 ppbv) shows that under these conditions uptake is reversible. The most important condensed phase products are hydrated oligomers of glyoxal, which are also formed reversibly under these conditions. Our studies show that organosulfates were not formed under dark conditions for neutral or acidified aerosol; similarly, Minerath et al. have recently shown that formation of a different class of organosulfates (alkyl sulfates) also proceeds very slowly even under acidic conditions (Environ. Sci. Technol. 42, 4410, 2008). The masses assigned to sulfate esters in previous work (Liggio et al. Environ. Sci. Technol. 39, 1532, 2005) via low resolution AMS studies were assigned as glyoxal oligomers in our study via high resolution AMS spectra. However, organosulfates were identified under irradiated conditions, and we present attempts to identify the specific species via comparison with lab synthesized organosulfates. The influence of irradiation on organosulfate formation is still under investigation. Under irradiated conditions we see clear evidence for active oxidative photochemistry. The aerosol phase becomes increasingly oxidized and oxidation products, such as organic acids, similar to those observed in studies using bulk samples by Carlton et al. (Atmos. Environ. 41, 7588, 2007) are formed. Overall uptake is reduced under our experimental conditions, likely due to increasing temperature and decreasing relative humidity. We also report observation of imidazoles (carbon-nitrogen containing aromatic heterocycles) resulting from reaction of glyoxal with the nitrogen component of the ammonium sulfate seed aerosol. The imidazoles form irreversibly under dark and irradiated conditions, in ammonium sulfate and acidified ammonium sulfate (pH~1) aerosol. The molecular framework of imidazoles is very stable as a result of the aromaticity. The primary imidazole product, which has a low vapor pressure estimated at 0.0014 Torr, is predicted to be present as a (protonated) cation, owing to its basicity (pKB = 7). It is thus likely not a candidate for repartitioning to the gas phase. Evidence for participation of ammonium in reactions with glyoxal using bulk samples has recently been reported by Noziere et al. (JPCA 113, 231, 2008; ACPD 9, 1, 2009). This study reveals the complex chemistry occurring within ammonium sulfate seed aerosol even for systems with greatly reduced complexity compared to atmospheric aerosol. The results increase our understanding of the contribution of glyoxal to SOA formation processes. More specifically, these results provide valuable insights into important aerosol processes, such as organosulfate and oligomer formation, as well as the formation of aromatic nitrogen containing heterocycles from reaction of a carbonyl with ammonium sulfate aerosol.

Effect of intravenous administration of D-lysergic acid diethylamide on initiation of protein synthesis in a cell-free system derived from brain.

PubMed

Cosgrove, J W; Brown, I R

1984-05-01

An initiating cell-free protein synthesis system derived from brain was utilized to demonstrate that the intravenous injection of D-lysergic acid diethylamide (LSD) to rabbits resulted in a lesion at the initiation stage of brain protein synthesis. Three inhibitors of initiation, edeine, poly(I), and aurintricarboxylic acid were used to demonstrate a reduction in initiation-dependent amino acid incorporation in the brain cell-free system. One hour after LSD injection, there was also a measurable decrease in the formation of 40S and 80S initiation complexes in vitro, using either [35S]methionine or [35S]Met-tRNAf. Analysis of the methionine pool size after LSD administration indicated there was no change in methionine levels. Analysis of the formation of initiation complexes in the brain cell-free protein synthesis system prepared 6 h after LSD administration indicated that there was a return to control levels at this time. The effects of LSD on steps in the initiation process are thus reversible.

Computational science: shifting the focus from tools to models

PubMed Central

Hinsen, Konrad

2014-01-01

Computational techniques have revolutionized many aspects of scientific research over the last few decades. Experimentalists use computation for data analysis, processing ever bigger data sets. Theoreticians compute predictions from ever more complex models. However, traditional articles do not permit the publication of big data sets or complex models. As a consequence, these crucial pieces of information no longer enter the scientific record. Moreover, they have become prisoners of scientific software: many models exist only as software implementations, and the data are often stored in proprietary formats defined by the software. In this article, I argue that this emphasis on software tools over models and data is detrimental to science in the long term, and I propose a means by which this can be reversed. PMID:25309728

Enantioseparation of mandelic acid derivatives by high performance liquid chromatography with substituted β-cyclodextrin as chiral mobile phase additive and evaluation of inclusion complex formation

PubMed Central

Tong, Shengqiang; Zhang, Hu; Shen, Mangmang

2014-01-01

The enantioseparation of ten mandelic acid derivatives was performed by reverse phase high performance liquid chromatography with hydroxypropyl-β-cyclodextrin (HP-β-CD) or sulfobutyl ether-β-cyclodextrin (SBE-β-CD) as chiral mobile phase additives, in which inclusion complex formations between cyclodextrins and enantiomers were evaluated. The effects of various factors such as the composition of mobile phase, concentration of cyclodextrins and column temperature on retention and enantioselectivity were studied. The peak resolutions and retention time of the enantiomers were strongly affected by the pH, the organic modifier and the type of β-cyclodextrin in the mobile phase, while the concentration of buffer solution and temperature had a relatively low effect on resolutions. Enantioseparations were successfully achieved on a Shimpack CLC-ODS column (150×4.6 mm i.d., 5 μm). The mobile phase was a mixture of acetonitrile and 0.10 mol L-1 of phosphate buffer at pH 2.68 containing 20 mmol L-1 of HP-β-CD or SBE-β-CD. Semi-preparative enantioseparation of about 10 mg of α-cyclohexylmandelic acid and α-cyclopentylmandelic acid were established individually. Cyclodextrin-enantiomer complex stoichiometries as well as binding constants were investigated. Results showed that stoichiomertries for all the inclusion complex of cyclodextrin-enantiomers were 1:1. PMID:24893270

Formation of hybrid phycobilisomes by association of phycobiliproteins from Nostoc and Fremyella

DOE Office of Scientific and Technical Information (OSTI.GOV)

Canaani, O.; Gantt, E.

1982-09-01

Formation of phycobilisomes has been accomplished in vitro from isolated phycobiliprotein fraction obtained from the same blue-green alga (intrageneric) and from different blue-green algae (intergeneric). Phycobilisomes, which are supramolecular complexes of phycobiliproteins, serve as major light-harvesting antennae for photosynthesis in blue-green and red algae. Intrageneric association into energetically functional phycobilisomes, previously reported to occur with Nostoc sp. allophycocyanin and phycoerythrin-phycocyanin complexes has been obtained with Fremyella diplosiphon. By their spectral propeties (absorption, fluorescence excitation, and emission) and electron microscopic images, the native and in vitro-associated phycobilisomes were virtually indistinguishable. Intergeneic phycobilisomes have been produced from allophycocyanin of Nostoc sp. strainmore » Mac, and phycoerythrin-phycocyanin of F. diplosiphon, as well as from the reverse mixtures. Phycobilisomes of Nostoc and Fremyella, analyzed by NaDodSO/sub 4//polyacrylamide gel electrophoresis, possessed a number of polypeptides having similar molecular weights: the usual ..cap alpha..- and ..beta..-phycobilin-containing polypeptides of M/sub r/ 15,000-22,000, a faint band at M/sub r/ ca. 95,000, and a prominent band at M/sub r/ ca. 31,000. The M/sub r/ 31,000 polypeptide is assumed to provide the recognition site for attachment of the phycoerythrin-phycocyanin complexes with the allophycocyanin core. In vitro association was not obtained between allophycocyanin from Nostoc and phycoerythrin-phycocyanin complexes from Phormidium persicinum or Porphyridium sordidum.« less

Analog modeling and kinematic restoration of inverted hangingwall synclinal basins developed above syn-kinematic salt: Application to the Lusitanian and Parentis basins

NASA Astrophysics Data System (ADS)

Roma, Maria; Vidal-Royo, Oskar; McClay, Ken; Ferrer, Oriol; Muñoz, Josep Anton

2017-04-01

The formation of hagingwall syncline basins is basically constrained by the geometry of the basement-involved fault, but also by salt distribution . The formation of such basins is common around the Iberian Peninsula (e.g. Lusitanian, Parentis, Basque-Cantabian, Cameros and Organyà basins) where Upper Triassic (Keuper) salt governed their polyphasic Mesozoic extension and their subsequent Alpine inversion. In this scenario, a precise interpretation of the sub-salt faults geometry and a reconstruction of the initial salt thickness are key to understand the kinematic evolution of such basins. Using an experimental approach (sandbox models) and these Mesozoic basins as natural analogues, the aim of this work is to: 1) investigate the main parameters that controlled the formation and evolution of hagingwall syncline basins analyzing the role of syn-kinematic salt during extension and subsequent inversion; and 2) quantify the deformation and salt mobilization based on restoration of analog model cross sections. The experimental results demonstrate that premature welds are developed by salt deflation with consequent upward propagation of the basal fault in salt-bearing rift systems with a large amount of extension,. In contrast, thicker salt inhibits the upward fault propagation, which results into a further salt migration and development of a hagingwall syncline basins flanked by salt walls. The inherited extensional architecture as well as salt continuity dramatically controlled subsequent inversion. Shortening initially produced the folding and the uplift of the synclinal basins. Minor reverse faults form as a consequence of overtightening of welded diapir stems. However, no trace of reverse faulting is found around diapirs stems, as ductile unit is still available for extrusion, squeezing and accommodation of shortening. Restoration of the sandbox models has demonstrated that this is a powerful tool to unravel the complex structures in the models and this may similarly be applied to the seismic interpretation of the natural complex salt structures.

Flux-trapping during the formation of field-reversed configurations

NASA Astrophysics Data System (ADS)

Armstrong, W. T.; Harding, D. G.; Crawford, E. A.; Hoffman, A. L.

1981-10-01

Optimized trapping of bias flux during the early formation phases of a Field Reversed Configuration was studied experimentally on the field reversed theta pinch TRX-1. An annular z-pinch preionizer was employed to permit ionization at high values of initial reverse bias flux. Octopole barrier fields are pulsed during field reversal to minimize plasma/wall contact and associated loss of reverse flux. Also, second half cycle operation was examined in obtaining very high values of reverse flux. Flux loss is generally observed to be governed by resistive diffusion through a current sheath at the plasma boundary, rather than flux convection to the plasma boundary. Trapped reverse flux at the time of field reversal, as well as after the radial implosion, is observed to increase with the applied bias field. This increase is greatest, and in fact nearly linear with bias field, when barrier fields are employed. Barrier fields also appear to broaden the current sheath, which results in some flux loss and a less dynamic radial implosion. A general model and one dimensional simulation of flux loss is described and correlated with experimental results.

Luminescence quenching by reversible ionization or exciplex formation/dissociation.

PubMed

Ivanov, Anatoly I; Burshtein, Anatoly I

2008-11-20

The kinetics of fluorescence quenching by both charge transfer and exciplex formation is investigated, with an emphasis on the reversibility and nonstationarity of the reactions. The Weller elementary kinetic scheme of bimolecular geminate ionization and the Markovian rate theory are shown to lead to identical results, provided the rates of the forward and backward reactions account for the numerous recontacts during the reaction encounter. For excitation quenching by the reversible exciplex formation, the Stern-Volmer constant is specified in the framework of the integral encounter theory. The bulk recombination affecting the Stern-Volmer quenching constant makes it different for pulse excited and stationary luminescence. The theory approves that the free energy gap laws for ionization and exciplex formation are different and only the latter fits properly the available data (for lumiflavin quenching by aliphatic amines and aromatic donors) in the endergonic region.

Folding Behaviors of Protein (Lysozyme) Confined in Polyelectrolyte Complex Micelle.

PubMed

Wu, Fu-Gen; Jiang, Yao-Wen; Chen, Zhan; Yu, Zhi-Wu

2016-04-19

The folding/unfolding behavior of proteins (enzymes) in confined space is important for their properties and functions, but such a behavior remains largely unexplored. In this article, we reported our finding that lysozyme and a double hydrophilic block copolymer, methoxypoly(ethylene glycol)5K-block-poly(l-aspartic acid sodium salt)10 (mPEG(5K)-b-PLD10), can form a polyelectrolyte complex micelle with a particle size of ∼30 nm, as verified by dynamic light scattering and transmission electron microscopy. The unfolding and refolding behaviors of lysozyme molecules in the presence of the copolymer were studied by microcalorimetry and circular dichroism spectroscopy. Upon complex formation with mPEG(5K)-b-PLD10, lysozyme changed from its initial native state to a new partially unfolded state. Compared with its native state, this copolymer-complexed new folding state of lysozyme has different secondary and tertiary structures, a decreased thermostability, and significantly altered unfolding/refolding behaviors. It was found that the native lysozyme exhibited reversible unfolding and refolding upon heating and subsequent cooling, while lysozyme in the new folding state (complexed with the oppositely charged PLD segments of the polymer) could unfold upon heating but could not refold upon subsequent cooling. By employing the heating-cooling-reheating procedure, the prevention of complex formation between lysozyme and polymer due to the salt screening effect was observed, and the resulting uncomplexed lysozyme regained its proper unfolding and refolding abilities upon heating and subsequent cooling. Besides, we also pointed out the important role the length of the PLD segment played during the formation of micelles and the monodispersity of the formed micelles. Furthermore, the lysozyme-mPEG(5K)-b-PLD10 mixtures prepared in this work were all transparent, without the formation of large aggregates or precipitates in solution as frequently observed in other protein-polyelectrolyte systems. Hence, the present protein-PEGylated poly(amino acid) mixture provides an ideal water-soluble model system to study the important role of electrostatic interaction in the complexation between proteins and polymers, leading to important new knowledge on the protein-polymer interactions. Moreover, the polyelectrolyte complex micelle formed between protein and PEGylated polymer may provide a good drug delivery vehicle for therapeutic proteins.

Bright, Multi-responsive, Sky-Blue Platinum(II) Phosphors Based on a Tetradentate Chelating Framework.

PubMed

Liu, Lijie; Wang, Xiang; Wang, Nan; Peng, Tai; Wang, Suning

2017-07-24

A new class of highly efficient and stable, blue-phosphorescent Pt II complexes based on a tetradentate chelating framework has been found to exhibit highly sensitive and reversible responses to multiple external stimuli including temperature, pressure, and UV irradiation with distinct phosphorescent color switching-from blue to red or white. Intermolecular excimer formation is the main origin of this intriguing multi-response phenomenon. Highly efficient singlet-oxygen sensitization by the Pt II compounds yields UV-light-induced phosphorescence enhancement and color switching. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Photochemical Reactions of (n(5)-Pentamethylcyclpentadienyl)-Dicarbonyliron-Alkyl and -Silyl Complexes: Reversible Ethylene Insertion into an Iron-Silicon Bond and Implications for the Mechanism of Transition Metal-Catalyzed Hydrosilation of Alkenes.

DTIC Science & Technology

1985-12-11

RD-R162 462 PHOTOCHEMICAL REACTIONS OF(N(S)-P NTANETNYLCVCLPENTADIENYL)-DICARRONVLIR.. (U) MASSACHUSETTS INST OF TECH CAMBRIDGE DEPT OF CHEMISTRY...34 Photochemical Reactions of (n5-Pentamethylcyclpentadienyl)- Dicarbonyliron-Alkyl and -Silyl Complexes: Reversible Ethylene Insertion into an Iron-Silicon Bond...Chemical Society) PHOTOCHEMICAL REACTIONS OF (n5-PENTAMETHYLCYCLOPENTADIENYL)- DICARBONYLIRON-ALKYL AND -SILYL COMPLEXES: REVERSIBLE ETHYLENE INSERTION INTO

Reversible Self-Assembly of Water-Soluble Gold(I) Complexes.

PubMed

Aguiló, Elisabet; Moro, Artur J; Gavara, Raquel; Alfonso, Ignacio; Pérez, Yolanda; Zaccaria, Francesco; Guerra, Célia Fonseca; Malfois, Marc; Baucells, Clara; Ferrer, Montserrat; Lima, João Carlos; Rodríguez, Laura

2018-02-05

The reaction of the gold polymers containing bipyridyl and terpyridyl units, [Au(C≡CC 15 H 10 N 3 )] n and [Au(C≡CC 10 H 7 N 2 )] n , with the water-soluble phosphines 1,3,5-triaza-7-phosphatricyclo[3.3.1.13.7]decane and 3,7-diacetyl-1,3,7-triaza-5-phosphabicyclo[3.3.1]nonane gives rise to the formation of four gold(I) alkynyl complexes that self-assemble in water (H 2 O) and dimethyl sulfoxide (DMSO), through different intermolecular interactions, with an impact on the observed luminescence displayed by the supramolecular assemblies. A detailed analysis carried out by NMR studies performed in different DMSO/deuterated H 2 O mixtures indicates the presence of two different assembly modes in the aggregates: (i) chain assemblies, which are based mainly on aurophilic interactions, and (ii) stacked assemblies, which are based on Au···π and π···π interactions. These different supramolecular environments can also be detected by their intrinsic optical properties (differences in absorption and emission spectra) and are predicted by the changes in the relative binding energy from density functional theory calculations carried out in DMSO and H 2 O. Small-angle X-ray scattering (SAXS) experiments performed in the same mixture of solvents are in agreement with the formation of aggregates in all cases. The aromatic units chosen, bipyridine and terpyridine, allow the use of external stimuli to reversibly change the aggregation state of the supramolecular assemblies. Interaction with the Zn 2+ cation is observed to disassemble the aggregates, while encapsulating agents competing for Zn 2+ complexation revert the process to the aggregation stage, as verified by SAXS and NMR. The adaptive nature of the supramolecular assemblies to the metal-ion content is accompanied by significant changes in the absorption and emission spectra, signaling the aggregation state and also the content on Zn 2+ .

Quantitative Analysis of HIV-1 Preintegration Complexes

PubMed Central

Engelman, Alan; Oztop, Ilker; Vandegraaff, Nick; Raghavendra, Nidhanapati K.

2009-01-01

Retroviral replication proceeds through the formation of a provirus, an integrated DNA copy of the viral RNA genome. The linear cDNA product of reverse transcription is the integration substrate and two different integrase activities, 3′ processing and DNA strand transfer, are required for provirus formation. Integrase nicks the cDNA ends adjacent to phylogenetically-conserved CA dinucleotides during 3′ processing. After nuclear entry and locating a suitable chromatin acceptor site, integrase joins the recessed 3′-OHs to the 5′-phosphates of a double-stranded staggered cut in the DNA target. Integrase functions in the context of a large nucleoprotein complex, called the preintegration complex (PIC), and PICs are analyzed to determine levels of integrase 3′ processing and DNA strand transfer activities that occur during acute virus infection. Denatured cDNA end regions are monitored by indirect end-labeling to measure the extent of 3′ processing. Native PICs can efficiently integrate their viral cDNA into exogenously added target DNA in vitro, and Southern blotting or nested PCR assays are used to quantify the resultant DNA strand transfer activity. This study details HIV-1 infection, PIC extraction, partial purification, and quantitative analyses of integrase 3′ processing and DNA strand transfer activities. PMID:19233280

Mechanisms and Kinetics of Alkaline Hydrolysis of the Energetic Nitroaromatic Compounds 2,4,6-Trinitrotoluene (TNT) and 2,4-Dinitroanisole (DNAN)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Salter-Blanc, Alexandra J.; Bylaska, Eric J.; Ritchie, Julia J.

2013-07-02

The environmental impacts of energetic compounds can be minimized through the design and selection of new energetic materials with favorable fate properties. Building predictive models to inform this process, however, is difficult because of uncertainties and complexities in some major fate-determining transformation reactions such as the alkaline hydrolysis of energetic nitroaromatic compounds (NACs). Prior work on the mechanisms of the reaction between NACs and OH– has yielded inconsistent results. In this study, the alkaline hydrolysis of 2,4,6-trinitrotoluene (TNT) and 2,4-dinitroanisole (DNAN) was investigated with coordinated experimental kinetic measurements and molecular modeling calculations. For TNT, the results suggest reversible formation ofmore » an initial product, which is likely either a Meisenheimer complex or a TNT anion formed by abstraction of a methyl proton by OH–. For DNAN, the results suggest that a Meisenheimer complex is an intermediate in the formation of 2,4-dinitrophenolate. Despite these advances, the remaining uncertainties in the mechanisms of these reactions—and potential variability between the hydrolysis mechanisms for different NACs—mean that it is not yet possible to generalize the results into predictive models (e.g., quantitative structure–activity relationships, QSARs) for hydrolysis of other NACs.« less

Mechanisms and kinetics of alkaline hydrolysis of the energetic nitroaromatic compounds 2,4,6-trinitrotoluene (TNT) and 2,4-dinitroanisole (DNAN).

PubMed

Salter-Blanc, Alexandra J; Bylaska, Eric J; Ritchie, Julia J; Tratnyek, Paul G

2013-07-02

The environmental impacts of energetic compounds can be minimized through the design and selection of new energetic materials with favorable fate properties. Building predictive models to inform this process, however, is difficult because of uncertainties and complexities in some major fate-determining transformation reactions such as the alkaline hydrolysis of energetic nitroaromatic compounds (NACs). Prior work on the mechanisms of the reaction between NACs and OH(-) has yielded inconsistent results. In this study, the alkaline hydrolysis of 2,4,6-trinitrotoluene (TNT) and 2,4-dinitroanisole (DNAN) was investigated with coordinated experimental kinetic measurements and molecular modeling calculations. For TNT, the results suggest reversible formation of an initial product, which is likely either a Meisenheimer complex or a TNT anion formed by abstraction of a methyl proton by OH(-). For DNAN, the results suggest that a Meisenheimer complex is an intermediate in the formation of 2,4-dinitrophenolate. Despite these advances, the remaining uncertainties in the mechanisms of these reactions-and potential variability between the hydrolysis mechanisms for different NACs-mean that it is not yet possible to generalize the results into predictive models (e.g., quantitative structure-activity relationships, QSARs) for hydrolysis of other NACs.

Synthesis, characterization, redox behavior, DNA and protein binding and antibacterial activity studies of ruthenium(II) complexes of bidentate schiff bases.

PubMed

Paul, Hena; Sen, Buddhadeb; Mondal, Tapan Kumar; Chattopadhyay, Pabitra

2017-08-03

Two new ruthenium(II) complexes of Schiff base ligands (L) derived from cinnamaldehyde and ethylenediamine formulated as [Ru(L)(bpy) 2 ](ClO 4 ) 2 , where L 1 = N,N'-bis(4-nitrocinnamald-ehyde)ethylenediamine and L 2 = N,N'-bis(2-nitrocinnamaldehyde)-ethylenediamine for complex 1 and 2, respectively, were isolated in pure form. The complexes were characterized by physicochemical and spectroscopic methods. The electrochemical behavior of the complexes showed the Ru(III)/Ru(II) couple at different potentials with quasi-reversible voltammograms. The interaction of the complexes with calf thymus DNA (CT-DNA) using absorption, emission spectral studies and electrochemical techniques have been used to determine the binding constant, K b and the linear Stern-Volmer quenching constant, K SV . The results indicate that the ruthenium(II) complexes interact with CT-DNA strongly in a groove binding mode. The interactions of bovine serum albumin (BSA) with the complexes were also investigated with the help of absorption and fluorescence spectroscopy tools. Absorption spectroscopy proved the formation of a ground state BSA-[Ru(L)(bpy) 2 ](ClO 4 ) 2 complex. The antibacterial study showed that the Ru(II) complexes (1 and 2) have better activity than the standard antibiotics but weak activity than the ligands.

Particle-in-cell simulations of Earth-like magnetosphere during a magnetic field reversal

NASA Astrophysics Data System (ADS)

Barbosa, M. V. G.; Alves, M. V.; Vieira, L. E. A.; Schmitz, R. G.

2017-12-01

The geologic record shows that hundreds of pole reversals have occurred throughout Earth's history. The mean interval between the poles reversals is roughly 200 to 300 thousand years and the last reversal occurred around 780 thousand years ago. Pole reversal is a slow process, during which the strength of the magnetic field decreases, become more complex, with the appearance of more than two poles for some time and then the field strength increases, changing polarity. Along the process, the magnetic field configuration changes, leaving the Earth-like planet vulnerable to the harmful effects of the Sun. Understanding what happens with the magnetosphere during these pole reversals is an open topic of investigation. Only recently PIC codes are used to modeling magnetospheres. Here we use the particle code iPIC3D [Markidis et al, Mathematics and Computers in Simulation, 2010] to simulate an Earth-like magnetosphere at three different times along the pole reversal process. The code was modified, so the Earth-like magnetic field is generated using an expansion in spherical harmonics with the Gauss coefficients given by a MHD simulation of the Earth's core [Glatzmaier et al, Nature, 1995; 1999; private communication to L.E.A.V.]. Simulations show the qualitative behavior of the magnetosphere, such as the current structures. Only the planet magnetic field was changed in the runs. The solar wind is the same for all runs. Preliminary results show the formation of the Chapman-Ferraro current in the front of the magnetosphere in all the cases. Run for the middle of the reversal process, the low intensity magnetic field and its asymmetrical configuration the current structure changes and the presence of multiple poles can be observed. In all simulations, a structure similar to the radiation belts was found. Simulations of more severe solar wind conditions are necessary to determine the real impact of the reversal in the magnetosphere.

Paleomagnetism of the Cretaceous Galula Formation and implications for vertebrate evolution

NASA Astrophysics Data System (ADS)

Widlansky, Sarah J.; Clyde, William C.; O'Connor, Patrick M.; Roberts, Eric M.; Stevens, Nancy J.

2018-03-01

This study uses magnetostratigraphy to help constrain the age of the paleontologically important Galula Formation (Rukwa Rift Basin, southwestern Tanzania). The formation preserves a Cretaceous vertebrate fauna, including saurischian dinosaurs, a putative gondwanatherian mammal, and notosuchian crocodyliforms. With better dating, the Galula Formation and its fossils help fill a temporal gap in our understanding of vertebrate evolution in continental Africa, enabling better evaluation of competing paleobiogeographic hypotheses concerning faunal exchange throughout Gondwana during the Cretaceous. Paleomagnetic samples for this study were collected from the Namba (higher in section) and Mtuka (lower in section) members of the Galula Formation and underwent stepwise thermal demagnetization. All samples displayed a strong normal magnetic polarity overprint, and maximum unblocking temperatures at approximately 690 °C. Three short reversed intervals were identified in the Namba Member, whereas the Mtuka Member lacked any clear reversals. Given the relatively limited existing age constraints, one interpretation correlates the Namba Member to Chron C32. An alternative correlation assigns reversals in the Namba Member to recently proposed short reversals near the end of the Cretaceous Normal Superchron (Chron C34), a time that is traditionally interpreted as having stable normal polarity. The lack of reversals in the Mtuka Member supports deposition within Chron C34. These data suggest that the Namba Member is no older than Late Cretaceous (Cenomanian-Campanian), with the Mtuka Member less well constrained to the middle Cretaceous (Aptian-Cenomanian). The paleomagnetic results are supported by the application of fold and reversal tests for paleomagnetic stability, and paleomagnetic poles for the Namba (246.4°/77.9°, α95 5.9°) and Mtuka (217.1°/72.2°, α95 11.1°) members closely matching the apparent polar wander path for Africa during the Late Cretaceous. These results confidently indicate a Late Creteceous age assignment for the Namba Member of the Galula Formation, a unit that has yielded key crocodyliform (e.g., Pakasuchus; Rukwasuchus) and dinosaur (e.g., Rukwatitan; Shingopana) fossils from eastern Africa.

Biasing hydrogen bond donating host systems towards chemical warfare agent recognition.

PubMed

Hiscock, Jennifer R; Wells, Neil J; Ede, Jayne A; Gale, Philip A; Sambrook, Mark R

2016-10-12

A series of neutral ditopic and negatively charged, monotopic host molecules have been evaluated for their ability to bind chloride and dihydrogen phosphate anions, and neutral organophosphorus species dimethyl methylphosphonate (DMMP), pinacolyl methylphosphonate (PMP) and the chemical warfare agent (CWA) pinacolyl methylphosphonofluoridate (GD, soman) in organic solvent via hydrogen bonding. Urea, thiourea and boronic acid groups are shown to bind anions and neutral guests through the formation of hydrogen bonds, with the urea and thiourea groups typically exhibiting higher affinity interactions. The introduction of a negative charge on the host structure is shown to decrease anion affinity, whilst still allowing for high stability host-GD complex formation. Importantly, the affinity of the host for the neutral CWA GD is greater than for anionic guests, thus demonstrating the potential for selectivity reversal based on charge repulsion.

Intercellular signaling in Stigmatella aurantiaca: Purification and characterization of stigmolone, a myxobacterial pheromone

PubMed Central

Plaga, Wulf; Stamm, Irmela; Schairer, Hans Ulrich

1998-01-01

The myxobacterium Stigmatella aurantiaca passes through a life cycle that involves formation of a multicellular fruiting body as the most complex stage. An early step in this differentiation process depends on a signal factor secreted by the cells when nutrients become limited. The formation of a fruiting body from a small cell population can be accelerated by addition of this secreted material. The bioactive compound was found to be steam volatile. It was purified to homogeneity by steam distillation followed by reversed-phase and normal-phase HPLC. The pheromone was named stigmolone, in accordance with the structure 2,5,8-trimethyl-8-hydroxy-nonan-4-one, as determined by NMR and mass spectrometry. Stigmolone represents a structurally unique and highly bioactive prokaryotic pheromone that is effective in the bioassay at 1 nM concentration. PMID:9736724

Intercellular signaling in Stigmatella aurantiaca: purification and characterization of stigmolone, a myxobacterial pheromone.

PubMed

Plaga, W; Stamm, I; Schairer, H U

1998-09-15

The myxobacterium Stigmatella aurantiaca passes through a life cycle that involves formation of a multicellular fruiting body as the most complex stage. An early step in this differentiation process depends on a signal factor secreted by the cells when nutrients become limited. The formation of a fruiting body from a small cell population can be accelerated by addition of this secreted material. The bioactive compound was found to be steam volatile. It was purified to homogeneity by steam distillation followed by reversed-phase and normal-phase HPLC. The pheromone was named stigmolone, in accordance with the structure 2,5, 8-trimethyl-8-hydroxy-nonan-4-one, as determined by NMR and mass spectrometry. Stigmolone represents a structurally unique and highly bioactive prokaryotic pheromone that is effective in the bioassay at 1 nM concentration.

Nitric Oxide Mediates Glutamate-Linked Enhancement of cGMP Levels in the Cerebellum

NASA Astrophysics Data System (ADS)

Bredt, David S.; Snyder, Solomon H.

1989-11-01

Nitric oxide, which mediates influences of numerous neurotransmitters and modulators on vascular smooth muscle and leukocytes, can be formed in the brain from arginine by an enzymatic activity that stoichiometrically generates citrulline. We show that glutamate and related amino acids, such as N-methyl-D-aspartate, markedly stimulate arginine-citrulline transformation in cerebellar slices stoichiometrically with enhancement of cGMP levels. Nω-monomethyl-L-arginine blocks the augmentation both of citrulline and cGMP with identical potencies. Arginine competitively reverses both effects of Nω-monomethyl-L-arginine with the same potencies. Hemoglobin, which complexes nitric oxide, prevents the stimulation by N-methyl-D-aspartate of cGMP levels, and superoxide dismutase, which elevates nitric oxide levels, increases cGMP formation. These data establish that nitric oxide mediates the stimulation by glutamate of cGMP formation.

Phase transitions and photoinduced transformations at high pressure in the molecular donor-acceptor fullerene complex (Cd(dedtc){sub 2}){sub 2} · C{sub 60}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Meletov, K. P., E-mail: mele@issp.ac.ru; Konarev, D. V.; Tolstikova, A. O.

2015-06-15

The Raman spectra of crystals of C{sub 60} fullerene-cadmium diethyldithiocarbamate molecular donor-acceptor complexes (Cd(dedtc){sub 2}){sub 2} · C{sub 60} were measured at pressures of up to 17 GPa, and the crystal lattice parameters of these complexes were determined at pressures of up to 6 GPa. An increase in pressure up to ∼2 GPa leads to changes in the Raman spectra, which are manifested by splitting of the intramolecular H{sub g}(1)-H{sub g}(8) phonon modes and by softening of the A{sub g}(2) mode of the C{sub 60} molecule. A further increase in pressure up to 17 GPa does not induce significant newmore » changes to the Raman spectra, while a decrease is accompanied by the reverse transformation at a pressure of about 2 GPa. The pressure dependence of the lattice parameters also exhibits a reversible feature at 2 GPa related to a jumplike decrease in compressibility. All these data are indicative of a phase transition in the vicinity of 2 GPa related to the formation of covalent bonds between C{sub 60} molecules and, probably, the appearance of C{sub 120} dimers in fullerene layers. It was also found that, in the pressure interval from 2 to 6.3 GPa, the Raman spectra of complexes exhibit photoinduced transformations under prolonged exposure to laser radiation with a wavelength of λ = 532 nm and power density up to 5000 W/cm{sup 2}. These changes are manifested by splitting and softening of the A{sub g}(2) mode and resemble analogous changes accompanying the photopolymerization of C{sub 60} fullerene. The intensity of new bands exhibits exponential growth with increasing exposure time. The photopolymer yield depends on both the laser radiation power and external pressure. The A{sub g}(2) mode splitting under irradiation can be related to the formation of photo-oligomers with various numbers of intermolecular covalent bonds per C{sub 60} molecule.« less

Reversible exposure of hydrophobic residues on albumin as a novel strategy for formulation of nanodelivery vehicles for taxanes

PubMed Central

Garro, AG; Beltramo, DM; Alasino, RV; Leonhard, V; Heredia, V; Bianco, ID

2011-01-01

Background: We report herein a novel strategy for the preparation of protein-based nanode-livery vehicles for hydrophobic active pharmaceutical ingredients. Methods: The procedure consisted of three steps, ie, exposure of hydrophobic residues of a protein to a pH-induced partial unfolding: interaction between hydrophobic residues on the protein and the hydrophobic active pharmaceutical ingredient, and a final step where the structure of the protein was reversed to a native-like state by returning to neutral pH. As proof of concept, the interaction of paclitaxel with partially unfolded states of human serum albumin was evaluated as a potential method for the preparation of water-soluble complexes of the taxane with albumin. Results: We found that paclitaxel readily binds to pH-induced partially unfolded albumin, leading to the formation of optically clear water-soluble complexes. The complexes thus formed were more stable in solution when the albumin native state was at least partially restored by neutralization of the solution to a pH around 7. It was also observed that the hydrodynamic radius of human serum albumin was only slightly increased after the cycle of pH changes, remaining in a monomeric state with a size according to paclitaxel binding. Furthermore, paclitaxel binding did not affect the overall exposure of charged groups of human serum albumin, as evaluated by its interaction with an ionic exchange resin. Conclusion: The in vitro biological activity of the complexes formed was qualitatively equivalent to that of a Cremophor®-based formulation. PMID:21822381

Reversible Thermoset Adhesives

NASA Technical Reports Server (NTRS)

Mac Murray, Benjamin C. (Inventor); Tong, Tat H. (Inventor); Hreha, Richard D. (Inventor)

2016-01-01

Embodiments of a reversible thermoset adhesive formed by incorporating thermally-reversible cross-linking units and a method for making the reversible thermoset adhesive are provided. One approach to formulating reversible thermoset adhesives includes incorporating dienes, such as furans, and dienophiles, such as maleimides, into a polymer network as reversible covalent cross-links using Diels Alder cross-link formation between the diene and dienophile. The chemical components may be selected based on their compatibility with adhesive chemistry as well as their ability to undergo controlled, reversible cross-linking chemistry.

Negative vortices: The formation of vortex rings with reversed rotation in viscoelastic liquids

NASA Astrophysics Data System (ADS)

Palacios-Morales, Carlos; Barbosa, Christophe; Solorio, Francisco; Zenit, Roberto

2015-05-01

The formation process of vortex rings in a viscoelastic liquid is studied experimentally considering a piston-cylinder arrangement. Initially, a vortex ring begins to form as fluid is injected from the cylinder into the tank in a manner similar to that observed for Newtonian liquids. For later times, when the piston ceases its motion, the flow changes dramatically. A secondary vortex with reversed spinning direction appears and grows to be as large in size as the original one. The formation process is studied by contrasting the evolution with that obtained for Newtonian liquids with equivalent Reynolds numbers and stroke ratios. We argue that the reversing flow, or negative vortex, results from the combined action of shear and extension rates produced during the vortex formation, in a process similar to that observed behind ascending bubbles and falling spheres in viscoelastic media.

Studies on G-protein alpha.betagamma heterotrimer formation reveal a putative S-prenyl-binding site in the alpha subunit.

PubMed Central

Dietrich, Alexander; Scheer, Alexander; Illenberger, Daria; Kloog, Yoel; Henis, Yoav I; Gierschik, Peter

2003-01-01

The alpha and betagamma subunits of heterotrimeric G-proteins contain specific lipid modifications, which are required for their biological function. However, the relevance of these modifications to the interactions within the heterotrimeric G-protein is not fully understood. In order to explore the role of the S-prenyl moiety of the isoprenylated betagamma dimer of retinal transducin, betagamma(t), in the formation of the heterotrimeric complex with the corresponding N-acylated alpha subunit, alpha(t), we employed purified fully processed subunits, which are soluble in aqueous solutions without detergents. Pertussis-toxin-mediated [(32)P]ADP-ribosylation of alpha(t) is strongly stimulated (approximately 10-fold) in the presence of betagamma(t) and can thus serve as a measure for heterotrimer formation. Using this assay, preincubation of alpha(t) with S-prenyl analogues containing farnesyl or geranylgeranyl moieties was found to inhibit heterotrimer formation in a dose-dependent manner. The inhibition was competitive and reversible, as indicated by its reversal upon increase of the betagamma(t) dimer concentration or by removal of the S-prenyl analogue using gel filtration. The competitive nature of the inhibition is supported by the marked attenuation of the inhibition when the S-prenyl analogue was added to alpha(t) together with or after betagamma(t). The inhibition does not involve interaction with the alpha(t) acyl group, since an S-prenyl analogue inhibited the [(32)P]ADP-ribosylation of an unlipidated alpha(t) mutant. These data suggest the existence of a hitherto unrecognized S-prenyl-binding site in alpha(t), which is critical for its interaction with prenylated betagamma(t). PMID:12952523

The role of water in the formation of reversed micelles: An antimicellization agent

USGS Publications Warehouse

Yu, Z.-J.; Zhou, N.-F.; Neuman, R.D.

1992-01-01

Micellization of sodium bis(2-ethylhexyl) phosphate in n-heptane has been studied under controlled environmental conditions by dynamic and static light scattering. The results clearly show that a trace amount of water has a very dramatic effect on reversed micellization. In contrast with results in the literature, water can function as an antimicellization agent. The generality of and the evidence for supporting the current view that water is a prerequisite for the formation of reversed micelles are discussed and criticized. ?? 1992 American Chemical Society.

Charge displacement in bacteriorhodopsin during the forward and reverse bR-K phototransition.

PubMed Central

Groma, G I; Hebling, J; Ludwig, C; Kuhl, J

1995-01-01

Dried oriented purple membrane samples of Halobacterium salinarium were excited by 150 fs laser pulses of 620 nm with a 7 kHz repetition rate. An unusual complex picosecond electric response signal consisting of a positive and a negative peak was detected by a sampling oscilloscope. The ratio of the two peaks was changed by 1) reducing the repetition rate, 2) varying the intensity of the excitation beam, and 3) applying background illumination by light of 647 nm or 511 nm. All of these features can be explained by the simultaneous excitation of the bacteriorhodopsin ground form and the K intermediate. The latter was populated by the (quasi)continuous excitation attributable to its prolonged lifetime in a dehydrated state. Least-square analysis resulted in a 5 ps upper and 2.5 ps lower limit for the time constant of the charge displacement process, corresponding to the forward reaction. That is in good agreement with the formation time of K. The charge separation driven by the reverse phototransition was faster, having a time constant of a 3.5 ps upper limit. The difference in the rates indicates the existence of different routes for the forward and the reverse photoreactions. PMID:8580349

Super strong dopamine hydrogels with shape memory and bioinspired actuating behaviours modulated by solvent exchange.

PubMed

Huang, Jiahe; Liao, Jiexin; Wang, Tao; Sun, Weixiang; Tong, Zhen

2018-03-28

Dopamine-containing hydrogels were synthesized by copolymerization of dopamine methacrylamide (DMA), N,N-dimethylacrylamide (DMAA), and an N,N'-methylenebisacrylamide (BIS) crosslinker in a mixed solvent of water and DMSO. The association of DMA was formed by simply immersing in water to facilely reinforce the hydrogel due to the introduction of the second physical crosslinking. The tensile strength of the hydrogels was increased greatly and regulated in a wide range from 200 kPa to over 2 MPa. The association of DMA was destroyed upon immersing in DMSO. This reversible formation and dissociation of the association structure endowed the hydrogel with shape memory and actuating capabilities. Rapid shape fixing in water and complete shape recovery in DMSO was realized within several minutes. Bioinspired functional soft actuators were designed based on the reversible association and metal ion coordination of DMA, including fast responsive hydrogel tentacles, programable multiple shape change, reversible and versatile painting and writing "hydrogel paper". The facile preparation and strength regulation provide a new way to design novel soft actuators through solvent exchange, and will inspire more complex applications upon combining the association with other properties of mussel inspired dopamine derivatives.

Achieving Reversible H2/H+ Interconversion at Room Temperature with Enzyme-Inspired Molecular Complexes: A Mechanistic Study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Priyadarshani, Nilusha; Dutta, Arnab; Ginovska-Pangovska, Bojana

Inspired by the contribution of the protein scaffold to the efficiency with which enzymes function, we report the first molecular complex that is reversible for electrocatalytic H2 production/oxidation at room temperature in methanol. [Ni(PCy2NPhe2)2]2+ (CyPhe; PR2NR’2 = 1,5-diaza-3,7-diphosphacyclooctane, Cy=cyclohexyl, Phe=phenylalanine), shows reversible behavior in acidic methanol with peripheral phenylalanine groups providing key contributions to the catalytic behavior. The importance of the aromatic rings is implicated in achieving reversibility, based on the lack of reversibility of similar complexes, [Ni(PCy2NAmino Acid2)2]2+, containing arginine (CyArg) or glycine (CyGly). A complex with an added OH group on the ring, (CyTyr; Tyr=Tyrosine), also shows similarmore » behavior. NMR studies reveal a significantly slower rate of chair-boat isomerization for the CyPhe relative to other derivatives, suggesting that the aromatic groups provide structural control by interacting with each other, an observation supported by molecular dynamics studies. NMR studies also show extremely fast proton movement, with a proton pathway from the Ni-H through the pendant amine to the –COOH group. Further, studies of acomplex without the –COOH group, [Ni(PCy2NTym2)2]2+ (CyTym; Tym=Tyramine), are not reversible and have slow proton movement from the pendant amine, demonstrating the essential nature of the –COOH group in achieving reversibility. Finally, methanol is demonstrated to play a critical contributing role. The influence of multiple factors on reversibility for this synthetic catalyst is a demonstration of the intricate interplay between the first, second, and outer coordination spheres and resembles the complexity observed in metalloenzymes.« less

Evidence of preorganization in quinonoid intermediate formation from L-Trp in H463F mutant Escherichia coli tryptophan indole-lyase from effects of pressure and pH.

PubMed

Phillips, Robert S; Kalu, Ukoha; Hay, Sam

2012-08-21

The effects of pH and hydrostatic pressure on the reaction of H463F tryptophan indole-lyase (TIL) have been evaluated. The mutant TIL shows very low activity for elimination of indole but is still competent to form a quinonoid intermediate from l-tryptophan [Phillips, R. S., Johnson, N., and Kamath, A. V. (2002) Biochemistry 41, 4012-4019]. Stopped-flow measurements show that the formation of the quinonoid intermediate at 505 nm is affected by pH, with a bell-shaped dependence for the forward rate constant, k(f), and dependence on a single basic group for the reverse rate constant, k(r), with the following values: pK(a1) = 8.14 ± 0.15, pK(a2) = 7.54 ± 0.15, k(f,min) = 18.1 ± 1.3 s(-1), k(f,max) = 179 ± 46.3 s(-1), k(r,min) = 11.4 ± 1.2 s(-1), and k(r,max) = 33 ± 1.6 s(-1). The pH effects may be due to ionization of Tyr74 as the base and Cys298 as the acid influencing the rate constant for deprotonation. High-pressure stopped-flow measurements were performed at pH 8, which is the optimum for the forward reaction. The rate constants show an increase with pressure up to 100 MPa and a subsequent decrease above 100 MPa. Fitting the pressure data gives the following values: k(f,0) = 15.4 ± 0.8 s(-1), ΔV(‡) = -29.4 ± 2.9 cm(3) mol(-1), and Δβ(‡) = -0.23 ± 0.03 cm(3) mol(-1) MPa(-1) for the forward reaction, and k(r,0) = 20.7 ± 0.8 s(-1), ΔV(‡) = -9.6 ± 2.3 cm(3) mol(-1), and Δβ(‡) = -0.05 ± 0.02 cm(3) mol(-1) MPa(-1) for the reverse reaction. The primary kinetic isotope effect on quinonoid intermediate formation at pH 8 is small (~2) and is not significantly pressure-dependent, suggesting that the effect of pressure on k(f) may be due to perturbation of an active site preorganization step. The negative activation volume is also consistent with preorganization of the ES complex prior to quinonoid intermediate formation, and the negative compressibility may be due to the effect of pressure on the enzyme conformation. These results support the conclusion that the preorganization of the H463F TIL Trp complex, which is probably dominated by motion of the l-Trp indole moiety of the aldimine complex, contributes to quinonoid intermediate formation.

Efficient whole cell biocatalyst for formate-based hydrogen production.

PubMed

Kottenhahn, Patrick; Schuchmann, Kai; Müller, Volker

2018-01-01

Molecular hydrogen (H 2 ) is an attractive future energy carrier to replace fossil fuels. Biologically and sustainably produced H 2 could contribute significantly to the future energy mix. However, biological H 2 production methods are faced with multiple barriers including substrate cost, low production rates, and low yields. The C1 compound formate is a promising substrate for biological H 2 production, as it can be produced itself from various sources including electrochemical reduction of CO 2 or from synthesis gas. Many microbes that can produce H 2 from formate have been isolated; however, in most cases H 2 production rates cannot compete with other H 2 production methods. We established a formate-based H 2 production method utilizing the acetogenic bacterium Acetobacterium woodii . This organism can use formate as sole energy and carbon source and possesses a novel enzyme complex, the hydrogen-dependent CO 2 reductase that catalyzes oxidation of formate to H 2 and CO 2 . Cell suspensions reached specific formate-dependent H 2 production rates of 71 mmol g protein -1 h -1 (30.5 mmol g CDW -1 h -1 ) and maximum volumetric H 2 evolution rates of 79 mmol L -1 h -1 . Using growing cells in a two-step closed batch fermentation, specific H 2 production rates reached 66 mmol g CDW -1 h -1 with a volumetric H 2 evolution rate of 7.9 mmol L -1  h -1 . Acetate was the major side product that decreased the H 2 yield. We demonstrate that inhibition of the energy metabolism by addition of a sodium ionophore is suitable to completely abolish acetate formation. Under these conditions, yields up to 1 mol H 2 per mol formate were achieved. The same ionophore can be used in cultures utilizing formate as specific switch from a growing phase to a H 2 production phase. Acetobacterium woodii reached one of the highest formate-dependent specific H 2 productivity rates at ambient temperatures reported so far for an organism without genetic modification and converted the substrate exclusively to H 2 . This makes this organism a very promising candidate for sustainable H 2 production and, because of the reversibility of the A. woodii enzyme, also a candidate for reversible H 2 storage.

Reversibility of electrochemical reactions of sulfur supported on inverse opal carbon in glyme-Li salt molten complex electrolytes.

PubMed

Tachikawa, Naoki; Yamauchi, Kento; Takashima, Eriko; Park, Jun-Woo; Dokko, Kaoru; Watanabe, Masayoshi

2011-07-28

Electrochemical reactions of sulfur supported on three-dimensionally ordered macroporous carbon in glyme-Li salt molten complex electrolytes exhibit good reversibility and large capacity based on the mass of sulfur, which suggests that glyme-Li salt molten complexes are suitable electrolytes for Li-S batteries.

Mitochondrial complex I inhibitor rotenone inhibits and redistributes vesicular monoamine transporter 2 via nitration in human dopaminergic SH-SY5Y cells.

PubMed

Watabe, Masahiko; Nakaki, Toshio

2008-10-01

Parkinson's disease is a progressive neurodegenerative disorder characterized by selective degeneration of nigrostriatal dopaminergic neurons. Long-term systemic mitochondrial complex I inhibition by rotenone induces selective degeneration of dopaminergic neurons in rats. We have reported dopamine redistribution from vesicles to the cytosol to play a crucial role in selective dopaminergic cell apoptosis. In the present study, we investigated how rotenone causes dopamine redistribution to the cytosol using an in vitro model of human dopaminergic SH-SY5Y cells. Rotenone stimulated nitration of the tyrosine residues of intracellular proteins. The inhibition of nitric-oxide synthase or reactive oxygen species decreased the amount of nitrotyrosine and attenuated rotenone-induced apoptosis. When we examined the intracellular localization of dopamine immunocytochemically using anti-dopamine/vesicular monoamine transporter 2 (VMAT2) antibodies and quantitatively using high-performance liquid chromatography, inhibiting nitration was found to suppress rotenone-induced dopamine redistribution from vesicles to the cytosol. We demonstrated rotenone to nitrate tyrosine residues of VMAT2 using an immunocytochemical method with anti-nitrotyrosine antibodies and biochemically with immunoprecipitation experiments. Rotenone inhibited the VMAT2 activity responsible for the uptake of dopamine into vesicles, and this inhibition was reversed by inhibiting nitration. Moreover, rotenone induced the accumulation of aggregate-like formations in the stained image of VMAT2, which was reversed by inhibiting nitration. Our findings demonstrate that nitration of the tyrosine residues of VMAT2 by rotenone leads to both functional inhibition and accumulation of aggregate-like formations of VMAT2 and consequently to the redistribution of dopamine to the cytosol and apoptosis of dopaminergic SH-SY5Y cells.

Complex surface rupturing and related formation mechanisms in the Xiaoyudong area for the 2008 Mw 7.9 Wenchuan Earthquake, China

NASA Astrophysics Data System (ADS)

Tan, Xi-bin; Yuan, Ren-mao; Xu, Xi-wei; Chen, Gui-hua; Klinger, Yann; Chang, Chung-Pai; Ren, Jun-jie; Xu, Chong; Li, Kang

2012-09-01

The large oblique reverse slip shock of the 2008 Mw = 7.9 Wenchuan earthquake, China, produced one of the longest and most complicated surface ruptures ever known. The complexity is particularly evident in the Xiaoyudong area, where three special phenomena occurred: the 7 km long Xiaoyudong rupture perpendicular to the Beichuan-Yingxiu fault; the occurrence of two parallel faults rupturing simultaneously, and apparent discontinuity of the Beichuan-Yingxiu rupture. This paper systematically documents these co-seismic rupture phenomena for the Xiaoyudong area. The discussion and results are based on field investigations and analyses of faulting mechanisms and prevalent stress conditions. The results show that the Beichuan-Yingxiu fault formed a 3.5 km wide restraining stepover at the Xiaoyudong area. The Xiaoyudong fault is not a tear fault suggested by previous researches, but a frontal reverse fault induced by the oblique compression at this stepover; it well accommodates the 'deformation gap' of the Beichuan-Yingxiu fault in the Xiaoyudong area. Further, stress along the Peng-Guan fault plane doubles due to a change in dip angle of the Beichuan-Yingxiu fault across the Xiaoyudong restraining stepover. This resulted in two faults rupturing the ground's surface simultaneously, to the north of the Xiaoyudong area. These results are helpful in deepening our understanding of the dynamic processes that produced surface ruptures during the Wenchuan earthquake. Furthermore, the results suggest more attention be focused on the influence of dextral slip component, the change of the control fault's attitude, and property differences in rocks on either side of faults when discussing the formation mechanism of surface ruptures.

Transition state characterization for the reversible binding of dihydrogen to bis(2,2'-bipyridine)rhodium(I) from temperature- and pressure-dependent experimental and theoretical studies.

PubMed

Fujita, Etsuko; Brunschwig, Bruce S; Creutz, Carol; Muckerman, James T; Sutin, Norman; Szalda, David; van Eldik, Rudi

2006-02-20

Thermodynamic and kinetic parameters for the oxidative addition of H2 to [Rh(I)(bpy)2]+ (bpy = 2,2'-bipyridine) to form [Rh(III)(H)2(bpy)2]+ were determined from either the UV-vis spectrum of equilibrium mixtures of [Rh(I)(bpy)2]+ and [Rh(III)(H)2(bpy)2]+ or from the observed rates of dihydride formation following visible-light irradiation of solutions containing [Rh(III)(H)2(bpy)2]+ as a function of H2 concentration, temperature, and pressure in acetone and methanol. The activation enthalpy and entropy in methanol are 10.0 kcal mol(-1) and -18 cal mol(-1) K(-1), respectively. The reaction enthalpy and entropy are -10.3 kcal mol(-1) and -19 cal mol(-1) K(-1), respectively. Similar values were obtained in acetone. Surprisingly, the volumes of activation for dihydride formation (-15 and -16 cm(3) mol(-1) in methanol and acetone, respectively) are very close to the overall reaction volumes (-15 cm(3) mol(-1) in both solvents). Thus, the volumes of activation for the reverse reaction, elimination of dihydrogen from the dihydrido complex, are approximately zero. B3LYP hybrid DFT calculations of the transition-state complex in methanol and similar MP2 calculations in the gas phase suggest that the dihydrogen has a short H-H bond (0.823 and 0.810 Angstroms, respectively) and forms only a weak Rh-H bond (1.866 and 1.915 Angstroms, respectively). Equal partial molar volumes of the dihydrogenrhodium(I) transition state and dihydridorhodium(III) can account for the experimental volume profile found for the overall process.

Bim Automation: Advanced Modeling Generative Process for Complex Structures

NASA Astrophysics Data System (ADS)

Banfi, F.; Fai, S.; Brumana, R.

2017-08-01

The new paradigm of the complexity of modern and historic structures, which are characterised by complex forms, morphological and typological variables, is one of the greatest challenges for building information modelling (BIM). Generation of complex parametric models needs new scientific knowledge concerning new digital technologies. These elements are helpful to store a vast quantity of information during the life cycle of buildings (LCB). The latest developments of parametric applications do not provide advanced tools, resulting in time-consuming work for the generation of models. This paper presents a method capable of processing and creating complex parametric Building Information Models (BIM) with Non-Uniform to NURBS) with multiple levels of details (Mixed and ReverseLoD) based on accurate 3D photogrammetric and laser scanning surveys. Complex 3D elements are converted into parametric BIM software and finite element applications (BIM to FEA) using specific exchange formats and new modelling tools. The proposed approach has been applied to different case studies: the BIM of modern structure for the courtyard of West Block on Parliament Hill in Ottawa (Ontario) and the BIM of Masegra Castel in Sondrio (Italy), encouraging the dissemination and interaction of scientific results without losing information during the generative process.

Effect of heparin and heparan sulphate on open promoter complex formation for a simple tandem gene model using ex situ atomic force microscopy.

PubMed

Chammas, Oliver; Bonass, William A; Thomson, Neil H

2017-05-01

The influence of heparin and heparan sulphate (HepS) on the appearance and analysis of open promoter complex (RP o ) formation by E. coli RNA polymerase (RNAP) holoenzyme (σ 70 RNAP) on linear DNA using ex situ imaging by atomic force microscopy (AFM) has been investigated. Introducing heparin or HepS into the reaction mix significantly reduces non-specific interactions of the σ 70 RNAP and RNAP after RP o formation allowing for better interpretation of complexes shown within AFM images, particularly on DNA templates containing more than one promoter. Previous expectation was that negatively charged polysaccharides, often used as competitive inhibitors of σRNAP binding and RP o formation, would also inhibit binding of the DNA template to the mica support surface and thereby lower the imaging yield of active RNAP-DNA complexes. We found that the reverse of this was true, and that the yield of RP o formation detected by AFM, for a simple tandem gene model containing two λ PR promoters, increased. Moreover and unexpectedly, HepS was more efficient than heparin, with both of them having a dispersive effect on the sample, minimising unwanted RNAP-RNAP interactions as well as non-specific interactions between the RNAP and DNA template. The success of this method relied on the observation that E. coli RNAP has the highest affinity for the mica surface of all the molecular components. For our system, the affinity of the three constituent biopolymers to muscovite mica was RNAP>Heparin or HepS>DNA. While we observed that heparin and HepS can inhibit DNA binding to the mica, the presence of E. coli RNAP overcomes this effect allowing a greater yield of RP o s for AFM analysis. This method can be extended to other DNA binding proteins and enzymes, which have an affinity to mica higher than DNA, to improve sample preparation for AFM studies. Copyright © 2017 The Authors. Published by Elsevier Inc. All rights reserved.

Attempt to rescue sex-reversal by transgenic expression of the PISRT1 gene in XX PIS-/- goats.

PubMed

Boulanger, L; Kocer, A; Daniel, N; Pannetier, M; Chesné, P; Heyman, Y; Renault, L; Mandon-Pépin, B; Chavatte-Palmer, P; Vignon, X; Vilotte, J-L; Cotinot, C; Renard, J-P; Pailhoux, E

2008-01-01

The Polled Intersex Syndrome (PIS mutation) in goats leads to an absence of horn and to an early sex-reversal of the XX gonads. This mutation is a deletion of an 11.7-kb DNA fragment showing a tissue-specific regulatory activity. Indeed, in XX PIS(-/-) gonads the deletion of PIS leads to the transcriptional extinction of at least 3 neighboring genes, FOXL2, PFOXic and PISRT1. Among them, only FOXL2 is a 'classical' gene, encoding a highly conserved transcription factor. On the other hand, knock-out of Foxl2 in mice results in an early blocking of follicle formation without sex-reversal. This phenotype discrepancy leads to two hypotheses, either FOXL2 is responsible for XX sex-reversal in goat assuming distinct functions of its protein during ovarian differentiation in different mammals, or other PIS-regulated genes are involved. To assess the second possibility, PISRT1 expression was constitutively restored in XX PIS(-/-) gonads. Six transgenic fetuses were obtained by nuclear transfer and studied at 2 developmental stages, 41 and 46 days post-reconstruction. The gonads of these fetuses appear phenotypically identical to those of cloned non-transgenic controls. Conclusively, this result argues for FOXL2 being responsible for the PIS gonad-associated phenotype. Its invalidation in goat will help to better understand this complex syndrome. Copyright 2008 S. Karger AG, Basel.

Quantitative 3D evolution of colloidal nanoparticle oxidation in solution

DOE PAGES

Sun, Yugang; Zuo, Xiaobing; Sankaranarayanan, Subramanian K. R. S.; ...

2017-04-21

Real-time tracking three-dimensional (3D) evolution of colloidal nanoparticles in solution is essential for understanding complex mechanisms involved in nanoparticle growth and transformation. We simultaneously use time-resolved small-angle and wide-angle x-ray scattering to monitor oxidation of highly uniform colloidal iron nanoparticles, enabling the reconstruction of intermediate 3D morphologies of the nanoparticles with a spatial resolution of ~5 Å. The in-situ probing combined with large-scale reactive molecular dynamics simulations reveals the transformational details from the solid metal nanoparticles to hollow metal oxide nanoshells via nanoscale Kirkendall process, for example, coalescence of voids upon their growth, reversing of mass diffusion direction depending onmore » crystallinity, and so forth. In conclusion, our results highlight the complex interplay between defect chemistry and defect dynamics in determining nanoparticle transformation and formation.« less

Polyelectrolyte-Surfactant Complexes: A New Class of Organogelators

NASA Astrophysics Data System (ADS)

Cavicchi, Kevin; Liu, Yuqing; Guzman, Gustavo

2011-03-01

Polyelectrolyte-surfactant complexes (PE-SURFs) are a class of polymers generated by neutralizing a polyelectrolyte with an oppositely charged surfactant. It has been found that PE-SURFs composed of polystyrene sulfonate and long chain alkyl dimethyl amines act as good organogelators for a range of hydrophobic, organic solvents. Thermo-reversible organogels are formed by heating and cooling PE-SURF/solvent solutions. The gel transition temperature is influenced by the degree of polymerization, the length of the alkyl side-chain, the solubility parameter of the solvent, and the concentration of the gelator. Freeze-drying and scanning electron microscopy characterization of the resultant xerogels shows the formation of rod- and plate-like network morphologies depending on the system parameters. This behavior is consistent with gelation driven by the self-assembly of the amphiphilic PE-SURFs into micellar networks.

Quantitative 3D evolution of colloidal nanoparticle oxidation in solution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sun, Yugang; Zuo, Xiaobing; Sankaranarayanan, Subramanian K. R. S.

Real-time tracking three-dimensional (3D) evolution of colloidal nanoparticles in solution is essential for understanding complex mechanisms involved in nanoparticle growth and transformation. We simultaneously use time-resolved small-angle and wide-angle x-ray scattering to monitor oxidation of highly uniform colloidal iron nanoparticles, enabling the reconstruction of intermediate 3D morphologies of the nanoparticles with a spatial resolution of ~5 Å. The in-situ probing combined with large-scale reactive molecular dynamics simulations reveals the transformational details from the solid metal nanoparticles to hollow metal oxide nanoshells via nanoscale Kirkendall process, for example, coalescence of voids upon their growth, reversing of mass diffusion direction depending onmore » crystallinity, and so forth. In conclusion, our results highlight the complex interplay between defect chemistry and defect dynamics in determining nanoparticle transformation and formation.« less

Processes Underlying Developmental Reversals in False-Memory Formation: Comment on Brainerd, Reyna, and Ceci (2008)

ERIC Educational Resources Information Center

Ghetti, Simona

2008-01-01

C. J. Brainerd, V. F. Reyna, and S. J. Ceci (2008) reviewed compelling evidence of developmental reversals in false-memory formation (i.e., younger children exhibit lower false-memory rates than do older children and adults) and proposed that this phenomenon depends on the development of gist processing (i.e., the ability to identify and process…

Observation of small cluster formation in concentrated monoclonal antibody solutions and its implications to solution viscosity.

PubMed

Yearley, Eric J; Godfrin, Paul D; Perevozchikova, Tatiana; Zhang, Hailiang; Falus, Peter; Porcar, Lionel; Nagao, Michihiro; Curtis, Joseph E; Gawande, Pradad; Taing, Rosalynn; Zarraga, Isidro E; Wagner, Norman J; Liu, Yun

2014-04-15

Monoclonal antibodies (mAbs) are a major class of biopharmaceuticals. It is hypothesized that some concentrated mAb solutions exhibit formation of a solution phase consisting of reversibly self-associated aggregates (or reversible clusters), which is speculated to be responsible for their distinct solution properties. Here, we report direct observation of reversible clusters in concentrated solutions of mAbs using neutron spin echo. Specifically, a stable mAb solution is studied across a transition from dispersed monomers in dilute solution to clustered states at more concentrated conditions, where clusters of a preferred size are observed. Once mAb clusters have formed, their size, in contrast to that observed in typical globular protein solutions, is observed to remain nearly constant over a wide range of concentrations. Our results not only conclusively establish a clear relationship between the undesirable high viscosity of some mAb solutions and the formation of reversible clusters with extended open structures, but also directly observe self-assembled mAb protein clusters of preferred small finite size similar to that in micelle formation that dominate the properties of concentrated mAb solutions. Copyright © 2014 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Simulation of Reversible Protein–Protein Binding and Calculation of Binding Free Energies Using Perturbed Distance Restraints

PubMed Central

2017-01-01

Virtually all biological processes depend on the interaction between proteins at some point. The correct prediction of biomolecular binding free-energies has many interesting applications in both basic and applied pharmaceutical research. While recent advances in the field of molecular dynamics (MD) simulations have proven the feasibility of the calculation of protein–protein binding free energies, the large conformational freedom of proteins and complex free energy landscapes of binding processes make such calculations a difficult task. Moreover, convergence and reversibility of resulting free-energy values remain poorly described. In this work, an easy-to-use, yet robust approach for the calculation of standard-state protein–protein binding free energies using perturbed distance restraints is described. In the binding process the conformations of the proteins were restrained, as suggested earlier. Two approaches to avoid end-state problems upon release of the conformational restraints were compared. The method was evaluated by practical application to a small model complex of ubiquitin and the very flexible ubiquitin-binding domain of human DNA polymerase ι (UBM2). All computed free energy differences were closely monitored for convergence, and the calculated binding free energies had a mean unsigned deviation of only 1.4 or 2.5 kJ·mol–1 from experimental values. Statistical error estimates were in the order of thermal noise. We conclude that the presented method has promising potential for broad applicability to quantitatively describe protein–protein and various other kinds of complex formation. PMID:28898077

Reversed-phase ion-pair liquid chromatography method for purification of duplex DNA with single base pair resolution

PubMed Central

Wysoczynski, Christina L.; Roemer, Sarah C.; Dostal, Vishantie; Barkley, Robert M.; Churchill, Mair E. A.; Malarkey, Christopher S.

2013-01-01

Obtaining quantities of highly pure duplex DNA is a bottleneck in the biophysical analysis of protein–DNA complexes. In traditional DNA purification methods, the individual cognate DNA strands are purified separately before annealing to form DNA duplexes. This approach works well for palindromic sequences, in which top and bottom strands are identical and duplex formation is typically complete. However, in cases where the DNA is non-palindromic, excess of single-stranded DNA must be removed through additional purification steps to prevent it from interfering in further experiments. Here we describe and apply a novel reversed-phase ion-pair liquid chromatography purification method for double-stranded DNA ranging in lengths from 17 to 51 bp. Both palindromic and non-palindromic DNA can be readily purified. This method has the unique ability to separate blunt double-stranded DNA from pre-attenuated (n-1, n-2, etc) synthesis products, and from DNA duplexes with single base pair overhangs. Additionally, palindromic DNA sequences with only minor differences in the central spacer sequence of the DNA can be separated, and the purified DNA is suitable for co-crystallization of protein–DNA complexes. Thus, double-stranded ion-pair liquid chromatography is a useful approach for duplex DNA purification for many applications. PMID:24013567

Field-induced assembly of colloidal ellipsoids into well-defined microtubules

PubMed Central

Crassous, Jérôme J.; Mihut, Adriana M.; Wernersson, Erik; Pfleiderer, Patrick; Vermant, Jan; Linse, Per; Schurtenberger, Peter

2014-01-01

Current theoretical attempts to understand the reversible formation of stable microtubules and virus shells are generally based on shape-specific building blocks or monomers, where the local curvature of the resulting structure is explicitly built-in via the monomer geometry. Here we demonstrate that even simple ellipsoidal colloids can reversibly self-assemble into regular tubular structures when subjected to an alternating electric field. Supported by model calculations, we discuss the combined effects of anisotropic shape and field-induced dipolar interactions on the reversible formation of self-assembled structures. Our observations show that the formation of tubular structures through self-assembly requires much less geometrical and interaction specificity than previously thought, and advance our current understanding of the minimal requirements for self-assembly into regular virus-like structures. PMID:25409686

Reversal of an Epigenetic Switch Governing Cell Chaining in Bacillus subtilis by Protein Instability

PubMed Central

Chai, Yunrong; Kolter, Roberto; Losick, Richard

2010-01-01

Bacillus subtilis forms long chains of cells during growth and biofilm formation. Cell separation is mediated by autolysins, whose genes are under the negative control of a heteromeric complex composed of the proteins SinR and SlrR. Formation of the SinR•SlrR complex is governed by a self-reinforcing, double-negative feedback loop in which SinR represses the gene for SlrR and SlrR, by forming the SinR•SlrR complex, titrates SinR and prevents it from repressing slrR. The loop is a bistable switch and exists in a SlrRLOW state in which autolysin genes are on, and a SlrRHIGH state in which autolysin genes are repressed by SinR•SlrR. Cells in the SlrRLOW state are driven into the SlrRHIGH state by SinI, an antirepressor that binds to and inhibits SinR. However, the mechanism by which cells in the SlrRHIGH state revert back to the SlrRLOW state is unknown. We report that SlrR is proteolytically unstable and present evidence that self-cleavage via a LexA-like autopeptidase and ClpC contribute to its degradation. Cells producing a self-cleavage-resistant mutant of SlrR exhibited more persistent chaining during growth and yielded biofilms with enhanced structural complexity. We propose that degradation of SlrR allows cells to switch from the SlrRHIGH to the SlrRLOW state. PMID:20923420

A conserved role for the ESCRT membrane budding complex in LINE retrotransposition

PubMed Central

Dong, Chun; Han, Jeffrey S.

2017-01-01

Long interspersed nuclear element-1s (LINE-1s, or L1s) are an active family of retrotransposable elements that continue to mutate mammalian genomes. Despite the large contribution of L1 to mammalian genome evolution, we do not know where active L1 particles (particles in the process of retrotransposition) are located in the cell, or how they move towards the nucleus, the site of L1 reverse transcription. Using a yeast model of LINE retrotransposition, we identified ESCRT (endosomal sorting complex required for transport) as a critical complex for LINE retrotransposition, and verified that this interaction is conserved for human L1. ESCRT interacts with L1 via a late domain motif, and this interaction facilitates L1 replication. Loss of the L1/ESCRT interaction does not impair RNP formation or enzymatic activity, but leads to loss of retrotransposition and reduced L1 endonuclease activity in the nucleus. This study highlights the importance of the ESCRT complex in the L1 life cycle and suggests an unusual mode for L1 RNP trafficking. PMID:28586350

HIV-1 Vif promotes the formation of high molecular mass APOBEC3G complexes

PubMed Central

Goila-Gaur, Ritu; Khan, Mohammad A.; Miyagi, Eri; Kao, Sandra; Opi, Sandrine; Takeuchi, Hiroaki; Strebel, Klaus

2008-01-01

HIV-1 Vif inhibits the antiviral activity of APOBEC3G (APO3G) by inducing proteasomal degradation. Here, we studied the effects of Vif on APO3G in vitro. In this system, Vif did not cause APO3G degradation. Instead, Vif induced changes in APO3G that affected immunoprecipitation of the native protein. This effect required wt Vif and was reversed by heat-denaturation of APO3G. Sucrose gradient analysis demonstrated that wt Vif induced the gradual transition of APO3G translated in vitro or expressed in HeLa cells from a low molecular mass conformation to puromycin-sensitive high molecular mass (HMM) complexes. In the absence of Vif or the presence of biologically inactive Vif APO3G failed to form HMM complexes. Our results expose a novel function of Vif that promotes the assembly of APO3G into presumably packaging-incompetent HMM complexes and may explain how Vif can overcome the APO3G-imposed block to HIV replication under conditions of no or inefficient APO3G degradation. PMID:18023836

PFN1 Induces drug resistance through Beclin1 Complex mediated autophagy in multiple myeloma.

PubMed

Lu, Yichen; Wang, Ya; Xu, He; Shi, Chen; Jin, Fengyan; Li, Wei

2018-06-26

Autophagy plays an important role in Multiple Myeloma (MM) for homeostasis, survival and drug resistance, but which genes participant in this process is unclear. We identified serval cytoskeleton genes upregulated in MM patients by GEP datasets, especially patients with high PFN1 expression had poor prognosis in MM. In vitro, overexpressed PFN1 promotes proliferation and Bortezomib (BTZ) resistance in MM cells. Further study indicated overexpression of PFN1 significantly promoted the process of autophagy and induced BTZ resistance in MM. Otherwise, knockdown of PFN1 blocked autophagy and sensitized MM to BTZ. Co-IP in MM cells demonstrated PFN1 could bind Beclin1 complex and promote the initiation of autophagy. Inhibition of autophagy via blocking the formation of Beclin1 complex could reverse the phenotype of BTZ resistance in MM. Our findings suggested that PFN1 could promote autophagy through taking part in Beclin1 complex and contribute to BTZ resistance, which may become a novel molecular target in the therapy of MM. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.

Computational study of pristine and titanium-doped sodium alanates for hydrogen storage applications

NASA Astrophysics Data System (ADS)

Dathar, Gopi Krishna Phani

The emphasis of this research is to study and elucidate the underlying mechanisms of reversible hydrogen storage in pristine and Ti-doped sodium aluminum hydrides using molecular modeling techniques. An early breakthrough in using complex metal hydrides as hydrogen storage materials is from the research on sodium alanates by Bogdanovic et al., in 1997 reporting reversible hydrogen storage is possible at moderate temperatures and pressures in transition metal doped sodium alanates. Anton reported titanium salts as the best catalysts compared to all other transition metal salts from his further research on transition metal doped sodium alanates. However, a few questions remained unanswered regarding the role of Ti in reversible hydrogen storage of sodium alanates with improved thermodynamics and kinetics of hydrogen desorption. The first question is about the position of transition metal dopants in the sodium aluminum hydride lattice. The position is investigated by identifying the possible sites for titanium dopants in NaAlH4 lattice and studying the structure and dynamics of possible compounds resulting from titanium doping in sodium alanates. The second question is the role of titanium dopants in improved thermodynamics of hydrogen desorption in Ti-doped NaAlH4. Though it is accepted in the literature that formation of TiAl alloys (Ti-Al and TiAl3) is favorable, reaction pathways are not clearly established. Furthermore, the source of aluminum for Ti-Al alloy formation is not clearly understood. The third question in this area is the role of titanium dopants in improved kinetics of hydrogen absorption and desorption in Ti-doped sodium alanates. This study is directed towards addressing the three longstanding questions in this area. Thermodynamic and kinetic pathways for hydrogen desorption in pristine NaAlH4 and formation of Ti-Al alloys in Ti-doped NaAlH 4, are elucidated to understand the underlying mechanisms of hydrogen desorption. Density functional theory formalism as implemented in CASTEP (Cambridge Serial Total Energy Package) is used to study the structure and energetics of pristine and Ti-doped sodium alanates. From investigations of various models of sodium alanates with Ti dopants, it is shown that the difference between the energy required for Ti→SNa (Ti-substituted Na at the lattice site on the surface) and Ti→TI (Ti placed on top of the surface interstitial SI site) is 0.003 eV atom-1, and is minimal compared to other models. Since less energy is required for Ti→S Na and Ti→TI, these two sites (SNa and T I) would be preferred by the Ti dopants. In Ti→SNa model, Ti is coordinated to two aluminum and seven hydrogen atoms resulting in the possible formation of a TiAl2H7 complex. At elevated temperatures (423 and 448 K), the number of aluminum atoms coordinating with titanium in the complex increase from two (at distances in the 2.6-2.7 A range) to five (at distances in the 2.6-2.7 A range). Besides the formation of a Ti-Al-H complex, Al-Al association (with a 2.97 A bond length) is also seen from the DFT-MD results. In the case of Ti→TI, Ti is coordinated to two aluminum and two hydrogen atoms resulting in the possible formation of a TiAl2H2 complex. TiAl2 H2 complex becomes TiAl3H6 and TiAl 3H7 at elevated temperatures of 423 and 448 K, respectively. The investigation of thermodynamics pathways in Ti-doped sodium alanates illustrates a three step reaction pathway to the formation of TiAl3 (Ti and AlH3 after the first reaction, TiAl after the second and finally TiAl3). This investigation also suggests aluminum in its +3 oxidation state present in aluminum hydride species is responsible in the formation of Ti-Al alloys. From kinetics studies, the proposed mechanism is related to transition from AlH4- to AlH6 3-. The rate limiting step is determined to be associated with hydrogen evolution from association of AlH3 species nucleating aluminum phase. This step is 15 kJ/mol higher than the nearest highest barrier in the reaction path related to transition from AlH52- to AlH63-. From the DFT-MD simulations, it is observed that the titanium dopants are present on the surface during the entire simulation time and exhibit the role in catalytic splitting of hydrogen from surrounding AlH4 groups. Besides the catalytic role, Ti dopants also form bonds with Al, and we also see that the AlH4 groups on the surface and that are present in the sub-surface layers are drawn towards the Ti dopants. This association of Al around titanium indicates the initiation of Al nucleation site facilitated by Ti dopants residing on the surface.

ALS/FTD Mutation-Induced Phase Transition of FUS Liquid Droplets and Reversible Hydrogels into Irreversible Hydrogels Impairs RNP Granule Function

PubMed Central

Murakami, Tetsuro; Qamar, Seema; Lin, Julie Qiaojin; Schierle, Gabriele S. Kaminski; Rees, Eric; Miyashita, Akinori; Costa, Ana R.; Dodd, Roger B.; Chan, Fiona T.S.; Michel, Claire H.; Kronenberg-Versteeg, Deborah; Li, Yi; Yang, Seung-Pil; Wakutani, Yosuke; Meadows, William; Ferry, Rodylyn Rose; Dong, Liang; Tartaglia, Gian Gaetano; Favrin, Giorgio; Lin, Wen-Lang; Dickson, Dennis W.; Zhen, Mei; Ron, David; Schmitt-Ulms, Gerold; Fraser, Paul E.; Shneider, Neil A.; Holt, Christine; Vendruscolo, Michele; Kaminski, Clemens F.; St George-Hyslop, Peter

2015-01-01

Summary The mechanisms by which mutations in FUS and other RNA binding proteins cause ALS and FTD remain controversial. We propose a model in which low-complexity (LC) domains of FUS drive its physiologically reversible assembly into membrane-free, liquid droplet and hydrogel-like structures. ALS/FTD mutations in LC or non-LC domains induce further phase transition into poorly soluble fibrillar hydrogels distinct from conventional amyloids. These assemblies are necessary and sufficient for neurotoxicity in a C. elegans model of FUS-dependent neurodegeneration. They trap other ribonucleoprotein (RNP) granule components and disrupt RNP granule function. One consequence is impairment of new protein synthesis by cytoplasmic RNP granules in axon terminals, where RNP granules regulate local RNA metabolism and translation. Nuclear FUS granules may be similarly affected. Inhibiting formation of these fibrillar hydrogel assemblies mitigates neurotoxicity and suggests a potential therapeutic strategy that may also be applicable to ALS/FTD associated with mutations in other RNA binding proteins. PMID:26526393

The mechanism of hydroaminoalkylation catalyzed by group 5 metal binaphtholate complexes.

PubMed

Reznichenko, Alexander L; Hultzsch, Kai C

2012-02-15

The intermolecular hydroaminoalkylation of unactivated alkenes and vinyl arenes with secondary amines occurs readily in the presence of tantalum and niobium binaphtholate catalysts with high regio- and enantioselectivity (up to 98% ee). Mechanistic studies have been conducted in order to determine the kinetic order of the reaction in all reagents and elucidate the rate- and stereodetermining steps. The effects of substrate steric and electronic properties on the overall reaction rate have been evaluated. The reaction is first order in amine and the catalyst, while exhibiting saturation in alkene at high alkene concentration. Unproductive reaction events including reversible amine binding and arene C-H activation have been observed. The formation of the metallaaziridine is a fast reversible nondissociative process and the overall reaction rate is limited either by amide exchange or alkene insertion, as supported by reaction kinetics, kinetic isotope effects, and isotopic labeling studies. These results suggest that the catalytic activity can be enhanced by employing a more electron-deficient ligand backbone.

Direct observation of oxygen vacancy-driven structural and resistive phase transitions in La2/3Sr1/3MnO3

NASA Astrophysics Data System (ADS)

Yao, Lide; Inkinen, Sampo; van Dijken, Sebastiaan

2017-02-01

Resistive switching in transition metal oxides involves intricate physical and chemical behaviours with potential for non-volatile memory and memristive devices. Although oxygen vacancy migration is known to play a crucial role in resistive switching of oxides, an in-depth understanding of oxygen vacancy-driven effects requires direct imaging of atomic-scale dynamic processes and their real-time impact on resistance changes. Here we use in situ transmission electron microscopy to demonstrate reversible switching between three resistance states in epitaxial La2/3Sr1/3MnO3 films. Simultaneous high-resolution imaging and resistance probing indicate that the switching events are caused by the formation of uniform structural phases. Reversible horizontal migration of oxygen vacancies within the manganite film, driven by combined effects of Joule heating and bias voltage, predominantly triggers the structural and resistive transitions. Our findings open prospects for ionotronic devices based on dynamic control of physical properties in complex oxide nanostructures.

Controllable self-assembly of sodium caseinate with a zwitterionic vitamin-derived bolaamphiphile.

PubMed

Sun, Li-Hui; Sun, Yu-Long; Yang, Li-Jun; Zhang, Jian; Chen, Zhong-Xiu

2013-11-06

The control of self-assembly of sodium caseinate (SC) including the formation of mixed layers, microspheres, or nanoparticles is highly relevant to the microstructure of food and the design of promising drug delivery systems. In this paper, we designed a structure-switchable zwitterionic bolaamphiphile, 1,12-diaminododecanediorotate (DDO), from orotic acid, which has special binding sites and can guide the self-assembly of SC. Complexation between SC and DDO was investigated using dynamic light scattering, transmission electron microscopy, differential scanning calorimetry, and fluorescence spectra measurements. Monomeric DDO was bound to the negatively charged sites on the SC micelle and made the structure of SC more compact with decreased electrostatic repulsion between the head groups. Vesicular DDO led to reassociation of vesicles with enlarged size via preferable hydrophobic interactions. Moreover, the aggregation between SC and DDO was found to be temperature-dependent and reversible. This research provides an effective way to control the reversible self-assembly of SC by the zwitterionic vitamin-derived bolaamphiphile.

Controlled Growth of CdS Quantum Dot in an Amphiphilic Diblock Copolymer Poly(2-Vinyl Pyridine)-b-Poly(n-Hexyl Isocyanate) Reversed Micelle Nanoreactor.

PubMed

Samal, Monica; Mohapatra, Priya Ranjan; Yun, Kyu Sik

2015-09-01

A diblock copolymer poly(2-vinyl pyridine)-b-poly(n-hexyl isocyanate) (P2VP-b-PHIC) is used for the present study. It has two blocks; a rod-shaped PHIC block that adopts a helical conformation, and a coil shaped P2VP block. In a polar solvent such as THF both PHIC and P2VP blocks are soluble. In mixtures of two solvents, such as THF and methanol, while the solubility of P2VP component is augmented that of PHIC is decreased leading to formation of reversed micelles. The pyridine nitrogen in P2VP block is a reactive site. It forms complexes with a suitable metal ion, such as Cd2+. The micelle is employed as a nanoreactor for synthesis of CdS quantum dot (QD). In this paper, the micellization behaviour of the copolymer and the use of the micelles for synthesis and controlled growth of CdS nanocrystals are demonstrated.

Flux-trapping during the formation of field-reversed configurations

NASA Astrophysics Data System (ADS)

Armstrong, W. T.; Harding, D. G.; Crawford, E. A.; Hoffman, A. L.

1982-11-01

Flux-trapping during the early formation phases of a field-reversed configuration has been studied experimentally on the field-reversed theta-pinch TRX-1. An annular z-pinch preionizer was employed to permit ionization at high values of reverse-bias flux. Contrary to previous analysis, the rate of flux loss was not governed exclusively by inertially limited plasma convection to the tube walls. At high reverse flux levels, a pressure bearing sheath was observed to form at the tube walls and the flux loss was restricted by resistive diffusion across this sheath. The characteristic time for flux loss was 0.08rt (cm) μsec, independent of the bias field and independent of the fill pressure for fill pressures above 15 mTorr D2. Octopole barrier fields were found to be effective in limiting the inertially governed flux loss at very early times before the wall sheath formed.

High Fidelity Modeling of Field Reversed Configuration (FRC) Thrusters

DTIC Science & Technology

2016-06-01

space propulsion . This effort consists of numerical model development, physical model development, and systematic studies of the non-linear plasma...studies of the physical characteristics of Field Reversed Configuration (FRC) plasma for advanced space propulsion . This effort consists of numerical...FRCs for propulsion application. Two of the most advanced designs are based on the theta-pinch formation and the RMF formation mechanism, which

Denitrification-derived nitric oxide modulates biofilm formation in Azospirillum brasilense.

PubMed

Arruebarrena Di Palma, Andrés; Pereyra, Cintia M; Moreno Ramirez, Lizbeth; Xiqui Vázquez, María L; Baca, Beatriz E; Pereyra, María A; Lamattina, Lorenzo; Creus, Cecilia M

2013-01-01

Azospirillum brasilense is a rhizobacterium that provides beneficial effects on plants when they colonize roots. The formation of complex bacterial communities known as biofilms begins with the interaction of planktonic cells with surfaces in response to appropriate signals. Nitric oxide (NO) is a signaling molecule implicated in numerous processes in bacteria, including biofilm formation or dispersion, depending on genera and lifestyle. Azospirillum brasilense Sp245 produces NO by denitrification having a role in root growth promotion. We analyzed the role of endogenously produced NO on biofilm formation in A. brasilense Sp245 and in a periplasmic nitrate reductase mutant (napA::Tn5; Faj164) affected in NO production. Cells were statically grown in media with nitrate or ammonium as nitrogen sources and examined for biofilm formation using crystal violet and by confocal laser microscopy. Both strains formed biofilms, but the mutant produced less than half compared with the wild type in nitrate medium showing impaired nitrite production in this condition. NO measurements in biofilm confirmed lower values in the mutant strain. The addition of a NO donor showed that NO influences biofilm formation in a dose-dependent manner and reverses the mutant phenotype, indicating that Nap positively regulates the formation of biofilm in A. brasilense Sp245. © 2012 Federation of European Microbiological Societies. Published by Blackwell Publishing Ltd. All rights reserved.

Polycomb group protein complexes exchange rapidly in living Drosophila.

PubMed

Ficz, Gabriella; Heintzmann, Rainer; Arndt-Jovin, Donna J

2005-09-01

Fluorescence recovery after photobleaching (FRAP) microscopy was used to determine the kinetic properties of Polycomb group (PcG) proteins in whole living Drosophila organisms (embryos) and tissues (wing imaginal discs and salivary glands). PcG genes are essential genes in higher eukaryotes responsible for the maintenance of the spatially distinct repression of developmentally important regulators such as the homeotic genes. Their absence, as well as overexpression, causes transformations in the axial organization of the body. Although protein complexes have been isolated in vitro, little is known about their stability or exact mechanism of repression in vivo. We determined the translational diffusion constants of PcG proteins, dissociation constants and residence times for complexes in vivo at different developmental stages. In polytene nuclei, the rate constants suggest heterogeneity of the complexes. Computer simulations with new models for spatially distributed protein complexes were performed in systems showing both diffusion and binding equilibria, and the results compared with our experimental data. We were able to determine forward and reverse rate constants for complex formation. Complexes exchanged within a period of 1-10 minutes, more than an order of magnitude faster than the cell cycle time, ruling out models of repression in which access of transcription activators to the chromatin is limited and demonstrating that long-term repression primarily reflects mass-action chemical equilibria.

Reversal of Apixaban Induced Alterations in Hemostasis by Different Coagulation Factor Concentrates: Significance of Studies In Vitro with Circulating Human Blood

PubMed Central

Arellano-Rodrigo, Eduardo; Roquer, Jaume; Reverter, Joan Carles; Sanz, Victoria Veronica; Molina, Patricia; Lopez-Vilchez, Irene; Diaz-Ricart, Maribel; Galan, Ana Maria

2013-01-01

Apixaban is a new oral anticoagulant with a specific inhibitory action on FXa. No information is available on the reversal of the antihemostatic action of apixaban in experimental or clinical settings. We have evaluated the effectiveness of different factor concentrates at reversing modifications of hemostatic mechanisms induced by moderately elevated concentrations of apixaban (200 ng/ml) added in vitro to blood from healthy donors (n = 10). Effects on thrombin generation (TG) and thromboelastometry (TEM) parameters were assessed. Modifications in platelet adhesive, aggregating and procoagulant activities were evaluated in studies with blood circulating through damaged vascular surfaces, at a shear rate of 600 s−1. The potential of prothrombin complex concentrates (PCCs; 50 IU/kg), activated prothrombin complex concentrates (aPCCs; 75 IU/kg), or activated recombinant factor VII (rFVIIa; 270 μg/kg), at reversing the antihemostatic actions of apixaban, were investigated. Apixaban interfered with TG kinetics. Delayed lag phase, prolonged time to peak and reduced peak values, were improved by the different concentrates, though modifications in TG patterns were diversely affected depending on the activating reagents. Apixaban significantly prolonged clotting times (CTs) in TEM studies. Prolongations in CTs were corrected by the different concentrates with variable efficacies (rFVIIa≥aPCC>PCC). Apixaban significantly reduced fibrin and platelet interactions with damaged vascular surfaces in perfusion studies (p<0.05 and p<0.01, respectively). Impairments in fibrin formation were normalized by the different concentrates. Only rFVIIa significantly restored levels of platelet deposition. Alterations in hemostasis induced by apixaban were variably compensated by the different factor concentrates investigated. However, effects of these concentrates were not homogeneous in all the tests, with PCCs showing more efficacy in TG, and rFVIIa being more effective on TEM and perfusion studies. Our results indicate that rFVIIa, PCCs and aPCCs have the potential to restore platelet and fibrin components of the hemostasis previously altered by apixaban. PMID:24244342

Evaluation of Multi-tRNA Synthetase Complex by Multiple Reaction Monitoring Mass Spectrometry Coupled with Size Exclusion Chromatography

PubMed Central

Kim, Jun Seok; Lee, Cheolju

2015-01-01

Eight aminoacyl-tRNA synthetases (M, K, Q, D, R, I, EP and LARS) and three auxiliary proteins (AIMP1, 2 and 3) are known to form a multi-tRNA synthetase complex (MSC) in mammalian cells. We combined size exclusion chromatography (SEC) with reversed-phase liquid chromatography multiple reaction monitoring mass spectrometry (RPLC-MRM-MS) to characterize MSC components and free ARS proteins in human embryonic kidney (HEK 293T) cells. Crude cell extract and affinity-purified proteins were fractionated by SEC in non-denaturing state and ARSs were monitored in each fraction by MRM-MS. The eleven MSC components appeared mostly in earlier SEC fractions demonstrating their participation in complex formation. TARSL2 and AIMP2-DX2, despite their low abundance, were co-purified with KARS and detected in the SEC fractions, where MSC appeared. Moreover, other large complex-forming ARS proteins, such as VARS and FARS, were detected in earlier fractions. The MRM-MS results were further confirmed by western blot analysis. Our study demonstrates usefulness of combined SEC-MRM analysis for the characterization of protein complexes and in understanding the behavior of minor isoforms or variant proteins. PMID:26544075

Visualization of a proteasome-independent intermediate during restriction of HIV-1 by rhesus TRIM5α

PubMed Central

Campbell, Edward M.; Perez, Omar; Anderson, Jenny L.; Hope, Thomas J.

2008-01-01

TRIM5 proteins constitute a class of restriction factors that prevent host cell infection by retroviruses from different species. TRIM5α restricts retroviral infection early after viral entry, before the generation of viral reverse transcription products. However, the underlying restriction mechanism remains unclear. In this study, we show that during rhesus macaque TRIM5α (rhTRIM5α)–mediated restriction of HIV-1 infection, cytoplasmic HIV-1 viral complexes can associate with concentrations of TRIM5α protein termed cytoplasmic bodies. We observe a dynamic interaction between rhTRIM5α and cytoplasmic HIV-1 viral complexes, including the de novo formation of rhTRIM5α cytoplasmic body–like structures around viral complexes. We observe that proteasome inhibition allows HIV-1 to remain stably sequestered into large rhTRIM5α cytoplasmic bodies, preventing the clearance of HIV-1 viral complexes from the cytoplasm and revealing an intermediate in the restriction process. Furthermore, we can measure no loss of capsid protein from viral complexes arrested at this intermediate step in restriction, suggesting that any rhTRIM5α-mediated loss of capsid protein requires proteasome activity. PMID:18250195

Evaluation of Multi-tRNA Synthetase Complex by Multiple Reaction Monitoring Mass Spectrometry Coupled with Size Exclusion Chromatography.

PubMed

Park, Seong-Jun; Ahn, Hee-Sung; Kim, Jun Seok; Lee, Cheolju

2015-01-01

Eight aminoacyl-tRNA synthetases (M, K, Q, D, R, I, EP and LARS) and three auxiliary proteins (AIMP1, 2 and 3) are known to form a multi-tRNA synthetase complex (MSC) in mammalian cells. We combined size exclusion chromatography (SEC) with reversed-phase liquid chromatography multiple reaction monitoring mass spectrometry (RPLC-MRM-MS) to characterize MSC components and free ARS proteins in human embryonic kidney (HEK 293T) cells. Crude cell extract and affinity-purified proteins were fractionated by SEC in non-denaturing state and ARSs were monitored in each fraction by MRM-MS. The eleven MSC components appeared mostly in earlier SEC fractions demonstrating their participation in complex formation. TARSL2 and AIMP2-DX2, despite their low abundance, were co-purified with KARS and detected in the SEC fractions, where MSC appeared. Moreover, other large complex-forming ARS proteins, such as VARS and FARS, were detected in earlier fractions. The MRM-MS results were further confirmed by western blot analysis. Our study demonstrates usefulness of combined SEC-MRM analysis for the characterization of protein complexes and in understanding the behavior of minor isoforms or variant proteins.

Polar Field Reversals and Active Region Decay

NASA Astrophysics Data System (ADS)

Petrie, Gordon; Ettinger, Sophie

2017-09-01

We study the relationship between polar field reversals and decayed active region magnetic flux. Photospheric active region flux is dispersed by differential rotation and turbulent diffusion, and is transported poleward by meridional flows and diffusion. We summarize the published evidence from observation and modeling of the influence of meridional flow variations and decaying active region flux's spatial distribution, such as the Joy's law tilt angle. Using NSO Kitt Peak synoptic magnetograms covering cycles 21-24, we investigate in detail the relationship between the transport of decayed active region flux to high latitudes and changes in the polar field strength, including reversals in the magnetic polarity at the poles. By means of stack plots of low- and high-latitude slices of the synoptic magnetograms, the dispersal of flux from low to high latitudes is tracked, and the timing of this dispersal is compared to the polar field changes. In the most abrupt cases of polar field reversal, a few activity complexes (systems of active regions) are identified as the main cause. The poleward transport of large quantities of decayed trailing-polarity flux from these complexes is found to correlate well in time with the abrupt polar field changes. In each case, significant latitudinal displacements were found between the positive and negative flux centroids of the complexes, consistent with Joy's law bipole tilt with trailing-polarity flux located poleward of leading-polarity flux. The activity complexes of the cycle 21 and 22 maxima were larger and longer-lived than those of the cycle 23 and 24 maxima, and the poleward surges were stronger and more unipolar and the polar field changes larger and faster. The cycle 21 and 22 polar reversals were dominated by only a few long-lived complexes whereas the cycle 23 and 24 reversals were the cumulative effects of more numerous, shorter-lived regions. We conclude that sizes and lifetimes of activity complexes are key to understanding the diversity of polar reversals.

Experimental study of the formation of field-reversed configurations employing high-order multipole fields

NASA Astrophysics Data System (ADS)

Slough, J. T.; Hoffman, A. L.

1990-04-01

A high-order multipole ``barrier'' field was applied at the vacuum tube wall in the TRX experiment [Phys. Fluids B 1, 840 (1989)] during both the preionization and field reversal phases of field-reversed configuration (FRC) formation. Use of this field during field reversal resulted in a significant reduction of impurities as well as increased flux trapping. With a large enough Bθ at the wall, sheath detachment from the wall became apparent, and flux loss through the sheath became negligible (<10%). At larger wall Bθ (>1.5 kG), destructive rotational spin-up occurred, driven by Hall current forces. When the multipole barrier field was also applied during either axial discharge or ringing theta current preionization, a very symmetric and uniform breakdown of the fill gas was achieved. In particular, using ringing theta preionization, complete ionization of the fill gas was accomplished with purely inductive fields of remarkably low magnitude, where Ez≤3 V/cm, and Eθ≤20 V/cm. Due to the improved ionization symmetry, about 65% to 75% of the lift-off flux (flux remaining after field reversal) could be retained through the remaining formation processes into an equilibrium FRC. Using the multipole field during both preionization and formation, it was possible to form FRC's with good confinement with greater than 3 mWb of trapped flux at 15 mTorr D2 or H2 in a 10 cm radius device. Values of s in excess of 4 could be achieved in this manner.

Negative-ion formation in the explosives RDX, PETN, and TNT by using the reversal electron attachment detection technique

NASA Technical Reports Server (NTRS)

Boumsellek, S.; Alajajian, S. H.; Chutjian, A.

1992-01-01

First results of a beam-beam, single-collision study of negative-ion mass spectra produced by attachment of zero-energy electrons to the molecules of the explosives RDX, PETN, and TNT are presented. The technique used is reversal electron attachment detection (READ) wherein the zero-energy electrons are produced by focusing an intense electron beam into a shaped electrostatic field which reverses the trajectory of electrons. The target beam is introduced at the reversal point, and attachment occurs because the electrons have essentially zero longitudinal and radial velocity. The READ technique is used to obtain the 'signature' of molecular ion formation and/or fragmentation for each explosive. Present data are compared with results from atmospheric-pressure ionization and negative-ion chemical ionization methods.

Iminoboronate Formation Leads to Fast and Reversible Conjugation Chemistry of α-Nucleophiles at Neutral pH

PubMed Central

Bandyopadhyay, Anupam

2015-01-01

Bioorthogonal reactions that are fast and reversible under physiologic conditions are in high demand for biological applications. Herein, we show that an ortho boronic acid substituent makes aryl ketones to rapidly conjugate with α-nucleophiles at neutral pH. Specifically, 2-acetylphenylboronic acid and derivatives were found to conjugate with phenylhydrazine with rate constants of 102 to 103 M−1 s−1, comparable to the fastest bioorthogonal conjugations known to date. 11B-NMR analysis reveals varied extent of iminoboronate formation of the conjugates, in which the imine nitrogen forms a dative bond with boron. The iminoboronate formation activates the imines for hydrolysis and exchange, rendering these oxime/hydrazone conjugations reversible and dynamic under physiologic conditions. The fast and dynamic nature of the iminoboronate chemistry should find wide applications in biology. PMID:26311464

In-situ neutron diffraction of LaCoO3 perovskite under uniaxial compression. I. Crystal structure analysis and texture development

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aman, Amjad; Chen, Yan; Lugovy, Mykola

2014-01-01

The dynamics of texture formation, changes in crystal structure and stress accommodation mechanisms are studied in R3c rhombohedral LaCoO3 perovskite during in-situ uniaxial compression experiment by neutron diffraction. The neutron diffraction revealed the complex crystallographic changes causing the texture formation and significant straining along certain crystallographic directions during in-situ compression, which are responsible for the appearance of hysteresis and non-linear ferroelastic deformation in LaCoO3 perovskite. The irreversible strain after the first loading was connected with the appearance of non-recoverable changes in the intensity ratio of certain crystallographic peaks, causing non-reversible texture formation. However in the second loading/unloading cycle the hysteresismore » loop was closed and no irreversible strain appears after deformation. The significant texture formation is responsible for increase in the Young s modulus of LaCoO3 at high compressive loads, where the reported values of Young s modulus increase from 76 GPa measured at the very beginning of the loading to 194 GPa at 900 MPa applied compressive stress measured at the beginning of the unloading curve.« less

Synthesis and spectral characterization of 2-((2-hydroxybenzylidene)amino)-2-methylpropane-1,3-diol derived complexes: Molecular docking and antimicrobial studies

NASA Astrophysics Data System (ADS)

Ansari, Istikhar A.; Sama, Farasha; Raizada, Mukul; Shahid, M.; Rajpoot, Ravi Kant; Siddiqi, Zafar A.

2017-01-01

A series of four homo-dinuclear transition metal complexes with stoichiometry [M2(HL)2(H2O)2] [M = Fe (1), Co (2), Ni (3) and Cu (4); H3L = 2-((2-hydroxybenzylidene)amino)-2-methylpropane-1,3-diol] has been prepared. Ligand (H3L) was obtained by the condensation of 2-amino-2-methyl-1,3-propanediol (H2ampd) with salicylaldehyde. The complexes (1-4) are characterized employing elemental analysis, FTIR, ESI mass, 1H &13C NMR, EPR, UV Visible, TGA, cyclic voltammetry, and magnetic studies. Spectral data ascertained the bonding features and the geometry of the complexes and revealed that all the complexes adopt distorted octahedral geometry with high spin state of metal ions. Thermal and ESI mass data confirmed the proposed stoichiometry of the complexes. Cyclic voltammetric (CV) studies ascertain the formation of MII/MIII quasi-reversible redox couples in solution. The antimicrobial activities of the present complexes have been examined against few bacteria (E. coli, B. subtilis, S. aureus and S. typhymurium) and fungi (C. albicans, A. fumigatus and P. marneffeiin) suggesting that the present compounds show moderate to high antimicrobial properties. Among all the compounds tested, complex (4) exhibited highest antibacterial as well as antifungal activity. Molecular docking studies of the free ligand and the complexes are performed with BDNA.

Conversion from CUL4-based COP1–SPA E3 apparatus to UVR8–COP1–SPA complexes underlies a distinct biochemical function of COP1 under UV-B

PubMed Central

Huang, Xi; Ouyang, Xinhao; Yang, Panyu; Lau, On Sun; Chen, Liangbi; Wei, Ning; Deng, Xing Wang

2013-01-01

The evolutionarily conserved CONSTITUTIVE PHOTOMORPHOGENESIS 1 (COP1) is a RING and WD40 protein that functions as a substrate receptor of CULLIN4–DAMAGED DNA BINDING PROTEIN 1 (CUL4–DDB1)–based E3 ubiquitin ligases in both plants and animals. In Arabidopsis, COP1 is a central repressor of photomorphogenesis in the form of COP1–SUPPRESSOR OF PHYA (SPA) complex(es). CUL4–DDB1–COP1–SPA suppresses the photomorphogenic program by targeting the transcription factor ELONGATED HYPOCOTYL 5 for degradation. Intriguingly, under photomorphogenic UV-B light, COP1 reverses its repressive role and promotes photomorphogenesis. However, the mechanism by which COP1 is functionally switched is still obscure. Here, we demonstrate that UV-B triggers the physical and functional disassociation of the COP1–SPA core complex(es) from CUL4–DDB1 and the formation of a unique complex(es) containing the UV-B receptor UV RESISTANCE LOCUS 8 (UVR8). The establishment of this UV-B–dependent COP1 complex(es) is associated with its positive modulation of ELONGATED HYPOCOTYL 5 stability and activity, which sheds light on the mechanism of COP1’s promotive action in UV-B–induced photomorphogenesis. PMID:24067658

Choline and dimethylglycine produce superoxide/hydrogen peroxide from the electron transport chain in liver mitochondria.

PubMed

Mailloux, Ryan J; Young, Adrian; Chalker, Julia; Gardiner, Danielle; O'Brien, Marisa; Slade, Liam; Brosnan, John T

2016-12-01

Here, we report that choline and dimethylglycine can stimulate reactive oxygen species (ROS) production in liver mitochondria. Choline stimulated O 2 ˙ - /H 2 O 2 formation at a concentration of 5 μm. We also observed that Complex II and III inhibitors, atpenin A5 and myxothiazol, collectively induced a 95% decrease in O 2 ˙ - /H 2 O 2 production indicating both sites serve as the main sources of ROS during choline oxidation. Dimethylglycine, an intermediate of choline oxidation, was a more effective ROS generator. Rates of production were ~ 43% higher than choline-mediated O 2 ˙ - /H 2 O 2 production. The main site for dimethylglycine-mediated ROS production was via reverse electron transfer to Complex I. Our results demonstrate that metabolism of essential metabolites involved in methionine and folic acid biosynthesis can stimulate mitochondrial ROS production. © 2016 Federation of European Biochemical Societies.

Phosphorylation-regulated Binding of RNA Polymerase II to Fibrous Polymers of Low Complexity Domains

PubMed Central

Xiang, Siheng; Wu, Leeju; Theodoropoulos, Pano; Mirzaei, Hamid; Han, Tina; Xie, Shanhai; Corden, Jeffry L.; McKnight, Steven L.

2014-01-01

SUMMARY The low complexity (LC) domains of the products of the fused in sarcoma (FUS), Ewings sarcoma (EWS) and TAF15 genes are translocated onto a variety of different DNA-binding domains and thereby assist in driving the formation of cancerous cells. In the context of the translocated fusion proteins, these LC sequences function as transcriptional activation domains. Here we show that polymeric fibers formed from these LC domains directly bind the C-terminal domain (CTD) of RNA polymerase II in a manner reversible by phosphorylation of the iterated, heptad repeats of the CTD. Mutational analysis indicates that the degree of binding between the CTD and the LC domain polymers correlates with the strength of transcriptional activation. These studies offer a simple means of conceptualizing how RNA polymerase II is recruited to active genes in its unphosphorylated state, and released for elongation following phosphorylation of the CTD. PMID:24267890

Evidence of a New Hydrogen Complex in Dilute Nitride Alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bisognin, G.; De Salvador, D.; Napolitani, E.

2007-04-10

By means of high resolution x-ray diffraction and photoluminescence measurements we demonstrate that, as a result of hydrogen irradiation of GaAs1-xNx/GaAs, the original tensile strain of the as-grown material is reversed into a compressive one and that, at the same time, N atoms are electronically passivated. We show that the amount of compressive strain is determined exclusively by N concentration. This compressive strain is caused by the formation of peculiar N-H complexes and disappears after moderate annealing, while N electronic passivation still holds. These experimental results demonstrate that the lattice properties of fully-hydrogenated GaAs1-xNx/GaAs are ruled by a H complexmore » which is different and less stable than that responsible for electronic passivation of N in GaAs1-xNx/GaAs.« less

miR-204 reverses temozolomide resistance and inhibits cancer initiating cells phenotypes by degrading FAP-α in glioblastoma.

PubMed

Yang, Yun-Na; Zhang, Xiang-Hua; Wang, Yan-Ming; Zhang, Xi; Gu, Zheng

2018-05-01

Malignant gliomas are treated with temozolomide (TMZ) at present, but often exhibit resistance to this agent. Cancer-initiating cells (CICs) have been suggested to lead to TMZ resistance. The mechanisms underlying CICs-based TMZ resistance are not fully understood. MicroRNAs (miRNAs) have been demonstrated to serve important roles in tumorigenesis and TMZ resistance. In the present study, a sphere forming assay and western blot analysis were performed to detect the formation of CICs and fibroblast activation protein α (FAP-α) protein expression. It was revealed that TMZ resistance promoted the formation of CICs and upregulated FAP-α expression in glioblastoma cells. Over-expressing FAP-α was also demonstrated to promote TMZ resistance and induce the formation of CICs in U251MG cells. In addition, using a reverse transcription-quantitative polymerase chain reaction, it was observed that miR-204 was downregulated in U251MG-resistant (-R) cells. miR-204 expression negatively correlated with the FAP-α levels in human glioblastoma tissues, and it may inhibit the formation of CICs and reverse TMZ resistance in U251MG-R cells. Therefore, it was concluded that miR-204 reversed temozolomide resistance and inhibited CICs phenotypes by degrading FAP-α in glioblastoma.

miR-204 reverses temozolomide resistance and inhibits cancer initiating cells phenotypes by degrading FAP-α in glioblastoma

PubMed Central

Yang, Yun-Na; Zhang, Xiang-Hua; Wang, Yan-Ming; Zhang, Xi; Gu, Zheng

2018-01-01

Malignant gliomas are treated with temozolomide (TMZ) at present, but often exhibit resistance to this agent. Cancer-initiating cells (CICs) have been suggested to lead to TMZ resistance. The mechanisms underlying CICs-based TMZ resistance are not fully understood. MicroRNAs (miRNAs) have been demonstrated to serve important roles in tumorigenesis and TMZ resistance. In the present study, a sphere forming assay and western blot analysis were performed to detect the formation of CICs and fibroblast activation protein α (FAP-α) protein expression. It was revealed that TMZ resistance promoted the formation of CICs and upregulated FAP-α expression in glioblastoma cells. Over-expressing FAP-α was also demonstrated to promote TMZ resistance and induce the formation of CICs in U251MG cells. In addition, using a reverse transcription-quantitative polymerase chain reaction, it was observed that miR-204 was downregulated in U251MG-resistant (-R) cells. miR-204 expression negatively correlated with the FAP-α levels in human glioblastoma tissues, and it may inhibit the formation of CICs and reverse TMZ resistance in U251MG-R cells. Therefore, it was concluded that miR-204 reversed temozolomide resistance and inhibited CICs phenotypes by degrading FAP-α in glioblastoma. PMID:29725461

The Feasibility of Formation and Kinetics of NMR Signal Amplification by Reversible Exchange (SABRE) at High Magnetic Field (9.4 T)

PubMed Central

2015-01-01

1H NMR signal amplification by reversible exchange (SABRE) was observed for pyridine and pyridine-d5 at 9.4 T, a field that is orders of magnitude higher than what is typically utilized to achieve the conventional low-field SABRE effect. In addition to emissive peaks for the hydrogen spins at the ortho positions of the pyridine substrate (both free and bound to the metal center), absorptive signals are observed from hyperpolarized orthohydrogen and Ir-complex dihydride. Real-time kinetics studies show that the polarization build-up rates for these three species are in close agreement with their respective 1H T1 relaxation rates at 9.4 T. The results suggest that the mechanism of the substrate polarization involves cross-relaxation with hyperpolarized species in a manner similar to the spin-polarization induced nuclear Overhauser effect. Experiments utilizing pyridine-d5 as the substrate exhibited larger enhancements as well as partial H/D exchange for the hydrogen atom in the ortho position of pyridine and concomitant formation of HD molecules. While the mechanism of polarization enhancement does not explicitly require chemical exchange of hydrogen atoms of parahydrogen and the substrate, the partial chemical modification of the substrate via hydrogen exchange means that SABRE under these conditions cannot rigorously be referred to as a non-hydrogenative parahydrogen induced polarization process. PMID:24528143

The feasibility of formation and kinetics of NMR signal amplification by reversible exchange (SABRE) at high magnetic field (9.4 T).

PubMed

Barskiy, Danila A; Kovtunov, Kirill V; Koptyug, Igor V; He, Ping; Groome, Kirsten A; Best, Quinn A; Shi, Fan; Goodson, Boyd M; Shchepin, Roman V; Coffey, Aaron M; Waddell, Kevin W; Chekmenev, Eduard Y

2014-03-05

(1)H NMR signal amplification by reversible exchange (SABRE) was observed for pyridine and pyridine-d5 at 9.4 T, a field that is orders of magnitude higher than what is typically utilized to achieve the conventional low-field SABRE effect. In addition to emissive peaks for the hydrogen spins at the ortho positions of the pyridine substrate (both free and bound to the metal center), absorptive signals are observed from hyperpolarized orthohydrogen and Ir-complex dihydride. Real-time kinetics studies show that the polarization build-up rates for these three species are in close agreement with their respective (1)H T1 relaxation rates at 9.4 T. The results suggest that the mechanism of the substrate polarization involves cross-relaxation with hyperpolarized species in a manner similar to the spin-polarization induced nuclear Overhauser effect. Experiments utilizing pyridine-d5 as the substrate exhibited larger enhancements as well as partial H/D exchange for the hydrogen atom in the ortho position of pyridine and concomitant formation of HD molecules. While the mechanism of polarization enhancement does not explicitly require chemical exchange of hydrogen atoms of parahydrogen and the substrate, the partial chemical modification of the substrate via hydrogen exchange means that SABRE under these conditions cannot rigorously be referred to as a non-hydrogenative parahydrogen induced polarization process.

The magnetic polarity stratigraphy of the Mauch Chunk Formation, Pennsylvania

PubMed Central

Opdyke, Neil D.; DiVenere, Victor J.

2004-01-01

Three sections of Chesterian Mauch Chunk Formation in Pennsylvania have been studied paleomagnetically to determine a Late Mississippian magnetic polarity stratigraphy. The upper section at Lavelle includes a conglomerate with abundant red siltstone rip-up clasts that yielded a positive conglomerate test. All samples were subjected to progressive thermal demagnetization to temperatures as high as 700°C. Two components of magnetization were isolated: a synfolding “B” component and the prefolding “C” component. The conglomerate test is positive, indicating that the C component was acquired very early in the history of the sediment. A coherent pattern of magnetic polarity reversals was identified. Five magnetozones were identified in the upper Lavelle section, which yields a pattern that is an excellent match with the pattern of reversals obtained from the upper Mauch Chunk at the original type section of the Mississippian/Pennsylvanian boundary at Pottsville, PA. The frequency of reversals in the upper Mississippian, as identified in the Mauch Chunk Formation, is approximately one to two per million years, which is an average for field reversal through time. PMID:15353597

The magnetic polarity stratigraphy of the Mauch Chunk Formation, Pennsylvania.

PubMed

Opdyke, Neil D; DiVenere, Victor J

2004-09-14

Three sections of Chesterian Mauch Chunk Formation in Pennsylvania have been studied paleomagnetically to determine a Late Mississippian magnetic polarity stratigraphy. The upper section at Lavelle includes a conglomerate with abundant red siltstone rip-up clasts that yielded a positive conglomerate test. All samples were subjected to progressive thermal demagnetization to temperatures as high as 700 degrees C. Two components of magnetization were isolated: a synfolding "B" component and the prefolding "C" component. The conglomerate test is positive, indicating that the C component was acquired very early in the history of the sediment. A coherent pattern of magnetic polarity reversals was identified. Five magnetozones were identified in the upper Lavelle section, which yields a pattern that is an excellent match with the pattern of reversals obtained from the upper Mauch Chunk at the original type section of the Mississippian/Pennsylvanian boundary at Pottsville, PA. The frequency of reversals in the upper Mississippian, as identified in the Mauch Chunk Formation, is approximately one to two per million years, which is an average for field reversal through time.

Thymidine phosphorylase exerts complex effects on bone resorption and formation in myeloma

PubMed Central

Liu, Huan; Liu, Zhiqiang; Du, Juan; He, Jin; Lin, Pei; Amini, Behrang; Starbuck, Michael W.; Novane, Nora; Shah, Jatin J.; Davis, Richard E.; Hou, Jian; Gagel, Robert F.; Yang, Jing

2016-01-01

Myelomatous bone disease is characterized by the development of lytic bone lesions and a concomitant reduction in bone formation, leading to chronic bone pain and fractures. To understand the underlying mechanism, we investigated the contribution of myeloma-expressed thymidine phosphorylase (TP) to bone lesions. In osteoblast progenitors, TP upregulated the methylation of RUNX2 and osterix, leading to decreased bone formation. In osteoclast progenitors, TP upregulated the methylation of IRF8, thereby enhanced expression of NFATc1, leading to increased bone resorption. TP reversibly catalyzes thymidine into thymine and 2DDR. Myeloma-secreted 2DDR bound to integrin αVβ3/α5β1 in the progenitors, activated PI3K/Akt signaling, and increased DNMT3A expression, resulting in hypermethylation of RUNX2, osterix, and IRF8. This study elucidates an important mechanism for myeloma-induced bone lesions, suggesting that targeting TP may be a viable approach to healing resorbed bone in patients. As TP overexpression is common in bone-metastatic tumors, our findings could have additional mechanistic implications. PMID:27559096

Minimising reversion, using seawater and magnesium chloride, caused by the dissolution of tricalcium aluminate hexahydrate.

PubMed

Palmer, Sara J; Frost, Ray L; Smith, Matthew K

2011-01-15

The increase in pH and aluminium concentration after the neutralisation of bauxite refinery residues is commonly known as reversion. This investigation reports the extent of reversion in synthetic supernatant liquor and possible methods to reduce reversion. This work is based on bauxite refinery residues produced from alumina refineries, where reversion is a real life situation in neutralised refinery residues. Tricalcium aluminate hexahydrate, a common phase in bauxite refinery residues, has been found to cause reversion. It has been established that reductions in both pH and aluminium from the seawater neutralisation process are due to the formation of 'Bayer' hydrotalcite Mg(7)Al(2)(OH)(18)(CO(3)(2-),SO(4)(2-))·xH(2)O. This is the primary mechanism involved in the removal of aluminium from solution. Increasing the volume of seawater used for the neutralisation process minimises the extent of reversion for both synthetic supernatant liquor and red mud slurry. The addition of MgCl(2)·6H(2)O also showed a reduction in reversion and confirmed that the decrease in aluminium and hydroxyl ions is due to the formation of Bayer hydrotalcite and not simply a dilution effect. Copyright © 2010 Elsevier Inc. All rights reserved.

Mechanism for Collective Cell Alignment in Myxococcus xanthus Bacteria

PubMed Central

Balagam, Rajesh; Igoshin, Oleg A.

2015-01-01

Myxococcus xanthus cells self-organize into aligned groups, clusters, at various stages of their lifecycle. Formation of these clusters is crucial for the complex dynamic multi-cellular behavior of these bacteria. However, the mechanism underlying the cell alignment and clustering is not fully understood. Motivated by studies of clustering in self-propelled rods, we hypothesized that M. xanthus cells can align and form clusters through pure mechanical interactions among cells and between cells and substrate. We test this hypothesis using an agent-based simulation framework in which each agent is based on the biophysical model of an individual M. xanthus cell. We show that model agents, under realistic cell flexibility values, can align and form cell clusters but only when periodic reversals of cell directions are suppressed. However, by extending our model to introduce the observed ability of cells to deposit and follow slime trails, we show that effective trail-following leads to clusters in reversing cells. Furthermore, we conclude that mechanical cell alignment combined with slime-trail-following is sufficient to explain the distinct clustering behaviors observed for wild-type and non-reversing M. xanthus mutants in recent experiments. Our results are robust to variation in model parameters, match the experimentally observed trends and can be applied to understand surface motility patterns of other bacterial species. PMID:26308508

The ζ Toxin Induces a Set of Protective Responses and Dormancy

PubMed Central

Tabone, Mariangela; Gonzalez-Pastor, José E.; Daugelavicius, Rimantas; Ayora, Silvia; Alonso, Juan C.

2012-01-01

The ζε module consists of a labile antitoxin protein, ε, which in dimer form (ε2) interferes with the action of the long-living monomeric ζ phosphotransferase toxin through protein complex formation. Toxin ζ, which inhibits cell wall biosynthesis and may be bactericide in nature, at or near physiological concentrations induces reversible cessation of Bacillus subtilis proliferation (protective dormancy) by targeting essential metabolic functions followed by propidium iodide (PI) staining in a fraction (20–30%) of the population and selects a subpopulation of cells that exhibit non-inheritable tolerance (1–5×10−5). Early after induction ζ toxin alters the expression of ∼78 genes, with the up-regulation of relA among them. RelA contributes to enforce toxin-induced dormancy. At later times, free active ζ decreases synthesis of macromolecules and releases intracellular K+. We propose that ζ toxin induces reversible protective dormancy and permeation to PI, and expression of ε2 antitoxin reverses these effects. At later times, toxin expression is followed by death of a small fraction (∼10%) of PI stained cells that exited earlier or did not enter into the dormant state. Recovery from stress leads to de novo synthesis of ε2 antitoxin, which blocks ATP binding by ζ toxin, thereby inhibiting its phosphotransferase activity. PMID:22295078

A novel double patterning approach for 30nm dense holes

NASA Astrophysics Data System (ADS)

Hsu, Dennis Shu-Hao; Wang, Walter; Hsieh, Wei-Hsien; Huang, Chun-Yen; Wu, Wen-Bin; Shih, Chiang-Lin; Shih, Steven

2011-04-01

Double Patterning Technology (DPT) was commonly accepted as the major workhorse beyond water immersion lithography for sub-38nm half-pitch line patterning before the EUV production. For dense hole patterning, classical DPT employs self-aligned spacer deposition and uses the intersection of horizontal and vertical lines to define the desired hole patterns. However, the increase in manufacturing cost and process complexity is tremendous. Several innovative approaches have been proposed and experimented to address the manufacturing and technical challenges. A novel process of double patterned pillars combined image reverse will be proposed for the realization of low cost dense holes in 30nm node DRAM. The nature of pillar formation lithography provides much better optical contrast compared to the counterpart hole patterning with similar CD requirements. By the utilization of a reliable freezing process, double patterned pillars can be readily implemented. A novel image reverse process at the last stage defines the hole patterns with high fidelity. In this paper, several freezing processes for the construction of the double patterned pillars were tested and compared, and 30nm double patterning pillars were demonstrated successfully. A variety of different image reverse processes will be investigated and discussed for their pros and cons. An economic approach with the optimized lithography performance will be proposed for the application of 30nm DRAM node.

Thermodynamics of natural selection III: Landauer's principle in computation and chemistry.

PubMed

Smith, Eric

2008-05-21

This is the third in a series of three papers devoted to energy flow and entropy changes in chemical and biological processes, and their relations to the thermodynamics of computation. The previous two papers have developed reversible chemical transformations as idealizations for studying physiology and natural selection, and derived bounds from the second law of thermodynamics, between information gain in an ensemble and the chemical work required to produce it. This paper concerns the explicit mapping of chemistry to computation, and particularly the Landauer decomposition of irreversible computations, in which reversible logical operations generating no heat are separated from heat-generating erasure steps which are logically irreversible but thermodynamically reversible. The Landauer arrangement of computation is shown to produce the same entropy-flow diagram as that of the chemical Carnot cycles used in the second paper of the series to idealize physiological cycles. The specific application of computation to data compression and error-correcting encoding also makes possible a Landauer analysis of the somewhat different problem of optimal molecular recognition, which has been considered as an information theory problem. It is shown here that bounds on maximum sequence discrimination from the enthalpy of complex formation, although derived from the same logical model as the Shannon theorem for channel capacity, arise from exactly the opposite model for erasure.

The ζ toxin induces a set of protective responses and dormancy.

PubMed

Lioy, Virginia S; Machon, Cristina; Tabone, Mariangela; Gonzalez-Pastor, José E; Daugelavicius, Rimantas; Ayora, Silvia; Alonso, Juan C

2012-01-01

The ζε module consists of a labile antitoxin protein, ε, which in dimer form (ε(2)) interferes with the action of the long-living monomeric ζ phosphotransferase toxin through protein complex formation. Toxin ζ, which inhibits cell wall biosynthesis and may be bactericide in nature, at or near physiological concentrations induces reversible cessation of Bacillus subtilis proliferation (protective dormancy) by targeting essential metabolic functions followed by propidium iodide (PI) staining in a fraction (20-30%) of the population and selects a subpopulation of cells that exhibit non-inheritable tolerance (1-5×10(-5)). Early after induction ζ toxin alters the expression of ∼78 genes, with the up-regulation of relA among them. RelA contributes to enforce toxin-induced dormancy. At later times, free active ζ decreases synthesis of macromolecules and releases intracellular K(+). We propose that ζ toxin induces reversible protective dormancy and permeation to PI, and expression of ε(2) antitoxin reverses these effects. At later times, toxin expression is followed by death of a small fraction (∼10%) of PI stained cells that exited earlier or did not enter into the dormant state. Recovery from stress leads to de novo synthesis of ε(2) antitoxin, which blocks ATP binding by ζ toxin, thereby inhibiting its phosphotransferase activity.

Stabilizing multicellularity through ratcheting

PubMed Central

Libby, Eric; Conlin, Peter L.; Kerr, Ben; Ratcliff, William C.

2016-01-01

The evolutionary transition to multicellularity probably began with the formation of simple undifferentiated cellular groups. Such groups evolve readily in diverse lineages of extant unicellular taxa, suggesting that there are few genetic barriers to this first key step. This may act as a double-edged sword: labile transitions between unicellular and multicellular states may facilitate the evolution of simple multicellularity, but reversion to a unicellular state may inhibit the evolution of increased complexity. In this paper, we examine how multicellular adaptations can act as evolutionary ‘ratchets’, limiting the potential for reversion to unicellularity. We consider a nascent multicellular lineage growing in an environment that varies between favouring multicellularity and favouring unicellularity. The first type of ratcheting mutations increase cell-level fitness in a multicellular context but are costly in a single-celled context, reducing the fitness of revertants. The second type of ratcheting mutations directly decrease the probability that a mutation will result in reversion (either as a pleiotropic consequence or via direct modification of switch rates). We show that both types of ratcheting mutations act to stabilize the multicellular state. We also identify synergistic effects between the two types of ratcheting mutations in which the presence of one creates the selective conditions favouring the other. Ratcheting mutations may play a key role in diverse evolutionary transitions in individuality, sustaining selection on the new higher-level organism by constraining evolutionary reversion. This article is part of the themed issue ‘The major synthetic evolutionary transitions’. PMID:27431522

Cladribine and Fludarabine Nucleotides Induce Distinct Hexamers Defining a Common Mode of Reversible RNR Inhibition.

PubMed

Wisitpitthaya, Somsinee; Zhao, Yi; Long, Marcus J C; Li, Minxing; Fletcher, Elaine A; Blessing, William A; Weiss, Robert S; Aye, Yimon

2016-07-15

The enzyme ribonucleotide reductase (RNR) is a major target of anticancer drugs. Until recently, suicide inactivation in which synthetic substrate analogs (nucleoside diphosphates) irreversibly inactivate the RNR-α2β2 heterodimeric complex was the only clinically proven inhibition pathway. For instance, this mechanism is deployed by the multifactorial anticancer agent gemcitabine diphosphate. Recently reversible targeting of RNR-α-alone coupled with ligand-induced RNR-α-persistent hexamerization has emerged to be of clinical significance. To date, clofarabine nucleotides are the only known example of this mechanism. Herein, chemoenzymatic syntheses of the active forms of two other drugs, phosphorylated cladribine (ClA) and fludarabine (FlU), allow us to establish that reversible inhibition is common to numerous drugs in clinical use. Enzyme inhibition and fluorescence anisotropy assays show that the di- and triphosphates of the two nucleosides function as reversible (i.e., nonmechanism-based) inhibitors of RNR and interact with the catalytic (C site) and the allosteric activity (A site) sites of RNR-α, respectively. Gel filtration, protease digestion, and FRET assays demonstrate that inhibition is coupled with formation of conformationally diverse hexamers. Studies in 293T cells capable of selectively inducing either wild-type or oligomerization-defective mutant RNR-α overexpression delineate the central role of RNR-α oligomerization in drug activity, and highlight a potential resistance mechanism to these drugs. These data set the stage for new interventions targeting RNR oligomeric regulation.

Interactions and reversal-field memory in complex magnetic nanowire arrays

NASA Astrophysics Data System (ADS)

Rotaru, Aurelian; Lim, Jin-Hee; Lenormand, Denny; Diaconu, Andrei; Wiley, John. B.; Postolache, Petronel; Stancu, Alexandru; Spinu, Leonard

2011-10-01

Interactions and magnetization reversal of Ni nanowire arrays have been investigated by the first-order reversal curve (FORC) method. Several series of samples with controlled spatial distribution were considered including simple wires of different lengths and diameters (70 and 110 nm) and complex wires with a single modulated diameter along their length. Subtle features of magnetic interactions are revealed through a quantitative analysis of the local interaction field profile distributions obtained from the FORC method. In addition, the FORC analysis indicates that the nanowire systems with a mean diameter of 70 nm appear to be organized in symmetric clusters indicative of a reversal-field memory effect.

Magnetic reversal frequency in the Lower Cambrian Niutitang Formation, Hunan Province, South China

NASA Astrophysics Data System (ADS)

Duan, Zongqi; Liu, Qingsong; Ren, Shoumai; Li, Lihui; Deng, Xiaolong; Liu, Jianxing

2018-05-01

The reversal frequency of the paleomagnetic field bears great information of evolution of the Earth's deep interior. However, there are still debates on the frequency pattern during the older periods of the Phanerozoic. This study investigated the Niutitang Formation (Lower Cambrian) of the Ciye 1 Hole from south China. Rock magnetic results indicate that the dominant magnetic carrier is magnetite. Characteristic remanence magnetizations have been successfully isolated for the weakly-magnetized shale rocks through stepwise alternated field demagnetization using the 2 G Enterprises Rapid System Magnetometer with a low-noise thin-walled quartz-glass sample holder. Constrained by radiometric ages, our paleomagnetic results indicated frequent polarity reversals during the period of ˜524-514 Ma, which backs up the speculation about the episode of the Ediacaran-Cambrian (˜550-500 Ma) with a character of reversal hyperactivity.

Iminoboronate Formation Leads to Fast and Reversible Conjugation Chemistry of α-Nucleophiles at Neutral pH.

PubMed

Bandyopadhyay, Anupam; Gao, Jianmin

2015-10-12

Bioorthogonal reactions that are fast and reversible under physiological conditions are in high demand for biological applications. Herein, it is shown that an ortho boronic acid substituent makes aryl ketones rapidly conjugate with α-nucleophiles at neutral pH. Specifically, 2-acetylphenylboronic acid and derivatives were found to conjugate with phenylhydrazine with rate constants of 10(2) to 10(3) M(-1) s(-1) , comparable to the fastest bioorthogonal conjugations known to date. (11) B NMR analysis revealed the varied extent of iminoboronate formation of the conjugates, in which the imine nitrogen forms a dative bond with boron. The iminoboronate formation activates the imines for hydrolysis and exchange, rendering these oxime/hydrazone conjugations reversible and dynamic under physiological conditions. The fast and dynamic nature of the iminoboronate chemistry should find wide applications in biology. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Formation and Sustainment of Flipped Spherical Torus Plasmas on HIST

NASA Astrophysics Data System (ADS)

Oguro, T.; Jinno, T.; Hasegawa, H.; Nagata, M.; Fukumoto, N.; Uyama, T.; Masamune, S.; Iida, M.; Katsurai, M.

2002-11-01

In order to understand comprehensively the relaxation and self-organization in the coaxial helicity injection system, we have investigated dynamics of ST plasmas produced in the HIST device by decreasing the external toroidal field (TF) and reversing its sign in time. In results, we have discovered that the ST relaxes towards flipped/reversed ST configurations. Surprisingly, it has been observed that not only toroidal flux but also poloidal flux reverses sign spontaneously during the relaxation process. This self-reversal of the poloidal field is thought to be evidence for global helicity conservation. Taylor helicity-driven relaxed theory predicts that there exists the relaxed state of the flipped ST plasma when the TF current is reversed. We found that when q_axis passes through the q_axis =1 rational barrier in the initial phase, the ST plasma becomes unstable and relaxes to flipped states through RFP states. The n=1 mode activities are essential in the formation and sustainment of the flipped ST.

Cucurbit[8]uril-Containing Multilayer Films for the Photocontrolled Binding and Release of a Guest Molecule.

PubMed

Nicolas, Henning; Yuan, Bin; Zhang, Xi; Schönhoff, Monika

2016-03-15

The powerful host-guest chemistry of cucurbit[8]uril (CB[8]) was employed to obtain photoresponsive polyelectrolyte multilayer films for the reversible and photocontrolled binding and release of an organic guest molecule. For this purpose, we designed and synthesized a polyelectrolyte with azobenzene side groups. Then, CB[8] was associated with the azo side group to obtain a supramolecular host-guest complex that was further used as building block in order to prepare photoresponsive and CB[8]-containing polyelectrolyte multilayer films. Ultraviolet spectroscopy and a dissipative quartz crystal microbalance are employed to monitor the formation of the host-guest complex and the layer-by-layer self-assembly of the multilayer films, respectively. We demonstrate that the photoresponsive properties of the azo side groups are maintained before and after host-guest complexation with CB[8] in solution and within the multilayer films, respectively. A guest molecule was then specifically included as second binding partner into the CB[8]-containing multilayer films. Subsequently, the release of the guest was performed by UV light irradiation due to the trans-cis isomerization of the adjacent azo side groups. Re-isomerization of the azo side groups was achieved by VIS light irradiation and enabled the rebinding of the guest into CB[8]. Finally, we demonstrate that the photocontrolled binding and release within CB[8]-containing multilayer films can reliably and reversibly be performed over a period of more than 2 weeks with constant binding efficiency. Therefore, we expect such novel type of photosensitive films to have promising future applications in the field of stimuli-responsive nanomaterials.

Self-Healing of Unentangled Polymer Networks with Reversible Bonds

PubMed Central

Stukalin, Evgeny B.; Cai, Li-Heng; Kumar, N. Arun; Leibler, Ludwik; Rubinstein, Michael

2013-01-01

Self-healing polymeric materials are systems that after damage can revert to their original state with full or partial recovery of mechanical strength. Using scaling theory we study a simple model of autonomic self-healing of unentangled polymer networks. In this model one of the two end monomers of each polymer chain is fixed in space mimicking dangling chains attachment to a polymer network, while the sticky monomer at the other end of each chain can form pairwise reversible bond with the sticky end of another chain. We study the reaction kinetics of reversible bonds in this simple model and analyze the different stages in the self-repair process. The formation of bridges and the recovery of the material strength across the fractured interface during the healing period occur appreciably faster after shorter waiting time, during which the fractured surfaces are kept apart. We observe the slowest formation of bridges for self-adhesion after bringing into contact two bare surfaces with equilibrium (very low) density of open stickers in comparison with self-healing. The primary role of anomalous diffusion in material self-repair for short waiting times is established, while at long waiting times the recovery of bonds across fractured interface is due to hopping diffusion of stickers between different bonded partners. Acceleration in bridge formation for self-healing compared to self-adhesion is due to excess non-equilibrium concentration of open stickers. Full recovery of reversible bonds across fractured interface (formation of bridges) occurs after appreciably longer time than the equilibration time of the concentration of reversible bonds in the bulk. PMID:24347684

Novel Application of a Reverse Triage Protocol Providing Increased Access to Care in an Outpatient, Primary Care Clinic Setting.

PubMed

Sacino, Amanda N; Shuster, Jonathan J; Nowicki, Kamil; Carek, Peter J; Wegman, Martin P; Listhaus, Alyson; Gibney, Joseph M; Chang, Ku-Lang

2016-02-01

As the number of patients with access to care increases, outpatient clinics will need to implement innovative strategies to maintain or enhance clinic efficiency. One viable alternative involves reverse triage. A reverse triage protocol was implemented during a student-run free clinic. Each patient's chief complaint(s) were obtained at the beginning of the clinic session and ranked by increasing complexity. "Complexity" was defined as the subjective amount of time required to provide a full, thorough evaluation of a patient. Less complex cases were prioritized first since they could be expedited through clinic processing and allow for more time and resources to be dedicated to complex cases. Descriptive statistics were used to characterize and summarize the data obtained. Categorical variables were analyzed using chi-square. A time series analysis of the outcome versus centered time in weeks was also conducted. The average number of patients seen per clinic session increased by 35% (9.5 versus 12.8) from pre-implementation of the reverse triage protocol to 6 months after the implementation of the protocol. The implementation of a reverse triage in an outpatient setting significantly increased clinic efficiency as noted by a significant increase in the number of patients seen during a clinic session.

Disruption of Specific RNA-RNA Interactions in a Double-Stranded RNA Virus Inhibits Genome Packaging and Virus Infectivity

PubMed Central

Fajardo, Teodoro; Sung, Po-Yu; Roy, Polly

2015-01-01

Bluetongue virus (BTV) causes hemorrhagic disease in economically important livestock. The BTV genome is organized into ten discrete double-stranded RNA molecules (S1-S10) which have been suggested to follow a sequential packaging pathway from smallest to largest segment during virus capsid assembly. To substantiate and extend these studies, we have investigated the RNA sorting and packaging mechanisms with a new experimental approach using inhibitory oligonucleotides. Putative packaging signals present in the 3’untranslated regions of BTV segments were targeted by a number of nuclease resistant oligoribonucleotides (ORNs) and their effects on virus replication in cell culture were assessed. ORNs complementary to the 3’ UTR of BTV RNAs significantly inhibited virus replication without affecting protein synthesis. Same ORNs were found to inhibit complex formation when added to a novel RNA-RNA interaction assay which measured the formation of supramolecular complexes between and among different RNA segments. ORNs targeting the 3’UTR of BTV segment 10, the smallest RNA segment, were shown to be the most potent and deletions or substitution mutations of the targeted sequences diminished the RNA complexes and abolished the recovery of viable viruses using reverse genetics. Cell-free capsid assembly/RNA packaging assay also confirmed that the inhibitory ORNs could interfere with RNA packaging and further substitution mutations within the putative RNA packaging sequence have identified the recognition sequence concerned. Exchange of 3’UTR between segments have further demonstrated that RNA recognition was segment specific, most likely acting as part of the secondary structure of the entire genomic segment. Our data confirm that genome packaging in this segmented dsRNA virus occurs via the formation of supramolecular complexes formed by the interaction of specific sequences located in the 3’ UTRs. Additionally, the inhibition of packaging in-trans with inhibitory ORNs suggests this that interaction is a bona fide target for the design of compounds with antiviral activity. PMID:26646790

Disruption of Specific RNA-RNA Interactions in a Double-Stranded RNA Virus Inhibits Genome Packaging and Virus Infectivity.

PubMed

Fajardo, Teodoro; Sung, Po-Yu; Roy, Polly

2015-12-01

Bluetongue virus (BTV) causes hemorrhagic disease in economically important livestock. The BTV genome is organized into ten discrete double-stranded RNA molecules (S1-S10) which have been suggested to follow a sequential packaging pathway from smallest to largest segment during virus capsid assembly. To substantiate and extend these studies, we have investigated the RNA sorting and packaging mechanisms with a new experimental approach using inhibitory oligonucleotides. Putative packaging signals present in the 3'untranslated regions of BTV segments were targeted by a number of nuclease resistant oligoribonucleotides (ORNs) and their effects on virus replication in cell culture were assessed. ORNs complementary to the 3' UTR of BTV RNAs significantly inhibited virus replication without affecting protein synthesis. Same ORNs were found to inhibit complex formation when added to a novel RNA-RNA interaction assay which measured the formation of supramolecular complexes between and among different RNA segments. ORNs targeting the 3'UTR of BTV segment 10, the smallest RNA segment, were shown to be the most potent and deletions or substitution mutations of the targeted sequences diminished the RNA complexes and abolished the recovery of viable viruses using reverse genetics. Cell-free capsid assembly/RNA packaging assay also confirmed that the inhibitory ORNs could interfere with RNA packaging and further substitution mutations within the putative RNA packaging sequence have identified the recognition sequence concerned. Exchange of 3'UTR between segments have further demonstrated that RNA recognition was segment specific, most likely acting as part of the secondary structure of the entire genomic segment. Our data confirm that genome packaging in this segmented dsRNA virus occurs via the formation of supramolecular complexes formed by the interaction of specific sequences located in the 3' UTRs. Additionally, the inhibition of packaging in-trans with inhibitory ORNs suggests this that interaction is a bona fide target for the design of compounds with antiviral activity.

The histone shuffle: histone chaperones in an energetic dance

PubMed Central

Das, Chandrima; Tyler, Jessica K.; Churchill, Mair E.A.

2014-01-01

Our genetic information is tightly packaged into a rather ingenious nucleoprotein complex called chromatin in a manner that enables it to be rapidly accessed during genomic processes. Formation of the nucleosome, which is the fundamental unit of chromatin, occurs via a stepwise process that is reversed to enable the disassembly of nucleosomes. Histone chaperone proteins have prominent roles in facilitating these processes as well as in replacing old histones with new canonical histones or histone variants during the process of histone exchange. Recent structural, biophysical and biochemical studies have begun to shed light on the molecular mechanisms whereby histone chaperones promote chromatin assembly, disassembly and histone exchange to facilitate DNA replication, repair and transcription. PMID:20444609

The kinetics of inhibition of erythrocyte cholinesterase by monomethylcarbamates

PubMed Central

Reiner, E.; Simeon-Rudolf, V.

1966-01-01

1. The kinetics of the interaction of erythrocyte cholinesterase with 1-naphthyl N-methylcarbamate, 2-isopropoxyphenyl N-methylcarbamate and phenyl N-methylcarbamate were studied. Rate constants for inhibition and rate constants for spontaneous reactivation were determined. The calculated rate constants for spontaneous reactivation agreed well with those obtained experimentally. 2. The degree of inhibition obtained after preincubation of enzyme and inhibitor was found to be independent of both the substrate concentration and the dilution of the inhibited enzyme. 3. The reaction between the enzyme and the inhibitor was consistent with carbamates being regarded as poor substrates of cholinesterases. There was no evidence for the formation of a reversible complex between the enzyme and the carbamate. PMID:5941343

Low temperature thermally regenerative electrochemical system

DOEpatents

Loutfy, Raouf O.; Brown, Alan P.; Yao, Neng-Ping

1983-01-01

A thermally regenerative electrochemical system including an electrochemical cell with two water-based electrolytes separated by an ion exchange membrane, at least one of the electrolytes containing a complexing agent and a salt of a multivalent metal whose respective order of potentials for a pair of its redox couples is reversible by a change in the amount of the complexing agent in the electrolyte, the complexing agent being removable by distillation to cause the reversal.

Using reversed phase high performance liquid chromatography to study the complexation of anthocyanins with β-cyclodextrin

NASA Astrophysics Data System (ADS)

Deineka, V. I.; Lapshova, M. S.; Deineka, L. A.

2014-06-01

It is shown by means of reversed phase high performance liquid chromatography (RP HPLC) with mobile phases containing additions of β-cyclodextrin that 5-glucosides of cyanidin and pelargonidin form stronger inclusion complexes than 3-glucosides; this is explained by the steric interference of the glucoside radical.

The 16.6 Ma Steens Mountain Geomagnetic Polarity Reversal: Additional Complexity From a Composite Record of Five Stratigraphic Sections.

NASA Astrophysics Data System (ADS)

Jarboe, N. A.; Coe, R. S.; Glen, J. M.; Paul, R. R.

2007-05-01

The best known record of the earth's magnetic field behavior during a geomagnetic polarity reversal preserved in volcanic rock is the reverse to normal (R-N) polarity reversal found in the Steens Basalts of SE Oregon. At three locations where reverse to normal sections are found (Steens Mountain, Catlow Peak, and Poker Jim Ridge), four high precision 40Ar/39Ar plateau ages of plagioclase separates from transitionally magnetized rocks were determined. The ages are the same within error and have a weighted mean age of 16.58 ± 0.14 Ma. Errors are two sigma. A more precise constraint on the youngest possible age of the reversal is 16.548 ± 0.050 Ma determined from the normally magnetized Oregon Canyon tuff capping the Catlow Peak section. Comparison of these ages to the new geomagnetic polarity time scale of Gradstein et al. (A Geologic Time Scale 2004, 589 pp., Cambridge University Press, 2004.), after adjustments due to differences in Fish Canyon sanidine (FCs) standard ages (28.02 Ma, this study; 28.24 Ma, Gradstein et al.), shows that the Steens reversal is uniquely identified as the top of the C5Cr chron. The high precision of the ages and the Steens' reversal location in the geomagnetic polarity timescale convincingly demonstrate that these stratigraphically uncorrelated transitional sections were erupted during the same transition and their transitional paths should be combined. The high-quality, detailed benchmark record of this reversal (Mankinen et al., JGR, 90(B), 10.393-10.416, 1985; Prevot et al., Nature, 316, 230-234, 1985) is a composite derived from two sampled sections 2 km apart on Steens Mountain that overlapped significantly, Steens A above and Steens B below. This study showed that the magnetic field during the reversal moved from reverse to normal and then bounced back to transitional before finally returning to normal (a R-T-N-T-N path). The unexamined upper part of the Steens B section was later sampled and revealed an additional bounce of the field during the transition (Camps et al., JGR, 104(B8), 17747- 58, 1999). This increased the reversal's complexity to a R-T-N-T-N-T-N pattern. We have studied a R-N volcanic section at Catlow Peak 70 km SSE of Steens Mountain with 32 flows erupted during the transition. The transitional directions trace a path very close to the Steens A and B reversal path but contain an additional large swing through the reversed field direction, demonstrating an even more complex R-T-N-T-N-T-R-T-N path. We will also report on two R-N sections recently sampled at Poker Jim Ridge 80 km west of Steens Mountain that add new directions to the Steens record. The complex composite Steens reversal path recorded in these high fidelity lavas gives some credence to suggestions of very complex magnetic field behavior during reversals, previously seen only in sediment records where the acquisition of magnetization is less well understood.

2-Oxoglutarate dehydrogenase is a more significant source of O2(·-)/H2O2 than pyruvate dehydrogenase in cardiac and liver tissue.

PubMed

Mailloux, Ryan J; Gardiner, Danielle; O'Brien, Marisa

2016-08-01

Pyruvate dehydrogenase (Pdh) and 2-oxoglutarate dehydrogenase (Ogdh) are vital for Krebs cycle metabolism and sources of reactive oxygen species (ROS). O2(·-)/H2O2 formation by Pdh and Ogdh from porcine heart were compared when operating under forward or reverse electron transfer conditions. Comparisons were also conducted with liver and cardiac mitochondria. During reverse electron transfer (RET) from NADH, purified Ogdh generated ~3-3.5× more O2(·-)/H2O2 in comparison to Pdh when metabolizing 0.5-10µM NADH. Under forward electron transfer (FET) conditions Ogdh generated ~2-4× more O2(·-)/H2O2 than Pdh. In both liver and cardiac mitochondria, Ogdh displayed significantly higher rates of ROS formation when compared to Pdh. Ogdh was also a significant source of ROS in liver mitochondria metabolizing 50µM and 500µM pyruvate or succinate. Finally, we also observed that DTT directly stimulated O2(·-)/H2O2 formation by purified Pdh and Ogdh and in cardiac or liver mitochondria in the absence of substrates and cofactors. Taken together, Ogdh is a more potent source of ROS than Pdh in liver and cardiac tissue. Ogdh is also an important ROS generator regardless of whether pyruvate or succinate serve as the sole source of carbon. Our observations provide insight into the ROS generating capacity of either complex in cardiac and liver tissue. The evidence presented herein also indicates DTT, a reductant that is routinely added to biological samples, should be avoided when assessing mitochondrial O2(·-)/H2O2 production. Copyright © 2016 Elsevier B.V. All rights reserved.

Thrusting Rates in the Early Eocene from the Sevier Hinterland, Idaho, USA

NASA Astrophysics Data System (ADS)

Anastasio, D. J.; Latta, D.; Kodama, K. P.; Idleman, B. D.

2011-12-01

The terminal motion on the Wildhorse thrust system was reconstructed from the Smiley Creek Formation in eastern Idaho, USA (UTM coordinates 11T 739950 m E, 4865190 m N). During the last 100 m of fault slip the calculated slip rate varied between 0.05 to 1.2 mm/yr averaged over time intervals of 300-800 kyrs. The emergent thrust fault overrode proximal fault scarp colluvium deposited as water poor debris flows and was buried by braided stream sheet flood facies sourced by out-of-sequence thrust motion further west. Paleomagnetic data (~100 cores from 27 horizons spaced ~5-60 m apart) showed both normal and reversed directions during progressive step-wise thermal demagnetization to 670° C. Principal component analysis was used to calculate characteristic remanent magnetization directions from which sample polarities were assigned. Correlation of the Smiley Creek Formation to the Geomagnetic Polarity Timescale requires an age older than 49.39±0.27 (n=7) Ma determined by 40Ar/39Ar dating of overlying Challis Volcanic samples and younger than 57±9 Ma, the youngest U/Pb zircon age from an included andesite cobble from a near by Smiley Creek conglomerate exposure (11T 766548 m E, 4874382 m N). The favored magnetostratigraphic correlation is most consistent with expected terrestrial fan facies accumulation rates, the reversal pattern, and calculated paleopole positions. The 183 m of Smiley Creek Formation west of Stag Creek, Idaho was deposited in 4.48 myrs during polarity chrons 24.3n to 23n2n. The terminal emplacement of the Wildhorse thrust was associated with the development of the Pioneer Metamorphic Core complex in the hinterland of the Montana Recess of the Idaho-Wyoming-Montana thrust belt.

Merging constitutional and motional covalent dynamics in reversible imine formation and exchange processes.

PubMed

Kovaříček, Petr; Lehn, Jean-Marie

2012-06-06

The formation and exchange processes of imines of salicylaldehyde, pyridine-2-carboxaldehyde, and benzaldehyde have been studied, showing that the former has features of particular interest for dynamic covalent chemistry, displaying high efficiency and fast rates. The monoimines formed with aliphatic α,ω-diamines display an internal exchange process of self-transimination type, inducing a local motion of either "stepping-in-place" or "single-step" type by bond interchange, whose rate decreases rapidly with the distance of the terminal amino groups. Control of the speed of the process over a wide range may be achieved by substituents, solvent composition, and temperature. These monoimines also undergo intermolecular exchange, thus merging motional and constitutional covalent behavior within the same molecule. With polyamines, the monoimines formed execute internal motions that have been characterized by extensive one-dimensional, two-dimensional, and EXSY proton NMR studies. In particular, with linear polyamines, nondirectional displacement occurs by shifting of the aldehyde residue along the polyamine chain serving as molecular track. Imines thus behave as simple prototypes of systems displaying relative motions of molecular moieties, a subject of high current interest in the investigation of synthetic and biological molecular motors. The motional processes described are of dynamic covalent nature and take place without change in molecular constitution. They thus represent a category of dynamic covalent motions, resulting from reversible covalent bond formation and dissociation. They extend dynamic covalent chemistry into the area of molecular motions. A major further step will be to achieve control of directionality. The results reported here for imines open wide perspectives, together with other chemical groups, for the implementation of such features in multifunctional molecules toward the design of molecular devices presenting a complex combination of motional and constitutional dynamic behaviors.

Ultrasonic Time Reversal Mirrors

NASA Astrophysics Data System (ADS)

Fink, Mathias; Montaldo, Gabriel; Tanter, Mickael

2004-11-01

For more than ten years, time reversal techniques have been developed in many different fields of applications including detection of defects in solids, underwater acoustics, room acoustics and also ultrasound medical imaging and therapy. The essential property that makes time reversed acoustics possible is that the underlying physical process of wave propagation would be unchanged if time were reversed. In a non dissipative medium, the equations governing the waves guarantee that for every burst of sound that diverges from a source there exists in theory a set of waves that would precisely retrace the path of the sound back to the source. If the source is pointlike, this allows focusing back on the source whatever the medium complexity. For this reason, time reversal represents a very powerful adaptive focusing technique for complex media. The generation of this reconverging wave can be achieved by using Time Reversal Mirrors (TRM). It is made of arrays of ultrasonic reversible piezoelectric transducers that can record the wavefield coming from the sources and send back its time-reversed version in the medium. It relies on the use of fully programmable multi-channel electronics. In this paper we present some applications of iterative time reversal mirrors to target detection in medical applications.

High fluorescence emission of carboxylic acid functionalized polystyrene/BaTiO{sub 3} nanocomposites and rare earth metal complexes: Preparation and characterization

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cao, X. T.; Showkat, A. M.; Wang, Z.

2015-03-30

Noble fluorescence nanocomposite compound based on barium titanate nanoparticles (BTO), polystyrene (PSt), and terbium ion (Tb{sup 3+}) was synthesized by a combination of surface-initiated reversible addition-fragmentation chain transfer (RAFT) polymerization, Friedel-Crafts alkylation reaction and coordinate chemistry. Initially, a modification of surface of BTO was conducted by an exchange process with S-benzyl S’-trimethoxysilylpropyltrithiocarbonate to create macro-initiator for polymerization of styrene. Subsequently, aryl carboxylic acid functionalized polystyrene grafted barium titanate (BTO-g-PSt-COOH) was generated by substitution reaction between 4-(Chloromethyl) benzoic acid and PSt chains. The coordination of the nanohybrids with Tb{sup 3+} ions afforded fluorescent Tb{sup 3+} tagged aryl carboxylic acid functionalized polystyrenemore » grafted barium titanate (BTO-g-PSt-Tb{sup 3+}) complexes. Structure, morphology, and fluorescence properties of nanohybrid complexes were investigated by respective physical and spectral studies. FT-IR and SEM analyses confirmed the formation of BTO-g-PSt-Tb{sup 3+}nanohybrids. Furthermore, TGA profiles demonstrated the grafting of aryl carboxylic acid functionalized polystyrene on BTO surface. Optical properties of BTO-g-PSt-Tb{sup 3+} complexes were investigated by fluorescence spectroscopy.« less

Bacopa monnieri Phytochemicals Mediated Synthesis of Platinum Nanoparticles and Its Neurorescue Effect on 1-Methyl 4-Phenyl 1,2,3,6 Tetrahydropyridine-Induced Experimental Parkinsonism in Zebrafish

PubMed Central

Nellore, Jayshree; Pauline, Cynthia; Amarnath, Kanchana

2013-01-01

Current discovery demonstrates the rapid formation of platinum nanoparticles using leaf extract of a neurobeneficial plant, Bacopa monnieri (BmE). The nanoparticles (BmE-PtNPs) were stabilized and then coated with varied phytochemicals present within the leaf extract. These nanoparticles demonstrated the same activity of Complex I, as that of oxidizing NADH to NAD+ using a spectrophotometric method. This suggests that BmE-PtNPs are a potential medicinal substance for oxidative stress mediated disease with suppressed mitochondrial complex I, namely, Parkinson's disease (PD). Hence, the neuroprotective potentials of the phytochemical coated nanoparticle were explored in 1-methyl 4-phenyl 1,2,3,6 tetrahydropyridine- (MPTP-)induced experimental Parkinsonism in zebrafish model. BmE-PtNPs pretreatment significantly reversed toxic effects of MPTP by increasing the levels of dopamine, its metabolites, GSH and activities of GPx, catalase, SOD and complex I, and reducing levels of MDA along with enhanced locomotor activity. Taken together, these findings suggest that BmE-PtNPs have protective effect in MPTP-induced neurotoxicity in this model of Parkinson's disease via their dual functions as mitochondrial complex I and antioxidant activity. PMID:26317003

Reversing the similarity effect: The effect of presentation format.

PubMed

Cataldo, Andrea M; Cohen, Andrew L

2018-06-01

A context effect is a change in preference that occurs when alternatives are added to a choice set. Models of preferential choice that account for context effects largely assume a within-dimension comparison process. It has been shown, however, that the format in which a choice set is presented can influence comparison strategies. That is, a by-alternative or by-dimension grouping of the dimension values encourage within-alternative or within-dimension comparisons, respectively. For example, one classic context effect, the compromise effect, is strengthened by a by-dimension presentation format. Extrapolation from this result suggests that a second context effect, the similarity effect, will actually reverse when stimuli are presented in a by-dimension format. In the current study, we presented participants with a series of apartment choice sets designed to elicit the similarity effect, with either a by-alternative or by-dimension presentation format. Participants in the by-alternative condition demonstrated a standard similarity effect; however, participants in the by-dimension condition demonstrated a strong reverse similarity effect. The present data can be accounted for by Multialternative Decision Field Theory (MDFT) and the Multiattribute Linear Ballistic Accumulator (MLBA), but not Elimination by Aspects (EBA). Indeed, when some weak assumptions of within-dimension processes are met, MDFT and the MLBA predict the reverse similarity effect. These modeling results suggest that the similarity effect is governed by either forgetting and inhibition (MDFT), or attention to positive or negative differences (MLBA). These results demonstrate that flexibility in the comparison process needs to be incorporated into theories of preferential choice. Copyright © 2018 Elsevier B.V. All rights reserved.

Conjugated polyelectrolyte based real-time fluorescence assay for phospholipase C.

PubMed

Liu, Yan; Ogawa, Katsu; Schanze, Kirk S

2008-01-01

A fluorescence turnoff assay for phospholipase C (PLC) from Clostridium perfringens is developed based on the reversible interaction between the natural substrate, phosphatidylcholine, and a fluorescent, water-soluble conjugated polyelectrolyte (CPE). The fluorescence intensity of the CPE in water is increased substantially by the addition of the phospholipid due to the formation of a CPE-lipid complex. Incubation of the CPE-lipid complex with the enzyme PLC causes the fluorescence intensity to decrease (turnoff sensor); the response arises due to PLC-catalyzed hydrolysis of the phosphatidylcholine, which effectively disrupts the CPE-lipid complex. The PLC assay operates with phospholipid substrate concentrations in the micromolar range, and the analytical detection limit for PLC is <1 nM. The optimized assay provides a convenient, rapid, and real-time sensor for PLC activity. The real-time fluorescence intensity from the CPE can be converted to substrate concentration by using an ex situ calibration curve, allowing PLC-catalyzed reaction rates and kinetic parameters to be determined. PLC activation by Ca2+ and inhibition by EDTA and fluoride ion are demonstrated using the optimized sensor.

Mechanism of cell alignment in groups of Myxococcus xanthus bacteria

NASA Astrophysics Data System (ADS)

Balgam, Rajesh; Igoshin, Oleg

2015-03-01

Myxococcus xanthus is a model for studying self-organization in bacteria. These flexible cylindrical bacteria move along. In groups, M. xanthus cells align themselves into dynamic cell clusters but the mechanism underlying their formation is unknown. It has been shown that steric interactions can cause alignment in self-propelled hard rods but it is not clear how flexibility and reversals affect the alignment and cluster formation. We have investigated cell alignment process using our biophysical model of M. xanthus cell in an agent-based simulation framework under realistic cell flexibility values. We observed that flexible model cells can form aligned cell clusters when reversals are suppressed but these clusters disappeared when reversals frequency becomes similar to the observed value. However, M. xanthus cells follow slime (polysaccharide gel like material) trails left by other cells and we show that implementing this into our model rescues cell clustering for reversing cells. Our results show that slime following along with periodic cell reversals act as positive feedback to reinforce existing slime trails and recruit more cells. Furthermore, we have observed that mechanical cell alignment combined with slime following is sufficient to explain the distinct clustering patterns of reversing and non-reversing cells as observed in recent experiments. This work is supported by NSF MCB 0845919 and 1411780.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Perumalla, Kalyan S.; Yoginath, Srikanth B.

Problems such as fault tolerance and scalable synchronization can be efficiently solved using reversibility of applications. Making applications reversible by relying on computation rather than on memory is ideal for large scale parallel computing, especially for the next generation of supercomputers in which memory is expensive in terms of latency, energy, and price. In this direction, a case study is presented here in reversing a computational core, namely, Basic Linear Algebra Subprograms, which is widely used in scientific applications. A new Reversible BLAS (RBLAS) library interface has been designed, and a prototype has been implemented with two modes: (1) amore » memory-mode in which reversibility is obtained by checkpointing to memory in forward and restoring from memory in reverse, and (2) a computational-mode in which nothing is saved in the forward, but restoration is done entirely via inverse computation in reverse. The article is focused on detailed performance benchmarking to evaluate the runtime dynamics and performance effects, comparing reversible computation with checkpointing on both traditional CPU platforms and recent GPU accelerator platforms. For BLAS Level-1 subprograms, data indicates over an order of magnitude better speed of reversible computation compared to checkpointing. For BLAS Level-2 and Level-3, a more complex tradeoff is observed between reversible computation and checkpointing, depending on computational and memory complexities of the subprograms.« less

Crystal Violet Lactone Salicylaldehyde Hydrazone Zn(II) Complex: a Reversible Photochromic Material both in Solution and in Solid Matrix

PubMed Central

Li, Kai; Li, Yuanyuan; Tao, Jing; Liu, Lu; Wang, Lili; Hou, Hongwei; Tong, Aijun

2015-01-01

Crystal violet lactone (CVL) is a classic halochromic dye which has been widely used as chromogenic reagent in thermochromic and piezochromic systems. In this work, a very first example of CVL-based reversible photochromic compound was developed, which showed distinct color change upon UV-visible light irradiation both in solution and in solid matrix. Moreover, metal complex of CVL salicylaldehyde hydrozone was facilely synthesized, exhibiting reversible photochromic properties with good fatigue resistance. It was served as promising solid material for photo-patterning. PMID:26412101

Time-reversed, flow-reversed ballistics simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zernow, L.; Chapyak, E. J.; Scheffler, D. R.

2001-01-01

Two-dimensional simulations of planar sheet jet formation are studied to examine the hydrodynamic issues involved when simulations are carried out in the inverse direction, that is, with reversed time and flow. Both a realistic copper equation of state and a shockless equation of state were used. These studies are an initial step in evaluating this technique as a ballistics design tool.

Aquifer composition and the tendency toward scale-deposit formation during reverse osmosis desalination - Examples from saline ground water in New Mexico, USA

USGS Publications Warehouse

Huff, G.F.

2006-01-01

Desalination is expected to make a substantial contribution to water supply in the United States by 2020. Currently, reverse osmosis is one of the most cost effective and widely used desalination technologies. The tendency to form scale deposits during reverse osmosis is an important factor in determining the suitability of input waters for use in desalination. The tendency toward scale formation of samples of saline ground water from selected geologic units in New Mexico was assessed using simulated evaporation. All saline water samples showed a strong tendency to form CaCO3 scale deposits. Saline ground water samples from the Yeso Formation and the San Andres Limestone showed relatively stronger tendencies to form CaSO4 2H2O scale deposits and relatively weaker tendencies to form SiO2(a) scale deposits than saline ground water samples from the Rio Grande alluvium. Tendencies toward scale formation in saline ground water samples from the Dockum Group were highly variable. The tendencies toward scale formation of saline waters from the Yeso Formation, San Andres Limestone, and Rio Grande alluvium appear to correlate with the mineralogical composition of the geologic units, suggesting that scale-forming tendencies are governed by aquifer composition and water-rock interaction. ?? 2006 Elsevier B.V. All rights reserved.

Knockdown of miR-27a sensitizes colorectal cancer stem cells to TRAIL by promoting the formation of Apaf-1-caspase-9 complex

PubMed Central

Zhang, Rui; Xu, Jian; Zhao, Jian; Bai, Jinghui

2017-01-01

MicroRNAs have been proved to participate in multiple biological processes in cancers. For developing resistance to cytotoxic drug, cancer cells, especially the cancer stem cells, usually change their microRNA expression profile to survive in hostile environments. In the present study, we found that expression of microRNA-27a was increased in colorectal cancer stem cells. High level of microRNA-27a was indicated to induce the resistance to TNF-related apoptosis-inducing ligand (TRAIL). Knockdown of microRNA-27a resensitized colorectal cancer stem cells to TRAIL-induced cell death. Mechanically, the gene of Apaf-1, which is associated with the mitochondrial apoptosis, was demonstrated to be the target of microRNA-27a in colorectal cancer stem cells. Knockdown of microRNA-27a increased the expression level of Apaf-1, thus enhancing the formation of Apaf-1-caspase-9 complex and subsequently promoting the TRAIL-induced apoptosis in colorectal cancer stem cells. These findings suggested that knockdown of microRNA-27a in colorectal cancer stem cells by the specific antioligonucleotides was potential to reverse the chemoresistance to TRAIL. It may represent a novel therapeutic strategy for treating the colorectal cancer more effectively. PMID:28423356

Knockdown of miR-27a sensitizes colorectal cancer stem cells to TRAIL by promoting the formation of Apaf-1-caspase-9 complex.

PubMed

Zhang, Rui; Xu, Jian; Zhao, Jian; Bai, Jinghui

2017-07-11

MicroRNAs have been proved to participate in multiple biological processes in cancers. For developing resistance to cytotoxic drug, cancer cells, especially the cancer stem cells, usually change their microRNA expression profile to survive in hostile environments. In the present study, we found that expression of microRNA-27a was increased in colorectal cancer stem cells. High level of microRNA-27a was indicated to induce the resistance to TNF-related apoptosis-inducing ligand (TRAIL). Knockdown of microRNA-27a resensitized colorectal cancer stem cells to TRAIL-induced cell death. Mechanically, the gene of Apaf-1, which is associated with the mitochondrial apoptosis, was demonstrated to be the target of microRNA-27a in colorectal cancer stem cells. Knockdown of microRNA-27a increased the expression level of Apaf-1, thus enhancing the formation of Apaf-1-caspase-9 complex and subsequently promoting the TRAIL-induced apoptosis in colorectal cancer stem cells. These findings suggested that knockdown of microRNA-27a in colorectal cancer stem cells by the specific antioligonucleotides was potential to reverse the chemoresistance to TRAIL. It may represent a novel therapeutic strategy for treating the colorectal cancer more effectively.

Optical monitoring of gases with cholesteric liquid crystals.

PubMed

Han, Yang; Pacheco, Katherine; Bastiaansen, Cees W M; Broer, Dirk J; Sijbesma, Rint P

2010-03-10

A new approach to optical monitors for gases is introduced using cholesteric liquid crystals doped with reactive chiral compounds. The approach is based on cholesteric pitch length changes caused by a change in helical twisting power (HTP) of the chiral dopants upon reaction with the analyte. The concept is demonstrated for monitoring carbon dioxide via reversible carbamate formation and for oxygen using the irreversible oxidation of a chiral dithiol to a disulfide. Monitoring of CO(2) was achieved by doping a commercial cholesteric liquid crystalline mixture (E7) with 1.6% mol of the 1:1 complex of an optically pure diamine with a TADDOL derivative. Upon exposure to carbon dioxide, the reflection band of a thin film of the mixture shifted from 637 to 495 nm as a consequence of dissociation of the complex after carbamate formation of the diamine. An O(2) monitor was obtained by doping E7 with a chiral binaphthyl dithiol derivative and a nonresponsive codopant. The reflection band of the oxygen monitor film changed from 542 to 600 nm, due to the conformational change accompanying oxidation of the dithiol to disulfide. These monitoring mechanisms hold promise for application in smart packaging, where carbon dioxide and oxygen are of special interest because of their roles in food preservation.

Phosphatase inhibition leads to histone deacetylases 1 and 2 phosphorylation and disruption of corepressor interactions.

PubMed

Galasinski, Scott C; Resing, Katheryn A; Goodrich, James A; Ahn, Natalie G

2002-05-31

The regulation of histone deacetylases (HDACs) by phosphorylation was examined by elevating intracellular phosphorylation in cultured cells with the protein phosphatase inhibitor okadaic acid. After fractionation of extracts from treated versus untreated cells, HDAC 1 and 2 eluted in several peaks of deacetylase activity, assayed using mixed acetylated histones or acetylated histone H4 peptide. Stimulation of cells with okadaic acid led to hyperphosphorylation of HDAC 1 and 2 as well as changes in column elution of both enzymes. Hyperphosphorylated HDAC2 was also observed in cells synchronized with nocodazole or taxol, demonstrating regulation of HDAC phosphorylation during mitosis. Phosphorylated HDAC1 and 2 showed a gel mobility retardation that correlated with a small but significant increase in activity, both of which were reversed upon phosphatase treatment in vitro. However, the most pronounced effect of HDAC phosphorylation was to disrupt protein complex formation between HDAC1 and 2 as well as complex formation between HDAC1 and corepressors mSin3A and YY1. In contrast, interactions between HDAC1/2 and RbAp46/48 were unaffected by okadaic acid. These results establish a novel link between HDAC phosphorylation and the control of protein-protein interactions and suggest a mechanism for relief of deacetylase-catalyzed transcriptional repression by phosphorylation-dependent signaling.

Comparative 13C Metabolic Flux Analysis of Pyruvate Dehydrogenase Complex-Deficient, l-Valine-Producing Corynebacterium glutamicum▿†

PubMed Central

Bartek, Tobias; Blombach, Bastian; Lang, Siegmund; Eikmanns, Bernhard J.; Wiechert, Wolfgang; Oldiges, Marco; Nöh, Katharina; Noack, Stephan

2011-01-01

l-Valine can be formed successfully using C. glutamicum strains missing an active pyruvate dehydrogenase enzyme complex (PDHC). Wild-type C. glutamicum and four PDHC-deficient strains were compared by 13C metabolic flux analysis, especially focusing on the split ratio between glycolysis and the pentose phosphate pathway (PPP). Compared to the wild type, showing a carbon flux of 69% ± 14% through the PPP, a strong increase in the PPP flux was observed in PDHC-deficient strains with a maximum of 113% ± 22%. The shift in the split ratio can be explained by an increased demand of NADPH for l-valine formation. In accordance, the introduction of the Escherichia coli transhydrogenase PntAB, catalyzing the reversible conversion of NADH to NADPH, into an l-valine-producing C. glutamicum strain caused the PPP flux to decrease to 57% ± 6%, which is below the wild-type split ratio. Hence, transhydrogenase activity offers an alternative perspective for sufficient NADPH supply, which is relevant for most amino acid production systems. Moreover, as demonstrated for l-valine, this bypass leads to a significant increase of product yield due to a concurrent reduction in carbon dioxide formation via the PPP. PMID:21784914

Modelling of Field-Reversed Configuration Experiment with Large Safety Factor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Steinhauer, L; Guo, H; Hoffman, A

2005-11-28

The Translation-Confinement-Sustainment facility has been operated in the 'translation-formation' mode in which a plasma is ejected at high-speed from a {theta}-pinch-like source into a confinement chamber where it settles into a field-reversed-configuration state. Measurements of the poloidal and toroidal field have been the basis of modeling to infer the safety factor. It is found that the edge safety factor exceeds two, and that there is strong forward magnetic shear. The high-q arises because the large elongation compensates for the modest ratio of toroidal-to-poloidal field in the plasma. This is the first known instance of a very high-{beta} plasma with amore » safety factor greater than unity. Two-fluid modeling of the measurements also indicate several other significant features: a broad 'transition layer' at the plasma boundary with probable line-tying effects, complex high-speed flows, and the appearance of a two-fluid minimum-energy state in the plasma core. All these features may contribute to both the stability and good confinement of the plasma.« less

Protein aggregation as bacterial inclusion bodies is reversible.

PubMed

Carrió, M M; Villaverde, A

2001-01-26

Inclusion bodies are refractile, intracellular protein aggregates usually observed in bacteria upon targeted gene overexpression. Since their occurrence has a major economical impact in protein production bio-processes, in vitro refolding strategies are under continuous exploration. In this work, we prove spontaneous in vivo release of both beta-galactosidase and P22 tailspike polypeptides from inclusion bodies resulting in their almost complete disintegration and in the concomitant appearance of soluble, properly folded native proteins with full biological activity. Since, in particular, the tailspike protein exhibits an unusually slow and complex folding pathway involving deep interdigitation of beta-sheet structures, its in vivo refolding indicates that bacterial inclusion body proteins are not collapsed into an irreversible unfolded state. Then, inclusion bodies can be observed as transient deposits of folding-prone polypeptides, resulting from an unbalanced equilibrium between in vivo protein precipitation and refolding that can be actively displaced by arresting protein synthesis. The observation that the formation of big inclusion bodies is reversible in vivo can be also relevant in the context of amyloid diseases, in which deposition of important amounts of aggregated protein initiates the pathogenic process.

[The effects of anterio-posterior and dorso-ventral inversions of the lateral mesoblast of the neurula on the formation of the mesonephric, medullary, and adrenal anlage of the common toad, Bufo bufo L. (Amphibia, Anoura)].

PubMed

Gipouloux, J D; Hakim, J

1975-10-13

The experimental results of cranio-caudal reversal and dorso-ventral reversal of the lateral mesoblast of the toad early neurula prove that, at this stage, the cranio-caudal polarity of this tissue is fixed but not the dorso-ventral one. External factors are responsible for the formation of mesonephric, adrenal and gonadal medullary anlage by the lateral mesoblast.

Dysfunctional nitric oxide signalling increases risk of myocardial infarction.

PubMed

Erdmann, Jeanette; Stark, Klaus; Esslinger, Ulrike B; Rumpf, Philipp Moritz; Koesling, Doris; de Wit, Cor; Kaiser, Frank J; Braunholz, Diana; Medack, Anja; Fischer, Marcus; Zimmermann, Martina E; Tennstedt, Stephanie; Graf, Elisabeth; Eck, Sebastian; Aherrahrou, Zouhair; Nahrstaedt, Janja; Willenborg, Christina; Bruse, Petra; Brænne, Ingrid; Nöthen, Markus M; Hofmann, Per; Braund, Peter S; Mergia, Evanthia; Reinhard, Wibke; Burgdorf, Christof; Schreiber, Stefan; Balmforth, Anthony J; Hall, Alistair S; Bertram, Lars; Steinhagen-Thiessen, Elisabeth; Li, Shu-Chen; März, Winfried; Reilly, Muredach; Kathiresan, Sekar; McPherson, Ruth; Walter, Ulrich; Ott, Jurg; Samani, Nilesh J; Strom, Tim M; Meitinger, Thomas; Hengstenberg, Christian; Schunkert, Heribert

2013-12-19

Myocardial infarction, a leading cause of death in the Western world, usually occurs when the fibrous cap overlying an atherosclerotic plaque in a coronary artery ruptures. The resulting exposure of blood to the atherosclerotic material then triggers thrombus formation, which occludes the artery. The importance of genetic predisposition to coronary artery disease and myocardial infarction is best documented by the predictive value of a positive family history. Next-generation sequencing in families with several affected individuals has revolutionized mutation identification. Here we report the segregation of two private, heterozygous mutations in two functionally related genes, GUCY1A3 (p.Leu163Phefs*24) and CCT7 (p.Ser525Leu), in an extended myocardial infarction family. GUCY1A3 encodes the α1 subunit of soluble guanylyl cyclase (α1-sGC), and CCT7 encodes CCTη, a member of the tailless complex polypeptide 1 ring complex, which, among other functions, stabilizes soluble guanylyl cyclase. After stimulation with nitric oxide, soluble guanylyl cyclase generates cGMP, which induces vasodilation and inhibits platelet activation. We demonstrate in vitro that mutations in both GUCY1A3 and CCT7 severely reduce α1-sGC as well as β1-sGC protein content, and impair soluble guanylyl cyclase activity. Moreover, platelets from digenic mutation carriers contained less soluble guanylyl cyclase protein and consequently displayed reduced nitric-oxide-induced cGMP formation. Mice deficient in α1-sGC protein displayed accelerated thrombus formation in the microcirculation after local trauma. Starting with a severely affected family, we have identified a link between impaired soluble-guanylyl-cyclase-dependent nitric oxide signalling and myocardial infarction risk, possibly through accelerated thrombus formation. Reversing this defect may provide a new therapeutic target for reducing the risk of myocardial infarction.

Towards reversible basic linear algebra subprograms: A performance study

DOE PAGES

Perumalla, Kalyan S.; Yoginath, Srikanth B.

2014-12-06

Problems such as fault tolerance and scalable synchronization can be efficiently solved using reversibility of applications. Making applications reversible by relying on computation rather than on memory is ideal for large scale parallel computing, especially for the next generation of supercomputers in which memory is expensive in terms of latency, energy, and price. In this direction, a case study is presented here in reversing a computational core, namely, Basic Linear Algebra Subprograms, which is widely used in scientific applications. A new Reversible BLAS (RBLAS) library interface has been designed, and a prototype has been implemented with two modes: (1) amore » memory-mode in which reversibility is obtained by checkpointing to memory in forward and restoring from memory in reverse, and (2) a computational-mode in which nothing is saved in the forward, but restoration is done entirely via inverse computation in reverse. The article is focused on detailed performance benchmarking to evaluate the runtime dynamics and performance effects, comparing reversible computation with checkpointing on both traditional CPU platforms and recent GPU accelerator platforms. For BLAS Level-1 subprograms, data indicates over an order of magnitude better speed of reversible computation compared to checkpointing. For BLAS Level-2 and Level-3, a more complex tradeoff is observed between reversible computation and checkpointing, depending on computational and memory complexities of the subprograms.« less

QRFP-43 inhibits lipolysis by preventing ligand-induced complex formation between perilipin A, caveolin-1, the catalytic subunit of protein kinase and hormone-sensitive lipase in 3T3-L1 adipocytes.

PubMed

Mulumba, Mukandila; Granata, Riccarda; Marleau, Sylvie; Ong, Huy

2015-05-01

QRFP (RFamide) peptides are neuropeptides involved in food intake and adiposity regulation in rodents. We have previously shown that QRFP-43 (43RFa) and QRFP-26 (26RFa) inhibited isoproterenol (ISO)-induced lipolysis in adipocytes. However, the antilipolytic signaling pathways activated by QRFP peptides have not been investigated. In the present study, 3T3-L1 adipocytes were used to identify the main pathways involved in QRFP-43 decreasing ISO-induced lipolysis. Our results show that QRFP-43 reduced ISO-induced phosphorylation of perilipin A (PLIN) and hormone-sensitive lipase (HSL) on Ser660 by 43 and 25%, respectively, but increased Akt phosphorylation by 44%. However, the inhibition of phosphodiesterase 3B (PDE3B), a regulator of lipolysis activated by Akt, did not reverse the antilipolytic effect of QRFP-43. PDE3B inhibition reversed the decrease of Ser660 HSL phosphorylation associated with QRFP-43 antilipolytic effect. QRFP-43 also prevented PKC activation and ISO-induced Src kinases activation leading to the inhibition of the caveolin-1 (CAV-1) translocation on lipid droplets. Indeed, QRFP-43 attenuated phorbol 12-myristate 13-acetate-induced lipolysis and ISO-induced extracellular signal-regulated and Src kinases by 28, 37 and 48%, respectively. The attenuation of ISO-induced lipolysis by QRFP-43 was associated with a decrease of phosphorylated Ser660 HSL, PKA-catalytic (PKA-c) subunit and CAV-1 translocation on lipid droplets by 37, 50 and 46%, respectively. The decrease in ISO-induced CAV-1 and PKA-c translocation was associated with a reduction of PLIN phosphorylation by 44% in QRFP-43-treated adipocytes. These results suggest that QRFP-43 attenuated ISO-induced lipolysis by preventing the formation of an active complex on lipid droplets and the activation of Src kinases and PKC. Copyright © 2015. Published by Elsevier B.V.

Compact toroid generation, lifetime, and stability studies in linear reversed-field theta pinch geometries, (TRX-1): Second annual and final report, June 1981-March 1983

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hoffman, A.L.; Slough, J.T.

1983-09-01

Four major areas have been investigated in the triggered reconnection experiment (TRX) program. These areas are flux trapping; formation (reconnection and axial dynamics); stability; and lifetime. This report describes the progress in each of these areas. Flux trapping for relatively slow field reversal rates due to the formation of a wall sheath has been accomplished and techniques have been developed for both triggered and programmed reconnection and the formation process has been optimized for maximum flux retention. Rotational n=2 instability has been controlled through the use of octopole barrier fields and long particle lifetimes have been achieved through optimization ofmore » the formation process. 46 refs., 63 figs., 4 tabs. (FI)« less

Apparatus for electrohydrodynamically assembling patterned colloidal structures

NASA Technical Reports Server (NTRS)

Trau, Mathias (Inventor); Aksay, Ilhan A. (Inventor); Saville, Dudley A. (Inventor)

2000-01-01

A method apparatus is provided for electrophoretically depositing particles onto an electrode, and electrohydrodynamically assembling the particles into crystalline structures. Specifically, the present method and apparatus creates a current flowing through a solution to cause identically charged electrophoretically deposited colloidal particles to attract each other over very large distances (<5 particle diameters) on the surface of electrodes to form two-dimensional colloidal crystals. The attractive force can be created with both DC and AC fields and can modulated by adjusting either the field strength or frequency of the current. Modulating this lateral attraction between the particles causes the reversible formation of two-dimensional fluid and crystalline colloidal states on the electrode surface. Further manipulation allows for the formation of two or three-dimensional colloidal crystals, as well as more complex designed structures. Once the required structures are formed, these three-dimension colloidal crystals can be permanently frozen or glued by controlled coagulation induced by to the applied field to form a stable crystalline structure.

In vivo imaging of Dauer-specific neuronal remodeling in C. elegans.

PubMed

Schroeder, Nathan E; Flatt, Kristen M

2014-09-04

The mechanisms controlling stress-induced phenotypic plasticity in animals are frequently complex and difficult to study in vivo. A classic example of stress-induced plasticity is the dauer stage of C. elegans. Dauers are an alternative developmental larval stage formed under conditions of low concentrations of bacterial food and high concentrations of a dauer pheromone. Dauers display extensive developmental and behavioral plasticity. For example, a set of four inner-labial quadrant (IL2Q) neurons undergo extensive reversible remodeling during dauer formation. Utilizing the well-known environmental pathways regulating dauer entry, a previously established method for the production of crude dauer pheromone from large-scale liquid nematode cultures is demonstrated. With this method, a concentration of 50,000 - 75,000 nematodes/ml of liquid culture is sufficient to produce a highly potent crude dauer pheromone. The crude pheromone potency is determined by a dose-response bioassay. Finally, the methods used for in vivo time-lapse imaging of the IL2Qs during dauer formation are described.

Method for electrohydrodynamically assembling patterned colloidal structures

NASA Technical Reports Server (NTRS)

Trau, Mathias (Inventor); Aksay, Ilhan A. (Inventor); Saville, Dudley A. (Inventor)

1999-01-01

A method apparatus is provided for electrophoretically depositing particles onto an electrode, and electrohydrodynamically assembling the particles into crystalline structures. Specifically, the present method and apparatus creates a current flowing through a solution to cause identically charged electrophoretically deposited colloidal particles to attract each other over very large distances (<5 particle diameters) on the surface of electrodes to form two-dimensional colloidal crystals. The attractive force can be created with both DC and AC fields and can modulated by adjusting either the field strength or frequency of the current. Modulating this lateral attraction between the particles causes the reversible formation of two-dimensional fluid and crystalline colloidal states on the electrode surface. Further manipulation allows for the formation of two or three-dimensional colloidal crystals, as well as more complex designed structures. Once the required structures are formed, these three-dimension colloidal crystals can be permanently frozen or glued by controlled coagulation induced by to the applied field to form a stable crystalline structure.

Assembly of porous hierarchical copolymers/resin proppants: New approaches to smart proppant immobilization via molecular anchors.

PubMed

Alexander, Shirin; Dunnill, Charles W; Barron, Andrew R

2016-03-15

The assembly of temperature/pH sensitive complex microparticle structures through chemisorption and physisorption provides a responsive system that offers application as routes to immobilization of proppants in-situ. Thermogravimetric analysis (TGA) and scanning electron microscopy (SEM) along with energy dispersive X-ray analysis (EDX) have been used to characterize a series of bi-functionalized monolayers and/or multilayers grown on alumina microparticles and investigate the reactive nature of both temperature sensitive cross-linker (epoxy resin) with the layers and pH-responsive bridging layer (polyetheramine). The bifunctional acids, behaving as molecular anchors, allow for a controlled reaction with a cross-linker (resin or polymer) with the formation of networks, which is either irreversible or reversible based on the nature of the cross-linker. The networks results in formation of porous hierarchical particles that offer a potential route to the creation of immobile proppant pack. Copyright © 2015 Elsevier Inc. All rights reserved.

Reactivity of molecular dioxygen towards a series of isostructural dichloroiron(III) complexes with tripodal tetraamine ligands: general access to mu-oxodiiron(III) complexes and effect of alpha-fluorination on the reaction kinetics.

PubMed

Thallaj, Nasser K; Rotthaus, Olaf; Benhamou, Leila; Humbert, Nicolas; Elhabiri, Mourad; Lachkar, Mohammed; Welter, Richard; Albrecht-Gary, Anne-Marie; Mandon, Dominique

2008-01-01

We have synthesized the mono, di-, and tri-alpha-fluoro ligands in the tris(2-pyridylmethyl)amine (TPA) series, namely, FTPA, F(2)TPA and F(3)TPA, respectively. Fluorination at the alpha-position of these nitrogen-containing tripods shifts the oxidation potential of the ligand by 45-70 mV per added fluorine atom. The crystal structures of the dichloroiron(II) complexes with FTPA and F(2)TPA reveal that the iron center lies in a distorted octahedral geometry comparable to that already found in TPAFeCl(2). All spectroscopic data indicate that the geometry is retained in solution. These three isostructural complexes all react with molecular dioxygen to yield stable mu-oxodiiron(III) complexes. Crystal structure analyses are reported for each of these three mu-oxo compounds. With TPA, a symmetrical structure is obtained for a dicationic compound with the tripod coordinated in the kappa(4)N coordination mode. With FTPA, the compound is a neutral mu-oxodiiron(III) complex with a kappa(3)N coordination mode of the ligand. Oxygenation of the F(2)TPA complex gave a neutral unsymmetrical compound, the structure of which is reminiscent of that already found with the trifluorinated ligand. On reduction, all mu-oxodiiron(III) complexes revert to the starting iron(II) species. The oxygenation reaction parallels the well-known formation of mu-oxo derivatives from dioxygen in the chemistry of porphyrins reported almost three decades ago. The striking feature of the series of iron(II) precursors is the effect of the ligand on the kinetics of oxygenation of the complexes. Whereas the parent complex undergoes 90 % conversion over 40 h, the monofluorinated ligand provides a complex that has fully reacted after 30 h, whereas the reaction time for the complex with the difluorinated ligand is only 10 h. Analysis of the spectroscopic data reveals that formation of the mu-oxo complexes proceeds in two distinct reversible kinetic steps with k(1) approximately 10 k(2). For TPAFeCl(2) and FTPAFeCl(2) only small variations in the k(1) and k(2) values are observed. By contrast, F(2)TPAFeCl(2) exhibits k(1) and k(2) values that are ten times higher. These differences in kinetics are interpreted in the light of structural and electronic effects, especially the Lewis acidity at the metal center. Our results suggest coordination of dioxygen as an initial step in the process leading to formation of mu-oxodiiron(III) compounds, by contrast with an unlikely outer-sphere reduction of dioxygen, which generally occurs at negative potentials.

Multi-Fluid Simulations of Field Reversed Configuration Formation

NASA Astrophysics Data System (ADS)

Sousa, Eder; Martin, Robert

2017-10-01

The use of field reversed configuration (FRC) have been studied extensively for fusion application but here we investigate them for propulsion purposes. FRCs have the potential to produce highly variable thrust and specific impulse using different gases as propellant. Aspects of the FRC formation physics, using a rotating magnetic field (RMF) at low power, are simulated using a multi-fluid plasma model. Results are compared with experimental observations with emphasis in the development of instabilities and robustness of the field reversal. The use of collisional radiative models are used to help compare experiment versus simulation results. Distribution A: Approved for public release; distribution unlimited; Clearance No. 17445. This work is supported by the Air Force Office of Scientific Research Grant Number 17RQCOR465.

Time-reversed waves and super-resolution

NASA Astrophysics Data System (ADS)

Fink, Mathias; de Rosny, Julien; Lerosey, Geoffroy; Tourin, Arnaud

2009-06-01

Time-reversal mirrors (TRMs) refocus an incident wavefield to the position of the original source regardless of the complexity of the propagation medium. TRMs have now been implemented in a variety of physical scenarios from GHz microwaves to MHz ultrasonics and to hundreds of Hz in ocean acoustics. Common to this broad range of scales is a remarkable robustness exemplified by observations at all scales that the more complex the medium (random or chaotic), the sharper the focus. A TRM acts as an antenna that uses complex environments to appear wider than it is, resulting for a broadband pulse, in a refocusing quality that does not depend on the TRM aperture. Moreover, when the complex environment is located in the near field of the source, time-reversal focusing opens completely new approaches to super-resolution. We will show that, for a broadband source located inside a random metamaterial, a TRM located in the far field radiated a time-reversed wave that interacts with the random medium to regenerate not only the propagating but also the evanescent waves required to refocus below the diffraction limit. This focusing process is very different from that developed with superlenses made of negative index material only valid for narrowband signals. We will emphasize the role of the frequency diversity in time-reversal focusing. To cite this article: M. Fink et al., C. R. Physique 10 (2009).

Dehydrogenation kinetics and reversibility of LiAlH4-LiBH4 doped with Ti-based additives and MWCNT

NASA Astrophysics Data System (ADS)

Thaweelap, Natthaporn; Utke, Rapee

2016-11-01

Dehydrogenation kinetics and reversibility of LiAlH4-LiBH4 doped with Ti-based additives (TiCl3 and Ti-isopropoxide), multiwall carbon nanotubes (MWCNT), and MWCNT impregnated with Ti-based additives are proposed. Reduction of dehydrogenation temperature as well as improvements of kinetics and reversibility, especially decomposition of thermodynamically stable hydride (LiBH4) is obtained from the samples doped with Ti-isopropoxide and MWCNT. This can be due to the fact that the formations of LixAl(1-x)B2 and LiH-Al containing phase during dehydrogenation favor decomposition of LiH, leading to increment of hydrogen capacity, and stabilization of boron in solid state, resulting in improvement of reversibility. Besides, the curvatures and thermal conductivity of MWCNT benefit hydrogen diffusion and heat transfer during de/rehydrogenation. Nevertheless, deficient hydrogen content reversible is observed in all samples due to the irreversible of LiAlH4 and/or Li3AlH6 as well as the formation of stable phase (Li2B12H12) during de/rehydrogenation.

"It Makes You Rethink Your Choice of the Pill": Theory-Based Formative Research to Design a Contraceptive Choice Campaign.

PubMed

Sundstrom, Beth; DeMaria, Andrea L; Meier, Stephanie; Jones, Annabel; Moxley, Grace E

2015-01-01

Half of all pregnancies in the United States remain unplanned despite improved access to highly effective long-acting reversible contraception, including the intrauterine device and the implant. This study conducted theory-based formative research to develop a contraceptive choice campaign aimed at increasing long-acting reversible contraception uptake by women ages 18-44 years in Charleston, South Carolina, an urban area in the southeastern United States. Researchers developed and tested message concepts and designs. Six focus groups and 18 interviews were conducted among reproductive-age women (n = 79). Qualitative data analysis revealed messages and designs that resonated with these women. Emphasizing long-acting reversible contraception as the healthy option, highlighting long-acting reversible contraception effectiveness, including relatable and trustworthy characters, and using language of control emerged as themes. Women reported a preference for statistics illustrating effectiveness combined with empowering messages of control over contraceptive decision making. Findings from this study offer practical recommendations for developing contraceptive choice campaigns targeting long-acting reversible contraception use and further the goal of reducing unintended pregnancy among women.

Antibodies Targeting Closely Adjacent or Minimally Overlapping Epitopes Can Displace One Another

PubMed Central

Abdiche, Yasmina Noubia; Yeung, Andy Yik; Ni, Irene; Stone, Donna; Miles, Adam; Morishige, Winse; Rossi, Andrea; Strop, Pavel

2017-01-01

Here we describe how real-time label-free biosensors can be used to identify antibodies that compete for closely adjacent or minimally overlapping epitopes on their specific antigen via a mechanism of antibody displacement. By kinetically perturbing one another’s binding towards their antigen via the formation of a transient trimolecular complex, antibodies can displace one another in a fully reversible and dose-dependent manner. Displacements can be readily identified when epitope binning assays are performed in a classical sandwich assay format whereby a solution antibody (analyte) is tested for binding to its antigen that is first captured via an immobilized antibody (ligand) because an inverted sandwiching response is observed when an analyte displaces a ligand, signifying the antigen’s unusually rapid dissociation from its ligand. In addition to classifying antibodies within a panel in terms of their ability to block or sandwich pair with one another, displacement provides a hybrid mechanism of competition. Using high-throughput epitope binning studies we demonstrate that displacements can be observed on any target, if the antibody panel contains appropriate epitope diversity. Unidirectional displacements occurring between disparate-affinity antibodies can generate apparent asymmetries in a cross-blocking experiment, confounding their interpretation. However, examining competition across a wide enough concentration range will often reveal that these displacements are reversible. Displacement provides a gentle and efficient way of eluting antigen from an otherwise high affinity binding partner which can be leveraged in designing reagents or therapeutic antibodies with unique properties. PMID:28060885

Antibodies Targeting Closely Adjacent or Minimally Overlapping Epitopes Can Displace One Another.

PubMed

Abdiche, Yasmina Noubia; Yeung, Andy Yik; Ni, Irene; Stone, Donna; Miles, Adam; Morishige, Winse; Rossi, Andrea; Strop, Pavel

2017-01-01

Here we describe how real-time label-free biosensors can be used to identify antibodies that compete for closely adjacent or minimally overlapping epitopes on their specific antigen via a mechanism of antibody displacement. By kinetically perturbing one another's binding towards their antigen via the formation of a transient trimolecular complex, antibodies can displace one another in a fully reversible and dose-dependent manner. Displacements can be readily identified when epitope binning assays are performed in a classical sandwich assay format whereby a solution antibody (analyte) is tested for binding to its antigen that is first captured via an immobilized antibody (ligand) because an inverted sandwiching response is observed when an analyte displaces a ligand, signifying the antigen's unusually rapid dissociation from its ligand. In addition to classifying antibodies within a panel in terms of their ability to block or sandwich pair with one another, displacement provides a hybrid mechanism of competition. Using high-throughput epitope binning studies we demonstrate that displacements can be observed on any target, if the antibody panel contains appropriate epitope diversity. Unidirectional displacements occurring between disparate-affinity antibodies can generate apparent asymmetries in a cross-blocking experiment, confounding their interpretation. However, examining competition across a wide enough concentration range will often reveal that these displacements are reversible. Displacement provides a gentle and efficient way of eluting antigen from an otherwise high affinity binding partner which can be leveraged in designing reagents or therapeutic antibodies with unique properties.

Reactions of the ionized enol tautomer of acetanilide: elimination of HNCO via a novel rearrangement.

PubMed

Heydorn, Lisa N; Carter, Lynn M; Bowen, Richard D; Terlouw, Johan K

2003-01-01

The reactions of ionised acetanilide, C(6)H(5)NH(=O)CH(3)(.+), and its enol, C(6)H(5)NH(OH)=CH(2)(.+), have been studied by a combination of tandem mass spectrometric and computational methods. These two isomeric radical cations have distinct chemistries at low internal energies. The keto tautomer eliminates exclusively CH(2)=C=O to give ionised aniline. In contrast, the enol tautomer loses H-N=C=O, via an unusual skeletal rearrangement, to form predominantly ionised methylene cyclohexadiene. Hydrogen atom loss also occurs from the enol tautomer, with the formation of protonated oxindole. The mechanisms for H-N=C=O and hydrogen atom loss both involve cyclisation; the former proceeds via a spiro transition state formed by attachment of the methylene group to the ipso position, whereas the latter entails the formation of a five-membered ring by attachment to the ortho position. The behaviour of labelled analogues reveals that these two processes have different site selectivities. Hydrogen atom loss involves a reverse critical energy and is subject to an isotope effect. Surprisingly, attempts to promote the enolisation of ionised acetanilide by proton-transport catalysis were unsuccessful. In a reversal of the usual situation for ionised carbonyl compounds, ionised acetanilide is actually more stable than its enol tautomer. The enol tautomer was resistant to proton-transport catalysed ketonisation to ionised acetanilide, possibly because the favoured geometry of the encounter complex with the base molecule is inappropriate for facilitating tautomerisation.

Reverse Induced Fit-Driven MAS-Downstream Transduction: Looking for Metabotropic Agonists.

PubMed

Pernomian, Larissa; Gomes, Mayara S; de Paula da Silva, Carlos H Tomich; Rosa, Joaquin M C

2017-01-01

Protective effects of MAS activation have spurred clinical interests in developing MAS agonists. However, current bases that drive this process preclude that physiological concentrations of peptide MAS agonists induce an atypical signaling that does not reach the metabotropic efficacy of constitutive activation. Canonical activation of MAS-coupled G proteins is only achieved by supraphysiological concentrations of peptide MAS agonists or physiological concentrations of chemically modified analogues. These pleiotropic differences are because of two overlapped binding domains: one non-metabotropic site that recognizes peptide agonists and one metabotropic domain that recognizes modified analogues. It is feasible that supraphysiological concentrations of peptide MAS agonists undergo to chemical modifications required for binding to metabotropic domain. Receptor oligomerization enhances pharmacological parameters coupled to metabotropic signaling. The formation of receptor-signalosome complex makes the transduction of agonists more adaptive. Considering the recent identification of MAS-signalosome, we aimed to postulate the reverse induced fit hypothesis in which MAS-signalosome would trigger chemical modifications required for agonists bind to MAS metabotropic domain. Here we cover rational perspectives for developing novel metabotropic MAS agonists in the view of the reverse induced-fit hypothesis. Predicting a 3D model of MAS metabotropic domain may guide the screening of chemical modifications required for metabotropic efficacy. Pharmacophore-based virtual screening would select potential metabotropic MAS agonists from virtual libraries from human proteome. Rational perspectives that consider reverse induced fit hypothesis during MAS activation for developing metabotropic MAS agonists represents the best approach in providing MAS ligands with constitutive efficacy at physiological concentrations. Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.org.

Linear pi-Acceptor-Templated Dynamic Clipping to Macrobicycles and[2]Rotaxanes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Klivansky, Liana M.; Koshkakaryan, Gayane; Cao, Dennis

2009-04-30

Functional rotaxanes are one of the representative nanoscale molecular machines that have found applications in many areas, including molecular electronics, nanoelectromechanical systems (NEMS), photo controllable smart surfaces, and nanovalves. With the advent of molecular recognition and self-assembly, such molecular compounds can now be obtained efficiently through template-directed synthesis. One of the common strategies of making [2]rotaxanes involves the clipping of a macrocycle around a preformed dumbbell-shaped template in a [1+1] or [2+2] manner. While early examples were based on irreversible kinetic pathway through covalent bond formation, recent advances on reversible dynamic covalent chemistry (DCC) has attracted great attention to thismore » field. By virtue of thermodynamically controlled equilibria, DCC has provided highly efficient and versatile synthetic routes in the selection of specific products from a complex system. Among the several reversible reactions in the category of DCC reactions, the imine formation has proven to be very versatile in macrocyclization to give complex interlocked molecular compounds. Cryptands are three dimensional bicyclic hosts with preorganized cavities capable of inclusion of ions and small molecules. Replacing the nitrogen bridgeheads in common cryptands with aromatic ring systems gives cyclophane-based macrobicycles. The introduction of aromatic ring systems into a preorganized cage-like geometry facilitates ion-{pi} interactions and {pi}-{pi} interactions, resulting in novel metal sandwiches, fluoride receptors, and host-guest complexes. In particular, the seminal work by Gibson, Huang and coworkers on cryptand complexation with paraquat and diquat guests have resulted in the efficient synthesis of mechanically interlocked rotaxanes. The synthesis of cyclophane-based macrobicycles, however, was mostly realized through multiple reaction steps and in high-dilution conditions, which often suffered from low yield and tedious workup. Thus, a one-step, five-component [2+3] clipping reaction that can give the desired macrobicycle is highly desirable. We are motivated by a {pi}-guest templating protocol, because not only {pi}-{pi} interactions can contribute to the formation of macrobicycles, but also the resulting host-guest system holds great promise as a forerunner in the construction of interlocked molecules. (Scheme 1c) Very simple precursors, namely 1,3,5-benzenetrialdehyde (1) and 2,2{prime}-(ethylenedioxy)diethylamine (2) were chosen as the components for desired macrobicycle. (Scheme 2) The formation of six imine bonds would connect the five components to give a macrobicycle while extending the conjugation in the C{sub 3}-symmetric aromatic 'ceiling' and 'floor', which is suitable for enhancing the {pi}-{pi} interactions with a complementary aromatic template. Meanwhile, the ethylene glycol 'pillars' can provide sufficient flexibility, proper spacing, and polar binding sites to assist guest encapsulation. Initial screening of ?-templates engaged several C{sub 3} symmetric aromatic compounds in order to match the symmetry of the desired macrobicycle, which only resulted in nonspecific mixtures. It was found instead that linear bipyridinium (BPY) containing guests effectively templated the [2+3] clipping reaction. Based on this protocol, a [2]rotaxane was successfully assembled as the single product from the six-component reaction.« less

Reverse Ecology: from systems to environments and back.

PubMed

Levy, Roie; Borenstein, Elhanan

2012-01-01

The structure of complex biological systems reflects not only their function but also the environments in which they evolved and are adapted to. Reverse Ecology-an emerging new frontier in Evolutionary Systems Biology-aims to extract this information and to obtain novel insights into an organism's ecology. The Reverse Ecology framework facilitates the translation of high-throughput genomic data into large-scale ecological data, and has the potential to transform ecology into a high-throughput field. In this chapter, we describe some of the pioneering work in Reverse Ecology, demonstrating how system-level analysis of complex biological networks can be used to predict the natural habitats of poorly characterized microbial species, their interactions with other species, and universal patterns governing the adaptation of organisms to their environments. We further present several studies that applied Reverse Ecology to elucidate various aspects of microbial ecology, and lay out exciting future directions and potential future applications in biotechnology, biomedicine, and ecological engineering.

Coagulation under flow: the influence of flow-mediated transport on the initiation and inhibition of coagulation.

PubMed

Fogelson, Aaron L; Tania, Nessy

2005-01-01

A mathematical model of intravascular coagulation is presented; it encompasses the biochemistry of the tissue factor pathway, platelet activation and deposition on the subendothelium, and flow- and diffusion-mediated transport of coagulation proteins and platelets. Simulation experiments carried out with the model indicate the predominant role played by the physical processes of platelet deposition and flow-mediated removal of enzymes in inhibiting coagulation in the vicinity of vascular injury. Sufficiently rapid production of factors IXa and Xa by the TF:VIIa complex can overcome this inhibition and lead to formation of significant amounts of the tenase complex on the surface of activated platelets and, as a consequence, to substantial thrombin production. Chemical inhibitors are seen to play almost no (TFPI) or little (AT-III and APC) role in determining whether substantial thrombin production will occur. The role of APC is limited by the necessity for diffusion of thrombin from the site of injury to nearby endothelial cells to form the thrombomodulin-thrombin complex and for diffusion in the reverse direction of the APC made by this complex. TFPI plays an insignificant part in inhibiting the TF:VIIa complex under the conditions studied whether its action involves sequential binding of TFPI to Xa and then TFPI:Xa to TF:VIIa, or direct binding of TFPI to Xa already bound to the TF:VIIa complex. Copyright 2005 S. Karger AG, Basel.

Global reverse supply chain design for solid waste recycling under uncertainties and carbon emission constraint.

PubMed

Xu, Zhitao; Elomri, Adel; Pokharel, Shaligram; Zhang, Qin; Ming, X G; Liu, Wenjie

2017-06-01

The emergence of concerns over environmental protection, resource conservation as well as the development of logistics operations and manufacturing technology has led several countries to implement formal collection and recycling systems of solid waste. Such recycling system has the benefits of reducing environmental pollution, boosting the economy by creating new jobs, and generating income from trading the recyclable materials. This leads to the formation of a global reverse supply chain (GRSC) of solid waste. In this paper, we investigate the design of such a GRSC with a special emphasis on three aspects; (1) uncertainty of waste collection levels, (2) associated carbon emissions, and (3) challenges posed by the supply chain's global aspect, particularly the maritime transportation costs and currency exchange rates. To the best of our knowledge, this paper is the first attempt to integrate the three above-mentioned important aspects in the design of a GRSC. We have used mixed integer-linear programming method along with robust optimization to develop the model which is validated using a sample case study of e-waste management. Our results show that using a robust model by taking the complex interactions characterizing global reverse supply chain networks into account, we can create a better GRSC. The effect of uncertainties and carbon constraints on decisions to reduce costs and emissions are also shown. Copyright © 2017 Elsevier Ltd. All rights reserved.

Glycal Formation in Crystals of Uridine Phosphorylase

DOE Office of Scientific and Technical Information (OSTI.GOV)

Paul, Debamita; O’Leary, Sen E.; Rajashankar, Kanagalaghatta

2010-06-22

Uridine phosphorylase is a key enzyme in the pyrimidine salvage pathway. This enzyme catalyzes the reversible phosphorolysis of uridine to uracil and ribose 1-phosphate (or 2{prime}-deoxyuridine to 2{prime}-deoxyribose 1-phosphate). Here we report the structure of hexameric Escherichia coli uridine phosphorylase treated with 5-fluorouridine and sulfate and dimeric bovine uridine phosphorylase treated with 5-fluoro-2{prime}-deoxyuridine or uridine, plus sulfate. In each case the electron density shows three separate species corresponding to the pyrimidine base, sulfate, and a ribosyl species, which can be modeled as a glycal. In the structures of the glycal complexes, the fluorouracil O2 atom is appropriately positioned to actmore » as the base required for glycal formation via deprotonation at C2{prime}. Crystals of bovine uridine phosphorylase treated with 2{prime}-deoxyuridine and sulfate show intact nucleoside. NMR time course studies demonstrate that uridine phosphorylase can catalyze the hydrolysis of the fluorinated nucleosides in the absence of phosphate or sulfate, without the release of intermediates or enzyme inactivation. These results add a previously unencountered mechanistic motif to the body of information on glycal formation by enzymes catalyzing the cleavage of glycosyl bonds.« less

Glutathione peroxidase: fact and fiction.

PubMed

Flohé, L

The present knowledge of glutathione (GSH) peroxidase is briefly reviewed: GSH peroxidase has a molecular weight of about 85,000, consists of four apparently-identical subunits and contains four g atom of selenium/mol. The enzyme-bound selenium can undergo a substrate-induced redox change and is obviously essential for activity. In accordance with the assumption that a selenol group is reversibly oxidized during catalysis, ping-pong kinetics are observed. Limiting maximum velocities and Michaelis constants, indicating the formation of an enzyme-substrate complex, are not detectable. The enzyme is highly specific for GSH but reacts with many hydroperoxides. It can be deduced from the kinetic analysis of GSH peroxidase that in physiological conditions removal of hydroperoxide is largely independent of fluctuations in the cellular concentration of GSH. However, the system will abruptly collapse if the rate of hydroperoxide formation exceeds that of regeneration of GSH. By these considerations, the pathophysiological manifestation of disorders in GSH metabolism and pentose-phosphate shunt may be explained. With regard to its low specificity for hydroperoxides, GSH peroxidase could be involved in various metabolic events such as H2O2 removal in compartments low in catalase, hydroperoxide-mediated mutagenesis, protection of unsaturated lipids in biomembranes, prostaglandin biosynthesis, and regulation of prostacyclin formation.

From a Dy(III) single molecule magnet (SMM) to a ferromagnetic [Mn(II)Dy(III)Mn(II)] trinuclear complex.

PubMed

Bhunia, Asamanjoy; Gamer, Michael T; Ungur, Liviu; Chibotaru, Liviu F; Powell, Annie K; Lan, Yanhua; Roesky, Peter W; Menges, Fabian; Riehn, Christoph; Niedner-Schatteburg, Gereon

2012-09-17

The Schiff base compound 2,2'-{[(2-aminoethyl)imino]bis[2,1-ethanediyl-nitriloethylidyne]}bis-2-hydroxy-benzoic acid (H(4)L) as a proligand was prepared in situ. This proligand has three potential coordination pockets which make it possible to accommodate from one to three metal ions allowing for the possible formation of mono-, di-, and trinuclear complexes. Reaction of in situ prepared H(4)L with Dy(NO(3))(3)·5H(2)O resulted in the formation of a mononuclear complex [Dy(H(3)L)(2)](NO(3))·(EtOH)·8(H(2)O) (1), which shows SMM behavior. In contrast, reaction of in situ prepared H(4)L with Mn(ClO(4))(2)·6H(2)O and Dy(NO(3))(3)·5H(2)O in the presence of a base resulted in a trinuclear mixed 3d-4f complex (NHEt(3))(2)[Dy{Mn(L)}(2)](ClO(4))·2(H(2)O) (2). At low temperatures, compound 2 is a weak ferromagnet. Thus, the SMM behavior of compound 1 can be switched off by incorporating two Mn(II) ions in close proximity either side of the Dy(III). This quenching behavior is ascribed to the presence of the weak ferromagnetic interactions between the Mn(II) and Dy(III) ions, which at T > 2 K act as a fluctuating field causing the reversal of magnetization on the dysprosium ion. Mass spectrometric ion signals related to compounds 1 and 2 were both detected in positive and negative ion modes via electrospray ionization mass spectrometry. Hydrogen/deuterium exchange (HDX) reactions with ND(3) were performed in a FT-ICR Penning-trap mass spectrometer.

Play: The Reversal Theory Perspective.

ERIC Educational Resources Information Center

Kerr, J. H.

The intention of this theoretical paper is to present a reversal theory interpretation of play phenomena. Reversal theory, a developing theory in psychology, concerns the complex relationship between experience and motivation. One of the central charactieristics of the theory is that it attempts to understand why so much of human behavior is…

Experimental and theoretical investigation of topological and energetic characteristics of Sb complexes reversibly binding molecular oxygen.

PubMed

Fukin, Georgy K; Baranov, Evgenii V; Jelsch, Christian; Guillot, Benoît; Poddel'sky, Andrey I; Cherkasov, Vladimir K; Abakumov, Gleb A

2011-07-28

The experimental distribution of electron density in Ph(3)(4,5-OMe-3,6-Bu(t)-Cat)Sb·MeCN (1*) and Ph(3)(4,5-N(2)C(4)H(6)-3,6-Bu(t)-Cat)Sb·MeOH (2*) complexes was studied. According to atoms in molecules theory, the Sb-C(Ph), Sb-O(catecholate), and Sb···N(O) bonds are intermediate, whereas the O-C and C-C bonds are covalent, respectively. The energy of the Sb···N(MeCN) and Sb···O(MeOH) bonds are 7.0 and 11.3 kcal/mol according to the Espinosa equation. Density functional theory and Hartree-Fock calculations were carried out for a series of catecholate and amidophenolate complexes of antimony(V). It was shown that such calculations reliably reproduce geometrical and topological parameters and therefore can be used for a criterion search of dioxygen reversible binding by the catecholate and amidophenolate complexes of antimony(V). It was found that the "critical" value of the HOMO energy vary in the range from -5.197 to -5.061 eV for reversible binding of dioxygen complexes. This can serve as a thermodynamic criterion to predict the possibility of the dioxygen reversible binding by the catecholate and amidophenolate complexes of Sb(V). The HOMO energies correlate with the conversion of the catecholate and amidophenolate complexes in corresponding spiroendoperoxide derivatives as well. The contribution of the atom orbitals of the carbon atoms in the five-membered metallocycle to HOMO in complexes with different substitutes in the 4- and 5-positions of the catecholate ligand allows predicting the place of dioxygen addition. © 2011 American Chemical Society

Nanocomplexes of Photolabile Polyelectrolyte and Upconversion Nanoparticles for Near-Infrared Light-Triggered Payload Release.

PubMed

Xiang, Jun; Ge, Feijie; Yu, Bing; Yan, Qiang; Shi, Feng; Zhao, Yue

2018-06-07

A new approach to encapsulating charged cargo molecules into a nanovector and subsequently using near-infrared (NIR) light to trigger the release is demonstrated. NIR light-responsive nanovector was prepared through electrostatic interaction-driven complexation between negatively charged silica-coated upconversion nanoparticles (UCNP@silica, 87 nm hydrodynamic diameter, polydispersity index ∼0.05) and a positively charged UV-labile polyelectrolyte bearing pendants of poly(ethylene glycol) and o-nitrobenzyl side groups; whereas charged fluorescein (FLU) was loaded through a co-complexation process. By controlling the amount of polyelectrolyte, UCNP@silica can be covered by the polymer, whereas remaining dispersed in aqueous solution. Under 980 nm laser excitation, UV light emitted by UCNP is absorbed by photolytic side groups within polyelectrolyte, which results in cleavage of o-nitrobenzyl groups and formation of carboxylic acid groups. Such NIR light-induced partial reversal of positive charge to negative charge on the polyelectrolyte layer disrupts the equilibrium among UCNP@silica, polyelectrolyte, and FLU and, consequently, leads to release of FLU molecules.

A network of epigenetic regulators guides developmental haematopoiesis in vivo.

PubMed

Huang, Hsuan-Ting; Kathrein, Katie L; Barton, Abby; Gitlin, Zachary; Huang, Yue-Hua; Ward, Thomas P; Hofmann, Oliver; Dibiase, Anthony; Song, Anhua; Tyekucheva, Svitlana; Hide, Winston; Zhou, Yi; Zon, Leonard I

2013-12-01

The initiation of cellular programs is orchestrated by key transcription factors and chromatin regulators that activate or inhibit target gene expression. To generate a compendium of chromatin factors that establish the epigenetic code during developmental haematopoiesis, a large-scale reverse genetic screen was conducted targeting orthologues of 425 human chromatin factors in zebrafish. A set of chromatin regulators was identified that target different stages of primitive and definitive blood formation, including factors not previously implicated in haematopoiesis. We identified 15 factors that regulate development of primitive erythroid progenitors and 29 factors that regulate development of definitive haematopoietic stem and progenitor cells. These chromatin factors are associated with SWI/SNF and ISWI chromatin remodelling, SET1 methyltransferase, CBP-p300-HBO1-NuA4 acetyltransferase, HDAC-NuRD deacetylase, and Polycomb repressive complexes. Our work provides a comprehensive view of how specific chromatin factors and their associated complexes play a major role in the establishment of haematopoietic cells in vivo.

Droplet Digital Enzyme-Linked Oligonucleotide Hybridization Assay for Absolute RNA Quantification.

PubMed

Guan, Weihua; Chen, Liben; Rane, Tushar D; Wang, Tza-Huei

2015-09-03

We present a continuous-flow droplet-based digital Enzyme-Linked Oligonucleotide Hybridization Assay (droplet digital ELOHA) for sensitive detection and absolute quantification of RNA molecules. Droplet digital ELOHA incorporates direct hybridization and single enzyme reaction via the formation of single probe-RNA-probe (enzyme) complex on magnetic beads. It enables RNA detection without reverse transcription and PCR amplification processes. The magnetic beads are subsequently encapsulated into a large number of picoliter-sized droplets with enzyme substrates in a continuous-flow device. This device is capable of generating droplets at high-throughput. It also integrates in-line enzymatic incubation and detection of fluorescent products. Our droplet digital ELOHA is able to accurately quantify (differentiate 40% difference) as few as ~600 RNA molecules in a 1 mL sample (equivalent to 1 aM or lower) without molecular replication. The absolute quantification ability of droplet digital ELOHA is demonstrated with the analysis of clinical Neisseria gonorrhoeae 16S rRNA to show its potential value in real complex samples.

Droplet Digital Enzyme-Linked Oligonucleotide Hybridization Assay for Absolute RNA Quantification

PubMed Central

Guan, Weihua; Chen, Liben; Rane, Tushar D.; Wang, Tza-Huei

2015-01-01

We present a continuous-flow droplet-based digital Enzyme-Linked Oligonucleotide Hybridization Assay (droplet digital ELOHA) for sensitive detection and absolute quantification of RNA molecules. Droplet digital ELOHA incorporates direct hybridization and single enzyme reaction via the formation of single probe-RNA-probe (enzyme) complex on magnetic beads. It enables RNA detection without reverse transcription and PCR amplification processes. The magnetic beads are subsequently encapsulated into a large number of picoliter-sized droplets with enzyme substrates in a continuous-flow device. This device is capable of generating droplets at high-throughput. It also integrates in-line enzymatic incubation and detection of fluorescent products. Our droplet digital ELOHA is able to accurately quantify (differentiate 40% difference) as few as ~600 RNA molecules in a 1 mL sample (equivalent to 1 aM or lower) without molecular replication. The absolute quantification ability of droplet digital ELOHA is demonstrated with the analysis of clinical Neisseria gonorrhoeae 16S rRNA to show its potential value in real complex samples. PMID:26333806

Nitrogenase of Klebsiella pneumoniae. Interaction of the component proteins studied by ultracentrifugation

PubMed Central

Eady, Robert R.

1973-01-01

Sedimentation-velocity analyses of mixtures of the component proteins of nitrogenase of Klebsiella pneumoniae at a 1:1 molar ratio, showed a single peak of sedimentation coefficient (12.4S) considerably greater than that obtained for the larger (Fe+Mo-containing) protein centrifuged alone (10.4S). When the ratio exceeded 1:1 (the smaller Fe-containing protein in excess) an additional peak corresponding in sedimentation coefficient (about 4.5S) to free Fe-containing protein appeared. When proteins, which had been inactivated by exposure to air were used, no interaction occurred. Na2S2O4 at 2mm both reversed and prevented interaction between the two proteins; sedimentation coefficients corresponded to those of the proteins when centrifuged alone. These results demonstrate the formation of a complex between the nitrogenase proteins, and, together with data of activity titration curves, are consistent with the formulation of the nitrogenase complex of K. pneumoniae as (Fe-containing protein)–(Fe+Mo-containing protein). ImagesFig. 1. PMID:4589392

Droplet Digital Enzyme-Linked Oligonucleotide Hybridization Assay for Absolute RNA Quantification

NASA Astrophysics Data System (ADS)

Guan, Weihua; Chen, Liben; Rane, Tushar D.; Wang, Tza-Huei

2015-09-01

We present a continuous-flow droplet-based digital Enzyme-Linked Oligonucleotide Hybridization Assay (droplet digital ELOHA) for sensitive detection and absolute quantification of RNA molecules. Droplet digital ELOHA incorporates direct hybridization and single enzyme reaction via the formation of single probe-RNA-probe (enzyme) complex on magnetic beads. It enables RNA detection without reverse transcription and PCR amplification processes. The magnetic beads are subsequently encapsulated into a large number of picoliter-sized droplets with enzyme substrates in a continuous-flow device. This device is capable of generating droplets at high-throughput. It also integrates in-line enzymatic incubation and detection of fluorescent products. Our droplet digital ELOHA is able to accurately quantify (differentiate 40% difference) as few as ~600 RNA molecules in a 1 mL sample (equivalent to 1 aM or lower) without molecular replication. The absolute quantification ability of droplet digital ELOHA is demonstrated with the analysis of clinical Neisseria gonorrhoeae 16S rRNA to show its potential value in real complex samples.

Structure of a Water Monolayer on the Anatase TiO2(101) Surface

NASA Astrophysics Data System (ADS)

Patrick, Christopher E.; Giustino, Feliciano

2014-07-01

Titanium dioxide (TiO2) plays a central role in the study of artificial photosynthesis, owing to its ability to perform photocatalytic water splitting. Despite over four decades of intense research efforts in this area, there is still some debate over the nature of the first water monolayer on the technologically relevant anatase TiO2(101) surface. In this work, we use first-principles calculations to reverse engineer the experimental high-resolution x-ray photoelectron spectra measured for this surface by Walle et al. [J. Phys. Chem. C 115, 9545 (2011)] and find evidence supporting the existence of a mix of dissociated and molecular water in the first monolayer. Using both semilocal and hybrid functional calculations, we revise the current understanding of the adsorption energetics by showing that the energetic cost of water dissociation is reduced via the formation of a hydrogen-bonded hydroxyl-water complex. We also show that such a complex can provide an explanation of an unusual superstructure observed in high-resolution scanning tunneling microscopy experiments.

Improving the Factor Structure of Psychological Scales: The Expanded Format as an Alternative to the Likert Scale Format

ERIC Educational Resources Information Center

Zhang, Xijuan; Savalei, Victoria

2016-01-01

Many psychological scales written in the Likert format include reverse worded (RW) items in order to control acquiescence bias. However, studies have shown that RW items often contaminate the factor structure of the scale by creating one or more method factors. The present study examines an alternative scale format, called the Expanded format,…

Design, syntheses, characterization, and cytotoxicity studies of novel heterobinuclear oxindolimine copper(II)-platinum(II) complexes.

PubMed

Aranda, Esther Escribano; Matias, Tiago Araújo; Araki, Koiti; Vieira, Adriana Pires; de Mattos, Elaine Andrade; Colepicolo, Pio; Luz, Carolina Portela; Marques, Fábio Luiz Navarro; da Costa Ferreira, Ana Maria

2016-12-01

Herein, the design and syntheses of two new mononuclear oxindolimine-copper(II) (1 and 2) and corresponding heterobinuclear oxindolimine Cu(II)Pt(II) complexes (3 and 4), are described. All the isolated complexes were characterized by spectroscopic techniques (UV/Vis, IR, EPR), in addition to elemental analysis and mass spectrometry. Cyclic voltammetry (CV) measurements showed that in all cases, one-electron quasi-reversible waves were observed, and ascribed to the formation of corresponding copper(I) complexes. Additionally, waves related to oxindolimine ligand reduction was verified, and confirmed using analogous oxindolimine-Zn(II) complexes. The Pt(IV/II) reduction, and corresponding oxidation, for complexes 3 and 4 occurred at very close values to those observed for cisplatin. By complementary fluorescence studies, it was shown that glutathione (GSH) cannot reduce any of these complexes, under the experimental conditions (room temperature, phosphate buffer 50mM, pH7.4), using an excess of 20-fold [GSH]. All these complexes showed characteristic EPR spectral profile, with parameters values g ǁ >g ⊥ suggesting an axially distorted environment around the copper(II) center. Interactions with calf thymus-DNA, monitored by circular dichroism (CD), indicated different effects modulated by the ligands. Finally, the cytotoxicity of each complex was tested toward different tumor cells, in comparison to cisplatin, and low values of IC 50 in the range 0.6 to 4.0μM were obtained, after 24 or 48h incubation at 37°C. The obtained results indicate that such complexes can be promising alternative antitumor agents. Copyright © 2016 Elsevier Inc. All rights reserved.

Structural and functional properties of the HIV-1 RNA-tRNA(Lys)3 primer complex annealed by the nucleocapsid protein: comparison with the heat-annealed complex.

PubMed Central

Brulé, Fabienne; Marquet, Roland; Rong, Liwei; Wainberg, Mark A; Roques, Bernard P; Le Grice, Stuart F J; Ehresmann, Bernard; Ehresmann, Chantal

2002-01-01

The conversion of the single-stranded RNA genome into double-stranded DNA by virus-coded reverse transcriptase (RT) is an essential step of the retrovirus life cycle. In human immunodeficiency virus type 1 (HIV-1), RT uses the cellular tRNA(Lys)3 to initiate the (-) strand DNA synthesis. Placement of the primer tRNA(Lys)3 involves binding of its 3'-terminal 18 nt to a complementary region of genomic RNA termed PBS. However, the PBS sequence is not the unique determinant of primer usage and additional contacts are important. This placement is believed to be achieved in vivo by the nucleocapsid domain of Gag or by the mature protein NCp. Up to now, structural information essentially arose from heat-annealed primer-template complexes (Isel et al., J Mol Biol, 1995, 247:236-250; Isel et al., EMBO J, 1999, 18:1038-1048). Here, we investigated the formation of the primer-template complex mediated by NCp and compared structural and functional properties of heat- and NCp-annealed complexes. We showed that both heat- and NCp-mediated procedures allow comparable high yields of annealing. Then, we investigated structural features of both kinds of complexes by enzymatic probing, and we compared their relative efficiency in (-) strong stop DNA synthesis. We did not find any significant differences between these complexes, suggesting that information derived from the heat-annealed complex can be transposed to the NCp-mediated complex and most likely to complexes formed in vivo. PMID:11873759

Adiabatic model of field reversal by fast ions in an axisymmetric open trap

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tsidulko, Yu. A., E-mail: tsidulko@mail.ru

2016-06-15

A model of field reversal by fast ions has been developed under the assumption of preservation of fast-ion adiabatic invariants. Analytical solutions obtained in the approximation of a narrow fast-ion layer and numerical solutions to the evolutionary problem are presented. The solutions demonstrate the process of formation of a field reversed configuration with parameters close to those of the planned experiment.

The conserved N-terminal basic residues and zinc-finger motifs of HIV-1 nucleocapsid restrict the viral cDNA synthesis during virus formation and maturation

PubMed Central

Didierlaurent, Ludovic; Houzet, Laurent; Morichaud, Zakia; Darlix, Jean-Luc; Mougel, Marylène

2008-01-01

Reverse transcription of the genomic RNA by reverse transcriptase occurs soon after HIV-1 infection of target cells. The viral nucleocapsid (NC) protein chaperones this process via its nucleic acid annealing activities and its interactions with the reverse transcriptase enzyme. To function, NC needs its two conserved zinc fingers and flanking basic residues. We recently reported a new role for NC, whereby it negatively controls reverse transcription in the course of virus formation. Indeed, deleting its zinc fingers causes reverse transcription activation in virus producer cells. To investigate this new NC function, we used viruses with subtle mutations in the conserved zinc fingers and its flanking domains. We monitored by quantitative PCR the HIV-1 DNA content in producer cells and in produced virions. Results showed that the two intact zinc-finger structures are required for the temporal control of reverse transcription by NC throughout the virus replication cycle. The N-terminal basic residues also contributed to this new role of NC, while Pro-31 residue between the zinc fingers and Lys-59 in the C-terminal region did not. These findings further highlight the importance of NC as a major target for anti-HIV-1 drugs. PMID:18641038

Kirkendall void formation in reverse step graded Si1-xGex/Ge/Si(001) virtual substrates

NASA Astrophysics Data System (ADS)

Sivadasan, Vineet; Rhead, Stephen; Leadley, David; Myronov, Maksym

2018-02-01

Formation of Kirkendall voids is demonstrated in the Ge underlayer of reverse step graded Si1-xGex/Ge buffer layers grown on Si(001) using reduced pressure chemical vapour deposition (RP-CVD). This phenomenon is seen when the constant composition Si1-xGex layer is grown at high temperatures and for x ≤ 0.7. The density and size of the spherical voids can be tuned by changing Ge content in the Si1-xGex and other growth parameters.

Annual National Test and Evaluation Conference (27th) Held in Tampa, Florida on March 14-17, 2011

DTIC Science & Technology

2011-03-17

Based Test & Evaluation PETALLINGFRAGMENTATION RADIAL FRACTUREBRITTLE FRACTURE DUCTILE HOLE GROWTH PLUGGING THREAT VELOCITY MATERIAL MATERIAL V50 TYPE...Less Complex Less Costly Testing More Complex More Costly PETALLINGFRAGMENTATION RADIAL FRACTUREBRITTLE FRACTURE DUCTILE HOLE GROWTH PLUGGING...Reversible injuries; medical attention required 3 Serious Fracture of skull, penetration < 2 cm Reversible injuries; hospitalization required 4 Severe

Contributions of Lateral and Orbital Frontal Regions to Abstract Rule Acquisition and Reversal in Monkeys

PubMed Central

La Camera, Giancarlo; Bouret, Sebastien; Richmond, Barry J.

2018-01-01

The ability to learn and follow abstract rules relies on intact prefrontal regions including the lateral prefrontal cortex (LPFC) and the orbitofrontal cortex (OFC). Here, we investigate the specific roles of these brain regions in learning rules that depend critically on the formation of abstract concepts as opposed to simpler input-output associations. To this aim, we tested monkeys with bilateral removals of either LPFC or OFC on a rapidly learned task requiring the formation of the abstract concept of same vs. different. While monkeys with OFC removals were significantly slower than controls at both acquiring and reversing the concept-based rule, monkeys with LPFC removals were not impaired in acquiring the task, but were significantly slower at rule reversal. Neither group was impaired in the acquisition or reversal of a delayed visual cue-outcome association task without a concept-based rule. These results suggest that OFC is essential for the implementation of a concept-based rule, whereas LPFC seems essential for its modification once established. PMID:29615854

Reversing Implicit First Impressions through Reinterpretation after a Two-Day Delay

PubMed Central

Mann, Thomas C.; Ferguson, Melissa J.

2016-01-01

People are adept at forming impressions of others, but how easily can impressions be updated? Although implicit first impressions have been characterized as difficult to overturn, recent work shows that they can be reversed through reinterpretation of earlier learning. However, such reversal has been demonstrated only in the same experimental session in which the impression formed, suggesting that implicit updating might be possible only within a brief temporal window, before impressions are consolidated and when memory about the initial information is strongest. Implicit impressions may be unable to be revised when reinterpreting details are learned later, due to memory consolidation or forgetting of the details to be reinterpreted. This study tested whether implicit first impressions can be reversed through reinterpretation after a two-day delay following the initial formation. Results showed that implicit revision emerged after the delay, even among those with poor explicit recall or who were not cued to recall. We discuss implications for theory on impression formation and updating. PMID:28017977

Reversing Implicit First Impressions through Reinterpretation after a Two-Day Delay.

PubMed

Mann, Thomas C; Ferguson, Melissa J

2017-01-01

People are adept at forming impressions of others, but how easily can impressions be updated? Although implicit first impressions have been characterized as difficult to overturn, recent work shows that they can be reversed through reinterpretation of earlier learning. However, such reversal has been demonstrated only in the same experimental session in which the impression formed, suggesting that implicit updating might be possible only within a brief temporal window, before impressions are consolidated and when memory about the initial information is strongest. Implicit impressions may be unable to be revised when reinterpreting details are learned later, due to memory consolidation or forgetting of the details to be reinterpreted. This study tested whether implicit first impressions can be reversed through reinterpretation after a two-day delay following the initial formation. Results showed that implicit revision emerged after the delay, even among those with poor explicit recall or who were not cued to recall. We discuss implications for theory on impression formation and updating.

Multifunctional QD-based co-delivery of siRNA and doxorubicin to HeLa cells for reversal of multidrug resistance and real-time tracking.

PubMed

Li, Jin-Ming; Wang, Yuan-Yuan; Zhao, Mei-Xia; Tan, Cai-Ping; Li, Yi-Qun; Le, Xue-Yi; Ji, Liang-Nian; Mao, Zong-Wan

2012-03-01

Co-delivery of siRNA and chemotherapeutic agents has been developed to combat multidrug resistance in cancer therapy. Recently, we developed a series of quantum dots (QDs) functionalized by β-cyclodextrin (β-CD) coupled to amino acids, some of which can be used to facilitate the delivery of siRNA. In this study, two CdSe/ZnSe QDs modified with β-CD coupled to L-Arg or L-His were used to simultaneously deliver doxorubicin (Dox) and siRNA targeting the MDR1 gene to reverse the multidrug resistance of HeLa cells. In this co-delivery system, Dox was firstly encapsulated into the hydrophobic cavities of β-CD, resulting in bypass of P-glycoprotein (P-gp)-mediated drug efflux. After complex formation of the mdr1 siRNA with Dox-loaded QDs via electrostatic interaction, significant down-regulation of mdr1 mRNA levels and P-gp expression was achieved as shown by RT-PCR and Western blotting experiments, respectively. The number of apoptotic HeLa cells after treatment with the complexes substantially exceeded the number of apoptotic cells induced by free Dox only. The intrinsic fluorescence of the QDs provided an approach to track the system by laser confocal microscopy. These multifunctional QDs are promising vehicles for the co-delivery of nucleic acids and chemotherapeutics and for real-time tracking of treatment. Copyright © 2011 Elsevier Ltd. All rights reserved.

Kinetics and Mechanism Study of Competitive Inhibition of Jack-Bean Urease by Baicalin

PubMed Central

Tan, Lirong; Su, Jiyan; Wu, Dianwei; Yu, Xiaodan; Su, Zuqing; Wu, Xiaoli; Kong, Songzhi; Lai, Xiaoping; Lin, Ji; Su, Ziren

2013-01-01

Baicalin (BA) is the principal component of Radix Scutellariae responsible for its pharmacological activity. In this study, kinetics and mechanism of inhibition by BA against jack-bean urease were investigated for its therapeutic potential. It was revealed that the IC50 of BA against jack-bean urease was 2.74 ± 0.51 mM, which was proved to be a competitive and concentration-dependent inhibition with slow-binding progress curves. The rapid formation of initial BA-urease complex with an inhibition constant of K i = 3.89 × 10−3 mM was followed by a slow isomerization into the final complex with an overall inhibition constant of K i* = 1.47 × 10−4 mM. High effectiveness of thiol protectors against BA inhibition indicated that the strategic role of the active-site sulfhydryl group of the urease was involved in the blocking process. Moreover, the inhibition of BA was proved to be reversible due to the fact that urease could be reactivated by dithiothreitol but not reactant dilution. Molecular docking assay suggested that BA made contacts with the important activating sulfhydryl group Cys-592 residues and restricted the mobility of the active-site flap. Taken together, it could be deduced that BA was a competitive inhibitor targeting thiol groups of urease in a slow-binding manner both reversibly and concentration-dependently, serving as a promising urease inhibitor for treatments on urease-related diseases. PMID:24198731

Insights into the mechanisms of RNA secondary structure destabilization by the HIV-1 nucleocapsid protein

PubMed Central

Belfetmi, Anissa; Zargarian, Loussiné; Tisné, Carine; Sleiman, Dona; Morellet, Nelly; Lescop, Ewen; Maskri, Ouerdia; René, Brigitte; Mély, Yves; Fossé, Philippe; Mauffret, Olivier

2016-01-01

The mature HIV-1 nucleocapsid protein NCp7 (NC) plays a key role in reverse transcription facilitating the two obligatory strand transfers. Several properties contribute to its efficient chaperon activity: preferential binding to single-stranded regions, nucleic acid aggregation, helix destabilization, and rapid dissociation from nucleic acids. However, little is known about the relationships between these different properties, which are complicated by the ability of the protein to recognize particular HIV-1 stem–loops, such as SL1, SL2, and SL3, with high affinity and without destabilizing them. These latter properties are important in the context of genome packaging, during which NC is part of the Gag precursor. We used NMR to investigate destabilization of the full-length TAR (trans activating response element) RNA by NC, which is involved in the first strand transfer step of reverse transcription. NC was used at a low protein:nucleotide (nt) ratio of 1:59 in these experiments. NMR data for the imino protons of TAR identified most of the base pairs destabilized by NC. These base pairs were adjacent to the loops in the upper part of the TAR hairpin rather than randomly distributed. Gel retardation assays showed that conversion from the initial TAR–cTAR complex to the fully annealed form occurred much more slowly at the 1:59 ratio than at the higher ratios classically used. Nevertheless, NC significantly accelerated the formation of the initial complex at a ratio of 1:59. PMID:26826129

Redox-switchable copper(I) metallogel: a metal-organic material for selective and naked-eye sensing of picric acid.

PubMed

Sarkar, Sougata; Dutta, Soumen; Chakrabarti, Susmita; Bairi, Partha; Pal, Tarasankar

2014-05-14

Thiourea (TU), a commercially available laboratory chemical, has been discovered to introduce metallogelation when reacted with copper(II) chloride in aqueous medium. The chemistry involves the reduction of Cu(II) to Cu(I) with concomitant oxidation of thiourea to dithiobisformamidinium dichloride. The gel formation is triggered through metal-ligand complexation, i.e., Cu(I)-TU coordination and extensive hydrogen bonding interactions involving thiourea, the disulfide product, water, and chloride ions. Entangled network morphology of the gel selectively develops in water, maybe for its superior hydrogen-bonding ability, as accounted from Kamlet-Taft solvent parameters. Complete and systematic chemical analyses demonstrate the importance of both Cu(I) and chloride ions as the key ingredients in the metal-organic coordination gel framework. The gel is highly fluorescent. Again, exclusive presence of Cu(I) metal centers in the gel structure makes the gel redox-responsive and therefore it shows reversible gel-sol phase transition. However, the reversibility does not cause any morphological change in the gel phase. The gel practically exhibits its multiresponsive nature and therefore the influences of different probable interfering parameters (pH, selective metal ions and anions, selective complexing agents, etc.) have been studied mechanistically and the results might be promising for different applications. Finally, the gel material shows a highly selective visual response to a commonly used nitroexplosive, picric acid among a set of 19 congeners and the preferred selectivity has been mechanistically interpreted with density functional theory-based calculations.

Toroidal equilibrium states with reversed magnetic shear and parallel flow in connection with the formation of Internal Transport Barriers

NASA Astrophysics Data System (ADS)

Kuiroukidis, Ap.; Throumoulopoulos, G. N.

2015-08-01

We construct nonlinear toroidal equilibria of fixed diverted boundary shaping with reversed magnetic shear and flows parallel to the magnetic field. The equilibria have hole-like current density and the reversed magnetic shear increases as the equilibrium nonlinearity becomes stronger. Also, application of a sufficient condition for linear stability implies that the stability is improved as the equilibrium nonlinearity correlated to the reversed magnetic shear gets stronger with a weaker stabilizing contribution from the flow. These results indicate synergetic stabilizing effects of reversed magnetic shear, equilibrium nonlinearity and flow in the establishment of Internal Transport Barriers (ITBs).

[Safety and efficacy of a prothrombin complex concentrate in patients with coagulopathy and hemorrhage].

PubMed

Martínez-Calle, N; Marcos-Jubilar, M; Alfonso, A; Hernández, M; Hidalgo, F; Lecumberri, R; Páramo, Ja

2014-01-01

Prothrombin complex concentrates (PCC) are approved for urgent reversal of vitamin K antagonists (VKA). Recently, PCC have been used in the management of massive bleeding-associated coagulopathy. The present work evaluates safety and efficacy of PCC in a case series of both VKA reversal and massive bleeding. Retrospective review of cases treated with CCP (January 2010 to February 2013). Safety endpoints were infusion reactions and incidence of thromboembolic events. Efficacy endpoints were: 1) VKA reversal efficacy and 2) Massive bleeding coagulopathy reversal and 24h mortality. Thirty-one patients were included (22 male), median age 61 years (range 30-86). No infusion reactions were detected, and only 1 thrombotic episode was observed. VKA reversal was effective in 100% of patients (6/6), all of them with complete reversal of INR value. In massive bleeding, 24-hour survival was 64% (16/25). Invasive hemostatic procedures were required in 28% of patients (7/25). CCP use was correlated with bleeding control in 44% of cases (11/25), and also significantly associated with survival (p=0.01). CCP are safe and effective for the novel indication of adjuvant treatment in massive bleeding patients, as well as for traditional urgent reversal of VKA.

Erythrocyte haemolysate interacts with ATP-Fe to form a complex containing iron, ATP and 13 800 MW polypeptide.

PubMed

Weaver, J; Zhan, H; Pollack, S

1993-01-01

Iron first entering the reticulocyte is bound to ATP in the low MW cytosolic pool; some is also 'loosely bound' to haemoglobin, coeluting with haemoglobin from a molecular sieve column though not incorporated into haem. When haemolysate is mixed with ATP-Fe in vitro a similar high MW iron-containing complex is formed: the ATP-Fe interacts with a non-haemoglobin constituent of the haemolysate to form a high MW ATP-Fe complex in which the ratio of ATP:Fe (originally 6:1) is reversed, so that the complex contains more iron than ATP. The high MW ATP-Fe complex is formed even when ATP is in 150-fold molar excess and is formed without detectable hydrolysis of the ATP. The activity of haemolysate in forming the high MW ATP-Fe complex is not diminished by dialysis; all of the activity is recovered in the haemoglobin-containing fraction obtained from an Ultrogel AcA 44 column. The activity does not derive from haemoglobin since 85% of the activity is removed when haemoglobin is purified from haemolysate with DEAE-Sephadex. The chelatable iron pool of the cell probably includes both the high MW ATP-Fe complex and low MW ATP-Fe. Shunting of ATP-Fe to a high MW aggregate reduces the amount of iron present in the highly reactive low MW form and thus probably serves to limit the formation of cell damaging radicals.

Use of reversed phase high pressure liquid chromatography for the physicochemical and thermodynamic characterization of oxyresveratrol/beta-cyclodextrin complexes.

PubMed

Rodríguez-Bonilla, Pilar; López-Nicolás, José Manuel; García-Carmona, Francisco

2010-06-01

Knowledge of the complexation process of oxyresveratrol with beta-cyclodextrin (beta-CD) under different physicochemical conditions is essential if this potent antioxidant compound is to be used successfully in both food and pharmaceutical industries as ingredient of functional foods or nutraceuticals, despite its poor stability and bioavailability. In this paper, the complexation of oxyresveratrol with natural CDs was investigated for first time using RP-HPLC and mobile phases to which alpha-, beta-, and gamma-CD were added. Among natural CDs, the interaction of oxyresveratrol with beta-CD was more efficient than with alpha- and gamma-CD. The decrease in the retention times with increasing concentrations of beta-CD (0-4 mM) showed that the formation constants (KF) of the oxyresveratrol/beta-CD complexes were strongly dependent on both the water-methanol proportion and the temperature of the mobile phase employed. However, oxyresveratrol formed complexes with beta-CD with a 1:1 stoichiometry in all the physicochemical conditions tested. Moreover, to obtain information about the mechanism of the oxyresveratrol affinity for beta-CD, the thermodynamic parameters DeltaG degrees, DeltaH degrees and DeltaS degrees were obtained. Finally, to gain information on the effect of the structure of different compounds belonging to the stilbenoids family on the KF values, the complexation of other molecules, resveratrol, pterostilbene and pinosylvin, was studied and compared with the results obtained for the oxyresveratrol/beta-CD complexes. Copyright 2010 Elsevier B.V. All rights reserved.

Effects of Acerola (Malpighia emarginata DC.) Juice Intake on Brain Energy Metabolism of Mice Fed a Cafeteria Diet.

PubMed

Leffa, Daniela Dimer; Rezin, Gislaine Tezza; Daumann, Francine; Longaretti, Luiza M; Dajori, Ana Luiza F; Gomes, Lara Mezari; Silva, Milena Carvalho; Streck, Emílio L; de Andrade, Vanessa Moraes

2017-03-01

Obesity is a multifactorial disease that comes from an imbalance between food intake and energy expenditure. Moreover, studies have shown a relationship between mitochondrial dysfunction and obesity. In the present study, we investigated the effect of acerola juices (unripe, ripe, and industrial) and its main pharmacologically active components (vitamin C and rutin) on the activity of enzymes of energy metabolism in the brain of mice fed a palatable cafeteria diet. Two groups of male Swiss mice were fed on a standard diet (STA) or a cafeteria diet (CAF) for 13 weeks. Afterwards, the CAF-fed animals were divided into six subgroups, each of which received a different supplement for one further month (water, unripe, ripe or industrial acerola juices, vitamin C, or rutin) by gavage. Our results demonstrated that CAF diet inhibited the activity of citrate synthase in the prefrontal cortex, hippocampus, and hypothalamus. Moreover, CAF diet decreased the complex I activity in the hypothalamus, complex II in the prefrontal cortex, complex II-III in the hypothalamus, and complex IV in the posterior cortex and striatum. The activity of succinate dehydrogenase and creatine kinase was not altered by the CAF diet. However, unripe acerola juice reversed the inhibition of the citrate synthase activity in the prefrontal cortex and hypothalamus. Ripe acerola juice reversed the inhibition of citrate synthase in the hypothalamus. The industrial acerola juice reversed the inhibition of complex I activity in the hypothalamus. The other changes were not reversed by any of the tested substances. In conclusion, we suggest that alterations in energy metabolism caused by obesity can be partially reversed by ripe, unripe, and industrial acerola juice.

Electrogelation of Biopolymers for New Functional Materials

DTIC Science & Technology

2013-08-31

System to Evaluate e-gel Properties As reported previously, we have designed and implemented microfluidic flow chambers with embedded electrodes...effort is as a new opportunity to use egel formation and reversibility as a mode for material coatings that would be reversible, such as for living skins

Reversible cluster formation in concentrated monoclonal antibody solutions

NASA Astrophysics Data System (ADS)

Godfrin, P. Douglas; Porcar, Lionel; Falus, Peter; Zarraga, Isidro; Wagner, Norm; Liu, Yun

2015-03-01

Protein cluster formation in solution is of fundamental interest for both academic research and industrial applications. Recently, industrial scientists are also exploring the effect of reversible cluster formation on biopharmaceutical processing and delivery. However, despite of its importance, the understanding of protein clusters at concentrated solutions remains scientifically very challenging. Using the neutron spin echo technique to study the short time dynamics of proteins in solutions, we have recently systematically studied cluster formation in a few monoclonal antibody (mAb) solutions and their relation with solution viscosity. We show that the existence of anisotropic attraction can cause the formation of finite sized clusters, which increases the solution viscosity. Interestingly, once clusters form at relatively low concentrations, the average size of clusters in solutions remains almost constant over a wide range of concentrations similar to that of micelle formation. For a different mAb we have also investigated, the attraction is mostly induced by hydrophobic patches. As a result, these mAbs form large clusters with loosely linked proteins. In both cases, the formation of clusters all increases the solution viscosity substantially. However, due to different physics origins of cluster formation, solutions viscosities for these two different types of mAbs need to be controlled by different ways.

Pattern-formation mechanisms in motility mutants of Myxococcus xanthus

PubMed Central

Starruß, Jörn; Peruani, Fernando; Jakovljevic, Vladimir; Søgaard-Andersen, Lotte; Deutsch, Andreas; Bär, Markus

2012-01-01

Formation of spatial patterns of cells is a recurring theme in biology and often depends on regulated cell motility. Motility of the rod-shaped cells of the bacterium Myxococcus xanthus depends on two motility machineries, type IV pili (giving rise to S-motility) and the gliding motility apparatus (giving rise to A-motility). Cell motility is regulated by occasional reversals. Moving M. xanthus cells can organize into spreading colonies or spore-filled fruiting bodies, depending on their nutritional status. To ultimately understand these two pattern-formation processes and the contributions by the two motility machineries, as well as the cell reversal machinery, we analyse spatial self-organization in three M. xanthus strains: (i) a mutant that moves unidirectionally without reversing by the A-motility system only, (ii) a unidirectional mutant that is also equipped with the S-motility system, and (iii) the wild-type that, in addition to the two motility systems, occasionally reverses its direction of movement. The mutant moving by means of the A-engine illustrates that collective motion in the form of large moving clusters can arise in gliding bacteria owing to steric interactions of the rod-shaped cells, without the need of invoking any biochemical signal regulation. The two-engine strain mutant reveals that the same phenomenon emerges when both motility systems are present, and as long as cells exhibit unidirectional motion only. From the study of these two strains, we conclude that unidirectional cell motion induces the formation of large moving clusters at low and intermediate densities, while it results in vortex formation at very high densities. These findings are consistent with what is known from self-propelled rod models, which strongly suggests that the combined effect of self-propulsion and volume exclusion interactions is the pattern-formation mechanism leading to the observed phenomena. On the other hand, we learn that when cells occasionally reverse their moving direction, as observed in the wild-type, cells form small but strongly elongated clusters and self-organize into a mesh-like structure at high enough densities. These results have been obtained from a careful analysis of the cluster statistics of ensembles of cells, and analysed in the light of a coagulation Smoluchowski equation with fragmentation. PMID:24312730

Enhanced bioelectricity generation and azo dye treatment in a reversible photo-bioelectrochemical cell by using novel anthraquinone-2,6-disulfonate (AQDS)/MnOx-doped polypyrrole film electrodes.

PubMed

Sun, Jian; Cai, Bihai; Xu, Wenjing; Huang, Yu; Zhang, Yaping; Peng, Yenping; Chang, Kenlin; Kuo, Jiahong; Chen, Kufan; Ning, Xunan; Liu, Guoguang; Wang, Yujie; Yang, Zuoyi; Liu, Jingyong

2017-02-01

A novel anthraquinone-2,6-disulfonate/MnO x -doped polypyrrole film (AQDS/Mn/PPy) electrode was prepared by one-step electropolymerization method and was used to improve performance of a reversible photo-bioelectrochemical cell (RPBEC). The RPBEC was operated in polarity reversion depended on dark/light reaction of alga Chlorella vulgaris by which sequential decolorization of azo dye and mineralization of decolorization products coupled with bioelectricity generation can be achieved. The results showed that formation of uniform AQDS/Mn/PPy film significantly enhanced electroactive surface area and electrocatalytic activity of carbon electrode. The RPBEC with AQDS/Mn/PPy electrodes demonstrated 77% increases in maximum power and 73% increases in Congo red decolorization rate before polarity reversion, and 198% increases in maximum power and 138% increases in decolorization products mineralization rate after polarity reversion, respectively, compared to the RPBEC with bare electrode. This was resulted from simultaneous dynamics improvement in half-reaction rate of anode and photo-biocathode due to enhanced electron transfer and algal-bacterial biofilm formation. Copyright © 2016 Elsevier Ltd. All rights reserved.

The impact of whole human blood on the kinetic inertness of platinum(iv) prodrugs - an HPLC-ICP-MS study.

PubMed

Theiner, Sarah; Grabarics, Márkó; Galvez, Luis; Varbanov, Hristo P; Sommerfeld, Nadine S; Galanski, Markus; Keppler, Bernhard K; Koellensperger, Gunda

2018-04-17

The potential advantage of platinum(iv) complexes as alternatives to classical platinum(ii)-based drugs relies on their kinetic stability in the body before reaching the tumor site and on their activation by reduction inside cancer cells. In this study, an analytical workflow has been developed to investigate the reductive biotransformation and kinetic inertness of platinum(iv) prodrugs comprising different ligand coordination spheres (respectively, lipophilicity and redox behavior) in whole human blood. The distribution of platinum(iv) complexes in blood pellets and plasma was determined by inductively coupled plasma-mass spectrometry (ICP-MS) after microwave digestion. An analytical approach based on reversed-phase (RP)-ICP-MS was used to monitor the parent compound and the formation of metabolites using two different extraction procedures. The ligand coordination sphere of the platinum(iv) complexes had a significant impact on their accumulation in red blood cells and on their degree of kinetic inertness in whole human blood. The most lipophilic platinum(iv) compound featuring equatorial chlorido ligands showed a pronounced penetration into blood cells and a rapid reductive biotransformation. In contrast, the more hydrophilic platinum(iv) complexes with a carboplatin- and oxaliplatin-core exerted kinetic inertness on a pharmacologically relevant time scale with notable amounts of the compound accumulated in the plasma fraction.

Formation of a physiological reverse shoulder joint.

PubMed

Lerner, Markus; Turkmen, Ismail; Bernd, Ludger

2016-01-20

Congenital shoulder deformities are rarely seen in orthopaedic practice. Proximal humeral defects and glenoid hypoplasia have been reported separately in the literature. We present a case involving a 31-year-old woman having a cosmetic problem with her upper arm who was diagnosed with reverse shoulder joint deformity. This article presents the clinical, radiological and biomechanical findings of a physiological reverse shoulder joint. This is the first such reported case. 2016 BMJ Publishing Group Ltd.

Precursor Ion–Ion Aggregation in the Brust–Schiffrin Synthesis of Alkanethiol Nanoparticles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Graham, Trent R.; Renslow, Ryan; Govind, Niranjan

Tetraoctylammonium bromide is used in the Brust-Schiffrin nanoparticle synthesis to phase-transfer chloroaurate ions from the aqueous phase to the organic phase. While it is established that the quaternary ammonium complex self-associates in the organic phase, the actual self-assembled structure is debated. We have confirmed the presence of ion-ion aggregates through quantitative 1H Nuclear Magnetic Resonance spectroscopy (NMR), pulsed field gradient, diffusion-ordered NMR (DOSY-NMR) and density functional theory (DFT) based NMR shift calculations. Tetraoctylammonium complexes (TOA-X, where X = Br, Cl, AuCl4-xBrx, AuBr4/Br and AuCl4-xBrx/Br) were investigated to measure the extraction of water into the organic phase. 1H NMR and DFTmore » based NMR shielding calculations indicated that deshielding of water is due to hydration of the anion and not the formation of the aqueous core of a reverse micelle. DOSYNMR results were consistent with the formation of small aggregates at typical Brust-Schiffrin synthesis concentrations. The extent of aggregation correlated with the size and electronegativity of the anion and was analyzed with a modified, isodesmic, indefinite aggregation model. The substitution of bromoauric acid for chlororoauric acid at conditions emulating the Brust-Schiffrin synthesis increased the aggregation of the quaternary ammonium complex. The increase in aggregation corresponded with an increase in the size of the produced nanoparticles from 4.3 to 4.6 nm. Understanding the selfassembly and supramolecular structure of precursors in the Brust-Schiffrin synthesis will enable further refinement of models that predict the growth of noble metal nanoparticles.« less

Simultaneous analysis and retention behavior of major isoflavonoids in Radix Puerariae lobatae and Radix Puerariae thomsonii by high performance liquid chromatography with cyclodextrins as a mobile phase modifier.

PubMed

Zeng, Aiguo; Xing, Jianfeng; Wang, Changhe; Song, Jie; Li, Cong; Yang, Xin; Yang, Guangde

2012-01-27

In order to differentiate two species of Radix Puerariae (Radix Puerariae lobatae and Radix Puerariae thomsonii) and to determine major isoflavonoids (puerarin, daidzin, daidzein and genistein) in the samples, a simple high performance liquid chromatography (HPLC) method with isocratic elution employing cyclodextrins (CDs) as mobile phase additives was developed. Various factors affecting the retention of isoflavonoids in the C(18) reversed-phase column, such as the nature of CDs, the concentration of hydroxypropyl-β-cyclodextrin (HP-β-CD) and the methanol percentage in the mobile phase, were studied. Experimental results confirmed that HP-β-CD, as a very effective mobile phase additive, could markedly reduce the retention of isoflavonoids, especially daidzein and genistein. The elution of four isoflavonoids could be achieved on a Kromasil(®) C(18) column within 56 min by using the methanol-water contained 5 mM HP-β-CD (25/75, v/v) mixture as the mobile phase. The formation of the inclusion complexes between isoflavonoids and HP-β-CD explained the modification of the retention of analytes. The apparent formation constants determined by HPLC confirmed that the stoichiometry of HP-β-CD-isoflavonoid complexes was 1:1, and the stability of the complexes depended on the size and property of isoflavonoids. The optimized method was successfully applied for the simultaneous determination of major isoflavonoids in P. lobatae and P. thomsonii samples. This work provides a useful method for the analysis of traditional Chinese herbs. Copyright © 2011 Elsevier B.V. All rights reserved.

The effects of isoprene and NOx on secondary organic aerosols formed through reversible and irreversible uptake to aerosol water

NASA Astrophysics Data System (ADS)

El-Sayed, Marwa M. H.; Ortiz-Montalvo, Diana L.; Hennigan, Christopher J.

2018-01-01

Isoprene oxidation produces water-soluble organic gases capable of partitioning to aerosol liquid water. The formation of secondary organic aerosols through such aqueous pathways (aqSOA) can take place either reversibly or irreversibly; however, the split between these fractions in the atmosphere is highly uncertain. The aim of this study was to characterize the reversibility of aqSOA formed from isoprene at a location in the eastern United States under substantial influence from both anthropogenic and biogenic emissions. The reversible and irreversible uptake of water-soluble organic gases to aerosol water was characterized in Baltimore, Maryland, USA, using measurements of particulate water-soluble organic carbon (WSOCp) in alternating dry and ambient configurations. WSOCp evaporation with drying was observed systematically throughout the late spring and summer, indicating reversible aqSOA formation during these times. We show through time lag analyses that WSOCp concentrations, including the WSOCp that evaporates with drying, peak 6 to 11 h after isoprene concentrations, with maxima at a time lag of 9 h. The absolute reversible aqSOA concentrations, as well as the relative amount of reversible aqSOA, increased with decreasing NOx / isoprene ratios, suggesting that isoprene epoxydiol (IEPOX) or other low-NOx oxidation products may be responsible for these effects. The observed relationships with NOx and isoprene suggest that this process occurs widely in the atmosphere, and is likely more important in other locations characterized by higher isoprene and/or lower NOx levels. This work underscores the importance of accounting for both reversible and irreversible uptake of isoprene oxidation products to aqueous particles.

Reverse lyotropic liquid crystals from europium nitrate and P123 with enhanced luminescence efficiency.

PubMed

Yi, Sijing; Li, Qintang; Liu, Hongguo; Chen, Xiao

2014-10-02

Fabrication of lyotropic aggregates containing the lanthanide ions is becoming a preferable way to prepare novel functional materials. Here, the lyotropic liquid crystals (LLCs) of reverse hexagonal, reverse bicontinuous cubic, and lamellar phases have been constructed in sequence directly from the mixtures of Eu(NO3)3·6H2O and Pluronic P123 amphiphilc block copolymer with increasing the salt proportion. Their phase types and structural characteristics were analyzed using polarized optical microscopy (POM) and small-angle X-ray scattering (SAXS) measurements. The driving forces of reverse LLC phase formation were investigated using Fourier-transformed infrared spectroscopy (FTIR) and rheological measurements. The hydrated europium salt was found to act not only as a solvent here, but also as the bridge to form hydrogen bonding between coordinated water molecules and PEO blocks, which played a key role in the reverse LLCs formation. Compared to those in aqueous solutions and solid state, the enhanced luminescence quantum yields and prolonged excited state lifetimes were observed in two europium containing reverse mesophases. The luminescence quenching effect of lanthanide ions was efficiently suppressed, probably due to the substitution of coordinated water molecules by oxyethyl groups of P123 and ordered phase structures of LLCs, where the coordinated europium ions were confined and isolated by PEO blocks. The optimum luminescence performance was then found to exist in the reverse hexagonal phase. The obtained results on such lanthanide-induced reverse LLCs should be referable for designing new luminescent soft materials construction to expand their application fields.

Experimental studies of applications of time-reversal acoustics to noncoherent underwater communications.

PubMed

Heinemann, M; Larraza, A; Smith, K B

2003-06-01

The most difficult problem in shallow underwater acoustic communications is considered to be the time-varying multipath propagation because it impacts negatively on data rates. At high data rates the intersymbol interference requires adaptive algorithms on the receiver side that lead to computationally intensive and complex signal processing. A novel technique called time-reversal acoustics (TRA) can environmentally adapt the acoustic propagation effects of a complex medium in order to focus energy at a particular target range and depth. Using TRA, the multipath structure is reduced because all the propagation paths add coherently at the intended target location. This property of time-reversal acoustics suggests a potential application in the field of noncoherent acoustic communications. This work presents results of a tank scale experiment using an algorithm for rapid transmission of binary data in a complex underwater environment with the TRA approach. A simple 15-symbol code provides an example of the simplicity and feasibility of the approach. Covert coding due to the inherent scrambling induced by the environment at points other than the intended receiver is also investigated. The experiments described suggest a high potential in data rate for the time-reversal approach in underwater acoustic communications while keeping the computational complexity low.

An ocular drug delivery system containing zinc diethyldithiocarbamate and HPbetaCD inclusion complex--corneal permeability, anti-cataract effects and mechanism studies.

PubMed

Wang, Siling; Li, Dexin; Ito, Yoshimasa; Liu, Xia; Zhang, Jinghai; Wu, Chunfu

2004-10-01

Our purpose was to study the formulation and anti-cataract effects of aqueous eye drops containing a high concentration of zinc diethyldithiocarbamate (Zn-DDC). A possible mechanism of the anti-cataract effect of Zn-DDC was also studied. Zn-DDC and hydroxypropyl-beta-cyclodextrin (HPbetaCD) inclusion complex (Zn-DDC/HPbetaCD) was studied using the saturation solution method and characterized by differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (IR). Suitable formulations for Zn-DDC eye drops were established by means of in-vitro trans-corneal penetration experiments. The anti-cataract effect of the selected formulation was demonstrated by the delay in lens opacity development in hereditary shumuya cataract rats (SCRs). Semiquantitative reverse transcription polymerase chain reaction (RT-PCR) was performed to study the effect of diethyldithiocarbamate (DDC), a metabolite of Zn-DDC, on the transcription inducible nitric oxide synthase (iNOS) mRNA in human lens epithelial cells (HLEC). In the presence of 22% (w/v) HPbetaCD, the solubility of Zn-DDC in water (0.2 mM) was increased almost 850 fold (to 17 mM), by the formation of Zn-DDC/HPbetaCD. The stoichiometry of Zn-DDC inclusion was 1:1. The Zn-DDC/HPbetaCD stability constant, Ks (1:1) was estimated to be 3453 M(-1). The ophthalmic preparation containing 0.1% HPMC and 0.1% poloxamer 188 (P188) exhibited better permeability than the others in-vitro, and significantly delayed cataract formation in SCRs compared with non-treated SCRs. DDC inhibits the transcription of iNOS mRNA in HLEC. We concluded that this drug delivery system increases both the drug solubility in aqueous eye drops and the permeability of drug through the rabbit cornea, by the formation of a drug-cyclodextrin inclusion complex and the addition of polymers and penetration enhancers. The preparation effectively prevented the development of cataracts in SCRs. DDC, the metabolite of Zn-DDC, may be one of the factors in the prevention of cataract formation because it inhibits the transcription of iNOS mRNA.

Insight into the molecular mechanism of the sulfur oxidation process by reverse sulfite reductase (rSiR) from sulfur oxidizer Allochromatium vinosum.

PubMed

Ghosh, Semanti; Bagchi, Angshuman

2018-04-26

Sulfur metabolism is one of the oldest known biochemical processes. Chemotrophic or phototrophic proteobacteria, through the dissimilatory pathway, use sulfate, sulfide, sulfite, thiosulfate or elementary sulfur by either reductive or oxidative mechanisms. During anoxygenic photosynthesis, anaerobic sulfur oxidizer Allochromatium vinosum forms sulfur globules that are further oxidized by dsr operon. One of the key redox enzymes in reductive or oxidative sulfur metabolic pathways is the DsrAB protein complex. However, there are practically no reports to elucidate the molecular mechanism of the sulfur oxidation process by the DsrAB protein complex from sulfur oxidizer Allochromatium vinosum. In the present context, we tried to analyze the structural details of the DsrAB protein complex from sulfur oxidizer Allochromatium vinosum by molecular dynamics simulations. The molecular dynamics simulation results revealed the various types of molecular interactions between DsrA and DsrB proteins during the formation of DsrAB protein complex. We, for the first time, predicted the mode of binding interactions between the co-factor and DsrAB protein complex from Allochromatium vinosum. We also compared the binding interfaces of DsrAB from sulfur oxidizer Allochromatium vinosum and sulfate reducer Desulfovibrio vulgaris. This study is the first to provide a comparative aspect of binding modes of sulfur oxidizer Allochromatium vinosum and sulfate reducer Desulfovibrio vulgaris.

Investigating pyridazine and phthalazine exchange in a series of iridium complexes in order to define their role in the catalytic transfer of magnetisation from para-hydrogen.

PubMed

Appleby, Kate M; Mewis, Ryan E; Olaru, Alexandra M; Green, Gary G R; Fairlamb, Ian J S; Duckett, Simon B

2015-07-01

The reaction of [Ir(IMes)(COD)Cl], [IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene, COD = 1,5-cyclooctadiene] with pyridazine (pdz) and phthalazine (phth) results in the formation of [Ir(COD)(IMes)(pdz)]Cl and [Ir(COD)(IMes)(phth)]Cl. These two complexes are shown by nuclear magnetic resonance (NMR) studies to undergo a haptotropic shift which interchanges pairs of protons within the bound ligands. When these complexes are exposed to hydrogen, they react to form [Ir(H) 2 (COD)(IMes)(pdz)]Cl and [Ir(H) 2 (COD)(IMes)(phth)]Cl, respectively, which ultimately convert to [Ir(H) 2 (IMes)(pdz) 3 ]Cl and [Ir(H) 2 (IMes)(phth) 3 ]Cl, as the COD is hydrogenated to form cyclooctane. These two dihydride complexes are shown, by NMR, to undergo both full N-heterocycle dissociation and a haptotropic shift, the rates of which are affected by both steric interactions and free ligand p K a values. The use of these complexes as catalysts in the transfer of polarisation from para -hydrogen to pyridazine and phthalazine via signal amplification by reversible exchange (SABRE) is explored. The possible future use of drugs which contain pyridazine and phthalazine motifs as in vivo or clinical magnetic resonance imaging probes is demonstrated; a range of NMR and phantom-based MRI measurements are reported.

REVERSAL LEARNING SET AND FUNCTIONAL EQUIVALENCE IN CHILDREN WITH AND WITHOUT AUTISM

PubMed Central

Lionello-DeNolf, Karen M.; McIlvane, William J.; Canovas, Daniela S.; de Souza, Deisy G.; Barros, Romariz S.

2009-01-01

To evaluate whether children with and without autism could exhibit (a) functional equivalence in the course of yoked repeated-reversal training and (b) reversal learning set, 6 children, in each of two experiments, were exposed to simple discrimination contingencies with three sets of stimuli. The discriminative functions of the set members were yoked and repeatedly reversed. In Experiment 1, all the children (of preschool age) showed gains in the efficiency of reversal learning across reversal problems and behavior that suggested formation of functional equivalence. In Experiment 2, 3 nonverbal children with autism exhibited strong evidence of reversal learning set and 2 showed evidence of functional equivalence. The data suggest a possible relationship between efficiency of reversal learning and functional equivalence test outcomes. Procedural variables may prove important in assessing the potential of young or nonverbal children to classify stimuli on the basis of shared discriminative functions. PMID:20186287

Fixed Versus Variable Dosing of 4-factor Prothrombin Complex Concentrate for Emergent Warfarin Reversal

ClinicalTrials.gov

2018-04-06

Acute Bleeding on Long-Term Anticoagulation Therapy; Hemorrhage; Significant Bleeding in Patients With a Coagulopathy (Prolonged Thrombin Time); Urgent Reversal of Vitamin K Antagonist (VKA) Anticoagulation

Systematic Underestimation of Earthquake Magnitudes from Large Intracontinental Reverse Faults: Historical Ruptures Break Across Segment Boundaries

NASA Technical Reports Server (NTRS)

Rubin, C. M.

1996-01-01

Because most large-magnitude earthquakes along reverse faults have such irregular and complicated rupture patterns, reverse-fault segments defined on the basis of geometry alone may not be very useful for estimating sizes of future seismic sources. Most modern large ruptures of historical earthquakes generated by intracontinental reverse faults have involved geometrically complex rupture patterns. Ruptures across surficial discontinuities and complexities such as stepovers and cross-faults are common. Specifically, segment boundaries defined on the basis of discontinuities in surficial fault traces, pronounced changes in the geomorphology along strike, or the intersection of active faults commonly have not proven to be major impediments to rupture. Assuming that the seismic rupture will initiate and terminate at adjacent major geometric irregularities will commonly lead to underestimation of magnitudes of future large earthquakes.

Role of Mediator and Effects of Temperature on ortho-C-N Bond Fusion Reactions of Aniline Using Ruthenium Templates: Isolation and Characterization of New Ruthenium Complexes of the in-Situ-Generated Ligands.

PubMed

Roy, Suman K; Sengupta, Debabrata; Rath, Santi Prasad; Saha, Tanushri; Samanta, Subhas; Goswami, Sreebrata

2017-05-01

In this work, ortho-C-N bond fusion reactions of aniline are followed by the use of two different ruthenium mediators. Reaction of aniline with [Ru III (terpy)Cl 3 ] (terpy = 2,2':6',2″-terpyridine) resulted in a trans bis-aniline ruthenium(II) complex [1] + which upon oxidation with H 2 O 2 produced compound [2] + of a bidentate ligand, N-phenyl-1,2-benzoquinonediimine, due to an oxidative ortho-C-N bond fusion reaction. Complex [1] + and aniline (neat) at 185 °C produced a bis-chelated ruthenium complex (3). A previously reported complex [Ru II (N-phenyl-1,2-benzoquinonediimine)(aniline) 2 (Cl) 2 ] (5) undergoes similar oxidation by air at 185 °C to produce complex [3]. A separate chemical reaction between aniline and strongly oxidizing tetra-n-propylammonium perruthenate [(n-pr) 4 N] + [RuO 4 ] - in air produced a ruthenium complex [4] of a N 4 -tetraamidophenylmacrocycle ligand via multiple ortho-C-N bond fusion reaction. Notably, the yield of this product is low (5%) at 100 °C but increases to 25% in refluxing aniline. All these complexes are characterized fully by their physicochemical characterizations and X-ray structure determination. From their structural parameters and other spectroscopic studies, complex [2] + is assigned as [Ru II (terpy)(N-phenyl-1,2-benzoquinonediimine)(Cl)] + whereas complex [4] is described as a ruthenium(VI) complex comprised of a reduced deprotonated N-phenyl-1,2-diamidobenzene and N 4 -tetraamidophenylmacrocyclic ligand. Complex [2] + exhibits one reversible oxidation at 1.32 V and one reversible reduction at -0.75 V vs Ag/AgCl reference electrode. EPR of the electrogenerated complexes has revealed that the oxidized complex is a ruthenium(III) complex with an axial EPR spectrum at g av = 2.06. The reduced complex [2], on the other hand, shows a single-line EPR signal at g av = 1.998. In contrast, complex [4] shows two successive one-electron oxidation waves at 0.5 and 0.8 V and an irreversible reduction wave at -0.9 V. EPR studies of the oxidized complexes [4] + and [4] 2+ reveal that oxidations are ligand centered. DFT calculations were employed to elucidate the electronic structures as well as the redox processes associated with the above complexes. Aerial ortho-C-N bond fusion reactions of aniline using two different mediators, viz. [Ru III (terpy)Cl 3 ] and [(n-pr) 4 N] + [RuO 4 ] - , have been followed. It is found that in the case of oxidizable Ru(III) mediator complex, C-N bond fusion is limited only to dimerization reaction whereas the high-valent Ru(VII) salt mediates multiple C-N bond fusion reactions leading to the formation of a novel tetradentate N 4 -tetraamidophenylmacrocyclic ligand. Valence ambiguity in the complexes of the resultant redox-active ligands is scrutinized.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sherman, Andrew J

A heterogeneous body having ceramic rich cermet regions in a more ductile metal matrix. The heterogeneous bodies are formed by thermal spray operations on metal substrates. The thermal spray operations apply heat to a cermet powder and project it onto a solid substrate. The cermet powder is composed of complex composite particles in which a complex ceramic-metallic core particle is coated with a matrix precursor. The cermet regions are generally comprised of complex ceramic-metallic composites that correspond approximately to the core particles. The cermet regions are approximately lenticular shaped with an average width that is at least approximately twice themore » average thickness. The cermet regions are imbedded within the matrix phase and generally isolated from one another. They have obverse and reverse surfaces. The matrix phase is formed from the matrix precursor coating on the core particles. The amount of heat applied during the formation of the heterogeneous body is controlled so that the core particles soften but do not become so fluid that they disperse throughout the matrix phase. The force of the impact on the surface of the substrate tends to flatten them. The flattened cermet regions tend to be approximately aligned with one another in the body.« less

Electron transport chain dysfunction by H(2)O (2) is linked to increased reactive oxygen species production and iron mobilization by lipoperoxidation: studies using Saccharomyces cerevisiae mitochondria.

PubMed

Cortés-Rojo, Christian; Estrada-Villagómez, Mirella; Calderón-Cortés, Elizabeth; Clemente-Guerrero, Mónica; Mejía-Zepeda, Ricardo; Boldogh, Istvan; Saavedra-Molina, Alfredo

2011-04-01

The mitochondrial electron transport chain (ETC) contains thiol groups (-SH) which are reversibly oxidized to modulate ETC function during H(2)O(2) overproduction. Since deleterious effects of H(2)O(2) are not limited to -SH oxidation, due to the formation of other H(2)O(2)-derived species, some processes like lipoperoxidation could enhance the effects of H(2)O(2) over ETC enzymes, disrupt their modulation by -SH oxidation and increase superoxide production. To verify this hypothesis, we tested the effects of H(2)O(2) on ETC activities, superoxide production and iron mobilization in mitochondria from lipoperoxidation-resistant native yeast and lipoperoxidation-sensitized yeast. Only complex III activity from lipoperoxidation-sensitive mitochondria exhibited a higher susceptibility to H(2)O(2) and increased superoxide production. The recovery of ETC activity by the thiol reductanct β-mercaptoethanol (BME) was also altered at complex III, and a role was attributed to lipoperoxidation, the latter being also responsible for iron release. A hypothetical model linking lipoperoxidation, increased complex III damage, superoxide production and iron release is given.

Stress Granule-Inducing Eukaryotic Translation Initiation Factor 4A Inhibitors Block Influenza A Virus Replication

PubMed Central

Slaine, Patrick D.; Kleer, Mariel; Smith, Nathan K.; Khaperskyy, Denys A.

2017-01-01

Eukaryotic translation initiation factor 4A (eIF4A) is a helicase that facilitates assembly of the translation preinitiation complex by unwinding structured mRNA 5′ untranslated regions. Pateamine A (PatA) and silvestrol are natural products that disrupt eIF4A function and arrest translation, thereby triggering the formation of cytoplasmic aggregates of stalled preinitiation complexes known as stress granules (SGs). Here we examined the effects of eIF4A inhibition by PatA and silvestrol on influenza A virus (IAV) protein synthesis and replication in cell culture. Treatment of infected cells with either PatA or silvestrol at early times post-infection resulted in SG formation, arrest of viral protein synthesis and failure to replicate the viral genome. PatA, which irreversibly binds to eIF4A, sustained long-term blockade of IAV replication following drug withdrawal, and inhibited IAV replication at concentrations that had minimal cytotoxicity. By contrast, the antiviral effects of silvestrol were fully reversible; drug withdrawal caused rapid SG dissolution and resumption of viral protein synthesis. IAV inhibition by silvestrol was invariably associated with cytotoxicity. PatA blocked replication of genetically divergent IAV strains, suggesting common dependence on host eIF4A activity. This study demonstrates that the core host protein synthesis machinery can be targeted to block viral replication. PMID:29258238

Forward genetics in Candida albicans that reveals the Arp2/3 complex is required for hyphal formation, but not endocytosis

PubMed Central

Epp, Elias; Walther, Andrea; Guylaine, Lépine; Leon, Zully; Mullick, Alaka; Raymond, Martine; Wendland, Jürgen; Whiteway, Malcolm

2014-01-01

Summary Candida albicans is a diploid fungal pathogen lacking a defined complete sexual cycle, and thus has been refractory to standard forward genetic analysis. Instead, transcription profiling and reverse genetic strategies based on Saccharomyces cerevisiae have typically been used to link genes to functions. To overcome restrictions inherent in such indirect approaches, we have investigated a forward genetic mutagenesis strategy based on the UAU1 technology. We screened 4700 random insertion mutants for defects in hyphal development and linked two new genes (ARP2 and VPS52) to hyphal growth. Deleting ARP2 abolished hyphal formation, generated round and swollen yeast phase cells, disrupted cortical actin patches and blocked virulence in mice. The mutants also showed a global lack of induction of hyphae-specific genes upon the yeast-to-hyphae switch. Surprisingly, both arp2Δ/Δ and arp2Δ/Δarp3Δ/Δ mutants were still able to endocytose FM4-64 and Lucifer Yellow, although as shown by time-lapse movies internalization of FM4-64 was somewhat delayed in mutant cells. Thus the non-essential role of the Arp2/3 complex discovered by forward genetic screening in C. albicans showed that uptake of membrane components from the plasma membrane to vacuolar structures is not dependent on this actin nucleating machinery. PMID:20141603

Formation of mixed-layer structures in smectites intercalated with tryptone

NASA Astrophysics Data System (ADS)

Block, K. A.; Trusiak, A.; Steiner, J. C.; Katz, A.; Gottlieb, P.; Alimova, A.

2012-12-01

Stable clay-protein complexes are fundamental to studies of the critical zone, terrestrial ecosystems, pharmacology, and industrial applications such as bioremediation. Two sets of montmorillonite clays were purified and made homoionic for Na and Mg. Mg-montmorillonite and Na-montmorillonite were mixed with tryptone (casein digest) in a 9:1 and 18:1 clay:tryptone ratio, resulting in the formation of reversible intercalated structures. X-ray diffraction analysis of the protein-clay complexes produced profiles consisting of two peaks associated with the smectite 001 reflection and a related tryptone-packet peak similar to that produced by a mixed layer clay structure. Shifts in the 002, 003, and 004 diffraction maxima are attributed to disorder caused by the interaction with the protein. Line broadening in the smectite-tryptone XRD spectra is interpreted to be the result of interlayer absorption. Adsorption produces coherent crystalline packets of regularly interbedded tryptone and smectite platelets. SEM images reveal clay platelets with upwardly rolled edges that tend toward cylindrical structures with the production of occasional tubes in the smaller platelet size range as noted for organic compound-kaolinite intercalation reported by Fenoll Hach-Ali and Weiss (1969). Reference: Fenoll Hach-Ali, P.F., Weiss, A., 1969. Estudio de la reaccion de caolinita y N-metilform- amida. Quimica LXV, 769-790. Scanning electron micrograph of tryptone-intercalated clay platelets exhibiting rolled edge structure.

Characterization of Mammalian Selenoprotein O: A Redox-Active Mitochondrial Protein

PubMed Central

Yim, Sun Hee; Gladyshev, Vadim N.; Lee, Seung-Rock

2014-01-01

Selenoproteins exhibit diverse biological functions, most of which are associated with redox control. However, the functions of approximately half of mammalian selenoproteins are not known. One such protein is Selenoprotein O (SelO), the largest mammalian selenoprotein with orthologs found in a wide range of organisms, including bacteria and yeast. Here, we report characterization of mammalian SelO. Expression of this protein could be verified in HEK 293T cells by metabolic labeling of cells with 75Se, and it was abolished when selenocysteine was replaced with serine. A CxxU motif was identified in the C-terminal region of SelO. This protein was reversibly oxidized in a time- and concentration-dependent manner in HEK 293T cells when cells were treated with hydrogen peroxide. This treatment led to the formation of a transient 88 kDa SelO-containing complex. The formation of this complex was enhanced by replacing the CxxU motif with SxxC, but abolished when it was replaced with SxxS, suggesting a redox interaction of SelO with another protein through its Sec residue. SelO was localized to mitochondria and expressed across mouse tissues. Its expression was little affected by selenium deficiency, suggesting it has a high priority for selenium supply. Taken together, these results show that SelO is a redox-active mitochondrial selenoprotein. PMID:24751718

Characterization of mammalian selenoprotein o: a redox-active mitochondrial protein.

PubMed

Han, Seong-Jeong; Lee, Byung Cheon; Yim, Sun Hee; Gladyshev, Vadim N; Lee, Seung-Rock

2014-01-01

Selenoproteins exhibit diverse biological functions, most of which are associated with redox control. However, the functions of approximately half of mammalian selenoproteins are not known. One such protein is Selenoprotein O (SelO), the largest mammalian selenoprotein with orthologs found in a wide range of organisms, including bacteria and yeast. Here, we report characterization of mammalian SelO. Expression of this protein could be verified in HEK 293T cells by metabolic labeling of cells with 75Se, and it was abolished when selenocysteine was replaced with serine. A CxxU motif was identified in the C-terminal region of SelO. This protein was reversibly oxidized in a time- and concentration-dependent manner in HEK 293T cells when cells were treated with hydrogen peroxide. This treatment led to the formation of a transient 88 kDa SelO-containing complex. The formation of this complex was enhanced by replacing the CxxU motif with SxxC, but abolished when it was replaced with SxxS, suggesting a redox interaction of SelO with another protein through its Sec residue. SelO was localized to mitochondria and expressed across mouse tissues. Its expression was little affected by selenium deficiency, suggesting it has a high priority for selenium supply. Taken together, these results show that SelO is a redox-active mitochondrial selenoprotein.

Controls on the Fate and Speciation of Np(V) During Iron (Oxyhydr)oxide Crystallization.

PubMed

Bots, Pieter; Shaw, Samuel; Law, Gareth T W; Marshall, Timothy A; Mosselmans, J Frederick W; Morris, Katherine

2016-04-05

The speciation and fate of neptunium as Np(V)O2(+) during the crystallization of ferrihydrite to hematite and goethite was explored in a range of systems. Adsorption of NpO2(+) to iron(III) (oxyhydr)oxide phases was reversible and, for ferrihydrite, occurred through the formation of mononuclear bidentate surface complexes. By contrast, chemical extractions and X-ray absorption spectroscopy (XAS) analyses showed the incorporation of Np(V) into the structure of hematite during its crystallization from ferrihydrite (pH 10.5). This occurred through direct replacement of octahedrally coordinated Fe(III) by Np(V) in neptunate-like coordination. Subsequent analyses on mixed goethite and hematite crystallization products (pH 9.5 and 11) showed that Np(V) was incorporated during crystallization. Conversely, there was limited evidence for Np(V) incorporation during goethite crystallization at the extreme pH of 13.3. This is likely due to the formation of a Np(V) hydroxide precipitate preventing incorporation into the goethite particles. Overall these data highlight the complex behavior of Np(V) during the crystallization of iron(III) (oxyhydr)oxides, and demonstrate clear evidence for neptunium incorporation into environmentally important mineral phases. This extends our knowledge of the range of geochemical conditions under which there is potential for long-term immobilization of radiotoxic Np in natural and engineered environments.

UV-Vis spectrophotometry of quinone flow battery electrolyte for in situ monitoring and improved electrochemical modeling of potential and quinhydrone formation.

PubMed

Tong, Liuchuan; Chen, Qing; Wong, Andrew A; Gómez-Bombarelli, Rafael; Aspuru-Guzik, Alán; Gordon, Roy G; Aziz, Michael J

2017-12-06

Quinone-based aqueous flow batteries provide a potential opportunity for large-scale, low-cost energy storage due to their composition from earth abundant elements, high aqueous solubility, reversible redox kinetics and their chemical tunability such as reduction potential. In an operating flow battery utilizing 9,10-anthraquinone-2,7-disulfonic acid, the aggregation of an oxidized quinone and a reduced hydroquinone to form a quinhydrone dimer causes significant variations from ideal solution behavior and of optical absorption from the Beer-Lambert law. We utilize in situ UV-Vis spectrophotometry to establish (a), quinone, hydroquinone and quinhydrone molar attenuation profiles and (b), an equilibrium constant for formation of the quinhydrone dimer (K QHQ ) ∼ 80 M -1 . We use the molar optical attenuation profiles to identify the total molecular concentration and state of charge at arbitrary mixtures of quinone and hydroquinone. We report density functional theory calculations to support the quinhydrone UV-Vis measurements and to provide insight into the dimerization conformations. We instrument a quinone-bromine flow battery with a Pd-H reference electrode in order to demonstrate how complexation in both the negative (quinone) and positive (bromine) electrolytes directly impacts measured half-cell and full-cell voltages. This work shows how accounting for electrolyte complexation improves the accuracy of electrochemical modeling of flow battery electrolytes.

Gelation-driven component selection in the generation of constitutional dynamic hydrogels based on guanine-quartet formation

PubMed Central

Sreenivasachary, Nampally; Lehn, Jean-Marie

2005-01-01

The guanosine hydrazide 1 yields a stable supramolecular hydrogel based on the formation of a guanine quartet (G-quartet) in presence of metal cations. The effect of various parameters (concentration, nature of metal ion, and temperature) on the properties of this gel has been studied. Proton NMR spectroscopy is shown to allow a molecular characterization of the gelation process. Hydrazide 1 and its assemblies can be reversibly decorated by acylhydrazone formation with various aldehydes, resulting in formation of highly viscous dynamic hydrogels. When a mixture of aldehydes is used, the dynamic system selects the aldehyde that leads to the most stable gel. Mixing hydrazides 1, 9 and aldehydes 6, 8 in 1:1:1:1 ratio generated a constitutional dynamic library containing the four acylhydrazone derivatives A, B, C, and D. The library constitution displayed preferential formation of the acylhydrazone B that yields the strongest gel. Thus, gelation redirects the acylhydrazone distribution in the dynamic library as guanosine hydrazide 1 scavenges preferentially aldehyde 8, under the pressure of gelation because of the collective interactions in the assemblies of G-quartets B, despite the strong preference of the competing hydrazide 9 for 8. Gel formation and component selection are thermoreversible. The process amounts to gelation-driven self-organization with component selection and amplification in constitutional dynamic hydrogels based on G-quartet formation and reversible covalent connections. The observed self-organization and component selection occur by means of a multilevel self-assembly involving three dynamic processes, two of supramolecular and one of reversible covalent nature. They extend constitutional dynamic chemistry to phase-organization and phase-transition events. PMID:15840720

Gelation-driven component selection in the generation of constitutional dynamic hydrogels based on guanine-quartet formation.

PubMed

Sreenivasachary, Nampally; Lehn, Jean-Marie

2005-04-26

The guanosine hydrazide 1 yields a stable supramolecular hydrogel based on the formation of a guanine quartet (G-quartet) in presence of metal cations. The effect of various parameters (concentration, nature of metal ion, and temperature) on the properties of this gel has been studied. Proton NMR spectroscopy is shown to allow a molecular characterization of the gelation process. Hydrazide 1 and its assemblies can be reversibly decorated by acylhydrazone formation with various aldehydes, resulting in formation of highly viscous dynamic hydrogels. When a mixture of aldehydes is used, the dynamic system selects the aldehyde that leads to the most stable gel. Mixing hydrazides 1, 9 and aldehydes 6, 8 in 1:1:1:1 ratio generated a constitutional dynamic library containing the four acylhydrazone derivatives A, B, C, and D. The library constitution displayed preferential formation of the acylhydrazone B that yields the strongest gel. Thus, gelation redirects the acylhydrazone distribution in the dynamic library as guanosine hydrazide 1 scavenges preferentially aldehyde 8, under the pressure of gelation because of the collective interactions in the assemblies of G-quartets B, despite the strong preference of the competing hydrazide 9 for 8. Gel formation and component selection are thermoreversible. The process amounts to gelation-driven self-organization with component selection and amplification in constitutional dynamic hydrogels based on G-quartet formation and reversible covalent connections. The observed self-organization and component selection occur by means of a multilevel self-assembly involving three dynamic processes, two of supramolecular and one of reversible covalent nature. They extend constitutional dynamic chemistry to phase-organization and phase-transition events.

Dynamics of Fos-Jun-NFAT1 complexes

PubMed Central

Ramirez-Carrozzi, Vladimir R.; Kerppola, Tom K.

2001-01-01

Transcription initiation in eukaryotes is controlled by nucleoprotein complexes formed through cooperative interactions among multiple transcription regulatory proteins. These complexes may be assembled via stochastic collisions or defined pathways. We investigated the dynamics of Fos-Jun-NFAT1 complexes by using a multicolor fluorescence resonance energy transfer assay. Fos-Jun heterodimers can bind to AP-1 sites in two opposite orientations, only one of which is populated in mature Fos-Jun-NFAT1 complexes. We studied the reversal of Fos-Jun binding orientation in response to NFAT1 by measuring the efficiencies of energy transfer from donor fluorophores linked to opposite ends of an oligonucleotide to an acceptor fluorophore linked to one subunit of the heterodimer. The reorientation of Fos-Jun by NFAT1 was not inhibited by competitor oligonucleotides or heterodimers. The rate of Fos-Jun reorientation was faster than the rate of heterodimer dissociation at some binding sites. The facilitated reorientation of Fos-Jun heterodimers therefore can enhance the efficiency of Fos-Jun-NFAT1 complex formation. We also examined the influence of the preferred orientation of Fos-Jun binding on the stability and transcriptional activity of Fos-Jun-NFAT1 complexes. Complexes formed at sites where Fos-Jun favored the same binding orientation in the presence and absence of NFAT1 exhibited an 8-fold slower dissociation rate than complexes formed at sites where Fos-Jun favored the opposite binding orientation. Fos-Jun-NFAT1 complexes also exhibited greater transcription activation at promoter elements that favored the same orientation of Fos-Jun binding in the presence and absence of NFAT1. Thus, the orientation of heterodimer binding can influence both the dynamics and promoter selectivity of multiprotein transcription regulatory complexes. PMID:11320240

Dynamics of Fos-Jun-NFAT1 complexes.

PubMed

Ramirez-Carrozzi, V R; Kerppola, T K

2001-04-24

Transcription initiation in eukaryotes is controlled by nucleoprotein complexes formed through cooperative interactions among multiple transcription regulatory proteins. These complexes may be assembled via stochastic collisions or defined pathways. We investigated the dynamics of Fos-Jun-NFAT1 complexes by using a multicolor fluorescence resonance energy transfer assay. Fos-Jun heterodimers can bind to AP-1 sites in two opposite orientations, only one of which is populated in mature Fos-Jun-NFAT1 complexes. We studied the reversal of Fos-Jun binding orientation in response to NFAT1 by measuring the efficiencies of energy transfer from donor fluorophores linked to opposite ends of an oligonucleotide to an acceptor fluorophore linked to one subunit of the heterodimer. The reorientation of Fos-Jun by NFAT1 was not inhibited by competitor oligonucleotides or heterodimers. The rate of Fos-Jun reorientation was faster than the rate of heterodimer dissociation at some binding sites. The facilitated reorientation of Fos-Jun heterodimers therefore can enhance the efficiency of Fos-Jun-NFAT1 complex formation. We also examined the influence of the preferred orientation of Fos-Jun binding on the stability and transcriptional activity of Fos-Jun-NFAT1 complexes. Complexes formed at sites where Fos-Jun favored the same binding orientation in the presence and absence of NFAT1 exhibited an 8-fold slower dissociation rate than complexes formed at sites where Fos-Jun favored the opposite binding orientation. Fos-Jun-NFAT1 complexes also exhibited greater transcription activation at promoter elements that favored the same orientation of Fos-Jun binding in the presence and absence of NFAT1. Thus, the orientation of heterodimer binding can influence both the dynamics and promoter selectivity of multiprotein transcription regulatory complexes.

Children's Understanding of Ambiguous Figures: Which Cognitive Developments Are Necessary to Experience Reversal

ERIC Educational Resources Information Center

Doherty, M.J.; Wimmer, M.C.

2005-01-01

In two experiments involving one hundred and thirty-eight 3- to 5-year-olds we examined the claim that a complex understanding of ambiguity is required to experience reversal of ambiguous stimuli [Gopnik, A., & Rosati, A. (2001). Duck or rabbit? Reversing ambiguous figures and understanding ambiguous representations. Developmental Science, 4,…

Formation, spin-up, and stability of field-reversed configurations

DOE PAGES

Omelchenko, Yuri A.

2015-08-24

Formation, spontaneous spin-up and stability of theta-pinch formed field-reversed configurations are studied self-consistently in three dimensions with a multiscale hybrid model that treats all plasma ions as full-orbit collisional macro-particles and the electrons as a massless quasineutral fluid. The end-to-end hybrid simulations for the first time reveal poloidal profiles of implosion-driven fast toroidal plasma rotation and demonstrate three well-known discharge regimes as a function of experimental parameters: the decaying stable configuration, the tilt unstable configuration and the nonlinear evolution of a fast growing tearing mode.

Smart nickel oxide materials for the applications of energy efficiency and storage

NASA Astrophysics Data System (ADS)

Lin, Feng

The present dissertation studies nickel oxide-based materials for the application of electrochromic windows and lithium-air batteries. The materials were fabricated via radio frequency magnetron sputtering and subsequently post-treated with thermal evaporation and ozone exposure. The strategies to improve electrochromic performance of nickel oxide materials were investigated including compositional control, morphology tuning, modification of electronic structure and interface engineering (i.e., Li2O 2, graphene). The electrochemical properties of the resulting materials were characterized in lithium ion electrolytes. Extremely high performing nickel oxide-based electrochromic materials were obtained in terms of optical modulation, switching kinetics, bleached-state transparency and durability, which promise the implementation of these materials for practical smart windows. With the aid of advanced synchrotron X-ray absorption spectroscopy, it is reported for the first time that the electrochromic effect in multicomponent nickel oxide-based materials arises from the reversible formation of hole states in the NiO6 cluster accompanying with the reversible formation of Li2O2. The reversible formation of Li2O 2 was successfully leveraged with the study of electro-catalysts and cathode materials for lithium-air batteries. The reversibility of Li 2O2 was thoroughly investigated using soft X-ray absorption spectroscopy and theoretical simulation, which substantiates the promise of using electrochromic films as electro-catalysts and/or cathode materials in lithium-air batteries.

The active site of hydroxynitrile lyase from Prunus amygdalus: Modeling studies provide new insights into the mechanism of cyanogenesis

PubMed Central

Dreveny, Ingrid; Kratky, Christoph; Gruber, Karl

2002-01-01

The FAD-dependent hydroxynitrile lyase from almond (Prunus amygdalus, PaHNL) catalyzes the cleavage of R-mandelonitrile into benzaldehyde and hydrocyanic acid. Catalysis of the reverse reaction—the enantiospecific formation of α-hydroxynitriles—is now widely utilized in organic syntheses as one of the few industrially relevant examples of enzyme-mediated C–C bond formation. Starting from the recently determined X-ray crystal structure, systematic docking calculations with the natural substrate were used to locate the active site of the enzyme and to identify amino acid residues involved in substrate binding and catalysis. Analysis of the modeled substrate complexes supports an enzymatic mechanism that includes the flavin cofactor as a mere "spectator" of the reaction and relies on general acid/base catalysis by the conserved His-497. Stabilization of the negative charge of the cyanide ion is accomplished by a pronounced positive electrostatic potential at the binding site. PaHNL activity requires the FAD cofactor to be bound in its oxidized form, and calculations of the pKa of enzyme-bound HCN showed that the observed inactivation upon cofactor reduction is largely caused by the reversal of the electrostatic potential within the active site. The suggested mechanism closely resembles the one proposed for the FAD-independent, and structurally unrelated HNL from Hevea brasiliensis. Although the actual amino acid residues involved in the catalytic cycle are completely different in the two enzymes, a common motif for the mechanism of cyanogenesis (general acid/base catalysis plus electrostatic stabilization of the cyanide ion) becomes evident. PMID:11790839

Epitope reactions can be gauged by relative antibody discriminating specificity (RADS) values supported by deletion, substitution and cysteine bridge formation analyses: potential uses in pathogenesis studies

PubMed Central

2012-01-01

Background Epitope-mapping of infectious agents is essential for pathogenesis studies. Since polyclonal antibodies (PAbs) and monoclonal antibodies (MAbs) are always polyspecific and can react with multiple epitopes, it is important to distinguish between specific and non-specific reactions. Relative antibody discriminating specificity (RADS) values, obtained from their relative ELISA reactions with L-amino acid peptides prepared in the natural versus reverse orientations (x-fold absorbance natural/absorbance reverse = RADS value) may be valuable for this purpose. PAbs generated against the dengue type-2 virus (DENV-2) nonstructural-1 (NS1) glycoprotein candidate vaccine also reacted with both DENV envelope (E) glycoproteins and blood-clotting proteins. New xKGSx/xSGKx amino acid motifs were identified on DENV-2 glycoproteins, HIV-1 gp41 and factor IXa. Their potential roles in DENV and HIV-1 antibody-enhanced replication (AER) and auto-immunity were assessed. In this study, a) RADS values were determined for MAbs and PAbs, generated in congeneic (H2: class II) mice against DENV NS1 glycoprotein epitopes, to account for their cross-reaction patterns, and b) MAb 1G5.3 reactions with xKGSx/xSGKx motifs present in the DENV-4 NS1, E and HIV-1 glycoproteins and factor IXa were assessed after the introduction of amino acid substitutions, deletions, or intra-/inter-cysteine (C-C) bridges. Results MAbs 1H7.4, 5H4.3, 3D1.4 and 1G5.3 had high (4.23- to 16.83-fold) RADS values against single epitopes on the DENV-2 NS1 glycoprotein, and MAb 3D1.4 defined the DENV complex-conserved LX1 epitope. In contrast, MAbs 1G5.4-A1-C3 and 1C6.3 had low (0.47- to 1.67-fold) RADS values against multiple epitopes. PAb DENV complex-reactions occurred through moderately-high (2.77- and 3.11-fold) RADS values against the LX1 epitope. MAb 1G5.3 reacted with xSGKx motifs present in DENV-4 NS1 and E glycoproteins, HIV-1 gp41 and factor IXa, while natural C-C bridge formations or certain amino acid substitutions increased its binding activity. Conclusions These results: i) were readily obtained using a standard 96-well ELISA format, ii) showed the LX1 epitope to be the immuno-dominant DENV complex determinant in the NS1 glycoprotein, iii) supported an antigenic co-evolution of the DENV NS1 and E glycoproteins, and iv) identified methods that made it possible to determine the role of anti-DENV PAb reactions in viral pathogenesis. PMID:22546090

Bidirectional juxtacrine ephrinB2/Ephs signaling promotes angiogenesis of ECs and maintains self-renewal of MSCs.

PubMed

Cao, Cen; Huang, Ying; Tang, Qingming; Zhang, Chenguang; Shi, Lei; Zhao, Jiajia; Hu, Li; Hu, Zhewen; Liu, Yun; Chen, Lili

2018-07-01

Co-transplantation of endothelial cells (ECs) and mesenchymal stem cells (MSCs) is an important strategy for repairing complex and large bone defects. However, the ways in which ECs and MSCs interact remain to be fully clarified. We found that forward ephrinB2/Ephs signaling from hBMSCs to hUVECs promoted the tube formation of hUVECs by activating the PI3K/AKT/mTOR pathway. Reverse ephrinB2/Ephs signaling from hUVECs to hBMSCs promoted the proliferation and maintenance of hBMSCs self-renewal via upregulation of OCT4, SOX2, and YAP1. Subcutaneous co-transplantation of ECs and MSCs in nude mice confirmed that forward ephrinB2/Ephs signaling could increase the cross-sectional area of blood vessels in the transplanted area, and reverse ephrinB2/Ephs signaling could maintain the self-renewal of transplanted hBMSCs in vivo. Based on these results, ephrinB2/Ephs bidirectional juxtacrine regulation between ECs and MSCs plays a pivotal role in improving the healing of bone defects by promoting angiogenesis and achieving a sufficient number of MSCs. Copyright © 2018 Elsevier Ltd. All rights reserved.

Pressure-Responsive, Surfactant-Free CO2-Based Nanostructured Fluids

PubMed Central

2017-01-01

Microemulsions are extensively used in advanced material and chemical processing. However, considerable amounts of surfactant are needed for their formulation, which is a drawback due to both economic and ecological reasons. Here, we describe the nanostructuration of recently discovered surfactant-free, carbon dioxide (CO2)-based microemulsion-like systems in a water/organic-solvent/CO2 pressurized ternary mixture. “Water-rich” nanodomains embedded into a “water-depleted” matrix have been observed and characterized by the combination of Raman spectroscopy, molecular dynamics simulations, and small-angle neutron scattering. These single-phase fluids show a reversible, pressure-responsive nanostructuration; the “water-rich” nanodomains at a given pressure can be instantaneously degraded/expanded by increasing/decreasing the pressure, resulting in a reversible, rapid, and homogeneous mixing/demixing of their content. This pressure-triggered responsiveness, together with other inherent features of these fluids, such as the absence of any contaminant in the ternary mixture (e.g., surfactant), their spontaneous formation, and their solvation capability (enabling the dissolution of both hydrophobic and hydrophilic molecules), make them appealing complex fluid systems to be used in molecular material processing and in chemical engineering. PMID:28846386

Iridium-Catalyzed Hydrogen Transfer Reactions

NASA Astrophysics Data System (ADS)

Saidi, Ourida; Williams, Jonathan M. J.

This chapter describes the application of iridium complexes to catalytic hydrogen transfer reactions. Transfer hydrogenation reactions provide an alternative to direct hydrogenation for the reduction of a range of substrates. A hydrogen donor, typically an alcohol or formic acid, can be used as the source of hydrogen for the reduction of carbonyl compounds, imines, and alkenes. Heteroaromatic compounds and even carbon dioxide have also been reduced by transfer hydrogenation reactions. In the reverse process, the oxidation of alcohols to carbonyl compounds can be achieved by iridium-catalyzed hydrogen transfer reactions, where a ketone or alkene is used as a suitable hydrogen acceptor. The reversible nature of many hydrogen transfer processes has been exploited for the racemization of alcohols, where temporary removal of hydrogen generates an achiral ketone intermediate. In addition, there is a growing body of work where temporary removal of hydrogen provides an opportunity for using alcohols as alkylating agents. In this chemistry, an iridium catalyst "borrows" hydrogen from an alcohol to give an aldehyde or ketone intermediate, which can be transformed into either an imine or alkene under the reaction conditions. Return of the hydrogen from the catalyst provides methodology for the formation of amines or C-C bonds where the only by-product is typically water.

Low-temperature thermally regenerative electrochemical system

DOEpatents

Loutfy, R.O.; Brown, A.P.; Yao, N.P.

1982-04-21

A thermally regenerative electrochemical system is described including an electrochemical cell with two water-based electrolytes separated by an ion exchange membrane, at least one of the electrolytes containing a complexing agent and a salt of a multivalent metal whose respective order of potentials for a pair of its redox couples is reversible by a change in the amount of the ocmplexing agent in the electrolyte, the complexing agent being removable by distillation to cause the reversal.

Structure of a group II intron in complex with its reverse transcriptase.

PubMed

Qu, Guosheng; Kaushal, Prem Singh; Wang, Jia; Shigematsu, Hideki; Piazza, Carol Lyn; Agrawal, Rajendra Kumar; Belfort, Marlene; Wang, Hong-Wei

2016-06-01

Bacterial group II introns are large catalytic RNAs related to nuclear spliceosomal introns and eukaryotic retrotransposons. They self-splice, yielding mature RNA, and integrate into DNA as retroelements. A fully active group II intron forms a ribonucleoprotein complex comprising the intron ribozyme and an intron-encoded protein that performs multiple activities including reverse transcription, in which intron RNA is copied into the DNA target. Here we report cryo-EM structures of an endogenously spliced Lactococcus lactis group IIA intron in its ribonucleoprotein complex form at 3.8-Å resolution and in its protein-depleted form at 4.5-Å resolution, revealing functional coordination of the intron RNA with the protein. Remarkably, the protein structure reveals a close relationship between the reverse transcriptase catalytic domain and telomerase, whereas the active splicing center resembles the spliceosomal Prp8 protein. These extraordinary similarities hint at intricate ancestral relationships and provide new insights into splicing and retromobility.

Examining the base stacking interaction in a dinucleotide context via reversible cyclobutane dimer analogue formation under UV irradiation.

PubMed

Liu, Degang; Li, Lei

2013-11-14

Substituted tolyl groups are considered as close isosteres of the thymine (T) residue. They can be recognized by DNA polymerases as if they were thymine. Although these toluene derivatives are relatively inert toward radical additions, our recent finding suggests that the dinucleotide analogue TpTo (To = 2'-deoxy-1-(3-tolyl)-β-D-ribofuranose) supports an ortho photocycloaddition reaction upon UV irradiation, producing two cyclobutane pyrimidine dimer (CPD) analogues 2 and 3 . Our report here further shows that formation of these CPD species is reversible under UVC irradiation, resembling the photochemical property of the CPD species formed between two Ts. Analyzing the stability of these CPD analogues suggests that one ( 2 ) is more stable than the other ( 3 ). The TpTo conformer responsible for 2 formation is also more stable than that responsible for 3 formation, as indicated by the Gibbs free energy change calculated from the constructed Bordwell thermodynamic cycle. These different stabilities are not due to the varying photochemical properties, as proved by quantum yields determined from the corresponding photoreactions. Instead, they are ascribed to the different stacking interaction between the T and the To rings both in the TpTo dinucleotide as well as in the formed CPD analogues. Factors contributing to the ring stacking interactions are also discussed. Our proof-of-concept approach suggests that a carefully designed Bordwell cycle coupled with reversible CPD formations under UV irradiation can be very useful in studying DNA base interactions.

Examining the base stacking interaction in a dinucleotide context via reversible cyclobutane dimer analogue formation under UV irradiation

PubMed Central

Liu, Degang; Li, Lei

2013-01-01

Substituted tolyl groups are considered as close isosteres of the thymine (T) residue. They can be recognized by DNA polymerases as if they were thymine. Although these toluene derivatives are relatively inert toward radical additions, our recent finding suggests that the dinucleotide analogue TpTo (To = 2'-deoxy-1-(3-tolyl)-β-D-ribofuranose) supports an ortho photocycloaddition reaction upon UV irradiation, producing two cyclobutane pyrimidine dimer (CPD) analogues 2 and 3. Our report here further shows that formation of these CPD species is reversible under UVC irradiation, resembling the photochemical property of the CPD species formed between two Ts. Analyzing the stability of these CPD analogues suggests that one (2) is more stable than the other (3). The TpTo conformer responsible for 2 formation is also more stable than that responsible for 3 formation, as indicated by the Gibbs free energy change calculated from the constructed Bordwell thermodynamic cycle. These different stabilities are not due to the varying photochemical properties, as proved by quantum yields determined from the corresponding photoreactions. Instead, they are ascribed to the different stacking interaction between the T and the To rings both in the TpTo dinucleotide as well as in the formed CPD analogues. Factors contributing to the ring stacking interactions are also discussed. Our proof-of-concept approach suggests that a carefully designed Bordwell cycle coupled with reversible CPD formations under UV irradiation can be very useful in studying DNA base interactions. PMID:24223299

An aqueous rechargeable formate-based hydrogen battery driven by heterogeneous Pd catalysis.

PubMed

Bi, Qing-Yuan; Lin, Jian-Dong; Liu, Yong-Mei; Du, Xian-Long; Wang, Jian-Qiang; He, He-Yong; Cao, Yong

2014-12-01

The formate-based rechargeable hydrogen battery (RHB) promises high reversible capacity to meet the need for safe, reliable, and sustainable H2 storage used in fuel cell applications. Described herein is an additive-free RHB which is based on repetitive cycles operated between aqueous formate dehydrogenation (discharging) and bicarbonate hydrogenation (charging). Key to this truly efficient and durable H2 handling system is the use of highly strained Pd nanoparticles anchored on graphite oxide nanosheets as a robust and efficient solid catalyst, which can facilitate both the discharging and charging processes in a reversible and highly facile manner. Up to six repeated discharging/charging cycles can be performed without noticeable degradation in the storage capacity. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

[Molecular mechanisms in sex determination: from gene regulation to pathology].

PubMed

Ravel, C; Chantot-Bastaraud, S; Siffroi, J-P

2004-01-01

Testis determination is the complex process by which the bipotential gonad becomes a normal testis during embryo development. As a consequence, this process leads to sexual differentiation corresponding to the masculinization of both genital track and external genitalia. The whole phenomenon is under genetic control and is particularly driven by the presence of the Y chromosome and by the SRY gene, which acts as the key initiator of the early steps of testis determination. However, many other autosomal genes, present in both males and females, are expressed during testis formation in a gene activation pathway, which is far to be totally elucidated. All these genes act in a dosage-sensitive manner by which quantitative gene abnormalities, due to chromosomal deletions, duplications or mosaicism, may lead to testis determination failure and sex reversal.

A supramolecular miktoarm star polymer based on porphyrin metal complexation in water.

PubMed

Hou, Zhanyao; Dehaen, Wim; Lyskawa, Joël; Woisel, Patrice; Hoogenboom, Richard

2017-07-25

A novel supramolecular miktoarm star polymer was successfully constructed in water from a pyridine end-decorated polymer (Py-PmDEGA) and a metalloporphyrin based star polymer (ZnTPP-(PEG) 4 ) via metal-ligand coordination. The Py-PmDEGA moiety was prepared via a combination of reversible addition-fragmentation chain transfer polymerization (RAFT) and subsequent aminolysis and Michael addition reactions to introduce the pyridine end-group. The ZnTPP(PEG) 4 star-polymer was synthesized by the reaction between tetrakis(p-hydroxyphenyl)porphyrin and toluenesulfonyl-PEG, followed by insertion of a zinc ion into the porphyrin core. The formation of a well-defined supramolecular AB 4 -type miktoarm star polymer was unambiguously demonstrated via UV-Vis spectroscopic titration, isothermal titration calorimetry (ITC) and diffusion ordered NMR spectroscopy (DOSY).

Homogeneously catalysed conversion of aqueous formaldehyde to H2 and carbonate.

PubMed

Trincado, M; Sinha, Vivek; Rodriguez-Lugo, Rafael E; Pribanic, Bruno; de Bruin, Bas; Grützmacher, Hansjörg

2017-04-28

Small organic molecules provide a promising solution for the requirement to store large amounts of hydrogen in a future hydrogen-based energy system. Herein, we report that diolefin-ruthenium complexes containing the chemically and redox non-innocent ligand trop 2 dad catalyse the production of H 2 from formaldehyde and water in the presence of a base. The process involves the catalytic conversion to carbonate salt using aqueous solutions and is the fastest reported for acceptorless formalin dehydrogenation to date. A mechanism supported by density functional theory calculations postulates protonation of a ruthenium hydride to form a low-valent active species, the reversible uptake of dihydrogen by the ligand and active participation of both the ligand and the metal in substrate activation and dihydrogen bond formation.

Reverse engineering by design: using history to teach.

PubMed

Fagette, Paul

2013-01-01

Engineering students rarely have an opportunity to delve into the historic antecedents of design in their craft, and this is especially true for biomedical devices. The teaching emphasis is always on the new, the innovative, and the future. Even so, over the last decade, I have coupled a research agenda with engineering special projects into a successful format that allows young biomedical engineering students to understand aspects of their history and learn the complexities of design. There is value in having knowledge of historic engineering achievements, not just for an appreciation of these accomplishments but also for understanding exactly how engineers and clinicians of the day executed their feats-in other words, how the design process works. Ultimately, this particular educational odyssey confirms that history and engineering education are not only compatible but mutually supportive.

A general method to eliminate laboratory induced recombinants during massive, parallel sequencing of cDNA library.

PubMed

Waugh, Caryll; Cromer, Deborah; Grimm, Andrew; Chopra, Abha; Mallal, Simon; Davenport, Miles; Mak, Johnson

2015-04-09

Massive, parallel sequencing is a potent tool for dissecting the regulation of biological processes by revealing the dynamics of the cellular RNA profile under different conditions. Similarly, massive, parallel sequencing can be used to reveal the complexity of viral quasispecies that are often found in the RNA virus infected host. However, the production of cDNA libraries for next-generation sequencing (NGS) necessitates the reverse transcription of RNA into cDNA and the amplification of the cDNA template using PCR, which may introduce artefact in the form of phantom nucleic acids species that can bias the composition and interpretation of original RNA profiles. Using HIV as a model we have characterised the major sources of error during the conversion of viral RNA to cDNA, namely excess RNA template and the RNaseH activity of the polymerase enzyme, reverse transcriptase. In addition we have analysed the effect of PCR cycle on detection of recombinants and assessed the contribution of transfection of highly similar plasmid DNA to the formation of recombinant species during the production of our control viruses. We have identified RNA template concentrations, RNaseH activity of reverse transcriptase, and PCR conditions as key parameters that must be carefully optimised to minimise chimeric artefacts. Using our optimised RT-PCR conditions, in combination with our modified PCR amplification procedure, we have developed a reliable technique for accurate determination of RNA species using NGS technology.

Edoxaban effects on bleeding following punch biopsy and reversal by a 4-factor prothrombin complex concentrate.

PubMed

Zahir, Hamim; Brown, Karen S; Vandell, Alexander G; Desai, Madhuri; Maa, Jen-Fue; Dishy, Victor; Lomeli, Barbara; Feussner, Annette; Feng, Wenqin; He, Ling; Grosso, Michael A; Lanz, Hans J; Antman, Elliott M

2015-01-06

The oral factor Xa inhibitor edoxaban has demonstrated safety and efficacy in stroke prevention in patients with atrial fibrillation and in the treatment and secondary prevention of venous thromboembolism. This study investigated the reversal of edoxaban's effects on bleeding measures and biomarkers by using a 4-factor prothrombin complex concentrate (4F-PCC). This was a phase 1 study conducted at a single site. This was a double-blind, randomized, placebo-controlled, 2-way crossover study to determine the reversal effect of descending doses of 4F-PCC on bleeding duration and bleeding volume following edoxaban treatment. A total of 110 subjects (17 in part 1, 93 in part 2) were treated. Intravenous administration of 4F-PCC 50, 25, or 10 IU/kg following administration of edoxaban (60 mg) dose-dependently reversed edoxaban's effects on bleeding duration and endogenous thrombin potential, with complete reversal at 50 IU/kg. Effects on prothrombin time were partially reversed at 50 IU/kg. A similar trend was seen for bleeding volume. The 4F-PCC dose-dependently reversed the effects of edoxaban (60 mg), with complete reversal of bleeding duration and endogenous thrombin potential and partial reversal of prothrombin time following 50 IU/kg. Edoxaban alone and in combination with 4F-PCC was safe and well tolerated in these healthy subjects. A dose of 50 IU/kg 4F-PCC may be suitable for reversing edoxaban anticoagulation. http://www.clinicaltrials.gov. Unique identifier: NCT02047565. © 2014 American Heart Association, Inc.

Reverse osmosis water purification system

NASA Technical Reports Server (NTRS)

Ahlstrom, H. G.; Hames, P. S.; Menninger, F. J.

1986-01-01

A reverse osmosis water purification system, which uses a programmable controller (PC) as the control system, was designed and built to maintain the cleanliness and level of water for various systems of a 64-m antenna. The installation operates with other equipment of the antenna at the Goldstone Deep Space Communication Complex. The reverse osmosis system was designed to be fully automatic; with the PC, many complex sequential and timed logic networks were easily implemented and are modified. The PC monitors water levels, pressures, flows, control panel requests, and set points on analog meters; with this information various processes are initiated, monitored, modified, halted, or eliminated as required by the equipment being supplied pure water.

Sub-surface structures and collapse mechanisms of summit pit craters

NASA Astrophysics Data System (ADS)

Roche, O.; van Wyk de Vries, B.; Druitt, T. H.

2001-01-01

Summit pit craters are found in many types of volcanoes and are generally thought to be the product of collapse into an underpressured reservoir caused by magma withdrawal. We investigate the mechanisms and structures associated with summit pit crater formation by scaled analogue experiments and make comparisons with natural examples. Models use a sand plaster mixture as analogue rock over a cylinder of silicone simulating an underpressured magma reservoir. Experiments are carried out using different roof aspect ratios (roof thickness/roof width) of 0.2-2. They reveal two basic collapse mechanisms, dependant on the roof aspect ratio. One occurs at low aspect ratios (≤1), as illustrated by aspect ratios of 0.2 and 1. Outward dipping reverse faults initiated at the silicone margins propagates through the entire roof thickness and cause subsidence of a coherent block. Collapse along the reverse faults is accommodated by marginal flexure of the block and tension fractures at the surface (aspect ratio of 0.2) or by the creation of inward dipping normal faults delimiting a terrace (aspect ratio of 1). At an aspect ratio of 1, overhanging pit walls are the surface expressions of the reverse faults. Experiments at high aspect ratio (>1.2) reveal a second mechanism. In this case, collapse occurs by stopping, which propagates upwards by a complex pattern of both reverse faults and tension fractures. The initial underground collapse is restricted to a zone above the reservoir and creates a cavity with a stable roof above it. An intermediate mechanism occurs at aspect ratios of 1.1-1.2. In this case, stopping leads to the formation of a cavity with a thin and unstable roof, which collapses suddenly. The newly formed depression then exhibits overhanging walls. Surface morphology and structure of natural examples, such as the summit pit craters at Masaya Volcano, Nicaragua, have many of the features created in the models, indicating that the internal structural geometry of experiments can be applied to real examples. In particular, the surface area and depth of the underpressured reservoir can be roughly estimated. We present a morphological analysis of summit pit craters at volcanoes such as Kilimanjaro (Tanzania), San Cristobal, Telica and Masaya (Nicaragua), and Ubinas (Peru), and indicate a likely type of subsidence and possible position of the former magma reservoir responsible for collapse in each case.

A Highly Reversible Room-Temperature Sodium Metal Anode

PubMed Central

2015-01-01

Owing to its low cost and high natural abundance, sodium metal is among the most promising anode materials for energy storage technologies beyond lithium ion batteries. However, room-temperature sodium metal anodes suffer from poor reversibility during long-term plating and stripping, mainly due to formation of nonuniform solid electrolyte interphase as well as dendritic growth of sodium metal. Herein we report for the first time that a simple liquid electrolyte, sodium hexafluorophosphate in glymes (mono-, di-, and tetraglyme), can enable highly reversible and nondendritic plating–stripping of sodium metal anodes at room temperature. High average Coulombic efficiencies of 99.9% were achieved over 300 plating–stripping cycles at 0.5 mA cm–2. The long-term reversibility was found to arise from the formation of a uniform, inorganic solid electrolyte interphase made of sodium oxide and sodium fluoride, which is highly impermeable to electrolyte solvent and conducive to nondendritic growth. As a proof of concept, we also demonstrate a room-temperature sodium–sulfur battery using this class of electrolytes, paving the way for the development of next-generation, sodium-based energy storage technologies. PMID:27163006

A Highly Reversible Room-Temperature Sodium Metal Anode.

PubMed

Seh, Zhi Wei; Sun, Jie; Sun, Yongming; Cui, Yi

2015-11-25

Owing to its low cost and high natural abundance, sodium metal is among the most promising anode materials for energy storage technologies beyond lithium ion batteries. However, room-temperature sodium metal anodes suffer from poor reversibility during long-term plating and stripping, mainly due to formation of nonuniform solid electrolyte interphase as well as dendritic growth of sodium metal. Herein we report for the first time that a simple liquid electrolyte, sodium hexafluorophosphate in glymes (mono-, di-, and tetraglyme), can enable highly reversible and nondendritic plating-stripping of sodium metal anodes at room temperature. High average Coulombic efficiencies of 99.9% were achieved over 300 plating-stripping cycles at 0.5 mA cm(-2). The long-term reversibility was found to arise from the formation of a uniform, inorganic solid electrolyte interphase made of sodium oxide and sodium fluoride, which is highly impermeable to electrolyte solvent and conducive to nondendritic growth. As a proof of concept, we also demonstrate a room-temperature sodium-sulfur battery using this class of electrolytes, paving the way for the development of next-generation, sodium-based energy storage technologies.

Temperature characteristics and magnetization mechanism of Fe1.2Co films

NASA Astrophysics Data System (ADS)

Dong, Dashun; Fang, Qingqing; Wang, Wenwen; Yang, Jingjing

2017-11-01

Fe1.2Co films with various thicknesses were prepared on glass substrates by pulsed laser deposition (PLD). The Fe1.2Co crystal structure exhibited a preferred orientation in the <1 1 0> direction. Also, we found that changing the film thickness affected its magnetic properties and the formation of its reversed nucleus. By measuring magnetism-temperature (M-T) curves under applied field cooling (FC) and zero-field cooling (ZFC), we found that the mechanism of the formation and growth of the reversed nucleus played a main role in blocking the motion of domain walls: the mechanism was competition between a ferromagnetic phase (FM) and an anti-ferromagnetic phase (AFM) at 10-300 K. Moreover, we found that the reversed nucleus blocked the motion of magnetic domains more at 10 K than at 300 K. We suggest that the reversed nucleus affects the magnetism more at low temperatures, which causes the coercivity to be higher at low temperature than at room temperature. These results will help us to understand the magnetic properties and temperature characteristics of FeCo thin films.

Trinuclear ruthenium dioxolene complexes based on the bridging ligand hexahydroxytriphenylene: electrochemistry, spectroscopy, and near-infrared electrochromic behaviour associated with a reversible seven-membered redox chain.

PubMed

Grange, Christopher S; Meijer, Anthony J H M; Ward, Michael D

2010-01-07

The trinuclear complexes [{(R2bipy)2Ru}3(mu3-HHTP)](PF6)3 [1(PF6)3, R = H; 2(PF6)3, R = 4-tBu] contain three {Ru(R2bipy)2}2+ fragments connected to the triangular tris-chelating ligand hexahydroxytriphenylene (H6HHTP). This bridging ligand contains three dioxolene-type binding sites, each of which can reversibly convert between dianionic catecholate (cat), monoanionic semiquinone (sq) or neutral quinone (q) redox states. The bridging ligand as a whole can therefore exist in seven different redox states from fully reduced [cat,cat,cat]6- through to fully oxidised, neutral [q,q,q]. Cyclic voltammetry of 1(PF6)3 in MeCN reveals six redox processes of which the three at more positive potentials (the sq/q couples) are reversible but the three at more negative potentials (the sq/cat couples) are irreversible with distorted wave shapes due to the insolubility of the reduced forms of the complex. In contrast, the more soluble complex 2(PF6)3 displays six reversible one-electron redox processes making all components of a seven-membered redox chain accessible. UV/Vis/NIR spectro-electrochemical studies reveal rich spectroscopic behaviour, with--in particular--very intense transitions in the near-IR region in many of the oxidation states associated with Ru(II)-->(dioxolene) MLCT and bridging ligand centred pi-pi* transitions. TDDFT calculations were used to analyse the electronic spectra in all seven oxidation states; the calculated spectra generally show very good agreement with experiment, which has allowed a fairly complete assignment of the low-energy transitions. The strong electrochromism of the complexes in the near-IR region has formed the basis of an optical window in which a thin film of 1(PF6)3 or 2(PF6)3 on a conductive glass surface can be reversibly and rapidly switched between redox states that alternate between strongly absorbing or near-transparent at 1100 nm, with--for 2(PF6)3--the switching being stable and reversible in water over thousands of cycles.

The group II intron maturase: a reverse transcriptase and splicing factor go hand in hand.

PubMed

Zhao, Chen; Pyle, Anna Marie

2017-12-01

The splicing of group II introns in vivo requires the assistance of a multifunctional intron encoded protein (IEP, or maturase). Each IEP is also a reverse-transcriptase enzyme that enables group II introns to behave as mobile genetic elements. During splicing or retro-transposition, each group II intron forms a tight, specific complex with its own encoded IEP, resulting in a highly reactive holoenzyme. This review focuses on the structural basis for IEP function, as revealed by recent crystal structures of an IEP reverse transcriptase domain and cryo-EM structures of an IEP-intron complex. These structures explain how the same IEP scaffold is utilized for intron recognition, splicing and reverse transcription, while providing a physical basis for understanding the evolutionary transformation of the IEP into the eukaryotic splicing factor Prp8. Copyright © 2017 Elsevier Ltd. All rights reserved.

Reverse Transfection Using Gold Nanoparticles

NASA Astrophysics Data System (ADS)

Yamada, Shigeru; Fujita, Satoshi; Uchimura, Eiichiro; Miyake, Masato; Miyake, Jun

Reverse transfection from a solid surface has the potential to deliver genes into various types of cell and tissue more effectively than conventional methods of transfection. We present a method for reverse transfection using a gold colloid (GC) as a nanoscaffold by generating nanoclusters of the DNA/reagentcomplex on a glass surface, which could then be used for the regulation of the particle size of the complex and delivery of DNA into nuclei. With this method, we have found that the conjugation of gold nanoparticles (20 nm in particle size) to the pEGFP-N1/Jet-PEI complex resulted in an increase in the intensity of fluorescence of enhanced green fluorescent protein (EGFP) (based on the efficiency of transfection) from human mesenchymal stem cells (hMSCs), as compared with the control without GC. In this manner, we constructed a method for reverse transfection using GC to deliver genes into the cells effectively.

Attractive design: an elution solvent optimization platform for magnetic-bead-based fractionation using digital microfluidics and design of experiments.

PubMed

Lafrenière, Nelson M; Mudrik, Jared M; Ng, Alphonsus H C; Seale, Brendon; Spooner, Neil; Wheeler, Aaron R

2015-04-07

There is great interest in the development of integrated tools allowing for miniaturized sample processing, including solid phase extraction (SPE). We introduce a new format for microfluidic SPE relying on C18-functionalized magnetic beads that can be manipulated in droplets in a digital microfluidic platform. This format provides the opportunity to tune the amount (and potentially the type) of stationary phase on-the-fly, and allows the removal of beads after the extraction (to enable other operations in same device-space), maintaining device reconfigurability. Using the new method, we employed a design of experiments (DOE) operation to enable automated on-chip optimization of elution solvent composition for reversed phase SPE of a model system. Further, conditions were selected to enable on-chip fractionation of multiple analytes. Finally, the method was demonstrated to be useful for online cleanup of extracts from dried blood spot (DBS) samples. We anticipate this combination of features will prove useful for separating a wide range of analytes, from small molecules to peptides, from complex matrices.

Low-Dimensional Oxygen Vacancy Ordering and Diffusion in SrCrO 3$-$δ

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ong, Phuong-Vu; Du, Yingge; Sushko, Peter V.

2017-04-06

We investigate the formation mechanisms of vacancy-ordered phase and collective mass transport in epitaxial SrCrO 3$-$δ films using ab initio simulations within the density functional theory formalism. We show that as concentration of oxygen vacancies (V O’s) increases, they form one-dimensional (1D) chains that feature Cr-centered tetrahedra. Aggregation of these 1D V O-chains results in the formation of (111)-oriented oxygen-deficient planes (V O-planes) and an extended vacancy-ordered phase observed in recent experiments. We discuss atomic scale mechanisms enabling the quasi-2D V O aggregates to expand along and translate across (111) planes. The corresponding lowest activation energy pathways necessarily involve rotationmore » of Cr-centered tetrahedra, which emerges as a universal feature of fast ionic conduction in complex oxides. These findings explain reversible oxidation and reduction in SrCrO 3$-$δ at low-temperatures and provide insights into transient behavior necessary to harness ionic conductive oxides for high performance and low-temperature electrochemical reactors.« less

Stimuli-responsive supramolecular micellar assemblies of cetylpyridinium chloride with cucurbit[5/7]urils.

PubMed

Choudhury, Sharmistha Dutta; Barooah, Nilotpal; Aswal, Vinod Kumar; Pal, Haridas; Bhasikuttan, Achikanath C; Mohanty, Jyotirmayee

2014-05-21

This article demonstrates, for the first time, construction of novel cucurbituril (CB)-adorned supramolecular micellar assemblies of a cationic surfactant, cetylpyridinium chloride (CPC), through noncovalent host-guest interactions. The distinct cation receptor features and cavity dimensions of the CB5 and CB7 homologues assert that the macrocyclic hosts remain complexed with the CPC monomers and take part in the micelle formation, a unique observation in contrast to that of the classical host, β-cyclodextrin. The cooperative contributions of the CB macrocycles in the micelle formation have been documented by the photochemical, surface tension, conductivity, DOSY NMR, and SANS measurements. The contrasting downward and upward shifts in the cmc of the CPC surfactant, respectively, with CB5 and CB7 hosts provide a unique opportunity for the controlled tuning of the micellization region for CPC from 0.57 to 1.6 mM, by using a combination of the macrocyclic hosts. The article also establishes the reversible response of these soft supramolecular micellar structures to thermal-stimuli, which projects their utility for on-demand smart drug-delivery vehicles.

Effects of various chemical compounds on spontaneous and hydrogen peroxide-induced reversion in strain TA104 of Salmonella typhimurium.

PubMed

Han, J S

1992-04-01

In experiments designed to determine which active oxygen species contribute to hydrogen peroxide (HP)-induced reversion in strain TA104 of Salmonella typhimurium, 1,10-phenanthroline (an iron chelator, which prevents the formation of hydroxyl radicals from HP and DNA-bound iron by the Fenton reaction), sodium azide (a singlet oxygen scavenger), and potassium iodide (an hydroxyl radical scavenger) inhibited HP-induced reversion. These results indicate that hydroxyl radicals generated from HP by the Fenton reaction, and perhaps singlet oxygen, contribute to HP-induced reversion in TA104. However, reduced glutathione (reduces Fe3+ to Fe2+ and/or HP to water), diethyldithiocarbamic acid (an inhibitor of superoxide dismutase), diethyl maleate (a glutathione scavenger), and 3-amino-1,2,4-triazole (an inhibitor of catalase) did not inhibit HP-induced reversion in TA104. Thus, superoxide radical anions and HP itself do not appear to be the cause of HP-induced reversion in this strain. In experiments on the effect of 5 common dietary compounds (beta-carotene, retinoic acid, and vitamins A, C and E), chlorophyllin (CHL), and ergothioneine, the frequency of revertants in TA104 increased above the spontaneous frequency in the presence of beta-carotene or vitamin C (about 2-fold) or vitamin A (about 3-fold). The 5 dietary antimutagens and CHL did not inhibit HP-induced reversion in TA104. However, L-ergothioneine inhibited HP-induced reversion in this strain. Therefore, it is likely that L-ergothioneine is a scavenger of hydroxyl radicals or an inhibitor of their formation, and perhaps of singlet oxygen, at the concentrations tested in TA104.

Chiral Symmetry Breaking in Peptide Systems During Formation of Life on Earth.

PubMed

Konstantinov, Konstantin K; Konstantinova, Alisa F

2018-03-01

Chiral symmetry breaking in complex chemical systems with a large number of amino acids and a large number of similar reactions was considered. It was shown that effective averaging over similar reaction channels may result in very weak effective enantioselectivity of forward reactions, which does not allow most of the known models to result in chiral symmetry breaking during formation of life on Earth. Models with simple and catalytic synthesis of a single amino acid, formation of peptides up to length five, and sedimentation of insoluble pair of substances were considered. It was shown that depending on the model and the values of the parameters, chiral symmetry breaking may occur in up to about 10% out of all possible unique insoluble pair combinations even in the absence of any catalytic synthesis and that minimum total number of amino acids in the pair is 5. If weak enantioselective forward catalytic synthesis of amino acids is present, then the number of possible variants, in which chiral symmetry breaking may occur, increases substantially. It was shown that that the most interesting catalysts have zero or one amino acid of "incorrect" chirality. If the parameters of the model are adjusted in such a way to result in an increase of concentration of longer peptides, then catalysts with two amino acids of incorrect chirality start to appear at peptides of length five. Models of chiral symmetry breaking in the presence of epimerization were considered for peptides up to length three. It was shown that the range of parameters in which chiral symmetry breaking could occur significantly shrinks in comparison to previously considered models with peptides up to length two. An experiment of chiral symmetry breaking was proposed. The experiment consists of a three-step cycle: reversible catalytic synthesis of amino acids, reversible synthesis of peptides, and irreversible sedimentation of insoluble substances.

Chiral Symmetry Breaking in Peptide Systems During Formation of Life on Earth

NASA Astrophysics Data System (ADS)

Konstantinov, Konstantin K.; Konstantinova, Alisa F.

2018-03-01

Chiral symmetry breaking in complex chemical systems with a large number of amino acids and a large number of similar reactions was considered. It was shown that effective averaging over similar reaction channels may result in very weak effective enantioselectivity of forward reactions, which does not allow most of the known models to result in chiral symmetry breaking during formation of life on Earth. Models with simple and catalytic synthesis of a single amino acid, formation of peptides up to length five, and sedimentation of insoluble pair of substances were considered. It was shown that depending on the model and the values of the parameters, chiral symmetry breaking may occur in up to about 10% out of all possible unique insoluble pair combinations even in the absence of any catalytic synthesis and that minimum total number of amino acids in the pair is 5. If weak enantioselective forward catalytic synthesis of amino acids is present, then the number of possible variants, in which chiral symmetry breaking may occur, increases substantially. It was shown that that the most interesting catalysts have zero or one amino acid of "incorrect" chirality. If the parameters of the model are adjusted in such a way to result in an increase of concentration of longer peptides, then catalysts with two amino acids of incorrect chirality start to appear at peptides of length five. Models of chiral symmetry breaking in the presence of epimerization were considered for peptides up to length three. It was shown that the range of parameters in which chiral symmetry breaking could occur significantly shrinks in comparison to previously considered models with peptides up to length two. An experiment of chiral symmetry breaking was proposed. The experiment consists of a three-step cycle: reversible catalytic synthesis of amino acids, reversible synthesis of peptides, and irreversible sedimentation of insoluble substances.

Bile Salt Mediated Growth of Reverse Wormlike Micelles in Nonpolar Liquids

NASA Astrophysics Data System (ADS)

Tung, Shih-Huang; Huang, Yi-En; Raghavan, Srinivasa

2006-03-01

We report the growth of reverse wormlike micelles induced by the addition of a bile salt in trace amounts to solutions of the phospholipid, lecithin in nonpolar organic solvents. Previous recipes for reverse wormlike micelles have usually required the addition of water to induce reverse micellar growth; here, we show that bile salts, due to their unique ``facially amphiphilic'' structure, can play a role analogous to water and promote the longitudinal aggregation of lecithin molecules into reverse micellar chains. The formation of transient entangled networks of these reverse micelles transforms low-viscosity lecithin organosols into strongly viscoelastic fluids. The zero-shear viscosity increases by more than five orders of magnitude, and it is the molar ratio of bile salt to lecithin that controls this viscosity enhancement. The growth of reverse wormlike micelles is also confirmed by small-angle neutron scattering (SANS) experiments on these fluids.

Algorithmic Complexity. Volume II.

DTIC Science & Technology

1982-06-01

digital computers, this improvement will go unnoticed if only a few complex products are to be taken, however it can become increasingly important as...computed in the reverse order. If the products are formed moving from the top of the tree downward, and then the divisions are performed going from the...the reverse order, going up the tree. (r- a mod m means that r is the remainder when a is divided by M.) The overall running time of the algorithm is

A flavanoid component of chocolate quickly reverses an imposed memory deficit.

PubMed

Knezevic, Bogdan; Komatsuzaki, Yoshimasa; de Freitas, Emily; Lukowiak, Ken

2016-03-01

The ability to remember is influenced by environmental and lifestyle factors, such as stress and diet. A flavanol contained in chocolate, epicatechin (Epi), has been shown to enhance long-term memory (LTM) formation in Lymnaea. Combining two stressors (low-calcium pond water and crowding) blocks learning and all forms of memory; that is, this combination of environmentally relevant stressors creates a memory-unfriendly state. We tested the hypothesis that Epi will immediately reverse the memory-unfriendly state, i.e. that snails in the memory-deficit state when trained in Epi will immediately become competent to learn and form memory. We found that Epi not only reverses the memory-deficit state but also further enhances LTM formation. Thus, a naturally occurring bioactive plant compound can overcome a memory-unfriendly state. This supports the idea that bioactive substances may mitigate memory-making deficits that, for example, occur with ageing. © 2016. Published by The Company of Biologists Ltd.

High-Performance of Gas Hydrates in Confined Nanospace for Reversible CH4 /CO2 Storage.

PubMed

Casco, Mirian E; Jordá, José L; Rey, Fernando; Fauth, François; Martinez-Escandell, Manuel; Rodríguez-Reinoso, Francisco; Ramos-Fernández, Enrique V; Silvestre-Albero, Joaquín

2016-07-11

The molecular exchange of CH4 for CO2 in gas hydrates grown in confined nanospace has been evaluated for the first time using activated carbons as a host structure. The nano-confinement effects taking place inside the carbon cavities and the exceptional physicochemical properties of the carbon structure allows us to accelerate the formation and decomposition process of the gas hydrates from the conventional timescale of hours/days in artificial bulk systems to minutes in confined nanospace. The CH4 /CO2 exchange process is fully reversible with high efficiency at practical temperature and pressure conditions. Furthermore, these activated carbons can be envisaged as promising materials for long-distance natural gas and CO2 transportation because of the combination of a high storage capacity, a high reversibility, and most important, with extremely fast kinetics for gas hydrate formation and release. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Turbulence and mechanism of resistance on spheres and cylinders

NASA Technical Reports Server (NTRS)

Ahlborn, FR

1932-01-01

The nature of turbulent flow through pipes and around obstacles is analyzed and illustrated by photographs of turbulence on screens and straighteners. It is shown that the reversal of flow and of the resistance law on spheres is not explainable by Prandtl's turbulence in the boundary layer. The investigation of the analogous phenomena on the cylinder yields a reversal of the total field of flow. The very pronounced changes in pressure distribution connected with it were affirmed by manometric measurements on spheres by Professor O. Krell. The reversal in a homogenous nonvortical flow is brought about by the advance of the stable arrangement of Karman's dead air vortices toward the test object and by the substitution of an alternatingly one-sided or rotating but stable vortex formation in place of the initially symmetrical formation. This also explains the marked variations of the models.

Modelling biofilm-induced formation damage and biocide treatment in subsurface geosystems

PubMed Central

Ezeuko, C C; Sen, A; Gates, I D

2013-01-01

Biofilm growth in subsurface porous media, and its treatment with biocides (antimicrobial agents), involves a complex interaction of biogeochemical processes which provide non-trivial mathematical modelling challenges. Although there are literature reports of mathematical models to evaluate biofilm tolerance to biocides, none of these models have investigated biocide treatment of biofilms growing in interconnected porous media with flow. In this paper, we present a numerical investigation using a pore network model of biofilm growth, formation damage and biocide treatment. The model includes three phases (aqueous, adsorbed biofilm, and solid matrix), a single growth-limiting nutrient and a single biocide dissolved in the water. Biofilm is assumed to contain a single species of microbe, in which each cell can be a viable persister, a viable non-persister, or non-viable (dead). Persisters describe small subpopulation of cells which are tolerant to biocide treatment. Biofilm tolerance to biocide treatment is regulated by persister cells and includes ‘innate’ and ‘biocide-induced’ factors. Simulations demonstrate that biofilm tolerance to biocides can increase with biofilm maturity, and that biocide treatment alone does not reverse biofilm-induced formation damage. Also, a successful application of biological permeability conformance treatment involving geologic layers with flow communication is more complicated than simply engineering the attachment of biofilm-forming cells at desired sites. PMID:23164434

Thymidine phosphorylase exerts complex effects on bone resorption and formation in myeloma.

PubMed

Liu, Huan; Liu, Zhiqiang; Du, Juan; He, Jin; Lin, Pei; Amini, Behrang; Starbuck, Michael W; Novane, Nora; Shah, Jatin J; Davis, Richard E; Hou, Jian; Gagel, Robert F; Yang, Jing

2016-08-24

Myelomatous bone disease is characterized by the development of lytic bone lesions and a concomitant reduction in bone formation, leading to chronic bone pain and fractures. To understand the underlying mechanism, we investigated the contribution of myeloma-expressed thymidine phosphorylase (TP) to bone lesions. In osteoblast progenitors, TP up-regulated the methylation of RUNX2 and osterix, leading to decreased bone formation. In osteoclast progenitors, TP up-regulated the methylation of IRF8 and thereby enhanced expression of NFATc1 (nuclear factor of activated T cells, cytoplasmic 1 protein), leading to increased bone resorption. TP reversibly catalyzes thymidine into thymine and 2-deoxy-d-ribose (2DDR). Myeloma-secreted 2DDR bound to integrin αVβ3/α5β1 in the progenitors, activated PI3K (phosphoinositide 3-kinase)/Akt signaling, and increased DNMT3A (DNA methyltransferase 3A) expression, resulting in hypermethylation of RUNX2, osterix, and IRF8 This study elucidates an important mechanism for myeloma-induced bone lesions, suggesting that targeting TP may be a viable approach to healing resorbed bone in patients. Because TP overexpression is common in bone-metastatic tumors, our findings could have additional mechanistic implications. Copyright © 2016, American Association for the Advancement of Science.

Computational and biochemical characterization of two partially overlapping interfaces and multiple weak-affinity K-Ras dimers

NASA Astrophysics Data System (ADS)

Prakash, Priyanka; Sayyed-Ahmad, Abdallah; Cho, Kwang-Jin; Dolino, Drew M.; Chen, Wei; Li, Hongyang; Grant, Barry J.; Hancock, John F.; Gorfe, Alemayehu A.

2017-01-01

Recent studies found that membrane-bound K-Ras dimers are important for biological function. However, the structure and thermodynamic stability of these complexes remained unknown because they are hard to probe by conventional approaches. Combining data from a wide range of computational and experimental approaches, here we describe the structure, dynamics, energetics and mechanism of assembly of multiple K-Ras dimers. Utilizing a range of techniques for the detection of reactive surfaces, protein-protein docking and molecular simulations, we found that two largely polar and partially overlapping surfaces underlie the formation of multiple K-Ras dimers. For validation we used mutagenesis, electron microscopy and biochemical assays under non-denaturing conditions. We show that partial disruption of a predicted interface through charge reversal mutation of apposed residues reduces oligomerization while introduction of cysteines at these positions enhanced dimerization likely through the formation of an intermolecular disulfide bond. Free energy calculations indicated that K-Ras dimerization involves direct but weak protein-protein interactions in solution, consistent with the notion that dimerization is facilitated by membrane binding. Taken together, our atomically detailed analyses provide unique mechanistic insights into K-Ras dimer formation and membrane organization as well as the conformational fluctuations and equilibrium thermodynamics underlying these processes.

Optimal setups for forced-choice staircases with fixed step sizes.

PubMed

García-Pérez, M A

2000-01-01

Forced-choice staircases with fixed step sizes are used in a variety of formats whose relative merits have never been studied. This paper presents a comparative study aimed at determining their optimal format. Factors included in the study were the up/down rule, the length (number of reversals), and the size of the steps. The study also addressed the issue of whether a protocol involving three staircases running for N reversals each (with a subsequent average of the estimates provided by each individual staircase) has better statistical properties than an alternative protocol involving a single staircase running for 3N reversals. In all cases the size of a step up was different from that of a step down, in the appropriate ratio determined by García-Pérez (Vision Research, 1998, 38, 1861 - 1881). The results of a simulation study indicate that a) there are no conditions in which the 1-down/1-up rule is advisable; b) different combinations of up/down rule and number of reversals appear equivalent in terms of precision and cost: c) using a single long staircase with 3N reversals is more efficient than running three staircases with N reversals each: d) to avoid bias and attain sufficient accuracy, threshold estimates should be based on at least 30 reversals: and e) to avoid excessive cost and imprecision, the size of the step up should be between 2/3 and 3/3 the (known or presumed) spread of the psychometric function. An empirical study with human subjects confirmed the major characteristics revealed by the simulations.

Reversible mechanochromic luminescence at room temperature in cationic platinum(II) terpyridyl complexes.

PubMed

Han, Ali; Du, Pingwu; Sun, Zijun; Wu, Haotian; Jia, Hongxing; Zhang, Rui; Liang, Zhenning; Cao, Rui; Eisenberg, Richard

2014-04-07

Reversible mechanochromic luminescence in cationic platinum(II) terpyridyl complexes is described. The complexes [Pt(Nttpy)Cl]X2 (Nttpy = 4'-(p-nicotinamide-N-methylphenyl)-2,2':6',2″-terpyridine, X = PF6 (1), SbF6 (2), Cl (3), ClO4 (4), OTf (5), BF4 (6)) exhibit different colors under ambient light in the solid state, going from red to orange to yellow. All of these complexes are brightly luminescent at both room temperature and 77 K. Upon gentle grinding, the yellow complexes (4-6) turn orange and exhibit bright red luminescence. The red luminescence can be changed back to yellow by the addition of a few drops of acetonitrile to the sample. Crystallographic studies of the yellow and red forms of complex 5 suggest that the mechanochromic response is likely the result of a change in intermolecular Pt···Pt distances upon grinding.

Insights into the mechanisms of RNA secondary structure destabilization by the HIV-1 nucleocapsid protein.

PubMed

Belfetmi, Anissa; Zargarian, Loussiné; Tisné, Carine; Sleiman, Dona; Morellet, Nelly; Lescop, Ewen; Maskri, Ouerdia; René, Brigitte; Mély, Yves; Fossé, Philippe; Mauffret, Olivier

2016-04-01

The mature HIV-1 nucleocapsid protein NCp7 (NC) plays a key role in reverse transcription facilitating the two obligatory strand transfers. Several properties contribute to its efficient chaperon activity: preferential binding to single-stranded regions, nucleic acid aggregation, helix destabilization, and rapid dissociation from nucleic acids. However, little is known about the relationships between these different properties, which are complicated by the ability of the protein to recognize particular HIV-1 stem-loops, such as SL1, SL2, and SL3, with high affinity and without destabilizing them. These latter properties are important in the context of genome packaging, during which NC is part of the Gag precursor. We used NMR to investigate destabilization of the full-length TAR (trans activating response element) RNA by NC, which is involved in the first strand transfer step of reverse transcription. NC was used at a low protein:nucleotide (nt) ratio of 1:59 in these experiments. NMR data for the imino protons of TAR identified most of the base pairs destabilized by NC. These base pairs were adjacent to the loops in the upper part of the TAR hairpin rather than randomly distributed. Gel retardation assays showed that conversion from the initial TAR-cTAR complex to the fully annealed form occurred much more slowly at the 1:59 ratio than at the higher ratios classically used. Nevertheless, NC significantly accelerated the formation of the initial complex at a ratio of 1:59. © 2016 Belfetmi et al.; Published by Cold Spring Harbor Laboratory Press for the RNA Society.

N-benzoylated 1,4,8,11-tetraazacyclotetradecane and their copper(II) and nickel(II) complexes: Spectral, magnetic, electrochemical, crystal structure, catalytic and antimicrobial studies

NASA Astrophysics Data System (ADS)

Nirmala, G.; Rahiman, A. Kalilur; Sreedaran, S.; Jegadeesh, R.; Raaman, N.; Narayanan, V.

2010-09-01

A series of N-benzoylated cyclam ligands incorporating three different benzoyl groups 1,4,8,11-tetra-(benzoyl)-1,4,8,11-tetraazacyclotetradecane (L 1), 1,4,8,11-tetra-(2-nitrobenzoyl)-1,4,8,11-tetraazacyclotetradecane (L 2) and 1,4,8,11-tetra-(4-nitrobenzoyl)-1,4,8,11-tetraazacyclotetradecane (L 3) and their nickel(II) and copper(II) complexes are described. Crystal structure of L 1 is also reported. The ligands and complexes were characterized by elemental analysis, electronic, IR, 1H NMR and 13C NMR spectral studies. N-benzoylation causes red shift in the λmax values of the complexes. The cyclic voltammogram of the complexes of ligand L 1 show one-electron, quasi-reversible reduction wave in the region -1.00 to -1.04 V, whereas that of L 2 and L 3 show two quasi-reversible reduction peaks. Nickel complexes show one-electron quasi-reversible oxidation wave at a positive potential in the range +1.05 to +1.15 V. The ESR spectra of the mononuclear copper(II) complexes show four lines, characteristic of square-planar geometry with nuclear hyperfine spin 3/2. All copper(II) complexes show a normal room temperature magnetic moment values μeff 1.70-1.73 BM which is close to the spin-only value of 1.73 BM. Kinetic studies on the oxidation of pyrocatechol to o-quinone using the copper(II) complexes as catalysts and hydrolysis of 4-nitrophenylphosphate using the copper(II) and nickel(II) complexes as catalysts were carried out. All the ligands and their complexes were also screened for antimicrobial activity against Gram-positive, Gram-negative bacteria and human pathogenic fungi.

Theoretical study of the coordination behavior of formate and formamidoximate with dioxovanadium( v ) cation: implications for selectivity towards uranyl

DOE PAGES

Mehio, Nada; Johnson, J. Casey; Dai, Sheng; ...

2015-10-28

Poly(acrylamidoxime)-based fibers bearing random mixtures of carboxylate and amidoxime groups are the most widely utilized materials for extracting uranium from seawater. However, the competition between uranyl (UO 2 2+) and vanadium ions poses a significant challenge to the industrial mining of uranium from seawater using the current generation of adsorbents. To design more selective adsorbents, a detailed understanding of how major competing ions interact with carboxylate and amidoxime ligands is required. In this work, we employ density functional theory (DFT) and wave-function methods to investigate potential binding motifs of the dioxovanadium ion, VO 2 +, with water, formate, and formamidoximatemore » ligands. Employing higher level of theory calculations (CCSD(T)) resolve the existing controversy between the experimental results and previous DFT calculations for the structure of the hydrated VO 2 + ion. Consistent with the EXAFS data, CCSD(T) calculations predict higher stability of the distorted octahedral geometry of VO 2 +(H 2O) 4 compared to the five-coordinate complex with a single water molecule in the second hydration shell, while all seven tested DFT methods yield the reverse stability of the two conformations. Analysis of the relative stabilities of formate-VO 2 + complexes indicates that both monodentate and bidentate forms may coexist in thermodynamic equilibrium in solution, with the equilibrium balance leaning more towards the formation of monodentate species. Investigations of VO 2 + coordination with the formamidoximate anion has revealed the existence of seven possible binding motifs, four of which are within ~ 4.0 kcal/mol of each other. Calculations establish that the most stable binding motif entails the coordination of oxime oxygen and amide nitrogen atoms via a tautomeric rearrangement of amidoxime to imino hydroxylamine. Lastly, the difference in the most stable VO 2 + and UO 2 2+ binding conformation has important implications for the design of more selective UO 2 2+ ligands.« less

Investigation of the Dynamics of Magnetic Vortices and Antivortices Using Micromagnetic Simulations

NASA Astrophysics Data System (ADS)

Asmat-Uceda, Martin Antonio

This thesis is focused on investigating the dynamic properties of spin textures in patterned magnetic structures by using micromagnetic simulations. These textures become particularly relevant at sub-micron length scales where the interplay between magnetostatic and exchange energy leads to unique properties that are of great interest both from a fundamental perspective and for the development of new technologies. Two different systems, a magnetic antivortex (AV) stabilized in the intersection of perpendicular microwires, and three interacting vortices in an equilateral arrangement, were considered for this study. For the first system, the AV, the formation process and the excitation spectra were investigated. Since the AV is a metastable state, the design of a host structure capable of stabilizing it requires careful consideration and it is desirable to have general guidelines that could help to optimize the AV formation rate. The role of the shape anisotropy and the field dependence of the AV formation process is discussed in detail. Micromagnetic simulations along with magneto-optical Kerr effect and magnetic force microscopy measurements demonstrated that the asymmetry in the structure can be used to promote the formation of such AV's and that regions with lower shape anisotropy lead the reversal process, while simulations of the dynamic response show that when the system is excited with in-plane and out-of-plane external magnetic fields, normal modes with azimuthal and radial characteristics are found, respectively, in addition to the low frequency gyrotropic mode. The modes are influenced by the spin texture in the intersection, which offers additional possibilities for manipulating spin waves (SW). For the second system, three interacting vortices are simulated and compared with a simple analytical model that considers only dipolar interactions. It was found that when a fitting parameter is introduced to the model, the main features of the simulations are captured better than more complex models, which suggest that this simple framework can be used to accurately model more complex vortex networks.

Reversibility of temperature driven discrete layer-by-layer formation of dioctyl-benzothieno-benzothiophene films.

PubMed

Dohr, M; Ehmann, H M A; Jones, A O F; Salzmann, I; Shen, Q; Teichert, C; Ruzié, C; Schweicher, G; Geerts, Y H; Resel, R; Sferrazza, M; Werzer, O

2017-03-22

Film forming properties of semiconducting organic molecules comprising alkyl-chains combined with an aromatic unit have a decisive impact on possible applications in organic electronics. In particular, knowledge on the film formation process in terms of wetting or dewetting, and the precise control of these processes, is of high importance. In the present work, the subtle effect of temperature on the morphology and structure of dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) films deposited on silica surfaces by spin coating is investigated in situ via X-ray diffraction techniques and atomic force microscopy. Depending on temperature, bulk C8-BTBT exhibits a crystalline, a smectic A and an isotropic phase. Heating of thin C8-BTBT layers at temperatures below the smectic phase transition temperature leads to a strong dewetting of the films. Upon approaching the smectic phase transition, the molecules start to rewet the surface in the form of discrete monolayers with a defined number of monolayers being present at a given temperature. The wetting process and layer formation is well defined and thermally stable at a given temperature. On cooling the reverse effect is observed and dewetting occurs. This demonstrates the full reversibility of the film formation behavior and reveals that the layering process is defined by an equilibrium thermodynamic state, rather than by kinetic effects.

Andrographolide sodium bisulphite-induced inactivation of urease: inhibitory potency, kinetics and mechanism.

PubMed

Mo, Zhi-Zhun; Wang, Xiu-Fen; Zhang, Xie; Su, Ji-Yan; Chen, Hai-Ming; Liu, Yu-Hong; Zhang, Zhen-Biao; Xie, Jian-Hui; Su, Zi-Ren

2015-07-16

The inhibitory effect of andrographolide sodium bisulphite (ASB) on jack bean urease (JBU) and Helicobacter pylori urease (HPU) was performed to elucidate the inhibitory potency, kinetics and mechanism of inhibition in 20 mM phosphate buffer, pH 7.0, 2 mM EDTA, 25 °C. The ammonia formations, indicator of urease activity, were examined using modified spectrophotometric Berthelot (phenol-hypochlorite) method. The inhibitory effect of ASB was characterized with IC50 values. Lineweaver-Burk and Dixon plots for JBU inhibition of ASB was constructed from the kinetic data. SH-blocking reagents and competitive active site Ni2+ binding inhibitors were employed for mechanism study. Molecular docking technique was used to provide some information on binding conformations as well as confirm the inhibition mode. The IC50 of ASB against JBU and HPU was 3.28±0.13 mM and 3.17±0.34 mM, respectively. The inhibition proved to be competitive and concentration- dependent in a slow-binding progress. The rapid formation of initial ASB-JBU complex with an inhibition constant of Ki=2.86×10(-3) mM was followed by a slow isomerization into the final complex with an overall inhibition constant of Ki*=1.33×10(-4) mM. The protective experiment proved that the urease active site is involved in the binding of ASB. Thiol reagents (L-cysteine and dithiothreithol) strongly protect the enzyme from the loss of enzymatic activity, while boric acid and fluoride show weaker protection, indicating that the active-site sulfhydryl group of JBU was potentially involved in the blocking process. Moreover, inhibition of ASB proved to be reversible since ASB-inactivated JBU could be reactivated by dithiothreitol application. Molecular docking assay suggested that ASB made contacts with the important sulfhydryl group Cys-592 residue and restricted the mobility of the active-site flap. ASB was a competitive inhibitor targeting thiol groups of urease in a slow-binding manner both reversibly and concentration-dependently, serving as a promising urease inhibitor for the treatment of urease-related diseases.

HuR interacts with human immunodeficiency virus type 1 reverse transcriptase, and modulates reverse transcription in infected cells

PubMed Central

Lemay, Julie; Maidou-Peindara, Priscilla; Bader, Thomas; Ennifar, Eric; Rain, Jean-Christophe; Benarous, Richard; Liu, Lang Xia

2008-01-01

Reverse transcription of the genetic material of human immunodeficiency virus type 1 (HIV-1) is a critical step in the replication cycle of this virus. This process, catalyzed by reverse transcriptase (RT), is well characterized at the biochemical level. However, in infected cells, reverse transcription occurs in a multiprotein complex – the reverse transcription complex (RTC) – consisting of viral genomic RNA associated with viral proteins (including RT) and, presumably, as yet uncharacterized cellular proteins. Very little is known about the cellular proteins interacting with the RTC, and with reverse transcriptase in particular. We report here that HIV-1 reverse transcription is affected by the levels of a nucleocytoplasmic shuttling protein – the RNA-binding protein HuR. A direct protein-protein interaction between RT and HuR was observed in a yeast two-hybrid screen and confirmed in vitro by homogenous time-resolved fluorescence (HTRF). We mapped the domain interacting with HuR to the RNAse H domain of RT, and the binding domain for RT to the C-terminus of HuR, partially overlapping the third RRM RNA-binding domain of HuR. HuR silencing with specific siRNAs greatly impaired early and late steps of reverse transcription, significantly inhibiting HIV-1 infection. Moreover, by mutagenesis and immunoprecipitation studies, we could not detect the binding of HuR to the viral RNA. These results suggest that HuR may be involved in and may modulate the reverse transcription reaction of HIV-1, by an as yet unknown mechanism involving a protein-protein interaction with HIV-1 RT. PMID:18544151

Publisher Correction: Bottom-up linking of carbon markets under far-sighted cap coordination and reversibility

NASA Astrophysics Data System (ADS)

Heitzig, Jobst; Kornek, Ulrike

2018-06-01

In the PDF version of this Article originally published, in equation (6) gi' was incorrectly formatted as gi', and at the end of the Methods section wi was incorrectly formatted as wi. These have now been corrected.

Exciplex formation accompanied with excitation quenching.

PubMed

Fedorenko, Stanislav G; Burshtein, Anatoly I

2010-04-08

The competence of the reversible exciplex formation and parallel quenching of excitation (by electron or energy transfer) was considered using a non-Markovian pi-forms approach, identical to integral encounter theory (IET). General equations accounting for the reversible quenching and exciplex formation are derived in the contact approximation. Their general solution was obtained and adopted to the most common case when the ground state particles are in great excess. Particular cases of only photoionization or just exciplex formation separately studied earlier by means of IET are reproduced. In the case of the irreversible excitation quenching, the theory allows specifying the yields of the fluorescence and exciplex luminescence, as well as the long time kinetics of excitation and exciplex decays, in the absence of quenching. The theory distinguishes between the alternative regimes of (a) fast equilibration between excitations and exciplexes followed by their decay with a common average rate and (b) the fastest and deep excitation decay followed by the weaker and slower delayed fluorescence, backed by exciplex dissociation.

Rapid reversible borane to boryl hydride exchange by metal shuttling on the carborane cluster surface† †Electronic supplementary information (ESI) available. CCDC 1545735 and 1545736. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c7sc01846k

PubMed Central

Eleazer, Bennett J.; Smith, Mark D.

2017-01-01

In this work, we introduce a novel concept of a borane group vicinal to a metal boryl bond acting as a supporting hemilabile ligand in exohedrally metalated three-dimensional carborane clusters. The (POBOP)Ru(Cl)(PPh3) pincer complex (POBOP = 1,7-OP(i-Pr)2-m-2-carboranyl) features extreme distortion of the two-center-two-electron Ru–B bond due to the presence of a strong three-center-two-electron B–H···Ru vicinal interaction. Replacement of the chloride ligand with a hydride afforded the (POBOP)Ru(H)(PPh3) pincer complex, which possesses B–Ru, B–H···Ru, and Ru–H bonds. This complex was found to exhibit a rapid exchange between hydrogen atoms of the borane and the terminal hydride through metal center shuttling between two boron atoms of the carborane cage. This exchange process, which involves sequential cleavage and formation of strong covalent metal–boron and metal–hydrogen bonds, is unexpectedly facile at temperatures above –50 °C corresponding to an activation barrier of 12.2 kcal mol–1. Theoretical calculations suggested two equally probable pathways for the exchange process through formally Ru(0) or Ru(iv) intermediates, respectively. The presence of this hemilabile vicinal B–H···Ru interaction in (POBOP)Ru(H)(PPh3) was found to stabilize a latent coordination site at the metal center promoting efficient catalytic transfer dehydrogenation of cyclooctane under nitrogen and air at 170 °C. PMID:28970919

TCTEX1D4, a novel protein phosphatase 1 interactor: connecting the phosphatase to the microtubule network

PubMed Central

Korrodi-Gregório, Luís; Vieira, Sandra I.; Esteves, Sara L. C.; Silva, Joana V.; Freitas, Maria João; Brauns, Ann-Kristin; Luers, Georg; Abrantes, Joana; Esteves, Pedro J.; da Cruz e Silva, Odete A. B.; Fardilha, Margarida; da Cruz e Silva, Edgar F.

2013-01-01

Summary Reversible phosphorylation plays an important role as a mechanism of intracellular control in eukaryotes. PPP1, a major eukaryotic Ser/Thr-protein phosphatase, acquires its specificity by interacting with different protein regulators, also known as PPP1 interacting proteins (PIPs). In the present work we characterized a physiologically relevant PIP in testis. Using a yeast two-hybrid screen with a human testis cDNA library, we identified a novel PIP of PPP1CC2 isoform, the T-complex testis expressed protein 1 domain containing 4 (TCTEX1D4) that has recently been described as a Tctex1 dynein light chain family member. The overlay assays confirm that TCTEX1D4 interacts with the different spliced isoforms of PPP1CC. Also, the binding domain occurs in the N-terminus, where a consensus PPP1 binding motif (PPP1BM) RVSF is present. The distribution of TCTEX1D4 in testis suggests its involvement in distinct functions, such as TGFβ signaling at the blood–testis barrier and acrosome cap formation. Immunofluorescence in human ejaculated sperm shows that TCTEX1D4 is present in the flagellum and in the acrosome region of the head. Moreover, TCTEX1D4 and PPP1 co-localize in the microtubule organizing center (MTOC) and microtubules in cell cultures. Importantly, the TCTEX1D4 PPP1BM seems to be relevant for complex formation, for PPP1 retention in the MTOC and movement along microtubules. These novel results open new avenues to possible roles of this dynein, together with PPP1. In essence TCTEX1D4/PPP1C complex appears to be involved in microtubule dynamics, sperm motility, acrosome reaction and in the regulation of the blood–testis barrier. PMID:23789093

Diffusion-Limited Cargo Loading of an Engineered Protein Container.

PubMed

Zschoche, Reinhard; Hilvert, Donald

2015-12-30

The engineered bacterial nanocompartment AaLS-13 is a promising artificial encapsulation system that exploits electrostatic interactions for cargo loading. In order to study its ability to take up and retain guests, a pair of fluorescent proteins was developed which allows spectroscopic determination of the extent of encapsulation by Förster resonance energy transfer (FRET). The encapsulation process is generally complete within a second, suggesting low energetic barriers for proteins to cross the capsid shell. Formation of intermediate aggregates upon mixing host and guest in vitro complicates capsid loading at low ionic strength, but can be sidestepped by increasing salt concentrations or diluting the components. Encapsulation of guests is completely reversible, and the position of the equilibrium is easily tuned by varying the ionic strength. These results, which challenge the notion that AaLS-13 is a continuous rigid shell, provide valuable information about cargo loading that will guide ongoing efforts to engineer functional host-guest complexes. Moreover, it should be possible to adapt the protein FRET pair described in this report to characterize functional capsid-cargo complexes generated by other encapsulation systems.

Structure transition in lipids and nucleic acids of tumor cells under anticancer drugs applications

NASA Astrophysics Data System (ADS)

Dovbeshko, G. I.; Repnytska, O. P.; Tryndiak, V. P.; Todor, I. N.

2003-12-01

Interaction of DNA and phospholipids from Carcinoma Guerina resistant and sensitive cells of Wistar line rats with anti-cancer drugs - cis-platin and doxorubicin (DOX) have been studied in vivo and in vitro experiments. Surface enhanced infrared absorption (SEIRA) spectroscopy was applied for registration of conformational changes in DNA and lipids induced by anti-cancer drugs. It has been shown in vivo experiment that doxorubicin influences less structural disordering of the membrane than cis-platin. Cis-platin creates irreversible complex with memebrane phospholipids, strongly interacting with phosophates and carbohydrate chains. Doxorubicin influences the ordering of carbohydrate chains and does not strongly influence phosphate heads. This change seems to be partially reversible. In contrast, in vivo experiment the doxorubicin strongly influences the DNA structure, leading to DNA stabilization and formation of new H-bonds in DNA-doxorubicin complex. We have not registered the interaction of DNA with cis-platin in vivo experiment. Experiment in vitro for cis-platin incubation with phospholipids from cancer cells during 0.5 hour at 37°C has not shown those drastic structural peculiarities that it was observed in vivo experiments.

A Coordination Network with Ligand-Centered Redox Activity Based on facial-[CrIII (2-mercaptophenolato)3 ]3- Metalloligands.

PubMed

Wakizaka, Masanori; Matsumoto, Takeshi; Kobayashi, Atsushi; Kato, Masako; Chang, Ho-Chol

2017-07-21

The design of redox-active metal-organic frameworks and coordination networks (CNs), which exhibit metal- and/or ligand-centered redox activity, has recently received increased attention. In this study, the redox-active metalloligand (RML) [Me 4 N] 3 fac-[Cr III (mp) 3 ] (1) (mp=2-mercaptophenolato) was synthesized and characterized by single-crystal X-ray diffraction analysis, and its reversible ligand-centered one-electron oxidation was examined by cyclic voltammetry and spectroelectrochemical measurements. Since complex 1 contains O/S coordination sites in three directions, complexation with K + ions led to the formation of the two-dimensional honeycomb sheet-structured [K 3 fac-{Cr III (mp) 3 }(H 2 O) 6 ] n (2⋅6 H 2 O), which is the first example of a redox-active CN constructed from a RML with o-disubstituted benzene ligands. Herein, we unambiguously demonstrate the ligand-centered redox activity of the RML within the CN 2⋅6 H 2 O in the solid state. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

An illustration of the complexity of continent formation

NASA Technical Reports Server (NTRS)

Burke, Kevin

1988-01-01

It was pointed out that a consensus may be emerging in crustal growth models, considering the clustering of most growth curves and their uncertainties. Curves most distant from this clustering represent models involving extensive recycling of continental material back into the mantle, but the author wondered if geochemical signatures for this would be recognizable considering the lack of evidence from seismic tomography for discrete mantle reservoirs, and the likelihood of core-mantle interaction based on recent high pressure experiments. Unreactivated Archean rocks represent only 2 percent of present continental area, and the author was uncomfortable about basing inferences on what the early Earth was like on such a small amount of information. He feels that the hypothesis of continental assembly that needs testing is that of banging together of island arcs, such as in Indonesia today. As an example of how complex this process can be, the author described the geology of the Caribbean arc system, which shows evidence for reversals of subduction polarity, numerous collisional events, and substantial strike-slip movements. It seemed unlikely to the author that Archean examples would have been less complicated.

Chemical Properties of Elements 99 and 100 [Einsteinium and Fermium

DOE R&D Accomplishments Database

Seaborg, G. T.; Thompson, S. G.; Harvey, B. G.; Choppin, G. R.

1954-07-23

A description of some of the chemical properties and of the methods used in the separations of elements 99 [Einsteinium] and 100 [Fermium] are given. The new elements exhibit the properties expected for the tenth and eleventh actinide elements. Attempts to produce an oxidation state greater than III of element 99 have been unsuccessful. In normal aqueous media only the III state of element 100 appears to exist. The relative spacings of the elution peaks of the new elements in some separations with ion exchange resin columns are the same as the relative spacings of the homologous lanthanide elements. The results of experiments involving cation exchange resins with very concentrated hydrochloric acid eluant show that the new elements, like the earlier actinides, are more strongly complexed than the lanthanides. The new elements also exist partially as anions in concentrated hydrochloric acid, as do earlier actinide elements, and they may be partially separated from each other by means of ion exchange resins. With some eluants interesting reversals of elution positions are observed in the region Bk-Cf-99-100, indicating complex ion formation involving unusual factors.

A Reusable Impedimetric Aptasensor for Detection of Thrombin Employing a Graphite-Epoxy Composite Electrode

PubMed Central

Ocaña, Cristina; Pacios, Mercè; del Valle, Manel

2012-01-01

Here, we report the application of a label-free electrochemical aptasensor based on a graphite-epoxy composite electrode for the detection of thrombin; in this work, aptamers were immobilized onto the electrodes surface using wet physical adsorption. The detection principle is based on the changes of the interfacial properties of the electrode; these were probed in the presence of the reversible redox couple [Fe(CN)6]3−/[Fe(CN)6]4− using impedance measurements. The electrode surface was partially blocked due to formation of aptamer-thrombin complex, resulting in an increase of the interfacial electron-transfer resistance detected by Electrochemical Impedance Spectroscopy (EIS). The aptasensor showed a linear response for thrombin in the range of 7.5 pM to 75 pM and a detection limit of 4.5 pM. The aptasensor was regenerated by breaking the complex formed between the aptamer and thrombin using 2.0 M NaCl solution at 42 °C, showing its operation for different cycles. The interference response caused by main proteins in serum has been characterized. PMID:22736991

Single-molecule analysis of diffusion and trapping of STIM1 and Orai1 at endoplasmic reticulum–plasma membrane junctions

PubMed Central

Wu, Minnie M.; Covington, Elizabeth D.; Lewis, Richard S.

2014-01-01

Following endoplasmic reticulum (ER) Ca2+ depletion, STIM1 and Orai1 complexes assemble autonomously at ER–plasma membrane (PM) junctions to trigger store-operated Ca2+ influx. One hypothesis to explain this process is a diffusion trap in which activated STIM1 diffusing in the ER becomes trapped at junctions through interactions with the PM, and STIM1 then traps Orai1 in the PM through binding of its calcium release-activated calcium activation domain. We tested this model by analyzing STIM1 and Orai1 diffusion using single-particle tracking, photoactivation of protein ensembles, and Monte Carlo simulations. In resting cells, STIM1 diffusion is Brownian, while Orai1 is slightly subdiffusive. After store depletion, both proteins slow to the same speeds, consistent with complex formation, and are confined to a corral similar in size to ER–PM junctions. While the escape probability at high STIM:Orai expression ratios is <1%, it is significantly increased by reducing the affinity of STIM1 for Orai1 or by expressing the two proteins at comparable levels. Our results provide direct evidence that STIM-Orai complexes are trapped by their physical connections across the junctional gap, but also reveal that the complexes are surprisingly dynamic, suggesting that readily reversible binding reactions generate free STIM1 and Orai1, which engage in constant diffusional exchange with extrajunctional pools. PMID:25057023

High fat, high sucrose diet causes cardiac mitochondrial dysfunction due in part to oxidative post-translational modification of mitochondrial complex II

PubMed Central

Sverdlov, Aaron L.; Elezaby, Aly; Behring, Jessica B.; Bachschmid, Markus M.; Luptak, Ivan; Tu, Vivian H.; Siwik, Deborah A.; Miller, Edward J.; Liesa, Marc; Shirihai, Orian S; Pimentel, David R.; Cohen, Richard A.; Colucci, Wilson S.

2014-01-01

Background Diet-induced obesity leads to metabolic heart disease (MHD) characterized by increased oxidative stress that may cause oxidative post-translational modifications (OPTM) of cardiac mitochondrial proteins. The functional consequences of OPTM of cardiac mitochondrial proteins in MHD are unknown. Our objective was to determine whether cardiac mitochondrial dysfunction in MHD due to diet-induced obesity is associated with cysteine OPTM. Methods and results Male C57Bl/6J mice were fed either a high-fat, high-sucrose (HFHS) or control diet for 8 months. Cardiac mitochondria from HFHS-fed mice (vs. control diet) had an increased rate of H2O2 production, a decreased GSH/GSSG ratio, a decreased rate of complex II substrate-driven ATP synthesis and decreased complex II activity. Complex II substrate-driven ATP synthesis and complex II activity were partially restored ex-vivo by reducing conditions. A biotin switch assay showed that HFHS feeding increased cysteine OPTM in complex II subunits A (SDHA) and B (SDHB). Using iodo-TMT multiplex tags we found that HFHS feeding is associated with reversible oxidation of cysteines 89 and 231 in SDHA, and 100, 103 and 115 in SDHB. Conclusions MHD due to consumption of a HFHS “Western” diet causes increased H2O2 production and oxidative stress in cardiac mitochondria associated with decreased ATP synthesis and decreased complex II activity. Impaired complex II activity and ATP production are associated with reversible cysteine OPTM of complex II. Possible sites of reversible cysteine OPTM in SDHA and SDHB were identified by iodo-TMT tag labeling. Mitochondrial ROS may contribute to the pathophysiology of MHD by impairing the function of complex II. PMID:25109264

Syntheses, structures and selective dye adsorption of five formic-based coordination polymers prepared by in-situ hydrolysis of N, N‧-dimethylformamide

NASA Astrophysics Data System (ADS)

Zhu, Zheng; Meng, Xiang-min; Zhang, Dong-mei; Zhang, Xia; Wang, Mei; Jin, Fan; Fan, Yu-hua

2017-04-01

Five functional coordination polymers (formic-based CPs) namely: {[Cu2(CHOO)3(bibp)2]·CHOO}n (1), {[Co2(CHOO)3(bibp)2]·NO3·H2O}n (2), {[Ni2(CHOO)3(bibp)2]·NO3·H2O}n (3) [Co(CHOO)2(bbibp)]n (4) and [Zn(CHOO)2(bbibp)]n (5) (bibp=4,4‧-bis(imidazolyl)biphenyl, bbibp=4,4‧-bis(benzoimidazo-1-yl)biphenyl) have been successfully hydrothermally synthesized using the in-situ hydrolysis of N, N‧-dimethylformamide (DMF) as the source of formate. All of these five polymers were characterized by single-crystal X-ray diffraction, elemental analysis, IR spectra, powder X-ray diffraction (PXRD), and thermogravimetric (TG) analysis. Complexes 1-3 have the similar three-dimensional 3D kag topological framework built from the bibp ligand as the support member between the neighboring formic planes. Both complexes 4 and 5 have the similar one-dimensional 1D linear chain which is further assembled into 3D supermolecular structure by C-H…O hydrogen bonds. The dyes adsorption experiments have also been investigated systematically. The results show that complexes 2 and 3 exhibit high selective adsorption ability towards anionic dyes in their aqueous solution. Moreover, complex 2 displays good reversibility in the process of the dyes adsorption-release. Meanwhile, the unusual blocking phenomenon was firstly observed when complex 2 was in MO/OIV aqueous solutions with different concentration.

Analytical ultracentrifugation with fluorescence detection system reveals differences in complex formation between recombinant human TNF and different biological TNF antagonists in various environments

PubMed Central

Krayukhina, Elena; Noda, Masanori; Ishii, Kentaro; Maruno, Takahiro; Wakabayashi, Hirotsugu; Tada, Minoru; Suzuki, Takuo; Ishii-Watabe, Akiko; Kato, Masahiko; Uchiyama, Susumu

2017-01-01

ABSTRACT A number of studies have attempted to elucidate the binding mechanism between tumor necrosis factor (TNF) and clinically relevant antagonists. None of these studies, however, have been conducted as close as possible to physiologic conditions, and so the relationship between the size distribution of TNF-antagonist complexes and the antagonists' biological activity or adverse effects remains elusive. Here, we characterized the binding stoichiometry and sizes of soluble TNF-antagonist complexes for adalimumab, infliximab, and etanercept that were formed in human serum and in phosphate-buffered saline (PBS). Fluorescence-detected sedimentation velocity analytical ultracentrifugation analyses revealed that adalimumab and infliximab formed a range of complexes with TNF, with the major complexes consisting of 3 molcules of the respective antagonist and one or 2 molcules of TNF. Considerably greater amounts of high-molecular-weight complexes were detected for infliximab in human serum. The emergence of peaks with higher sedimentation coefficients than the adalimumab monomer as a function of added human serum albumin (HSA) concentration in PBS suggested weak reversible interactions between HSA and immunoglobulins. Etanerept exclusively formed 1:1 complexes with TNF in PBS, and a small amount of complexes with higher stoichiometry was detected in human serum. Consistent with these biophysical characterizations, a reporter assay showed that adalimumab and infliximab, but not etanercept, exerted FcγRIIa- and FcγRIIIa-mediated cell signaling in the presence of TNF and that infliximab exhibited higher potency than adalimumab. This study shows that assessing distribution profiles in serum will contribute to a more comprehensive understanding of the in vivo behavior of therapeutic proteins. PMID:28387583

Chemically Reversible Reactions of Hydrogen Sulfide with Metal Phthalocyanines

PubMed Central

2015-01-01

Hydrogen sulfide (H2S) is an important signaling molecule that exerts action on various bioinorganic targets. Despite this importance, few studies have investigated the differential reactivity of the physiologically relevant H2S and HS– protonation states with metal complexes. Here we report the distinct reactivity of H2S and HS– with zinc(II) and cobalt(II) phthalocyanine (Pc) complexes and highlight the chemical reversibility and cyclability of each metal. ZnPc reacts with HS–, but not H2S, to generate [ZnPc-SH]−, which can be converted back to ZnPc by protonation. CoPc reacts with HS–, but not H2S, to form [CoIPc]−, which can be reoxidized to CoPc by air. Taken together, these results demonstrate the chemically reversible reaction of HS– with metal phthalocyanine complexes and highlight the importance of H2S protonation state in understanding the reactivity profile of H2S with biologically relevant metal scaffolds. PMID:24785654

The mechano-chemistry of a monomeric reverse transcriptase

PubMed Central

Malik, Omri; Khamis, Hadeel; Rudnizky, Sergei

2017-01-01

Abstract Retroviral reverse transcriptase catalyses the synthesis of an integration-competent dsDNA molecule, using as a substrate the viral RNA. Using optical tweezers, we follow the Murine Leukemia Virus reverse transcriptase as it performs strand-displacement polymerization on a template under mechanical force. Our results indicate that reverse transcriptase functions as a Brownian ratchet, with dNTP binding as the rectifying reaction of the ratchet. We also found that reverse transcriptase is a relatively passive enzyme, able to polymerize on structured templates by exploiting their thermal breathing. Finally, our results indicate that the enzyme enters the recently characterized backtracking state from the pre-translocation complex. PMID:29165701

A reversed-phase compatible thin-layer chromatography autography for the detection of acetylcholinesterase inhibitors.

PubMed

Ramallo, I Ayelen; García, Paula; Furlan, Ricardo L E

2015-11-01

A dual readout autographic assay to detect acetylcholinesterase inhibitors present in complex matrices adsorbed on reversed-phase or normal-phase thin-layer chromatography plates is described. Enzyme gel entrapment with an amphiphilic copolymer was used for assay development. The effects of substrate and enzyme concentrations, pH, incubation time, and incubation temperature on the sensitivity and the detection limit of the assay were evaluated. Experimental design and response surface methodology were used to optimize conditions with a minimum number of experiments. The assay allowed the detection of 0.01% w/w of physostigmine in both a spiked Sonchus oleraceus L. extract chromatographed on normal phase and a spiked Pimenta racemosa (Mill.) J.W. Moore leaf essential oil chromatographed on reversed phase. Finally, the reversed-phase thin-layer chromatography assay was applied to reveal the presence of an inhibitor in the Cymbopogon citratus (DC.) Stapf essential oil. The developed assay is able to detect acetylcholinesterase inhibitors present in complex matrixes that were chromatographed in normal phase or reversed-phase thin-layer chromatography. The detection limit for physostigmine on both normal and reversed phase was of 1×10(-4) μg. The results can be read by a change in color and/or a change in fluorescence. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Reversible Hydrogen Activation by a Pyridonate Borane Complex: Combining Frustrated Lewis Pair Reactivity with Boron-Ligand Cooperation.

PubMed

Gellrich, Urs

2018-04-16

A pyridone borane complex that liberates dihydrogen under mild conditions is described. The reverse reaction, dihydrogen activation by the formed pyridonate borane complex, is achieved under moderate H 2 pressure (2 bar) at room temperature. DFT and DLPNO-CCSD(T) computations reveal that the active form of the pyridonate borane complex is a boroxypyridine that can be described as a single component frustrated Lewis pair (FLP). Significantly, the boroxypyridine undergoes a chemical transformation to a neutral pyridone donor ligand in the course of the hydrogen activation. This unprecedented mode of action may thus, in analogy to metal-ligand cooperation, be regarded as an example of boron-ligand cooperation. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Direct Observation of Energy Detrapping in LH1-RC Complex by Two-Dimensional Electronic Spectroscopy.

PubMed

Ma, Fei; Yu, Long-Jiang; Hendrikx, Ruud; Wang-Otomo, Zheng-Yu; van Grondelle, Rienk

2017-01-18

The purple bacterial core light harvesting antenna-reaction center (LH1-RC) complex is the simplest system able to achieve the entire primary function of photosynthesis. During the past decade, a variety of photosynthetic proteins were studied by a powerful technique, two-dimensional electronic spectroscopy (2DES). However, little attention has been paid to LH1-RC, although its reversible uphill energy transfer, trapping, and backward detrapping processes, represent a crucial step in the early photosynthetic reaction dynamics. Thus, in this work, we employed 2DES to study two LH1-RC complexes of Thermochromatium (Tch.) tepidum. By direct observation of detrapping, the complex reversible process was clearly identified and an overall scheme of the excitation evolution in LH1-RC was obtained.

Binding Modes of Phthalocyanines to Amyloid β Peptide and Their Effects on Amyloid Fibril Formation.

PubMed

Valiente-Gabioud, Ariel A; Riedel, Dietmar; Outeiro, Tiago F; Menacho-Márquez, Mauricio A; Griesinger, Christian; Fernández, Claudio O

2018-03-13

The inherent tendency of proteins to convert from their native states into amyloid aggregates is associated with a range of human disorders, including Alzheimer's and Parkinson's diseases. In that sense, the use of small molecules as probes for the structural and toxic mechanism related to amyloid aggregation has become an active area of research. Compared with other compounds, the structural and molecular basis behind the inhibitory interaction of phthalocyanine tetrasulfonate (PcTS) with proteins such as αS and tau has been well established, contributing to a better understanding of the amyloid aggregation process in these proteins. We present here the structural characterization of the binding of PcTS and its Cu(II) and Zn(II)-loaded forms to the amyloid β-peptide (Aβ) and the impact of these interactions on the peptide amyloid fibril assembly. Elucidation of the PcTS binding modes to Aβ 40 revealed the involvement of specific aromatic and hydrophobic interactions in the formation of the Aβ 40 -PcTS complex, ascribed to a binding mode in which the planarity and hydrophobicity of the aromatic ring system in the phthalocyanine act as main structural determinants for the interaction. Our results demonstrated that formation of the Aβ 40 -PcTS complex does not interfere with the progression of the peptide toward the formation of amyloid fibrils. On the other hand, conjugation of Zn(II) but not Cu(II) at the center of the PcTS macrocyclic ring modified substantially the binding profile of this phthalocyanine to Aβ 40 and became crucial to reverse the effects of metal-free PcTS on the fibril assembly of the peptide. Overall, our results provide a firm basis to understand the structural rules directing phthalocyanine-protein interactions and their implications on the amyloid fibril assembly of the target proteins; in particular, our results contradict the hypothesis that PcTS might have similar mechanisms of action in slowing the formation of a variety of pathological aggregates. Copyright © 2018 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Biomechanics of Reverse Shoulder Arthroplasty: 
Current Concepts.

PubMed

Lorenzetti, Adam J; Stone, Geoffrey P; Simon, Peter; Frankle, Mark A

2016-01-01

The evolution of reverse shoulder arthroplasty has provided surgeons with new solutions for many complex shoulder problems. A primary goal of orthopaedics is the restoration or re-creation of functional anatomy to reduce pain and improve function, which can be accomplished by either repairing injured structures or replacing them as anatomically as possible. If reconstructible tissue is lacking or not available, which is seen in patients who have complex shoulder conditions such as an irreparable rotator cuff-deficient shoulder, cuff tear arthropathy, or severe glenoid bone loss, substantial problems may arise. Historically, hemiarthroplasty or glenoid grafting with total shoulder arthroplasty yielded inconsistent and unsatisfactory results. Underlying pathologies in patients who have an irreparable rotator cuff-deficient shoulder, cuff tear arthropathy, or severe glenoid bone loss can considerably alter the mechanical function of the shoulder and create treatment dilemmas that are difficult to overcome. A better biomechanical understanding of these pathologic adaptations has improved treatment options. In the past three decades, reverse total shoulder arthroplasty was developed to treat these complex shoulder conditions not by specifically re-creating the anatomy but by using the remaining functional tissue to improve shoulder balance. Reverse total shoulder arthroplasty has achieved reliable improvements in both pain and function. Initial implant designs lacked scientific evidence to support the design rationale, and many implants failed because surgeons did not completely understand the forces involved or the pathology being treated. Implant function and clinical results will continue to improve as surgeons' biomechanical understanding of shoulder disease and reverse shoulder arthroplasty implants increases.

Kinetically inert Cu in coastal waters.

PubMed

Kogut, Megan B; Voelker, Bettina M

2003-02-01

Many studies have shown that Cu and other metals in natural waters are mostly bound by unidentified compounds interpreted to be strong ligands reversibly complexing a given metal. However, commonly applied analytical techniques are not capable of distinguishing strongly but reversibly complexed metal from metal bound in kinetically inert compounds. In this work, we use a modified competitive ligand exchange adsorptive cathodic stripping voltammetry method combined with size fractionation to show that most if not all of the apparently very strongly (log K > or = 13) bound Cu in samples from five New England coastal waters (1-18 nM, 10-60% of total Cu) is actually present as kinetically inert compounds. In three of the five samples examined by ultrafiltration, a significant portion of the 0.2-microm-filtrable inert Cu was retained by a 0.02-microm-pore size filter, suggesting that at least some of the Cu was kinetically inert because it was physically sequestered in colloidal material. The rest of the ambient Cu, and Cu added in titrations, were reversibly bound in complexes that could be modeled as having conditional stability constants of 10(10)-10(13). The Cu-binding ability of these complexes was equivalent to that of seawater containing reasonable concentrations of humic substances from terrestrial sources, approximately 0.15-0.45 mg of C/L. Both the inert compounds and the reversible ligands were important for determining [Cu2+] at ambient Cu levels in our samples.

Calcineurin inhibitor-induced complement system activation via ERK1/2 signalling is inhibited by SOCS-3 in human renal tubule cells.

PubMed

Loeschenberger, Beatrix; Niess, Lea; Würzner, Reinhard; Schwelberger, Hubert; Eder, Iris E; Puhr, Martin; Guenther, Julia; Troppmair, Jakob; Rudnicki, Michael; Neuwirt, Hannes

2018-02-01

One factor that significantly contributes to renal allograft loss is chronic calcineurin inhibitor (CNI) nephrotoxicity (CIN). Among other factors, the complement (C-) system has been proposed to be involved CIN development. Hence, we investigated the impact of CNIs on intracellular signalling and the effects on the C-system in human renal tubule cells. In a qPCR array, CNI treatment upregulated C-factors and downregulated SOCS-3 and the complement inhibitors CD46 and CD55. Additionally, ERK1/-2 was required for these regulations. Following knock-down and overexpression of SOCS-3, we found that SOCS-3 inhibits ERK1/-2 signalling. Finally, we assessed terminal complement complex formation, cell viability and apoptosis. Terminal complement complex formation was induced by CNIs. Cell viability was significantly decreased, whereas apoptosis was increased. Both effects were reversed under complement component-depleted conditions. In vivo, increased ERK1/-2 phosphorylation and SOCS-3 downregulation were observed at the time of transplantation in renal allograft patients who developed a progressive decline of renal function in the follow-up compared to stable patients. The progressive cohort also had lower total C3 levels, suggesting higher complement activity at baseline. In conclusion, our data suggest that SOCS-3 inhibits CNI-induced ERK1/-2 signalling, thereby blunting the negative control of C-system activation. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Involvement of heme oxygenase-1 in β-cyclodextrin-hemin complex-induced cucumber adventitious rooting process.

PubMed

Lin, Yuting; Li, Meiyue; Huang, Liqin; Shen, Wenbiao; Ren, Yong

2012-09-01

Our previous results showed that β-cyclodextrin-hemin complex (CDH) exhibited a vital protective role against cadmium-induced oxidative damage and toxicity in alfalfa seedling roots by the regulation of heme oxygenase-1 (HO-1) gene expression. In this report, we further test whether CDH exhibited the hormonal-like response. The application of CDH and an inducer of HO-1, hemin, were able to induce the up-regulation of cucumber HO-1 gene (CsHO1) expression and thereafter the promotion of adventitious rooting in cucumber explants. The effect is specific for HO-1 since the potent HO-1 inhibitor zinc protoporphyrin IX (ZnPP) blocked the above responses triggered by CDH, and the inhibitory effects were reversed further when 30% saturation of CO aqueous solution was added together. Further, molecular evidence showed that CDH triggered the increases of the HO-1-mediated target genes responsible for adventitious rooting, including one DnaJ-like gene (CsDNAJ-1) and two calcium-dependent protein kinase (CDPK) genes (CsCDPK1 and CsCDPK5), and were inhibited by ZnPP and reversed by CO. The calcium (Ca2+) chelator ethylene glycol-bis (2-aminoethylether)-N,N,N',N'-tetraacetic acid (EGTA) and the Ca2+ channel blocker lanthanum chloride (LaCl3) not only compromised the induction of adventitious rooting induced by CDH but also decreased the transcripts of above three target genes. However, the application of ascorbic acid (AsA), a well-known antioxidant in plants, failed to exhibit similar inducible effect on adventitious root formation. In short, above results illustrated that the response of CDH in the induction of cucumber adventitious rooting might be through HO-1-dependent mechanism and calcium signaling. Physiological, pharmacological and molecular evidence showed that β-cyclodextrin-hemin complex (CDH) was able to induce cucumber adventitious rooting through heme oxygenase-1 (HO-1)-dependent mechanism and calcium signaling.

Dynamics of the solute-solvent interactions of electronically excited 4-N,N-dimethylaminobenzonitrile (DMABN) and of 3,5,N,N-tetramethyl-4-aminobenzonitrile (TMABN) dissolved in viscous alcohols and in a viscous nitrile

NASA Astrophysics Data System (ADS)

Weisenborn, Petra C. M.; Huizer, A. Herbert; Varma, Cyril A. G. O.

1989-06-01

The time dependence of the fluorescence of solutions of 4-N,N-dimethylaminobenzonitrile (DMABN) and 3,5,N,N-tetramethyl-4-aminobenzonitrile (TMA BN) in neat polar solvents has been investigated, using a 25 ps UV-laser pulse for excitation and a streak camera for detection. Both the compounds DMABN and TMABN exhibit normal fluorescence F N and anomalous fluorescence F A, but all the solutions of TMABN show merely a single band in the fluorescence spectrum, which is a superposition of the bands F N and F A. In the case of DMABN the fluorescence in the region λ < 400 nm, where F N dominates, the fluorescence decays tri-exponentially due to fluorescence from three types of species, namely excited solute-solvent complexes, excited bare solutes and solute-solvent exciplexes. Within the lifetime of these emitting species there is probably no reverse reaction from exciplexes to excited solute-solvent complexes or excited bare solutes. This is in contrast with a previously presented picture, which includes such a reverse reaction. In the case of the solution of DMABN in n-butanol, the fluorescence at λ < 400 nm is bi-exponential. We show that this is due to an accidental degeneracy of two lifetimes. In contrast to a previous conclusion, we find that DMABN exists partially in the form of ground state solute-solvent complexes also in the solution in nitriles. The anomalous fluorescence develops in two phases, in the first one solute-solvent exciplexes are formed and in the second one the dielectric polarization of the solvent around the exciplex builds up. The rate constant for the formation of the anomalously fluorescing species, i.e. solute-solvent exciplexes, bears no relation with the longitudinal relaxation time, as claimed to have been shown previously.

Three reversible polymorphic copper(I) complexes triggered by ligand conformation: insights into polymorphic crystal habit and luminescent properties.

PubMed

Chai, Wenxiang; Hong, Mingwei; Song, Li; Jia, Guohua; Shi, Hongsheng; Guo, Jiayu; Shu, Kangying; Guo, Bing; Zhang, Yicheng; You, Wenwu; Chen, Xueyuan

2015-05-04

Three luminescent polymorphs based on a new copper(I) complex Cu(2-QBO)(PPh3)PF6 (1, PPh3 = triphenylphosphine, 2-QBO = 2-(2'-quinolyl)benzoxazole) have been synthesized and characterized by FT-IR, UV-vis, elemental analyses, and single-crystal X-ray diffraction analyses. Each polymorph can reversibly convert from one to another through appropriate procedures. Interestingly, such interconversion can be distinguished by their intrinsic crystal morphologies and colors (namely α, dark yellow plate, β, orange block, γ, light yellow needle) as well as photoluminescent (PL) properties. X-ray crystal structure analyses of these three polymorphs show three different supramolecular structures from 1D to 3D, which are expected to be responsible for the formation of three different crystal morphologies such as needle, plate, and block. Combination of the experimental data with DFT calculations on these three polymorphs reveals that the polymorphic interconversion is triggered by the conformation isomerization of the 2-QBO ligand and can be successfully controlled by the polarity of the process solvents (affecting the molecular dipole moment) and thermodynamics (affecting the molecular total energy). It is also found that the different crystal colors of polymorphs and their PL properties are derived from different θ values (dihedral angle between benzoxazolyl and quinolyl group of the 2-QBO ligand) and P-Cu-P angles based on TD-DFT calculations. Moreover, an interesting phase interconversion between γ and β has also been found under different temperature, and this result is consistent with the DFT calculations in which the total energy of β is larger than that of γ. This polymorphism provides a good model to study the relationship between the structure and the physical properties in luminescent copper(I) complexes as well as some profound insights into their PL properties.

Effect of Thermal Shock During Legionella Bacteria Removal on the Corrosion Properties of Zinc-Coated Steel Pipes

NASA Astrophysics Data System (ADS)

Orlikowski, Juliusz; Ryl, Jacek; Jazdzewska, Agata; Krakowiak, Stefan

2016-07-01

The purpose of this investigation was to conduct the failure analysis of a water-supply system made from zinc-coated steel. The observed corrosion process had an intense and complex character. The brownish deposits and perforations were present after 2-3 years of exploitation. The electrochemical study based on the Tafel polarization, corrosion potential monitoring, and electrochemical impedance spectroscopy together with microscopic analysis via SEM and EDX were performed in order to identify the cause of such intense corrosion. The performed measurements allowed us to determine that thermal shock was the source of polarity-reversal phenomenon. This process had begun the corrosion of steel which later led to the formation of deposits and perforations in the pipes. The work includes appropriate action in order to efficiently identify the described corrosion threat.

Epigenetic dysregulation in cognitive disorders.

PubMed

Gräff, Johannes; Mansuy, Isabelle M

2009-07-01

Epigenetic mechanisms are not only essential for biological functions requiring stable molecular changes such as the establishment of cell identity and tissue formation, they also constitute dynamic intracellular processes for translating environmental stimuli into modifications in gene expression. Over the past decade it has become increasingly clear that both aspects of epigenetic mechanisms play a pivotal role in complex brain functions. Evidence from patients with neurodegenerative and neurodevelopmental disorders such as Alzheimer's disease and Rett syndrome indicated that epigenetic mechanisms and chromatin remodeling need to be tightly controlled for proper cognitive functions, and their dysregulation can have devastating consequences. However, because they are dynamic, epigenetic mechanisms are also potentially reversible and may provide powerful means for pharmacological intervention. This review outlines major cognitive disorders known to be associated with epigenetic dysregulation, and discusses the potential of 'epigenetic medicine' as a promising cure.

High affinity binding of a fungal oligopeptide elicitor to parsley plasma membranes triggers multiple defense responses.

PubMed

Nürnberger, T; Nennstiel, D; Jabs, T; Sacks, W R; Hahlbrock, K; Scheel, D

1994-08-12

An oligopeptide of 13 amino acids (Pep-13) identified within a 42 kDa glycoprotein elicitor from P. mega-sperma was shown to be necessary and sufficient to stimulate a complex defense response in parsley cells comprising H+/Ca2+ influxes, K+/Cl- effluxes, an oxidative burst, defense-related gene activation, and phytoalexin formation. Binding of radiolabeled Pep-13 to parsley microsomes and protoplasts was specific, reversible, and saturable. Identical structural features of Pep-13 were found to be responsible for specific binding and initiation of all plant responses analyzed. The high affinity binding site recognizing the peptide ligand (KD = 2.4 nM) may therefore represent a novel class of receptors in plants, and the rapidly induced ion fluxes may constitute elements of the signal transduction cascade triggering pathogen defense in plants.

Affinity labeling of a cysteine at or near the catalytic center of Escherichia coli B DNA-dependent RNA polymerase.

PubMed

Miller, J A; Serio, G F; Bear, J L; Howard, R A; Kimball, A P

1980-03-14

9-beta-D-Arabinofuranosyl-6-thiopurine was used to affinity label DNA-dependent RNA polymerase isolated from Escherichia coli B. This substrate analogue displayed competitive type inhibition which could be reversed by addition of a thiol reagent, such as dithiothreitol, while exposure to hydrogen peroxide, a mild oxidizing agent, caused an increase in both the inhibitory and enzyme binding capability of arabinofuranosyl thiopurine. Chromatographic analysis of the products obtained by pronase digestion of the 9-beta-D-arabinofuranosyl-6-[35S]thiopurine-enzyme complex suggests that disulfide bond formation occurs between the inhibitor and a cysteine residue located in or near the active center of the enzyme. In addition, polyacrylamide gel electrophoresis indicated that the arabinofuranosyl thiopurine moeity was bound to the beta' subunit of the enzyme.

Algorithm 937: MINRES-QLP for Symmetric and Hermitian Linear Equations and Least-Squares Problems.

PubMed

Choi, Sou-Cheng T; Saunders, Michael A

2014-02-01

We describe algorithm MINRES-QLP and its FORTRAN 90 implementation for solving symmetric or Hermitian linear systems or least-squares problems. If the system is singular, MINRES-QLP computes the unique minimum-length solution (also known as the pseudoinverse solution), which generally eludes MINRES. In all cases, it overcomes a potential instability in the original MINRES algorithm. A positive-definite pre-conditioner may be supplied. Our FORTRAN 90 implementation illustrates a design pattern that allows users to make problem data known to the solver but hidden and secure from other program units. In particular, we circumvent the need for reverse communication. Example test programs input and solve real or complex problems specified in Matrix Market format. While we focus here on a FORTRAN 90 implementation, we also provide and maintain MATLAB versions of MINRES and MINRES-QLP.

Ileostomy Complications in Infants less than 1500 grams - Frequent but Manageable.

PubMed

Kargl, Simon; Wagner, Oliver; Pumberger, Wolfgang

2017-01-01

In very low birth weight infants abdominal emergency surgery may result in ileostomy formation. We observed a frequent stoma complications in these patients. This retrospective analysis put light on ileostomy-related problems and complications in very low birth weight (VLBW) infants. In a seven-year retrospective chart review (2008 - 2014) infants with ileostomy formation weighing less than 1500 grams at time of operation were identified and reviewed. Data analysis included demographic data, complications and short term outcomes. Thirty patients were included. Ileostomy was formed for spontaneous intestinal perforation (SIP) (n=17), meconium obstruction of prematurity (MOP) (n=6), midgut volvulus (MV) (n=5), necrotizing enterocolitis (NEC) (n=1) and Hirschsprung's disease (HD) (n=1). Three patients died before ileostomy reversal was considered. In seven patients planned ileostomy reversal was done. Twenty infants had stoma related complications (stoma prolapse, prestomal obstruction, stoma retraction, high output stoma, peristomal skin excoriation, and stomal ischemia). Complications did not correlate with underlying diseases. Stomal complications necessitated earlier stoma reversal (mean 62 days). Postoperative complications after stoma reversal occurred in three children (wound dehiscence, adhesion ileus, anastomotic stricture). Although ileostomy related complications are frequent in very low birth weight infants, mortality is low. Morbidity is manageable.

A highly reversible room-temperature sodium metal anode

DOE PAGES

Seh, Zhi Wei; Sun, Jie; Sun, Yongming; ...

2015-11-02

Owing to its low cost and high natural abundance, sodium metal is among the most promising anode materials for energy storage technologies beyond lithium ion batteries. However, room-temperature sodium metal anodes suffer from poor reversibility during long-term plating and stripping, mainly due to formation of nonuniform solid electrolyte interphase as well as dendritic growth of sodium metal. Herein we report for the first time that a simple liquid electrolyte, sodium hexafluorophosphate in glymes (mono-, di-, and tetraglyme), can enable highly reversible and nondendritic plating–stripping of sodium metal anodes at room temperature. High average Coulombic efficiencies of 99.9% were achieved overmore » 300 plating–stripping cycles at 0.5 mA cm –2. In this study, the long-term reversibility was found to arise from the formation of a uniform, inorganic solid electrolyte interphase made of sodium oxide and sodium fluoride, which is highly impermeable to electrolyte solvent and conducive to nondendritic growth. As a proof of concept, we also demonstrate a room-temperature sodium–sulfur battery using this class of electrolytes, paving the way for the development of next-generation, sodium-based energy storage technologies.« less

Synthesis and Reactivity of Tripodal Complexes Containing Pendant Bases

DOE Office of Scientific and Technical Information (OSTI.GOV)

Blacquiere, Johanna M.; Pegis, Michael L.; Raugei, Simone

2014-09-02

The synthesis of a new tripodal ligand family is reported, with tertiary-amine groups in the second-coordination sphere. The ligands are tris(amido)amine derivatives, with the pendant amines attached via a peptide coupling strategy. They were designed to be used in new catalysts for the oxygen reduction reaction (ORR), in which the pendant acid/base group could improve catalyst performance. Two members of the new ligand family were each metallated with Co(II) and Zn(II) to afford trigonal monopyramidal complexes. Reaction of the cobalt complexes, [Co(L)]-, with dioxygen reversibly generates a small amount of a Co(III)-superoxo species, which was characterized by EPR. Protonation ofmore » the zinc complex Zn[N{CH2CH2NC(O)CH2N(CH2Ph)2}3)-– ([Zn(TNBn)]-) with one equivalent of acid occurs with displacement and dissociation of an amide ligand. Addition of excess acid to the any of the complexes [M(L)]- results in complete proteolysis and formation of the ligands H3L. This decomposition limits the use of these complexes as catalysts for the ORR. An alternative ligand with two pyridyl arms was also prepared but could not be metallated. These studies highlight the importance of stability of the primary-coordination sphere of ORR electrocatalysts to both oxidative and acidic conditions. This research was supported as part of the Center for Molecular Electrocatalysis, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences.« less

Charge-mediated Fab-Fc interactions in an IgG1 antibody induce reversible self-association, cluster formation, and elevated viscosity.

PubMed

Arora, Jayant; Hu, Yue; Esfandiary, Reza; Sathish, Hasige A; Bishop, Steven M; Joshi, Sangeeta B; Middaugh, C Russell; Volkin, David B; Weis, David D

Concentration-dependent reversible self-association (RSA) of monoclonal antibodies (mAbs) poses a challenge to their pharmaceutical development as viable candidates for subcutaneous delivery. While the role of the antigen-binding fragment (Fab) in initiating RSA is well-established, little evidence supports the involvement of the crystallizable fragment (Fc). In this report, a variety of biophysical tools, including hydrogen exchange mass spectrometry, are used to elucidate the protein interface of such non-covalent protein-protein interactions. Using dynamic and static light scattering combined with viscosity measurements, we find that an IgG1 mAb (mAb-J) undergoes RSA primarily through electrostatic interactions and forms a monomer-dimer-tetramer equilibrium. We provide the first direct experimental mapping of the interface formed between the Fab and Fc domains of an antibody at high protein concentrations. Charge distribution heterogeneity between the positively charged interface spanning complementarity-determining regions CDR3H and CDR2L in the Fab and a negatively charged region in C H 3/Fc domain mediates the RSA of mAb-J. When arginine and NaCl are added, they disrupt RSA of mAb-J and decrease the solution viscosity. Fab-Fc domain interactions between mAb monomers may promote the formation of large transient antibody complexes that ultimately cause increases in solution viscosity. Our findings illustrate how limited specific arrangements of amino-acid residues can cause mAbs to undergo RSA at high protein concentrations and how conserved regions in the Fc portion of the antibody can also play an important role in initiating weak and transient protein-protein interactions.

Production of alpha-amylase from Aspergillus oryzae for several industrial applications in a single step.

PubMed

Porfirif, María C; Milatich, Esteban J; Farruggia, Beatriz M; Romanini, Diana

2016-06-01

A one-step method as a strategy of alpha-amylase concentration and purification was developed in this work. This methodology requires the use of a very low concentration of biodegradable polyelectrolyte (Eudragit(®) E-PO) and represents a low cost, fast, easy to scale up and non-polluting technology. Besides, this methodology allows recycling the polymer after precipitation. The formation of reversible soluble/insoluble complexes between alpha-amylase and the polymer Eudragit(®) E-PO was studied, and their precipitation in selected conditions was applied with bioseparation purposes. Turbidimetric assays allowed to determine the pH range where the complexes are insoluble (4.50-7.00); pH 5.50 yielded the highest turbidity of the system. The presence of NaCl (0.05M) in the medium totally dissociates the protein-polymer complexes. When the adequate concentration of polymer was added under these conditions to a liquid culture of Aspergillus oryzae, purification factors of alpha-amylase up to 7.43 and recoveries of 88% were obtained in a simple step without previous clarification. These results demonstrate that this methodology is suitable for the concentration and production of alpha-amylase from this source and could be applied at the beginning of downstream processing. Copyright © 2016 Elsevier B.V. All rights reserved.

Structure-sensitive film materials based on polyvinyl alcohol compositions with polyacids

NASA Astrophysics Data System (ADS)

Lazareva, Tatjana G.; Iljushenko, Irina A.

1995-05-01

The influence of polyacidic additives (silicotungstic acid -- STA, carboxymethylcellulose -- Na-CMC, polymethacrylic acid -- PMA, polyacrylic acid -- PAA) on the molecular mobility of film composition based on polyvinyl alcohol (PVA) in the temperature range 20 - 200 degree(s)C has been evaluated. It has been concluded that interpolymer complexes are formed due to hydrogen bonding of the PVA and polyacidic additive molecules, which results in the change of the PVA stereoregularity. The formation of the complexes depends on the type and concentration of the polyacidic additive, the process of (alpha) -relaxation and, in a certain concentration range of the additive, increases the molecular mobility of the kinetic segments surrounding the complex. The influence of short-term UV-irradiation on the structure and properties of such materials has been investigated. A possibility of the reversible change of molecular mobility and stereoregularity of the examined compositions as a result of short-term UV-irradiation has been established. Introduction of polyacids into the PVA structure gives rise to the electrosensitivity, i.e., the ability to change structure under the action of an electric field. In this case the distinguishing feature is the relation between the molecular mobility and electrosensitivity in the range of parameters where the (alpha) - relaxation occurs.

Biogenic Manganese-Oxide Mineralization is Enhanced by an Oxidative Priming Mechanism for the Multi-Copper Oxidase, MnxEFG.

PubMed

Tao, Lizhi; Simonov, Alexandr N; Romano, Christine A; Butterfield, Cristina N; Fekete, Monika; Tebo, Bradley M; Bond, Alan M; Spiccia, Leone; Martin, Lisandra L; Casey, William H

2017-01-26

In a natural geochemical cycle, manganese-oxide minerals (MnO x ) are principally formed through a microbial process, where a putative multicopper oxidase MnxG plays an essential role. Recent success in isolating the approximately 230 kDa, enzymatically active MnxEFG protein complex, has advanced our understanding of biogenic MnO x mineralization. Here, the kinetics of MnO x formation catalyzed by MnxEFG are examined using a quartz crystal microbalance (QCM), and the first electrochemical characterization of the MnxEFG complex is reported using Fourier transformed alternating current voltammetry. The voltammetric studies undertaken using near-neutral solutions (pH 7.8) establish the apparent reversible potentials for the Type 2 Cu sites in MnxEFG immobilized on a carboxy-terminated monolayer to be in the range 0.36-0.40 V versus a normal hydrogen electrode. Oxidative priming of the MnxEFG protein complex substantially enhances the enzymatic activity, as found by in situ electrochemical QCM analysis. The biogeochemical significance of this enzyme is clear, although the role of an oxidative priming of catalytic activity might be either an evolutionary advantage or an ancient relic of primordial existence. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Theoretical study of the kinetics of chlorine atom abstraction from chloromethanes by atomic chlorine.

PubMed

Brudnik, Katarzyna; Twarda, Maria; Sarzyński, Dariusz; Jodkowski, Jerzy T

2013-10-01

Ab initio calculations at the G3 level were used in a theoretical description of the kinetics and mechanism of the chlorine abstraction reactions from mono-, di-, tri- and tetra-chloromethane by chlorine atoms. The calculated profiles of the potential energy surface of the reaction systems show that the mechanism of the studied reactions is complex and the Cl-abstraction proceeds via the formation of intermediate complexes. The multi-step reaction mechanism consists of two elementary steps in the case of CCl4 + Cl, and three for the other reactions. Rate constants were calculated using the theoretical method based on the RRKM theory and the simplified version of the statistical adiabatic channel model. The temperature dependencies of the calculated rate constants can be expressed, in temperature range of 200-3,000 K as [Formula: see text]. The rate constants for the reverse reactions CH3/CH2Cl/CHCl2/CCl3 + Cl2 were calculated via the equilibrium constants derived theoretically. The kinetic equations [Formula: see text] allow a very good description of the reaction kinetics. The derived expressions are a substantial supplement to the kinetic data necessary to describe and model the complex gas-phase reactions of importance in combustion and atmospheric chemistry.

Reversible Redox Activity by Ion-pH Dually Modulated Duplex Formation of i-Motif DNA with Complementary G-DNA.

PubMed

Chang, Soyoung; Kilic, Tugba; Lee, Chang Kee; Avci, Huseyin; Bae, Hojae; Oskui, Shirin Mesbah; Jung, Sung Mi; Shin, Su Ryon; Kim, Seon Jeong

2018-04-08

The unique biological features of supramolecular DNA have led to an increasing interest in biomedical applications such as biosensors. We have developed an i-motif and G-rich DNA conjugated single-walled carbon nanotube hybrid materials, which shows reversible conformational switching upon external stimuli such as pH (5 and 8) and presence of ions (Li⁺ and K⁺). We observed reversible electrochemical redox activity upon external stimuli in a quick and robust manner. Given the ease and the robustness of this method, we believe that pH- and ion-driven reversible DNA structure transformations will be utilized for future applications for developing novel biosensors.

Molecular interactions between lecithin and bile salts/acids in oils and their effects on reverse micellization.

PubMed

Njauw, Ching-Wei; Cheng, Chih-Yang; Ivanov, Viktor A; Khokhlov, Alexei R; Tung, Shih-Huang

2013-03-26

It has been known that the addition of bile salts to lecithin organosols induces the formation of reverse wormlike micelles and that the worms are similar to long polymer chains that entangle each other to form viscoelastic solutions. In this study, we further investigated the effects of different bile salts and bile acids on the growth of lecithin reverse worms in cyclohexane and n-decane. We utilized rheological and small-angle scattering techniques to analyze the properties and structures of the reverse micelles. All of the bile salts can transform the originally spherical lecithin reverse micelles into wormlike micelles and their rheological behaviors can be described by the single-relaxation-time Maxwell model. However, their efficiencies to induce the worms are different. In contrast, before phase separation, bile acids can induce only short cylindrical micelles that are not long enough to impart viscoelasticity. We used Fourier transform infrared spectroscopy to investigate the interactions between lecithin and bile salts/acids and found that different bile salts/acids employ different functional groups to form hydrogen bonds with lecithin. Such effects determine the relative positions of the bile salts/acids in the headgroups of lecithin, thus resulting in varying efficiencies to alter the effective critical packing parameter for the formation of wormlike micelles. This work highlights the importance of intermolecular interactions in molecular self-assembly.

Photolithography and Fluorescence Correlation Spectroscopy used to examine the rates of exchange in reverse micelle systems

NASA Astrophysics Data System (ADS)

Norris, Zach; Mawson, Cara; Johnson, Kyron; Kessler, Sarah; Rebecca, Anne; Wolf, Nathan; Lim, Michael; Nucci, Nathaniel

Reverse micelles are molecular complexes that encapsulate a nanoscale pool of water in a surfactant shell dissolved in non-polar solvent. These complexes have a wide range of applications, and in all cases, the degree to which reverse micelles (RM) exchange their contents is relevant for their use. Despite its importance, this aspect of RM behavior is poorly understood. Photolithography is employed here to create micro and nano scale fluidic systems in which mixing rates can be precisely measured using fluorescence correlation spectroscopy (FCS). Micro-channel patterns are etched using reactive ion etching process into a layer of silicon dioxide on crystalline silicon substrates. Solutions containing mixtures of reverse micelles, proteins, and fluorophores are placed into reservoirs in the patterns, while diffusion and exchange between RMs is monitored using a FCS system built from a modified confocal Raman spectrometer. Using this approach, the diffusion and exchange rates for RM systems are measured as a function of the components of the RM mixture. Funding provided by Rowan University.

Reverse weathering in marine sediments and the geochemical cycle of potassium in seawater: Insights from the K isotopic composition (41K/39K) of deep-sea pore-fluids

USGS Publications Warehouse

Santiago Ramos, Danielle P.; Morgan, Leah; Lloyd, Nicholas S.; Higgins, John A.

2018-01-01

In situ Al-silicate formation, also known as “reverse weathering,” is an important sink of many of the major and minor cations in seawater (e.g. Mg, K, and Li). However, the importance of this sink in global geochemical cycles and isotopic budgets of these elements remains poorly constrained. Here, we report on the potassium isotopic composition (41">41K/39">39K) of deep-sea sediment pore-fluids from four (Integrated) Ocean Drilling Program sites (1052, U1378, U1395 and U1403) to characterize potassium isotopic fractionation associated with the formation of authigenic Al-silicate minerals in marine sediments and its role in elevating the 41">41K/39">39K of seawater relative to bulk silicate Earth. Isotopic ratios are obtained by high-resolution multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) in cold plasma conditions with a long-term external reproducibility of ca. 0.17‰. We find that, although all sites are characterized by pore-fluid K concentrations that decline with increasing depth, their K isotopic profiles vary systematically from site-to-site; at sites characterized by rapid sedimentation rates, pore-fluid profiles of 41">41K/39">39K are relatively invariant whereas at sites characterized by slow sedimentation rates, 41">41K/39">39K declines with depth by up to 1.8‰. Results from 1-D diffusion-advection-reaction models suggest that these differences may result from a complex interplay between sedimentation rate and fractionation of K isotopes during diffusion, Al-silicate authigenesis, and ion exchange. Model simulations suggest fractionation factors between 0.9980 and 1.0000 for reverse weathering reactions in deep-sea sediments. Although deep-sea sites do not constitute major sinks of K in seawater, some of the processes responsible for K isotopic fractionation at these sites (diffusion and Al-silicate authigenesis) likely play a role in determining the 41">41K/39">39K of seawater.

Rapid and reversible epigenome editing by endogenous chromatin regulators.

PubMed

Braun, Simon M G; Kirkland, Jacob G; Chory, Emma J; Husmann, Dylan; Calarco, Joseph P; Crabtree, Gerald R

2017-09-15

Understanding the causal link between epigenetic marks and gene regulation remains a central question in chromatin biology. To edit the epigenome we developed the FIRE-Cas9 system for rapid and reversible recruitment of endogenous chromatin regulators to specific genomic loci. We enhanced the dCas9-MS2 anchor for genome targeting with Fkbp/Frb dimerizing fusion proteins to allow chemical-induced proximity of a desired chromatin regulator. We find that mSWI/SNF (BAF) complex recruitment is sufficient to oppose Polycomb within minutes, leading to activation of bivalent gene transcription in mouse embryonic stem cells. Furthermore, Hp1/Suv39h1 heterochromatin complex recruitment to active promoters deposits H3K9me3 domains, resulting in gene silencing that can be reversed upon washout of the chemical dimerizer. This inducible recruitment strategy provides precise kinetic information to model epigenetic memory and plasticity. It is broadly applicable to mechanistic studies of chromatin in mammalian cells and is particularly suited to the analysis of endogenous multi-subunit chromatin regulator complexes.Understanding the link between epigenetic marks and gene regulation requires the development of new tools to directly manipulate chromatin. Here the authors demonstrate a Cas9-based system to recruit chromatin remodelers to loci of interest, allowing rapid, reversible manipulation of epigenetic states.

Self-Assembly of Molecular Threads into Reversible Gels

NASA Astrophysics Data System (ADS)

Sayar, Mehmet; Stupp, Samuel I.

2001-03-01

Reversible gels formed by low concentrations of molecular gelators that self-assemble into fibers with molecular width and extremely long length have been studied via Monte Carlo simulations. The gelators of interest have two kinds of interactions, one governs self-assembly into fibers and the other provides inter-fiber connectivity to drive the formation of a network. The off-lattice Monte Carlo simulation presented here is based on a point particle representation of gelators. In this model each particle can form only two strong bonds, that enable linear fiber formation, but a variable number of weak bonds which provide inter-fiber connectivity. The gel formation has been studied as a function of concentration of monomers, the strength of interactions, number of bonding sites per particle for weak interactions, and the stiffness of the fibers. The simulation results are compared with two experimental systems synthesized in our group in order to understand gelation mechanisms.

[Reverse learning in WAG/Rij rats with depression-like behavior].

PubMed

Malyshev, A V; Zakharov, A M; Sarkisova, K Iu; Dubynin, V A

2012-01-01

Learning and reverse learning in a complex maze, behavior in the open field test, novelty-suppressed feeding test, and forced swimming test were studies in WAG/Rij and Wistar rats. As compared with Wistar rats, WAG/Rij rats more slowly learned the spatial task, more slowly performed in the learning and reverse learning tasks, and made more errors in the complex maze (18% of WAG/Rij rats didn't reach learning criterion). Moreover, WAG/Rij rats exhibited reduced grooming reactions in the open field test, longer latency of approaching to food in the novel open field, reduced amount of food consumed in the home cage in the novelty-suppressed feeding test, and increased immobility time in the forced swimming test. The results suggest cognitive impaiment in WAG/Rij rats with depression-like behavior.

Adaptable Hydrogel Networks with Reversible Linkages for Tissue Engineering

PubMed Central

Wang, Huiyuan

2015-01-01

Adaptable hydrogels have recently emerged as a promising platform for three-dimensional (3D) cell encapsulation and culture. In conventional, covalently crosslinked hydrogels, degradation is typically required to allow complex cellular functions to occur, leading to bulk material degradation. In contrast, adaptable hydrogels are formed by reversible crosslinks. Through breaking and re-forming of the reversible linkages, adaptable hydrogels can be locally modified to permit complex cellular functions while maintaining their long-term integrity. In addition, these adaptable materials can have biomimetic viscoelastic properties that make them well suited for several biotechnology and medical applications. In this review, adaptable hydrogel design considerations and linkage selections are overviewed, with a focus on various cell compatible crosslinking mechanisms that can be exploited to form adaptable hydrogels for tissue engineering. PMID:25989348

Topological formation of a multiply charged vortex in the Rb Bose-Einstein condensate: Effectiveness of the gravity compensation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kumakura, M.; PRESTO, JST, 4-1-8 Honcho Kawaguchi, Saitama 332-0012; CREST, JST, 4-1-8 Honcho Kawaguchi, Saitama 332-0012

2006-06-15

In a Bose-Einstein condensate of {sup 87}Rb (F=2,m{sub F}=2) atoms we have topologically created a quantized vortex with a charge of 4 by reversing the magnetic field of the trap. Experimental conditions of reversal time and initial magnetic field strength for the successful vortex creation were restricted within narrower ranges, compared to those in the case of the {sup 23}Na condensate. The experimental difficulty was explained in terms of a non-negligible gravitational sag arising from its large atomic mass. We have successfully stabilized the vortex formation by compensating gravity with a blue-detuned laser beam.

Hydrogen storage compositions

DOEpatents

Li, Wen; Vajo, John J.; Cumberland, Robert W.; Liu, Ping

2011-04-19

Compositions for hydrogen storage and methods of making such compositions employ an alloy that exhibits reversible formation/deformation of BH.sub.4.sup.- anions. The composition includes a ternary alloy including magnesium, boron and a metal and a metal hydride. The ternary alloy and the metal hydride are present in an amount sufficient to render the composition capable of hydrogen storage. The molar ratio of the metal to magnesium and boron in the alloy is such that the alloy exhibits reversible formation/deformation of BH.sub.4.sup.- anions. The hydrogen storage composition is prepared by combining magnesium, boron and a metal to prepare a ternary alloy and combining the ternary alloy with a metal hydride to form the hydrogen storage composition.

Reversible five-coordinate ⇄ six-coordinate transformation in cobalt(II) complexes

NASA Astrophysics Data System (ADS)

Xiao, Linda; Bhadbhade, Mohan; Baker, Anthony T.

2018-04-01

The heterocyclic ligands 2,6-bis(pyrazol-1-yl)pyridine (L1) and 2,6-bis(benzimidazol-2-yl)pyridine (L2) and their cobalt(II) complexes were synthesized. The blue five-coordinate complex [Co(L1)Cl2] isolated initially from the reaction mixture rapidly absorbed water vapour from the atmosphere to yield the pink six-coordinate complex [Co(L1)(H2O)3]Cl2. This change is reversible upon desiccation or transferring [Co(L1)(H2O)3]Cl2 into acetonitrile. The five coordinate complex [Co(L2)Cl2], however, remains stable under similar conditions. The structures of the complexes [Co(L1)Cl2], [Co(L1)(H2O)3]Cl2 and [Co(L2)Cl2] have been determined by x-ray crystallography. The magnetic susceptibilities and the electronic spectra for [Co(L1)Cl2], [Co(L2)Cl2] and [Co(L1)(H2O)3]Cl2 are presented.

Telomerase Reverse Transcriptase Deficiency Prevents Neointima Formation Through Chromatin Silencing of E2F1 Target Genes.

PubMed

Endorf, Elizabeth B; Qing, Hua; Aono, Jun; Terami, Naoto; Doyon, Geneviève; Hyzny, Eric; Jones, Karrie L; Findeisen, Hannes M; Bruemmer, Dennis

2017-02-01

Aberrant proliferation of smooth muscle cells (SMC) in response to injury induces pathological vascular remodeling during atherosclerosis and neointima formation. Telomerase is rate limiting for tissue renewal and cell replication; however, the physiological role of telomerase in vascular diseases remains to be determined. The goal of the present study was to determine whether telomerase reverse transcriptase (TERT) affects proliferative vascular remodeling and to define the molecular mechanism by which TERT supports SMC proliferation. We first demonstrate high levels of TERT expression in replicating SMC of atherosclerotic and neointimal lesions. Using a model of guidewire-induced arterial injury, we demonstrate decreased neointima formation in TERT-deficient mice. Studies in SMC isolated from TERT-deficient and TERT overexpressing mice with normal telomere length established that TERT is necessary and sufficient for cell proliferation. TERT deficiency did not induce a senescent phenotype but resulted in G1 arrest albeit hyperphosphorylation of the retinoblastoma protein. This proliferative arrest was associated with stable silencing of the E2F1-dependent S-phase gene expression program and not reversed by ectopic overexpression of E2F1. Finally, chromatin immunoprecipitation and accessibility assays revealed that TERT is recruited to E2F1 target sites and promotes chromatin accessibility for E2F1 by facilitating the acquisition of permissive histone modifications. These data indicate a previously unrecognized role for TERT in neointima formation through epigenetic regulation of proliferative gene expression in SMC. © 2016 American Heart Association, Inc.

A model complex of a possible intermediate in the mechanism of action of peptide deformylase: first example of an (N2S)zinc(II)-formate complex.

PubMed

Chang, S C; Sommer, R D; Rheingold, A L; Goldberg, D P

2001-11-21

The synthesis and crystallographic characterization of a new (N2S)zinc-alkyl complex and (N2S)zinc-formate complex is described; the bonding mode of the formate complex has implications for the mechanism of action of the enzyme peptide deformylase.

trans-[Pt(BCat')Me(PCy3)2]: an experimental case study of reductive elimination processes in Pt-Boryls through associative mechanisms.

PubMed

Braunschweig, Holger; Bertermann, Rüdiger; Brenner, Peter; Burzler, Michael; Dewhurst, Rian D; Radacki, Krzysztof; Seeler, Fabian

2011-10-10

A stable trans-(alkyl)(boryl) platinum complex trans-[Pt(BCat')Me(PCy(3))(2)] (Cat'=Cat-4-tBu; Cy=cyclohexyl=C(6)H(11)) was synthesised by salt metathesis reaction of trans-[Pt(BCat')Br(PCy(3))(2)] with LiMe and was fully characterised. Investigation of the reactivity of the title compound showed complete reductive elimination of Cat'BMe at 80 °C within four weeks. This process may be accelerated by the addition of a variety of alkynes, thereby leading to the formation of the corresponding η(2) -alkyne platinum complexes, of which [Pt(η(2)-MeCCMe)(PCy(3))(2)] was characterised by X-ray crystallography. Conversion of the trans-configured title compound to a cis derivative remained unsuccessful due to an instantaneous reductive elimination process during the reaction with chelating phosphines. Treatment of trans-[Pt(BCat')Me(PCy(3))(2)] with Cat(2)B(2) led to the formation of CatBMe and Cat'BMe. In the course of further investigations into this reaction, indications for two indistinguishable reaction mechanisms were found: 1) associative formation of a six-coordinate platinum centre prior to reductive elimination and 2) σ-bond metathesis of B-B and C-Pt bonds. Mechanism 1 provides a straightforward explanation for the formation of both methylboranes. Scrambling of diboranes(4) Cat(2)B(2) and Cat'(2)B(2) in the presence of [Pt(PCy(3))(2)], fully reductive elimination of CatBMe or Cat'BMe from trans-[Pt(BCat')Me(PCy(3))(2)] in the presence of sub-stoichiometric amounts of Cat(2)B(2), and evidence for the reversibility of the oxidative addition of Cat(2)B(2) to [Pt(PCy(3))(2)] all support mechanism 2, which consists of sequential equilibria reactions. Furthermore, the solid-state molecular structure of cis-[Pt(BCat)(2)(PCy(3))(2)] and cis-[Pt(BCat')(2)(PCy(3))(2)] were investigated. The remarkably short B-B separations in both bis(boryl) complexes suggest that the two boryl ligands in each case are more loosely bound to the Pt(II) centre than in related bis(boryl) species. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Fungus hyphae-supported alumina: An efficient and reclaimable adsorbent for fluoride removal from water.

PubMed

Yang, Weichun; Tian, Shunqi; Tang, Qiongzhi; Chai, Liyuan; Wang, Haiying

2017-06-15

A reclaimable adsorbent of fungus hyphae-supported alumina (FHSA) bio-nanocomposites was developed, characterized and applied in fluoride removal from water. This adsorbent can be fast assembled and disassemble reversibly, promising efficient reclamation and high accessible surface area for fluoride adsorption. Adsorption experiments demonstrate that the FHSA performed well over a considerable wide pH range of 3-10 with high fluoride removal efficiencies (>66.3%). The adsorption capacity was 105.60mgg -1 for FHSA, much higher than that for the alumina nanoparticles (50.55mgg -1 ) and pure fungus hyphae (22.47mgg -1 ). The adsorption capacity calculated by the pure content of alumina in the FHSA is 340.27mgg -1 of alumina. Kinetics data reveal that the fluoride adsorption process on the FHSA was fast, nearly 90% fluoride adsorption can be achieved within 40min. The fluoride adsorption on the FHSA is mainly due to the surface complexes formation of fluoride with AlOH and the attraction between protonated NH 2 and fluoride through hydrogen bonding. Findings demonstrate that the FHSA has potential applicability in fluoride removal due to its strong fluoride adsorbility and the easy reclamation by its fast reversible assembly and disassembly feature. Copyright © 2017 Elsevier Inc. All rights reserved.

High-Performance Hydrogen Storage Nanoparticles Inside Hierarchical Porous Carbon Nanofibers with Stable Cycling.

PubMed

Xia, Guanglin; Chen, Xiaowei; Zhao, Yan; Li, Xingguo; Guo, Zaiping; Jensen, Craig M; Gu, Qinfen; Yu, Xuebin

2017-05-10

An effective route based on space-confined chemical reaction to synthesize uniform Li 2 Mg(NH) 2 nanoparticles is reported. The hierarchical pores inside the one-dimensional carbon nanofibers (CNFs), induced by the creation of well-dispersed Li 3 N, serve as intelligent nanoreactors for the reaction of Li 3 N with Mg-containing precursors, resulting in the formation of uniformly discrete Li 2 Mg(NH) 2 nanoparticles. The nanostructured Li 2 Mg(NH) 2 particles inside the CNFs are capable of complete hydrogenation and dehydrogenation at a temperature as low as 105 °C with the suppression of ammonia release. Furthermore, by virtue of the nanosize effects and space-confinement by the porous carbon scaffold, no degradation was observed after 50 de/rehydrogenation cycles at a temperature as low as 130 °C for the as-prepared Li 2 Mg(NH) 2 nanoparticles, indicating excellent reversibility. Moreover, the theoretical calculations demonstrate that the reduction in particle size could significantly enhance the H 2 sorption of Li 2 Mg(NH) 2 by decreasing the relative activation energy barrier, which agrees well with our experimental results. This method could represent an effective, general strategy for synthesizing nanoparticles of complex hydrides with stable reversibility and excellent hydrogen storage performance.

Role of mitochondrial dysfunction in neurotoxicity of MPP+: partial protection of PC12 cells by acetyl-L-carnitine.

PubMed

Virmani, Ashraf; Gaetani, Franco; Binienda, Zbigniew; Xu, Alex; Duhart, Helen; Ali, Syed F

2004-10-01

The damage to the central nervous system that is observed after administration of either methamphetamine (METH) or 1-methyl-4-phenylpyridinium (MPP+), the neurotoxic metabolite of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), is known to be linked to dopamine (DA). The underlying neurotoxicity mechanism for both METH and MPP+ seem to involve free radical formation and impaired mitochondrial function. The MPP+ is thought to selectively kill nigrostriatal dopaminergic neurons by inhibiting mitochondrial complex I, with cell death being attributed to oxidative stress damage to these vulnerable DA neurons. In the present study, MPP+ was shown to significantly inhibit the response to MTT by cultured PC12 cells. This inhibitory action of MPP+ could be partially reversed by the co-incubation of the cells with the acetylated form of carnitine, acetyl-L-carnitine (ALC). Since at least part of the toxic action of MPP+ is related to mitochondrial inhibition, the partial reversal of the inhibition of MTT response by ALC could involve a partial restoration of mitochondrial function. The role carnitine derivatives, such as ALC, play in attenuating MPP+ and METH-evoked toxicity is still under investigation to elucidate the contribution of mitochondrial dysfunction in mechanisms of neurotoxicity.

Green tea and cocoa enhance cognition in Lymnaea

PubMed Central

Swinton, Erin; de Freitas, Emily; Swinton, Cayley; Shymansky, Tamila; Hiles, Emily; Zhang, Jack; Rothwell, Cailin; Lukowiak, Ken

2018-01-01

ABSTRACT A flavonoid, (-)-epicatechi (Epi), enhances long-term memory (LTM) formation in Lymnaea and reverses memory obstruction caused by stress. Many foods contain substantial amounts of Epi, (e.g. green tea and cocoa). In humans eating such foods may directly or indirectly enhance cognition. We directly test whether operant conditioning training Lymnaea in these natural foods result in the same effects as training snails in pure Epi. We found that exposure to products containing high concentrations of Epi (e.g. green tea and cocoa) during training enhanced memory formation and could even reverse a learning and memory deficit brought about by stress. Epi can be photo-inactivated by exposure to ultraviolet light. We found that following photo-inactivation of Epi, memory enhancement did not occur. Photo-inactivation of foods containing Epi (e,g. green tea) blocked their ability to enhance LTM. Our data are thus consistent with the hypothesis that dietary sources of Epi can have positive benefits on cognitive ability and be able to reverse memory aversive states. PMID:29497476

Nucleophilic catalysis of acylhydrazone equilibration for protein-directed dynamic covalent chemistry

PubMed Central

Bhat, Venugopal T.; Caniard, Anne M.; Luksch, Torsten; Brenk, Ruth; Campopiano, Dominic J.; Greaney, Michael F.

2010-01-01

Dynamic covalent chemistry uses reversible chemical reactions to set up an equilibrating network of molecules at thermodynamic equilibrium, which can adjust its composition in response to any agent capable of altering the free energy of the system. When the target is a biological macromolecule, such as a protein, the process corresponds to the protein directing the synthesis of its own best ligand. Here, we demonstrate that reversible acylhydrazone formation is an effective chemistry for biological dynamic combinatorial library formation. In the presence of aniline as a nucleophilic catalyst, dynamic combinatorial libraries equilibrate rapidly at pH 6.2, are fully reversible, and may be switched on or off by means of a change in pH. We have interfaced these hydrazone dynamic combinatorial libraries with two isozymes from the glutathione S-transferase class of enzyme, and observed divergent amplification effects, where each protein selects the best-fitting hydrazone for the hydrophobic region of its active site. PMID:20489719

Optical reversible programmable Boolean logic unit.

PubMed

Chattopadhyay, Tanay

2012-07-20

Computing with reversibility is the only way to avoid dissipation of energy associated with bit erase. So, a reversible microprocessor is required for future computing. In this paper, a design of a simple all-optical reversible programmable processor is proposed using a polarizing beam splitter, liquid crystal-phase spatial light modulators, a half-wave plate, and plane mirrors. This circuit can perform 16 logical operations according to three programming inputs. Also, inputs can be easily recovered from the outputs. It is named the "reversible programmable Boolean logic unit (RPBLU)." The logic unit is the basic building block of many complex computational operations. Hence the design is important in sense. Two orthogonally polarized lights are defined here as two logical states, respectively.

Formation of the acrosome complex in the bush cricket Gampsocleis gratiosa (Orthoptera: Tettigoniidae).

PubMed

Su, Cai Xia; Chen, Jie; Shi, Fu Ming; Guo, Ming Shen; Chang, Yan Lin

2017-07-01

The acrosome complex plays an indispensable role in the normal function of mature spermatozoa. However, the dynamic process of acrosome complex formation in insect remains poorly understood. Gampsocleis gratiosa Brunner von Wattenwyl possesses the typical characteristic of insect sperms, which is tractable in terms of size, and therefore was selected for the acrosome formation study in this report. The results show that acrosome formation can be divided into six phases: round, rotating, rhombic, cylindrical, transforming and mature phase, based on the morphological dynamics of acrosome complex and nucleus. In addition, the cytoskeleton plays a critical role in the process of acrosome formation. The results from this study indicate that: (1) glycoprotein is the major component of the acrosome proper; (2) the microfilament is one element of the acrosome complex, and may mediate the morphologic change of the acrosome complex; (3) the microtubules might also shape the nucleus and acrosome complex during the acrosome formation. Copyright © 2017 Elsevier Ltd. All rights reserved.

Reversible double oxidation and protonation of the non-innocent bridge in a nickel(II) salophen complex.

PubMed

de Bellefeuille, David; Askari, Mohammad S; Lassalle-Kaiser, Benedikt; Journaux, Yves; Aukauloo, Ally; Orio, Maylis; Thomas, Fabrice; Ottenwaelder, Xavier

2012-12-03

Substitution on the aromatic bridge of a nickel(II) salophen complex with electron-donating dimethylamino substituents creates a ligand with three stable, easily and reversibly accessible oxidation states. The one-electron-oxidized product is characterized as a nickel(II) radical complex with the radical bore by the central substituted aromatic ring, in contrast to other nickel(II) salen or salophen complexes that oxidize on the phenolate moieties. The doubly oxidized product, a singlet species, is best described as having an iminobenzoquinone bridge with a vinylogous distribution of bond lengths between the dimethylamino substituents. Protonation of the dimethylamino substituents inhibits these redox processes on the time scale of cyclovoltammetry, but electrolysis and chemical oxidation are consistent with deprotonation occurring concomitantly with electron transfer to yield the mono- and dioxidized species described above.

Recycling tires? Reversible crosslinking of poly(butadiene).

PubMed

Trovatti, Eliane; Lacerda, Talita M; Carvalho, Antonio J F; Gandini, Alessandro

2015-04-01

Furan-modified poly(butadiene) prepared by the thiol-ene click reaction is crosslinked with bismaleimides through the Diels-Alder reaction, giving rise to a novel recyclable elastomer. This is possible because of the thermal reversibility of the adducts responsible for the formation of the network. The use of this strategy provides the possibility to produce recyclable tires. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Nano-encrypted Morse code: a versatile approach to programmable and reversible nanoscale assembly and disassembly.

PubMed

Wong, Ngo Yin; Xing, Hang; Tan, Li Huey; Lu, Yi

2013-02-27

While much work has been devoted to nanoscale assembly of functional materials, selective reversible assembly of components in the nanoscale pattern at selective sites has received much less attention. Exerting such a reversible control of the assembly process will make it possible to fine-tune the functional properties of the assembly and to realize more complex designs. Herein, by taking advantage of different binding affinities of biotin and desthiobiotin toward streptavidin, we demonstrate selective and reversible decoration of DNA origami tiles with streptavidin, including revealing an encrypted Morse code "NANO" and reversible exchange of uppercase letter "I" with lowercase "i". The yields of the conjugations are high (>90%), and the process is reversible. We expect this versatile conjugation technique to be widely applicable with different nanomaterials and templates.

Molecular and biochemical characterization of two tungsten- and selenium-containing formate dehydrogenases from Eubacterium acidaminophilum that are associated with components of an iron-only hydrogenase.

PubMed

Graentzdoerffer, Andrea; Rauh, David; Pich, Andreas; Andreesen, Jan R

2003-01-01

Two gene clusters encoding similar formate dehydrogenases (FDH) were identified in Eubacterium acidaminophilum. Each cluster is composed of one gene coding for a catalytic subunit ( fdhA-I, fdhA-II) and one for an electron-transferring subunit ( fdhB-I, fdhB-II). Both fdhA genes contain a TGA codon for selenocysteine incorporation and the encoded proteins harbor five putative iron-sulfur clusters in their N-terminal region. Both FdhB subunits resemble the N-terminal region of FdhA on the amino acid level and contain five putative iron-sulfur clusters. Four genes thought to encode the subunits of an iron-only hydrogenase are located upstream of the FDH gene cluster I. By sequence comparison, HymA and HymB are predicted to contain one and four iron-sulfur clusters, respectively, the latter protein also binding sites for FMN and NAD(P). Thus, HymA and HymB seem to represent electron-transferring subunits, and HymC the putative catalytic subunit containing motifs for four iron-sulfur clusters and one H-cluster specific for Fe-only hydrogenases. HymD has six predicted transmembrane helices and might be an integral membrane protein. Viologen-dependent FDH activity was purified from serine-grown cells of E. acidaminophilum and the purified protein complex contained four subunits, FdhA and FdhB, encoded by FDH gene cluster II, and HymA and HymB, identified after determination of their N-terminal sequences. Thus, this complex might represent the most simple type of a formate hydrogen lyase. The purified formate dehydrogenase fraction contained iron, tungsten, a pterin cofactor, and zinc, but no molybdenum. FDH-II had a two-fold higher K(m) for formate (0.37 mM) than FDH-I and also catalyzed CO(2) reduction to formate. Reverse transcription (RT)-PCR pointed to increased expression of FDH-II in serine-grown cells, supporting the isolation of this FDH isoform. The fdhA-I gene was expressed as inactive protein in Escherichia coli. The in-frame UGA codon for selenocysteine incorporation was read in the heterologous system only as stop codon, although its potential SECIS element exhibited a quite high similarity to that of E. coli FDH.

The Development of Ambiguous Figure Perception

ERIC Educational Resources Information Center

Wimmer, Marina C.; Doherty, Martin J.

2011-01-01

Ambiguous figures have fascinated researchers for almost 200 years. The physical properties of these figures remain constant, yet two distinct interpretations are possible; these reverse (switch) from one percept to the other. The consensus is that reversal requires complex interaction of perceptual bottom-up and cognitive top-down elements. The…

Inclusion Complexes of Diisopropyl Fluorophosphate with Cyclodextrins.

DTIC Science & Technology

1987-09-01

SUPPLEMENTARY NOTATION For Submission to Journal of Catalysis. 17. COSATI CODES 18. SUBJECT TERMS (Continue on reverse if necessary and identify by block...number) FIELD GROUP SUB-GROUP 19. ABSTRACT (Continue on reverse if necessary and identify by block number) See Attached DTIC S ELECTESNOV 2 3 1987D 20

Membrane fusion and exocytosis.

PubMed

Jahn, R; Südhof, T C

1999-01-01

Membrane fusion involves the merger of two phospholipid bilayers in an aqueous environment. In artificial lipid bilayers, fusion proceeds by means of defined transition states, including hourglass-shaped intermediates in which the proximal leaflets of the fusing membranes are merged whereas the distal leaflets are separate (fusion stalk), followed by the reversible opening of small aqueous fusion pores. Fusion of biological membranes requires the action of specific fusion proteins. Best understood are the viral fusion proteins that are responsible for merging the viral with the host cell membrane during infection. These proteins undergo spontaneous and dramatic conformational changes upon activation. In the case of the paradigmatic fusion proteins of the influenza virus and of the human immunodeficiency virus, an amphiphilic fusion peptide is inserted into the target membrane. The protein then reorients itself, thus forcing the fusing membranes together and inducing lipid mixing. Fusion of intracellular membranes in eukaryotic cells involves several protein families including SNAREs, Rab proteins, and Sec1/Munc-18 related proteins (SM-proteins). SNAREs form a novel superfamily of small and mostly membrane-anchored proteins that share a common motif of about 60 amino acids (SNARE motif). SNAREs reversibly assemble into tightly packed helical bundles, the core complexes. Assembly is thought to pull the fusing membranes closely together, thus inducing fusion. SM-proteins comprise a family of soluble proteins that bind to certain types of SNAREs and prevent the formation of core complexes. Rab proteins are GTPases that undergo highly regulated GTP-GDP cycles. In their GTP form, they interact with specific proteins, the effector proteins. Recent evidence suggests that Rab proteins function in the initial membrane contact connecting the fusing membranes but are not involved in the fusion reaction itself.

The controlled formation and cleavage of an intramolecular d8-d8 Pt-Pt interaction in a dinuclear cycloplatinated molecular "pivot-hinge".

PubMed

Koo, Chi-Kin; Wong, Ka-Leung; Lau, Kai-Cheung; Wong, Wai-Yeung; Lam, Michael Hon-Wah

2009-08-03

The bis(diphenylphosphino)methane (dppm)-bridged dinuclear cycloplatinated complex {[Pt(L)](2)(mu-dppm)}(2+) (Pt(2)dppm; HL: 2-phenyl-6-(1H-pyrazol-3-yl)-pyridine) demonstrates interesting reversible "pivot-hinge"-like intramolecular motions in response to the protonation/deprotonation of L. In its protonated "closed" configuration, the two platinum(II) centers are held in position by intramolecular d(8)-d(8) Pt-Pt interaction. In its deprotonated "open" configuration, such Pt-Pt interaction is cleaved. To further understand the mechanism behind this hingelike motion, an analogous dinuclear cycloplatinated complex, {[Pt(L)](2)(mu-dchpm)}(2+) (Pt(2)dchpm) with bis(dicyclohexylphosphino)methane (dchpm) as the bridging ligand, was synthesized. From its protonation/deprotonation responses, it was revealed that aromatic pi-pi interactions between the phenyl moieties of the mu-dppm and the deprotonated pyrazolyl rings of L was essential to the reversible cleavage of the intramolecular Pt-Pt interaction in Pt(2)dppm. In the case of Pt(2)dchpm, spectroscopic and spectrofluorometric titrations as well as X-ray crystallography indicated that the distance between the two platinum(II) centers shrank upon deprotonation, thus causing a redshift in its room-temperature triplet metal-metal-to-ligand charge-transfer emission from 614 to 625 nm. Ab initio calculations revealed the presence of intramolecular hydrogen bonding between the deprotonated and negatively charged 1-pyrazolyl-N moiety and the methylene CH and phenyl C-H of the mu-dppm. The "open" configuration of the deprotonated Pt(2)dppm was estimated to be 19 kcal mol(-1) more stable than its alternative "closed" configuration. On the other hand, the open configuration of the deprotonated Pt(2)dchpm was 6 kcal mol(-1) less stable than its alternative closed configuration.

Inconsistent magnetic polarities in magnetite- and greigite-bearing sediments: Understanding complex magnetizations in the late Messinian in the Adana Basin (southern Turkey)

NASA Astrophysics Data System (ADS)

Lucifora, Stella; Cifelli, Francesca; Mattei, Massimo; Sagnotti, Leonardo; Cosentino, Domenico; Roberts, Andrew P.

2012-10-01

We present paleomagnetic, rock magnetic and scanning electron microscope data from three upper Messinian stratigraphic sections from the Adana Basin (southern Turkey). The collected samples are from fine-grained units, which were deposited during the Messinian Salinity Crisis (within subchron C3r). Paleomagnetic results reveal an inconsistent polarity record, related to a mixture of magnetite and greigite that hinders determination of a reliable magnetostratigraphy. Three classes of samples are recognized on the basis of paleomagnetic results. The first is characterized by a single magnetization component, with normal polarity, that is stable up to 530-580°C and is carried by magnetite. The second is characterized by a single magnetization component, with reversed polarity, that is stable up to 330-420°C. This magnetization is due to greigite, which developed after formation of slumps and before tectonic tilting of the studied successions. The third is characterized by reversed polarity, which is stable up to 530-580°C. We interpret this component as a primary magnetization carried by fine-grained and magnetically stable detrital magnetite. Results indicate that in the Adana Basin the assumption that a primary magnetization is carried by magnetite, and a magnetic overprint carried by greigite, does not hold because a late magnetic overprint has also been found for magnetite-bearing samples. Our data illustrate the complexity of magnetostratigraphic reconstructions in successions characterized by variable mixtures of magnetic minerals with different magnetic stability that formed at different stages. We demonstrate the need to perform detailed magnetic mineralogy analyses when conducting magnetostratigraphic studies of clay-rich sediments from marine or lacustrine environments.

Effects of the incorporation of ε-aminocaproic acid/chitosan particles to fibrin on cementoblast differentiation and cementum regeneration.

PubMed

Park, Chan Ho; Oh, Joung-Hwan; Jung, Hong-Moon; Choi, Yoonnyoung; Rahman, Saeed Ur; Kim, Sungtae; Kim, Tae-Il; Shin, Hong-In; Lee, Yun-Sil; Yu, Frank H; Baek, Jeong-Hwa; Ryoo, Hyun-Mo; Woo, Kyung Mi

2017-10-01

Cementum formation on the exposed tooth-root surface is a critical process in periodontal regeneration. Although various therapeutic approaches have been developed, regeneration of integrated and functional periodontal complexes is still wanting. Here, we found that the OCCM30 cementoblasts cultured on fibrin matrix express substantial levels of matrix proteinases, leading to the degradation of fibrin and the apoptosis of OCCM30 cells, which was reversed upon treatment with a proteinase inhibitor, ε-aminocaproic acid (ACA). Based on these findings, ACA-releasing chitosan particles (ACP) were fabricated and ACP-incorporated fibrin (fibrin-ACP) promoted the differentiation of cementoblasts in vitro, as confirmed by bio-mineralization and expressions of molecules associated with mineralization. In a periodontal defect model of beagle dogs, fibrin-ACP resulted in substantial cementum formation on the exposed root dentin in vivo, compared to fibrin-only and enamel matrix derivative (EMD) which is used clinically for periodontal regeneration. Remarkably, the fibrin-ACP developed structural integrations of the cementum-periodontal ligament-bone complex by the Sharpey's fiber insertion. In addition, fibrin-ACP promoted alveolar bone regeneration through increased bone volume of tooth roof-of-furcation defects and root coverage. Therefore, fibrin-ACP can promote cementogenesis and osteogenesis by controlling biodegradability of fibrin, implicating the feasibility of its therapeutic use to improve periodontal regeneration. Cementum, the mineralized layer on root dentin surfaces, functions to anchor fibrous connective tissues on tooth-root surfaces with the collagenous Sharpey's fibers integration, of which are essential for periodontal functioning restoration in the complex. Through the cementum-responsible fiber insertions on tooth-root surfaces, PDLs transmit various mechanical responses to periodontal complexes against masticatory/occlusal stimulations to support teeth. In this study, periodontal tissue regeneration was enhanced by use of modified fibrin biomaterial which significantly promoted cementogenesis within the periodontal complex with structural integration by collagenous Sharpey's fiber insertions in vivo by controlling fibrin degradation and consequent cementoblast apoptosis. Furthermore, the modified fibrin could improve repair and regeneration of tooth roof-of-furcation defects, which has spatial curvatures and geometrical difficulties and hardly regenerates periodontal tissues. Copyright © 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

A composite of complex and chemical hydrides yields the first Al-based amidoborane with improved hydrogen storage properties.

PubMed

Dovgaliuk, Iurii; Jepsen, Lars H; Safin, Damir A; Łodziana, Zbigniew; Dyadkin, Vadim; Jensen, Torben R; Devillers, Michel; Filinchuk, Yaroslav

2015-10-05

The first Al-based amidoborane Na[Al(NH2 BH3 )4 ] was obtained through a mechanochemical treatment of the NaAlH4 -4 AB (AB=NH3 BH3 ) composite releasing 4.5 wt % of pure hydrogen. The same amidoborane was also produced upon heating the composite at 70 °C. The crystal structure of Na[Al(NH2 BH3 )4 ], elucidated from synchrotron X-ray powder diffraction and confirmed by DFT calculations, contains the previously unknown tetrahedral ion [Al(NH2 BH3 )4 ](-) , with every NH2 BH3 (-) ligand coordinated to aluminum through nitrogen atoms. Combination of complex and chemical hydrides in the same compound was possible due to both the lower stability of the AlH bonds compared to the BH ones in borohydride, and due to the strong Lewis acidity of Al(3+) . According to the thermogravimetric analysis-differential scanning calorimetry-mass spectrometry (TGA-DSC-MS) studies, Na[Al(NH2 BH3 )4 ] releases in two steps 9 wt % of pure hydrogen. As a result of this decomposition, which was also supported by volumetric studies, the formation of NaBH4 and amorphous product(s) of the surmised composition AlN4 B3 H(0-3.6) were observed. Furthermore, volumetric experiments have also shown that the final residue can reversibly absorb about 27 % of the released hydrogen at 250 °C and p(H2 )=150 bar. Hydrogen re-absorption does not regenerate neither Na[Al(NH2 BH3 )4 ] nor starting materials, NaAlH4 and AB, but rather occurs within amorphous product(s). Detailed studies of the latter one(s) can open an avenue for a new family of reversible hydrogen storage materials. Finally, the NaAlH4 -4 AB composite might become a starting point towards a new series of aluminum-based tetraamidoboranes with improved hydrogen storage properties such as hydrogen storage density, hydrogen purity, and reversibility. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Myasthenia gravis: the role of complement at the neuromuscular junction.

PubMed

Howard, James F

2018-01-01

Generalized myasthenia gravis (gMG) is a rare autoimmune disorder characterized by skeletal muscle weakness caused by disrupted neurotransmission at the neuromuscular junction (NMJ). Approximately 74-88% of patients with gMG have acetylcholine receptor (AChR) autoantibodies. Complement plays an important role in innate and antibody-mediated immunity, and activation and amplification of complement results in the formation of membrane attack complexes (MACs), lipophilic proteins that damage cell membranes. The role of complement in gMG has been demonstrated in animal models and patients. Studies in animals lacking specific complement proteins have confirmed that MAC formation is required to induce experimental autoimmune MG (EAMG) and NMJ damage. Complement inhibition in EAMG models can prevent disease induction and reverse its progression. Patients with anti-AChR + MG have autoantibodies and MACs present at NMJs. Damaged NMJs are associated with more severe disease, fewer AChRs, and MACs in synaptic debris. Current MG therapies do not target complement directly. Eculizumab is a humanized monoclonal antibody that inhibits cleavage of complement protein C5, preventing MAC formation. Eculizumab treatment improved symptoms compared with placebo in a phase II study in patients with refractory gMG. Direct complement inhibition could preserve NMJ physiology and muscle function in patients with anti-AChR + gMG. © 2017 The Authors. Annals of the New York Academy of Sciences published by Wiley Periodicals Inc. on behalf of The New York Academy of Sciences.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Itoh, Masahiko; Nelson, Celeste M.; Myers, Connie A.

Maintenance of apico-basal polarity in normal breast epithelial acini requires a balance between cell proliferation, cell death, and proper cell-cell and cell-extracellular matrix signaling. Aberrations in any of these processes can disrupt tissue architecture and initiate tumor formation. Here we show that the small GTPase Rap1 is a crucial element in organizing acinar structure and inducing lumen formation. Rap1 activity in malignant HMT-3522 T4-2 cells is appreciably higher than in S1 cells, their non-malignant counterparts. Expression of dominant-negative Rap1 resulted in phenotypic reversion of T4-2 cells, led to formation of acinar structures with correct apico-basal polarity, and dramatically reduced tumormore » incidence despite the persistence of genomic abnormalities. The resulting acini contained prominent central lumina not observed when other reverting agents were used. Conversely, expression of dominant-active Rap1 in T4-2 cells inhibited phenotypic reversion and led to increased invasiveness and tumorigenicity. Thus, Rap1 acts as a central regulator of breast architecture, with normal levels of activation instructing apical polarity during acinar morphogenesis, and increased activation inducing tumor formation and progression to malignancy.« less

The significance of ACTH for the process of formation of complex heparin compounds in the blood during immobilization stress

NASA Technical Reports Server (NTRS)

Kudryashov, B. A.; Shapiro, F. B.; Lomovskaya, F. B.; Lyapina, L. A.

1979-01-01

Adrenocorticotropin (ACTH) was administered to rats at different times following adrenalectomy. Adrenocorticotropin caused a significant increase in the formation of heparin complexes even in the absence of stress factor. When ACTH secretion is blocked, immobilization stress is not accompanied by an increase in the process of complex formation. The effect of ACTH on the formation of heparin complexes was mediated through its stimulation of the adrenal cortex.

Time-reversal in geophysics: the key for imaging a seismic source, generating a virtual source or imaging with no source (Invited)

NASA Astrophysics Data System (ADS)

Tourin, A.; Fink, M.

2010-12-01

The concept of time-reversal (TR) focusing was introduced in acoustics by Mathias Fink in the early nineties: a pulsed wave is sent from a source, propagates in an unknown media and is captured at a transducer array termed a “Time Reversal Mirror (TRM)”. Then the waveforms received at each transducer are flipped in time and sent back resulting in a wave converging at the original source regardless of the complexity of the propagation medium. TRMs have now been implemented in a variety of physical scenarios from GHz microwaves to MHz ultrasonics and to hundreds of Hz in ocean acoustics. Common to this broad range of scales is a remarkable robustness exemplified by observations that the more complex the medium (random or chaotic), the sharper the focus. A TRM acts as an antenna that uses complex environments to appear wider than it is, resulting for a broadband pulse, in a refocusing quality that does not depend on the TRM aperture. We show that the time-reversal concept is also at the heart of very active research fields in seismology and applied geophysics: imaging of seismic sources, passive imaging based on noise correlations, seismic interferometry, monitoring of CO2 storage using the virtual source method. All these methods can indeed be viewed in a unified framework as an application of the so-called time-reversal cavity approach. That approach uses the fact that a wave field can be predicted at any location inside a volume (without source) from the knowledge of both the field and its normal derivative on the surrounding surface S, which for acoustic scalar waves is mathematically expressed in the Helmholtz Kirchhoff (HK) integral. Thus in the first step of an ideal TR process, the field coming from a point-like source as well as its normal derivative should be measured on S. In a second step, the initial source is removed and monopole and dipole sources reemit the time reversal of the components measured in the first step. Instead of directly computing the resulting HK integral along S, physical arguments can be used to straightforwardly predict that the time-reversed field in the cavity writes as the difference of advanced and retarded Green’s functions centred on the initial source position. This result is in some way disappointing because it means that reversing a field using a closed TRM is not enough to realize a perfect time-reversal experiment. In practical applications, the converging wave is always followed by a diverging one (see figure). However we will show that this result is of great importance since it furnishes the basis for imaging methods in media with no active source. We will focus more especially on the virtual source method showing that it can be used for implementing the DORT method (Decomposition of the time reversal operator) in a passive way. The passive DORT method could be interesting for monitoring changes in a complex scattering medium, for example in the context of CO2 storage. Time-reversal imaging applied to the giant Sumatra earthquake

Effects of the resistivity profile on the formation of a reversed configuration and single helicity states in compressible simulations of the reversed-field pinch

DOE Office of Scientific and Technical Information (OSTI.GOV)

Onofri, M.; Malara, F.

2013-10-15

Compressible magnetohydrodynamics simulations of the reversed-field pinch (RFP) are presented. Previous simulations of the RFP, including density and pressure evolution, showed that a stationary state with a reversed toroidal magnetic field could not be obtained, contrary to the results produced with numerical codes neglecting density and pressure dynamics. The simulations described in the present paper show that including density and pressure evolution, a stationary RFP configuration can be obtained if the resistivity has a radial profile steeply increasing close to the wall. Such resistivity profile is more realistic than a uniform resistivity, since the temperature at the wall is lowermore » than in the plasma core.« less

Transitional paleointensities from Kauai, Hawaii, and geomagnetic reversal models

USGS Publications Warehouse

Bogue, Scott W.; Coe, Robert S.

1984-01-01

Previously presented paleointensity results from an R-N transition zone in Kauai, Hawaii, show that field intensity dropped from 0. 431 Oe to 0. 101 Oe while the field remained within 30 degree of the reversed axial dipole direction. A recovery in intensity and the main directional change followed this presumably short period of low field strength. As the reversal neared completion, the field has an intensity of 0. 217 Oe while still 40 degree from the final direction. The relationship of paleointensity to field direction during the early part of the reversal thus differs from that toward the end, a feature that only some reversal models are consistent with. For example, a model in which a standing nondipole component persists through the dipole reversal predicts only symmetric intensity patterns. In contrast, zonal flooding models generate suitably complex field behavior if multiple flooding schemes operate during a single reversal or if the flooding process is itself asymmetric.

Structural complexity at and around the Triassic-Jurassic GSSP at Kuhjoch, Northern Calcareous Alps, Austria

NASA Astrophysics Data System (ADS)

Palotai, M.; Pálfy, J.; Sasvári, Á.

2017-10-01

One of the key requirements for a Global Stratotype Section and Point (GSSP) is the absence of tectonic disturbance. The GSSP for the Triassic-Jurassic system boundary was recently defined at Kuhjoch, Northern Calcareous Alps, Austria. New field observations in the area of the Triassic-Jurassic boundary GSSP site demonstrate that the overturned, tight, and almost upright Karwendel syncline was formed at semibrittle deformation conditions, confirmed by axial planar foliation. Tight to isoclinal folds at various scales were related to a tectonic transport to the north. Brittle faulting occurred before and after folding as confirmed by tilt tests (the rotation of structural data by the average bedding). Foliation is ubiquitous in the incompetent units, including the Kendlbach Formation at the GSSP. A reverse fault (inferred to be formed as a normal fault before folding) crosscuts the GSSP sections, results in the partial tectonic omission of the Schattwald Beds, and thus makes it impossible to measure a complete and continuous stratigraphic section across the whole Kendlbach Formation. Based on these observations, the Kuhjoch sections do not fulfil the specific requirement for a GSSP regarding the absence of tectonic disturbances near boundary level.

Unsteady RANS/DES analysis of flow around helicopter rotor blades at forword flight conditions

NASA Astrophysics Data System (ADS)

Zhang, Zhenyu; Qian, Yaoru

2018-05-01

In this paper, the complex flows around forward-flying helicopter blades are numerically investigated. Both the Reynolds-averaged Navier-Stokes (RANS) and the Detached Eddy Simulation (DES) methods are used for the analysis of characteristics like local dynamic flow separation, effects of radial sweeping and reversed flow. The flow was solved by a highly efficient finite volume solver with multi-block structured grids. Focusing upon the complexity of the advance ratio effects, above properties are fully recognized. The current results showed significant agreements between both RANS and DES methods at phases with attached flow phases. Detailed information of separating flow near the withdrawal phases are given by DES results. The flow analysis of these blades under reversed flow reveals a significant interaction between the reversed flow and the span-wise sweeping.