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1

Detection of low-populated reaction intermediates with hyperpolarized NMR.  

PubMed

Hyperpolarized (13)C NMR spectroscopy can provide the sensitivity and spectral resolution to detect, identify and quantify low-populated reaction intermediates, thus yielding direct chemical information on reaction mechanisms in real-time assays. PMID:20448982

Jensen, Pernille R; Meier, Sebastian; Ardenkjaer-Larsen, Jan H; Duus, Jens Ø; Karlsson, Magnus; Lerche, Mathilde H

2009-07-20

2

Nitroxyl disulfides, novel intermediates in transnitrosation reactions.  

PubMed

A novel anionic RSN(O)SR species, the intermediate in transnitrosation reactions, was explored computationally with B3LYP and CBS-QB3 methods. The species resembles a nitroxyl coordinated to a highly distorted disulfide, and it differs significantly from intermediates in nucleophilic acyl substitution. Reactions of the following species were computed for comparison: MeS(-) + MeSNO; MeO(-) + MeONO; MeS(-) + MeSCHO; MeO(-) + MeOCHO. The last two have very different intermediates from the first two. Mass spectrometric experimental evidence is presented that is consistent with the formation of a nitroxyl disulfide in the gas phase. The calculated proton affinity and redox potentials of the intermediate are also reported. PMID:12783550

Houk, K N; Hietbrink, Bruce N; Bartberger, Michael D; McCarren, Patrick R; Choi, Bo Yoon; Voyksner, Robert D; Stamler, Jonathan S; Toone, Eric J

2003-06-11

3

Transfer and breakup reactions at intermediate energies  

SciTech Connect

The origin of the quasi-elastic peak in peripheral heavy-ion reactions is discussed in terms of inelastic scattering and transfer reactions to unbound states of the primary projectile-like fragment. The situation is analogous to the use of reverse kinematics in fusion reactions, a technique in which the object of study is moving with nearly the beam velocity. It appears that several important features of the quasi-elastic peak may be explained by this approach. Projectile-breakup reactions have attractive features for the study of nuclear structure. They may also be used to determine the partition of excitation energy in peripheral reactions. At intermediate energies, neutron-pickup reactions leading to four-body final states become important. Examples of experiments are presented that illustrate these points. 15 refs., 14 figs.

Stokstad, R.G.

1986-04-01

4

A new intermediate in the Prins reaction  

PubMed Central

Summary Two Prins reactions were investigated by the use of DFT calculations. A model composed of R–CH=CH2 + H3O+(H2O)13 + (H2C=O)2, R = Me and Ph, was adopted to trace reaction paths. For both alkenes, the concerted path forming 1,3-diols was obtained as the rate determining step (TS1). TS stands for a transition state. From the 1,3-diol, a bimolecular elimination (TS2) leads to the allylic alcohol as the first channel. In the second channel, the 1,3-diol was converted via TS3 into an unprecedented hemiacetal intermediate, HO–CH2–O–CH(R)–CH2–CH2–OH. This intermediate undergoes ring closure (TS4), affording the 1,3-dioxane product. The intermediate is of almost the same stability as the product, and two species were suggested to be in a state of equilibrium. While the geometry of TS1 appears to be forwarded to that of a carbocation intermediate, the cation disappeared through the enlargement of the water cluster. Dynamical calculations of a classical trajectory using the atom-centered density matrix propagation molecular dynamics model on the four TSs were carried out, and results of IRC calculations were confirmed by them.

Fukuda, Takeshi; Yamazaki, Shoko

2013-01-01

5

A new intermediate in the Prins reaction.  

PubMed

Two Prins reactions were investigated by the use of DFT calculations. A model composed of R-CH=CH2 + H3O(+)(H2O)13 + (H2C=O)2, R = Me and Ph, was adopted to trace reaction paths. For both alkenes, the concerted path forming 1,3-diols was obtained as the rate determining step (TS1). TS stands for a transition state. From the 1,3-diol, a bimolecular elimination (TS2) leads to the allylic alcohol as the first channel. In the second channel, the 1,3-diol was converted via TS3 into an unprecedented hemiacetal intermediate, HO-CH2-O-CH(R)-CH2-CH2-OH. This intermediate undergoes ring closure (TS4), affording the 1,3-dioxane product. The intermediate is of almost the same stability as the product, and two species were suggested to be in a state of equilibrium. While the geometry of TS1 appears to be forwarded to that of a carbocation intermediate, the cation disappeared through the enlargement of the water cluster. Dynamical calculations of a classical trajectory using the atom-centered density matrix propagation molecular dynamics model on the four TSs were carried out, and results of IRC calculations were confirmed by them. PMID:23532354

Yamabe, Shinichi; Fukuda, Takeshi; Yamazaki, Shoko

2013-03-05

6

Suppressing the formation of stable intermediates in hydride destabilization reactions  

NASA Astrophysics Data System (ADS)

Comprehensive computational screening efforts have identified numerous candidates for hydride destabilization reactions with reaction enthalpies that fall in the range of interest for engineering requirements (20 to 40 kJ/mol H2). Less certain are the actual kinetic pathways of the solid--state reactions under consideration. Of particular interest are LiBH4--based reactions. We have studied a number of destabilization reactions based on LiBH4 and note that the B12H12 closo--borane is a commonly formed intermediate. Moreover, formation of M2/nB12H12 phases as major intermediate species is observed in hydrogen desorption reaction of various M(BH4)n systems before further conversion to either MBn or B+MHn. We have also examined a number of possible reactions that might destabilize B12H12 phases using reactions suggested in the recent literature but even under severe processing conditions, this closo--borane phase remains. Our inability to destabilize the closo--borane is particularly puzzling given that the initial work of Vajo on the LiBH4--MgH2 with dehydrogenation into several bar pressure showed complete reversibility. Our work however has generally been done under static vacuum. We have re-examined the reactions in the LiBH4--MgH2 and through the use of ^11B NMR, note that when dehydrogenated under 4 bar hydrogen pressure, no amorphous boron or B12H12 can be detected. When dehydrogenated into pressures below 1.5 bar hydrogen however, the closo--borane structure is formed. We will discuss these results and consider other possible reaction pathways that dictate the way in which these solid--state reaction experiments are conducted.

Ahn, Channing

2010-03-01

7

Removal of Bisphenol A and its Reaction-Intermediates from Aqueous Solution by Ozonation  

Microsoft Academic Search

In this study, the oxidation of Bisphenol A (BPA) and its reaction-intermediates in aqueous solution by ozonation was investigated. The results of the study indicated that ozonation is effective in oxidizing BPA. Catechol, resorcinol, acetone, formaldehyde and organic acids, acetic, formic, maleic, and oxalic acid, are identified as reaction-intermediates. Ozonation of 51 ?M (770 ?M C) of BPA resulted in

T. Garoma; S. A. Matsumoto; Y. Wu; R. Klinger

2010-01-01

8

Investigation of Unexpected Reaction Intermediates in the Alkaline Hydrolysis of Methyl 3,5-Dinitrobenzoate  

ERIC Educational Resources Information Center

|An experimental project aimed at identifying stable reaction intermediates is described. Initially, the studied reaction appears to involve the simple hydrolysis, by aqueous sodium hydroxide, of methyl 3,5-dinitrobenzoate dissolved in dimethyl sulfoxide. On mixing the substrates, however, the reaction mixture unexpectedly turns an intense red in…

Silva, Clesia C.; Silva, Ricardo O.; Navarro, Daniela M. A. F.; Navarro, Marcelo

2009-01-01

9

In Vivo Identification of Intermediate Stages of the DNA Inversion Reaction Catalyzed by the Salmonella Hin Recombinase  

Microsoft Academic Search

The Hin recombinase catalyzes a site-specific recombination reaction that results in the reversible inversion of a 1-kbp segment of the Salmonella chromosome. The DNA inversion reaction catalyzed by the Salmonella Hin recombinase is a dynamic process proceeding through many intermediate stages, requiring multiple DNA sites and the Fis accessory protein. Biochemical analysis of this reaction has identified intermediate steps in

Oliver Z. Nanassy; Kelly T. Hughes

10

Intermediate Phenotypes Identify Divergent Pathways to Alzheimer's Disease  

PubMed Central

Background Recent genetic studies have identified a growing number of loci with suggestive evidence of association with susceptibility to Alzheimer's disease (AD). However, little is known of the role of these candidate genes in influencing intermediate phenotypes associated with a diagnosis of AD, including cognitive decline or AD neuropathologic burden. Methods/Principal Findings Thirty-two single nucleotide polymorphisms (SNPs) previously implicated in AD susceptibility were genotyped in 414 subjects with both annual clinical evaluation and completed brain autopsies from the Religious Orders Study and the Rush Memory and Aging Project. Regression analyses evaluated the relation of SNP genotypes to continuous measures of AD neuropathology and cognitive function proximate to death. A SNP in the zinc finger protein 224 gene (ZNF224, rs3746319) was associated with both global AD neuropathology (p?=?0.009) and global cognition (p?=?0.002); whereas, a SNP at the phosphoenolpyruvate carboxykinase locus (PCK1, rs8192708) was selectively associated with global cognition (p?=?3.57×10?4). The association of ZNF224 with cognitive impairment was mediated by neurofibrillary tangles, whereas PCK1 largely influenced cognition independent of AD pathology, as well as Lewy bodies and infarcts. Conclusions/Significance The findings support the association of several loci with AD, and suggest how intermediate phenotypes can enhance analysis of susceptibility loci in this complex genetic disorder.

Shulman, Joshua M.; Chibnik, Lori B.; Aubin, Cristin; Schneider, Julie A.; Bennett, David A.; De Jager, Philip L.

2010-01-01

11

(Ligand intermediates in metal-catalyzed reactions)  

SciTech Connect

This report consists of sections on sigma bond complexes of alkenes, a new carbon-hydrogen bond activation reaction of alkene complexes, carbon-hydrogen bond migrations in alkylidene complexes, carbon- hydrogen bond migrations in alkyne complexes, synthesis, structure and reactivity of C{sub x} complexes, synthesis and reactivity of alcohol and ether complexes, new catalysts for the epimerization of secondary alcohols; carbon-hydrogen bond activation in alkoxide complexes, pi/sigma equilibria in metal/O=CXX' complexes, and other hydrocarbon ligands; miscellaneous.(WET)

Not Available

1992-01-01

12

Fission decay in intermediate heavy ion reactions  

SciTech Connect

Results are presented on cross sections, parallel and perpendicular momentum transfers, charge loss and velocity systematics for fission following reactions of Fe and Nb projectiles at 50--100 MeV/A on targets of Ta, Au, and Th. The results at 100 MeV/A are compared to a detailed multistage deexcitation model. The initial collision is modeled with an intranuclear cascade. The resultant excited target residues then undergo a fast preequilibrium decay stage followed by a statistical decay involving nucleon evaporation and fission. Results from this modeling are in reasonable agreement with experimental data. 14 refs., 11 figs.

Britt, H.C.

1990-10-03

13

Recent results on intermediate-energy nucleon knockout reactions  

NASA Astrophysics Data System (ADS)

Nucleon knockout reactions using fast rare isotope beams are a well-suited tool to study single-particle properties of exotic nuclei and the evolution of nuclear shell structure towards the drip-lines. In particular the sudden removal of two protons from an intermediate-energy neutron-rich projectile has been shown to proceed as a direct reaction. In addition to giving spectroscopic information, this type of reaction promises a rather unique tool assign spins by measuring the momentum distributions of the heavy reaction residues. In the present experiment, the heavy reaction residues were measured in coincidence with the removed. These more final-state-exclusive measurements are key for further validation of this direct reaction and its use for quantitative spectroscopy of highly neutron-rich nuclei.

Wimmer, K.

2013-04-01

14

Ligandless, Anionic, Arylpalladium Halide Intermediates in the Heck Reaction  

PubMed Central

We report the isolation and reactivity of a series of “ligandless,” anionic arylpalladium complexes of the general structure [Pd(Ar)Br2]22- by the reaction of (tBu3P)Pd(Ar)(Br) and bromide. These anionic complexes insert olefins at room temperature, and these fast insertions indicate that the anionic complexes are kinetically competent as intermediates in Heck-Mizoroki reactions conducted under “ligandless” conditions (lacking added dative ligand). Kinetic studies showed that the anionic complexes insert olefins much faster than the corresponding neutral, P(t-Bu)3-ligated complexes. Addition of halide to the reaction of the neutral complex (tBu3P)Pd(Ar)(Br) and styrene led to a significant rate acceleration, suggesting that the anionic complex forms rapidly and reversibly in situ from the neutral species prior to migratory insertion. These data, along with studies on the regioselectivity for reaction of aryl halides with butyl vinyl ether in the presence of the different starting catalysts, are consistent with the intermediacy of the same anionic, arylpalladium intermediates in Heck reactions catalyzed by palladium complexes containing bulky trialkylphosphine ligands as in reactions conducted under ligandless conditions.

Carrow, Brad P.

2010-01-01

15

Identifying surface intermediates with TPD: Methylchlorosilanes on Cu(001)  

NASA Astrophysics Data System (ADS)

Various methylchlorosilane molecules (SiHx Mey Clz , x+y+z=4) were exposed to a Cu(001) surface. Dissociative adsorption was observed for several hydrogen containing species, at surface temperatures above 160K. The chemistry and thermal stability of the surface bound fragments were then studied as a means for understanding intermediates of the commercially important ``Direct Process,'' namely production of Cl2(CH3)2Si, from Si and CH3Cl, with a Cu catalyst. Temperature programmed desorption indicates that methyl groups are readily transferred between absorbed Si-containing species. A large fraction of Cl remains on the surface after observation of typically 2 or 3 distinct TPD features below 450K. By a comparison of the product species distributions to the parent species, we are then able to propose key intermediates common to many of the adsorption/desorption mechanisms.

Lallo, James; Lee, Everett; Hinch, B. J.; Strongin, Dan

2009-03-01

16

Photocatalytic degradation of paracetamol: intermediates and total reaction mechanism.  

PubMed

The advanced oxidation of paracetamol (PAM) promoted by TiO(2)/UV system in aqueous medium was investigated. Monitoring this reaction by HPLC and TOC, it was demonstrated that while oxidation of paracetamol is quite efficient under these conditions, its mineralization is not complete. HPLC indicated the formation of hydroquinone, benzoquinone, p-aminophenol and p-nitrophenol in the reaction mixtures. Further evidence of p-nitrophenol formation was obtained following the reaction by UV-vis spectroscopy. Continuous monitoring by IR spectroscopy demonstrated the breaking of the aromatic amide present in PAM and subsequent formation of several aromatic intermediate compounds such as p-aminophenol and p-nitrophenol. These aromatic compounds were eventually converted into trans-unsaturated carboxylic acids. Based on these experimental results, an alternative deacylation mechanism for the photocatalytic oxidation of paracetamol is proposed. Our studies also demonstrated IR spectroscopy to be a useful technique to investigate oxidative mechanisms of pharmaceutical compounds. PMID:23123003

Moctezuma, Edgar; Leyva, Elisa; Aguilar, Claudia A; Luna, Raúl A; Montalvo, Carlos

2012-10-13

17

Binary reactions inbar pp collisions at intermediate energies  

NASA Astrophysics Data System (ADS)

We discuss here the binary reactions of strange and charmed particle production inbar pp collisions at intermediate energies. In the case of baryon production with only one strange or charmed quark the cross section is determined by planar diagrams with K *, K ** or D *, D **-meson poles in the t-channel. We calculated these diagrams in the frame of quark-gluon string model (QGSM) proposed earlier. We obtained also the cross-sections for reactions with baryon exchange in the t-channel withKbar K andDbar D pair in the final state. Predicted cross-sections for the reactions ofbar ? _c ? _c production are of the order of hundred nanobarns. Using reggeon calculus we estimated cross-sections of binary reactions with two or three strange quarks in the final state:bar pp to ? bar ? ,? bar ? and ??. We discuss also the possible manifestation of color transparency effects in reactions with antiprotons on nuclei where all antiproton quarks annihilate.

Kaidalov, A. B.; Volkovitsky, P. E.

1994-09-01

18

Direct measurement of Criegee intermediate (CH2OO) reactions with acetone, acetaldehyde, and hexafluoroacetone.  

PubMed

Criegee biradicals, i.e., carbonyl oxides, are critical intermediates in ozonolysis and have been implicated in autoignition chemistry and other hydrocarbon oxidation systems, but until recently the direct measurement of their gas-phase kinetics has not been feasible. Indirect determinations of Criegee intermediate kinetics often rely on the introduction of a scavenger molecule into an ozonolysis system and analysis of the effects of the scavenger on yields of products associated with Criegee intermediate reactions. Carbonyl species, in particular hexafluoroacetone (CF(3)COCF(3)), have often been used as scavengers. In this work, the reactions of the simplest Criegee intermediate, CH(2)OO (formaldehyde oxide), with three carbonyl species have been measured by laser photolysis/tunable synchrotron photoionization mass spectrometry. Diiodomethane photolysis produces CH(2)I radicals, which react with O(2) to yield CH(2)OO + I. The formaldehyde oxide is reacted with a large excess of a carbonyl reactant and both the disappearance of CH(2)OO and the formation of reaction products are monitored. The rate coefficient for CH(2)OO + hexafluoroacetone is k(1) = (3.0 ± 0.3) × 10(-11) cm(3) molecule(-1) s(-1), supporting the use of hexafluoroacetone as a Criegee-intermediate scavenger. The reactions with acetaldehyde, k(2) = (9.5 ± 0.7) × 10(-13) cm(3) molecule(-1) s(-1), and with acetone, k(3) = (2.3 ± 0.3) × 10(-13) cm(3) molecule(-1) s(-1), are substantially slower. Secondary ozonides and products of ozonide isomerization are observed from the reactions of CH(2)OO with acetone and hexafluoroacetone. Their photoionization spectra are interpreted with the aid of quantum-chemical and Franck-Condon-factor calculations. No secondary ozonide was observable in the reaction of CH(2)OO with acetaldehyde, but acetic acid was identified as a product under the conditions used (4 Torr and 293 K). PMID:22481381

Taatjes, Craig A; Welz, Oliver; Eskola, Arkke J; Savee, John D; Osborn, David L; Lee, Edmond P F; Dyke, John M; Mok, Daniel W K; Shallcross, Dudley E; Percival, Carl J

2012-04-05

19

Characterization of Anionic Cluster Nucleophilic Substitution Reaction Intermediates  

NASA Astrophysics Data System (ADS)

Recent theoretical and experimental developments in the arena of the gas phase S_{rm N}2 reaction (X^- + RY to RX + Y^-) has rekindled interest in this classic chemical reaction. Consideration of the gas phase S_{rm N} 2 double minima potential surface from a valence bond perspective, advocated by Shaik et. al., predicts the presence of a low lying excited electronic state corresponding to electron transfer. In this work we take advantage of long range ion-molecule induced forces to stabilize the S_{rm N}2 reactants in a complex, X^-cdot RY, allowing us to search for this charge transfer excited state from the well defined location on the potential energy surface. Photoelectron spectroscopy of X^ - cdot RY confirms the identification of the species as essentially charge-localized. Vibrational fine structure observed in the case of I^- cdot CH_3I is found to be consistent with small distortions of the CH_3I neutral upon complexation to form a stable intermediate in the S_{rm N}2 identity reaction. A narrow photofragmentation band lies just below the vertical electron detachment energy and is assigned to the X^- cdot RY to X cdotcdot (RY) ^- charge transfer excited state. More detailed study of the photofragmentation band reveals the photoexcitation mechanism is not direct charge transfer but is mediated by a weakly bound negative ion state. The excited state photochemistry of the X ^- cdot RY reaction intermediates is characterized by the formation of the endothermic halide abstraction product XY^-. Trends in the formation of the dihalide product are strongly dependent of the nature of the R group and these results are consistent with a preferential ion binding site in the complex. Search for the XY^- dihalide product in the bimolecular ground state reaction at supra-thermal collision energies revealed halide abstraction as a competitive product channel to the well known Walden inversion mechanism. All of these results are integrated in the development a picture of the X^- cdot RY photofragmentation dynamics in the context of the diabatic (charge-localized) states invoked to interpret the structure of the (ground state) S_{rm N}2 potential surface.

Cyr, Donna Marie

20

Mechanistic insight into the hydrazine decomposition on Rh(111): effect of reaction intermediate on catalytic activity.  

PubMed

Periodic density functional theory (DFT) calculations have been performed to systematically investigate the effect of reaction intermediate on catalytic activity for hydrazine (N2H4) decomposition on Rh(111). Reaction mechanisms via intramolecular and NH2-assisted N2H4 decompositions are comparatively analyzed, including adsorption configuration, reaction energy and barrier of elementary step, and reaction network. Our results show that the most favorable N2H4 decomposition pathway starts with the initial N-N bond scission to the NH2 intermediate, followed by stepwise H stripping from adsorbed N2Hx (x = 1-4) species, and finally forms the N2 and NH3 products. Comparatively, the stepwise intramolecular dehydrogenation via N2H4? N2H3? N2H2? N2H ? N2, and N2H4? NH2? NH ? N with or without NH2 promotion effect, are unfavorable due to higher energy barriers encountered. Energy barrier analysis, reaction rate constants, and electronic structures are used to identify the crucial competitive route. The promotion effect of the NH2 intermediate is structurally reflected in the weakening of the N-H bond and strengthening of the N-N bond in N2Hx in the coadsorption system; it results intrinsically from the less structural deformation of the adsorbate, and weakening of the interaction between dehydrogenated fragment and departing H in transition state. Our results highlight the crucial effect of reaction intermediate on catalytic activity and provide a theoretical approach to analyze the effect. PMID:23990024

Deng, Zhigang; Lu, Xiaoqing; Wen, Zengqiang; Wei, Shuxian; Liu, Yunjie; Fu, Dianling; Zhao, Lianming; Guo, Wenyue

2013-08-29

21

Crystal structures of intermediates in the nitroalkane oxidase reaction.  

PubMed

The flavoenzyme nitroalkane oxidase is a member of the acyl-CoA dehydrogenase superfamily. Nitroalkane oxidase catalyzes the oxidation of neutral nitroalkanes to nitrite and the corresponding aldehydes or ketones. Crystal structures to 2.2 A resolution or better of enzyme complexes with bound substrates and of a trapped substrate-flavin adduct are described. The D402N enzyme has no detectable activity with neutral nitroalkanes [Valley, M. P., and Fitzpatrick, P. F. (2003) J. Am. Chem. Soc. 125, 8738-8739]. The structure of the D402N enzyme crystallized in the presence of 1-nitrohexane or 1-nitrooctane shows the presence of the substrate in the binding site. The aliphatic chain of the substrate extends into a tunnel leading to the enzyme surface. The oxygens of the substrate nitro group interact both with amino acid residues and with the 2'-hydroxyl of the FAD. When nitroalkane oxidase oxidizes nitroalkanes in the presence of cyanide, an electrophilic flavin imine intermediate can be trapped [Valley, M. P., Tichy, S. E., and Fitzpatrick, P. F. (2005) J. Am. Chem. Soc. 127, 2062-2066]. The structure of the enzyme trapped with cyanide during oxidation of 1-nitrohexane shows the presence of the modified flavin. A continuous hydrogen bond network connects the nitrogen of the CN-hexyl-FAD through the FAD 2'-hydroxyl to a chain of water molecules extending to the protein surface. Together, our complementary approaches provide strong evidence that the flavin cofactor is in the appropriate oxidation state and correlates well with the putative intermediate state observed within each of the crystal structures. Consequently, these results provide important structural descriptions of several steps along the nitroalkane oxidase reaction cycle. PMID:19265437

Héroux, Annie; Bozinovski, Dragana M; Valley, Michael P; Fitzpatrick, Paul F; Orville, Allen M

2009-04-21

22

Mapping chemical bonding of reaction intermediates with femtosecond X-ray laser spectroscopy  

NASA Astrophysics Data System (ADS)

We determine the pathways in the photo-dissociation reactions of Fe(CO)5 both in the gas phase and in solution by mapping the valence electronic structure of the reaction intermediates with femtosecond X-ray laser spectroscopy.

Wernet, Ph.; Beye, M.; de Groot, F.; Düsterer, S.; Gaffney, K.; Grübel, S.; Hartsock, R.; Hennies, F.; Josefsson, I.; Kennedy, B.; Kunnus, K.; Leitner, T.; Mazza, T.; Meyer, M.; Nordlund, D.; Odelius, M.; Quevedo, W.; Radcliffe, P.; Rajkovic, I.; Schlotter, B.; Scholz, M.; Schreck, S.; Suljoti, E.; Techert, S.; Turner, J.; Weniger, C.; Zhang, W.; Föhlisch, A.

2013-03-01

23

Capturing fleeting intermediates in a catalytic C-H amination reaction cycle  

PubMed Central

We have applied an ambient ionization technique, desorption electrospray ionization MS, to identify transient reactive species of an archetypal C–H amination reaction catalyzed by a dirhodium tetracarboxylate complex. Using this analytical method, we have detected previously proposed short-lived reaction intermediates, including two nitrenoid complexes that differ in oxidation state. Our findings suggest that an Rh-nitrene oxidant can react with hydrocarbon substrates through a hydrogen atom abstraction pathway and raise the intriguing possibility that two catalytic C–H amination pathways may be operative in a typical bulk solution reaction. As highlighted by these results, desorption electrospray ionization MS should have broad applicability for the mechanistic study of catalytic processes.

Perry, Richard H.; Cahill, Thomas J.; Roizen, Jennifer L.; Du Bois, Justin; Zare, Richard N.

2012-01-01

24

Spectroscopic features of cytochrome P450 reaction intermediates  

PubMed Central

Preface Cytochromes P450 constitute a broad class of heme monooxygenase enzymes with more than 11,500 isozymes which have been identified in organisms from all biological kingdoms [1]. These enzymes are responsible for catalyzing dozens chemical oxidative transformations such as hydroxylation, epoxidation, N-demethylation, etc., with very broad range of substrates [2-3]. Historically these enzymes received their name from ‘pigment 450’ due to the unusual position of the Soret band in UV-Vis absorption spectra of the reduced CO-saturated state [4-5]. Despite detailed biochemical characterization of many isozymes, as well as later discoveries of other ‘P450-like heme enzymes’ such as nitric oxide synthase and chloroperoxidase, the phenomenological term ‘cytochrome P450’ is still commonly used as indicating an essential spectroscopic feature of the functionally active protein which is now known to be due to the presence of a thiolate ligand to the heme iron [6]. Heme proteins with an imidazole ligand such as myoglobin and hemoglobin as well as an inactive form of P450 are characterized by Soret maxima at 420 nm [7]. This historical perspective highlights the importance of spectroscopic methods for biochemical studies in general, and especially for heme enzymes, where the presence of the heme iron and porphyrin macrocycle provides rich variety of specific spectroscopic markers available for monitoring chemical transformations and transitions between active intermediates of catalytic cycle.

Luthra, Abhinav; Denisov, Ilia G.; Sligar, Stephen G.

2010-01-01

25

Structural characterization of the reaction pathway in phosphoserine phosphatase: crystallographic "snapshots" of intermediate states.  

PubMed

Phosphoserine phosphatase (PSP) is a member of a large class of enzymes that catalyze phosphoester hydrolysis using a phosphoaspartate-enzyme intermediate. PSP is a likely regulator of the steady-state d-serine level in the brain, which is a critical co-agonist of the N-methyl-d-aspartate type of glutamate receptors. Here, we present high-resolution (1.5-1.9 A) structures of PSP from Methanococcus jannaschii, which define the open state prior to substrate binding, the complex with phosphoserine substrate bound (with a D to N mutation in the active site), and the complex with AlF3, a transition-state analog for the phospho-transfer steps in the reaction. These structures, together with those described for the BeF3- complex (mimicking the phospho-enzyme) and the enzyme with phosphate product in the active site, provide a detailed structural picture of the full reaction cycle. The structure of the apo state indicates partial unfolding of the enzyme to allow substrate binding, with refolding in the presence of substrate to provide specificity. Interdomain and active-site conformational changes are identified. The structure with the transition state analog bound indicates a "tight" intermediate. A striking structure homology, with significant sequence conservation, among PSP, P-type ATPases and response regulators suggests that the knowledge of the PSP reaction mechanism from the structures determined will provide insights into the reaction mechanisms of the other enzymes in this family. PMID:12051918

Wang, Weiru; Cho, Ho S; Kim, Rosalind; Jancarik, Jaru; Yokota, Hisao; Nguyen, Henry H; Grigoriev, Igor V; Wemmer, David E; Kim, Sung-Hou

2002-05-31

26

Reaction of coordinated dinitrogen. 12. Identification of intermediates in the conversion of molybdenum-bound dinitrogen into ammonia and hydrazine. Factors affecting the ammonia-forming reaction  

Microsoft Academic Search

When bis(dinitrogen) complexes of molybdenum and tungsten are treated with an excess of strong acid, with few exceptions, a complex containing the hydrazido(2-) ligand has been identified either as a product in the reaction or as an intermediate on the way to the formation of ammonia and hydrazine. In the case of those molybdenum complexes that produce ammonia, the stoichiometry

G. E. Bossard; T. Adrian George; Daniel B. Howell; Lenore M. Koczon; Richard K. Lester

1983-01-01

27

Trapping of Reactive Intermediates to Study Reaction Mechanisms in Cellulose Chemistry  

Microsoft Academic Search

Reaction with specific scavenger agents, so-called trapping, is\\u000a a direct way to prove the occurrence of reactive intermediates in a reaction system, and thus\\u000a to elucidate the underlying reaction mechanisms. After an introduction on chemical intermediates, chemical\\u000a trapping and the peculiarities of trapping methodology in the presence of cellulose, four chapters from\\u000a cellulose chemistry were selected to illustrate how trapping can be

Thomas Rosenau; Antje Potthast; Paul Kosma

28

Time delays in reactions with intermediate and compound nuclear structure  

Microsoft Academic Search

We present a simple model, analytically solvable, of the time evolution of the scattering of a wave packet, which exhibits and clarifies the compound nucleus process, and can be easily extended to the study of the time delays involved when intermediate structure is present.

E. Rosengaus; P. A. Mello; M. Bauer

1978-01-01

29

Metamorphic dehydration reactions control the location of intermediate-depth seismicity  

NASA Astrophysics Data System (ADS)

The cause of intermediate-depth seismicity in subduction zones is not well understood. The viability of proposed mechanisms, that include dehydration embrittlement, shear instablities, and the presence of fluids in general, depends significantly on local conditions, including pressure, temperature, and composition. A number of high resolution seismic studies have improved the location of earthquakes within the slab in Japan, Alaska and Cascadia. Intriguingly, the warm subduction zones of Nankai and Cascadia show that intermediate depth seismicity is located below the oceanic crust. In contrast, the colder subduction zones Alaska, Tohoku and Hokkaido have the upper plane of seismicity confined to the subducting crust, with a systematic deepening of the seismic belt with respect to the top of the slab with depth. We use high resolution thermal-petrological models to determine the metamorphic facies in the downgoing slab and to identify the main phase changes that cause dehydration. In Alaska and Northern Japan, the seismicity occurs at, or at shallower depths than, the blueschist-out boundary. In Nankai and Cascadia the seismicity disappears above the antigorite-out boundary. Seismicity in the lower plane of the double seismic zone in Northern Japan also occurs at pressures and temperatures below the antigorite-out boundary. These observations strongly suggest that intermediate-depth seismicity is limited by the first major dehydration reaction in the crust and mantle and that fluids liberated by this phase change are primarily responsible for causing the earthquakes.

van Keken, Peter E.; Kita, Saeko; Nakajima, Junichi; Abers, Geoff; Hacker, Brad

2013-04-01

30

Compound nuclei, binary decay, and multifragmentation in intermediate-energy heavy-ion reactions  

SciTech Connect

Hot compound nuclei, frequently produced in intermediate-energy reactions through a variety of processes, are shown to be an important and at times dominant source of complex fragments. 13 refs., 12 figs.

Moretto, L.G.; Wozniak, G.J.

1988-07-01

31

CONSIDERATION OF REACTION INTERMEDIATES IN STRUCTURE-ACTIVITY RELATIONSHIPS: A KEY TO UNDERSTANDING AND PREDICTION  

EPA Science Inventory

Consideration of Reaction Intermediates in Structure- Activity Relationships: A Key to Understanding and Prediction A structure-activity relationship (SAR) represents an empirical means for generalizing chemical information relative to biological activity, and is frequent...

32

Investigation of the intermediate-energy deuteron breakup reaction  

SciTech Connect

The Udagawa-Tamura formalism is employed to calculate the proton singles both in the bound and unbound regions. Both the Elastic-Breakup (EB) and the Breakup-Fusion (BF) processes are considered to calculate the doubly-differential cross section for light and intermediate mass nuclei. The calculated spectra for 25 and 56 MeV deuterons reproduce the experimental spectra very well except for the spectra at large angle and at low energies, of the outgoing particle. Contributions due to precompound and evaporation processes are estimated to supplement the spectral results based on the Elastic-Breakup and Breakup-Fusion mechanisms. An extension of the model calculations to higher deuteron energies is being made to test the (EB + BF) model limitations. 5 refs., 1 fig.

Divadeenam, M.; Ward, T.E.; Mustafa, M.G.; Udagawa, T.; Tamura, T.

1989-01-01

33

Temperature-scan cryocrystallography reveals reaction intermediates in bacteriophytochrome  

SciTech Connect

Light is a fundamental signal that regulates important physiological processes such as development and circadian rhythm in living organisms. Phytochromes form a major family of photoreceptors responsible for red light perception in plants, fungi and bacteria. They undergo reversible photoconversion between red-absorbing (Pr) and far-red-absorbing (Pfr) states, thereby ultimately converting a light signal into a distinct biological signal that mediates subsequent cellular responses. Several structures of microbial phytochromes have been determined in their dark-adapted Pr or Pfr states. However, the structural nature of initial photochemical events has not been characterized by crystallography. Here we report the crystal structures of three intermediates in the photoreaction of Pseudomonas aeruginosa bacteriophytochrome (PaBphP). We used cryotrapping crystallography to capture intermediates, and followed structural changes by scanning the temperature at which the photoreaction proceeded. Light-induced conformational changes in PaBphP originate in ring D of the biliverdin (BV) chromophore, and E-to-Z isomerization about the C{sub 15} = C{sub 16} double bond between rings C and D is the initial photochemical event. As the chromophore relaxes, the twist of the C{sub 15} methine bridge about its two dihedral angles is reversed. Structural changes extend further to rings B and A, and to the surrounding protein regions. These data indicate that absorption of a photon by the Pfr state of PaBphP converts a light signal into a structural signal via twisting and untwisting of the methine bridges in the linear tetrapyrrole within the confined protein cavity.

Yang, Xiaojing; Ren, Zhong; Kuk, Jane; Moffat, Keith (UC)

2012-03-27

34

Temperature-scan cryocrystallography reveals reaction intermediates in bacteriophytochrome.  

PubMed

Light is a fundamental signal that regulates important physiological processes such as development and circadian rhythm in living organisms. Phytochromes form a major family of photoreceptors responsible for red light perception in plants, fungi and bacteria. They undergo reversible photoconversion between red-absorbing (Pr) and far-red-absorbing (Pfr) states, thereby ultimately converting a light signal into a distinct biological signal that mediates subsequent cellular responses. Several structures of microbial phytochromes have been determined in their dark-adapted Pr or Pfr states. However, the structural nature of initial photochemical events has not been characterized by crystallography. Here we report the crystal structures of three intermediates in the photoreaction of Pseudomonas aeruginosa bacteriophytochrome (PaBphP). We used cryotrapping crystallography to capture intermediates, and followed structural changes by scanning the temperature at which the photoreaction proceeded. Light-induced conformational changes in PaBphP originate in ring D of the biliverdin (BV) chromophore, and E-to-Z isomerization about the C(15) = C(16) double bond between rings C and D is the initial photochemical event. As the chromophore relaxes, the twist of the C(15) methine bridge about its two dihedral angles is reversed. Structural changes extend further to rings B and A, and to the surrounding protein regions. These data indicate that absorption of a photon by the Pfr state of PaBphP converts a light signal into a structural signal via twisting and untwisting of the methine bridges in the linear tetrapyrrole within the confined protein cavity. PMID:22002602

Yang, Xiaojing; Ren, Zhong; Kuk, Jane; Moffat, Keith

2011-10-16

35

Incomplete Combustion of Hydrogen: Trapping a Reaction Intermediate  

ERIC Educational Resources Information Center

|The combustion of hydrogen in air is quite complex with at least 28 mechanistic steps and twelve reaction species. Most of the species involved are radicals (having unpaired electrons) in nature. Among the various species generated, a few are stable, including hydrogen peroxide. In a normal hydrogen flame, the hydrogen peroxide goes on to further…

Mattson, Bruce; Hoette, Trisha

2007-01-01

36

Neutron Spectra from Intermediate-Energy Nucleus-Nucleus Reactions  

SciTech Connect

Double-differential cross sections of neutron production at angles from 0 to 110 degrees from many reactions induced by light and medium nuclei on targets from 12C to 208Pb, at several incident energies from 95 to 600 MeV/nucleon have been measured recently at the Institute of Physical and Chemical Research (RIKEN) Ring Cyclotron in Japan and at the Heavy-Ion Medical Accelerator of the National Institute of Radiological Science in Chiba, Japan using the time-of-flight technique. We have analyzed all these new measurements using the Quantum Molecular Dynamics (QMD) model, the Oak Ridge intranuclear cascade model HIC, the ISABEL intranuclear cascade model from LAHET, and the Los Alamos version of the Quark-Gluon String Model code LAQGSM03. On the whole, all four models used here describe reasonably well most of the measured neutron spectra, although different models agree differently with data from specific reactions and some serious discrepances are observed for some reactions. We present here some illustrative results from our study, discuss possible reasons for some of the observed discrepancies and try to outline ways to further improve the tested codes in order to address these problems.

Iwase, Hiroshi [GSI, Planckstr. 1, 64291 Darmstadt (Germany); Iwata, Yoshiyuki [National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage, Chiba 263-8555 (Japan); Nakamura, Takashi [Tohoku University, Aoba, Aramaki, Aoba-ku, Sendai 980-8579 (Japan); Gudima, Konstantin [Institute of Applied Physics, Academy of Science of Moldova, Chisinau, MD-2028 (Moldova, Republic of); Mashnik, Stepan; Sierk, Arnold; Prael, Richard [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States)

2005-05-24

37

Asymmeric Formal [3+3]-Cycloaddition Reactions of Nitrones with Electrophilic Vinylcarbene Intermediates  

PubMed Central

With metal carbene access to dipolar intermediates, 3,6-dihydro-1,2-oxazines are produced in high yields by dirhodium(II) carboxylate catalyzed reactions between nitrones and a ?-TBSO-substituted vinyldiazoacetate. High enantiocontrol occurs with catalysis by N-phthaloyl-(S)-(amino acid)-ligated dirhodium carboxylates for [3+3]-cycloaddition reactions with both acyclic and cyclic nitrones.

Wang, Xiaochen; Xu, Xinfang; Zavalij, Peter Y.; Doyle, Michael P.

2011-01-01

38

Asymmeric formal [3 + 3]-cycloaddition reactions of nitrones with electrophilic vinylcarbene intermediates.  

PubMed

With metal carbene access to dipolar intermediates, 3,6-dihydro-1,2-oxazines are produced in high yields by dirhodium(II) carboxylate catalyzed reactions between nitrones and a ?-TBSO-substituted vinyldiazoacetate. High enantiocontrol occurs with catalysis by N-phthaloyl-(S)-(amino acid)-ligated dirhodium carboxylates for [3 + 3]-cycloaddition reactions with both acyclic and cyclic nitrones. PMID:21932856

Wang, Xiaochen; Xu, Xinfang; Zavalij, Peter Y; Doyle, Michael P

2011-09-27

39

Mössbauer and EPR Study of Reaction Intermediates of Cytochrome P450  

NASA Astrophysics Data System (ADS)

We present a complementary Mössbauer and EPR study on reaction intermediates of substrate-free and substrate-bound cytochrome P450cam from Pseudomonas putida prepared by the freeze-quench method from 57Fe-labeled P450cam using peroxy acetic acid as oxidizing agent. When reacting the substrate-free P450cam for 8 ms reaction time the reaction mixture consists of ˜85% of ferric low-spin iron (Fe(III)) with g-factors and hyperfine parameters of the starting material; the remaining ˜15% are identified as ferryl iron (Fe(IV); S Fe=1) by its Mössbauer signature. Parallel to the ferryl iron a tyrosine radical ( S rad=1/2) is formed. The two paramagnetic species are not exchange-coupled; however, they are close enough to significantly influence the (EPR) relaxation behavior of the radical spin. In the case of substrate-bound P450cam only trace amounts of the tyrosine radical are formed within 8 ms (<3%); within the accuracy of Mössbauer spectroscopy (5%) iron(IV) can not be detected. The results point to Tyr-96, which is hydrogen-bonded to the substrate camphor, as the candidate for the observed tyrosine radical.

Schünemann, V.; Trautwein, A. X.; Jung, C.; Terner, J.

2002-06-01

40

Study of intermediates from transition metal excited-state electron-transfer reactions  

SciTech Connect

Conventional and fast-kinetics techniques of photochemistry, photophysics, radiation chemistry, and electrochemistry were used to study the intermediates involved in transition metal excited-state electron-transfer reactions. These intermediates were excited state of Ru(II) and Cr(III) photosensitizers, their reduced forms, and species formed in reactions of redox quenchers and electron-transfer agents. Of particular concern was the back electron-transfer reaction between the geminate pair formed in the redox quenching of the photosensitizers, and the dependence of its rate on solution medium and temperature in competition with transformation and cage escape processes. (DLC)

Hoffman, M.Z.

1992-07-31

41

Parameterization of ?-nucleus total reaction cross section at intermediate energies  

NASA Astrophysics Data System (ADS)

Applying a Coulomb correction factor to the Glauber model we have derived a closed expression for ?-nucleus total reaction cross section, ? R. Under the approximation of rigid projectile model, the elastic S-matrix element Sel(b) is evaluated from the phenomenological N-? amplitude and a Gaussian fit to the Helm's model form factor. Excellent agreements with the experimental data have been achieved by performing two-parameter fits to the ?-nucleus ? R data in the energy range about 75 to 193 MeV. One of the parameters was found to be energy independent while the other, as expected, shows the energy dependence similar to that of N-? total cross section.

Alvi, M. A.; Abdulmomen, M. A.

2008-12-01

42

Population of bound excited states in intermediate-energy fragmentation reactions  

SciTech Connect

Fragmentation reactions with intermediate-energy heavy-ion beams exhibit a wide range of reaction mechanisms, ranging from direct reactions to statistical processes. We examine this transition by measuring the relative population of excited states in several sd-shell nuclei produced by fragmentation with the number of removed nucleons ranging from two to sixteen. The two-nucleon removal is consistent with a non-dissipative process, whereas the removal of more than five nucleons appears to be mainly statistical.

Obertelli, A.; Gade, A.; Bazin, D.; Hansen, P.G.; Hoagland, T.; Lecouey, J.-L.; Mueller, W.F.; Yoneda, K. [National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824 (United States); Campbell, C.M.; Cook, J.M.; Davies, A.D.; Dinca, D.-C.; Glasmacher, T.; Terry, J.R.; Zwahlen, H. [National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824 (United States); Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824 (United States); Cottle, P.D.; Kemper, K.W.; Reynolds, R.R.; Roeder, B.T. [Department of Physics, Florida State University, Tallahassee, Florida 32306 (United States); Tostevin, J.A. [Department of Physics, School of Electronics and Physical Sciences, University of Surrey, Guildford, Surrey GU2 7XH (United Kingdom)

2006-04-15

43

Mechanism of light cluster production in nucleon induced reactions at intermediate energy  

NASA Astrophysics Data System (ADS)

A dynamical model dedicated to the nucleon induced reaction between 30 and 150 MeV is presented. It considers different stages of the reaction: the approaching phase, the in-medium nucleon-nucleon collisions, the cluster formation, and the secondary deexcitation process. The notions of influence area and phase-space exploration during the reaction are introduced. The importance of the reaction geometry and the conservation laws is emphasized. The model is able to globally reproduce the absolute cross sections for the emission of neutron and light charged particles for proton- and neutron induced reactions on heavy and intermediate targets (56Fe and 208Pb).

Lacroix, Denis; Blideanu, Valentin; Durand, Dominique

2005-02-01

44

Crystal Structure of Reaction Intermediates in Pyruvate Class II Aldolase  

PubMed Central

Crystal structures of divalent metal-dependent pyruvate aldolase, HpaI, in complex with substrate and cleavage products were determined to 1.8–2.0 Å resolution. The enzyme·substrate complex with 4-hydroxy-2-ketoheptane-1,7-dioate indicates that water molecule W2 bound to the divalent metal ion initiates C3–C4 bond cleavage. The binding mode of the aldehyde donor delineated a solvent-filled capacious binding locus lined with predominantly hydrophobic residues. The absence of direct interactions with the aldehyde aliphatic carbons accounts for the broad specificity and lack of stereospecific control by the enzyme. Enzymatic complex structures formed with keto acceptors, pyruvate, and 2-ketobutyrate revealed bidentate interaction with the divalent metal ion by C1-carboxyl and C2-carbonyl oxygens and water molecule W4 that is within close contact of the C3 carbon. Arg70 assumes a multivalent role through its guanidinium moiety interacting with all active site enzymatic species: C2 oxygen in substrate, pyruvate, and ketobutyrate; substrate C4 hydroxyl; aldehyde C1 oxygen; and W4. The multiple interactions made by Arg70 stabilize the negatively charged C4 oxygen following proton abstraction, the aldehyde alignment in aldol condensation, and the pyruvate enolate upon aldol cleavage as well as support proton exchange at C3. This role is corroborated by loss of aldol cleavage ability and pyruvate C3 proton exchange activity and by a 730-fold increase in the dissociation constant toward the pyruvate enolate analog oxalate in the R70A mutant. Based on the crystal structures, a mechanism is proposed involving the two enzyme-bound water molecules, W2 and W4, in acid/base catalysis that facilitates reversible aldol cleavage. The same reaction mechanism promotes decarboxylation of oxaloacetate.

Coincon, Mathieu; Wang, Weijun; Sygusch, Jurgen; Seah, Stephen Y. K.

2012-01-01

45

Nucleon radiative capture and the inverse reaction at intermediate energies  

SciTech Connect

The processes which can lead to the radiative capture of fast nucleons include direct transitions in the nuclear potential, transitions in which coherent multipole resonances are excited, transitions by nucleons which are excited in early intranuclear collisions, bremsstrahlung from nucleon-nucleon collisions and photon evaporation'' from a thermally equilibrated nucleus. Corresponding processes occur when an energetic photon ejects fast nucleons from a nucleus. As experimental information from capture and photoreactions has become more detailed, inconsistencies and uncertainties have appeared which reflect difficulties in identifying and separating the responsible processes. This has led to more sophisticated and more complicated theoretical treatments which in turn have promoted new and more demanding experiments. 38 refs. 10 figs.

Halpern, I.

1991-01-01

46

A specific polymerase chain reaction method to identify Stenotrophomonas maltophilia.  

PubMed

Stenotrophomonas maltophilia is a multidrug-resistant nosocomial pathogen that is difficult to identify unequivocally using current methods. Accordingly, because the presence of this microorganism in a patient may directly determine the antimicrobial treatment, conventional polymerase chain reaction (PCR) and real-time PCR assays targeting 23S rRNA were developed for the specific identification of S. maltophilia. The PCR protocol showed high specificity when tested against other species of Stenotrophomonas, non-fermentative Gram-negative bacilli and 100 clinical isolates of S. maltophilia previously identified using the Vitek system. PMID:23778655

Gallo, Stephanie Wagner; Ramos, Patrícia Locosque; Ferreira, Carlos Alexandre Sanchez; de Oliveira, Sílvia Dias

2013-05-01

47

Trapping and Characterization of a Reaction Intermediate in Carbapenem Hydrolysis by B. cereus Metallo-?-lactamase  

PubMed Central

Metallo-?-lactamases hydrolyze most ?-lactam antibiotics. The lack of a successful inhibitor for them is related to the previous failure to characterize a reaction intermediate with a clinically useful substrate. Stopped-flow experiments together with rapid freeze-quench EPR and Raman spectroscopies were used to characterize the reaction of Co(II)-BcII with imipenem. These studies show that Co(II)-BcII is able to hydrolyze imipenem both in the mono- and dinuclear forms. In contrast to the situation met for penicillin, the species that accumulates during turnover is an enzyme-intermediate adduct in which the ?-lactam bond has already been cleaved. This intermediate is a metal-bound anionic species, with a novel resonant structure, that is stabilized by the metal ion at the DCH or Zn2 site. This species has been characterized based on its spectroscopic features. This represents a novel, previously unforeseen intermediate, that is related to the chemical nature of carbapenems, as confirmed by the finding of a similar intermediate for meropenem. Since carbapenems are the only substrates cleaved by B1, B2 and B3 lactamases, the identification of this intermediate could be exploited as a first step towards the design of transition state based inhibitors for all three classes of metallo-?-lactamases.

Tioni, Mariana F.; Llarrull, Leticia I.; Poeylaut-Palena, Andres A.; Marti, Marcelo A.; Saggu, Miguel; Periyannan, Gopal R.; Mata, Ernesto G.; Bennett, Brian; Murgida, Daniel H.; Vila, Alejandro J.

2009-01-01

48

Synthesis of a Potential Intermediate for TMC-95A via an Organocatalyzed Aldol Reaction.  

PubMed

N-Prolinylanthranilamide-based pseudopeptide organocatalyst 14 was shown to promote enantioselective direct aldol reaction of 7-iodoisatin and 2,2-dimethyl-1,3-dioxan-5-one with 90% conversion (75% isolated yield), 90% enantioselectivity, and 23:1 diastereoselectivity. To demonstrate the synthetic utility of this chemistry, the racemic aldol reaction product was converted in five steps to a potential intermediate for construction of the natural product TMC-95A. PMID:24024913

Pearson, Anthony J; Panda, Santanu; Bunge, Scott D

2013-09-24

49

(Intermediate energy studies of polarization transfer, polarized deuteron scattering, and (p,. pi. /sup + -/) reactions: Rapporteur's report)  

SciTech Connect

An overview of intermediate energy (80 to 1000 MeV) study contributions to the International Polarization Symposium in Osaka, Japan, August 1985 is presented in this report. Contributions fall into three categories: polarization transfer, polarized deuteron scattering and polarized (p,..pi../sup + -/) reactions. (WRF)

Moss, J.M.

1985-01-01

50

Possible genotoxicity of melanin synthesis intermediates: Tyrosinase reaction products interact with DNA in vitro  

Microsoft Academic Search

The actual cellular target of the cytotoxic intermediates of melanin synthesis is not yet known. In the present paper it is shown that eukaryotic DNA binds in vitro to soluble reaction products of tyrosinase (EC 1.14.18.1) and is physically modified, as ascertained by the following criteria: (a) buoyant density in cesium chloride density gradients; (b) polyacrylamide gel electrophoresis: (c) deoxyribonuclease

M. Miranda; D. Botti; M. Cola

1984-01-01

51

Theoretical insights into the superior activity of gold catalysts and reactions of organogold intermediates with electrophiles.  

PubMed

Three fundamental steps of homogeneous gold catalysis, the activiation of substrates by coordination to gold, the protodeauration after the nucleophilic addition and the transmetalation to palladium in palladium-catalysed C-C bond forming reactions using organogold intermediates have been studied and discussed in detail. PMID:22455045

Hashmi, A Stephen K; Pernpointner, Markus; Hansmann, Max M

2011-01-01

52

Benchmarking of activation reaction distribution in an intermediate energy neutron field.  

PubMed

Neutron-induced reaction rate depth profiles inside concrete shield irradiated by intermediate energy neutron were calculated using a Monte-Carlo code and compared with an experiment. An irradiation field of intermediate neutron produced in the forward direction from a thick (stopping length) target bombarded by 400 MeV nucleon(-1) carbon ions was arranged at the heavy ion medical accelerator in Chiba. Ordinary concrete shield of 90 cm thickness was installed 50 cm downstream the iron target. Activation detectors of aluminum, gold and gold covered with cadmium were inserted at various depths. Irradiated samples were extracted after exposure and gamma-ray spectrometry was performed for each sample. Comparison of experimental and calculated shows good agreement for both low- and high-energy neutron-induced reaction except for (27)Al(n,X)(24)Na reaction at the surface. PMID:21515619

Ogawa, Tatsuhiko; Morev, Mikhail N; Hirota, Masahiro; Abe, Takuya; Koike, Yuya; Iwai, Satoshi; Iimoto, Takeshi; Kosako, Toshiso

2011-04-22

53

Production of projectile-like-fragments with light systems in mass asymmetric, intermediate energy reactions  

NASA Astrophysics Data System (ADS)

The reactions ^40,48Ca + ^112,124Sn at a bombarding energy of 45 MeV/A were studied with the 4? charged particle detector array, CHIMERA, at the Laboratori Nazionali del Sud in Catania, Italy. Measured observables were the charged particle multiplicities, their individual energy, charge, and in some cases, isotopic identity. Of particular interest is the production of intermediate mass fragments and their correlations with projectile-like fragments (PLFs) formed in the reaction. Data concerning the production of PLFs will be presented; specifically their charge, energy, and angular distributions. The reaction mechanism and isotopic effects with be discussed.

Quinlan, Michael; Pawelczak, Iwona; T\\ Oke, Jan; Schr"Oder, Udo

2009-05-01

54

Crystal Structure of the Plant PPC Decarboxylase AtHAL3a Complexed with an Ene-thiol Reaction Intermediate  

Microsoft Academic Search

The Arabidopsis thaliana protein AtHAL3a decarboxylates 4?-phosphopantothenoylcysteine to 4?-phosphopantetheine, a step in coenzyme A biosynthesis. Surprisingly, this decarboxylation reaction is carried out as an FMN-dependent redox reaction. In the first half-reaction, the side-chain of the cysteine residue of 4?-phosphopantothenoylcysteine is oxidised and the thioaldehyde intermediate decarboxylates spontaneously to the 4?-phosphopantothenoyl-aminoethenethiol intermediate. In the second half-reaction this compound is reduced to

Stefan Steinbacher; Pilar Hernández-Acosta; Bastian Bieseler; Michael Blaesse; Robert Huber; Francisco Antonio Culiáñez-Macià; Thomas Kupke

2003-01-01

55

Global assessment of molecularly identified Anisakis Dujardin, 1845 (Nematoda: Anisakidae) in their teleost intermediate hosts.  

PubMed

Here, we present the ITS ribosomal DNA (rDNA) sequence data on 330 larvae of nematodes of the genus Anisakis Dujardin, 1845 collected from 26 different bony fish species from 21 sampling locations and different climatic zones. New host records are provided for Anisakis simplex (Rudolphi, 1809) sensu stricto (s.s.) and A. pegreffli Campana-Rouget et Biocca, 1955 from Anoplopoma fimbria (Pallas) (Santa Barbara, East Pacific), A. typica (Diesing, 1860) from Caesio cuning (Bloch), Lepturacanthus savala (Cuvier) and Katsuwonus pelamis (Linnaeus) (Indonesia, West Pacific), A. simplex s.s. from Cololabis saira (Brevoort) (Hawaii, Central Pacific), A. simplex C of Nascetti et al. (1986) from Sebastolobus alascanus Bean (Santa Barbara, East Pacific) and A. physeteris Baylis, 1923 from Synaphobranchus kaupii Johnson (Namibia, East Atlantic). Comparison with host records from 60 previous molecular studies of Anisakis species reveals the teleost host range so far recorded for the genus. Perciform (57 species) and gadiform (21) fishes were the most frequently infected orders, followed by pleuronectiforms (15) and scorpaeniforms (15). Most commonly infected fish families were Scombridae (12), Gadidae (10), Carangidae (8) and Clupeidae (7), with Merluccius merluccius (Linnaeus) alone harbouring eight Anisakis species. Different intermediate host compositions implicate differing life cycles for the so far molecularly identified Anisakis sibling species. PMID:23724731

Kuhn, Thomas; Hailer, Frank; Palm, Harry W; Klimpel, Sven

2013-05-01

56

Insights into the Mechanism of Type I Dehydroquinate Dehydratases from Structures of Reaction Intermediates  

SciTech Connect

The biosynthetic shikimate pathway consists of seven enzymes that catalyze sequential reactions to generate chorismate, a critical branch point in the synthesis of the aromatic amino acids. The third enzyme in the pathway, dehydroquinate dehydratase (DHQD), catalyzes the dehydration of 3-dehydroquinate to 3-dehydroshikimate. We present three crystal structures of the type I DHQD from the intestinal pathogens Clostridium difficile and Salmonella enterica. Structures of the enzyme with substrate and covalent pre- and post-dehydration reaction intermediates provide snapshots of successive steps along the type I DHQD-catalyzed reaction coordinate. These structures reveal that the position of the substrate within the active site does not appreciably change upon Schiff base formation. The intermediate state structures reveal a reaction state-dependent behavior of His-143 in which the residue adopts a conformation proximal to the site of catalytic dehydration only when the leaving group is present. We speculate that His-143 is likely to assume differing catalytic roles in each of its observed conformations. One conformation of His-143 positions the residue for the formation/hydrolysis of the covalent Schiff base intermediates, whereas the other conformation positions the residue for a role in the catalytic dehydration event. The fact that the shikimate pathway is absent from humans makes the enzymes of the pathway potential targets for the development of non-toxic antimicrobials. The structures and mechanistic insight presented here may inform the design of type I DHQD enzyme inhibitors.

Light, Samuel H.; Minasov, George; Shuvalova, Ludmilla; Duban, Mark-Eugene; Caffrey, Michael; Anderson, Wayne F.; Lavie, Arnon (NWU); (UIC)

2012-02-27

57

Role of the PR intermediate in the reaction of cytochrome c oxidase with O2.  

PubMed

The first discernible intermediate when fully reduced cytochrome c oxidase reacts with O2 is a dioxygen adduct (compound A) of the binuclear heme iron-copper center. The subsequent decay of compound A is associated with transfer of an electron from the low-spin heme a to this center. This reaction eventually produces the ferryl state (F) of this center, but whether an intermediate state may be observed between A and F has been the subject of some controversy. Here we show, using both optical and EPR spectroscopy, that such an intermediate (P(R)) indeed exists and that it exhibits spectroscopic properties quite distinct from F. The optical spectrum of P(R) is similar or identical to the spectrum of the P(M) intermediate that is formed after compound A when two-electron-reduced enzyme reacts with O2. An unusual EPR spectrum with features of a CuB(II) ion that interacts magnetically with a nearby paramagnet [cf. Hansson, O., Karlsson, B., Aasa, R., Vänngård, T., and Malmström, B.G (1982) EMBO J. 1, 1295-1297; Blair, D. F., Witt, S. N., and Chan, S. I. (1985) J. Am. Chem. Soc. 107, 7389-7399] can be uniquely assigned to the P(R) intermediate, not being found in either the P(M) or F intermediate. The binuclear center in the P(R) state may be assigned as having an Fe(a3)(IV)=O CuB(II) structure, as in both the P(M) and F states. The spectroscopic differences between these three intermediates are evaluated. The P(R) state has a key role as an initiator of proton translocation by the enzyme, and the thermodynamic and electrostatic bases for this are discussed. PMID:11389603

Morgan, J E; Verkhovsky, M I; Palmer, G; Wikström, M

2001-06-12

58

New observations concerning the chloroacetaldehyde reaction with some tRNA constituents. Stable intermediates, kinetics and selectivity of the reaction.  

PubMed Central

The stable intermediates formed in the reaction of cytosine, cytidine and adenosine with chloracetaldehyde were isolated. The -CH2CH/OH/- bridge between the exo and endo nitrogen atoms of the parent base was found in these compounds by means of PMR spectroscopy. Their acid-induced dehydration resulted in formation of appropriate ethenoderivatives. The rate constants of the intermediate formation and its dehydration were found to be 38x10(-4) and 47x10(-4) /min-1/ for adenosine, and 33x10(-4) and 10x10(-4) /min-1/ for cytidine. The PH range of 4.5--5.0 was found to be optimum for both adenosine and cytidine reactions. The quantitative modification of these two nucleosides in the presence of guanosine may be achieved with high selectivity only at a low pH of 3.0--4.0 N6-methyladenosine and N4-methylcytidine react quantitatively with chloroacetaldehyde and the reaction rate is higher than in the case of the parent nucleosides. The structure of the reaction products was assigned on the basis of PMR spectroscopy.

Biernat, J; Ciesiolka, J; Gornicki, P; Adamiak, R W; Kryzosiak, W J; Wiewiorowski, M

1978-01-01

59

The Low Temperature Thermal Decomposition of Ammonium Perchlorate: Nitryl Perchlorate as the Reaction Intermediate  

Microsoft Academic Search

We identify nitryl perchlorate as the essential intermediate in the low temperature thermal decomposition of ammonium perchlorate AP. Evidence supporting this identification includes the analytical detection of an oxidized nitrogenous species in partly reacted AP and the ability of ammonium nitrate and several other nitrates to markedly reduce the induction period to decomposition of AP and to accelerate the subsequent

A. K. Galwey; M. A. Mohamed

1984-01-01

60

Stabilization of the peroxy intermediate in the oxygen splitting reaction of cytochrome cbb 3  

Microsoft Academic Search

The proton-pumping cbb3-type cytochrome c oxidases catalyze cell respiration in many pathogenic bacteria. For reasons not yet understood, the apparent dioxygen (O2) affinity in these enzymes is very high relative to other members of the heme-copper oxidase (HCO) superfamily. Based on density functional theory (DFT) calculations on intermediates of the oxygen scission reaction in active-site models of cbb3- and aa3-type

Vivek Sharma; Mårten Wikström; Ville R. I. Kaila

2011-01-01

61

Production of projectile-like-fragments with light systems in mass asymmetric, intermediate energy reactions  

Microsoft Academic Search

The reactions ^40,48Ca + ^112,124Sn at a bombarding energy of 45 MeV\\/A were studied with the 4pi charged particle detector array, CHIMERA, at the Laboratori Nazionali del Sud in Catania, Italy. Measured observables were the charged particle multiplicities, their individual energy, charge, and in some cases, isotopic identity. Of particular interest is the production of intermediate mass fragments and their

Michael Quinlan; Iwona Pawelczak; Jan T Oke; Schr

2009-01-01

62

Formation of covalent ?-linked carbohydrate–enzyme intermediates during the reactions catalyzed by ?-amylases  

Microsoft Academic Search

Porcine pancreatic and Bacillus amyloliquefaciens ?-amylases were examined for the formation of covalent carbohydrate intermediates during reaction. The enzymes were precipitated and denatured by adding 10 volumes of acetone. When these denatured enzymes were mixed with methyl ?-6-[3H]-maltooligosaccharide glycosides and chromatographed on BioGel P-2, no carbohydrate was found in the protein void volume peak. When the enzymes were added to

Seung-Heon Yoon; D. Bruce Fulton; John F. Robyt

2007-01-01

63

The reactions of possible intermediates in the selective catalytic reduction of nitrogen oxides by hydrocarbons  

Microsoft Academic Search

The reactions of formamide and nitromethane, two possible intermediates in the selective catalytic reduction of nitrogen oxides by methane, have been studied over Co-ZSM5, H-ZSM5 and Cu-ZSM5. Formamide, a possible surrogate for nitrosomethane, reacts completely below 250°C over Co-ZSM5 with formation of NH3 and CO by one route and HCN and H2O by another. Inclusion of NO causes partial conversion

N. W. Cant; A. D. Cowan; I. O. Y. Liu; A. Satsuma

1999-01-01

64

Identifying a new intermediate polar using XMM-Newton and INTEGRAL  

NASA Astrophysics Data System (ADS)

The bright X-ray source 2XMMi J180438.7-145647 is fortunate to have long baseline observations in INTEGRAL that complement observations taken by other missions. Optical spectroscopy of this object has suggested a distance of ˜7 kpc and an identification with a low-mass X-ray binary. We instead use the X-ray data from 0.3 to 40 keV to identify the source as a bright intermediate polar (IP) with an estimate for the white dwarf mass of ˜0.60 M?. This identification is supported by the presence of an iron triplet, the component lines of which are some of the strongest seen in IPs, and the signature of the spin period of the white dwarf at ˜24 min. We note that the lack of broad-band variability may suggest that this object is a stream-fed IP, similar in many respects to the well-studied IP, V2400 Oph. Phase binning has allowed us to create spectra corresponding to the peaks and troughs of the light curve from which we determine that the spectra appear harder in the troughs, consistent with the behaviour of other IPs binned on their spin periods. This work strongly suggests a misidentification in the optical due to the presence of large columns of enshrouding material. We instead propose a distance to the source of <2.5 kpc to be consistent with the luminosities of other IPs in the dim, hard state. The considerable flux of the source together with the strength of the iron lines may, in future, allow the source to be used to diagnose the properties of the shock-heated plasma and the reflected component of the emission.

Middleton, Matthew J.; Cackett, Edward M.; Shaw, Craig; Ramsay, Gavin; Roberts, Timothy P.; Wheatley, Peter J.

2012-01-01

65

A new paramagnetic intermediate formed during the reaction of nitrite with deoxyhemoglobin  

PubMed Central

The reduction of nitrite by deoxygenated hemoglobin chains has been implicated in red cell induced vasodilation, although the mechanism for this process has not been established. We have previously demonstrated that the reaction of nitrite with deoxyhemoglobin produces a hybrid intermediate with properties of Hb(II)NO+ and Hb(III)NO that builds up during the reaction retaining potential NO bioactivity. To explain the unexpected stability of this intermediate, which prevents NO release from the Hb(III)NO component, we had implicated the transfer of an electron from the ?-93 thiol to NO+ producing •SHb(II)NO. In order to determine if this species is formed and to characterize its properties, we have investigated the electron paramagnetic resonance (EPR) changes taking place during the nitrite reaction. The EPR effects of blocking the thiol group with N-ethyl-maleimide and using carboxypeptidase-A to stabilize the R-quaternary conformation have demonstrated that •SHb(II)NO is formed and that it has the EPR spectrum expected for NO bound to the heme in the ?-chain plus that of a thiyl radical. This new NO-related paramagnetic species is in equilibrium with the hybrid intermediate “Hb(II)NO+ ? Hb(III)NO” thereby further inhibiting the release of NO from Hb(III)NO. The formation of an NO-related paramagnetic species other than the tightly bound NO in Hb(II)NO was also confirmed by a decrease in the EPR signal by ?20°C incubation, which shifts the equilibrium back to the “Hb(II)NO+ ? Hb(III)NO” intermediate. This previously unrecognized NO hemoglobin species explains the stability of the intermediates and the buildup of a pool of potentially bioactive NO during nitrite reduction. It also provides a pathway for the formation of ?-93 cysteine S-nitrosylated hemoglobin [SNOHb:S-nitrosohemoglobin], which has been shown to induce vasodilation, by a rapid radical-radical reaction of any free NO with the thiyl radical of this new paramagnetic intermediate.

Salgado, Maria T.; Ramasamy, Somasundaram; Tsuneshige, Antonio; Manoharan, Periakaruppan T.; Rifkind, Joseph M.

2011-01-01

66

Investigations of the structure and reactions of the intermediate in the chlorination of resorcinol  

SciTech Connect

The investigation reported here describes an attempt to establish the structure of the intermediate that undergoes ring-opening in the chlorination of resorcinol and its chloro-derivatives in a nucleophilic solvent such as H[sub 2]O or CH[sub 3]OH. The evidence suggests that the pentachloride and not the tetrachloride is the intermediate that reacts with the nucleophiles. Chlorination reactions were conducted in Ch[sub 3]OH/H[sub 2]O. The structures of the early-generation products from incorporation of CH[sub 3]OH were sufficiently stable to be characterized. These products implicated the pentachloride. Resorcinol, di- and trichlororesorcinol, and the pentachloride gave the same products. The mechanisms of the ring-opening and the reactions leading to the products are described in detail. The assumption is made that the same or similar reactions are involved in the aqueous chlorination of resorcinol, but that decarboxylation and solvolysis reactions rapidly degrade the products immediately following ring-opening.

Heasley, V.L.; Anderson, M.E.; Combes, D.S.; Elias, D.S.; Gardner, J.T.; Hernandez, M.L.; Moreland, R.J.; Shellhamer, D.F. (Point Loma Nazarene College, San Diego, CA (United States). Dept. of Chemistry)

1993-09-01

67

Catching catalysis in the act: using single crystal kinetics to trap methylamine dehydrogenase reaction intermediates.  

PubMed

Methylamine dehydrogenase (MADH) is produced by a range of gram-negative methylotrophic and autotrophic bacteria, and allows the organisms to utilise methylamine as the sole source of carbon. The enzyme catalyses the oxidation of methylamine to formaldehyde and ammonia, leaving it in a two-electron reduced state. To complete the catalytic cycle, MADH is reoxidised via an electron transfer (ET) chain. The redox center in the enzyme is the organic cofactor tryptophan tryptophylquinone (TTQ) derived from the posttranslational modification of two Trp residues in the protein. This cofactor has spectral features in the visible region, which change during catalytic turnover, defining spectrally distinct reaction intermediates that reflect the electronic state of the TTQ. In the case of the Paracoccus denitrificans enzyme the physiologic ET chain involves the protein redox partner amicyanin (a blue copper protein). A stable binary (MADH/amicyanin) complex can be formed, and its crystal structure has been solved to 2.5 A resolution by Chen et al. [Biochemistry 21 (1992) 4959]. These crystals were shown to be competent for catalysis and ET by Merli et al. [J. Biol. Chem. 271 (1996) 9177] using single crystal polarised absorption spectroscopy. Through a novel combination of single crystal visible microspectrophotometry, X-ray crystallography and freeze-trapping, we have trapped reaction intermediates of the enzyme in complex with its physiological redox partner amicyanin in the crystalline state. We will present data confirming that catalysis and ET in the binary complex crystals can be tracked by single crystal visible microspectrophotometry. We will also show that the reaction pathway is unperturbed by the presence of cryoprotectant solution, enabling direct freeze-trapping of reaction intermediates within the crystal. We will present new data demonstrating that the binary complex crystals are also capable of exhibiting UV light-dependent oxidase activity, as observed in solution [Biochim. Biophys. Acta 1364 (1998) 297]. PMID:12686162

Pearson, Arwen R; Wilmot, Carrie M

2003-04-11

68

Exploiting Acyl and Enol Azolium Intermediates via NHeterocyclic Carbene Catalyzed Reactions of Alpha-Reducible Aldehydes  

PubMed Central

N-heterocyclic carbenes are well known for their role in catalyzing benzoin and Stetter reactions: the generation of acyl anion equivalents from simple aldehydes to react with a variety of electrophiles. However, when an aldehyde bearing a leaving group or unsaturation adjacent to the acyl anion equivalent is subjected to an NHC, a new avenue of reactivity is unlocked, leading to a number of novel transformations which can generate highly complex products from simple starting materials, many of which are assembled through unconventional bond disconnections. The field of these new reactions - those utilizing ?-reducible aldehydes to access previously unexplored catalytic intermediates – has expanded rapidly in the past eight years. This review aims to provide the reader with a historical perspective on the underlying discoveries that led to the current state of the art, a mechanistic description of these reactions, and a summary of the recent advances in this area.

Vora, Harit U.; Wheeler, Philip

2013-01-01

69

Progress in applyiong the FKK multistep reaction theory to intermediate-energy data evaluation  

SciTech Connect

Recent developments to the physics modeling in the FKK-GNASH code system are reviewed. We describe modifications to include a linking of multistep direct and multistep compound processes, which are important when the incident energy is less than about 30 MeV. A model for multiple preequilibrium emission is given, and compared with experimental measurements of proton reactions on {sup 90}Zr at 160 MeV. We also give some preliminary observations concerning FKK calculations which use both normal and non-normal DWBA matrix elements. We describe the application of the FKK-GNASH code to a range of nuclear data applications, including intermediate energy reactions of importance in the accelerator transmutation of waste, and fast neutron and proton cancer radiation treatment. We outline areas where further work is needed for the accurate modeling of nuclear reactions using the FKK theory.

Chadwick, M.B. [Lawrence Livermore National Lab., CA (United States); Young, P.G. [Los Alamos National Lab., NM (United States)

1994-07-01

70

Consequences of a covariant description of heavy-ion reactions at intermediate energies  

SciTech Connect

Heavy-ion collisions at intermediate energies are studied by using a new relativistic quantum molecular dynamics (RQMD) code, which is a covariant generalization of the quantum molecular dynamics (QMD) approach. We show that this new implementation is able to produce the same results in the nonrelativistic limit (i.e., 50 MeV/nucleon) as the noncovariant QMD. Such a comparison is not available in the literature. At higher energies (i.e., 1.5 GeV/nucleon and 2 GeV/nucleon) RQMD and QMD give different results in respect to the time evolution of the phase space, for example for the directed transverse flow. These differences show that consequences of a covarient description of heavy-ion reactions within the framework of RQMD exist even at intermediate energies.

Lehmann, E.; Puri, R.K.; Faessler, A.; Batko, G.; Huang, S.W. (Institut fuer Theoretische Physik, Universitaet Tuebingen, Auf der Morgenstelle 14, D-72706 Tuebingen (Germany))

1995-04-01

71

The role of long-lived reactive oxygen intermediates in the reaction of ozone with aerosol particles  

Microsoft Academic Search

The heterogeneous reactions of O3 with aerosol particles are of central importance to air quality. They are studied extensively, but the molecular mechanisms and kinetics remain unresolved. Based on new experimental data and calculations, we show that long-lived reactive oxygen intermediates (ROIs) are formed. The chemical lifetime of these intermediates exceeds 100 seconds, which is much longer than the surface

Manabu Shiraiwa; Yulia Sosedova; Aurélie Rouvière; Hong Yang; Yingyi Zhang; Jonathan P. D. Abbatt; Markus Ammann; Ulrich Pöschl

2011-01-01

72

Isotopic-yield ratios of complex fragments from intermediate-energy heavy-ion reactions  

SciTech Connect

Isotopically resolved yields of intermediate-mass fragments from /sup 12/C- and /sup 18/O-induced reactions on /sup 58,64/Ni, /sup nat/Ag, and /sup 197/Au at E/A = 84 MeV were measured. The systematic variation of the yield ratios with projectile and target shows that these fragments are produced by a mechanism that involves the whole target nucleus. It is demonstrated that, within a statistical interpretation, the isotope-yield ratios are a measure of the entropy and determine a relation between temperature and density at breakup.

Wada, R.; Hildenbrand, K.D.; Lynen, U.; Mueller, W.F.J.; Rabe, H.J.; Sann, H.; Stelzer, H.; Trautmann, W.; Trockel, R.; Brummund, N.; and others

1987-05-04

73

First-Principles Prediction of Crystal Structures, Reaction Pathways, and Intermediate Products in Hydrogen Storage Reactions  

NASA Astrophysics Data System (ADS)

Practical hydrogen storage for mobile applications requires materials that exhibit high hydrogen densities, low decomposition temperatures, and fast kinetics for absorption and desorption. Unfortunately, no reversible materials are currently known that possess all of these attributes. Here we present an overview of our recent efforts aimed at developing a first-principles computational approach to the discovery of novel hydrogen storage materials. We have developed computational tools which enable accurate prediction of decomposition thermodynamics, crystal structures for unknown hydrides, and thermodynamically preferred decomposition pathways. We present examples that illustrate each of these three capabilities. Specifically, we focus on recent work on crystal structure and dehydriding reactions of (i) borohydride materials, such as Ca(BH4)2 and Mg(BH4)2, (ii) amidoboranes and their decomposition products, and (iii) mixtures of complex hydrides. [4pt] [1] J. Yang, A. Sudik, C. Wolverton, and D. J. Siegel, Chem. Soc. Rev. 39, 656 (2010). [0pt] [2] D. E. Farrell, D. Shin, and C. Wolverton, Phys. Rev. B 80, 224201 (2009). [0pt] [3] C. Weidenthaler, A. Pommerin, M. Felderhoff, W. Sun, C. Wolverton, B. Bogdanovic, and F. Schuth, J. Amer. Chem. Soc. 131, 16735 (2009). [0pt] [4] A. R. Akbarzadeh, C. Wolverton, and V. Ozolins, Phys. Rev. B 79, 184102 (2009). [0pt] [5] Y. S. Lee, Y. Kim, Y. W. Cho, D. Shapiro, C. Wolverton, and V. Ozolins, Phys. Rev. B 79, 104107 (2009). [0pt] [6] V. Ozolins, E. H. Majzoub, and C. Wolverton, J. Amer. Chem. Soc. 131, 230 (2009). [0pt] [7] V. Ozolins, E. H. Majzoub, and C. Wolverton, Phys. Rev. Lett. 100, 135501 (2008). [0pt] [8] Y. Zhang, E. Majzoub, V. Ozolins, and C. Wolverton, Phys. Rev. B 82, 174107 (2010).

Wolverton, Chris

2011-03-01

74

Reaction of a copper(II)-nitrosyl complex with hydrogen peroxide: putative formation of a copper(I)-peroxynitrite intermediate.  

PubMed

The reaction of a Cu(II)-nitrosyl complex (1) with hydrogen peroxide at -20 °C in acetonitrile results in the formation of the corresponding Cu(I)-peroxynitrite intermediate. The reduction of the Cu(II) center was monitored by UV-visible spectroscopic studies. Formation of the peroxynitrite intermediate has been confirmed by its characteristic phenol ring nitration reaction as well as isolation of corresponding Cu(I)-nitrate (2). On air oxidation, 2 resulted in the corresponding Cu(II)-nitrate (3). Thus, these results demonstrate a possible decomposition pathway for H(2)O(2) and NO through the formation of a peroxynitrite intermediate in biological systems. PMID:22466785

Kalita, Apurba; Kumar, Pankaj; Mondal, Biplab

2012-03-30

75

Multifragmentation in intermediate energy {sup 129}Xe-induced heavy-ion reactions  

SciTech Connect

The {sup 129}Xe-induced reactions on {sup nat}Cu, {sup 89}Y, {sup 165}Ho, and {sup 197}Au at bombarding energies of E/A = 40 & 60 MeV have been studied theoretically and experimentally in order to establish the underlying mechanism of multifragmentation at intermediate energy heavy-Ion collisions. Nuclear disks formed in central heavy-ion collisions, as simulated by means of Boltzmann-like kinetic equations, break up into several fragments due to a new kind of Rayleigh-like surface instability. A sheet of liquid, stable in the limit of non-interacting surfaces, is shown to become unstable due to surface-surface interactions. The onset of this instability is determined analytically. A thin bubble behaves like a sheet and is susceptible to the surface instability through the crispation mode. The Coulomb effects associated with the depletion of charges in the central cavity of nuclear bubbles are investigated. The onset of Coulomb instability is demonstrated for perturbations of the radial mode. Experimental intermediate-mass-fragment multiplicity distributions for the {sup 129}Xe-induced reactions are shown to be binomial at each transverse energy. From these distributions, independent of the specific target, an elementary binary decay probability p can be extracted that has a thermal dependence. Thus it is inferred that multifragmentation is reducible to a combination of nearly independent emission processes. If sequential decay is assumed, the increase of p with transverse energy implies a contraction of the emission time scale. The sensitivity of p to the lower Z threshold in the definition of intermediate-mass-fragments points to a physical Poisson simulations of the particle multiplicities show that the weak auto-correlation between the fragment multiplicity and the transverse energy does not distort a Poisson distribution into a binomial distribution. The effect of device efficiency on the experimental results has also been studied.

Tso, Kin

1996-05-01

76

Reactions of peroxynitrite with uric acid: formation of reactive intermediates, alkylated products and triuret, and in vivo production of triuret under conditions of oxidative stress.  

PubMed

Hyperuricemia is associated with hypertension, metabolic syndrome, preeclampsia, cardio-vascular disease and renal disease, all conditions associated with oxidative stress. We hypothesized that uric acid, a known antioxidant, might become prooxidative following its reaction with oxidants; and, thereby contribute to the pathogenesis of these diseases. Uric acid and 1,3-(15)N(2)-uric acid were reacted with peroxynitrite in different buffers and in the presence of alcohols, antioxidants and in human plasma. The reaction products were identified using liquid chromatography-mass spectrometry (LC-MS) analyses. The reactions generate reactive intermediates that yielded triuret as their final product. We also found that the antioxidant, ascorbate, could partially prevent this reaction. Whereas triuret was preferentially generated by the reactions in aqueous buffers, when uric acid or 1,3-(15)N(2)-uric acid was reacted with peroxynitrite in the presence of alcohols, it yielded alkylated alcohols as the final product. By extension, this reaction can alkylate other biomolecules containing OH groups and others containing labile hydrogens. Triuret was also found to be elevated in the urine of subjects with preeclampsia, a pregnancy-specific hypertensive syndrome that is associated with oxidative stress, whereas very little triuret is produced in normal healthy volunteers. We conclude that under conditions of oxidative stress, uric acid can form reactive intermediates, including potential alkylating species, by reacting with peroxynitrite. These reactive intermediates could possibly explain how uric acid contributes to the pathogenesis of diseases such as the metabolic syndrome and hypertension. PMID:19219741

Gersch, Christine; Palii, Sergiu P; Imaram, Witcha; Kim, Kyung Mee; Karumanchi, S Ananth; Angerhofer, Alexander; Johnson, Richard J; Henderson, George N

2009-02-01

77

REACTIONS OF PEROXYNITRITE WITH URIC ACID: FORMATION OF REACTIVE INTERMEDIATES, ALKYLATED PRODUCTS AND TRIURET, AND IN VIVO PRODUCTION OF TRIURET UNDER CONDITIONS OF OXIDATIVE STRESS  

PubMed Central

Hyperuricemia is associated with hypertension, metabolic syndrome, preeclampsia, cardiovascular disease and renal disease, all conditions associated with oxidative stress. We hypothesized that uric acid, a known antioxidant, might become prooxidative following its reaction with oxidants; and, thereby contribute to the pathogenesis of these diseases. Uric acid and 1,3-15N2-uric acid were reacted with peroxynitrite in different buffers and in the presence of alcohols, antioxidants and in human plasma. The reaction products were identified using liquid chromatography-mass spectrometry (LC-MS) analyses. The reactions generate reactive intermediates that yielded triuret as their final product. We also found that the antioxidant, ascorbate, could partially prevent this reaction. Whereas triuret was preferentially generated by the reactions in aqueous buffers, when uric acid or 1,3-15N2-uric acid was reacted with peroxynitrite in the presence of alcohols, it yielded alkylated alcohols as the final product. By extension, this reaction can alkylate other biomolecules containing OH groups and others containing labile hydrogens. Triuret was also found to be elevated in the urine of subjects with preeclampsia, a pregnancy-specific hypertensive syndrome that is associated with oxidative stress, whereas very little triuret is produced in normal healthy volunteers. We conclude that under conditions of oxidative stress, uric acid can form reactive intermediates, including potential alkylating species, by reacting with peroxynitrite. These reactive intermediates could possibly explain how uric acid contributes to the pathogenesis of diseases such as the metabolic syndrome and hypertension.

Gersch, Christine; Palii, Sergiu P.; Imaram, Witcha; Kim, Kyung Mee; Karumanchi, S. Ananth; Angerhofer, Alexander; Johnson, Richard J.; Henderson, George N.

2009-01-01

78

General aspect of catalytic hydrogenation and isomerization reactions on oxide catalyst. Characteristics of the reactions via ionic and nonionic intermediates  

SciTech Connect

An analysis of new and available data, mostly published by Tanaka and Okuhara, on the hydrogenation of alkenes and conjugated dienes and the hydrogen-deuterium exchange on the oxides of cadmium, magnesium, zinc, cobalt, chromium, thorium, zirconium, and lanthanum, and on molybdenum disulfide suggested that the partial hydrogenation of conjugated dienes catalyzed by cadmium and magnesium oxide proceeds by a mechanism which is similar to that of diene hydrogenation on supported alkali metals or on alkali metal hydride and involves allyl carbanion intermediates. The same ionic mechanism apparently also occurs in the double-bond migration of n-alkenes on cadmium oxide, and the isomerization catalyzed by molybdenum disulfide. The nonionic reaction mechanism via o-alkyl and o- or m-allyl intermediates apparently proceeds on active sites of a definite structure, i.e., a specific degree of coordination, but the ionic mechanism seems to depend only on the acidity or basicity of the sites. The nonspecific nature of the site for the ionic mechanism may result in high resistance to poisoning.

Tanaka, K.; Okuhara, T.

1980-09-01

79

The Physics Classroom: Identifying Action and Reaction Force Pairs  

NSDL National Science Digital Library

This website, from the Physics Classroom, offers a detailed physics tutorial for high school students explaining Newton's Third Law of Motion. The page gives a thorough description of action-reaction force pairs with illustrations and example exercises. Links are provided to tutorials on Newton's other laws of motion.

2009-02-26

80

Synthesis of Y1BaCu3O(x) Superconducting Powders by Intermediate Phase Reactions.  

National Technical Information Service (NTIS)

A procedure for synthesizing Y1Ba2Cu3O(x) by solid state reactions was developed. The method is based on the use of barium compounds, previously synthesized, as intermediate phases for the process. The reaction kinetics of this procedure were established ...

C. Moure J. F. Fernandez J. Tartaj P. Recio P. Duran

1991-01-01

81

Automatic Method for Identifying Reaction Coordinates in Complex Systems †  

Microsoft Academic Search

To interpret simulations of a complex system to determine the physical mechanism of a dynamical process, it is necessary to identify the small number of coordinates that distinguish the stable states from the transition states. We develop an automatic method for identifying these degrees of freedom from a database of candidate physical variables. In the method neural networks are used

Ao Ma; Aaron R. Dinner

2005-01-01

82

The reaction network of the selective oxidation of n-butane on (VO) 2P 2O 7 catalysts: Nature of oxygen containing intermediates  

Microsoft Academic Search

The reaction network of the partial oxidation of n-butane to maleic anhydride on (VO)2P2O7 has been investigated using steady-state and transient experiments in a Temporal-Analysis-of-Products (TAP) reactor under vacuum conditions to identify by mass spectrometry possible intermediate products and in a tubular fixed bed reactor at atmospheric pressure to derive information on the role of the detected and other potential

B. Kubias; U. Rodemerck; H.-W. Zanthoff; M. Meisel

1996-01-01

83

Investigation of the O+allyl addition/elimination reaction pathways from the OCH2CHCH2 radical intermediate  

NASA Astrophysics Data System (ADS)

These experiments study the preparation of and product channels resulting from OCH2CHCH2, a key radical intermediate in the O+allyl bimolecular reaction. The data include velocity map imaging and molecular beam scattering results to probe the photolytic generation of the radical intermediate and the subsequent pathways by which the radicals access the energetically allowed product channels of the bimolecular reaction. The photodissociation of epichlorohydrin at 193.3 nm produces chlorine atoms and c-OCH2CHCH2 radicals; these undergo a facile ring opening to the OCH2CHCH2 radical intermediate. State-selective resonance-enhanced multiphoton ionization (REMPI) detection resolves the velocity distributions of ground and spin-orbit excited state chlorine independently, allowing for a more accurate determination of the internal energy distribution of the nascent radicals. We obtain good agreement detecting the velocity distributions of the Cl atoms with REMPI, vacuum ultraviolet (VUV) photoionization at 13.8 eV, and electron bombardment ionization; all show a bimodal distribution of recoil kinetic energies. The dominant high recoil kinetic energy feature peaks near 33 kcal/mol. To elucidate the product channels resulting from the OCH2CHCH2 radical intermediate, the crossed laser-molecular beam experiment uses VUV photoionization and detects the velocity distribution of the possible products. The data identify the three dominant product channels as C3H4O (acrolein)+H, C2H4+HCO (formyl radical), and H2CO (formaldehyde)+C2H3. A small signal from C2H2O (ketene) product is also detected. The measured velocity distributions and relative signal intensities at m/e=27, 28, and 29 at two photoionization energies show that the most exothermic product channel, C2H5+CO, does not contribute significantly to the product branching. The higher internal energy onset of the acrolein+H product channel is consistent with the relative barriers en route to each of these product channels calculated at the CCSD(T)/aug-cc-pVQZ level of theory, although a clean determination of the barrier energy to H+acrolein is precluded by the substantial partitioning into rotational energy during the photolytic production of the nascent radicals. We compare the measured branching fraction to the H+acrolein product channel with a statistical prediction based on the calculated transition states.

Fitzpatrick, Benjamin L.; Lau, Kai-Chung; Butler, Laurie J.; Lee, Shih-Huang; Lin, Jim-Min, Jr.

2008-08-01

84

Snapshot of a reaction intermediate: analysis of benzoylformate decarboxylase in complex with a benzoylphosphonate inhibitor  

PubMed Central

Benzoylformate decarboxylase (BFDC) is a thiamin diphosphate (ThDP)-dependent enzyme acting on aromatic substrates. In addition to its metabolic role in the mandelate pathway, BFDC shows broad substrate specificity coupled with tight stereocontrol in the carbon-carbon bond-forming reverse reaction, making it a useful biocatalyst for the production of chiral ?-hydroxyketones. The reaction of methyl benzoylphosphonate (MBP), an analogue of the natural substrate benzoylformate, with BFDC results in the formation of a stable analogue (C2?-phosphonomandelylThDP) of the covalent ThDP-substrate adduct C2?-mandelylThDP. Formation of the stable adduct is confirmed both by formation of a circular dichroism band characteristic of the 1’,4’-iminopyrimidine tautomeric form of ThDP (commonly observed when ThDP forms tetrahedral complexes with its substrates), and by high resolution mass spectrometry of the reaction mixture. In addition, the structure of BFDC with the MBP inhibitor was solved by X-ray crystallography, to a spatial resolution of 1.37 Å. The electron density clearly shows formation of a tetrahedral adduct between the C2 atom of ThDP and the carbonyl carbon atom of the MBP. This adduct resembles the intermediate from the penultimate step of the carboligation reaction between benzaldehyde and acetaldehyde. The combination of real-time kinetic information via stopped-flow circular dichroism with steady-state data from equilibrium circular dichroism measurements and X-ray crystallography reveals details of the first step of the reaction catalyzed by BFDC. The MBP-ThDP adduct on BFDC is compared to the recently solved structure of the same adduct on benzaldehyde lyase, another ThDP-dependent enzyme capable of catalyzing aldehyde condensation with high stereospecificity.

Brandt, Gabriel S.; Kneen, Malea M.; Chakraborty, Sumit; Baykal, Ahmet T.; Nemeria, Natalia; Yep, Alejandra; Ruby, David I.; Petsko, Gregory A.; Kenyon, George L.; McLeish, Michael J.; Jordan, Frank; Ringe, Dagmar

2009-01-01

85

Snapshot of a Reaction Intermediate: Analysis of Benzoylformate Decarboxylase in Complex with a Benzoylphosphonate Inhibitor  

SciTech Connect

Benzoylformate decarboxylase (BFDC) is a thiamin diphosphate- (ThDP-) dependent enzyme acting on aromatic substrates. In addition to its metabolic role in the mandelate pathway, BFDC shows broad substrate specificity coupled with tight stereo control in the carbon-carbon bond-forming reverse reaction, making it a useful biocatalyst for the production of chiral-hydroxy ketones. The reaction of methyl benzoylphosphonate (MBP), an analogue of the natural substrate benzoylformate, with BFDC results in the formation of a stable analogue (C2{alpha}-phosphonomandelyl-ThDP) of the covalent ThDP-substrate adduct C2{alpha}-mandelyl-ThDP. Formation of the stable adduct is confirmed both by formation of a circular dichroism band characteristic of the 1',4'-iminopyrimidine tautomeric form of ThDP (commonly observed when ThDP forms tetrahedral complexes with its substrates) and by high-resolution mass spectrometry of the reaction mixture. In addition, the structure of BFDC with the MBP inhibitor was solved by X-ray crystallography to a spatial resolution of 1.37 {angstrom} (PDB ID 3FSJ). The electron density clearly shows formation of a tetrahedral adduct between the C2 atom of ThDP and the carbonyl carbon atom of the MBP. This adduct resembles the intermediate from the penultimate step of the carboligation reaction between benzaldehyde and acetaldehyde. The combination of real-time kinetic information via stopped-flow circular dichroism with steady-state data from equilibrium circular dichroism measurements and X-ray crystallography reveals details of the first step of the reaction catalyzed by BFDC. The MBP-ThDP adduct on BFDC is compared to the recently solved structure of the same adduct on benzaldehyde lyase, another ThDP-dependent enzyme capable of catalyzing aldehyde condensation with high stereospecificity.

Brandt, Gabriel S.; Kneen, Malea M.; Chakraborty, Sumit; Baykal, Ahmet T.; Nemeria, Natalia; Yep, Alejandra; Ruby, David I.; Petsko, Gregory A.; Kenyon, George L.; McLeish, Michael J.; Jordan, Frank; Ringe, Dagmar; (Michigan); (Rutgers); (Brandeis)

2009-04-22

86

An Homogeneous Fluorescence Polymerase Chain Reaction Assay to Identify Salmonella  

Microsoft Academic Search

We have developed a semiquantitative homogeneous fluorescence assay that combines polymerase chain reaction (PCR) amplification with direct fluorescence detection (HF-PCR). The assay eliminates the need to perform gel electrophoresis on test samples. Using a set ofSalmonella-specific primers, this system was used to verify suspect colonies from culture plates asSalmonella.The fluorescence signal is generated by a nucleic acid dye, YO-PRO-1, that

Susan Y. Tseng; Dan Macool; Viki Elliott; George Tice; Ray Jackson; Mark Barbour; Douglas Amorese

1997-01-01

87

Reaction of coordinated dinitrogen. 12. Identification of intermediates in the conversion of molybdenum-bound dinitrogen into ammonia and hydrazine. Factors affecting the ammonia-forming reaction  

SciTech Connect

When bis(dinitrogen) complexes of molybdenum and tungsten are treated with an excess of strong acid, with few exceptions, a complex containing the hydrazido(2-) ligand has been identified either as a product in the reaction or as an intermediate on the way to the formation of ammonia and hydrazine. In the case of those molybdenum complexes that produce ammonia, the stoichiometry of the reaction can be represented by eq 1 and 2: (1) )Mo/sup 0/(N/sub 2/)/sub 2/) ..-->../sup H/sup +// )Mo(NNH/sub 2/)) + N/sub 2/, (2) )Mo(NNH/sub 2/)) ..-->../sup H/sup +// 1/2N/sub 2/ + HN/sub 4//sup +/ + )Mo(III)), with a molybdenum(III) complex as the final molybdenum-containing product. Here the identification of two isomeric hydrazido(2-) complexes are reported upon, that are formed as a mixture in the reaction of excess HBr in tetrahydrofuran (THF) solution with trans-(Mo(N/sub 2/)/sub 2/(triphos)(PPh/sub 3/)), where triphos = PhP(CH/sub 2/CH/sub 2/PPh/sub 2/)/sub 2/. From this mixture of hydrazido(2-) complexes ammonia and a trace of hydrazine are produced in THF solution, but in benzene or toluene solution more hydrazine than ammonia is produced. On the basis of data presented, reversible phosphine dissociation is the next recognizable step toward ammonia formation.

Bossard, G.E.; George, T.A.; Howell, D.B.; Koczon, L.M.; Lester, R.K.

1983-07-06

88

Plant ALDH10 family: identifying critical residues for substrate specificity and trapping a thiohemiacetal intermediate.  

PubMed

Plant ALDH10 family members are aminoaldehyde dehydrogenases (AMADHs), which oxidize ?-aminoaldehydes to the corresponding acids. They have been linked to polyamine catabolism, osmoprotection, secondary metabolism (fragrance), and carnitine biosynthesis. Plants commonly contain two AMADH isoenzymes. We previously studied the substrate specificity of two AMADH isoforms from peas (PsAMADHs). Here, two isoenzymes from tomato (Solanum lycopersicum), SlAMADHs, and three AMADHs from maize (Zea mays), ZmAMADHs, were kinetically investigated to obtain further clues to the catalytic mechanism and the substrate specificity. We also solved the high resolution crystal structures of SlAMADH1 and ZmAMADH1a because these enzymes stand out from the others regarding their activity. From the structural and kinetic analysis, we can state that five residues at positions 163, 288, 289, 444, and 454 (PsAMADHs numbering) can, directly or not, significantly modulate AMADH substrate specificity. In the SlAMADH1 structure, a PEG aldehyde derived from the precipitant forms a thiohemiacetal intermediate, never observed so far. Its absence in the SlAMADH1-E260A structure suggests that Glu-260 can activate the catalytic cysteine as a nucleophile. We show that the five AMADHs studied here are capable of oxidizing 3-dimethylsulfoniopropionaldehyde to the cryo- and osmoprotectant 3-dimethylsulfoniopropionate. For the first time, we also show that 3-acetamidopropionaldehyde, the third aminoaldehyde besides 3-aminopropionaldehyde and 4-aminobutyraldehyde, is generally oxidized by AMADHs, meaning that these enzymes are unique in metabolizing and detoxifying aldehyde products of polyamine degradation to nontoxic amino acids. Finally, gene expression profiles in maize indicate that AMADHs might be important for controlling ?-aminoaldehyde levels during early stages of the seed development. PMID:23408433

Kope?ny, David; Kon?itíková, Radka; Tylichová, Martina; Vigouroux, Armelle; Moskalíková, Hana; Soural, Miroslav; Šebela, Marek; Moréra, Solange

2013-02-13

89

The millisecond intermediate in the reaction of nitric oxide with oxymyoglobin is an iron(III)--nitrato complex, not a peroxynitrite.  

PubMed

The dioxygenation of nitric oxide by oxyheme in globin proteins is a major route for NO detoxification in aerobic biological systems. In myoglobin, this reaction is thought to proceed through an iron(III)-bound peroxynitrite before homolytic cleavage of the O-O bond to form an iron(IV)-oxo and NO(2) radical followed by recombination and nitrate production. Single turnover experiments at alkaline pH have revealed the presence of a millisecond high-spin heme intermediate. It is widely presumed that this species is an iron(III)-peroxynitrite species, but detailed characterization of the intermediate is lacking. Using resonance Raman spectroscopy and rapid-freeze quench techniques, we identify the millisecond intermediate as an iron(III)-nitrato complex with a symmetric NO(2) stretch at 1282 cm(-1). Greater time resolution techniques will be required to detect the putative iron(III) peroxynitrite complex. PMID:19469573

Yukl, Erik T; de Vries, Simon; Moënne-Loccoz, Pierre

2009-06-01

90

The Millisecond Intermediate in the Reaction of Nitric Oxide with Oxymyoglobin is an iron(III)-Nitrato Complex, not a Peroxynitrite  

PubMed Central

The dioxygenation of nitric oxide by oxyheme in globin proteins is a major route for NO detoxification in aerobic biological systems. In myoglobin, this reaction is thought to proceed through an iron(III)-bound peroxynitrite before homolytic cleavage of the O-O bond to form an iron(IV)-oxo and NO2 radical followed by recombination and nitrate production. Single turnover experiments at alkaline pH have revealed the presence of a millisecond high-spin heme intermediate. It is widely presumed that this species is an iron(III)-peroxynitrite species, but detailed characterization of the intermediate is lacking. Using resonance Raman spectroscopy and rapid-freeze quench techniques, we identify the millisecond intermediate as an iron(III)-nitrato complex with a symmetric NO2 stretch at 1282 cm?1. Greater time resolution techniques will be required to detect the putative iron(III) peroxynitrite complex.

Yukl, Erik T.; de Vries, Simon; Moenne-Loccoz, Pierre

2009-01-01

91

Identifying Predictors of Negative Psychological Reactions to Stalking Victimization  

ERIC Educational Resources Information Center

|Victims of stalking often experience a number of negative psychological problems including such things as fear, symptoms of depression, and anger. However, research on factors that lead to these outcomes is limited. The goal of this study was to first identify distinct subgroups of stalking victims based on measures of psychological problems…

Johnson, Matthew C.; Kercher, Glen A.

2009-01-01

92

Structure and quantum chemical characterization of chloroperoxidase compound 0, a common reaction intermediate of diverse heme enzymes  

Microsoft Academic Search

We have determined the crystal structure of the chloroperoxidase (CPO) hydroperoxo reaction intermediate (CPO compound 0) at 1.75-Å resolution. The intermediate was generated through controlled photoreduction of the CPO oxygen complex during x-ray data collection, which was monitored by recording of the crystal absorption spectra. Initially, the peroxo-anion species was formed and then protonated to yield compound 0. Quantum chemical

Karin Kühnel; Etienne Derat; James Terner; Sason Shaik; Ilme Schlichting

2007-01-01

93

Studies on the transglucosylation reactions of cassava and Thai rosewood ?-glucosidases using 2-deoxy-2-fluoro-glycosyl-enzyme intermediates  

Microsoft Academic Search

?-Glucosidases from cassava and Thai rosewood can synthesize a variety of alkyl glucosides using various alcohols as glucosyl acceptors for transglucosylation. Both enzymes were inactivated by 2-deoxy-2-fluoro-sugar analogues to form the covalent glycosyl-enzyme intermediates, indicating that the reaction mechanism was of the double-replacement type. The trapped enzyme intermediates were used for investigating transglucosylation specificity, by measuring the rate of reactivation

Greanggrai Hommalai; Pimchai Chaiyen; Jisnuson Svasti

2005-01-01

94

Intermediates detected by visible spectroscopy during the reaction of nitrite with deoxyhemoglobin: the effect of nitrite concentration and diphosphoglycerate.  

PubMed

The reaction of nitrite with deoxyhemoglobin (deoxyHb) results in the reduction of nitrite to NO, which binds unreacted deoxyHb forming Fe(II)-nitrosylhemoglobin (Hb(II)NO). The tight binding of NO to deoxyHb is, however, inconsistent with reports implicating this reaction with hypoxic vasodilation. This dilemma is resolved by the demonstration that metastable intermediates are formed in the course of the reaction of nitrite with deoxyHb. The level of intermediates is quantitated by the excess deoxyHb consumed over the concentrations of the final products formed. The dominant intermediate has a spectrum that does not correspond to that of Hb(III)NO formed when NO reacts with methemoglobin (MetHb), but is similar to metHb resulting in the spectroscopic determinations of elevated levels of metHb. It is a delocalized species involving the heme iron, the NO, and perhaps the beta-93 thiol. The putative role for red cell reacted nitrite on vasodilation is associated with reactions involving the intermediate. (1) The intermediate is less stable with a 10-fold excess of nitrite and is not detected with a 100-fold excess of nitrite. This observation is attributed to the reaction of nitrite with the intermediate producing N2O3. (2) The release of NO quantitated by the formation of Hb(II)NO is regulated by changes in the distal heme pocket as shown by the 4.5-fold decrease in the rate constant in the presence of 2,3-diphosphoglycerate. The regulated release of NO or N2O3 as well as the formation of the S-nitroso derivative of hemoglobin, which has also been reported to be formed from the intermediates generated during nitrite reduction, should be associated with any hypoxic vasodilation attributed to the RBC. PMID:17880185

Nagababu, Enika; Ramasamy, Somasundaram; Rifkind, Joseph M

2007-09-20

95

Combining Meyer-Schuster rearrangement with aldol and Mannich reactions: theoretical study of the intermediate interception strategy.  

PubMed

Interception of the transient allenyl enolate intermediate of the vanadium-catalyzed Meyer-Schuster rearrangement with aldehydes and imines has been studied computationally using density functional theory. Mechanistic details of the catalytic cycles for each of the reaction variants are established. In particular, it is shown that the active form of the catalyst contains two triphenylsiloxy ligands, the transesterification of vanadate occurs via ?-bond metathesis, and vanadium enolate is directly involved in the key C-C bond formation. The calculations also provide support for the dissociative course of the key 1,3-shift step. The stereochemistry of the reaction is thoroughly investigated, and the obtained energy barriers reproduce and rationalize the experimentally observed (Z)-, (E)-selectivity. The calculated free energy profiles are analyzed in terms of efficiency of the intermediate enolate interception. It is shown that the investigated reactions represent borderline cases, in which the intermediate trapping is only slightly favored over the undesired isomerization pathway. PMID:23106444

Kalek, Marcin; Himo, Fahmi

2012-11-08

96

Direct kinetic measurements of Criegee intermediate (CH?OO) formed by reaction of CH?I with O?.  

PubMed

Ozonolysis is a major tropospheric removal mechanism for unsaturated hydrocarbons and proceeds via "Criegee intermediates"--carbonyl oxides--that play a key role in tropospheric oxidation models. However, until recently no gas-phase Criegee intermediate had been observed, and indirect determinations of their reaction kinetics gave derived rate coefficients spanning orders of magnitude. Here, we report direct photoionization mass spectrometric detection of formaldehyde oxide (CH(2)OO) as a product of the reaction of CH(2)I with O(2). This reaction enabled direct laboratory determinations of CH(2)OO kinetics. Upper limits were extracted for reaction rate coefficients with NO and H(2)O. The CH(2)OO reactions with SO(2) and NO(2) proved unexpectedly rapid and imply a substantially greater role of carbonyl oxides in models of tropospheric sulfate and nitrate chemistry than previously assumed. PMID:22246773

Welz, Oliver; Savee, John D; Osborn, David L; Vasu, Subith S; Percival, Carl J; Shallcross, Dudley E; Taatjes, Craig A

2012-01-13

97

Dehydration reactions and intermediate depth earthquakes: Is gypsum the right analog material for an experimental investigation?  

NASA Astrophysics Data System (ADS)

In addition to melting or runaway creep along shear zones, plastic instabilities and solid-solid phase transitions, the mechanical effect of dehydration reactions has been suggested as a process responsible for the occurrence of intermediate depth earthquakes: If the porosity and permeability of the source region are low and the overall molar volume change of the reaction is positive the effective pressure acting on the rock is significantly reduced. Rocks initially deforming in their ductile field could then embrittle and fail. Experimental investigations have previously been performed on both dehydrating gypsum as an analog material and natural rock samples like serpentinite (antigorite). Dehydration in nature occurs syntectonically and the occurrence of earthquakes always requires at least a partial release of stored elastic energy associated with a drop in stress. Therefore only those deformation experiments are significant that are performed in parallel with the progressing reaction. In addition, at constant strain rate, the measured stress-strain curve must show a significant and rapid stress drop which is symptomatic for brittle failure. If this feature is not observed for a specific analog material, it is not suitable for the investigation of the above process in the context of earthquakes. For this reaction induced embrittlement to be expected the hydrous material should show brittle failure at low confining pressures. Nominally dry cylindrical samples of finegrained natural gypsum were strained up to 15% in a gas-medium apparatus at 0.1 to 50 MPa confining pressure, 20 to 110^oC and a strain rate of 1.5 \\cdot 10-6 to 1.5 \\cdot 10-5 1/s. The samples showed nearly ideally ductile behavior suggesting cataclastic flow. The flow stress was independent of strain rate, decreased with decreasing confining pressure and increasing temperature and had a maximum of 80 MPa. Only at room temperature and ambient pressure did the samples show slow strain weakening indicating ductile stress relaxation. The maximum flow stress in this case was only 30 MPa. This raises the question if for the case of gypsum a reaction induced reduction in effective pressure can initiate embrittlement. Results on clarifying deformation experiments under reaction conditions will be presented in addition to the results summarized above.

Milsch, H.; Scholz, C.

2003-04-01

98

IR spectroscopic characterization of intermediates in a gas-phase ionic reaction  

NASA Astrophysics Data System (ADS)

Decarbonylation of acetophenone is a facile process mediated by Co+ complexation. Structures of two species on the gas-phase reaction path have been characterized by their infrared photodissociation spectroscopy, namely the Co+(acetophenone) complex itself, and the decarbonylated but still complexed product ion Co+(C7H8). Infrared spectra over the 500-1800 cm-1 frequency range were obtained by wavelength-dependent multiple-photon dissociation using the FELIX free electron laser and a Fourier-transform ion cyclotron resonance mass spectrometer. Structural characterizations were made by comparison with predicted spectra calculated by density functional theory (DFT) using the B3LYP functional. The initial complex Co+(acetophenone) was found to be intact, with little or no presence of rearrangement or bond-inserted structures. The spectrum indicates a mixture of O-bound and ring-bound isomers of this complex. The decarbonylated product ion was assigned to have the most stable structure, namely Co+(toluene), with no indication of the presence of possible bond-inserted isomers having a two-coordinate metal ion. A decarbonylation path involving metal ion insertion adjacent to the carbonyl group was suggested, and the corresponding bond-inserted complexes were computed to be energetically reasonable intermediate structures on the reaction path.

Dunbar, Robert C.; Moore, David T.; Oomens, Jos

2007-09-01

99

Intermediate mass fragment emission and iso-scaling in dissipative Ca+Sn reactions at 45 AMeV  

NASA Astrophysics Data System (ADS)

The production mechanism of intermediate-mass fragments (IMFs) with atomic numbers Z = 3 - 7 is explored in the intermediate energy regime, studying dissipative 48Ca+112Sn and 48Ca+124Sn reactions at E/A = 45MeV. Various aspects of IMF emission patterns point to an inelastic break-up type production mechanism involving excited projectile-like fragment from dissipative interactions. Isotopic yield ratios of identical IMFs from the above two dissipative reactions have been analysed using the "isoscaling" method. Observed trends are correlated with ground-state binding energy systematics and their relevance for an evaluation of the symmetry energy is discussed.

Singh, H.; Quinlan, M. J.; To~ke, J.; Pawelczak, I.; Henry, E.; Schröder, W. U.; Amorini, F.; Anzalone, A.; Maiolino, C.; Auditore, L.; Loria, D.; Trifiro, A.; Trimarchi, M.; Cardella, G.; De Filippo, E.; Pagano, A.; Chatterjee, M. B.; Cavallaro, S.; Geraci, E.; Papa, M.; Pirrone, S.; Verde, G.; Grzeszczuk, A.; Guazzoni, P.; Zetta, L.; La Guidara, E.; Lanzalone, G.; Lo Nigro, S.; Politi, G.; Loria, D.; Porto, F.; Rizzo, F.; Russotto, P.; Vigilante, M.

2013-04-01

100

The Stopped-flow Method and Chemical Intermediates in Enzyme Reactions - A Personal Essay.  

PubMed

My perspective does not deal directly with photosynthesis research. However, the methods evolved have played an important role in several areas of biochemistry and biophysics including photosynthesis. Improvements of rapid reaction methods, based upon the pioneering studies of Hamilton Hartridge and F.J.W. Roughton, and Glenn Millikan, required a detailed study of the hydraulics of small-bore tubes and jet mixers, taking into account, that economy of reactants was demanded by the sparcity of enzyme preparations in the 1930s. This Personal perspective recites the steps taken to minimize the volumes expended in rapid flow studies, together with the improvements in electronic technology of rapid and sensitive spectrophotometry of labile intermediates in enzyme reactions. Of the methods studied, continuous, accelerated and stopped flow, the latter was designed for the highest fluid economy and subsequently proved to be of wide use for studying biochemical kinetics. Advances in fast spectrophotometry of dilute solutions led to great improvements in Millikan's dual-wavelength system, both in speed of recording and decreases of background noise level, largely due to electronic stabilization of light sources and sensitive amplifiers. The application of these technologies to studies of hemoglobin, myoglobin and heme enzymes was, more recently, followed by studies of suspensions of organelles, cells, and tissues not only in vivo but also at low temperatures with cryoprotectants, leading to the use of flash activation in carbon monoxide inhibited heme enzymes. Laser technology allowed photosynthetic systems to be studied at cryotemperatures, leading to the development of electron tunneling theories for biological reactions (not discussed in this paper). All in all, the many fundamental developments of electronics, optics and hydraulics indicate how technology can respond effectively to the needs of biology in general, and photobiology in particular. PMID:16328835

Chance, Britton

2004-01-01

101

The thermodynamic properties of 2-aminobiphenyl (an intermediate in the carbazole/hydrogen reaction network)  

SciTech Connect

Catalytic hydrodenitrogenation (HDN) is a key step in upgrading processes for conversion of heavy petroleum, shale oil, tar sands, and the products of the liquefaction of coal to economically viable products. This research program provides accurate experimental thermochemical and thermophysical properties for key organic nitrogen-containing compounds present in the range of alternative feedstocks, and applies the experimental information to thermodynamic analyses of key HDN reaction networks. This report is the first in a series that will lead to an analysis of a three-ring HDN system; the carbazole/hydrogen reaction network. 2-Aminobiphenyl is the initial intermediate in the HDN pathway for carbazole, which consumes the least hydrogen possible. Measurements leading to the calculation of the ideal-gas thermodynamic properties for 2-aminobiphenyl are reported. Experimental methods included combustion calorimetry, adiabatic heat-capacity calorimetry, comparative ebulliometry, inclined-piston gauge manometry, and differential-scanning calorimetry (d.s.c). Entropies, enthalpies, and Gibbs energies of formation were derived for the ideal gas for selected temperatures between 298.15 K and 820 K. The critical temperature and critical density were determined for 2-aminobiphenyl with the d.s.c., and the critical pressure was derived. The Gibbs energies of formation are used in thermodynamic calculations to compare the feasibility of the initial hydrogenolysis step in the carbazole/H{sub 2} network with that of its hydrocarbon and oxygen-containing analogous; i.e., fluorene/H{sub 2} and dibenzofuran/H{sub 2}. Results of the thermodynamic calculations are compared with those of batch-reaction studies reported in the literature. 57 refs., 8 figs., 18 tabs.

Steele, W.V.; Chirico, R.D.; Knipmeyer, S.E.; Nguyen, A.

1990-12-01

102

The structure of the biliverdin radical intermediate in phycocyanobilin:ferredoxin oxidoreductase identified by high-field EPR and DFT  

PubMed Central

The cyanobacterial enzyme phycocyanobilin:ferredoxin oxidoreductase (PcyA) catalyzes the two-step four-electron reduction of biliverdin IX? to phycocyanobilin, the precursor of biliprotein chromophores found in phycobilisomes. It is known that catalysis proceeds via paramagnetic radical intermediates, but the structure of these intermediates and the transfer pathways for the four protons involved are not known. In this study, high-field electron paramagnetic resonance (EPR) spectroscopy of frozen solutions and single crystals of the one-electron reduced protein-substrate complex of two PcyA mutants D105N from the cyanobacteria Synechocystis sp. PCC6803 and Nostoc sp. PCC7120 are examined. Detailed analysis of Synechocystis D105N mutant spectra at 130 GHz and 406 GHz reveals a biliverdin radical with a very narrow g tensor with principal values 2.00359(5), 2.00341(5) and 2.00218(5). Using density-functional theory (DFT) computations to explore the possible protonation states of the biliverdin radical, it is shown that this g tensor is consistent with a biliverdin radical where the carbonyl oxygen atoms on both the A and the D pyrrole rings are protonated. This experimentally confirms the reaction mechanism recently proposed (Tu et al, Biochemistry 2007, 46, 1484).

Stoll, Stefan; Gunn, Alexander; Brynda, Marcin; Sughrue, Wesley; Kohler, Amanda C.; Ozarowski, Andrew; Fisher, Andrew J.; Lagarias, J. Clark; Britt, R. David

2009-01-01

103

Weak interaction processes in supernovae: New probes using charge exchange reaction at intermediate energies  

NASA Astrophysics Data System (ADS)

Spin-isospin-flip excitations in nuclei at vanishing momentum transfer are generally referred to as Gamov-Teller (GT) transitions. They are being studied because the simplicity of the excitation makes them an ideal probe for testing nuclear structure models. In astrophysics, GT transitions provide an important input for model calculations and element formation during the explosive phase of a massive star at the end of its life-time. GT transitions in the ?- direction (also referred to as isospin lowering T< transitions) have extensively been studied through (p,n) and (3He,t) charge-exchange reactions [B.D. Anderson et al., Phys. Rev. C 36 (1987) 2195, B.D. Anderson et al., Phys. Rev. C 43 (1991) 50, J. Rapaport et al., Phys. Rev. C 24 (1981) 335, H. Akimune et al., Nucl. Phys. A 569 (1994) 245c, Y. Fujita et al., Phys. Lett. B 365 (1996) 29]. The generally good resolution allows easy extraction of the GT distribution and the total B(GT-) strength in the final nucleus. On the other hand, determination of B(GT+) strength through a charge-exchange reaction in the T> direction were mostly done with secondary neutron beams, and as such, they come with significant experimental difficulties. TRIUMF has pioneered this field in the late 80's and early 90's with a rich and highly successful (n,p) program using a several hundred MeV neutron beam from a 7Li(p,n)7Be reaction [R. Helmer, Can. J. Phys. 65 (1987) 588]. In this paper we present the (d,2He) reaction at intermediate energies as another and potentially even more powerful tool for charge-exchange reactions in the T>, resp. ?+ direction. The key issue here will be the high resolution of order 100 keV, which provides new and sometimes unexpected insight into nuclear structure phenomena. This program has been launched at the AGOR Superconducting Cyclotron Facility at the KVI Groningen. By now, it covers a wide field of physics questions ranging from few-body physics, the structure of halo-nuclei, to questions pertaining to the dynamics of supernova explosions and nuclear synthesis, and more recently to the measurements of (??) decay matrix elements and the determination of half-lives of (??) decaying nuclei.

Frekers, Dieter

2005-04-01

104

Capturing reaction paths and intermediates in Cre-loxP recombination using single-molecule fluorescence.  

PubMed

Site-specific recombination plays key roles in microbe biology and is exploited extensively to manipulate the genomes of higher organisms. Cre is a well studied site-specific recombinase, responsible for establishment and maintenance of the P1 bacteriophage genome in bacteria. During recombination, Cre forms a synaptic complex between two 34-bp DNA sequences called loxP after which a pair of strand exchanges forms a Holliday junction (HJ) intermediate; HJ isomerization then allows a second pair of strand exchanges and thus formation of the final recombinant product. Despite extensive work on the Cre-loxP system, many of its mechanisms have remained unclear, mainly due to the transient nature of complexes formed and the ensemble averaging inherent to most biochemical work. Here, we address these limitations by introducing tethered fluorophore motion (TFM), a method that monitors large-scale DNA motions through reports of the diffusional freedom of a single fluorophore. We combine TFM with Förster resonance energy transfer (FRET) and simultaneously observe both large- and small-scale conformational changes within single DNA molecules. Using TFM-FRET, we observed individual recombination reactions in real time and analyzed their kinetics. Recombination was initiated predominantly by exchange of the "bottom-strands" of the DNA substrate. In productive complexes we used FRET distributions to infer rapid isomerization of the HJ intermediates and that a rate-limiting step occurs after this isomerization. We also observed two nonproductive synaptic complexes, one of which was structurally distinct from conformations in crystals. After recombination, the product synaptic complex was extremely stable and refractory to subsequent rounds of recombination. PMID:23184986

Pinkney, Justin N M; Zawadzki, Pawel; Mazuryk, Jaroslaw; Arciszewska, Lidia K; Sherratt, David J; Kapanidis, Achillefs N

2012-11-26

105

A Pivotal Heme-transfer Reaction Intermediate in Cytochrome c Biogenesis*  

PubMed Central

c-Type cytochromes are widespread proteins, fundamental for respiration or photosynthesis in most cells. They contain heme covalently bound to protein in a highly conserved, highly stereospecific post-translational modification. In many bacteria, mitochondria, and archaea this heme attachment is catalyzed by the cytochrome c maturation (Ccm) proteins. Here we identify and characterize a covalent, ternary complex between the heme chaperone CcmE, heme, and cytochrome c. Formation of the complex from holo-CcmE occurs in vivo and in vitro and involves the specific heme-binding residues of both CcmE and apocytochrome c. The enhancement and attenuation of the amounts of this complex correlates completely with known consequences of mutations in genes for other Ccm proteins. We propose the complex is a trapped catalytic intermediate in the cytochrome c biogenesis process, at the point of heme transfer from CcmE to the cytochrome, the key step in the maturation pathway.

Mavridou, Despoina A. I.; Stevens, Julie M.; Monkemeyer, Leonie; Daltrop, Oliver; di Gleria, Katalin; Kessler, Benedikt M.; Ferguson, Stuart J.; Allen, James W. A.

2012-01-01

106

Bacillus anthracis o-succinylbenzoyl-CoA synthetase: reaction kinetics and a novel inhibitor mimicking its reaction intermediate  

PubMed Central

O-succinylbenzoyl-CoA (OSB-CoA) synthetase (EC 6.2.1.26) catalyzes the ATP-dependent condensation of o-succinylbenzoate (OSB) and CoA to form OSB-CoA, the fourth step of the menaquinone biosynthetic pathway in Bacillus anthracis. Gene knockout studies have highlighted this enzyme as a potential target for the discovery of new antibiotics. Here we report the first studies on the kinetic mechanism of B. anthracis OSB-CoA synthetase, classifying it as an ordered Bi Uni Uni Bi ping-pong mechanism. Through a series of pre-steady-state and steady-state kinetic studies in conjunction with direct-binding studies, it is demonstrated that CoA, the last substrate to bind, strongly activates the first half-reaction after the first round of turnover. The activation of the first-half reaction is most likely achieved by CoA stabilizing conformations of the enzyme in the ‘F’ form, which slowly isomerize back to the E form. Thus, the kinetic mechanism of OSB-CoA synthetase may be more accurately described as an ordered Bi Uni Uni Bi Iso ping-pong mechanism. The substrate specificity of OSB-CoA synthetase was probed using a series of OSB analogs with alterations in the carboxylate groups. OSB-CoA shows a strong preference for OSB over all of the analogs tested as none were active except 4-(2-trifluoromethylphenyl)-4-oxobutyric acid which exhibited a 100-fold decrease in kcat/Km. Based on an understanding of OSB-CoA synthetase’s kinetic mechanism and substrate specificity, a reaction intermediate analog of OSB-AMP, 5’-O-(N-(2-trifluoromethylphenyl)-4-oxobutyl) adenosine sulfonamide (TFMP-butyl-AMS), was designed and synthesized. This inhibitor was found to be an uncompetitive inhibitor to CoA and a mixed-type inhibitor to ATP and OSB with low micromolar inhibition constants. Collectively, these results should serve as an important forerunner to more detailed and extensive inhibitor design studies aimed at developing lead compounds against the OSB-CoA synthetase class of enzymes.

Tian, Yang; Suk, Dae-Hwan; Cai, Feng; Crich, David; Mesecar, Andrew D.

2009-01-01

107

Observation of all the intermediate steps of a chemical reaction on an oxide surface by scanning tunneling microscopy.  

PubMed

By means of high-resolution scanning tunneling microscopy (STM), we have revealed unprecedented details about the intermediate steps for a surface-catalyzed reaction. Specifically, we studied the oxidation of H adatoms by O(2) molecules on the rutile TiO(2)(110) surface. O(2) adsorbs and successively reacts with the H adatoms, resulting in the formation of water species. Using time-lapsed STM imaging, we have unraveled the individual reaction intermediates of HO(2), H(2)O(2), and H(3)O(2) stoichiometry and the final reaction product-pairs of water molecules, [H(2)O](2). Because of their different appearance and mobility, these four species are discernible in the time-lapsed STM images. The interpretation of the STM results is corroborated by density functional theory calculations. The presented experimental and theoretical results are discussed with respect to previous reports where other reaction mechanisms have been put forward. PMID:19309169

Matthiesen, Jesper; Wendt, Stefan; Hansen, Jonas Ø; Madsen, Georg K H; Lira, Estephania; Galliker, Patrick; Vestergaard, Ebbe K; Schaub, Renald; Laegsgaard, Erik; Hammer, Bjørk; Besenbacher, Flemming

2009-03-24

108

A Combined DFT and NMR Investigation of the Zinc Organometallic Intermediate Proposed in the Syn-Selective Tandem Chain Extension-Aldol Reaction of ?-Keto Esters  

PubMed Central

The tandem chain extension-aldol (TCA) reaction of ?-keto esters provides a ?-substituted ?-keto ester with an average syn:anti selectivity of 10:1. It is proposed that the reaction proceeds via a carbon-zinc bound organometallic intermediate potentially bearing mechanistic similarity to the Reformatsky reaction. Evidence, derived from control Reformatsky reactions and a study of the structure of the TCA intermediate utilizing DFT methods and NMR-spectroscopy, suggests the ?-keto group of the TCA intermediate plays a significant role in diastereoselectivity observed in this reaction. Such coordination effects have design implications for future zinc mediated reactions.

Aiken, Karelle S.; Eger, Wilhelm A.; Williams, Craig M.; Spencer, Carley M.

2012-01-01

109

Direct observation of the unstable intermediates in radical addition reaction by using an interfacing microchip combined with an NMR.  

PubMed

Direct observation of the unstable intermediate in the radical addition reaction of the oxime ether 1 mediated by triethylborane (Et(3)B) is described using (1)H and (11)B micro channeled cell for synthesis monitoring (MICCS), which was recently developed as an interfacing microchip for NMR. It was possible that the signal of the intermediate was observed as a result of using MICCS technique with a standard NMR instrument. This result supports the structure of the intermediate analyzed by diffusion-ordered spectroscopy (DOSY) NMR method in a previous paper. The procedure of micro channeled cell for synthesis monitoring-nuclear magnetic resonance (MICCS-NMR) was much easier than that of DOSY method. It was proven that it could be applied to the reaction in an anhydrous condition. PMID:17924352

Nakakoshi, Masamichi; Ueda, Masafumi; Sakurai, Satoshi; Asakura, K; Utsumi, Hiroshi; Miyata, Okiko; Naito, Takeaki; Takahashi, Yutaka

2007-11-01

110

A study of the atmospherically relevant reaction between molecular chlorine and dimethylsulfide (DMS): Establishing the reaction intermediate and measurement of absolute photoionization cross-sections  

NASA Astrophysics Data System (ADS)

In a study using UV photoelectron spectroscopy (PES) of the atmospherically relevant reaction CH3SCH3 + Cl2 ? CH3SCH2Cl + HCl bands associated with a reaction intermediate have been observed. These have been assigned to ionization of the covalently bound molecule (CH3)2SCl2 on the basis of the intensity of the observed bands as a function of reaction time, molecular orbital calculations of vertical ionization energies and evidence from infrared spectroscopy. A method has also been developed, with the flow-tube/PE spectrometer combination used, to measure photoionization cross-sections of the reagents and products at the photon energy utilized and this has allowed the photoionization cross-section of the intermediate to be estimated. This work augments an earlier study in which the rate constant of the reaction between CH3SCH3 (DMS) and Cl2 has been measured at room temperature.

Dyke, J. M.; Ghosh, M. V.; Goubet, M.; Lee, E. P. F.; Levita, G.; Miqueu, K.; Shallcross, D. E.

2006-05-01

111

Radicals in the Reaction between Peroxynitrite and Uric Acid Identified by Electron Spin Resonance Spectroscopy and Liquid Chromatography Mass Spectrometry  

PubMed Central

Peroxynitrite is a reactive oxidant produced in vivo in response to oxidative and other stress by the diffusion-limited reaction of nitric oxide and superoxide. This contribution is focused on the identification of free radical intermediates of uric acid formed during its reaction with peroxynitrite. The experimental approach included the ESR spin trapping of the radical generated from the reaction between uric acid and peroxynitrite at pH 7.4 and mass spectrometry studies of the trapped radicals. Using PBN (N-tert-butyl-?-phenylnitrone) as the spin trapping agent, a six-line ESR spectrum was obtained and its hyperfine coupling constants, a(N) = 15.6 G; and a(H) = 4.4 G, revealed the presence of carbon-based radicals. Further structural identification of the PBN-radical adducts was carried out using liquid chromatography-mass spectrometry. After comparison with the control reactions, two species were identified corresponding to the protonated molecules (M+1) at m/z 352 and 223, respectively. The ions of m/z 352 were characterized as the PBN-triuretcarbonyl radical adduct and the m/z 223 ion was identified as the PBN-aminocarbonyl radical adduct. Their mechanism of formation is discussed.

Imaram, Witcha; Gersch, Christine; Kim, Kyung Mee; Johnson, Richard J.; Henderson, George N.; Angerhofer, Alexander

2010-01-01

112

The GC-MS Observation of Intermediates in a Stepwise Grignard Addition Reaction  

ERIC Educational Resources Information Center

|Preparation of phenylmagnesium bromide described by Eckert, addition of three equivalents of Grignard reagent to diethyl carbonate to form triphenylmethanol and a series of GC-MS procedures that form intermediates. The analysis is consistent with a gas chromatogram and mass spectrum for each of the expected intermediates and final product of the…

Latimer, Devin

2007-01-01

113

Mechanistic Studies on the Reaction of Nitroxylcobalamin with Dioxygen: Evidence for Formation of a Peroxynitritocob(III)alamin Intermediate.  

PubMed

Studies by others suggest that the reduced vitamin B12 complex, cob(II)alamin, scavenges nitric oxide to form air-sensitive nitroxylcobalamin (NO(-)-Cbl(III); NOCbl) in vivo. The fate of newly formed NOCbl is not known. A detailed mechanistic investigation of the oxidation of NOCbl by oxygen is presented. Only base-on NOCbl reacts with O2, and the reaction proceeds via an associative mechanism involving a peroxynitritocob(III)alamin intermediate, Co(III)-N(O)OO(-). The intermediate undergoes O-O bond homolysis and ligand isomerization to ultimately yield NO2Cbl and H2OCbl(+)/HOCbl, respectively. Ligand isomerization may potentially occur independent of O-O bond homolysis. Formation of (•)OH and (•)NO2 intermediates from O-O bond homolysis is demonstrated using phenol and tyrosine radical traps and the characterization of small amounts of a corrinoid product with minor modifications to the corrin ring. PMID:24050193

Subedi, Harishchandra; Brasch, Nicola E

2013-09-19

114

Computational characterization of reaction intermediates in the photocycle of the sensory domain of the AppA blue light photoreceptor.  

PubMed

The AppA protein with the BLUF (blue light using flavin adenine dinucleotide) domain is a blue light photoreceptor that cycle between dark-adapted and light-induced functional states. We characterized possible reaction intermediates in the photocycle of AppA BLUF. Molecular dynamics (MD), quantum chemical and quantum mechanical-molecular mechanical (QM/MM) calculations were carried out to describe several stable structures of a molecular system modeling the protein. The coordinates of heavy atoms from the crystal structure (PDB code 2IYG) of the protein in the dark state served as starting point for 10 ns MD simulations. Representative MD frames were used in QM(B3LYP/cc-pVDZ)/MM(AMBER) calculations to locate minimum energy configurations of the model system. Vertical electronic excitation energies were estimated for the molecular clusters comprising the quantum subsystems of the QM/MM optimized structures using the SOS-CIS(D) quantum chemistry method. Computational results support the occurrence of photoreaction intermediates that are characterized by spectral absorption bands between those of the dark and light states. They agree with crystal structures of reaction intermediates (PDB code 2IYI) observed in the AppA BLUF domain. Transformations of the Gln63 side chain stimulated by photo-excitation and performed with the assistance of the chromophore and the Met106 side chain are responsible for these intermediates. PMID:21155828

Khrenova, Maria G; Domratcheva, Tatiana; Schlichting, Ilme; Grigorenko, Bella L; Nemukhin, Alexander V

2010-12-13

115

Graph-theoretical identifi-cation of pathways for biochemical reactions  

Microsoft Academic Search

Abstract A rigorous method for identifying biochemical reaction or metabolic pathways through its systematic synthesis has been established. The current method for synthesizing networks of metabolic pathways follows the general frame- work of a highly exacting combinatorial method. The method is capable of generating not only all combinatorially independent, feasible reaction networks only once, but also those combinations of independent

H. Seo; D. Y. Lee; L. T. Fan; S. Shafie; B. Bertok; F. Friedler

2001-01-01

116

L-myo-inosose-1 as a probable intermediate in the reaction catalyzed by myo-inositol oxygenase  

SciTech Connect

In previous investigations, it was necessary to have Fe(II) and cysteine present in order to assay the catalytic activity of purified hog kidney myo-inositol oxygenase. In the present study it was found that, if this purified nonheme iron enzyme is slowly frozen in solution with glutathione and stored at -20 degrees C, it is fully active in the absence of activators if catalase is present to remove adventitious H/sub 2/O/sub 2/. With this simpler assay system it was possible to clarify the effects of several variables on the enzymic reaction. Thus, the maximum velocity is pH-dependent with a maximum around pH 9.5, but the apparent Km for myo-inositol (air atmosphere) remains constant at 5.0 mM throughout a broad pH range. The enzyme is quite specific for its substrate myo-inositol, is very sensitive to oxidants and reductants, but is not affected by a variety of complexing agents, nucleotides, sulfhydryl reagents, etc. In other experiments it was found that L-myo-inosose-1, a potential intermediate in the enzymic reaction, is a potent competitive inhibitor (Ki = 62 microM), while other inososes and a solution thought to contain D-glucodialdehyde, another potential intermediate, are weak inhibitors. Also, both a kinetic deuterium isotope effect (kH/kD = 2.1) and a tritium isotope effect (kH/kT = 7.5) are observed for the enzymic reaction when (1-2H)- and (1-3H)-myo-inositol are used as reactants. These latter results are considered strong evidence that the oxygenase reaction proceeds by a pathway involving L-myo-inosose-1 as an intermediate rather than by an alternative pathway that would have D-glucodialdehyde as the intermediate.

Naber, N.I.; Swan, J.S.; Hamilton, G.A.

1986-11-04

117

Evidence for a proton halo in 27 P through measurements of reaction cross-sections at intermediate energies  

Microsoft Academic Search

:   Measurements of reaction cross-sections ( ?R's) for some proton-rich nuclei ( N = 11–15 isotones) on carbon target at intermediate energies have been performed on RIBLL of HIRFL. A larger enhancement of\\u000a the ?R for 27P has been observed than for its neighboring nuclei. A large difference between the proton and neutron density distributions\\u000a (proton halo) is necessary to

D. Q. Fang; W. Q. Shen; J. Feng; X. Z. Cai; H. Y. Zhang; Y. G. Ma; C. Zhong; Z. Y. Zhu; W. Z. Jiang; W. L. Zhan; Z. Y. Guo; G. Q. Xiao; J. S. Wang; J. Q. Wang; J. X. Li; M. Wang; J. F. Wang; Z. J. Ning; Q. J. Wang; Z. Q. Chen

2001-01-01

118

NO3 radical production from the reaction between the Criegee intermediate CH2OO and NO2.  

PubMed

Formation of the NO3 radical was observed following photolysis of the CH2I2 + O2 system at 248 nm under ambient atmospheric boundary layer conditions (?760 Torr and 297 K) in the presence of NO2. The Criegee intermediate (CI) CH2OO is believed to be responsible for the NO3 production. The potential of such reactions to enhance the rate of NO3 production in the atmosphere is discussed. PMID:24030640

Ouyang, Bin; McLeod, Matthew W; Jones, Roderic L; Bloss, William J

2013-09-25

119

Subcellular fractionation of TGF-beta1-stimulated lung epithelial cells: a novel proteomic approach for identifying signaling intermediates.  

PubMed

Members of the transforming growth factor (TGF)-beta superfamily are key regulators of lung development and homeostasis, in particular by controlling alveolar/bronchial epithelial cell function. TGF-beta signaling involves ligand-dependent activation of receptor serine/threonine kinases, activation and subsequent nuclear translocation of pathway-specific transcription factors (Smads), and ultimately, modulation of gene expression. While Smad-dependent responses represent the primary signaling components activated by TGF-beta receptors, their function is controlled by a variety of cofactors. In addition, alternative signaling systems mediating TGF-beta-induced effects have recently been described such as MAP kinase pathways. To uncover novel proteins that participate in TGF-beta signaling via nuclear/cytoplasmic shuttling in lung epithelial cells, we have analyzed A549 human lung epithelial cells, using subcellular fractionation combined with 2-D PAGE, tryptic digestion, and MS. We identified a rapid increase in the cytosolic localization of KH-type splicing regulatory protein (KHSRP), far upstream element-binding protein (FUBP1), hnRNP-L, and hnRNP-H1, concomitant with a decrease in their nuclear localization in response to TGF-beta1. Proteomic data were confirmed by immunofluorescence and immunoblot analyses. In summary, we represent a powerful novel technology for the identification of previously unknown signaling intermediates. PMID:19253281

Milosevic, Jadranka; Bulau, Patrick; Mortz, Ejvind; Eickelberg, Oliver

2009-03-01

120

Elucidation of the order of oxidations and identification of an intermediate in the multistep clavaminate synthase reaction.  

PubMed

The enzyme clavaminate synthase (CS) catalyzes the formation of the first bicyclic intermediate in the biosynthetic pathway to the potent beta-lactamase inhibitor clavulanic acid. Our previous work has led to the proposal that the cyclization/desaturation of the substrate proclavaminate proceeds in two oxidative steps, each coupled to a decarboxylation of alpha-ketoglutarate and a reduction of dioxygen to water [Salowe, S. P., Marsh, E. N., & Townsend, C. A. (1990) Biochemistry 29, 6499-6508]. We have now employed kinetic isotope effect studies to determine the order of oxidations for CS purified from Streptomyces clavuligerus. By using (4'RS)-[4'-3H,1-14C]-rac-proclavaminate, a primary T(V/K) = 8.3 +/- 0.2 was measured from [3H]water release data, while an alpha-secondary T(V/K) = 1.06 +/- 0.01 was determined from the changing 3H/14C ratio of the product clavaminate. Values for the primary and alpha-secondary effects of 11.9 +/- 1.7 and 1.12 +/- 0.07, respectively, were obtained from the changing 3H/14C ratio of the residual proclavaminate by using new equations derived for a racemic substrate bearing isotopic label at both primary and alpha-secondary positions. Since only the first step of consecutive irreversible reactions will exhibit a V/K isotope effect, we conclude that C-4' is the initial site of oxidation in proclavaminate. As expected, no significant changes in the 3H/14C ratio of residual substrate were observed with [3-3H,1-14C]-rac-proclavaminate. However, two new tritiated compounds were produced in this incubation, apparently the result of isotope-induced branching brought about by the presence of tritium at the site of the second oxidation. One of these compounds was identified by comparison to authentic material as dihydroclavaminate, a stable intermediate that normally remains enzyme-bound. On the basis of the body of information available and the similarities to alpha-ketoglutarate-dependent dioxygenases, a comprehensive mechanistic scheme for CS is proposed to account for this unusual enzymatic transformation. PMID:1998687

Salowe, S P; Krol, W J; Iwata-Reuyl, D; Townsend, C A

1991-02-26

121

"Dba-free" palladium intermediates of the Heck-Matsuda reaction.  

PubMed

The "dba-free" Heck-Matsuda reaction was investigated via direct ESI-MS(/MS) monitoring. Palladium species involved in the reduction of Pd(II) during a Wacker type reaction and several "dba-free" arylpalladium transient complexes were detected and characterized. Based on these findings, a more comprehensible catalytic cycle for this pivotal reaction is suggested. PMID:23511838

Machado, Angelo H L; Milagre, Humberto M S; Eberlin, Livia S; Sabino, Adão A; Correia, Carlos Roque D; Eberlin, Marcos N

2013-05-28

122

New model catalysts (platinum nanoparticles) and new techniques (SFG and STM) for studies of reaction intermediates and surface restructuring at high pressures during catalytic reactions  

NASA Astrophysics Data System (ADS)

Single-crystal surfaces have long served us well as model catalysts; however, a new type of model catalyst has been prepared using electron beam lithography. Ordered arrays of platinum nano-particles in the 2.5-50 nm size range are deposited on oxide substrates (silica, alumina, and titania) of 1 cm 2 surface area, and are used in catalyzed surface reactions at high pressures (atmospheres). Their preparation, cleaning, and reactivity is discussed. Scanning tunneling microscopy (STM) and vibrational spectroscopy by sum frequency generation (SFG) can be utilized to monitor the substrate and adsorbate structure, respectively, over a fourteen order of magnitude pressure range (10 -10-10 4 Torr). As a consequence, we can monitor the surface structure and reaction intermediates during high pressure catalytic reactions. An STM that operates at both high pressure (atmosphere) and high temperature has been constructed and utilized to monitor platinum (111) and (110) surface structure during chemisorption of H 2, O 2 and CO, and during catalytic reactions of olefin hydrogenation and hydrogenolysis. Changes of surface structure upon chemisorption and during reactions have been monitored. Catalysis by the platinum tip was also detected in the presence of H 2 or O 2 at high pressures and 300 K, leading to hydrogenation or oxidation of carbonaceous deposits with nanometer spatial resolution. Vibrational spectroscopy using SFG has been used to monitor pressure dependent changes in the chemisorption of CO and NO over Pt(111). Bonding — which is similar to that in Pt m(CO) n (where n/m > 1 ) clusters and for an incommensurate CO overlayer — is observed above 100 Torr. Reaction intermediates that form during ethylene, propylene, and isobutene hydrogenation, as well as CO oxidation, at atmospheric pressures and 300 K were monitored by SFG. The dominant reacting species that hydrogenate are the weakly ?-bonded olefins, while the strongly chemisorbed alkylidyne and di-? bonded species are spectators during the reaction. From quantitative measurement of coverages, the absolute turnover rates can be determined.

Somorjai, G. A.

1997-11-01

123

The role of long-lived reactive oxygen intermediates in the reaction of ozone with aerosol particles  

NASA Astrophysics Data System (ADS)

The heterogeneous reactions of O3 with aerosol particles are of central importance to air quality. They are studied extensively, but the molecular mechanisms and kinetics remain unresolved. Based on new experimental data and calculations, we show that long-lived reactive oxygen intermediates (ROIs) are formed. The chemical lifetime of these intermediates exceeds 100 seconds, which is much longer than the surface residence time of molecular O3 (~10-9 s). The ROIs explain and resolve apparent discrepancies between earlier quantum mechanical calculations and kinetic experiments. They play a key role in the chemical transformation and adverse health effects of toxic and allergenic air-particulate matter, such as soot, polycyclic aromatic hydrocarbons and proteins. ROIs may also be involved in the decomposition of O3 on mineral dust and in the formation and growth of secondary organic aerosols. Moreover, ROIs may contribute to the coupling of atmospheric and biospheric multiphase processes.

Shiraiwa, Manabu; Sosedova, Yulia; Rouvière, Aurélie; Yang, Hong; Zhang, Yingyi; Abbatt, Jonathan P. D.; Ammann, Markus; Pöschl, Ulrich

2011-04-01

124

Reaction of a Copper(II)-Nitrosyl Complex with Hydrogen Peroxide: Phenol Ring Nitration through a Putative Peroxynitrite Intermediate.  

PubMed

Copper(II) complex, 1, with the histidine-derived ligand L (L = methyl 2-(2-hydroxybenzylamino)-3-(1H-imidazol-5-yl)propanoate) has been synthesized and characterized. Single-crystal structure determination reveals a diphenolato-bridged dicopper(II) core in 1. Addition of (•)NO to an acetonitrile solution of 1 affords the corresponding mononuclear copper(II)-nitrosyl complex, 2. In the presence of H2O2, 2 results in formation of the corresponding copper(I)-peroxynitrite. Formation of peroxynitrite ((-)OONO) intermediate is evident from its characteristic phenol ring nitration reaction which resembles the tyrosine nitration in biological systems. Further, isolation of nitrate (NO3(-)) as the decomposition product from 2 at room temperature also supports the involvement of (-)OONO intermediate. PMID:24059697

Kalita, Apurba; Deka, Ramesh C; Mondal, Biplab

2013-09-23

125

Increase in Three ?,?-Dicarbonyl Compound Levels in Human Uremic Plasma: Specific in VivoDetermination of Intermediates in Advanced Maillard Reaction  

Microsoft Academic Search

Methylglyoxal (MGO), glypxal (GO) and 3-deoxyglucosone (3-DG) are reactive ?,?-dicarbonyl intermediates in advanced Maillard reaction, which form advanced glycation and oxidation end products (AGEs) by reaction with both lysine and arginine residues in protein. We measured these three dicarbonyl compound levels in human plasma to estimate the relationship between accumulation of ?,?-dicarbonyl compounds and AGE formation reactions in uremia and

Hiroko Odani; Toru Shinzato; Yoshihiro Matsumoto; Jun Usami; Kenji Maeda

1999-01-01

126

Two progressive substrates of the M-intermediate can be identified in glucose-embedded, wild-type bacteriorhodopsin.  

PubMed Central

Glucose-embedded bacteriorhodopsin shows M-intermediates with different Amide I infrared bands when samples are illuminated at 240 or 260 K, in contrast with fully hydrated samples where a single M-intermediate is formed at all temperatures. In hydrated, but not in glucose-embedded specimens, the N intermediate is formed together with M at 260 K. Both Fourier transform infrared and electron diffraction data from glucose-embedded bacteriorhodopsin suggest that at 260 K a mixture is formed of the M-state that is trapped at 240 K, and a different M-intermediate (MN) that is also formed by mutant forms of bacteriorhodopsin that lack a carboxyl group at the 96 position, necessary for the M to N transition. The fact that an MN species is trapped in glucose-embedded, wild-type bacteriorhodopsin suggests that the glucose samples lack functionally important water molecules that are needed for the proton transfer aspartate 96 to the Schiff base (and, thus, to form the N-intermediate); thus, aspartate 96 is rendered ineffective as a proton donor.

Vonck, J; Han, B G; Burkard, F; Perkins, G A; Glaeser, R M

1994-01-01

127

Interplay Of Mean Field And Individual Nucleon Collisions Effects At Intermediate Energy Heavy Ion Reactions  

SciTech Connect

In our study of the reaction 20Ne+27Al at energy of 84 A MeV, the track detectors were used to select the target like fragments arising from processes in which the interacting system becomes disintegrated into a large number of constituent nucleons and one massive fragment. Heavy ion reaction studies at bombarding energies of several tens of MeV/nucleon have provided the evidence that most of reaction cross section, in this energy range, is associated with the production of primary projectile like and target like fragment in the first step of the nuclear reaction. The subsequent evolution of the studied reaction systems, has been usually described either using low energy models based on mean field effects (MFE), or high energy models where reaction proceeds by independent collisions (INC) of individual nucleons in the overlap region between target and projectile. The analysis of our results in terms of different MFE and INC models, prescribing consistent timings, has shown that the reaction mechanism may be defined of interplay of the mean field and individual nucleon collisions effects.

Subotic, K.; Jordanov, D.; Durasevic, M.; Dragosavac, D. [VINCA Institute of Nuclear Sciences, P.O. Box 522, 11001 Belgrade (Serbia and Montenegro); Grabez, B. [Institute of Physics, P.O. Box 57, 11080 Belgrade (Serbia and Montenegro)

2007-04-23

128

Development and evaluation of a multiplex polymerase chain reaction assay to identify Salmonella serogroups and serotypes  

Microsoft Academic Search

To improve limitations of Salmonella serotyping, 2 multiplex polymerase chain reaction (M-PCR) were developed using a strategy that identifies first the genes encoding serogroups (rfbJ, wzx). According to the serogroup determined, a second M-PCR identifies serotype (fliC, fljB, wcdB, and sdf-I sequence). Standardization and evaluation of both M-PCRs were carried out.

Nora Cardona-Castro; Miryan Sánchez-Jiménez; Lelia Lavalett; Nélida Múñoz; Jaime Moreno

2009-01-01

129

Nuclear symmetry energy and proton-rich reactions at intermediate energies  

SciTech Connect

Based on an isospin-dependent Boltzmann-Uehling-Uhlenbeck transport model, effects of high-density behavior of nuclear symmetry energy in the proton-rich reaction {sup 22}Si+{sup 22}Si at a beam energy of 400 MeV/nucleon are studied. It is found that the symmetry energy affects {pi}{sup +} production more than {pi}{sup -}. More interestingly, compared to neutron-rich reactions, for {pi}{sup -}/{pi}{sup +} and dense matter's N/Z ratios, effects of symmetry energy in the proton-rich reaction show contrary behaviors. The practical experiment by using the proton-rich reaction {sup 22}Si+{sup 40}Ca to study nuclear symmetry energy is also provided.

Yong Gaochan [Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000 (China)

2011-07-15

130

Probing elastic and inelastic breakup contributions to intermediate-energy two-proton removal reactions  

NASA Astrophysics Data System (ADS)

The two-proton removal reaction from 28Mg projectiles has been studied at 93 MeV/u. First coincidence measurements of the heavy 26Ne projectile residues, the removed protons, and other light charged particles enabled the relative cross sections from each of the three possible elastic and inelastic proton removal mechanisms to be determined. These more final-state-exclusive measurements are key for further interrogation of these reaction mechanisms and use of the reaction channel for quantitative spectroscopy of very neutron-rich nuclei. The relative and absolute yields of the three contributing mechanisms are compared to reaction model expectations based on the use of eikonal dynamics and sd-shell-model structure amplitudes.

Wimmer, K.; Bazin, D.; Gade, A.; Tostevin, J. A.; Baugher, T.; Chajecki, Z.; Coupland, D.; Famiano, M. A.; Ghosh, T. K.; Grinyer, G. F.; Hodges, R.; Howard, M. E.; Kilburn, M.; Lynch, W. G.; Manning, B.; Meierbachtol, K.; Quarterman, P.; Ratkiewicz, A.; Sanetullaev, A.; Stroberg, S. R.; Tsang, M. B.; Weisshaar, D.; Winkelbauer, J.; Winkler, R.; Youngs, M.

2012-05-01

131

K+ Scattering on Nuclei at Intermediate Energy: Standard Nuclear Reaction Theory vs. New Physics  

SciTech Connect

The search for signals of new phenomenon is an important trend in the contemporary strong interaction physics. Two observations-color transparency and nuclear J/{psi} suppression are considered as candidates for the signals of unusual events (nonexponential attenuation of a colored hadron in nuclear matter and quark-gluon plasma, both predicted by QCD). They were explained in the framework of Glauber approximation. On the contrary, we show that new experimental data on the total cross section of K+-nuclei interaction at intermediate energies (IE) cannot be described by the well-elaborated Glauber model.

Eliseev, S.M. [Bogoliubov Laboratory of Theoretical Physics, Joint Institute for Nuclear Research, 141980 Dubna (Russian Federation)

2005-10-26

132

Nuclear spin polarization following intermediate-energy heavy-ion reactions  

SciTech Connect

Intermediate-energy heavy-ion collisions can produce a spin polarization of the projectile-like species. Spin polarization has been observed for both nucleon removal and nucleon pickup processes. Qualitative agreement with measured spin polarization as a function of the momentum of the projectile-like fragment is found in a kinematical model that considers conservation of linear and angular momentum and assumes peripheral interactions between the fast projectile and target. Improvements to the kinematical model are discussed that aim to achieve quantitative agreement with spin polarization data from both the nucleon removal and pickup processes.

Mantica, P. F.; Groh, D. E.; Pinter, J. S. [Department of Chemistry, Michigan State University, East Lansing, MI 48824 (United States); NSCL, Michigan State University, East Lansing, MI 48824 (United States); Mertzimekis, T. J. [NSCL, Michigan State University, East Lansing, MI 48824 (United States); Stuchbery, A. E. [Department of Nuclear Physics, Research School for Physical Sciences and Engineering, Australian National University, Canberra, ACT 0200 (Australia)

2007-06-13

133

High Resolution Reaction Intermediates of rabbit Muscle Fructose-1,6-bisphosphate Aldolase: Substrate Cleavage and Induced Fit  

SciTech Connect

Crystal structures were determined to 1.8-Angstrom resolution of the glycolytic enzyme fructose-1, 6-bis(phosphate) aldolase trapped in complex with its substrate and a competitive inhibitor, mannitol-1, 6-bis(phosphate). The enzyme substrate complex corresponded to the postulated Schiff base intermediate and has reaction geometry consistent with incipient C3-C4 bond cleavage catalyzed by Glu-187, which is adjacent to the Schiff base forming Lys-229. Atom arrangement about the cleaved bond in the reaction intermediate mimics a pericyclic transition state occurring in non-enzymatic aldol condensations. Lys-146 hydrogen bonds the substrate C4 hydroxyl and assists substrate cleavage by stabilizing the developing negative charge on the C4 hydroxyl during proton abstraction. Mannitol-1, 6-bis(phosphate) forms a non-covalent complex in the active site whose binding geometry mimics the covalent carbinolamine precursor. Glu-187 hydrogen bonds the C2 hydroxyl of the inhibitor in the enzyme complex substantiating a proton transfer role by Glu-187 in catalyzing the conversion of the carbinolamine intermediate to Schiff base. Modeling of the acyclic substrate configuration into the active site shows Glu-187, in acid form, hydrogen bonding both substrate C2 carbonyl and C4 hydroxyl, thereby aligning the substrate ketose for nucleophilic attack by Lys-229. The multi-functional role by Glu-187 epitomizes a canonical mechanistic feature conserved in Schiff base forming aldolases catalyzing carbohydrate metabolism. Trapping of tagatose-1, 6-bis(phosphate), a diastereoisomer of fructose-1, 6-bis(phosphate), displayed stereospecific discrimination and reduced ketohexose binding specificity. Each ligand induces homologous conformational changes in two adjacent a-helical regions that promote phosphate binding in the active site.

St-Jean,M.; Lafrance-Vanasse, J.; Liotard, B.; Sygusch, J.

2005-01-01

134

Hydrogen bonding to the cysteine ligand of superoxide reductase: acid-base control of the reaction intermediates.  

PubMed

Superoxide reductase (SOR) is a non-heme iron metalloenzyme that detoxifies superoxide radical in microorganisms. Its active site consists of an unusual non-heme Fe(2+) center in a [His4Cys1] square pyramidal pentacoordination, with the axial cysteine ligand proposed to be an essential feature in catalysis. Two NH peptide groups from isoleucine 118 and histidine 119 establish hydrogen bonds involving the sulfur ligand (Desulfoarculus baarsii SOR numbering). To investigate the catalytic role of these hydrogen bonds, the isoleucine 118 residue of the SOR from Desulfoarculus baarsii was mutated into alanine, aspartate, or serine residues. Resonance Raman spectroscopy showed that the mutations specifically induced an increase of the strength of the Fe(3+)-S(Cys) and S-C?(Cys) bonds as well as a change in conformation of the cysteinyl side chain, which was associated with the alteration of the NH hydrogen bonding involving the sulfur ligand. The effects of the isoleucine mutations on the reactivity of SOR with O2 (•-) were investigated by pulse radiolysis. These studies showed that the mutations induced a specific increase of the pK a of the first reaction intermediate, recently proposed to be an Fe(2+)-O2 (•-) species. These data were supported by density functional theory calculations conducted on three models of the Fe(2+)-O2 (•-) intermediate, with one, two, or no hydrogen bonds involving the sulfur ligand. Our results demonstrated that the hydrogen bonds between the NH (peptide) and the cysteine ligand tightly control the rate of protonation of the Fe(2+)-O2 (•-) reaction intermediate to form an Fe(3+)-OOH species. PMID:23917995

Tremey, Emilie; Bonnot, Florence; Moreau, Yohann; Berthomieu, Catherine; Desbois, Alain; Favaudon, Vincent; Blondin, Geneviève; Houée-Levin, Chantal; Nivière, Vincent

2013-08-06

135

Electron shuttling effect of the intermediate quinones in phenol oxidation by Fenton reaction  

SciTech Connect

Fenton-type reactions have been developed for destruction of organic contaminants in water. This advanced oxidation process (AOP) shows promise for onsite destruction of hazardous organic compounds in water without generating secondary pollutants commonly associated with conventional treatment processes. Fenton-type reactions generate hydroxyl radical by iron(II) decomposition of hydrogen peroxide. Hydroxyl radical reacts rapidly and non-selectively with most organic compounds, so deep, even complete degradation may be achieved. The overall oxidation of organic compounds by Fenton-type reactions is, however, complex and may involve a series of steps. Understanding the oxidation mechanism, therefore, is prerequisite to proper engineering of Fenton based remediation technologies. We present here the results of a kinetic investigation on iron catalyzed oxidation of phenol by hydrogen peroxide in water in the dark.

Chen, Ruzhong; Pignatello, J.J. [Connecticut Agricultural Experimental Station, New Haven, CT (United States)

1996-12-31

136

Reaction of Aryl Diazonium Salts and Diiron(I) Dithiolato Carbonyls: Evidence for Radical Intermediates  

PubMed Central

Treatment of Fe2(pdt)(CO)4(dppv) (1) with aryldiazonium salts affords the 34e? adducts [Fe2(pdt)(?-N2Ar)(CO)4(dppv)]+ (pdt2? = 1,3-propanedithiolate, dppv = cis-C2H2(PPh2)2). Under some conditions, the same reaction gave substantial amounts of [1]+, the product of electron-transfer. Consistent with the influence of electron transfer in the reactions of some electrophiles with Fe(I)Fe(I) dithiolates, the reaction of [Me3S2]+ and Fe2(pdt)(CO)4(dppbz) was found to give [Fe2(pdt)(CO)4(dppbz)]+ as well as Me2S and Me2S2 (dppbz = 1,2-bis(diphenylphosphino)benzene).

Olsen, Matthew T.; Zaffaroni, Riccardo

2012-01-01

137

An explanation of the ABC enhancement in the dd --> ?X reaction at intermediate energies  

NASA Astrophysics Data System (ADS)

The dd --> ?X reaction is studied in a model where each pair of nucleons in the projectile and target deuterons undergoes pion production through the NN -->d? reaction. The condition that the two deuterons fuse to form an ?-particle then leads to peaks at small missing masses, the well-known ABC enhancement, but also a broad structure around the maximum missing mass. With a simplified input amplitude the model gives a quantitative description of both the ?-particle momentum and angular distributions for a deuteron beam energy of 1250 MeV.

Gårdestig, Anders; Fäldt, Göran; Wilkin, Colin

1998-03-01

138

Emission of high-energy, light particles from intermediate-energy heavy-ion reactions  

SciTech Connect

One of the early surprises in examining reaction products from heavy ion reactions at 10 MeV/nucleon and above was the large yield of light particles emitted and the high energies to which the spectra of these particles extended. The interpretation of the origin of the high energy light ions has evolved from a picture of projectile excitation and subsequent evaporation to one of pre-equilibrium (or nonequilibrium) emission. The time scale for particle emission has thus moved from one that occurs following the initial collision to one that occurs at the very early stages of the collision. Research at ORNL on this phenomenon is reviewed. (WHK)

Ball, J.B.; Auble, R.L.

1982-01-01

139

Vibrational spectrum of the lumi intermediate in the room temperature rhodopsin photo-reaction.  

PubMed Central

The vibrational spectrum (650-1750 cm(-1)) of the lumi-rhodopsin (lumi) intermediate formed in the microsecond time regime of the room-temperature rhodopsin (RhRT) photoreaction is measured for the first time using picosecond time-resolved coherent anti-Stokes Raman spectroscopy (PTR/CARS). The vibrational spectrum of lumi is recorded 2.5 micros after the 3-ps, 500-nm excitation of RhRT. Complementary to Fourier transform infrared spectra recorded at Rh sample temperatures low enough to freeze lumi, these PTR/CARS results provide the first detailed view of the vibrational degrees of freedom of room-temperature lumi (lumiRT) through the identification of 21 bands. The exceptionally low intensity (compared to those observed in bathoRT) of the hydrogen out-of-plane (HOOP) bands, the moderate intensity and absolute positions of C-C stretching bands, and the presence of high-intensity C==C stretching bands suggest that lumiRT contains an almost planar (nontwisting), all-trans retinal geometry. Independently, the 944-cm(-1) position of the most intense HOOP band implies that a resonance coupling exists between the out-of-plane retinal vibrations and at least one group among the amino acids comprising the retinal binding pocket. The formation of lumiRT, monitored via PTR/CARS spectra recorded on the nanosecond time scale, can be associated with the decay of the blue-shifted intermediate (BSI(RT)) formed in equilibrium with the bathoRT intermediate. PTR/CARS spectra measured at a 210-ns delay contain distinct vibrational features attributable to BSI(RT), which suggest that the all-trans retinal in both BSI(RT) and lumiRT is strongly coupled to part of the retinal binding pocket. With regard to the energy storage/transduction mechanism in RhRT, these results support the hypothesis that during the formation of lumiRT, the majority of the photon energy absorbed by RhRT transfers to the apoprotein opsin.

Ujj, L; Jager, F; Atkinson, G H

1998-01-01

140

Astrophysically Important Reaction Rates For Novae And X-ray Bursts From Proton Breakup At Intermediate Energies  

SciTech Connect

We discuss the use of one-nucleon removal reactions of loosely bound nuclei at intermediate energies as an indirect method in nuclear astrophysics. The breakup reactions are proved to be good spectroscopic tools and can be used to study a large number of loosely bound proton- or neutron-rich nuclei over a wide range of beam energies. As peripheral processes, they can be used to extract asymptotic normalization coefficients (ANCs) from which non-resonant capture reaction rates of astrophysical interest can be calculated parameter free. In this talk, we present results of a proton-breakup experiment carried out at GANIL (France) with a cocktail beam centered around {sup 23}Al at 50 MeV/nucleon. Momentum distributions of the breakup fragments, inclusive and in coincidence with gamma rays detected by EXOGAM Germanium clover array, were measured in the focal plan of SPEG energy-loss spectrometer. We present in particular the investigations of reaction rates for {sup 22}Mg(p,{gamma}){sup 23}Al and {sup 23}Al(p,{gamma}){sup 24}Si important for novae and X-ray bursts, respectively.

Banu, A.; Trache, L. [Cyclotron Institute, Texas A and M University, College Station, Texas 77843-3366 (United States); National Institute of Physics and Nuclear Engineering, 'Horia Hulubei' (IFIN-HH), R-077125 Magurele-Bucharest (Romania); Carstoiu, F.; Negoita, F.; Rotaru, F. [National Institute of Physics and Nuclear Engineering, 'Horia Hulubei' (IFIN-HH), R-077125 Magurele-Bucharest (Romania); Orr, N. A.; Achouri, N. L.; Laurent, B. [Laboratoire de Physique Corpusculaire, IN2P3-CNRS, ISMRA et Universite, F-14050 Caen (France); Bonaccorso, A. [Instituto Nazionale di Fisica Nucleare, Sez. Di Pisa, I-56127 Pisa (Italy); Catford, W. N.; Patterson, N.; Thomas, J. S. [Department of Physics, University of Surrey, Guildford GU2 5XH (United Kingdom); Chartier, M.; Fernandez-Dominguez, B.; Paschalis, S.; Pietras, B. [Oliver Lodge Laboratory, University of Liverpool, Liverpool L69 7ZE (United Kingdom); Freer, M. [School of Physics and Astronomy, University of Birmingham, Birmingham B15 2TT (United Kingdom); Gaudefroy, L.; Roussel-Chomaz, P. [Grand Accelerateur d'Ions Lourds, BP 55027, 14076 Caen Cedex 5 (France); Horoi, M. [Department of Physics, Central Michigan University, Mount Pleasant, Michigan 48859 (United States)

2010-11-24

141

Intermediates in Hin-mediated DNA inversion: a role for Fis and the recombinational enhancer in the strand exchange reaction.  

PubMed Central

The site-specific inversion reaction controlling flagellin synthesis in Salmonella involves the function of three proteins: Hin, Fis and HU. The DNA substrate must be supercoiled and contain a recombinational enhancer sequence in addition to the two recombination sites. Using mutant substrates or modified reaction conditions, large amounts of complexes can be generated which are recognized by double-stranded breaks within both recombination sites upon quenching. The cleaved molecules contain 2-bp staggered cuts within the central dinucleotide of the recombination site. Hin is covalently associated with the 5' end while the protruding 3' end contains a free hydoxyl. We demonstrate that complexes generated in the presence of an active enhancer are intermediates that have advanced past the major rate limiting step(s) of the reaction. In the absence of a functional enhancer, Hin is also able to assemble and catalyze site-specific cleavages within the two recombination sites. However, these complexes are kinetically distinct from the complexes assembled with a functional enhancer and cannot generate inversion without an active enhancer. The results suggest that strand exchange leading to inversion is mediated by double-stranded cleavage of DNA at both recombination sites followed by the rotation of strands to position the DNA into the recombinant configuration. The role of the enhancer and DNA supercoiling in these reactions is discussed. Images

Johnson, R C; Bruist, M F

1989-01-01

142

Nuclear spin polarization following intermediate-energy heavy-ion reactions  

SciTech Connect

Intermediate-energy heavy-ion collisions can produce a spin polarization of the projectile-like species. Spin polarization has been observed for both nucleon removal and nucleon pickup processes. Qualitative agreement with measured spin polarization as a function of the momentum of the projectile-like fragment is found in a kinematic model that considers conservation of linear and angular momentum and assumes peripheral interactions between the fast projectile and target. Better quantitative agreement was reached by including more realistic angular distributions and deorientation caused by {gamma}-ray emission and by correcting for the out-of-plane acceptance. The newly introduced corrections were found to apply to both nucleon removal and nucleon pickup processes.

Groh, D. E.; Pinter, J. S.; Mantica, P. F. [Department of Chemistry, Michigan State University, East Lansing, Michigan 48824 (United States); National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824 (United States); Mertzimekis, T. J. [National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824 (United States); Stuchbery, A. E. [Department of Nuclear Physics, Research School for Physical Sciences and Engineering, Australian National University, Canberra, ACT 0200 (Australia); Khoa, D. T. [Institute for Nuclear Science and Technique, VAEC, P. O. Box 5T-160, Nghia Do, Hanoi, (Viet Nam)

2007-11-15

143

Studies of intermediates, in catalytic reactions, catalysts and catalytic combustion using laser and mass spectrometry.  

National Technical Information Service (NTIS)

We have in this project focused our research on a study of the most simple model reaction, that includes OH-radicals, which is the oxidation of hydrogen to water on a metal catalyst. The OH radical is formed at the surface of the catalyst when molecular h...

A. Rosen

1993-01-01

144

Plastic Scintillator Detectors for the Study of Transfer and Breakup Reactions at Intermediate Energies.  

National Technical Information Service (NTIS)

The detection of light particles associated with projectile like fragments can be used to separate transfer and breakup reactions provided the detectors cover a large solid angle. Three detection systems are described: (1) a pi detector in the shape of a ...

H. R. Schmidt M. Bantel Y. D. Chan S. M. Gazes R. Kamermans

1984-01-01

145

The cyclic dipeptide CI-4 [cyclo-(l-Arg-d-Pro)] inhibits family 18 chitinases by structural mimicry of a reaction intermediate.  

PubMed Central

Family 18 chitinases are attractive targets for the development of new inhibitors with chemotherapeutic potential against fungi, insects and protozoan/nematodal parasites. Although several inhibitors have been identified, these are based on complex chemistry, which hampers iterative structure-based optimization. Here we report the details of chitinase inhibition by the natural product peptide CI-4 [ cyclo -(L-Arg-D-Pro)], which possesses activity against the human pathogenic fungus Candida albicans, and describe a 1.7 A (0.17 nm) crystal structure of CI-4 in complex with the enzyme. The structure reveals that the cyclic dipeptide inhibits chitinases by structurally mimicking a reaction intermediate, and could, on the basis of its accessible chemistry, be a candidate for further optimization.

Houston, Douglas R; Eggleston, Ian; Synstad, Bj?rnar; Eijsink, Vincent G H; van Aalten, Daan M F

2002-01-01

146

Spectral and Kinetic Characterization of Intermediates in the Aromatization Reaction Catalyzed by NikD, an Unusual Amino Acid Oxidase†  

PubMed Central

The flavoenzyme nikD, a 2-electron acceptor, catalyzes a remarkable aromatization of piperideine-2-carboxylate (P2C) to picolinate, an essential component of nikkomycin antibiotics. Steady-state kinetic data are indicative of a sequential mechanism where oxygen reacts with a reduced enzyme•dihydropicolinate (DHP) complex. The kinetics observed for complex formation with competitive inhibitors are consistent with a one-step binding mechanism. The anaerobic reaction with P2C involves three steps. The first step yields an enzyme•substrate charge transfer complex likely to contain the electron-rich P2C enamine. Calculated rates of formation and dissociation of the nikD•P2C complex are similar to those observed for the enzyme•1-cyclohexenoate complex. Formation of a reduced enzyme•DHP complex, (EH2•DHP)ini, occurs in a second step that exhibits a hyperbolic dependence on substrate concentration. The limiting rate of nikD reduction is at least 10-fold faster than the turnover rate observed with unlabeled or [4, 4, 5, 5, 6, 6-D6]-P2C and exhibits a kinetic isotope effect (KIE = 6.4). The observed KIE on Kd apparent (4.7) indicates that P2C is a sticky substrate. Formation of a final reduced species, (EH2•DHP)fin, occurs in a third step that is independent of P2C concentration and equal to the observed turnover rate. The observed KIE (3.3) indicates that the final step involves cleavage of at least one C-H bond. Tautomerization, followed by isomerization, of the initial DHP intermediate can produce an isomer that could be oxidized to picolinate in a reaction that satisfies known steric constraints of flavoenzyme reactions without the need to reposition a covalently tethered flavin or tightly bound intermediate.

Bruckner, Robert C.; Jorns, Marilyn Schuman

2009-01-01

147

Formula for Proton-Nucleus Reaction Cross Section at Intermediate Energies and Its Application  

NASA Astrophysics Data System (ADS)

We construct a formula for proton-nucleus total reaction cross section as a function of the mass and neutron excess of the target nucleus and the proton incident energy. We deduce the dependence of the cross section on the mass number and the proton incident energy from a simple argument involving the proton optical depth within the framework of a black sphere approximation of nuclei, while we describe the neutron excess dependence by introducing the density derivative of the symmetry energy, L, on the basis of a radius formula constructed from macroscopic nuclear models. We find that the cross section formula can reproduce the energy dependence of the cross section measured for stable nuclei without introducing any adjustable energy dependent parameter. We finally discuss whether or not the reaction cross section is affected by an extremely low density tail of the neutron distribution for halo nuclei.

Iida, Kei; Kohama, Akihisa; Oyamatsu, Kazuhiro

2007-04-01

148

Evidence for a Tetraoxo Intermediate in a Reaction Between a Superoxometal Complex and Acylperoxyl Radicals  

SciTech Connect

The superoxo complex Cr{sub aq}({sup 18}O{sup 18}O){sup 2+} reacts with (CH{sub 3}){sub 3}C(O){sup 16}O{sup 16}O{sup {center_dot}} to generate quantitative yields of mixed-label dioxygen, {sup 18}O{sup 16}O, demonstrating that this cross-reaction involves head-to-head interaction between the metal-activated and alkyl-activated dioxygen.

Pestovsky, Oleg; Harrata, Kamel A.; Bakac, Andreja

2008-08-05

149

Reactions and Intermediates at the Metal-Polymer Interface as Observed by XPS and NEXAFS Spectroscopy  

Microsoft Academic Search

Potassium or chromium were evaporated by means of a Knudsen effusion cell under ultra-high vacuum conditions onto a number of common polymers, prepared as stretched foils and spin-coated films. The metal-polymer interface was studied by X-ray Absorption and X-ray Photoelectron Spectroscopy. Evaporated samples were analyzed without exposure to the atmosphere. Different general types of reactions of the metal atoms with

J. F. Friedrich; I. Koprinarov; R. Giebler; A. Lippitz; W. E. S. Unger

1999-01-01

150

Identifying genomic and developmental causes of adverse drug reactions in children  

PubMed Central

Adverse drug reactions are a concern for all clinicians who utilize medications to treat adults and children; however, the frequency of adult and pediatric adverse drug reactions is likely to be under-reported. In this age of genomics and personalized medicine, identifying genetic variation that results in differences in drug biotransformation and response has contributed to significant advances in the utilization of several commonly used medications in adults. In order to better understand the variability of drug response in children however, we must not only consider differences in genotype, but also variation in gene expression during growth and development, namely ontogeny. In this article, recommendations for systematically approaching pharmacogenomic studies in children are discussed, and several examples of studies that investigate the genomic and developmental contribution to adverse drug reactions in children are reviewed.

Becker, Mara L; Leeder, J Steven

2011-01-01

151

Study of intermediates from transition metal excited-state electron-transfer reactions. [Annual] progress report, August 1, 1989--July 31, 1992  

SciTech Connect

Conventional and fast-kinetics techniques of photochemistry, photophysics, radiation chemistry, and electrochemistry were used to study the intermediates involved in transition metal excited-state electron-transfer reactions. These intermediates were excited state of Ru(II) and Cr(III) photosensitizers, their reduced forms, and species formed in reactions of redox quenchers and electron-transfer agents. Of particular concern was the back electron-transfer reaction between the geminate pair formed in the redox quenching of the photosensitizers, and the dependence of its rate on solution medium and temperature in competition with transformation and cage escape processes. (DLC)

Hoffman, M.Z.

1992-07-31

152

Structure of amidase from Pseudomonas aeruginosa showing a trapped acyl transfer reaction intermediate state.  

PubMed

Microbial amidases belong to the thiol nitrilases family and have potential biotechnological applications in chemical and pharmaceutical industries as well as in bioremediation. The amidase from Pseudomonas aeruginosa isa6 x 38-kDa enzyme that catalyzes the hydrolysis of a small range of short aliphatic amides. The hereby reported high resolution crystallographic structure shows that each amidase monomer is formed by a globular four-layer alphabetabetaalpha sandwich domain with an additional 81-residue long C-terminal segment. This wraps arm-in-arm with a homologous C-terminal chain of another monomer, producing a strongly packed dimer. In the crystal, the biological active homo-hexameric amidase is built grouping three such dimers around a crystallographic 3-fold axis. The structure also elucidates the structural basis for the enzyme activity, with the nitrilases catalytic triad at the bottom of a 13-A deep, funnel-shaped pocket, accessible from the solvent through a narrow neck with 3-A diameter. An acyl transfer intermediate, resulting from the purification protocol, was found bound to the amidase nucleophilic agent, Cys(166). These results suggest that some pocket defining residues should undergo conformational shifts to allow substrates and products to access and leave the catalytic pocket, for turnover to occur. PMID:17442671

Andrade, Jorge; Karmali, Amin; Carrondo, Maria A; Frazão, Carlos

2007-04-17

153

Investigation of the O+allyl addition/elimination reaction pathways from the OCH{sub 2}CHCH{sub 2} radical intermediate  

SciTech Connect

These experiments study the preparation of and product channels resulting from OCH{sub 2}CHCH{sub 2}, a key radical intermediate in the O+allyl bimolecular reaction. The data include velocity map imaging and molecular beam scattering results to probe the photolytic generation of the radical intermediate and the subsequent pathways by which the radicals access the energetically allowed product channels of the bimolecular reaction. The photodissociation of epichlorohydrin at 193.3 nm produces chlorine atoms and c-OCH{sub 2}CHCH{sub 2} radicals; these undergo a facile ring opening to the OCH{sub 2}CHCH{sub 2} radical intermediate. State-selective resonance-enhanced multiphoton ionization (REMPI) detection resolves the velocity distributions of ground and spin-orbit excited state chlorine independently, allowing for a more accurate determination of the internal energy distribution of the nascent radicals. We obtain good agreement detecting the velocity distributions of the Cl atoms with REMPI, vacuum ultraviolet (VUV) photoionization at 13.8 eV, and electron bombardment ionization; all show a bimodal distribution of recoil kinetic energies. The dominant high recoil kinetic energy feature peaks near 33 kcal/mol. To elucidate the product channels resulting from the OCH{sub 2}CHCH{sub 2} radical intermediate, the crossed laser-molecular beam experiment uses VUV photoionization and detects the velocity distribution of the possible products. The data identify the three dominant product channels as C{sub 3}H{sub 4}O (acrolein)+H, C{sub 2}H{sub 4}+HCO (formyl radical), and H{sub 2}CO (formaldehyde)+C{sub 2}H{sub 3}. A small signal from C{sub 2}H{sub 2}O (ketene) product is also detected. The measured velocity distributions and relative signal intensities at m/e=27, 28, and 29 at two photoionization energies show that the most exothermic product channel, C{sub 2}H{sub 5}+CO, does not contribute significantly to the product branching. The higher internal energy onset of the acrolein+H product channel is consistent with the relative barriers en route to each of these product channels calculated at the CCSD(T)/aug-cc-pVQZ level of theory, although a clean determination of the barrier energy to H+acrolein is precluded by the substantial partitioning into rotational energy during the photolytic production of the nascent radicals. We compare the measured branching fraction to the H+acrolein product channel with a statistical prediction based on the calculated transition states.

FitzPatrick, Benjamin L.; Lau, K.-C.; Butler, Laurie J. [James Franck Institute and Department of Chemistry, University of Chicago, Chicago, Illinois 60637 (United States); Lee, S.-H. [National Synchrotron Radiation Research Center, Hsinchu, 30076 Taiwan (China); Lin, Jim Jr-Min [Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, 10617 Taiwan (China)

2008-08-28

154

Intermediate- and high-energy reactions of uranium with neon and carbon  

SciTech Connect

Target fragment production from the interactions of 1.0, 3.0, 4.8, and 12 GeV /sup 12/C and 5.0, 8.0, 20, and 42 GeV /sup 20/Ne with uranium has been measured using off-line gamma-ray spectroscopic techniques. The experimental charge and mass yield distributions are generally consistent with the concepts of limiting fragmentation and factorization at energies of 3.0 GeV and above. The total projectile kinetic energy was found to be the relevant scaling parameter for the comparison of reactions induced by projectiles of different sizes. Light fragments with mass number less than 60 were found to violate limiting fragmentation, and had excitation functions that were strongly increasing with projectile energy until 8.0 to 12.0 GeV. With the 1.0 GeV /sup 12/C beam the pattern of mass yields was quite different from that of all the other reactions, with the normal peak in the fission mass region (80 < A < 145), but with much lower yields below mass number 60 and between mass numbers 145 and 210, indicating that these fragments are formed primarily in very energetic reactions in which large excitation energies are transferred to and significant amounts of mass are removed from the target nucleus. Theoretical predictions of the intra-nuclear cascade, nuclear fireball, and nuclear firestreak models are compared with the experimental results. The intra-nuclear cascade and nuclear firestreak models are both able to predict the general shapes of the experimental distributions, with the exception of the yields for the lightest fragments.

McGaughey, P.L.

1982-11-01

155

Catecholase activity of dicopper(II)-bispidine complexes: stabilities and structures of intermediates, kinetics and reaction mechanism.  

PubMed

A mechanism for the oxidation of 3,5-di-tert-butylcatechol (dtbc) with dioxygen to the corresponding quinone (dtbq), catalyzed by bispidine-dicopper complexes (bispidines are various mono- and dinucleating derivatives of 3,7-diazabicyclo[3.3.1]nonane with bis-tertiary-amine-bispyridyl or bis-tertiary-amine-trispyridyl donor sets), is proposed on the basis of (1) the stoichiometry of the reaction as well as the stabilities and structures [X-ray, density functional theory (B3LYP, TZV)] of the bispidine-dicopper(II)-3,4,5,6-tetrachlorcatechol intermediates, (2) formation kinetics and structures (molecular mechanics, MOMEC) of the end-on peroxo-dicopper(II) complexes and (3) kinetics of the stoichiometric (anaerobic) and catalytic (aerobic) copper-complex-assisted oxidation of dtbc. This involves (1) the oxidation of the dicopper(I) complexes with dioxygen to the corresponding end-on peroxo-dicopper(II) complexes, (2) coordination of dtbc as a bridging ligand upon liberation of H(2)O(2) and (3) intramolecular electron transfer to produce dtbq, which is liberated, and the dicopper(I) catalyst. Although the bispidine complexes have reactivities comparable to those of recently published catalysts with macrocyclic ligands, which seem to reproduce the enzyme-catalyzed process in various reaction sequences, a strikingly different oxidation mechanism is derived from the bispidine-dicopper-catalyzed reaction. PMID:16964505

Born, Karin; Comba, Peter; Daubinet, André; Fuchs, Alexander; Wadepohl, Hubert

2006-09-09

156

Weak electron-induced charged current reactions in /sup 12/C at intermediate energies  

SciTech Connect

The reaction e/sup -/+/sup 12/C..--> nu../sub e/+/sup 12/B is studied for electron energies of 0.5, 1.5, 3.0, and 6.0 GeV. Differential cross sections as a function of outgoing nucleus angle are obtained for these energies. The differential cross sections for the 0.5 and 3.0 GeV cases are analyzed in detail and contributions from the various form factors are determined. The results of the calculation are discussed in detail.

Mintz, S.L.

1987-08-01

157

[Ligand intermediates in metal-catalyzed reactions]. Progress report, July 1, 1989--June 30, 1992  

SciTech Connect

This report consists of sections on sigma bond complexes of alkenes, a new carbon-hydrogen bond activation reaction of alkene complexes, carbon-hydrogen bond migrations in alkylidene complexes, carbon- hydrogen bond migrations in alkyne complexes, synthesis, structure and reactivity of C{sub x} complexes, synthesis and reactivity of alcohol and ether complexes, new catalysts for the epimerization of secondary alcohols; carbon-hydrogen bond activation in alkoxide complexes, pi/sigma equilibria in metal/O=CXX` complexes, and other hydrocarbon ligands; miscellaneous.(WET)

Not Available

1992-08-01

158

Cobalt catalysis in the gas phase: experimental characterization of cobalt(i) complexes as intermediates in regioselective diels-alder reactions.  

PubMed

In situ-formed cobalt(I) complexes are proposed to act as efficient catalysts in regioselective Diels-Alder reactions of unactivated substrates such as 1,3-dienes and alkynes. We report the first experimental evidence for the in situ reduction of CoBr2(dppe) [dppe = 1,2-bis(diphenylphosphino)ethane] by Zn/ZnI2 to [Co(I)(dppe)](+) by means of electrospray MS(n) experiments. Additionally, the reactivities of Co(II) and Co(I) dppe complexes toward the Diels-Alder substrates isoprene and phenylacetylene were probed in gas-phase ion/molecule reactions (IMRs). Isoprene and phenylacetylene were introduced into the mass spectrometer via the buffer gas flow of a linear ion trap. The IMR experiments revealed a significantly higher substrate affinity of [Co(I)(dppe)](+) compared with [Co(II)Br(dppe)](+). Furthermore, the central intermediate of the solution-phase cobalt-catalyzed Diels-Alder reaction, [Co(I)(dppe)(isoprene)(phenylacetylene)](+), could be generated via IMR and examined in the gas phase. Collision activation of this complex ion delivered evidence for the gas-phase reaction of isoprene with phenylacetylene in the coordination sphere of the cobalt ion. The experimental findings are consistent with the results of quantum-chemical calculations on all of the observed Co(I) dppe complex ions. The results constitute strong analytical evidence for the formation and importance of different cobalt(I) species in regioselective Diels-Alder reactions of unactivated substrates and identify [Co(I)(dppe)](+) as the active Diels-Alder catalyst. PMID:24044877

Fiebig, Lukas; Kuttner, Julian; Hilt, Gerhard; Schwarzer, Martin C; Frenking, Gernot; Schmalz, Hans-Günther; Schäfer, Mathias

2013-09-26

159

Prompt fission neutron emission in neutron and proton induced reactions at intermediate energies  

SciTech Connect

The generalized model for the description of the prompt fission neutron spectra and multiplicities at neutron and proton energies up to about 100 MeV is described. The three main emission mechanisms considered are the precompound emission, the pre-scission particle evaporation before the saddle point and at descent to the scission point, and the emission from excited fission fragments. The two-component exciton model is used for the description of the preequilibrium stage of the reaction. The time-dependent statistical model with inclusion of the nuclear friction effects describes particle evaporation starting just after the precompound emission stage and lasting for the duration of the evolution of the compound nucleus toward scission. The fragment mass distribution and fission fragment kinetic and excitation energies are determined from the properties of the composite system at the scission point. The particle spectra from the fission fragments are calculated within the statistical approach. These spectra are then transformed into the laboratory rest frame using the calculated fragment kinetic energies and are averaged over the calculated fragment mass distributions. The model was applied to analyze the prompt fission neutron characteristics in the proton and neutron induced fission of actinide nuclei, and comparisons with the experimental data in {sup 238}U(n,f), {sup 238}U(p,f), and {sup 242}Pu(p,f) reactions are presented.

Rubchenya, V. A. [Department of Physics, University of Jyvaeskylae, FIN-40014, Jyvaeskylae, Finland and V. G. Khlopin Radium Institute, RU-194021 St. Petersburg (Russian Federation)

2007-05-15

160

Chemistry of low-valent molybdenum phosphite complexes: Models of seven-coordinate reaction intermediates.  

PubMed

A simple synthesis of the zerovalent complex Mo[P(OCH(3))(3)](6) has been devised from a potassium reduction of MoCl(4)(tetrahydrofuran)(2) followed by reaction with trimethyl phosphite at 70 degrees . Protonation of this octahedral complex gave only low yields of the expected seven-coordinate hydride, HMo[P(OCH(3))(3)](6) (+). The major product was an octahedral nonhydridic cation, Mo[P(OCH(3))(3)](5)P(OCH(3))(2) (+), derived from proton cleavage of the P-O phosphite ester bond. This octahedral cation was stereochemically nonrigid, apparently through facile methoxy group migration. Close packing by methoxy groups in this fluxional cation was established through an x-ray crystallographic study of Mo[P(OCH(3))(3)](5)P(OCH(3))(2) (+)-PF(6) (-). Extended reaction of trifluoroactic acid with Mo[P(OCH(3))(3)](6) yielded the seven-coordinate hydride, HMo[P(OCH(3))(3)](4)(O(2)CCF(3)), which was near pentagonal bipyramidal and was stereochemically nonrigid. PMID:16592505

Muetterties, E L; Kirner, J F; Evans, W J; Watson, P L; Abdel-Meguid, S; Tavanaiepour, I; Day, V W

1978-03-01

161

Chemistry of low-valent molybdenum phosphite complexes: Models of seven-coordinate reaction intermediates  

PubMed Central

A simple synthesis of the zerovalent complex Mo[P(OCH3)3]6 has been devised from a potassium reduction of MoCl4(tetrahydrofuran)2 followed by reaction with trimethyl phosphite at 70°. Protonation of this octahedral complex gave only low yields of the expected seven-coordinate hydride, HMo[P(OCH3)3]6+. The major product was an octahedral nonhydridic cation, Mo[P(OCH3)3]5P(OCH3)2+, derived from proton cleavage of the P—O phosphite ester bond. This octahedral cation was stereochemically nonrigid, apparently through facile methoxy group migration. Close packing by methoxy groups in this fluxional cation was established through an x-ray crystallographic study of Mo[P(OCH3)3]5P(OCH3)2+-PF6-. Extended reaction of trifluoroactic acid with Mo[P(OCH3)3]6 yielded the seven-coordinate hydride, HMo[P(OCH3)3]4(O2CCF3), which was near pentagonal bipyramidal and was stereochemically nonrigid.

Muetterties, E. L.; Kirner, J. F.; Evans, W. J.; Watson, P. L.; Abdel-Meguid, S.; Tavanaiepour, I.; Day, V. W.

1978-01-01

162

Detection of spirorchiid trematodes in gastropod tissues by polymerase chain reaction: preliminary identification of an intermediate host of Learedius learedi.  

PubMed

Marine spirorchiid trematodes are associated with morbidity and mortality in sea turtles worldwide. The intermediate hosts remain unknown, and discovery efforts are hindered by the large number and great diversity of potential hosts within sea turtle habitats, as well the potential for low prevalence and overdispersion. A high-throughput DNA extraction and polymerase chain reaction-based method was developed to detect the internal transcribed spacer 2 (ITS2) region of the ribosomal gene of 2 spirorchiid genera, Learedius and Hapalotrema , within pooled samples of gastropod tissues. A model system consisting of freshwater snail ( Pomacea bridgesii ) tissues and DNA extracts spiked with adult Learedius learedi and known quantities of spirorchiid DNA was used to develop and test the technique. Threshold of detection was found to be equivalent to an early prepatent infection within 1.5 g of gastropod tissue. This technique was used to screen approximately 25 species of marine gastropods at a captive facility where green turtles ( Chelonia mydas ) become infected by L. learedi . The parasite was detected in a sample of knobby keyhole limpet ( Fissurella nodosa ), thus providing the first evidence of an intermediate host for a marine spirorchiid trematode. This technique has many potential applications in trematode life cycle discovery studies. PMID:20496958

Stacy, Brian A; Frankovich, Thomas; Greiner, Ellis; Alleman, A Rick; Herbst, Lawrence H; Klein, Paul; Bolten, Alan; McIntosh, Antoinette; Jacobson, Elliott R

2010-08-01

163

Extending the Kawai-Kerman-McVoy Statistical Theory of Nuclear Reactions to Intermediate Structure via Doorways  

NASA Astrophysics Data System (ADS)

Kawai, Kerman, and McVoy have shown that a statistical treatment of many open channels that are coupled by direct reactions leads to modifications of the Hauser-Feshbach expression for energy-averaged cross section [Ann. of Phys. 75, 156 (1973)]. The energy averaging interval for this cross section is on the order of the width of single particle resonances, ? 1 MeV, revealing only a gross structure in the cross section. When the energy-averaging interval is decreased down to a width of a doorway state, ? 0.1 MeV, a so-called intermediate structure may be observed in cross sections. We extend the Kawai-Kerman-McVoy theory into the intermediate structure by leveraging a theory of doorway states developed by Feshbach, Kerman, and Lemmer [Ann. of Phys. 41, 230 (1967)]. As a by-product of the extension, an alternative derivation of the central result of the Kawai-Kerman-McVoy theory is suggested. We quantify the effect of the approximations used in derivation by performing numerical computations for a large set of compound nuclear states.

Arbanas, G.; Bertulani, C. A.; Dean, D. J.; Kerman, A. K.; Roche, K. J.

2012-02-01

164

Extending the Kawai-Kerman-McVoy Statistical Theory of Nuclear Reactions to Intermediate Structure via Doorways  

SciTech Connect

Kawai, Kerman, and McVoy have shown that a statistical treatment of many open channels that are coupled by direct reactions leads to modifications of the Hauser- Feshbach expression for energy-averaged cross section (Ann. of Phys. 75 (1973) 156). The energy averaging interval for this cross section is on the order of the width of single particle resonances, 1MeV, revealing only a gross structure in the cross section. When the energy-averaging interval is decreased down to a width of a doorway state 0.1 MeV, a so-called intermediate structure may be observed in cross sections. We extend the Kawai-Kerman-McVoy theory into the intermediate structure by leveraging a theory of doorway states developed by Feshbach, Kerman, and Lemmer (Ann. of Phys. 42 (1967) 230). As a byproduct of the extension, an alternative derivation of the central result of the Kawai-Kerman-McVoy theory is suggested. We quantify the effect of the approximations used in derivation by performing numerical computations for a large set of compound nuclear states.

Arbanas, Goran [ORNL; Bertulani, C. A. [Texas A& M University-Commerce, Commerce, Texas; Dean, D. J. [U.S. Department of Energy; Kerman, A. K. [Massachusetts Institute of Technology (MIT); Roche, K. J. [Pacific Northwest National Laboratory (PNNL)

2011-01-01

165

A dianionic phosphorane intermediate and transition states in an associative A(N)+D(N) mechanism for the ribonucleaseA hydrolysis reaction.  

PubMed

The RNaseA enzyme efficiently cleaves phosphodiester bonds in the RNA backbone. Phosphoryl transfer plays a central role in many biochemical reactions, and this is one of the most studied enzymes. However, there remains considerable controversy about the reaction mechanism. Most of this debate centers around the roles of the conserved residues, structures of the transition state or states, the possibility of a stable intermediate, and the charge and structure of this intermediate. In this communication we report calculations of the mechanism of the hydrolysis step in this reaction using a comprehensive QM/MM theoretical approach that includes a high level calculation of the interactions in the QM region, free energy estimates along an NEB optimized reaction path, and the inclusion of the interaction of the protein surroundings and solvent. Contrary to prior calculations we find a stable pentacoordinated dianionic phosphorane intermediate in the reaction path supporting an A(N)+D(N) reaction mechanism. In the transition state in the path from the reactant to the intermediate state (with barrier of 3.96 kcal/mol and intermediate stability of 2.21 kcal/mol) a proton from the attacking water is partially transferred to the His119 residue and the PO bond only partially formed from the remaining nucleophilic OH(-) species (bond order (BO) 0.11). In passing from the intermediate to the product state (barrier 13.22 kcal/mol) the PO bond on the cyclic phosphorane intermediate is nearly broken (BO 0.28) and the transfer of the proton from the Lys41 is almost complete (Lys41-H BO 0.87). In the product state a proton has been transferred from Lys41 to the O2' position of the sugar. The role of Lys41 as the catalytic acid is a result of the relative positioning of the Lys41 and His12 in the catalytic site. This configuration is supported by calculations and docking studies. PMID:19245210

Elsässer, Brigitta; Valiev, Marat; Weare, John H

2009-03-25

166

A Dianionic Phosphorane Intermediate and Transition States in an Associative AN+DN Mechanism for the RibonucleaseA Hydrolysis Reaction  

SciTech Connect

The RNaseA enzyme efficiently cleaves phosphodiester bonds in the RNA backbone. Phosphoryl transfer plays a central role in many biochemical reactions, and this is one of the most studied enzymes. However, there remains considerable controversy about the reaction mechanism. Most of this debate centers around the roles of the conserved residues, structures of the transition state or states, the possibility of a stable intermediate, and the charge and structure of this intermediate. In this communication we report calculations of the mechanism of the hydrolysis step in this reaction using a comprehensive QM/MM theoretical approach that includes a high level calculation of the interactions in the QM region, free energy estimates along an NEB optimized reaction path, and the inclusion of the interaction of the protein surroundings and solvent. Contrary to prior calculations we find a stable pentacoordinated dianionic phosphorane intermediate in the reaction path supporting an AN+DN reaction mechanism. In the transition state in the path from the reactant to the intermediate state (with barrier of 3.96 kcal/mol and intermediate stability of 2.21 kcal/mol) a proton from the attacking water is partially transferred to the His119 residue and the PO bond only partially formed from the remaining nucleophilic OH? species (bond order (BO) 0.11). In passing from the intermediate to the product state (barrier 13.22 kcal/mol) the PO bond on the cyclic phosphorane intermediate is nearly broken (BO 0.28) and the transfer of the proton from the Lys41 is almost complete (Lys41-H BO 0.87). In the product state a proton has been transferred from Lys41 to the O2? position of the sugar. The role of Lys41 as the catalytic acid is a result of the relative positioning of the Lys41 and His12 in the catalytic site. This configuration is supported by calculations and docking studies.

Elsasser, Brigitta M.; Valiev, Marat; Weare, John H.

2009-03-25

167

Acute allergy reaction after posterior sub-Tenon's triamcinolone injection in the treatment of intermediate uveitis in the asthmatic patient.  

PubMed

We report the case of a 21-year-old female patient afflicted with atopic asthma admitted to hospital in order to diagnose and treat bilateral uveitis. After diagnostic examination: serological tests for Candida and Aspergillus antigens, analysis of direct vitreous preparation and of culture searching for fungal and bacterial etiology, tests for antinuclear antibodies and for boreliosis, the diagnosis of idiopathic intermediate uveitis (pars planitis) were made. Routine treatment with Polcortolon in sub-Tenon's triamcinolone injection was applied. It resulted in acute allergic reaction characterized by blepharedema and chemosis. Hydrocortisone, Clemastin, Zyrtec, Calcium and locally Dexamethasone and Emadine in drops instilled to conjunctival sac were administered resulting in symptom disappearance. PMID:15314977

Mackiewicz, Jerzy; Biziorek, Barbara; Mackiewicz, Barbara; Zagórski, Zbigniew

2003-01-01

168

Mass scaling of reaction mechanisms in intermediate energy heavy ion collisions  

NASA Astrophysics Data System (ADS)

Reaction mechanisms have been studied for two nearly symmetrical systems of different total mass, between 25 and 74 AMeV. It is shown that collisions are mostly binary whatever the system mass and the bombarding energy. From the slowing-down of the partners, it is possible to establish the continuous evolution from quasielastic to (completely) damped collisions. It turns out that results are independent of the total system mass if involved energies are expressed in AMeV. The occurrence of mid-rapidity emission is also considered and may be used to establish a link between mechanisms observed at low and high bombarding energy. Part of it corresponds to a fast decay of outgoing partners.

Métivier, V.; Tamain, B.; Auger, G.; Bacri, C. O.; Benlliure, J.; Bocage, F.; Borderie, B.; Bougault, R.; Brou, R.; Buchet, P.; Charvet, J. L.; Chbihi, A.; Colin, J.; Cussol, D.; Dayras, R.; Demeyer, A.; Doré, D.; Durand, D.; Ecomard, P.; Eudes, P.; Gourio, D.; Guinet, D.; Laforest, R.; Lautesse, P.; Laville, J. L.; Lebreton, L.; Lecolley, J. F.; Le Fèvre, A.; Legrain, R.; Lopez, O.; Louvel, M.; Marie, N.; Nalpas, L.; Parlog, M.; Péter, J.; Plagnol, E.; Rahmani, A.; Reposeur, T.; Rivet, M. F.; Rosato, E.; Saint-Laurent, F.; Steckmeyer, J. C.; Tassan-Got, L.; Vient, E.; Volant, C.; Wieleczko, J. P.

2000-06-01

169

Isospin diffusion in {sup 58}Ni-induced reactions at intermediate energies. II. Dynamical simulations  

SciTech Connect

We study isospin effects in semiperipheral collisions above the Fermi energy by considering the symmetric {sup 58}Ni+{sup 58}Ni and the asymmetric {sup 58}Ni+{sup 197}Au reactions over the incident energy range 52A-74A MeV. A microscopic transport model with two different parametrizations of the symmetry energy term is used to investigate the isotopic content of pre-equilibrium emission and the N/Z diffusion process. Simulations are also compared to experimental data obtained with the INDRA array and provide information on the degree of isospin equilibration observed in Ni+Au collisions. A better overall agreement between data and simulations is obtained when using a symmetry term that linearly increases with nuclear density.

Galichet, E. [Institut de Physique Nucleaire, Universite Paris-Sud 11, CNRS/IN2P3, F-91406 Orsay Cedex (France); Conservatoire National des Arts et Metiers, F-75141 Paris Cedex 03 (France); INFN Laboratori Nazionali del Sud, I-95123 Catania (Italy); INFN Sez. di Catania and Dipartimento di Fisica, Universita di Catania (Italy); Colonna, M. [INFN Laboratori Nazionali del Sud, I-95123 Catania (Italy); Borderie, B.; Rivet, M. F. [Institut de Physique Nucleaire, Universite Paris-Sud 11, CNRS/IN2P3, F-91406 Orsay Cedex (France)

2009-06-15

170

Plastic scintillator detectors for the study of transfer and breakup reactions at intermediate energies  

NASA Astrophysics Data System (ADS)

The detection of light particles associated with projectile like fragments can be used to separate transfer and breakup reactions provided the detectors cover a large solid angle. Three detection systems are described: (1) 4-pi detector in the shape of a cube, 20 cm on a side, (2) a X-Y position sensitive (delta) E-E detector having an area of 20 x 20 cm, and (3) a multielement detector consisting of eight position sensitive strips. The latter two detectors are of the phoswich type having the thin element of NE102 (tau = 2.5 ns) and the thick element of NE115 (tau = 225 ns). The performance characteristics of the three detectors are described.

Schmidt, H. R.; Bantel, M.; Chan, Y. D.; Gazes, S. M.; Kamermans, R.; Albiston, C.; Wald, S.; Stokstad, R. G.

1984-10-01

171

Direct-semidirect and multistep processes in radiative proton capture reactions at intermediate energies  

SciTech Connect

The energy dependence of the 60/sup 0/ proton capture differential cross sections for /sup 11/B and /sup 27/Al targets in the proton bombarding energy range of 20 to 100 MeV were measured. The angular distributions and analyzing powers at proton bombarding energies 28.3, 49.2 MeV (/sup 11/B target) and 20.8 MeV (/sup 27/Al target) were measured. A direct-semidirect model using a global optical model parameters was used to compare with experimental data. The calculations with an energy-dependent set of OMP produce reasonable fits to the experimental data from the region of the GDR up to approximately 40 MeV. However, at energies above approx.40 MeV, the DSD differential cross sections overestimate the experimental value. The calculations with a fixed set of OMP fit the experimental data for the entire energy region. The DSD model predicts angular distributions and analyzing powers reasonably well. The second excited state of the /sup 7/Be from the reaction /sup 6/Li(p,..gamma..) was investigated to explore whether multistep processes are important in radiative capture reactions. The energy dependence, angular distributions, and analyzing powers for the 7/2/sup -/ state were obtained. It was found that this state cannot be explained by a DSD model. A theoretical model was developed and a computer program was made to calculate multistep processes. It was found that the results from the theoretical calculation failed to match the experimental data.

Kim, W.

1986-01-01

172

Catecholase activity of a mu-hydroxodicopper(II) macrocyclic complex: structures, intermediates and reaction mechanism.  

PubMed

The monohydroxo-bridged dicopper(II) complex (1), its reduced dicopper(I) analogue (2) and the trans-mu-1,2-peroxo-dicopper(II) adduct (3) with the macrocyclic N-donor ligand [22]py4pz (9,22-bis(pyridin-2'-ylmethyl)-1,4,9,14,17,22,27,28,29,30- decaazapentacyclo -[22.2.1(14,7).1(11,14).1(17,20)]triacontane-5,7(28),11(29),12,18,20(30), 24(27),25-octaene), have been prepared and characterized, including a 3D structure of 1 and 2. These compounds represent models of the three states of the catechol oxidase active site: met, deoxy (reduced) and oxy. The dicopper(II) complex 1 catalyzes the oxidation of catechol model substrates in aerobic conditions, while in the absence of dioxygen a stoichiometric oxidation takes place, leading to the formation of quinone and the respective dicopper(I) complex. The catalytic reaction follows a Michaelis-Menten behavior. The dicopper(I) complex binds molecular dioxygen at low temperature, forming a trans-mu-1,2-peroxo-dicopper adduct, which was characterized by UV-Vis and resonance Raman spectroscopy and electrochemically. This peroxo complex stoichiometrically oxidizes a second molecule of catechol in the absence of dioxygen. A catalytic mechanism of catechol oxidation by 1 has been proposed, and its relevance to the mechanisms earlier proposed for the natural enzyme and other copper complexes is discussed. PMID:16208496

Koval, Iryna A; Belle, Catherine; Selmeczi, Katalin; Philouze, Christian; Saint-Aman, Eric; Schuitema, Anna Maria; Gamez, Patrick; Pierre, Jean-Louis; Reedijk, Jan

2005-11-08

173

Crystal structure of bifunctional aldos-2-ulose dehydratase/isomerase from Phanerochaete chrysosporium with the reaction intermediate ascopyrone M.  

PubMed

The enzyme aldos-2-ulose dehydratase/isomerase (AUDH) participates in carbohydrate secondary metabolism, catalyzing the conversion of glucosone and 1,5-d-anhydrofructose to the secondary metabolites cortalcerone and microthecin, respectively. AUDH is a homo-dimeric enzyme with subunits of 900 amino acids. The subunit consists of a seven-bladed ?-propeller domain, two cupin folds and a C-terminal lectin domain. AUDH contains a structural Zn(2+) and Mg(2+) located in loop regions and two zinc ions at the bottom of two putative active-site clefts in the propeller and the cupin domain, respectively. Catalysis is dependent on these two zinc ions, as their specific removal led to loss of enzymatic activity. The structure of the Zn(2)(+)-depleted enzyme is very similar to that of native AUDH, and structural changes upon metal removal as the cause for the catalytic deficiencies can be excluded. The complex with the reaction intermediate ascopyrone M shows binding of this compound at two different sites, with direct coordination to Zn(2+) in the propeller domain and as second sphere ligand of the metal ion in the cupin domain. These observations suggest that the two reactions of AUDH might be catalyzed in two different active sites, about 60 Å apart. The dehydration reaction most likely follows an elimination mechanism, where Zn(2+) acts as a Lewis acid polarizing the C2 keto group of 1,5-d-anhydrofructose. Abstraction of the proton at the C3 carbon atom and protonation of the leaving group, the C4 hydroxyl moiety, could potentially be catalyzed by the side chain of the suitably positioned residue His155. PMID:22330145

Claesson, Magnus; Lindqvist, Ylva; Madrid, Susan; Sandalova, Tatyana; Fiskesund, Roland; Yu, Shukun; Schneider, Gunter

2012-02-08

174

Oxo iron(IV) as an oxidative active intermediate of p-chlorophenol in the Fenton reaction: a DFT study.  

PubMed

Debate continues over which active species plays the role of oxidative agent during the Fenton reaction-the HO? radical or oxo iron [Fe(IV)O](2+). In this context, the present study investigates the oxidation of p-chlorophenol by [Fe(IV)O(H(2)O)(5)](2+) using DFT calculations, within gas-phase and micro-solvated models, in order to explore the possible role of oxo iron as a reactant. The results show that the chlorine atom substitution of p-chlorophenol by oxo iron is a highly stabilising step (?H = -83 kcal mol(-1)) with a free energy barrier of 5.8 kcal mol(-1) in the micro-solvated model. This illustrates the high oxidising power of the [Fe(IV)O(H(2)O)(5)](2+) complex. On the other hand, the breaking of the Fe-O bond, leading to the formation of hydroquinone, is observed to be the rate-determining step of the reaction. The rather large free energy barrier corresponding to this bond cleavage amounts to 10.2 and 9.3 kcal mol(-1) in the gas-phase and micro-solvated models, respectively. Elsewhere, the lifetime of the HO? radical has previously been shown to be extremely small. These facts, combined with observations of oxo iron under certain experimental conditions, suggest that oxo iron is a highly plausible oxidative species of the reaction. In addition, a trigonal bipyramidal iron complex, coordinated either by hydroxyl groups and/or by water molecules, has been found in all described mechanisms. This structure appears to be a stable intermediate; and to our knowledge, it has not been characterised by previous studies. PMID:22322483

Mignon, Pierre; Pera-Titus, Marc; Chermette, Henry

2012-02-09

175

Tandem Processes Identified from Reaction Screening: Nucleophilic Addition to Aryl N-Phosphinylimines Employing La(III)-TFAA activation  

PubMed Central

Reaction screening of nucleophilic reaction partners for addition to N-diphenylphosphinylimines employing lanthanum (III) triflate as catalyst and trifluoroacetic anhydride (TFAA) as activator is reported. A number of tandem processes leading to novel chemotypes including aza-Prins/intramolecular Friedel-Crafts annulations have been identified and both reaction scope and mechanism further investigated.

Kinoshita, Hidenori; Ingham, Oscar J.; Ong, Winnie W.; Beeler, Aaron B.

2010-01-01

176

A simple method for analysis of consecutive reactions with a second order formation and a first order decay of an intermediate  

Microsoft Academic Search

A simple method is developed to evaluate rate constants from absorbance-time traces for a pair of consecutive reactions consisting\\u000a of a second order formation and a first order decay of an intermediate. Initially, a first order profile is simulated utilizing\\u000a the data near the end of the reaction. The difference between this simulated and observed profiles provides the absorbance-time\\u000a data

N. J. Matuska; R. N. Bose

1997-01-01

177

Photofragment imaging study of the CH{sub 2}CCH{sub 2}OH radical intermediate of the OH+allene reaction  

SciTech Connect

These velocity map imaging experiments characterize the photolytic generation of one of the two radical intermediates formed when OH reacts via an addition mechanism with allene. The CH{sub 2}CCH{sub 2}OH radical intermediate is generated photolytically from the photodissociation of 2-chloro-2-propen-1-ol at 193 nm. Detecting the Cl atoms using [2+1] resonance-enhanced multiphoton ionization evidences an isotropic angular distribution for the Cl+CH{sub 2}CCH{sub 2}OH photofragments, a spin-orbit branching ratio for Cl({sup 2}P{sub 1/2}):Cl({sup 2}P{sub 3/2}) of 0.28, and a bimodal recoil kinetic energy distribution. Conservation of momentum and energy allows us to determine from this data the internal energy distribution of the nascent CH{sub 2}CCH{sub 2}OH radical cofragment. To assess the possible subsequent decomposition pathways of this highly vibrationally excited radical intermediate, we include electronic structure calculations at the G3//B3LYP level of theory. They predict the isomerization and dissociation transition states en route from the initial CH{sub 2}CCH{sub 2}OH radical intermediate to the three most important product channels for the OH+allene reaction expected from this radical intermediate: formaldehyde+C{sub 2}H{sub 3}, H+acrolein, and ethene+CHO. We also calculate the intermediates and transition states en route from the other radical adduct, formed by addition of the OH to the center carbon of allene, to the ketene+CH{sub 3} product channel. We compare our results to a previous theoretical study of the O+allyl reaction conducted at the CBS-QB3 level of theory, as the two reactions include several common intermediates.

Raman, Arjun S.; Justine Bell, M.; Lau, K.-C.; Butler, Laurie J. [James Franck Institute and Department of Chemistry, University of Chicago, Chicago, Illinois 60637 (United States)

2007-10-21

178

Structure-sensitivity and ensemble effects in reactions of strongly adsorbed intermediates. Catalytic dehydrogenation and dehydration of formic acid on nickel  

Microsoft Academic Search

Formic acid (HCOOH) dehydrogenates and dehydrates catalytically on Ni surfaces by unimolecular decomposition of strongly adsorbed formate intermediates. The rate of these reactions and the identity and decomposition selectivity of surface formate are not affected by Ni dispersion or by changes in Ni ensemble size resulting from Cu alloying or from coadsorption of Co and oxygen. Dehydrogenation and dehydration occur

Enrique Iglesia; Michel Boudart

1991-01-01

179

Differential inhibition of class I and class II 5-enolpyruvylshikimate-3-phosphate synthases by tetrahedral reaction intermediate analogues.  

PubMed

The shikimate pathway enzyme 5-enolpyruvylshikimate-3-phosphate synthase (EPSP synthase or EPSPS) is best known as the target of the herbicide glyphosate. EPSPS is also considered an attractive target for the development of novel antibiotics since the pathogenicity of many microorganisms depends on the functionality of the shikimate pathway. Here, we have investigated the inhibitory potency of stable fluorinated or phosphonate-based analogues of the tetrahedral reaction intermediate (TI) in a parallel study utilizing class I (glyphosate-sensitive) and class II (glyphosate-tolerant) EPSPS. The (R)-difluoromethyl and (R)-phosphonate analogues of the TI are the most potent inhibitors of EPSPS described to date. However, we found that class II EPSPS are up to 400 times less sensitive to inhibition by these TI analogues. X-ray crystallographic data revealed that the conformational changes of active site residues observed upon inhibitor binding to the representative class I EPSPS from Escherichia coli do not occur in the prototypical class II enzyme from Agrobacterium sp. strain CP4. It appears that because the active sites of class II EPSPS do not possess the flexibility to accommodate these TI analogues, the analogues themselves undergo conformational changes, resulting in less favorable inhibitory properties. Since pathogenic microorganisms such as Staphylococcus aureus utilize class II EPSPS, we conclude that the rational design of novel EPSPS inhibitors with potential as broad-spectrum antibiotics should be based on the active site structures of class II EPSP synthases. PMID:17958399

Funke, Todd; Healy-Fried, Martha L; Han, Huijong; Alberg, David G; Bartlett, Paul A; Schönbrunn, Ernst

2007-10-25

180

A novel microfluidic rapid freeze-quench device for trapping reactions intermediates for high field EPR analysis  

NASA Astrophysics Data System (ADS)

Rapid freeze quench electron paramagnetic resonance (RFQ)-EPR is a method for trapping short lived intermediates in chemical reactions and subjecting them to EPR spectroscopy investigation for their characterization. Two (or more) reacting components are mixed at room temperature and after some delay the mixture is sprayed into a cold trap and transferred into the EPR tube. A major caveat in using commercial RFQ-EPR for high field EPR applications is the relatively large amount of sample needed for each time point, a major part of which is wasted as the dead volume of the instrument. The small sample volume (˜2 ?l) needed for high field EPR spectrometers, such as W-band (˜3.5 T, 95 GHz), that use cavities calls for the development of a microfluidic based RFQ-EPR apparatus. This is particularly important for biological applications because of the difficulties often encountered in producing large amounts of intrinsically paramagnetic proteins and spin labeled nucleic acid and proteins. Here we describe a dedicated microfluidic based RFQ-EPR apparatus suitable for small volume samples in the range of a few ?l. The device is based on a previously published microfluidic mixer and features a new ejection mechanism and a novel cold trap that allows collection of a series of different time points in one continuous experiment. The reduction of a nitroxide radical with dithionite, employing the signal of Mn2+ as an internal standard was used to demonstrate the performance of the microfluidic RFQ apparatus.

Kaufmann, Royi; Yadid, Itamar; Goldfarb, Daniella

2013-05-01

181

Structure-sensitivity and ensemble effects in reactions of strongly adsorbed intermediates. Catalytic dehydrogenation and dehydration of formic acid on nickel  

SciTech Connect

Formic acid (HCOOH) dehydrogenates and dehydrates catalytically on Ni surfaces by unimolecular decomposition of strongly adsorbed formate intermediates. The rate of these reactions and the identity and decomposition selectivity of surface formate are not affected by Ni dispersion or by changes in Ni ensemble size resulting from Cu alloying or from coadsorption of Co and oxygen. Dehydrogenation and dehydration occur via identical intermediates that require small Ni ensembles (1-2 surface atoms) and that decompose with similar activation energy, a surprising result because the required molecular rearrangements differ markedly in the two decomposition modes. The authors suggest that reaction trajectories bifurcate after the formation of the activated complex in the rate-determining formate-decomposition step, leading to two kinetically indistinguishable decomposition paths. The decomposition selectivity on metal catalysts is controlled by entropy differences between the two reaction paths and by the binding energy of adsorbed oxygen atoms on these metal surfaces.

Iglesia, E. (Exxon Research and Engineering Co., Annandale, NJ (United States)); Boudart, M. (Stanford Univ., CA (United States))

1991-09-05

182

Prescription Surveillance and Polymerase Chain Reaction Testing to Identify Pathogens during Outbreaks of Infection  

PubMed Central

Syndromic surveillance, including prescription surveillance, offers a rapid method for the early detection of agents of bioterrorism and emerging infectious diseases. However, it has the disadvantage of not considering definitive diagnoses. Here, we attempted to definitively diagnose pathogens using polymerase chain reaction (PCR) immediately after the prescription surveillance system detected an outbreak. Specimens were collected from 50 patients with respiratory infections. PCR was used to identify the pathogens, which included 14 types of common respiratory viruses and Mycoplasma pneumoniae. Infectious agents including M. pneumoniae, respiratory syncytial virus (RSV), rhinovirus, enterovirus, and parainfluenza virus were detected in 54% of patients. For the rapid RSV diagnosis kit, sensitivity was 80% and specificity was 85%. For the rapid adenovirus diagnosis kit, no positive results were obtained; therefore, sensitivity could not be calculated and specificity was 100%. Many patients were found to be treated for upper respiratory tract infections without the diagnosis of a specific pathogen. In Japan, an outbreak of M. pneumoniae infection began in 2011, and our results suggested that this outbreak may have included false-positive cases. By combining syndromic surveillance and PCR, we were able to rapidly and accurately identify causative pathogens during a recent respiratory infection outbreak.

Sugiura, Hiroaki; Fujimoto, Tsuguto; Sugawara, Tamie; Hanaoka, Nozomu; Konagaya, Masami; Kikuchi, Kiyoshi; Hanada, Eisuke; Okabe, Nobuhiko; Ohkusa, Yasushi

2013-01-01

183

Prescription surveillance and polymerase chain reaction testing to identify pathogens during outbreaks of infection.  

PubMed

Syndromic surveillance, including prescription surveillance, offers a rapid method for the early detection of agents of bioterrorism and emerging infectious diseases. However, it has the disadvantage of not considering definitive diagnoses. Here, we attempted to definitively diagnose pathogens using polymerase chain reaction (PCR) immediately after the prescription surveillance system detected an outbreak. Specimens were collected from 50 patients with respiratory infections. PCR was used to identify the pathogens, which included 14 types of common respiratory viruses and Mycoplasma pneumoniae. Infectious agents including M. pneumoniae, respiratory syncytial virus (RSV), rhinovirus, enterovirus, and parainfluenza virus were detected in 54% of patients. For the rapid RSV diagnosis kit, sensitivity was 80% and specificity was 85%. For the rapid adenovirus diagnosis kit, no positive results were obtained; therefore, sensitivity could not be calculated and specificity was 100%. Many patients were found to be treated for upper respiratory tract infections without the diagnosis of a specific pathogen. In Japan, an outbreak of M. pneumoniae infection began in 2011, and our results suggested that this outbreak may have included false-positive cases. By combining syndromic surveillance and PCR, we were able to rapidly and accurately identify causative pathogens during a recent respiratory infection outbreak. PMID:23509772

Sugiura, Hiroaki; Fujimoto, Tsuguto; Sugawara, Tamie; Hanaoka, Nozomu; Konagaya, Masami; Kikuchi, Kiyoshi; Hanada, Eisuke; Okabe, Nobuhiko; Ohkusa, Yasushi

2013-02-07

184

Use of a nonradioactive genetic probe identified, synthesized, and labeled in the polymerase chain reaction.  

PubMed

This study introduces a strategy to identify and produce sequences useful as genetic markers, or native genetic probes for DNA-DNA hybridization in bacterial strains where the genetics is not well described. Actinobacillus actinomy-cetemcomitans (A.a.) was used as an example. Fifty ng genomic DNA from A.a. ATCC 33384 and Haemophilus aphrophilus ATCC 33389 was amplified in a thermocycler using a single 10-mer primer. The PCR products were separated by electrophoresis on a 1% submarine agarose gel containing ethidium bromide and visualized by UV illumination, and the strain-specific amplitypes were compared. DNA from two bands, 0.9 and 4 kb, unique for the A.a. strain, was cut out, amplified under high stringency with the same primer and labeled by replacing 33.3 microM dTTP with digoxigenin-labeled dUTP in the reaction mixture. The labeled probe was then repeatedly used for hybridization to DNA from various A.a., H. aphrophilus, and other bacterial strains of the Pasteurellaceae family. The results showed that the 0.9-kb probe detected all A.a. tested, and distinguished it from other closely related bacterial species. We conclude that the described strategy is useful for identifying and selecting genetic sequences useful as genetic markers in A.a. PMID:7521967

Preus, H R; Russell, D T

1994-06-01

185

Multiple Reaction Monitoring as a Method for Identifying Protein Posttranslational Modifications  

PubMed Central

The activity of many transcriptional regulators is significantly altered by posttranslational modifications of specific sites. For example, the activity of the muscle-restricted transcription factor family myocyte enhancer factor 2 (MEF2) is tightly controlled by phosphorylation. This modification is responsible for either an increase or a decrease in transcriptional activity, depending on the specific amino acid residues that are phosphorylated by signal-dependent kinases. Although mass spectrometry-based methods, such as precursor ion and neutral loss scans, are extremely useful for identifying unknown phosphopeptides from a complex mixture, they do not take advantage of any prior knowledge about the protein being investigated. Quite often a significant amount of information is available. This may include the primary sequence, type of phosphorylation (serine/threonine vs. tyrosine), or predicted phosphoacceptor sites (consensus peptide that is targeted by a kinase). This information can be used to predict precursor and fragment ion m/z values for a multiple reaction monitoring (MRM) experiment. By using these highly sensitive MRM experiments to trigger dependent product ion scans on a hybrid quadrupole linear ion-trap instrument, we were able to identify low levels of phosphorylation of MEF2A (a member of the MEF2 family), and ?-casein. This method of monitoring protein phosphorylation at specific phosphoacceptor sites may prove useful in understanding the physiological regulation of protein function.

Cox, David M.; Zhong, F.; Du, M.; Duchoslav, E.; Sakuma, T.; McDermott, J. C.

2005-01-01

186

Large kinetic isotope effects in methane oxidation catalyzed by methane monooxygenase: evidence for C-H bond cleavage in a reaction cycle intermediate.  

PubMed

The reduced hydroxylase component (MMOH) of soluble methane monooxygenase (MMO) from Methylosinus trichosporium OB3b reacts with O2 and CH4 to produce CH3OH and H2O in a single-turnover reaction. Transient kinetic analysis of this reaction has revealed at least five and probably six intermediates during the turnover [Lee, S.-K., Nesheim, J. C., & Lipscomb, J. D. (1993) J. Biol. Chem. 268, 21569-21577; Liu, Y., Nesheim, J. C., Lee, S.-K., & Lipscomb, J. D. (1995) J. Biol. Chem. 270, 24662-24665]. One intermediate, termed compound Q, reacts with CH4 to yield enzyme-bound product. It is shown here that the deuterium kinetic isotope effect (KIE) for the reaction of compound Q with CH4 is 50-100, which is one of the largest effects observed to date. The rate constants for the reactions of the deuterated homologs of methane decrease monotonically as the deuterium content increases, suggesting that a large primary isotope effect dominates. The KIEs determined by analyzing the products after a single turnover have the following values: 1:1 CH4:CD4 (19); CD3H (12); CD2H2 (9); and CH3D (4). The KIE values determined by directly observing the reactive intermediate and by monitoring product ratios are all large, consistent with complete C-H bond breaking in the oxygenation step of the reaction. However, the differences in the KIE values determined by these two methods suggest that the reaction is more complex than currently proposed. A modified mechanism introducing the possibility of hydrogen-atom reabstraction by an intermediate methyl radical is proposed. PMID:8756490

Nesheim, J C; Lipscomb, J D

1996-08-01

187

Chlorinations catalyzed by chloroperoxidase occur via diffusible intermediate(s) and the reaction components play multiple roles in the overall process  

Microsoft Academic Search

The chlorination mechanism of the fungal enzyme chloroperoxidase (CPO) has been debated for (1) active site chlorination and (2) diffusible species mediated chlorination. Based upon the conversion of ?35 different substrates belonging to different reactive groups, it was found that substrate dimensions and topography had no pronounced effect on rates of CPO chlorination reaction. Epoxidation of indene was dependent on

Kelath Murali Manoj

2006-01-01

188

A test for the coexistence of reactive intermediates with different molecular composition in chiral Lewis acid-catalysed reactions: the case of Ti-TADDOLate-catalysed Diels–Alder reactions  

Microsoft Academic Search

The Diels–Alder reactions between cyclopentadiene 2 and (E)-3-butenoyl-1,3-oxazolidin-2-one 1 catalysed by several TADDOL-TiCl2 complexes have been studied with different [dienophile]\\/[catalyst] ratios and different concentrations of reagents and catalyst. The enantioselectivity of some of the reactions depends on these factors, which indicates the participation of intermediate complexes with different catalyst and dienophile compositions (1:1, 1:2 and 2:1). The best results are

Belén Altava; M. Isabel Burguete; José I. Garc??a; Santiago V. Luis; José A. Mayoral; Maria J. Vicent

2001-01-01

189

Developing species-specific primers to identify Bulinus truncatus and Bulinus beccari, the intermediate hosts of Schistosoma haematobium in Saudi Arabia.  

PubMed

This work aimed to determine the inter- and intra-specific variations in populations of Bulinus truncatus and Bulinus beccari, the intermediate hosts of Schistosoma haematobium in Saudi Arabia, and to develop species-specific primers to identify these snails as a first step in the development of multiplex PCR for simultaneously identifying the snails and diagnosing its infections in a single step. Two populations of B. truncatus were collected from Asser and Bisha (A and B), and two B. beccari populations were collected from Mahial Asser and Merba (C and D). The snails' genomic DNA was extracted and amplified using 5 different primers. The primers displayed variable intra- and inter-specific differences across the populations. The largest RAPD-PCR fragments were cloned into a vector as a preparatory step for sequencing. Similarity searches for the sequenced cloned inserts revealed no similar sequences in the GenBank database or its associated databases. Specific primers used to target the B. truncatus and B. beccari genomes were designed using the Gene Runner program and based on the DNA sequences obtained from RAPD fragment sequence analyses. Using these primers for specific PCRs resulted in expected single-band PCR products of 536 bp for B. beccari and 478 bp for B. truncatus. These results will be helpful for simultaneously identifying B. truncatus and B. beccari snails and diagnosing S. haematobium infections within the snails using single step multiplex PCR. PMID:22441124

Mostafa, Osama M S; Bin Dajem, Saad M; Al-Qahtani, Ahmed; Ibrahim, Essam H; Al-Quraishy, Saleh A S

2012-03-10

190

Studies on the mechanism of the peroxyoxalate chemiluminescence reaction: part 2. Further identification of intermediates using 2D EXSY 13C nuclear magnetic resonance spectroscopy.  

PubMed

Further consideration has been given to the reaction pathway of a model peroxyoxalate chemiluminescence system. Again utilising doubly labelled oxalyl chloride and anhydrous hydrogen peroxide, 2D EXSY (13)C nuclear magnetic resonance (NMR) spectroscopy experiments allowed for the characterisation of unknown products and key intermediate species on the dark side of the peroxyoxalate chemiluminescence reaction. Exchange spectroscopy afforded elucidation of a scheme comprised of two distinct mechanistic pathways, one of which contributes to chemiluminescence. (13)C NMR experiments carried out at varied reagent molar ratios demonstrated that excess amounts of hydrogen peroxide favoured formation of 1,2-dioxetanedione: the intermediate that, upon thermolysis, has been long thought to interact with a fluorophore to produce light. PMID:18420048

Tonkin, Sarah A; Bos, Richard; Dyson, Gail A; Lim, Kieran F; Russell, Richard A; Watson, Simon P; Hindson, Christopher M; Barnett, Neil W

2008-03-13

191

A Dianionic Phosphorane Intermediate and Transition States in an Associative AN+DN Mechanism for the RibonucleaseA Hydrolysis Reaction  

SciTech Connect

The ubiquitous presence of phosphoryl transfer as central step in many metabolic, signaling, energy storage, etc. enzymatic reactions requires that the details of the reaction mechanisms (e.g. reaction paths, transition state stabilization and structure, etc.) that leads to their remarkable rates in protein catalytic environments be understood1. It is expected that most of these reactions proceed through a pathway that includes a penta- coordinated phosphorane species. However, the nature of the bonding and the protonation of the structure in this region and the possibility of stable intermediates as the system passes along the reaction path through the transitions state (TS) are currently topics of considerable debate1a,b,c. Typically nucleophilic substitution reactions are classified in terms of extremes of two bonding situations along the reaction path: in a dissociative mechanism the substrate phosphate bridging bond is broken and the bond to the entering nucleophilic group is not yet formed leaving a metastable metaphosphate (PO3?) intermediate (a DN+AN reaction); in an associative mechanism in the extreme case a metastable pentacoordinated phosphorane species with nearly equivalent bonds is present in the TS, whose subsequent dissociation leads to the product state (an AN+DN reaction). Recently we published a computational study of the phosphoryl transfer step of a major class of enzymes, the serine kinases2a,b involved in signal transduction. These calculations2b support a dissociative mechanism (DNAN,) for this family of enzymes with unstable metaphosphate structure in loose transition state with total bond order of 22%.

Elsasser, Brigitta M.; Valiev, Marat; Weare, John H.

2009-02-26

192

Density functional theory calculation of cyclic carboxylic phosphorus mixed anhydrides as possible intermediates in biochemical reactions: implications for the Pro-Tide approach.  

PubMed

Cyclic acyl phosphoramidates (CAPAs) are important components in several fundamental biological reactions such as protein synthesis and phosphorylation. These structures are particularly interesting in the nucleotide pro-drug approach, Pro-Tide, since they are putative intermediates in one of the hydrolysis steps required for activation. The central role played by the amino acid carboxylate function suggests first the formation of a cyclic mixed phosphorus anhydride, rapidly followed by water attack. To investigate such speculations, we performed quantum mechanical calculations using the B3LYP/6-311+G** level of theory for the plausible mechanisms of action considered. In the five-membered ring case, transition state theory demonstrated how the overall, gas-phase, mechanism of action could be split into two in-line addition-elimination (A-E) steps separated by a penta-coordinate phosphorane intermediate. The difference between five-membered and six-membered ring first A-E was also explored, revealing a single step, unimolecular reaction for the six-membered ring A-E profile. Implicit solvent contribution further confirmed the importance of CAPAs as reactive intermediates in such kind of reactions. Lastly, the second A-E pathway was analyzed to understand the complete pathway of the reaction. This analysis is the first attempt to clarify the putative mechanism of action involved in the activation of Pro-Tides and casts light also on the possible mechanism of action involved in primordial protein syntheses, strengthening the hypothesis of a common cyclic mixed phosphorus anhydride species as a common intermediate. PMID:22318882

Ricci, Antonio; Brancale, Andrea

2012-02-08

193

Measurements of Total Reaction Cross Sections for Exotic Nuclei Close to the Proton Drip-line at Intermediate Energies and Observation of a Proton Halo in 27P  

Microsoft Academic Search

Measurements of the total reaction cross sections (sigmaR) for some proton-rich nuclei (N = 11-15 isotones) on a carbon target at intermediate energies have been performed on the Radioactive Ion Beam Line of the Heavy Ion Research Facility in Lanzhou. A larger enhancement of sigmaR for 27P has been observed than for its neighbours. Evidence for a proton halo in

De-Qing Fang; Wen-Qing Shen; Jun Feng; Xiang-Zhou Cai; Yu-Gang Ma; Hu-Yong Zhang; Chen Zhong; Wen-Long Zhan; Zhong-Yan Guo; Guo-Qing Xiao; Jian-Song Wang; Jin-Chuan Wang; Jia-Xing Li; Meng Wang; Jian-Feng Wang; Zhen-Jiang Ning; Quan-Jin Wang; Zhi-Qiang Chen

2001-01-01

194

Mechanistic and kinetic investigation on the formation of palladacyclopentadiene complexes. A novel interpretation involving a bimolecular self-reaction of a monoalkyne intermediate  

Microsoft Academic Search

The stoichiometric reaction between the complex [Pd(eta(2)-dmfu)(BiPy)] (dmfu = dimethylfumarate; BiPy = 2,2'-bipyridine) and the deactivated alkynes dmbd (dimethyl-2-butynedioate) and pna (methyl (4-nitrophenyl)propynoate), providing the respective palladacyclopentadienes, was investigated. The mechanism leading to the palladacyclopentadiene derivative involves a bimolecular self-rearrangement of the monoalkyne intermediate [Pd(eta(2)-alk)(BiPy)] (alk = dmbd, pna), followed by the customary attack of the free alkyne on the

A. Holuigue; J. M. Ernsting; F. Visentin; C. Levi; L. Canovese; C. J. Elsevier

2008-01-01

195

Protein vivisection reveals elusive intermediates in folding  

PubMed Central

Although most folding intermediates escape detection, their characterization is crucial to the elucidation of folding mechanisms. Here we outline a powerful strategy to populate partially unfolded intermediates: A buried aliphatic residue is substituted with a charged residue (e.g., Leu?Glu?) to destabilize and unfold a specific region of the protein. We apply this strategy to Ubiquitin, reversibly trapping a folding intermediate in which the ?5 strand is unfolded. The intermediate refolds to a native-like structure upon charge neutralization under mildly acidic conditions. Characterization of the trapped intermediate using NMR and hydrogen exchange methods identifies a second folding intermediate and reveals the order and free energies of the two major folding events on the native side of the rate-limiting step. This general strategy may be combined with other methods and have broad applications in the study of protein folding and other reactions that require trapping of high energy states.

Zheng, Zhongzhou; Sosnick, Tobin R.

2010-01-01

196

Protein vivisection reveals elusive intermediates in folding.  

PubMed

Although most folding intermediates escape detection, their characterization is crucial to the elucidation of folding mechanisms. Here, we outline a powerful strategy to populate partially unfolded intermediates: A buried aliphatic residue is substituted with a charged residue (e.g., Leu-->Glu(-)) to destabilize and unfold a specific region of the protein. We applied this strategy to ubiquitin, reversibly trapping a folding intermediate in which the beta5-strand is unfolded. The intermediate refolds to a native-like structure upon charge neutralization under mildly acidic conditions. Characterization of the trapped intermediate using NMR and hydrogen exchange methods identifies a second folding intermediate and reveals the order and free energies of the two major folding events on the native side of the rate-limiting step. This general strategy may be combined with other methods and have broad applications in the study of protein folding and other reactions that require trapping of high-energy states. PMID:20144618

Zheng, Zhongzhou; Sosnick, Tobin R

2010-02-06

197

Protein Vivisection Reveals Elusive Intermediates in Folding  

SciTech Connect

Although most folding intermediates escape detection, their characterization is crucial to the elucidation of folding mechanisms. Here, we outline a powerful strategy to populate partially unfolded intermediates: A buried aliphatic residue is substituted with a charged residue (e.g., Leu {yields} Glu{sup -}) to destabilize and unfold a specific region of the protein. We applied this strategy to ubiquitin, reversibly trapping a folding intermediate in which the {beta}5-strand is unfolded. The intermediate refolds to a native-like structure upon charge neutralization under mildly acidic conditions. Characterization of the trapped intermediate using NMR and hydrogen exchange methods identifies a second folding intermediate and reveals the order and free energies of the two major folding events on the native side of the rate-limiting step. This general strategy may be combined with other methods and have broad applications in the study of protein folding and other reactions that require trapping of high-energy states.

Zheng, Zhongzhou; Sosnick, Tobin R. (UC)

2010-05-25

198

Identifying reaction of stock price to public information based on fuzzy c-means clustering  

Microsoft Academic Search

The efficient markets hypothesis (EMH) maintains that market prices fully reflect all available information such as public or private information. Therefore, the study of analyzing the reaction of stock price to the information has attracted more and more attention. Here we proposed an effective measuring method using fuzzy c-means (FCM) for describing the reaction to public information, and further analyzing

Li Chao-Chao; Chi Kai; Fu Fang-Ping; Che Wen-Gang; Zhao Qing-Jiang

2010-01-01

199

Detection of short-lived intermediates in electrochemical reactions using time-resolved surface-enhanced Raman spectroscopy  

SciTech Connect

p-Nitrobenzoic acid (PNBA) is studied by real-time detection of SERS spectra during time-resolved optical multichannel recording following the application of a double potential step to a Ag electrode. The spectral bands of three stable intermediate products, p-nitrosobenzoate, hydroxylamine, and azoxy compounds are observed. In addition, the transient bands of an unstable intermediate are seen at 996, 1233, and 1580 cm{sup {minus}1} with a lifetime of about 70 ms during the oxidation process of the hydroxylamine compound which itself is generated electrochemically by a 200-ms potential pulse. We suggest these bands represent the p-nitrosobenzoate free-radical anion intermediate formed during the oxidation of the hydroxylamine compound.

Shi, Chongtie,; Zhang, Wei; Birke, R.L.; Lombardi, J.R. (The City College of The City Univ. of New York, NY (USA))

1990-06-14

200

Kinetics and Spectroscopic Evidence that the Cu(I) - Semiquinone Intermediate Reduces Molecular Oxygen in the Oxidative Half-Reaction of Arthrobacter globiformis Amine Oxidase†  

PubMed Central

The role of copper during the reoxidation of substrate-reduced amine oxidases by O2 has not yet been definitively established. Both outer-sphere and inner-sphere pathways for the reduction of O2 to H2O2 have been proposed. A key step in the inner-sphere mechanism is the reaction of O2 directly with the Cu(I) center of a [Cu(I) ? semiquinone] intermediate. To thoroughly examine this possibility, we have measured the spectral changes associated with single-turnover reoxidation by O2 of substrate-reduced Arthrobacter globiformis amine oxidase (AGAO) under a wide range of conditions. We have previously demonstrated that the internal electron-transfer reaction [Cu(II) ? TPQAMQ ? Cu(I) ? TPQSQ] (where TPQAMQ is the aminoquinol form of reduced TPQ and TPQSQ is the semiquinone form) occurs at a rate that could permit the reaction of O2 with both species to be observed on the stopped-flow time scale (Shepard EM and Dooley DM (2006) JBIC 11:1039-1048). The transient absorption spectra observed for the reaction of O2 with substrate-reduced AGAO provide compelling support for the reaction of the Cu(I) ? TPQSQ form. Further, global analysis of the kinetics and the transient absorption spectra are fully consistent with an inner-sphere reaction of the Cu(I)-semiquinone intermediate with O2 and are inconsistent with an outer-sphere mechanism for the reaction of the reduced enzyme with O2.

Shepard, Eric M.; Okonski, Kristina M.; Dooley, David M.

2009-01-01

201

Experimental study and baryonic exchange interpretation of the reaction 2H(d, n)3He in the intermediate energy region  

NASA Astrophysics Data System (ADS)

We present a complete set of eight differential cross sections of the reactions 2H(d, n)3He and 2H(d, p)3H in the 0-60° c.m. angular range for incident deuteron momenta between 1.1 and 2.5 GeV/c. A simple phenomenological interpretation of the energy dependence of the total cross section ?T and of d?dt at fixed t shows, in the reaction, the contribution of a nucleon exchange process to which we must add a mechanism implying the ?33 resonance excitation in the direct channel. NUCLEAR REACTION 2H(d, n)3He, 2H(d, p)3H Ed=0.3-1.25 GeV; measured ?(Ed, ?) intermediate energy; phenomenological analysis of the baryonic exchange mechanisms.

Bizard, G.; Laville, J. L.; Le Brun, C.; Lecolley, J. F.; Lefebvres, F.; Osmont, A.; Regimbart, R.; Steckmeyer, J. C.; Berger, J.; Duflo, J.; Goldzahl, L.; Oostens, J.; Plouin, F.; Fabbri, F. L.; Picozza, P.; Satta, L.

1980-10-01

202

Modeling of a gas–liquid reactor in batch conditions. Study of the intermediate regime when part of the reaction occurs within the film and part within the bulk  

Microsoft Academic Search

A model is proposed for irreversible gas–liquid reactions, especially in the so-called ‘intermediate regime’ where the liquid phase mass transfer coefficient and the chemical reaction rate lead to a situation where part of the reaction occurs within the bulk and part occurs within the film. Firstly, the film theory is used but a new parameter, the depletion factor, is introduced

Hassen Benbelkacem; Hubert Debellefontaine

2003-01-01

203

Identifying genetic risk factors for serious adverse drug reactions: current progress and challenges  

Microsoft Academic Search

Serious adverse drug reactions (SADRs) are a major cause of morbidity and mortality worldwide. Some SADRs may be predictable, based upon a drug's pharmacodynamic and pharmacokinetic properties. Many, however, appear to be idiosyncratic. Genetic factors may underlie susceptibility to SADRs and the identification of predisposing genotypes may improve patient management through the prospective selection of appropriate candidates. Here we discuss

Russell A. Wilke; Debbie W. Lin; Dan M. Roden; Paul B. Watkins; David Flockhart; Issam Zineh; Kathleen M. Giacomini; Ronald M. Krauss

2007-01-01

204

Identifi cation of a 27 kDa Protein in Patients With Anaphylactic Reactions to Mango  

Microsoft Academic Search

? Abstract Mango fruit has become increasingly popular in recent years. We report on 2 patients who developed anaphylactic reactions after the ingestion of fresh mango. Allergy to mango was confi rmed by a positive skin prick test result and positive cellular allergen stimulation test results. Neither of the patients had detectable mango-specifi c immunoglobulin (Ig) E levels. Results were

R Renner; C Hipler; R Treudler; W Harth; JC Simon

205

From Bis(silylene) and Bis(germylene) Pincer-Type Nickel(II) Complexes to Isolable Intermediates of the Nickel-Catalyzed Sonogashira Cross-Coupling Reaction.  

PubMed

The first [ECE]Ni(II) pincer complexes with E = Si(II) and E = Ge(II) metallylene donor arms were synthesized via C-X (X = H, Br) oxidative addition, starting from the corresponding [EC(X)E] ligands. These novel complexes were fully characterized (NMR, MS, and XRD) and used as catalyst for Ni-catalyzed Sonogashira reactions. These catalysts allowed detailed information on the elementary steps of this catalytic reaction (transmetalation ? oxidative addition ? reductive elimination), resulting in the isolation and characterization of an unexpected intermediate in the transmetalation step. This complex, {[ECE]Ni acetylide ? CuBr} contains both nickel and copper, with the copper bound to the alkyne ?-system. Consistent with these unusual structural features, DFT calculations of the {[ECE]Ni acetylide ? CuBr} intermediates revealed an unusual E-Cu-Ni three-center-two-electron bonding scheme. The results reveal a general reaction mechanism for the Ni-based Sonogashira coupling and broaden the application of metallylenes as strong ?-donor ligands for catalytic transformations. PMID:24053603

Gallego, Daniel; Brück, Andreas; Irran, Elisabeth; Meier, Florian; Kaupp, Martin; Driess, Matthias; Hartwig, John F

2013-10-04

206

The synthesis of buprenorphine intermediates by regioselective microbial N- and O-demethylation reactions using Cunninghamella echinulata NRRL 1384  

Microsoft Academic Search

A biotransformation procedure, using the filamentous fungus Cunninghamella echinulata NRRL 1384, for the high yielding regioselective demethylation of a thebaine derivative to give intermediates for the synthesis of buprenorphine is reported. The thebaine derived substrate can be converted to a mixture of N-demethylated and N,O-demethylated products. Manipulation of the growth conditions of the organism and time of substrate addition resulted

Anthony M Abel; Andrew J Carnell; J. Alf Davis; Michael Paylor

2003-01-01

207

Polymerase chain reaction analyses identify two distinct classes of Borrelia burgdorferi.  

PubMed Central

We sequenced homologous chromosomal loci from several North American and European isolates of the Lyme disease spirochete Borrelia burgdorferi, as well as from the relapsing fever spirochete Borrelia hermsii. Inter- and intraspecies sequence comparisons permitted the design of B. burgdorferi-specific polymerase chain reaction primers that detected all strains tested (n = 31) from diverse geographical and biological origins. Polymerase chain reaction "typing" with other unique sets of primers subdivided B. burgdorferi isolates into two groups: all North American isolates and a few European isolates made up one group, while the majority of the European and Asian isolates made up the second group. This classification may have a clinical correlate reflected in differences between "typical" Lyme borreliosis in North America and Europe. Images

Rosa, P A; Hogan, D; Schwan, T G

1991-01-01

208

Isolation, Characterization of an Intermediate in an Oxygen Atom-Transfer Reaction, and the Determination of the Bond Dissociation Energy  

SciTech Connect

Redox reactions coupled with the formal loss or gain of an oxygen atom are ubiquitous in chemical processes. Such reactions proceed through the reduction of the donor center (XO) and the oxidation of the acceptor (Y) molecule. Among many examples of the metal centered oxygen atom transfer (OAT) reactivity, those involving molybdenum complexes have been widely investigated due to their involvement in mononuclear molybdenum enzymes. The heat of reaction of the overall atom transfer process can be expressed as a difference between the bond dissociation energies (BDEs) of the oxygen-donor(X) and oxygen-acceptor(Y) bond, i.e., H=DX=o-DY=O.

Nemykin, Victor N.; Laskin, Julia; Basu, Partha

2004-07-19

209

Homoaromatics as intermediates in the substitution reactions of 1,2,4,5-tetrazines with ammonia and hydrazine  

Microsoft Academic Search

This thesis describes some nucleophilic substitution reactions between the red 1,2,4,5-tetrazines and hydrazine-hydrate or ammonia. Special attention was paid to the occurrence of the S

A. D. Counotte-Potman

1981-01-01

210

Reaction cross sections of intermediate energy 3He-particles on targets from 9Be to 208Pb  

Microsoft Academic Search

Reaction cross sections for 3He-particles have been measured for 9Be, 12C, 16O, 28Si, 40Ca, 58,60Ni, 112,116,118,120,124Sn, and 208Pb at 96, 138 and 167 MeV. The results are compared with predictions from optical model calculations using phenomenological and global optical potentials. The behaviour of the wavefunctions and of the contributions to the reaction cross sections from different regions in the nucleus is

A. Ingemarsson; G. J. Arendse; A. Auce; R. F. Carlson; A. A. Cowley; A. J. Cox; S. V. Förtsch; R. Johansson; B. R. Karlson; M. Lantz; J. Peavy; J. A. Stander; G. F. Steyn; G. Tibell

2001-01-01

211

Anionic Pd(0) and Pd(II) Intermediates in Palladium-Catalyzed Heck and Cross-Coupling Reactions  

Microsoft Academic Search

The anions of PdCl2L2 and Pd(OAc)2, precursors of palladium(0) used in cross-coupling and Heck reactions, play a crucial role in these reactions. Tricoordinated anionic complexes Pd 0 L2Cl - and Pd0L2(OAc)- are the effective catalysts instead of the usually postulated Pd 0 L2 complex. The anion ligated to the palladium(0) affects the kinetics of the oxidative addition to ArI as

Christian Amatore; Anny Jutand

2000-01-01

212

Calculated and measured battery voltages - thermodynamics aids in identifying electrochemical reactions. Final report, March-June 1984  

SciTech Connect

Both the open- and closed-circuit voltages of a battery depend on the thermodynamic conditions inside the cell. When the actual electrochemical reaction of a particular battery is unknown, thermodynamic calculations can help to identify it. Using thermodynamics data, the open-circuit voltages for alternatively electrochemical reactions can be calculated. When accurate data are available, the calculated voltage for the correct electrochemical reaction will agree to within millivolts with the measured value. For the Cl/sub 2/-Li molten salt system, the calculated and measured values are both 3.612V. For alkaline zinc batteries, the data indicate that Zn0 is the discharge product at the anode under ambient conditions. For the acid Mn02-Zn system, under the thermodynamic conditions, a two-electron reduction of MnO/sub 2/ occurs. Initially, in the alkaline MnO/sub 2/-Zn system. Mn(OH)/sub 4/ is the discharge product at the cathode.

DeVries, L.E.

1985-02-01

213

High-valent intermediates in the reaction of N alpha-acetyl microperoxidase-8 with hydrogen peroxide: models for compounds 0, I and II of horseradish peroxidase.  

PubMed

N-acetyl microperoxidase-8 (Ac-MP-8) is a water soluble, ferric heme model for the peroxidases. The reaction of Ac-MP-8 with H2O2 in 10 mM potassium phosphate over the pH range of 7-11 gives rise sequentially to relatively stable green and red species with properties that closely mimic those of HRP compounds I and II, respectively. Low-temperature stopped-flow studies of this reaction carried out in 50% v/v methanol/10 mM potassium phosphate, pH* 9.1 at -25.8 degrees C indicate that the pseudo-first-order rate constant, kobs, that describes the formation of the green intermediate exhibits saturation kinetics as a function of [H2O2] with kmaxobs = 95 s-1 and KM = 87 mM. Rapid-scan studies carried out with [H2O2] = 200 mM at -38.0 degrees C show that a compound 0 species with a characteristic band near 340 nm is formed whose conversion to the green species is rate limiting. Thus, Ac-MP-8 has high-valent forms that are models for all three known intermediates in the peroxidase cycle of horseradish peroxidase. PMID:1656947

Wang, J S; Baek, H K; Van Wart, H E

1991-09-30

214

Reactions of 1,2-catechol with t Bu 3M (M = Ga, In). Structures of intermediate products  

Microsoft Academic Search

Reactions of 1,2-catechol with tBu3M (M=Ga, In) have been studied. Trinuclear compounds [tBu5M3(OC6H4O)2] [M=Ga (1), M=In (2)] were synthesised in the reaction of 2 equiv. of C6H4(OH)2 with 3 equiv. of tBu3M in refluxing solvents. At room temperature the reaction of 1,2-catechol with tBu3In in Et2O leads to the formation of a binuclear complex [tBu4In2(OC6H4OH)2·2Et2O] (3) possessing a four-membered In2O2

Wanda Ziemkowska; Piotr Stella; Romana Anulewicz-Ostrowska

2005-01-01

215

A novel fault-tree approach for identifying potential causes of satellite reaction wheel failure  

Microsoft Academic Search

Due to unforeseen circumstances and naturally occurring faults, it is desired that an on-board fault-diagnosis system of a space vehicle be capable of detecting, isolating, identifying or classifying faults in the system. In this paper, a novel approach is proposed which strengthens existing efficient fault-detection mechanisms with an additional ability to classify different types of faults to effectively determine potential

A. Barua; P. Sinha; K. Khorasani; S. Tafazoli

2005-01-01

216

Human immunodeficiency virus-1 protease. 1. Initial velocity studies and kinetic characterization of reaction intermediates by sup 18 O isotope exchange  

SciTech Connect

The peptidolytic reaction HIV-1 protease has been investigated by using four oligopeptide substrates, Ac-Ser-Gln-Asn-Pro-Val-Val-NH{sub 2}, Ac-Arg-Ala-Ser-Gln-Asn-Tyr-Pro-Val-Val-NH{sub 2}, Ac-Ser-Gln-Ser-Tyr-Pro-Val-Val-NH{sub 2}, and Ac-Arg-Lys-Ile-Leu-Phe-Leu-Asp-Gly-NH{sub 2} that resemble two cleavage sites found within the naturally occurring polyprotein substrates Pr55{sup gag} and Pr160{sup gag-pol}. By use of a variety of inorganic salts, it was concluded that the peptidolytic reaction is nonspecifically activated by increasing ionic strength. V/K increased in an apparently parabolic fashion with increasing ionic strength, while V was either increased or decreased slightly. From product inhibition studies, the kinetic mechanism of the protease is either random or ordered uni-bi, depending on the substrate studied. The protease-catalyzed exchange of an atom of {sup 18}O from H{sub 2}{sup 18}O into the re-formed substrates occurred at a rate which was 0.01-0.12 times that the forward peptidolytic reaction. The results of these studies are in accord with the formation of a kinetically competent enzyme-bound amide hydrate intermediate, the collapse of which is the rate-limiting chemical step in the reaction pathway.

Hyland, L.J.; Tomaszek, T.A. Jr.; Roberts, G.D.; Carr, S.A.; Magaard, V.W.; Bryan, H.L.; Fakhoury, S.A.; Moore, M.L.; Minnich, M.D.; Culp, J.S.; DesJarlais, R.L.; Meek, T.D. (Smline Beecham Pharmaceuticals, King of Prussia, PA (United States))

1991-08-27

217

Delayed hemolytic transfusion reaction with multiple alloantibody (Anti S, N, K) and a monospecific autoanti-JKb in intermediate ?-thalassemia patient in Tabriz  

PubMed Central

It appears that delayed hemolytic transfusion reactions may occur several days after the administration of donor red cells is true even though they have been shown to be compatible in cross match tests by the antiglobulin technique. A specific case was observed in our center, which confirms the fact. The patient was a 37-year-old male suffering from intermediate ?-thalassemia. He had a history of two previous transfusions, with unknown transfusion reaction. In the last transfusion, laboratory data showed: Hb 7.8 g/dL and Hematocrit (Hct) 24.2%. The patient received two units of cross matched, compatible concentrated red blood cells (RBCs). After eight days a severe reaction was observed with clinical evidence of tachycardia, fatigue, fever, back pain, chest discomfort, jaundice, nausea and anorexia. Accordingly delayed hemolytic transfusion reaction was suspected, and anti-RBC antibodies were tested. Laboratory tests revealed the presence of three alloantibodies: Anti-N, anti-S, anti-K, and a monospecific autoanti-JKb.

Dolatkhah, Roya; Esfahani, Ali; Torabi, Seyed Esmaeil; Kermani, Iraj Asvadi; Sanaat, Zohreh; Ziaei, Jamal Eivazei; Nikanfar, Alireza; Chavoshi, Seyed Hadi; Ghoreishi, Zohreh; Kermani, Atabak Asvadi

2013-01-01

218

Delayed hemolytic transfusion reaction with multiple alloantibody (Anti S, N, K) and a monospecific autoanti-JK(b) in intermediate ?-thalassemia patient in Tabriz.  

PubMed

It appears that delayed hemolytic transfusion reactions may occur several days after the administration of donor red cells is true even though they have been shown to be compatible in cross match tests by the antiglobulin technique. A specific case was observed in our center, which confirms the fact. The patient was a 37-year-old male suffering from intermediate ?-thalassemia. He had a history of two previous transfusions, with unknown transfusion reaction. In the last transfusion, laboratory data showed: Hb 7.8 g/dL and Hematocrit (Hct) 24.2%. The patient received two units of cross matched, compatible concentrated red blood cells (RBCs). After eight days a severe reaction was observed with clinical evidence of tachycardia, fatigue, fever, back pain, chest discomfort, jaundice, nausea and anorexia. Accordingly delayed hemolytic transfusion reaction was suspected, and anti-RBC antibodies were tested. Laboratory tests revealed the presence of three alloantibodies: Anti-N, anti-S, anti-K, and a monospecific autoanti-JK(b). PMID:24014947

Dolatkhah, Roya; Esfahani, Ali; Torabi, Seyed Esmaeil; Kermani, Iraj Asvadi; Sanaat, Zohreh; Ziaei, Jamal Eivazei; Nikanfar, Alireza; Chavoshi, Seyed Hadi; Ghoreishi, Zohreh; Kermani, Atabak Asvadi

2013-07-01

219

Intermediates in Reactions of Copper(I) Complexes with N-Oxides: From Formation of Stable Adducts to Oxo Transfer  

PubMed Central

Reactions of Cu(I) complexes of bidentate N-donor supporting ligands with pyridine- and trimethylamine-N-oxides or PhIO were explored. Key results include the identification of novel Cu(I)-N-oxide adducts, aryl substituent hydroxylation, and bis(?-oxo)dicopper complex formation via a route involving oxo transfer.

Hong, Sungjun; Gupta, Aalo K.; Tolman, William B.

2009-01-01

220

Reaction Times Identify a Pavlovian Component in a Two-Choice Discrimination  

PubMed Central

Six pigeons discriminated on discrete trials between two colors. In Experiment 1, two luminous spots were both either blue or green and the reinforced responses were “peck left” for blue and “peck right” for green. In Experiment 2, the hue of a center spot controlled subsequent choice pecks to left or right. In both experiments response bias was manipulated in two ways. During stimulus frequency (“SF”) sessions correct responses brought food on 40% of trials; in “imbalanced” blocks of sessions one hue appeared on 80% of trials and the other on 20%. During reinforcement probability (“RNF”) sessions the hues appeared equally often, but in imbalanced blocks the hues signaled different reinforcement probabilities, either 64% or 16%. In “balanced” control blocks the hues appeared equally often and were both reinforced at 40%. The experiments gave similar results. When bias was computed from choice percentages the imbalanced conditions yielded substantial response bias, and the amount of bias was about the same under RNF and SF treatments, However, reaction times (RTs) gave a different outcome. RNF imbalance slowed responses directed at the less reinforced stimulus, but SF imbalance had little RT effect (Experiment 1) or no effect (Experiment 2). These results suggest that choice was controlled by an instrumental stimulus-response-reinforcement association, whereas RTs were controlled by a Pavlovian stimulus-reinforcement association.

Blough, Donald S.

2009-01-01

221

Reaction times identify a Pavlovian component in a two-choice discrimination.  

PubMed

Six pigeons discriminated on discrete trials between two colors. In Experiment 1, two luminous spots were both either blue or green and the reinforced responses were "peck left" for blue and "peck right" for green. In Experiment 2, the hue of a center spot controlled subsequent choice pecks to left or right. In both experiments response bias was manipulated in two ways. During stimulus frequency ("SF") sessions correct responses brought food on 40% of trials; in "imbalanced" blocks of sessions one hue appeared on 80% of trials and the other on 20%. During reinforcement probability ("RNF") sessions the hues appeared equally often, but in imbalanced blocks the hues signaled different reinforcement probabilities, either 64% or 16%. In "balanced" control blocks the hues appeared equally often and were both reinforced at 40%. The experiments gave similar results. When bias was computed from choice percentages the imbalanced conditions yielded substantial response bias, and the amount of bias was about the same under RNF and SF treatments. However, reaction times (RTs) gave a different outcome. RNF imbalance slowed responses directed at the less reinforced stimulus, but SF imbalance had little RT effect (Experiment 1) or no effect (Experiment 2). These results suggest that choice was controlled by an instrumental stimulus-response-reinforcement association, whereas RTs were controlled by a Pavlovian stimulus-reinforcement association. PMID:19429212

Blough, Donald S

2009-02-03

222

NO reduction by nitric-oxide reductase from denitrifying bacterium Pseudomonas aeruginosa: characterization of reaction intermediates that appear in the single turnover cycle.  

PubMed

Nitric-oxide reductase (NOR) of a denitrifying bacterium catalyzes NO reduction to N(2)O at the binuclear catalytic center consisting of high spin heme b(3) and non-heme Fe(B). The structures of the reaction intermediates in the single turnover of the NO reduction by NOR from Pseudomonas aeruginosa were investigated using optical absorption and EPR spectroscopies combined with an originally designed freeze-quench device. In the EPR spectrum of the sample, in which the fully reduced NOR was mixed with an NO solution and quenched at 0.5 ms after the mixing, two characteristic signals for the ferrous Fe(B)-NO and the penta-coordinated ferrous heme b(3)-NO species were observed. The CO inhibition of its formation indicated that two NO molecules were simultaneously distributed into the two irons of the same binuclear center of the enzyme in this state. The time- and temperature-dependent EPR spectral changes indicated that the species that appeared at 0.5 ms is a transient reaction intermediate prior to the N(2)O formation, in good agreement with the so-called "trans" mechanism. It was also found that the final state of the enzyme in the single turnover cycle is the fully oxidized state, in which the mu-oxo-bridged ligand is absent between the two irons of its binuclear center, unlike the resting form of NOR as isolated. On the basis of these present findings, we propose a newly developed mechanism for the NO reduction reaction conducted by NOR. PMID:15504726

Kumita, Hideyuki; Matsuura, Koji; Hino, Tomoya; Takahashi, Satoshi; Hori, Hiroshi; Fukumori, Yoshihiro; Morishima, Isao; Shiro, Yoshitsugu

2004-10-25

223

Photocatalytic degradation of methylene blue on nanocrystalline TiO 2: Surface mass spectrometry of reaction intermediates  

Microsoft Academic Search

Photocatalytic degradation reactions of methylene blue on nanocrystalline TiO2 (nc-TiO2) films were studied in situ by surface mass spectrometric techniques including secondary ion mass spectrometry, laser desorption direct ion mass spectrometry, and laser desorption\\/laser photoion mass spectrometry. The parent ion of methylene blue and\\/or its reduced form leucomethylene blue was observed with little fragmentation by all methods prior to ultraviolet

Hubert Gnaser; Michael R. Savina; Wallis F. Calaway; C. Emil Tripa; Igor V. Veryovkin; Michael J. Pellin

2005-01-01

224

Photocatalytic degradation of methylene blue on nanocrystalline TiO2: Surface mass spectrometry of reaction intermediates  

Microsoft Academic Search

Photocatalytic degradation reactions of methylene blue on nanocrystalline TiO2 (nc-TiO2) films were studied in situ by surface mass spectrometric techniques including secondary ion mass spectrometry, laser desorption direct ion mass spectrometry, and laser desorption\\/laser photoion mass spectrometry. The parent ion of methylene blue and\\/or its reduced form leucomethylene blue was observed with little fragmentation by all methods prior to ultraviolet

Hubert Gnaser; Michael R. Savina; Wallis F. Calaway; C. Emil Tripa; Igor V. Veryovkin; Michael J. Pellin

2005-01-01

225

A scale for identifying "Stockholm syndrome" reactions in young dating women: factor structure, reliability, and validity.  

PubMed

The factor structure, reliability, and validity of a 49-item scale designed to measure Stockholm Syndrome (also referred to as "traumatic bonding" and "terror bonding"), that is, bonding with an abusive partner, were assessed for college women in heterosexual dating relationships. Factor analysis identified three major factors: Core Stockholm Syndrome, characterized by cognitive distortions and other strategies for coping with abuse; Psychological Damage, marked by depression, low self-esteem, and loss of sense of self; and Love-Dependence, typified by the feeling that one cannot survive without one's partner's love. The scale and factors had excellent internal consistency and good test-retest reliabilities. They correlated negatively with the Marlowe-Crowne Social Desirability scale and positively with Horowitz, Wilner, & Alvarez' (1979) Impact of Event Scale, Hyler and Rieder's (1987) Borderline Personality Disorder Scale, Hatfield and Sprecher's (1986) Passionate Love Scale, and Straus' (1979) Verbal Aggression and Violence scales of the Conflict Tactics Scales. PMID:8555117

Graham, D L; Rawlings, E I; Ihms, K; Latimer, D; Foliano, J; Thompson, A; Suttman, K; Farrington, M; Hacker, R

1995-01-01

226

Synthesis of anionic hypervalent cyclic selenenate esters: relevance to the hypervalent intermediates in nucleophilic substitution reactions at the selenium(II) center.  

PubMed

The synthesis of a diaryl diselenide that contains 2,6-dicarboxylic acid groups, 2,2'-diselanediylbis(5-tert-butylisophthalic acid) (10), is described. Diselenide 10 undergoes intramolecular cyclization in methanol to form a cyclic selenenate ester, 5-tert-butyl-3-oxo-3H-benzo[c][1,2]oxaselenole-7-carboxylic acid (11). The cyclization reaction proceeds more rapidly in the presence of organic bases, such as pyridine, adenine, and 4,4'-bipyridine, to form pyridinium 5-tert-butyl-3-oxo-3H-benzo[c][1,2]oxaselenole-7-carboxylate (14), adeninium 5-tert-butyl-3-oxo-3H-benzo[c][1,2]oxaselenole-7-carboxylate (15), and 4,4'-bipyridiniumbis(5-tert-butyl-3-oxo-3H-benzo[c][1,2]oxaselenole-7-carboxylate) (16), respectively. However, 2,2'-diselanediyldibenzoic acid (22) does not undergo cyclization under similar conditions. Structural studies on cyclic selenenate esters 14-16 revealed that the Se···O (COO(-)) secondary distances (2.170, 2.075, and 2.176 Å) were significantly shorter than the corresponding Se···O distances (2.465, 2.472, and 2.435 Å) observed for the selenenate esters stabilized by the neutral donors (CHO, COOH, and COOEt). (1)H, (13)C, and (77)Se NMR spectroscopy of compounds 11 and 14-16 reveal that the aryl protons of compound 11 and the organic cations of compounds 14-16 exchange between the two carboxylate groups via a hypercoordinate intermediate. The corresponding hypercoordinate intermediate (14b, pyridinium selenuranide) for compound 14 was detected at low temperatures using (77)Se NMR spectroscopy. The presumed hypercoordinate intermediates in the carboxylate-exchange reactions at the selenium(II) center for a set of model reactions were optimized using DFT-B3LYP/6-311+g(d) calculations and their structural features compared with the X-ray structure of anionic selenenate esters 14-16. PMID:22190290

Selvakumar, Karuthapandi; Singh, Harkesh B; Goel, Nidhi; Singh, Udai P; Butcher, Ray J

2011-12-21

227

New model catalysts (platinum nanoparticles) and new techniques (SFG and STM) for studies of reaction intermediates and surface restructuring at high pressures during catalytic reactions  

Microsoft Academic Search

Single-crystal surfaces have long served us well as model catalysts; however, a new type of model catalyst has been prepared using electron beam lithography. Ordered arrays of platinum nano-particles in the 2.5–50 nm size range are deposited on oxide substrates (silica, alumina, and titania) of 1 cm2 surface area, and are used in catalyzed surface reactions at high pressures (atmospheres).

G. A. Somorjai

1997-01-01

228

Electronic and steric effects on the mechanism of the inverse electron demand Diels-Alder reaction of 2-aminopyrroles with 1,3,5-triazines: identification of five intermediates by 1H, 13C, 15N, and 19F NMR spectroscopy.  

PubMed

The inverse electron demand Diels-Alder (IEDDA) reaction of 1-tert-butyl-2-aminopyrrole with 2,4,6-tris(trifluoromethyl)-1,3,5-triazine in THF-d(8) to give a pyrrolo[2,3-d]pyrimidine was studied by (1)H, (13)C, (15)N, and (19)F NMR spectroscopy, and five intermediates were identified. A zwitterion was the first intermediate detected, and it cyclized to a tricyclic adduct and its conjugate acid. It also gave a neutral imine via a proton switch. The tricyclic adduct underwent a retro-Diels-Alder reaction, but the expected CF(3)CN was not detected. NMR indicated that the amino group of the 2-aminopyrrole was bonded to the CF(3)CN to form a trifluoroacetoamidinium ion. The products of the retro-Diels-Alder reaction reacted rapidly with each other to give the final intermediate observed. Acid-catalyzed loss of an amidine gave the final aromatic product. This is the first study in which direct experimental evidence for the order of the steps in the IEDDA cascade reaction of 1,3,5-triazines with amino-containing dienophiles has been obtained. This study and analogous 1,3-dipolar cycloaddition reactions, in which zwitterions have been detected or proposed, have two factors in common: electronic effects that stabilize the zwitterions and steric effects that inhibit their cyclization. PMID:19053577

De Rosa, Michael; Arnold, David

2009-01-01

229

Catecholase activity of dicopper(II)-bispidine complexes: stabilities and structures of intermediates, kinetics and reaction mechanism  

Microsoft Academic Search

A mechanism for the oxidation of 3,5-di-tert-butylcatechol (dtbc) with dioxygen to the corresponding quinone (dtbq), catalyzed by bispidine-dicopper complexes (bispidines\\u000a are various mono- and dinucleating derivatives of 3,7-diazabicyclo[3.3.1]nonane with bis-tertiary-amine–bispyridyl or bis-tertiary-amine–trispyridyl\\u000a donor sets), is proposed on the basis of (1) the stoichiometry of the reaction as well as the stabilities and structures [X-ray,\\u000a density functional theory (B3LYP, TZV)] of

Karin Born; Peter Comba; André Daubinet; Alexander Fuchs; Hubert Wadepohl

2007-01-01

230

Elucidation of the order of oxidations and identification of an intermediate in the multistep clavaminate synthase reaction  

SciTech Connect

The enzyme clavaminate synthase (CS) catalyzes the formation of the first bicyclic intermediate in the biosynthetic pathway to the potent {beta}-lactamase inhibitor clavulanic acid. Previous work has led to the proposal that the cyclization/desaturation of the substrate proclavaminate proceeds in two oxidative steps, each coupled to a decarboxylation of {alpha}-ketoglutarate and a reduction of dioxygen to water. The authors have now employed kinetic isotope effect studies to determine the order of oxidations for CS purified from Streptomyces clavuligerus. Using (4{prime}RS)-(4{prime}-{sup 3}H,1-{sup 14}C)-rac-proclavaminate, a primary {sup T}(V/K) = 8.3 {plus minus} 0.2 was measured from ({sup 3}H)water release data, while an {alpha}-secondary {sup T}(V/K) = 1.06 {plus minus} 0.01 was determined from the changing {sup 3}H/{sup 14}C ratio of the product clavaminate. Values for the primary and {alpha}-secondary effects of 11.9 {plus minus} 1.7 and 1.12 {plus minus} 0.07, respectively, were obtained from the changing {sup 3}H/{sup 14}C ratio of the residual proclavaminate by using new equations derived for a racemic substrate bearing isotopic label at both primary and {alpha}-secondary positions. On the basis of the body of information available and the similarities to {alpha}-ketoglutarate-dependent dioxygenases, a comprehensive mechanistic scheme for CS is proposed to account for this unusual enzymatic transformation.

Salowe, S.P.; Krol, W.J.; Iwata-Reuyl, D.; Townsend, C.A. (Johns Hopkins Univ., Baltimore, MD (United States))

1991-02-26

231

Formation of gold and gold sulfide nanoparticles and mesoscale intermediate structures in the reactions of aqueous HAuCl4 with sulfide and citrate ions.  

PubMed

The effects of the molar ratio of sodium sulfide to chloroauric acid in the range of 0.5 to 5 and the time factor on the formation of the nanoparticles (NPs) of metallic Au, Au(2)S or their mixtures have been studied applying in situ and ex situ techniques (UV-Vis absorption spectroscopy, potentiometry, TEM, SPM, SERS, XPS). The products and intermediates have been compared with those for the reduction of chloroaurate with citrate ions and combinations of citrate and sulfide ions. An increase in the concentration of sulfide ions accelerates the reduction of Au(iii) complexes but hinders the nucleation and growth of Au NPs, resulting in a prolonged period before the appearance of plasmon peaks. The electrochemical potential is not directly associated with the plasmon intensities, although the potential sharply decreases simultaneously with a blue shift of the near-IR peak emerging with the Na(2)S/HAuCl(4) ratios of 0.5 to 1.5. It was concluded that the peak is due to longitudinal plasmon resonance of gold nanoplates. Au(2)S NPs, the nucleation of which is effectively inhibited, and probably some structures and fragments visible in TEM and AFM, including 2-5 nm Au NPs, crystallize in part outside the solutions. The evidence of partially liquid mesoscale structures comprising intermediate gold species as precursors of nanoparticles is presented, and their origin, ex situ transformation and role in the reaction mechanisms are discussed. PMID:19551214

Mikhlin, Yuri; Likhatski, Maxim; Karacharov, Anton; Zaikovski, Vladimir; Krylov, Alexander

2009-04-20

232

Construction of the Octose 8-Phosphate Intermediate in Lincomycin A Biosynthesis: Characterization of the Reactions Catalyzed by LmbR and LmbN  

PubMed Central

Lincomycin A is a potent antimicrobial agent noted for its unusual C1 methylmercapto-substituted eight-carbon sugar. Despite its long clinical history for the treatment of Grampositive infections, the biosynthesis of the C8-sugar, methylthiolincosamide (MTL), is poorly understood. Here, we report our studies of the two initial enzymatic steps in the MTL biosynthetic pathway leading to the identification of D-erythro-D-gluco-octose 8-phosphate as a key intermediate. Our experiments demonstrate that this intermediate is formed via a transaldol reaction catalyzed by LmbR using D-fructose 6-phosphate or D-sedoheptulose 7-phosphate as the C3 donor and D-ribose 5-phosphate as the C5 acceptor. Subsequent 1,2-isomerization catalyzed by LmbN converts the resulting 2-keto C8-sugar (octulose 8-phosphate) to octose 8-phosphate. These results provide, for the first time, in vitro evidence revealing the biosynthetic origin of the C8 backbone of MTL.

Sasaki, Eita; Lin, Chia-I; Lin, Ke-Yi; Liu, Hung-wen

2012-01-01

233

On the origin of cytotoxicity of the natural product varacin. A novel example of a pentathiepin reaction that provides evidence for a triatomic sulfur intermediate.  

PubMed

A density functional theoretical study is presented, which implicates a novel S(3)-cleavage in the decomposition of a pentathiepin. This study predicts an interconversion between a pentathiepin and an open-chain polysulfur ion intermediate from which a key determinant in the chemistry then follows. Expulsion of diatomic sulfur, S(2), is unlikely from the unimolecular collapse of the open-chain polysulfur ion. Instead, S(3) can dissociate due to an unusually long and weak sulfur-sulfur (S4-S5) bond. A mechanistic picture now emerges which predicts that the novel S-S cleavage reaction and the unanticipated S(3) fragmentation are a result of delocalization of the negative charge within the remaining carbon-sulfur fragment. The computed results presented here reveal a new aspect to the chemistry of pentathiepins, that of S(3) unit transfer, which is proposed to have significance in the mechanism of cytotoxicity of the natural product varacin, 1. PMID:11603989

Greer, A

2001-10-24

234

Preparation and characterization of bonded silica hydride intermediate from triethoxysilane and dimethylmethoxysilane using supercritical carbon dioxide and dioxane as reaction medium.  

PubMed

This research examines bonding methodology, surface coverage and silanol conversion efficiencies on the preparation of silica hydride (SiH) intermediate from triethoxysilane (TES) and dimethylmethoxysilane (DMMS) using sc-CO(2) and dioxane as reaction solvent. Under sc-CO(2) reaction conditions (at temperature and pressure of 100 °C, 414 bar, respectively and 3h reaction time), the surface coverages of SiH (evaluated from %C obtained from elemental analysis) prepared with DMMS (3.39 ?mol/m(2)) and TES (4.46 ?mol/m(2)) increased by 2- and 4-folds respectively, when compared to reaction performed in dioxane (2.66 ?mol/m(2), SiH, DMMS and 0.69 ?mol/m(2), SiH, TES). The relatively higher surface coverage of SiH from TES over DMMS generated in sc-CO(2) is due to the inherent trialkoxy moiety of the TES that favours siloxane crosslinkage, forming polymeric surface attachments to yield a higher ligand density than the monomeric DMMS ligand. A conversion efficiency of ?84.4% of SiH prepared from TES in sc-CO(2) estimated from (29)Si CP/MAS NMR analysis is comparable to TES silanization in dioxane or toluene. Moreover, silica hydride (SiH) conversion efficiency of ca. 42.4% achieved for the hydride intermediate prepared from DMMS in sc-CO(2) is more superior to 33.3% efficiency obtained in dioxane. The differences in conversion efficiencies is attributed to the ability of sc-CO(2) being able to access silica pores that are inaccessible in organic solvents. Bonded silica hydride from TES, DMMS prepared in sc-CO(2) were characterized using elemental analysis, thermogravimetric analysis (TGA), BET surface area, Fourier transform infrared (FI-IR) and solid state NMR spectroscopy. Silica hydride technology/chemical functionalization of silica in sc-CO(2) avoid extended purification steps (i.e. filtration and washing), generation of waste organic solvent and the need of costly or energy consuming drying processing with improved modification efficiency. PMID:22446079

Ashu-Arrah, Benjamin A; Glennon, Jeremy D; Albert, Klaus

2012-03-03

235

On the accuracy of different theoretical models in the prediction of neutron induced reaction cross-sections at intermediate energies  

SciTech Connect

An extensive assessment of the predictive capabilities of different nuclear models in the reproduction of experimental activation and transmutation cross-sections for neutron induced reactions is presented. Experimental EXFOR data have been processed and treated in order to systematically analyze all the available measurements for target nuclei from {sup 27}Al to {sup 209}Bi with energy of the projectile above 0.1 MeV. Experimental data have been compared with the correspondent simulations performed by means of the TALYS code and the ALICE/ASH code using different models for the description of the nuclear level densities at equilibrium states, these being both phenomenological and microscopic ones. The comparison between measurements and calculations is quantified by means of different statistical deviation factors, which are given as functions of the target nuclei mass number and of different channels. Recommendations are provided to the users on the best combinations of codes and models to optimize the accuracy of the simulations. Furthermore, the calculation of a of a 'mean model error' deviation factor has also been performed, making the results of this work also useful for the construction of covariance matrixes of 'model deficiencies' for a wide number of nuclides. (authors)

Mercatali, L.; Konobeyev, A.; Broeders, C. [Forschungszentrum Karlsruhe, Inst. for Reactor Safety, Hermann von Helmotz Platz 1, Eggenstein-Leopoldshafen D-76344 (Germany)

2006-07-01

236

[Intermediate phenotype of schizophrenia].  

PubMed

Genes are major contributors to schizophrenia. The intermediate phenotype concept represents a strategy for identifying risk genes for schizophrenia and for characterizing the neural systems affected by risk gene variants to elucidate quantitative, mechanistic aspects of brain function implicated in schizophrenia. Intermediate phenotypes are defined by being heritable, being able to measure quantitatively; being related to the disorder and its symptoms in the general population; being stable over time; showing increased expression in unaffected relatives of probands; and cosegregation with the disorder in families. Intermediate phenotypes in schizophrenia are neurocognition, neuroimaging, neurophysiology, etc. In this review, we present concept, recent work, and future perspective of intermediate phenotype. PMID:23678587

Hashimoto, Ryota

2013-04-01

237

Crystal structure of reaction intermediates in pyruvate class II aldolase: substrate cleavage, enolate stabilization, and substrate specificity.  

PubMed

Crystal structures of divalent metal-dependent pyruvate aldolase, HpaI, in complex with substrate and cleavage products were determined to 1.8-2.0 Å resolution. The enzyme·substrate complex with 4-hydroxy-2-ketoheptane-1,7-dioate indicates that water molecule W2 bound to the divalent metal ion initiates C3-C4 bond cleavage. The binding mode of the aldehyde donor delineated a solvent-filled capacious binding locus lined with predominantly hydrophobic residues. The absence of direct interactions with the aldehyde aliphatic carbons accounts for the broad specificity and lack of stereospecific control by the enzyme. Enzymatic complex structures formed with keto acceptors, pyruvate, and 2-ketobutyrate revealed bidentate interaction with the divalent metal ion by C1-carboxyl and C2-carbonyl oxygens and water molecule W4 that is within close contact of the C3 carbon. Arg(70) assumes a multivalent role through its guanidinium moiety interacting with all active site enzymatic species: C2 oxygen in substrate, pyruvate, and ketobutyrate; substrate C4 hydroxyl; aldehyde C1 oxygen; and W4. The multiple interactions made by Arg(70) stabilize the negatively charged C4 oxygen following proton abstraction, the aldehyde alignment in aldol condensation, and the pyruvate enolate upon aldol cleavage as well as support proton exchange at C3. This role is corroborated by loss of aldol cleavage ability and pyruvate C3 proton exchange activity and by a 730-fold increase in the dissociation constant toward the pyruvate enolate analog oxalate in the R70A mutant. Based on the crystal structures, a mechanism is proposed involving the two enzyme-bound water molecules, W2 and W4, in acid/base catalysis that facilitates reversible aldol cleavage. The same reaction mechanism promotes decarboxylation of oxaloacetate. PMID:22908224

Coincon, Mathieu; Wang, Weijun; Sygusch, Jurgen; Seah, Stephen Y K

2012-08-20

238

Unimolecular dissociation of the propargyl radical intermediate of the CH+C2H2 and C+C2H3 reactions  

NASA Astrophysics Data System (ADS)

This paper examines the unimolecular dissociation of propargyl (HCCCH2) radicals over a range of internal energies to probe the CH+HCCH and C+C2H3 bimolecular reactions from the radical intermediate to products. The propargyl radical was produced by 157 nm photolysis of propargyl chloride in crossed laser-molecular beam scattering experiments. The H-loss and H2 elimination channels of the nascent propargyl radicals were observed. Detection of stable propargyl radicals gave an experimental determination of 71.5 (+5/-10) kcal/mol as the lowest barrier to dissociation of the radical. This barrier is significantly lower than predictions for the lowest barrier to the radical's dissociation and also lower than calculated overall reaction enthalpies. Products from both H2+HCCC and H+C3H2 channels were detected at energies lower than what has been theoretically predicted. An HCl elimination channel and a minor C-H fission channel were also observed in the photolysis of propargyl chloride.

McCunn, Laura R.; Fitzpatrick, Benjamin L.; Krisch, Maria J.; Butler, Laurie J.; Liang, Chi-Wei; Lin, Jim J.

2006-10-01

239

Reaction pathways of 2-iodoacetic acid on Cu(100): coverage-dependent competition between C-I bond scission and COOH deprotonation and identification of surface intermediates.  

PubMed

The chemistry of 2-iodoacetic acid on Cu(100) has been studied by a combination of reflection-absorption infrared spectroscopy (RAIRS), X-ray photoelectron spectroscopy (XPS), temperature-programmed reaction/desorption (TPR/D), and theoretical calculations based on density functional theory for the optimized intermediate structures. In the thermal decomposition of ICH(2)COOH on Cu(100) with a coverage less than a half monolayer, three surface intermediates, CH(2)COO, CH(3)COO, and CCOH, are generated and characterized spectroscopically. Based on their different thermal stabilities, the reaction pathways of ICH(2)COOH on Cu(100) at temperatures higher than 230 K are established to be ICH(2)COOH --> CH(2)COO + H + I, CH(2)COO + H --> CH(3)COO, and CH(3)COO --> CCOH. Theoretical calculations suggest that the surface CH(2)COO has the skeletal plane, with delocalized pi electrons, approximately parallel to the surface. The calculated Mulliken charges agree with the detected binding energies for the two carbon atoms in CH(2)COO on Cu(100). The CCOH derived from CH(3)COO decomposition has a CC stretching frequency at 2025 cm(-1), reflecting its triple-bond character which is consistent with the calculated CCOH structure on Cu(100). Theoretically, CCOH at the bridge and hollow sites has a similar stability and is adsorbed with the molecular axis approximately perpendicular to the surface. The TPR/D study has shown the evolution of the products of H(2), CH(4), H(2)O, CO, CO(2), CH(2)CO, and CH(3)COOH from CH(3)COO decomposition between 500 and 600 K and the formation of H(2) and CO from CCOH between 600 and 700 K. However, at a coverage near one monolayer, the major species formed at 230 and 320 K are proposed to be ICH(2)COO and CH(3)COO. CH(3)COO becomes the only species present on the surface at 400 K. That is, there are two reaction pathways of ICH(2)COOH --> ICH(2)COO + H and ICH(2)COO + H --> CH(3)COO + I (possibly via CH(2)COO), which are different from those observed at lower coverages. Because the C-I bond dissociation of iodoethane on copper single crystal surfaces occurs at approximately 120 K and that the deprotonation of CH(3)COOH on Cu(100) occurs at approximately 220 K, the preferential COOH dehydrogenation of monolayer ICH(2)COOH is an interesting result, possibly due to electronic and/or steric effects. PMID:20356026

Lin, Yi-Shiue; Lin, Jain-Shiun; Liao, Yung-Hsuan; Yang, Che-Ming; Kuo, Che-Wei; Lin, Hong-Ping; Fan, Liang-Jen; Yang, Yaw-Wen; Lin, Jong-Liang

2010-06-01

240

Synthesis of a new intermediate for bioactive Lamellarins.  

PubMed

This paper reports two methods of synthesis for 1,2,4-trimethoxy-5-(1-methyl-2-phenyl-vinyl)-benzene, which was a key intermediate to synthesize the various Lamellarins. One method is by using the Wittig-Horner reaction and another is by the Grignard reaction. By conducting contrast experiments, we got the optimal reaction parameters for high yields. The newly formed intermediate was identified by means of IR spectrum, (1)H-NMR, (13)C-NMR and melting point measurements. PMID:18458442

He, Yu-Rong; You, Ye-Cheng; Hu, Jie-Han; Wang, Ai-Ling; Yu, Xiao-Song; Hu, Dai-Hua

2007-03-14

241

A Novel Tool for Studying Auxin-Metabolism: The Inhibition of Grapevine Indole-3-Acetic Acid-Amido Synthetases by a Reaction Intermediate Analogue  

PubMed Central

An important process for the regulation of auxin levels in plants is the inactivation of indole-3-acetic acid (IAA) by conjugation to amino acids. The conjugation reaction is catalysed by IAA-amido synthetases belonging to the family of GH3 proteins. Genetic approaches to study the biological significance of these enzymes have been hampered by large gene numbers and a high degree of functional redundancy. To overcome these difficulties a chemical approach based on the reaction mechanism of GH3 proteins was employed to design a small molecule inhibitor of IAA-amido synthetase activity. Adenosine-5?-[2-(1H-indol-3-yl)ethyl]phosphate (AIEP) mimics the adenylated intermediate of the IAA-conjugation reaction and was therefore proposed to compete with the binding of MgATP and IAA in the initial stages of catalysis. Two grapevine IAA-amido synthetases with different catalytic properties were chosen to test the inhibitory effects of AIEP in vitro. GH3-1 has previously been implicated in the grape berry ripening process and is restricted to two amino acid substrates, whereas GH3-6 conjugated IAA to 13 amino acids. AIEP is the most potent inhibitor of GH3 enzymes so far described and was shown to be competitive against MgATP and IAA binding to both enzymes with Ki-values 17-68-fold lower than the respective Km-values. AIEP also exhibited in vivo activity in an ex planta test system using young grape berries. Exposure to 5–20 µM of the inhibitor led to decreased levels of the common conjugate IAA-Asp and reduced the accumulation of the corresponding Asp-conjugate upon treatment with a synthetic auxin. AIEP therefore represents a novel chemical probe with which to study IAA-amido synthetase function.

Bottcher, Christine; Dennis, Eric G.; Booker, Grant W.; Polyak, Steven W.; Boss, Paul K.; Davies, Christopher

2012-01-01

242

First case series of emerging Rickettsial neonatal sepsis identified by polymerase chain reaction-based deoxyribonucleic acid sequencing.  

PubMed

Purpose: To detect and identify the aetiological agent in the peripheral blood from the cases of neonatal sepsis. Materials and Methods: Four neonates from geographically different regions of South India presented with signs of neonatal sepsis and all the routine clinical and laboratory investigations were performed. Blood culture by Bac T Alert 3D was negative. To establish the aetiology, polymerase chain reaction (PCR) for eubacterial genome and subsequent amplification with Gram positive and Gram negative primers were performed followed by deoxyribonucleic acid (DNA) sequencing. Results: PCR for the detection of eubacterial genome was positive in all the four neonates and further amplification with designed Gram positive and Gram negative primers revealed the presence of Gram negative bacteria. The amplicons were identified as Orientia tsutsugamushi in three neonates and Coxiella burnetti in the other neonate. Multalin analysis was done to further characterise the strain variation among the three strains. Conclusion: PCR-based DNA sequencing is a rapid and reliable diagnostic tool to identify the aetiological agents of neonatal sepsis. This is the first case series of emerging Rickettsial neonatal sepsis in India . PMID:24064639

Aarthi, P; Bagyalakshmi, R; Mohan, K R; Krishna, M; Nitin, M; Madhavan, H N; Kalyani, S

243

The thiolase reaction mechanism: the importance of Asn316 and His348 for stabilizing the enolate intermediate of the Claisen condensation.  

PubMed

The biosynthetic thiolase catalyzes a Claisen condensation reaction between acetyl-CoA and the enzyme acetylated at Cys89. Two oxyanion holes facilitate this catalysis: oxyanion hole I stabilizes the enolate intermediate generated from acetyl-CoA, whereas oxyanion hole II stabilizes the tetrahedral intermediate of the acetylated enzyme. The latter intermediate is formed when the alpha-carbanion of acetyl-CoA enolate reacts with the carbonyl carbon of acetyl-Cys89, after which C-C bond formation is completed. Oxyanion hole II is made of two main chain peptide NH groups, whereas oxyanion hole I is formed by a water molecule (Wat82) and NE2(His348). Wat82 is anchored in the active site by an optimal set of hydrogen bonding interactions, including a hydrogen bond to ND2(Asn316). Here, the importance of Asn316 and His348 for catalysis has been studied; in particular, the properties of the N316D, N316A, N316H, H348A, and H348N variants have been determined. For the N316D variant, no activity could be detected. For each of the remaining variants, the k(cat)/K(m) value for the Claisen condensation catalysis is reduced by a factor of several hundred, whereas the thiolytic degradation catalysis is much less affected. The crystal structures of the variants show that the structural changes in the active site are minimal. Our studies confirm that oxyanion hole I is critically important for the condensation catalysis. Removing either one of the hydrogen bond donors causes the loss of at least 3.4 kcal/mol of transition state stabilization. It appears that in the thiolytic degradation direction, oxyanion hole I is not involved in stabilizing the transition state of its rate limiting step. However, His348 has a dual role in the catalytic cycle, contributing to oxyanion hole I and activating Cys89. The analysis of the hydrogen bonding interactions in the very polar catalytic cavity shows the importance of two conserved water molecules, Wat82 and Wat49, for the formation of oxyanion hole I and for influencing the reactivity of the catalytic base, Cys378, respectively. Cys89, Asn316, and His348 form the CNH-catalytic triad of the thiolase superfamily. Our findings are also discussed in the context of the importance of this triad for the catalytic mechanism of other enzymes of the thiolase superfamily. PMID:19842716

Meriläinen, Gitte; Poikela, Visa; Kursula, Petri; Wierenga, Rik K

2009-11-24

244

Demonstration of spatial light modulation by using reversible photochemical reaction of bacteriorhodopsin between ground state and K intermediate at room temperature  

NASA Astrophysics Data System (ADS)

We have experimentally studied about spatial light modulation by using the early photochemical product of bacteriorhodopsin(bR) called K intermediate at room temperature. In general, it is necessary for using K intermediate to lower the temperature of bR under 77 K. In this paper, we propose a new technique to use K intermediate at room temperature. We demonstrated experimentally spatial light modulation by using K intermediate at room temperature.

Iwamoto, Kyohei; Konishi, Tsuyoshi; Okada-Shudo, Yoshiko; Itoh, Kazuyoshi; Ichioka, Yoshiki

245

MCNP{trademark} simulations for identifying environmental contaminants using prompt gamma-rays from thermal neutron capture reactions  

SciTech Connect

The primary purposes of the Multispectral Neutron Logging Project, (MSN Project, funded by the U.S. Department of Energy), were to assess the effectiveness of existing neutron- induced spectral gamma-ray logging techniques for identifying environmental contaminants along boreholes, to further improve the technology, and to transfer that technology to industry. Using a pulsed neutron source with a high-resolution gamma-ray detector, spectra from thermal neutron capture reactions may be used to identify contaminants in the borehole environment. Direct borehole measurements such as this complement physical sampling and are useful in environmental restoration projects where characterization of contaminated sites is required and long-term monitoring may be needed for many years following cleanup or stabilization. In the MSN Project, a prototype logging instrument was designed which incorporated a pulsed 14-MeV neutron source and HPGe detector. Experimental measurements to determine minimum detection thresholds with the prototype instrument were conducted in the variable-contaminant test model for Cl, Cd, Sm, Gd, and Hg. We benchmarked an enhanced version of the Monte Carlo N-Particle computer code MCNP{trademark} using experimental data for Cl provide by our collaborators and experimental data from the variable-contaminant test model. MCNP was then used to estimate detection thresholds for the other contaminants used in the variable-contaminant model with the goal of validating the use of MCNP to estimate detection thresholds for many other contaminants that were not measured.

Frankle, S.C.; Conaway, J.G.

1996-12-31

246

Crystal structures of I-SceI complexed to nicked DNA substrates: snapshots of intermediates along the DNA cleavage reaction pathway  

SciTech Connect

I-SceI is a homing endonuclease that specifically cleaves an 18-bp double-stranded DNA. I-SceI exhibits a strong preference for cleaving the bottom strand DNA. The published structure of I-SceI bound to an uncleaved DNA substrate provided a mechanism for bottom strand cleavage but not for top strand cleavage. To more fully elucidate the I-SceI catalytic mechanism, we determined the X-ray structures of I-SceI in complex with DNA substrates that are nicked in either the top or bottom strands. The structures resemble intermediates along the DNA cleavage reaction. In a structure containing a nick in the top strand, the spatial arrangement of metal ions is similar to that observed in the structure that contains uncleaved DNA, suggesting that cleavage of the bottom strand occurs by a common mechanism regardless of whether this strand is cleaved first or second. In the structure containing a nick in the bottom strand, a new metal binding site is present in the active site that cleaves the top strand. This new metal and a candidate nucleophilic water molecule are correctly positioned to cleave the top strand following bottom strand cleavage, providing a plausible mechanism for top strand cleavage.

Moure, Carmen M.; Gimble, Frederick S.; Quiocho, Florante A. (Baylor); (Purdue)

2008-07-28

247

A new experimental approach to investigate intermediate-energy proton elastic scattering and breakup reactions on exotic nuclei in inverse kinematics  

NASA Astrophysics Data System (ADS)

We report on a new experimental setup for the investigation of proton induced reactions on exotic nuclei in inverse kinematics. It was installed and successfully used in the scattering study of intermediate-energy protons (˜700MeV/u) on neutron-rich nuclei 6,8He produced with the FRagment Separator (FRS) at the GSI facility, Darmstadt. A new pure liquid-hydrogen target was successfully adapted allowing to obtain low-background data as compared to commonly used (CH2)n targets.Absolute differential cross-sections for elastic (p,6,8He) scattering were obtained at angles corresponding to 0.05?|t|?0.125 (GeV/c)2 of the four-momentum transfer squared (-t) leading to the first diffraction minimum and spanning more than two orders of magnitude. They complement an earlier measurement at smaller angles 0.0025?|t|?0.05 (GeV/c)2 performed at the same energy with an active target. Both data sets agree well in the overlap region t?0.05 (GeV/c)2 and enable a refined and comparative study of the radial distribution of the nuclear matter density.

Kiselev, O. A.; Aksouh, F.; Bleile, A.; Bochkarev, O. V.; Chulkov, L. V.; Cortina-Gil, D.; Dobrovolsky, A. V.; Egelhof, P.; Geissel, H.; Hellström, M.; Isaev, N. B.; Komkov, B. G.; Matoš, M.; Moroz, F. V.; Münzenberg, G.; Mutterer, M.; Mylnikov, V. A.; Neumaier, S. R.; Pribora, V. N.; Seliverstov, D. M.; Sergueev, L. O.; Shrivastava, A.; Sümmerer, K.; Weick, H.; Winkler, M.; Yatsoura, V. I.

2011-06-01

248

Ab initio study of hypervalent sulfur hydrides as model intermediates in the interconversion reactions of compounds containing sulfur-sulfur bonds  

SciTech Connect

Ab initio MO calculations involving the 4-31G* basis set have been used to predict the equilibrium geometries of the hypervalent sulfur hydrides H/sub 2/SS, (HS)/sub 2/SS, H/sub 2/S(SH)/sub 2/, H/sub 2/S(SSH)/sub 2/, and the cyclic H/sub 4/S/sub 4/. The energy changes in their formation from appropriate sulfanes H/sub 2/S/sub n/ (n = 1-4) have been studied with the 6-31G* basis set including the correction for the electron correlation by the second- and third-order Moeller-Plesset perturbation theory. The results are used to discuss the possible pathways in the interconversion reactions between various sulfur compounds containing cumulated SS bonds, for example, the formation of S/sub 7/ from S/sub 8/ for which hypervalent intermediates have been proposed recently. Comparison with experimental evidence is made whenever possible.

Laitinen, R.S.; Pakkanen, T.A.; Steudel, R.

1987-02-04

249

Photocatalytic degradation of propachlor in aqueous TiO2 suspensions. Determination of the reaction pathway and identification of intermediate products by various analytical methods.  

PubMed

The light-induced degradation of propachlor (2-chloro-N-isopropylacetanilide) under simulated solar irradiation has been investigated in aqueous solutions containing TiO2 suspensions as photocatalysts. The study focuses on the identification of possible intermediate products and the determination of inorganic ions formed during the process, using several powerful analytical techniques such as gas chromatography mass-spectrometry (GC-MS) and ion chromatography. The primary degradation of propachlor has been a fast process with a half-live time of 2.3 min and followed pseudo-first-order kinetics according to the Langmuir-Hinshelwood model. The mineralization of the organic carbon to CO2 after 240 min of irradiation was found to be < 63%. The corresponding stoichiometric transformation of organic chlorine into chloride ion was reached in 30 min, whereas oxidation of nitrogen to nitrate ions took place at delayed irradiation times. Various aromatic intermediates have been identified by GC/MS techniques during the treatment, which were involved into three tentative degradation routes. One, was based on the dechlorination through positive holes or solvated electrons to form the hydroxy or aliphatic derivative. The second route consists of the rupture of amide bond or the N-C bond via nitrogen ionization by positive holes and through the ring hydroxylation, respectively. Finally, the third possible degradation route was based on hydrogen abstraction by the hydroxyl radicals or positive holes, followed either by the addition of oxygen to the alkyl radical or the decomposition of the peroxyl radical formed. From the analytical data, a possible multi-step degradation scheme was proposed. This work points to the necessity of extended knowledge of the successive steps in a solar-assisted detoxification process. PMID:12146860

Konstantinou, Ioannis K; Sakkas, Vasilios A; Albanis, Triantafyllos A

2002-06-01

250

Chromophoric spin-labeled beta-lactam antibiotics for ENDOR structural characterization of reaction intermediates of class A and class C beta-lactamases.  

PubMed

The chromophoric spin-label substrate 6-N-[3-(2,2,5,5-tetramethyl-1-oxypyrrolin-3-yl)-propen-2-oyl]penicillanic acid (SLPPEN) was synthesized by acylation of 6-aminopenicillanic acid with the acid chloride of 3-(2,2,5,5-tetramethyl-1-oxypyrrolinyl)-2-propenoic acid and characterized by physical methods. By application of angle-selected electron nuclear double resonance (ENDOR), we have determined the molecular structure of SLPPEN in solution. SLPPEN exhibited UV absorption properties that allowed accurate monitoring of the kinetics of its enzyme-catalyzed hydrolysis. The maximum value of the (substrate-product) difference extinction coefficient was 2824 M(-1) cm(-1) at 275 nm compared to 670 M(-1) cm(-1) at 232 nm for SLPEN [J. Am. Chem. Soc. 117 (1995) 6739]. For SLPPEN, the steady-state kinetic parameters kcat and kcat/KM, determined under initial velocity conditions, were 637 +/- 36 s(-1) and 13.8 +/- 1.4 x 10(6) M(-1) s(-1), respectively, for hydrolysis catalyzed by TEM-1 beta-lactamase of E. coli, and 0.5 +/- 0.04 s(-1) and 3.9 +/- 0.4 x 10(4) M(-1) s(-1) for hydrolysis catalyzed by the beta-lactamase of Enterobacter cloacae P99. We have also observed "burst kinetics" for the hydrolysis of SLPPEN with P99 beta-lactamase, indicative of formation of an acylenzyme reaction intermediate. In DMSO:H2O (30:70, v:v) cryosolvent mixtures buffered to pH* 7.0, the half-life of the acylenzyme intermediate formed with the P99 enzyme at -5 degrees C was > or = 3 min, suitable for optical characterization. The observation of burst kinetics in the hydrolysis of SLPPEN catalyzed by P99 beta-lactamase suggests that this chromophoric spin-labeled substrate is differentially sensitive to active site interactions underlying the cephalosporinase and penicillinase reactivity of this class C enzyme. PMID:15134725

Mustafi, Devkumar; Hofer, Jennifer E; Huang, Wanzhi; Palzkill, Timothy; Makinen, Marvin W

2004-05-01

251

Demonstration of spatial light modulation by using reversible photochemical reaction of bacteriorhodopsin between ground state and K intermediate at room temperature  

Microsoft Academic Search

We have experimentally studied about spatial light modulation by using the early photochemical product of bacteriorhodopsin(bR) called K intermediate at room temperature. In general, it is necessary for using K intermediate to lower the temperature of bR under 77 K. In this paper, we propose a new technique to use K intermediate at room temperature. We demonstrated experimentally spatial light

Kyohei Iwamoto; Tsuyoshi Konishi; Yoshiko Okada-Shudo; Kazuyoshi Itoh; Yoshiki Ichioka

2002-01-01

252

Isoporphyrin Intermediate in Heme Oxygenase Catalysis  

PubMed Central

Human heme oxygenase-1 (hHO-1) catalyzes the O2- and NADPH-dependent oxidation of heme to biliverdin, CO, and free iron. The first step involves regiospecific insertion of an oxygen atom at the ?-meso carbon by a ferric hydroperoxide and is predicted to proceed via an isoporphyrin ?-cation intermediate. Here we report spectroscopic detection of a transient intermediate during oxidation by hHO-1 of ?-meso-phenylheme-IX, ?-meso-(p-methylphenyl)-mesoheme-III, and ?-meso-(p-trifluoromethylphenyl)-mesoheme-III. In agreement with previous experiments (Wang, J., Niemevz, F., Lad, L., Huang, L., Alvarez, D. E., Buldain, G., Poulos, T. L., and Ortiz de Montellano, P. R. (2004) J. Biol. Chem. 279, 42593–42604), only the ?-biliverdin isomer is produced with concomitant formation of the corresponding benzoic acid. The transient intermediate observed in the NADPH-P450 reductase-catalyzed reaction accumulated when the reaction was supported by H2O2 and exhibited the absorption maxima at 435 and 930 nm characteristic of an isoporphyrin. Product analysis by reversed phase high performance liquid chromatography and liquid chromatography electrospray ionization mass spectrometry of the product generated with H2O2 identified it as an isoporphyrin that, on quenching, decayed to benzoylbiliverdin. In the presence of H218O2, one labeled oxygen atom was incorporated into these products. The hHO-1-isoporphyrin complexes were found to have half-lives of 1.7 and 2.4 h for the p-trifluoromethyl- and p-methyl-substituted phenylhemes, respectively. The addition of NADPH-P450 reductase to the H2O2-generated hHO-1-isoporphyrin complex produced ?-biliverdin, confirming its role as a reaction intermediate. Identification of an isoporphyrin intermediate in the catalytic sequence of hHO-1, the first such intermediate observed in hemoprotein catalysis, completes our understanding of the critical first step of heme oxidation.

Evans, John P.; Niemevz, Fernando; Buldain, Graciela; de Montellano, Paul Ortiz

2008-01-01

253

Hydrogen storage in LiAlH4: predictions of the crystal structures and reaction mechanisms of intermediate phases from quantum mechanics.  

PubMed

We use the density functional theory and x-ray and neutron diffraction to investigate the crystal structures and reaction mechanisms of intermediate phases likely to be involved in decomposition of the potential hydrogen storage material LiAlH(4). First, we explore the decomposition mechanism of monoclinic LiAlH(4) into monoclinic Li(3)AlH(6) plus face-centered cubic (fcc) Al and hydrogen. We find that this reaction proceeds through a five-step mechanism with an overall activation barrier of 36.9 kcal/mol. The simulated x ray and neutron diffraction patterns from LiAlH(4) and Li(3)AlH(6) agree well with experimental data. On the other hand, the alternative decomposition of LiAlH(4) into LiAlH(2) plus H(2) is predicted to be unstable with respect to that through Li(3)AlH(6). Next, we investigate thermal decomposition of Li(3)AlH(6) into fcc LiH plus Al and hydrogen, occurring through a four-step mechanism with an activation barrier of 17.4 kcal/mol for the rate-limiting step. In the first and second steps, two Li atoms accept two H atoms from AlH(6) to form the stable Li-H-Li-H complex. Then, two sequential H(2) desorption steps are followed, which eventually result in fcc LiH plus fcc Al and hydrogen: Li(3)AlH(6)(monoclinic)-->3 LiH(fcc)+Al(fcc)+3/2 H(2) is endothermic by 15.8 kcal/mol. The dissociation energy of 15.8 kcal/mol per formula unit compares to experimental enthalpies in the range of 9.8-23.9 kcal/mol. Finally, we explore thermal decomposition of LiH, LiH(s)+Al(s)-->LiAl(s)+12H(2)(g) is endothermic by 4.6 kcal/mol. The B32 phase, which we predict as the lowest energy structure for LiAl, shows covalent bond characters in the Al-Al direction. Additionally, we determine that transformation of LiH plus Al into LiAlH is unstable with respect to transformation of LiH through LiAl. PMID:15549945

Kang, Jeung Ku; Lee, Jai Young; Muller, Richard P; Goddard, William A

2004-12-01

254

Hydrogen storage in LiAlH4 : predictions of the crystal structures and reaction mechanisms of intermediate phases from quantum mechanics.  

SciTech Connect

We use the density functional theory and x-ray and neutron diffraction to investigate the crystal structures and reaction mechanisms of intermediate phases likely to be involved in decomposition of the potential hydrogen storage material LiAlH{sub 4}. First, we explore the decomposition mechanism of monoclinic LiAlH4 into monoclinic Li{sub 3}AlH{sub 6} plus face-centered cubic (fcc) Al and hydrogen. We find that this reaction proceeds through a five-step mechanism with an overall activation barrier of 36.9 kcal/mol. The simulated x ray and neutron diffraction patterns from LiAlH{sub 4} and Li{sub 3}AlH{sub 6} agree well with experimental data. On the other hand, the alternative decomposition of LiAlH{sub 4} into LiAlH2 plus H2 is predicted to be unstable with respect to that through Li{sub 3}AlH{sub 6}. Next, we investigate thermal decomposition of Li{sub 3}AlH{sub 6} into fcc LiH plus Al and hydrogen, occurring through a four-step mechanism with an activation barrier of 17.4 kcal/mol for the rate-limiting step. In the first and second steps, two Li atoms accept two H atoms from AlH{sub 6} to form the stable Li-H-Li-H complex. Then, two sequential H2 desorption steps are followed, which eventually result in fcc LiH plus fcc Al and hydrogen: Li{sub 3}AlH{sub 6}(monoclinic) {yields} 3 LiH(fcc) + Al(fcc) + 3/2 H{sub 2} is endothermic by 15.8 kcal/mol. The dissociation energy of 15.8 kcal/mol per formula unit compares to experimental enthalpies in the range of 9.8-23.9 kcal/mol. Finally, we explore thermal decomposition of LiH, LiH(s) + Al(s) {yields} LiAl(s) + 1/2 H{sub 2}(g) is endothermic by 4.6 kcal/mol. The B32 phase, which we predict as the lowest energy structure for LiAl, shows covalent bond characters in the Al-Al direction. Additionally, we determine that transformation of LiH plus Al into LiAlH is unstable with respect to transformation of LiH through LiAl.

Lee, Jai Young (KAIST, Republic of Korea); Muller, Richard Partain; Kang, Jeung Ku (KAIST, Republic of Korea); Goddard, William A., III (California Institute of Technology, Pasadena, CA)

2005-06-01

255

Intermediates in wet oxidation of cellulose: identification of hydroxyl radical and characterization of hydrogen peroxide  

Microsoft Academic Search

Some intermediates were identified during the course of non-catalytic wet air oxidation (WAO) of cellulose. Concentrations of by-products were determined in function of temperature and reaction time. This study also showed that hydroxyl radicals (HO) and hydrogen peroxide (H2O2) play the role of intermediates in the initial phase of the oxidation reactions. Hydroxyl radicals were detected by the electron spin

Raphaël Robert; Stéphane Barbati; Natacha Ricq; Maurice Ambrosio

2002-01-01

256

Identification of intermediates in the catalytic cycle of chloroperoxidase  

Microsoft Academic Search

Background: Chloroperoxidase (CPO) is the most versatile of the hemethiolate proteins, catalyzing the chlorination of activated C?H bonds and reactions reminiscent of peroxidase, catalase, and cytochrome P450. Despite 30 years of continuous efforts, no intermediates of the enzyme's catalytic cycle have been identified except for compound I. Thus, in the absence of conclusive evidence it is generally believed that the

Hans-Achim Wagenknecht; Wolf-Dietrich Woggon

1997-01-01

257

Use of polymerase chain reaction to identify Brucella abortus strain RB51 among Brucella field isolates from cattle in Italy.  

PubMed

Brucella abortus strain RB51, a rough mutant of the B. abortus 2308 virulent strain, was recently approved in the United States as the official vaccine for brucellosis in cattle. Following recent evidence of unauthorized use of RB51 vaccine in Italy, where the use of vaccines for brucellosis is no longer allowed, the suitability of an RB51-specific polymerase chain reaction assay for identifying the RB51 strain among Brucella field isolates from cattle in Italy was investigated. The oligonucleotide primers used in this study, belonging to a six-primer cocktail for Brucella species previously described by other authors, allowed the amplification of a 364-base pair (bp) fragment specific for RB51 and its parent strain 2308, and a 498-bp product specific for B. abortus. In addition, unresolved bands ranging from 600 to 700 bp were observed from RB51 strain. Brucella abortus biovars 1, 2 and 4 have only one specific sensitive 498-bp band. The B. abortus biovars 3, 5 and 6 did not give any signal. The 498-bp product from a reference Brucella strain was sequenced and submitted to EMBL with the accession number AJ271969 while the 364-bp fragment from RB51 strain was submitted to EMBL database with accession number AJ271968. The sequence studies confirmed the specificity of the detected fragments. No amplification was obtained by testing DNA from strains antigenically related to Brucella, such as Yersinia enterocolitica O:9, Escherichia coli O:157, Salmonella urbana and Pasteurella multocida. The results of this study indicate that this technique, in combination with specific serological tests, could be a useful diagnostic method to verify the use of RB51 vaccine and can contribute to the creation of a databank of circulating strains. PMID:11315520

Adone, R; Ciuchini, F; La Rosa, G; Marianelli, C; Muscillo, M

2001-03-01

258

Detection and identification of intermediates in the reaction of L-serine with Escherichia coli tryptophan synthase via rapid-scanning ultraviolet-visible spectroscopy  

SciTech Connect

Rapid-scanning stopped-flow (RSSF) UV-visible spectroscopy has been used to investigate the UV-visible absorption changes (300-550 nm) that occur in the spectrum of enzyme-bound pyridoxal 5'-phosphate during the reaction of L-serine with the alpha 2 beta 2 and beta 2 forms of Escherichia coli tryptophan synthase. In agreement with previous kinetic studies the reaction with alpha 2 beta 2 was found to occur in three detectable relaxations (1/tau 1 greater than 1/tau 2 greater than 1/tau 3). The RSSF data reveal that during tau 1, the internal aldimine, E(PLP), with lambda max = 412 nm (pH 7.8), undergoes rapid conversion to two transient species, one with lambda max congruent to 420 nm and one with lambda max congruent to 460 nm. These species decay in a biphasic process to a complicated final spectrum with lambda max congruent to 350 nm and with a broad envelope of absorbance extending out to approximately 525 nm. Analysis of the time-resolved spectra establishes that the spectral changes in tau 2 are nearly identical with the spectral changes in tau 3. These findings identify the serine Schiff base (the external aldimine) as the 420 nm absorbing, highly fluorescent transient; the species with lambda max congruent to 460 nm is the delocalized carbanion (quinoidal) species derived from abstraction of the alpha proton from the external aldimine. The reaction of L-serine with beta 2 consists of two relaxations and yields a quasi-stable species with lambda max = 420 nm, in good agreement with a previous report.

Drewe, W.F. Jr.; Dunn, M.F.

1985-07-16

259

Diminished CAGE Effect in {p}-H2: IR Identification of Intermediates in Addition Reactions of CL Atom with Unsaturated Hydrocarbons  

NASA Astrophysics Data System (ADS)

We report infrared absorption spectra of several free radicals produced upon reaction of Cl atoms with unsaturated hydrocarbons isolated in solid {p}-H2. Cl atoms were produced by in situ photodissociation of Cl2 isolated in solid {p}-H2 at 365 nm. In experiments with the Cl2/C6H6/{p}-H2 matrices, intense absorption features at 617.0, 719.8, 956.0, and 1430.5 Cm-1 and weaker ones at 577.1, 833.6, 876.8, 833.6, 983.0, 993.5, 1008.0, 1026.4, 1112.5, 1118.5, 1179.0, 1406.5, 1509.4, 2967.2, 3054.3, 3063.4, 3070.9, and 3083.9 Cm-1 appeared upon irradiation of the matrix at 365 nm and increased in intensity upon subsequent annealing of the matrix at 4.8 K for a few minutes. By comparison of vibrational wavenumbers and deuterium isotopic shifts predicted with the B3PW91 and MPW1PW91/aug-cc-pVTZ methods, these features are readily assigned to the ?-complex of ClC6H6 (chlorocyclohexadienyl radical), rather than the previously proposed ?-complex. In experiments with the Cl2/C2H2/{p}-H2 matrices, the 1-chloroethyl radicals (CHClCH3) and chloroethene (C2H3Cl) are identified as the main products of the Cl + C2H2 reaction in solid {p}-H2. The assignments of IR absorption lines at 738.2, 1027.6, 1283.4, 1377.1, 1426.6, 1442.6, and 2861.2 Cm-1 to 1-chloroethyl radicals are based on comparison of the observed vibrational wavenumbers and 13C- and D-isotopic shifts with those predicted with the B3LYP and MP2/aug-cc-pVDZ methods. These results indicate that the primary products of the addition reaction Cl + C2H2, the 2-chlorovinyl radicals, are unstable; they react readily with {p}-H2 to form CHClCH3 and C2H3Cl. If time permits, other examples such as Cl + 1, 3-butadien and H + C6H6 or C6H5Cl will be discussed. These results serve as excellent examples to demonstrate that the diminished cage effect of solid {p}-H2 makes production of free radicals via bimolecular reactions feasible.

Lee, Yuan-Pern; Bahou, Mohammed; Golec, Barbara

2011-06-01

260

A General Method for Identifying Recessive Diploid-Specific Mutations in Saccharomyces Cerevisiae, Its Application to the Isolation of Mutants Blocked at Intermediate Stages of Meiotic Prophase and Characterization of a New Gene Sae2  

PubMed Central

We describe a general new approach for identifying recessive mutations that affect diploid strains of yeast Saccharomyces cerevisiae and the application of this method to the identification of mutations that confer an intermediate block in meiotic prophase chromosome metabolism. The method uses a temperature-sensitive conjugation mutation ste7-1 in combination with homothallism. The mutations of interest confer a defect in spore formation that is dependent upon a gene required for initiation of meiotic recombination and development of meiosis-specific chromosome structure (SPO11). Identified in this screen were null mutations of the DMC1 gene, nonnull mutations of RAD50 (rad50S), and mutations in three new genes designated SAE1, SAE2 and SAE3 (Sporulation in the Absence of Spo Eleven). Molecular characterization of the SAE2 gene and characterization of meiotic and mitotic phenotypes of sae2 mutants are also presented. The phenotypes conferred by a sae2 null mutation are virtually indistinguishable from those conferred by the previously identified nonnull mutations of RAD50 (rad50S). Most notably, both mutations confer only weak sensitivity to the radiomimetic agent methyl methane sulfonate (MMS) but completely block resection and turnover of meiosis-specific double-strand breaks. These observations provide further evidence that this constellation of phenotypes identifies a specific molecular function.

McKee, AHZ.; Kleckner, N.

1997-01-01

261

Choice reaction times for identifying the direction of first-order motion and different varieties of second-order motion  

Microsoft Academic Search

This study sought to quantify the temporal properties of the human visual system by measuring forced-choice reaction times for discriminating the drift direction of first-order motion (luminance-modulated noise) and a variety of second-order motion patterns (modulations of either the contrast, polarity, orientation or spatial length of a noise carrier) over a range of stimulus modulation depths. In general, reaction times

Tim Ledgeway; Claire V. Hutchinson

2008-01-01

262

An optimization framework for identifying reaction activation\\/inhibition or elimination candidates for overproduction in microbial systems  

Microsoft Academic Search

We introduce a computational framework termed OptReg that determines the optimal reaction activations\\/inhibitions and eliminations for targeted biochemical production. A reaction is deemed up- or downregulated if it is constrained to assume flux values significantly above or below its steady-state before the genetic manipulations. The developed framework is demonstrated by studying the overproduction of ethanol in Escherichia coli. Computational results

Priti Pharkya; Costas D. Maranas

2006-01-01

263

Use of the Ligase Detection Reaction-Polymerase Chain Reaction to Identify Point Mutations in Extended-Spectrum Beta-Lactamases  

Microsoft Academic Search

The aim of this study was to detect point mutations in extended-spectrum ?-lactamase (ESBL) genes in a background of wild-type\\u000a (non-ESBL-producing) bacteria using a highly sensitive and specific method developed for this purpose. The ligase detection\\u000a reaction-polymerase chain reaction (LDR-PCR) method was used to test different ESBL-producing strains and clinical isolates\\u000a for a specific point mutation in the bla SHV-ESBL

C. Niederhauser; L. Kaempf; I. Heinzer

2000-01-01

264

Heterologous expression and characterization of a "Pseudomature" form of taxadiene synthase involved in paclitaxel (Taxol) biosynthesis and evaluation of a potential intermediate and inhibitors of the multistep diterpene cyclization reaction.  

PubMed

The diterpene cyclase taxadiene synthase from yew (Taxus) species transforms geranylgeranyl diphosphate to taxa-4(5),11(12)-diene as the first committed step in the biosynthesis of the anti-cancer drug Taxol. Taxadiene synthase is translated as a preprotein bearing an N-terminal targeting sequence for localization to and processing in the plastids. Overexpression of the full-length preprotein in Escherichia coli and purification are compromised by host codon usage, inclusion body formation, and association with host chaperones, and the preprotein is catalytically impaired. Since the transit peptide-mature enzyme cleavage site could not be determined directly, a series of N-terminally truncated enzymes was created by expression of the corresponding cDNAs from a suitable vector, and each was purified and kinetically evaluated. Deletion of up to 79 residues yielded functional protein; however, deletion of 93 or more amino acids resulted in complete elimination of activity, implying a structural or catalytic role for the amino terminus. The pseudomature form of taxadiene synthase having 60 amino acids deleted from the preprotein was found to be superior with respect to level of expression, ease of purification, solubility, stability, and catalytic activity with kinetics comparable to the native enzyme. In addition to the major product, taxa-4(5),11(12)-diene (94%), this enzyme produces a small amount of the isomeric taxa-4(20), 11(12)-diene ( approximately 5%), and a product tentatively identified as verticillene ( approximately 1%). Isotopically sensitive branching experiments utilizing (4R)-[4-(2)H(1)]geranylgeranyl diphosphate confirmed that the two taxadiene isomers, and a third (taxa-3(4),11(12)-diene), are derived from the same intermediate taxenyl C4-carbocation. These results, along with the failure of the enzyme to utilize 2, 7-cyclogeranylgeranyl diphosphate as an alternate substrate, indicate that the reaction proceeds by initial ionization of the diphosphate ester and macrocyclization to the verticillyl intermediate, followed by a secondary cyclization to the taxenyl cation and deprotonation (i.e., formation of the A-ring prior to B/C-ring closure). Two potential mechanism-based inhibitors were tested with recombinant taxadiene synthase but neither provided time-dependent inactivation nor afforded more than modest competitive inhibition. PMID:10864451

Williams, D C; Wildung, M R; Jin, A Q; Dalal, D; Oliver, J S; Coates, R M; Croteau, R

2000-07-01

265

Caffeoylquinic acid derived free radicals identified during antioxidant reactions of bitter tea (Ilex latifolia and Ilex kudincha).  

PubMed

In order to provide some insight into the chemical basis for the antioxidant behaviour of bitter tea, the Chinese medicinal beverage derived from leaves of Ilex kudincha or Ilex latifolia, free radicals generated during the oxidation of aqueous extracts of dried leaves have been investigated by electron paramagnetic resonance (EPR) spectroscopy. With both beverages, the major components in the EPR spectra after accelerated autoxidation under alkaline conditions or oxidation with the superoxide anion radical were comparable to those derived from reactions of caffeoylquinic acids. Thus these reaction products have sufficient stability for biological activity, and the present results suggest that such molecules contribute appreciably to the antioxidant chemistry of these beverages. PMID:21776475

Pirker, Katharina Franziska; Goodman, Bernard Albert

2010-11-18

266

Study on the Pp Implies p + X Reaction at 36 GeV/C on Events with an Identified Proton.  

National Technical Information Service (NTIS)

The experimental results of the pp implies p (slow) + X reaction at 36 GeV/c are presented. The cross sections of single and double diffraction dissociation (epsilon/sub s/=2.07+-0.21 mn, epsilon/sub D/=4.70+-0.44 mb, respectively) were obtained which are...

I. V. Boguslavskii I. M. Gramenitskii Z. Zlatanov R. Lednicky V. I. Rud

1978-01-01

267

Electrospray ionization mass spectrometric investigations of [alpha]-dicarbonyl compounds--Probing intermediates formed in the course of the nonenzymatic browning reaction of l-ascorbic acid  

NASA Astrophysics Data System (ADS)

A new method is presented which allows the simultaneous detection of various [alpha]-dicarbonyl compounds generated in the course of the nonenzymatic browning reaction initiated by thermal treatment of l-ascorbic acid, namely: glyoxal, methylglyoxal, diacetyl, 3-deoxy-l-pentosone, and l-threosoneE 3-Deoxy-l-threosone was successfully identified as a new C4-[alpha]-dicarbonyl structure for the first time in the degradation of Vitamin C by application of this non-chromatographic mass spectrometric approach. Moreover, a more detailed elucidation of the mechanistic scenario with respect to the oxidative and nonoxidative pathways is presented by using dehydro-l-ascorbic acid and 2,3-diketo-l-gulonic acid instead of l-ascorbic acid as a starting material. Furthermore, the postulated pathways are corroborated with the aid of 13C-isotopic labeling studies. The investigations were extended to baby food, and the successful detection of [alpha]-dicarbonyl compounds characteristic for Vitamin C degradation proved the matrix tolerance of the introduced method.

Schulz, Anke; Trage, Claudia; Schwarz, Helmut; Kroh, Lothar W.

2007-05-01

268

Evaluation of the applicability of polymerase chain reaction (PCR) to sex identifi cation in Eurasian blackbirds (Turdus merula)  

Microsoft Academic Search

Turdus merula is one of most common bird species in Europe. This study verifi ed a method for its sex identifi cation by PCR with P2\\/P8 primers, based on the CHD1 gene polymorphism, proposed in earlier studies as a universal tool for sex identifi cation in most bird species. Although there are some reports that PCR cannot determine sex in

ANDRZEJ DYBUS; ANNA SIEMIERZ; DARIUSZ WYSOCKI; IWONA SZATKOWSKA; SEBASTIAN GUENZEL

269

Unique stepwise substitution reaction of a mono(guanidinate)tetraplatinum complex with amidines, giving mono(amidinate)tetraplatinum complexes through mixed-ligand intermediate complexes.  

PubMed

A mono(guanidinate)tetraplatinum complex [Pt4(?-OCOCH3)7(?-(TolN)2CN(i)Pr2)] (5: Tol = C6H4Me-4) was prepared by treating [Pt4(?-OCOCH3)8] (1) with excess amounts of N,N?-bis(p-tolyl)-N??-diisopropylguanidine (4a). A substitution reaction of the guanidinate moiety of 5 with N,N?-bis(aryl)formamidine (10: aryl = C6H4Me-4, C6H4COMe-4, and C6H4OMe-4) via mixed-ligand intermediates, trans-[Pt4(?-OCOCH3)6(?-(TolN)2CN(i)Pr2)(?-ArNCHNAr)] (11: Tol = C6H4Me-4; Ar = C6H4Me-4, C6H4COMe-4, and C6H4OMe-4), as a stepwise substitution mechanism, afforded the corresponding mono(amidinate)tetraplatinum complexes [Pt4(?-OCOCH3)7(?-ArNCHNAr)] (2a: Ar = C6H4Me-4; 2b: Ar = C6H4COMe-4; 2c: Ar = C6H4OMe-4) along with trans-bis(amidinate)tetraplatinum complexes trans-[Pt4(?-OCOCH3)6(?-ArNCHNAr)2] (3a: Ar = C6H4Me-4; 3b: Ar = C6H4COMe-4; 3c: Ar = C6H4OMe-4) as minor products. A Pt4 dimer complex [Pt4(?-OCOCH3)7]2-{?-(ArN)2C(C6H4)2C(NAr)2} (13: Ar = C6H4(t)Bu-4) was selectively obtained upon treatment of 5 with a bis(amidine) linker ligand, N4,N4,N4?,N4?-tetrakis(p-(tert-butyl)phenyl)-[1,1?-biphenyl]-4,4?-dicarboxamidine (12). All in-plane acetates of the two Pt4 cores in 13 were fully substituted by 2,6-dimethylbenzoic acid, 2,4,6-triisopropylbenzoic acid, and ferrocenecarboxylic acid while maintaining its dimer structure to give the corresponding derivatives [Pt4(?-OCOCH3)4(?-OCOC6H3Me2-2,6)3]2-{?-(ArN)2C(C6H4)2C(NAr)2} (14: Ar = C6H4(t)Bu-4), [Pt4(?-OCOCH3)4(?-OCOC6H2(i)Pr3-2,4,6)3]2-{?-(ArN)2C(C6H4)2C(NAr)2} (15: Ar = C6H4(t)Bu-4), and [Pt4(?-OCOCH3)4(?-OCOC5H4FeCp)3]2-{?-(ArN)2C(C6H4)2C(NAr)2} (16: Ar = C6H4(t)Bu-4). The electrochemistry of the four Pt4 dimer complexes 13–16 displayed a one-electron process attributed to Pt4(9+)/Pt4(8+), and another one-electron process due to Fe3+/Fe2+ was observed for the hexaferrocenyl derivative 16. PMID:23254781

Tanaka, Shinji; Mashima, Kazushi

2013-02-28

270

PAH Intermediates: Links between the Atmosphere and Biological Systems  

PubMed Central

China is now the world's largest emitter of polycyclic aromatic hydrocarbons (PAHs). In addition, PAHs, and their reactive intermediates, undergo trans-Pacific atmospheric transport to the Western U.S. The objectives of our research are to predict, identify and quantify novel PAH intermediates in the atmosphere and biological systems, using computational methods, as well as laboratory and field experiments. Gaussian is used to predict the thermodynamic properties of parent structure PAHs, as well as the associated nitro-, oxy-, and hydroxy- PAH intermediates. Based on these predictions, state-of-the-art analytical chemistry techniques are used to identify and quantify these potential intermediates on Asian particulate matter before and after reaction in a continuous flow photochemical reactor. These same techniques are used to identify the relative proportion of PAH intermediates in PAH source regions (such as Beijing, China) and during long-range atmospheric transport to the Western U.S. PAH personal exposure studies in China and the Confederated Tribes of the Umatilla Indian Reservation in Oregon will be used to assess the similarities and differences in the PAH intermediates in biological systems relative to the atmosphere.

SIMONICH, STACI L. MASSEY; MOTORYKIN, OLEKSII; JARIYASOPIT, NARUMOL

2010-01-01

271

Computer-aided design of chiral ligands. Part I. Database search methods to identify chiral ligand types for asymmetric reactions.  

PubMed

The utility of database searching to identify chiral ligand motifs is outlined. The key elements of three known chiral ligands have been described as bond vectors. The CAVEAT program was then used to screen the Cambridge Structural Database (CSD), portions of the Chemical Abstracts Services three-dimensional database (CAS-3D), and the TRIAD tricyclic structure database for scaffolds containing these elements. Scaffolds corresponding to the known starting points were identified indicating that this method can be used to identify chiral ligand structural motifs. In addition, alternate structural motifs were found that suggested alternative possible ligands. PMID:11885961

Kozlowski, Marisa C; Panda, Manoranjan

2002-03-01

272

The Chemoselective Reduction of Isoxazoline ?-Lactams Through Iminium Aza-Diels-Alder Reactions: A Short-Cut Synthesis of Aminols as Valuable Intermediates towards Nucleoside Derivatives  

PubMed Central

Isoxazoline ?-lactams are prepared starting from the regioisomeric cycloadducts of benzonitrile oxide to the N-alkyl 2-azanorbornenes taking advantage of the efficient catalytic oxidation by RuO4. The reduction of the amide groups is easily conducted in the presence of LiAlH4 under mild conditions, which allowed for the chemoselective reduction of the amide moiety followed by ring opening to afford the desired conformationally locked isoxazoline-carbocyclic aminols, as valuable intermediates for nucleoside synthesis.

Memeo, Misal Giuseppe; Mella, Mariella; Quadrelli, Paolo

2012-01-01

273

Detection of covalent and non-covalent intermediates in the polymerization reaction catalyzed by a C149S-class III polyhydroxybutyrate synthase§  

PubMed Central

Polyhydroxybutyrate (PHB) synthases catalyze the conversion of 3-hydroxybutyryl coenzyme A (HBCoA) to PHB of molecular weight 1.5 million. The class III synthase from Allochromatium vinosum is a tetramer of PhaEPhaC (each 40 KDa). The polymerization involves covalent catalysis using C149 of PhaC with one PHB chain per PhaEC dimer. Two mechanisms for elongation have been proposed. The first involves an active site composed of two monomers where the growing hydroxybutyrate (HB) chain alternates between C149 on each monomer. The second involves C149 and covalent and non-covalent (HB)nCoA intermediates. Two approaches were investigated to distinguish between these models. The first involved the wt-PhaEC primed with sTCoA (a CoA ester of (HB)3 in which the terminal HO is replaced with an H) which uniformly loads the enzyme. The primed synthase was reacted with [1-14C] HBCoA by a rapid chemical quench method and analyzed for covalent and non-covalent intermediates. Radiolabel was found only with the protein. The second approach used C149S-PhaEC which catalyzes polymer formation at 1/2200 the rate of wt PhaEC (1.79 min?1 vs 3900 min?1). C149S-PhaEC was incubated with [1-14C] HBCoA and chemically quenched on the min time scale to reveal non-covalently bound [1-14C] (HB)2CoA and (HB)3CoA as well as covalently labeled protein. Synthesized (HB)nCoA (n = 2, 3) were shown to acylate PhaEC with rate constants of 1 to 2 min?1 and these species are converted into polymer. The (HB)n-CoA function as kinetically and chemically competent intermediates. These results support the mechanism involving covalently and non-covalently bound intermediates.

Li, Ping; Chakraborty, Sumit; Stubbe, JoAnne

2009-01-01

274

Ethanol electro-oxidation over Pt( h k l): Comparative study on the reaction intermediates probed by FTIR and SFG spectroscopies  

Microsoft Academic Search

We have investigated the adsorbed intermediates of ethanol electro-oxidation at Pt(111), Pt(100) and Pt(110) using FTIR and SFG spectroscopies. Mainly, we focus on the CO formation. The aim of the present work is to compare the responses coming from two different surface probes: FTIR spectroscopy and SFG spectroscopy. Between 1800cm?1 and 2300cm?1, our FTIR and SFG results are in good

Janaina Fernandes Gomes; Bertrand Busson; Abderrahmane Tadjeddine; Germano Tremiliosi-Filho

2008-01-01

275

Studies on the fine structural localization of zinc-iodide-osmium reaction in the brain I. Some characteristics of localization in the perikarya of identified neurons  

Microsoft Academic Search

Summary Samples of different brain areas fixed with aldehyde-perfusion were impregnated in zinc-iodide-osmium solution. In attempting to classify nerve cells on the basis of their zinc-iodide-osmium positivity, reactive sites confined to the perikaryal organelles of identified nerve cells were studied electron-microscopically. It was revealed that the Golgi apparatus, the smooth endoplasmic reticulum and the synaptic vesicles contained reaction product of

Ferenc Joó; Norbert Halász; Árpád Párducz

1973-01-01

276

Impetigo-Like Tinea Faciei Around the Nostrils Caused by Arthroderma vanbreuseghemii Identified Using Polymerase Chain Reaction-Based Sequencing of Crusts.  

PubMed

We report a case of Arthroderma vanbreuseghemii (a teleomorph of Trichophyton interdigitale) infection around the nostrils in a 3-year-old girl. The culture was negative, so the pathogenic agent was identified using polymerase chain reaction-based sequencing of the crusts taken from the lesion on the nostril. Treatment with oral itraconazole and topical 1% naftifine/0.25% ketoconazole cream after a topical wash with ketoconazole shampoo was effective. PMID:23278484

Kang, Daoxian; Ran, Yuping; Li, Conghui; Dai, Yaling; Lama, Jebina

2012-12-26

277

Toward unique identifiers  

Microsoft Academic Search

This paper discusses the creation and use of unique identifiers for intellectual property. General concepts applicable to unique identifiers are defined and discussed [identifier, digital object, dumb and intelligent identifiers, readability, affordance or computability, multiple identification, resolution, metadata, persistence, granularity, derivatives (e.g., versions, formats, manifestations, and copies), check digits, and intermediate objects]. Requirements for unique identifiers are reviewed. Capacity issues

NORMAN PASKIN

1999-01-01

278

Study of Intermediates from Transition Metal Excited-State Electron-Transfer Reactions. Progress Report, April 1, 1984-March 31, 1985.  

National Technical Information Service (NTIS)

Excited-state inter- and intramolecular electron-transfer reactions lie at the heart of most photochemical solar energy conversion schemes. Our research, which utilizes the techniques of continuous and pulsed photolysis and radiolysis, has focused on thre...

M. Z. Hoffman

1985-01-01

279

Detection and identification of intermediates in the reaction of L-serine with Escherichia coli tryptophan synthase via rapid-scanning ultraviolet-visible spectroscopy  

Microsoft Academic Search

Rapid-scanning stopped-flow (RSSF) UV-visible spectroscopy has been used to investigate the UV-visible absorption changes (300-550 nm) that occur in the spectrum of enzyme-bound pyridoxal 5'-phosphate during the reaction of L-serine with the alpha 2 beta 2 and beta 2 forms of Escherichia coli tryptophan synthase. In agreement with previous kinetic studies the reaction with alpha 2 beta 2 was found

William Frederick Drewe; Michael F. Dunn

1985-01-01

280

Intermediate inputs and economic productivity.  

PubMed

Many models of economic growth exclude materials, energy and other intermediate inputs from the production function. Growing environmental pressures and resource prices suggest that this may be increasingly inappropriate. This paper explores the relationship between intermediate input intensity, productivity and national accounts using a panel dataset of manufacturing subsectors in the USA over 47 years. The first contribution is to identify sectoral production functions that incorporate intermediate inputs, while allowing for heterogeneity in both technology and productivity. The second contribution is that the paper finds a negative correlation between intermediate input intensity and total factor productivity (TFP)--sectors that are less intensive in their use of intermediate inputs have higher productivity. This finding is replicated at the firm level. We propose tentative hypotheses to explain this association, but testing and further disaggregation of intermediate inputs is left for further work. Further work could also explore more directly the relationship between material inputs and economic growth--given the high proportion of materials in intermediate inputs, the results in this paper are suggestive of further work on material efficiency. Depending upon the nature of the mechanism linking a reduction in intermediate input intensity to an increase in TFP, the implications could be significant. A third contribution is to suggest that an empirical bias in productivity, as measured in national accounts, may arise due to the exclusion of intermediate inputs. Current conventions of measuring productivity in national accounts may overstate the productivity of resource-intensive sectors relative to other sectors. PMID:23359736

Baptist, Simon; Hepburn, Cameron

2013-01-28

281

Microeconomic Concepts Students Should Learn before Intermediate Macroeconomics.  

ERIC Educational Resources Information Center

Identifies four microeconomic concepts students should learn before entering the study of intermediate macroeconomics. Included are relative prices, general versus partial equilibrium, constrained optimization, and the nature of production concepts. Recommends making intermediate microeconomics a prerequisite for intermediate macroeconomics. (MJP)

Salemi, Michael K.

1996-01-01

282

Monoclonal antibody MS13 identifies a plasmatocyte membrane protein and inhibits encapsulation and spreading reactions of Manduca sexta hemocytes.  

PubMed

Lepidopterans generally can successfully defend themselves against a variety of parasites or parasitoids. One mechanism they use is to encapsulate the invader in many layers of hemocytes. For encapsulation to occur, the hemocytes must attach to the foreign material, spread, and adhere to each other. The molecules that mediate these processes are not known. One method to identify proteins potentially necessary for adhesion, spreading, and, thus, encapsulation is to use monoclonal antibodies that interfere with these functions. In this paper, we report that a monoclonal antibody against Manduca sexta plasmatocytes effectively inhibited encapsulation of synthetic beads in vitro and in vivo. Furthermore, it inhibited plasmatocyte spreading in vitro. Other anti-hemocyte antibodies did not have these effects. The plasmatocyte-specific monoclonal antibody, mAb MS13, recognized a protein of approximately 90,000 daltons as indicated by Western blot analysis of hemocyte lysate proteins. The epitope recognized by mAb MS13 was present on the exterior surface of plasmatocytes. Using indirect immunohistochemistry with hemocyte-specific antibodies, we also determined that during encapsulation plasmatocytes were the first cells bound to latex beads and later layers consisted of both plasmatocytes and granular cells. Arch. PMID:11169749

Wiegand, C; Levin, D; Gillespie, J; Willott, E; Kanost, M; Trenczek, T

2000-11-01

283

Novel CYP2D6 and CYP2C19 variants identified in a patient with adverse reactions towards venlafaxine monotherapy and dual therapy with nortriptyline and fluoxetine.  

PubMed

We present a case report of novel variants of CYP2D6 and CYP2C19 identified in a patient who experienced adverse effects during antidepressant therapy. CYP2D6 DNA sequencing revealed that the patient was most likely an intermediate metabolizer, owing to the presence of a novel variant (2579C>T), which gives rise to a premature stop codon in exon 5. Because defects in CYP2C19 may also be important, we sequenced the promoter region and all exons of CYP2C19 and identified a cluster of three novel variants (-13G>A, 7C>T and 10T>C) around exon 1, as well as the more common CYP2C19*2 allele. The presence of multiple genetic lesions in CYP2C19 implies that this patient is potentially a CYP2C19 poor metabolizer, and this was confirmed by haplotype analysis. Combined impairment of CYP2D6 and CYP2C19 activities, we believe, may have contributed to the development of the observed drug responses in the present report. PMID:23799451

Chua, Eng Wee; Foulds, James; Miller, Allison L; Kennedy, Martin A

2013-09-01

284

Eleven new heaviest isotopes of elements Z = 105 to Z = 117 identified among the products of 249Bk+48Ca reactions  

SciTech Connect

The heaviest isotopes of elements Z = 117 to Z = 105, 294117, 293117, 290115, 289115, 286113, 285113, 282Rg, 281Rg, 278Mt, 274Bh, and 270Db, were identified by means of the Dubna gas-filled recoil separator among the products of the 249Bk + 48Ca reaction. The details of the observed six decay chains, indicating the production and decay of isotopes 293117 and 294117, are presented and discussed. The decay energies and resulting half-lives of these new nuclei show a strong rise of stability with increasing neutron number, validating the concept of the island of enhanced stability for superheavy nuclei.

Oganessian, Yuri Ts. [FLNR-JINR, Russia; Abdullin, F. Sh. [Joint Institute for Nuclear Research, Dubna, Russia; Bailey, P. D. [Oak Ridge National Laboratory (ORNL); Benker, D. E. [Oak Ridge National Laboratory (ORNL); Bennett, M. E. [University of Nevada, Las Vegas; Dmitriev, S. [FLNR-JINR, Russia; Ezold, Julie G. [Oak Ridge National Laboratory (ORNL); Hamilton, J. H. [Vanderbilt University; Henderson, R. [Lawrence Livermore National Laboratory (LLNL); Itkis, M. G. [FLNR-JINR, Russia; Lobanov, Yu. V. [Joint Institute for Nuclear Research, Dubna, Russia; Mezentsev, A. N. [Joint Institute for Nuclear Research, Dubna, Russia; Moody, K. [Lawrence Livermore National Laboratory (LLNL); Nelson, S. L. [Lawrence Livermore National Laboratory (LLNL); Polyakov, A. N. [Joint Institute for Nuclear Research, Dubna, Russia; Porter, C. E. [Oak Ridge National Laboratory (ORNL); Ramayya, A. V. [Vanderbilt University; Riley, F. D. [Oak Ridge National Laboratory (ORNL); Roberto, James B [ORNL; Ryabinin, M. A. [Research Institute of Atomic Reactors, Dimitrovgrad, Russia; Rykaczewski, Krzysztof Piotr [ORNL; Taylor, R [Oak Ridge National Laboratory (ORNL); Tsyganov, Yu. S. [Joint Institute for Nuclear Research, Dubna, Russia; Utyonkov, V. [FLNR-JINR, Russia; Voinov, A. A. [Joint Institute for Nuclear Research, Dubna, Russia; Vostokin, G. K. [Joint Institute for Nuclear Research, Dubna, Russia; Wilk, P. A. [Lawrence Livermore National Laboratory (LLNL)

2011-01-01

285

Ni/Fe-supported over hydrotalcites precursors as catalysts for clean and selective oxidation of Basic Yellow 11: reaction intermediates determination.  

PubMed

In this work, Basic Yellow 11 (BY 11) was employed as model compound to study catalytic wet air oxidation as a pre-treatment step to the conventional biological oxidation. Ni and Fe catalysts supported over hydrotalcite (HT) were prepared by incipient wetness and excess impregnation to obtain catalysts with different metal loadings (from 1 to 10 wt.%). HTs were synthesized by co-precipitation and characterized with XRD, X-ray fluorescence (XRF), BET, thermogravimetric analysis and SEM. Results showed that dye conversion increased with Ni and Fe content up to 7 wt.% and that the most effective catalyst were prepared by incipient wetness impregnation. The influence of metal loading in the catalyst, and the preparation method as well as the reaction conditions was investigated. A mechanism and reaction pathways for BY 11 during catalytic liquid phase oxidation have also been proposed. PMID:22960061

Ovejero, G; Rodríguez, A; Vallet, A; García, J

2012-09-07

286

Crossed beam study of the charge-transfer reaction of Ar/sup +/ with N/sub 2/ at low and intermediate energies  

SciTech Connect

The charge-transfer reaction Ar/sup +/(N/sub 2/,Ar) N/sup +//sub 2/ was studied in a crossed beam experiment at 1.73 and 4.01 eV collision energies. A weak plasma ion source was used to generate a nearly pure Ar/sup +/ (/sup 2/P/sub 3//sub ///sub 2/) ion beam, which is crossed at 90/sup 0/ by a He-seeded supersonic jet N/sub 2/ beam. Detailed analysis of the results demonstrates that the reaction proceeds cleanly to generate N/sup +//sub 2/(X ..sigma../sup +//sub g/, v = 1) with a distribution of rotational states. A direct mechanism, qualitatively described as electron jump with negligible momentum transfer, is followed at collision energies of 1.7 and 4 eV.

Friedrich, B.; Trafton, W.; Rockwood, A.; Howard, S.; Futrell, J.H.

1984-03-15

287

Structural changes without stable intermediate state in inelastic material. Part II. Applications to displacive and diffusional–displacive phase transformations, strain-induced chemical reactions and ductile fracture  

Microsoft Academic Search

A number of simple examples demonstrate the applicability of the general theory developed in Part I of this paper to various structural changes in solids, namely to displacive and generalized second-order phase transformations, twinning and reorientation of crystal lattice, ductile fracture, and strain-induced chemical reactions. The theory is extended to diffusional-displacive phase transitions. The following problems for elastic and elastoplastic

Valery I. Levitas

2000-01-01

288

On the Configurational Stability of Chiral Heteroatom-Substituted [D1]Methylpalladium Complexes as Intermediates of Stille and Suzuki-Miyaura Cross-Coupling Reactions  

PubMed Central

Enantiomerically pure (S)-tributylstannyl[D1]methanol and (R)- and (S)-tributylstannyl[D1]methyl benzoates were Stille-coupled with bromobenzene and benzoyl chloride in 1,4-dioxane and toluene using [(Ph3P)4Pd] or [(Ph3P)2PdCl2] either alone or in combination with CuCN as cocatalyst at temperatures up to 80 °C. The products were found to be enantiomerically pure. (R)- and (S)-N-(tributylstannyl[D1]methyl)phthalimides gave enantiomerically pure products with benzoyl chloride, but with bromobenzene protected phenyl[D1]methylamines gave products of only 52–69?% ee depending on the solvent used. Tributyl(thio[D1]methyl)stannanes could not be Stille-coupled with benzoyl chloride or with bromobenzene. Similarly, dimethyl phenyl[D1]methylboronate underwent a Suzuki–Miyaura coupling with bromobenzene to give phenyl[D1]methylsilane with 99?% ee. All couplings followed a retentive course and, except in one case, the intermediate [XCHDPdLn] complexes were found to be microscopically configurationally stable.

Malova Krizkova, Petra; Hammerschmidt, Friedrich

2013-01-01

289

Reactions of C{sub 2}H{sub 5} radicals with O, O{sub 3}, and NO{sub 3}: Decomposition pathways of the intermediate C{sub 2}H{sub 5}O radical  

SciTech Connect

Alkoxy radicals are important species in the atmospheric degradation of hydrocarbons as well as in combustion processes. Additionally, they play a crucial role in the pyrolysis of oxygen-containing hydrocarbons. The reactions of C{sub 2}H{sub 5} with O, O{sub 3}, and NO{sub 3} have been investigated in a discharge flow reactor at room temperature and pressures between 1 and 3 mbar. The reaction products were detected by mass spectrometry with electron-impact ionization. The product pattern observed is explained in terms of the decomposition of an intermediately formed, chemically activated ethoxy radical. It is shown that, with this assumption, the experimentally determined branching ratios of the different product channels can be reproduced nearly quantitatively by RRKM calculations based on ab initio results for the stationary points of the potential energy surface of C{sub 2}H{sub 5}O. For C{sub 2}H{sub 5} + O and C{sub 2}H{sub 5} + O{sub 3}, the existence of an additional, parallel channel leading to OH has to be assumed.. High-pressure Arrhenius parameters for the unimolecular reactions of the ethoxy radical are given and discussed.

Hoyermann, K.; Seeba, J. [Univ. Goettingen (Germany). Inst. fuer Physikalische Chemie; Olzmann, M.; Viskolcz [Univ. Halle-Wittenberg (Germany). Inst. fuer Physikalische Chemie

1999-07-22

290

Thermally-generated reactive intermediates: Trapping of the parent ferrocene-based o-quinodimethane and reactions of diradicals generated by hydrogen-atom transfers  

SciTech Connect

Ferrocenocyclobutene is prepared by flash vacuum pyrolysis (FVP) of the N-amino-2-phenylaziridine hydrazone of 2-methylferrocenealdehyde. In the second section of this dissertation, a series of hydrocarbon rearrangements were observed. FVP of o-allyltoluene at 0.1 Torr (700--900 C) gives 2-methylindan and indene, accompanied by o-propenyltoluene. FVP of 2-methyl-2`-vinylbiphenyl gives 9-methyl-9,10-dihydrophenanthrene, which fits the proposed mechanism. However, FVP of 2-(o-methylbenzyl)styrene gives mainly anthracene and 1-methylanthracene. This cyclization reaction was also successful with o-allylphenol and o-(2-methylallyl)phenol.

Ferguson, J.M.

1993-09-01

291

Intermediate Nuclear Structure for 2v 2{beta} Decay of {sup 48}Ca Studied by (p, n) and (n, p) Reactions at 300 MeV  

SciTech Connect

Angular distributions of the double differential cross sections for the {sup 48}Ca(p,n) and the {sup 48}Ti(n,p) reactions were measured at 300 MeV. A multipole decomposition technique was applied to the spectra to extract the Gamow-Teller (GT) transition strengths. In the (n, p) spectrum beyond 8 MeV excitation energy extra B(GT{sup +}) strengths which are not predicted by the shell model calculation. This extra B(GT{sup +}) strengths significantly contribute to the nuclear matrix element of the 2v2{beta}-decay.

Sakai, H.; Yako, K. [University of Tokyo, Department of Physics, Hongo 7-3-1, Bunkyo, Tokyo 113-0033 (Japan)

2009-08-26

292

One-electron transfer reactions of diquat radical to different reduction intermediates of oxygen. Formation of hydroxyl radical and electronically excited states  

SciTech Connect

The one-electron transfer activation of DQ++ by microsomal fractions comprises an aerobic phase and an anaerobic phase. The aerobic phase is characterized by O2 consumption, formation of electronically excited states with main emission below 600 nm, and H2O2 formation. The anaerobic phase is characterized by H2O2 consumption, DQ+ accumulation, HO. formation, and also electronically excited state formation with main emission beyond 600 nm. Superoxide dismutase abolishes the photoemission during the aerobic phase, whereas it has no effect on the photoemission originating during the anaerobic phase. The hydroxylation products of the aromatic compound salicylate, mainly 2,3- and 2,5-dihydroxybenzoic acids--indicative of the occurrence of HO.-, were detected by h.p.l.c. with oxidative electrochemical detection during the anaerobic phase, but not during the aerobic phase. Neither H2O2 consumption nor HO. are prevented by desferrioxamine. These experimental observations are interpreted on the grounds of two main electron-transfer reactions of DQ.+: under aerobic conditions, two one-electron transfer steps to molecular O2 and O2.- to yield H2O2. Under anaerobic conditions, one-electron transfer step to contaminating iron or any ferrioxamine formed to a ferrous complex which can support a Fenton-like reduction of H2O2 with formation of HO.. The toxicological relevance for the occurrence of such reactions is also discussed in terms of the formation of electronically excited states.

Mira, D.; Brunk, U.; Boveris, A.; Cadenas, E. (Univ. of Linkoeping (Sweden))

1988-01-01

293

The Children's Interaction Matrix: Intermediate Form, Primary Form. Preliminary Manual. Research Edition 1975.  

ERIC Educational Resources Information Center

|The Children's Interaction Matrix, Intermediate and Primary Forms, are designed to identify the preferred work and content styles of children in group situations. These factors aid the researcher, teacher, and counselor in understanding the individual's preferred mode of behavior in groups as well as indicating the students' reaction to group…

Drummond, Robert J.; And Others

294

Hybrid model analysis of intermediate energy (20< E ?<140 MeV) photonuclear reactions on232Th and235,238U  

NASA Astrophysics Data System (ADS)

The hybrid model code ALICE/LIVERMORE 82 (with fission option) has been used in the study of photonuclear reactions on232Th and235,238U (20< E ?<140 MeV). The total fission probabilities P f were calculated. A model was established for the decay of the fission fragments. This model, together with the code ALICE, allowed the calculation of the cross sections ? (i) for emission of at least i neutrons, and of the average multiplicity ¯v and width W of the neutron distribution for238U. The theoretical results for P f , ? (i) , ¯v and W show very good agreement with existing experimental data. It is shown that a comparison of the calculations with the available experimental data does not allow for a discrimination between the various photon absorption mechanisms proposed (single-particle absorption vs. quasi-deuteron mechanism).

Ryckbosch, D.; Carlos, P.; Leprêtre, A.

1988-12-01

295

THE EFFECT OF THE {sup 14}N(p, {gamma}){sup 15}O REACTION ON THE BLUE LOOPS IN INTERMEDIATE-MASS STARS  

SciTech Connect

We present stellar evolutionary sequences of stars in the mass range 5-12 M{sub Sun }, having solar-like initial composition. The stellar models are obtained using updated input physics, including recent rates of thermonuclear reactions. We investigate the effects of a modification of the {sup 14}N(p, {gamma}){sup 15}O reaction rate, as suggested by recent evaluations, on the formation and extension of the blue loops encountered during the evolution of the stars in the above mass range. We find that a reduced {sup 14}N(p, {gamma}){sup 15}O rate, as described in the text, has a striking impact on the physical conditions of burning and mixing during shell hydrogen burning when the blue loops are formed. In particular, we find that the efficiency of shell hydrogen burning is crucial for the formation of an extended blue loop. We show that a significantly reduced {sup 14}N(p, {gamma}){sup 15}O rate affects severely the extension of the blue loops and the time spent by the star in the blue part of the Hertzsprung-Russell diagram in the mass range 5-7 M{sub Sun} if the treatment of convection is based on the Schwarzschild criterion only. In this case, envelope overshooting helps to restore well-extended blue loops as supported by the observations of the Cepheid stars. If core overshooting is included during the core hydrogen and core helium burning phases, the loop formation and its properties depend on how this overshooting is treated for a given stellar mass range, as well as on its efficiency.

Halabi, Ghina M.; El Eid, Mounib F. [Department of Physics, American University of Beirut, Beirut (Lebanon); Champagne, Arthur [Department of Physics and Astronomy, University of North Carolina, Chapel Hill, NC (United States)

2012-12-10

296

Reaction intermediates in the selective reduction of NO with propene over Ga 2O 3Al 2O 3 and In 2O 3Al 2O 3 catalysts  

Microsoft Academic Search

Minor products formed in the reaction of NO+C3H6+O2 over Ga2O3-Al2O3 and In2O3-Al2O3 were identified by using GC–MS technique. A lot of minor products, such as oxygenated, nitrile, nitrite compounds and higher hydrocarbons were detected on both catalysts. The formation of surface nitrile species in the NO+C3H6+O2 reaction was also recognized in the diffuse reflectance FT–IR spectra. FT–IR spectra showed that

Masaaki Haneda; Emmanuel Joubert; Jean-Christophe Ménézo; Daniel Duprez; Jacques Barbier; Nicolas Bion; Marco Daturi; Jacques Saussey; Jean-Claude Lavalley; Hideaki Hamada

2001-01-01

297

Study of intermediates from transition metal excited-state electron-transfer reactions. Final report, August 4, 1986--August 31, 1997  

SciTech Connect

The techniques of continuous photolysis and pulsed laser flash photolysis, continuous and pulse radiolysis, fast-scan cyclic voltammetry, and time-resolved fluorimetry have been used to examine intramolecular electron transfer within the solvent quenching cage, photodynamics of quenching of the excited states of transition-metal photosensitizers, the properties of excites states and one-electron reduced forms, ground- and excited-state interactions with solutes, and photoinduced oxidations of organic solutes in aqueous solution. The following specific areas were examined: (1) the parameters that govern the yields of redox products from excited-state electron-transfer quenching reactions; (2) the mediation of the properties of excited states and one-electron reduced forms by the ligands and the solution medium; (3) the effect of the interactions between the ground state of the complex and the solution components on the behavior of the excited state; (4) the yields of singlet oxygen from excited-state energy-transfer quenching by O{sub 2}; and (5) the oxidations of solutes by singlet oxygen, excited-state electron-transfer quenching, and free radicals. This report contains the abstracts of 50 publications describing the studies.

Hoffman, M.Z.

1997-12-31

298

Polymerase chain reaction assay identifies Culex nigripalpus: part of an assay for molecular identification of the common Culex (Culex) mosquitoes of the eastern United States.  

PubMed

Nucleotide sequence information on internal transcribed spacer (ITS) 1 and ITS 2 regions of the nuclear ribosomal DNA multigene family was used to develop a polymerase chain reaction assay that identifies Culex nigripalpus Theobald. The assay uses species-specific forward and reverse primers for Cx. nigripalpus and can be used along with previously described primers to distinguish among 4 common taxa of Culex (Culex) of the eastern USA with a single thermal cycler program. The assay distinguishes among the 4 taxa Cx. nigripalpus, Cx. restuans Theobald, Cx. salinarius Coquillett, and members of the Cx. pipiens Linnaeus complex. This assay may be used to verify the morphological identification of individual specimens of Culex or to confirm the species composition of mosquito pools. PMID:12825660

Aspen, Stephen; Crabtree, Mary B; Savage, Harry M

2003-06-01

299

Eleven new heaviest isotopes of elements Z=105 to Z=117 identified among the products of {sup 249}Bk+{sup 48}Ca reactions  

SciTech Connect

The heaviest isotopes of elements Z=117 to Z=105, {sup 294}117, {sup 293}117, {sup 290}115, {sup 289}115, {sup 286}113, {sup 285}113, {sup 282}Rg, {sup 281}Rg, {sup 278}Mt, {sup 274}Bh, and {sup 270}Db, were identified by means of the Dubna gas-filled recoil separator among the products of the {sup 249}Bk + {sup 48}Ca reaction. The details of the observed six decay chains, indicating the production and decay of isotopes {sup 293}117 and {sup 294}117, are presented and discussed. The decay energies and resulting half-lives of these new nuclei show a strong rise of stability with increasing neutron number, validating the concept of the island of enhanced stability for superheavy nuclei [Oganessian et al., Phys. Rev. Lett. 104, 142502 (2010)].

Oganessian, Yu. Ts.; Abdullin, F. Sh.; Dmitriev, S. N.; Itkis, M. G.; Lobanov, Yu. V.; Mezentsev, A. N.; Polyakov, A. N.; Sagaidak, R. N.; Shirokovsky, I. V.; Subbotin, V. G.; Sukhov, A. M.; Tsyganov, Yu. S.; Utyonkov, V. K.; Voinov, A. A.; Vostokin, G. K. [Joint Institute for Nuclear Research, RU-141980 Dubna (Russian Federation); Bailey, P. D.; Benker, D. E.; Ezold, J. G.; Porter, C. E.; Riley, F. D. [Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States)

2011-05-15

300

Intramolecular charge transfer of 4-(dimethylamino)benzonitrile probed by time-resolved fluorescence and transient absorption: No evidence for two ICT states and a {pi}{sigma}{sup *} reaction intermediate  

SciTech Connect

For the double exponential fluorescence decays of the locally excited (LE) and intramolecular charge transfer (ICT) states of 4-(dimethylamino)benzonitrile (DMABN) in acetonitrile (MeCN) the same times {tau}{sub 1} and {tau}{sub 2} are observed. This means that the reversible LE<-->ICT reaction, starting from the initially excited LE state, can be adequately described by a two state mechanism. The most important factor responsible for the sometimes experimentally observed differences in the nanosecond decay time, with {tau}{sub 1}(LE)<{tau}{sub 1}(ICT), is photoproduct formation. By employing a global analysis of the LE and ICT fluorescence response functions with a time resolution of 0.5 ps/channel in 1200 channels reliable kinetic and thermodynamic data can be obtained. The arguments presented in the literature in favor of a {pi}{sigma}* state with a bent CN group as an intermediate in the ICT reaction of DMABN are discussed. From the appearance of an excited state absorption (ESA) band in the spectral region between 700 and 800 nm in MeCN for N,N-dimethylanilines with CN, Br, F, CF{sub 3}, and C(=O)OC{sub 2}H{sub 2} p-substituents, it is concluded that this ESA band cannot be attributed to a {pi}{sigma}{sup *} state, as only the C-C{identical_to}N group can undergo the required 120 deg. bending.

Zachariasse, Klaas A.; Druzhinin, Sergey I.; Senyushkina, Tamara [Max-Planck-Institut fuer biophysikalische Chemie, Spektroskopie und Photochemische Kinetik, 37070 Goettingen (Germany); Kovalenko, Sergey A. [Institut fuer Chemie, Humboldt Universitaet zu Berlin, Brook-Taylor Strasse 2, 12489 Berlin (Germany)

2009-12-14

301

Unimolecular dissociation of the propargyl radical intermediate of the CH+C{sub 2}H{sub 2} and C+C{sub 2}H{sub 3} reactions  

SciTech Connect

This paper examines the unimolecular dissociation of propargyl (HCCCH{sub 2}) radicals over a range of internal energies to probe the CH+HCCH and C+C{sub 2}H{sub 3} bimolecular reactions from the radical intermediate to products. The propargyl radical was produced by 157 nm photolysis of propargyl chloride in crossed laser-molecular beam scattering experiments. The H-loss and H{sub 2} elimination channels of the nascent propargyl radicals were observed. Detection of stable propargyl radicals gave an experimental determination of 71.5 (+5/-10) kcal/mol as the lowest barrier to dissociation of the radical. This barrier is significantly lower than predictions for the lowest barrier to the radical's dissociation and also lower than calculated overall reaction enthalpies. Products from both H{sub 2}+HCCC and H+C{sub 3}H{sub 2} channels were detected at energies lower than what has been theoretically predicted. An HCl elimination channel and a minor C-H fission channel were also observed in the photolysis of propargyl chloride.

McCunn, Laura R.; FitzPatrick, Benjamin L.; Krisch, Maria J.; Butler, Laurie J.; Liang, C.-W.; Lin, Jim J. [James Franck Institute and Department of Chemistry, University of Chicago, Chicago, Illinois 60637 (United States); Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, Taiwan 106 (China)

2006-10-07

302

Transient Ru-methyl formate intermediates generated with bifunctional transfer hydrogenation catalysts.  

PubMed

Desorption electrospray ionization (DESI) coupled to high-resolution Orbitrap mass spectrometry (MS) was used to study the reactivity of a (?-amino alcohol)(arene)RuCl transfer hydrogenation catalytic precursor in methanol (CH(3)OH). By placing [(p-cymene)RuCl(2)](2) on a surface and spraying a solution of ?-amino alcohol in methanol, two unique transient intermediates having lifetimes in the submillisecond to millisecond range were detected. These intermediates were identified as Ru (II) and Ru (IV) complexes incorporating methyl formate (HCOOCH(3)). The Ru (IV) intermediate is not observed when the DESI spray solution is sparged with Ar gas, indicating that O(2) dissolved in the solvent is necessary for oxidizing Ru (II) to Ru (IV). These proposed intermediates are supported by high-resolution and high mass accuracy measurements and by comparing experimental to calculated isotope profiles. Additionally, analyzing the bulk reaction mixture using gas chromatography-MS and nuclear magnetic resonance spectroscopy confirms the formation of HCOOCH(3). These results represent an example that species generated from the (?-amino alcohol)(arene)RuCl (II) catalytic precursor can selectively oxidize CH(3)OH to HCOOCH(3). This observation leads us to propose a pathway that can compete with the hydrogen transfer catalytic cycle. Although bifunctional hydrogen transfer with Ru catalysts has been well-studied, the ability of DESI to intercept intermediates formed in the first few milliseconds of a chemical reaction allowed identification of previously unrecognized intermediates and reaction pathways in this catalytic system. PMID:22315417

Perry, Richard H; Brownell, Kristen R; Chingin, Konstantin; Cahill, Thomas J; Waymouth, Robert M; Zare, Richard N

2012-02-06

303

Kinetic study of photocatalytic degradation of carbamazepine, clofibric acid, iomeprol and iopromide assisted by different TiO2 materials--determination of intermediates and reaction pathways.  

PubMed

The light-induced degradation of clofibric acid, carbamazepine, iomeprol and iopromide under simulated solar irradiation has been investigated in aqueous solutions suspended with different TiO2 materials (P25 and Hombikat UV100). Kinetic studies showed that P25 had a better photocatalytic activity for clofibric acid and carbamazepine than Hombikat UV100. For photocatalytic degradation of iomeprol Hombikat UV100 was more suitable than P25. The results can be explained by the higher adsorption capacity of Hombikat UV100 for iomeprol. The study also focuses on the identification and quantification of possible degradation products. The degradation process was monitored by determination of sum parameters and inorganic ions. In case of clofibric acid various aromatic and aliphatic degradation products have been identified and quantified. A possible multi-step degradation scheme for clofibric acid is proposed. This study proves the high potential of the photocatalytic oxidation process to transform and mineralize environmentally relevant pharmaceuticals and contrast media in water. PMID:14769415

Doll, Tusnelda E; Frimmel, Fritz H

2004-02-01

304

MHD intermediate shock discontinuities. I - Rankine-Hugoniot conditions  

Microsoft Academic Search

Recent numerical investigations have focused attention once more on the role of intermediate shocks in MHD. Four types of intermediate shock are identified using a graphical representation of the MHD Rankine-Hugoniot conditions. This same representation can be used to exhibit the close relationship of intermediate shocks to switch-on shocks and rotational discontinuities. The conditions under which intermediate discontinuities can be

C. F. Kennel; R. D. Blandford; P. Coppi

1989-01-01

305

Tandem mass spectrometry identifies proteins phosphorylated by cyclic AMP-dependent protein kinase when sea urchin sperm undergo the acrosome reaction.  

PubMed

The exocytotic acrosome reaction (AR), which is required for fertilization, occurs when sea urchin sperm contact the egg jelly (EJ) layer. Among other physiological changes, increases in adenylyl cyclase activity, cAMP and cAMP-dependent protein kinase (PKA) activity occur coincident with the AR. By using inhibitors of PKA, a permeable analog of cAMP and the phosphodiesterase inhibitor IBMX, we show that PKA activity is required for AR induction by EJ. A minimum of six sperm proteins are phosphorylated by PKA upon exposure to EJ, as detected by a PKA substrate-specific antibody. The phosphorylation of these proteins and the percentage of acrosome reacted sperm can be regulated by PKA modulators. The fucose sulfate polymer (FSP), a major component of EJ, is the molecule that triggers sperm PKA activation. Extracellular Ca(2+) is required for PKA activation. Six sperm proteins phosphorylated by PKA were identified by tandem mass spectrometry (MS/MS) utilizing the emerging sea urchin genome. Based on their identities and localizations in sperm head and flagellum, the putative functions of these proteins in sperm physiology and AR induction are discussed. PMID:16038896

Su, Yi-Hsien; Chen, Sheng-Hong; Zhou, Huilin; Vacquier, Victor D

2005-09-01

306

Studies of intermediate-mass fragment emission in the [sup 3]He+[sup nat]Ag, [sup 197]Au reactions between 0. 48 and 3. 6 GeV  

SciTech Connect

Intermediate-mass fragments formed in reactions of [sup 3]He ions with [sup nat]Ag and [sup 197]Au targets have been studied at five energies between 0.48 and 3.6 GeV. Inclusive measurements show that as the bombarding energy increases, there is a strong enhancement in fragment cross sections and a trend toward isotropic angular distributions. Between 0.90 and 1.8 GeV, a change in the emission mechanism is suggested by (1) kinetic energy spectra with high-energy tails that become distinctly flatter, (2) a broadening of the spectral Coulomb peaks toward lower energies, and (3) charge distributions that become constant, exhibiting a power-law exponent [tau][approx]2.0. Exclusive studies of the [sup 3]He+[sup nat]Ag system at 0.90 and 3.6 GeV detected multifragment events with multiplicities up to four. The probability for high-multiplicity events increases about 40-fold between 0.90 and 3.6 GeV. At both energies, the kinetic energy spectra depend on multiplicity, especially when triggering on backward-emitted fragments. For multiplicity three events, a rapidity analysis of the data at 3.6 GeV is consistent with a single, relatively low source velocity, [ital v][sub [ital S

Yennello, S.J.; Kwiatkowski, K.; Pollacco, E.C.; Volant, C.; Cassagnou, Y.; Dayras, R.; Fields, D.E.; Harar, S.; Hourani, E.; Legrain, R.; Norbeck, E.; Planeta, R.; Wile, J.L.; Yoder, N.R.; Viola, V.E. (Indiana University, Bloomington, Indiana 47405 (United States) DAPNIA/Service de Physique Nucleaire, Centre d'Etudes Nucleaires de Saclay, F-91191, Gif-sur-Yvette (France) Grand Accelerateur National d'Ions Lourds (GANIL), Boite Postale No. 5027, boulevard Henri Becquerel, 14021 Caen Cedex (France) Institut de Physique Nucleaire Orsay, Boite Postale F-91406, Orsay (France) Iowa University, Iowa City, Iowa 52242 (United States) Jagellonian University, Krakow (Poland))

1993-09-01

307

Functionalization of the corrole ring: the role of isocorrole intermediates  

PubMed Central

Bromination of 3-nitro-5,10,15-triarylcorrole selectively provides two regioisomers, depending on the reaction pathway. An isocorrole species is the key intermediate to drive the reaction towards the 2-Br-17-nitro regioisomer.

Tortora, Luca; Nardis, Sara; Fronczek, Frank R.; Smith, Kevin M.; Paolesse, Roberto

2011-01-01

308

Genome-wide association study identifies HLA-A*3101 allele as a genetic risk factor for carbamazepine-induced cutaneous adverse drug reactions in Japanese population.  

PubMed

An anticonvulsant, carbamazepine (CBZ), is known to show incidences of cutaneous adverse drug reactions (cADRs) including Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN) and drug-induced hypersensitivity syndrome (DIHS). To identify a gene(s) susceptible to CBZ-induced cADRs, we conducted a genome-wide association study (GWAS) in 53 subjects with the CBZ-induced cADRs, including SJS, TEN and DIHS, and 882 subjects of a general population in Japan. Among the single nucleotide polymorphisms (SNPs) analyzed in the GWAS, 12 SNPs showed significant association with CBZ-induced cADRs, and rs1633021 showed the smallest P-value for association with CBZ-induced cADRs (P = 1.18 × 10?¹³). These SNPs were located within a 430 kb linkage disequilibrium block on chromosome 6p21.33, including the HLA-A locus. Thus, we genotyped the individual HLA-A alleles in 61 cases and 376 patients who showed no cADRs by administration of CBZ (CBZ-tolerant controls) and found that HLA-A*3101 was present in 60.7% (37/61) of the patients with CBZ-induced cADRs, but in only 12.5% (47/376) of the CBZ-tolerant controls (odds ratio = 10.8, 95% confidence interval 5.9-19.6, P = 3.64 × 10?¹?), implying that this allele has the 60.7% sensitivity and 87.5% specificity when we apply HLA-A*3101 as a risk predictor for CBZ-induced cADRs. Although DIHS is clinically distinguished from SJS and TEN, our data presented here have indicated that they share a common genetic factor as well as a common pathophysiological mechanism. Our findings should provide useful information for making a decision of individualized medication of anticonvulsants. PMID:21149285

Ozeki, Takeshi; Mushiroda, Taisei; Yowang, Amara; Takahashi, Atsushi; Kubo, Michiaki; Shirakata, Yuji; Ikezawa, Zenro; Iijima, Masafumi; Shiohara, Tetsuo; Hashimoto, Koji; Kamatani, Naoyuki; Nakamura, Yusuke

2010-12-10

309

Intermediate Sanctions in Sentencing Guidelines.  

National Technical Information Service (NTIS)

Table of Contents: Foreword; Acknowledgments; Executive summary; Intermediate sanctions in sentencing guidelines; Intermediate sanctions; Sentencing guidelines; Incorporating intermediate sanctions in sentencing guidelines; Problems and prospects; and Lis...

M. Tonry

1997-01-01

310

Data requirements for intermediate energy nuclear applications  

SciTech Connect

Several applications that include spallation neutron sources, space radiation effects, biomedical isotope production, accelerator shielding and radiation therapy make use of intermediate energy nuclear data extending to several GeV. The overlapping data needs of these applications are discussed in terms of what projectiles, targets and reactions are of interest. Included is a discussion of what is generally known about these data and what is needed to facilitate their use in intermediate energy applications. 40 refs., 2 figs., 2 tabs.

Pearlstein, S.

1990-01-01

311

Effect of Bonding Temperature on Interfacial Reaction and Mechanical Properties of Diffusion-Bonded Joint Between Ti-6Al-4V and 304 Stainless Steel Using Nickel as an Intermediate Material  

NASA Astrophysics Data System (ADS)

An investigation was carried out on the solid-state diffusion bonding between Ti-6Al-4V (TiA) and 304 stainless steel (SS) using pure nickel (Ni) of 200-?m thickness as an intermediate material prepared in vacuum in the temperature range from 973 K to 1073 K (700 °C to 800 °C) in steps of 298 K (25 °C) using uniaxial compressive pressure of 3 MPa and 60 minutes as bonding time. Scanning electron microscopy images, in backscattered electron mode, had revealed existence of layerwise Ti-Ni-based intermetallics such as either Ni3Ti or both Ni3Ti and NiTi at titanium alloy-nickel (TiA/Ni) interface, whereas nickel-stainless steel (Ni/SS) diffusion zone was free from intermetallic phases for all joints processed. Chemical composition of the reaction layers was determined in atomic percentage by energy dispersive spectroscopy and confirmed by X-ray diffraction study. Room-temperature properties of the bonded joints were characterized using microhardness evaluation and tensile testing. The maximum hardness value of ~800 HV was observed at TiA/Ni interface for the bond processed at 1073 K (800 °C). The hardness value at Ni/SS interface for all the bonds was found to be ~330 HV. Maximum tensile strength of ~206 MPa along with ~2.9 pct ductility was obtained for the joint processed at 1023 K (750 °C). It was observed from the activation study that the diffusion rate at TiA/Ni interface is lesser than that at the Ni/SS interface. From microhardness profile, fractured surfaces and fracture path, it was demonstrated that failure of the joints was initiated and propagated apparently at the TiA/Ni interface near Ni3Ti intermetallic phase.

Thirunavukarasu, Gopinath; Kundu, Sukumar; Mishra, Brajendra; Chatterjee, Subrata

2013-08-01

312

1,2-Oxopalladation versus pi-allyl palladium route. A regioconvergent approach to a key intermediate for cyclopentanoids synthesis. New insights into the Pd(II)-catalyzed lactonization reaction.  

PubMed

Regioconvergent synthesis of the key lactone 1 from an equimolar mixture of the two olefins 4 and 5 was achieved by unique Pd(II) chemistry. The synthetic versatility of lactone 1 has been demonstrated in the synthesis of iridoids and of the endo-Corey lactone 2, which is a key intermediate for the F(2)-isoprostane synthesis. Upon exposure of the sodium salts of 4 and 5 to a catalytic amount of Pd(OAc)(2) under oxygen, in the presence of AcOH, an isomeric lactone 12 was obtained in addition to the title compound 1. The Pd(II) lactonization was optimized by fine-tuning all the factors participating in the catalytic cycle: solvent, oxidant, co-oxidant, and Pd(II) source. The Hosokawa's heterobimetallic couple emerged as the catalyst of choice. With a Cu(II)-Pd(II) couple, the redox process was transferred to copper, and the formal oxidation state of palladium remained constant during the reaction. By virtue of this new methodology, lactone 1 was obtained in a rewarding 60% yield, along with isomeric lactone 12 in 30% yield. A detailed mechanistic study was carried out in order to elucidate the formation of lactones 1 and 12. Lactone 1 was formed from either olefin 8 or olefin 10; on the other hand, lactone 12 was formed exclusively from olefin 10. An intramolecular 1,2-acyloxypalladiation was invoked for the transformation of 8 into 1, whereas the pi-allyl complexes 13 and 11 were involved in the transformation of olefin 10 into 12 and 1, respectively. PMID:12182643

Zanoni, Giuseppe; Porta, Alessio; Meriggi, Alessia; Franzini, Maurizio; Vidari, Giovanni

2002-08-23

313

Properties of Swift's intermediate bursts  

Microsoft Academic Search

Gamma-ray bursts are usually classified through their high-energy emission into short-duration and long-duration bursts. A third intermediate group has been identified on statistical grounds but its individual properties have not yet been studied in detail. Using the large sample of follow-up observations of GRBs produced during the Swift era we analyze the individual characteristics of this group. We find that

A. de Ugarte Postigo; I. Horváth; P. Veres; Z. Bagoly; D. A. Kann; C. C. Thöne; L. G. Balazs; P. D'Avanzo; M. A. Aloy; S. Foley; S. Campana; J. Mao; P. Jakobsson; S. Covino; J. P. U. Fynbo; J. Gorosabel; A. J. Castro-Tirado; L. Amati; M. Nardini

2010-01-01

314

The Intermediate Unit.  

ERIC Educational Resources Information Center

An appraisal of Washington's modern legislation indicates that the county as an educational intermediate unit needs to be reevaluated. It is suggested in this document that the service functions of the unit are of first importance in such a reevaluation. Fourteen service functions are suggested in pointing out that the function of the intermediate

Babcock, Chester D.

315

Intermediate Filament Diseases: Desminopathy  

PubMed Central

Desminopathy is one of the most common intermediate filament human disorders associated with mutations in closely interacting proteins, desmin and alphaB-crystallin. The inheritance pattern in familial desminopathy is characterized as autosomal dominant or autosomal recessive, but many cases have no family history. At least some and likely most sporadic desminopathy cases are associated with de novo DES mutations. The age of disease onset and rate of progression may vary depending on the type of inheritance and location of the causative mutation. Typically, the illness presents with lower and later upper limb muscle weakness slowly spreading to involve truncal, neck-flexor, facial and bulbar muscles. Skeletal myopathy is often combined with cardiomyopathy manifested by conduction blocks, arrhythmias and chronic heart failure resulting in premature sudden death. Respiratory muscle weakness is a major complication in some patients. Sections of the affected skeletal and cardiac muscles show abnormal fibre areas containing chimeric aggregates consisting of desmin and other cytoskeletal proteins. Various DES gene mutations: point mutations, an insertion, small in-frame deletions and a larger exon-skipping deletion, have been identified in desminopathy patients. The majority of these mutations are located in conserved alpha-helical segments, but additional mutations have recently been identified in the tail domain. Filament and network assembly studies indicate that most but not all disease-causing mutations make desmin assembly-incompetent and able to disrupt a pre-existing filamentous network in dominant-negative fashion. AlphaB-crystallin serves as a chaperone for desmin preventing its aggregation under various forms of stress; mutant CRYAB causes cardiac and skeletal myopathies identical to those resulting from DES mutations.

Goldfarb, Lev G.; Olive, Montse; Vicart, Patrick; Goebel, Hans H.

2009-01-01

316

Discovery-Oriented Approach To Organic Synthesis: Tandem Aldol Condensation-Michael Addition Reactions. Identifying Diastereotopic Hydrogens in an Achiral Molecule by NMR Spectroscopy  

NASA Astrophysics Data System (ADS)

We have found a beautiful example of anisochrony of diastereotopic acyclic methylene hydrogens in a symmetric diketone, synthesized by techniques traditionally performed in an introductory organic laboratory course. Synthesis of the diketone is high-yielding and easy to carry out, and the products can be directly isolated with a good degree of purity with no need of further manipulation. The reaction can be accomplished in a single laboratory session.

Wachter-Jurcsak, Nanette; Reddin, Kendra

2001-09-01

317

A diagnostic multiplex polymerase chain reaction method to identify Japanese internal apple-feeding Lepidopteran pests: Grapholita molesta , Grapholita dimorpha (Lepidoptera: Tortricidae), and Carposina sasakii (Lepidoptera: Carposinidae)  

Microsoft Academic Search

We present a multiplex polymerase chain reaction method to differentiate between three Japanese internal apple-feeding pests:\\u000a the oriental fruit moth, Grapholita molesta (Busck), Grapholita dimorpha Komai, and the peach fruit moth, Carposina sasakii Matsumura. A 1,342-bp fragment of mitochondrial cytochrome oxidase subunit I (COI) was sequenced in each species. The three\\u000a species showed consistent and diagnostic differences in the region

Hiroshi Hada; Ken-Taro Sekine

2011-01-01

318

Intermediate energy nuclear data for applications  

NASA Astrophysics Data System (ADS)

A comprehensive review of the data needs for various applications was performed by the participants of the meeting. The status of compilation and evaluation of the needed data in the intermediate energy range of incident particles was discussed. The following broad application areas were identified and considered by the participants: intermediate energy nuclear data needed for accelerators; intermediate energy nuclear data needed for space applications; and intermediate energy nuclear data for medical applications. The role of nuclear model calculations in data evaluations in this energy range was considered. The possibilities of existing model codes were considered from the point of view of reliability, accuracy, cost of computer time, and availability to specialists in the Member States. The Meeting presentations were divided into the following three sessions: nuclear data needs in the intermediate energy range (6 papers), progress of nuclear data computations and evaluations in the intermediate energy range (6 papers), and progress of experimental data measurements in the intermediate energy range. A separate abstract was prepared for each paper. The ways of further improvement of the status of nuclear data in the intermediate energy range were discussed and the results of these discussions can be found in the conclusions and recommendations of this meeting.

Kocherov, N. P.

1991-02-01

319

Properties of Swift`s intermediate bursts  

NASA Astrophysics Data System (ADS)

Based on their prompt, high-energy emission, gamma-ray bursts are usually classified into short-duration and long-duration classes. A third intermediate group has been identified on statistical grounds but its individual properties have not yet been studied in detail. Using the large sample of follow-up observations of GRBs produced during the Swift era we analyze the individual characteristics of this group. We find that intermediate bursts are significantly different from short GRBs but share many properties with long bursts, probably pointing to a common progenitor type. However, we find that intermediate bursts are significantly dimmer and have on average lower redshifts.

Veres, P.; de Ugarte Postigo, A.; Horvath, I.; Bagoly, Z.; Kann, D. A.; Thöne, C. C.; Balazs, L. G.; D'Avanzo, P.; Aloy, M. A.; Foley, S.; Campana, S.; Mao, J.; Jakobsson, P.; Covino, S.; Fynbo, J. P. U.; Gorosabel, J.; Castro-Tirado, A. J.; Nardini, M.; Amati, L.

2011-08-01

320

Peroxo-type intermediates in class I ribonucleotide reductase and related binuclear non-heme iron enzymes.  

PubMed

We have performed a systematic study of chemically possible peroxo-type intermediates occurring in the non-heme di-iron enzyme class Ia ribonucleotide reductase, using spectroscopically calibrated computational chemistry. Density functional computations of equilibrium structures, Fe-O and O-O stretch frequencies, Mossbauer isomer shifts, absorption spectra, J-coupling constants, electron affinities, and free energies of O(2) and proton or water binding are presented for a series of possible intermediates. The results enable structure-property correlations and a new rationale for the changes in carboxylate conformations occurring during the O(2) reaction of this class of non-heme iron enzymes. Our procedure identifies and characterizes various possible candidates for peroxo intermediates experimentally observed along the ribonucleotide reductase dioxygen activation reaction. The study explores how water or a proton can bind to the di-iron site of ribonucleotide reductase and facilitate changes that affect the electronic structure of the iron sites and activate the site for further reaction. Two potential reaction pathways are presented: one where water adds to Fe1 of the cis-mu-1,2 peroxo intermediate P causing opening of a bridging carboxylate to form intermediate P' that has an increased electron affinity and is activated for proton-coupled electron transfer to form the Fe(III)Fe(IV) intermediate X; and one that is more energetically favorable where the P to P' conversion involves addition of a proton to a terminal carboxylate ligand in the site which increases the electron affinity and triggers electron transfer to form X. Both pathways provide a mechanism for the activation of peroxy intermediates in binuclear non-heme iron enzymes for reactivity. The studies further show that water coordination can induce the conformational changes observed in crystal structures of the met state. PMID:19663382

Jensen, Kasper P; Bell, Caleb B; Clay, Michael D; Solomon, Edward I

2009-09-01

321

Repair of gaps in retroviral DNA integration intermediates.  

PubMed

Diverse mobile DNA elements are believed to pirate host cell enzymes to complete DNA transfer. Prominent examples are provided by retroviral cDNA integration and transposon insertion. These reactions initially involve the attachment of each element 3' DNA end to staggered sites in the host DNA by element-encoded integrase or transposase enzymes. Unfolding of such intermediates yields DNA gaps at each junction. It has been widely assumed that host DNA repair enzymes complete attachment of the remaining DNA ends, but the enzymes involved have not been identified for any system. We have synthesized DNA substrates containing the expected gap and 5' two-base flap structure present in retroviral integration intermediates and tested candidate enzymes for the ability to support repair in vitro. We find three required activities, two of which can be satisfied by multiple enzymes. These are a polymerase (polymerase beta, polymerase delta and its cofactor PCNA, or reverse transcriptase), a nuclease (flap endonuclease), and a ligase (ligase I, III, or IV and its cofactor XRCC4). A proposed pathway involving retroviral integrase and reverse transcriptase did not carry out repair under the conditions tested. In addition, prebinding of integrase protein to gapped DNA inhibited repair reactions, indicating that gap repair in vivo may require active disassembly of the integrase complex. PMID:11070016

Yoder, K E; Bushman, F D

2000-12-01

322

Mechanisms of Deterioration of Intermediate Moisture Food Systems.  

National Technical Information Service (NTIS)

A study of shelf stability in intermediate moisture foods was made. Major efforts were made to control lipid oxidation and nonenzymatic browning. In order to determine means of preventing these reactions, model systems were developed having the same water...

T. P. Labuza

1972-01-01

323

Multifragmentation in intermediate energy heavy ion collisions  

SciTech Connect

The GSL/LBL plastic ball/wall detector system was used to gain insight into the fragment production mechanism in Au + Au and Au + Fe reactions. Full azimuthal coverage for light particles (p,d,t,/sup 3/He,/sup 4/He) and intermediate mass fragments (z greater than 10) is achieved in the forward hemisphere in the center of mass system. The complete measurement of light particles allowed a global analysis of the events and a search for collective effects in fragment emission by comparing to flow effects seen in the light particles. The large acceptance for intermediate mass fragments allowed a measurements of their multiplicities event-by-event.

Jacak, B.V.; Britt, H.C.; Claesson, G.; Doss, K.G.R.; Ferguosn, R.; Gavron, A.I.; Gustafsson, H.A.; Gutbrod, H.; Harris, J.W.; Kampert, K.H.

1986-04-14

324

[The application of monoclonal peroxidase conjugates to identify comma bacillus of serum groups 01 and 0139 in the reaction of dot-immune analysis].  

PubMed

The source of monoclonal antibodies was chosen the cultural fluid of hybridoma-producers deposited in the specialized collection of cell cultures of vertebrates (St. Petersburg) with numbers RKKK(P) 386D and RKKK(P) 674D. The specific immunoglobulin (Ig) from cultural fluid was concentrated by precipitation with saturated solution of ammonium sulfate. The scheme of obtaining monoclonal antibodies included activation of peroxidase, conjugation of activated peroxidase with Ig, removal of unbounded proteins, storage and control. The preservation of activity of conjugates was supported with BSA (10%) or glycerin (50%). The last on is preferable to be applied for this purpose. The test of monoclonal antibody-01 and monoclonal antibody-0139 of peroxidase conjugates with kit of strains of comma bacillus 01 and 0139 demonstrated their strict specificity because they interacted only with corresponding serum groups under absence of crossed reactions with representatives of geterologic microorganisms. The direct dot-immune analysis is carried out during 1.5 hour and its sensitivity is within the limits 105-106. The application of diagnostic monoclonal peroxidase conjugates 01, 0139 in laboratory practice can promote the increase of specificity of serologic analysis of cholera and saving time-frame of its application. PMID:23808022

Alekseeva, L P; Kozlova, G A; Markina, O V; Kretenchuk, O F; Iagovkin, M E; Bursha, O S

2013-03-01

325

Polymerase chain reaction-based mutageneses identify key transporters belonging to multigene families involved in Na+ and pH homeostasis of Synechocystis sp. PCC 6803.  

PubMed

Primary ion pumps and antiporters exist as multigene families in the Synechocystis sp. PCC 6803 genome and show very strong homologies to those found in higher plants. The gene knock-outs of five putative Na+/H+ antiporters (slr1727, sll0273, sll0689, slr1595 and slr0415) and seven cation ATPases (sll1614, sll1920, slr0671-72, slr0822, slr1507-08-09, slr1728- 29 and slr1950) in the model cyanobacterium (http://www.kazusa.or.jp/cyano/cyano.html) were performed in this study relying on homologous recombination with mutagenenic fragments constructed using a fusion polymerase chain reaction (PCR) approach. The impacts of these gene knock-outs were evaluated in terms of Na+ and pH, and light-induced acidification and alkalization that are asso-ciated with inorganic carbon uptake. Two of the five putative antiporter mutants exhibit a characteristic interplay between the pH and Na+ dependence of growth, but only one of the antiporters appears to be necessary for high NaCl tolerance. On the other hand, the mutation of one of the two copper-trafficking ATPases produces a cell line that shows acute NaCl sensitivity. Additionally, disruptions of a putative Ca2+-ATPase and a gene cluster encoding a putative Na+-ATPase subunit also cause high NaCl sensitivity. The findings and possible mechanisms are discussed in relation to the potential roles of these transporters in Synechocystis sp. PCC 6803. PMID:12067339

Wang, Hong-Liang; Postier, Bradley L; Burnap, Robert L

2002-06-01

326

Epidemiology of Imported Cutaneous Leishmaniasis at the Hospital for Tropical Diseases, London, United Kingdom: Use of Polymerase Chain Reaction to Identify the Species  

PubMed Central

This study reviewed all patients diagnosed with imported cutaneous leishmaniasis (CL) at the Hospital for Tropical Diseases in London, United Kingdom, over an 11-year period. Diagnostic and epidemiologic information was collected prospectively for all patients with imported CL to this hospital during 1998–2009. A total of 223 patients were given a diagnosis of CL. Ninety patients were diagnosed with Old World CL, which was caused most commonly by Leishmania donovani complex (n = 20). A total of 71% were tourists to the Mediterranean region, 36% were migrants or visiting friends and relatives, and 17% were soldiers. One hundred thirty-three patients were given a diagnosis of New World CL. The Leishmania subgenus Viannia caused 97 of these cases; 44% of these were in backpackers and 29% were in soldiers. Polymerase chain reaction was more sensitive and faster for detecting Leishmania DNA (86% for Old World CL and 96% for New World CL) than culture. This is the largest study of imported leishmaniasis, and demonstrates that tourists to the Mediterranean and backpackers in Central and South America are at risk for this disease.

Wall, Emma C.; Watson, Julie; Armstrong, Margaret; Chiodini, Peter L.; Lockwood, Diana N.

2012-01-01

327

Separation of intermediates of iron-catalyzed dopamine oxidation reactions using reversed-phase ion-pairing chromatography coupled in tandem with UV-visible and ESI-MS detections.  

PubMed

Reversed-phase ion-pairing chromatography (RP-IPC) is coupled on-line with electrospray ionization-mass spectrometry (ESI-MS) through an interface comprising a four-way switch valve and an anion exchange column. Regeneration of the anion exchange column can be accomplished on-line by switching the four-way switch valve to interconnect the column to a regeneration solution. Positioning the anion exchange column between the RP-IPC and ESI-MS instruments allows the ion-pairing reagent (IPR) sodium octane sulfonate to be removed. The IPC-ESI-MS method enabled us to separate and detect four intermediates of the Fe(III)-catalyzed dopamine oxidation. In particular, 6-hydroxydopamine, which is short-lived and highly neurotoxic, was detected and quantified. Together with the separation of other intermediates, gaining insight into the mechanism and kinetics of the Fe(III)-catalyzed dopamine oxidation becomes possible. PMID:23217306

Zhang, Lin; Yagnik, Gargey; Jiang, Dianlu; Shi, Shuyun; Chang, Peter; Zhou, Feimeng

2012-10-29

328

Intermediate Pulsewidth Laser System.  

National Technical Information Service (NTIS)

The report is the second in the series of semiannual technical reports on Contract N00014-66-C-0056. It begins discussion on phase two of the contract which consists of the design, construction and delivery of an intermediate pulsewidth laser system. Subj...

J. W. Kantorski C. G. Young

1971-01-01

329

SPACE: Intermediate Level Modules.  

ERIC Educational Resources Information Center

|These modules were developed to assist teachers at the intermediate level to move away from extensive skill practice and toward more meaningful interdisciplinary learning. This packet, to be used by teachers in the summer Extended Learning Program, provides detailed thematic lesson plans matched to the Indiana Curriculum Proficiency Guide. The…

Indiana State Dept. of Education, Indianapolis. Center for School Improvement and Performance.

330

Lens Intermediate Filaments  

PubMed Central

The ocular lens assembles two separate Intermediate Filament systems sequentially with differentiation. Canonical 8–11 nm IFs composed of Vimentin are assembled in lens epithelial cells and younger fiber cells, while the fiber cell-specific Beaded Filaments are switched on as fiber cell elongation initiates. Some of the key features of both filament systems are reviewed.

2009-01-01

331

Intermediate band photovoltaics overview  

Microsoft Academic Search

Intermediate band photovoltaics bases its theoretical superior performance over single gap solar cells on enhancing the photogenerated solar cell current thanks to the two-step absorption of photons with energy lower than the semiconductor gap without degrading the output voltage. Its presumably better utilisation of the solar spectrum has lately become a topic of research, not only because of that of

L. Cuadra; A. Marti; N. Lopez; A. Luque

2003-01-01

332

Molecular detection of breast cancer metastasis in sentinel lymph nodes by reverse transcriptase polymerase chain reaction (RT-PCR): identifying, evaluating and establishing multi-marker panels.  

PubMed

The potential advantage of using quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) methodology to detect metastasis in sentinel lymph nodes (SLNs) of breast cancer (BC) patients was evaluated in this prospective study. We measured the expression of relevant gene transcripts in SLNs using an innovative algorithm and compared the results of single-marker assays versus multi-marker assays with conventional histological detection methods. SLNs from women aged ? 18 years diagnosed with unilateral BC were examined by haematoxylin-eosin staining and immunohistochemistry and analysed for transcripts of several relevant genes using qRT-PCR (learning group). Four candidate panels of expressed transcript combinations with high sensitivity and specificity were selected for further investigation. The candidate panels were then validated using SLNs from a second group of BC patients (validation group). In the learning group, 74/314 SLN sections from 150 patients were positive for metastasis by histology. The transcripts analysed showed the following individual sensitivities/specificities: cytokeratin 19 (CK19) 94.6%/97.9%; mammaglobin 1 (MGB1) 82.4%/91.7%; mammaglobin 2 (MGB2) 82.4%/96.7%; carcinoembryonic antigen (CEA) 71.6%/97.5%; EPCAM (epithelial cell adhesion molecule) 91.9%/97.1%; and NY-BR-1 82.4%/93.8%. The optimal panel based on the predefined criteria comprised four markers: CK19, MGB1, EPCAM, and NY-BR-1, of which ? 2 had to be positive (95.9% sensitivity, 95.0% specificity, 85.5% positive predictive value (PPV), and 98.7% negative predictive value (NPV)). Overall concordance with histology was 95.2%. In the validation group, 84/315 SLN sections from 235 patients were histologically positive, and panel sensitivity, specificity and overall accuracy were 88.1, 95.2 and 93.3%, respectively, at the SLN section level. In conclusion, molecular staging using expression patterns of relevant transcripts in SLNs could serve as a useful complement to standard diagnostic work-up in BC patients. The proposed flexible multi-parametric approach does not improve the overall accuracy compared with the single-marker approach. However, it overcomes several limitations of the previously reported molecular assays for SLN diagnosis. PMID:21858660

Wallwiener, Christian W; Wallwiener, Markus; Kurth, Ralf R; Röhm, Carmen; Neubauer, Hans; Banys, Malgorzata J; Staebler, Annette; Schönfisch, Birgitt; Meuer, Stefan C; Giese, Thomas; Fehm, Tanja N

2011-08-21

333

[Intermediate lymphocytic lymphoma].  

PubMed

The characteristic features are presented of intermediate lymphocytic lymphomas which have suggested the pathomorphological and clinical peculiarity of this disease entity. They occur in two forms: diffuse and nodular which are two phases in the development of the disease. The phenotypic and karyotypic characteristics of these lymphomas resemble those of chronic lymphocytic leukaemia, but their more malignant course is similar to that of centrocytic lymphomas. PMID:1413789

Ko?czalik, P; Hyjek, E

1992-02-01

334

Rupture disc. [LMFBR intermediate heat transport system  

Microsoft Academic Search

The intermediate heat transport system for a sodium-cooled fast breeder reactor includes a device for rapidly draining the sodium therefrom should a sodium-water reaction occur within the system. This device includes a rupturable member in a drain line in the system and means for cutting a large opening therein and for positively removing the sheared-out portion from the opening cut

1977-01-01

335

Carbonylation as a Key Reaction in Anaerobic Acetone Activation by Desulfococcus biacutus.  

PubMed

Acetone is activated by aerobic and nitrate-reducing bacteria via an ATP-dependent carboxylation reaction to form acetoacetate as the first reaction product. In the activation of acetone by sulfate-reducing bacteria, acetoacetate has not been found to be an intermediate. Here, we present evidence of a carbonylation reaction as the initial step in the activation of acetone by the strictly anaerobic sulfate reducer Desulfococcus biacutus. In cell suspension experiments, CO was found to be a far better cosubstrate for acetone activation than CO2. The hypothetical reaction product, acetoacetaldehyde, is extremely reactive and could not be identified as a free intermediate. However, acetoacetaldehyde dinitrophenylhydrazone was detected by mass spectrometry in cell extract experiments as a reaction product of acetone, CO, and dinitrophenylhydrazine. In a similar assay, 2-amino-4-methylpyrimidine was formed as the product of a reaction between acetoacetaldehyde and guanidine. The reaction depended on ATP as a cosubstrate. Moreover, the specific activity of aldehyde dehydrogenase (coenzyme A [CoA] acylating) tested with the putative physiological substrate was found to be 153 ± 36 mU mg(-1) protein, and its activity was specifically induced in extracts of acetone-grown cells. Moreover, acetoacetyl-CoA was detected (by mass spectrometry) after the carbonylation reaction as the subsequent intermediate after acetoacetaldehyde was formed. These results together provide evidence that acetoacetaldehyde is an intermediate in the activation of acetone by sulfate-reducing bacteria. PMID:23913429

Gutiérrez Acosta, Olga B; Hardt, Norman; Schink, Bernhard

2013-08-02

336

Development of a multiplexed polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) assay to identify common members of the Subgenera Culex (Culex) and Culex (Phenacomyia) in Guatemala.  

PubMed

Morphological differentiation of mosquitoes in the subgenera Culex (Culex) and Culex (Phenacomyia) in Guatemala is difficult, with reliable identification ensured only through examination of larval skins from individually reared specimens and associated male genitalia. We developed a multiplexed polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) assay to identify common Cx. (Cux.) and Cx. (Phc.). Culex (Cux.) chidesteri, Cx. (Cux.) coronator, Cx. (Cux.) interrogator, Cx. (Cux.) quinquefasciatus, Cx. (Cux.) nigripalpus/Cx. (Cux.) thriambus, and Cx. (Phc.) lactator were identified directly with a multiplexed primer cocktail comprising a conserved forward primer and specific reverse primers targeting ribosomal DNA (rDNA). Culex nigripalpus and Cx. thriambus were differentiated by restriction digest of homologous amplicons. The assay was developed and optimized using well-characterized specimens from Guatemala and the United States and field tested with unknown material from Guatemala. This assay will be a valuable tool for mosquito identification in entomological and arbovirus ecology studies in Guatemala. PMID:20682869

Kent, Rebekah J; Deus, Stephen; Williams, Martin; Savage, Harry M

2010-08-01

337

Mössbauer- and EPR-Snapshots of an Enzymatic Reaction: The Cytochrome P450 Reaction Cycle  

NASA Astrophysics Data System (ADS)

In this communication we present a complimentary Mössbauer- and EPR-study of the time dependance of the reaction of substrate free P450cam with peracetic acid within a time region ranging from 8 ms up to 5 min. An Fe(IV) species as well as a tyrosyl radical residing on the amino acid residue Tyr96 have been identified as reaction intermediates. These species possibly are formed by the reduction of compound I by means of transferring an electron from Tyr 96 to the heme moiety.

Schünemann, V.; Jung, C.; Lendzian, F.; Barra, A.-L.; Teschner, T.; Trautwein, A. X.

2004-12-01

338

Evidence for the two phosphate binding sites of an analogue of the thioacyl intermediate for the Trypanosoma cruzi glyceraldehyde-3-phosphate dehydrogenase-catalyzed reaction, from its crystal structure.  

PubMed

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) catalyzes the reversible oxidative phosphorylation of d-glyceraldehyde 3-phosphate (GAP) into d-glycerate 1,3-bisphosphate (1,3-diPG) in the presence of NAD(+) and inorganic phosphate (P(i)). Within the active site, two anion-binding sites were ascribed to the binding of the C3 phosphate of GAP (P(s)) and to the binding of the attacking phosphate ion (P(i)). The role played by these two sites in the catalytic mechanism in connection with the functional role of coenzyme exchange (NADH-NAD(+) shuttle) has been investigated by several studies leading to the C3 phosphate flipping model proposed by Skarzynski et al. [Skarzynski, T., Moody, P. C., and Wonacott, A. J. (1987) J. Mol. Biol. 193, 171-187]. This model has not yet received direct confirmation. To gain further insight into the role of both sites, we synthesized irreversible inhibitors which form with the essential cysteine residue a thioacyl enzyme analogue of the catalytic intermediate. Here we report the refined glycosomal Trypanosoma cruzi GAPDH in complex with a covalently bound GAP analogue at an improved resolution of 2.0-2.5 A. For this holo-thioacyl enzyme complex, a flip-flop movement is clearly characterized, the change from the P(i) to the P(s) binding site being correlated with the coenzyme exchange step: the weaker interaction of the intermediate when bound at the P(s) site with the cofactor allows its release and also the binding of the inorganic phosphate for the next catalytic step. This result gives strong experimental support for the generally accepted flip-flop model of the catalytic mechanism in GAPDH. PMID:12795610

Castilho, Marcelo S; Pavão, Fernando; Oliva, Glaucius; Ladame, Sylvain; Willson, Michèle; Périé, Jacques

2003-06-17

339

Mesoscopic statistical properties of multistep enzyme-mediated reactions.  

PubMed

Enzyme-mediated reactions may proceed through multiple intermediate conformational states before creating a final product molecule, and one often wishes to identify such intermediate structures from observations of the product creation. In this study, the authors address this problem by solving the chemical master equations for various enzymatic reactions. A perturbation theory analogous to that used in quantum mechanics allows the determination of the first (n) and the second (?2) cumulants of the distribution of created product molecules as a function of the substrate concentration and the kinetic rates of the intermediate processes. The mean product flux V=d(n)/dt (or 'dose-response' curve) and the Fano factor F= ?2/(n) are both realistically measurable quantities, and whereas the mean flux can often appear the same for different reaction types, the Fano factor can be quite different. This suggests both qualitative and quantitative ways to discriminate between different reaction schemes, and the authors explore this possibility in the context of four sample multistep enzymatic reactions. Measuring both the mean flux and the Fano factor can not only discriminate between reaction types, but can also provide some detailed information about the internal, unobserved kinetic rates, and this can be done without measuring single-molecule transition events. PMID:21028932

de Ronde, W H; Daniels, B C; Mugler, A; Sinitsyn, N A; Nemenman, I

2009-09-01

340

Statistical properties of multistep enzyme-mediated reactions  

SciTech Connect

Enzyme-mediated reactions may proceed through multiple intermediate conformational states before creating a final product molecule, and one often wishes to identify such intermediate structures from observations of the product creation. In this paper, we address this problem by solving the chemical master equations for various enzymatic reactions. We devise a perturbation theory analogous to that used in quantum mechanics that allows us to determine the first () and the second (variance) cumulants of the distribution of created product molecules as a function of the substrate concentration and the kinetic rates of the intermediate processes. The mean product flux V=d/dt (or 'dose-response' curve) and the Fano factor F=variance/ are both realistically measurable quantities, and while the mean flux can often appear the same for different reaction types, the Fano factor can be quite different. This suggests both qualitative and quantitative ways to discriminate between different reaction schemes, and we explore this possibility in the context of four sample multistep enzymatic reactions. We argue that measuring both the mean flux and the Fano factor can not only discriminate between reaction types, but can also provide some detailed information about the internal, unobserved kinetic rates, and this can be done without measuring single-molecule transition events.

Nemenman, Ilya [Los Alamos National Laboratory; Sinitsyn, Nikolai A [Los Alamos National Laboratory; De Ronde, Wiet H [AMOLF; Daniels, Bryan C [CORNELL; Mugler, Andrew [COLUMBIA

2008-01-01

341

Incoherence in the South African Labour Market for Intermediate Skills  

ERIC Educational Resources Information Center

This article is concerned with the production and employment of technically skilled labour at the intermediate level in South Africa. Three differing labour market pathways to intermediate skilling are identified. These are: the traditional apprenticeship route, the new "Learnerships" pathway (similar to the "modern apprenticeship" schemes adopted…

Kraak, Andre

2008-01-01

342

Formation of ammonia and hydrazine from the reactions of acids with bis(dinitrogen) complexes of molybdenum. Identification and isolation of intermediates. Possible analogy with the hydrazine-forming property of nitrogenase  

Microsoft Academic Search

The reactions of anhydrous HBr and HCl with trans-(Mo(Nâ)â(triphos)(PRâ)), where triphos = PhP(CHâCHâPPhâ)â(PRâ = PPhâ(1), PMePhâ (2)), in tetrahydrofuran (THF) solution to produce ammonia and in benzene solution to produce hydrazine and ammonia have been examined. Complex 1 reacted with HBr in THF to produce 1.5 mol of Nâ\\/mol of 1 and routinely ca. 0.72 mol of NHâ\\/mol of 1,

J. A. Baumann; G. E. Bossard; T. A. George; D. B. Howell; L. M. Koczon; R. K. Lester; C. M. Noddings

1985-01-01

343

Nature and dynamics of the charge-separated intermediate in reaction centers in which bacteriochlorophyll replaces the photoactive bacteriopheophytin. 2. The rates and yields of charge separation and recombination  

Microsoft Academic Search

The primary photochemistry of the (M)L214H and (M)L214H\\/(L)E104V mutant bacterial reaction centers (RCs) from Rhodobacter sphaeroides has been investigated at room and cryogenic temperatures. In both mutants the native bacteriopheophytin electron acceptor (BPh{sub L}) is replaced with a bacteriochlorophyll (BChl) molecule denoted by Î; in the double mutant a hydrogen-bonding interaction of Î-is removed. The initial stage of charge separation,

Christine Kirmaier; Laurent Laporte; D. Holten; C. C. Schenck

1995-01-01

344

Identifying harms.  

PubMed

Moral disagreements often revolve around the issue of harm to others. Identifying harms, however, is a contested enterprise. This paper provides a conceptual toolbox for identifying harms, and so possible wrongdoing, by drawing several distinctions. First, I distinguish between four modes of human vulnerability, forming four ways in which one can be in a harmed state. Second, I argue for the intrinsic disvalue of harm and so distinguish the presence of harm from the fact that it is instrumental to or constitutive of a valued act, practice or way of life. Finally, I distinguish between harm and wrongdoing, arguing that while harm is a normative concept requiring justification, not all harmed states are automatically unjustified. The advantage of this view is that it refocuses the moral debate on the normative issues involved while establishing a common basis to which both sides can agree: the presence of harm to others. PMID:21434956

Harrosh, Shlomit

2011-03-25

345

Identify Symmetry  

NSDL National Science Digital Library

This unit will teach you how to identify symmetry in everyday objects and mathematical shapes in lines and rotational symmetry. What is line symmetry? Click on the link to find out: Line Symmetry Here is a line activity to see if you understand it: Line Symmetry Class Zone See if you understand the concepts by doing the following quiz: Line Symmetry Work Now for rotational symmetry: Rotational Symmetry See if you understand rotational symmetry by taking this quiz: Rotational Symmetry Work ...

Neubert, Mrs.

2011-03-03

346

Identifying Erosion  

NSDL National Science Digital Library

In this environmental science activity (page 3 of the PDF), leaners will identify and explain the causes of erosion. They will observe the effects of erosion on the surrounding area and further explore examples of erosion online. An extension activity allows learners to make a hands-on model of soil erosion. Though this was created as a pre-visit activity for a workshop about water flow and erosion, it makes a great stand-alone activity as well!

Cosi

2009-01-01

347

Formation of a stalled early intermediate of pseudouridine synthesis monitored by real-time FRET.  

PubMed

Pseudouridine is the most abundant of more than 100 chemically distinct natural ribonucleotide modifications. Its synthesis consists of an isomerization reaction of a uridine residue in the RNA chain and is catalyzed by pseudouridine synthases. The unusual reaction mechanism has become the object of renewed research effort, frequently involving replacement of the substrate uridines with 5-fluorouracil (f(5)U). f(5)U is known to be a potent inhibitor of pseudouridine synthase activity, but the effect varies among the target pseudouridine synthases. Derivatives of f(5)U have previously been detected, which are thought to be either hydrolysis products of covalent enzyme-RNA adducts, or isomerization intermediates. Here we describe the interaction of pseudouridine synthase 1 (Pus1p) with f(5)U-containing tRNA. The interaction described is specific to Pus1p and position 27 in the tRNA anticodon stem, but the enzyme neither forms a covalent adduct nor stalls at a previously identified reaction intermediate of f(5)U. The f(5)U27 residue, as analyzed by a DNAzyme-based assay using TLC and mass spectrometry, displayed physicochemical properties unaltered by the reversible interaction with Pus1p. Thus, Pus1p binds an f(5)U-containing substrate, but, in contrast to other pseudouridine synthases, leaves the chemical structure of f(5)U unchanged. The specific, but nonproductive, interaction demonstrated here thus constitutes an intermediate of Pus turnover, stalled by the presence of f(5)U in an early state of catalysis. Observation of the interaction of Pus1p with fluorescence-labeled tRNA by a real-time readout of fluorescence anisotropy and FRET revealed significant structural distortion of f(5)U-tRNA structure in the stalled intermediate state of pseudouridine catalysis. PMID:20106954

Hengesbach, Martin; Voigts-Hoffmann, Felix; Hofmann, Benjamin; Helm, Mark

2010-01-27

348

Experiments in intermediate energy physics  

SciTech Connect

Research in experimental nuclear physics was done from 1979 to 2002 primarily at intermediate energy facilities that provide pion, proton, and kaon beams. Particularly successful has been the work at the Los Alamos Meson Physics Facility (LAMPF) on unraveling the neutron and proton contributions to nuclear ground state and transition densities. This work was done on a wide variety of nuclei and with great detail on the carbon, oxygen, and helium isotopes. Some of the investigations involved the use of polarized targets which allowed the extraction of information on the spin-dependent part of the triangle-nucleon interaction. At the Indiana University Cyclotron Facility (IUCF) we studied proton-induced charge exchange reactions with results of importance to astrophysics and the nuclear few-body problem. During the first few years, the analysis of heavy-ion nucleus scattering data that had been taken prior to 1979 was completed. During the last few years we created hypernuclei by use of a kaon beam at Brookhaven National Laboratory (BNL) and an electron beam at Jefferson Laboratory (JLab). The data taken at BNL for a study of the non-mesonic weak decay of the A particle in a nucleus are still under analysis by our collaborators. The work at JLab resulted in the best resolution hypernuclear spectra measured thus far with magnetic spectrometers.

Dehnhard, D.

2003-02-28

349

Ultrasound biomicroscopic imaging in intermediate uveitis  

PubMed Central

BACKGROUND—Clinical examination of the region of the eye mainly affected in patients with intermediate uveitis is difficult and often hampered by media opacities. In that perspective ultrasound biomicroscopy (UBM) promises to be a valuable additional diagnostic tool.?METHODS—UBM was performed at a sound frequency of 50 MHz on 26 eyes of 13 patients with intermediate uveitis in order to determine configuration of pars plana, peripheral retina, and vitreous. Findings of ophthalmoscopy with scleral indentation and UBM were compared.?RESULTS—In 18 of 26 eyes pathological structures such as membraneous or fluffy vitreous condensations were identified by UBM. Among these UBM revealed pathological findings which were not visible on funduscopy in nine eyes. Most importantly, vitreoretinal adhesions with traction on the retina were imaged in four eyes. However, in three eyes vitreous opacities being visible on funduscopy were not identified by UBM.?CONCLUSION—UBM seems to be a valuable diagnostic technique for the evaluation of patients with intermediate uveitis. Longitudinal studies will have to determine the relevance of UBM findings for the individual clinical course and their influence on therapeutic decisions.?? Keywords: intermediate uveitis; ultrasound biomicroscopy; vitreous opacities

Haring, G.; Nolle, B.; Wiechens, B.

1998-01-01

350

Formation of ammonia and hydrazine from the reactions of acids with bis(dinitrogen) complexes of molybdenum. Identification and isolation of intermediates. Possible analogy with the hydrazine-forming property of nitrogenase  

SciTech Connect

The reactions of anhydrous HBr and HCl with trans-(Mo(N/sub 2/)/sub 2/(triphos)(PR/sub 3/)), where triphos = PhP(CH/sub 2/CH/sub 2/PPh/sub 2/)/sub 2/(PR/sub 3/ = PPh/sub 3/(1), PMePh/sub 2/ (2)), in tetrahydrofuran (THF) solution to produce ammonia and in benzene solution to produce hydrazine and ammonia have been examined. Complex 1 reacted with HBr in THF to produce 1.5 mol of N/sub 2//mol of 1 and routinely ca. 0.72 mol of NH/sub 3//mol of 1, respectively, and MoBr/sub 3/(triphos) (greater than or equal to94% yield). No more than a trace of hydrazine was detected. Total nitrogen balance was increased to 100% when amounts of HBr were added periodically during the reaction. The reaction of 1 or 2 with HBr or HCl led to the rapid loss of 1 mol of N/sub 2/ and the formation of a pair of isomeric hydrazido(2-) complexes, (MoX(NNH/sub 2/)(triphos)(PR/sub 3/))X (PR/sub 3/ = PPh/sub 3/ for 1 A(X) and 1 B(X), PPh/sub 2/Me for 2A(X) and 2B(X); X = Br, Cl). The same mixtures were formed in the absence of solvent. The presence of two isomers was the result of the position of the phenyl group on the central phosphorus atom of the triphos ligand relative to the hydrazido(2-) ligand. 48 references, 3 figures, 3 tables.

Baumann, J.A.; Bossard, G.E.; George, T.A.; Howell, D.B.; Koczon, L.M.; Lester, R.K.; Noddings, C.M.

1985-10-23

351

The sonochemical degradation of azobenzene and related azo dyes: Rate enhancements via Fenton's reactions  

Microsoft Academic Search

The sonochemical degradation of aqueous solutions of azobenzene and related azo dyes (methyl orange, o-methyl red, and p-methyl red) was performed at 500 kHz and 50 W, under air, Oâ, or Ar saturation at 288 K. Reaction products and intermediates were identified by HPLC-ES-MS. Total organic carbon (TOC) was also determined as a function of reaction time. The authors propose

Jiju M. Joseph; Hugo Destaillats; Hui-Ming Hung; Michael R. Hoffmann

2000-01-01

352

Communications: Elementary oxygen electrode reactions in the aprotic Li-air battery  

NASA Astrophysics Data System (ADS)

We discuss the electrochemical reactions at the oxygen electrode of an aprotic Li-air battery. Using density functional theory to estimate the free energy of intermediates during the discharge and charge of the battery, we introduce a reaction free energy diagram and identify possible origins of the overpotential for both processes. We also address the question of electron conductivity through the Li2O2 electrode and show that in the presence of Li vacancies Li2O2 becomes a conductor.

Hummelshøj, J. S.; Blomqvist, J.; Datta, S.; Vegge, T.; Rossmeisl, J.; Thygesen, K. S.; Luntz, A. C.; Jacobsen, K. W.; Nørskov, J. K.

2010-02-01

353

Development of a polymerase chain reaction assay for differentiation between Culex pipiens pipiens and Cx. p. quinquefasciatus (Diptera: Culicidae) in North America based on genomic differences identified by subtractive hybridization.  

PubMed

Culex pipiens is a complex of mosquitoes that are involved in the transmission of pathogens, including St. Louis encephalitis virus in North America. The 2 major taxa in the complex, Cx. p. pipiens and Cx. p. quinquefasciatus, are nearly identical morphologically, making identification of field-collected specimens difficult, and attempts at differentiation based on biochemical and molecular techniques have been unsuccessful. We report here the use of genomic subtractive hybridization to identify a region of nucleic acid heterology between the genomes of Cx. p. pipiens and Cx. p. quinquefasciatus and the development of a polymerase chain reaction (PCR) assay to discriminate between them. PCR primers based on the nucleic acid sequence of a Cx. p. pipiens-unique DNA fragment were used to differentiate Cx. p. pipiens and Cx. p. pipiens/quinquefasciatus hybrids from Cx. p. quinquefasciatus by using extracted individual mosquito genomic DNA, crude DNA preparations from a mosquito head or legs, and DNA from triturated mosquito pools. PMID:9379458

Crabtree, M B; Savage, H M; Miller, B R

1997-09-01

354

Radiolysis studies on reactive intermediates. Technical progress report, November 1, 1975--November 1, 1976  

SciTech Connect

During the past year we have focused on the development of new experimental electron magnetic resonance methods and new theoretical models to study reactive reaction intermediates and on the application of these and other methods to study radical and ionic intermediates produced by high energy radiation. We have continued development of electron spin echo spectrometry for studying molecular orientation around trapped radicals, have suggested a new electron spin-lattice relaxation mechanism applicable to glasses, have shown a correlation between electron spin-lattice relaxation times and trapped radical decay and have shown how electron-electron double resonance measurements of cross relaxation can be analyzed to give radical-radical correlation distances. A new model of electron localization in alkanes has been developed, electron solvation in alcohol-alkane mixtures has been studied theoretically and an improved model of electron solvation times has been formulated. Radical reaction intermediates have been detected and identified by spin trapping in methanol, cyanoalkyl and fluoroalcohol liquids, and by X and Q band ESR in methyltetrahydrofuran glass. In aqueous glasses the electronic structure of O/sup -/ and the first solvation shell geometry of e/sup -//sub t/ have been deduced by /sup 17/O substitution. Electron tunneling as a function of the e/sup -//sub t/ energy state and the photoionization mechanism of indole in solution have been investigated.

Kevan, L.

1976-11-01

355

Oxidation of sulfoxides and arsenic(III) in corrosion of nanoscale zero valent iron by oxygen: evidence against ferryl ions (Fe(IV)) as active intermediates in Fenton reaction.  

PubMed

Previous studies have shown that the corrosion of zerovalent iron (ZVI) by oxygen (O(2)) via the Fenton reaction can lead to the oxidation of various organic and inorganic compounds. However, the nature of the oxidants involved (i.e., ferryl ion (Fe(IV)) versus hydroxyl radical (HO(•))) is still a controversial issue. In this work, we reevaluated the relative importance of these oxidants and their role in As(III) oxidation during the corrosion of nanoscale ZVI (nZVI) in air-saturated water. It was shown that Fe(IV) species could react with sulfoxides (e.g., dimethyl sulfoxide, methyl phenyl sulfoxide, and methyl p-tolyl sulfoxide) through a 2-electron transfer step producing corresponding sulfones, which markedly differed from their HO(•)-involved products. When using these sulfoxides as probe compounds, the formation of oxidation products indicative of HO(•) but no generation of sulfone products supporting Fe(IV) participation were observed in the nZVI/O(2) system over a wide pH range. As(III) could be completely or partially oxidized by nZVI in air-saturated water. Addition of scavengers for solution-phase HO(•) and/or Fe(IV) quenched As(III) oxidation at acidic pH but had little effect as solution pH increased, highlighting the importance of the heterogeneous iron surface reactions for As(III) oxidation at circumneutral pH. PMID:21133375

Pang, Su-Yan; Jiang, Jin; Ma, Jun

2010-12-06

356

Stabilization of labile carbonyl addition intermediates by a synthetic receptor.  

PubMed

Products of unfavorable chemical equilibria are not readily observed because their high energy and increased reactivity result in low concentrations. Biological macromolecules use binding forces to access unfavorable equilibria and stabilize reactive intermediates by isolating them from the medium. In a similar vein, we describe here a synthetic receptor that allows direct observation of labile tetrahedral intermediates: hemiaminals formed in the reaction of an aldehyde carbonyl group with amines. The receptor encapsulates alkyl-substituted primary amines, then orients them toward a covalently tethered aldehyde function. The hemiaminal intermediates appear at high concentration, confined from the bulk solution and observable at ambient temperature by conventional nuclear magnetic resonance spectroscopy. PMID:17656719

Iwasawa, Tetsuo; Hooley, Richard J; Rebek, Julius

2007-07-27

357

Non-heme Fe(IV)-oxo intermediates.  

PubMed

High-valent non-heme iron-oxo intermediates have been proposed for decades as the key intermediates in numerous biological oxidation reactions. In the past three years, the first direct characterization of such intermediates has been provided by studies of several alphaKG-dependent oxygenases that catalyze either hydroxylation or halogenation of their substrates. In each case, the Fe(IV)-oxo intermediate is implicated in cleavage of the aliphatic C-H bond to initiate hydroxylation or halogenation. The observation of non-heme Fe(IV)-oxo intermediates and Fe(II)-containing product(s) complexes with almost identical spectroscopic parameters in the reactions of two distantly related alphaKG-dependent hydroxylases suggests that members of this subfamily follow a conserved mechanism for substrate hydroxylation. In contrast, for the alphaKG-dependent non-heme iron halogenase, CytC3, two distinct Fe(IV) complexes form and decay together, suggesting that they are in rapid equilibrium. The existence of two distinct conformers of the Fe site may be the key factor accounting for the divergence of the halogenase reaction from the more usual hydroxylation pathway after C-H bond cleavage. Distinct transformations catalyzed by other mononuclear non-heme enzymes are likely also to involve initial C-H bond cleavage by Fe(IV)-oxo complexes, followed by diverging reactivities of the resulting Fe(III)-hydroxo/substrate radical intermediates. PMID:17542550

Krebs, Carsten; Galoni? Fujimori, Danica; Walsh, Christopher T; Bollinger, J Martin

2007-06-02

358

Identifying Species  

NSDL National Science Digital Library

This two part activity will allow students to investigate biological diversity in the area of their school. They will first prepare a taxonomic key to distinguish between the four insects or spiders that they have selected. All of the keys are combined and students then perform a transect study of a neighborhood field or school playing ground. Finally as a class students will compile a list of the animals and plants that are found within a mile of their school. They may need to use field guides, local resources, taxonomic keys, and species lists to help identify these organisms. Once they have compiled their list they will organize the species into the taxonomic groups they have studied.

Dispezio, Michael

359

Properties of Swift`s intermediate bursts  

Microsoft Academic Search

Based on their prompt, high-energy emission, gamma-ray bursts are usually classified into short-duration and long-duration classes. A third intermediate group has been identified on statistical grounds but its individual properties have not yet been studied in detail. Using the large sample of follow-up observations of GRBs produced during the Swift era we analyze the individual characteristics of this group. We

P. Veres; A. de Ugarte Postigo; I. Horvath; Z. Bagoly; D. A. Kann; C. C. Thöne; L. G. Balazs; P. D'Avanzo; M. A. Aloy; S. Foley; S. Campana; J. Mao; P. Jakobsson; S. Covino; J. P. U. Fynbo; J. Gorosabel; A. J. Castro-Tirado; M. Nardini; L. Amati

2011-01-01

360

Isoporphyrin intermediate in heme oxygenase catalysis. Oxidation of alpha-meso-phenylheme.  

PubMed

Human heme oxygenase-1 (hHO-1) catalyzes the O2- and NADPH-dependent oxidation of heme to biliverdin, CO, and free iron. The first step involves regiospecific insertion of an oxygen atom at the alpha-meso carbon by a ferric hydroperoxide and is predicted to proceed via an isoporphyrin pi-cation intermediate. Here we report spectroscopic detection of a transient intermediate during oxidation by hHO-1 of alpha-meso-phenylheme-IX, alpha-meso-(p-methylphenyl)-mesoheme-III, and alpha-meso-(p-trifluoromethylphenyl)-mesoheme-III. In agreement with previous experiments (Wang, J., Niemevz, F., Lad, L., Huang, L., Alvarez, D. E., Buldain, G., Poulos, T. L., and Ortiz de Montellano, P. R. (2004) J. Biol. Chem. 279, 42593-42604), only the alpha-biliverdin isomer is produced with concomitant formation of the corresponding benzoic acid. The transient intermediate observed in the NADPH-P450 reductase-catalyzed reaction accumulated when the reaction was supported by H2O2 and exhibited the absorption maxima at 435 and 930 nm characteristic of an isoporphyrin. Product analysis by reversed phase high performance liquid chromatography and liquid chromatography electrospray ionization mass spectrometry of the product generated with H2O2 identified it as an isoporphyrin that, on quenching, decayed to benzoylbiliverdin. In the presence of H218O2, one labeled oxygen atom was incorporated into these products. The hHO-1-isoporphyrin complexes were found to have half-lives of 1.7 and 2.4 h for the p-trifluoromethyl- and p-methyl-substituted phenylhemes, respectively. The addition of NADPH-P450 reductase to the H2O2-generated hHO-1-isoporphyrin complex produced alpha-biliverdin, confirming its role as a reaction intermediate. Identification of an isoporphyrin intermediate in the catalytic sequence of hHO-1, the first such intermediate observed in hemoprotein catalysis, completes our understanding of the critical first step of heme oxidation. PMID:18487208

Evans, John P; Niemevz, Fernando; Buldain, Graciela; de Montellano, Paul Ortiz

2008-05-16

361

Reactive intermediates revealed in secondary organic aerosol formation from isoprene  

PubMed Central

Isoprene is a significant source of atmospheric organic aerosol; however, the oxidation pathways that lead to secondary organic aerosol (SOA) have remained elusive. Here, we identify the role of two key reactive intermediates, epoxydiols of isoprene (IEPOX = ?-IEPOX + ?-IEPOX) and methacryloylperoxynitrate (MPAN), which are formed during isoprene oxidation under low- and high-NOx conditions, respectively. Isoprene low-NOx SOA is enhanced in the presence of acidified sulfate seed aerosol (mass yield 28.6%) over that in the presence of neutral aerosol (mass yield 1.3%). Increased uptake of IEPOX by acid-catalyzed particle-phase reactions is shown to explain this enhancement. Under high-NOx conditions, isoprene SOA formation occurs through oxidation of its second-generation product, MPAN. The similarity of the composition of SOA formed from the photooxidation of MPAN to that formed from isoprene and methacrolein demonstrates the role of MPAN in the formation of isoprene high-NOx SOA. Reactions of IEPOX and MPAN in the presence of anthropogenic pollutants (i.e., acidic aerosol produced from the oxidation of SO2 and NO2, respectively) could be a substantial source of “missing urban SOA” not included in current atmospheric models.

Surratt, Jason D.; Chan, Arthur W. H.; Eddingsaas, Nathan C.; Chan, ManNin; Loza, Christine L.; Kwan, Alan J.; Hersey, Scott P.; Flagan, Richard C.; Wennberg, Paul O.; Seinfeld, John H.

2010-01-01

362

The MHD intermediate shock interaction with an intermediate wave: Are intermediate shocks physical  

SciTech Connect

Contrary to the usual belief that MHD intermediate shocks are extraneous, the authors have recently shown by numerical solutions of dissipative MHD equations that intermediate shocks are admissible and can be formed through nonlinear steepening from a continuous wave. In this paper, he clarifies the differences between the conventional view and the results by studying the interaction of an MHD intermediate shock with an intermediate wave. The study reaffirms his results. In addition, the study shows that there exists a larger class of shocklike solutions in the time-dependent dissiaptive MHD equations than are given by the MHD Rankine-Hugoniot relations. it also suggests a mechanism for forming rotational discontinuities through the interaction of an intermediate shock with an intermediate wave. The results are of importance not only to the MHD shock theory but also to studies such as magnetic field reconnection models.

Wu, C.C. (Univ. of California, Los Angeles (United States))

1988-02-01

363

Welding. Performance Objectives. Intermediate Course.  

ERIC Educational Resources Information Center

|Several intermediate performance objectives and corresponding criterion measures are listed for each of nine terminal objectives for an intermediate welding course. The materials were developed for a 36-week (3 hours daily) course designed to prepare the student for employment in the field of welding. Electric welding and specialized (TIG & MIG)…

Vincent, Kenneth

364

Wealth, Financial Intermediation and Growth  

Microsoft Academic Search

This paper presents empirical support for the existence of wealth effects in the contribution of financial intermediation to economic growth, and offers a theoretical explanation for these effects. Using GMM dynamic panel data techniques applied to study the growth-promoting effects of financial intermediation, we show that the exogenous contribution of financial development on economic growth has different effects for different

Alejandro Gaytan; Romain Ranciere

2004-01-01

365

Masonry. Performance Objectives. Intermediate Course.  

ERIC Educational Resources Information Center

|Several intermediate performance objectives and corresponding criterion measures are listed for each of 13 terminal objectives for an intermediate masonry course. These materials, developed for a two-semester (3 hours daily) course, are designed to provide the student with the skills and knowledge necessary for entry level employment in the field…

Thompson, Moses

366

Remotely adjustable intermediate seismic support  

Microsoft Academic Search

An intermediate seismic support system is described for use in conjunction with a nuclear reactor, comprising: a nuclear reactor closure head; control rod drive mechanisms (CRDMs) projecting upwardly from the nuclear reactor closure head. Each of the control rod drive mechanisms include a latch housing within which are respectively disposed control rod drive rods; and an intermediate seismic support capable

1987-01-01

367

The Theory of Financial Intermediation  

Microsoft Academic Search

Traditional theories of intermediation are based on transaction costs and asymmetric information. They are designed to account for institutions which take deposits or issue insurance policies and channel funds to firms. However, in recent decades there have been significant changes. Although transaction costs and asymmetric information have declined, intermediation has increased. New markets for financial futures and options are mainly

Franklin Allen; Anthony M. Santomero

1996-01-01

368

A Fluorogenic Aromatic Nucleophilic Substitution Reaction for Demonstrating Normal-Phase Chromatography and Isolation of Nitrobenzoxadiazole Chromophores  

ERIC Educational Resources Information Center

Normal-phase chromatography is an essential technique for monitoring chemical reactions, identifying the presence of specific components, as well as the purification of organic compounds. An experiment to facilitate the instruction and understanding of the concepts behind normal-phase chromatography at the introductory and intermediate

Key, Jessie A.; Li, Matthew D.; Cairo, Christopher W.

2011-01-01

369

A Fluorogenic Aromatic Nucleophilic Substitution Reaction for Demonstrating Normal-Phase Chromatography and Isolation of Nitrobenzoxadiazole Chromophores  

ERIC Educational Resources Information Center

|Normal-phase chromatography is an essential technique for monitoring chemical reactions, identifying the presence of specific components, as well as the purification of organic compounds. An experiment to facilitate the instruction and understanding of the concepts behind normal-phase chromatography at the introductory and intermediate

Key, Jessie A.; Li, Matthew D.; Cairo, Christopher W.

2011-01-01

370

Degradation pathway of the naphthalene azo dye intermediate 1-diazo-2- naphthol-4-sulfonic acid using Fenton's reagent.  

PubMed

Degradation of naphthalene dye intermediate 1-diazo-2- naphthol-4-sulfonic acid (1,2,4-Acid) by Fenton process has been studied in depth for the purpose of learning more about the reactions involved in the oxidation of 1,2,4-Acid. During 1,2,4-Acid oxidation, the solution color initially takes on a dark red, then to dark black associated with the formation of quinodial-type structures, and then goes to dark brown and gradually disappears, indicating a fast degradation of azo group. The observed color changes of the solution are a result of main reaction intermediates, which can be an indicator of the level of oxidization reached. Nevertheless, complete TOC removal is not accomplished, in accordance with the presence of resistant carboxylic acids at the end of the reaction. The intermediates generated along the reaction time have been identified and quantified. UPLC-(ESI)-TOF-HRMS analysis allows the detection of 19 aromatic compounds of different size and complexity. Some of them share the same accurate mass but appear at different retention time, evidencing their different molecular structures. Heteroatom oxidation products like SO(4)(2-) have also been quantified and explanations of their release are proposed. Short-chain carboxylic acids are detected at long reaction time, as a previous step to complete the process of dye mineralization. Finally, considering all the findings of the present study and previous related works, the evolution from the original 1,2,4-Acid to the final products is proposed in a general reaction scheme. PMID:22608610

Zhu, Nanwen; Gu, Lin; Yuan, Haiping; Lou, Ziyang; Wang, Liang; Zhang, Xin

2012-05-02

371

Photocatalytic degradation of metoprolol tartrate in suspensions of two TiO2-based photocatalysts with different surface area. Identification of intermediates and proposal of degradation pathways.  

PubMed

This study investigates the efficiency of the photocatalytic degradation of metoprolol tartrate (MET), a widely used ?(1)-blocker, in TiO(2) suspensions of Wackherr's "Oxyde de titane standard" and Degussa P25. The study encompasses transformation kinetics and efficiency, identification of intermediates and reaction pathways. In the investigated range of initial concentrations (0.01-0.1 mM), the photocatalytic degradation of MET in the first stage of the reaction followed approximately a pseudo-first order kinetics. The TiO(2) Wackherr induced a significantly faster MET degradation compared to TiO(2) Degussa P25 when relatively high substrate concentrations were used. By examining the effect of ethanol as a scavenger of hydroxyl radicals (OH), it was shown that the reaction with OH played the main role in the photocatalytic degradation of MET. After 240 min of irradiation the reaction intermediates were almost completely mineralized to CO(2) and H(2)O, while the nitrogen was predominantly present as NH(4)(+). Reaction intermediates were studied in detail and a number of them were identified using LC-MS/MS (ESI+), which allowed the proposal of a tentative pathway for the photocatalytic transformation of MET as a function of the TiO(2) specimen. PMID:22035693

Abramovi?, Biljana; Kler, Sanja; Soji?, Daniela; Lauševi?, Mila; Radovi?, Tanja; Vione, Davide

2011-10-08

372

Validation of the reaction thermodynamics associated with NaSc(BH4)4 from first-principles calculations: Detecting metastable paths and identifying the minimum free energy path  

NASA Astrophysics Data System (ADS)

A critical drawback with first-principles thermodynamic calculations is the absence of the vibrational and entropic contributions to the prediction of reaction mechanisms, which could conclusively show that the predicted reaction mechanism might be not the most stable reaction path. This study focused on providing an answer to this problem by examining possible metastable paths for five reactant mixtures whose reaction mechanisms were previously predicted using first-principles thermodynamic calculations. The aim of this study was to find a minimum free energy path among all the possible paths of each reactant mixture. This effort provided the clear conclusion that the original reaction paths predicted from first-principles thermodynamic calculations were the most stable reaction paths at an appropriate H2 pressure range for all cases. An additional examination associated with density functional theory uncertainty suggests how the ambiguity of reaction mechanisms predicted based on thermodynamic calculations should be understood and dealt with.

Kim, Ki Chul

2012-08-01

373

Intermediate-statistics spin waves  

NASA Astrophysics Data System (ADS)

In this paper, we show that spin waves, the elementary excitation of the Heisenberg magnetic system, obey a kind of intermediate statistics with a finite maximum occupation number n. We construct an operator realization for the intermediate statistics obeyed by magnons, the quantized spin waves, and then construct a corresponding intermediate-statistics realization for the angular momentum algebra in terms of the creation and annihilation operators of the magnons. In other words, instead of the Holstein-Primakoff representation, a bosonic representation subject to a constraint on the occupation number, we present an intermediate-statistics representation with no constraints. In this realization, the maximum occupation number is naturally embodied in the commutation relation of creation and annihilation operators, while the Holstein-Primakoff representation is a bosonic operator relation with an additional putting-in-by-hand restriction on the occupation number. We deduce the intermediate-statistics distribution function for magnons from the intermediate-statistics commutation relation of the creation and annihilation operators directly, which is a modified Bose-Einstein distribution. On the basis of these results, we calculate the dispersion relations for ferromagnetic and antiferromagnetic spin waves. The relations between the intermediate statistics that magnons obey and the other two important kinds of intermediate statistics, Haldane-Wu statistics and the fractional statistics of anyons, are discussed. We also compare the spectrum of the intermediate-statistics spin wave with the exact solution of the one-dimensional s = 1/2 Heisenberg model, which is obtained by the Bethe ansatz method. For ferromagnets, we take the contributions from the interaction between magnons (the quartic contribution), the next-to-nearest-neighbor interaction, and the dipolar interaction into account for comparison with the experiment.

Dai, Wu-Sheng; Xie, Mi

2009-04-01

374

Reactive intermediates and carbohydrate fragmentation in Maillard chemistry  

Microsoft Academic Search

Much research is devoted to the elucidation of mechanisms in the Maillard reaction. Model studies with reactive intermediates and 13C-labelled precursors have contributed significantly to our understanding of flavour formation in the Maillard reaction. Several examples are discussed here: The formation of methyl pyrazines and 2-acetyl-1-pyrroline, the role of ARP's and deoxyglycosones and the formation of carbohydrate fragments from reducing

H. Weenen

1998-01-01

375

Photoreactions of cyclic sulfite esters: Evidence for diradical intermediates  

PubMed Central

Summary The photochemistry of a phenyl and 1,2-diphenyl substituted sulfite ester is reported. The performance of photoreactions under relatively mild reaction conditions enables the detection of products that have not been observed in previous studies. It is concluded that, complementary to the initially proposed carbene intermediates, diradicals may also be considered.

Arney, Benny E; Ihmels, Heiko

2012-01-01

376

Kinetic Theory of Adsorption of Intermediates in Electrochemical Catalysis  

Microsoft Academic Search

The behavior of adsorbed intermediates in consecutive electrochemical reactions is discussed in terms of the steady-state rate equations, and a comparison with results obtained using the quasiequilibrium assumption is made. The adsorption pseudocapacitance vs potential plot is shown to be symmetrical only when the quasiequilibrium assumption is made, namely when the ratio of specific rate constants for the desorption step

E. Gileadi; B. E. Conway

1963-01-01

377

Storage Stability and Improvement of Intermediate Moisture Foods.  

National Technical Information Service (NTIS)

The rates of chemical reactions which deteriorate foods prepared to an intermediate moisture content and water activity (A sub w 0.6 to 0.9) were studied. The phenomenon of sorption hysteresis was used to prepare model systems and foods to similar A sub w...

T. P. Labuza

1973-01-01

378

Structural relations for time-dependent intermediate shocks  

SciTech Connect

A quantitative description of time-dependent (MHD) intermediate shocks is formulated. In non-coplanar Riemann problems, time-dependent 2 yields 3 intermediate shocks evolve in time as a localized self-similar structure whose strength decreases as 1/sq rt t, and whose width expands as sq rt t. We derive structural relations, similar to Rankine-Hugoniot relations, between the plasma properties and the magnitude of the transverse magnetic field, which we hope can help identify time-dependent 2 yields 3 intermediate shocks at the magnetopause, in the solar wind, and elsewhere in space. The analytic forms of the structural relations agree with our numerical results. 15 refs.

Wu, C.C.; Kennel, C.F. (California Univ., Los Angeles (United States))

1992-10-01

379

Heterogeneous Degradation of Oxygenated Intermediates.  

National Technical Information Service (NTIS)

Issues surrounding the importance of including heterogeneous processes when determining the fate of oxygenated intermediates in the troposphere are discussed. Results of recent investigations are reviewed and preliminary data from a laboratory study are p...

E. O. Edney

1994-01-01

380

Plasticity of Intermediate Filament Subunits  

PubMed Central

Intermediate filaments (IFs) assembled in vitro from recombinantly expressed proteins have a diameter of 8–12 nm and can reach several micrometers in length. IFs assemble from a soluble pool of subunits, tetramers in the case of vimentin. Upon salt addition, the subunits form first unit length filaments (ULFs) within seconds and then assembly proceeds further by end-to-end fusion of ULFs and short filaments. So far, IF subunits have mainly been observed by electron microscopy of glycerol sprayed and rotary metal shadowed specimens. Due to the shear forces during spraying the IF subunits appear generally as straight thin rods. In this study, we used atomic force microscopy (AFM), cryo-electron microscopy (cryo-EM) combined with molecular modeling to investigate the conformation of the subunits of vimentin, desmin and keratin K5/K14 IFs in various conditions. Due to their anisotropic shape the subunits are difficult to image at high resolution by cryo-EM. In order to enhance contrast we used a cryo-negative staining approach. The subunits were clearly identified as thin, slightly curved rods. However the staining agent also forced the subunits to aggregate into two-dimensional networks of dot-like structures. To test this conformational change further, we imaged dried unfixed subunits on mica by AFM revealing a mixture of extended and dot-like conformations. The use of divalent ions such as calcium and magnesium, as well as glutaraldehyde exposure favored compact conformations over elongated ones. These experimental results as well as coarse-grained molecular dynamics simulations of a vimentin tetramer highlight the plasticity of IF subunits.

Hoenger, Andrea; Buehler, Markus J.; Kreplak, Laurent

2010-01-01

381

BB Seminar: Prediction of Survival Incorporating Intermediate Event Info  

Cancer.gov

In recent years, an increasing number of predictive markers have been identified as useful for risk prediction. When interest lies in predicting long term survival, it has often been argued that intermediate event information may be very helpful in improving the prediction. Most existing methods for incorporating potentially censored intermediate event information in predicting long term survival focus on modeling the disease process and are derived under restrictive parametric models in a multi-state survival setting.

382

Modeling the Reaction of Fe Atoms with CCl4  

SciTech Connect

The reaction of zero-valent iron with carbon tetrachloride (CCl4) in gas phase was studied using density functional theory. Temperature programmed desorption experiments over a range of Fe and CCl4 coverages on a FeO(111) surface, demonstrate a rich surface chemistry with several reaction products (C2Cl4, C2Cl6, OCCl2, CO, FeCl2, FeCl3) observed. The reactivity of Fe and CCl4 was studied under three stoichiometries, one Fe with one CCl4, one Fe with two CCl4 molecules and two Fe with one CCl4, modeling the environment of the experimental work. The electronic structure calculations give insight into the reactions leading to the experimentally observed products and suggest that novel Fe-C-Cl containing species are important intermediates in these reactions. The intermediate complexes are formed in highly exothermic reactions, in agreement with the experimentally observed reactivity with the surface at low temperature (30 K). This initial survey of the reactivity of Fe with CCl4 identifies some potential reaction pathways that are important in the effort to use Fe nano-particles to differentiate harmful pathways that lead to the formation of contaminants like chloroform (CHCl3) from harmless pathways that lead to products such as formate (HCO2-) or carbon oxides in water and soil. The Pacific Northwest National Laboratory is operated by Battelle for the U.S. Department of Energy.

Camaioni, Donald M.; Ginovska, Bojana; Dupuis, Michel

2009-01-05

383

Noncanonical Reactions of Flavoenzymes  

PubMed Central

Enzymes containing flavin cofactors are predominantly involved in redox reactions in numerous cellular processes where the protein environment modulates the chemical reactivity of the flavin to either transfer one or two electrons. Some flavoenzymes catalyze reactions with no net redox change. In these reactions, the protein environment modulates the reactivity of the flavin to perform novel chemistries. Recent mechanistic and structural data supporting novel flavin functionalities in reactions catalyzed by chorismate synthase, type II isopentenyl diphosphate isomerase, UDP-galactopyranose mutase, and alkyl-dihydroxyacetonephosphate synthase are presented in this review. In these enzymes, the flavin plays either a direct role in acid/base reactions or as a nucleophile or electrophile. In addition, the flavin cofactor is proposed to function as a “molecular scaffold” in the formation of UDP-galactofuranose and alkyl-dihydroxyacetonephosphate by forming a covalent adduct with reaction intermediates.

Sobrado, Pablo

2012-01-01

384

Cost-effectiveness of diagnostic strategies to identify Mycobacterium avium subspecies paratuberculosis super-shedder cows in a large dairy herd using antibody enzyme-linked immunosorbent assays, quantitative real-time polymerase chain reaction, and bacterial culture.  

PubMed

Diagnostic strategies to detect Mycobacterium avium subsp. paratuberculosis (MAP) super-shedder cows in dairy herds have been minimally studied. The objective of the current study was to compare the cost-effectiveness of strategies for identification of MAP super-shedders on a California dairy herd of 3,577 cows housed in free-stall pens. Eleven strategies that included serum or milk enzyme-linked immunosorbent assay (ELISA), quantitative real-time polymerase chain reaction (qPCR) or culture of environmental samples, pooled or individual cow fecal samples, or combinations thereof were compared. Nineteen super-shedders (0.5%) were identified by qPCR and confirmed by culture as cows shedding ? 10,000 colony forming units (CFU)/g feces (median of 30,000 CFU/g feces). A stratified random sample of the study herd based on qPCR results of fecal pools was the most sensitive (74%) strategy and had the highest cost ($5,398/super-shedder). The reference strategy with the lowest cost ($1,230/super-shedder) and sensitivity (47%) included qPCR testing of fecal samples from ELISA-positive lactating (milk) and nonlactating (serum) cows housed in pens with the highest MAP bioburden. The most cost-effective alternative to the reference was to perform qPCR testing of fecal samples from ELISA-positive cows (milk and serum for milking and dry cows, respectively) for a sensitivity of 68% and cost of $2,226/super-shedder. In conclusion, diagnostic strategies varied in their cost-effectiveness depending on the tests, specimen type, and labor costs. Initial qPCR testing of environmental samples from free-stall pens to target cows in pens with the highest MAP bioburden for further testing can improve the cost-effectiveness of strategies for super-shedder identification. PMID:22807510

Aly, Sharif S; Anderson, Randall J; Whitlock, Robert H; Fyock, Terry L; McAdams, Susan C; Byrem, Todd M; Jiang, Jiming; Adaska, John M; Gardner, Ian A

2012-07-17

385

Time-resolved heme protein intermediates  

NASA Astrophysics Data System (ADS)

To determine the enzymatic mechanisms of heme proteins, it is necessary to identify the intermediates along the catalytic pathway and measure the times of their formation and decay. Resonance Raman scattering spectra are especially powerful for obtaining such information as the electronic structure of the heme group and the nature of the ligand coordinated to the heme iron atom may be monitored. The oxygen intermediates of two physiologically important enzymes will be presented. Nitric oxide synthase (NOS) uses oxygen to convert arginine to NO and citrulline; and cytochrome c oxidase (CcO) reduces oxygen to water to support oxidative phosphorylation. The fate or the oxygen in each of these enzymes has been followed by resonance Raman scattering. In NOS the oxygen is slowly converted to an activated species that then reacts fast, whereas in CcO the oxygen is rapidly converted to a reactive species that subsequently reacts slowly. The properties of the intermediates and the origin of the differences between these enzymes will be discussed.

Rousseau, Denis

2005-03-01

386

Reaction coordinates for electron transfer reactions  

SciTech Connect

The polarization fluctuation and energy gap formulations of the reaction coordinate for outer sphere electron transfer are linearly related to the constant energy constraint Lagrangian multiplier m in Marcus' theory of electron transfer. The quadratic dependence of the free energies of the reactant and product intermediates on m and m+1, respectively, leads to similar dependence of the free energies on the reaction coordinates and to the same dependence of the activation energy on the reorganization energy and the standard reaction free energy. Within the approximations of a continuum model of the solvent and linear response of the longitudinal polarization to the electric field in Marcus' theory, both formulations of the reaction coordinate are expected to lead to the same results.

Rasaiah, Jayendran C. [Department of Chemistry, University of Maine, Orono, Maine 04469 (United States); Zhu Jianjun [Department of Chemistry, State University of New York, Stonybrook, New York 11790 (United States) and Department of Chemistry, Henan Normal University, Xinxiang, Henan (China)

2008-12-07

387

One-pot Synthesis of Lactams Using Domino Reactions: Combination of Schmidt Reaction with Sakurai and Aldol Reactions  

PubMed Central

A series of domino reactions in which the intramolecular Schmidt reaction is combined with either a Sakurai reaction, an aldol reaction, or both is reported. The Sakurai reaction of an allylsilane with an azido-containing enone under Lewis acidic conditions followed by protonation of the resulting titanium enolate species allowed for a subsequent intramolecular Schmidt reaction. Alternatively, the intermediate titanium enolate could undergo an aldol reaction, followed by the intramolecular Schmidt reaction to form lactam products with multiple stereogenic centers. The stereochemical features of the titanium enolate aldol reaction with several 3-azidoaldehyde substrates during this domino process is discussed.

Huh, Chan Woo; Somal, Gagandeep K.; Katz, Christopher E.; Pei, Huaxing; Zeng, Yibin; Douglas, Justin T.; Aube, Jeffrey

2009-01-01

388

Incomplete and complete fusion in intermediate energy heavy ion reactions  

SciTech Connect

The yields, angular distributions and differential range spectra have been measured for individual target residues from the interaction of 8.5 MeV/A /sup 16/O, 19 MeV/A /sup 16/O, 35 MeV/A /sup 12/C and 86 MeV/A /sup 12/C with /sup 154/Sm. From the measured data, fragment isobaric yields and velocity spectra were deduced. The results are compared to the sum rule model of Wilczyski et al. and the nuclear firestreak model. 18 references.

Aleklett, K.; Loveland, W.; Sugihara, T.T.; Morrissey, D.J.; Wenxin, L.; Kot, W.; Seaborg, G.T.

1984-03-01

389

Artificial reaction coordinate "tunneling" in free-energy calculations: the catalytic reaction of RNase H.  

PubMed

We describe a method for the systematic improvement of reaction coordinates in quantum mechanical/molecular mechanical (QM/MM) calculations of reaction free-energy profiles. In umbrella-sampling free-energy calculations, a biasing potential acting on a chosen reaction coordinate is used to sample the system in reactant, product, and transition states. Sharp, nearly discontinuous changes along the resulting reaction path are used to identify coordinates that are relevant for the reaction but not properly sampled. These degrees of freedom are then included in an extended reaction coordinate. The general formalism is illustrated for the catalytic cleavage of the RNA backbone of an RNA/DNA hybrid duplex by the RNase H enzyme of Bacillus halodurans. We find that in the initial attack of the phosphate diester by water, the oxygen-phosphorus distances alone are not sufficient as reaction coordinates, resulting in substantial hysteresis in the proton degrees of freedom and a barrier that is too low (approximately 10 kcal/mol). If the proton degrees of freedom are included in an extended reaction coordinate, we obtain a barrier of 21.6 kcal/mol consistent with the experimental rates. As the barrier is approached, the attacking water molecule transfers one of its protons to the O1P oxygen of the phosphate group. At the barrier top, the resulting hydroxide ion forms a penta-coordinated phosphate intermediate. The method used to identify important degrees of freedom, and the procedure to optimize the reaction coordinate are general and should be useful both in classical and in QM/MM free-energy calculations. PMID:19462398

Rosta, Edina; Woodcock, H Lee; Brooks, Bernard R; Hummer, Gerhard

2009-08-01

390

Key intermediates of iodine-mediated electrophilic cyclization: isolation and characterization in an osmabenzene system.  

PubMed

Caught in the act: Key intermediates in an iodine-mediated electrophilic cyclization reaction was isolated by introducing metallabenzenes as the starting material. The unique structure of the intermediate should be described as the intimate ion pair form, instead of the widely accepted iodonium ion form. PMID:23897550

Wang, Tongdao; Zhang, Hong; Han, Feifei; Long, Lipeng; Lin, Zhenyang; Xia, Haiping

2013-07-29

391

1,2-DIHYDROXYPROPYL-3-ARSONIC ACID: A KEY INTERMEDIATE FOR ARSONOLIPIDS  

Microsoft Academic Search

The synthesis and properties of a key intermediate for arsonolipids, rac-1,2-dihydroxypropyl-3-arsonic acid and its salts, are described. The mechanism of the Meyer reaction with ?-hydroxy alkyl halides is discussed.

Gerasimos M. Tsivgoulis; Demetrios N. Sotiropoulos; Panayiotis V. Ioannou

1991-01-01

392

Redox isomerization via azomethine ylide intermediates: N-alkyl indoles from indolines and aldehydes.  

PubMed

Indolines react with aromatic and heteroaromatic aldehydes to yield N-alkyl indoles in a benzoic acid catalyzed redox isomerization reaction. Azomethine ylides are intermediates in this process which was established by intramolecular [3 + 2] trapping experiments. PMID:21247142

Deb, Indubhusan; Das, Deepankar; Seidel, Daniel

2011-01-19

393

A temporal intermediate stimulus problem.  

PubMed

Pigeons discriminated the serial position of a target duration among a sequence of 3 stimulus durations; the specific duration sequences changed across trials. In different conditions, the target duration was the shortest, intermediate, or longest duration in the sequence. Conditions involved a series of transitions in which new duration sequences were added to the stimulus set, providing an assessment of transfer. Pigeons learned and transferred the discrimination when the target was the shortest or longest duration. When, however, the target was the intermediate duration, the birds had great difficulty learning the task and exhibited little transfer to novel sequences. These findings are similar to those observed with nontemporal stimuli in a classic discrimination task, the intermediate stimulus problem. They provide an extension of work on relational timing to a more complex situation. PMID:9805788

Fetterman, J G

1998-10-01

394

Materials System for Intermediate Temperature Solid Oxide Fuel Cell  

SciTech Connect

AC complex impedance spectroscopy studies were conducted between 600-800 C on symmetrical cells that employed strontium-and-magnesium-doped lanthanum gallate electrolyte, La{sub 0.9}Sr{sub 0.1}Ga{sub 0.8}Mg{sub 0.2}O{sub 3} (LSGM). The objective of the study was to identify the materials system for fabrication and evaluation of intermediate temperature (600-800 C) solid oxide fuel cells (SOFCs). The slurry-coated electrode materials had fine porosity to enhance catalytic activity. Cathode materials investigated include La{sub 1-x}Sr{sub x}MnO{sub 3} (LSM), LSCF (La{sub 1-x}Sr{sub x}Co{sub y}Fe{sub 1-y}O{sub 3}), a two-phase particulate composite consisting of LSM-doped-lanthanum gallate (LSGM), and LSCF-LSGM. The anode materials were Ni-Ce{sub 0.85}Gd{sub 0.15}O{sub 2} (Ni-GDC) and Ni-Ce{sub 0.6}La{sub 0.4}O{sub 2} (Ni-LDC) composites. Experiments conducted with the anode materials investigated the effect of having a barrier layer of GDC or LDC in between the LSGM electrolyte and the Ni-composite anode to prevent adverse reaction of the Ni with lanthanum in LSGM. For proper interpretation of the beneficial effects of the barrier layer, similar measurements were performed without the barrier layer. The ohmic and the polarization resistances of the system were obtained over time as a function of temperature (600-800 C), firing temperature, thickness, and the composition of the electrodes. The study revealed important details pertaining to the ohmic and the polarization resistances of the electrode as they relate to stability and the charge-transfer reactions that occur in such electrode structures.

Uday B. Pal; Srikanth Gopalan

2005-01-24

395

Monoclonal antibodies against myofibrillar components of rat skeletal muscle decorate the intermediate filaments of cultured cells.  

PubMed Central

Monospecific antibodies were produced in vitro by fusing mouse myeloma cells with spleen cells from a BALB/c mouse immunized with rat skeletal myofibrils. After cloning 3 times on agarose, two stable clones were obtained and chosen for further characterization. The first clone, JLB1, produced an antibody that recognizing an antigen distributed in the M-line region and on either site of the Z line of myofibrils. The second clone, JLB7, produced an antibody reacting only with an antigen located at the M-line region of myofibrils. Both JLB1 and JLB7 antibodies decorate the typical intermediate filaments of a variety of cultured cells. Colcemid treatment of cells before reaction with both antibodies resulted in the coiling or capping (or both) of the fibers around the nucleus. Brief treatment of cells with cytochalasin B did not affect the integrity of the fibers stained by both antibodies whereas, under the same conditions, microfilament bundles visualized by another monoclonal antibody (JLA20) against actin were disassembled into many aggregates in the cytoplasm. Identical staining patterns of the intermediate filaments are obtained by double-label immunofluorescence microscopy of the same cell stained with these monoclonal antibodies and rabbit autoimmune serum (which has been shown to react with the components of the intermediate filaments). By using immunoprecipitation, protein bands at 210,000 and 95,000 daltons from chicken embryo fibroblasts were identified as the potential antigens recognized by JLB1 and JLB7 monoclonal antibodies, respectively. The widespread occurrence of these antigenic determinants in different cultured cells suggests the highly conservative property of these intermediate-filament components. Images

Lin, J J

1981-01-01

396

Learning to predict chemical reactions.  

PubMed

Being able to predict the course of arbitrary chemical reactions is essential to the theory and applications of organic chemistry. Approaches to the reaction prediction problems can be organized around three poles corresponding to: (1) physical laws; (2) rule-based expert systems; and (3) inductive machine learning. Previous approaches at these poles, respectively, are not high throughput, are not generalizable or scalable, and lack sufficient data and structure to be implemented. We propose a new approach to reaction prediction utilizing elements from each pole. Using a physically inspired conceptualization, we describe single mechanistic reactions as interactions between coarse approximations of molecular orbitals (MOs) and use topological and physicochemical attributes as descriptors. Using an existing rule-based system (Reaction Explorer), we derive a restricted chemistry data set consisting of 1630 full multistep reactions with 2358 distinct starting materials and intermediates, associated with 2989 productive mechanistic steps and 6.14 million unproductive mechanistic steps. And from machine learning, we pose identifying productive mechanistic steps as a statistical ranking, information retrieval problem: given a set of reactants and a description of conditions, learn a ranking model over potential filled-to-unfilled MO interactions such that the top-ranked mechanistic steps yield the major products. The machine learning implementation follows a two-stage approach, in which we first train atom level reactivity filters to prune 94.00% of nonproductive reactions with a 0.01% error rate. Then, we train an ensemble of ranking models on pairs of interacting MOs to learn a relative productivity function over mechanistic steps in a given system. Without the use of explicit transformation patterns, the ensemble perfectly ranks the productive mechanism at the top 89.05% of the time, rising to 99.86% of the time when the top four are considered. Furthermore, the system is generalizable, making reasonable predictions over reactants and conditions which the rule-based expert does not handle. A web interface to the machine learning based mechanistic reaction predictor is accessible through our chemoinformatics portal ( http://cdb.ics.uci.edu) under the Toolkits section. PMID:21819139

Kayala, Matthew A; Azencott, Chloé-Agathe; Chen, Jonathan H; Baldi, Pierre

2011-09-02

397

Communication Networks in Intermediate Markets  

Microsoft Academic Search

Most commodities move from points of production through successive stages of processing or manufacture and further stages of intermediate distribution before reaching points of final purchase. The final value of a commodity, in fact, is often analyzed by observing the amounts of labor and capital services that are added to it at each of these stages by the firm which

F. E. Balderston

1958-01-01

398

Intermediate filaments mediate cytoskeletal crosstalk  

Microsoft Academic Search

Intermediate filaments, actin-containing microfilaments and microtubules are the three main cytoskeletal systems of vertebrate and many invertebrate cells. Although these systems are composed of distinctly different proteins, they are in constant and intimate communication with one another. Understanding the molecular basis of this cytoskeletal crosstalk is essential for determining the mechanisms that underlie many cell-biological phenomena. Recent studies have revealed

Lynne Chang; Robert D. Goldman

2004-01-01

399

AIDS Elementary/Intermediate Curriculum.  

ERIC Educational Resources Information Center

|This Acquired Immune Deficiency Syndrome (AIDS) Curriculum was developed for intermediate elementary (5th, 6th, and 7th grade) students. It is an integrated unit that encompasses health, science, social studies, math, and language arts. The curriculum is comprised of nine class activities designed to meet the following objectives: (1) to…

Kellogg, Nancy Rader

400

Intermediate Filaments: A Historical Perspective  

PubMed Central

Intracellular protein filaments intermediate in size between actin microfilaments and microtubules are composed of a surprising variety of tissue specific proteins commonly interconnected with other filamentous systems for mechanical stability and decorated by a variety of proteins that provide specialized functions. The sequence conservation of the coiled-coil, alpha-helical structure responsible for polymerization into individual 10 nm filaments defines the classification of intermediate filament proteins into a large gene family. Individual filaments further assemble into bundles and branched cytoskeletons visible in the light microscope. However, it is the diversity of the variable terminal domains that likely contributes most to different functions. The search for the functions of intermediate filament proteins has led to discoveries of roles in diseases of the skin, heart, muscle, liver, brain, adipose tissues and even premature aging. The diversity of uses of intermediate filaments as structural elements and scaffolds for organizing the distribution of decorating molecules contrasts with other cytoskeletal elements. This review is an attempt to provide some recollection of how such a diverse field emerged and changed over about 30 years.

Oshima, Robert G.

2007-01-01

401

Intermediate Mechanics Tutorials: The Lagrangian  

NSDL National Science Digital Library

This set of tutorial materials focuses on explaining the use of the Lagrangian in classical mechanics. In the tutorial, students describe a basic physics problem using a Newtonian notation, then using the Lagrangian, and then compare the two. This material includes a tutorial and example homework. This is part of a large collection of similar tutorial materials in intermediate classical mechanics.

Wittmann, Michael C.; Ambrose, Bradley S.

2009-07-26

402

Identification of the intermediate hosts of Habronema microstoma and Habronema muscae under field conditions.  

PubMed

A polymerase chain reaction (PCR)-based assay was used for the specific detection of Habronema microstoma and Habronema muscae (Nematoda, Spirurida) in order to identify the intermediate hosts of both nematode species under field conditions. A total of 1087 netted and 165 laboratory-bred flies were tested. Flies were identified as Musca domestica Linnaeus 1758, Musca autumnalis De Geer 1776, Haematobia irritans (Linnaeus 1758), Haematobia titillans (De Geer 1907) and Stomoxys calcitrans (Linnaeus 1758) (Muscidae). Genomic DNA was extracted from pools of fly heads, thoraces and abdomens, and 703 samples were subjected to a duplex two-step semi-nested PCR assay to specifically detect diagnostic regions within the ribosomal ITS2 sequence of both H. microstoma and H. muscae. Stomoxys calcitrans specimens were positive for H. microstoma DNA and M. domestica specimens were positive for H. muscae DNA. In particular, PCR-positive samples derived from both farm-netted and laboratory-bred flies. The present study represents the first evidence of the vectorial competence of different fly species as intermediate hosts of Habronema stomachworms under field conditions. We discuss the roles of S. calcitrans and M. domestica in transmitting H. microstoma and H. muscae. PMID:18816277

Traversa, D; Otranto, D; Iorio, R; Carluccio, A; Contri, A; Paoletti, B; Bartolini, R; Giangaspero, A

2008-09-01

403

Proline-catalysed Mannich reactions of acetaldehyde  

Microsoft Academic Search

Small organic molecules recently emerged as a third class of broadly useful asymmetric catalysts that direct reactions to yield predominantly one chiral product, complementing enzymes and metal complexes. For instance, the amino acid proline and its derivatives are useful for the catalytic activation of carbonyl compounds via nucleophilic enamine intermediates. Several important carbon-carbon bond-forming reactions, including the Mannich reaction, have

Jung Woon Yang; Carley Chandler; Michael Stadler; Daniela Kampen; Benjamin List

2008-01-01

404

Noneczematous Contact Reactions  

Microsoft Academic Search

\\u000a Not all skin contact reactions present as eczema or dermatitis. There are several distinct noneczematous contact reactions\\u000a which are more commonly seen. The mechanisms of these reactions are not clearly elucidated yet. It is very useful to clinicians\\u000a to be able to identify these dermatoses as contact reactions so that they may be confirmed with patch testing and other unnecessary

Anthony Goon; Chee-Leok Goh

405

Intermediate Temperature Solid Oxide Fuel Cell Development  

SciTech Connect

Solid oxide fuel cells (SOFCs) are high efficiency energy conversion devices. Present materials set, using yttria stabilized zirconia (YSZ) electrolyte, limit the cell operating temperatures to 800 C or higher. It has become increasingly evident however that lowering the operating temperature would provide a more expeditious route to commercialization. The advantages of intermediate temperature (600 to 800 C) operation are related to both economic and materials issues. Lower operating temperature allows the use of low cost materials for the balance of plant and limits degradation arising from materials interactions. When the SOFC operating temperature is in the range of 600 to 700 C, it is also possible to partially reform hydrocarbon fuels within the stack providing additional system cost savings by reducing the air preheat heat-exchanger and blower size. The promise of Sr and Mg doped lanthanum gallate (LSGM) electrolyte materials, based on their high ionic conductivity and oxygen transference number at the intermediate temperature is well recognized. The focus of the present project was two-fold: (a) Identify a cell fabrication technique to achieve the benefits of lanthanum gallate material, and (b) Investigate alternative cathode materials that demonstrate low cathode polarization losses at the intermediate temperature. A porous matrix supported, thin film cell configuration was fabricated. The electrode material precursor was infiltrated into the porous matrix and the counter electrode was screen printed. Both anode and cathode infiltration produced high performance cells. Comparison of the two approaches showed that an infiltrated cathode cells may have advantages in high fuel utilization operations. Two new cathode materials were evaluated. Northwestern University investigated LSGM-ceria composite cathode while Caltech evaluated Ba-Sr-Co-Fe (BSCF) based pervoskite cathode. Both cathode materials showed lower polarization losses at temperatures as low as 600 C than conventional manganite or cobaltite cathodes.

S. Elangovan; Scott Barnett; Sossina Haile

2008-06-30

406

NICMOS Intermediate Focus/Alignment  

NASA Astrophysics Data System (ADS)

# The purpose of this activity is to perform a series of iterative adjustments of the NICMOS pupil alignment mechanism to establish the initial optical alignment in focus and tilt for all three cameras. This proposal has been broken down into 4 sub-proposals to make implementation easier. The four phases of the NICMOS Focus/Alignment activity are: # 1} Pre-Alignment Check-out {prop 7134} 2} Coarse Optical Alignment {Initial Focus Sweep} {prop 7041} 3} Intermediate Focus/Alignment {prop 7135} 4} Fine Optical Alignment {prop 7042} # This is proposal 7135; Intermediate Focus/Alignment -------------------------- Objectives: a} Estimate PAM focus and X/Y tilt for each camera b} Check performance over camera fields of view c} Allow sufficient time for dewar temperatures to equilibrate before next activity

Schneider, Glenn

1997-12-01

407

Intermediate phenotypes in psychiatric disorders  

PubMed Central

The small effect size of most individual risk factors for psychiatric disorders likely reflects biological heterogeneity and diagnostic imprecision, which has encouraged genetic studies of intermediate biologic phenotypes that are closer to the molecular effects of risk genes than are the clinical symptoms. Neuroimaging-based intermediate phenotypes have emerged as particularly promising because they map risk associated gene effects onto physiological processes in brain that are altered in patients and in their healthy relatives. Recent evidence using this approach has elucidated discrete, dissociable biological mechanisms of risk genes at the level of neural circuitries, and their related cognitive functions. This approach may greatly contribute to our understanding of the genetics and pathophysiology of psychiatric disorders.

Rasetti, Roberta; Weinberger, Daniel R.

2011-01-01

408

Oxidation at intermediate moisture contents  

Microsoft Academic Search

In the study of the oxidation rate of methyl linoleate in protein and cellulose systems, a prooxidant effect was found at\\u000a intermediate moisture contents. At low water content, water hydrates metals and hydrogen bonds with peroxides, and an overall\\u000a decrease in the rate of lipid oxidation results. With an increase in the water content to the region with a water

T. P. Labuza; N. D. Heidelbaugh; M. Silver; M. Karel

1971-01-01

409

Price Theory: An Intermediate Text  

NSDL National Science Digital Library

David D. Friedman, Professor of Law at Santa Clara University, has made his textbook, "Price Theory: An Intermediate Text" available on the web. The book focuses on trying to teach students the "economic way of thinking" and the "analytical core of economics -- price theory." Topics covered include consumer choice, market structure and economic efficiency. Price Theory also contains chapters on less conventional topics such as the political marketplace, the economics of law and law breaking; and the economics of love and marriage.

Friedman, David D.

1990-01-01

410

Intermediate filaments in nervous tissues  

Microsoft Academic Search

Intermediate filaments have been isolated from rabbit intradural spinal nerve roots by the axonal flotation method. This method was modified to avoid exposure of axons to low ionic strength medium. The purified filaments are morphologically 75-80% pure. The gel electrophoretogr am shows four major bands migrating at 200,000, 145,000, 68,000, and 60,000 daltons, respectively. A similar preparation from rabbit brain

RONALD K. H. LIEM; SHU-HUI YEN; GARY D. SALOMON; MICHAEL L. SHELANSKI

1978-01-01

411

Fundamentals of flight, intermediate text  

NSDL National Science Digital Library

This website is an intermediate on-line textbook on the fundamentals of flight. Initially, this resource examines different kinds of flight. Specifically gliding and true flight are explored. Further topics in the principles of flight will cover aeronautics, the movement of fluids, water and liquids, movement of air, measurements, properties of flight, air moving objects, and forces in flight. This resource also provides fundamentals of flight references. Copyright 2005 International Technology Education Association

Aerospace, Cislunar

1996-01-01

412

Intermediate care. It takes two.  

PubMed

An intermediate care scheme launched by a primary care trust in April 2000 is now receiving 90 referrals a month, mainly from GPs and community staff. Patients receive an assessment within two hours of referral and care within four hours. Patients can refer themselves and ambulance crews can also refer patients to the scheme, preventing hospital admissions. The scheme operates from 8 am to 8 pm, seven days a week and it is hoped to extend it to 24 hours. PMID:12596491

Altoft, Lesley; Raven, Debbie

2003-02-01

413

Controlling reaction specificity in pyridoxal phosphate enzymes  

PubMed Central

Pyridoxal 5'-phosphate enzymes are ubiquitous in the nitrogen metabolism of all organisms. They catalyze a wide variety of reactions including racemization, transamination, decarboxylation, elimination, retro-aldol cleavage, Claisen condensation, and others on substrates containing an amino group, most commonly ?-amino acids. The wide variety of reactions catalyzed by PLP enzymes is enabled by the ability of the covalent aldimine intermediate formed between substrate and PLP to stabilize carbanionic intermediates at C? of the substrate. This review attempts to summarize the mechanisms by which reaction specificity can be achieved in PLP enzymes by focusing on three aspects of these reactions: stereoelectronic effects, protonation state of the external aldimine intermediate, and interaction of the carbanionic intermediate with the protein side chains present in the active site.

Toney, Michael D.

2012-01-01

414

Cyclohexanone Conversion Catalyzed by Pt\\/?-Al 2 O 3 : Evidence of Oxygen Removal and Coupling Reactions  

Microsoft Academic Search

\\u000a Abstract  The conversion of cyclohexanone, often identified as an intermediate in the conversion of lignin-derived compounds, was catalyzed\\u000a by Pt\\/?-Al2O3 in the presence of H2 at 573 K. Dehydrogenation was a kinetically significant reaction, indicated by a high selectivity for phenol. Oxygen-removal\\u000a reactions are indicated by products including benzene, cyclohexene, and cyclohexene. Bimolecular reactions involving cyclohexanone\\u000a and\\/or products of its conversion led

Tarit Nimmanwudipong; Ron C. Runnebaum; Kevin Tay; David E. Block; Bruce C. Gates

415

Ozonation and peroxone oxidation of benzophenone-3 in water: effect of operational parameters and identification of intermediate products.  

PubMed

The goal of this study was to bring forward new data and insights with respect to the effect of operational variables and reaction pathways during ozonation and peroxone oxidation of the UV filter compound benzophenone-3 (BP3) in water. A systematic parameter study, investigating the effect of the ozone inlet concentration, temperature, pH, H(2)O(2) and t-butanol addition in a lab-scale bubble reactor, showed the promising potential of ozonation towards BP3 degradation. pH showed to be a major process parameter, with half-life times (5.1-15.0 min) being more than two times shorter at pH10 compared to neutral and acid conditions. This indicates the important role of hydroxyl radicals as supported by the addition of H(2)O(2) and t-butanol as HO promoter and scavenger, respectively. Ozonation intermediate products were identified by liquid chromatography coupled to quadrupole-time-of-flight mass spectrometry (HPLC-QqTOF-MS/MS). Demethylation and non-selective HO attack proved to be the major reaction mechanisms. Where available, identified intermediates were confirmed using analytical standards, and concentration profiles along the ozonation process were determined through selective targeted MS/MS analysis. Benzophenone-1 (BP1), also being a UV-filter compound, and 2,2'-dihydroxy-4-methoxybenzophenone (DHM