Conformational dynamics in fluorophenylcarbamoyl-alpha-chymotrypsins.

PubMed

Kairi, M; Gerig, J T

1990-06-19

A series of fluorine-substituted diphenylcarbamoyl chlorides have been synthesized and used to prepare corresponding diphenylcarbamoylated derivatives of alpha-chymotrypsin. The enzyme is rapidly inactivated by these compounds, as has been previously observed for the unsubstituted chloride, and the derivatives are stable enough to permit extensive studies by fluorine NMR spectroscopy. In combination with previously reported results, these NMR experiments suggest that the aromatic rings of a diphenylcarbamoyl group attached to chymotrypsin may be found in two magnetically and dynamically distinguishable sites, with exchange between these sites taking place by a process that involves rotation about the carbamoyl N-CO bond and localized unfolding of the enzyme. The extent to which a given fluoroaromatic ring is found in one of these sites is dependent on the position of the fluorine substituent and the nature of the partner aromatic ring. It is found that a 2-fluorophenyl ring, when present, dominantly determines site occupation, while a 3-fluorophenyl ring has no effects that are detectably different from those of an unsubstituted phenyl ring. There is evidence for slow aromatic ring rotation within at least one of the phenyl ring interaction sites. Saturation transfer and lineshape methods provide information about the rates of interconversion of the N-phenyl groups between these sites. Line-width, spin-lattice relaxation times and fluorine-proton nuclear Overhauser effects determined at 282 and 470 MHz are reported for each system examined.

New Polybenzimidazole Architectures by Diels Alder Polymerization

DTIC Science & Technology

2012-02-14

stable organic polymers known.9 This class of polymers is aromatic with the heterocyclic benzimidazole group, a five membered imidazole ring...will allow benzimidazole ring systems to be prepared from the cycloaddition with an imidazole diene. The goals of the project included synthesis

Does the concept of Clar's aromatic sextet work for dicationic forms of polycyclic aromatic hydrocarbons?--testing the model against charged systems in singlet and triplet states.

PubMed

Dominikowska, Justyna; Palusiak, Marcin

2011-07-07

The concept of Clar's π-electron aromatic sextet was tested against a set of polycyclic aromatic hydrocarbons in neutral and doubly charged forms. Systems containing different types of rings (in the context of Clar's concept) were chosen, including benzene, naphthalene, anthracene, phenanthrene and triphenylene. In the case of dicationic structures both singlet and triplet states were considered. It was found that for singlet state dicationic structures the concept of aromatic sextet could be applied and the local aromaticity could be discussed in the context of that model, whereas in the case of triplet state dicationic structures Clar's model rather failed. Different aromaticity indices based on various properties of molecular systems were applied for the purpose of the studies. The discussion about the interdependence between the values of different aromaticity indices applied to neutral and charged systems in singlet and triplet states is also included. This journal is © the Owner Societies 2011

Protonation at the aromatic ring of samarium benzophenone dianion species. Isolation and structural characterization of a samarium(III) enolate complex

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

Hou, Z.; Yoshimura, Takashi; Wakatsuki, Yasuo

1994-11-30

The reduction of aromatic compounds into their dihydro derivatives by dissolving metal/alcohol systems (the Birch reduction) is a useful methodology in organic synthesis. Of particular importance is the reduction of aromatic carbonyl compounds such as aromatic acids, esters, amides, and monoaryl ketones, which usually generates in situ useful metal enolate intermediates that upon further reaction with electrophiles yield a variety of cyclohexadiene derivatives. One of the possible processes to generate these metal enolate intermediates is thought to be the monoprotonation of dianionic species at the para position of the aromatic rings. On the other hand, the reduction of diaryl ketonesmore » by alkali metals in liquid ammonia or by lanthanide metals in THF/HMPA or DME has been well known to afford the corresponding ketone dianions. The first X-ray structure of metal ketone dianion complexes, [Yb([mu]-[eta][sup 1],[eta][sup 2]-OCPh[sub 2]) (HMPA)[sub 2

Infrared spectroscopy of protonated trimethylamine-(benzene)(n) (n = 1-4) as model clusters of the quaternary ammonium-aromatic ring interaction.

PubMed

Shishido, Ryunosuke; Kawai, Yuki; Fujii, Asuka

2014-09-04

The essence of the molecular recognition of the neurotransmitter acetylcholine has been attributed to the attractive interaction between a quaternary ammonium and aromatic rings. We employed protonated trimethylamine-(benzene)n clusters (n = 1-4) in the gas phase as a model to study the recognition mechanism of acetylcholine at the microscopic level. We applied size-selective infrared spectroscopy to the clusters and observed the NH and CH stretching vibrational regions. We also performed density functional theory calculations of stable structures, charge distributions, and infrared spectra of the clusters. It was shown that the methyl groups of protonated trimethylamine are solvated by benzene one at a time in the n > 1 clusters, and the validity of these clusters as a model system of the acetylcholine recognition was demonstrated. The nature of the interactions between a quaternary ammonium and aromatic rings is discussed on the basis of the observed infrared spectra and the theoretical calculations.

Can Baird's and Clar's Rules Combined Explain Triplet State Energies of Polycyclic Conjugated Hydrocarbons with Fused 4nπ- and (4n + 2)π-Rings?

PubMed

Ayub, Rabia; Bakouri, Ouissam El; Jorner, Kjell; Solà, Miquel; Ottosson, Henrik

2017-06-16

Compounds that can be labeled as "aromatic chameleons" are π-conjugated compounds that are able to adjust their π-electron distributions so as to comply with the different rules of aromaticity in different electronic states. We used quantum chemical calculations to explore how the fusion of benzene rings onto aromatic chameleonic units represented by biphenylene, dibenzocyclooctatetraene, and dibenzo[a,e]pentalene modifies the first triplet excited states (T 1 ) of the compounds. Decreases in T 1 energies are observed when going from isomers with linear connectivity of the fused benzene rings to those with cis- or trans-bent connectivities. The T 1 energies decreased down to those of the parent (isolated) 4nπ-electron units. Simultaneously, we observe an increased influence of triplet state aromaticity of the central 4n ring as given by Baird's rule and evidenced by geometric, magnetic, and electron density based aromaticity indices (HOMA, NICS-XY, ACID, and FLU). Because of an influence of triplet state aromaticity in the central 4nπ-electron units, the most stabilized compounds retain the triplet excitation in Baird π-quartets or octets, enabling the outer benzene rings to adapt closed-shell singlet Clar π-sextet character. Interestingly, the T 1 energies go down as the total number of aromatic cycles within a molecule in the T 1 state increases.

Role of methyl group number on SOA formation from aromatic hydrocarbons photooxidation under low NOx conditions

NASA Astrophysics Data System (ADS)

Li, L.; Tang, P.; Nakao, S.; Chen, C.-L.; Cocker, D. R., III

2015-11-01

Substitution of methyl groups onto the aromatic ring determines the SOA formation from the aromatic hydrocarbon precursor. This study links the number of methyl groups on the aromatic ring to SOA formation from aromatic hydrocarbons photooxidation under low NOx conditions (HC / NO > 10 ppb C : ppb). Aromatic hydrocarbons with increasing numbers of methyl groups are systematically studied. SOA formation from pentamethylbenzene and hexamethylbenzene are reported for the first time. A decreasing SOA yield with increasing number of methyl groups is observed. Linear trends are found in both f44 vs. f43 and O / C vs. H / C for SOA from aromatic hydrocarbons with zero to six methyl groups. An SOA oxidation state predictive method based on benzene is used to examine the effect of added methyl groups on aromatic oxidation under low NOx conditions. Further, the impact of methyl group number on density and volatility of SOA from aromatic hydrocarbons is explored. Finally, a mechanism for methyl group impact on SOA formation is suggested. Overall, this work suggests as more methyl groups are attached on the aromatic ring, SOA products from these aromatic hydrocarbons become less oxidized per mass/carbon.

A Multistep Synthesis Incorporating a Green Bromination of an Aromatic Ring

ERIC Educational Resources Information Center

Cardinal, Pascal; Greer, Brandon; Luong, Horace; Tyagunova, Yevgeniya

2012-01-01

Electrophilic aromatic substitution is a fundamental topic taught in the undergraduate organic chemistry curriculum. A multistep synthesis that includes a safer and greener method for the bromination of an aromatic ring than traditional bromination methods is described. This experiment is multifaceted and can be used to teach students about…

The effect of perfluorination on the aromaticity of benzene and heterocyclic six-membered rings.

PubMed

Wu, Judy I; Pühlhofer, Frank G; Schleyer, Paul von Ragué; Puchta, Ralph; Kiran, Boggavarapu; Mauksch, Michael; Hommes, Nico J R van Eikema; Alkorta, Ibon; Elguero, José

2009-06-18

Despite having six highly electronegative F's, perfluorobenzene C(6)F(6) is as aromatic as benzene. Ab initio block-localized wave function (BLW) computations reveal that both C(6)F(6) and benzene have essentially the same extra cyclic resonance energies (ECREs). Localized molecular orbital (LMO)-nucleus-independent chemical shifts (NICS) grids demonstrates that the F's induce only local paratropic contributions that are not related to aromaticity. Thus, all of the fluorinated benzenes (C(6)F(n)H((6-n)), n = 1-6) have similar ring-LMO-NICS(pi zz) values. However, 1,3-difluorobenzene 2b and 1,3,5-trifluorobenzene 3c are slightly less aromatic than their isomers due to a greater degree of ring charge alternation. Isoelectronic C(5)H(5)Y heterocycles (Y = BH(-), N, NH(+)) are as aromatic as benzene, based on their ring-LMO-NICS(pi zz) and ECRE values, unless extremely electronegative heteroatoms (e.g., Y = O(+)) are involved.

Four faces of the interaction between ions and aromatic rings.

PubMed

Papp, Dóra; Rovó, Petra; Jákli, Imre; Császár, Attila G; Perczel, András

2017-07-15

Non-covalent interactions between ions and aromatic rings play an important role in the stabilization of macromolecular complexes; of particular interest are peptides and proteins containing aromatic side chains (Phe, Trp, and Tyr) interacting with negatively (Asp and Glu) and positively (Arg and Lys) charged amino acid residues. The structures of the ion-aromatic-ring complexes are the result of an interaction between the large quadrupole moment of the ring and the charge of the ion. Four attractive interaction types are proposed to be distinguished based on the position of the ion with respect to the plane of the ring: perpendicular cation-π (CP ⊥ ), co-planar cation-π (CP ∥ ), perpendicular anion-π (AP ⊥ ), and co-planar anion-π (AP ∥ ). To understand more than the basic features of these four interaction types, a systematic, high-level quantum chemical study is performed, using the X -  + C 6 H 6 , M +  + C 6 H 6 , X -  + C 6 F 6 , and M +  + C 6 F 6 model systems with X -  = H - , F - , Cl - , HCOO - , CH 3 COO - and M +  = H + , Li + , Na + , NH4+, CH 3 NH3+, whereby C 6 H 6 and C 6 F 6 represent an electron-rich and an electron-deficient π system, respectively. Benchmark-quality interaction energies with small uncertainties, obtained via the so-called focal-point analysis (FPA) technique, are reported for the four interaction types. The computations reveal that the interactions lead to significant stabilization, and that the interaction energy order, given in kcal mol -1 in parentheses, is CP ⊥ (23-37) > AP ⊥ (14-21) > CP ∥ (9-22) > AP ∥ (6-16). A natural bond orbital analysis performed leads to a deeper qualitative understanding of the four interaction types. To facilitate the future quantum chemical characterization of ion-aromatic-ring interactions in large biomolecules, the performance of three density functional theory methods, B3LYP, BHandHLYP, and M06-2X, is tested against the FPA benchmarks, with the result that the M06-2X functional performs best. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

Bond Length Equalization with molecular aromaticity-A new measurement of aromaticity.

PubMed

Shen, Chen-Fei; Liu, Zi-Zhong; Liu, Hong-Xia; Zhang, Hui-Qing

2018-05-08

A new method to measure the amount of aromaticity is presented through the process of Bond Length Equalization (BLE). Degree of Aromaticity (DOA), a two-dimensional intensive quantity including geometric and energetic factors, as a new measurement of aromaticity is proposed. The unique characteristic of DOA and the formation of DOA will be displayed. The calculation of the geometrical optimization, DOA, Nucleus Independent Chemical Shifts (NICS) and Ring Stretching Vibration Raman Spectroscopy Frequency (RSVRSF) for the aromatic ring molecules - G n H n m (G = C, Si, Ge, n = 3, 5-8, m = +1, -1, 0, +1, +2) were calculated using the method of Density Functional Theory (DFT). The correlation between radius angle and molecular energy is absolute quadratic in the process of BLE. As the increasing of the number of ring atoms, the value of DOA decreasing gradually, the aromaticity decreased gradually, which was a same conclusion as NICS and RSVRSF concluded. Copyright © 2018 Elsevier B.V. All rights reserved.

Stacking interactions between nitrogen-containing six-membered heterocyclic aromatic rings and substituted benzene: studies in solution and in the solid state.

PubMed

Gung, Benjamin W; Wekesa, Francis; Barnes, Charles L

2008-03-07

The stacking interactions between an aromatic ring and a pyridine or a pyrimidine ring are studied by using a series of triptycene-derived scaffolds. The indicative ratios of the syn and anti conformers were determined by variable-temperature NMR spectroscopy. The syn conformer aligns the attached aromatic ring and the heterocycle in a parallel-displaced orientation while the anti conformer sets the two rings apart from each other. Comparing to the corresponding control compounds where a benzene ring is in the position of the heterocycle, higher attractive interactions are observed as indicated by the higher syn/anti ratios. In general, the attractive interactions are much less sensitive to the substituent effects than the corresponding nonheterocycles. The greatest attractive interactions were observed between a pyrimidine ring and a N,N-dimethylaminobenzene, consistent with a predominant donor-acceptor interaction. The interactions between a pyridine ring and a substituted benzene ring show that the pyridine is comparable to that of a NO2- or a CN-substituted benzene ring except for the unpredictable substituent effects.

Polyimides with carbonyl and ether connecting groups between the aromatic rings

NASA Technical Reports Server (NTRS)

Hergenrother, Paul M. (Inventor); Havens, Stephen J. (Inventor)

1992-01-01

New polyimides have been prepared from the reaction of aromatic dianhydrides with novel aromatic diamines containing carbonyl and ether connecting groups between the aromatic rings. Several of these polyimides are shown to be semi-crystalline as evidenced by wide angle x ray diffraction and differential scanning calorimetry. Most of the polyimides form tough solvent resistant films with high tensile properties. Several of these materials can be thermally processed to form solvent and base resistant moldings.

Supramolecular aromaticity

NASA Astrophysics Data System (ADS)

Karabıyık, Hande; Sevinçek, Resul; Karabıyık, Hasan

2014-05-01

We report experimental and theoretical evidences for supramolecular aromaticity as a new concept to be widely used in researches about molecular crystals. CSD survey regarding frequently encountered resonance-assisted H-bonds (RAHBs) in formic acid, formamide, formimidamide, formic acid-formamide, and formamide-formimidamide dimers shows that supramolecular quasirings formed by RAHBs have remarkable electronic delocalization within themselves, which is reminiscent of aromaticity at supramolecular level. This study criticizes and reevaluates the validity of conventional judgment which states that ring systems formed by intermolecular H-bonds cannot be aromatic. Thus, the term aromaticity can be extended to supramolecular systems formed by RAHBs. Supramolecular aromaticity has a multi-fold nature involving both σ- and π-delocalization, and σ-delocalization through RAHBs takes on a task of compensating σ-deficiency within quasirings. Atomic composition in donor-acceptor set of the dimers is descriptive for supramolecular aromaticity. We revised bond-valence parameters for RAHBs and they suggest that hypervalent character of H atoms is more pronounced than their hypovalent character in RAHBs. The σ-delocalized bonding within H-bonded quasirings necessitates hypervalent character of H atoms. Quantum chemical calculations based on adiabatic Hydrogen Atom Transfer (HAT) between the monomers reveal that topological parameters at ring critical points (RCPs) of the quasirings correlate well with Shannon's entropic aromaticity index. The presence of additional LP orbital on O atoms implying more diffused LP-orbitals in donor-acceptor set leads to the formation of resonance-disabling states reducing supramolecular aromaticity of a quasiring and energetic cost of the electron transfer between the monomers. There is a nonignorable electron transfer between the monomers even in the cases where H atoms are close to donor or acceptor atom. NBO analyses have revealed that formally vacant LP* orbitals on H-atoms in TS geometries mediate intermolecular electron transfer as a result of the hyperconjugative stereoelectronic interactions.

Virtual Exploration of the Ring Systems Chemical Universe.

PubMed

Visini, Ricardo; Arús-Pous, Josep; Awale, Mahendra; Reymond, Jean-Louis

2017-11-27

Here, we explore the chemical space of all virtually possible organic molecules focusing on ring systems, which represent the cyclic cores of organic molecules obtained by removing all acyclic bonds and converting all remaining atoms to carbon. This approach circumvents the combinatorial explosion encountered when enumerating the molecules themselves. We report the chemical universe database GDB4c containing 916 130 ring systems up to four saturated or aromatic rings and maximum ring size of 14 atoms and GDB4c3D containing the corresponding 6 555 929 stereoisomers. Almost all (98.6%) of these ring systems are unknown and represent chiral 3D-shaped macrocycles containing small rings and quaternary centers reminiscent of polycyclic natural products. We envision that GDB4c can serve to select new ring systems from which to design analogs of such natural products. The database is available for download at www.gdb.unibe.ch together with interactive visualization and search tools as a resource for molecular design.

Opioid receptor probes derived from cycloaddition of the hallucinogen natural product salvinorin A.

PubMed

Lozama, Anthony; Cunningham, Christopher W; Caspers, Michael J; Douglas, Justin T; Dersch, Christina M; Rothman, Richard B; Prisinzano, Thomas E

2011-04-25

As part of our continuing efforts toward more fully understanding the structure-activity relationships of the neoclerodane diterpene salvinorin A, we report the synthesis and biological characterization of unique cycloadducts through [4+2] Diels-Alder cycloaddition. Microwave-assisted methods were developed and successfully employed, aiding in functionalizing the chemically sensitive salvinorin A scaffold. This demonstrates the first reported results for both cycloaddition of the furan ring and functionalization via microwave-assisted methodology of the salvinorin A skeleton. The cycloadducts yielded herein introduce electron-withdrawing substituents and bulky aromatic groups into the C-12 position. Kappa opioid (KOP) receptor space was explored through aromatization of the bent oxanorbornadiene system possessed by the cycloadducts to a planar phenyl ring system. Although dimethyl- and diethylcarboxylate analogues 5 and 6 retain some affinity and selectivity for KOP receptors and are full agonists, their aromatized counterparts 13 and 14 have reduced affinity for KOP receptors. The methods developed herein signify a novel approach toward rapidly probing the structure-activity relationships of furan-containing natural products.

Molecular mechanisms in the pyrolysis of unsaturated chlorinated hydrocarbons: formation of benzene rings. 1. Quantum chemical studies.

PubMed

McIntosh, Grant J; Russell, Douglas K

2013-05-23

Analogues of important aromatic growth mechanisms in hydrocarbon pyrolysis and combustion systems are extended to chlorinated systems. We consider the addition of C2Cl2 to both C4Cl3 and C4Cl5 radicals at the M06-2X/6-311+G(3df,3p)//B3LYP/6-31G(d) level of theory, and we demonstrate that these reaction systems have much in common with those of nonchlorinated species. In particular, we find that these radicals appear to lead preferentially to fulvenes, and not to the observed aromatic products, as is found in nonchlorinated systems. We have therefore also considered nonradical C4/C2 channels by way of Diels-Alder cyclization of C4Cl4/C2Cl2 and C4H2Cl2/C2HCl pairs to describe aromatic formation. While the latter pair readily leads to the formation of partially chlorinated benzenes, the fully chlorinated congeners are sterically prohibited from ring closing directly; this leads to a series of novel rearrangement processes which predict the formation of hexachloro-1,5-diene-3-yne, in addition to hexachlorobenzene, in good agreement with experiment. This suggests, for the first time, that facile nonradical routes to aromatic formation are operative in partially and fully chlorinated pyrolysis and combustion systems.

Simulation of SOA formation and composition from oxidation of toluene and m-xylene in chamber experiments

NASA Astrophysics Data System (ADS)

Xu, J.; Liu, Y.; Nakao, S.; Cocker, D.; Griffin, R. J.

2013-12-01

Aromatic hydrocarbons contribute an important fraction of anthropogenic reactive volatile organic compounds (VOCs) in the urban atmosphere. Photo-oxidation of aromatic hydrocarbons leads to secondary organic products that have decreased volatilities or increased solubilities and can form secondary organic aerosol (SOA). Despite the crucial role of aromatic-derived SOA in deteriorating air quality and harming human health, its formation mechanism is not well understood and model simulation of SOA formation still remains difficult. The dependence of aromatic SOA formation on nitrogen oxides (NOx) is not captured fully by most SOA formation models. Most models predict SOA formation under high NOx levels well but underestimate SOA formation under low NOx levels more representative of the ambient atmosphere. Thus, it is crucial to investigate the NOx-dependent chemistry in aromatic photo-oxidation systems and correspondingly update SOA formation models. In this study, NOx-dependent mechanisms of toluene and m-xylene SOA formation are updated using the gas-phase Caltech Atmospheric Chemistry Mechanism (CACM) coupled to a gas/aerosol partitioning model. The updated models were optimized by comparing to eighteen University of California, Riverside United States Environmental Protection Agency (EPA) chamber experiment runs under both high and low NOx conditions. Correction factors for vapor pressures imply uncharacterized aerosol-phase association chemistry. Simulated SOA speciation implies the importance of ring-opening products in governing SOA formation (up to 40%~60% for both aromatics). The newly developed model can predict strong decreases of m-xylene SOA yield with increasing NOx. Speciation distributions under varied NOx levels implies that the well-known competition between RO2 + HO2 and RO2 + NO (RO2 = peroxide bicyclic radical) may not be the only factor influencing SOA formation. The reaction of aromatic peroxy radicals with NO competing with its self-cyclization also affects NOx-dependence of SOA formation. Comparison of SOA formation yield and composition between two aromatics implies aldehyde/ketone chemistry from ring-opening route and chemistry for phenolic route play important roles in governing SOA formation and that ring-opening aldehydes and phenolic nitrates are produced to a greater extent in the toluene system, leading to higher SOA yields for toluene than for m-xylene.

1-Methyl-4-(4-nitro­benzo­yl)pyridinium perchlorate

PubMed Central

Gruber, Tobias; Eissmann, Frank; Weber, Edwin; Schüürmann, Gerrit

2011-01-01

In the main mol­ecule of the title compound, C13H11N2O3 +·ClO4 −, the two aromatic rings are twisted by 56.19 (3)° relative to each other and the nitro group is not coplanar with the benzene ring [36.43 (4)°]. The crystal packing is dominated by infinite aromatic stacks in the a-axis direction. These are formed by the benzene units of the mol­ecule featuring an alternating arrangement, which explains the two different distances of 3.3860 (4) and 3.4907 (4) Å for the aromatic units (these are the perpendicular distances of the centroid of one aromatic ring on the mean plane of the other other aromatic ring). Adjacent stacks are connected by π–π stacking between two pyridinium units [3.5949 (4) Å] and weak C—H⋯O inter­actions. The perchlorate anions are accomodated in the lattice voids connected to the cation via weak C—H⋯O contacts between the O atoms of the anion and various aromatic as well as methyl H atoms. PMID:22059070

Illuminating the dark side of DOM: A bottom up approach to understanding the structure and composition of DOM.

NASA Astrophysics Data System (ADS)

Zito, P.; Tarr, M. A.; Spencer, R. G.; Podgorski, D. C.

2017-12-01

Dissolved organic matter (DOM) is one of the most complex natural mixtures on Earth. It is generally comprised of hydrocarbons incorporating a diverse subset of oxygen-containing functional groups along with a small amount of nitrogen, sulfur and phosphorous heteroatoms all of which make it very difficult to chromatographically separate. The only way to directly characterize and quantify these structural and compositional changes is by separating the DOM continuum into defined bins of structure and chemistry. In this study, we take an alternate bottom-up approach that utilizes petroleum to work toward identifying the molecular structures of DOM. Although petroleum is the most structurally diverse mixture in nature, it is almost exclusively comprised of hydrocarbons with only trace quantities of heteroatoms, including oxygen. Here, crude oil was chromatographically separated into bins based on the number of aromatic rings to be used as a starting carbon source. Photochemically produced DOM from these aromatic ring bins provides unique opportunities to gain insight in the compositional controls associated with transport, processing and fate of DOM in natural systems. Here, we present EEMs data from individual ring fractions that were subjected to 24 hours of sunlight to use as a model to fingerprint specific aromatic regions in the DOM fraction. Results illustrate that the 1-, 2-, 3-, 4- and 5- ring fractions exhibit a wide range of structurally dependent excitation and emission spectra. A well-known red-shift in the emission and excitation occurs as the number of rings increase. In order to understand changes in the elemental composition of the data, ultra high-resolution mass spectrometry was used to obtain molecular level information. Together, these data will provide a tool to help understand the relationship of the composition and structure of DOM released into the environment in terms of aromaticity. It is well known that aromaticity is an important indicator of the chemical characteristics of DOM and can be used to explain the role of DOM in environmental processes. Thus, identifying these compounds in terms of aromaticity after photodegradation will provide information about the fate, transport and mechanisms of the photolabile and recalcitrant compounds in the environment.

Toward a more complete understanding of noncovalent interactions involving aromatic rings.

PubMed

Wheeler, Steven E; Bloom, Jacob W G

2014-08-14

Noncovalent interactions involving aromatic rings, which include π-stacking interactions, anion-π interactions, and XH-π interactions, among others, are ubiquitous in chemical and biochemical systems. Despite dramatic advances in our understanding of these interactions over the past decade, many aspects of these noncovalent interactions have only recently been uncovered, with many questions remaining. We summarize our computational studies aimed at understanding the impact of substituents and heteroatoms on these noncovalent interactions. In particular, we discuss our local, direct interaction model of substituent effects in π-stacking interactions. In this model, substituent effects are dominated by electrostatic interactions of the local dipoles associated with the substituents and the electric field of the other ring. The implications of the local nature of substituent effects on π-stacking interactions in larger systems are discussed, with examples given for complexes with carbon nanotubes and a small graphene model, as well as model stacked discotic systems. We also discuss related issues involving the interpretation of electrostatic potential (ESP) maps. Although ESP maps are widely used in discussions of noncovalent interactions, they are often misinterpreted. Next, we provide an alternative explanation for the origin of anion-π interactions involving substituted benzenes and N-heterocycles, and show that these interactions are well-described by simple models based solely on charge-dipole interactions. Finally, we summarize our recent work on the physical nature of substituent effects in XH-π interactions. Together, these results paint a more complete picture of noncovalent interactions involving aromatic rings and provide a firm conceptual foundation for the rational exploitation of these interactions in a myriad of chemical contexts.

Positron annihilation studies in solid substituted aromatic compounds

NASA Astrophysics Data System (ADS)

Oliveira, F. C.; Oliveira, A. M.; Donnici, C. L.; Machado, J. C.; Magalhães, W. F.; Windmöller, D.; Fulgêncio, F. H.; Souza, L. R.

2011-04-01

Positronium formation was investigated in benzene and naphthalene compounds with electron donating (sbnd NH2 and sbnd OH) and electron withdrawing (sbnd CN and sbnd NO2) substituents. The results exhibit an increase in the positronium formation yield whenever donating groups are bound to the ring and a decrease with withdrawing groups. These results can be attributed to the π-system electronic density variation in the aromatic ring. The amount of positronium obtained, I3 parameter, has been correlated with the Hammett (σ) and Brown-Okamoto (σp+) constants and adjusted through the modified Hammett equation, which employs the ratio I3/I3ϕ, yielding a satisfactory fit.

Characteristics of microbial community functional structure of a biological coking wastewater treatment system.

PubMed

Joshi, Dev Raj; Zhang, Yu; Zhang, Hong; Gao, Yingxin; Yang, Min

2018-01-01

Nitrogenous heterocyclic compounds are key pollutants in coking wastewater; however, the functional potential of microbial communities for biodegradation of such contaminants during biological treatment is still elusive. Herein, a high throughput functional gene array (GeoChip 5.0) in combination with Illumina HiSeq2500 sequencing was used to compare and characterize the microbial community functional structure in a long run (500days) bench scale bioreactor treating coking wastewater, with a control system treating synthetic wastewater. Despite the inhibitory toxic pollutants, GeoChip 5.0 detected almost all key functional gene (average 61,940 genes) categories in the coking wastewater sludge. With higher abundance, aromatic ring cleavage dioxygenase genes including multi ring1,2diox; one ring2,3diox; catechol represented significant functional potential for degradation of aromatic pollutants which was further confirmed by Illumina HiSeq2500 analysis results. Response ratio analysis revealed that three nitrogenous compound degrading genes- nbzA (nitro-aromatics), tdnB (aniline), and scnABC (thiocyanate) were unique for coking wastewater treatment, which might be strong cause to increase ammonia level during the aerobic process. Additionally, HiSeq2500 elucidated carbozole and isoquinoline degradation genes in the system. These findings expanded our understanding on functional potential of microbial communities to remove organic nitrogenous pollutants; hence it will be useful in optimization strategies for biological treatment of coking wastewater. Copyright © 2017. Published by Elsevier B.V.

Biodegradation of high-molecular-weight polycyclic aromatic hydrocarbons under anaerobic conditions: Overview of studies, proposed pathways and future perspectives.

PubMed

Nzila, Alexis

2018-05-07

The biodegradation of low- and high-molecular-weight polycyclic aromatic hydrocarbons (PAHs) (LWM-PAHs and HMW-PAHs, respectively) has been studied extensively under aerobic conditions. Molecular O 2 plays 2 critical roles in this biodegradation process. O 2 activates the aromatic rings through hydroxylation prior to ring opening and serves as a terminal electron acceptor (TEA). However, several microorganisms have devised ways of activating aromatic rings, leading to ring opening (and thus biodegradation) when TEAs other than O 2 are used (under anoxic conditions). These microorganisms belong to the sulfate-, nitrate-, and metal-ion-reducing bacteria and the methanogens. Although the anaerobic biodegradation of monocyclic aromatic hydrocarbons and LWM-PAH naphthalene have been studied, little information is available about the biodegradation of HMW-PAHs. This manuscript reviews studies of the anaerobic biodegradation of HMW-PAHs and identifies gaps that limit both our understanding and the efficiency of this biodegradation process. Strategies that can be employed to overcome these limitations are also discussed. Copyright © 2018 Elsevier Ltd. All rights reserved.

Role of methyl group number on SOA formation from monocyclic aromatic hydrocarbons photooxidation under low-NOx conditions

NASA Astrophysics Data System (ADS)

Li, L.; Tang, P.; Nakao, S.; Chen, C.-L.; Cocker, D. R., III

2016-02-01

Substitution of methyl groups onto the aromatic ring determines the secondary organic aerosol (SOA) formation from the monocyclic aromatic hydrocarbon precursor (SOA yield and chemical composition). This study links the number of methyl groups on the aromatic ring to SOA formation from monocyclic aromatic hydrocarbons photooxidation under low-NOx conditions (HC/NO > 10 ppbC : ppb). Monocyclic aromatic hydrocarbons with increasing numbers of methyl groups are systematically studied. SOA formation from pentamethylbenzene and hexamethylbenzene are reported for the first time. A decreasing SOA yield with increasing number of methyl groups is observed. Linear trends are found in both f44 vs. f43 and O / C vs. H / C for SOA from monocyclic aromatic hydrocarbons with zero to six methyl groups. An SOA oxidation state predictive method based on benzene is used to examine the effect of added methyl groups on aromatic oxidation under low-NOx conditions. Further, the impact of methyl group number on density and volatility of SOA from monocyclic aromatic hydrocarbons is explored. Finally, a mechanism for methyl group impact on SOA formation is suggested. Overall, this work suggests that, as more methyl groups are attached on the aromatic ring, SOA products from these monocyclic aromatic hydrocarbons become less oxidized per mass/carbon on the basis of SOA yield or chemical composition.

Chemical and thermal stability of N-heterocyclic ionic liquids in catalytic C-H activation reactions.

PubMed

Chen, Guanyi; Kang, Shujuan; Ma, Qisheng; Chen, Weiqun; Tang, Yongchun

2014-11-01

(1)H-NMR spectrum analyses are applied to study the chemical and thermal stability of selected N-heterocyclic ionic liquids within the reaction system that can highly efficiently activate a C-H bond of methane and convert it into the C-O bond in methanol. Our results indicate that under such reaction conditions involving using a powerful Pt-based catalyst and strong acidic solvent, the aromatic ring of an imidazolium cation becomes unstable generating an ammonium ion (NH(4)(+)). Our results also suggest that the instability of the imidazolium ring is more chemically (participation in reactions) than thermally based. Modifications of the aromatic ring structure such as pyrazolium and triazolium cations can increase the chemical/thermal stability of ionic liquids under these reaction conditions. Copyright © 2014 John Wiley & Sons, Ltd.

Towards the Rational Design of Ionic Liquid Matrices for Secondary Ion Mass Spectrometry: Role of the Anion

NASA Astrophysics Data System (ADS)

Dertinger, Jennifer J.; Walker, Amy V.

2013-08-01

The role of the ionic liquid (IL) anion structure on analyte signal enhancements has been systematically investigated in secondary ion mass spectrometry (SIMS) using a variety of samples, including lipids, sterols, polymers, and peptides. Twenty-four ILs were synthesized. The 12 matrix acids were cinnamic acid derivatives. Two bases were employed: 1-methylimidazole and tripropylamine. Three matrices, methylimmidazolium o-coumarate, tripropylammonium o-coumarate, and tripropylammonium 3,4,5-trimethoxycinnamate, were "universal" matrices enhancing all analytes tested. The pKa of the matrix acid does not appear to have a strong effect on analyte ion intensities. Rather, it is observed that a single hydroxyl group on the anion aromatic ring leads to significantly increased molecular ion intensities. No analyte signal enhancements were observed for -CH3, -CF3 and -OCH3 groups present on the aromatic ring. The position of the -OH group on the aromatic ring also alters molecular ion intensity enhancements. As well as the chemical identity and position of substituents, the number of moieties on the aromatic ring may affect the analyte signal enhancements observed. These observations suggest that the activation of the IL anion aromatic ring is important for optimizing analyte signal intensities. The implications for SIMS imaging of complex structures, such as biological samples, are discussed.

Oxidation of Oil Sands Process-Affected Water by Potassium Ferrate(VI).

PubMed

Wang, Chengjin; Klamerth, Nikolaus; Huang, Rongfu; Elnakar, Haitham; Gamal El-Din, Mohamed

2016-04-19

This paper investigates the oxidation of oil sands process-affected water (OSPW) by potassium ferrate(VI). Due to the selectivity of ferrate(VI) oxidation, two-ring and three-ring fluorescing aromatics were preferentially removed at doses <100 mg/L Fe(VI), and one-ring aromatics were removed only at doses ≥100 mg/L Fe(VI). Ferrate(VI) oxidation achieved 64.0% and 78.4% removal of naphthenic acids (NAs) at the dose of 200 mg/L and 400 mg/L Fe(VI) respectively, and NAs with high carbon number and ring number were removed preferentially. (1)H nuclear magnetic resonance ((1)H NMR) spectra indicated that the oxidation of fluorescing aromatics resulted in the opening of some aromatic rings. Electron paramagnetic resonance (EPR) analysis detected signals of organic radical intermediates, indicating that one-electron transfer is one of the probable mechanisms in the oxidation of NAs. The inhibition effect of OSPW on Vibrio fischeri and the toxicity effect on goldfish primary kidney macrophages (PKMs) were both reduced after ferrate(VI) oxidation. The fluorescing aromatics in OSPW were proposed to be an important contributor to this acute toxicity. Degradation of model compounds with ferrate(VI) was also investigated and the results confirmed our findings in OSPW study.

Aromatic C=C bonds as dipolarophiles: facile reactions of uncomplexed electron-deficient benzene derivatives and other aromatic rings with a non-stabilized azomethine ylide.

PubMed

Lee, Sunyoung; Diab, Sonia; Queval, Pierre; Sebban, Muriel; Chataigner, Isabelle; Piettre, Serge R

2013-05-27

Non-stabilized azomethine ylide 4a reacts smoothly at room temperature with a variety of uncomplexed aromatic heterocycles and carbocycles on the condition that the ring contains at least one or two electron-withdrawing substituents, respectively. Aromatic substrates, including pyridine and benzene derivatives, participate as 2π components in [3+2] cycloaddition reactions and interact with one, two, or three equivalent(s) of the ylide, depending on their structure and substitution pattern. Thus, this process affords highly functionalized polycyclic structures that contain between one and three pyrrolidinyl ring(s) in useful yields. These results indicate that the site selectivity of the cycloaddition reactions strongly depends on both the nature and the positions of the substituents. In most cases, the second 1,3-dipolar reaction occurs on the opposite face to the one that contains the first pyrrolidinyl ring. DFT calculations on model compounds indicate that a concerted mechanism features a low activation barrier. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Writing with ring currents: selectively hydrogenated polycyclic aromatics as finite models of graphene and graphane

PubMed Central

Fowler, Patrick W.; Gibson, Christopher M.; Bean, David E.

2014-01-01

Alternating partial hydrogenation of the interior region of a polycyclic aromatic hydrocarbon gives a finite model system representing systems on the pathway from graphene to the graphane modification of the graphene sheet. Calculations at the DFT and coupled Hartree–Fock levels confirm that sp2 cycles of bare carbon centres isolated by selective hydrogenation retain the essentially planar geometry and electron delocalization of the annulene that they mimic. Delocalization is diagnosed by the presence of ring currents, as detected by ipsocentric calculation and visualization of the current density induced in the π system by a perpendicular external magnetic field. These induced ‘ring’ currents have essentially the same sense, strength and orbital origin as in the free hydrocarbon. Subjected to the important experimental proviso of the need for atomic-scale control of hydrogenation, this finding predicts the possibility of writing single, multiple and concentric diatropic and/or paratropic ring currents on the graphene/graphane sheet. The implication is that pathways for free flow of ballistic current can be modelled in the same way. PMID:24611026

Polycyclic aromatic hydrocarbon formation during the gasification of sewage sludge in sub- and supercritical water: Effect of reaction parameters and reaction pathways.

PubMed

Gong, Miao; Wang, Yulan; Fan, Yujie; Zhu, Wei; Zhang, Huiwen; Su, Ying

2018-02-01

The formation of polycyclic aromatic hydrocarbon is a widespread issue during the supercritical water gasification of sewage sludge, which directly reduces the gasification efficiency and restricts the technology practical application. The changes of the concentrations and forms as well as the synthesis rate of polycyclic aromatic hydrocarbons in the residues from supercritical water gasification of dewatered sewage sludge were investigated to understand influence factors and the reaction pathways. Results showed that the increase of reaction temperature during the heating period favours directly concentration of polycyclic aromatic hydrocarbon (especially higher-molecular-weight), especially when it raise above 300 °C. Lower heating and cooling rate essentially extend the total reaction time. Higher polycyclic aromatic hydrocarbon concentration and higher number of rings were generally promoted by lower heating and cooling rate, longer reaction time and higher reaction temperature. The lower-molecular-weight polycyclic aromatic hydrocarbons can be directly generated through the decomposition of aromatic-containing compounds in sewage sludge, as well as 3-ring and 4-ring polycyclic aromatic hydrocarbons can be formed by aromatization of steroids. Possible mechanisms of reaction pathways of supercritical water gasification of sewage sludge were also proposed. Copyright © 2017 Elsevier Ltd. All rights reserved.

Electron energy loss spectra of polycyclic aromatic hydrocarbons

NASA Technical Reports Server (NTRS)

Keller, John W.; Coplan, M. A.; Goruganthu, R.

1992-01-01

A survey of the electron energy-loss spectroscopy is reported of gas-phase polycyclic aromatic hydrocarbon (PAH) molecules consisting of up to seven rings where the study is limited to the more thermodynamically stable pericondensed systems. The aim of this work is to obtain absorption profiles (proportional to the oscillator strengths) from the visible to the soft X-ray region near 30 eV.

No-carrier-added (NCA) aryl ([sup 18]F) fluorides via the nucleophilic aromatic substitution of electron rich aromatic rings

DOEpatents

Yushin Ding; Fowler, J.S.; Wolf, A.P.

1993-10-19

A method for synthesizing no-carrier-added (NCA) aryl [.sup.18 F] fluoride substituted aromatic aldehyde compositions bearing an electron donating group is described. The method of the present invention includes the step of reacting aromatic nitro aldehydes having a suitably protected hydroxyl substitutent on an electron rich ring. The reaction is The U.S. Government has rights in this invention pursuant to Contract Number DE-AC02-76CH00016, between the U.S. Department of Energy and Associated Universities Inc.

No-carrier-added (NCA) aryl (18E) fluorides via the nucleophilic aromatic substitution of electron rich aromatic rings

DOEpatents

Ding, Yu-Shin; Fowler, Joanna S.; Wolf, Alfred P.

1993-01-01

A method for synthesizing no-carrier-added (NCA) aryl [.sup.18 F] fluoride substituted aromatic aldehyde compositions bearing an electron donating group is described. The method of the present invention includes the step of reacting aromatic nitro aldehydes having a suitably protected hydroxyl substitutent on an electron rich ring. The reaction is The U.S. Government has rights in this invention pursuant to Contract Number DE-AC02-76CH00016, between the U.S. Department of Energy and Associated Universities Inc.

CHEMISTRY OF OXIDATION OF POLYCYCLIC AROMATIC HYDROCARBONS BY SOIL PSEUDOMONADS

PubMed Central

Rogoff, Martin H.

1962-01-01

Rogoff, Martin H. (U.S. Bureau of Mines, Pittsburgh, Pa.). Oxidation of polycyclic aromatic hydrocarbons by soil pseudomonads. J. Bacteriol. 83:998–1004. 1962.—Substitution of phenanthrene by a methyl group at the 9-carbon blocks oxidation of the compound by a resting-cell suspension of a phenanthrene-grown soil pseudomonad. When 2-methylphenanthrene is provided, the oxidation rate is considerably higher; 3-methylphenanthrene is oxidized at a rate intermediate between the other two, even though the methyl group is attached to a carbon directly involved in ring splitting. Cells grown on naphthalene or anthracene oxidize phenanthrene at a much lower rate than cells grown with phenanthrene or 2-methylnaphthalene as the source of carbon. Naphthalene-grown cells also absorb less phenanthrene from aqueous solution than do their phenanthrene-grown counterparts. The data are in keeping with the hypothesis that polynuclear aromatic hydrocarbons attach to the relevant bacterial enzymes at carbon-carbon bonds of high electron density (K regions; localized double bonds), and that the ring-splitting reactions then occur at other bonds on the substrate molecule. The actual bond that undergoes fission is determined by the electronic and steric configurations of the enzyme-substrate complex. When linearly arranged aromatic compounds such as naphthalene or anthracene are attacked, attachment to an enzyme and ring splitting may take place on the same ring; angular aromatic compounds such as phenanthrene afford attachment to an enzyme at a bond in a ring other than the one containing the ring-splitting site. PMID:14493381

Redox shuttles for overcharge protection of lithium batteries

DOEpatents

Amine, Khalil; Chen, Zonghai; Wang, Qingzheng

2010-12-14

The present invention is generally related to electrolytes containing novel redox shuttles for overcharge protection of lithium-ion batteries. The redox shuttles are capable of thousands hours of overcharge tolerance and have a redox potential at about 3-5.5 V vs. Li and particularly about 4.4-4.8 V vs. Li. Accordingly, in one aspect the invention provides electrolytes comprising an alkali metal salt; a polar aprotic solvent; and a redox shuttle additive that is an aromatic compound having at least one aromatic ring with four or more electronegative substituents, two or more oxygen atoms bonded to the aromatic ring, and no hydrogen atoms bonded to the aromatic ring; and wherein the electrolyte solution is substantially non-aqueous. Further there are provided electrochemical devices employing the electrolyte and methods of making the electrolyte.

Separation of alkylphenols by normal-phase and reversed-phase high-performance liquid chromatography

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

Schabron, J.F.; Hurtubise, R.J.; Silver, H.F.

1978-11-01

Empirical correlation factors were developed which relate log k' values for alkylphenols, the naphthols, and two phenylphenols to structural features. Both normal-phase and reversed-phase chromatographic systems were studied. The stationary phases employed in the normal-phase work were ..mu..-Bondapak CN, ..mu..-Bondapak NH/sub 2/, and ..mu..-Porasil. The structural features which affect retention in the normal-phase chromatographic systems are the number of ortho substituents, the number of aliphatic carbons, and the number of aromatic rings. The stationary phases employed in the reversed-phase work were ..mu..-Bondapak C/sub 18/ and ..mu..-Bondapak CN. The structural features which affect retention in the reversed-phase chromatographic systems are themore » number of aliphatic carbons and the number of aromatic double bonds. On ..mu..-Bondapak C/sub 18/, the presence or absence of a nonaromatic ring is of added importance.« less

Opioid Receptor Probes Derived from Cycloaddition of the Hallucinogen Natural Product Salvinorin A†

PubMed Central

Lozama, Anthony; Cunningham, Christopher W.; Caspers, Michael J.; Douglas, Justin T.; Dersch, Christina M.; Rothman, Richard B.; Prisinzano, Thomas E.

2011-01-01

As part of our continuing efforts toward more fully understanding the structure-activity relationships of the neoclerodane diterpene salvinorin A, we report the synthesis and biological characterization of unique cycloadducts through [4+2] Diels-Alder cycloaddition. Microwave-assisted methods were developed and successfully employed, aiding in functionalizing the chemically sensitive salvinorin A scaffold. This demonstrates the first reported results for both cycloaddition of the furan ring and functionalization via microwave-assisted methodology of the salvinorin A skeleton. The cycloadducts yielded herein introduce electron-withdrawing substituents and bulky aromatic groups into the C-12 position. Kappa opioid (KOP) receptor space was explored through aromatization of the bent oxanorbornadiene system possessed by the cycloadducts to a planar phenyl ring system. Although dimethyl- and diethylcarboxylate analogues 5 and 6 retain some affinity and selectivity for KOP receptors and are full agonists, their aromatized counterparts 13 and 14 have reduced affinity for KOP receptors. The methods developed herein signify a novel approach toward rapidly probing the structure-activity relationships of furan containing natural products. PMID:21338114

Studies on non-steroidal inhibitors of aromatase enzyme; 4-(aryl/heteroaryl)-2-(pyrimidin-2-yl)thiazole derivatives.

PubMed

Sahin, Zafer; Ertas, Merve; Berk, Barkın; Biltekin, Sevde Nur; Yurttas, Leyla; Demirayak, Seref

2018-05-01

Steroidal and non-steroidal aromatase inhibitors target the suppression of estrogen biosynthesis in the treatment of breast cancer. Researchers have increasingly focused on developing non-steroidal derivatives for their potential clinical use avoiding steroidal side-effects. Non-steroidal derivatives generally have planar aromatic structures attached to the azole ring system. One part of this ring system comprises functional groups that inhibit aromatization through the coordination of the haem group of the aromatase enzyme. Replacement of the triazole ring system and development of aromatic/cyclic structures of the side chain can increase selectivity over aromatase enzyme inhibition. In this study, 4-(aryl/heteroaryl)-2-(pyrimidin-2-yl)thiazole derivatives were synthesized and physical analyses and structural determination studies were performed. The IC 50 values were determined by a fluorescence-based aromatase inhibition assay and compound 1 (4-(2-hydroxyphenyl)-2-(pyrimidine-2-yl)thiazole) were found potent inhibitor of enzyme (IC 50 :0.42 nM). Then, their antiproliferative activity over MCF-7 and HEK-293 cell lines was evaluated using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Compounds 1, 7, 8, 13, 15, 18, 21 were active against MCF-7 breast cancer cells. Lastly, a series of docking experiments were undertaken to analyze the crystal structure of human placental aromatase and identify the possible interactions between the most active structure and the active site. Copyright © 2018 Elsevier Ltd. All rights reserved.

Aromaticity of strongly bent benzene rings: persistence of a diatropic ring current and its shielding cone in [5]paracyclophane.

PubMed

Jenneskens, Leonardus W; Havenith, Remco W A; Soncini, Alessandro; Fowler, Patrick W

2011-10-06

Direct evaluation of the induced π current density in [5]paracyclophane (1) shows that, despite the significant non-planarity (α = 23.2°) enforced by the pentamethylene bridge, there is only a modest (ca. 17%) reduction in the π ring current, justifying the use of shielding-cone arguments for the assignment of (1)H NMR chemical shifts of 1 and the claim that the non-planar benzene ring in 1 retains its aromaticity (on the magnetic criterion).

Centrohexaindane: six benzene rings mutually fixed in three dimensions - solid-state structure and six-fold nitration.

PubMed

Kuck, Dietmar; Linke, Jens; Teichmann, Lisa Christin; Barth, Dieter; Tellenbröker, Jörg; Gestmann, Detlef; Neumann, Beate; Stammler, Hans-Georg; Bögge, Hartmut

2016-04-28

The solid-state molecular structure of centrohexaindane (), a unique hydrocarbon comprising six benzene rings clamped to each other in three dimensions around a neopentane core, and the molecular packing in crystals of ·CHCl3 are reported. The molecular Td-symmetry and the Cartesian orientation of the six indane wings of in the solid state have been confirmed. The course and limitation of electrophilic aromatic substitution of are demonstrated for the case of nitration. Based on nitration experiments of a lower congener of , tribenzotriquinacene , the six-fold nitrofunctionalisation of has been achieved in excellent yield, giving four constitutional isomers, two nonsymmetrical ( and ) and two C3-symmetrical ones ( and ), all of which contain one single nitro group in each of the six benzene rings. The relative yields of the four isomers (∼3 : 1 : 1 : 3) point to a random electrophilic attack of the electrophiles at the twelve formally equivalent outer positions of the aromatic periphery of , suggesting electronic independence of its six aromatic π-electron systems. In turn, the pronounced conformational rigidity of the centrohexacyclic framework of enables the unequivocal structural identification of the isomeric hexanitrocentrohexaindanes by (1)H NMR spectroscopy.

Disordered organic electronic materials based on non-benzenoid 1,6-methano[10]annulene rings

DOEpatents

Tovar, John D; Streifel, Benjamin C; Peart, Patricia A

2014-10-07

Conjugated polymers and small molecules including the nonplanar aromatic 1,6-methano[10]annulene ring structure along with aromatic subunits, such as diketopyrrolopyrrole, and 2,1,3-benzothiadiazole, substituted with alkyl chains in a "Tail In," "Tail Out," or "No Tail" regiochemistry are disclosed.

Multifunctional receptor model for dioxin and related compound toxic action: possible thyroid hormone-responsive effector-linked site.

PubMed Central

McKinney, J D

1989-01-01

Molecular/theoretical modeling studies have revealed that thyroid hormones and toxic chlorinated aromatic hydrocarbons of environmental significance (for which dioxin or TCDD is the prototype) have similar structural properties that could be important in molecular recognition in biochemical systems. These molecular properties include a somewhat rigid, sterically accessible and polarizable aromatic ring and size-limited, hydrophobic lateral substituents, usually contained in opposite adjoining rings of a diphenyl compound. These molecular properties define the primary binding groups thought to be important in molecular recognition of both types of structures in biochemical systems. Similar molecular reactivities are supported by the demonstration of effective specific binding of thyroid hormones and chlorinated aromatic hydrocarbons with four different proteins, enzymes, or receptor preparations that are known or suspected to be involved in the expression of thyroid hormone activity. These binding interactions represent both aromatic-aromatic (stacking) and molecular cleft-type recognition processes. A multiple protein or multifunctional receptor-ligand binding mechanism model is proposed as a way of visualizing the details and possible role of both the stacking and cleft type molecular recognition factors in the expression of biological activity. The model suggests a means by which hormone-responsive effector-linked sites (possible protein-protein-DNA complexes) can maintain highly structurally specific control of hormone action. Finally, the model also provides a theoretical basis for the design and conduct of further biological experimentation on the molecular mechanism(s) of action of toxic chlorinated aromatic hydrocarbons and thyroid hormones. Images FIGURE 3. A FIGURE 3. B FIGURE 3. C FIGURE 3. D PMID:2551666

Electronic distributions within protein phenylalanine aromatic rings are reflected by the three-dimensional oxygen atom environments.

PubMed Central

Thomas, K A; Smith, G M; Thomas, T B; Feldmann, R J

1982-01-01

The atomic environments of 170 phenylalanine-residue aromatic rings from 28 protein crystal structures are transformed into a common orientation and combined to calculate an average three-dimensional environment. The spatial distribution of atom types in this environment reveals a preferred interaction between oxygen atoms and the edge of the planar aromatic rings. From the difference in frequency of interaction of oxygen atoms with the edge and the top of the ring, an apparent net free energy difference of interaction favoring the edge of the ring is estimated to be about -1 kcal/mol (1 cal = 4.184 J). Ab initio quantum mechanical calculations, performed on a model consisting of benzene and formamide, indicate that the observed geometry is stabilized by a favorable enthalpic interaction. Although benzene rings are considered to be nonpolar, the electron distribution is a complex multipole with no net dipole moment. The observed interaction orientation frequencies demonstrate that these multipolar electron distributions, when occurring at the short distances encountered in densely packed protein molecules, are significant determinants of internal packing geometries. PMID:6956896

1-(Hydroxy­meth­yl)pyrene

PubMed Central

Gruber, Tobias; Seichter, Wilhelm; Weber, Edwin

2010-01-01

The asymmetric unit of the title compound, C17H12O, contains two molecules, in which the fused aromatic ring systems are almost planar [maximum deviations = 0.0529 (9) and 0.0256 (9) Å]. In the crystal, aromatic π–π stacking inter­actions (perpendicular distance of centroids of about 3.4 Å) and strong O—H⋯O hydrogen bonds result in a helical arrangement of pyrenyl dimers. PMID:21579858

Two Aromatic Rings Coupled a Sulfur-Containing Group to Favor Protein Electron Transfer by Instantaneous Formations of π∴S:π↔π:S∴π or π∴π:S↔π:π∴S Five-Electron Bindings

PubMed Central

Sun, Weichao; Ren, Haisheng; Tao, Ye; Xiao, Dong; Qin, Xin; Deng, Li; Shao, Mengyao; Gao, Jiali; Chen, Xiaohua

2015-01-01

The cooperative interactions among two aromatic rings with a S-containing group are described, which may participate in electron hole transport in proteins. Ab initio calculations reveal the possibility for the formations of the π∴S:π↔π:S∴π and π∴π:S↔π:π∴S five-electron bindings in the corresponding microsurrounding structures in proteins, both facilitating electron hole transport as efficient relay stations. The relay functionality of these two special structures comes from their low local ionization energies and proper binding energies, which varies with the different aromatic amino acids, S-containing residues, and the arrangements of the same aromatic rings according to the local microsurroundings in proteins. PMID:26120374

Mechanism for Ring-Opening of Aromatic Polymers by Remote Atmospheric Pressure Plasma

NASA Astrophysics Data System (ADS)

Gonzalez, Eleazar; Barankin, Michael; Guschl, Peter; Hicks, Robert

2009-10-01

A low-temperature, atmospheric pressure oxygen and helium plasma was used to treat the surfaces of polyetheretherketone, polyphenylsulfone, polyethersulfone, and polysulfone. These aromatic polymers were exposed to the afterglow of the plasma, which contained oxygen atoms, and to a lesser extent metastable oxygen (^1δg O2) and ozone. After less than 2.5 seconds treatment, the polymers were converted from a hydrophobic state with a water contact angle of 85±5 to a hydrophilic state with a water contact angle of 13±5 . It was found that plasma activation increased the bond strength to adhesives by as much as 4 times. X-ray photoelectron spectroscopy revealed that between 7% and 27% of the aromatic carbon atoms on the polymer surfaces was oxidized and converted into aldehyde and carboxylic acid groups. Analysis of polyethersulfone by internal reflection infrared spectroscopy showed that a fraction of the aromatic carbon atoms were transformed into C=C double bonds, ketones, and carboxylic acids after plasma exposure. It was concluded that the oxygen atoms generated by the atmospheric pressure plasma insert into the double bonds on the aromatic rings, forming a 3-member epoxy ring, which subsequently undergoes ring opening and oxidation to yield an aldehyde and a carboxylic acid group.

Where does the electron go? The nature of ortho/para and meta group directing in electrophilic aromatic substitution

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

Liu, Shubin, E-mail: shubin@email.unc.edu

Electrophilic aromatic substitution as one of the most fundamental chemical processes is affected by atoms or groups already attached to the aromatic ring. The groups that promote substitution at the ortho/para or meta positions are, respectively, called ortho/para and meta directing groups, which are often characterized by their capability to donate electrons to or withdraw electrons from the ring. Though resonance and inductive effects have been employed in textbooks to explain this phenomenon, no satisfactory quantitative interpretation is available in the literature. Here, based on the theoretical framework we recently established in density functional reactivity theory (DFRT), where electrophilicity andmore » nucleophilicity are simultaneously quantified by the Hirshfeld charge, the nature of ortho/para and meta group directing is systematically investigated for a total of 85 systems. We find that regioselectivity of electrophilic attacks is determined by the Hirshfeld charge distribution on the aromatic ring. Ortho/para directing groups have most negative charges on the ortho/para positions, while meta directing groups often possess the largest negative charge on the meta position. Our results do not support that ortho/para directing groups are electron donors and meta directing groups are electron acceptors. Most neutral species we studied here are electron withdrawal in nature. Anionic systems are always electron donors. There are also electron donors serving as meta directing groups. We predicted ortho/para and meta group directing behaviors for a list of groups whose regioselectivity is previously unknown. In addition, strong linear correlations between the Hirshfeld charge and the highest occupied molecular orbital have been observed, providing the first link between the frontier molecular orbital theory and DFRT.« less

The Effect of n vs. iso Isomerization on the Thermophysical Properties of Aromatic and Non-aromatic Ionic Liquids.

PubMed

Rodrigues, Ana S M C; Almeida, Hugo F D; Freire, Mara G; Lopes-da-Silva, José A; Coutinho, João A P; Santos, Luís M N B F

2016-09-15

This work explores the n vs. iso isomerization effects on the physicochemical properties of different families of ionic liquids (ILs) with variable aromaticity and ring size. This study comprises the experimental measurements, in a wide temperature range, of the ILs' thermal behavior, heat capacities, densities, refractive indices, surface tensions, and viscosities. The results here reported show that the presence of the iso -alkyl group leads to an increase of the temperature of the glass transition, T g . The iso- pyrrolidinium (5 atoms ring cation core) and iso -piperidinium (6 atoms ring cation core) ILs present a strong differentiation in the enthalpy and entropy of melting. Non-aromatic ILs have higher molar heat capacities due to the increase of the atomic contribution, whereas it was not found any significant differentiation between the n and iso -alkyl isomers. A small increase of the surface tension was observed for the non-aromatic ILs, which could be related to their higher cohesive energy of the bulk, while the lower surface entropy observed for the iso isomers indicates a structural resemblance between the IL bulk and surface. The significant differentiation between ILs with a 5 and 6 atoms ring cation in the n -alkyl series (where 5 atoms ring cations have higher surface entropy) is an indication of a more efficient arrangement of the non-polar region at the surface in ILs with smaller cation cores. The ILs constituted by non-aromatic piperidinium cation, and iso -alkyl isomers were found to be the most viscous among the studied ILs due to their higher energy barriers for shear stress.

Magnetic Response of Aromatic Rings Under Rotation: Aromatic Shielding Cone of Benzene Upon Different Orientations of the Magnetic Field.

PubMed

Papadopoulos, A G; Charistos, N D; Muñoz-Castro, A

2017-06-20

The induced shielding cone is one of the most characteristic aspects of aromatic species. Herein, we explore its behavior under different orientations of the applied magnetic field by evaluating the overall and dissected π- and σ-electron contributions. Our results shed light onto the orientation dependence behavior of the shielding cone, unraveling a characteristic pattern upon rotation of the aromatic ring. This pattern decreases the long range of the magnetic response, such that it resembles the behavior under constant molecular tumbling in solution. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Copper Causes Regiospecific Formation of C4F8-Containing Six-Membered Rings and their Defluorination/Aromatization to C4F4-Containing Rings in Triphenylene/1,4-C4F8I2 Reactions

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

Rippy, Kerry C.; Bukovsky, Eric V.; Clikeman, Tyler T.

The presence of Cu in reactions of triphenylene (TRPH) and 1,4-C4F8I2 at 360 °C led to regiospecific substitution of TRPH ortho C(β) atoms to form C4F8-containing rings, completely suppressing substitution on C(α) atoms. In addition, Cu caused selective reductive-defluorination/aromatization (RD/A) to form C4F4- containing aromatic rings. Without Cu, the reactions of TRPH and 1,4- C4F8I2 were not regiospecific and no RD/A was observed. These results, supported by DFT calculations, are the first examples of Cupromoted (i) regiospecific perfluoroannulation, (ii) preparative C–F activation, and (iii) RD/A. HPLC-purified products were characterized by X-ray diffraction, low-temperature PES, and 1H/19F NMR.

Resveratrol and para-coumarate serve as ring precursors for coenzyme Q biosynthesis[S

PubMed Central

Xie, Letian X.; Williams, Kevin J.; He, Cuiwen H.; Weng, Emily; Khong, San; Rose, Tristan E.; Kwon, Ohyun; Bensinger, Steven J.; Marbois, Beth N.; Clarke, Catherine F.

2015-01-01

Coenzyme Q (Q or ubiquinone) is a redox-active polyisoprenylated benzoquinone lipid essential for electron and proton transport in the mitochondrial respiratory chain. The aromatic ring 4-hydroxybenzoic acid (4HB) is commonly depicted as the sole aromatic ring precursor in Q biosynthesis despite the recent finding that para-aminobenzoic acid (pABA) also serves as a ring precursor in Saccharomyces cerevisiae Q biosynthesis. In this study, we employed aromatic 13C6-ring-labeled compounds including 13C6-4HB, 13C6-pABA, 13C6-resveratrol, and 13C6-coumarate to investigate the role of these small molecules as aromatic ring precursors in Q biosynthesis in Escherichia coli, S. cerevisiae, and human and mouse cells. In contrast to S. cerevisiae, neither E. coli nor the mammalian cells tested were able to form 13C6-Q when cultured in the presence of 13C6-pABA. However, E. coli cells treated with 13C6-pABA generated 13C6-ring-labeled forms of 3-octaprenyl-4-aminobenzoic acid, 2-octaprenyl-aniline, and 3-octaprenyl-2-aminophenol, suggesting UbiA, UbiD, UbiX, and UbiI are capable of using pABA or pABA-derived intermediates as substrates. E. coli, S. cerevisiae, and human and mouse cells cultured in the presence of 13C6-resveratrol or 13C6-coumarate were able to synthesize 13C6-Q. Future evaluation of the physiological and pharmacological responses to dietary polyphenols should consider their metabolism to Q. PMID:25681964

Synthesis of Aromatic Aza-metallapentalenes from Metallabenzene via Sequential Ring Contraction/Annulation

NASA Astrophysics Data System (ADS)

Wang, Tongdao; Han, Feifei; Huang, Haiping; Li, Jinhua; Zhang, Hong; Zhu, Jun; Lin, Zhenyang; Xia, Haiping

2015-04-01

The concept of aromaticity has long played an important role in chemistry and continues to fascinate both experimentalists and theoreticians. Among the archetypal aromatic compounds, heteroaromatics are particularly attractive. Recently, substitution of a transition-metal fragment for a carbon atom in the anti-aromatic hydrocarbon pentalene has led to the new heteroaromatic osmapentalenes. However, construction of the aza-homolog of osmapentalenes cannot be accomplished by a similar synthetic manipulation. Here, we report the synthesis of aza-osmapentalenes by sequential ring contraction/annulation reactions of osmabenzenes via osmapentafulvenes. Nuclear magnetic resonance spectra, X-ray crystallographic analysis, and DFT calculations all suggest that these aza-osmapentalenes exhibit aromatic character. Thus, the stepwise transformation of metallabenzenes to metallapentafulvenes and then aza-metallapentalenes provides an efficient and facile synthetic route to these bicyclic heteroaromatics.

Precise through-space control of an abiotic electrophilic aromatic substitution reaction

NASA Astrophysics Data System (ADS)

Murphy, Kyle E.; Bocanegra, Jessica L.; Liu, Xiaoxi; Chau, H.-Y. Katharine; Lee, Patrick C.; Li, Jianing; Schneebeli, Severin T.

2017-04-01

Nature has evolved selective enzymes for the efficient biosynthesis of complex products. This exceptional ability stems from adapted enzymatic pockets, which geometrically constrain reactants and stabilize specific reactive intermediates by placing electron-donating/accepting residues nearby. Here we perform an abiotic electrophilic aromatic substitution reaction, which is directed precisely through space. Ester arms--positioned above the planes of aromatic rings--enable it to distinguish between nearly identical, neighbouring reactive positions. Quantum mechanical calculations show that, in two competing reaction pathways, both [C-H...O]-hydrogen bonding and electrophile preorganization by coordination to a carbonyl group likely play a role in controlling the reaction. These through-space-directed mechanisms are inspired by dimethylallyl tryptophan synthases, which direct biological electrophilic aromatic substitutions by preorganizing dimethylallyl cations and by stabilizing reactive intermediates with [C-H...N]-hydrogen bonding. Our results demonstrate how the third dimension above and underneath aromatic rings can be exploited to precisely control electrophilic aromatic substitutions.

Selective Oxidation of Lignin Model Compounds.

PubMed

Gao, Ruili; Li, Yanding; Kim, Hoon; Mobley, Justin K; Ralph, John

2018-05-02

Lignin, the planet's most abundant renewable source of aromatic compounds, is difficult to degrade efficiently to welldefined aromatics. We developed a microwave-assisted catalytic Swern oxidation system using an easily prepared catalyst, MoO 2 Cl 2 (DMSO) 2 , and DMSO as the solvent and oxidant. It demonstrated high efficiency in transforming lignin model compounds containing the units and functional groups found in native lignins. The aromatic ring substituents strongly influenced the selectivity of β-ether phenolic dimer cleavage to generate sinapaldehyde and coniferaldehyde, monomers not usually produced by oxidative methods. Time-course studies on two key intermediates provided insight into the reaction pathway. Owing to the broad scope of this oxidation system and the insight gleaned with regard to its mechanism, this strategy could be adapted and applied in a general sense to the production of useful aromatic chemicals from phenolics and lignin. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Design of aromatic-containing cell-penetrating peptide mimics with structurally modified π electronics.

PubMed

deRonde, Brittany M; Birke, Alexander; Tew, Gregory N

2015-02-09

Cell-penetrating peptides (CPPs) and their synthetic mimics (CPPMs) represent a class of molecules that facilitate the intracellular delivery of various cargo. Previous studies indicated that the presence of aromatic functionalities improved CPPM activity. Given that aromatic functionalities play prominent roles in membrane biology and participate in various π interactions, we explored whether these interactions could be optimized for improved CPPM activity. CPPMs were synthesized by ring-opening metathesis polymerization by using monomers that contained aromatic rings substituted with electron-donating and electron-withdrawing groups and covered an electrostatic potential range from -29.69 to +15.57 kcal mol(-1) . These groups altered the quadrupole moments of the aromatic systems and were used to test if such structural modifications changed CPPM activity. CPPMs were added to dye-loaded vesicles and the release of carboxyfluorescein was monitored as a function of polymer concentration. Changes in the effective polymer concentration to release 50% of the dye (effective concentration, EC50 ) were monitored. Results from this assay showed that the strength of the electron-donating and electron-withdrawing groups incorporated in the CPPMs did not alter polymer EC50 values or activity. This suggests that other design parameters may have a stronger impact on CPPM activity. In addition, these results indicate that a wide range of aromatic groups can be incorporated without negatively impacting polymer activity. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Modulation of ethoxyresorufin O-deethylase and glutathione S-transferase activities in Nile tilapia (Oreochromis niloticus) by polycyclic aromatic hydrocarbons containing two to four rings: implications in biomonitoring aquatic pollution.

PubMed

Pathiratne, Asoka; Hemachandra, Chamini K

2010-08-01

Despite ubiquity of polycyclic aromatic hydrocarbons (PAHs) in the tropical environments, little information is available concerning responses of tropical fish to PAHs and associated toxicity. In the present study, effects of five PAHs containing two to four aromatic rings on hepatic CYP1A dependent ethoxyresorufin O-deethylase (EROD), glutathione S-transferase (GST) and serum sorbitol dehydrogenase (SDH) activities in Nile tilapia, a potential fish species for biomonitoring pollution in tropical waters, were evaluated. Results showed that EROD activities were induced by the PAHs containing four aromatic rings (pyrene and chrysene) in a dose dependent manner. However PAHs with two to three aromatic rings (naphthalene, phenanthrene and fluoranthene) caused no effect or inhibition of EROD activities depending on the dose and the duration. Fluoranthene was the most potent inhibitor. SDH results demonstrated that high doses of fluoranthene induced hepatic damage. GST activity was induced by the lowest dose of phenanthrene, fluoranthene and chrysene but high doses had no effect. The results indicate that induction of EROD enzyme in Nile tilapia is a useful biomarker of exposure to PAHs such as pyrene and chrysene. However EROD inhibiting PAHs such as fluoranthene in the natural environment may modulate the EROD inducing potential of other PAHs thereby influencing PAH exposure assessments.

All-metal aromatic cationic palladium triangles can mimic aromatic donor ligands with Lewis acidic cations† †Electronic supplementary information (ESI) available: Reaction procedures, characterization of complexes, copies of all spectra and cif files, modelling details and XYZ coordinates. CCDC 1410440–1410442. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c7sc03475j Click here for additional data file. Click here for additional data file.

PubMed Central

Wang, Yanlan; Monfredini, Anna; Deyris, Pierre-Alexandre; Blanchard, Florent; Derat, Etienne; Malacria, Max

2017-01-01

We present that cationic rings can act as donor ligands thanks to suitably delocalized metal–metal bonds. This could grant parent complexes with the peculiar properties of aromatic rings that are crafted with main group elements. We assembled Pd nuclei into equilateral mono-cationic triangles with unhindered faces. Like their main group element counterparts and despite their positive charge, these noble-metal rings form stable bonding interactions with other cations, such as positively charged silver atoms, to deliver the corresponding tetranuclear dicationic complexes. Through a mix of modeling and experimental techniques we propose that this bonding mode is an original coordination-like one rather than a 4-centre–2-electron bond, which have already been observed in three dimensional aromatics. The present results thus pave the way for the use of suitable metal rings as ligands. PMID:29163890

Aromatic hydroxylation by cytochrome P450: model calculations of mechanism and substituent effects.

PubMed

Bathelt, Christine M; Ridder, Lars; Mulholland, Adrian J; Harvey, Jeremy N

2003-12-10

The mechanism and selectivity of aromatic hydroxylation by cytochrome P450 enzymes is explored using new B3LYP density functional theory computations. The calculations, using a realistic porphyrin model system, show that rate-determining addition of compound I to an aromatic carbon atom proceeds via a transition state with partial radical and cationic character. Reactivity is shown to depend strongly on ring substituents, with both electron-withdrawing and -donating groups strongly decreasing the addition barrier in the para position, and it is shown that the calculated barrier heights can be reproduced by a new dual-parameter equation based on radical and cationic Hammett sigma parameters.

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

Keeratitham, Waralee, E-mail: waralee.ke@student.chula.ac.th; Somwangthanaroj, Anongnat, E-mail: anongnat.s@chula.ac.th

Herein, our main objective is to prepare the fast curing epoxy system with high glass transition temperature (T{sub g}) by incorporating the multifunctional epoxy resin into the mixture of diglycidyl ether of bisphenol A (DGEBA) as a major epoxy component and aromatic diamine as a hardener. Furthermore, the curing behavior as well as thermal and thermomechanical properties were investigated by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and thermomechanical analysis (TMA). It was found that T{sub g} obtained from tan δ of DGEBA/aromatic diamine system increased from 100 °C to 205 °C with the presence of 30 percentage bymore » weight of multifunctional epoxy resin. Additionally, the isothermal DSC results showed that the multifunctional epoxy resin can accelerate the curing reaction of DGEBA/aromatic diamine system. Namely, a high degree of curing (∼90%) was achieved after a few minutes of curing at low temperature of 130 °C, owing to a large number of epoxy ring of multifunctional epoxy resin towards the active hydrogen atoms of aromatic diamine.« less

Fungal bioremediation of the creosote-contaminated soil: influence of Pleurotus ostreatus and Irpex lacteus on polycyclic aromatic hydrocarbons removal and soil microbial community composition in the laboratory-scale study.

PubMed

Byss, Marius; Elhottová, Dana; Tříska, Jan; Baldrian, Petr

2008-11-01

The aim of this study was to determine the efficacy of selected basidiomycetes in the removing of polycyclic aromatic hydrocarbons (PAH) from the creosote-contaminated soil. Fungi Pleurotus ostreatus and Irpex lacteus were supplemented with creosote-contaminated (50-200 mg kg(-1) PAH) soil originating from a wood-preserving plant and incubated at 15 °C for 120 d. Either fungus degraded PAH with 4-6 aromatic rings more efficiently than the microbial community present initially in the soil. PAH removal was higher in P. ostreatus treatments (55-67%) than in I. lacteus treatments (27-36%) in general. P. ostreatus (respectively, I. lacteus) removed 86-96% (47-59%) of 2-rings PAH, 63-72% (33-45%) of 3-rings PAH, 32-49% (9-14%) of 4-rings PAH and 31-38% (11-13%) of 5-6-rings PAH. MIS (Microbial Identification System) Sherlock analysis of the bacterial community determined the presence of dominant Gram-negative bacteria (G-) Pseudomonas in the inoculated soil before the application of fungi. Complex soil microbial community was characterized by phospholipid fatty acids analysis followed by GC-MS/MS. Either fungus induced the decrease of bacterial biomass (G- bacteria in particular), but the soil microbial community was influenced by P. ostreatus in a different way than by I. lacteus. The bacterial community was stressed more by the presence of I. lacteus than P. ostreatus (as proved by the ratio of the fungal/bacterial markers and by the ratio of trans/cis mono-unsaturated fatty acids). Moreover, P. ostreatus stimulated the growth of Gram-positive bacteria (G+), especially actinobacteria and these results indicate the potential of the positive synergistic interaction of this fungus and actinobacteria in creosote biodegradation.

Normal-phase liquid chromatography retention behavior of polycyclic aromatic hydrocarbon and their methyl-substituted derivatives on an aminopropyl stationary phase.

PubMed

Wilson, Walter B; Hayes, Hugh V; Sander, Lane C; Campiglia, Andres D; Wise, Stephen A

2017-09-01

Retention indices for 124 polycyclic aromatic hydrocarbons (PAHs) and 62 methyl-substituted (Me-) PAHs were determined using normal-phase liquid chromatography (NPLC) on a aminopropyl (NH 2 ) stationary phase. PAH retention behavior on the NH 2 phase is correlated to the total number of aromatic carbons in the PAH structure. Within an isomer group, non-planar isomers generally elute earlier than planar isomers. MePAHs generally elute slightly later but in the same region as the parent PAHs. Correlations between PAH retention behavior on the NH 2 phase and PAH thickness (T) values were investigated to determine the influence of non-planarity for isomeric PAHs with four to seven aromatic rings. Correlation coefficients ranged from r = 0.19 (five-ring peri-condensed molecular mass (MM) 252 Da) to r = -0.99 (five-ring cata-condensed MM 278 Da). In the case of the smaller PAHs (MM ≤ 252 Da), most of the PAHs had a planar structure and provided a low correlation. In the case of larger PAHs (MM ≥ 278 Da), nonplanarity had a significant influence on the retention behavior and good correlation between retention and T was obtained for the MM 278 Da, MM 302 Da, MM 328 Da, and MM 378 Da isomer sets. Graphical abstract NPLC separation of the three-, four-, five-, and six-ring PAH isomers with different number of aromatic carbon atoms and degrees of non-planarity (Thickness, T). The inserted figure plots the number of aromatic carbon atoms vs. the log I value for the 124 parent PAHs.

Stability and molecular properties of the boron-nitrogen alternating analogs of azulene and naphthalene: a computational study.

PubMed

Catão, Anderson José Lopes; López-Castillo, Alejandro

2017-04-01

In this work, the spectroscopic information, stability and aromaticity of the boron-nitrogen azulene and naphthalene molecules are provided by the use of CC2 (geometry optimization, dipole moment, UV-vis spectrum calculations) and DFT (vibrational spectrum and NMR calculations) methodologies. One isomer of the investigated boron-nitrogen naphthalene (boroazanaphthalene) and two isomers of boron-nitrogen azulene, 1,3,4,6,8-pentaaza-2,3a,5,7,8a-pentaboraazulene (BN-azulene) and 2,3a,5,7,8a-pentaaza-1,3,4,6,8- pentaboraazulene (NB-azulene), are stable systems. However, these molecules have different properties, i.e., different stability, dipole moment, and aromaticity based on the NICS approach. BN-naphthalene has a high dipole moment magnitude showing high polar character, while naphthalene is apolar. BN- and NB-azulene are weakly polar, while ordinary azulene is highly polar in character. Also, substitution of C atoms by B and N atoms decreases the aromaticity. In the case of NB-azulene, the seven-membered ring has anti-aromaticity behavior while both rings of BN-azulene exhibit aromaticity. We expect that the new theoretical data provided in this work will be useful in identifying and characterizing experimentally the compounds investigated, and in helping our understanding of the chemistry of boron-nitrogen molecules. Graphical abstract Boron-nitrogen alternating analogs of azulene. Spectral distinction between isomers.

Cyclic terpenoids of contemporary resinous plant detritus and of fossil woods, ambers and coals

USGS Publications Warehouse

Simoneit, B.R.T.; Grimalt, J.O.; Wang, T.-G.; Cox, R.E.; Hatcher, P.G.; Nissenbaum, A.

1986-01-01

Cyclic terpenoids present in the solvent extractable material of fossil woods, ambers and brown coals have been analyzed. The sample series chosen consisted of wood remains preserved in Holocene to Jurassic sediments and a set of of ambers from the Philippines (copalite), Israel, Canada and Dominican Republic. The brown coals selected were from the Fortuna Garsdorf Mine and Miocene formations on Fiji. The fossil wood extracts contained dominant diterpenoid or sesquiterpenoid skeletons, and aromatized species were present at high concentrations, with a major amount of two-ring aromatic compounds. Tricyclic diterpenoids were the predominant compounds in the ambers. Aromatized derivatives were the major components, consisting of one or two aromatic ring species with the abietane and occasionally pimarane skeletons. The saturated structures were comprised primarily of the abietane and pimarane skeletons having from three to five carbon (C1, C2, etc.) substituents. Kaurane and phyllocladane isomers were present in only minor amounts. Bicyclic sesquiterpenoids as saturated and partial or fully aromatized forms were also common in these samples, but only traces of sesterterpenoids and triterpenoid derivatives were found. The brown coal extracts were composed of major amounts of one- and two-ring aromatized terpenoids, with a greater proportion of triterpenoid derivatives than in the case of the woods and ambers. This was especially noticeable for the German coal, where the triterpenoids were predominant. Open C-ring aromatized structures were also present in this coal. Steroid compounds were not detectable, but some hopanes were found as minor components in the German brown coal. An overview of the skeletal structure classes identified in each sample, as well as the general mass spectrometric characteristics of the unknown compounds are included in the present paper. It can be concluded from these structural distributions that aromatization is the main process for the transformation of terrestrial cyclic terpenoids during diagenesis, constituting a general pathway for all terpenoids. ?? 1986 Pergamon Journals Ltd.

Band gaps and the possible effect on impact sensitivity for some nitro aromatic explosive materials

NASA Astrophysics Data System (ADS)

Zhang, Hong; Cheung, Frankie; Zhao, Feng; Cheng, Xin-Lu

The first principle density functional theory method SIESTA has been used to compute the band gap of several polynitroaromatic explosives, such as TATB, DATB, TNT, and picric acid. In these systems, the weakest bond is the one between an NO2 group and the aromatic ring. The bond dissociation energy (BDE) alone cannot predicate the relative sensitivity to impact of these four systems correctly. It was found that their relative impact sensitivity could be explained by considering the BDE and the band gap value of the crystal state together.

2,3-Dimethyl-6-nitro-2H-indazole

PubMed Central

Chen, Yan; Fang, Zheng; Wei, Ping

2009-01-01

In the mol­ecule of the title compound, C9H9N3O2, the indazole ring system is almost planar [maximum deviation = 0.019 (3) Å for the C atom bearing the nitro group]. In the crystal structure, inter­molecular C—H⋯O inter­actions link the mol­ecules into centrosymmetric dimers, forming R 2 2(18) ring motifs. Aromatic π–π contacts between indazole rings [centroid–centroid distances = 3.632 (1) and 3.705 (1) Å] may further stabilize the structure. PMID:21583483

Functional electrolyte for lithium-ion batteries

DOEpatents

Zhang, Lu; Zhang, Zhengcheng; Amine, Khalil

2015-04-14

Functional electrolyte solvents include compounds having at least one aromatic ring with 2, 3, 4 or 5 substituents, at least one of which is a substituted or unsubstituted methoxy group, at least one of which is a tert-butyl group and at least one of which is a substituted or unsubstituted polyether or poly(ethylene oxide) (PEO) group bonded through oxygen to the aromatic ring, are provided.

A highly sensitive monoclonal antibody based biosensor for quantifying 3-5 ring polycyclic aromatic hydrocarbons (PAHs) in aqueous environmental samples.

PubMed

Li, Xin; Kaattari, Stephen L; Vogelbein, Mary A; Vadas, George G; Unger, Michael A

2016-03-01

Immunoassays based on monoclonal antibodies (mAbs) are highly sensitive for the detection of polycyclic aromatic hydrocarbons (PAHs) and can be employed to determine concentrations in near real-time. A sensitive generic mAb against PAHs, named as 2G8, was developed by a three-step screening procedure. It exhibited nearly uniformly high sensitivity against 3-ring to 5-ring unsubstituted PAHs and their common environmental methylated PAHs, with IC 50 values between 1.68-31 μg/L (ppb). 2G8 has been successfully applied on the KinExA Inline Biosensor system for quantifying 3-5 ring PAHs in aqueous environmental samples. PAHs were detected at a concentration as low as 0.2 μg/L. Furthermore, the analyses only required 10 min for each sample. To evaluate the accuracy of the 2G8-based biosensor, the total PAH concentrations in a series of environmental samples analyzed by biosensor and GC-MS were compared. In most cases, the results yielded a good correlation between methods. This indicates that generic antibody 2G8 based biosensor possesses significant promise for a low cost, rapid method for PAH determination in aqueous samples.

Stereodynamics and edge-to-face CH-π aromatic interactions in imino compounds containing heterocyclic rings.

PubMed

González-Rosende, M Eugenia; Castillo, Encarna; Jennings, W Brian; Malone, John F

2017-02-07

By comparison with close contact interactions between benzene rings there is a paucity of experimental data available for attractive interactions involving aromatic heterocyclic rings, especially for small molecules in solution. Herein we describe aromatic heterocyclic and carbocyclic edge-to face interactions and conformational stereodynamics of N-1,2-diphenylethyl imines bearing a phenyl group and either a 2-pyridyl, 3-pyridyl, 2-thiophene or 2-furanyl moiety on the imino carbon. X-ray crystal structures have been determined for two compounds. Slow rotation about the phenyl-imino bond in the E-isomers and around the heterocycle-imino bond in the Z-isomers of the pyridyl compounds was observed at low temperatures by NMR. Abnormally large shielding of one ortho hydrogen indicates that both the imino phenyl and heterocycle rings can engage in an edge-to-face interaction with the N-terminal phenyl moiety in the appropriate isomer. Some rotational barriers around the phenyl-imino and heterocycle-imino bonds were measured.

Diverse Reactions of Thiophenes, Selenophenes, and Tellurophenes with Strongly Oxidizing I(III) PhI(L)2 Reagents.

PubMed

Egalahewa, Sathsara; Albayer, Mohammad; Aprile, Antonino; Dutton, Jason L

2017-02-06

We report the outcomes of the reactions of aromatic group 16 thiophene, selenophene, and tellurophene rings with the I(III) oxidants PhI(OAc)(OTf) and [PhI(Pyr) 2 ][OTf] 2 (Pyr = pyridine). In all reactions, oxidative processes take place, with generation of PhI as the reduction product. However, with the exception of tellurophene with PhI(OAc)(OTf), +4 oxidation state complexes are not observed, but rather a variety of other processes occur. In general, where a C-H unit is available on the 5-membered ring, an electrophilic aromatic substitution reaction of either -IPh or pyridine onto the ring occurs. When all positions are blocked, reactions with PhI(OAc)(OTf) give acetic and triflic anhydride as the identifiable oxidative byproducts, while [PhI(Pyr) 2 ][OTf] 2 gives pyridine electrophilic aromatic substitution onto the peripheral rings. Qualitative mechanistic studies indicate that the presence of the oxidizable heteroatom is required for pyridine to act as an electrophile in a substantial manner.

Urea-Aromatic Stacking and Concerted Urea Transport: Conserved Mechanisms in Urea Transporters Revealed by Molecular Dynamics.

PubMed

Padhi, Siladitya; Priyakumar, U Deva

2016-10-11

Urea transporters are membrane proteins that selectively allow urea molecules to pass through. It is not clear how these transporters allow rapid conduction of urea, a polar molecule, in spite of the presence of a hydrophobic constriction lined by aromatic rings. The current study elucidates the mechanism that is responsible for this rapid conduction by performing free energy calculations on the transporter dvUT with a cumulative sampling time of about 1.3 μs. A parallel arrangement of aromatic rings in the pore enables stacking of urea with these rings, which, in turn, lowers the energy barrier for urea transport. Such interaction of the rings with urea is proposed to be a conserved mechanism across all urea-conducting proteins. The free energy landscape for the permeation of multiple urea molecules reveals an interplay between interurea interaction and the solvation state of the urea molecules. This is for the first time that multiple molecule permeation through any small molecule transporter has been modeled.

The formation of quasi-alicyclic rings in alkyl-aromatic compounds

NASA Astrophysics Data System (ADS)

Straka, Pavel; Buryan, Petr; Bičáková, Olga

2018-02-01

The alkyl side chains of n-alkyl phenols, n-alkyl benzenes and n-alkyl naphthalenes are cyclised, as demonstrated by GC measurements, FTIR spectroscopy and molecular mechanics calculations. Cyclisation occurs due to the intramolecular interaction between an aromatic ring (-δ) and a hydrogen of the terminal methyl group (+δ) of an alkyl chain. In fact, conventional molecules are not aliphatic-aromatic, but quasi-alicyclic-aromatic. With the aromatic molecules formed with a quasi-alicyclic ring, the effect of van der Waals attractive forces increases not only intramolecularly but also intermolecularly. This effect is strong in molecules with propyl and higher alkyl substituents. The increase of intermolecular van der Waals attractive forces results in bi-linearity in the GC retention time of the compounds in question, observed in the dependence of the logarithm of the relative retention time on the number of carbons in a molecule in both polar and nonpolar stationary phases with both capillary and packed columns. The role of van der Waals forces has been demonstrated using the potential energies of covalent and noncovalent interactions for 2-n-alkyl phenols, n-alkyl benzenes and 1-n-alkyl- and 2-n-alkyl naphthalenes.

Implementation of GPC characterization of asphalt binders at Louisiana materials laboratory : tech summary.

DOT National Transportation Integrated Search

2013-10-01

Asphalt is a mixture of a wide variety of chemical compounds that include aliphatic hydrocarbons and highly fused : aromatic ring systems. They are classi ed as asphaltenes (medium molecular weight) and maltenes (low molecular : weight). To improv...

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

Ijam, M.J.; Qatami, S.Y.A.; Arif, S.F.

For several decades removal of aromatics from crude oil fractions (e.g. kerosene and lubricating oils) has been practiced in oil refining to produce fuels and lubricants of lower aromatic content and hence of improved quality. These aromatics are suitable raw materials for the manufacture of aromatic solvents, aromatic process oils, high octane gasoline, and as basic materials for making detergents, perfumes and dyes. Detailed study of molecular structure and substituent effects on the retention characteristics of aromatic hydrocarbons have been reported on alumina, silica and various chemically bonded silicas containing -C/sub 18/, -NH/sub 2/, -R(NH)/sub 2//sub 2/, -CN, RCN, RONmore » and phenyl-mercuric acetate for the compound class (ring-numbered) high performance liquid chromatography (2, 3, 8, 12, 24, 28). Previous work in this laboratory has demonstrated that individual normal and branched aliphatic hydrocarbons from kerosene and light gas oil were isolated and identified. This paper describes the extension of this work to cover the separation and identification of aromatic ring classes (mono-, di-, and tri-aromatics) in the gas oil fraction of Kuwait petroleum. Characterization and identification of the major components in the dinuclear aromatics is our primary objective in this study.« less

3-Ethyl-5-(4-meth­oxy­phen­oxy)-2-(pyridin-4-yl)-3H-imidazo[4,5-b]pyridine

PubMed Central

Ranjith, S.; SubbiahPandi, A.; Suresh, A. D.; Pitchumani, K.

2011-01-01

In the title compound, C20H18N4O2, the imidazopyridine fused ring system is almost perpendicular to the benzene ring [dihedral angle = 87.6 (5)°]. The pyridine ring makes a dihedral angle of 35.5 (5)° with the mean plane of the imidazopyridine fragment. The crystal structure is stabilized by an aromatic π–π stacking inter­action between the phenyl rings of neighbouring mol­ecules [centroid–centroid distance = 3.772 (2) Å, inter­planar distance = 3.546 (2) Å and slippage = 1.286 (2) Å]. PMID:21837144

The Misuse of the Circle Notation to Represent Aromatic Rings.

ERIC Educational Resources Information Center

Belloli, Robert C.

1983-01-01

Discusses the confusion and erroneous conclusions that can result from the overuse and misuse of the circle notation to represent aromaticity in polycylic aromatic hydrocarbons. Includes nature of the problem, textbook treatment, and a possible compromise method of representation. (Author/JN)

Crystallization and preliminary crystallographic analysis of the catechol 2,3-dioxygenase PheB from Bacillus stearothermophilus BR219

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

Sugimoto, Keisuke; Matsufuzi, Kazuki; Ohnuma, Hiroaki

2006-02-01

PheB, an extradiol-cleaving catecholic dioxygenase, was crystallized by the hanging-drop vapour-diffusion method using PEG 4000 as a precipitant. The crystal belongs to the orthorhombic system, space group P2{sub 1}2{sub 1}2{sub 1}, and diffracts to 2.3 Å resolution. Class II extradiol-cleaving catecholic dioxygenase, a key enzyme of aromatic compound degradation in bacteria, cleaves the aromatic ring of catechol by adding two O atoms. PheB is one of the class II extradiol-cleaving catecholic dioxygenases and shows a high substrate specificity for catechol derivatives, which have one aromatic ring. In order to reveal the mechanism of the substrate specificity of PheB, PheB hasmore » been crystallized by the hanging-drop vapour-diffusion method using PEG 4000 as a precipitant. The space group of the obtained crystal was P2{sub 1}2{sub 1}2{sub 1}, with unit-cell parameters a = 65.5, b = 119.2, c = 158.7 Å. The crystal diffracted to 2.3 Å resolution.« less

Bio-electrochemical remediation of real field petroleum sludge as an electron donor with simultaneous power generation facilitates biotransformation of PAH: effect of substrate concentration.

PubMed

Chandrasekhar, K; Venkata Mohan, S

2012-04-01

Remediation of real-field petroleum sludge was studied under self-induced electrogenic microenvironment with the function of variable organic loads (OLs) in bio-electrochemical treatment (BET) systems. Operation under various OLs documented marked influence on both electrogenic activity and remediation efficiency. Both total petroleum hydrocarbons (TPH) and its aromatic fraction documented higher removal with OL4 operation followed by OL3, OL2, OL1 and control. Self-induced biopotential and associated multiple bio-electrocatalytic reactions during BET operation facilitated biotransformation of higher ring aromatics (5-6) to lower ring aromatic (2-3) compounds. Asphaltenes and NSO fractions showed negligible removal during BET operation. Higher electrogenic activity was recorded at OL1 (343mV; 53.11mW/m(2), 100Ω) compared to other three OLs operation. Bioaugmentation to anodic microflora with anaerobic culture documented enhanced electrogenic activity at OL4 operation. Voltammetric profiles, Tafel analysis and VFA generation were in agreement with the observed power generation and degradation efficiency. Copyright © 2012 Elsevier Ltd. All rights reserved.

Water flow in carbon-based nanoporous membranes impacted by interactions between hydrated ions and aromatic rings.

PubMed

Liu, Jian; Shi, Guosheng; Fang, Haiping

2017-02-24

Carbon-based nanoporous membranes, such as carbon nanotubes (CNTs), graphene/graphene oxide and graphyne, have shown great potential in water desalination and purification, gas and ion separation, biosensors, and lithium-based batteries, etc. A deep understanding of the interaction between hydrated ions in an aqueous solution and the graphitic surface in systems composed of water, ions and a graphitic surface is essential for applications with carbon-based nanoporous membrane platforms. In this review, we describe the recent progress of the interaction between hydrated ions and aromatic ring structures on the carbon-based surface and its applications in the water flow in a carbon nanotube. We expect that these works can be extended to the understanding of water flow in other nanoporous membranes, such as nanoporous graphene, graphyne and stacked sheets of graphene oxide.

Structures and properties of molecular torsion balances to decipher the nature of substituent effects on the aromatic edge-to-face interaction.

PubMed

Gardarsson, Haraldur; Schweizer, W Bernd; Trapp, Nils; Diederich, François

2014-04-14

Various recent computational studies initiated this systematic re-investigation of substituent effects on aromatic edge-to-face interactions. Five series of Tröger base derived molecular torsion balances (MTBs), initially introduced by Wilcox and co-workers, showing an aromatic edge-to-face interaction in the folded, but not in the unfolded form, were synthesized. A fluorine atom or a trifluoromethyl group was introduced onto the edge ring in ortho-, meta-, and para-positions to the C-H group interacting with the face component. The substituents on the face component were varied from electron-donating to electron-withdrawing. Extensive X-ray crystallographic data allowed for a discussion on the conformational behavior of the torsional balances in the solid state. While most systems adopt the folded conformation, some were found to form supramolecular intercalative dimers, lacking the intramolecular edge-to-face interaction, which is compensated by the gain of aromatic π-stacking interactions between four aryl rings of the two molecular components. This dimerization does not take place in solution. The folding free enthalpy ΔG(fold) of all torsion balances was determined by (1)H NMR measurements by using 10 mM solutions of samples in CDCl3 and C6D6. Only the ΔG(fold) values of balances bearing an edge-ring substituent in ortho-position to the interacting C-H show a steep linear correlation with the Hammett parameter (σ(meta)) of the face-component substituent. Thermodynamic analysis using van't Hoff plots revealed that the interaction is enthalpy-driven. The ΔG(fold) values of the balances, in addition to partial charge calculations, suggest that increasing the polarization of the interacting C-H group makes a favorable contribution to the edge-to-face interaction. The largest contribution, however, seems to originate from local direct interactions between the substituent in ortho-position to the edge-ring C-H and the substituted face ring. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Retardation effect of nitrogen compounds and condensed aromatics on shale oil catalytic cracking processing and their characterization.

PubMed

Li, Nan; Chen, Chen; Wang, Bin; Li, Shaojie; Yang, Chaohe; Chen, Xiaobo

Untreated shale oil, shale oil treated with HCl aqueous solution and shale oil treated with HCl and furfural were used to do comparative experiments in fixed bed reactors. Nitrogen compounds and condensed aromatics extracted by HCl and furfural were characterized by electrospray ionization Fourier transform cyclotron resonance mass spectrometry and gas chromatography and mass spectrometry, respectively. Compared with untreated shale oil, the conversion and yield of liquid products increased considerably after removing basic nitrogen compounds by HCl extraction. Furthermore, after removing nitrogen compounds and condensed aromatics by both HCl and furfural, the conversion and yield of liquid products further increased. In addition, N 1 class species are predominant in both basic and non-basic nitrogen compounds, and they are probably indole, carbazole, cycloalkyl-carbazole, pyridine and cycloalkyl-pyridine. As for the condensed aromatics, most of them possess aromatic rings with two to three rings and zero to four carbon atom.

Oxidation of Naphthenoaromatic and Methyl-Substituted Aromatic Compounds by Naphthalene 1,2-Dioxygenase

PubMed Central

Selifonov, S. A.; Grifoll, M.; Eaton, R. W.; Chapman, P. J.

1996-01-01

Oxidation of acenaphthene, acenaphthylene, and fluorene was examined with recombinant strain Pseudomonas aeruginosa PAO1(pRE695) expressing naphthalene dioxygenase genes cloned from plasmid NAH7. Acenaphthene underwent monooxygenation to 1-acenaphthenol with subsequent conversion to 1-acenaphthenone and cis- and trans-acenaphthene-1,2-diols, while acenaphthylene was dioxygenated to give cis-acenaphthene-1,2-diol. Nonspecific dehydrogenase activities present in the host strain led to the conversion of both of the acenaphthene-1,2-diols to 1,2-acenaphthoquinone. The latter was oxidized spontaneously to naphthalene-1,8-dicarboxylic acid. No aromatic ring dioxygenation products were detected from acenaphthene and acenaphthylene. Mixed monooxygenase and dioxygenase actions of naphthalene dioxygenase on fluorene yielded products of benzylic 9-monooxygenation, aromatic ring dioxygenation, or both. The action of naphthalene dioxygenase on a variety of methyl-substituted aromatic compounds, including 1,2,4-trimethylbenzene and isomers of dimethylnaphthalene, resulted in the formation of benzylic alcohols, i.e., methyl group monooxygenation products, which were subsequently converted to the corresponding carboxylic acids by dehydrogenase(s) in the host strain. Benzylic monooxygenation of methyl groups was strongly predominant over aromatic ring dioxygenation and essentially nonspecific with respect to the substitution pattern of the aromatic substrates. In addition to monooxygenating benzylic methyl and methylene groups, naphthalene dioxygenase behaved as a sulfoxygenase, catalyzing monooxygenation of the sulfur heteroatom of 3-methylbenzothiophene. PMID:16535238

Quantum coherent π-electron rotations in a non-planar chiral molecule induced by using a linearly polarized UV laser pulse

NASA Astrophysics Data System (ADS)

Mineo, Hirobumi; Fujimura, Yuichi

2015-06-01

We propose an ultrafast quantum switching method of π-electron rotations, which are switched among four rotational patterns in a nonplanar chiral aromatic molecule (P)-2,2’- biphenol and perform the sequential switching among four rotational patterns which are performed by the overlapped pump-dump laser pulses. Coherent π-electron dynamics are generated by applying the linearly polarized UV pulse laser to create a pair of coherent quasidegenerated excited states. We also plot the time-dependent π-electron ring current, and discussed ring current transfer between two aromatic rings.

Synthesis and activity of novel analogs of hemiasterlin as inhibitors of tubulin polymerization: modification of the A segment.

PubMed

Yamashita, Ayako; Norton, Emily B; Kaplan, Joshua A; Niu, Chuan; Loganzo, Frank; Hernandez, Richard; Beyer, Carl F; Annable, Tami; Musto, Sylvia; Discafani, Carolyn; Zask, Arie; Ayral-Kaloustian, Semiramis

2004-11-01

Analogs of hemiasterlin (1) and HTI-286 (2), which contain various aromatic rings in the A segment, were synthesized as potential inhibitors of tubulin polymerization. The structure-activity relationships related to stereo- and regio-chemical effects of substituents on the aromatic ring in the A segment were studied. Analogs, which carry a meta-substituted phenyl ring in the A segment show comparable activity for inhibition of tubulin polymerization to 2, as well as in the cell proliferation assay using KB cells containing P-glycoprotein, compared to those of 1 and 2.

Analogies between Vanadoborates and Planar Aromatic Hydrocarbons: A High-Spin Analogue of Aromaticity.

PubMed

King, R Bruce

2017-12-23

The vanadium-vanadium interactions in the polygonal aggregates of d¹ vanadium(IV) atoms, with a total of 4 k + 2 vanadium electrons ( k an integer) imbedded in an electronically inactive borate matrix in certain vanadoborate structures are analogous to the ring carbon-carbon interactions in diamagnetic planar cyclic hydrocarbons. They thus represent a high-spin analogue of aromaticity. Thus, the vanadoborate anion [V₆B 20 O 50 H₈] 8- with six V(IV) electrons (i.e., 4 k + 2 for k = 1) contains a macrohexagon of d¹ V(IV) atoms with four unpaired electrons. This high-spin system is related to the low-spin aromaticity in the diamagnetic benzene having six π electrons. Similarly, the vanadoborate anion [V 10 B 28 O 74 H₈] 16- with ten V(IV) electrons (i.e., 4 k + 2 for k = 2) contains a macrodecagon of d¹ V(IV) atoms with eight unpaired electrons. Again, this high-spin system is related to the aromaticity in the diamagnetic 1,6-methanol[10]annulene, having ten π electrons.

In silico and experimental methods revealed highly diverse bacteria with quorum sensing and aromatics biodegradation systems--a potential broad application on bioremediation.

PubMed

Huang, Yili; Zeng, Yanhua; Yu, Zhiliang; Zhang, Jing; Feng, Hao; Lin, Xiuchun

2013-11-01

Phylogenetic overlaps between aromatics-degrading bacteria and acyl-homoserine-lactone (AHL) or autoinducer (AI) based quorum-sensing (QS) bacteria were evident in literatures; however, the diversity of bacteria with both activities had never been finely described. In-silico searching in NCBI genome database revealed that more than 11% of investigated population harbored both aromatic ring-hydroxylating-dioxygenase (RHD) gene and AHL/AI-synthetase gene. These bacteria were distributed in 10 orders, 15 families, 42 genus and 78 species. Horizontal transfers of both genes were common among them. Using enrichment and culture dependent method, 6 Sphingomonadales and 4 Rhizobiales with phenanthrene- or pyrene-degrading ability and AHL-production were isolated from marine, wetland and soil samples. Thin-layer-chromatography and gas-chromatography-mass-spectrum revealed that these Sphingomonads produced various AHL molecules. This is the first report of highly diverse bacteria that harbored both aromatics-degrading and QS systems. QS regulation may have broad impacts on aromatics biodegradation, and would be a new angle for developing bioremediation technology. Copyright © 2013 Elsevier Ltd. All rights reserved.

Laboratory Studies of Stabilities of Heterocyclic Aromatic Molecules: Suggested Gas Phase Ion-Molecule Routes to Production in Interstellar Gas Clouds

NASA Technical Reports Server (NTRS)

Adams, Nigel G.; Fondren, L. Dalila; McLain, Jason L.; Jackson, Doug M.

2006-01-01

Several ring compounds have been detected in interstellar gas clouds, ISC, including the aromatic, benzene. Polycyclic aromatic hydrocarbons, PAHs, have been implicated as carriers of diffuse interstellar bands (DIBs) and unidentified infrared (UIR) bands. Heterocyclic aromatic rings of intermediate size containing nitrogen, possibly PreLife molecules, were included in early searches but were not detected and a recent search for Pyrimidine was unsuccessful. Our laboratory investigations of routes to such molecules could establish their existence in ISC and suggest conditions under which their concentrations would be maximized thus aiding the searches. The stability of such ring compounds (C5H5N, C4H4N2, C5H11N and C4H8O2) has been tested in the laboratory using charge transfer excitation in ion-molecule reactions. The fragmentation paths, including production of C4H4(+), C3H3N(+) and HCN, suggest reverse routes to the parent molecules, which are presently under laboratory investigation as production sources.

New insights into thermal decomposition of polycyclic aromatic hydrocarbon oxyradicals.

PubMed

Liu, Peng; Lin, He; Yang, Yang; Shao, Can; Gu, Chen; Huang, Zhen

2014-12-04

Thermal decompositions of polycyclic aromatic hydrocarbon (PAH) oxyradicals on various surface sites including five-membered ring, free-edge, zigzag, and armchair have been systematically investigated by using ab initio density functional theory B3LYP/6-311+G(d,p) basis set. The calculation based on Hückel theory indicates that PAHs (3H-cydopenta[a]anthracene oxyradical) with oxyradicals on a five-membered ring site have high chemical reactivity. The rate coefficients of PAH oxyradical decomposition were evaluated by using Rice-Ramsperger-Kassel-Marcus theory and solving the master equations in the temperature range of 1500-2500 K and the pressure range of 0.1-10 atm. The kinetic calculations revealed that the rate coefficients of PAH oxyradical decomposition are temperature-, pressure-, and surface site-dependent, and the oxyradical on a five-membered ring is easier to decompose than that on a six-membered ring. Four-membered rings were found in decomposition of the five-membered ring, and a new reaction channel of PAH evolution involving four-membered rings is recommended.

A simple methodological validation of the gas/particle fractionation of polycyclic aromatic hydrocarbons in ambient air

NASA Astrophysics Data System (ADS)

Kim, Yong-Hyun; Kim, Ki-Hyun

2015-07-01

The analysis of polycyclic aromatic hydrocarbons (PAH) in ambient air requires the tedious experimental steps of both sampling and pretreatment (e.g., extraction or clean-up). To replace pre-existing conventional methods, a simple, rapid, and novel technique was developed to measure gas-particle fractionation of PAH in ambient air based on ‘sorbent tube-thermal desorption-gas chromatograph-mass spectrometer (ST-TD-GC-MS)’. The separate collection and analysis of ambient PAHs were achieved independently by two serially connected STs. The basic quality assurance confirmed good linearity, precision, and high sensitivity to eliminate the need for complicated pretreatment procedures with the detection limit (16 PAHs: 13.1 ± 7.04 pg). The analysis of real ambient PAH samples showed a clear fractionation between gas (two-three ringed PAHs) and particulate phases (five-six ringed PAHs). In contrast, for intermediate (four ringed) PAHs (fluoranthene, pyrene, benz[a]anthracene, and chrysene), a highly systematic/gradual fractionation was established. It thus suggests a promising role of ST-TD-GC-MS as measurement system in acquiring a reliable database of airborne PAH.

Revisiting shape selectivity in liquid chromatography for polycyclic aromatic hydrocarbons (PAHs) - six-ring and seven-ring Cata-condensed PAH isomers of molecular mass 328 Da and 378 Da.

PubMed

Oña-Ruales, Jorge O; Sander, Lane C; Wilson, Walter B; Wise, Stephen A

2018-01-01

The relationship of reversed-phase liquid chromatography (RPLC) retention on a polymeric C 18 stationary phase and the shape of polycyclic aromatic hydrocarbons (PAHs) was investigated for three-ring to seven-ring cata-condensed isomers. We report the first RPLC separation for six-ring and seven-ring cata-condensed PAH isomers. Correlations of LC retention and shape parameters (length-to-breath ratio, L/B and thickness, T) were investigated for 2 three-ring isomers (molecular mass 178 Da), 5 four-ring isomers (molecular mass 228 Da), 11 five-ring isomers (molecular mass 278 Da), 17 six-ring isomers (molecular mass 328 Da), and 20 seven-ring isomers (molecular mass 378 Da). Significant linear correlations were found for all isomer groups (r = 0.71 to 0.94). Nonplanarity of the PAH isomers was found to influence retention (i.e., nonplanar isomers eluting earlier than expected based on L/B) and linear correlations of retention vs. T for isomer groups containing nonplanar isomers were significant (r = 0.71 to 0.86). Graphical abstract.

Comparison of molecular structure of alkali metal o-, m- and p-nitrobenzoates

NASA Astrophysics Data System (ADS)

Regulska, E.; Świsłocka, R.; Samsonowicz, M.; Lewandowski, W.

2008-09-01

The influence of nitro-substituent in ortho, meta and para positions as well as lithium, sodium, potassium, rubidium and cesium on the electronic system of aromatic ring and the distribution of electronic charge in carboxylic group of the nitrobenzoates were estimated. Optimized geometrical structures were calculated (B3LYP/6-311++G ∗∗). To make quantitative evaluation of aromaticity of studied molecules the geometric (A J, BAC, I 6 and HOMA) as well as magnetic (NICS) aromaticity indices were calculated. Electronic charge distribution was also examined by molecular spectroscopic study, which may be the source of quality criterion for aromaticity. Experimental and theoretical FT-IR, FT-Raman and NMR ( 1H and 13C) spectra of the title compounds were analyzed. The calculated parameters were compared to experimental characteristics of these molecules.

Synthesis of Secondary Aromatic Amides via Pd-Catalyzed Aminocarbonylation of Aryl Halides Using Carbamoylsilane as an Amide Source.

PubMed

Tong, Wenting; Cao, Pei; Liu, Yanhong; Chen, Jianxin

2017-11-03

Using N-methoxymethyl-N-organylcarbamoyl(trimethyl)silanes as secondary amides source, the direct transformation of aryl halides into the corresponding secondary aromatic amides via palladium-catalyzed aminocarbonylation is described. The reactions tolerated a broad range of functional groups on the aryl ring except big steric hindrance of substituent. The types and the relative position of substituents on the aryl ring impact the coupling efficiency.

Polycyclic aromatic hydrocarbons in soils and crops after irrigation of wastewater discharged from domestic sewage treatment plants.

PubMed

Chung, N J; Cho, J Y; Park, S W; Park, B J; Hwang, S A; Park, T I

2008-08-01

The effects of domestic wastewater application on the translocation and accumulation of polycyclic aromatic hydrocarbons (PAHs) in soil and crops (rice, lettuce, and barley) were investigated by Wagner's pot experiment. In the soils and crops after domestic wastewater irrigation, high-molecular weight PAHs (5 to 6 ring) were not detected, but low-molecular weight PAHs (3 to 4 ring) were only detected at trace levels.

Spectroscopic study of the charge-transfer complexes TiCl4/styrene and TiCl4/polystyrene

NASA Astrophysics Data System (ADS)

Gonçalves, Norberto S.; Noda, Lúcia. K.

2017-10-01

In this work, solutions of TiCl4/styrene and TiCl4/polystyrene charge-transfer complexes in CHCl3 or CDCl3 were investigated by UV-vis, resonance Raman and 1H NMR spectroscopies in order to study their molecular and electronic structures. Both show a yellow colour due to absorption in the 400 nm region, related to a charge-transfer transition. In Raman spectra, as the excitation approaches the resonance region, the primary enhancement of aromatic ring modes was mainly observed, rather than intensification of the vinylic double-bond stretch. Under the experimental conditions it was observed that formation of polystyrene takes place, as showed by 1H NMR spectra, and the most significant interaction occurs at the aromatic ring, as supported by the results from interaction of TiCl4 with polystyrene, as indicated by the charge-transfer band and resonant intensification of the aromatic ring modes.

Secondary Structures in a Freeze-Dried Lignite Humic Acid Fraction Caused by Hydrogen-Bonding of Acidic Protons with Aromatic Rings.

PubMed

Cao, Xiaoyan; Drosos, Marios; Leenheer, Jerry A; Mao, Jingdong

2016-02-16

A lignite humic acid (HA) was separated from inorganic and non-HA impurities (i.e., aluminosilicates, metals) and fractionated by a combination of dialysis and XAD-8 resin. Fractionation revealed a more homogeneous structure of lignite HA. New and more specific structural information on the main lignite HA fraction is obtained by solid-state nuclear magnetic resonance (NMR) spectroscopy. Quantitative (13)C multiple cross-polarization (multiCP) NMR indicated oxidized phenyl propane structures derived from lignin. MultiCP experiments, conducted on potassium HA salts titrated to pH 10 and pH 12, revealed shifts consistent with carboxylate and phenolate formation, but structural changes associated with enolate formation from aromatic beta keto acids were not detected. Two-dimensional (1)H-(13)C heteronuclear correlation (2D HETCOR) NMR indicated aryl-aliphatic ketones, aliphatic and aromatic carboxyl groups, phenol, and methoxy phenyl ethers. Acidic protons from carboxyl groups in both the lignite HA fraction and a synthetic HA-like polycondensate were found to be hydrogen-bonded with electron-rich aromatic rings. Our results coupled with published infrared spectra provide evidence for the preferential hydrogen bonding of acidic hydrogens with electron-rich aromatic rings rather than adjacent carbonyl groups. These hydrogen-bonding interactions likely result from stereochemical arrangements in primary structures and folding.

Quantum control of coherent π -electron ring currents in polycyclic aromatic hydrocarbons

NASA Astrophysics Data System (ADS)

Mineo, Hirobumi; Fujimura, Yuichi

2017-12-01

We present results for quantum optimal control (QOC) of the coherent π electron ring currents in polycyclic aromatic hydrocarbons (PAHs). Since PAHs consist of a number of condensed benzene rings, in principle, there exist various coherent ring patterns. These include the ring current localized to a designated benzene ring, the perimeter ring current that flows along the edge of the PAH, and the middle ring current of PAHs having an odd number of benzene rings such as anthracene. In the present QOC treatment, the best target wavefunction for generation of the ring current through a designated path is determined by a Lagrange multiplier method. The target function is integrated into the ordinary QOC theory. To demonstrate the applicability of the QOC procedure, we took naphthalene and anthracene as the simplest examples of linear PAHs. The mechanisms of ring current generation were clarified by analyzing the temporal evolutions of the electronic excited states after coherent excitation by UV pulses or (UV+IR) pulses as well as those of electric fields of the optimal laser pulses. Time-dependent simulations of the perimeter ring current and middle ring current of anthracene, which are induced by analytical electric fields of UV pulsed lasers, were performed to reproduce the QOC results.

Oxidation of cinnamic acid derivatives: A pulse radiolysis and theoretical study

NASA Astrophysics Data System (ADS)

Yadav, Pooja; Mohan, Hari; Maity, Dilip Kumar; Suresh, Cherumuttathu H.; Rao, B. S. Madhav

2008-07-01

Second order rate constants in the range of ( k = 1.6-4.5) × 10 9 dm 3 mol -1 s -1 were obtained for the rad OH induced oxidation of nitro- and methoxycinnamic acid derivatives in neutral solutions using pulse radiolysis. The transient absorption spectra exhibited a broad peak around 360-410 nm in o-methoxy, o- and p-nitrocinnamates or two peaks around 310-330 and 370-410 nm in other isomers. Quantum chemical calculations revealed that addition of rad OH to olefinic moiety yielded considerably more stable structures than ring addition products and the para system among the latter is the most stable. Spin density analysis suggested that olefinic adducts retained the aromaticity in contrast to its loss in ring rad OH adducts. An excellent linear correlation between the relative stabilities of the rad OH adducts (after accounting for the aromatic stabilization in olefinic adducts) and the maximum Sd values is also obtained.

Understanding of assembly phenomena by aromatic-aromatic interactions: benzene dimer and the substituted systems.

PubMed

Lee, Eun Cheol; Kim, Dongwook; Jurecka, Petr; Tarakeshwar, P; Hobza, Pavel; Kim, Kwang S

2007-05-10

Interactions involving aromatic rings are important in molecular/biomolecular assembly and engineering. As a consequence, there have been a number of investigations on dimers involving benzene or other substituted pi systems. In this Feature Article, we examine the relevance of the magnitudes of their attractive and repulsive interaction energy components in governing the geometries of several pi-pi systems. The geometries and the associated binding energies were evaluated at the complete basis set (CBS) limit of coupled cluster theory with singles, doubles, and perturbative triples excitations [CCSD(T)] using a least biased scheme for the given data set. The results for the benzene dimer indicate that the floppy T-shaped structure (center-to-center distance: 4.96 A, with an axial benzene off-centered above the facial benzene) is isoenergetic in zero-point-energy (ZPE) corrected binding energy (D0) to the displaced-stacked structure (vertical interplanar distance: 3.54 A). However, the T-shaped structure is likely to be slightly more stable (D0 approximately equal to 2.4-2.5 kcal/mol) if quadruple excitations are included in the coupled cluster calculations. The presence of substituents on the aromatic ring, irrespective of their electron withdrawing or donating nature, leads to an increase in the binding energy, and the displaced-stacked conformations are more stabilized than the T-shaped conformers. This explains the wide prevalence of displaced stacked structures in organic crystals. Despite that the dispersion energy is dominating, the substituent as well as the conformational effects are correlated to the electrostatic interaction. This electrostatic origin implies that the substituent effect would be reduced in polar solution, but important in apolar media, in particular, for assembling processes.

Inhibition of carboxylesterases by benzil (diphenylethane-1,2-dione) and heterocyclic analogues is dependent upon the aromaticity of the ring and the flexibility of the dione moiety.

PubMed

Hyatt, Janice L; Stacy, Vanessa; Wadkins, Randy M; Yoon, Kyoung Jin P; Wierdl, Monika; Edwards, Carol C; Zeller, Matthias; Hunter, Allen D; Danks, Mary K; Crundwell, Guy; Potter, Philip M

2005-08-25

Benzil has been identified as a potent selective inhibitor of carboxylesterases (CEs). Essential components of the molecule required for inhibitory activity include the dione moiety and the benzene rings, and substitution within the rings affords increased selectivity toward CEs from different species. Replacement of the benzene rings with heterocyclic substituents increased the K(i) values for the compounds toward three mammalian CEs when using o-nitrophenyl acetate as a substrate. Logarithmic plots of the K(i) values versus the empirical resonance energy, the heat of union of formation energy, or the aromatic stabilization energy determined from molecular orbital calculations for the ring structures yielded linear relationships that allowed prediction of the efficacy of the diones toward CE inhibition. Using these data, we predicted that 2,2'-naphthil would be an excellent inhibitor of mammalian CEs. This was demonstrated to be correct with a K(i) value of 1 nM being observed for a rabbit liver CE. In addition, molecular simulations of the movement of the ring structures around the dione dihedral indicated that the ability of the compounds to inhibit CEs was due, in part, to rotational constraints enforced by the dione moiety. Overall, these studies identify subdomains within the aromatic ethane-1,2-diones, that are responsible for CE inhibition.

A highly sensitive monoclonal antibody based biosensor for quantifying 3-5 ring polycyclic aromatic hydrocarbons (PAHs) in aqueous environmental samples

PubMed Central

Li, Xin; Kaattari, Stephen L.; Vogelbein, Mary A.; Vadas, George G.; Unger, Michael A.

2016-01-01

Immunoassays based on monoclonal antibodies (mAbs) are highly sensitive for the detection of polycyclic aromatic hydrocarbons (PAHs) and can be employed to determine concentrations in near real-time. A sensitive generic mAb against PAHs, named as 2G8, was developed by a three-step screening procedure. It exhibited nearly uniformly high sensitivity against 3-ring to 5-ring unsubstituted PAHs and their common environmental methylated PAHs, with IC50 values between 1.68–31 μg/L (ppb). 2G8 has been successfully applied on the KinExA Inline Biosensor system for quantifying 3-5 ring PAHs in aqueous environmental samples. PAHs were detected at a concentration as low as 0.2 μg/L. Furthermore, the analyses only required 10 min for each sample. To evaluate the accuracy of the 2G8-based biosensor, the total PAH concentrations in a series of environmental samples analyzed by biosensor and GC-MS were compared. In most cases, the results yielded a good correlation between methods. This indicates that generic antibody 2G8 based biosensor possesses significant promise for a low cost, rapid method for PAH determination in aqueous samples. PMID:26925369

Light-induced yellowing of selectively 13C-enriched dehydrogenation polymers (DHPs). Part 2, NMR assignments and photoyellowing of aromatic ring 1-, 3-, 4-, and 5-13C DHPs

Treesearch

Jim Parkas; Magnus Paulsson; Terashima Noritsugu; Ulla Westermark; Sally Ralph

2004-01-01

Light-induced yellowing of lignocellulosicmaterials has been studied using 13C-enriched DHP (dehydrogenation polymer), selectively 13C-enriched at positions 1, 3, 4, and 5 in the aromatic ring, and quantitative solution state 13C NMR spectroscopy. The NMR study confirmed the results of previous studies using side-chain labeled DHP, mainly that coniferyl alcohol end...

Methyl substituted polyimides containing carbonyl and ether connecting groups

NASA Technical Reports Server (NTRS)

Hergenrother, Paul M. (Inventor); Havens, Stephen J. (Inventor)

1992-01-01

Polyimides were prepared from the reaction of aromatic dianhydrides with novel aromatic diamines having carbonyl and ether groups connecting aromatic rings containing pendant methyl groups. The methyl substituent polyimides exhibit good solubility and form tough, strong films. Upon exposure to ultraviolet irradiation and/or heat, the methyl substituted polyimides crosslink to become insoluble.

Conformational behavior of phenylglycines and hydroxyphenylglycines and non-planarity of phenyl rings.

PubMed

Nandel, Fateh S; Shafique, Mohd

2014-10-01

The non-proteinogenic amino acids--phenylglycine (PG) and hydroxyphenylglycine (HPG) are crucial components of certain peptidic natural products and are important for the preparation of various medicines. In this, study, the conformation of model dipeptides Ac-X-NHMe of PG, p-HPG and 3, 5-di-hydroxyphenylglycine (3, 5-DHPG) was studied both in R and S form by quantum mechanical (QM) and molecular dynamics approaches. On the energy scale, the conformational states of these molecules in both the R and S were found to be degenerate by QM studies, stabilized by non-covalent interactions like carbonyl--carbonyl interactions, carbonyl-lp .. π (aromatic ring) interactions etc. These interactions disappeared/weakened due to interaction of water molecules with carbonyl groups of backbone in simulation and water was found to interact with the aromatic ring through O(w)-H .. π or O(w)lp .. π interactions. The degeneracy of conformational states was lifted in favor of R-form of PG and DHPG and water molecules interactions with aromatic ring led to non-planarity of the aromatic ring. In simulation studies, irrespective of the starting geometry, the Φ, ψ values for the R form correspond to inverse β/inverse collagen region and for the S-form, the Φ, ψ values correspond to β/collagen region i.e., adopt single conformation. The obtained results were in conformity with the CD spectroscopic data on D-PG and D-p-HPG. The conformational behavior of the unusual amino acids might be of great help in designing of bioactive peptides/peptide based drugs to be realized in single conformation--an essential requirement.

3-Phenyl-6-(2-pyrid-yl)-1,2,4,5-tetra-zine.

PubMed

Chartrand, Daniel; Laverdière, François; Hanan, Garry

2007-12-06

The title compound, C(13)H(9)N(5), is the first asymmetric diaryl-1,2,4,5-tetra-zine to be crystallographically characterized. We have been inter-ested in this motif for incorporation into supra-molecular assemblies based on coordination chemistry. The solid state structure shows a centrosymmetric mol-ecule, forcing a positional disorder of the terminal phenyl and pyridyl rings. The mol-ecule is completely planar, unusual for aromatic rings with N atoms in adjacent ortho positions. The stacking observed is very common in diaryl-tetra-zines and is dominated by π stacking [centroid-to-centroid distance between the tetrazine ring and the aromatic ring of an adjacent molecule is 3.6 Å, perpendicular (centroid-to-plane) distance of about 3.3 Å].

Polycyclic aromatic hydrocarbon (PAH) emissions from a coal-fired pilot FBC system.

PubMed

Liu, K; Han, W; Pan, W P; Riley, J T

2001-06-29

Due to the extensive amount of data suggesting the hazards of these compounds, 16 polycyclic aromatic hydrocarbons (PAHs) are on the Environmental Protection Agency (EPA) Priority Pollutant List. Emissions of these PAHs in the flue gas from the combustion of four coals were measured during four 1000h combustion runs using the 0.1MW heat-input (MWth) bench-scale fluidized bed combustor (FBC). An on-line sampling system was designed for the 16 PAHs, which consisted of a glass wool filter, condenser, glass fiber filter, Teflon filter, and a Tenax trap. The filters and Tenax were extracted by methylene chloride and hexane, respectively, followed by GC/MS analysis using the selective ion monitoring (SIM) mode. In this project, the effects of operating parameters, limestone addition, chlorine content in the coal, and Ca/S molar ratio on the emissions of PAHs were studied. The results indicated that the emissions of PAHs in an FBC system are primarily dependent on the combustion temperature and excess air ratio. The injection of secondary air with high velocity in the freeboard effectively reduces PAH emissions. The addition of extra limestone can promote the formation of PAHs in the FBC system. Chlorine in the coal can possibly lead to large benzene ring PAH formation during combustion. The total PAH emission increases with an increase in the sulfur content of coal. Incomplete combustion results in PAHs with four or more benzene rings. High efficiency combustion results in PAHs with two or three benzene rings.

Polycyclic aromatic hydrocarbons profiles of spent drilling fluids deposited at Emu-Uno, Delta State, Nigeria.

PubMed

Iwegbue, Chukwujindu M A

2011-10-01

The concentrations and profiles of polycyclic aromatic hydrocarbons were determined in spent drilling fluid deposited at Emu-Uno, Delta State of Nigeria. The total concentrations of polycyclic aromatic hydrocarbons in the spent drilling fluid deposits ranged between 40 and 770 μg kg(-1). The PAHs profile were predominantly 2- and 3-rings with acenaphthalene, phenanthrene, fluorene being the predominant PAHs. The prevalence of 2- and 3-rings PAHs in the spent drilling fluid deposits indicate contamination of the drilling fluids with crude oil during drilling. Incorporation of spent drilling fluids into the soil has serious implication for soil, surface water and groundwater quality. © Springer Science+Business Media, LLC 2011

Nuclear Magnetic Resonance Studies of an N2-Guanine Adduct Derived from the Tumorigen Dibenzo[a,l]pyrene in DNA: Impact of Adduct Stereochemistry, Size, and Local DNA Sequence on Solution Conformations

PubMed Central

2015-01-01

The dimensions and arrangements of aromatic rings (topology) in adducts derived from the reactions of polycyclic aromatic hydrocarbon (PAH) diol epoxide metabolites with DNA influence the distortions and stabilities of double-stranded DNA, and hence their recognition and processing by the human nucleotide excision repair (NER) system. Dibenzo[a,l]pyrene (DB[a,l]P) is a highly tumorigenic six-ring PAH, which contains a nonplanar and aromatic fjord region that is absent in the structurally related bay region five-ring PAH benzo[a]pyrene (B[a]P). The PAH diol epoxide–DNA adducts formed include the stereoisomeric 14S and 14Rtrans-anti-DB[a,l]P-N2-dG and the stereochemically analogous 10S- and 10R-B[a]P-N2-dG (B[a]P-dG) guanine adducts. However, nuclear magnetic resonance (NMR) solution studies of the 14S-DB[a,l]P-N2-dG adduct in DNA have not yet been presented. Here we have investigated the 14S-DB[a,l]P-N2-dG adduct in two different sequence contexts using NMR methods with distance-restrained molecular dynamics simulations. In duplexes with dC opposite the adduct deleted, a well-resolved base-displaced intercalative adduct conformation can be observed. In full duplexes, in contrast to the intercalated 14R stereoisomeric adduct, the bulky DB[a,l]P residue in the 14S adduct is positioned in a greatly widened and distorted minor groove, with significant disruptions and distortions of base pairing at the lesion site and two 5′-side adjacent base pairs. These unique structural features are significantly different from those of the stereochemically analogous but smaller B[a]P-dG adduct. The greater size and different topology of the DB[a,l]P aromatic ring system lead to greater structurally destabilizing DNA distortions that are partially compensated by stabilizing DB[a,l]P-DNA van der Waals interactions, whose combined effects impact the NER response to the adduct. These structural results broaden our understanding of the structure–function relationship in NER. PMID:24617538

Ring flips revisited: (13)C relaxation dispersion measurements of aromatic side chain dynamics and activation barriers in basic pancreatic trypsin inhibitor.

PubMed

Weininger, Ulrich; Modig, Kristofer; Akke, Mikael

2014-07-22

Intramolecular motions of proteins are critical for biological function. Transient structural fluctuations underlie a wide range of processes, including enzyme catalysis, ligand binding to buried sites, and generic protein motions, such as 180° rotation of aromatic side chains in the protein interior, but remain poorly understood. Understanding the dynamics and molecular nature of concerted motions requires characterization of their rates and energy barriers. Here we use recently developed (13)C transverse relaxation dispersion methods to improve our current understanding of aromatic ring flips in basic pancreatic trypsin inhibitor (BPTI). We validate these methods by benchmarking ring-flip rates against the three previously characterized cases in BPTI, namely, Y23, Y35, and F45. Further, we measure conformational exchange for one additional aromatic ring, F22, which can be interpreted in terms of a flip rate of 666 s(-1) at 5 °C. Upon inclusion of our previously reported result that Y21 also flips slowly [Weininger, U., et al. (2013) J. Phys. Chem. B 117, 9241-9247], the (13)C relaxation dispersion experiments thus reveal relatively slow ring-flip rates for five of eight aromatic residues in BPTI. These results are in contrast with previous reports, which have estimated that all rings, except Y23, Y35, and F45, flip with a high rate at ambient temperature. The (13)C relaxation dispersion data result in an updated rank order of ring-flip rates in BPTI, which agrees considerably better with that estimated from a recent 1 ms molecular dynamics trajectory than do previously published NMR data. However, significant quantitative differences remain between experiment and simulation, in that the latter yields flip rates that are in many cases too fast by 1-2 orders of magnitude. By measuring flip rates across a temperature range of 5-65 °C, we determined the activation barriers of ring flips for Y23, Y35, and F45. Y23 and F45 have identical activation parameters, suggesting that the fluctuations of the protein core around these residues are similar in character. Y35 differs from the other two in its apparent activation entropy. These results might be rationalized by the fact that Y23 and F45 are located in the same region of the structure while Y35 is remote from the other two rings. As indicated by our new results for the exceptionally well-characterized protein BPTI, (13)C relaxation dispersion experiments open the possibility of studying ring flips in a range of cases wider than that previously possible.

Comparison of UV/hydrogen peroxide, potassium ferrate(VI), and ozone in oxidizing the organic fraction of oil sands process-affected water (OSPW).

PubMed

Wang, Chengjin; Klamerth, Nikolaus; Messele, Selamawit Ashagre; Singh, Arvinder; Belosevic, Miodrag; Gamal El-Din, Mohamed

2016-09-01

The efficiency of three different oxidation processes, UV/H2O2 oxidation, ferrate(VI) oxidation, and ozonation with and without hydroxyl radical (OH) scavenger tert-butyl alcohol (TBA) on the removal of organic compounds from oil sands process-affected water (OSPW) was investigated and compared. The removal of aromatics and naphthenic acids (NAs) was explored by synchronous fluorescence spectra (SFS), ion mobility spectra (IMS), proton and carbon nuclear magnetic resonance ((1)H and (13)C NMR), and ultra-performance liquid chromatography coupled with time-of-flight mass spectrometry (UPLC TOF-MS). UV/H2O2 oxidation occurred through radical reaction and photolysis, transforming one-ring, two-ring, and three-ring fluorescing aromatics simultaneously and achieving 42.4% of classical NAs removal at 2.0 mM H2O2 and 950 mJ/cm(2) UV dose provided with medium pressure mercury lamp. Ferrate(VI) oxidation exhibited high selectivity, preferentially removing two-ring and three-ring fluorescing aromatics, sulfur-containing NAs (NAs + S), and NAs with high carbon and high hydrogen deficiency. At 2.0 mM Fe(VI), 46.7% of classical NAs was removed. Ozonation achieved almost complete removal of fluorescing aromatics, NAs + S, and classical NAs (NAs with two oxygen atoms) at the dose of 2.0 mM O3. Both molecular ozone reaction and OH reaction were important pathways in transforming the organics in OSPW as supported by ozonation performance with and without TBA. (1)H NMR analyses further confirmed the removal of aromatics and NAs both qualitatively and quantitatively. All the three oxidation processes reduced the acute toxicity towards Vibrio fischeri and on goldfish primary kidney macrophages (PKMs), with ozonation being the most efficient. Copyright © 2016 Elsevier Ltd. All rights reserved.

Normal-phase liquid chromatography retention behavior of polycyclic aromatic sulfur heterocycles and alkyl-substituted polycyclic aromatic sulfur heterocycle isomers on an aminopropyl stationary phase.

PubMed

Wilson, Walter B; Hayes, Hugh V; Sander, Lane C; Campiglia, Andres D; Wise, Stephen A

2018-02-01

Retention indices for 67 polycyclic aromatic sulfur heterocycles (PASHs) and 80 alkyl-substituted PASHs were determined using normal-phase liquid chromatography (NPLC) on an aminopropyl (NH 2 ) stationary phase. The retention behavior of PASH on the NH 2 phase is correlated with the number of aromatic carbon atoms and two structural characteristics have a significant influence on their retention: non-planarity (thickness, T) and the position of the sulfur atom in the bay-region of the structure. Correlations between solute retention on the NH 2 phase and T of PASHs were investigated for three cata-condensed (cata-) PASH isomer groups: (a) 13 four-ring molecular mass (MM) 234 Da cata-PASHs, (b) 20 five-ring MM 284 Da cata-PASHs, and (c) 12 six-ring MM 334 Da cata-PASHs. Correlation coefficients ranged from r = -0.49 (MM 234 Da) to r = -0.65 (MM 334 Da), which were significantly lower than structurally similar PAH isomer groups (r = -0.70 to r = -0.99). The NPLC retention behavior of the PASHs are compared to similar results for PAHs.

Cation induced electrochromism in 2,4-dinitrophenylhydrazine (DNPH): Tuning optical properties of aromatic rings

NASA Astrophysics Data System (ADS)

Sanader, Željka; Brunet, Claire; Broyer, Michel; Antoine, Rodolphe; Dugourd, Philippe; Mitrić, Roland; Bonačić-Koutecký, Vlasta

2013-05-01

We have theoretically investigated the influence of protons and noble metal cations on optical properties of 2,4-dinitrophenylhydrazine (DNPH). We show that optical properties of aromatic rings can be tuned by cation-induced electrochromism in DNPH due to binding to specific NO2 groups. Our findings on cation-induced electrochromism in DNPH may open new routes in two different application areas, due to the fact that DNPH can easily bind to biological molecules and surface materials through carbonyl groups.

Synthesis and antifungal activity of C-21 steroids with an aromatic D ring.

PubMed

Sonego, Juan M; Cirigliano, Adriana M; Cabrera, Gabriela M; Burton, Gerardo; Veleiro, Adriana S

2013-07-01

Six analogues of salpichrolides with a simplified side chain (6-11) were synthesized using a new methodology to obtain steroids with an aromatic D-ring. The key step was the elimination of HBr in a vicinal dibromo D-homosteroid by treatment with 1,4-diazabicyclo[2.2.2]octane (DABCO). All new compounds were completely characterized by 2D NMR techniques and tested on two fungal pathogenic species, Fusarium virguliforme and Fusarium solani. Copyright © 2013 Elsevier Inc. All rights reserved.

Isomer effects on polyimide properties

NASA Technical Reports Server (NTRS)

Stump, B. L.

1978-01-01

Thermally stable polyimide polymers were prepared. Parameters explored include asymmetry of substitution, addition of alkyl substituents to an aromatic ring, and an increase in the number of aromatic rings present in the diamine monomer. It is shown that the use of an asymmetrical diamine in the preparation of a polyimide produces a polymer with a markedly lowered glass transition temperature. This is achieved with little or no sacrifice of thermal stability. An alternate approach taken was to prepare imide monomers which are capable of addition-type polymerization.

Effect of ZSM-5 acidity on aromatic product selectivity during upgrading of pine pyrolysis vapors

DOE PAGES

Engtrakul, Chaiwat; Mukarakate, Calvin; Starace, Anne K.; ...

2015-11-14

The impact of catalyst acidity on the selectivity of upgraded biomass pyrolysis products was studied by passing pine pyrolysis vapors over five ZSM-5 catalysts of varying acidity at 500 degrees C. The SiO 2-to-Al 2O 3 ratio (SAR) of the ZSM-5 zeolite was varied from 23 to 280 to control the acidity of the catalyst and the composition of upgraded products. The upgraded product stream was analyzed by GCMS. Additionally, catalysts were characterized using temperature programmed desorption, diffuse-reflectance FTIR spectroscopy, N 2 physisorption, and X-ray diffraction. The results showed that the biomass pyrolysis vapors were highly deoxygenated to form amore » slate of aromatic hydrocarbons over all of the tested ZSM-5 catalysts. As the overall acidity of the ZSM-5 increased the selectivity toward alkylated (substituted) aromatics (e.g., xylene, dimethyl-naphthalene, and methyl-anthracene) decreased while the selectivity toward unsubstituted aromatics (e.g., benzene, naphthalene, and anthracene) increased. Additionally, the selectivity toward polycyclic aromatic compounds (2-ring and 3-ring) increased as catalyst acidity increased, corresponding to a decrease in acid site spacing. The increased selectivity toward less substituted polycyclic aromatic compounds with increasing acidity is related to the relative rates of cyclization and alkylation reactions within the zeolite structure. As the acid site concentration increases and sites become closer to each other, the formation of additional cyclization products occurs at a greater rate than alkylated products. The ability to adjust product selectivity within 1-, 2-, and 3-ring aromatic families, as well as the degree of substitution, by varying ZSM-5 acidity could have significant benefits in terms creating a slate of upgraded biomass pyrolysis products to meet specific target market demands.« less

Dimethandrolone (7α,11β-dimethyl-19-nortestosterone) and 11β-methyl-19-nortestosterone are not converted to aromatic A-ring products in the presence of recombinant human aromatase☆

PubMed Central

Attardi, Barbara J.; Pham, Trung C.; Radler, Lisa M.; Burgenson, Janet; Hild, Sheri A.; Reel, Jerry R.

2008-01-01

Dimethandrolone undecanoate (DMAU: 7α,11β-dimethyl-19-nortestosterone 17β-undecanoate) is a potent orally active androgen in development for hormonal therapy in men. Cleavage of the 17β-ester bond by esterases in vivo leads to liberation of the biologically active androgen, dimethandrolone (DMA), a 19-norandrogen. For hormone replacement in men, administration of C19 androgens such as testosterone (T) may lead to elevations in circulating levels of estrogens due to aromatization. As several reports have suggested that certain 19-norandrogens may serve as substrates for the aromatase enzyme and are converted to the corresponding aromatic A-ring products, it was important to investigate whether DMA, the related compound, 11β-methyl-19-nortestosterone (11β-MNT), also being tested for hormonal therapy in men, and other 19-norandrogens can be converted to aromatic A-ring products by human aromatase. The hypothetical aromatic A-ring product corresponding to each substrate was obtained by chemical synthesis. These estrogens bound with high affinity to purified recombinant human estrogen receptors (ER) α and β in competitive binding assays (IC50's: 5−12 × 10−9 M) and stimulated transcription of 3XERE-luciferase in T47Dco human breast cancer cells with a potency equal to or greater than that of estradiol (E2) (EC50's: 10−12 to 10−11 M). C19 androgens (T, 17α-methyltestosterone (17α-MT), androstenedione (AD), and 16α-hydroxyandrostenedione (16α-OHAD)), 19-norandrogens (DMA, 11β-MNT, 19-nortestosterone (19-NT), and 7α-methyl-19-nortestosterone (MENT)) or the structurally similar 19-norprogestin, norethindrone (NET) were incubated at 50 μM with recombinant human aromatase for 10−180 min at 37 °C. The reactions were terminated by extraction with acetonitrile and centrifugation, and substrate and potential product were separated by HPLC. Retention times were monitored by UV absorption, and UV peaks were quantified using standard curves. Aromatization of the positive controls, T, AD, and 16α-OHAD was linear for 40−60 min, and conversion of T or AD was complete by 120 min. The nonsteroidal aromatase inhibitor, letrozole, demonstrated concentration-dependent suppression of T aromatization. Under the same conditions, there was no detectable conversion of DMA, 11β-MNT, or NET to their respective hypothetical aromatic A-ring products during incubation times up to 180 min. Aromatization of MENT and 19-NT proceeded slowly and was limited. Collectively, these data support the notion that in the absence of the C19-methyl group, which is the site of attack by oxygen, aromatization of androgenic substrates proceeds slowly or not at all and that this reaction is impeded by the presence of a methyl group at the 11β position. PMID:18555683

Activation of a Carbon-Oxygen Bond of Benzofuran by Precoordination of Manganese to the Carbocyclic Ring: A Model for Hydrodeoxygenation.

PubMed

Zhang; Watson; Dullaghan; Gorun; Sweigart

1999-08-01

Stable unsaturated heterocycles such as benzofuran are difficult to remove from petroleum by conventional catalytic hydrotreating. However, in a model system, coordination of Mn(CO)(3)(+) to the aromatic ring of benzofuran activates the C-O bond towards insertion of [Pt(PPh(3))(2)] [Eq. (1)]. The insertion is preceded by precoordination to the furan C=C bond; thus, the 2,3-dihydro analogue of 1, which lacks this double bond, does not undergo insertion of the Pt moiety.

(2E)-1-(2,6-Dichloro-3-fluoro-phen-yl)-3-phenyl-prop-2-en-1-one.

PubMed

Praveen, Aletti S; Yathirajan, Hemmige S; Narayana, Badiadka; Gerber, Thomas; Hosten, Eric; Betz, Richard

2012-04-01

In the title compound, C(15)H(9)Cl(2)FO, the F atom shows positional disorder over two positions, with site-occupancy factors of 0.747 (4) and 0.253 (4). The dihedral angle between the rings is 86.37 (10)°. In the crystal, C-H⋯O contacts connect the mol-ecules into chains along the c axis. The shortest inter-centroid distance between two aromatic systems is 3.6686 (12) Å and is apparent between the halogenated rings.

Actions of a versatile fluorene-degrading bacterial isolate on polycyclic aromatic compounds.

PubMed Central

Grifoll, M; Selifonov, S A; Gatlin, C V; Chapman, P J

1995-01-01

Pseudomonas cepacia F297 grew with fluorene as a sole source of carbon and energy; its growth yield corresponded to an assimilation of about 40% of fluorene carbon. The accumulation of a ring meta-cleavage product during growth and the identification of 1-indanone in growth media and washed-cell suspensions suggest that strain F297 metabolizes fluorene by mechanisms analogous to those of naphthalene degradation. In addition to fluorene, strain F297 utilized for growth a wide variety of polycyclic aromatic compounds (PACs), including naphthalene, 2,3-dimethylnaphthalene, phenanthrene, anthracene, and dibenzothiophene. Fluorene-induced cells of the strain also transformed 2,6-dimethylnaphthalene, biphenyl, dibenzofuran, acenaphthene, and acenaphthylene. The identification of products formed from those substrates (by gas chromatography-mass spectrometry) in washed-cell suspensions indicates that P. cepacia F297 carries out the following reactions: (i) aromatic ring oxidation and cleavage, apparently using the pyruvate released for growth, (ii) methyl group oxidations, (iii) methylenic oxidations, and (iv) S oxidations of aromatic sulfur heterocycles. Strain F297 grew with a creosote-PAC mixture, producing an almost complete removal of all aromatic compounds containing 2 to 3 rings in 14 days, as demonstrated by gas chromatography analysis of the remaining PACs recovered from cultures. The identification of key chemicals confirmed that not only are certain compounds depleted but also the anticipated reaction products are found. PMID:7487007

Actions of a versatile fluorene-degrading bacterial isolate on polycyclic aromatic compounds.

PubMed

Grifoll, M; Selifonov, S A; Gatlin, C V; Chapman, P J

1995-10-01

Pseudomonas cepacia F297 grew with fluorene as a sole source of carbon and energy; its growth yield corresponded to an assimilation of about 40% of fluorene carbon. The accumulation of a ring meta-cleavage product during growth and the identification of 1-indanone in growth media and washed-cell suspensions suggest that strain F297 metabolizes fluorene by mechanisms analogous to those of naphthalene degradation. In addition to fluorene, strain F297 utilized for growth a wide variety of polycyclic aromatic compounds (PACs), including naphthalene, 2,3-dimethylnaphthalene, phenanthrene, anthracene, and dibenzothiophene. Fluorene-induced cells of the strain also transformed 2,6-dimethylnaphthalene, biphenyl, dibenzofuran, acenaphthene, and acenaphthylene. The identification of products formed from those substrates (by gas chromatography-mass spectrometry) in washed-cell suspensions indicates that P. cepacia F297 carries out the following reactions: (i) aromatic ring oxidation and cleavage, apparently using the pyruvate released for growth, (ii) methyl group oxidations, (iii) methylenic oxidations, and (iv) S oxidations of aromatic sulfur heterocycles. Strain F297 grew with a creosote-PAC mixture, producing an almost complete removal of all aromatic compounds containing 2 to 3 rings in 14 days, as demonstrated by gas chromatography analysis of the remaining PACs recovered from cultures. The identification of key chemicals confirmed that not only are certain compounds depleted but also the anticipated reaction products are found.

Pyridine-substituted thiazolylphenol derivatives: Synthesis, modeling studies, aromatase inhibition, and antiproliferative activity evaluation.

PubMed

Ertas, Merve; Sahin, Zafer; Berk, Barkin; Yurttas, Leyla; Biltekin, Sevde N; Demirayak, Seref

2018-04-01

Drugs used in breast cancer treatments target the suppression of estrogen biosynthesis. During this suppression, the main goal is to inhibit the aromatase enzyme that is responsible for the cyclization and structuring of estrogens either with steroid or non-steroidal-type inhibitors. Non-steroidal derivatives generally have a planar aromatic structure attached to the triazole ring system in their structures, which inhibits hydroxylation reactions during aromatization by coordinating the heme group. Bioisosteric replacement of the triazole ring system and development of aromatic/cyclic structures of the side chain can increase the selectivity for aromatase enzyme inhibition. In this study, pyridine-substituted thiazolylphenol derivatives, which are non-steroidal triazole bioisosteres, were synthesized using the Hantzsch method, and physical analysis and structural determination studies were performed. The IC 50 values of the compounds were determined by a fluorescence-based aromatase inhibition assay. Then, their antiproliferative activities on the MCF7 and HEK 293 cell lines were evaluated with the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Furthermore, the crystal structure of human placental aromatase was subjected to a series of docking experiments to identify the possible interactions between the most active structure and the active site. Lastly, an in silico technique was performed to analyze and predict the drug-likeness, molecular and ADME properties of the synthesized molecules. © 2018 Deutsche Pharmazeutische Gesellschaft.

Fluorinated Aromatic Amino Acids Distinguish Cation-π Interactions from Membrane Insertion*

PubMed Central

He, Tao; Gershenson, Anne; Eyles, Stephen J.; Lee, Yan-Jiun; Liu, Wenshe R.; Wang, Jiangyun; Gao, Jianmin; Roberts, Mary F.

2015-01-01

Cation-π interactions, where protein aromatic residues supply π systems while a positive-charged portion of phospholipid head groups are the cations, have been suggested as important binding modes for peripheral membrane proteins. However, aromatic amino acids can also insert into membranes and hydrophobically interact with lipid tails. Heretofore there has been no facile way to differentiate these two types of interactions. We show that specific incorporation of fluorinated amino acids into proteins can experimentally distinguish cation-π interactions from membrane insertion of the aromatic side chains. Fluorinated aromatic amino acids destabilize the cation-π interactions by altering electrostatics of the aromatic ring, whereas their increased hydrophobicity enhances membrane insertion. Incorporation of pentafluorophenylalanine or difluorotyrosine into a Staphylococcus aureus phosphatidylinositol-specific phospholipase C variant engineered to contain a specific PC-binding site demonstrates the effectiveness of this methodology. Applying this methodology to the plethora of tyrosine residues in Bacillus thuringiensis phosphatidylinositol-specific phospholipase C definitively identifies those involved in cation-π interactions with phosphatidylcholine. This powerful method can easily be used to determine the roles of aromatic residues in other peripheral membrane proteins and in integral membrane proteins. PMID:26092728

In Vitro Antifungal Activity of New and Known Geranylated Phenols against Phytophthora cinnamomi Rands.

PubMed

Chavez, María I; Soto, Mauricio; Cimino, Franco A; Olea, Andrés F; Espinoza, Luis; Díaz, Katy; Taborga, Lautaro

2018-05-29

A series of new and known geranylated phenol/methoxyphenol derivatives has been tested in vitro as inhibitor agents of mycelial growth of Phytophthora cinnamomi . The activity of tested compounds is correlated with the nature, number, and position of the substituent group on the aromatic ring. Results indicate that the most active geranylated derivatives are those having two hydroxyl groups (or one ⁻OH and one ⁻OCH₃) attached to the aromatic ring. Interestingly, these derivatives are as active as Metalaxil ® , a commonly used commercial fungicide. Thus, our results suggest that some of these compounds might be of agricultural interest due to their potential use as fungicides against P. cinnamomi . The effect of structure on fungicide activity is discussed in terms of electronic distribution on both the aromatic ring and side geranyl chain. All tested compounds have been synthesized by direct coupling of geraniol and the respective phenol. Interestingly, new digeranylated derivatives were obtained by increasing the reaction time.

3-Phenyl-6-(2-pyrid­yl)-1,2,4,5-tetra­zine

PubMed Central

Chartrand, Daniel; Laverdière, François; Hanan, Garry

2008-01-01

The title compound, C13H9N5, is the first asymmetric diaryl-1,2,4,5-tetra­zine to be crystallographically characterized. We have been inter­ested in this motif for incorporation into supra­molecular assemblies based on coordination chemistry. The solid state structure shows a centrosymmetric mol­ecule, forcing a positional disorder of the terminal phenyl and pyridyl rings. The mol­ecule is completely planar, unusual for aromatic rings with N atoms in adjacent ortho positions. The stacking observed is very common in diaryl­tetra­zines and is dominated by π stacking [centroid-to-centroid distance between the tetrazine ring and the aromatic ring of an adjacent molecule is 3.6 Å, perpendicular (centroid-to-plane) distance of about 3.3 Å]. PMID:21200916

Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS): A National Analysis of Data from 10-Year Post-marketing Surveillance.

PubMed

Renda, Francesca; Landoni, Giovanni; Bertini Malgarini, Renato; Assisi, Alessandro; Azzolini, Maria Luisa; Mucchetti, Marta; Pimpinella, Giuseppe; Pani, Luca

2015-12-01

Drug reaction with eosinophilia and systemic symptoms (DRESS) is a rare, severe and potentially fatal cutaneous adverse drug reaction (the mortality rate is up to 10 %) associated with numerous and apparently heterogeneous drugs. The aetiology is unknown. To report Italian cases of DRESS over a 10-year period. We searched the National Pharmacovigilance Network (NPN) for the term 'drug reaction with eosinophilia and systemic symptoms' from 1 January 2004 to 1 January 2014, to identify all reports of DRESS. Each case was checked to avoid duplication. In the NPN, we identified 91 serious cases of DRESS: 68 were spontaneous, still-unpublished reports, while 23 additional cases were derived from screening of the scientific literature, performed by marketing authorization holders. Notably, the single common element linking all cases of DRESS was intake of a drug containing an aromatic ring. Thanks to the largest national DRESS case series ever reported, we were able to hypothesize, for the first time, that there is an association between use of drugs containing an aromatic ring in their chemical structure and DRESS. This might aid understanding of the aetiology of DRESS and facilitate diagnosis.

Analysis of the magnetically induced current density of molecules consisting of annelated aromatic and antiaromatic hydrocarbon rings.

PubMed

Sundholm, Dage; Berger, Raphael J F; Fliegl, Heike

2016-06-21

Magnetically induced current susceptibilities and current pathways have been calculated for molecules consisting of two pentalene groups annelated with a benzene (1) or naphthalene (2) moiety. Current strength susceptibilities have been obtained by numerically integrating separately the diatropic and paratropic contributions to the current flow passing planes through chosen bonds of the molecules. The current density calculations provide novel and unambiguous current pathways for the unusual molecules with annelated aromatic and antiaromatic hydrocarbon moieties. The calculations show that the benzene and naphthalene moieties annelated with two pentalene units as in molecules 1 and 2, respectively, are unexpectedly antiaromatic sustaining only a local paratropic ring current around the ring, whereas a weak diatropic current flows around the C-H moiety of the benzene ring. For 1 and 2, the individual five-membered rings of the pentalenes are antiaromatic and a slightly weaker semilocal paratropic current flows around the two pentalene rings. Molecules 1 and 2 do not sustain any net global ring current. The naphthalene moiety of the molecule consisting of a naphthalene annelated with two pentalene units (3) does not sustain any strong ring current that is typical for naphthalene. Instead, half of the diatropic current passing the naphthalene moiety forms a zig-zag pattern along the C-C bonds of the naphthalene moiety that are not shared with the pentalene moieties and one third of the current continues around the whole molecule partially cancelling the very strong paratropic semilocal ring current of the pentalenes. For molecule 3, the pentalene moieties and the individual five-membered rings of the pentalenes are more antiaromatic than for 1 and 2. The calculated current patterns elucidate why the compounds with formally [4n + 2] π-electrons have unusual aromatic properties violating the Hückel π-electron count rule. The current density calculations also provide valuable information for interpreting the measured (1)H NMR spectra.

Development of a detailed chemical mechanism (MCMv3.1) for the atmospheric oxidation of aromatic hydrocarbons

NASA Astrophysics Data System (ADS)

Bloss, C.; Wagner, V.; Jenkin, M. E.; Volkamer, R.; Bloss, W. J.; Lee, J. D.; Heard, D. E.; Wirtz, K.; Martin-Reviejo, M.; Rea, G.; Wenger, J. C.; Pilling, M. J.

2005-03-01

The Master Chemical Mechanism has been updated from MCMv3 to MCMv3.1 in order to take into account recent improvements in the understanding of aromatic photo-oxidation. Newly available kinetic and product data from the literature have been incorporated into the mechanism. In particular, the degradation mechanisms for hydroxyarenes have been revised following the observation of high yields of ring-retained products, and product studies of aromatic oxidation under relatively low NOx conditions have provided new information on the branching ratios to first generation products. Experiments have been carried out at the European Photoreactor (EUPHORE) to investigate key subsets of the toluene system. These results have been used to test our understanding of toluene oxidation, and, where possible, refine the degradation mechanisms. The evaluation of MCMv3 and MCMv3.1 using data on benzene, toluene, p-xylene and 1,3,5-trimethylbenzene photosmog systems is described in a companion paper, and significant model shortcomings are identified. Ideas for additional modifications to the mechanisms, and for future experiments to further our knowledge of the details of aromatic photo-oxidation are discussed.

Development of a detailed chemical mechanism (MCMv3.1) for the atmospheric oxidation of aromatic hydrocarbons

NASA Astrophysics Data System (ADS)

Bloss, C.; Wagner, V.; Jenkin, M. E.; Volkamer, R.; Bloss, W. J.; Lee, J. D.; Heard, D. E.; Wirtz, K.; Martin-Reviejo, M.; Rea, G.; Wenger, J. C.; Pilling, M. J.

2004-09-01

The Master Chemical Mechanism has been updated from MCMv3 to MCMv3.1 in order to take into account recent improvements in the understanding of aromatic photo-oxidation. Newly available kinetic and product data from the literature has been incorporated into the mechanism. In particular, the degradation mechanisms for hydroxyarenes have been revised following the observation of high yields of ring-retained products, and product studies of aromatic oxidation under relatively low NOx conditions have provided new information on the branching ratios to first generation products. Experiments have been carried out at the European Photoreactor (EUPHORE) to investigate key subsets of the toluene system. These results have been used to test our understanding of toluene oxidation, and where possible, refine the degradation mechanisms. The evaluation of MCMv3 and MCMv3.1 using data on benzene, toluene, p-xylene and 1,3,5-trimethylbenzene photosmog systems is described in a companion paper, and significant model shortcomings are identified. Ideas for additional modifications to the mechanisms, and for future experiments to further our knowledge of the details of aromatic photo-oxidation are discussed.

Ab initio molecular orbital and infrared spectroscopic study of the conformation of secondary amides: derivatives of formanilide, acetanilide and benzylamides

NASA Astrophysics Data System (ADS)

Ilieva, S.; Hadjieva, B.; Galabov, B.

1999-09-01

Ab initio molecular orbital calculations at HF/4-31G level and infrared spectroscopic data for the frequencies are applied to analyse the grouping in a series model aromatic secondary amides: formanilide; acetanilide; o-methylacetanilide; 2,6-dimethylformanilide, 2,6-dimethylacetanilide; N-benzylacetamide and N-benzylformamide. The theoretical and experimental data obtained show that the conformational state of the molecules studied is determined by the fine balance of several intramolecular factors: resonance effect between the amide group and the aromatic ring, steric interaction between various substituents around the -NH-CO- grouping in the aromatic ring, conjugation between the carbonyl bond and the nitrogen lone pair as well as direct field influences inside the amide group.

Assessing Uncertainty of Interspecies Correlation Estimation Models for Aromatic Compounds

EPA Science Inventory

We developed Interspecies Correlation Estimation (ICE) models for aromatic compounds containing 1 to 4 benzene rings to assess uncertainty in toxicity extrapolation in two data compilation approaches. ICE models are mathematical relationships between surrogate and predicted test ...

Chemical and nanometer-scale structure of kerogen and its change during thermal maturation investigated by advanced solid-state 13C NMR spectroscopy

USGS Publications Warehouse

Mao, J.; Fang, X.; Lan, Y.; Schimmelmann, A.; Mastalerz, Maria; Xu, L.; Schmidt-Rohr, K.

2010-01-01

We have used advanced and quantitative solid-state nuclear magnetic resonance (NMR) techniques to investigate structural changes in a series of type II kerogen samples from the New Albany Shale across a range of maturity (vitrinite reflectance R0 from 0.29% to 1.27%). Specific functional groups such as CH3, CH2, alkyl CH, aromatic CH, aromatic C-O, and other nonprotonated aromatics, as well as "oil prone" and "gas prone" carbons, have been quantified by 13C NMR; atomic H/C and O/C ratios calculated from the NMR data agree with elemental analysis. Relationships between NMR structural parameters and vitrinite reflectance, a proxy for thermal maturity, were evaluated. The aromatic cluster size is probed in terms of the fraction of aromatic carbons that are protonated (???30%) and the average distance of aromatic C from the nearest protons in long-range H-C dephasing, both of which do not increase much with maturation, in spite of a great increase in aromaticity. The aromatic clusters in the most mature sample consist of ???30 carbons, and of ???20 carbons in the least mature samples. Proof of many links between alkyl chains and aromatic rings is provided by short-range and long-range 1H-13C correlation NMR. The alkyl segments provide most H in the samples; even at a carbon aromaticity of 83%, the fraction of aromatic H is only 38%. While aromaticity increases with thermal maturity, most other NMR structural parameters, including the aromatic C-O fractions, decrease. Aromaticity is confirmed as an excellent NMR structural parameter for assessing thermal maturity. In this series of samples, thermal maturation mostly increases aromaticity by reducing the length of the alkyl chains attached to the aromatic cores, not by pronounced growth of the size of the fused aromatic ring clusters. ?? 2010 Elsevier Ltd. All rights reserved.

Fluorescent aromatic sensors and their methods of use

NASA Technical Reports Server (NTRS)

Meador, Michael A. (Inventor); Tyson, Daniel S. (Inventor); Ilan, Ulvi F. (Inventor)

2012-01-01

Aromatic molecules that can be used as sensors are described. The aromatic sensors include a polycyclic aromatic hydrocarbon core with a five-membered imide rings fused to the core and at least two pendant aryl groups. The aromatic sensor molecules can detect target analytes or molecular strain as a result of changes in their fluorescence, in many cases with on-off behavior. Aromatic molecules that fluoresce at various frequencies can be prepared by altering the structure of the aromatic core or the substituents attached to it. The aromatic molecules can be used as sensors for various applications such as, for example, the detection of dangerous chemicals, biomedical diagnosis, and the detection of damage or strain in composite materials. Methods of preparing aromatic sensor molecules are also described.

Structure of aryl O -demethylase offers molecular insight into a catalytic tyrosine-dependent mechanism

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

Kohler, Amanda C.; Mills, Matthew J. L.; Adams, Paul D.

Some strains of soil and marine bacteria have evolved intricate metabolic pathways for using environmentally derived aromatics as a carbon source. Many of these metabolic pathways go through intermediates such as vanillate, 3-O-methylgallate, and syringate. Demethylation of these compounds is essential for downstream aryl modification, ring opening, and subsequent assimilation of these compounds into the tricarboxylic acid (TCA) cycle, and, correspondingly, there are a variety of associated aryl demethylase systems that vary in complexity. Intriguingly, only a basic understanding of the least complex system, the tetrahydrofolate-dependent aryl demethylase LigM from Sphingomonas paucimobilis, a bacterial strain that metabolizes lignin-derived aromatics, wasmore » previously available. LigM-catalyzed demethylation enables further modification and rin g opening of the single-ring aromatics vanillate and 3-Omethylgallate, which are common byproducts of biofuel production. We characterize aryl O-demethylation by LigM and report its 1.81-Å crystal structure, revealing a unique demethylase fold and a canonical folate-binding domain. Structural homology and geometry optimization calculations enabled the identification of LigM's tetrahydrofolate-binding site and protein-folate interactions. Computationally guided mutagenesis and kinetic analyses allowed the identification of the enzyme's aryl-binding site location and determination of its unique, catalytic tyrosine-dependent reaction mechanism. This work defines LigM as a distinct demethylase, both structurally and functionally, and provides insight into demethylation and its reaction requirements. Our results afford the mechanistic details required for efficient utilization of LigM as a tool for aryl O-demethylation and as a component of synthetic biology efforts to valorize previously underused aromatic compounds.« less

Structure of aryl O -demethylase offers molecular insight into a catalytic tyrosine-dependent mechanism

DOE PAGES

Kohler, Amanda C.; Mills, Matthew J. L.; Adams, Paul D.; ...

2017-04-03

Some strains of soil and marine bacteria have evolved intricate metabolic pathways for using environmentally derived aromatics as a carbon source. Many of these metabolic pathways go through intermediates such as vanillate, 3-O-methylgallate, and syringate. Demethylation of these compounds is essential for downstream aryl modification, ring opening, and subsequent assimilation of these compounds into the tricarboxylic acid (TCA) cycle, and, correspondingly, there are a variety of associated aryl demethylase systems that vary in complexity. Intriguingly, only a basic understanding of the least complex system, the tetrahydrofolate-dependent aryl demethylase LigM from Sphingomonas paucimobilis, a bacterial strain that metabolizes lignin-derived aromatics, wasmore » previously available. LigM-catalyzed demethylation enables further modification and rin g opening of the single-ring aromatics vanillate and 3-Omethylgallate, which are common byproducts of biofuel production. We characterize aryl O-demethylation by LigM and report its 1.81-Å crystal structure, revealing a unique demethylase fold and a canonical folate-binding domain. Structural homology and geometry optimization calculations enabled the identification of LigM's tetrahydrofolate-binding site and protein-folate interactions. Computationally guided mutagenesis and kinetic analyses allowed the identification of the enzyme's aryl-binding site location and determination of its unique, catalytic tyrosine-dependent reaction mechanism. This work defines LigM as a distinct demethylase, both structurally and functionally, and provides insight into demethylation and its reaction requirements. Our results afford the mechanistic details required for efficient utilization of LigM as a tool for aryl O-demethylation and as a component of synthetic biology efforts to valorize previously underused aromatic compounds.« less

Performance of 3D-space-based atoms-in-molecules methods for electronic delocalization aromaticity indices.

PubMed

Heyndrickx, Wouter; Salvador, Pedro; Bultinck, Patrick; Solà, Miquel; Matito, Eduard

2011-02-01

Several definitions of an atom in a molecule (AIM) in three-dimensional (3D) space, including both fuzzy and disjoint domains, are used to calculate electron sharing indices (ESI) and related electronic aromaticity measures, namely, I(ring) and multicenter indices (MCI), for a wide set of cyclic planar aromatic and nonaromatic molecules of different ring size. The results obtained using the recent iterative Hirshfeld scheme are compared with those derived from the classical Hirshfeld method and from Bader's quantum theory of atoms in molecules. For bonded atoms, all methods yield ESI values in very good agreement, especially for C-C interactions. In the case of nonbonded interactions, there are relevant deviations, particularly between fuzzy and QTAIM schemes. These discrepancies directly translate into significant differences in the values and the trends of the aromaticity indices. In particular, the chemically expected trends are more consistently found when using disjoint domains. Careful examination of the underlying effects reveals the different reasons why the aromaticity indices investigated give the expected results for binary divisions of 3D space. Copyright © 2010 Wiley Periodicals, Inc.

Are Anion/π Interactions Actually a Case of Simple Charge–Dipole Interactions?†

PubMed Central

Wheeler, Steven E.; Houk, K. N.

2011-01-01

Substituent effects in Cl− ••• C6H6−nXn complexes, models for anion/π interactions, have been examined using density functional theory and robust ab initio methods paired with large basis sets. Predicted interaction energies for 83 model Cl− ••• C6H6−nXn complexes span almost 40 kcal mol−1 and show an excellent correlation (r = 0.99) with computed electrostatic potentials. In contrast to prevailing models of anion/π interactions, which rely on substituent-induced changes in the aryl π-system, it is shown that substituent effects in these systems are due mostly to direct interactions between the anion and the substituents. Specifically, interaction energies for Cl− ••• C6H6−nXn complexes are recovered using a model system in which the substituents are isolated from the aromatic ring and π-resonance effects are impossible. Additionally, accurate potential energy curves for Cl− interacting with prototypical anion-binding arenes can be qualitatively reproduced by adding a classical charge–dipole interaction to the Cl− ••• C6H6 interaction potential. In substituted benzenes, binding of anions arises primarily from interactions of the anion with the local dipoles induced by the substituents, not changes in the interaction with the aromatic ring itself. When designing anion-binding motifs, phenyl rings should be viewed as a scaffold upon which appropriate substituents can be placed, because there are no attractive interactions between anions and the aryl π-system of substituted benzenes. PMID:20433187

Homologation process making higher alcohols

DOEpatents

Leung, Tak W.; Dombek, Bernard D.

1990-01-01

A liquid phase process for the manufacture of C.sub.2+ alkanols by the reaction of hydrogen with carbon monoxide in the presence of a catalyst containing ruthenium, cobalt, a halide-containing compound, and an aromatic compound substituted in adjacent ring positions by nitrogen atoms. The process embraces the use of rhodium as an additive to the catalyst system.

Endophytic Diaporthe sp. LG23 Produces a Potent Antibacterial Tetracyclic Triterpenoid.

PubMed

Li, Gang; Kusari, Souvik; Kusari, Parijat; Kayser, Oliver; Spiteller, Michael

2015-08-28

A new lanostanoid, 19-nor-lanosta-5(10),6,8,24-tetraene-1α,3β,12β,22S-tetraol (1), characterized by the presence of an aromatic B ring and hydroxylated at C-1, C-3, C-12, and C-22, was isolated from an endophytic fungus, Diaporthe sp. LG23, inhabiting leaves of the Chinese medicinal plant Mahonia fortunei. Six biosynthetically related known steroids were also isolated in parallel. Their structures were confirmed on the basis of detailed spectroscopic analysis in conjunction with the published data. Compound 1, an unusual fungus-derived 19-nor-lanostane tetracyclic triterpenoid with an aromatic B-ring system, exhibited pronounced antibacterial efficacy against both Gram-positive and -negative bacteria, especially the clinical isolates of Streptococcus pyogenes and Pseudomonas aeruginosa as well as a human pathogenic strain of Staphylococcus aureus. Our results reveal the potential of endophytes not only in conferring host fitness but also in contributing toward traditional host plant medicines.

Low severity coal conversion by ionic hydrogenation: Quarterly report, October--December 1988

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

Maioriello, J.; Larsen, J.W.

1988-12-31

A newly developed reaction system consisting of H/sub 2/O:BF/sub 3//H/sub 2//(CH/sub 3/CN)/sub 2/PtCl/sub 2/ was applied to the ionic hydrogenation of aromatic and functionalized aromatic compounds. Hydrogenations were carried out in this aqueous system at 50/degree/C and 500 psi H/sub 2/. Aryl ethers were hydrogenated and cleaved, yielding deoxygenated, fully saturated compounds as the major products. Reactions of nitrogen-containing aromatic compounds resulted in partial saturation of aromatic rings without cleavage of the C-N bonds. Aromatic and PNA compounds can be fully or partially hydrogenated depending on their structures. Aromatic thiols, sulfides and thiophenes poison the catalyst; the oxidized sulfur formsmore » (sulfonic acids, sulfones) were not reduced and did not poison the catalyst. It was found that certain aromatic compounds were easier to hydrogenate than others. Ionic hydrogenation of Wyodak cola using a H/sub 2/O:BF/sub 3//H/sub 2//(MeCN)/sub 2/PtCl/sub 2/ resulted in no significant increase in THF extractability (5.8--9.6% THF-extractables, wt) over that of the parent coal (4.6--6.7% THF-extractables, wt). Ionic hydrogenation of a demineralized Wyodak coal (1 M aq. citric acid, reflux 1 day) resulted in a slight increase in THF extractability (10.4%) over the untreated parent coal (5.6--5.8%). 4 refs., 1 fig., 1 tab.« less

The influence of the nature of a substituent on the parameters of the intra- and intermolecular interactions in molecules of cross-conjugated ketones

NASA Astrophysics Data System (ADS)

Kompaneets, V. V.; Vasilieva, I. A.

2017-08-01

We have quantitatively analyzed the vibronic parameters of two cross-conjugated δ-dimethylaminoketones. The presence of the -N(CH3)2, C=O, and -NO2 groups in the benzene ring has been shown to affect the manifestation of the vibronic parameters of characteristic bands that describe the state (vibrations, types of deformation upon excitation) of polyene systems with aromatic rings. Data on the influence of the nature of the substituent on the parameters of intra- and intermolecular interactions in the examined compounds have been presented.

The Broken Ring: Reduced Aromaticity in Lys-Trp Cations and High pH Tautomer Correlates with Lower Quantum Yield and Shorter Lifetimes

PubMed Central

2015-01-01

Several nonradiative processes compete with tryptophan fluorescence emission. The difficulty in spectral interpretation lies in associating specific molecular environmental features with these processes and thereby utilizing the fluorescence spectral data to identify the local environment of tryptophan. Here, spectroscopic and molecular modeling study of Lys-Trp dipeptide charged species shows that backbone-ring interactions are undistinguished. Instead, quantum mechanical ground state isosurfaces reveal variations in indole π electron distribution and density that parallel charge (as a function of pK1, pK2, and pKR) on the backbone and residues. A pattern of aromaticity-associated quantum yield and fluorescence lifetime changes emerges. Where quantum yield is high, isosurfaces have a charge distribution similar to the highest occupied molecular orbital (HOMO) of indole, which is the dominant fluorescent ground state of the 1La transition dipole moment. Where quantum yield is low, isosurface charge distribution over the ring is uneven, diminished, and even found off ring. At pH 13, the indole amine is deprotonated, and Lys-Trp quantum yield is extremely low due to tautomer structure that concentrates charge on the indole amine; the isosurface charge distribution bears scant resemblance to the indole HOMO. Such greatly diminished fluorescence has been observed for proteins where the indole nitrogen is hydrogen bonded, lending credence to the association of aromaticity changes with diminished quantum yield in proteins as well. Thus tryptophan ground state isosurfaces are an indicator of indole aromaticity, signaling the partition of excitation energy between radiative and nonradiative processes. PMID:24882092

Oxidation kinetics of polycyclic aromatic hydrocarbons by permanganate.

PubMed

Forsey, Steven P; Thomson, Neil R; Barker, James F

2010-04-01

The reactivity of permanganate towards polycyclic aromatics hydrocarbons (PAHs) is well known but little kinetic information is available. This study investigated the oxidation kinetics of a selected group of coal tar creosote compounds and alkylbenzenes in water using permanganate, and the correlation between compound reactivity and physical/chemical properties. The oxidation of naphthalene, phenanthrene, chrysene, 1-methylnaphthalene, 2-methylnaphthalene, acenaphthene, fluorene, carbazole isopropylbenzene, ethylbenzene and methylbenzene closely followed pseudo first-order reaction kinetics. The oxidation of pyrene was initially very rapid and did not follow pseudo first-order kinetics at early times. Fluoranthene was only partially oxidized and the oxidation of anthracene was too fast to be captured. Biphenyl, dibenzofuran, benzene and tert-butylbenzene were non-reactive under the study conditions. The oxidation rate was shown to increase with increasing number of polycyclic rings because less energy is required to overcome the aromatic character of a polycyclic ring than is required for benzene. Thus the rate of oxidation increased in the series naphthalene

Aromatic ring generation as a dust precursor in acetylene discharges

NASA Astrophysics Data System (ADS)

De Bleecker, Kathleen; Bogaerts, Annemie; Goedheer, Wim

2006-04-01

Production of aromatic hydrocarbon compounds as an intermediate step for particle formation in low-pressure acetylene discharges is investigated via a kinetic approach. The detailed chemical reaction mechanism contains 140 reactions among 55 species. The cyclic hydrocarbon chemistry is mainly based on studies of polycyclic aromatic hydrocarbon formation in cosmic environments. The model explicitly includes organic chain, cyclic molecules, radicals, and ions up to a size of 12 carbon atoms. The calculated density profiles show that the aromatic formation yields are quite significant, suggesting that aromatic compounds play a role in the underlying mechanisms of particle formation in hydrocarbon plasmas.

Superposed Redox Chemistry of Fused Carbon Rings in Cyclooctatetraene-Based Organic Molecules for High-Voltage and High-Capacity Cathodes.

PubMed

Zhao, Xiaolin; Qiu, Wujie; Ma, Chao; Zhao, Yingqin; Wang, Kaixue; Zhang, Wenqing; Kang, Litao; Liu, Jianjun

2018-01-24

Even though many organic cathodes have been developed and have made a significant improvement in energy density and reversibility, some organic materials always generate relatively low voltage and limited discharge capacity because their energy storage mechanism is solely based on redox reactions of limited functional groups [N-O, C═X (X = O, N, S)] linking to aromatic rings. Here, a series of cyclooctatetraene-based (C 8 H 8 ) organic molecules were demonstrated to have electrochemical activity of high-capacity and high-voltage from carbon rings by means of first-principles calculations and electronic structure analysis. Fused molecules of C 8 -C 4 -C 8 (C 16 H 12 ) and C 8 -C 4 -C 8 -C 4 -C 8 (C 24 H 16 ) contain, respectively, four and eight electron-deficient carbons, generating high-capacity by their multiple redox reactions. Our sodiation calculations predict that C 16 H 12 and C 24 H 16 exhibit discharge capacities of 525.3 and 357.2 mA h g -1 at the voltage change from 3.5 to 1.0 V and 3.7 to 1.3 V versus Na + /Na, respectively. Electronic structure analysis reveals that the high voltages are attributed to superposed electron stabilization mechanisms, including double-bond reformation and aromatization from carbon rings. High thermodynamic stability of these C 24 H 16 -based systems strongly suggests feasibility of experimental realization. The present work provides evidence that cyclooctatetraene-based organic molecules fused with the C 4 ring are promising in designing high-capacity and high-voltage organic rechargeable cathodes.

Outer-valence Electron Spectra of Prototypical Aromatic Heterocycles from an Optimally Tuned Range-Separated Hybrid Functional

PubMed Central

2014-01-01

Density functional theory with optimally tuned range-separated hybrid (OT-RSH) functionals has been recently suggested [Refaely-Abramson et al. Phys. Rev. Lett.2012, 109, 226405] as a nonempirical approach to predict the outer-valence electronic structure of molecules with the same accuracy as many-body perturbation theory. Here, we provide a quantitative evaluation of the OT-RSH approach by examining its performance in predicting the outer-valence electron spectra of several prototypical gas-phase molecules, from aromatic rings (benzene, pyridine, and pyrimidine) to more complex organic systems (terpyrimidinethiol and copper phthalocyanine). For a range up to several electronvolts away from the frontier orbital energies, we find that the outer-valence electronic structure obtained from the OT-RSH method agrees very well (typically within ∼0.1–0.2 eV) with both experimental photoemission and theoretical many-body perturbation theory data in the GW approximation. In particular, we find that with new strategies for an optimal choice of the short-range fraction of Fock exchange, the OT-RSH approach offers a balanced description of localized and delocalized states. We discuss in detail the sole exception found—a high-symmetry orbital, particular to small aromatic rings, which is relatively deep inside the valence state manifold. Overall, the OT-RSH method is an accurate DFT-based method for outer-valence electronic structure prediction for such systems and is of essentially the same level of accuracy as contemporary GW approaches, at a reduced computational cost. PMID:24839410

Single-molecule conductance through multiple π-π-stacked benzene rings determined with direct electrode-to-benzene ring connections.

PubMed

Schneebeli, Severin T; Kamenetska, Maria; Cheng, Zhanling; Skouta, Rachid; Friesner, Richard A; Venkataraman, Latha; Breslow, Ronald

2011-02-23

Understanding electron transport across π-π-stacked systems will help to answer fundamental questions about biochemical redox processes and benefit the design of new materials and molecular devices. Herein we employed the STM break-junction technique to measure the single-molecule conductance of multiple π-π-stacked aromatic rings. We studied electron transport through up to four stacked benzene rings held together in an eclipsed fashion via a paracyclophane scaffold. We found that the strained hydrocarbons studied herein couple directly to gold electrodes during the measurements; hence, we did not require any heteroatom binding groups as electrical contacts. Density functional theory-based calculations suggest that the gold atoms of the electrodes bind to two neighboring carbon atoms of the outermost cyclophane benzene rings in η(2) fashion. Our measurements show an exponential decay of the conductance with an increasing number of stacked benzene rings, indicating a nonresonant tunneling mechanism. Furthermore, STM tip-substrate displacement data provide additional evidence that the electrodes bind to the outermost benzene rings of the π-π-stacked molecular wires.

Polycyclic aromatic hydrocarbons in sediments and mussels of Corral Bay, south central Chile.

PubMed

Palma-Fleming, Hernan; P, Adalberto J Asencio; Gutierrez, Elena

2004-03-01

PAHs were measured in sediments and mussels (Mytilus chilensis) from Carboneros and Puerto Claro, located in Corral Bay, Valdivia. According to the ratio of phenanthrene/anthracene and fluoranthene/pyrene concentrations, these sites are medium polluted with PAHs originating mainly from pyrolytic sources. Fluoranthene was the major component measured in mussels (3.1-390 ng g(-1) dry weight) and sediments (6.9-74.1 ng g(-1) dry weight). In general, mussels were mainly exposed to the dissolved fraction of the lower molecular weight PAHs (tri- and tetra-aromatics) while the higher molecular ring systems (penta- and hexa-aromatics) were more bioavailable to sediments. Mussel PAHs content was relatively constant, with the exception of the 1999 summer season (March), when higher concentration values were found in both sites; however, PAHs residues in sediments showed a temporal variation.

Aniline-containing guests recognized by α,α',δ,δ'-tetramethyl-cucurbit[6]uril host.

PubMed

Lin, Rui-Lian; Fang, Guo-Sheng; Sun, Wen-Qi; Liu, Jing-Xin

2016-12-13

The host-guest complexation of symmetrical α,α',δ,δ'-tetramethyl-cucurbit[6]uril (TMeQ[6]) and cucurbit[7]uril (Q[7]) with a series of aniline-containing guests has been investigated by various experimental techniques including NMR, ITC, and X-ray crystallography. Experimental results indicate that both TMeQ[6] and Q[7] hosts can encapsulate aniline-containing guests to form stable inclusion complexes. However, the oval cavity of TMeQ[6] is more complementary in size and shape to the aromatic ring of the guests than the spherical cavity of Q[7]. Shielding and deshielding effects of the aromatic ring on guests lead to the remarkable chemical shifts of the TMeQ[6] host protons. The rotational restriction of the guests in the oval cavity of TMeQ[6] results in the large negative values of entropy. The X-ray crystal structure of the 1:1 inclusion complex between TMeQ[6] and N,N'-diethyl-benzene-1,4-diamine unambiguously reveals that the aromatic ring of the guest resides in the oval cavity of TMeQ[6].

Chirality of the 1,4-phenylene-silica nanoribbons at the nano and angstrom levels

NASA Astrophysics Data System (ADS)

Li, Yi; Wang, Sibing; Xiao, Min; Wang, Mingliang; Huang, Zhibin; Li, Baozong; Yang, Yonggang

2013-01-01

We reported the preparation of chiral 1,4-phenylene-silicas, using a sol-gel transcription approach, by self-assembly using low-molecular-weight gelators as templates. The silicas exhibited chirality at both the nano and angstrom levels. However, the relation between the chirality at the nano level and that at the angstrom levels has not been well studied. In this study, chiral 1,4-phenylene-silica nanoribbons were prepared by the self-assemblies of three chiral cationic gelators derived from amino acids as templates. These samples were characterized using field-emission scanning electron microscopy, transmission electron microscopy, x-ray diffraction, and circular dichroism. The results indicated that the handedness of the nanoribbons and the stacking of the aromatic rings were controllable. Although the nanoribbons exhibited left-handedness at the nano level, the stacking of the aromatic rings could exhibit left- or right-handedness. The handedness of the nanoribbons at the nano level was controlled by the organic self-assembly of the gelator. However, the stacking of the aromatic rings seemed to be controlled by the gelator itself.

Polycyclic aromatic hydrocarbons (PAH) formation from the pyrolysis of different municipal solid waste fractions.

PubMed

Zhou, Hui; Wu, Chunfei; Onwudili, Jude A; Meng, Aihong; Zhang, Yanguo; Williams, Paul T

2015-02-01

The formation of 2-4 ring polycyclic aromatic hydrocarbons (PAH) from the pyrolysis of nine different municipal solid waste fractions (xylan, cellulose, lignin, pectin, starch, polyethylene (PE), polystyrene (PS), polyvinyl chloride (PVC), and polyethylene terephthalate (PET)) were investigated in a fixed bed furnace at 800 °C. The mass distribution of pyrolysis was also reported. The results showed that PS generated the most total PAH, followed by PVC, PET, and lignin. More PAH were detected from the pyrolysis of plastics than the pyrolysis of biomass. In the biomass group, lignin generated more PAH than others. Naphthalene was the most abundant PAH, and the amount of 1-methynaphthalene and 2-methynaphthalene was also notable. Phenanthrene and fluorene were the most abundant 3-ring PAH, while benzo[a]anthracene and chrysene were notable in the tar of PS, PVC, and PET. 2-ring PAH dominated all tar samples, and varied from 40 wt.% to 70 wt.%. For PS, PET and lignin, PAH may be generated directly from the aromatic structure of the feedstock. Copyright © 2014 Elsevier Ltd. All rights reserved.

Hydrocarbons on Saturns Satellites: Relationship to Interstellar Dust and the Solar Nebula

NASA Technical Reports Server (NTRS)

Cruikshank, D. P.

2012-01-01

To understand the origin and evolution of our Solar System, and the basic components that led to life on Earth, we study interstellar and planetary spectroscopic signatures. The possible relationship of organic material detected in carbonaceous meteorites, interplanetary dust particles (IDPs), comets and the interstellar medium have been the source of speculation over the years as the composition and processes that governed the early solar nebula have been explored to understand the extent to which primitive material survived or became processed. The Cassini VIMS has provided new data relevant to this problem. Three of Saturn's satellites, Phoebe, Iapetus, and Hyperion, are found to have aromatic and aliphatic hydrocarbons on their surfaces. The aromatic hydrocarbon signature (C-H stretching mode at 3.28 micrometers) is proportionally significantly stronger (relative to the aliphatic bands) than that seen in other Solar System bodies (e.g., comets) and materials (Stardust samples, IDPs, meteorites) and the distinctive sub-features of the 3.4 micrometer aliphatic band (CH2 and CH3 groups) are reminiscent of those widely detected throughout the diffuse ISM. Phoebe may be a captured object that originated in the region beyond the present orbit of Neptune, where the solar nebula contained a large fraction of original interstellar ice and dust that was less processed than material closer to the Sun. Debris from Phoebe now resident on Iapetus and Hyperion, as well as o Phoebe itself, thus presents a unique blend of hydrocarbons, amenable to comparisons with interstellar hydrocarbons and other Solar System materials. The dust ring surrounding Saturn, in which Phoebe is embedded, probably originated from a collision with Phoebe. Dust ring particles are the likely source of the organic-bearing materials, and perhaps the recently identified small particles of Fe detected on Saturn's satellites. Lab measurements of the absolute band strengths of representative aliphatic and aromatic molecules, together with measurements from the VIMS data, allow us to calculate the number of C atoms to find the relative abundances of C atoms in the two kinds of organic molecules. The strength of the prominent aromatic C-H stretch band relative to the aliphatic band complex in Phoebe and Iapetus indicates that the relative abundance of aromatic to aliphatic carbon is very large (greater than 200). In contract, the aromatic band is nearly imperceptible in spectra of interplanetary dust particles (IDP), returned samples from comet 91P/Wild 2, insoluable carbonaceous material in most meteorites, and the diffuse interstellar dust (DISM) (although aromatics are known in all these materials-here we consider only the spectroscopic signature)

Transformation of toluene and benzene by mixed methanogenic cultures.

PubMed Central

Grbić-Galić, D; Vogel, T M

1987-01-01

The aromatic hydrocarbons toluene and benzene were anaerobically transformed by mixed methanogenic cultures derived from ferulic acid-degrading sewage sludge enrichments. In most experiments, toluene or benzene was the only semicontinuously supplied carbon and energy source in the defined mineral medium. No exogenous electron acceptors other than CO2 were present. The cultures were fed 1.5 to 30 mM unlabeled or 14C-labeled aromatic substrates (ring-labeled toluene and benzene or methyl-labeled toluene). Gas production from unlabeled substrates and 14C activity distribution in products from the labeled substrates were monitored over a period of 60 days. At least 50% of the substrates were converted to CO2 and methane (greater than 60%). A high percentage of 14CO2 was recovered from the methyl group-labeled toluene, suggesting nearly complete conversion of the methyl group to CO2 and not to methane. However, a low percentage of 14CO2 was produced from ring-labeled toluene or from benzene, indicating incomplete conversion of the ring carbon to CO2. Anaerobic transformation pathways for unlabeled toluene and benzene were studied with the help of gas chromatography-mass spectrometry. The intermediates detected are consistent with both toluene and benzene degradation via initial oxidation by ring hydroxylation or methyl oxidation (toluene), which would result in the production of phenol, cresols, or aromatic alcohol. Additional reactions, such as demethylation and ring reduction, are also possible. Tentative transformation sequences based upon the intermediates detected are discussed. PMID:3105454

The boron conundrum: Bonding in the bowl B30 and B36, fullerene B40 and triple ring B42 clusters

NASA Astrophysics Data System (ADS)

Pham, Hung Tan; Duong, L. V.; Tam, Nguyen Minh; Pham-Ho, M. P.; Nguyen, Minh Tho

2014-07-01

Geometries and bonding of B30, B36, B40 and B42 clusters were studied using quantum chemical computations. The bowl B30 and B36 and planar B42 clusters exhibit disk aromaticity. Diatropic ring current is strong in B30 and weaker in B42. A fullerene-like B40 (D2d) having two hexagons and four heptagons was found as the lowest-lying isomer. Such a fullerene whose MOs closely mimic those of the buckyball B80, represents novel structural feature of boron clusters. The most stable B42 (C2h) isomer is a triple ring tube with consistent σ + π diatropic magnetic responses making it a tubular aromatic species.

Evidence for a strong sulfur-aromatic interaction derived from crystallographic data.

PubMed

Zauhar, R J; Colbert, C L; Morgan, R S; Welsh, W J

2000-03-01

We have uncovered new evidence for a significant interaction between divalent sulfur atoms and aromatic rings. Our study involves a statistical analysis of interatomic distances and other geometric descriptors derived from entries in the Cambridge Crystallographic Database (F. H. Allen and O. Kennard, Chem. Design Auto. News, 1993, Vol. 8, pp. 1 and 31-37). A set of descriptors was defined sufficient in number and type so as to elucidate completely the preferred geometry of interaction between six-membered aromatic carbon rings and divalent sulfurs for all crystal structures of nonmetal-bearing organic compounds present in the database. In order to test statistical significance, analogous probability distributions for the interaction of the moiety X-CH(2)-X with aromatic rings were computed, and taken a priori to correspond to the null hypothesis of no significant interaction. Tests of significance were carried our pairwise between probability distributions of sulfur-aromatic interaction descriptors and their CH(2)-aromatic analogues using the Smirnov-Kolmogorov nonparametric test (W. W. Daniel, Applied Nonparametric Statistics, Houghton-Mifflin: Boston, New York, 1978, pp. 276-286), and in all cases significance at the 99% confidence level or better was observed. Local maxima of the probability distributions were used to define a preferred geometry of interaction between the divalent sulfur moiety and the aromatic ring. Molecular mechanics studies were performed in an effort to better understand the physical basis of the interaction. This study confirms observations based on statistics of interaction of amino acids in protein crystal structures (R. S. Morgan, C. E. Tatsch, R. H. Gushard, J. M. McAdon, and P. K. Warme, International Journal of Peptide Protein Research, 1978, Vol. 11, pp. 209-217; R. S. Morgan and J. M. McAdon, International Journal of Peptide Protein Research, 1980, Vol. 15, pp. 177-180; K. S. C. Reid, P. F. Lindley, and J. M. Thornton, FEBS Letters, 1985, Vol. 190, pp. 209-213), as well as studies involving molecular mechanics (G. Nemethy and H. A. Scheraga, Biochemistry and Biophysics Research Communications, 1981, Vol. 98, pp. 482-487) and quantum chemical calculations (B. V. Cheney, M. W. Schulz, and J. Cheney, Biochimica Biophysica Acta, 1989, Vol. 996, pp.116-124; J. Pranata, Bioorganic Chemistry, 1997, Vol. 25, pp. 213-219)-all of which point to the possible importance of the sulfur-aromatic interaction. However, the preferred geometry of the interaction, as determined from our analysis of the small-molecule crystal data, differs significantly from that found by other approaches. Copyright 2000 John Wiley & Sons, Inc.

Regulation of the Feruloyl Esterase (faeA) Gene from Aspergillus niger

PubMed Central

de Vries, Ronald P.; Visser, Jaap

1999-01-01

Feruloyl esterases can remove aromatic residues (e.g., ferulic acid) from plant cell wall polysaccharides (xylan, pectin) and are essential for complete degradation of these polysaccharides. Expression of the feruloyl esterase-encoding gene (faeA) from Aspergillus niger depends on d-xylose (expression is mediated by XlnR, the xylanolytic transcriptional activator) and on a second system that responds to aromatic compounds with a defined ring structure, such as ferulic acid and vanillic acid. Several compounds were tested, and all of the inducing compounds contained a benzene ring which had a methoxy group at C-3 and a hydroxy group at C-4 but was not substituted at C-5. Various aliphatic groups occurred at C-1. faeA expression in the presence of xylose or ferulic acid was repressed by glucose. faeA expression in the presence of ferulic acid and xylose was greater than faeA expression in the presence of either compound alone. The various inducing systems allow A. niger to produce feruloyl esterase not only during growth on xylan but also during growth on other ferulic acid-containing cell wall polysaccharides, such as pectin. PMID:10584009

Polycyclic aromatic hydrocarbons in the atmospheres of Titan and Jupiter

NASA Technical Reports Server (NTRS)

Sagan, Carl; Khare, B. N.; Thompson, W. R.; Mcdonald, G. D.; Wing, Michael R.; Bada, Jeffrey L.; Vo-Dinh, Tuan; Arakawa, E. T.

1993-01-01

PAHs are important components of the interstellar medium and carbonaceous chondrites, but have never been identified in the reducing atmospheres of the outer solar system. Incompletely characterized complex organic solids (tholins) produced by irradiating simulated Titan atmospheres reproduce well the observed UV/visible/IR optical constants of the Titan stratospheric haze. Titan tholin and a tholin generated in a crude simulation of the atmosphere of Jupiter are examined by two-step laser desorption/multiphoton ionization mass spectrometry. A range of two- to four-ring PAHs, some with one to four alkylation sites, are identified, with a net abundance of about 0.0001 g/g (grams per gram) of tholins produced. Synchronous fluorescence techniques confirm this detection. Titan tholins have proportionately more one- and two-ring PAHs than do Jupiter tholins, which in turn have more four-ring and larger PAHs. The four-ringed PAH chrysene, prominent in some discussions of interstellar grains, is found in Jupiter tholins.

Significance of Cytochrome P450 System Responses and Levels of Bile Fluorescent Aromatic Compounds in Marine Wildlife Following Oil Spills

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

Lee, Richard F.; Anderson, Jack W.

2005-07-01

The relationships among cytochrome P450 induction in marine wildlife species, levels of fluorescent aromatic compounds (FAC) in their bile, the chemical composition of the inducing compounds, the significance of the exposure pathway, and any resulting injury, as a consequence of exposure to crude oil following a spill, are reviewed. Fish collected after oil spills often show increases in cytochrome P450 system activity, cytochrome P4501A (CYP1A) and bile fluorescent aromatic compounds (FAC), that are correlated with exposure to polycyclic aromatic hydrocarbons (PAH) in the oil. There is also some evidence for increases in bile FAC and induction of cytochrome P450 inmore » marine birds and mammals after oil spills. However, when observed, increases in these exposure indicators are transitory and generally decrease to background levels within one year after the exposure. Laboratory studies have shown induction of cytochrome P450 systems occurs after exposure of fish to crude oil in water, sediment or food. Most of the PAH found in crude oil (dominantly 2- and 3-ring PAH) are not strong inducers of cytochrome P450. Exposure to the 4-ring chrysenes or the photooxidized products of the PAH may account for the cytochrome P450 responses in fish collected from oil-spill sites. The contribution of non-spill background PAH, particularly combustion-derived (pyrogenic) PAH, to bile FAC and cytochrome P450 system responses can be confounding and needs to be considered when evaluating oil spill effects. The ubiquity of pyrogenic PAH makes it important to fully characterize all sources of PAH, including PAH from natural resources, e.g. retene, in oil spill studies. In addition, such parameters as species, sex, age, ambient temperature and season need to be taken into account. While increases in fish bile FAC and cytochrome P450 system responses, can together, be sensitive general indicators of PAH exposure after an oil spill, there is little unequivocal evidence to suggest a linkage to higher order biological effects, e.g. toxicity, lesions, reproductive failure.« less

Origin of organic matter in the early solar system. VII - The organic polymer in carbonaceous chondrites

NASA Technical Reports Server (NTRS)

Hayatsu, R.; Matsuoka, S.; Anders, E.; Scott, R. G.; Studier, M. H.

1977-01-01

Degradation techniques, including pyrolysis, depolymerization, and oxidation, were used to study the insoluble polymer from the Murchison C2 chondrite. Oxidation with Cr2O7(2-) or O2/UV led to the identification of 15 aromatic ring systems. Of 11 aliphatic acids identified, three dicarboxylic acids presumably came from hydroaromatic portions of the polymer, whereas eight monocarboxylic acids probably derive from bridging groups or ring substituents. Depolymerization with CF3COO4 yielded some of the same ring systems, as well as alkanes (C1 through C8) and alkenes (C2 through C8), alkyl (C1 through C5) benzenes and naphthalenes, and methyl- or dimethyl -indene, -indane, -phenol, -pyrrole, and -pyridine. All these compounds were detected below 200 C, and are therefore probably indigenous constituents. The properties of the meteoritic polymer were compared with the properties of a synthetic polymer produced by the Fischer-Tropsch reaction. It is suggested that the meteoritic polymer was also produced by surface catalysis.

Initial Reductive Reactions in Aerobic Microbial Metabolism of 2,4,6-Trinitrotoluene

PubMed Central

Vorbeck, Claudia; Lenke, Hiltrud; Fischer, Peter; Spain, Jim C.; Knackmuss, Hans-Joachim

1998-01-01

Because of its high electron deficiency, initial microbial transformations of 2,4,6-trinitrotoluene (TNT) are characterized by reductive rather than oxidation reactions. The reduction of the nitro groups seems to be the dominating mechanism, whereas hydrogenation of the aromatic ring, as described for picric acid, appears to be of minor importance. Thus, two bacterial strains enriched with TNT as a sole source of nitrogen under aerobic conditions, a gram-negative strain called TNT-8 and a gram-positive strain called TNT-32, carried out nitro-group reduction. In contrast, both a picric acid-utilizing Rhodococcus erythropolis strain, HL PM-1, and a 4-nitrotoluene-utilizing Mycobacterium sp. strain, HL 4-NT-1, possessed reductive enzyme systems, which catalyze ring hydrogenation, i.e., the addition of a hydride ion to the aromatic ring of TNT. The hydride-Meisenheimer complex thus formed (H−-TNT) was further converted to a yellow metabolite, which by electrospray mass and nuclear magnetic resonance spectral analyses was established as the protonated dihydride-Meisenheimer complex of TNT (2H−-TNT). Formation of hydride complexes could not be identified with the TNT-enriched strains TNT-8 and TNT-32, or with Pseudomonas sp. clone A (2NT−), for which such a mechanism has been proposed. Correspondingly, reductive denitration of TNT did not occur. PMID:16349484

The Radio Spectra and - Inertial Defects Behavior of Planar Aromatic Heterocycles

NASA Astrophysics Data System (ADS)

McNaughton, Don; Jahn, Michaela K.; Grabow, Jens-Uwe; Godfrey, Peter; Travers, Michael; Wachsmuth, Dennis

2016-06-01

The simplest tricyclic aromatic nitrogen heterocyclic molecules 5,6 benzoquinoline and 7,8 benzoquinoline are possible candidates for detection of aromatic systems in the interstellar medium. Therefore the pure rotational spectra have been recorded using frequency-scanned Stark modulated, jet-cooled millimetre wave absorption spectroscopy (48-87 GHz) and Fourier Transform Microwave (FT MW) spectroscopy (2-26 GHz) of a supersonic rotationally cold molecular jet. Guided by ab initio molecular orbital predictions, spectral analysis of mm wave spectra, and higher resolution FT MW spectroscopy provided accurate rotational and centrifugal distortion constants together with 14N nuclear quadrupole coupling constants for both species. The determined inertial defects, along with those of similar species are used to develop an empirical formula for calculation of inertial defects of aromatic ring systems. The predictive ability of the formula is shown to be excellent for planar species with a number of pronounced out of plane vibrations. The resultant constants are of sufficient accuracy to be used in potential astrophysical searches. We gratefully acknowledge support from the Deutsche Forschungsgemeinschaft, the Deutsche Akademische Austauschdienst, as well as the Land Niedersachsen (J.-U.G). DMcN also thanks the Royal Society of Chemistry for their generous travel support.

Correlations of the Specific Rates of Solvolysis of Aromatic Carbamoyl Chlorides, Chloroformates, Chlorothionoformates, and Chlorodithioformates Revisited

PubMed Central

Kevill, Dennis N.; Koyoshi, Fumie; D’Souza, Malcolm J.

2007-01-01

Additional specific rates of solvolysis are determined for phenyl chloroformate. These values are combined with literature values to give a total of 49 data points, which are used within simple and extended Grunwald-Winstein treatments. Literature values are also brought together to allow treatments in more solvents than previously for three N-aryl-N-methylcarbamoyl chlorides, phenyl chlorothionoformate, phenyl chlorodithioformate, and N,N-diphenylcarbamoyl chloride. For the last two listed, moderately strong evidence for a meaningful inclusion of a term governed by the aromatic ring parameter (I) was indicated. No evidence was found requiring inclusion of this parameter for ionization reactions with only one aromatic ring on the nitrogen of carbamoyl chlorides or for the solvolyses of the chloroformate or chlorothionoformate proceeding by an addition-elimination (association-dissociation) mechanism.

Interactions between manganese oxides and multiple-ringed aromatic compounds

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

Whelan, G.; Sims, R.C.

1992-08-01

Objective is to determine whether Mn reductive dissolution can oxidize multiple-ringed aromatics, such as PAHs, in an oxic environment Research indicated that certain PAHs (eg, dihydrodiols and diones that form free-radical intermediates) are susceptible to oxidation and polymerization. Over 14 days, 83, 76, 54, 70, and 20% of the Mn was reduced by 2,3-, 1,3-, and 1,4-naphthalenediol, quinizarin, and 1,4-naphthoquinone, respectively. 100, 100, and 65% of the first three PAHs were oxidized, respectively. Aromatics with diol functional groups were more easily oxidized than those with only dione groups. Relatively insoluble compounds like quinizarin can be oxidized; insoluble ''humic-like'' material precipitated,more » indicating a polymerization-humification process. Results suggest that electron transfer/organic release from the oxide surface is the rate-limiting step.« less

Interactions between manganese oxides and multiple-ringed aromatic compounds

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

Whelan, G.; Sims, R.C.

1992-08-01

Objective is to determine whether Mn reductive dissolution can oxidize multiple-ringed aromatics, such as PAHs, in an oxic environment? Research indicated that certain PAHs (eg, dihydrodiols and diones that form free-radical intermediates) are susceptible to oxidation and polymerization. Over 14 days, 83, 76, 54, 70, and 20% of the Mn was reduced by 2,3-, 1,3-, and 1,4-naphthalenediol, quinizarin, and 1,4-naphthoquinone, respectively. 100, 100, and 65% of the first three PAHs were oxidized, respectively. Aromatics with diol functional groups were more easily oxidized than those with only dione groups. Relatively insoluble compounds like quinizarin can be oxidized; insoluble ``humic-like`` material precipitated,more » indicating a polymerization-humification process. Results suggest that electron transfer/organic release from the oxide surface is the rate-limiting step.« less

Polymeric molecular sieve membranes for gas separation

DOEpatents

Dai, Sheng; Qiao, Zhenan; Chai, Songhai

2017-08-15

A porous polymer membrane useful in gas separation, the porous polymer membrane comprising a polymeric structure having crosslinked aromatic groups and a hierarchical porosity in which micropores having a pore size less than 2 nm are present at least in an outer layer of the porous polymer membrane, and macropores having a pore size of over 50 nm are present at least in an inner layer of the porous polymer membrane. Also described are methods for producing the porous polymer membrane in which a non-porous polymer membrane containing aromatic rings is subjected to a Friedel-Crafts crosslinking reaction in which a crosslinking molecule crosslinks the aromatic rings in the presence of a Friedel-Crafts catalyst and organic solvent under sufficiently elevated temperature, as well as methods for using the porous polymer membranes for gas or liquid separation, filtration, or purification.

1-(Benzyl­ideneamino)pyridinum iodide

PubMed Central

Cui, Yong-Tao; Wang, Jian-Qiang; Ji, Chun-Xiang; Wu, Cong-Ren; Guo, Cheng

2009-01-01

In the title compound, C12H11N2 +·I−, the aromatic rings are oriented at a dihedral angle of 73.40 (3)°. In the crystal structure, π–π contacts between the pyridine rings and the benzene and pyridine rings [centroid–centroid distances = 3.548 (3) and 4.211 (3) Å] may stabilize the structure. PMID:21581846

The angular electronic band structure and free particle model of aromatic molecules: High-frequency photon-induced ring current

NASA Astrophysics Data System (ADS)

Öncan, Mehmet; Koç, Fatih; Şahin, Mehmet; Köksal, Koray

2017-05-01

This work introduces an analysis of the relationship of first-principles calculations based on DFT method with the results of free particle model for ring-shaped aromatic molecules. However, the main aim of the study is to reveal the angular electronic band structure of the ring-shaped molecules. As in the case of spherical molecules such as fullerene, it is possible to observe a parabolic dispersion of electronic states with the variation of angular quantum number in the planar ring-shaped molecules. This work also discusses the transition probabilities between the occupied and virtual states by analyzing the angular electronic band structure and the possibility of ring currents in the case of spin angular momentum (SAM) or orbital angular momentum (OAM) carrying light. Current study focuses on the benzene molecule to obtain its angular electronic band structure. The obtained electronic band structure can be considered as a useful tool to see the transition probabilities between the electronic states and possible contribution of the states to the ring currents. The photoinduced current due to the transfer of SAM into the benzene molecule has been investigated by using analytical calculations within the frame of time-dependent perturbation theory.

Reflectance spectroscopy (350-2500 nm) of solid-state polycyclic aromatic hydrocarbons (PAHs)

NASA Astrophysics Data System (ADS)

Izawa, M. R. M.; Applin, D. M.; Norman, L.; Cloutis, E. A.

2014-07-01

Polycyclic aromatic hydrocarbons (PAHs) are organic compounds based on fused aromatic rings, and are formed in a variety of astrophysical, solar nebula and planetary processes. Polycyclic aromatic hydrocarbons are known or suspected to occur in a wide variety of planetary settings including icy satellites, Titan’s hazes, carbonaceous meteorites, comet nuclei, ring particles; and terrestrial organic-rich lithologies such as coals, asphaltites, and bituminous sands. Relatively few measurements of the visible and near-infrared spectra of PAHs exist, yet this wavelength region (350-2500 nm) is widely used for remote sensing. This study presents detailed analyses of the 350-2500 nm reflectance spectra of 47 fine-grained powders of different high-purity solid-state PAHs. Spectral properties of PAHs change with variations in the number and connectivity of linked aromatic rings and the presence and type of side-groups and heterocycles. PAH spectra are characterized by three strong features near ∼880 nm, ∼1145 nm, and ∼1687 nm due to overtones of νCH fundamental stretching vibrations. Some PAHs are amenable to remote detection due to the presence of diagnostic spectral features, including: Nsbnd H stretching overtones at 1490-1515 nm in NH- and NH2-bearing PAHs, aliphatic or saturated bond Csbnd H overtone vibrations at ∼1180-1280 nm and ∼1700-1860 nm; a broad asymmetric feature between ∼1450 nm and ∼1900 nm due to Osbnd H stretching overtones in aromatic alcohols, Csbnd H and Cdbnd O combinations near ∼2000-2010 nm and ∼2060-2270 nm in acetyl and carboxyl-bearing PAHs. Other substituents such as sulphonyl, thioether ether and carboxyl heterocycles, or cyano, nitrate, and aromatic side groups, do not produce well-resolved diagnostic spectral features but do cause shifts in the positions of the aromatic Csbnd H vibrational overtone features. Fluorescence is commonly suppressed by the presence of heterocycles, side-groups and in many non-alternant PAHs. The spectral characteristics of PAHs offer the potential, under suitable circumstances, for remote characterization of the classes of PAH present and in some cases, identification of particular heterocyclic or side-group substituents.

PERSONAL EXPOSURE TO FINE PARTICLE POLYCYCLIC AROMATIC HYDROCARBONS: OUTDOOR SOURCE TRACERS

EPA Science Inventory

The most carcinogenic and toxic polycyclic aromatic hydrocarbons (PAH) are the 4-5 ring PAH found preferentially adsorbed to the fine particles (<2.54u in urban ambient air and personal air. Personal exposure to the carcinogenic particle bound PAH is also highly correlated ...

Aromatic Rings Commonly Used in Medicinal Chemistry: Force Fields Comparison and Interactions With Water Toward the Design of New Chemical Entities.

PubMed

Polêto, Marcelo D; Rusu, Victor H; Grisci, Bruno I; Dorn, Marcio; Lins, Roberto D; Verli, Hugo

2018-01-01

The identification of lead compounds usually includes a step of chemical diversity generation. Its rationale may be supported by both qualitative (SAR) and quantitative (QSAR) approaches, offering models of the putative ligand-receptor interactions. In both scenarios, our understanding of which interactions functional groups can perform is mostly based on their chemical nature (such as electronegativity, volume, melting point, lipophilicity etc.) instead of their dynamics in aqueous, biological solutions (solvent accessibility, lifetime of hydrogen bonds, solvent structure etc.). As a consequence, it is challenging to predict from 2D structures which functional groups will be able to perform interactions with the target receptor, at which intensity and relative abundance in the biological environment, all of which will contribute to ligand potency and intrinsic activity. With this in mind, the aim of this work is to assess properties of aromatic rings, commonly used for drug design, in aqueous solution through molecular dynamics simulations in order to characterize their chemical features and infer their impact in complexation dynamics. For this, common aromatic and heteroaromatic rings were selected and received new atomic charge set based on the direction and module of the dipole moment from MP2/6-31G * calculations, while other topological terms were taken from GROMOS53A6 force field. Afterwards, liquid physicochemical properties were simulated for a calibration set composed by nearly 40 molecules and compared to their respective experimental data, in order to validate each topology. Based on the reliance of the employed strategy, we expanded the dataset to more than 100 aromatic rings. Properties in aqueous solution such as solvent accessible surface area, H-bonds availability, H-bonds residence time, and water structure around heteroatoms were calculated for each ring, creating a database of potential interactions, shedding light on features of drugs in biological solutions, on the structural basis for bioisosterism and on the enthalpic/entropic costs for ligand-receptor complexation dynamics.

Molecular mechanisms in the pyrolysis of unsaturated chlorinated hydrocarbons: formation of benzene rings. 2. Experimental and kinetic modeling studies.

PubMed

McIntosh, Grant J; Russell, Douglas K

2013-05-23

The mechanism of formation of benzene rings during the pyrolysis of dichloro- and trichloroethylenes has been investigated by the method of laser powered homogeneous pyrolysis coupled with product analysis by gas chromatography. Additionally, selected (co)pyrolyses between the chlorinated ethylenes, CH2Cl2, C4Cl4, C4Cl6, and C2H2 have been performed to explicitly probe the roles of 2C3 and C4/C2 reaction pairs in aromatic growth. The presence of odd-carbon products in neat C4Cl6 pyrolyses indicates that 2C3 processes are operative in these systems; however, comparison with product yields from C2HCl3 suggests that C4/C2 processes dominate most other systems. This is further evidenced by an absence of C3 and other odd-carbon species in (co)pyrolyses with dichloromethane which should seed C3-based growth. The reactions of perchlorinated C4 species C4Cl5, C4Cl3, and C4Cl4 with C2Cl2 were subsequently explored through extensive kinetic simulations of the possible reaction pathways based on previous kinetic models and the exhaustive quantum chemical investigations of our preceding work. The experimental and theoretical results strongly suggest that, at moderate temperatures, aromatic ring formation from chlorinated ethylenes normally follows a Diels-Alder coupling of C4 and C2 molecular units followed by internal shifts; the one exception is the C4Cl4 + C2Cl2 system, where steric factors lead to the formation of nonaromatic products. There is little evidence for radical-based routes in these systems.

Structure-function correlation of chloroquine and analogues as transgene expression enhancers in nonviral gene delivery.

PubMed

Cheng, Jianjun; Zeidan, Ryan; Mishra, Swaroop; Liu, Aijie; Pun, Suzie H; Kulkarni, Rajan P; Jensen, Gregory S; Bellocq, Nathalie C; Davis, Mark E

2006-11-02

To understand how chloroquine (CQ) enhances transgene expression in polycation-based, nonviral gene delivery systems, a number of CQ analogues with variations in the aliphatic amino side chain or in the aromatic ring are synthesized and investigated. Our studies indicate that the aliphatic amino moiety of CQ is essential to provide increased gene expression. Further, the enhancements are more dramatically affected by changes to the aromatic ring and are positively correlated to the strength of intercalation between DNA and the CQ analogues. Quinacrine (QC), a CQ analogue with a fused acridinyl structure that can strongly intercalate DNA, enhances transfection similarly to CQ at a concentration 10 times lower, while N(4)-(4-pyridinyl)-N(1),N(1)-diethyl-1,4-pentanediamine (CP), a CQ analogue that has a weakly intercalating pyridinyl ring, shows no effect on gene expression. Subtle change on the 7-substituent of the chloroquine aromatic structure can also greatly affect the ability of the CQ analogues to enhance transgene expression. Transfection in the presence of N(4)-(7-trifluoromethyl-4-quinolinyl)-N(1),N(1)-diethyl-1,4-pentanediamin e (CQ7a) shows expression efficiency 10 times higher than in the presence of CQ at same concentration, while transfection in the presence of N(4)-(4-quinolinyl)-N(1),N(1)-diethyl-1,4-pentanediamine (CQ7b) does not reveal any enhancing effects on expression. Through a number of comparative studies with CQ and its analogues, we conclude that there are at least three mechanistic features of CQ that lead to the enhancement in gene expression: (i) pH buffering in endocytic vesicles, (ii) displacement of polycations from the nucleic acids in polyplexes, and (iii) alteration of the biophysical properties of the released nucleic acid.

Adsorption of guaiacol on Fe (110) and Pd (111) from first principles

NASA Astrophysics Data System (ADS)

Hensley, Alyssa J. R.; Wang, Yong; McEwen, Jean-Sabin

2016-06-01

The catalytic properties of surfaces are highly dependent upon the effect said surfaces have on the geometric and electronic structure of adsorbed reactants, products, and intermediates. It is therefore crucial to have a surface-level understanding of the adsorption of the key species in a reaction in order to design active and selective catalysts. Here, we study the adsorption of guaiacol on Fe (110) and Pd (111) using dispersion-corrected density functional theory calculations as both of these metals are of interest as hydrodeoxygenation catalysts for the conversion of bio-oils to useable biofuels. Both vertical (via the oxygen functional groups) and horizontal (via the aromatic ring) adsorption configurations were examined and the resulting adsorption and molecular distortion energies showed that the vertical sites were only physisorbed while the horizontal sites were chemisorbed on both metal surfaces. A comparison of guaiacol's horizontal adsorption on Fe (110) and Pd (111) showed that guaiacol had a stronger adsorption on Pd (111) while the Fe (110) surface distorted the Csbnd O bonds to a greater degree. Electronic analyses on the horizontal systems showed that the greater adsorption strength for guaiacol on Pd (111) was likely due to the greater charge transfer between the aromatic ring and the surface Pd atoms. Additionally, the greater distortion of the Csbnd O bonds in adsorbed guaiacol on Fe (110) is likely due to the greater degree of interaction between the oxygen and surface Fe atoms. Overall, our results show that the Fe (110) surface has a greater degree of interaction with the functional groups and the Pd (111) surface has a greater degree of interaction with the aromatic ring.

A divergent route to core- and peripherally functionalized diazacoronenes that act as colorimetric and fluorescence proton sensors

DOE PAGES

He, Bo; Dai, Jing; Zherebetskyy, Danylo; ...

2015-03-31

Combining core annulation and peripheral group modification, we have demonstrated a divergent synthesis of a family of highly functionalized coronene derivatives from a readily accessible dichlorodiazaperylene intermediate. Various reactions, such as aromatic nucleophilic substitution, Kumada coupling and Suzuki coupling proceed effectively on α-positions of the pyridine sites, giving rise to alkoxy, thioalkyl, alkyl or aryl substituted polycyclic aromatic hydrocarbons. In addition to peripheral group modulation, the aromatic core structures can be altered by annulation with thiophene or benzene ring systems. Corresponding single crystal X-ray diffraction and optical studies indicate that the heteroatom linkages not only impact the solid state packing,more » but also significantly influence the optoelectronic properties. Moreover, these azacoronene derivatives display significant acid-induced spectroscopic changes, suggesting their great potential as colorimetric and fluorescence proton sensors.« less

Models of S/π interactions in protein structures: Comparison of the H2S–benzene complex with PDB data

PubMed Central

Ringer, Ashley L.; Senenko, Anastasia; Sherrill, C. David

2007-01-01

S/π interactions are prevalent in biochemistry and play an important role in protein folding and stabilization. Geometries of cysteine/aromatic interactions found in crystal structures from the Brookhaven Protein Data Bank (PDB) are analyzed and compared with the equilibrium configurations predicted by high-level quantum mechanical results for the H2S–benzene complex. A correlation is observed between the energetically favorable configurations on the quantum mechanical potential energy surface of the H2S–benzene model and the cysteine/aromatic configurations most frequently found in crystal structures of the PDB. In contrast to some previous PDB analyses, configurations with the sulfur over the aromatic ring are found to be the most important. Our results suggest that accurate quantum computations on models of noncovalent interactions may be helpful in understanding the structures of proteins and other complex systems. PMID:17766371

Detecting aromatic compounds on planetary surfaces using ultraviolet time-resolved fluorescence spectroscopy

NASA Astrophysics Data System (ADS)

Eshelman, E.; Daly, M. G.; Slater, G.; Cloutis, E.

2018-02-01

Many aromatic organic molecules exhibit strong and characteristic fluorescence when excited with ultraviolet radiation. As laser excitation in the ultraviolet generates both fluorescence and resonantly enhanced Raman scattering of aromatic vibrational modes, combined Raman and fluorescence instruments have been proposed to search for organic compounds on Mars. In this work the time-resolved fluorescence of a suite of 24 compounds composed of 2-5 ringed alternant, non-alternant, and heterocyclic PAHs was measured. Fluorescence instrumentation with similar specifications to a putative flight instrument was capable of observing the fluorescence decay of these compounds with a sub-ns resolution. Incorporating time-resolved capabilities was also found to increase the ability to discriminate between individual PAHs. Incorporating time-resolved fluorescence capabilities into an ultraviolet gated Raman system intended for a rover or lander can increase the ability to detect and characterize PAHs on planetary surfaces.

Ultrahigh Molecular Weight Aromatic Siloxane Polymers

NASA Technical Reports Server (NTRS)

Ludwick, L. M.

1983-01-01

Silphenylene-siloxane polymers can be prepared by a condensation reaction of a diol 1,4-bis(hydroxydimethylsilyl)benzene and a silane bis(dimethylamino)dimethylsilane. Using a stepwise condensation technique, a polymer (R=CH3) with a molecular weight in excess of 1.0 x 1 million has been produced. The polymer exhibits increased thermal stability, compared to a methyl siloxane polymer without the aromatic phenyl ring in the backbone. The use of bis(dimethylamino)methylvinylsilane should allow for ready crosslinking at the vinyl sites (R=-CH=CH2) introduced into the backbone. However, under the conditions of the reaction system a high molecular weight polymer was not obtained or the polymer underwent a crosslinking process during the synthesis.

Beyond the benzene dimer: an investigation of the additivity of pi-pi interactions.

PubMed

Tauer, Tony P; Sherrill, C David

2005-11-24

The benzene dimer is the simplest prototype of pi-pi interactions and has been used to understand the fundamental physics of these interactions as they are observed in more complex systems. In biological systems, however, aromatic rings are rarely found in isolated pairs; thus, it is important to understand whether aromatic pairs remain a good model of pi-pi interactions in clusters. In this study, ab initio methods are used to compute the binding energies of several benzene trimers and tetramers, most of them in 1D stacked configurations. The two-body terms change only slightly relative to the dimer, and except for the cyclic trimer, the three- and four-body terms are negligible. This indicates that aromatic clusters do not feature any large nonadditive effects in their binding energies, and polarization effects in benzene clusters do not greatly change the binding that would be anticipated from unperturbed benzene-benzene interactions, at least for the 1D stacked systems considered. Three-body effects are larger for the cyclic trimer, but for all systems considered, the computed binding energies are within 10% of what would be estimated from benzene dimer energies at the same geometries.

Supramolecular liquid crystalline π-conjugates: the role of aromatic π-stacking and van der Waals forces on the molecular self-assembly of oligophenylenevinylenes.

PubMed

Goel, Mahima; Jayakannan, M

2010-10-07

Here, we report a unique design strategy to trace the role of aromatic π-stacking and van der Waals interactions on the molecular self-organization of π-conjugated building blocks in a single system. A new series of bulky oligophenylenevinylenes (OPVs) bearing a tricyclodecanemethylene (TCD) unit in the aromatic π-core with flexible long methylene chains (n = 0-12 and 16) in the longitudinal position were designed and synthesized. The OPVs were found to be liquid crystalline, and their enthalpies of phase transitions (also entropies) showed odd-even oscillation with respect to the number of carbon atoms in alkyl chains. OPVs with an even number of methylene units in the side chains showed higher enthalpies with respect to their highly packed solid structures compared to odd-numbered ones. Polarized light microscopic analysis confirmed the formation of cholesteric liquid crystalline (LC) phases of fan shaped textures with focal conics in OPVs with 5 ≤ n ≤ 9. OPVs with longer alkyl chains (OPV-10 to OPV-12) produced a birefringence pattern consisting of dark and bright ring-banded suprastructures. The melting temperature followed a sigmoidal trend, indicating the transformation of molecular self-organization in OPVs from solid to ring-banded suprastructures via cholesteric LC intermediates. At longer alkyl chain lengths, the van der Waals interactions among the alkyl chains became predominant and translated the mesogenic effect across the lamellae; as a consequence, the lamellae underwent twisted self-organization along the radial growth direction of the spherulites to produce bright and dark bands. Scanning electron microscope (SEM) analysis of cholesteric LC and ring-banded textures strongly supported the existence of twisted lamellae in the OPVs with ring-banded textures. Variable temperature X-ray diffraction analysis confirmed the reversibility of the molecular self-organization in the solid state and also showed the existence of the higher ordered lamellar structure in ring-banded OPVs. Photophysical characterizations such as excitation, emission, and time resolved fluorescence decay measurements were employed to trace molecular self-organization in their liquid crystalline phases. The emission spectra of the OPV samples showed odd-even oscillation in their emission wavelengths with respect to the length of alkyl chains. Highly packed even-OPVs showed more blue shift compared to that of less crystalline odd-OPVs. Time dependent fluorescence decay of OPVs followed a biexponential fit, and their lifetimes (τ(1) and τ(2) values) revealed that the decay is faster for odd-OPVs compared to even-OPVs. Among all the OPVs, the τ(2) values for OPV-8 and OPV-12 were found to be much higher, indicating their high luminescent characteristics. In a nut shell, bulky liquid crystalline OPV chromophores were cleverly utilized, for the first time, to probe the aromatic π-stacking versus van der Waals interactions on the molecular self-organization of π-conjugated system.

A Naphtho- p-quinodimethane Exhibiting Baird’s (Anti)Aromaticity, Broken Symmetry, and Attractive Photoluminescence

DOE PAGES

Shokri, Siamak; Li, Jingbai; Manna, Manoj K.; ...

2017-08-24

In this paper, we report a novel reductive desulfurization reaction involving π-acidic naphthalene diimides 1 (NDI) using thionating agents such as Lawesson’s reagent. Along with the expected thionated NDI derivatives 2-6, new heterocyclic naphtho-p-quinodimethane compounds 7 depicting broken/reduced symmetry were successfully isolated and fully characterized. Empirical studies and theoretical modeling suggest that was formed via a six-membered ring oxathiaphosphenine intermediate rather than the usual four-membered ring oxathiaphosphetane of 2-6. Aside from the reduced symmetry in 7 as confirmed by single-crystal XRD analysis, we established that the ground state UV-vis absorption of 7 is red-shifted in comparison to the parent NDImore » 1. This result was expected in the case of thionated polycyclic diimides. However, unusual low energy transitions originate from Baird 4nπ aromaticity of compounds 7 in lieu of the intrinsic Huckel (4n + 2)π aromaticity as encountered in NDI 1. Moreover, complementary theoretical modeling results also corroborate this change in aromaticity of 7. Consequently, photophysical investigations show that, compared to parent NDI 1, 7 can easily access and emit from its T 1 state with a phosphorescence 3(7a)* lifetime of τ P = 395 μs at 77 K indicative of the formation of the corresponding “aromatic triplet” species according to the Baird’s rule of aromaticity.« less

Metal-sulfur type cell having improved positive electrode

DOEpatents

Dejonghe, Lutgard C.; Visco, Steven J.; Mailhe, Catherine C.; Armand, Michel B.

1989-01-01

An novel metal-sulfur type cell operable at a temperature of 200.degree. C. or less with an energy density of 150 Whrs/Kg or better is disclosed characterized by an organo-sulfur cathode formed from an organic-sulfur compound having the general formula, in its charged state, of (R(S).sub.y).sub.n wherein y=1 to 6; n=2 to 20; and R is one or more different aliphatic or aromatic organic moieties having 1 to 20 carbon atoms, which may include one or more oxygen, sulfur, or nitrogen heteroatoms when R comprisises one of more aromatic rings, or one or more oxygen, sulfur, nitrogen, or fluorine atoms associtated with the chain when R comprises an aliphatic chain, wherein the aliphatic group may be linear or branched, saturated or unsaturated, and wherein either the aliphatic chain or the aromatic ring may have substituted groups thereon.

Metal-sulfur type cell having improved positive electrode

DOEpatents

DeJonghe, L.C.; Visco, S.J.; Mailhe, C.C.; Armand, M.B.

1988-03-31

A novel metal-sulfur type cell operable at a temperature of 200/degree/C or less with an energy density of 150 Whrs/Kg or better is disclosed characterized by an organo-sulfur cathode formed from an organic-sulfur compound having the general formula, in its charged state, of (R(S)/sub y/)n wherein y = 1 to 6; n = 2 to 20; and R is one or more different aliphatic or aromatic organic moieties having 1 to 20 carbon atoms, which may include one or more oxygen, sulfur, or nitrogen heteroatoms when R comprises one or more aromatic rings, or one or more oxygen, sulfur, nitrogen, or fluorine atoms associated with the chain when R comprises an aliphatic chain, wherein the aliphatic group may be linear or branched, saturated or unsaturated, and wherein either the aliphatic chain or the aromatic ring may have substituted groups thereon. 4 figs.

Determination of Aromatic Ring Number Using Multi-Channel Deep UV Native Fluorescence

NASA Technical Reports Server (NTRS)

Bhartia, R.; McDonald, G. D.; Salas, E.; Conrad, P.

2004-01-01

The in situ detection of organic material on an extraterrestrial surface requires both effective means of searching a relatively large surface area or volume for possible organic carbon, and a more specific means of identifying and quantifying compounds in indicated samples. Fluorescence spectroscopy fits the first requirement well, as it can be carried out rapidly, with minimal or no physical contact with the sample, and with sensitivity unmatched by any other organic analytical technique. Aromatic organic compounds with know fluorescence signatures have been identified in several extraterrestrial samples, including carbonaceous chondrites, interplanetary dust particles, and Martian meteorites. The compound distributions vary among these sources, however, with clear differences in relative abundances by number of aromatic rings and by degree of alkylation. This relative abundance information, therefore, can be used to infer the source of organic material detected on a planetary surface.

Nature of the water/aromatic parallel alignment interactions.

PubMed

Mitoraj, Mariusz P; Janjić, Goran V; Medaković, Vesna B; Veljković, Dušan Ž; Michalak, Artur; Zarić, Snežana D; Milčić, Miloš K

2015-01-30

The water/aromatic parallel alignment interactions are interactions where the water molecule or one of its O-H bonds is parallel to the aromatic ring plane. The calculated energies of the interactions are significant, up to ΔE(CCSD)(T)(limit) = -2.45 kcal mol(-1) at large horizontal displacement, out of benzene ring and CH bond region. These interactions are stronger than CH···O water/benzene interactions, but weaker than OH···π interactions. To investigate the nature of water/aromatic parallel alignment interactions, energy decomposition methods, symmetry-adapted perturbation theory, and extended transition state-natural orbitals for chemical valence (NOCV), were used. The calculations have shown that, for the complexes at large horizontal displacements, major contribution to interaction energy comes from electrostatic interactions between monomers, and for the complexes at small horizontal displacements, dispersion interactions are dominant binding force. The NOCV-based analysis has shown that in structures with strong interaction energies charge transfer of the type π → σ*(O-H) between the monomers also exists. © 2014 Wiley Periodicals, Inc.

The study of azaarene behavior over atmosphere of subtropical city(Keelung)

NASA Astrophysics Data System (ADS)

Liu, Chih Yun

2017-04-01

In this study, we collected the Total Suspended Particulates (TSP) from July 2014 to February 2016 in the subtropical city (Keelung), and researched azaarene behavior over atmosphere. Polycyclic Aromatic Compounds (PAHs) are ubiquitous pollutants in the environment; they have known carcinogens and/or mutagens, mainly produce from incomplete combustion. Azaarenes are polycyclic aromatic hydrocarbon derivative compounds in which a carbon atom in one of the aromatic rings is substituted by a nitrogen atom. Organism exposure to azaarenes occurs through inhalation of polluted air and by ingestion of food and/or water containing combustion products and accumulate in the body. Total azaarene concentration (16 individual compound concentration of the aggregate) is between 0.92 to 3.76 μg/m3, results showed that the concentration of azaarenes have significant seasonal variation, they have higher concentration in the cold month. In molecular weight, the highest proportion is the molecular weight equal to 143(ΣMQ) and then the molecular weight equal to 179(BAP), ΣMQ would rise from 30% 40% to 40% 50% during the cold month and warm months. Compared to ring number, 2-rings are biggest part, the smallest is 4-rings, its ratio has slight variation, but primary species is 2-rings. Emissions from transportation, local housing heating, factories burning fossil fuels and dust from Mainland south air mass are pollutant, their sources and climate conditions can affect concentration and composition of compound. There are highly significant correlation between 3-rings and 4-rings, which suggests that there are similar source strengths and transport mechanisms for these compounds. Correlation between concentration of azaarenes and ambient temperature is negative moderation, with concentration of atmospheric suspended particles is positive moderate correlation. Finally, we establish the relationship between the three parameters to predict concentration of azaarenes over atmosphere of subtropical regions. Key words: azaarenes, atmospheric suspended particles, subtropical city, multiple regression analysis.

Formation of polycyclic aromatic hydrocarbons in circumstellar envelopes

NASA Technical Reports Server (NTRS)

Frenklach, Michael; Feigelson, Eric D.

1989-01-01

Production of polycyclic aromatic hydrocarbons in carbon-rich circumstellar envelopes was investigated using a kinetic approach. A detailed chemical reaction mechanism of gas-phase PAH formation and growth, containing approximately 100 reactions of 40 species, was numerically solved under the physical conditions expected in cool stellar winds. The chemistry is based on studies of soot production in hydrocarbon pyrolysis and combustion. Several first-ring and second-ring cyclization processes were considered. A linear lumping algorithm was used to describe PAH growth beyond the second aromatic ring. PAH production using this mechanism was examined with respect to a grid of idealized constant velocity stellar winds as well as several published astrophysical models. The basic result is that the onset of PAH production in the interstellar envelopes is predicted to occur within the temperature interval of 1100 to 900 K. The absolute amounts of the PAHs formed, however, are very sensitive to a number of parameters, both chemical and astrophysical, whose values are not accurately known. Astrophysically meaningful quantities of PAHs require particularly dense and slow stellar winds and high initial acetylene abundance. It is suggested that most of the PAHs may be produced in a relatively small fraction of carbon-rich red giants.

A Computational Study of Structure and Reactivity of N-Substitued-4-Piperidones Curcumin Analogues and Their Radical Anions.

PubMed

Martínez-Cifuentes, Maximiliano; Weiss-López, Boris; Araya-Maturana, Ramiro

2016-12-02

In this work, a computational study of a series of N -substitued-4-piperidones curcumin analogues is presented. The molecular structure of the neutral molecules and their radical anions, as well as their reactivity, are investigated. N -substituents include methyl and benzyl groups, while substituents on the aromatic rings cover electron-donor and electron-acceptor groups. Substitutions at the nitrogen atom do not significantly affect the geometry and frontier molecular orbitals (FMO) energies of these molecules. On the other hand, substituents on the aromatic rings modify the distribution of FMO. In addition, they influence the capability of these molecules to attach an additional electron, which was studied through adiabatic (AEA) and vertical electron affinities (VEA), as well as vertical detachment energy (VDE). To study electrophilic properties of these structures, local reactivity indices, such as Fukui ( f ⁺) and Parr ( P ⁺) functions, were calculated, and show the influence of the aromatic rings substituents on the reactivity of α,β-unsaturated ketones towards nucleophilic attack. This study has potential implications for the design of curcumin analogues based on a 4-piperidone core with desired reactivity.

Energetic factors determining the binding of type I inhibitors to c-Met kinase: experimental studies and quantum mechanical calculations.

PubMed

Yu, Zhe; Ma, Yu-chi; Ai, Jing; Chen, Dan-qi; Zhao, Dong-mei; Wang, Xin; Chen, Yue-lei; Geng, Mei-yu; Xiong, Bing; Cheng, Mao-sheng; Shen, Jing-Kang

2013-11-01

To decipher the molecular interactions between c-Met and its type I inhibitors and to facilitate the design of novel c-Met inhibitors. Based on the prototype model inhibitor 1, four ligands with subtle differences in the fused aromatic rings were synthesized. Quantum chemistry was employed to calculate the binding free energy for each ligand. Symmetry-adapted perturbation theory (SAPT) was used to decompose the binding energy into several fundamental forces to elucidate the determinant factors. Binding free energies calculated from quantum chemistry were correlated well with experimental data. SAPT calculations showed that the predominant driving force for binding was derived from a sandwich π-π interaction with Tyr-1230. Arg-1208 was the differentiating factor, interacting with the 6-position of the fused aromatic ring system through the backbone carbonyl with a force pattern similar to hydrogen bonding. Therefore, a hydrogen atom must be attached at the 6-position, and changing the carbon atom to nitrogen caused unfavorable electrostatic interactions. The theoretical studies have elucidated the determinant factors involved in the binding of type I inhibitors to c-Met.

Quantifying reactivity for electrophilic aromatic substitution reactions with Hirshfeld charge.

PubMed

Liu, Shubin

2015-03-26

An electrophilic aromatic substitution is a process where one atom or group on an aromatic ring is replaced by an incoming electrophile. The reactivity and regioselectivity of this category of reactions is significantly impacted by the group that is already attached to the aromatic ring. Groups promoting substitution at the ortho/para and meta position are called ortho/para and meta directing groups, respectively. Earlier, we have shown that regioselectivity of the electrophilic aromatic substitution is dictated by the nucleophilicity of the substituted aromatic ring, which is proportional to the Hirshfeld charge on the regioselective site. Ortho/para directing groups have the largest negative charge values at the ortho/para positions, whereas meta directing groups often have the largest negative charge value at the meta position. The electron donation or acceptance feature of a substitution group is irrelevant to the regioselectivity. In this contribution, we extend our previous study by quantifying the reactivity for this kind of reactions. To that end, we examine the transition-state structure and activation energy of an identity reaction for a series of monosubstituted-benzene molecules reacting with hydrogen fluoride using BF3 as the catalyst in the gas phase. A total of 18 substitution groups will be considered, nine of which are ortho/para directing and the other nine groups meta directing. From this study, we found that the barrier height of these reactions strongly correlates with the Hirshfeld charge on the regioselective site for both ortho/para and meta directing groups, with the correlation coefficient R(2) both better than 0.96. We also discovered a less accurate correlation between the barrier height and HOMO energy. These results reconfirm the validity and effectiveness of employing the Hirshfeld charge as a reliable descriptor of both reactivity and regioselectivity for this vastly important category of chemical transformations.

Benzoyl radicals from (hetero)aromatic aldehydes. Decatungstate photocatalyzed synthesis of substituted aromatic ketones.

PubMed

Ravelli, Davide; Zema, Michele; Mella, Mariella; Fagnoni, Maurizio; Albini, Angelo

2010-09-21

Benzoyl radicals are generated directly from (hetero)aromatic aldehydes upon tetrabutylammonium decatungstate ((n-Bu(4)N)(4)W(10)O(32)), TBADT) photocatalysis under mild conditions. In the presence of alpha,beta-unsaturated esters, ketones and nitriles radical conjugate addition ensues and gives the corresponding beta-functionalized aryl alkyl ketones in moderate to good yields (stereoselectively in the case of 3-methylene-2-norbornanone). Due to the mild reaction conditions the presence of various functional groups on the aromatic ring is tolerated (e.g. methyl, methoxy, chloro). The method can be applied to hetero-aromatic aldehydes whether electron-rich (e.g. thiophene-2-carbaldehyde) or electron-poor (e.g. pyridine-3-carbaldehyde).

Photophysical Properties of Aromatic and Antiaromatic Porphyrinoids

DTIC Science & Technology

2011-04-14

possible to control the number of conjugated π-electrons by changing the number of connected pyrrole rings, ii) by providing a comparable set of [4n...Hexaphyrins: Effects of Confusion of Pyrrole Rings and Molecular Shape on Electronic Structures  Jong Min Lim, Jae Seok Lee, Hyun Woo Chung, Hee Won

Aromaticity of benzene derivatives: an exploration of the Cambridge Structural Database.

PubMed

Majerz, Irena; Dziembowska, Teresa

2018-04-01

The harmonic oscillator model of aromaticity (HOMA) index, one of the most popular aromaticity indices for solid-state benzene rings in the Cambridge Structural Database (CSD), has been analyzed. The histograms of HOMA for benzene, for benzene derivatives with one formyl, nitro, amino or hydroxy group as well as the histograms for the derivatives with two formyl, nitro, amino or hydroxy groups in ortho, meta and para positions were investigated. The majority of the substituted benzene derivatives in the CSD are characterized by a high value of HOMA, indicating fully aromatic character; however, the distribution of the HOMA value from 1 to about 0 indicates decreasing aromaticity down to non-aromatic character. Among the benzene derivatives investigated, a significant decrease in aromaticity can be related to compounds with diamino and dinitro groups in the meta position.

Development of a screening tool to prioritize testing for the carcinogenic hazard of residual aromatic extracts and related petroleum streams.

PubMed

Goyak, Katy O; Kung, Ming H; Chen, Min; Aldous, Keith K; Freeman, James J

2016-12-15

Residual aromatic extracts (RAE) are petroleum substances with variable composition predominantly containing aromatic hydrocarbons with carbon numbers greater than C25. Because of the high boiling nature of RAEs, the aromatics present are high molecular weight, with most above the range of carcinogenic polycyclic aromatic hydrocarbons (PAHs). However, refinery distillations are imperfect; some PAHs and their heteroatom-containing analogs (collectively referred to as polycyclic aromatic content or PAC) may remain in the parent stream and be extracted into the RAE, and overall PAC content is related to the carcinogenic potential of an RAE. We describe here a real-time analytical chemistry-based tool to assess the carcinogenic hazard of RAE via the development of a functional relationship between carcinogenicity and boiling point. Samples representative of steps along the RAE manufacturing process were obtained from five refineries to evaluate relationships between mutagenicity index (MI), PAC ring content and gas chromatographic distillation (GCD) curves. As expected, a positive linear relationship between MI and PAC ring content occurred, most specifically for 3-6 ring PAC (R 2 =0.68). A negative correlation was found between MI and temperature at 5% vaporization by GCD (R 2 =0.72), indicating that samples with greater amounts of lower boiling constituents were more likely to be carcinogenic. The inverse relationship between boiling range and carcinogenicity was further demonstrated by fractionation of select RAE samples (MI=0.50+0.07; PAC=1.70+0.51wt%; n=5) into low and high boiling fractions, where lower boiling fractions were both more carcinogenic than the higher boiling fractions (MI=2.36±0.55 and 0.17±0.11, respectively) and enriched in 3-6 ring PACs (5.20+0.70wt% and 0.97+0.35wt%, respectively). The criteria defining carcinogenicity was established as 479°C for the 5% vaporization points by GCD, with an approximate 95% probability of a future sample having an MI below the recommended limit of 0.4 for RAEs. Overall, these results provide a cost-efficient and real-time tool by which the carcinogenic potential of RAEs can be assessed at the refinery level, ultimately providing a means to readily monitor and minimize the carcinogenic potential of RAEs. Copyright © 2016. Published by Elsevier Ireland Ltd.

Quasi-aromatic Möbius Metal Chelates.

PubMed

Mahmoudi, Ghodrat; Afkhami, Farhad A; Castiñeiras, Alfonso; García-Santos, Isabel; Gurbanov, Atash; Zubkov, Fedor I; Mitoraj, Mariusz P; Kukułka, Mercedes; Sagan, Filip; Szczepanik, Dariusz W; Konyaeva, Irina A; Safin, Damir A

2018-04-16

We report the design as well as structural and spectroscopic characterizations of two new coordination compounds obtained from Cd(NO 3 ) 2 ·4H 2 O and polydentate ligands, benzilbis(pyridin-2-yl)methylidenehydrazone (L I ) and benzilbis(acetylpyridin-2-yl)methylidenehydrazone (L II ), in a mixture with two equivalents of NH 4 NCS in MeOH, namely [Cd(SCN)(NCS)(L I )(MeOH)] (1) and [Cd(NCS) 2 (L II )(MeOH)] (2). Both L I and L II are bound via two pyridyl-imine units yielding a tetradentate coordination mode giving rise to the 12 π electron chelate ring. It has been determined for the first time (qualitatively and quantitatively), using the EDDB electron population-based method, the HOMA index, and the ETS-NOCV charge and energy decomposition scheme, that the chelate ring containing Cd II can be classified as a quasi-aromatic Möbius motif. Notably, using the methyl-containing ligand L II controls the exclusive presence of the NCS - connected with the Cd II atom (structure 2), while applying L I allows us to simultaneously coordinate NCS - and SCN - ligands (structure 1). Both systems are stabilized mostly by hydrogen bonding, C-H···π interactions, aromatic π···π stacking, and dihydrogen C-H···H-C bonds. The optical properties have been investigated by diffused reflectance spectroscopy as well as molecular and periodic DFT/TD-DFT calculations. The DFT-based ETS-NOCV analysis as well as periodic calculations led us to conclude that the monomers which constitute the obtained chelates are extremely strongly bonded to each other, and the calculated interaction energies are found to be in the regime of strong covalent connections. Intramolecular van der Waals dispersion forces, due to the large size of L I and L II , appeared to significantly stabilize these systems as well as amplify the aromaticity phenomenon.

The influence of arene-ring size on stacking interaction with canonical base pairs

NASA Astrophysics Data System (ADS)

Formánek, Martin; Burda, Jaroslav V.

2014-04-01

Stacking interactions between aromatic molecules (benzene, p-cymene, biphenyl, and di- and tetra-hydrogen anthracene) and G.C and A.T canonical Watson-Crick (WC) base pairs are explored. Two functionals with dispersion corrections: ω-B97XD and B3LYP-D3 are used. For a comparison also the MP2 and B3LYP-D3/PCM methods were used for the most stable p-cymene…WC geometries. It was found that the stacking interaction increases with the size of π-conjugation system. Its extent is in agreement with experimental finding on anticancer activity of Ru(II) piano-stool complexes where intercalation of these aromatic molecules should play an important role. The explored structures are considered as ternary system so that decomposition of the interaction energy to pairwise and non-additivity contributions is also examined.

Mechanism of alkoxy groups substitution by Grignard reagents on aromatic rings and experimental verification of theoretical predictions of anomalous reactions.

PubMed

Jiménez-Osés, Gonzalo; Brockway, Anthony J; Shaw, Jared T; Houk, K N

2013-05-01

The mechanism of direct displacement of alkoxy groups in vinylogous and aromatic esters by Grignard reagents, a reaction that is not observed with expectedly better tosyloxy leaving groups, is elucidated computationally. The mechanism of this reaction has been determined to proceed through the inner-sphere attack of nucleophilic alkyl groups from magnesium to the reacting carbons via a metalaoxetane transition state. The formation of a strong magnesium chelate with the reacting alkoxy and carbonyl groups dictates the observed reactivity and selectivity. The influence of ester, ketone, and aldehyde substituents was investigated. In some cases, the calculations predicted the formation of products different than those previously reported; these predictions were then verified experimentally. The importance of studying the actual system, and not simplified models as computational systems, is demonstrated.

Mechanism of Alkoxy Groups Substitution by Grignard Reagents on Aromatic Rings and Experimental Verification of Theoretical Predictions of Anomalous Reactions

PubMed Central

Jiménez-Osés, Gonzalo; Brockway, Anthony J.; Shaw, Jared T.; Houk, K. N.

2013-01-01

The mechanism of direct displacement of alkoxy groups in vinylogous and aromatic esters by Grignard reagents, a reaction that is not observed with expectedly better tosyloxy leaving groups, is elucidated computationally. The mechanism of this reaction has been determined to proceed through the inner-sphere attack of nucleophilic alkyl groups from magnesium to the reacting carbons via a metalaoxetane transition state. The formation of a strong magnesium chelate with the reacting alkoxy and carbonyl groups dictates the observed reactivity and selectivity. The influence of ester, ketone and aldehyde substituents was investigated. In some cases, the calculations predicted the formation of products different than those previously reported; these predictions were then verified experimentally. The importance of studying the actual system, and not simplified models as computational systems, is demonstrated. PMID:23601086

(S)-N-{1-[5-(4-Chloro-benzyl-sulfanyl)-1,3,4-oxadiazol-2-yl]eth-yl}-4-methyl-benzene-sulfonamide.

PubMed

Syed, Tayyaba; Hameed, Shahid; Jones, Peter G

2011-10-01

The title compound, C(18)H(18)ClN(3)O(3)S(2), adopts by folding the form of a distorted disc. Inter-planar angles are 29.51 (7) and 63.43 (7)° from the five-membered ring to the aromatic systems and 34.80 (6)° between these two latter rings. The absolute configuration was confirmed by determination of the Flack parameter. In the crystal, the mol-ecules are linked by four hydrogen bonds, one classical (N-H⋯N) and three 'weak' (C-H⋯O), forming layers parallel to the ac plane; these are in turn linked in the third dimension by Cl⋯N [3.1689 (16) Å] and Cl⋯O [3.3148 (13) Å] contacts to the heterocyclic ring.

Crystal structure of N-{[3-bromo-1-(phenyl-sulfon-yl)-1H-indol-2-yl]meth-yl}benzene-sulfonamide.

PubMed

Umadevi, M; Raju, P; Yamuna, R; Mohanakrishnan, A K; Chakkaravarthi, G

2015-10-01

In the title compound, C21H17BrN2O4S2, the indole ring system subtends dihedral angles of 85.96 (13) and 9.62 (16)° with the planes of the N- and C-bonded benzene rings, respectively. The dihedral angles between the benzene rings is 88.05 (17)°. The mol-ecular conformation is stabilized by intra-molecular N-H⋯O and C-H⋯O hydrogen bonds and an aromatic π-π stacking [centroid-to-centroid distance = 3.503 (2) Å] inter-action. In the crystal, short Br⋯O [2.9888 (18) Å] contacts link the mol-ecules into [010] chains. The chains are cross-linked by weak C-H⋯π inter-actions, forming a three-dimensional network.

Function of Coenzyme F420 in Aerobic Catabolism of 2,4,6-Trinitrophenol and 2,4-Dinitrophenol by Nocardioides simplex FJ2-1A

PubMed Central

Ebert, Sybille; Rieger, Paul-Gerhard; Knackmuss, Hans-Joachim

1999-01-01

2,4,6-Trinitrophenol (picric acid) and 2,4-dinitrophenol were readily biodegraded by the strain Nocardioides simplex FJ2-1A. Aerobic bacterial degradation of these π-electron-deficient aromatic compounds is initiated by hydrogenation at the aromatic ring. A two-component enzyme system was identified which catalyzes hydride transfer to picric acid and 2,4-dinitrophenol. Enzymatic activity was dependent on NADPH and coenzyme F420. The latter could be replaced by an authentic preparation of coenzyme F420 from Methanobacterium thermoautotrophicum. One of the protein components functions as a NADPH-dependent F420 reductase. A second component is a hydride transferase which transfers hydride from reduced coenzyme F420 to the aromatic system of the nitrophenols. The N-terminal sequence of the F420 reductase showed high homology with an F420-dependent NADP reductase found in archaea. In contrast, no N-terminal similarity to any known protein was found for the hydride-transferring enzyme. PMID:10217752

Separation and characterization of polycyclic aromatic hydrocarbons and alkylphenols in coal derived solvents

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

Hurtubise, R.J.; Allen, T.W.; Hussain, A.

1981-03-29

Dry-column chromatography with an aluminum oxide stationary phase and a n-hexane-ether (19:1) mobile phase was used to separate polycyclic aromatic hydrocarbons (PAH) by ring size. Prior to the dry-column chromatography step, the coal derived solvents were added to an acid treated silica gel column and eluted with chloroform. This step removed pyridine-type nitrogen heterocycles. After separation of the individual ring fractions, the fractions were further separated by either thin layer chromatography (TLC) or high performance liquid chromatography (HPLC). If TLC was used, then after separation fluorescence profiles of each PAH ring fraction distributed on 30%-acetylated cellulose chromatoplates were obtained withmore » a spectrodensitometer. Measurement of fluorescence peak heights gave an approximate measure of the amount of the 3-, 4-, 5-, and 6- ring PAH. For HPLC separation, the 3- and 4- ring PAH fractions obtained from the dry-column chromatography step were separated with a ..mu..-Bondapak C/sub 18/ column and methanol:water (65:35) mobile phase. The HPLC separated PAH were characterized by chromatographic correlation factors and corrected fluorescence excitation spectra. Alkylphenols were identified in coal recycle solvent sample following separation by HPLC.« less

Formation and characterization of a multicomponent equilibrium system derived from cis- and trans-1-aminomethylcyclohexane-1,2-diol.

PubMed

Hetényi, Anasztázia; Szakonyi, Zsolt; Klika, Karel D; Pihlaja, Kalevi; Fülöp, Ferenc

2003-03-21

Both cis and trans isomers of amino diols 3-6 were prepared stereoselectively. In the reactions between 3-6 and phenyl isothiocyanate, the ring closure proceeded regioselectively and resulted only in spiro derivatives of 2-phenyliminooxazolidines 9, 10, 13, and 14. The reaction of cis- (or trans-)1-aminomethylcyclohexane-1,2-diol 4 (or 6) with 1 equiv of an aromatic aldehyde 15a-g in EtOH at room temperature resulted in a complex, multicomponent equilibrium mixture of 16a-g and 18a-g (or 17a-g and 19a-g), in each case consisting of a five-component, ring-chain tautomeric system 16A-E (or 17A-E), involving the Schiff base, two epimeric spirooxazolidines, two epimeric condensed 1,3-oxazines, and some of the four tricyclic compounds 18A-D (or 19A-D). The five-component, ring-chain equilibria were found to be adequately described by the Hammett-Brown linear free energy equation.

Analysis of polycyclic aromatic hydrocarbons in tree-rings of Masson pine (Pinus massoniana L.) from two industrial sites in the Pearl River Delta, south China.

PubMed

Kuang, Yuan-wen; Zhou, Guo-yi; Wen, Da-zhi; Li, Jiong; Sun, Fang-fang

2011-09-01

Concentrations of polycyclic aromatic hydrocarbons (PAHs) were examined and potential sources of PAHs were identified from the dated tree-rings of Masson pine (Pinus massoniana L.) near two industrial sites (Danshuikeng, DSK and Xiqiaoshan, XQS) in the Pearl River Delta of south China. Total concentrations of PAHs (∑PAHs) were revealed with similar patterns of temporal trends in the tree-rings at both sites, suggesting tree-rings recorded the historical variation in atmospheric PAHs. The differences of individual PAHs and of ∑PAHs detected in the tree-rings between the two sites reflected the historical differences of airborne PAHs. Regional changes in industrial activities might contribute to the site-specific and period-specific patterns of the tree-ring PAHs. The diagnostic PAH ratios of Ant/(Ant + PA), FL/(FL + Pyr), and BaA/(BaA + Chr)) revealed that PAHs in the tree-rings at both sites mainly stemmed from the combustion process (pyrogenic sources). Principal component analysis further confirmed that wood burning, coal combustion, diesel, and gasoline-powered vehicular emissions were the dominant contributors of PAHs sources at DSK, while diesel combustion, gasoline and natural gas combustion, and incomplete coal combustion were responsible for the main origins of PAHs at XQS. Tree-ring analysis of PAHs was indicative of PAHs from a mixture of sources of combustion, thus minimizing the bias of short-term active air sampling.

Chlorination of lignin by ubiquitous fungi has a likely role in global organochlorine production

Treesearch

Patricia Ortiz-Bermudez; Kolby C. Hirth; Ewald Srebotnik; Kenneth E. Hammel

2007-01-01

Soils and decayed plant litter contain significant quantities of chlorinated aromatic polymers that have a natural but largely unknown origin. We used cupric oxide ligninolysis coupled with gas chromatography/mass spectrometry to show that Curvularia inaequalis, a widely distributed litter ascomycete, chlorinated the aromatic rings of lignin in wood that it was...

Influence of fused aromatic ring on the stability of charge transfer complex between iodine and some five membered heterocyclic molecules through ultrasonic and spectral studies

NASA Astrophysics Data System (ADS)

Ulagendran, V.; Balu, P.; Kannappan, V.; Kumar, R.; Jayakumar, S.

2017-08-01

The charge transfer (CT) interaction between two fused heterocyclic compounds with basic pyrrole group as donors, viz., indole (IND) and carbazole (CAR), and iodine (acceptor) in DMSO medium is investigated by ultrasonic and UV-visible spectral methods at 303 K. The formation of CT complex in these systems is established from the trend in acoustical and excess thermo acoustical properties with molar concentration. The frequency acoustic spectra (FAS) is also carried out on these two systems for two fixed concentrations 0.002 M and 0.02 M, and in the frequency range 1 MHz-10 MHz to justify the frequency chosen for ultrasonic study. The absorption coefficient values in solution are computed and discussed. The formation constants of these complexes are determined using Kannappan equation in ultrasonic method. The formation of 1:1 complexes between iodine and IND, CAR was established by the theory of Benesi - Hildebrand in the UV-visible spectroscopic method. The stability constants of the CT complexes determined by spectroscopic and ultrasonic methods show a similar trend. These values also indicate that the presence of fused aromatic ring influences significantly when compared with K values of similar CT complexes of parent five membered heterocyclic compound (pyrrole) reported by us earlier.

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

Ijam, M.J.; Al-Qatami, S.Y.; Arif, S.F.

For several decades removal of aromatics from crude oil fractions has been practiced in oil refining to produce fuels and lubricants of lower aromatic content and hence of improved quality. These aromatics are suitable raw materials for the manufacture of aromatic solvents, aromatic process oils, high octane gasoline, and as basic materials for making detergents, perfumes and dyes. A study for the UV and IR spectra of the aromatic hydrocarbons showed them to consist mainly of bi-, tri-, tetra-, and penta-substituted benzene, bicyclic and tricyclic compounds. Detailed studies have been reported of molecular structure and substituent effects have been reportedmore » on the retention characteristics of aromatic hydrocarbons on alumina, silica and various chemically bonded silicas containing {minus}C{sub 18}, {minus}NH{sub 2}, {minus}R(NH){sub 2}, {minus}CN, RCN, and phenyl-mercuric acetate for compound class (ring-numbered) high performance liquid chromatography separation. With the aid of a Finnegan type 9612-4000 GC/MS apparatus, the mixture of neutral + basic aromatic hydrocarbons was qualitatively identified and revealed the presence of more than 112 peaks. The neutral + basic aromatic hydrocarbons consist mainly of: 3.68% monoaromatics (C{sub 3} - C{sub 6} alkyl benzenes), 52.81% bicycloaromatics (C{sub 0} - C{sub 4} alkylnaphthalenes), 6.20% tricycloaromatics (C{sub 0} - C{sub 4} alkyl phenanthrenes), and 37.32% nonhydrocarbons aromatic compounds. The components in major HPLC peaks corresponding to bicycloaromatics were further separated into small groups (3-4 components in each) by HPLC using an ODS-reverse phase-C{sub 18} column. To separate a single component from the mixture is a difficult problem. The individual compounds in the separated fractions were identified by GC/MS (Hewlett Packard 5993 system).« less

Aromatic aldehyde-catalyzed gas-phase decarboxylation of amino acid anion via imine intermediate: An experimental and theoretical study

NASA Astrophysics Data System (ADS)

Xiang, Zhang

2013-10-01

It is generally appreciated that carbonyl compound can promote the decarboxylation of the amino acid. In this paper, we have performed the experimental and theoretical investigation into the gas-phase decarboxylation of the amino acid anion catalyzed by the aromatic aldehyde via the imine intermediate on the basis of the tandem mass spectrometry (MS/MS) technique and density functional theory (DFT) calculation. The results show that the aromatic aldehyde can achieve a remarkable catalytic effect. Moreover, the catalytic mechanism varies according to the type of amino acid: (i) The decarboxylation of α-amino acid anion is determined by the direct dissociation of the Csbnd C bond adjacent to the carboxylate, for the resulting carbanion can be well stabilized by the conjugation between α-carbon, Cdbnd N bond and benzene ring. (ii) The decarboxylation of non-α-amino acid anion proceeds via a SN2-like transition state, in which the dissociation of the Csbnd C bond adjacent to the carboxylate and attacking of the resulting carbanion to the Cdbnd N bond or benzene ring take place at the same time. Specifically, for β-alanine, the resulting carbanion preferentially attacks the benzene ring leading to the benzene anion, because attacking the Cdbnd N bond in the decarboxylation can produce the unstable three or four-membered ring anion. For the other non-α-amino acid anion, the Cdbnd N bond preferentially participates in the decarboxylation, which leads to the pediocratic nitrogen anion.

Oxidations of N-(3-indoleethyl) cyclic aliphatic amines by horseradish peroxidase: the indole ring binds to the enzyme and mediates electron-transfer amine oxidation.

PubMed

Ling, Ke-Qing; Li, Wen-Shan; Sayre, Lawrence M

2008-01-23

Although oxidations of aromatic amines by horseradish peroxidase (HRP) are well-known, typical aliphatic amines are not substrates of HRP. In this study, the reactions of N-benzyl and N-methyl cyclic amines with HRP were found to be slow, but reactions of N-(3-indoleethyl) cyclic amines were 2-3 orders of magnitude faster. Analyses of pH-rate profiles revealed a dominant contribution to reaction by the amine-free base forms, the only species found to bind to the enzyme. A metabolic study on a family of congeneric N-(3-indoleethyl) cyclic amines indicated competition between amine and indole oxidation pathways. Amine oxidation dominated for the seven- and eight-membered azacycles, where ring size supports the change in hybridization from sp3 to sp2 that occurs upon one-electron amine nitrogen oxidation, whereas only indole oxidation was observed for the six-membered ring congener. Optical difference spectroscopic binding data and computational docking simulations suggest that all the arylalkylamine substrates bind to the enzyme through their aromatic termini with similar binding modes and binding affinities. Kinetic saturation was observed for a particularly soluble substrate, consistent with an obligatory role of an enzyme-substrate complexation preceding electron transfer. The significant rate enhancements seen for the indoleethylamine substrates suggest the ability of the bound indole ring to mediate what amounts to medium long-range electron-transfer oxidation of the tertiary amine center by the HRP oxidants. This is the first systematic investigation to document aliphatic amine oxidation by HRP at rates consistent with normal metabolic turnover, and the demonstration that this is facilitated by an auxiliary electron-rich aromatic ring.

Contraction of π-Conjugated Rings upon Oxidation from Cyclooctatetraene to Benzene via the Tropylium Cation.

PubMed

Tamoto, Akira; Aratani, Naoki; Yamada, Hiroko

2017-11-16

We have serendipitously discovered a unique transformation of a cyclooctatetraene derivative 1 into a cycloheptatriene spirolactone 3 upon oxidation, which is the first such transformation reported in 60 years. Product 3 could be reversibly interconverted into the aromatic tropylium cation 3H + by acid/base treatment, which was accompanied by drastic spectroscopic changes. The resultant cycloheptatriene could be further converted into benzene upon oxidation. We characterized all the key structures by X-ray studies. Eventually, the π-conjugated ring size shrinks from 8 to 7, then finally to 6 upon oxidation, in the direction of the stronger aromatization. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Crystal structure of 3-(2,5-di-meth-oxy-phen-yl)propionic acid.

PubMed

Bugenhagen, Bernhard; Al Jasem, Yosef; AlAzani, Mariam; Thiemann, Thies

2015-05-01

In the crystal of the title compound, C11H14O4, the aromatic ring is almost coplanar with the 2-position meth-oxy group with which it subtends a dihedral of 0.54 (2)°, while the 5-position meth-oxy group makes a corresponding dihedral angle of just 5.30 (2)°. The angle between the mean planes of the aromatic ring and the propionic acid group is 78.56 (2)°. The fully extended propionic side chain is in a trans configuration with a C-C-C-C torsion angle of -172.25 (7)°. In the crystal, hydrogen bonding is limited to dimer formation via R 2 (2)(8) rings. The hydrogen-bonded dimers are stacked along the b axis. The average planes of the two benzene rings in a dimer are parallel to each other, but at an offset of 4.31 (2) Å. Within neighbouring dimers along the [101] direction, the average mol-ecular benzene planes are almost perpendicular to each other, with a dihedral angle of 85.33 (2)°.

Selective Ring Opening of 1-Methylnaphthalene Over NiW-Supported Catalyst Using Dealuminated Beta Zeolite.

PubMed

Kim, Eun-Sang; Lee, You-Jin; Kim, Jeong-Rang; Kim, Joo-Wan; Kim, Tae-Wan; Chae, Ho-Jeong; Kim, Chul-Ung; Lee, Chang-Ha; Jeong, Soon-Yong

2016-02-01

Nanoporous Beta zeolite was dealuminated by weak acid treatment for reducing the acidity. Bi-functional catalysts were prepared using commercial Beta zeolites and the dealuminated zeolites for acidic function, NiW for metallic function. 1-Methylnaphthalene was selected as a model compound for multi-ring aromatics in heavy oil, and its selective ring opening reaction has been investigated using the prepared bi-functional catalysts with different acidity in fixed bed reaction system. The dealuminated Beta zeolites, which crystal structure and nanoporosity were maintained, showed the higher SiO2/Al2O3 ratio and smaller acidity than their original zeolite. NiW-supported catalyst using the dealuminated Beta zeolite with SiO2/Al203 mole ratio of 55 showed the highest performance for the selective ring opening. The acidity of catalyst seemed to play an important role as active sites for the selective ring opening of 1-methylnaphthalene but there should be some optimum catalyst acidity for the reaction. The acidity of Beta zeolite could be controlled by the acid treatment and the catalyst with the optimum acidity for the selective ring opening could be prepared.

Studies Toward the Total Synthesis of Eletefine

NASA Astrophysics Data System (ADS)

Rugg, Kyle William

Eletefine is a natural product of the stephaoxocane family of alkaloids. It possesses an isoquinoline moiety functionalized with three methoxy groups forming an electron rich aromatic system. Eletefine also possesses a ten-membered ring with a novel bridged vinyl ether functionality, and a remote chiral alcohol, making it a conspicuous and desirable target for the synthetic organic chemist. The plant from which eletefine was first isolated (Cissampelos glaberrima ) has been used in traditional medicine for the relief of symptoms from urinary tract infections and asthma. The proposed synthesis of eletefine is a convergent route which features a Sonogashira coupling and a novel alkyne hydration. Herein, methods towards the synthesis of the model system des-hydroxyeletefine are described, in particular attempts towards formation of the AB ring system of des-hydroxyeletefine, as well as C8-C9 bond formation methodology via acylation and Sonogashira coupling.

Single kernel method for detection of 2-acetyl-1-pyrroline in aromatic rice germplasm using SPME-GC/MS

USDA-ARS?s Scientific Manuscript database

INTRODUCTION Aromatic rice or fragrant rice, (Oryza sativa L.), has a strong popcorn-like aroma due to the presence of a five-membered N-heterocyclic ring compound known as 2-acetyl-1-pyrroline (2-AP). To date, existing methods for detecting this compound in rice require the use of several kernels. ...

Fungal lactone ring opening of 6', 7'-dihydroxybergamottin diminishes cytochrome P450 3A4 inhibitory activity

USDA-ARS?s Scientific Manuscript database

Furanocoumarins (FCs) are a class of aromatic compounds in grapefruit that inhibit human intestinal cytochrome P450 3A4 (CYP3A4). Since fungi metabolize polycyclic aromatic hydrocarbons, we hypothesized that certain fungi might also metabolize FCs into forms that may be inactive as CYP3A4 inhibitors...

Aerobic Biodegradation of Trichloroethylene.

DTIC Science & Technology

1987-07-01

into C02 and unidentified nonvolatile products. Phenol, 41 toiin- andq- cresol were found to replace the site water requirement for TCE metabolism...identified as phenol. Other aromatic compounds that could support TCE degradation were toluene, o- cresol , and m- cresol . The degradation could be...Production...... .. .. .. . 17 4. Test for the Catechol Ortho °Ring-Fission Pathway . 18 5. Oxidation of Aromatic Compounds ............. .18 6

Research to Significantly Enhance Composite Survivability at 550 F in Oxidative Environments

NASA Technical Reports Server (NTRS)

Byrd, Jim; Guinn, LaToya; Tilley, Kendra; Carson, Laura; Carty, Antoine; Meador, Michael (Technical Monitor)

2001-01-01

Prairie View A&M University using the NASA FAR grant has embarked on several paths to accomplish the initial goals of: (1) synthesizing three ring aromatic diamines to be used as monomers in the synthesis of polyamide resins; and (2) study hydrothermal aging behaviors and glass transition changes of composites synthesized at NASA Glenn Research Center. In establishing the synthesis of the three ring aromatic diamine, it has become necessary to conduct preliminary synthesis to include the nitration of diphenylmethane. The concentration and temperature were altered to assess the effect of purity of isomeric product distribution in such electrophilic aromatic substitution reaction. Products were analyzed using H and C-NMR, Thin Layer Chromatography, High Pressure Liquid Chromatography and GC-Mass Spectrometry (in progress). Results indicate that by varying the concentration of the reaction, a mixture of products can be obtained. Other electrophilic aromatic substitution reactions are also in progress such as Friedel-Craft acylation reaction using diphenylmethane with 4-nitrobenzoyl chloride to afford other diamine products. Furthermore, PVAMU has nearly completed the hydrothermal studies to assess the oxidative stability of DSP443B and DSP442A panels formulated at NASA Glenn Research Center.

Effect of collector molecular structure on the wettability of gold for froth flotation

NASA Astrophysics Data System (ADS)

Moncayo-Riascos, Ivan; Hoyos, Bibian A.

2017-10-01

Molecular dynamics simulations were conducted to evaluate the alteration of the hydrophilic state of gold surfaces caused by the adsorption of collectors with different molecular structures, using the contact angle of water droplets as an evaluation parameter. Four collectors were evaluated: SDS (with twelve hydrogenated carbon atoms), PAX (with five hydrogenated carbon atoms), DTP (with two branched aliphatic chains) and MBT (with an aromatic ring). The contact angle was evaluated for coatings of a monolayer (ML) and for surface densities of 2.89 μmol/m2 for each collector. For a ML, the hydrophobic effect generated by the aromatic ring of the MBT collector is comparable with the effect of the non-polar short chain of the PAX collector. The increase in hydrophobicity for the gold surfaces achieved by collectors with aliphatic chains is because the water-collector interaction energy is significantly higher (repulsive) than the water-gold interactions (attractive). The lowest increase in hydrophobicity was achieved with the MBT collector, since the carbon-water interaction energy of the aromatic ring is stronger than the interaction with the carbon atoms in the aliphatic chains. The calculated contact angles of the water droplets deviated less than 4% with respect to the experimental values.

Adsorbed States of phosphonate derivatives of N-heterocyclic aromatic compounds, imidazole, thiazole, and pyridine on colloidal silver: comparison with a silver electrode.

PubMed

Podstawka, Edyta; Olszewski, Tomasz K; Boduszek, Bogdan; Proniewicz, Leonard M

2009-09-03

Here, we report a systematic surface-enhanced Raman spectroscopy (SERS) study of the structures of phosphonate derivatives of the N-heterocyclic aromatic compounds imidazole (ImMeP ([hydroxy(1H-imidazol-5-yl)methyl]phosphonic acid) and (ImMe)(2)P (bis[hydroxy-(1H-imidazol-4-yl)-methyl]phosphinic acid)), thiazole (BAThMeP (butylaminothiazol-2-yl-methyl)phosphonic acid) and BzAThMeP (benzylaminothiazol-2-yl-methyl)phosphonic acid)), and pyridine ((PyMe)(2)P (bis[(hydroxypyridin-3-yl-methyl)]phosphinic acid)) adsorbed on nanometer-sized colloidal particles. We compared these structures to those on a roughened silver electrode surface to determine the relationship between the adsorption strength and the geometry. For example, we showed that all of these biomolecules interact with the colloidal surface through aromatic rings. However, for BzAThMeP, a preferential interaction between the benzene ring and the colloidal silver surface is observed more so than that between the thiazole ring and this substrate. The PC(OH)C fragment does not take part in the adsorption process, and the phosphonate moiety of ImMeP and (ImMe)(2)P, being removed from the surface, only assists in this process.

NMR studies of multiple conformations in complexes of Lactobacillus casei dihydrofolate reductase with analogues of pyrimethamine

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

Birdsall, B.; Tendler, S.J.B.; Feeney, J.

1990-10-01

{sup 1}H and {sup 19}F NMR signals from bound ligands have been assigned in one- and two-dimensional NMR spectra of complexes of Lactobacillus casei dihydrofolate reductase with various pyrimethamine analogues. The signals were identified mainly by correlating signals from bound and free ligands by using 2D exchange experiments. Analogues with symmetrically substituted phenyl rings give rise to {sup 1}H signals from four nonequivalent aromatic protons, clearly indicating the presence of hindered rotation about the pyrimidine-phenyl bond. Analogues with symmetrically substituted phenyl rings give rise to {sup 1}H signals from four nonequivalent aromatic protons, clearly indicating the presence of hindered rotationmore » about the pyrimidine-phenyl bond. Analogues containing asymmetrically substituted aromatic rings exist as mixtures of two rotational isomers (an enantiomeric pair) because of this hindered rotation and the NMR spectra revealed that both isomers (forms A and B) bind to the enzyme with comparable, though unequal, binding energies. In this case two complete sets of bound proton signals were observed. The relative orientations of the two forms have been determined from NOE through-space connections between protons on the ligand and protein. Ternary complexes with NADP{sup {plus}} were also examined.« less

Quantized Self-Assembly of Discotic Rings in a Liquid Crystal Confined in Nanopores

NASA Astrophysics Data System (ADS)

Sentker, Kathrin; Zantop, Arne W.; Lippmann, Milena; Hofmann, Tommy; Seeck, Oliver H.; Kityk, Andriy V.; Yildirim, Arda; Schönhals, Andreas; Mazza, Marco G.; Huber, Patrick

2018-02-01

Disklike molecules with aromatic cores spontaneously stack up in linear columns with high, one-dimensional charge carrier mobilities along the columnar axes, making them prominent model systems for functional, self-organized matter. We show by high-resolution optical birefringence and synchrotron-based x-ray diffraction that confining a thermotropic discotic liquid crystal in cylindrical nanopores induces a quantized formation of annular layers consisting of concentric circular bent columns, unknown in the bulk state. Starting from the walls this ring self-assembly propagates layer by layer towards the pore center in the supercooled domain of the bulk isotropic-columnar transition and thus allows one to switch on and off reversibly single, nanosized rings through small temperature variations. By establishing a Gibbs free energy phase diagram we trace the phase transition quantization to the discreteness of the layers' excess bend deformation energies in comparison to the thermal energy, even for this near room-temperature system. Monte Carlo simulations yielding spatially resolved nematic order parameters, density maps, and bond-orientational order parameters corroborate the universality and robustness of the confinement-induced columnar ring formation as well as its quantized nature.

Microwave-Assisted Synthesis of Phenothiazine and Quinoline Derivatives

PubMed Central

Găină, Luiza; Cristea, Castelia; Moldovan, Claudia; Porumb, Dan; Surducan, Emanoil; Deleanu, Călin; Mahamoud, Abdalah; Barbe, Jacques; Silberg, Ioan A.

2007-01-01

Application of a dynamic microwave power system in the chemical synthesis of some phenothiazine and quinoline derivatives is described. Heterocyclic ring formation, aromatic nucleophilic substitution and heterocyclic aldehydes/ketones condensation reactions were performed on solid support, or under solvent free reaction conditions. The microwave-assisted Duff formylation of phenothiazine was achieved. Comparison of microwave-assisted synthesis with the conventional synthetic methods demonstrates advantages related to shorter reaction times and in some cases better reaction yields.

Photophysical Properties on Functional Pi-Electronic Molecular Systems

DTIC Science & Technology

2012-08-01

the aromaticity; i) it is possible to control the number of conjugated π-electrons by changing the number of connected pyrrole rings, ii) by...flexibilities, and facile capture and release of two pyrrolic protons upon two-electron oxidation and reduction, respectively. Scheme 2. (a...nitrogen atoms of pyrrole A, B, C and D, and the ortho-carbon atom of meso-pentafluorophenyl group in a trigonal bipyramidal manner. The 1 H NMR spectrum

Application of SAIL phenylalanine and tyrosine with alternative isotope-labeling patterns for protein structure determination.

PubMed

Takeda, Mitsuhiro; Ono, Akira M; Terauchi, Tsutomu; Kainosho, Masatsune

2010-01-01

The extensive collection of NOE constraint data involving the aromatic ring signals is essential for accurate protein structure determination, although it is often hampered in practice by the pervasive signal overlapping and tight spin couplings for aromatic rings. We have prepared various types of stereo-array isotope labeled phenylalanines (epsilon- and zeta-SAIL Phe) and tyrosine (epsilon-SAIL Tyr) to overcome these problems (Torizawa et al. 2005), and proven that these SAIL amino acids provide dramatic spectral simplification and sensitivity enhancement for the aromatic ring NMR signals. In addition to these SAIL aromatic amino acids, we recently synthesized delta-SAIL Phe and delta-SAIL Tyr, which allow us to observe and assign delta-(13)C/(1)H signals very efficiently. Each of the various types of SAIL Phe and SAIL Tyr yields well-resolved resonances for the delta-, epsilon- or zeta-(13)C/(1)H signals, respectively, which can readily be assigned by simple and robust pulse sequences. Since the delta-, epsilon-, and zeta-proton signals of Phe/Tyr residues give rise to complementary NOE constraints, the concomitant use of various types of SAIL-Phe and SAIL-Tyr would generate more accurate protein structures, as compared to those obtained by using conventional uniformly (13)C, (15)N-double labeled proteins. We illustrated this with the case of an 18.2 kDa protein, Escherichia coli peptidyl-prolyl cis-trans isomerase b (EPPIb), and concluded that the combined use of zeta-SAIL Phe and epsilon-SAIL Tyr would be practically the best choice for protein structural determinations.

Low-Temperature Molecular Layer Deposition Using Monofunctional Aromatic Precursors and Ozone-Based Ring-Opening Reactions.

PubMed

Svärd, Laura; Putkonen, Matti; Kenttä, Eija; Sajavaara, Timo; Krahl, Fabian; Karppinen, Maarit; Van de Kerckhove, Kevin; Detavernier, Christophe; Simell, Pekka

2017-09-26

Molecular layer deposition (MLD) is an increasingly used deposition technique for producing thin coatings consisting of purely organic or hybrid inorganic-organic materials. When organic materials are prepared, low deposition temperatures are often required to avoid decomposition, thus causing problems with low vapor pressure precursors. Monofunctional compounds have higher vapor pressures than traditional bi- or trifunctional MLD precursors, but do not offer the required functional groups for continuing the MLD growth in subsequent deposition cycles. In this study, we have used high vapor pressure monofunctional aromatic precursors in combination with ozone-triggered ring-opening reactions to achieve sustained sequential growth. MLD depositions were carried out by using three different aromatic precursors in an ABC sequence, namely with TMA + phenol + O 3 , TMA + 3-(trifluoromethyl)phenol + O 3 , and TMA + 2-fluoro-4-(trifluoromethyl)benzaldehyde + O 3 . Furthermore, the effect of hydrogen peroxide as a fourth step was evaluated for all studied processes resulting in a four-precursor ABCD sequence. According to the characterization results by ellipsometry, infrared spectroscopy, and X-ray reflectivity, self-limiting MLD processes could be obtained between 75 and 150 °C with each of the three aromatic precursors. In all cases, the GPC (growth per cycle) decreased with increasing temperature. In situ infrared spectroscopy indicated that ring-opening reactions occurred in each ABC sequence. Compositional analysis using time-of-flight elastic recoil detection indicated that fluorine could be incorporated into the film when 3-(trifluoromethyl)phenol and 2-fluoro-4-(trifluoromethyl)benzaldehyde were used as precursors.

Control of π-Electron Rotations in Chiral Aromatic Molecules Using Intense Laser Pulses

NASA Astrophysics Data System (ADS)

Kanno, Manabu; Kono, Hirohiko; Fujimura, Yuichi

Our recent theoretical studies on laser-induced π-electron rotations in chiral aromatic molecules are reviewed. π electrons of a chiral aromatic molecule can be rotated along its aromatic ring by a nonhelical, linearly polarized laser pulse. An ansa aromatic molecule with a six-membered ring, 2,5-dichloro[n](3,6) pyrazinophane, which belongs to a planar-chiral molecule group, and its simplified molecule 2,5-dichloropyrazine are taken as model molecules. Electron wavepacket simulations in the frozen-molecular-vibration approximation show that the initial direction of π-electron rotation depends on the polarization direction of a linearly polarized laser pulse applied. Consecutive unidirectional rotation can be achieved by applying a sequence of linearly polarized pump and dump pulses to prevent reverse rotation. Optimal control simulations of π-electron rotation show that another controlling factor for unidirectional rotation is the relative optical phase between the different frequency components of an incident pulse in addition to photon polarization direction. Effects of nonadiabatic coupling between π-electron rotation and molecular vibrations are also presented, where the constraints of the frozen approximation are removed. The angular momentum gradually decays mainly owing to nonadiabatic coupling, while the vibrational amplitudes greatly depend on their rotation direction. This suggests that the direction of π-electron rotation on an attosecond timescale can be identified by detecting femtosecond molecular vibrations.

A preference for edgewise interactions between aromatic rings and carboxylate anions: the biological relevance of anion-quadrupole interactions.

PubMed

Jackson, Michael R; Beahm, Robert; Duvvuru, Suman; Narasimhan, Chandrasegara; Wu, Jun; Wang, Hsin-Neng; Philip, Vivek M; Hinde, Robert J; Howell, Elizabeth E

2007-07-19

Noncovalent interactions are quite important in biological structure-function relationships. To study the pairwise interaction of aromatic amino acids (phenylalanine, tyrosine, tryptophan) with anionic amino acids (aspartic and glutamic acids), small molecule mimics (benzene, phenol or indole interacting with formate) were used at the MP2 level of theory. The overall energy associated with an anion-quadrupole interaction is substantial (-9.5 kcal/mol for a benzene-formate planar dimer at van der Waals contact distance), indicating the electropositive ring edge of an aromatic group can interact with an anion. Deconvolution of the long-range coplanar interaction energy into fractional contributions from charge-quadrupole interactions, higher-order electrostatic interactions, and polarization terms was achieved. The charge-quadrupole term contributes between 30 to 45% of the total MP2 benzene-formate interaction; most of the rest of the interaction arises from polarization contributions. Additional studies of the Protein Data Bank (PDB Select) show that nearly planar aromatic-anionic amino acid pairs occur more often than expected from a random angular distribution, while axial aromatic-anionic pairs occur less often than expected; this demonstrates the biological relevance of the anion-quadrupole interaction. While water may mitigate the strength of these interactions, they may be numerous in a typical protein structure, so their cumulative effect could be substantial.

Catalytic ethanolysis and gasification of kraft lignin into aromatic alcohols and H2-rich gas over Rh supported on La2O3/CeO2-ZrO2.

PubMed

Yang, Jing; Zhao, Liang; Liu, Chunze; Wang, Yuanyuan; Dai, Liyi

2016-10-01

Efficient catalytic ethanolysis and gasification of kraft lignin were conducted over a versatile supported catalyst Rh/La2O3/CeO2-ZrO2 to give high-value aromatic alcohols and H2-rich gas. The removal of phenolic hydroxyl group was the most prevalent reaction, and importantly, almost no phenols, undesired char and saturating the aromatic ring were detected. Meanwhile, the feedstock and solvent both played key roles in H2 generation that contributed to the hydrodeoxygenation of liquid components and made the whole catalytic process out of H2 supply. Reusability tests of catalyst indicated that the crystalline phase transition and agglomeration of support, the loss of noble metal Rh and carbon deposition were the possible reasons for its deactivation in supercritical ethanol. Comparing with water, methanol and isopropanol system, ethanol was the only effective solvent for the depolymerization process. Copyright © 2016 Elsevier Ltd. All rights reserved.

2-[(4-Benzhydrylpipérazin-1-yl)méthyl]acrylonitrile

PubMed Central

Ben Amor, Fatma; Ould M’hamed, Mohamed; Mrabet, Hédi; Driss, Ahmed; Efrit, Mohamed Lotfi

2008-01-01

In the title compound, 2-[(4-benz­hydryl­piperazin-1-yl)­methyl]­acrylo­nitrile, C21H23N3, the substituted piperazine ring adopts a chair conformation and the dihedral angle between the mean planes of the aromatic rings is 71.61 (8)°. PMID:21201087

Aromatic Ring Currents Illustrated--NMR Spectra of Tin(IV) Porphyrin Complexes. An Advanced Undergraduate Experiment.

ERIC Educational Resources Information Center

Arnold, Dennis P.

1988-01-01

Attempts to show that in the closed loops of cyclic structures the protons situated in conic regions above and below the ring will be shielded. Uses the diamagnetic and air stable octahedral tin(IV) complexes of porphyrins for study. Notes complexes crystallize easily and offer spectacular purple colors. (MVL)

NMR analysis and tacticity determination of poly(lactic acid) in C5D5N

USDA-ARS?s Scientific Manuscript database

In this work tacticity assignments of poly(lactic acid), (PLA), are reported for the NMR peaks from CH carbon and CH3 proton at the tetrad level in deuterated pyridine. The methyl protons are better resolved in pyridine due to solvent effects such as ring current shielding of the aromatic ring and ...

Aromaticity of graphene nanoflakes in a new way: fragment analysis by combination of the nucleus-independent chemical shifts and the anisotropy of current induced density.

PubMed

Li, Qing; Li, Chun-Min; Xu, Hong-Liang; Su, Zhong-Min

2017-08-01

A graphene nanoflake (GNF) is a polycyclic aromatic hydrocarbon (PAH) with a huge two-dimensional π-conjugated carbon material in which a central benzene ring is surrounded by identical benzene-type rings through infinite alternant method. In this paper, we explore the structure-aromaticity relationship of the GNFs and the GNFs with hollow sites (GNFHs) by combining the nucleus-independent chemical shifts (NICS) with the anisotropy of the current induced density (ACID). Firstly, the benzene is a typical aromatic molecule (NICS = -9.671 ppm), GNFs 1-6 is darned with benzene and the corresponding GNFHs 1'-6'. Secondly, the NICS values of GNFs 1-6 alternately vary: -1.214 (1) > -13.847 (2) < -2.662 (3) > -14.530 (4) < -3.932 (5) > -13.978 (6) ppm, the GNFs (2, 4, 6) with even fragments of annulene have larger aromaticity than that of GNFs (1, 3, 5) with odd fragments of annulene. Significantly, the NICS values of GNFs 1-6 can also be fragment analyzed by the NICS values and ACID of benzene and corresponding GNFHs 1'-6'. The NICS values for GNFs (2, 4, 6) can be roughly estimated by the NICS value of benzene minus the NICS value of the GNFHs (2', 4', 6'), respectively. The NICS values for GNFs (1, 3, 5) can be roughly estimated by the NICS value of the GNFHs (1', 3', 5') minus the NICS value of benzene, respectively. We hope that the present work can provide a simple and reliable method for the rational design of the GNF with aromaticity, which may be used to understand the origin of the graphene nanoflake aromatic properties.

Polycyclic aromatic hydrocarbons (PAHs) in water from three estuaries of China: Distribution, seasonal variations and ecological risk assessment.

PubMed

Yan, Jinxia; Liu, Jingling; Shi, Xuan; You, Xiaoguang; Cao, Zhiguo

2016-08-15

The distribution, seasonal variations and ecological risk assessment of polycyclic aromatic hydrocarbons (PAHs) in water from three estuaries in Hai River Basin of China, which has been suffering from different anthropogenic pressures, were investigated. In three estuaries, the average concentration of ΣPAHs was the lowest in Luan River estuary, followed by Hai River estuary, and the highest in Zhangweixin River estuary. There were significant seasonal variations in ΣPAHs, the concentrations of ΣPAHs were higher in November than in May and August. The composition profiles of PAHs in different sites were significantly different, and illustrated seasonal variations. Generally, 2-ring (Nap) and 3-ring PAHs (Acp, Fl and Phe) were the most abundant components at most sampling sites in three estuaries. The PAHs in three estuaries were mainly originated from pyrogenic sources. A method based on toxic equivalency factors (TEFs) and risk quotient (RQ) was proposed to assess the ecological risk of ΣPAHs, with the ecological risk of individual PAHs being considered separately. The results showed that the ecological risks caused by ΣPAHs were high in Hai River estuary and Zhangweixin River estuary, and moderate in Luan River estuary. The mean values of ecological risk in August were lower than those in November. The contributions of individual PAHs to ecological risk were different in May, August and November. 3-ring and 4-ring PAHs accounted for much more ecological risk than 2-ring, 5-ring and 6-ring, although the contributions of 5-ring and 6-ring to ecological risk were higher than these to PAHs concentrations. Copyright © 2016 Elsevier Ltd. All rights reserved.

Bond cleavage of lignin model compounds into aromatic monomers using supported metal catalysts in supercritical water

PubMed Central

Yamaguchi, Aritomo; Mimura, Naoki; Shirai, Masayuki; Sato, Osamu

2017-01-01

More efficient use of lignin carbon is necessary for carbon-efficient utilization of lignocellulosic biomass. Conversion of lignin into valuable aromatic compounds requires the cleavage of C–O ether bonds and C–C bonds between lignin monomer units. The catalytic cleavage of C–O bonds is still challenging, and cleavage of C–C bonds is even more difficult. Here, we report cleavage of the aromatic C–O bonds in lignin model compounds using supported metal catalysts in supercritical water without adding hydrogen gas and without causing hydrogenation of the aromatic rings. The cleavage of the C–C bond in bibenzyl was also achieved with Rh/C as a catalyst. Use of this technique may greatly facilitate the conversion of lignin into valuable aromatic compounds. PMID:28387304

Metal-Organic Framework with Aromatic Rings Tentacles: High Sulfur Storage in Li-S Batteries and Efficient Benzene Homologues Distinction.

PubMed

Li, Meng-Ting; Sun, Yu; Zhao, Kai-Sen; Wang, Zhao; Wang, Xin-Long; Su, Zhong-Min; Xie, Hai-Ming

2016-12-07

We designed and fabricated a fluorophore-containing tetradentate carboxylate ligand-based metal-organic framework (MOF) material with open and semiopen channels, which acted as the host for sulfur trapped in Li-S batteries and sensor of benzene homologues. These channels efficiently provide a π-π* conjugated matrix for the charge transfer and guest molecule trapping. The open channel ensured a much higher loading quantitative of sulfur (S content-active material, 72 wt %; electrode, 50.4 wt %) than most of the MOF/sulfur composites, while the semiopen channel possessing aromatic rings tentacles guaranteed an outstanding specific discharge capacity (1092 mA h g -1 at 0.1 C) accompanied by good cycling stability. To our surprise, benefiting from special π-π* conjugated conditions, compound 1 could be a chemical sensor for benzene homologues, especially for 1,2,4-trimethylbenzene (1,2,4-TMB). This is the first example of MOFs materials serving as a sensor of 1,2,4-TMB among benzene homologues. Our works may be worthy of use for references in other porous materials systems to manufacture more long-acting Li-S batteries and sensitive chemical sensors.

Energetic factors determining the binding of type I inhibitors to c-Met kinase: experimental studies and quantum mechanical calculations

PubMed Central

Yu, Zhe; Ma, Yu-chi; Ai, Jing; Chen, Dan-qi; Zhao, Dong-mei; Wang, Xin; Chen, Yue-lei; Geng, Mei-yu; Xiong, Bing; Cheng, Mao-sheng; Shen, Jing-kang

2013-01-01

Aim: To decipher the molecular interactions between c-Met and its type I inhibitors and to facilitate the design of novel c-Met inhibitors. Methods: Based on the prototype model inhibitor 1, four ligands with subtle differences in the fused aromatic rings were synthesized. Quantum chemistry was employed to calculate the binding free energy for each ligand. Symmetry-adapted perturbation theory (SAPT) was used to decompose the binding energy into several fundamental forces to elucidate the determinant factors. Results: Binding free energies calculated from quantum chemistry were correlated well with experimental data. SAPT calculations showed that the predominant driving force for binding was derived from a sandwich π–π interaction with Tyr-1230. Arg-1208 was the differentiating factor, interacting with the 6-position of the fused aromatic ring system through the backbone carbonyl with a force pattern similar to hydrogen bonding. Therefore, a hydrogen atom must be attached at the 6-position, and changing the carbon atom to nitrogen caused unfavorable electrostatic interactions. Conclusion: The theoretical studies have elucidated the determinant factors involved in the binding of type I inhibitors to c-Met. PMID:24056705

Aqueous photolysis of niclosamide

USGS Publications Warehouse

Graebing, P.W.; Chib, J.S.; Hubert, T.D.; Gingerich, W.H.

2004-01-01

The photodegradation of [14C]niclosamide was studied in sterile, pH 5, 7, and 9 buffered aqueous solutions under artificial sunlight at 25.0 A? 1.0 A?C. Photolysis in pH 5 buffer is 4.3 times faster than in pH 9 buffer and 1.5 times faster than in pH 7 buffer. In the dark controls, niclosamide degraded only in the pH 5 buffer. After 360 h of continuous irradiation in pH 9 buffer, the chromatographic pattern of the degradates was the same regardless of which ring contained the radiolabel. An HPLC method was developed that confirmed these degradates to be carbon dioxide and two- and four-carbon aliphatic acids formed by cleavage of both aromatic rings. Carbon dioxide was the major degradate, comprising 40% of the initial radioactivity in the 360 h samples from both labels. The other degradates formed were oxalic acid, maleic acid, glyoxylic acid, and glyoxal. In addition, in the chloronitroaniline-labeled irradiated test solution, 2-chloro-4-nitroaniline was observed and identified after 48 h of irradiation but was not detected thereafter. No other aromatic compounds were isolated or observed in either labeled test system.

Novel mechanisms of biotransformation of p-tert-amylphenol by bacteria and fungi with special degradation abilities and simultaneous detoxification of the disinfectant.

PubMed

Schlueter, Rabea; Röder, Anja; Czekalski, Nadine; Gliesche, Daniel; Mikolasch, Annett; Schauer, Frieder

2014-01-01

The compound p-tert-amylphenol (p-(1,1-dimethylpropyl)phenol) is a widely used disinfectant belonging to the group of short branched-chain alkylphenols. It is produced in or imported into the USA with more than one million pounds per year and can be found in the environment in surface water, sediments, and soil. We have investigated for the first time the biotransformation of this disinfectant and the accumulation of metabolites by five bacterial strains, three yeast strains, and three filamentous fungi, selected because of their ability to transform either aromatic or branched-chain compounds. Of the 11 microorganisms tested, one yeast strain and three bacteria could not transform the disinfectant despite of a very low concentration applied (0.005%). None of the other seven organisms was able to degrade the short branched alkyl chain of p-tert-amylphenol. However, two yeast strains, two filamentous fungi, and two bacterial strains attacked the aromatic ring system of the disinfectant via the hydroxylated intermediate 4-(1,1-dimethyl-propyl)-benzene-1,2-diol resulting in two hitherto unknown ring fission products with pyran and furan structures, 4-(1,1-dimethyl-propyl)-6-oxo-6-H-pyran-2-carboxylic acid and 2-[3-(1,1-dimethyl-propyl)-5-oxo-2H-furan-2-yl]acetic acid. While the disinfectant was toxic to the organisms applied, one of the ring cleavage products was not. Thus, a detoxification of the disinfectant was achieved by ring cleavage. Furthermore, one filamentous fungus formed sugar conjugates with p-tert-amylphenol as another mechanism of detoxification of toxic environmental pollutants. With this work, we can also contribute to the allocation of unknown chemical compounds within environmental samples to their parent compounds.

Solid polymer battery electrolyte and reactive metal-water battery

DOEpatents

Harrup, Mason K.; Peterson, Eric S.; Stewart, Frederick F.

2000-01-01

In one implementation, a reactive metal-water battery includes an anode comprising a metal in atomic or alloy form selected from the group consisting of periodic table Group 1A metals, periodic table Group 2A metals and mixtures thereof. The battery includes a cathode comprising water. Such also includes a solid polymer electrolyte comprising a polyphosphazene comprising ligands bonded with a phosphazene polymer backbone. The ligands comprise an aromatic ring containing hydrophobic portion and a metal ion carrier portion. The metal ion carrier portion is bonded at one location with the polymer backbone and at another location with the aromatic ring containing hydrophobic portion. The invention also contemplates such solid polymer electrolytes use in reactive metal/water batteries, and in any other battery.

Finding Inspiration in the Protein Data Bank to Chemically Antagonize Readers of the Histone Code.

PubMed

Campagna-Slater, Valérie; Schapira, Matthieu

2010-04-12

Members of the Royal family of proteins are readers of the histone code that contain aromatic cages capable of recognizing specific sequences and lysine methylation states on histone tails. These binding modules play a key role in epigenetic signalling, and are part of a larger group of epigenetic targets that are becoming increasingly attractive for drug discovery. In the current study, pharmacophore representations of the aromatic cages forming the methyl-lysine (Me-Lys) recognition site were used to search the Protein Data Bank (PDB) for ligand binding pockets possessing similar chemical and geometrical features in unrelated proteins. The small molecules bound to these sites were then extracted from the PDB, and clustered based on fragments binding to the aromatic cages. The compounds collected are numerous and structurally diverse, but point to a limited set of preferred chemotypes; these include quaternary ammonium, sulfonium, and primary, secondary and tertiary amine moieties, as well as aromatic, aliphatic or orthogonal rings, and bicyclic systems. The chemical tool-kit identified can be used to design antagonists of the Royal family and related proteins. Copyright © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Structural and functional characterization of solute binding proteins for aromatic compounds derived from lignin: p-coumaric acid and related aromatic acids.

PubMed

Tan, Kemin; Chang, Changsoo; Cuff, Marianne; Osipiuk, Jerzy; Landorf, Elizabeth; Mack, Jamey C; Zerbs, Sarah; Joachimiak, Andrzej; Collart, Frank R

2013-10-01

Lignin comprises 15-25% of plant biomass and represents a major environmental carbon source for utilization by soil microorganisms. Access to this energy resource requires the action of fungal and bacterial enzymes to break down the lignin polymer into a complex assortment of aromatic compounds that can be transported into the cells. To improve our understanding of the utilization of lignin by microorganisms, we characterized the molecular properties of solute binding proteins of ATP-binding cassette transporter proteins that interact with these compounds. A combination of functional screens and structural studies characterized the binding specificity of the solute binding proteins for aromatic compounds derived from lignin such as p-coumarate, 3-phenylpropionic acid and compounds with more complex ring substitutions. A ligand screen based on thermal stabilization identified several binding protein clusters that exhibit preferences based on the size or number of aromatic ring substituents. Multiple X-ray crystal structures of protein-ligand complexes for these clusters identified the molecular basis of the binding specificity for the lignin-derived aromatic compounds. The screens and structural data provide new functional assignments for these solute-binding proteins which can be used to infer their transport specificity. This knowledge of the functional roles and molecular binding specificity of these proteins will support the identification of the specific enzymes and regulatory proteins of peripheral pathways that funnel these compounds to central metabolic pathways and will improve the predictive power of sequence-based functional annotation methods for this family of proteins. Copyright © 2013 Wiley Periodicals, Inc.

Structural and functional characterization of solute binding proteins for aromatic compounds derived from lignin: p-coumaric acid and related aromatic acids

PubMed Central

Tan, Kemin; Chang, Changsoo; Cuff, Marianne; Osipiuk, Jerzy; Landorf, Elizabeth; Mack, Jamey C.; Zerbs, Sarah; Joachimiak, Andrzej; Collart, Frank R.

2013-01-01

Lignin comprises 15.25% of plant biomass and represents a major environmental carbon source for utilization by soil microorganisms. Access to this energy resource requires the action of fungal and bacterial enzymes to break down the lignin polymer into a complex assortment of aromatic compounds that can be transported into the cells. To improve our understanding of the utilization of lignin by microorganisms, we characterized the molecular properties of solute binding proteins of ATP.binding cassette transporter proteins that interact with these compounds. A combination of functional screens and structural studies characterized the binding specificity of the solute binding proteins for aromatic compounds derived from lignin such as p-coumarate, 3-phenylpropionic acid and compounds with more complex ring substitutions. A ligand screen based on thermal stabilization identified several binding protein clusters that exhibit preferences based on the size or number of aromatic ring substituents. Multiple X-ray crystal structures of protein-ligand complexes for these clusters identified the molecular basis of the binding specificity for the lignin-derived aromatic compounds. The screens and structural data provide new functional assignments for these solute.binding proteins which can be used to infer their transport specificity. This knowledge of the functional roles and molecular binding specificity of these proteins will support the identification of the specific enzymes and regulatory proteins of peripheral pathways that funnel these compounds to central metabolic pathways and will improve the predictive power of sequence-based functional annotation methods for this family of proteins. PMID:23606130

Facile construction of substituted pyrimido[4,5-d]pyrimidones by transformation of enaminouracil

PubMed Central

Hamama, Wafaa S.; Ismail, Mohamed A.; Al-Saman, Hanaa A.; Zoorob, Hanafi H.

2012-01-01

The reaction of 6-amino-1,3-dimethylpyrimidine-2,4(1H,3H)-dione (1) as a binucleophile with primary aromatic or heterocyclic amines and formaldehyde or aromatic (heterocyclic) aldehydes in a molar ratio (1:1:2) gave the pyrimido[4,5-d]pyrimidin-2,4-dione ring systems 2–5. Treatment of 1 with diamines and formalin in molar ratio (2:1:4) gave the bis-pyrimido[4,5-d]pyrimidin-2,4-diones 6–8. Furthermore, substituted pyrimido[4,5-d]pyrimidin-2,4-diones with uracil derivative 11 or spiro indole 16 were synthesized. Synthesis of pyrimido[4,5-d]pyrimidin-2,4-diones with different substitution at C-5 and C-7 was achieved to give 13 and 18, respectively. PMID:25685408

Expedited Synthesis of Fluorine-18 Labeled Phenols. A Missing Link in PET Radiochemistry

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

Katzenellenbogen, John A.; Zhou, Dong

Fluorine-18 (F-18) is arguably the most valuable radionuclide for positron emission tomographic (PET) imaging. However, while there are many methods for labeling small molecules with F-18 at aliphatic positions and on electron-deficient aromatic rings, there are essentially no reliable and practical methods to label electron-rich aromatic rings such as phenols, with F-18 at high specific activity. This is disappointing because fluorine-labeled phenols are found in many drugs; there are also many interesting plant metabolites and hormones that contain either phenols or other electron-rich aromatic systems such as indoles whose metabolism, transport, and distribution would be interesting to study if theymore » could readily be labeled with F-18. Most approaches to label phenols with F-18 involve the labeling of electron-poor precursor arenes by nucleophilic aromatic substitution, followed by subsequent conversion to phenols by oxidation or other multi-step sequences that are often inefficient and time consuming. Thus, the lack of good methods for labeling phenols and other electron-rich aromatics with F-18 at high specific activity represents a significant methodological gap in F-18 radiochemistry that can be considered a “Missing Link in PET Radiochemistry”. The objective of this research project was to develop and optimize a series of unusual synthetic transformations that will enable phenols (and other electron-rich aromatic systems) to be labeled with F-18 at high specific activity, rapidly, reliably, and conveniently, thereby bridging this gap. Through the studies conducted with support of this project, we have substantially advanced synthetic methodology for the preparation of fluorophenols. Our progress is presented in detail in the sections below, and much has been published or presented publication; other components are being prepared for publication. In essence, we have developed a completely new method to prepare o-fluorophenols from non-aromatic precursors (diazocyclohexenones) by a novel reaction sequence that uses fluoride ion as a precursor and various activating electrophiles, and we have improved methods for the preparation of heterodiaryl iodonium salts. Both methods have been used to prepare interesting potential radiotracers. Other advances have been made in labeling dendrimeric nanoparticle structures of increasing interest for multimodal imaging and in advancing labeling through fluorosilane bonds. Thus, the progress we have made substantially fills the significant gap in PET radiochemistry that we originally identified, and it provides for the field new methodology that can be applied to a number of current challenges, including the preparation of several molecules of interest as radiotracers, such as 2-[18F]Fluoroestradiol (2-FES) and m-fluorotyrosine, which we have illustrated. These methods can be used by any skilled radiochemist interesting in preparing these agents or similar fluorine-18 labeled electron-rich arene systems of interested for PET biological imaging in the most general sense.« less

The source apportionment of polycyclic aromatic hydrocarbons (PAHs) in the topsoil in Xiaodian sewage irrigation area, North of China.

PubMed

Li, Jia-Le; Wang, Yan-Xin; Zhang, Cai-Xiang; Dong, Yi-Hui; Du, Bin; Liao, Xiao-Ping

2014-12-01

31 topsoil samples were collected by grid method in Xiaodian sewage irrigation area, Taiyuan City, North of China. The concentrations of 16 kinds of polycyclic aromatic hydrocarbons (PAHs) were determined by gas chromatograph coupled with mass spectrum. Generally speaking, the distribution order of PAHs in the area is: those with five and six rings > those with four rings > those with two and three rings. Source apportionment shows a significant zonation of the source of PAHs: the civil coal pollution occurred in the north part, the local and far factory pollution happened in the middle area and the mixed pollution sources from coal and wood combustion, automotive emission, presented in the south area. The distribution of PAHs has a definite relationship with the sewage water flow and soil adsorption. The related coefficient between PAHs and physicochemical property showed there was a negative correlation between pH, silt, clay and PAHs while there was a positive correlation between total organic carbon, sand and PAHs.

A physically interpretable quantum-theoretic QSAR for some carbonic anhydrase inhibitors with diverse aromatic rings, obtained by a new QSAR procedure.

PubMed

Clare, Brian W; Supuran, Claudiu T

2005-03-15

A QSAR based almost entirely on quantum theoretically calculated descriptors has been developed for a large and heterogeneous group of aromatic and heteroaromatic carbonic anhydrase inhibitors, using orbital energies, nodal angles, atomic charges, and some other intuitively appealing descriptors. Most calculations have been done at the B3LYP/6-31G* level of theory. For the first time we have treated five-membered rings by the same means that we have used for benzene rings in the past. Our flip regression technique has been expanded to encompass automatic variable selection. The statistical quality of the results, while not equal to those we have had with benzene derivatives, is very good considering the noncongeneric nature of the compounds. The most significant correlation was with charge on the atoms of the sulfonamide group, followed by the nodal orientation and the solvation energy calculated by COSMO and the charge polarization of the molecule calculated as the mean absolute Mulliken charge over all atoms.

Seasonal variation in diffusive exchange of polycyclic aromatic hydrocarbons across the air-seawater interface in coastal urban area.

PubMed

Kim, Seung-Kyu; Chae, Doo Hyun

2016-08-15

Concentrations of 15 polycyclic aromatic hydrocarbons (PAHs) in air-seawater interface were measured over 1year in the coastal region of Incheon, South Korea. Most individual PAHs and total PAHs in air displayed statistically significant negative correlations with temperature, but not significant in seawater. Less hydrophobic compounds with three rings were at or near equilibrium in summer, while PAHs with four to six rings were in disequilibrium in all seasons, with higher fugacity gradients in colder seasons and for more hydrophobic compounds. Differently from fugacity gradients, the highest net fluxes occurred for some three- and four-ring PAHs showing the highest atmospheric concentrations. Net gaseous exchange, which was higher in winter, occurred from air to seawater with an annual cumulative flux of 2075μg/m(2)/year (for Σ15PAHs), indicating that atmospheric PAHs in this region, originating from coal/biomass combustion, can deteriorate the quality of seawater and sediment. Copyright © 2016 Elsevier Ltd. All rights reserved.

Reconciling Experiment and Theory in the Use of Aryl-Extended Calix[4]pyrrole Receptors for the Experimental Quantification of Chloride–π Interactions in Solution

PubMed Central

Bauzá, Antonio; Quiñonero, David; Frontera, Antonio; Ballester, Pablo

2015-01-01

In this manuscript we consider from a theoretical point of view the recently reported experimental quantification of anion–π interactions (the attractive force between electron deficient aromatic rings and anions) in solution using aryl extended calix[4]pyrrole receptors as model systems. Experimentally, two series of calix[4]pyrrole receptors functionalized, respectively, with two and four aryl rings at the meso positions, were used to assess the strength of chloride–π interactions in acetonitrile solution. As a result of these studies the contribution of each individual chloride–π interaction was quantified to be very small (<1 kcal/mol). This result is in contrast with the values derived from most theoretical calculations. Herein we report a theoretical study using high-level density functional theory (DFT) calculations that provides a plausible explanation for the observed disagreement between theory and experiment. The study reveals the existence of molecular interactions between solvent molecules and the aromatic walls of the receptors that strongly modulate the chloride–π interaction. In addition, the obtained theoretical results also suggest that the chloride-calix[4]pyrrole complex used as reference to dissect experimentally the contribution of the chloride–π interactions to the total binding energy for both the two and four-wall aryl-extended calix[4]pyrrole model systems is probably not ideal. PMID:25913375

Condensed tannins: Quinone methide intermediates in procyanidin synthesis

Treesearch

Richard W. Hemingway; L. Y. Foo

1983-01-01

Proanthocyanidins (condensed tanruns) are widely distributed in plants and are found in sufficiently high concentration in some tree barks to encourage their industrial utilization. These polymers consist of flavanoid units linked through the C-4 of the pyran ring to the C-6 or C-8 carbons of the aromatic A-ring. Recent advances in the chemistry of condensed tannins...

Formal radical cyclization onto benzene rings: a general method and its use in the synthesis of ent-nocardione A.

PubMed

Clive, Derrick L J; Fletcher, Stephen P; Liu, Dazhan

2004-05-14

An indirect method is described for effecting radical cyclization onto a benzene ring. Cross-conjugated dienones 6, which are readily prepared from phenols, undergo radical cyclization (6 --> 7 --> 8), and the products (8) are easily aromatized. The method has been applied to the synthesis of ent-nocardione A (21).

Synthesis of tetra- and octa-aurated heteroaryl complexes towards probing aromatic indoliums

PubMed Central

Yuan, Jun; Sun, Tingting; He, Xin; An, Ke; Zhu, Jun; Zhao, Liang

2016-01-01

Polymetalated aromatic compounds are particularly challenging synthetic goals because of the limited thermodynamic stability of polyanionic species arising from strong electrostatic repulsion between adjacent carbanionic sites. Here we describe a facile synthesis of two polyaurated complexes including a tetra-aurated indole and an octa-aurated benzodipyrrole. The imido trinuclear gold(I) moiety exhibits nucleophilicity and undergoes an intramolecular attack on a gold(I)-activated ethynyl to generate polyanionic heteroaryl species. Their computed magnetic properties reveal the aromatic character in the five-membered ring. The incorporation of the aurated substituents at the nitrogen atom can convert non-aromaticity in the parent indolium into aromaticity in the aurated one because of hyperconjugation. Thus, the concept of hyperconjugative aromaticity is extended to heterocycles with transition metal substituents. More importantly, further analysis indicates that the aurated substituents can perform better than traditional main-group substituents. This work highlights the difference in aromaticity between polymetalated aryls and their organic prototypes. PMID:27186982

13C chemical-shift anisotropy of alkyl-substituted aromatic carbon in anthracene derivatives.

PubMed

Hoop, Cody L; Iuliucci, Robbie J

2013-06-01

The (13)C chemical-shift anisotropy in anthracene derivatives (9,10-dimethylanthracene, 9,10-dihydroanthracene, dianthracene, and triptycene) has been measured by the 2D FIREMAT timed pulse sequence and the corresponding set of principal values has been determined by the TIGER processing method. These molecules expand the data base of (13)C CSA measurements of fused aromatic rings some bridged by sp(3) carbon resulting in an unusual bonding configuration, which leads to distinctive aromatic (13)C CSA values. Crystal lattice distortions to the CSA were observed to change the isotropic shift by 2.5 to 3.3 ppm and changes as large as 8.3 ppm in principal components. Modeling of the CSA data by GIPAW DFT (GGA-PBE/ultrafine) shielding calculations resulted in an rms chemical-shift distance of 2.8 ppm after lattice including geometry optimization of the diffraction structures by the GIPAW method at GGA-PBE/ultrafine level. Attention is given to the substituted aromatic carbon in the phenyl groups (here forth referred to as the α-carbon) with respect to CSA modeling with electronic methods. The (13)C CSA of this position is accurately determined due to its spectral isolation of the isotropic shift that limits overlap in the FIREMAT spectrum. In cases where the bridging ring is sp(3) carbon, the current density is reduced from extending beyond the peripheral phenyl groups; this plays a significant role in the magnetic shielding of the α-position. Nuclear independent chemical-shift calculations based on GIAO DFT (B3LYP/6-31G(d)) shielding calculations were used to model the intramolecular π-interactions in dianthracene and triptycene. These NICS results estimate the isotropic shift of the α-position in dianthracene to be insignificantly affected by the presence of the neighboring aromatic rings. However, a notable change in isotropic shielding, Δσ(iso)=-2.1 ppm, is predicted for the α- position of triptycene. Experimentally, the δ22 principal component at the α-position for both dianthracene and triptycene increases by at least 12 ppm compared to 9,10-dihydroanthracene. To rationalize this change, shielding calculations in idealized structures are explored. The spatial position of the bicyclic scaffolding of the bridging ring plays a key role in the large increase in δ22 for the α-carbon. Copyright © 2013 Elsevier Inc. All rights reserved.

Polycyclic aromatic hydrocarbon metabolic network in Mycobacterium vanbaalenii PYR-1.

PubMed

Kweon, Ohgew; Kim, Seong-Jae; Holland, Ricky D; Chen, Hongyan; Kim, Dae-Wi; Gao, Yuan; Yu, Li-Rong; Baek, Songjoon; Baek, Dong-Heon; Ahn, Hongsik; Cerniglia, Carl E

2011-09-01

This study investigated a metabolic network (MN) from Mycobacterium vanbaalenii PYR-1 for polycyclic aromatic hydrocarbons (PAHs) from the perspective of structure, behavior, and evolution, in which multilayer omics data are integrated. Initially, we utilized a high-throughput proteomic analysis to assess the protein expression response of M. vanbaalenii PYR-1 to seven different aromatic compounds. A total of 3,431 proteins (57.38% of the genome-predicted proteins) were identified, which included 160 proteins that seemed to be involved in the degradation of aromatic hydrocarbons. Based on the proteomic data and the previous metabolic, biochemical, physiological, and genomic information, we reconstructed an experiment-based system-level PAH-MN. The structure of PAH-MN, with 183 metabolic compounds and 224 chemical reactions, has a typical scale-free nature. The behavior and evolution of the PAH-MN reveals a hierarchical modularity with funnel effects in structure/function and intimate association with evolutionary modules of the functional modules, which are the ring cleavage process (RCP), side chain process (SCP), and central aromatic process (CAP). The 189 commonly upregulated proteins in all aromatic hydrocarbon treatments provide insights into the global adaptation to facilitate the PAH metabolism. Taken together, the findings of our study provide the hierarchical viewpoint from genes/proteins/metabolites to the network via functional modules of the PAH-MN equipped with the engineering-driven approaches of modularization and rationalization, which may expand our understanding of the metabolic potential of M. vanbaalenii PYR-1 for bioremediation applications.

Effect of iodide on transformation of phenolic compounds by nonradical activation of peroxydisulfate in the presence of carbon nanotube: Kinetics, impacting factors, and formation of iodinated aromatic products.

PubMed

Guan, Chaoting; Jiang, Jin; Pang, Suyan; Luo, Congwei; Yang, Yi; Ma, Jun; Yu, Jing; Zhao, Xi

2018-06-04

Our recent study has demonstrated that iodide (I - ) can be easily and almost entirely oxidized to hypoiodous acid (HOI) but not to iodate by nonradical activation of peroxydisulfate (PDS) in the presence of a commercial carbon nanotube (CNT). In this work, the oxidation kinetics of phenolic compounds by the PDS/CNT system in the presence of I - were examined and potential formation of iodinated aromatic products was explored. Experimental results suggested that I - enhanced the transformation of six selected substituted phenols, primarily attributed to the generation of HOI that was considerably reactive toward these phenolic compounds. More significant enhancement was obtained at higher I - concentrations or lower pH values, while the change of PDS or CNT dosages exhibited a slight impact on the enhancing effect of I - . Product analyses with liquid chromatography tandem mass spectrometry clearly revealed the production of iodinated aromatic products when p-hydroxybenzoic acid (p-HBA, a model phenol) was treated by the PDS/CNT/I - system in both synthetic and real waters. Their formation pathways probably involved the substitution of HOI on aromatic ring of p-HBA, as well as the generation of iodinated p-HBA phenoxyl radicals and subsequent coupling of these radicals. Given the considerable toxicity and harmful effects of these iodinated aromatic products, particular attention should be paid when the novel PDS/CNT oxidation technology is applied for treatment of phenolic contaminants in iodide-containing waters. Copyright © 2018 Elsevier Ltd. All rights reserved.

Stabilization of flat aromatic Si6 rings analogous to benzene: ab initio theoretical prediction.

PubMed

Zdetsis, Aristides D

2007-12-07

It is shown by ab initio calculations, based on density functional (DFT/B3LYP), and high level coupled-cluster [CCSD(T)] and quadratic CI [QCISD(T)] methods, that flat aromatic silicon structures analogous to benzene (C6H6) can be stabilized in the presence of lithium. The resulting planar Si6Li6 structure is both stable and aromatic, sharing many key characteristics with benzene. To facilitate possible synthesis and characterization of these species, routes of formation with high exothermicity are suggested and several spectral properties (including optical absorption, infrared, and Raman) are calculated.

Influence of Fluorine Atoms and Aromatic Rings on the Acidity of Ethanol

NASA Astrophysics Data System (ADS)

Ramírez, Ramsés E.; García-Martínez, Cirilo; Méndez, Francisco

2009-09-01

Absolute gas-phase acidities ΔacidG0(OH) and ΔacidG0(CH) were calculated at the B3LYP and MP2 levels using six different standard basis sets for the OH and CH heterolytic bond cleavage of ethanol and twelve derivatives of the type CH3-nFnCHXrOH, where n ranges from zero to three and represents the number of fluorine atoms and r represents hydrogen and the type of aromatic ring, namely: X0 = hydrogen, X1 = phenyl, X2 = 1-naphthyl, and X3 = 9-anthryl. The similarity between calculated and experimental ΔacidG0(OH) values for ethanol (1a), 2-fluoroethanol (1b), 2,2-difluoroethanol (1c), 2,2,2-trifluoroethanol (1d), and 1-phenylethanol (2a) was used to validate the right theoretical method for this study. Substituent partial contributions to hydroxyl-, methylene-, and methine-hydrogen acidities were evaluated by linear combination. Good parameter fittings of the primary and secondary alcohols were obtained and interpreted as additive contribution of the substituent effects. The nonlinear contributions were identified. Calculations prove that fluoroalcohols exhibit C-H acidity, which is usually lower than O-H acidity. In principle, the inversion of this acidity order is possible by the introduction of a large aromatic ring instead to increase the number of fluorine atoms.

Deviation of the typical AAA substrate-threading pore prevents fatal protein degradation in yeast Cdc48.

PubMed

Esaki, Masatoshi; Islam, Md Tanvir; Tani, Naoki; Ogura, Teru

2017-07-14

Yeast Cdc48 is a well-conserved, essential chaperone of ATPases associated with diverse cellular activity (AAA) proteins, which recognizes substrate proteins and modulates their conformations to carry out many cellular processes. However, the fundamental mechanisms underlying the diverse pivotal roles of Cdc48 remain unknown. Almost all AAA proteins form a ring-shaped structure with a conserved aromatic amino acid residue that is essential for proper function. The threading mechanism hypothesis suggests that this residue guides the intrusion of substrate proteins into a narrow pore of the AAA ring, thereby becoming unfolded. By contrast, the aromatic residue in one of the two AAA rings of Cdc48 has been eliminated through evolution. Here, we show that artificial retrieval of this aromatic residue in Cdc48 is lethal, and essential features to support the threading mechanism are required to exhibit the lethal phenotype. In particular, genetic and biochemical analyses of the Cdc48 lethal mutant strongly suggested that when in complex with the 20S proteasome, essential proteins are abnormally forced to thread through the Cdc48 pore to become degraded, which was not detected in wild-type Cdc48. Thus, the widely applicable threading model is less effective for wild-type Cdc48; rather, Cdc48 might function predominantly through an as-yet-undetermined mechanism.

Gasoline Particulate Filters as an Effective Tool to Reduce Particulate and Polycyclic Aromatic Hydrocarbon Emissions from Gasoline Direct Injection (GDI) Vehicles: A Case Study with Two GDI Vehicles.

PubMed

Yang, Jiacheng; Roth, Patrick; Durbin, Thomas D; Johnson, Kent C; Cocker, David R; Asa-Awuku, Akua; Brezny, Rasto; Geller, Michael; Karavalakis, Georgios

2018-03-06

We assessed the gaseous, particulate, and genotoxic pollutants from two current technology gasoline direct injection vehicles when tested in their original configuration and with a catalyzed gasoline particulate filter (GPF). Testing was conducted over the LA92 and US06 Supplemental Federal Test Procedure (US06) driving cycles on typical California E10 fuel. The use of a GPF did not show any fuel economy and carbon dioxide (CO 2 ) emission penalties, while the emissions of total hydrocarbons (THC), carbon monoxide (CO), and nitrogen oxides (NOx) were generally reduced. Our results showed dramatic reductions in particulate matter (PM) mass, black carbon, and total and solid particle number emissions with the use of GPFs for both vehicles over the LA92 and US06 cycles. Particle size distributions were primarily bimodal in nature, with accumulation mode particles dominating the distribution profile and their concentrations being higher during the cold-start period of the cycle. Polycyclic aromatic hydrocarbons (PAHs) and nitrated PAHs were quantified in both the vapor and particle phases of the PM, with the GPF-equipped vehicles practically eliminating most of these species in the exhaust. For the stock vehicles, 2-3 ring compounds and heavier 5-6 ring compounds were observed in the PM, whereas the vapor phase was dominated mostly by 2-3 ring aromatic compounds.

Polycyclic aromatic hydrocarbons (PAH) formation from the pyrolysis of different municipal solid waste fractions

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

Zhou, Hui; Energy Research Institute, University of Leeds, Leeds LS2 9JT; Wu, Chunfei, E-mail: c.wu@leeds.ac.uk

2015-02-15

Highlights: • PAH from pyrolysis of 9 MSW fractions was investigated. • Pyrolysis of plastics released more PAH than that of biomass. • Naphthalene was the most abundant PAH in the tar. • The mechanism of PAH release from biomass and plastics was proposed. - Abstract: The formation of 2–4 ring polycyclic aromatic hydrocarbons (PAH) from the pyrolysis of nine different municipal solid waste fractions (xylan, cellulose, lignin, pectin, starch, polyethylene (PE), polystyrene (PS), polyvinyl chloride (PVC), and polyethylene terephthalate (PET)) were investigated in a fixed bed furnace at 800 °C. The mass distribution of pyrolysis was also reported. Themore » results showed that PS generated the most total PAH, followed by PVC, PET, and lignin. More PAH were detected from the pyrolysis of plastics than the pyrolysis of biomass. In the biomass group, lignin generated more PAH than others. Naphthalene was the most abundant PAH, and the amount of 1-methynaphthalene and 2-methynaphthalene was also notable. Phenanthrene and fluorene were the most abundant 3-ring PAH, while benzo[a]anthracene and chrysene were notable in the tar of PS, PVC, and PET. 2-ring PAH dominated all tar samples, and varied from 40 wt.% to 70 wt.%. For PS, PET and lignin, PAH may be generated directly from the aromatic structure of the feedstock.« less

Release behavior and formation mechanism of polycyclic aromatic hydrocarbons during coal pyrolysis.

PubMed

Gao, Meiqi; Wang, Yulong; Dong, Jie; Li, Fan; Xie, Kechang

2016-09-01

Polycyclic aromatic hydrocarbons (PAHs) are major environmental pollutants. They have attracted considerable attention due to their severe potential carcinogenic, mutagenic and genotoxic effects on human health. In this study, five different rank coals from China were pyrolyzed using pyro-probe CDS 5250 and the release behavior of 16 PAHs under different pyrolysis conditions were studied by Gas Chromatography-Mass Spectrometer (GC-MS). The structural characteristics of the five coals were determined by Cross-Polarization/Magic Angle Spinning Carbon-13 Nuclear Magnetic Resonance (CP/MAS (13)C NMR) spectroscopy, and then the factors influencing the formation of PAHs during coal pyrolysis were discussed together with the coal structural data. It was shown that the amount of PAHs generated during coal pyrolysis was largely related to coal rank and followed the order of medium metamorphic coal > low metamorphic coal > high metamorphic coal. The amount of total PAHs varied as the temperature was increased from 400 °C to 1200 °C, which showed a trend of first increasing and then decreasing, with the maximum value at 800 °C. Moreover, the species of PAHs released varied with pyrolysis temperatures. When the temperature was lower than 800 °C, the small ring PAHs were the most abundant, while the proportion of heavy rings increased at higher temperature. The results indicate that the formation of PAHs during coal pyrolysis depends on the structure of the coal. The species and amounts of PAHs generated during coal pyrolysis are closely related to the contents of protonated aromatic carbons and bridging ring junction aromatic carbons present in the coal structure. Copyright © 2016 Elsevier Ltd. All rights reserved.

Aromatic derivatives of 1H-2,3-dihydropyrazolo(4,5-b)-1,5-diazepine

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

Orlov, V.D.; Kiroga, Kh.; Kolos, N.N.

1987-09-01

Aromatic derivatives of 1H-2,3-dihydropyrazole(4,5-b)-1,5-diazepine were obtained by the reaction of 1-phenyl-3-methyl-4,5-diaminopyrazole with chalcones and acetylarenes, catalyzed by acetic or sulfuric acid. The seven-membered ring in these compounds has a conformation of the boat type. The IR, UV, PMR, and mass spectra of the compounds are discussed.

Sorption of the Aircraft Deicing Fluid Component Methyl-Benzotriazole in Soil

DTIC Science & Technology

1999-03-01

Atlas , Ronald M., Bartha , Richard, Microbial Ecology : Fundamentals and Applications. Benjamin Cummings: Redwood City, 1993. Ball, William P., Roberts...cell; transfer of substances from one medium to another [ Atlas and Bartha , 533; Fetter, 117]. (2) The process by which a compound in solution or...oxygen, low redox potential. [ Atlas and Bartha , 534; Schwarzenbach et al, 410] Aromatic compound - Carbon skeletons containing aromatic benzene ring and

Polyimides containing amide and perfluoroisopropylidene connecting groups

NASA Technical Reports Server (NTRS)

Dezern, James F. (Inventor)

1993-01-01

New, thermooxidatively stable polyimides were prepared from the reaction of aromatic dianhydrides containing isopropylidene bridging groups with aromatic diamines containing amide connecting groups between the rings. Several of these polyimides were shown to be semi-crystalline as evidenced by wide angle x ray scattering and differential scanning calorimetry. Most of the polyimides form tough, flexible films with high tensile properties. These polyimide films exhibit enhanced solubility in organic solvents.

Square Wave Voltammetry of TNT at Gold Electrodes Modified with Self-Assembled Monolayers Containing Aromatic Structures

PubMed Central

Trammell, Scott A.; Zabetakis, Dan; Moore, Martin; Verbarg, Jasenka; Stenger, David A.

2014-01-01

Square wave voltammetry for the reduction of 2,4,6-trinitrotoluene (TNT) was measured in 100 mM potassium phosphate buffer (pH 8) at gold electrodes modified with self-assembled monolayers (SAMs) containing either an alkane thiol or aromatic ring thiol structures. At 15 Hz, the electrochemical sensitivity (µA/ppm) was similar for all SAMs tested. However, at 60 Hz, the SAMs containing aromatic structures had a greater sensitivity than the alkane thiol SAM. In fact, the alkane thiol SAM had a decrease in sensitivity at the higher frequency. When comparing the electrochemical response between simulations and experimental data, a general trend was observed in which most of the SAMs had similar heterogeneous rate constants within experimental error for the reduction of TNT. This most likely describes a rate limiting step for the reduction of TNT. However, in the case of the alkane SAM at higher frequency, the decrease in sensitivity suggests that the rate limiting step in this case may be electron tunneling through the SAM. Our results show that SAMs containing aromatic rings increased the sensitivity for the reduction of TNT when higher frequencies were employed and at the same time suppressed the electrochemical reduction of dissolved oxygen. PMID:25549081

Methanogenic degradation of lignin-derived monoaromatic compounds by microbial enrichments from rice paddy field soil.

PubMed

Kato, Souichiro; Chino, Kanako; Kamimura, Naofumi; Masai, Eiji; Yumoto, Isao; Kamagata, Yoichi

2015-09-24

Anaerobic degradation of lignin-derived aromatics is an important metabolism for carbon and nutrient cycles in soil environments. Although there are some studies on degradation of lignin-derived aromatics by nitrate- and sulfate-reducing bacteria, knowledge on their degradation under methanogenic conditions are quite limited. In this study, methanogenic microbial communities were enriched from rice paddy field soil with lignin-derived methoxylated monoaromatics (vanillate and syringate) and their degradation intermediates (protocatechuate, catechol, and gallate) as the sole carbon and energy sources. Archaeal community analysis disclosed that both aceticlastic (Methanosarcina sp.) and hydrogenotrophic (Methanoculleus sp. and Methanocella sp.) methanogens dominated in all of the enrichments. Bacterial community analysis revealed the dominance of acetogenic bacteria (Sporomusa spp.) only in the enrichments on the methoxylated aromatics, suggesting that Sporomusa spp. initially convert vanillate and syringate into protocatechuate and gallate, respectively, with acetogenesis via O-demethylation. As the putative ring-cleavage microbes, bacteria within the phylum Firmicutes were dominantly detected from all of the enrichments, while the dominant phylotypes were not identical between enrichments on vanillate/protocatechuate/catechol (family Peptococcaceae bacteria) and on syringate/gallate (family Ruminococcaceae bacteria). This study demonstrates the importance of cooperation among acetogens, ring-cleaving fermenters/syntrophs and aceticlastic/hydrogenotrophic methanogens for degradation of lignin-derived aromatics under methanogenic conditions.

Methanogenic degradation of lignin-derived monoaromatic compounds by microbial enrichments from rice paddy field soil

PubMed Central

Kato, Souichiro; Chino, Kanako; Kamimura, Naofumi; Masai, Eiji; Yumoto, Isao; Kamagata, Yoichi

2015-01-01

Anaerobic degradation of lignin-derived aromatics is an important metabolism for carbon and nutrient cycles in soil environments. Although there are some studies on degradation of lignin-derived aromatics by nitrate- and sulfate-reducing bacteria, knowledge on their degradation under methanogenic conditions are quite limited. In this study, methanogenic microbial communities were enriched from rice paddy field soil with lignin-derived methoxylated monoaromatics (vanillate and syringate) and their degradation intermediates (protocatechuate, catechol, and gallate) as the sole carbon and energy sources. Archaeal community analysis disclosed that both aceticlastic (Methanosarcina sp.) and hydrogenotrophic (Methanoculleus sp. and Methanocella sp.) methanogens dominated in all of the enrichments. Bacterial community analysis revealed the dominance of acetogenic bacteria (Sporomusa spp.) only in the enrichments on the methoxylated aromatics, suggesting that Sporomusa spp. initially convert vanillate and syringate into protocatechuate and gallate, respectively, with acetogenesis via O-demethylation. As the putative ring-cleavage microbes, bacteria within the phylum Firmicutes were dominantly detected from all of the enrichments, while the dominant phylotypes were not identical between enrichments on vanillate/protocatechuate/catechol (family Peptococcaceae bacteria) and on syringate/gallate (family Ruminococcaceae bacteria). This study demonstrates the importance of cooperation among acetogens, ring-cleaving fermenters/syntrophs and aceticlastic/hydrogenotrophic methanogens for degradation of lignin-derived aromatics under methanogenic conditions. PMID:26399549

Molecular Static Third-Order Polarizabilities of Carbon-Cage Fullerene and Their Correlation with Three Geometric Properties: Symmetry, Aromaticity, and Size

NASA Technical Reports Server (NTRS)

Moore, C. E.; Cardelino, B. H.; Frazier, D. O.; Niles, J.; Wang, X.-Q.

1998-01-01

The static third-order polarizabilities (gamma) of C60, C70, five isomers of C78 and two isomers of C84 were analyzed in terms of three properties, from a geometric point of view: symmetry, aromaticity and size. The polarizability values were based on the finite field approximation using a semiempirical Hamiltonian (AM1) and applied to molecular structures obtained from density functional theory calculations. Symmetry was characterized by the molecular group order. The selection of 6-member rings as aromatic was determined from an analysis of bond lengths. Maximum interatomic distance and surface area were the parameters considered with respect to size. Based on triple linear regression analysis, it was found that the static linear polarizability (alpha) and gamma in these molecules respond differently to geometrical properties: alpha depends almost exclusively on surface area while gamma is affected by a combination of number of aromatic rings, length and group order, in decreasing importance. In the case of alpha, valence electron contributions provide the same information as all-electron estimates. For gamma, the best correlation coefficients are obtained when all-electron estimates are used and when the dependent parameter is ln(gamma) instead of gamma.

Transformations of Aromatic Compounds by Nitrosomonas europaea

PubMed Central

Keener, William K.; Arp, Daniel J.

1994-01-01

Benzene and a variety of substituted benzenes inhibited ammonia oxidation by intact cells of Nitrosomonas europaea. In most cases, the inhibition was accompanied by transformation of the aromatic compound to a more oxidized product or products. All products detected were aromatic, and substituents were often oxidized but were not separated from the benzene ring. Most transformations were enhanced by (NH4)2SO4 (12.5 mM) and were prevented by C2H2, a mechanism-based inactivator of ammonia monooxygenase (AMO). AMO catalyzed alkyl substituent hydroxylations, styrene epoxidation, ethylbenzene desaturation to styrene, and aniline oxidation to nitrobenzene (and unidentified products). Alkyl substituents were preferred oxidation sites, but the ring was also oxidized to produce phenolic compounds from benzene, ethylbenzene, halobenzenes, phenol, and nitrobenzene. No carboxylic acids were identified. Ethylbenzene was oxidized via styrene to two products common also to oxidation of styrene; production of styrene is suggestive of an electron transfer mechanism for AMO. Iodobenzene and 1,2-dichlorobenzene were oxidized slowly to halophenols; 1,4-dichlorobenzene was not transformed. No 2-halophenols were detected as products. Several hydroxymethyl (-CH2OH)-substituted aromatics and p-cresol were oxidized by C2H2-treated cells to the corresponding aldehydes, benzaldehyde was reduced to benzyl alcohol, and o-cresol and 2,5-dimethylphenol were not depleted. PMID:16349282

Spectroscopic and theoretical studies on the aromaticity of pyrrol-2-yl-carbonyl conformers

NASA Astrophysics Data System (ADS)

Dubis, Alina T.; Wojtulewski, Sławomir; Filipkowski, Karol

2013-06-01

The aromaticity of s-cis and s-trans pyrrol-2-yl carbonyl conformers was studied by FT-IR, 1H NMR spectroscopy and DFT calculations at the B3LYP/6-311++G(d,p) level of theory. The Harmonic Oscillator Model of Aromaticity (HOMA) and Nucleus Independent Chemical Shift (NICS) indices were calculated to estimate π-electron delocalization in the pyrrole ring. The usefulness of infrared spectroscopy in the evaluation of the aromaticity of the homogeneous set of pyrroles is discussed. The influence of 2-substitution on different aspects of aromaticity and stability of the pyrrol-2-yl carbonyl conformers is also discussed. It is concluded that the substitution effect of the title pyrrole derivatives can be explained on the basis of theoretical and experimental measurements of π-electron delocalization, including IR data.

Computational Study of Chemical Reactivity Using Information-Theoretic Quantities from Density Functional Reactivity Theory for Electrophilic Aromatic Substitution Reactions.

PubMed

Wu, Wenjie; Wu, Zemin; Rong, Chunying; Lu, Tian; Huang, Ying; Liu, Shubin

2015-07-23

The electrophilic aromatic substitution for nitration, halogenation, sulfonation, and acylation is a vastly important category of chemical transformation. Its reactivity and regioselectivity is predominantly determined by nucleophilicity of carbon atoms on the aromatic ring, which in return is immensely influenced by the group that is attached to the aromatic ring a priori. In this work, taking advantage of recent developments in quantifying nucleophilicity (electrophilicity) with descriptors from the information-theoretic approach in density functional reactivity theory, we examine the reactivity properties of this reaction system from three perspectives. These include scaling patterns of information-theoretic quantities such as Shannon entropy, Fisher information, Ghosh-Berkowitz-Parr entropy and information gain at both molecular and atomic levels, quantitative predictions of the barrier height with both Hirshfeld charge and information gain, and energetic decomposition analyses of the barrier height for the reactions. To that end, we focused in this work on the identity reaction of the monosubstituted-benzene molecule reacting with hydrogen fluoride using boron trifluoride as the catalyst in the gas phase. We also considered 19 substituting groups, 9 of which are ortho/para directing and the other 9 meta directing, besides the case of R = -H. Similar scaling patterns for these information-theoretic quantities found for stable species elsewhere were disclosed for these reactions systems. We also unveiled novel scaling patterns for information gain at the atomic level. The barrier height of the reactions can reliably be predicted by using both the Hirshfeld charge and information gain at the regioselective carbon atom. The energy decomposition analysis ensued yields an unambiguous picture about the origin of the barrier height, where we showed that it is the electrostatic interaction that plays the dominant role, while the roles played by exchange-correlation and steric effects are minor but indispensable. Results obtained in this work should shed new light for better understanding of the factors governing the reactivity for this class of reactions and assisting ongoing efforts for the design of new and more efficient catalysts for such kind of transformations.

Chromatographic selectivity of poly(alkyl methacrylate-co-divinylbenzene) monolithic columns for polar aromatic compounds by pressure-driven capillary liquid chromatography.

PubMed

Lin, Shu-Ling; Wang, Chih-Chieh; Fuh, Ming-Ren

2016-10-05

In this study, divinylbenzene (DVB) was used as the cross-linker to prepare alkyl methacrylate (AlMA) monoliths for incorporating π-π interactions between the aromatic analytes and AlMA-DVB monolithic stationary phases in capillary LC analysis. Various AlMA/DVB ratios were investigated to prepare a series of 30% AlMA-DVB monolithic stationary phases in fused-silica capillaries (250-μm i.d.). The physical properties (such as porosity, permeability, and column efficiency) of the synthesized AlMA-DVB monolithic columns were investigated for characterization. Isocratic elution of phenol derivatives was first employed to evaluate the suitability of the prepared AlMA-DVB columns for small molecule separation. The run-to-run (0.16-1.20%, RSD; n = 3) and column-to-column (0.26-2.95%, RSD; n = 3) repeatabilities on retention times were also examined using the selected AlMA-DVB monolithic columns. The π-π interactions between the aromatic ring and the DVB-based stationary phase offered better recognition on polar analytes with aromatic moieties, which resulted in better separation resolution of aromatic analytes on the AlMA-DVB monolithic columns. In order to demonstrate the capability of potential environmental and/or food safety applications, eight phenylurea herbicides with single benzene ring and seven sulfonamide antibiotics with polyaromatic moieties were analyzed using the selected AlMA-DVB monolithic columns. Copyright © 2016. Published by Elsevier B.V.

Molecular and electronic structure, magnetotropicity and absorption spectra of benzene-trinuclear copper(I) and silver(I) trihalide columnar binary stacks.

PubMed

Tsipis, A C; Stalikas, A V

2012-02-20

The molecular and electronic structures, stabilities, bonding features, magnetotropicity and absorption spectra of benzene-trinuclear Cu(I) and Ag(I) trihalide columnar binary stacks with the general formula [c-M(3)(μ(2)-X)(3)](n)(C(6)H(6))(m) (M = Cu, Ag; X = halide; n, m ≤ 2) have been investigated by means of electronic structure calculation methods. The interaction of c-M(3)(μ(2)-X)(3) clusters with one and two benzene molecules yields 1:1 and 1:2 binary stacks, while benzene sandwiched 2:1 stacks are formed upon interaction of two c-M(3)(μ(2)-X)(3) clusters with one benzene molecule. In all binary stacks the plane of the alternating c-M(3)(μ(2)-X)(3) and benzene components adopts an almost parallel orientation. The separation distance between the centroids of the benzene and the proximal c-M(3)(μ(2)-X)(3) metallic cluster found in the range 2.97-3.33 Å at the B97D/Def2-TZVP level is indicative of a π···π stacking interaction mode, for the centroid separation distance is very close to the sum of the van der Waals radii of Cu···C (3.10 Å) and Ag···C (3.44 Å). Energy decomposition analysis (EDA) at the SSB-D/TZP level revealed that the dominant term in the c-M(3)(μ(2)-X)(3)···C(6)H(6) interaction arises from dispersion and electrostatic forces while the covalent interactions are predicted to be negligible. On the other hand, charge decomposition analysis (CDA) illustrated very small charge transfer from C(6)H(6) toward the c-M(3)(μ(2)-X)(3) clusters, thus reflecting weak π-base/π-acid interactions which are further corroborated by the respective electrostatic potentials and the fact that the total dipole moment vector points to the center of the metallic ring of the c-M(3)(μ(2)-X)(3) cluster. The absorption spectra of all aromatic columnar binary stacks simulated by means of TD-DFT calculations showed strong absorptions in the UV region. The main features of the simulated absorption spectra are thoroughly analyzed, and assignments of the contributing electronic transitions are given. The magnetotropicity of the binary stacks evaluated by the NICS(zz)-scan curves indicated an enhancement of the diatropicity of the inorganic ring upon interaction with the aromatic benzene molecule. Noteworthy is the slight enhancement of the diatropicity of the benzene ring, particularly in the region between the interacting rings, probably due to the superposition (coupling) of the diamagnetic ring currents of the interacting aromatic ring systems.

Structure of Cryptosporidium IMP dehydrogenase bound to an inhibitor with in vivo antiparasitic activity

DOE PAGES

Kim, Youngchang; Makowska-Grzyska, Magdalena; Gorla, Suresh Kumar; ...

2015-04-21

Inosine 5´-monophosphate dehydrogenase (IMPDH) is a promising target for the treatment of Cryptosporidium infections. Here, the structure of C. parvum IMPDH ( CpIMPDH) in complex with inosine 5´-monophosphate (IMP) and P131, an inhibitor with in vivo anticryptosporidial activity, is reported. P131 contains two aromatic groups, one of which interacts with the hypoxanthine ring of IMP, while the second interacts with the aromatic ring of a tyrosine in the adjacent subunit. In addition, the amine and NO 2 moieties bind in hydrated cavities, forming water-mediated hydrogen bonds to the protein. The design of compounds to replace these water molecules is amore » new strategy for the further optimization of C. parvum inhibitors for both antiparasitic and antibacterial applications.« less

Structure of Cryptosporidium IMP dehydrogenase bound to an inhibitor with in vivo antiparasitic activity

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

Kim, Youngchang; Makowska-Grzyska, Magdalena; Gorla, Suresh Kumar

2015-04-21

Inosine 5'-monophosphate dehydrogenase (IMPDH) is a promising target for the treatment ofCryptosporidiuminfections. Here, the structure ofC. parvumIMPDH (CpIMPDH) in complex with inosine 5'-monophosphate (IMP) and P131, an inhibitor within vivoanticryptosporidial activity, is reported. P131 contains two aromatic groups, one of which interacts with the hypoxanthine ring of IMP, while the second interacts with the aromatic ring of a tyrosine in the adjacent subunit. In addition, the amine and NO 2moieties bind in hydrated cavities, forming water-mediated hydrogen bonds to the protein. The design of compounds to replace these water molecules is a new strategy for the further optimization ofC. parvuminhibitorsmore » for both antiparasitic and antibacterial applications.« less

The oxidation degradation of aromatic compounds

NASA Technical Reports Server (NTRS)

Brezinsky, Kenneth; Glassman, Irvin

1987-01-01

A series of experiments were conducted which focused on understanding the role that the O atom addition to aromatic rings plays in the oxidation of benzene and toluene. Flow reactor studies of the oxidation of toluene gave an indication of the amount of O atoms available during an oxidation and the degree to which the O atom adds to the ring. Flow reactor studies of the oxidation of toluene and benzene to which NO2 was added, have shown that NO2 appears to suppress the formation of O atoms and consequently reduce the amount of phenols and cresols formed by O atom addition. A high temperature pyrolysis study of phenol has confirmed that the major decomposition products are carbon monoxide and cyclopentadiene. A preliminary value for the overall decomposition rate constant was also obtained.

Microbial Toluene Removal in Hypoxic Model Constructed Wetlands Occurs Predominantly via the Ring Monooxygenation Pathway.

PubMed

Martínez-Lavanchy, P M; Chen, Z; Lünsmann, V; Marin-Cevada, V; Vilchez-Vargas, R; Pieper, D H; Reiche, N; Kappelmeyer, U; Imparato, V; Junca, H; Nijenhuis, I; Müller, J A; Kuschk, P; Heipieper, H J

2015-09-01

In the present study, microbial toluene degradation in controlled constructed wetland model systems, planted fixed-bed reactors (PFRs), was queried with DNA-based methods in combination with stable isotope fractionation analysis and characterization of toluene-degrading microbial isolates. Two PFR replicates were operated with toluene as the sole external carbon and electron source for 2 years. The bulk redox conditions in these systems were hypoxic to anoxic. The autochthonous bacterial communities, as analyzed by Illumina sequencing of 16S rRNA gene amplicons, were mainly comprised of the families Xanthomonadaceae, Comamonadaceae, and Burkholderiaceae, plus Rhodospirillaceae in one of the PFR replicates. DNA microarray analyses of the catabolic potentials for aromatic compound degradation suggested the presence of the ring monooxygenation pathway in both systems, as well as the anaerobic toluene pathway in the PFR replicate with a high abundance of Rhodospirillaceae. The presence of catabolic genes encoding the ring monooxygenation pathway was verified by quantitative PCR analysis, utilizing the obtained toluene-degrading isolates as references. Stable isotope fractionation analysis showed low-level of carbon fractionation and only minimal hydrogen fractionation in both PFRs, which matches the fractionation signatures of monooxygenation and dioxygenation. In combination with the results of the DNA-based analyses, this suggests that toluene degradation occurs predominantly via ring monooxygenation in the PFRs. Copyright © 2015, American Society for Microbiology. All Rights Reserved.

Novel insights into the fungal oxidation of monoaromatic and biarylic environmental pollutants by characterization of two new ring cleavage enzymes.

PubMed

Schlüter, Rabea; Lippmann, Ramona; Hammer, Elke; Gesell Salazar, Manuela; Schauer, Frieder

2013-06-01

The phenol-degrading yeast Trichosporon mucoides can oxidize and detoxify biarylic environmental pollutants such as dibenzofuran, diphenyl ether and biphenyl by ring cleavage. The degradation pathways are well investigated, but the enzymes involved are not. The high similarity of hydroxylated biphenyl derivatives and phenol raised the question if the enzymes of the phenol degradation are involved in ring cleavage or whether specific enzymes are necessary. Purification of enzymes from T. mucoides with catechol cleavage activity demonstrated the existence of three different enzymes: a classical catechol-1,2-dioxygenase (CDO), not able to cleave the aromatic ring system of 3,4-dihydroxybiphenyl, and two novel enzymes with a high affinity towards 3,4-dihydroxybiphenyl. The comparison of the biochemical characteristics and mass spectrometric sequence data of these three enzymes demonstrated that they have different substrate specificities. CDO catalyzes the ortho-cleavage of dihydroxylated monoaromatic compounds, while the two novel enzymes carry out a similar reaction on biphenyl derivatives. The ring fission of 3,4-dihydroxybiphenyl by the purified enzymes results in the formation of (5-oxo-3-phenyl-2,5-dihydrofuran-2-yl)acetic acid. These results suggest that the ring cleavage enzymes catalyzing phenol degradation are not involved in the ring cleavage of biarylic compounds by this yeast, although some intermediates of the phenol metabolism may function as inducers.

Dipolar-dephasing 13C NMR studies of decomposed wood and coalified xylem tissue: Evidence for chemical structural changes associated with defunctionalization of lignin structural units during coalification

USGS Publications Warehouse

Hatcher, P.G.

1988-01-01

A series of decomposed and coalified gymnosperm woods was examined by conventional solid-state 13C nuclear magnetic resonance (NMR) and by dipolar-dephasing NMR techniques. The results of these NMR studies for a histologically related series of samples provide clues as to the nature of codification reactions that lead to the defunctionalization of lignin-derived aromatic structures. These reactions sequentially involve the following: (1) loss of methoxyl carbons from guaiacyl structural units with replacement by hydroxyls and increased condensation; (2) loss of hydroxyls or aryl ethers with replacement by hydrogen as rank increases from lignin to high-volatile bituminous coal; (3) loss of alkyl groups with continued replacement by hydrogen. The dipolar-dephasing data show that the early stages of coalification in samples examined (lignin to lignite) involve a decreasing degree of protonation on aromatic rings and suggest that condensation is significant during coalification at this early stage. An increasing degree of protonation on aromatic rings is observed as the rank of the sample increases from lignite to anthracite.

Catalytic trimerization of aromatic nitriles and triaryl-s-triazine ring cross-linked high temperature resistant polymers and copolymers made thereby

NASA Technical Reports Server (NTRS)

Hsu, L. C. (Inventor)

1979-01-01

Triazine compounds and cross-linked polymer compositions are made by heating aromatic nitriles to a temperature in the range of from about 100 C to about 700 C, and preferably in the range of from about 200 C to about 350 C, in the presence of a catalyst or mixture of catalysts selected from one or more of the following groups: (1) organic sulfonic and sulfinic acids, (2) organic phosphonic and phosphinic acids, and (3)metallic acetylacetonates, at a pressure in the range of from about atmospheric pressure to about 10,000 psi and preferably in the range of from about 200 psi to about 750 psi. Aromatic nitrile-modified (terminated and/or appended) imide, benzimidazole, imidazopyrrolone, quinoxaline, and other condensation type prepolymers or their precopolymers are made which are trimerized with or without a filler by the aforementioned catalytic trimerization process into triaryl-s-triazine ring containing or cross-linked polymeric or copolymeric products useful in applications requiring high thermal-oxidative stability and high performance structural properties at elevated temperatures.

Study of the slope of the linear relationship between retention and mobile phase composition (Snyder-Soczewiñski model) in normal phase liquid chromatography with bonded and charge-transfer phases.

PubMed

Wu, Di; Lucy, Charles A

2016-12-02

The Snyder model and the Soczewiñski model are compared on classic NPLC bonded phases using literature data, and on the charge transfer 2, 4-dinitroanilinopropyl (DNAP) column using experimentally collected data. Overall, the Snyder model slightly better predicts the n-slope than the Soczewiñski model. However, both models give comparable uncertainty in predicting n-slope for a given compound. The number of aromatic double bonds was the most suitable descriptor for estimating the relative n-slope of PAHs, as it correlated with behavior better than the number of aromatic rings and is simpler to calculate than the solute adsorption area. On the DNAP phase, a modified Soczewiñski model is suggested to allow for the significant contribution of the aromatic rings to the n-slope. For classic NPLC bonded phases and DNAP columns, the contribution of polar group to the n-slope parallels the adsorption energy of each polar group. Copyright © 2016 Elsevier B.V. All rights reserved.

Nucleophilic substitution at centers other than carbon: reaction at the chlorine of N-chloroacetanilides with triethylamine as the nucleophile

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

Underwood, G.R.; Dietze, P.E.

1984-12-28

The reaction between triethylamine (TEA) and a series of para-substituted N-chloroacetanilides has been studied in aqueous solution buffered to pHs between 1 and 5. The exclusive product derived from the aromatic moiety is the corresponding acetanilide. The reaction occurs via two parallel pseudo-second-order paths, one acid catalyzed (the Orton-like mechanism), the other uncatalyzed. The uncatalyzed reaction is accelerated by the presence of electron-withdrawing substituents on the aromatic ring and can best be represented as nucleophilic displacement at chlorine. It therefore appears to be the prototype of a convenient class of reactions for the study of displacement reactions at chlorine. Themore » rho value for this reaction is 3.87, indicating substantial negative charge buildup in the aromatic ring during of the transition state. The acid-catalyzed reaction is more complex, presumable involving a protonation equilibrium for the N-chloroacetanilide prior to the rate-determining step similar to that in the Orton reaction. 15 references, 2 figures, 3 tables.« less

A quantum chemical study for exploring the inhibitory effect of nitrogen containing species on the adsorption of polynuclear aromatic hydrocarbons over a Bronsted acid site

NASA Astrophysics Data System (ADS)

Celis-Cornejo, C. M.; Garnica Mantilla, M. M.; Baldovino-Medrano, V. G.; Ramírez-Caballero, G. E.

2016-08-01

The analysis of the inhibitory effect of nitrogenated compounds on the hydroprocessing and hydropurification of oil derived fuels is important to produce cleaner fuels. In this work, density functional theory calculations were performed to investigate the effect of the nitrogen containing molecules on the adsorption of Polynuclear Aromatic Hydrocarbons (PAHs). Mordenite was chosen as a zeolitic structure for simulating a Bronsted acid site. The character of the acid site was confirmed by both a vibrational frequency calculation and a Bader charge analysis. From the adsorption calculations, it was found that the adsorption energy of PAHs increases with the number of aromatic rings in the structure. Also, the nitrogen containing species possibly inhibit more extensively two and three rings PAHs because of their lower adsorption energies. Finally, it was observed that the nitrogen species tend to drag the proton from the mordenite acid site. This explains the inhibitory effect in the adsorption of PAHs and contributes to understanding the dynamics of hydrocarbon hydroprocessing in refineries.

Insertion of benzene rings into the amide bond: one-step synthesis of acridines and acridones from aryl amides.

PubMed

Pintori, Didier G; Greaney, Michael F

2010-01-01

Insertion of benzene rings into the amide bond using the reactive intermediate benzyne is described. Aromatic amides undergo smooth insertion when treated with O-triflatophenyl silane benzyne precursors, producing versatile aminobenzophenone products in good to excellent yield. The process is entirely metal-free and has been exemplified on the synthesis of biologically active acridones and acridines.

Quantifying Functional Group Interactions that Determine Urea Effects on Nucleic Acid Helix Formation

PubMed Central

Guinn, Emily J.; Schwinefus, Jeffrey J.; Cha, Hyo Keun; McDevitt, Joseph L.; Merker, Wolf E.; Ritzer, Ryan; Muth, Gregory W.; Engelsgjerd, Samuel W.; Mangold, Kathryn E.; Thompson, Perry J.; Kerins, Michael J.; Record, Thomas

2013-01-01

Urea destabilizes helical and folded conformations of nucleic acids and proteins, as well as protein-nucleic acid complexes. To understand these effects, extend previous characterizations of interactions of urea with protein functional groups, and thereby develop urea as a probe of conformational changes in protein and nucleic acid processes, we obtain chemical potential derivatives (μ23 = dμ2/dm3) quantifying interactions of urea (component 3) with nucleic acid bases, base analogs, nucleosides and nucleotide monophosphates (component 2) using osmometry and hexanol-water distribution assays. Dissection of these μ23 yields interaction potentials quantifying interactions of urea with unit surface areas of nucleic acid functional groups (heterocyclic aromatic ring, ring methyl, carbonyl and phosphate O, amino N, sugar (C,O)); urea interacts favorably with all these groups, relative to interactions with water. Interactions of urea with heterocyclic aromatic rings and attached methyl groups (as on thymine) are particularly favorable, as previously observed for urea-homocyclic aromatic ring interactions. Urea m-values determined for double helix formation by DNA dodecamers near 25°C are in the range 0.72 to 0.85 kcal mol−1 m−1 and exhibit little systematic dependence on nucleobase composition (17–42% GC). Interpretation of these results using the urea interaction potentials indicates that extensive (60–90%) stacking of nucleobases in the separated strands in the transition region is required to explain the m-value. Results for RNA and DNA dodecamers obtained at higher temperatures, and literature data, are consistent with this conclusion. This demonstrates the utility of urea as a quantitative probe of changes in surface area (ΔASA) in nucleic acid processes. PMID:23510511

Heteroaromatic π-Stacking Energy Landscapes

PubMed Central

2014-01-01

In this study we investigate π-stacking interactions of a variety of aromatic heterocycles with benzene using dispersion corrected density functional theory. We calculate extensive potential energy surfaces for parallel-displaced interaction geometries. We find that dispersion contributes significantly to the interaction energy and is complemented by a varying degree of electrostatic interactions. We identify geometric preferences and minimum interaction energies for a set of 13 5- and 6-membered aromatic heterocycles frequently encountered in small drug-like molecules. We demonstrate that the electrostatic properties of these systems are a key determinant for their orientational preferences. The results of this study can be applied in lead optimization for the improvement of stacking interactions, as it provides detailed energy landscapes for a wide range of coplanar heteroaromatic geometries. These energy landscapes can serve as a guide for ring replacement in structure-based drug design. PMID:24773380

Single Benzene Green Fluorophore: Solid-State Emissive, Water-Soluble, and Solvent- and pH-Independent Fluorescence with Large Stokes Shifts.

PubMed

Beppu, Teruo; Tomiguchi, Kosuke; Masuhara, Akito; Pu, Yong-Jin; Katagiri, Hiroshi

2015-06-15

Benzene is the simplest aromatic hydrocarbon with a six-membered ring. It is one of the most basic structural units for the construction of π conjugated systems, which are widely used as fluorescent dyes and other luminescent materials for imaging applications and displays because of their enhanced spectroscopic signal. Presented herein is 2,5-bis(methylsulfonyl)-1,4-diaminobenzene as a novel architecture for green fluorophores, established based on an effective push-pull system supported by intramolecular hydrogen bonding. This compound demonstrates high fluorescence emission and photostability and is solid-state emissive, water-soluble, and solvent- and pH-independent with quantum yields of Φ=0.67 and Stokes shift of 140 nm (in water). This architecture is a significant departure from conventional extended π-conjugated systems based on a flat and rigid molecular design and provides a minimum requirement for green fluorophores comprising a single benzene ring. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Biodegradation of trichloroethylene and involvement of an aromatic biodegradative pathway.

PubMed Central

Nelson, M J; Montgomery, S O; Mahaffey, W R; Pritchard, P H

1987-01-01

Biodegradation of trichloroethylene (TCE) by bacterial strain G4 resulted in complete dechlorination of the compound, as indicated by the production of inorganic chloride. A component of the water from which strain G4 was isolated that was required for TCE degradation was identified as phenol. Strain G4 degraded TCE in the presence of chloramphenicol only when preinduced with phenol. Toluene, o-cresol. and m-cresol could replace the phenol requirement. Two of the inducers of TCE metabolism, phenol and toluene, apparently induced the same aromatic degradative pathway that cleaved the aromatic ring by meta fission. Cells induced with either phenol or toluene had similar oxidation rates for several aromatic compounds and had similar levels of catechol-2,3-dioxygenase. The results indicate that one or more enzymes of an inducible pathway for aromatic degradation in strain G4 are responsible for the degradation of TCE. PMID:3606099

Testing of molded high temperature plastic actuator road seals for use in advanced aircraft hydraulic systems

NASA Technical Reports Server (NTRS)

Waterman, A. W.; Huxford, R. L.; Nelson, W. G.

1976-01-01

Molded high temperature plastic first and second stage rod seal elements were evaluated in seal assemblies to determine performance characteristics. These characteristics were compared with the performance of machined seal elements. The 6.35 cm second stage Chevron seal assembly was tested using molded Chevrons fabricated from five molding materials. Impulse screening tests conducted over a range of 311 K to 478 K revealed thermal setting deficiencies in the aromatic polyimide molding materials. Seal elements fabricated from aromatic copolyester materials structurally failed during impulse cycle calibration. Endurance testing of 3.85 million cycles at 450 K using MIL-H-83283 fluid showed poorer seal performance with the unfilled aromatic polyimide material than had been attained with seals machined from Vespel SP-21 material. The 6.35 cm first stage step-cut compression loaded seal ring fabricated from copolyester injection molding material failed structurally during impulse cycle calibration. Molding of complex shape rod seals was shown to be a potentially controllable technique, but additional molding material property testing is recommended.

Acyclic Cucurbit[n]uril-type Molecular Containers: Influence of Aromatic Walls on their Function as Solubilizing Excipients for Insoluble Drugs

PubMed Central

2015-01-01

We studied the influence of the aromatic sidewalls on the ability of acyclic CB[n]-type molecular containers (1a–1e) to act as solubilizing agents for 19 insoluble drugs including the developmental anticancer agent PBS-1086. All five containers exhibit good water solubility and weak self-association (Ks ≤ 624 M–1). We constructed phase solubility diagrams to extract Krel and Ka values for the container·drug complexes. The acyclic CB[n]-type containers generally display significantly higher Ka values than HP-β-CD toward drugs. Containers 1a–1e bind the steroidal ring system and aromatic moieties of insoluble drugs. Compound 1b displays highest affinity toward most of the drugs studied. Containers 1a and 1b are broadly applicable and can be used to formulate a wider variety of insoluble drugs than was previously possible with cyclodextrin technology. For drugs that are solubilized by both HP-β-CD and 1a–1e, lower concentrations of 1a–1e are required to achieve identical [drug]. PMID:25369565

Acyclic cucurbit[n]uril-type molecular containers: influence of aromatic walls on their function as solubilizing excipients for insoluble drugs.

PubMed

Zhang, Ben; Isaacs, Lyle

2014-11-26

We studied the influence of the aromatic sidewalls on the ability of acyclic CB[n]-type molecular containers (1a-1e) to act as solubilizing agents for 19 insoluble drugs including the developmental anticancer agent PBS-1086. All five containers exhibit good water solubility and weak self-association (Ks ≤ 624 M(-1)). We constructed phase solubility diagrams to extract Krel and Ka values for the container·drug complexes. The acyclic CB[n]-type containers generally display significantly higher Ka values than HP-β-CD toward drugs. Containers 1a-1e bind the steroidal ring system and aromatic moieties of insoluble drugs. Compound 1b displays highest affinity toward most of the drugs studied. Containers 1a and 1b are broadly applicable and can be used to formulate a wider variety of insoluble drugs than was previously possible with cyclodextrin technology. For drugs that are solubilized by both HP-β-CD and 1a-1e, lower concentrations of 1a-1e are required to achieve identical [drug].

Presence and potential significance of aromatic-ketone groups in aquatic humic substances

USGS Publications Warehouse

Leenheer, J.A.; Wilson, M.A.; Malcolm, R.L.

1987-01-01

Aquatic humic- and fulvic-acid standards of the International Humic Substances Society were characterized, with emphasis on carbonyl-group nature and content, by carbon-13 nuclear-magnetic-resonance spectroscopy, proton nuclear-magnetic-resonance spectroscopy, and infrared spectroscopy. After comparing spectral results of underivatized humic and fulvic acids with spectral results of chemically modified derivatives, that allow improved observation of the carbonyl group, the data clearly indicated that aromatic ketone groups comprised the majority of the carbonyl-group content. About one ketone group per monocyclic aromatic ring was determined for both humic and fulvic acids. Aromatic-ketone groups were hypothesized to form by photolytic rearrangements and oxidation of phenolic ester and hydrocarbon precursors; these groups have potential significance regarding haloform formation in water, reactivity resulting from active hydrogen of the methyl and methylene adjacent to the ketone groups, and formation of hemiketal and lactol structures. Aromatic-ketone groups also may be the point of attachment between aliphatic and aromatic moieties of aquatic humic-substance structure. ?? 1987.

Identification and quantification of seven fused aromatic rings C26H14 peri-condensed benzenoid polycyclic aromatic hydrocarbons in a complex mixture of polycyclic aromatic hydrocarbons from coal tar.

PubMed

Oña-Ruales, Jorge O; Ruiz-Morales, Yosadara; Wise, Stephen A

2016-04-15

A methodology for the characterization of groups of polycyclic aromatic hydrocarbons (PAHs) using a combination of normal phase liquid chromatography with ultraviolet-visible spectroscopy (NPLC/UV-vis) and gas chromatography with mass spectrometry (GC/MS) was used for the identification and quantification of seven fused aromatic rings C26H14 peri-condensed benzenoid polycyclic aromatic hydrocarbons, PAHs, in standard reference material (SRM) 1597a, complex mixture of PAHs from coal tar. The NPLC/UV-vis isolated the fractions based on the number of aromatic carbons and the GC/MS allowed the identification and quantification of five of the nine C26H14 PAH isomers; naphtho[1,2,3,4-ghi]perylene, dibenzo[b,ghi]perylene, dibenzo[b,pqr]perylene, naphtho[8,1,2-bcd]perylene, and dibenzo[cd,lm]perylene using a retention time comparison with authentic reference standards. For the other four benzenoid isomers with no available reference standards the following two approaches were used. First, the annellation theory was used to achieve the potential identification of benzo[qr]naphtho[3,2,1,8-defg]chrysene, and second, the elution distribution in the GC fractions was used to support the potential identification of benzo[qr]naphtho[3,2,1,8-defg]chrysene and to reach the tentative identifications of dibenzo[a,ghi]perylene, naphtho[7,8,1,2,3-pqrst]pentaphene, and anthra[2,1,9,8-opqra]naphthacene. It is the first time that naphtho[1,2,3,4-ghi]perylene, dibenzo[b,ghi]perylene, dibenzo[b,pqr]perylene, naphtho[8,1,2-bcd]perylene, and dibenzo[cd,lm]perylene are quantified, and the first time that benzo[qr]naphtho[3,2,1,8-defg]chrysene is potentially identified, in any sample, in any context. Copyright © 2016 Elsevier B.V. All rights reserved.

Spectroscopic study of proflavine adsorption on the carbon nanotube surface.

PubMed

Buchelnikov, Anatoly S; Dovbeshko, Galina I; Voronin, Dmitry P; Trachevsky, Vladimir V; Kostjukov, Viktor V; Evstigneev, Maxim P

2014-01-01

Despite the fact that non-covalent interactions between various aromatic compounds and carbon nanotubes are being extensively investigated now, there is still a lack of understanding about the nature of such interactions. The present paper sheds light on one of the possible mechanisms of interaction between the typical aromatic dye proflavine and the carbon nanotube surface, namely, π-stacking between aromatic rings of these compounds. To investigate such a complexation, a qualitative analysis was performed by means of ultraviolet visible, infrared, and nuclear magnetic resonance spectroscopy. The data obtained suggest that π-stacking brings the major contribution to the stabilization of the complex between proflavine and the carbon nanotube.

Determination and source identification of priority polycyclic aromatic hydrocarbons in PM2.5 in Taiyuan, China

NASA Astrophysics Data System (ADS)

Zhang, Meng; Xie, Jingfang; Wang, Zhentao; Zhao, Lijuan; Zhang, Hong; Li, Meng

2016-09-01

Sixteen polycyclic aromatic hydrocarbons (PAHs) present in PM2. 5 were analyzed in 2012 in Taiyuan (China) using high performance liquid chromatography (HPLC) with fluorescence and ultraviolet detectors. The average daily mass concentrations of ΣPAHs in different seasons ranged from 10.36 ng/m3 to 215.93 ng/m3 and had strong seasonal variation, with highest values in winter and lowest in summer. Over the whole year, PAHs appeared in the following order of frequency: 4-ring > 6-ring > 5-ring > 3-ring; in winter, the percentage of 4-ring PAHs was the highest (62.68%), while in summer, the percentages of 5-ring and 6-ring PAHs (cumulative total of 50.57%) were higher. The ratio method was employed to investigate potential source categories of PAHs in PM2.5 in Taiyuan, with data suggesting that the main PAH sources are coal and wood combustion and vehicle emissions. Finally, a risk assessment of PAHs was performed based on benzo(a)pyrene equivalent (BaPeq) values and individual cancer risk ratios, with results suggesting that the toxicity of PAHs was high during winter and spring time in Taiyuan. The values of incremental lifetime cancer risk (ILCR) induced by whole year inhalation exposure(Ri) for all age groups were larger than 10- 6 in spring and winter, while Ri values for male and female adults in summer and autumn were also larger than 10- 6, indicating high potential carcinogenic risk. During the same season, the ILCR of adults was greater than that of other age groups and that of females was a little higher than of males. With respect to the season, the ranking of ILCR in decreasing order was as follows: winter, spring, autumn, and summer.

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

Kuz'mina, L. G., E-mail: kuzmina@igic.ras.ru; Gunina, M. A.; Churakov, A. V.

Two aromatic esters with the formulas C{sub 6}H{sub 13}-O-C{sub 6}H{sub 4}-C(O)O-C{sub 6}H{sub 4}-O-C{sub 7}H{sub 15} (1) and C{sub 7}H{sub 15}-O-C{sub 6}H{sub 4}-C(O)O-C{sub 6}H{sub 4}-O-C{sub 4}H{sub 9} (2) belonging to nematic liquid-crystal compounds were studied by X-ray diffraction. Compound 1 crystallizes in two modifications: monoclinic (1-m) and triclinic (1-tr). The crystal packing of 1 and 2 is built from alternating loosely packed aliphatic regions and closely packed aromatic regions. In crystal structures 1-m and 2, the aromatic regions are linked into chains by hydrogen bonds with the participation of the carbonyl oxygen atom of the ester group and the C-H fragmentmore » of the benzene ring, but these hydrogen bonds in 1-m are much weaker than in 2. In 1-m there are {pi}-stacking interactions between the molecules, resulting in the formation of centrosymmetric dimers with an interplanar distance of 3.45 A. In 1-tr, the aromatic fragments form a herringbone packing motif favorable for a two-dimensional network of directional C-H...{pi}-system interactions.« less

Polycyclic aromatic hydrocarbons in water, sediment, soil, and plants of the Aojiang River waterway in Wenzhou, China

PubMed Central

Li, Jianwang; Shang, Xu; Zhao, Zhixu; Tanguay, Robert L.; Dong, Qiaoxiang; Huang, Changjiang

2012-01-01

The town of Shuitou was renowned as the leather capital of China because of its large-scale tanning industry, but the industry’s lack of pollution controls has caused severe damage to the local water system. This study determined 15 priority polycyclic aromatic hydrocarbons (PAHs) in water, sediment, soil, and plant samples collected from Aojiang River and its estuary. The total PAHs ranged from 910 to 1520 ng/L in water samples. The total PAH in sediments were moderate to low in comparison with other rivers and estuaries in China, but the relative proportions of PAHs per million people are high when considering the population size associated with each watershed. Ratios of fluoranthene/pyrene and PAHs with low/high molecular weight suggest a petrogenic PAH origin. The PAH composition profile in soil was similar to that in sediment with 4–6 ring PAHs being dominant. The PAHs with 2–3 rings were the dominant species in plant leaves. There were no correlations between PAHs in soils and in plants, suggesting that PAHs accumulate in plant leaves through absorption from the air. The general observation of elevated PAH concentrations in all matrix suggests a possible contribution by the local leather industry on the PAH concentrations in the Aojiang watershed. PMID:19726127

Distribution, partition and removal of polycyclic aromatic hydrocarbons (PAHs) during coking wastewater treatment processes.

PubMed

Zhang, Wanhui; Wei, Chaohai; An, Guanfeng

2015-05-01

In this study, we report the performance of a full-scale conventional activated sludge (A-O1-O2) treatment in eliminating polycyclic aromatic hydrocarbons (PAHs). Both aqueous and solid phases along with the coking wastewater treatment processes were analyzed for the presence of 18 PAHs. It was found that the target compounds occurred widely in raw coking wastewater, treated effluent and sludge samples. In the coking wastewater treatment system, 4-5 ring PAHs were the dominant compounds, while 4 rings PAHs predominated in the sludge samples. Over 98% of the PAH removal was achieved in the coking wastewater treatment plant (WWTP), with the total concentration of PAHs being 21.3 ± 1.9 μg L(-1) in the final effluent. During the coking wastewater treatment processes, the association of the lower molecular weight PAH with suspended solids was generally less than 60%, while the association of higher molecular weight PAHs was greater than 90%. High distribution efficiencies (Kdp and Kds) were found, suggesting that adsorption was the potential removal pathway of PAHs. Finally, the mass balances of PAHs in various stages of the coking WWTP were obtained, and the results indicated that adsorption to sludge was the main removal pathway for PAHs in the coking wastewater treatment processes.

The docking of chiral analytes on proline-based chiral stationary phases: A molecular dynamics study of selectivity.

PubMed

Ashtari, M; Cann, N M

2015-08-28

Molecular dynamics simulations are employed to examine the selectivity of four proline-based chiral stationary phases in two solvent environments, a relatively apolar n-hexane/2-propanol solvent and a polar water/methanol solvent. The four chiral surfaces are based on a BOC-terminated diproline, a TMA-terminated diproline, a TMA-terminated triproline and a TMA-terminated hexaproline. This range of chiral selectors allows an analysis of the impact of oligomer length and terminal group on selectivity while the two solvent environments indicate the impact of solvent hydrogen bonding and polarity. The selector-analyte interactions are examined for six closely related analytes that each have an aromatic moiety, a hydrogen, and an alcohol group directly bonded to the stereocenter. The analytes differ in the nature of the aromatic group (phenyl or anthracyl), in the attachment point (to the central ring or a side ring in the anthracyl), and in the fourth group bonded to the carbon (CH3, CF3, or C2H5). For each of the 48 solvent+selector+analyte systems, selectivity factors are calculated and, when possible, compared to experiment. The docking mode for these proline-based selectors is analyzed. Copyright © 2015 Elsevier B.V. All rights reserved.

Effect of Hartree-Fock exact exchange on intramolecular magnetic coupling constants of organic diradicals

NASA Astrophysics Data System (ADS)

Cho, Daeheum; Ko, Kyoung Chul; Ikabata, Yasuhiro; Wakayama, Kazufumi; Yoshikawa, Takeshi; Nakai, Hiromi; Lee, Jin Yong

2015-01-01

The intramolecular magnetic coupling constant (J) of diradical systems linked with five- or six-membered aromatic rings was calculated to obtain the scaling factor (experimental J/calculated J ratio) for various density functional theory (DFT) functionals. Scaling factors of group A (PBE, TPSSh, B3LYP, B97-1, X3LYP, PBE0, and BH&HLYP) and B (M06-L, M06, M06-2X, and M06-HF) were shown to decrease as the amount of Hartree-Fock exact exchange (HFx) increases, in other words, overestimation of calculated J becomes more severe as the HFx increases. We further investigated the effect of HFx fraction of DFT functional on J value, spin contamination, and spin density distributions by comparing the B3LYP analogues containing different amount of HFx. It was revealed that spin contamination and spin densities at each atom increases as the HFx increases. Above all, newly developed BLYP-5 functional, which has 5% of HFx, was found to have the scaling factor of 1.029, indicating that calculated J values are very close to that of experimental values without scaling. BLYP-5 has potential to be utilized for accurate evaluation of intramolecular magnetic coupling constant (J) of diradicals linked by five- or six-membered aromatic ring couplers.

Effect of Hartree-Fock exact exchange on intramolecular magnetic coupling constants of organic diradicals.

PubMed

Cho, Daeheum; Ko, Kyoung Chul; Ikabata, Yasuhiro; Wakayama, Kazufumi; Yoshikawa, Takeshi; Nakai, Hiromi; Lee, Jin Yong

2015-01-14

The intramolecular magnetic coupling constant (J) of diradical systems linked with five- or six-membered aromatic rings was calculated to obtain the scaling factor (experimental J/calculated J ratio) for various density functional theory (DFT) functionals. Scaling factors of group A (PBE, TPSSh, B3LYP, B97-1, X3LYP, PBE0, and BH&HLYP) and B (M06-L, M06, M06-2X, and M06-HF) were shown to decrease as the amount of Hartree-Fock exact exchange (HFx) increases, in other words, overestimation of calculated J becomes more severe as the HFx increases. We further investigated the effect of HFx fraction of DFT functional on J value, spin contamination, and spin density distributions by comparing the B3LYP analogues containing different amount of HFx. It was revealed that spin contamination and spin densities at each atom increases as the HFx increases. Above all, newly developed BLYP-5 functional, which has 5% of HFx, was found to have the scaling factor of 1.029, indicating that calculated J values are very close to that of experimental values without scaling. BLYP-5 has potential to be utilized for accurate evaluation of intramolecular magnetic coupling constant (J) of diradicals linked by five- or six-membered aromatic ring couplers.

Use of Biomarkers in Oil Spill Risk Assessment in the marine environment

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

Anderson, Jack W.; Lee, Richard F.

2006-12-01

Numerous molecular, cellular and physiological biomarkers have been used to assess the responses of marine animals to petroleum compounds. To be used in ecological risk assessment after an oil spill, a biomarker response needs to be linked to petroleum exposure and not strongly influenced by internal and external confounding factors. Biomarker responses to petroleum PAH, dominated by alkylated two- and three-ringed aromatics, can be quite different than responses to pyrogenic PAH, dominated by four- and five-ringed aromatics. In many field sites there is a mixture of petrogenic and pyrogenic PAH, along with other contaminant, making it difficult to relate biomarkermore » responses to a particular contaminant class. Biomarkers used to assess marine animal responses in the field include the cytochrome P450 system, heat stress protein, histopathology and bile fluorescent compounds (FAC). Other biomarkers, including DNA/chromosomal damage and phase 2 enzymes, have been shown to respond after laboratory exposure, but more works needs to be done to demonstrate their usefulness in the field. One of the most useful biomarkers of petroleum exposure are the FAC responses in fish, which can be used to distinguish between petrogenic and pyrogenic PAH exposure. Few of the presently used biomarkers are linked to higher order biological effects, e.g toxicity, reproductive failure.« less

A 3D QSAR pharmacophore model and quantum chemical structure--activity analysis of chloroquine(CQ)-resistance reversal.

PubMed

Bhattacharjee, Apurba K; Kyle, Dennis E; Vennerstrom, Jonathan L; Milhous, Wilbur K

2002-01-01

Using CATALYST, a three-dimensional QSAR pharmacophore model for chloroquine(CQ)-resistance reversal was developed from a training set of 17 compounds. These included imipramine (1), desipramine (2), and 15 of their analogues (3-17), some of which fully reversed CQ-resistance, while others were without effect. The generated pharmacophore model indicates that two aromatic hydrophobic interaction sites on the tricyclic ring and a hydrogen bond acceptor (lipid) site at the side chain, preferably on a nitrogen atom, are necessary for potent activity. Stereoelectronic properties calculated by using AM1 semiempirical calculations were consistent with the model, particularly the electrostatic potential profiles characterized by a localized negative potential region by the side chain nitrogen atom and a large region covering the aromatic ring. The calculated data further revealed that aminoalkyl substitution at the N5-position of the heterocycle and a secondary or tertiary aliphatic aminoalkyl nitrogen atom with a two or three carbon bridge to the heteroaromatic nitrogen (N5) are required for potent "resistance reversal activity". Lowest energy conformers for 1-17 were determined and optimized to afford stereoelectronic properties such as molecular orbital energies, electrostatic potentials, atomic charges, proton affinities, octanol-water partition coefficients (log P), and structural parameters. For 1-17, fairly good correlation exists between resistance reversal activity and intrinsic basicity of the nitrogen atom at the tricyclic ring system, frontier orbital energies, and lipophilicity. Significantly, nine out of 11 of a group of structurally diverse CQ-resistance reversal agents mapped very well on the 3D QSAR pharmacophore model.

Flame propagation in heterogeneous mixtures of fuel drops and air

NASA Technical Reports Server (NTRS)

Myers, G. D.; Lefebvre, A. H.

1984-01-01

Photographic methods are used to measure flame speeds in flowing mixtures of fuel props and air at atmospheric pressure. The fuels employed include a conventional fuel oil plus various blends JP 7 with stocks containing single-ring and mullti-ring aromatics. The results for stoichiometric mixtures show that flame propagation cannot occur in mixtures containing mean drop sizes larger than 300 to 400 microns, depending on the fuel type. For smaller drop sizes, down to around 60 microns, flame speed is inversely proportional to drop size, indicating that evaporation rates are limiting to flame speed. Below around 60 microns, the curves of flame speed versus mean drop size flatten out, thereby demonstrating that for finely atomized sprays flame speeds are much less dependent on evaporation rates, and are governed primarily by mixing and/or chemical reaction rates. The fuels exhibiting the highest flame speeds are those containing multi-ring aromatics. This is attributed to the higher radiative heat flux emanating from their soot-bearing flames which enhances the rate of evaporation of the fuel drops approaching the flame front.

Carbon-supported bimetallic Pd–Fe catalysts for vapor-phase hydrodeoxygenation of guaiacol

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

Sun, Junming; Karim, Ayman M.; Zhang, He

2013-10-01

Abstract Carbon supported metal catalysts (Cu/C, Fe/C, Pd/C, Pt/C, PdFe/C and Ru/C) have been prepared, characterized and tested for vapor-phase hydrodeoxygenation (HDO) of guaiacol (GUA) at atmospheric pressure. Phenol was the major intermediate on all catalysts. Over the noble metal catalysts saturation of the aromatic ring was the major pathway observed at low temperature (250 °C), forming predominantly cyclohexanone and cyclohexanol. Substantial ring opening reaction was observed on Pt/C and Ru/C at higher reaction temperatures (e.g., 350 °C). Base metal catalysts, especially Fe/C, were found to exhibit high HDO activity without ring-saturation or ring-opening with the main products being benzene,more » phenol along with small amounts of cresol, toluene and trimethylbenzene (TMB). A substantial enhancement in HDO activity was observed on the PdFe/C catalysts. Compared with Fe/C, the yield to oxygen-free aromatic products (i.e., benzene/toluene/TMB) on PdFe/C increased by a factor of four at 350 °C, and by approximately a factor of two (83.2% versus 43.3%) at 450 °C. The enhanced activity of PdFe/C is attributed to the formation of PdFe alloy as evidenced by STEM, EDS and TPR.« less

A cluster of bacterial genes for anaerobic benzene ring biodegradation

PubMed Central

Egland, Paul G.; Pelletier, Dale A.; Dispensa, Marilyn; Gibson, Jane; Harwood, Caroline S.

1997-01-01

A reductive benzoate pathway is the central conduit for the anaerobic biodegradation of aromatic pollutants and lignin monomers. Benzene ring reduction requires a large input of energy and this metabolic capability has, so far, been reported only in bacteria. To determine the molecular basis for this environmentally important process, we cloned and analyzed genes required for the anaerobic degradation of benzoate and related compounds from the phototrophic bacterium, Rhodopseudomonas palustris. A cluster of 24 genes was identified that includes twelve genes likely to be involved in anaerobic benzoate degradation and additional genes that convert the related compounds 4-hydroxybenzoate and cyclohexanecarboxylate to benzoyl-CoA. Genes encoding benzoyl-CoA reductase, a novel enzyme able to overcome the resonance stability of the aromatic ring, were identified by directed mutagenesis. The gene encoding the ring-cleavage enzyme, 2-ketocyclohexanecarboxyl-CoA hydrolase, was identified by assaying the enzymatic activity of the protein expressed in Escherichia coli. Physiological data and DNA sequence analyses indicate that the benzoate pathway consists of unusual enzymes for ring reduction and cleavage interposed among enzymes homologous to those catalyzing fatty acid degradation. The cloned genes should be useful as probes to identify benzoate degradation genes from other metabolically distinct groups of anaerobic bacteria, such as denitrifying bacteria and sulfate-reducing bacteria. PMID:9177244

Polycyclic aromatic hydrocarbons associated with road deposited solid and their ecological risk: Implications for road stormwater reuse.

PubMed

Liu, Liang; Liu, An; Li, Yang; Zhang, Lixun; Zhang, Guijuan; Guan, Yuntao

2016-09-01

Reusing stormwater is becoming popular worldwide. However, urban road stormwater commonly contains toxic pollutants, such as polycyclic aromatic hydrocarbons (PAHs), which could undermine reuse safety. This study investigated pollution level of PAHs and their composition build-up on urban roads in a typical megacity in South China. The potential ecological risk posed by PAHs associated with road deposited solid (RDS) was also assessed. Results showed that ecological risk levels varied based on different land use types, which could be significantly influenced by the composition of PAHs and characteristics of RDS. A higher percentage of high-ring PAHs, such as more than four rings, could pose higher ecological risk and are more likely to undermine stormwater reuse safety. Additionally, the degree of traffic congestion rather than traffic volume was found to exert a more significant influence on the generation of high-ring PAH generation. Therefore, stormwater from more congested roads might need proper treatment (particularly for removing high-ring PAHs) before reuse or could be suitable for purposes requiring low-water-quality. The findings of this study are expected to contribute to adequate stormwater reuse strategy development and to enhance the safety of urban road stormwater reuse. Copyright © 2016 Elsevier B.V. All rights reserved.

Retention behavior of isomeric polycyclic aromatic sulfur heterocycles in gas chromatography on stationary phases of different selectivity

PubMed Central

Wilson, Walter B.; Sander, Lane C.; Oña-Ruales, Jorge O.; Mössner, Stephanie G.; Sidisky, Leonard M.; Lee, Milton L.; Wise, Stephen A.

2017-01-01

Retention indices for 48 polycyclic aromatic sulfur heterocycles (PASHs) were determined using gas chromatography with three different stationary phases: a 50% phenyl phase, a 50% liquid crystalline dimethylpolysiloxane (LC-DMPS) phase, and an ionic liquid (IL) phase. Correlations between the retention behavior on the three stationary phases and PASH geometry (L/B and T, i.e., length-to-breadth ratio and thickness, respectively) were investigated for the following four isomer sets: (1) 4 three-ring molecular mass (MM) 184 Da PASHs, (2) 13 four-ring MM 234 Da PASHs, (3) 10 five-ring MM 258 Da PASHs, and (4) 20 five-ring MM 284 Da PASHs. Correlation coefficients for retention on the 50% LC-DMPS vs L/B ranged from r = 0.50 (MM 284 Da) to r = 0.77 (MM 234 Da). Correlation coefficients for retention on the IL phase vs L/B ranged from r = 0.31 (MM 234 Da) to r = 0.54 (MM 284 Da). Correlation coefficients for retention on the 50% phenyl vs L/B ranged from r = 0.14 (MM 258 Da) to r = 0.59 (MM 284 Da). Several correlation trends are discussed in detail for the retention behavior of PASH on the three stationary phases. PMID:28089272

Retention behavior of isomeric polycyclic aromatic sulfur heterocycles in gas chromatography on stationary phases of different selectivity.

PubMed

Wilson, Walter B; Sander, Lane C; Oña-Ruales, Jorge O; Mössner, Stephanie G; Sidisky, Leonard M; Lee, Milton L; Wise, Stephen A

2017-02-17

Retention indices for 48 polycyclic aromatic sulfur heterocycles (PASHs) were determined using gas chromatography with three different stationary phases: a 50% phenyl phase, a 50% liquid crystalline dimethylpolysiloxane (LC-DMPS) phase, and an ionic liquid (IL) phase. Correlations between the retention behavior on the three stationary phases and PASH geometry (L/B and T, i.e., length-to-breadth ratio and thickness, respectively) were investigated for the following four isomer sets: (1) 4 three-ring molecular mass (MM) 184Da PASHs, (2) 13 four-ring MM 234Da PASHs, (3) 10 five-ring MM 258Da PASHs, and (4) 20 five-ring MM 284Da PASHs. Correlation coefficients for retention on the 50% LC-DMPS vs L/B ranged from r=0.50 (MM 284Da) to r=0.77 (MM 234Da). Correlation coefficients for retention on the IL phase vs L/B ranged from r=0.31 (MM 234Da) to r=0.54 (MM 284Da). Correlation coefficients for retention on the 50% phenyl vs L/B ranged from r=0.14 (MM 258Da) to r=0.59 (MM 284Da). Several correlation trends are discussed in detail for the retention behavior of PASH on the three stationary phases. Published by Elsevier B.V.

Molecular simulation insights on the in vacuo adsorption of amino acids on graphene oxide surfaces with varying surface oxygen densities

NASA Astrophysics Data System (ADS)

Rahmani, Farzin; Nouranian, Sasan; Mahdavi, Mina; Al-Ostaz, Ahmed

2016-11-01

In this fundamental study, a series of molecular dynamics simulations were performed in vacuo to investigate the energetics and select geometries of 20 standard amino acids (AAs) on pristine graphene (PG) and graphene oxide (GO) surfaces as a function of graphene surface oxygen density. These interactions are of key interest to graphene/biomolecular systems. Our results indicate that aromatic AAs exhibit the strongest total interactions with the PG surfaces due to π-π stacking. Tryptophan (Trp) has the highest aromaticity due to its indole side chain and, hence, has the strongest interaction among all AAs (-16.66 kcal/mol). Aliphatic, polar, and charged AAs show various levels of affinity to the PG sheets depending on the strength of their side chain hydrophobic interactions. For example, arginine (Arg) with its guanidinium side chain exhibits the strongest interaction with the PG sheets (-13.81 kcal/mol) following aromatic AAs. Also, glycine (Gly; a polar AA) has the weakest interaction with the PG sheets (-7.29 kcal/mol). When oxygen-containing functional groups are added to the graphene sheets, the π-π stacking in aromatic AAs becomes disrupted and perfect parallelism of the aromatic rings is lost. Moreover, hydrogen bonding and/or electrostatic interactions become more pronounced. Charged AAs exhibit the strongest interactions with the GO surfaces. In general, the AA-GO interactions increase with increasing surface oxygen density, and the effect is more pronounced at higher O/C ratios. This study provides a quantitative measure of AA-graphene interactions for the design and tuning of biomolecular systems suitable for biosensing, drug delivery, and gene delivery applications.

Recent advances in oxidative valorization of lignin

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

Ma, Ruoshui; Guo, Mond; Zhang, Xiao

Lignin, an aromatic macromolecule synthesized by all higher plants, is one of the most intriguing natural materials for utilization across a wide range of applications. Depolymerization and fragmentation of lignin into small chemicals constituents which can either replace current market products or be used building blocks for new material synthesis is a focus of current lignin valorization strategies. And among the variety of lignin degradation chemistries, catalytic oxidation of lignin presents an energy efficient means of lignin depolymerization and generating selective reaction products. Our review provides a summary of the recent advancements in oxidative lignin valorization couched in a discussionmore » on how these chemistries may contribute to the degradation of the lignin macromolecule through three major approaches: 1) inter-unit linkages cleavage; 2) propanyl side-chain oxidative modification; and 3) oxidation of the aromatic ring and ring cleavage reactions.« less

Recent advances in oxidative valorization of lignin

DOE PAGES

Ma, Ruoshui; Guo, Mond; Zhang, Xiao

2017-07-21

Lignin, an aromatic macromolecule synthesized by all higher plants, is one of the most intriguing natural materials for utilization across a wide range of applications. Depolymerization and fragmentation of lignin into small chemicals constituents which can either replace current market products or be used building blocks for new material synthesis is a focus of current lignin valorization strategies. And among the variety of lignin degradation chemistries, catalytic oxidation of lignin presents an energy efficient means of lignin depolymerization and generating selective reaction products. Our review provides a summary of the recent advancements in oxidative lignin valorization couched in a discussionmore » on how these chemistries may contribute to the degradation of the lignin macromolecule through three major approaches: 1) inter-unit linkages cleavage; 2) propanyl side-chain oxidative modification; and 3) oxidation of the aromatic ring and ring cleavage reactions.« less

Study on the interaction between typical phthalic acid esters (PAEs) and human haemoglobin (hHb) by molecular docking.

PubMed

Tan, Songwen; Wang, Donglin; Chi, Zhenxing; Li, Weiguo; Shan, Ye

2017-07-01

This work has evaluated the binding force between hHb and typcial PAEs (DMP, DEP, DPRP, DBP, DIBP, DHP and DPHP) using molecule docking technique. The DPHP with 3 aromatic rings has the strongest binding (-ΔG binding : 6.0kcalmol -1 ) than other PAEs (-ΔG binding : 2.91∼4.48kcalmol -1 ). The DMP with the lowest molecular weight has a high binding force (-ΔG binding : 4.48kcalmol -1 ), while the DHP with the highest molecular weight has the lowest binding force (-ΔG binding : 2.91kcalmol -1 ). When the length of side chain increases, the binding force trend to decrease, regarding the VDW forces and H-bonding. The lgK ow -ΔG binding plotting figure shows that a higher K ow value is accompanied by a lower binding force. The aromatic ring existed in PAEs largely increases the binding force between the hHb and the PAEs. On the other hand, the PAEs with higher number of carbon, meaning a higher hydrophobicity, can enter into the hydrophobic space of hHb centre deeper and bond to different position. The aromatic ring decreases the depth of binding position in the hydrophobic space. This work provides basic data and a theoretical method to assess the transport and accumulation of PAEs in human body, and the cytotoxicity of PAEs to hBRCs. Copyright © 2017 Elsevier B.V. All rights reserved.

Antioxidant activity of selenenamide-based mimic as a function of the aromatic thiols nucleophilicity, a DFT-SAPE model.

PubMed

Kheirabadi, Ramesh; Izadyar, Mohammad

2018-05-18

The mechanism of action of the selenenamide 1 as a mimic of the glutathione peroxidase (GPx) was investigated by the density functional theory. The solvent-assisted proton exchange procedure was applied to model the catalytic behavior and antioxidant activity of this mimic. To have an insight into the charge transfer effect, different aromatic thiols, including electron donating substituents on the phenyl ring were considered. The catalytic behavior of the selenenamide was modeled in a four-step mechanism, described by the oxidation of the mimic, the reduction of the obtained product, selenoxide, the reduction of the selenenylsulfide and dehydration of selenenic acid. On the basis of the activation parameters, the final step of the proposed mechanism is the rate determining states of the catalytic cycle. Turnover frequency (TOF) analysis showed that the electron donating groups at the para-position of the phenyl ring of the PhSH do not affect the catalytic activity of the selenenamide in contrast to p-methyl thiophenol which indicates the highest nucleophilicity. The evaluation of the electronic contribution of the various donating groups on the phenyl ring of the aromatic thiols shows that the antioxidant activity of the selenenamide sufficiently increases in the presence of the electron-donating substitutions. Finally, the charge transfer process at the rate-determining state was investigated based on the natural bond orbital analysis. Copyright © 2018 Elsevier Ltd. All rights reserved.

One-pot, two-step desymmetrization of symmetrical benzils catalyzed by the methylsulfinyl (dimsyl) anion.

PubMed

Ragno, Daniele; Bortolini, Olga; Giovannini, Pier Paolo; Massi, Alessandro; Pacifico, Salvatore; Zaghi, Anna

2014-08-14

An operationally simple one-pot, two-step procedure for the desymmetrization of benzils is herein described. This consists in the chemoselective cross-benzoin reaction of symmetrical benzils with aromatic aldehydes catalyzed by the methyl sulfinyl (dimsyl) anion, followed by microwave-assisted oxidation of the resulting benzoylated benzoins with nitrate, avoiding the costly isolation procedure. Both electron-withdrawing and electron-donating substituents may be accommodated on the aromatic rings of the final unsymmetrical benzil.

Oxygen activation by mononuclear nonheme iron dioxygenases involved in the degradation of aromatics.

PubMed

Wang, Yifan; Li, Jiasong; Liu, Aimin

2017-04-01

Molecular oxygen is utilized in numerous metabolic pathways fundamental for life. Mononuclear nonheme iron-dependent oxygenase enzymes are well known for their involvement in some of these pathways, activating O 2 so that oxygen atoms can be incorporated into their primary substrates. These reactions often initiate pathways that allow organisms to use stable organic molecules as sources of carbon and energy for growth. From the myriad of reactions in which these enzymes are involved, this perspective recounts the general mechanisms of aromatic dihydroxylation and oxidative ring cleavage, both of which are ubiquitous chemical reactions found in life-sustaining processes. The organic substrate provides all four electrons required for oxygen activation and insertion in the reactions mediated by extradiol and intradiol ring-cleaving catechol dioxygenases. In contrast, two of the electrons are provided by NADH in the cis-dihydroxylation mechanism of Rieske dioxygenases. The catalytic nonheme Fe center, with the aid of active site residues, facilitates these electron transfers to O 2 as key elements of the activation processes. This review discusses some general questions for the catalytic strategies of oxygen activation and insertion into aromatic compounds employed by mononuclear nonheme iron-dependent dioxygenases. These include: (1) how oxygen is activated, (2) whether there are common intermediates before oxygen transfer to the aromatic substrate, and (3) are these key intermediates unique to mononuclear nonheme iron dioxygenases?

Determination of particle-bound polycyclic aromatic hydrocarbons emitted from co-pelletization combustion of lignite and rubber wood sawdust

NASA Astrophysics Data System (ADS)

Kan, R.; Kaosol, T.; Tekasakul, P.; Tekasakul, S.

2017-09-01

Determination of particle-bound Polycyclic Aromatic Hydrocarbons (PAHs) emitted from co-pelletization combustion of lignite and rubber wood sawdust in a horizontal tube furnace is investigated using High Performance Liquid Chromatography with coupled Diode Array and Fluorescence Detection (HPLC-DAD/FLD). The particle-bound PAHs based on the mass concentration and the toxicity degree are discussed in the different size ranges of the particulate matters from 0.07-11 μm. In the present study, the particle-bound PAHs are likely abundant in the fine particles. More than 70% of toxicity degree of PAHs falls into PM1.1 while more than 80% of mass concentration of PAHs falls into PM2.5. The addition of lignite amount in the co-pelletization results in the increasing concentration of either 4-6 aromatic ring PAHs or high molecular weight PAHs. The high contribution of 4-6 aromatic ring PAHs or high molecular weight PAHs in the fine particles should be paid much more attention because of high probability of human carcinogenic. Furthermore, the rubber wood sawdust pellets emit high mass concentration of PAHs whereas the lignite pellets emit high toxicity degree of PAHs. By co-pelletized rubber wood sawdust with lignite (50% lignite pellets) has significant effect to reduce the toxicity degree of PAHs by 70%.

Comparing Urinary Biomarkers of Airborne and Dermal Exposure to Polycyclic Aromatic Compounds in Asphalt-Exposed Workers

PubMed Central

Sobus, Jon R.; McClean, Michael D.; Herrick, Robert F.; Waidyanatha, Suramya; Nylander-French, Leena A.; Kupper, Lawrence L.; Rappaport, Stephen M.

2009-01-01

When working with hot mix asphalt, road pavers are exposed to polycyclic aromatic hydrocarbons (PAHs) through the inhalation of vapors and particulate matter (PM) and through dermal contact with PM and contaminated surfaces. Several PAHs with four to six rings are potent carcinogens which reside in these particulate emissions. Since urinary biomarkers of large PAHs are rarely detectable in asphalt workers, attention has focused upon urinary levels of the more volatile and abundant two-ring and three-ring PAHs as potential biomarkers of PAH exposure. Here, we compare levels of particulate polycyclic aromatic compounds (P-PACs, a group of aromatic hydrocarbons containing PAHs and heterocyclic compounds with four or more rings) in air and dermal patch samples from 20 road pavers to the corresponding urinary levels of naphthalene (U-Nap) (two rings), phenanthrene (U-Phe) (three rings), monohydroxylated metabolites of naphthalene (OH-Nap) and phenanthrene (OH-Phe), and 1-hydroxypyrene (OH-Pyr) (four rings), the most widely used biomarker of PAH exposure. For each worker, daily breathing-zone air (n = 55) and dermal patch samples (n = 56) were collected on three consecutive workdays along with postshift, bedtime, and morning urine samples (n = 149). Measured levels of P-PACs and the urinary analytes were used to statistically model exposure–biomarker relationships while controlling for urinary creatinine, smoking status, age, body mass index, and the timing of urine sampling. Levels of OH-Phe in urine collected postshift, at bedtime, and the following morning were all significantly associated with levels of P-PACs in air and dermal patch samples. For U-Nap, U-Phe, and OH-Pyr, both air and dermal patch measurements of P-PACs were significant predictors of postshift urine levels, and dermal patch measurements were significant predictors of bedtime urine levels (all three analytes) and morning urine levels (U-Nap and OH-Pyr only). Significant effects of creatinine concentration were observed for all analytes, and modest effects of smoking status and body mass index were observed for U-Phe and OH-Pyr, respectively. Levels of OH-Nap were not associated with P-PAC measurements in air or dermal patch samples but were significantly affected by smoking status, age, day of sample collection, and urinary creatinine. We conclude that U-Nap, U-Phe, OH-Phe, and OH-Pyr can be used as biomarkers of exposure to particulate asphalt emissions, with OH-Phe being the most promising candidate. Indications that levels of U-Nap, U-Phe, and OH-Pyr were significantly associated with dermal patch measurements well into the evening after a given work shift, combined with the small ratios of within-person variance components to between-person variance components at bedtime, suggest that bedtime measurements may be useful for investigating dermal PAH exposures. PMID:19602502

Effect of B-ring substitution pattern on binding mode of propionamide selective androgen receptor modulators.

PubMed

Bohl, Casey E; Wu, Zengru; Chen, Jiyun; Mohler, Michael L; Yang, Jun; Hwang, Dong Jin; Mustafa, Suni; Miller, Duane D; Bell, Charles E; Dalton, James T

2008-10-15

Selective androgen receptor modulators (SARMs) are essentially prostate sparing androgens, which provide therapeutic potential in osteoporosis, male hormone replacement, and muscle wasting. Herein we report crystal structures of the androgen receptor (AR) ligand-binding domain (LBD) complexed to a series of potent synthetic nonsteroidal SARMs with a substituted pendant arene referred to as the B-ring. We found that hydrophilic B-ring para-substituted analogs exhibit an additional region of hydrogen bonding not seen with steroidal compounds and that multiple halogen substitutions affect the B-ring conformation and aromatic interactions with Trp741. This information elucidates interactions important for high AR binding affinity and provides new insight for structure-based drug design.

Biotechnological production of aromatic compounds of the extended shikimate pathway from renewable biomass.

PubMed

Lee, Jin-Ho; Wendisch, Volker F

2017-09-10

Aromatic chemicals that contain an unsaturated ring with alternating double and single bonds find numerous applications in a wide range of industries, e.g. paper and dye manufacture, as fuel additives, electrical insulation, resins, pharmaceuticals, agrochemicals, in food, feed and cosmetics. Their chemical production is based on petroleum (BTX; benzene, toluene, and xylene), but they can also be obtained from plants by extraction. Due to petroleum depletion, health compliance, or environmental issues such as global warming, the biotechnological production of aromatics from renewable biomass came more and more into focus. Lignin, a complex polymeric aromatic molecule itself, is a natural source of aromatic compounds. Many microorganisms are able to catabolize a plethora of aromatic compounds and interception of these pathways may lead to the biotechnological production of value-added aromatic compounds which will be discussed for Corynebacterium glutamicum. Biosynthesis of aromatic amino acids not only gives rise to l-tryptophan, L-tyrosine and l-phenylalanine, but also to aromatic intermediates such as dehydroshikimate or chorismate from which value-added aromatic compounds can be derived. In this review, we will summarize recent strategies for the biotechnological production of aromatic and related compounds from renewable biomass by Escherichia coli, Pseudomonas putida, C. glutamicum and Saccharomyces cerevisiae. In particular, we will focus on metabolic engineering of the extended shikimate pathway. Copyright © 2016 Elsevier B.V. All rights reserved.

Flammability and Photo-Stability of Selected Polymer Systems

NASA Technical Reports Server (NTRS)

Lo, Jeelin

1981-01-01

A systematic approach to the improvement of the flammability of epoxy resins, bisphenol-A polycarbonate poly(butylene terephthalate), and Nylon 6.6 by introducing halogens and loop functionality into the flame retardants is described. The phthalides (the loop functionality containing molecules) include 3,3-bis(4-bromophenyl)-phthalide, 3,3-bis(4-chlorophenyl)phthalide, and phenolphthalein. The phthalide containing epoxy resins are synthesized and characterized in comparison with the bisphenol-A epoxy resins in terms of flammability in the copolymer systems. The resins include diglycidyl ethers of phenolphthalein, bisphenol-A. tetrabromobisphenol-A, and tetraoromophenolphthalein. The vaporization of the phthalide additive in the polymers is observed in Thermal Gravimetric Analysis. The flame retardancy is primarily due to the presence of halogens. In the poly(butylene terephthalate) system, the cleavage of the C(sub aromatic) -B bond of the flame retardant additive enhances the crosslinking react ions between the aromatic rings resulting in an increase of char formation. In the epoxy resin systems, loop functionality contributes to char formation to a larger extent. The interaction between the epoxy resin and poly-(butylene terephthalate) follows the mechanism of insertion of the oxirane ring into the ester bond. This mechanism is studied by FT-IR. The investigation of the thermal properties of the char-forming phenol-formaldehyde resins is conducted to provide information for the systematic design of high temperature flame-resistant phenolics. NMR and FT-IR are used to characterize the oligomeric resins and the cured resins. The curing agents used in the study include formaldehyde, s-trioxane and terephthaloyl chloride. The brominated phenolic resins are found to have higher oxygen indices with lower char yields.

Heterocyclic replacements for benzene: Maximising ADME benefits by considering individual ring isomers.

PubMed

Ritchie, Timothy J; Macdonald, Simon J F

2016-11-29

The impact of replacing a mono-substituted benzene (phenyl) ring with thirty three aromatic and nine aliphatic heterocycles on nine ADME-related screens (solubility, lipophilicity, permeability, protein binding CYP450 inhibition and metabolic clearance) was assessed using matched molecular pair analysis. The results indicate that the influence on the ADME profile can differ significantly depending on the ring identity and importantly on the individual regioisomers that are possible for some rings. This information enables the medicinal chemist to make an informed choice about which rings and regioisomers to employ as mono-substituted benzene replacements, based upon the knowledge of how such replacements are likely to influence ADME-related parameters, for example to target higher solubility whilst avoiding CYP450 liabilities. Copyright © 2016 Elsevier Masson SAS. All rights reserved.

1-(4-Methyl-1-naphth­yl)ethanone

PubMed Central

Hu, Yong-Hong; Zhao, Xiao-Lei; Yang, Wen-Ge; Yao, Jin-Feng; Lu, Xiu-Tao

2008-01-01

In the mol­ecule of the title compound, C13H12O, the two aromatic rings are oriented at a dihedral angle of 2.90 (3)°. An intra­molecular C—H⋯O hydrogen bond results in the formation of a non-planar six-membered ring, which adopts an envelope conformation. In the crystal structure, inter­molecular C—H⋯O hydrogen bonds link the mol­ecules. PMID:21581284

Paramagnetic or diamagnetic persistent currents? A topological point of view

NASA Astrophysics Data System (ADS)

Waintal, Xavier

2009-03-01

A persistent current flows at low temperatures in small conducting rings when they are threaded by a magnetic flux. I will discuss the sign of this persistent current (diamagnetic or paramagnetic response) in the special case of N electrons in a one dimensional ring [1]. One dimension is very special in the sense that the sign of the persistent current is entirely controlled by the topology of the system. I will establish lower bounds for the free energy in the presence of arbitrary electron-electron interactions and external potentials. Those bounds are the counterparts of upper bounds derived by Leggett using another topological argument. Rings with odd (even) numbers of polarized electrons are always diamagnetic (paramagnetic). The situation is more interesting with unpolarized electrons where Leggett upper bound breaks down: rings with N=4n exhibit either paramagnetic behavior or a superconductor-like current-phase relation. The topological argument provides a rigorous justification for the phenomenological Huckel rule which states that cyclic molecules with 4n + 2 electrons like benzene are aromatic while those with 4n electrons are not. [4pt] [1] Xavier Waintal, Geneviève Fleury, Kyryl Kazymyrenko, Manuel Houzet, Peter Schmitteckert, and Dietmar Weinmann Phys. Rev. Lett.101, 106804 (2008).

A supramolecular approach to fabricate highly emissive smart materials

PubMed Central

Liu, Kai; Yao, Yuxing; Kang, Yuetong; Liu, Yu; Han, Yuchun; Wang, Yilin; Li, Zhibo; Zhang, Xi

2013-01-01

The aromatic chromophores, for example, perylene diimides (PDIs) are well known for their desirable absorption and emission properties. However, their stacking nature hinders the exploitation of these properties and further applications. To fabricate emissive aggregates or solid-state materials, it has been common practice to decrease the degree of stacking of PDIs by incorporating substituents into the parent aromatic ring. However, such practice often involves difficultorganic synthesis with multiple steps. A supramolecular approach is established here to fabricate highly fluorescent and responsive soft materials, which has greatly decreases the number of required synthetic steps and also allows for a system with switchable photophysical properties. The highly fluorescent smart material exhibits great adaptivity and can be used as a supramolecular sensor for the rapid detection of spermine with high sensitivity and selectivity, which is crucial for the early diagnosis of malignant tumors. PMID:23917964

Design of Novel Organic Thin Film Transistors for Wearable Electronics

DTIC Science & Technology

2012-08-01

from the Pc ring pyrrole C-N bond. This is also indicated by the red shift of 480 band to 586 broad band in optical absorption spectra. Bromine is...bending 1230 1237 1229 Aromatic C-H bending 1259 Aromatic C-H bending 1335 1352 1325 1345 pyrrole stretching 1402 1406 1403 1405 isoindole...stretching 1510 1519 1511 1519 Coupling of C=C pyrrole and aza C=N stretching 1603 1609 1592 1608 benzene stretching Distribution A: Approved for

Conformational preferences of 1-amino-2-phenylcyclohexanecarboxylic acid, a phenylalanine cyclohexane analogue

PubMed Central

Alemán, Carlos; Jiménez, Ana I.; Cativiela, Carlos; Nussinov, Ruth; Casanovas, Jordi

2009-01-01

The intrinsic conformational preferences of the restricted phenylalanine analogue generated by including the α and β carbon atoms into a cyclohexane ring (1-amino-2-phenylcyclohexanecarboxylic acid, c6Phe) have been determined using quantum mechanical calculations. Specifically, the conformational profile of the N-acetyl-N’-methylamide derivative of the c6Phe stereoisomers exhibiting either a cis or a trans relative orientation between the amino and phenyl substituents has been analyzed in different environments (gas phase, chloroform and aqueous solutions). Calculations were performed using B3LYP, MP2 and HF methods combined with the 6-31+G(d,p) and 6-311++G(d,p) basis sets, and a self-consistent reaction-field (SCRF) method was applied to analyze the influence of the solvent. The amino acids investigated can be viewed as constrained phenylalanine analogues with a rigidly oriented aromatic side chain that may interact with the peptide backbone not only sterically but also electronically through the aromatic π orbitals. Their conformational propensities have been found to be strongly influenced by the specific orientation of the aromatic substituent in each stereoisomer and the conformation adopted by the cyclohexane ring, as well as by the environment. PMID:19772338

Comparative study of the affinity and metabolism of type I and type II binding quinoline carboxamide analogs by cytochrome P450 3A4

PubMed Central

Dahal, Upendra P.; Joswig-Jones, Carolyn; Jones, Jeffrey P.

2011-01-01

Compounds that coordinate to the heme-iron of cytochrome P450 (CYP) enzymes are assumed to increase metabolic stability. However, recently we observed that the type II binding quinoline carboxamide (QCA) compounds were metabolically less stable. To test if the higher intrinsic clearance of type II binding compounds relative to type I binding compounds is general for other metabolic transformations, we synthesized a library of QCA compounds that could undergo N-dealkylation, O-dealkylation, benzylic hydroxylation and aromatic hydroxylation. The results demonstrated that type II binding QCA analogs were metabolically less stable (2 to 12 fold) at sub-saturating concentration compared to type I binding counterparts for all the transformations. When the rates of different metabolic transformations between type I and type II binding compounds were compared, they were found to be in the order of N-demethylation>benzylic hydroxylation> O-demethylation> aromatic hydroxylation. Finally, for the QCA analogs with aza-heteroaromatic rings, we did not detect metabolism in aza-aromatic rings (pyridine, pyrazine, pyrimidine) indicating electronegativity of the nitrogen can change regioselectivity in CYP metabolism. PMID:22087535

Forming a Two-Ring Polycyclic Aromatic Hydrocarbon without a Benzene Intermediate: the Reaction of Propargyl with Acetylene

NASA Astrophysics Data System (ADS)

Osborn, David; Savee, John; Selby, Talitha; Welz, Oliver; Taatjes, Craig

The reaction of acetylene (HCCH) with a resonance-stabilized free radical is a commonly invoked mechanism for the generation of polycyclic aromatic hydrocarbons (PAH), which are likely precursors of soot particles in combustion. In this work, we examine the sequential addition of acetylene to the propargyl radical (H2CCCH) at temperatures of 800 and 1000 K. Using time-resolved multiplexed photoionization mass spectrometry with tunable ionizing radiation, we identified the isomeric forms of the C5H5 and C7H7 intermediates in this reaction sequence, and confirmed that the final C9H8 product is the two-ring aromatic compound indene. We identified two different resonance-stabilized C5H5 intermediates, with different temperature dependencies. Furthermore, the C7H7 intermediate is the tropyl radical (c-C7H7) , not the benzyl radical (C6H5CH2) , as is usually assumed in combustion environments. These experimental results are in general agreement with the latest electronic structure / master equation results of da Silva et al. This work shows a pathway for PAH formation that bypasses benzene / benzyl intermediates.

Lignin degradation in wood-feeding insects.

PubMed

Geib, Scott M; Filley, Timothy R; Hatcher, Patrick G; Hoover, Kelli; Carlson, John E; Jimenez-Gasco, Maria del Mar; Nakagawa-Izumi, Akiko; Sleighter, Rachel L; Tien, Ming

2008-09-02

The aromatic polymer lignin protects plants from most forms of microbial attack. Despite the fact that a significant fraction of all lignocellulose degraded passes through arthropod guts, the fate of lignin in these systems is not known. Using tetramethylammonium hydroxide thermochemolysis, we show lignin degradation by two insect species, the Asian longhorned beetle (Anoplophora glabripennis) and the Pacific dampwood termite (Zootermopsis angusticollis). In both the beetle and termite, significant levels of propyl side-chain oxidation (depolymerization) and demethylation of ring methoxyl groups is detected; for the termite, ring hydroxylation is also observed. In addition, culture-independent fungal gut community analysis of A. glabripennis identified a single species of fungus in the Fusarium solani/Nectria haematococca species complex. This is a soft-rot fungus that may be contributing to wood degradation. These results transform our understanding of lignin degradation by wood-feeding insects.

Structure-activity relationships among substituted N-benzoyl derivatives of phenylalanine and its analogs in a microbial antitumor prescreen I: Derivatives of o-fluoro-DL-phenylalanine.

PubMed

Otani, T T; Briley, M R

1982-02-01

Twelve derivatives of 0-fluoro-dl-phenylalanine containing fluorine, chlorine, methoxy, and nitro radicals in various positions of the aromatic ring of the benzoyl group were prepared and tested in a Lactobacillus casei system. It was found that most substitutions in the benzoyl phenyl ring resulted in a compound exhibiting greater growth-inhibiting activity than the nonsubstituted benzoyl-o-fluorophenylalanine. The greatest activity was observed in the ortho-substituted fluoro compound and the meta- and para-substituted chloro and nitro compounds. With the methoxy group, the position of substitution appeared unimportant, since all three methoxy isomers exhibited essentially equal inhibition. Nitro substitution in the ortho position had a protective effect in that the product was less active than the unsubstituted benzoyl-o-fluoro-dl-phenylalanine.

Isotopic exchange of hydrogen in aromatic amino acids

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

Pshenichnikova, A.B.; Karnaukhova, E.N.; Mitsner, B.I.

The kinetics of the isotopic replacement of hydrogen in the aromatic amino acids L-tryptophan, L-tyrosine, and L-phenylalanine in solutions of deuterochloric and deuterosulfuric acids in deuterium oxide were investigated by PMR spectroscopy. The reactions were shown to be of first orders with respect both to the concentration of the substrate and to the activity of the deuterium ion. The isotopic effects of hydrogen and the values of the activation energy of H-D exchange in different positions of the aromatic ring in tryptophan and tyrosine were determined. The effect of properties of the medium on the rate of the isotopic exchangemore » of hydrogen is discussed. 17 refs., 2 figs., 2 tabs.« less

Selective conversion of polyenes to monoenes by RuCl(3) -catalyzed transfer hydrogenation: the case of cashew nutshell liquid.

PubMed

Perdriau, Sébastien; Harder, Sjoerd; Heeres, Hero J; de Vries, Johannes G

2012-12-01

Cardanol, a constituent of cashew nutshell liquid (CNSL), was subjected to transfer hydrogenation catalyzed by RuCl(3) using isopropanol as a reductant. The side chain of cardanol, which is a mixture of a triene, a diene, and a monoene, was selectively reduced to the monoene. Surprisingly, it is the C8-C9 double bond that is retained with high selectivity. A similar transfer hydrogenation of linoleic acid derivatives succeeded only if the substrate contained an aromatic ring, such as a benzyl ester. TEM and a negative mercury test showed that the catalyst was homogeneous. By using ESI-MS, ruthenium complexes were identified that contained one, two, or even three molecules of substrate, most likely as allyl complexes. The interaction between ruthenium and the aromatic ring determines selectivity in the hydrogenation reaction. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Evidence of benzenoid domains in nanographenes.

PubMed

Baldoni, Matteo; Mercuri, Francesco

2015-01-21

Calculations based on density functional theory demonstrate the occurrence of local deformations of the perfect honeycomb lattice in nanographenes to form arrangements, with triangular symmetry, composed of six-membered ring patterns. The formation of these locally regular superstructures, which can be considered as benzenoid-like domains on the 2D graphene lattice, is ascribed to the gain in resonance energy deriving from aromaticity. The relationship between the atomic morphology of nanographenes and details of the relaxed structure is rationalized in terms of Clar's theory of the aromatic sextet and by extending concepts borrowed from valence bond theory to 2D carbon nanostructures. Namely, two regular arrangements can be evidenced, defined as Clar (fully benzenoid) and Kekulé domains, which correspond to two different regular bond patterns in sets of adjacent six-membered rings. Our findings are compatible with recent experiments and have potentially relevant consequences in the development of novel electronic devices based on graphene materials.

Dithiopheneindenofluorene (TIF) Semiconducting Polymers with Very High Mobility in Field-Effect Transistors.

PubMed

Chen, Hu; Hurhangee, Michael; Nikolka, Mark; Zhang, Weimin; Kirkus, Mindaugas; Neophytou, Marios; Cryer, Samuel J; Harkin, David; Hayoz, Pascal; Abdi-Jalebi, Mojtaba; McNeill, Christopher R; Sirringhaus, Henning; McCulloch, Iain

2017-09-01

The charge-carrier mobility of organic semiconducting polymers is known to be enhanced when the energetic disorder of the polymer is minimized. Fused, planar aromatic ring structures contribute to reducing the polymer conformational disorder, as demonstrated by polymers containing the indacenodithiophene (IDT) repeat unit, which have both a low Urbach energy and a high mobility in thin-film-transistor (TFT) devices. Expanding on this design motif, copolymers containing the dithiopheneindenofluorene repeat unit are synthesized, which extends the fused aromatic structure with two additional phenyl rings, further rigidifying the polymer backbone. A range of copolymers are prepared and their electrical properties and thin-film morphology evaluated, with the co-benzothiadiazole polymer having a twofold increase in hole mobility when compared to the IDT analog, reaching values of almost 3 cm 2 V -1 s -1 in bottom-gate top-contact organic field-effect transistors. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Catalytic hydrogenation rate of polycyclic aromatic hydrocarbons in supercritical carbon dioxide containing polymer-stabilized palladium nanoparticles.

PubMed

Liao, Weisheng; Liu, Hsin-Wang; Chen, Hsing-Jung; Chang, Wen-Yen; Chiu, Kong-Hwa; Wai, Chien M

2011-01-01

Catalytic hydrogenation of polycyclic aromatic hydrocarbons (PAHs) with up to four fused benzene rings over high-density-polyethylene-stabilized palladium nanoparticles in supercritical carbon dioxide via in situ UV/Vis spectroscopy is presented. PAHs can be efficiently converted to saturated polycyclic hydrocarbons using this green technique under mild conditions at 20 MPa of CO₂ containing 1 MPa of H₂ at 40-50°C. Kinetic studies based on in situ UV/Vis spectra of the CO₂ phase reveal that the initial hydrogenation of a given PAH and the subsequent hydrogenations of its intermediates are pseudo-first-order. The hydrogenation rate of the latter is always much smaller than that of the former probably due to increasing steric hindrance introduced by the hydrogenated benzene rings of PAHs which impedes the adsorption process and hydrogen access to PAHs on catalyst surfaces. Copyright © 2010 Elsevier Ltd. All rights reserved.

Pseudomonads biodegradation of aromatic compounds in oil sands process-affected water.

PubMed

Zhang, Yanyan; McPhedran, Kerry N; Gamal El-Din, Mohamed

2015-07-15

Aromatic naphthenic acids (NAs) have been shown to be more toxic than the classical NAs found in oil sands process-affected water (OSPW). To reduce this toxicity, Pseudomonas fluorescens and Pseudomonas putida were used to determine their ability to biodegrade aromatic compounds including treatments considering the impacts of external carbon and iron addition. Results showed that with added carbon P. fluorescens and P. putida have the capability of biodegrading these aromatics. In the presence of external carbon, gene expression of a functional PAH-ring hydroxylating dioxygenase (PAH-RHDα) was determined through reverse transcription real-time PCR, suggesting active degradation of OSPW aromatic compounds. Although no significant classical NAs removal was observed during this process, toxicity was reduced by 49.3% under optimal conditions. OSPW toxicity was eliminated with the combination of ozonation at a dose of 80 mg/L followed by biodegradation, indicating that it is a promising combined OSPW treatment approach for the safe discharge to the aquatic environment. Copyright © 2015 Elsevier B.V. All rights reserved.

Application of calculated NMR parameters, aromaticity indices and wavefunction properties for evaluation of corrosion inhibition efficiency of pyrazine inhibitors

NASA Astrophysics Data System (ADS)

Behzadi, Hadi; Manzetti, Sergio; Dargahi, Maryam; Roonasi, Payman; Khalilnia, Zahra

2018-01-01

In light of the importance of developing novel corrosion inhibitors, a series of quantum chemical calculations were carried out to evaluate 15N chemical shielding CS tensors as well as aromaticity indexes including NICS, HOMA, FLU, and PDI of three pyrazine derivatives, 2-methylpyrazine (MP), 2-aminopyrazine (AP) and 2-amino-5-bromopyrazine (ABP). The NICS parameters have been shown in previous studies to be paramount to the prediction of anti-corrosion properties, and have been combined here with HOMA, FLU and PDI and detailed wavefunction analysis to determine the effects from bromination and methylation on pyrazine. The results show that the electron density around the nitrogens, represented by CS tensors, can be good indicators of anti-corrosion efficiency. Additionally, the NICS, FLU and PDI, as aromaticity indicators of molecule, are well correlated with experimental corrosion inhibition efficiencies of the studied inhibitors. Bader sampling and detailed wavefunction analysis shows that the major effects from bromination on the pyrazine derivatives affect the Laplacian of the electron density of the ring, delocalizing the aromatic electrons of the carbon atoms into lone pairs and increasing polarization of the Laplacian values. This feature is well agreement with empirical studies, which show that ABP is the most efficient anti-corrosion compound followed by AP and MP, a property which can be attributed and predicted by derivation of the Laplacian of the electron density of the ring nuclei. This study shows the importance of devising DFT methods for development of new corrosion inhibitors, and the strength of electronic and nuclear analysis, and depicts most importantly how corrosion inhibitors composed of aromatic moieties may be modified to increase anti-corrosive properties.

Distribution of polycyclic aromatic hydrocarbons in riverine waters after Mediterranean forest fires.

PubMed

Olivella, M A; Ribalta, T G; de Febrer, A R; Mollet, J M; de Las Heras, F X C

2006-02-15

Extensive forest fires occurred in Catalonia, northern Spain, in 1994. In our study, concentrations and profiles of 12 parent polycyclic aromatic hydrocarbons (PAHs) were determined in riverine waters, ash and sediment samples at nine sampling sites (W1-W9) and at three sampling dates from Llobregat hydrographic basin: in August, 1994, one month after the extensive forest fires; in September, 1994, after the first heavy autumn rainfalls and in January, 1995, six months after forest fires. In August 1994, the total concentrations of 12 PAHs measured in riverine waters varied from 2 ng/l to 336 ng/l. In September 1994, the total PAH concentrations decreased to 0.2-31 ng/l and in January 1995, from 9 ng/l to 73 ng/l. In August, the composition pattern of PAHs showed a distribution dominated by 4-ring PAHs (pyrene, chrysene+triphenylene, benzo(a)anthracene) at W3-W6, W8 and W9 and 3-ring PAHs (phenanthrene) at W1, W2 and W7. In September, a preference by 3-ring PAHs (phenanthrene) at all sampling sites except W5 was shown and in January was clearly dominated by 4-ring PAHs (chrysene+triphenylene, pyrene, benzo(a)anthracene) at all sampling sites. In ash and sediment samples, the total concentrations of 12 PAHs ranged from 1.3 ng/g to 19 ng/g. The dominant compound was phenanthrene.

[Pollution characteristics and sources of polycyclic aromatic hydrocarbons in urban rivers of Wenzhou city].

PubMed

Zhou, Jie-Cheng; Chen, Zhen-Lou; Bi, Chun-Juan; Lü, Jin-Gang; Xu, Shi-Yuan; Pan, Qi

2012-12-01

Concentrations of 18 polycyclic aromatic hydrocarbons (PAHs) in water and surface sediments collected from the urban rivers of Wenzhou city in spring and summer were measured by GC-MS. The results showed that the total PAHs concentrations in water and sediments of the studied rivers varied in ranges of 146.74-3 047.89 ng x L(-1) and 21.01-11 990.48 ng x g(-1), respectively. Higher concentrations occurred in spring. The low and middle rings of 2-4-ring were dominant in both water and sediments, but the concentrations of 5-ring and 6-ring PAHs in sediments were relatively higher than those in water. The EBaP values of PAHs in water of the studied rivers in spring and summer were 1.69-51.95 ng x L(-1) and 0-3.03 ng x L(-1), respectively. Eighty percent of water samples in spring surpassed the limits of BaP in surface water of China. The concentrations of sigma PAHs in the sediments both in spring and summer were lower than the ERM value, but part of the components of PAHs had values higher than the ERM, suggesting possible toxic effect on living organisms. Based on the PAHs molecule ratios and principal component analysis, a mixed PAHs source of petroleum and combustion in water and sediments was diagnosed, while sediments showed a greater proportion of combustion sources.

Variations in the bioavailability of polycyclic aromatic hydrocarbons in industrial and agricultural soils after bioremediation.

PubMed

Guo, Meixia; Gong, Zongqiang; Allinson, Graeme; Tai, Peidong; Miao, Renhui; Li, Xiaojun; Jia, Chunyun; Zhuang, Jie

2016-02-01

The aim of this study was to demonstrate the variations in bioavailability remaining in industrial and agricultural soils contaminated by polycyclic aromatic hydrocarbons (PAHs) after bioremediation. After inoculation of Mycobacterium sp. and Mucor sp., PAH biodegradation was tested on a manufactured gas plant (MGP) soil and an agricultural soil. PAH bioavailability was assessed before and after biodegradation using solid-phase extraction (Tenax-TA extraction) and solid-phase micro-extraction (SPME) to represent bioaccessibility and chemical activity of PAHs, respectively. Only 3- and 4-ring PAHs were noticeably biodegradable in the MGP soil. PAH biodegradation in the agricultural soil was different from that in the MGP soil. The rapidly desorbing fractions (F(rap)) extracted by Tenax-TA and the freely dissolved concentrations of 3- and 4-ring PAHs determined by SPME from the MGP soil decreased after 30 days biodegradation; those values of the 5- and 6-ring PAHs changed to a lesser degree. For the agricultural soil, the F(rap) values of the 3- and 4-ring PAHs also decreased after the biodegradation experiment. The Tenax-TA extraction and the SPME have the potential to assess variations in the bioavailability of PAHs and the degree of biodegradation in contaminated MGP soils. In addition, Tenax-TA extraction is more sensitive than SPME when used in the agricultural soil. Copyright © 2015 Elsevier Ltd. All rights reserved.

Functional and Structural Analysis of Phenazine O-Methyltransferase LaPhzM from Lysobacter antibioticus OH13 and One-Pot Enzymatic Synthesis of the Antibiotic Myxin.

PubMed

Jiang, Jiasong; Guiza Beltran, Daisy; Schacht, Andrew; Wright, Stephen; Zhang, Limei; Du, Liangcheng

2018-04-20

Myxin is a well-known antibiotic that had been used for decades. It belongs to the phenazine natural products that exhibit various biological activities, which are often dictated by the decorating groups on the heteroaromatic three-ring system. The three rings of myxin carry a number of decorations, including an unusual aromatic N5, N10-dioxide. We previously showed that phenazine 1,6-dicarboxylic acid (PDC) is the direct precursor of myxin, and two redox enzymes (LaPhzS and LaPhzNO1) catalyze the decarboxylative hydroxylation and aromatic N-oxidations of PDC to produce iodinin (1.6-dihydroxy- N5, N10-dioxide phenazine). In this work, we identified the LaPhzM gene from Lysobacter antibioticus OH13 and demonstrated that LaPhzM encodes a SAM-dependent O-methyltransferase converting iodinin to myxin. The results further showed that LaPhzM is responsible for both monomethoxy and dimethoxy formation in all phenazine compounds isolated from strain OH13. LaPhzM exhibits relaxed substrate selectivity, catalyzing O-methylation of phenazines with non-, mono-, or di- N-oxide. In addition, we demonstrated a one-pot biosynthesis of myxin by in vitro reconstitution of the three phenazine-ring decorating enzymes. Finally, we determined the X-ray crystal structure of LaPhzM with a bound cofactor at 1.4 Å resolution. The structure provided molecular insights into the activity and selectivity of the first characterized phenazine O-methyltransferase. These results will facilitate future exploitation of the thousands of phenazines as new antibiotics through metabolic engineering and chemoenzymatic syntheses.

Up-regulation of CYP1A1 and phase II enzymes by 5-ring isomeric polycyclic aromatic hydrocarbons in precision-cut rat hepatic slices: Importance of molecular shape.

PubMed

Pushparajah, Daphnee; Lewis, Dfv; Ioannides, Costas

2017-04-01

The objectives of the present study were two-fold: (a) to evaluate the role of molecular shape on the interaction of polycyclic aromatic hydrocarbons (PAHs) with the Ah receptor and CYP1A1 upregulation, and (b) to evaluate the potential of PAHs to induce epoxide hydrolase and glutathione S-transferase, two major enzymes involved in their metabolism. In order to achieve these objectives, precision-cut rat liver slices were incubated with a range of concentrations of seven 5-ring isomeric PAHs, namely benzo[c]chrysene, benzo[b]chrysene, benzo[g]chrysene, dibenzo[a,j]anthracene, dibenzo[a,c]anthracene, picene and pentacene, for 24h. All compounds, with the exception of pentacene, elevated the O-deethylation of ethoxyresorufin, an activity associated with CYP1A1; induction of this enzyme by the various PAHs correlated with their avidity for the Ah receptor. None of the PAHs studied increased epoxide hydrolase activity, monitored using benzo[a]pyrene 4,5-oxide. Of the seven PAHs, only benzo[g]chrysene elevated glutathione S-transferase activity, measured using 1-chloro-2,4-dinitrobenzene or 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole as substrates. No relationship could be established between length or length/width and interaction with the Ah receptor and CYP1A1 up-regulation indicating that other structural or electronic factors are likely to be more important. Finally, 5-ring PAHs are poor inducers of the epoxide hydrolase and glutathione S-transferase enzyme systems. Copyright © 2017 Elsevier Ltd. All rights reserved.

Effects of aromaticity in cations and their functional groups on the temperature dependence of low-frequency spectrum

DOE PAGES

Kakinuma, Shohei; Ramati, Sharon; Wishart, James F.; ...

2018-05-21

We investigate the temperature dependence of low-frequency spectra in the frequency range of 0.3–200 cm -1 for ionic liquids (ILs) whose cations possess two systematically different cyclic groups, using femtosecond Raman-induced Kerr effect spectroscopy. The target ILs are bis(trifluoromethylsulfonyl)amide [NTf 2]– salts of 1-cyclohexylmethyl-1-methylpyrrolidinium [CHxmMPyrr] +, 1-cyclohexylmethyl-3-methylimidazolium [CHxmMIm] +, N-cyclohexylmethylpyridinium [CHxmPy]+, 1-benzyl-1-methylpyrrolidinium [BzMPyrr] +, 1-benzyl-3-methylimidazolium [BzMIm] +, and N-benzylpyridinium [BzPy] + cations. The aim of this study is to better understand the effects of aromaticity in the cations’ constituent groups on the temperature-dependent low-frequency spectral features of the ILs. The low-frequency spectra of these ILs are temperature dependent, but themore » temperature-dependent spectrum of [CHxmMPyrr][NTf 2] is different from that of other ILs. While [CHxmMPyrr][NTf 2] shows spectral changes with temperature in the low-frequency region below 50 cm -1, the other ILs also show spectral changes in the high-frequency region above 80 cm -1 (above 50 cm -1 in the case of [BzMPyrr][NTf 2]). We conclude that the spectral change in the low-frequency region is due to both the cation and anion, while the change in the high-frequency region is attributed to the red shift of the aromatic ring librations. On the basis of the plots of the first moment of the spectra vs. temperature, we found that the first moment of the low-frequency spectrum of the IL whose cation does not have an aromatic ring is less temperature dependent than that of the other ILs. However, the intrinsic first moment, the first moment at 0 K, of the low-frequency spectrum is governed by the absence or presence of a charged aromatic group, while a neutral aromatic group does not have much influence on determining the intrinsic first moment.« less

Effects of aromaticity in cations and their functional groups on the temperature dependence of low-frequency spectrum

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

Kakinuma, Shohei; Ramati, Sharon; Wishart, James F.

We investigate the temperature dependence of low-frequency spectra in the frequency range of 0.3–200 cm -1 for ionic liquids (ILs) whose cations possess two systematically different cyclic groups, using femtosecond Raman-induced Kerr effect spectroscopy. The target ILs are bis(trifluoromethylsulfonyl)amide [NTf 2]– salts of 1-cyclohexylmethyl-1-methylpyrrolidinium [CHxmMPyrr] +, 1-cyclohexylmethyl-3-methylimidazolium [CHxmMIm] +, N-cyclohexylmethylpyridinium [CHxmPy]+, 1-benzyl-1-methylpyrrolidinium [BzMPyrr] +, 1-benzyl-3-methylimidazolium [BzMIm] +, and N-benzylpyridinium [BzPy] + cations. The aim of this study is to better understand the effects of aromaticity in the cations’ constituent groups on the temperature-dependent low-frequency spectral features of the ILs. The low-frequency spectra of these ILs are temperature dependent, but themore » temperature-dependent spectrum of [CHxmMPyrr][NTf 2] is different from that of other ILs. While [CHxmMPyrr][NTf 2] shows spectral changes with temperature in the low-frequency region below 50 cm -1, the other ILs also show spectral changes in the high-frequency region above 80 cm -1 (above 50 cm -1 in the case of [BzMPyrr][NTf 2]). We conclude that the spectral change in the low-frequency region is due to both the cation and anion, while the change in the high-frequency region is attributed to the red shift of the aromatic ring librations. On the basis of the plots of the first moment of the spectra vs. temperature, we found that the first moment of the low-frequency spectrum of the IL whose cation does not have an aromatic ring is less temperature dependent than that of the other ILs. However, the intrinsic first moment, the first moment at 0 K, of the low-frequency spectrum is governed by the absence or presence of a charged aromatic group, while a neutral aromatic group does not have much influence on determining the intrinsic first moment.« less

Effects of aromaticity in cations and their functional groups on the temperature dependence of low-frequency spectrum

NASA Astrophysics Data System (ADS)

Kakinuma, Shohei; Ramati, Sharon; Wishart, James F.; Shirota, Hideaki

2018-05-01

In this study, we investigate the temperature dependence of low-frequency spectra in the frequency range of 0.3-200 cm-1 for ionic liquids (ILs) whose cations possess two systematically different cyclic groups, using femtosecond Raman-induced Kerr effect spectroscopy. The target ILs are bis(trifluoromethylsulfonyl)amide [NTf2]- salts of 1-cyclohexylmethyl-1-methylpyrrolidinium [CHxmMPyrr]+, 1-cyclohexylmethyl-3-methylimidazolium [CHxmMIm]+, N-cyclohexylmethylpyridinium [CHxmPy]+, 1-benzyl-1-methylpyrrolidinium [BzMPyrr]+, 1-benzyl-3-methylimidazolium [BzMIm]+, and N-benzylpyridinium [BzPy]+ cations. The aim of this study is to better understand the effects of aromaticity in the cations' constituent groups on the temperature-dependent low-frequency spectral features of the ILs. The low-frequency spectra of these ILs are temperature dependent, but the temperature-dependent spectrum of [CHxmMPyrr][NTf2] is different from that of other ILs. While [CHxmMPyrr][NTf2] shows spectral changes with temperature in the low-frequency region below 50 cm-1, the other ILs also show spectral changes in the high-frequency region above 80 cm-1 (above 50 cm-1 in the case of [BzMPyrr][NTf2]). We conclude that the spectral change in the low-frequency region is due to both the cation and anion, while the change in the high-frequency region is attributed to the red shift of the aromatic ring librations. On the basis of the plots of the first moment of the spectra vs. temperature, we found that the first moment of the low-frequency spectrum of the IL whose cation does not have an aromatic ring is less temperature dependent than that of the other ILs. However, the intrinsic first moment, the first moment at 0 K, of the low-frequency spectrum is governed by the absence or presence of a charged aromatic group, while a neutral aromatic group does not have much influence on determining the intrinsic first moment.

Breaking Benzene Aromaticity-Computational Insights into the Mechanism of the Tungsten-Containing Benzoyl-CoA Reductase.

PubMed

Culka, Martin; Huwiler, Simona G; Boll, Matthias; Ullmann, G Matthias

2017-10-18

Aromatic compounds are environmental pollutants with toxic and carcinogenic properties. Despite the stability of aromatic rings, bacteria are able to degrade the aromatic compounds into simple metabolites and use them as growth substrates under oxic or even under anoxic conditions. In anaerobic microorganisms, most monocyclic aromatic growth substrates are converted to the central intermediate benzoyl-coenzyme A, which is enzymatically reduced to cyclohexa-1,5-dienoyl-CoA. The strictly anaerobic bacterium Geobacter metallireducens uses the class II benzoyl-CoA reductase complex for this reaction. The catalytic BamB subunit of this complex harbors an active site tungsten-bis-pyranopterin cofactor with the metal being coordinated by five protein/cofactor-derived sulfur atoms and a sixth, so far unknown, ligand. Although BamB has been biochemically and structurally characterized, its mechanism still remains elusive. Here we use continuum electrostatic and QM/MM calculations to model benzoyl-CoA reduction by BamB. We aim to elucidate the identity of the sixth ligand of the active-site tungsten ion together with the interplay of the electron and proton transfer events during the aromatic ring reduction. On the basis of our calculations, we propose that benzoyl-CoA reduction is initiated by a hydrogen atom transfer from a W(IV) species with an aqua ligand, yielding W(V)-[OH - ] and a substrate radical intermediate. In the next step, a proton-assisted second electron transfer takes place with a conserved active-site histidine serving as the second proton donor. Interestingly, our calculations suggest that the electron for the second reduction step is taken from the pyranopterin cofactors rather than from the tungsten ion. The resulting cationic radical, which is distributed over both pyranopterins, is stabilized by conserved anionic amino acid residues. The stepwise mechanism of the reduction shows similarities to the Birch reduction known from organic chemistry. However, the strict coupling of protons and electrons allows the reaction to proceed under milder conditions.

Co-Aromatization of Methane with Olefins: The Role of Inner Pore and External Surface Catalytic Sites

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

Yung, Matthew M; He, Peng; Jarvis, Jack

The co-aromatization of methane with olefins is investigated using Ag-Ga/HZSM-5 as the catalyst at 400 degrees C. The presence of methane has a pronounced effect on the product distribution in terms of increased average carbon number and substitution index and decreased aromatic carbon fraction compared with its N2 environment counterpart. The participation of methane during the co-aromatization over the Ag-Ga/HZSM-5 catalyst diminishes as the co-fed olefin feedstock molecule becomes larger, from 1-hexene to 1-octene and 1-decene, in diameter. The effect of suppressed methane participation with larger olefinic molecules is not as significant when Ag-Ga/HY is employed as the catalyst, whichmore » might be attributed to the larger pore size of HY that gives more room to hold olefin and methane molecules within the inner pores and reduces the diffusion limitation of olefin molecules. The effect of olefin feedstock on the methane participation during the co-aromatization over Ag-Ga/HZSM-5 is experimentally evidenced by 13C and 2D NMR. The incorporation of the methane carbon atoms into the phenyl ring of product molecules is reduced significantly with larger co-fed olefins, whereas its incorporation into the substitution groups of the formed aromatic molecules is not notably affected, suggesting that the methane participation in the phenyl ring formation might preferably occur within inner pores, while its incorporation into substitution groups may mainly take place on external catalytic sites. This hypothesis is well supported by the product selectivity obtained over Ag-Ga/HZSM-5 catalysts prepared using conventional ZSM-5, ZSM-5 with the external catalytic sites deactivated, nanosize ZSM-5, ZSM-5 with a micro/meso pore structure and ZSM-5 with the inner pores blocked, and further confirmed by the isotopic labeling studies.« less

Proteomic Characterization of Plasmid pLA1 for Biodegradation of Polycyclic Aromatic Hydrocarbons in the Marine Bacterium, Novosphingobium pentaromativorans US6-1

PubMed Central

Yun, Sung Ho; Choi, Chi-Won; Lee, Sang-Yeop; Lee, Yeol Gyun; Kwon, Joseph; Leem, Sun Hee; Chung, Young Ho; Kahng, Hyung-Yeel; Kim, Sang Jin; Kwon, Kae Kyoung; Kim, Seung Il

2014-01-01

Novosphingobium pentaromativorans US6-1 is a halophilic marine bacterium able to degrade polycyclic aromatic hydrocarbons (PAHs). Genome sequence analysis revealed that the large plasmid pLA1 present in N. pentaromativorans US6-1 consists of 199 ORFs and possess putative biodegradation genes that may be involved in PAH degradation. 1-DE/LC-MS/MS analysis of N. pentaromativorans US6-1 cultured in the presence of different PAHs and monocyclic aromatic hydrocarbons (MAHs) identified approximately 1,000 and 1,400 proteins, respectively. Up-regulated biodegradation enzymes, including those belonging to pLA1, were quantitatively compared. Among the PAHs, phenanthrene induced the strongest up-regulation of extradiol cleavage pathway enzymes such as ring-hydroxylating dioxygenase, putative biphenyl-2,3-diol 1,2-dioxygenase, and catechol 2,3-dioxygenase in pLA1. These enzymes lead the initial step of the lower catabolic pathway of aromatic hydrocarbons through the extradiol cleavage pathway and participate in the attack of PAH ring cleavage, respectively. However, N. pentaromativorans US6-1 cultured with p-hydroxybenzoate induced activation of another extradiol cleavage pathway, the protocatechuate 4,5-dioxygenase pathway, that originated from chromosomal genes. These results suggest that N. pentaromativorans US6-1 utilizes two different extradiol pathways and plasmid pLA1 might play a key role in the biodegradation of PAH in N. pentaromativorans US6-1. PMID:24608660

Stabilizing interactions between aromatic and basic side chains in alpha-helical peptides and proteins. Tyrosine effects on helix circular dichroism.

PubMed

Andrew, Charles D; Bhattacharjee, Samita; Kokkoni, Nicoleta; Hirst, Jonathan D; Jones, Gareth R; Doig, Andrew J

2002-10-30

Here we investigate the structures and energetics of interactions between aromatic (Phe or Tyr) and basic (Lys or Arg) amino acids in alpha-helices. Side chain interaction energies are measured using helical peptides, by quantifying their helicities with circular dichroism at 222 nm and interpreting the results with Lifson-Roig-based helix/coil theory. A difficulty in working with Tyr is that the aromatic ring perturbs the CD spectrum, giving an incorrect helicity. We calculated the effect of Tyr on the CD at 222 nm by deriving the intensities of the bands directly from the electronic and magnetic transition dipole moments through the rotational strengths corresponding to each excited state of the polypeptide. This gives an improved value of the helix preference of Tyr (from 0.48 to 0.35) and a correction to the helicity for the peptides containing Tyr. We find that Phe-Lys, Lys-Phe, Phe-Arg, Arg-Phe, and Tyr-Lys are all stabilizing by -0.10 to -0.18 kcal.mol-1 when placed i, i + 4 on the surface of a helix in aqueous solution, despite the great difference in polarity between these residues. Interactions between these side chains have previously been attributed to cation-pi bonds. A survey of protein structures shows that they are in fact predominantly hydrophobic interactions between the CH2 groups of Lys or Arg and the aromatic rings.

The effect of β-saturated pyrrolic rings on the electronic structures and aromaticity of magnesium porphyrin derivatives: a density functional study.

PubMed

Wan, Liang; Qi, Dongdong; Zhang, Yuexing

2011-09-01

Density functional theory (DFT) calculation on the molecular structures, molecular orbitals, electronic absorption spectra, and magnetic properties of magnesium porphyrin (MgPor) and a series of five hydrogenated magnesium porphyrin complexes with different number of β-saturated pyrrolic rings, namely MgPor-β-1Hy, MgPor-β-opp-2Hy, MgPor-β-adj-2Hy, MgPor-β-3Hy, and MgPor-β-4Hy, clarifies the red-shift of the lowest energy absorption band from chlorophyll a to bacteriochlorophyll and reveals the strong chemical stability for both of them. The energy levels of highest occupied molecular orbitals (HOMO) and HOMO-1 for MgPor are reversed upon hydrogenation at β-positions (2 and 3, 7 and 8, 12 and 13, and 17 and 18) of porphyrin ring. Along with the increase of β-saturated pyrrolic rings from 1, 2, 3, to 4, the HOMO energy increases from -4.78 eV to -3.10 eV in a regular manner. In contrast, the lowest unoccupied molecular orbitals (LUMO) energy levels of MgPor, MgPor-β-1Hy, and MgPor-β-opp-2Hy are very similar with each other. As a result, the lowest energy absorption band involving main transition from HOMO to LUMO is red-shifted from MgPor-β-1Hy to MgPor-β-opp-2Hy which is representative of chlorophyll a and bacteriochlorophyll, respectively. Natural hydroporphyrins represented by MgPor, MgPor-β-1Hy, and MgPor-β-opp-2Hy have turned out to be aromatic and stable enough, in good accordance with the ubiquity of their derivatives in the nature. In contrast, MgPor-β-adj-2Hy, MgPor-β-3Hy, and MgPor-β-4Hy with relatively weak aromaticity seem to be unstable and therefore were not found in nature. Copyright © 2011 Elsevier Inc. All rights reserved.

2-aminophenol 1,6-dioxygenase: a novel aromatic ring cleavage enzyme purified from Pseudomonas pseudoalcaligenes JS45.

PubMed Central

Lendenmann, U; Spain, J C

1996-01-01

Most bacterial pathways for the degradation of aromatic compounds involve introduction of two hydroxyl groups either ortho or para to each other. Ring fission then occurs at the bond adjacent to one of the hydroxyl groups. In contrast, 2-aminophenol is cleaved to 2-aminomuconic acid semialdehyde in the nitrobenzene-degrading strain Pseudomonas pseudoalcaligenes JS45. To examine the relationship between this enzyme and other dioxygenases, 2-aminophenol 1,6-dioxygenase has been purified by ethanol precipitation, gel filtration, and ion exchange chromatography. The molecular mass determined by gel filtration was 140,000 Da. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed two subunits of 35,000 and 39,000 Da, which suggested an alpha2beta2 subunit structure. Studies with inhibitors indicated that ferrous iron was the sole cofactor. The Km values for 2-aminophenol and oxygen were 4.2 and 710 microM, respectively. The enzyme catalyzed the oxidation of catechol, 6-amino-m-cresol, 2-amino-m-cresol, and 2-amino-4-chlorophenol. 3-Hydroxyanthranilate, protocatechuate, gentisate, and 3- and 4-methylcatechol were not substrates. The substrate range and the subunit structure are unique among those of the known ring cleavage dioxygenases. PMID:8892823

Identifying the Tautomeric Form of a Deoxyguanosine-Estrogen Quinone Intermediate.

PubMed

Stack, Douglas E

2015-09-10

Mechanistic insights into the reaction of an estrogen o-quinone with deoxyguanosine has been further investigated using high level density functional calculations in addition to the use of 4-hyroxycatecholestrone (4-OHE₁) regioselectivity labeled with deuterium at the C1-position. Calculations using the M06-2X functional with large basis sets indicate the tautomeric form of an estrogen-DNA adduct present when glycosidic bonds cleavage occurs is comprised of an aromatic A ring structure. This tautomeric form was further verified by use of deuterium labelling of the catechol precursor use to form the estrogen o-quinone. Regioselective deuterium labelling at the C1-position of the estrogen A ring allows discrimination between two tautomeric forms of a reaction intermediate either of which could be present during glycosidic bond cleavage. HPLC-MS analysis indicates a reactive intermediate with a m/z of 552.22 consistent with a tautomeric form containing no deuterium. This intermediate is consistent with a reaction mechanism that involves: (1) proton assisted Michael addition; (2) re-aromatization of the estrogen A ring; and (3) glycosidic bond cleavage to form the known estrogen-DNA adduct, 4-OHE₁-1-N7Gua.

5-Amino-3-methyl-1-phenyl-1H-pyrazole-4-carbaldehyde hemihydrate: a polarized electronic structure within hydrogen-bonded sheets of R(10)(8)(34) rings.

PubMed

Quiroga, Jairo; Trilleras, Jorge; Cobo, Justo; Glidewell, Christopher

2010-01-01

In the title compound, C(11)H(11)N(3)O.0.5H(2)O, the water molecule lies across a twofold rotation axis in the space group Pbcn. The bond distances in the organic component provide evidence for polarization of the electronic structure. The molecular components are linked into puckered sheets of R(10)(8)(34) rings by a combination of O-H...N and N-H...O hydrogen bonds; adjacent sheets are weakly linked by an aromatic pi-pi stacking interaction. Comparisons are made with some fused-ring analogues.

Polycyclic Aromatic Hydrocarbons Adsorption onto Graphene: A DFT and AIMD Study.

PubMed

Li, Bing; Ou, Pengfei; Wei, Yulan; Zhang, Xu; Song, Jun

2018-05-03

Density functional theory (DFT) calculations and ab-initio molecular dynamics (AIMD) simulations were performed to understand graphene and its interaction with polycyclic aromatic hydrocarbons (PAHs) molecules. The adsorption energy was predicted to increase with the number of aromatic rings in the adsorbates, and linearly correlate with the hydrophobicity of PAHs. Additionally, the analysis of the electronic properties showed that PAHs behave as mild n-dopants and introduce electrons into graphene; but do not remarkably modify the band gap of graphene, indicating that the interaction between PAHs and graphene is physisorption. We have also discovered highly sensitive strain dependence on the adsorption strength of PAHs onto graphene surface. The AIMD simulation indicated that a sensitive and fast adsorption process of PAHs can be achieved by choosing graphene as the adsorbent. These findings are anticipated to shed light on the future development of graphene-based materials with potential applications in the capture and removal of persistent aromatic pollutants.

Quantum switching of π-electron rotations in a nonplanar chiral molecule by using linearly polarized UV laser pulses.

PubMed

Mineo, Hirobumi; Yamaki, Masahiro; Teranishi, Yoshiaki; Hayashi, Michitoshi; Lin, Sheng Hsien; Fujimura, Yuichi

2012-09-05

Nonplanar chiral aromatic molecules are candidates for use as building blocks of multidimensional switching devices because the π electrons can generate ring currents with a variety of directions. We employed (P)-2,2'-biphenol because four patterns of π-electron rotations along the two phenol rings are possible and theoretically determine how quantum switching of the π-electron rotations can be realized. We found that each rotational pattern can be driven by a coherent excitation of two electronic states under two conditions: one is the symmetry of the electronic states and the other is their relative phase. On the basis of the results of quantum dynamics simulations, we propose a quantum control method for sequential switching among the four rotational patterns that can be performed by using ultrashort overlapped pump and dump pulses with properly selected relative phases and photon polarization directions. The results serve as a theoretical basis for the design of confined ultrafast switching of ring currents of nonplanar molecules and further current-induced magnetic fluxes of more sophisticated systems.

Synthesis and characterization of a novel long-alkyl-chain ester-substituted benzimidazole gelator and its octan-1-ol solvate.

PubMed

Geiger, H Cristina; Zick, Patricia L; Roberts, William R; Geiger, David K

2017-04-01

The synthesis of a novel benzimidazole derivative with a long-chain-ester substituent, namely methyl 8-[4-(1H-benzimidazol-2-yl)phenoxy]octanoate, (3), is reported. Ester (3) shows evidence of aggregation in solution and weak gelation ability with toluene. The octan-1-ol solvate, methyl 8-[4-(1H-benzimidazol-2-yl)phenoxy]octanoate octan-1-ol monosolvate, C 22 H 26 N 2 O 3 ·C 8 H 18 O, (4), exhibits a four-molecule hydrogen-bonded motif in the solid state, with N-H...O hydrogen bonds between benzimidazole molecules and O-H...N hydrogen bonds between the octan-1-ol solvent molecules and the benzimidazole unit. The alkyl chains of the ester and the octan-1-ol molecules are in unfolded conformations. The phenylene ring is canted by 10.27 (6)° from the plane of the benzimidazole ring system. H...C contacts make up 20.7% of the Hirshfeld surface coverage. Weak C-H...π interactions involving the benzimidazole alkyl chain and three aromatic rings are observed.

Effect of alkali metal ions on the pyrrole and pyridine π-electron systems in pyrrole-2-carboxylate and pyridine-2-carboxylate molecules: FT-IR, FT-Raman, NMR and theoretical studies

NASA Astrophysics Data System (ADS)

Świderski, G.; Wojtulewski, S.; Kalinowska, M.; Świsłocka, R.; Lewandowski, W.

2011-05-01

The FT-IR, FT-Raman and 1H and 13C NMR spectra of pyrrole-2-carboxylic acid (PCA) and lithium, sodium, potassium, rubidium and caesium pyrrole-2-carboxylates were recorded, assigned and compared in the Li → Na → K → Rb → Cs salt series. The effect of alkali metal ions on the electronic system of ligands was discussed. The obtained results were compared with previously reported ones for pyridine-2-carboxylic acid and alkali metal pyridine-2-carboxylates. Calculations for pyrrole-2-carboxylic acid and Li, Na, K pyrrole-2-carboxylates in B3LYP/6-311++G ** level and Møller-Plesset method in MP2/6-311++G ** level were made. Bond lengths, angles and dipole moments as well as aromaticity indices (HOMA, EN, GEO, I 6) for the optimized structures of pyrrole-2-carboxylic acid (PCA) and lithium, sodium, potassium pyrrole-2-carboxylates were also calculated. The degree of perturbation of the aromatic system of ligand under the influence of metals in the Li → Cs series was investigated with the use of statistical methods (linear correlation), calculated aromaticity indices and Mulliken, NBO and ChelpG population analysis method. Additionally, the Bader theory (AIM) was applied to setting the characteristic of the bond critical points what confirmed the influence of alkali metals on the pyrrole ring.

Gas-phase cationic benzoylation of ambient aromatic substrates studied with the decay technique

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

Occhiucci, G.; Cacace, F.; Speranza, M.

1986-03-05

The gas-phase benzoylation of typical ambient aromatic substrates PhY (Y = OH, OMe, and NH/sub 2/) has been investigated by a combination of the decay technique and of FT ICR mass spectrometry. Labeled phenylium ions, C/sub 6/X/sub 5//sup +/ (X = H and T), from the decay of multiply tritiated benzene, C/sub 6/X/sub 6/, have been allowed to react with excess CO-containing traces of PhY (Y = OH, OMe, and NH/sub 2/), in the pressure range from 90 to 650 torr. Radio GLC and HPLC of the tritiated products demonstrate two competitive reaction channels, i.e., phenylation and benzoylation of themore » aromatic substrates. The results indicate a sharp kinetic bias of the gaseous phenylium ions for the aromatic substrates, measured by an apparent k/sub CO//k/sub PhY/ ratio of 0.12 (Y = OH), 0.13 (Y = OMe), and 0.04 (Y = NH/sub 2/) in the systems at nearly atmospheric pressure. Gas-phase benzoylation displays a high intramolecular selectivity, occurring exclusively at the n-type center of PhOH and PhNH/sub 2/. In the case of PhOMe, appreciable ring benzoylation is observed, characterized by a remarkably high (up to 30:1) bias for the para position. The mechanistic features of the gas-phase benzoylation and phenylation processes, deduced from the decay and the ICR experiments, are discussed and compared with those of related aromatic acylation and alkylation reactions occurring in the dilute gas state. 30 references, 2 tables.« less

HST-STIS Spectra of Saturn's Rings and Implications for Their Reddening Agent

NASA Technical Reports Server (NTRS)

Cuzzi, Jeff

2016-01-01

We obtained HST-STIS spectra of Saturn's main rings in May 2011, using the G230L (and G430L) gratings, with final averaged radial resolution of 160 (and 330) km/pixel. The dataset filled a previous 200-330nm "spectral gap" between Cassini and ground-based spectra. The data provide radial profiles as a function of wavelength, but our most basic product at this point is a set of very low-noise spectra, radially averaged over broad regions of the rings (A, B, C, and Cassini Division). The raw spectra required special processing to remove artifacts due to extended-source grating scatter. We have modeled the spectra using a new particle surface model, which corrects for on-surface shadowing due to the likely very rough ring particle surfaces, and avoids overestimation of intra-mixed "neutral absorber". We correct for non-classical layer effects and finite ring optical depth, and relate our observed reflectivities to the spherical albedos of individual smooth particles. We model these smooth particle albedos using standard Hapke theory for regolith grain mixtures that are either homogeneous and "intramixed" (nonicy absorbers dispersed in water ice regolith grains) or heterogeneous "intimate" mixtures. As candidates for the nonicy contaminants we have considered amorphous carbon, aromatic-rich and aliphatic-rich organic tholins, silicates, hematite and iron metal. For the A and B rings, we find that iron metal (including a new theoretical estimate of the refractive indices of nanometer-sized grains of iron) is not spectrally steep enough in the 200-300nm range, and that aliphatic-rich tholins are either too steep at short wavelengths or too flat at long wavelengths. However, less than 1% by mass of aromatic-rich tholins provides a very good fit across the entire spectral range with no gratuitous "neutral absorber" needed, and a minimum of additional free parameters. The best fits require forward-scattering regolith grains. For the C Ring and Cassini Division, additional absorbers are needed (updated results will be given).

Unusual para-substituent effects on the intramolecular hydrogen-bond in hydrazone-based switches.

PubMed

Su, Xin; Lõkov, Märt; Kütt, Agnes; Leito, Ivo; Aprahamian, Ivan

2012-11-04

A "V"-shaped Hammett plot shows that resonance-assisted hydrogen bonding does not dictate the strength of the intramolecular hydrogen bond in the E isomers of hydrazone-based switches because it involves an aromatic pyridyl ring.

Recent discoveries of anticancer flavonoids.

PubMed

Raffa, Demetrio; Maggio, Benedetta; Raimondi, Maria Valeria; Plescia, Fabiana; Daidone, Giuseppe

2017-12-15

In this review we report the recent advances in anticancer activity of the family of natural occurring flavonoids, covering the time span of the last five years. The bibliographic data will be grouped, on the basis of biological information, in two great categories: reports in which the extract plants bioactivity is reported and the identification of each flavonoid is present or not, and reports in which the anticancer activity is attributable to purified and identified flavonoids from plants. Wherever possible, the targets and mechanisms of action as well as the structure-activity relationships of the molecules will be reported. Also, in the review it was thoroughly investigated the recent discovery on flavonoids containing the 2-phenyl-4H-chromen-4-one system even if some examples of unusual flavonoids, bearing a non-aromatic B-ring or other ring condensed to the base structure are reported. Copyright © 2017 Elsevier Masson SAS. All rights reserved.

Synthesis, characterization and catalytic oxidation properties of multi-wall carbon nanotubes with a covalently attached copper(II) salen complex

NASA Astrophysics Data System (ADS)

Salavati-Niasari, Masoud; Bazarganipour, Mehdi

2009-06-01

Hydroxyl functionalized copper(II) Schiff-base, N,N'-bis(4-hydroxysalicylidene)-ethylene-1,2-diaminecopper(II), [Cu((OH) 2-salen)], has been covalently anchored on modified MWCNTs. The new modified MWCNTs ([Cu((OH) 2-salen)]-MWCNTs) have been characterized by TEM, thermal analysis, XRD, XPS, UV-vis, DRS, FT-IR spectroscopy and elemental analysis. The modified copper(II) MWCNTs solid was used to affect the catalytic oxidation of ethylbenzene with tert-butylhydroperoxide as the oxidant at 333 K. The system is truly heterogeneous (no leaching observed) and reusable (no decrease in activity) in three consecutive runs. Acetophenone was the major product though small amounts of o- and p-hydroxyacetophenones were also formed revealing that C-H bond activation takes place both at benzylic and aromatic ring carbon atoms. Ring hydroxylation was more over the "neat" complexes than over the encapsulated complexes.

A novel withanolide with an unprecedented carbon skeleton from Physalis angulata.

PubMed

Sun, Cheng-Peng; Kutateladze, Andrei G; Zhao, Feng; Chen, Li-Xia; Qiu, Feng

2017-02-01

A novel withanolide, aromaphysalin A (1), possessing an exceptional C(11)-C(15) bond and an unprecedented 4,9-cyclized aromatic ring (ring A), is isolated from stems and leaves of Physalis angulata L. Its structure was determined by a combination of HRESIMS, 2D NMR spectra, and theoretical calculations. Compound 1 exhibited inhibitory activity on NO production with an IC 50 value of 51.64 μM. A plausible biosynthetic pathway for 1 is also discussed.

Relationship between structure and antiproliferative activity of 1-azaflavanones.

PubMed

Kawaii, Satoru; Endo, Kotaro; Tokiwano, Tetsuo; Yoshizawa, Yuko

2012-07-01

The synthesis of 19 derivatives of 2-phenyl-3,4-dihydroquinolin-4(1H)-one, as aza analogs of flavanones, was carried out and these compounds were further screened for their antiproliferative activity toward HL60 promyelocytic leukemia cells. In comparison with flavanone the replacement of C-ring ether oxygen atom with a nitrogen atom potentiated activity by more than 100-fold. It was suggested that the aromaticity of the B-ring contributes greatly to the activity of 1-azaflavanones.

4-Nitro­benzyl 2-bromo­acetate

PubMed Central

Zhu, Kai; Liu, Hui; Wang, Yan-Hua; Han, Ping-Fang; Wei, Ping

2009-01-01

In the mol­ecule of the title compound, C9H8BrNO4, the acetate group is close to planar [maximum deviation = 0.042 (3) Å] and is oriented at a dihedral angle of 73.24 (3)° with respect to the aromatic ring. In the crystal structure, inter­molecular C—H⋯O inter­actions link the mol­ecules into a three-dimensional network, forming R 2 2(10) ring motifs. PMID:21582813

Synthesis, Structural Characterization and Physicochemical Properties of Polymers Formed by Diazotization of 3-Amino-L-tyrosine and Closely Related Compounds

DTIC Science & Technology

1998-07-06

the possibility that a diazotization at the aliphatic (alpha) amino group might lead to deamination with the formation of a cinnamic acid derivative...symmetric chlorinated/nitrated cinnamic acid derivative, and might not provide unequivocal connectivity information, although it could suggest ring...substituted aromatic ring, i.e., it is more like the spectrum of p-coumaric acid than the desired 3-amino-4-hydroxy- cinnamic acid , which would be

Synthesis of Potential Metaboliters in the 1,2,3,4, and 5,6,7,8 Benzo Ring Positions of the Polycyclic Aromatic Hydrocarbon Benzo(G)Chrysene.

DTIC Science & Technology

1986-01-01

biological activity. Pullman, in 1945 , noted that active compounds contained angular benzo rings. She introduced the terminology "K- region" to refer to...Figure 1.6) give .... ~~~~~. .. .. .. . ........ . _............ . _.-.•.-•.. . ..... ... ,. 12 .xcellent correlation when measured reactivity ( hydrolysis ...molecular plane, the diol epoxide is trans or series 2. Early studies indicated that isomer 1 is the more reactive diol epoxide in hydrolysis reactions

An x-ray diffraction study of some mesoionic 2,3-diphenyltetrazoles

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

Luboradzki, R.; Kozminski, W.; Stefaniak, L.

1993-02-01

An X-my diffraction study is reported for four molecules of mesoionic 2,3-diphenyltetrazoles. The results confirm a dipolar [open quotes]mesoionic[close quotes] structure, aromatic character of the tetrazole ring and no conjugation between the phenyl and tetrazole rings. The geometry of the exocyclic group is discussed in detail. The molecular parameters of the compounds investigated are correlated with [sup 13]C and [sup 15]N nmr data. The results obtained are compared with similar structures which have already been studied.

3-(2,4-Dichloro­anilino)iso­benzo­furan-1(3H)-one1

PubMed Central

Odabaşoğlu, Mustafa; Büyükgüngör, Orhan

2008-01-01

In the mol­ecule of the title compound, C14H9Cl2NO2, the essentially planar phthalide group is oriented at a dihedral angle of 63.23 (5)° with respect to the substituted aromatic ring. In the crystal structure, inter­molecular C—H⋯O and N—H⋯O hydrogen bonds link the mol­ecules, generating R 4 4(21) ring motifs to form a three-dimensional network. PMID:21202144

Organic chemistry in Titan's upper atmosphere and its astrobiological consequences: I. Views towards Cassini plasma spectrometer (CAPS) and ion neutral mass spectrometer (INMS) experiments in space

NASA Astrophysics Data System (ADS)

Ali, A.; Sittler, E. C.; Chornay, D.; Rowe, B. R.; Puzzarini, C.

2015-05-01

The discovery of carbocations and carbanions by Ion Neutral Mass Spectrometer (INMS) and the Cassini Plasma Spectrometer (CAPS) instruments onboard the Cassini spacecraft in Titan's upper atmosphere is truly amazing for astrochemists and astrobiologists. In this paper we identify the reaction mechanisms for the growth of the complex macromolecules observed by the CAPS Ion Beam Spectrometer (IBS) and Electron Spectrometer (ELS). This identification is based on a recently published paper (Ali et al., 2013. Planet. Space Sci. 87, 96) which emphasizes the role of Olah's nonclassical carbonium ion chemistry in the synthesis of the organic molecules observed in Titan's thermosphere and ionosphere by INMS. The main conclusion of that work was the demonstration of the presence of the cyclopropenyl cation - the simplest Huckel's aromatic molecule - and its cyclic methyl derivatives in Titan's atmosphere at high altitudes. In this study, we present the transition from simple aromatic molecules to the complex ortho-bridged bi- and tri-cyclic hydrocarbons, e.g., CH2+ mono-substituted naphthalene and phenanthrene, as well as the ortho- and peri-bridged tri-cyclic aromatic ring, e.g., perinaphthenyl cation. These rings could further grow into tetra-cyclic and the higher order ring polymers in Titan's upper atmosphere. Contrary to the pre-Cassini observations, the nitrogen chemistry of Titan's upper atmosphere is found to be extremely rich. A variety of N-containing hydrocarbons including the N-heterocycles where a CH group in the polycyclic rings mentioned above is replaced by an N atom, e.g., CH2+ substituted derivative of quinoline (benzopyridine), are found to be dominant in Titan's upper atmosphere. The mechanisms for the formation of complex molecular anions are discussed as well. It is proposed that many closed-shell complex carbocations after their formation first, in Titan's upper atmosphere, undergo the kinetics of electron recombination to form open-shell neutral radicals. These radical species subsequently might form carbanions via radiative electron attachment at low temperatures with thermal electrons. The classic example is the perinaphthenyl anion in Titan's upper atmosphere. Therefore, future astronomical observations of selected carbocations and corresponding carbanions are required to settle the key issue of molecular anion chemistry on Titan. Other than earth, Titan is the only planetary body in our solar system that is known to have reservoirs of permanent liquids on its surface. The synthesis of complex biomolecules either by organic catalysis of precipitated solutes “on hydrocarbon solvent” on Titan or through the solvation process indeed started in its upper atmosphere. The most notable examples in Titan's prebiotic atmospheric chemistry are conjugated and aromatic polycyclic molecules, N-heterocycles including the presence of imino >Cdbnd N-H functional group in the carbonium chemistry. Our major conclusion in this paper is that the synthesis of organic compounds in Titan's upper atmosphere is a direct consequence of the chemistry of carbocations involving the ion-molecule reactions. The observations of complexity in the organic chemistry on Titan from the Cassini-Huygens mission clearly indicate that Titan is so far the only planetary object in our solar system that will most likely provide an answer to the question of the synthesis of complex biomolecules on the primitive earth and the origin of life.

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

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

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

2009-04-30

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

Degradation of herbicide 2,4-dichlorophenoxybutanoic acid in the photolysis of [FeOH]2+ and [Fe(Ox)3]3- complexes: A mechanistic study.

PubMed

Pozdnyakov, Ivan; Sherin, Peter; Grivin, Vjacheslav; Plyusnin, Victor

2016-03-01

In the present work the Fe(III)-assisted photodegradation of the herbicide 2,4-dichlorophenoxybutanoic acid (2,4-DB) has been studied by means of stationary (308 nm) and laser flash (355 nm) photolysis. The initial quantum yield of 2,4-DB photodegradation in [FeOH](2+) and [Fe(Ox)3](3-) systems was evaluated to be 0.11 and 0.17 upon 308 nm exposure, respectively. The prolonged photolysis of [FeOH](2+) and [Fe(Ox)3](3-) systems results in the complete degradation of 2,4-DB with almost complete mineralization of herbicide and its aromatic products in the case of [FeOH](2+) photolysis and the accumulation of some persistent aromatic products in the case of [Fe(Ox)3](3-) photolysis. For both systems the main primary products of 2,4-DB photolysis determined by liquid chromatography - mass spectrometry are products of the hydroxylation, the substitution of chlorine atom to OH group, the loss of aliphatic tail and the opening of benzene ring. The obtained results indicate ROS species (mainly OH radical) to be responsible for the herbicide photodegradation. Copyright © 2015 Elsevier Ltd. All rights reserved.

Spectroscopic Signatures and Structural Motifs of Dopamine: a Computational Study

NASA Astrophysics Data System (ADS)

Srivastava, Santosh Kumar; Singh, Vipin Bahadur

2016-06-01

Dopamine (DA) is an essential neurotransmitter in the central nervous system and it plays integral role in numerous brain functions including behaviour, cognition, emotion, working memory and associated learning. In the present work the conformational landscapes of neutral and protonated dopamine have been investigated in the gas phase and in aqueous solution by MP2 and DFT (M06-2X, ωB97X-D, B3LYP and B3LYP-D3) methods. Twenty lowest energy structures of neutral DA were subjected to geometry optimization and the gauche conformer, GIa, was found to be the lowest gas phase structure at the each level of theory in agreement with the experimental rotational spectroscopy. All folded gauche conformers (GI) where lone electron pair of the NH2 group is directed towards the π system of the aromatic ring ( 'non up' ) are found more stable in the gas phase. While in aqueous solution, all those gauche conformers (GII) where lone electron pair of the NH2 group is directed opposite from the π system of the aromatic ring ('up' structures) are stabilized significantly.Nine lowest energy structures, protonated at the amino group, are optimized at the same MP2/aug-cc-pVDZ level of theory. In the most stable gauche structures, g-1 and g+1, mainly electrostatic cation - π interaction is further stabilized by significant dispersion forces as predicted by the substantial differences between the DFT and dispersion corrected DFT-D3 calculations. In aqueous environment the intra-molecular cation- π distance in g-1 and g+1 isomers, slightly increases compared to the gas phase and the magnitude of the cation- π interaction is reduced relative to the gas phase, because solvation of the cation decreases its interaction energy with the π face of aromatic system. The IR intensity of the bound N-H+ stretching mode provides characteristic 'IR spectroscopic signatures' which can reflect the strength of cation- π interaction energy. The CC2 lowest lying S1 ( 1ππ* ) excited state of neutral dopamine is significantly red shifted upon protonation at amino site. E. Dragicevic, J. Schiemann and B. Liss, Neuroscience, 2015, 284, 798. Y. T. Chien et al. Science, 2010, 330, 1091. Cabezas etal., J. Phys. Chem. Lett. 2013, 4, 486.

Why Do Simple Molecules with "Isolated" Phenyl Rings Emit Visible Light?

PubMed

Zhang, Haoke; Zheng, Xiaoyan; Xie, Ni; He, Zikai; Liu, Junkai; Leung, Nelson L C; Niu, Yingli; Huang, Xuhui; Wong, Kam Sing; Kwok, Ryan T K; Sung, Herman H Y; Williams, Ian D; Qin, Anjun; Lam, Jacky W Y; Tang, Ben Zhong

2017-11-15

π-Bonds connected with aromatic rings were generally believed as the standard structures for constructing highly efficient fluorophores. Materials without these typical structures, however, exhibited only low fluorescence quantum yields and emitted in the ultraviolet spectral region. In this work, three molecules, namely bis(2,4,5-trimethylphenyl)methane, 1,1,2,2-tetrakis(2,4,5-trimethylphenyl)ethane, and 1,1,2,2-tetraphenylethane, with nonconjugated structures and isolated phenyl rings were synthesized and their photophysical properties were systematically investigated. Interestingly, the emission spectra of these three molecules could be well extended to 600 nm with high solid-state quantum yields of up to 70%. Experimental and theoretical analyses proved that intramolecular through-space conjugation between the "isolated" phenyl rings played an important role for this abnormal phenomenon.

Recent Advances in Ring-Opening Functionalization of Cycloalkanols by C-C σ-Bond Cleavage.

PubMed

Wu, Xinxin; Zhu, Chen

2018-06-01

Cycloalkanols prove to be privileged precursors for the synthesis of distally substituted alkyl ketones and polycyclic aromatic hydrocarbons (PAHs) by virtue of cleavage of their cyclic C-C bonds. Direct functionalization of cyclobutanols to build up other chemical bonds (e. g., C-F, C-Cl, C-Br, C-N, C-S, C-Se, C-C, etc.) has been achieved by using the ring-opening strategy. Mechanistically, the C-C cleavage of cyclobutanols can be involved in two pathways: (a) transition-metal catalyzed β-carbon elimination; (b) radical-mediated 'radical clock'-type ring opening. The recent advances of our group for the ring-opening functionalization of tertiary cycloalkanols are described in this account. © 2018 The Chemical Society of Japan & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Effect of central ventilation and air conditioner system on the concentration and health risk from airborne polycyclic aromatic hydrocarbons.

PubMed

Lv, Jinze; Zhu, Lizhong

2013-03-01

Central ventilation and air conditioner systems are widely utilized nowadays in public places for air exchange and temperature control, which significantly influences the transfer of pollutants between indoors and outdoors. To study the effect of central ventilation and air conditioner systems on the concentration and health risk from airborne pollutants, a spatial and temporal survey was carried out using polycyclic aromatic hydrocarbons (PAHs) as agent pollutants. During the period when the central ventilation system operated without air conditioning (AC-off period), concentrations of 2-4 ring PAHs in the model supermarket were dominated by outdoor levels, due to the good linearity between indoor air and outdoor air (r(p) > 0.769, p < 0.05), and the slopes (1.2-4.54) indicated that ventilating like the model supermarket increased the potential health risks from low molecular weight PAHs. During the period when the central ventilation and air conditioner systems were working simultaneously (AC-on period), although the total levels of PAHs were increased, the concentrations and percentage of the particulate PAHs indoors declined significantly. The BaP equivalency (BaPeq) concentration indicated that utilization of air conditioning reduced the health risks from PAHs in the model supermarket.

Molecular mechanism and genetic determinants of buprofezin degradation.

PubMed

Chen, Xueting; Ji, Junbin; Zhao, Leizhen; Qiu, Jiguo; Dai, Chen; Wang, Weiwu; He, Jian; Jiang, Jiandong; Hong, Qing; Yan, Xin

2017-07-14

Buprofezin is a widely used insect growth regulator whose residue has been frequently detected in the environment, posing a threat to aquatic organisms and non-target insects. Microorganisms play an important role in the degradation of buprofezin in the natural environment. However, the relevant catabolic pathway has not been fully characterized, and the molecular mechanism of catabolism is still completely unknown. Rhodococcus qingshengii YL-1 can utilize buprofezin as a sole source of carbon and energy for growth. In this study, the upstream catabolic pathway in strain YL-1 was identified using tandem mass spectrometry. Buprofezin is composed of a benzene ring and a heterocyclic ring. The degradation is initiated by the dihydroxylation of the benzene ring and continues via dehydrogenation, aromatic ring cleavage, breaking of an amide bond and the release of the heterocyclic ring 2- tert -butylimino-3-isopropyl-1,3,5-thiadiazinan-4-one (2-BI). A buprofezin degradation-deficient mutant strain YL-0 was isolated. Comparative genomic analysis combined with gene deletion and complementation experiments revealed that the gene cluster bfzBA3A4A1A2C is responsible for the upstream catabolic pathway of buprofezin. bfzA3A4A1A2 encodes a novel Rieske non-heme iron oxygenase (RHO) system that is responsible for the dihydroxylation of buprofezin at the benzene ring; bfzB is involved in dehydrogenation, and bfzC is in charge of benzene ring cleavage. Furthermore, the products of bfzBA3A4A1A2C can also catalyze dihydroxylation, dehydrogenation and aromatic ring cleavage of biphenyl, flavanone, flavone and bifenthrin. In addition, a transcriptional study revealed that bfzBA3A4A1A2C is organized in one transcriptional unit that is constitutively expressed in strain YL-1. Importance There is an increasing concern about the residue and environmental fate of buprofezin. Microbial metabolism is an important mechanism responsible for the buprofezin degradation in natural environment. However, the molecular mechanism and genetic determinants of microbial degradation of buprofezin has not been well identified. This work revealed that gene cluster bfzBA3A4A1A2C is responsible for the upstream catabolic pathway of buprofezin in R. qingshengii YL-1. The products of bfzBA3A4A1A2C could also degrade bifenthrin, a widely used pyrethroid insecticide. These findings enhance our understanding of the microbial degradation mechanism of buprofezin and benefit the application of strain YL-1 and bfzBA3A4A1A2C in the bioremediation of buprofezin contamination. Copyright © 2017 American Society for Microbiology.

Molecular Mechanism and Genetic Determinants of Buprofezin Degradation

PubMed Central

Chen, Xueting; Ji, Junbin; Zhao, Leizhen; Qiu, Jiguo; Dai, Chen; Wang, Weiwu; He, Jian; Jiang, Jiandong; Hong, Qing

2017-01-01

ABSTRACT Buprofezin is a widely used insect growth regulator whose residue has been frequently detected in the environment, posing a threat to aquatic organisms and nontarget insects. Microorganisms play an important role in the degradation of buprofezin in the natural environment. However, the relevant catabolic pathway has not been fully characterized, and the molecular mechanism of catabolism is still completely unknown. Rhodococcus qingshengii YL-1 can utilize buprofezin as a sole source of carbon and energy for growth. In this study, the upstream catabolic pathway in strain YL-1 was identified using tandem mass spectrometry. Buprofezin is composed of a benzene ring and a heterocyclic ring. The degradation is initiated by the dihydroxylation of the benzene ring and continues via dehydrogenation, aromatic ring cleavage, breaking of an amide bond, and the release of the heterocyclic ring 2-tert-butylimino-3-isopropyl-1,3,5-thiadiazinan-4-one (2-BI). A buprofezin degradation-deficient mutant strain YL-0 was isolated. A comparative genomic analysis combined with gene deletion and complementation experiments revealed that the gene cluster bfzBA3A4A1A2C is responsible for the upstream catabolic pathway of buprofezin. The bfzA3A4A1A2 cluster encodes a novel Rieske nonheme iron oxygenase (RHO) system that is responsible for the dihydroxylation of buprofezin at the benzene ring; bfzB is involved in dehydrogenation, and bfzC is in charge of benzene ring cleavage. Furthermore, the products of bfzBA3A4A1A2C can also catalyze dihydroxylation, dehydrogenation, and aromatic ring cleavage of biphenyl, flavanone, flavone, and bifenthrin. In addition, a transcriptional study revealed that bfzBA3A4A1A2C is organized in one transcriptional unit that is constitutively expressed in strain YL-1. IMPORTANCE There is an increasing concern about the residue and environmental fate of buprofezin. Microbial metabolism is an important mechanism responsible for the buprofezin degradation in the natural environment. However, the molecular mechanism and genetic determinants of microbial degradation of buprofezin have not been well identified. This work revealed that gene cluster bfzBA3A4A1A2C is responsible for the upstream catabolic pathway of buprofezin in Rhodococcus qingshengii YL-1. The products of bfzBA3A4A1A2C could also degrade bifenthrin, a widely used pyrethroid insecticide. These findings enhance our understanding of the microbial degradation mechanism of buprofezin and benefit the application of strain YL-1 and bfzBA3A4A1A2C in the bioremediation of buprofezin contamination. PMID:28710269

Multiple Functions of Aromatic-Carbohydrate Interactions in a Processive Cellulase Examined with Molecular Simulation*

PubMed Central

Payne, Christina M.; Bomble, Yannick J.; Taylor, Courtney B.; McCabe, Clare; Himmel, Michael E.; Crowley, Michael F.; Beckham, Gregg T.

2011-01-01

Proteins employ aromatic residues for carbohydrate binding in a wide range of biological functions. Glycoside hydrolases, which are ubiquitous in nature, typically exhibit tunnels, clefts, or pockets lined with aromatic residues for processing carbohydrates. Mutation of these aromatic residues often results in significant activity differences on insoluble and soluble substrates. However, the thermodynamic basis and molecular level role of these aromatic residues remain unknown. Here, we calculate the relative ligand binding free energy by mutating tryptophans in the Trichoderma reesei family 6 cellulase (Cel6A) to alanine. Removal of aromatic residues near the catalytic site has little impact on the ligand binding free energy, suggesting that aromatic residues immediately upstream of the active site are not directly involved in binding, but play a role in the glucopyranose ring distortion necessary for catalysis. Removal of aromatic residues at the entrance and exit of the Cel6A tunnel, however, dramatically impacts the binding affinity, suggesting that these residues play a role in chain acquisition and product stabilization, respectively. The roles suggested from differences in binding affinity are confirmed by molecular dynamics and normal mode analysis. Surprisingly, our results illustrate that aromatic-carbohydrate interactions vary dramatically depending on the position in the enzyme tunnel. As aromatic-carbohydrate interactions are present in all carbohydrate-active enzymes, these results have implications for understanding protein structure-function relationships in carbohydrate metabolism and recognition, carbon turnover in nature, and protein engineering strategies for biomass utilization. Generally, these results suggest that nature employs aromatic-carbohydrate interactions with a wide range of binding affinities for diverse functions. PMID:21965672

Natural bond orbital approach to the transmission of substituent effect through the fulvene and benzene ring systems.

PubMed

Oziminski, Wojciech P; Krygowski, Tadeusz M

2011-03-01

Electronic structure of 22 monosubstituted derivatives of benzene and exocyclically substituted fulvene with substituents: B(OH)(2), BH(2), CCH, CF(3), CH(3), CHCH(2), CHO, Cl, CMe(3), CN, COCH(3), CONH(2), COOH, F, NH(2), NMe(2), NO, NO(2), OCH(3), OH, SiH(3), SiMe(3) were studied theoretically by means of Natural Bond Orbital analysis. It is shown, that sum of π-electron population of carbon atoms of the fulvene and benzene rings, pEDA(F) and pEDA(B), respectively correlate well with Hammett substituent constants [Formula in text] and aromaticity index NICS. The substituent effect acting on pi-electron occupation at carbon atoms of the fulvene ring is significantly stronger than in the case of benzene. Electron occupations of ring carbon atoms (except C1) in fulvene plotted against each other give linear regressions with high correlation coefficients. The same is true for ortho- and para-carbon atoms in benzene. Positive slopes of the regressions indicate similar for fulvene and benzene kind of substituent effect - mostly resonance in nature. Only the regressions of occupation at the carbon atom in meta- position of benzene against ortho- and para-positions gives negative slopes and low correlation coefficients.

The effect of aromatization on the isotopic compositions of hydrocarbons during early diagenesis

NASA Technical Reports Server (NTRS)

Freeman, K. H.; Boreham, C. J.; Summons, R. E.; Hayes, J. M.

1994-01-01

Polycyclic aromatic hydrocarbons with varying degrees of aromatization were isolated from the Eocene Messel Shale (Rheingraben, Germany). The high abundances of these compounds and their structural resemblances to cyclic triterpenoid lipids are consistent with derivation from microbial rather than thermal processes. Compounds structurally related to oleanane contain from five to nine double bonds; those within a series of aromatized hopanoids contain from three to nine. All are products of diagenetic reactions that remove hydrogen or methyl groups, and, in several cases, break carbon-carbon bonds to open rings. Aromatized products are on average depleted in 13C relative to possible precursors by l.2% (range: l.5% enrichment to 4% depletion, n = 9). The dependence of 13C content on the number of double bonds is not, however, statistically significant and it must be concluded that there is no strong evidence for isotopic fractionation accompanying diagenetic aromatization. Isotopic differences between series (structures related to ursane, des-A-ursane, des-A-lupane, des-A-arborane, and possibly, des-A-gammacerane are present) are much greater, indicating that 13C contents are controlled primarily by source effects. Fractionations due to chromatographic isotope effects during HPLC ranged from 0.1 to 2.8%.

Catalytic oxidation of o-aminophenols and aromatic amines by mushroom tyrosinase.

PubMed

Muñoz-Muñoz, Jose Luis; Garcia-Molina, Francisco; Garcia-Ruiz, Pedro Antonio; Varon, Ramon; Tudela, Jose; Rodriguez-Lopez, Jose N; Garcia-Canovas, Francisco

2011-12-01

The kinetics of tyrosinase acting on o-aminophenols and aromatic amines as substrates was studied. The catalytic constants of aromatic monoamines and o-diamines were both low, these results are consistent with our previous mechanism in which the slow step is the transfer of a proton by a hydroxyl to the peroxide in oxy-tyrosinase (Fenoll et al., Biochem. J. 380 (2004) 643-650). In the case of o-aminophenols, the hydroxyl group indirectly cooperates in the transfer of the proton and consequently the catalytic constants in the action of tyrosinase on these compounds are higher. In the case of aromatic monoamines, the Michaelis constants are of the same order of magnitude than for monophenols, which suggests that the monophenols bind better (higher binding constant) to the enzyme to facilitate the π-π interactions between the aromatic ring and a possible histidine of the active site. In the case of aromatic o-diamines, both the catalytic and Michaelis constants are low, the values of the catalytic constants being lower than those of the corresponding o-diphenols. The values of the Michaelis constants of the aromatic o-diamines are slightly lower than those of their corresponding o-diphenols, confirming that the aromatic o-diamines bind less well (lower binding constant) to the enzyme. Copyright © 2011 Elsevier B.V. All rights reserved.

Raman and i.r. studies of the antileprotic drug Dapsone

NASA Astrophysics Data System (ADS)

D'Cunha, Romola; Kartha, V. B.; Gurnani, S.

No information is available on the mode of action of Dapsone in leprosy treatment, the phenomena of drug resistance and toxicity. Information on the interaction of Dapsone with serum proteins can be obtained at the molecular level by spectroscopic investigations on structural changes of the system. As a first step in these investigations, the i.r. and laser Raman spectra of Dapsone and N-deutero Dapsone have been obtained. The characteristic vibrational frequencies of the NH 2 group, the SO 2 group and the aromatic ring have been identified and assigned from isotope shifts and studies in various solvents.

Cocrystals of kaempferol, quercetin and myricetin with 4,4‧-bipyridine: Crystal structures, analyses of intermolecular interactions and antibacterial properties

NASA Astrophysics Data System (ADS)

Zhang, Yu-Nan; Yin, He-Mei; Zhang, Yu; Zhang, Da-Jun; Su, Xin; Kuang, Hai-Xue

2017-02-01

With an aim to explore the interactions of Osbnd H⋯N between hydroxyl moiety of the flavonoids and the pyridyl ring of N-containing aromatic amines, three flavonols with varying B-ring-hydroxyl groups (kaempferol, quercetin, and myricetin) were selected to combine with 4,4‧-bipyridine. As a result, three new cocrystals of flavonols were obtained with a solution evaporation approach. These three cocrystals were characterized by single crystal X-ray diffraction, XPRD, IR and NMR methods. The resulting cocrystals were kaempferol: 4,4‧-bipyridine (2:1) (KAE·BPY·2H2O), quercetin: 4,4‧-bipyridine (1:1.5) (QUE·BPY), and myricetin: 4,4‧-bipyridine (1:2) (MYR·BPY·H2O). Structural analyses show that an array of hydrogen bonds and π-π stacking interactions interconnect the molecules to form a two-dimensional (2D) supramolecular layer in KAE·BPY·2H2O, QUE·BPY, and MYR·BPY·H2O. In the three cocrystals, they present as three different synthons-ⅠR88(58), Ⅳ R44(42) and, Ⅶ R66(29) with 4,4‧-bipyridine, respectively-which may yield a strategy for constructing the supramolecule. Cocrystals of flavonols combined with N-containing aromatic amines, 7-OH, B-ring-hydroxyl number and/or the location of the flavonols to play a significant part in extending the dimensionality of the cocrystals. The resulting motif formation and crystal packing in these flavonols cocrystals has combined with N-containing aromatic amines. Additionally, the antibacterial properties of the three cocrystals against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) have been investigated.

Biotransformation of the high-molecular weight polycyclic aromatic hydrocarbon (PAH) benzo[k]fluoranthene by Sphingobium sp. strain KK22 and identification of new products of non-alternant PAH biodegradation by liquid chromatography electrospray ionization tandem mass spectrometry

PubMed Central

Maeda, Allyn H; Nishi, Shinro; Hatada, Yuji; Ozeki, Yasuhiro; Kanaly, Robert A

2014-01-01

A pathway for the biotransformation of the environmental pollutant and high-molecular weight polycyclic aromatic hydrocarbon (PAH) benzo[k]fluoranthene by a soil bacterium was constructed through analyses of results from liquid chromatography negative electrospray ionization tandem mass spectrometry (LC/ESI(–)-MS/MS). Exposure of Sphingobium sp. strain KK22 to benzo[k]fluoranthene resulted in transformation to four-, three-and two-aromatic ring products. The structurally similar four-and three-ring non-alternant PAHs fluoranthene and acenaphthylene were also biotransformed by strain KK22, and LC/ESI(–)-MS/MS analyses of these products confirmed the lower biotransformation pathway proposed for benzo[k]fluoranthene. In all, seven products from benzo[k]fluoranthene and seven products from fluoranthene were revealed and included previously unreported products from both PAHs. Benzo[k]fluoranthene biotransformation proceeded through ortho-cleavage of 8,9-dihydroxy-benzo[k]fluoranthene to 8-carboxyfluoranthenyl-9-propenic acid and 9-hydroxy-fluoranthene-8-carboxylic acid, and was followed by meta-cleavage to produce 3-(2-formylacenaphthylen-1-yl)-2-hydroxy-prop-2-enoic acid. The fluoranthene pathway converged with the benzo[k]fluoranthene pathway through detection of the three-ring product, 2-formylacenaphthylene-1-carboxylic acid. Production of key downstream metabolites, 1,8-naphthalic anhydride and 1-naphthoic acid from benzo[k]fluoranthene, fluoranthene and acenaphthylene biotransformations provided evidence for a common pathway by strain KK22 for all three PAHs through acenaphthoquinone. Quantitative analysis of benzo[k]fluoranthene biotransformation by strain KK22 confirmed biodegradation. This is the first pathway proposed for the biotransformation of benzo[k]fluoranthene by a bacterium. PMID:24325265

Cardiac toxicity of 5-ring polycyclic aromatic hydrocarbons is differentially dependent on the aryl hydrocarbon receptor 2 isoform during zebrafish development

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

Incardona, John P., E-mail: john.incardona@noaa.gov; Linbo, Tiffany L.; Scholz, Nathaniel L.

Petroleum-derived compounds, including polycyclic aromatic hydrocarbons (PAHs), commonly occur as complex mixtures in the environment. Recent studies using the zebrafish experimental model have shown that PAHs are toxic to the embryonic cardiovascular system, and that the severity and nature of this developmental cardiotoxicity varies by individual PAH. In the present study we characterize the toxicity of the relatively higher molecular weight 5-ring PAHs benzo[a]pyrene (BaP), benzo[e]pyrene (BeP), and benzo[k]fluoranthene (BkF). While all three compounds target the cardiovascular system, the underlying role of the ligand-activated aryl hydrocarbon receptor (AHR2) and the tissue-specific induction of the cytochrome p450 metabolic pathway (CYP1A) weremore » distinct for each. BaP exposure (40 {mu}M) produced AHR2-dependent bradycardia, pericardial edema, and myocardial CYP1A immunofluorescence. By contrast, BkF exposure (4-40 {mu}M) caused more severe pericardial edema, looping defects, and erythrocyte regurgitation through the atrioventricular valve that were AHR2-independent (i.e., absent myocardial or endocardial CYP1A induction). Lastly, exposure to BeP (40 {mu}M) yielded a low level of CYP1A+ signal in the vascular endothelium of the head and trunk, without evident toxic effects on cardiac function or morphogenesis. Combined with earlier work on 3- and 4-ring PAHs, our findings provide a more complete picture of how individual PAHs may drive the cardiotoxicity of mixtures in which they predominate. This will improve toxic injury assessments and risk assessments for wild fish populations that spawn in habitats altered by overlapping petroleum-related human impacts such as oil spills, urban stormwater runoff, or sediments contaminated by legacy industrial activities. -- Highlights: Black-Right-Pointing-Pointer PAH compounds with 5 rings in different arrangements caused differential tissue-specific patterns of CYP1A induction in zebrafish embryos. Black-Right-Pointing-Pointer These compounds produced differential cardiac developmental toxicity that did not strictly correlate with associated CYP1A induction. Black-Right-Pointing-Pointer Cardiotoxicity of benzo(a)pyrene was partially dependent on the AHR2 isoform, while benzo(k)fluoranthene cardiotoxicity was not. Black-Right-Pointing-Pointer Individual PAH compounds have distinct toxicokinetic pathways in fish embryos, and act through different toxic mechanisms.« less

Computer-aided rational design of novel EBF analogues with an aromatic ring.

PubMed

Wang, Shanshan; Sun, Yufeng; Du, Shaoqing; Qin, Yaoguo; Duan, Hongxia; Yang, Xinling

2016-06-01

Odorant binding proteins (OBPs) are important in insect olfactory recognition. These proteins bind specifically to insect semiochemicals and induce their seeking, mating, and alarm behaviors. Molecular docking and molecular dynamics simulations were performed to provide computational insight into the interaction mode between AgamOBP7 and novel (E)-β-farnesene (EBF) analogues with an aromatic ring. The ligand-binding cavity in OBP7 was found to be mostly hydrophobic due to the presence of several nonpolar residues. The interactions between the EBF analogues and the hydrophobic residues in the binding cavity increased in strength as the distance between them decreased. The EBF analogues with an N-methyl formamide or ester linkage had higher docking scores than those with an amide linkage. Moreover, delocalized π-π and electrostatic interactions were found to contribute significantly to the binding between the ligand benzene ring and nearby protein residues. To design new compounds with higher activity, four EBF analogues D1-D4 with a benzene ring were synthesized and evaluated based on their docking scores and binding affinities. D2, which had an N-methyl formamide group linkage, exhibited stronger binding than D1, which had an amide linkage. D4 exhibited particularly strong binding due to multiple hydrophobic interactions with the protein. This study provides crucial foundations for designing novel EBF analogues based on the OBP structure. Graphical abstract The design strategy of new EBF analogues based on the OBP7 structure.

Single base substitution causing the fragrant phenotype and development of a type-specific marker in aromatic coconut (Cocos nucifera).

PubMed

Vongvanrungruang, A; Mongkolsiriwatana, C; Boonkaew, T; Sawatdichaikul, O; Srikulnath, K; Peyachoknagul, S

2016-09-19

The fragrance gene, betaine aldehyde dehydrogenase 2 (Badh2), has been well studied in many plant species. The objectives of this study were to clone Badh2 and compare the sequences between aromatic and non-aromatic coconuts. The complete coding region was cloned from cDNA of both aromatic and non-aromatic coconuts. The nucleotide sequences were highly homologous to Badh2 genes of other plants. Badh2 consisted of a 1512-bp open reading frame encoding 503 amino acids. A single nucleotide difference between aromatic and non-aromatic coconuts resulted in the conversion of alanine (non-aromatic) to proline (aromatic) at position 442, which was the substrate binding site of BADH2. The ring side chain of proline could destabilize the structure leading to a non-functional enzyme. Badh2 genomic DNA was cloned from exon 1 to 4, and from exon 5 to 15 from the two coconut types, except for intron 4 that was very long. The intron sequences of the two coconut groups were highly homologous. No differences in Badh2 expression were found among the tissues of aromatic coconut or between aromatic and non-aromatic coconuts. The amino acid sequences of BADH2 from coconut and other plants were compared and the genetic relationship was analyzed using MEGA 7.0. The phylogenetic tree reconstructed by the Bayesian information criterion consisted of two distinct groups of monocots and dicots. Among the monocots, coconut (Cocos nucifera) and oil palm (Elaeis guineensis) were the most closely related species. A marker for coconut differentiation was developed from one-base substitution site and could be successfully used.

Experimental (FT-IR, FT-Raman, 1H NMR) and theoretical study of magnesium, calcium, strontium, and barium picolinates.

PubMed

Swiderski, G; Kalinowska, M; Wojtulewski, S; Lewandowski, W

2006-05-01

The experimental IR, Raman, and 1H NMR spectra of picolinic acid, as well as magnesium, calcium, strontium, and barium picolinates were registered, assigned and studied. Characteristic changes in the spectra of metal picolinates in comparison with the spectrum of ligand were observed, which lead to the conclusion that perturbation of the aromatic system of picolinates increases along with the series Mg-->Ca-->Sr-->Ba. Theoretical structures of beryllium and magnesium picolinates, as well as theoretical IR spectrum of magnesium picolinate were calculated in B3PW91/6-311++G(d, p) level. On the basis of calculated bond lengths in pyridine ring geometric, aromaticity indexes HOMA were calculated. The idea of these indexes is based on the fact that the essential factor in aromatic stabilization is the pi delocalization manifested in: planar geometry, equalization of the bond lengths and angles, and symmetry. The decidedly lower value of HOMA for magnesium picolinate (i.e. 0.545; 0.539) than that for beryllium picolinate (i.e. 0.998; 0.998) indicate higher aromatic properties of Be picolinate than of Mg picolinate. The comparison of theoretical and literature experimental structures of magnesium picolinate was done. The experimental structure contains two water molecules, so the calculations for hydrated magnesium picolinate were carried on, and the influence of coordinated water molecule on the structure of picolinates was discussed. The HOMAs for hydrated experimental and calculated Mg picolinate amount to 0.870; 0.743, and 0.900; 0.890, respectively, whereas for anhydrous structure, it is as described above, i.e. 0.545; 0.539. Thus, the calculations clearly showed that water molecules coordinated to the central atom weakens the effect of metal on the electronic system of ligand.

Experimental (FT-IR, FT-Raman, 1H NMR) and theoretical study of magnesium, calcium, strontium, and barium picolinates

NASA Astrophysics Data System (ADS)

Świderski, G.; Kalinowska, M.; Wojtulewski, S.; Lewandowski, W.

2006-05-01

The experimental IR, Raman, and 1H NMR spectra of picolinic acid, as well as magnesium, calcium, strontium, and barium picolinates were registered, assigned and studied. Characteristic changes in the spectra of metal picolinates in comparison with the spectrum of ligand were observed, which lead to the conclusion that perturbation of the aromatic system of picolinates increases along with the series Mg → Ca → Sr → Ba. Theoretical structures of beryllium and magnesium picolinates, as well as theoretical IR spectrum of magnesium picolinate were calculated in B3PW91/6-311++G(d, p) level. On the basis of calculated bond lengths in pyridine ring geometric, aromaticity indexes HOMA were calculated. The idea of these indexes is based on the fact that the essential factor in aromatic stabilization is the π delocalization manifested in: planar geometry, equalization of the bond lengths and angles, and symmetry. The decidedly lower value of HOMA for magnesium picolinate (i.e. 0.545; 0.539) than that for beryllium picolinate (i.e. 0.998; 0.998) indicate higher aromatic properties of Be picolinate than of Mg picolinate. The comparison of theoretical and literature experimental structures of magnesium picolinate was done. The experimental structure contains two water molecules, so the calculations for hydrated magnesium picolinate were carried on, and the influence of coordinated water molecule on the structure of picolinates was discussed. The HOMAs for hydrated experimental and calculated Mg picolinate amount to 0.870; 0.743, and 0.900; 0.890, respectively, whereas for anhydrous structure, it is as described above, i.e. 0.545; 0.539. Thus, the calculations clearly showed that water molecules coordinated to the central atom weakens the effect of metal on the electronic system of ligand.

CYP63A2, a catalytically versatile fungal P450 monooxygenase capable of oxidizing higher-molecular-weight polycyclic aromatic hydrocarbons, alkylphenols, and alkanes.

PubMed

Syed, Khajamohiddin; Porollo, Aleksey; Lam, Ying Wai; Grimmett, Paul E; Yadav, Jagjit S

2013-04-01

Cytochrome P450 monooxygenases (P450s) are known to oxidize hydrocarbons, albeit with limited substrate specificity across classes of these compounds. Here we report a P450 monooxygenase (CYP63A2) from the model ligninolytic white rot fungus Phanerochaete chrysosporium that was found to possess a broad oxidizing capability toward structurally diverse hydrocarbons belonging to mutagenic/carcinogenic fused-ring higher-molecular-weight polycyclic aromatic hydrocarbons (HMW-PAHs), endocrine-disrupting long-chain alkylphenols (APs), and crude oil aliphatic hydrocarbon n-alkanes. A homology-based three-dimensional (3D) model revealed the presence of an extraordinarily large active-site cavity in CYP63A2 compared to the mammalian PAH-oxidizing (CYP3A4, CYP1A2, and CYP1B1) and bacterial aliphatic-hydrocarbon-oxidizing (CYP101D and CYP102A1) P450s. This structural feature in conjunction with ligand docking simulations suggested potential versatility of the enzyme. Experimental characterization using recombinantly expressed CYP63A2 revealed its ability to oxidize HMW-PAHs of various ring sizes, including 4 rings (pyrene and fluoranthene), 5 rings [benzo(a)pyrene], and 6 rings [benzo(ghi)perylene], with the highest enzymatic activity being toward the 5-ring PAH followed by the 4-ring and 6-ring PAHs, in that order. Recombinant CYP63A2 activity yielded monohydroxylated PAH metabolites. The enzyme was found to also act as an alkane ω-hydroxylase that oxidized n-alkanes with various chain lengths (C9 to C12 and C15 to C19), as well as alkyl side chains (C3 to C9) in alkylphenols (APs). CYP63A2 showed preferential oxidation of long-chain APs and alkanes. To our knowledge, this is the first P450 identified from any of the biological kingdoms that possesses such broad substrate specificity toward structurally diverse xenobiotics (PAHs, APs, and alkanes), making it a potent enzyme biocatalyst candidate to handle mixed pollution (e.g., crude oil spills).

CYP63A2, a Catalytically Versatile Fungal P450 Monooxygenase Capable of Oxidizing Higher-Molecular-Weight Polycyclic Aromatic Hydrocarbons, Alkylphenols, and Alkanes

PubMed Central

Syed, Khajamohiddin; Porollo, Aleksey; Lam, Ying Wai; Grimmett, Paul E.

2013-01-01

Cytochrome P450 monooxygenases (P450s) are known to oxidize hydrocarbons, albeit with limited substrate specificity across classes of these compounds. Here we report a P450 monooxygenase (CYP63A2) from the model ligninolytic white rot fungus Phanerochaete chrysosporium that was found to possess a broad oxidizing capability toward structurally diverse hydrocarbons belonging to mutagenic/carcinogenic fused-ring higher-molecular-weight polycyclic aromatic hydrocarbons (HMW-PAHs), endocrine-disrupting long-chain alkylphenols (APs), and crude oil aliphatic hydrocarbon n-alkanes. A homology-based three-dimensional (3D) model revealed the presence of an extraordinarily large active-site cavity in CYP63A2 compared to the mammalian PAH-oxidizing (CYP3A4, CYP1A2, and CYP1B1) and bacterial aliphatic-hydrocarbon-oxidizing (CYP101D and CYP102A1) P450s. This structural feature in conjunction with ligand docking simulations suggested potential versatility of the enzyme. Experimental characterization using recombinantly expressed CYP63A2 revealed its ability to oxidize HMW-PAHs of various ring sizes, including 4 rings (pyrene and fluoranthene), 5 rings [benzo(a)pyrene], and 6 rings [benzo(ghi)perylene], with the highest enzymatic activity being toward the 5-ring PAH followed by the 4-ring and 6-ring PAHs, in that order. Recombinant CYP63A2 activity yielded monohydroxylated PAH metabolites. The enzyme was found to also act as an alkane ω-hydroxylase that oxidized n-alkanes with various chain lengths (C9 to C12 and C15 to C19), as well as alkyl side chains (C3 to C9) in alkylphenols (APs). CYP63A2 showed preferential oxidation of long-chain APs and alkanes. To our knowledge, this is the first P450 identified from any of the biological kingdoms that possesses such broad substrate specificity toward structurally diverse xenobiotics (PAHs, APs, and alkanes), making it a potent enzyme biocatalyst candidate to handle mixed pollution (e.g., crude oil spills). PMID:23416995

Sediment record of polycyclic aromatic hydrocarbons in the Liaohe River Delta wetland, Northeast China: Implications for regional population migration and economic development.

PubMed

Ma, Chuanliang; Lin, Tian; Ye, Siyuan; Ding, Xigui; Li, Yuanyuan; Guo, Zhigang

2017-03-01

The polycyclic aromatic hydrocarbons (PAHs) of a 210 Pb-dated sediment core extracted from the Liaohe River Delta wetland were measured to reconstruct the sediment record of PAHs and its response to human activity for the past 300 years in Northeast China. The concentrations of the 16 U.S. Environmental Protection Agency priority PAHs (∑16PAHs) ranged from 46 to 1167 ng g -1 in this sediment core. The concentrations of the 16 PAHs (especially 4- and 5+6-ring PAHs) after the 1980s (surface sediments 0-6 cm) were one or two orders of magnitudes higher than those of the down-core samples. The exponential growth of 4-ring and 5+6-ring PAH concentrations after the 1980s responded well to the increased energy consumption and number of civil vehicles resulting from the rapid economic development in China. Prior to 1950, relatively low levels of the 16 PAHs and a high proportion of 2+3-ring PAHs was indicative of biomass burning as the main source of the PAHs. A significant increase in the 2 + 3 ring PAH concentration from the 1860s-1920s was observed and could be attributed to a constant influx of population migration into Northeast China. It was suggested that the link between historical trend of PAHs and population or energy use involves two different economic stages. Typically, in an agricultural economy, the greater the population size, the greater the emission of PAHs from biomass burning, while in an industrial economy, the increase in sedimentary PAH concentrations is closely related to increasing energy consumption of fossil fuels. Copyright © 2016 Elsevier Ltd. All rights reserved.

Polycyclic aromatic hydrocarbons (PAHs) in wetland soils under different land uses in a coastal estuary: toxic levels, sources and relationships with soil organic matter and water-stable aggregates.

PubMed

Xiao, Rong; Bai, Junhong; Wang, Junjing; Lu, Qiongqiong; Zhao, Qingqing; Cui, Baoshan; Liu, Xinhui

2014-09-01

The concentrations of 16 polycyclic aromatic hydrocarbons (PAHs) were determined in the soils from industrial, wharf, cropland, milldam and natural wetland sites to characterize their distributions, toxic levels and possible sources in the Pearl River Estuary and identify their relationships with soil organic matter (SOM) and water-stable aggregates (WSAs). Our results indicate that the average concentration of total PAHs in this region reached a moderate pollution level, which was higher than that in other larger estuaries in Asia. The average level of total PAHs in industrial soils was 1.2, 1.5, 1.6 and 2.3 times higher than those in soils from wharf, cropland, milldam and natural wetland sites, respectively. Greater accumulation of PAHs occurred in the middle and/or bottom soil layers where 3-ring PAHs were dominant. Industrial soils also exhibited the highest toxic levels with the highest toxic equivalent concentrations of PAHs, followed by wharf and milldam soils, and the cropland and wetland soils had the lowest toxicity. The diagnostic ratios suggested that PAHs primarily originated from biomass and coal combustion at industrial and milldam sites, and petroleum combustion was determined to be the primary source of PAHs at the wharf, cropland and wetland sites. Both 3-ring and 4-ring PAHs in the milldam and wharf soils were significantly positively correlated with the SOM, whereas the 4,5,6-ring PAHs and total PAHs in industrial soils and the 2-ring PAHs in cropland soils were significantly negatively correlated with the SOM. In addition, large WSAs also exhibited a significant positive correlation with PAHs. Copyright © 2014 Elsevier Ltd. All rights reserved.

Characterization of a Naphthalene Dioxygenase Endowed with an Exceptionally Broad Substrate Specificity Toward Polycyclic Aromatic Hydrocarbons

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

Jouanneau,Y.; Meyer, C.; Jakoncic, J.

In Sphingomonas CHY-1, a single ring-hydroxylating dioxygenase is responsible for the initial attack of a range of polycyclic aromatic hydrocarbons (PAHs) composed of up to five rings. The components of this enzyme were separately purified and characterized. The oxygenase component (ht-PhnI) was shown to contain one Rieske-type [2Fe-2S] cluster and one mononuclear Fe center per {alpha} subunit, based on EPR measurements and iron assay. Steady-state kinetic measurements revealed that the enzyme had a relatively low apparent Michaelis constant for naphthalene (K{sub m} = 0.92 {+-} 0.15 {mu}M) and an apparent specificity constant of 2.0 {+-} 0.3 M{sup -1} s{sup -1}.more » Naphthalene was converted to the corresponding 1,2-dihydrodiol with stoichiometric oxidation of NADH. On the other hand, the oxidation of eight other PAHs occurred at slower rates and with coupling efficiencies that decreased with the enzyme reaction rate. Uncoupling was associated with hydrogen peroxide formation, which is potentially deleterious to cells and might inhibit PAH degradation. In single turnover reactions, ht-PhnI alone catalyzed PAH hydroxylation at a faster rate in the presence of organic solvent, suggesting that the transfer of substrate to the active site is a limiting factor. The four-ring PAHs chrysene and benz[a]anthracene were subjected to a double ring-dihydroxylation, giving rise to the formation of a significant proportion of bis-cis-dihydrodiols. In addition, the dihydroxylation of benz[a]anthracene yielded three dihydrodiols, the enzyme showing a preference for carbons in positions 1,2 and 10,11. This is the first characterization of a dioxygenase able to dihydroxylate PAHs made up of four and five rings.« less

π-Extended Star-Shaped Polycyclic Aromatic Hydrocarbons based on Fused Truxenes: Synthesis, Self-Assembly, and Facilely Tunable Emission Properties.

PubMed

Cheng, Cheng; Jiang, Yi; Liu, Cheng-Fang; Zhang, Jian-Dong; Lai, Wen-Yong; Huang, Wei

2016-12-19

A new set of star-shaped polycyclic aromatic hydrocarbons (PAHs) based on naphthalene-fused truxenes, TrNaCn (n=1-4), were synthesized and characterized. The synthesis involved a microwave-assisted six-fold Suzuki coupling reaction, followed by oxidative cyclodehydrogenation. Multiple dehydrocyclization products could be effectively isolated in a single reaction, thus suggesting that the oxidative cyclodehydrogenation reaction involved a stepwise ring-closing process. The thermal, optical, and electrochemical properties and the self-assembly behavior of the resulting oxidized samples were investigated to understand the impact of the ring-fusing process on the properties of the star-shaped PAHs. Distinct bathochromic shift of the absorption maxima (λ max ) revealed that the molecular conjugation extended with the stepwise ring-closing reactions. The optical band-gap energy of these PAHs varied significantly on increasing the number of fused rings, thereby resulting in readily tunable emissive properties of the resultant star-shaped PAHs. Interestingly, the generation of rigid "arms" by using perylene analogues caused TrNaC2 and TrNaC3 to show significantly enhanced photoluminescence quantum yields (PLQYs) in solution (η=0.65 and 0.66, respectively) in comparison with those of TrNa and TrNaC1 (η=0.08 and 0.16, respectively). Owing to strong intermolecular interactions, the TrNa precursor was able to self-assemble into rod-like microcrystals, which could be facilely identified by the naked eye, whilst TrNaC1 self-assembled into nanosheets once the naphthalene rings had fused. This study offers a unique platform to gain further insight into-and a better understanding of-the photophysical and self-assembly properties of π-extended star-shaped PAHs. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

QSAR and molecular modelling studies on B-DNA recognition of minor groove binders.

PubMed

de Oliveira, André Mauricio; Custódio, Flávia Beatriz; Donnici, Cláudio Luis; Montanari, Carlos Alberto

2003-02-01

Aromatic bisamidines have been proved to be efficient compounds against Leishmania spp. and Pneumocystis carinii. Although the mode of action is still not known, these molecules are supposed to be DNA minor groove binders (MGBs). This paper describes a molecular modelling study for a set of MGBs in order to rank them through their complementarity to the Dickerson Drew Dodecamer (DDD) according to their interaction energies with B-DNA. A comparative molecular field analysis (CoMFA) has shown the importance of relatively bulky positively charged groups attached to the MGB aromatic rings, and small and negatively charged substituents into the middle chain. Models were obtained for DNA denaturation related to H-bonding processes of binding modes. Validation of the model demonstrated the robustness of CoMFA in terms of independent test set of similar MGBs. GRID results allotted bioisosteric substitution of z.sbnd;Oz.sbnd; by z.sbnd;NHz.sbnd; in furan ring of furamidine and related compounds as being capable to enhance the binding to DDD.

Common Pharmacophore of Structurally Distinct Small-Molecule Inhibitors of Intracellular Retrograde Trafficking of Ribosome Inactivating Proteins

NASA Astrophysics Data System (ADS)

Yu, Shichao; Park, Jewn Giew; Kahn, Jennifer Nielsen; Tumer, Nilgun E.; Pang, Yuan-Ping

2013-12-01

We reported previously (+/-)-2-(5-methylthiophen-2-yl)-3-phenyl-2,3-dihydroquinazolin-4(1H)-one [(+/-)-Retro-2cycl] as the chemical structure of Retro-2 that showed mouse protection against ricin, a notorious ribosome inactivating protein (RIP). Herein we report our chemical resolution of (+/-)-Retro-2cycl, analog synthesis, and cell-based evaluation showing that the two optically pure enantiomers and their achiral analog have nearly the same degree of cell protection against ricin as (+/-)-Retro-2cycl. We also report our computational studies explaining the lack of stereo preference and revealing a common pharmacophore of structurally distinct inhibitors of intracellular retrograde trafficking of RIPs. This pharmacophore comprises a central aromatic ring o-substituted by an aromatic ring and a moiety bearing an O or S atom attached to sp2 C atom(s). These results offer new insights into lead identification and optimization for RIP antidote development to minimize the global health threat caused by ribosome-inactivating proteins.

Surface water polycyclic aromatic hydrocarbons (PAH) in urban areas of Nanjing, China.

PubMed

Wang, Chunhui; Zhou, Shenglu; Wu, Shaohua; Song, Jing; Shi, Yaxing; Li, Baojie; Chen, Hao

2017-10-01

The concentration, sources and environmental risks of polycyclic aromatic hydrocarbons (PAHs) in surface water in urban areas of Nanjing were investigated. The range of ∑ 16 PAHs concentration is between 4,076 and 29,455 ng/L, with a mean of 17,212 ng/L. The composition of PAHs indicated that 2- and 3-ring PAHs have the highest proportion in all PAHs, while the 5- and 6-ring PAHs were the least in proportion. By diagnostic ratio analysis, combustion and petroleum were a mixture input that contributed to the water PAH in urban areas of Nanjing. Positive matrix factorization quantitatively identified four factors, including coke oven, coal combustion, oil source, and vehicle emission, as the main sources. Toxic equivalency factors of BaP (BaP eq ) evaluate the environmental risks of PAHs and indicate the PAH concentration in surface water in urban areas of Nanjing had been polluted and might cause potential environmental risks. Therefore, the PAH contamination in surface water in urban areas of Nanjing should draw considerable attention.

The effect of high pressure on the lattice structure and dynamics of phenacenes

NASA Astrophysics Data System (ADS)

Capitani, F.; Höppner, M.; Malavasi, L.; Marini, C.; Dore, P.; Boeri, L.; Postorino, Paolo

2017-10-01

We studied the effect of high pressure on three phenacenes, aromatic molecules with a zig-zag configuration of the benzene rings. The lattice structure and vibrational dynamics of crystalline phenanthrene (C14H10, three benzene rings), chrysene (C18H12, four), and picene (C22H14, five) were investigated by means of X-ray diffraction and Raman measurements. Raman spectra were compared with theoretical ones obtained from ab-initio Density Functional Theory calculations. Experimental and theoretical results allowed to identify the onset of a structural transition in phenanthrene at 7.8 GPa under hydrostatic conditions and at 5.7 GPa under non-hydrostatic conditions. We found that this transition is related to a reorientantion of the molecules in the ab plane. On the contrary, chrysene and picene do not undergo any phase transition in the investigated pressure range, thus suggesting that molecular size plays an important role in the occurence of pressure induced structural modifications in aromatic compounds.

Syntheses of cytotoxic novel arctigenin derivatives bearing halogen and alkyl groups on aromatic rings.

PubMed

Yamauchi, Satoshi; Wukirsari, Tuti; Ochi, Yoshiaki; Nishiwaki, Hisashi; Nishi, Kosuke; Sugahara, Takuya; Akiyama, Koichi; Kishida, Taro

2017-09-01

The new lignano-9,9'-lactones (α,β-dibenzyl-γ-butyrolactone lignans), which showed the higher cytotoxicity than arctigenin, were synthesized. The well-known cytotoxic arctigenin showed activity against HL-60 cells (EC 50 =12μM), however, it was inactive against HeLa cells (EC 50 >100μM). The synthesized (3,4-dichloro, 2'-butoxy)-derivative 55 and (3,4-dichloro, 4'-butyl)-derivative 66 bearing the lignano-9,9'-lactone structures showed the EC 50 values of 10μM and 9.4μM against HL-60 cells, respectively. Against HeLa cells, the EC 50 value of the derivative 66 was 27μM. By comparing the activities with the corresponding 9,9'-epoxy structure (tetrahydrofuran compounds), the importance of the lactone structure of 55 and 66 for the higher activities was shown. The substituents on the aromatic ring of the lignano-9,9'-lactones affected the cytotoxicity level, observing more than 10-fold difference. Copyright © 2017. Published by Elsevier Ltd.

Treatability of phenol-production wastewater: Rate constant and pathway of dimethyl phenyl carbinol oxidation by hydroxyl radicals.

PubMed

Boonrattanakij, Nonglak; Joysampao, Atsawin; Pobsuktanasub, Tuksinaiya; Anotai, Jin; Ruangchainikom, Chalermchai

2017-12-15

Phenol-production wastewater is difficult to treat biologically by aerobic processes to meet the effluent standard COD of 120 mg L -1 because it contains several highly refractory aromatic pollutants, particularly dimethyl phenyl carbinol. Pretreatment revealed that dimethyl phenyl carbinol was slowly oxidized by molecular ozone; however, it readily reacted with hydroxyl radicals to yield acetophenone as a primary product. Acetophenone was further oxidized, first through five different pathways to form benzoic acid, phenyl glyoxalic acid, 4-4'-diacetyl biphenyl, and several hydroxylated aromatic compounds, and later to aliphatic carboxylic acids via ring cleavage. Regardless of system configuration (homogeneous vs heterogeneous), operating mode (batch vs continuous), and chemical concentration, the average intrinsic rate constants were 1.05 × 10 10 and 9.29 × 10 9  M -1  s -1 for dimethyl phenyl carbinol and acetophenone, respectively. Copyright © 2017 Elsevier Ltd. All rights reserved.

Li7(BH)5(+): a new thermodynamically favored star-shaped molecule.

PubMed

Torres-Vega, Juan J; Vásquez-Espinal, Alejandro; Beltran, Maria J; Ruiz, Lina; Islas, Rafael; Tiznado, William

2015-07-15

The potential energy surfaces (PESs) of Lin(BH)5(n-6) systems (where n = 5, 6, and 7) were explored using the gradient embedded genetic algorithm (GEGA) program, in order to find their global minima conformations. This search predicts that the lowest-energy isomers of Li6(BH)5 and Li7(BH)5(+) contain a (BH)5(6-) pentagonal fragment, which is isoelectronic and structurally analogous to the prototypical aromatic hydrocarbon anion C5H5(-). Li7(BH)5(+), along with Li7C5(+), Li7Si5(+) and Li7Ge5(+), joins a select group of clusters that adopt a seven-peak star-shape geometry, which is favored by aromaticity in the central five-membered ring, and by the preference of Li atoms for bridging positions. The theoretical analysis of chemical bonding, based on magnetic criteria, supports the notion that electronic delocalization is an important stabilization factor in all these star-shaped clusters.

A phenylalanine rotameric switch for signal-state control in bacterial chemoreceptors

NASA Astrophysics Data System (ADS)

Ortega, Davi R.; Yang, Chen; Ames, Peter; Baudry, Jerome; Parkinson, John S.; Zhulin, Igor B.

2013-12-01

Bacterial chemoreceptors are widely used as a model system for elucidating the molecular mechanisms of transmembrane signalling and have provided a detailed understanding of how ligand binding by the receptor modulates the activity of its associated kinase CheA. However, the mechanisms by which conformational signals move between signalling elements within a receptor dimer and how they control kinase activity remain unknown. Here, using long molecular dynamics simulations, we show that the kinase-activating cytoplasmic tip of the chemoreceptor fluctuates between two stable conformations in a signal-dependent manner. A highly conserved residue, Phe396, appears to serve as the conformational switch, because flipping of the stacked aromatic rings of an interacting F396-F396‧ pair in the receptor homodimer takes place concomitantly with the signal-related conformational changes. We suggest that interacting aromatic residues, which are common stabilizers of protein tertiary structure, might serve as rotameric molecular switches in other biological processes as well.

FORMATION OF POLYCYCLIC AROMATIC HYDROCARBONS AND CARBONACEOUS SOLIDS IN GAS-PHASE CONDENSATION EXPERIMENTS

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

Jaeger, C.; Huisken, F.; Henning, Th.

2009-05-01

Carbonaceous grains represent a major component of cosmic dust. In order to understand their formation pathways, they have been prepared in the laboratory by gas-phase condensation reactions such as laser pyrolysis and laser ablation. Our studies demonstrate that the temperature in the condensation zone determines the formation pathway of carbonaceous particles. At temperatures lower than 1700 K, the condensation by-products are mainly polycyclic aromatic hydrocarbons (PAHs) that are also the precursors or building blocks for the condensing soot grains. The low-temperature condensates contain PAH mixtures that are mainly composed of volatile three to five ring systems. At condensation temperatures highermore » than 3500 K, fullerene-like carbon grains and fullerene compounds are formed. Fullerene fragments or complete fullerenes equip the nucleating particles. Fullerenes can be identified as soluble components. Consequently, condensation products in cool and hot astrophysical environments such as cool and hot asymptotic giant branch stars or Wolf-Rayet stars should be different and should have distinct spectral properties.« less

Evidence of C-F-P and aromatic π-F-P weak interactions in imidazolium ionic liquids and its consequences

NASA Astrophysics Data System (ADS)

Panja, Sumit Kumar; Srivastava, Nitin; Srivastava, Jyoti; Prasad, Namburi Eswara; Noothalapati, Hemanth; Shigeto, Shinsuke; Saha, Satyen

2018-04-01

A simple change from alkyl group to alkene in side chain of imidazolium cation with same anion resulted in a drastic impact on physical properties (e.g., melting point) from bmimPF6 IL to cmimPF6 IL. The underlying reasons have been elucidated by structural and interaction studies with the help of DSC, SCXRD, vibrational and multi-nuclear NMR spectroscopic techniques. Experiments reveal existence of new weak interactions involving the carbon and π cloud of the imidazolium aromatic ring with fluoride of PF6 anion (i.e., C2-F-P and π-F-P) in cmimPF6 but are absent in structurally similar prototype IL, bmimPF6. Though weak, these interactions helped to form ladder type supramolecular arrangement, resulting in quite high melting point for cmimPF6 IL compared to bmimPF6 IL. These findings emphasize that an IL system can behave uniquely because of the existence of uncommon weak interactions.

Emission, distribution and toxicity of polycyclic aromatic hydrocarbons (PAHs) during municipal solid waste (MSW) and coal co-combustion.

PubMed

Peng, Nana; Li, Yi; Liu, Zhengang; Liu, Tingting; Gai, Chao

2016-09-15

Emission and distribution characteristics of polycyclic aromatic hydrocarbons (PAHs) were investigated during municipal solid waste (MSW) and coal combustion alone and MSW/coal blend (MSW weight fraction of 25%) co-combustion within a temperature range of 500°C-900°C. The results showed that for all combustion experiments, flue gas occupied the highest proportion of total PAHs and fly ash contained more high-ring PAHs. Moreover, the 3- and 4-ring PAHs accounted for the majority of total PAHs and Ant or Phe had the highest concentrations. Compared to coal, MSW combustion generated high levels of total PAHs with the range of 111.28μg/g-10,047.22μg/g and had high toxicity equivalent value (TEQ). MSW/coal co-combustion generated the smallest amounts of total PAHs and had the lowest TEQ than MSW and coal combustion alone. Significant synergistic interactions occurred between MSW and coal during co-combustion and the interactions suppressed the formation of PAHs, especially hazardous high-ring PAHs and decreased the TEQ. The present study indicated that the reduction of the yield and toxicity of PAHs can be achieved by co-combustion of MSW and coal. Copyright © 2016 Elsevier B.V. All rights reserved.

New type of bonding formed from an overlap between pi aromatic and pi C=O molecular orbitals stabilizes the coexistence in one molecule of the ionic and neutral meso-ionic forms of imidazopyridine.

PubMed

Hoffmann, Marcin; Plutecka, Agnieszka; Rychlewska, Urszula; Kucybala, Zdzislaw; Paczkowski, Jerzy; Pyszka, Ilona

2005-05-26

New bis(imidazo)pyridine dye has been synthesized and tested as a potential photoinitaitor for free-radical polymerization induced with the visible emission of an argon ion laser. The X-ray analysis based on data collected at 170 and 130 K, as well as density functional theory (DFT) calculations, revealed the presence of two different forms of imidazopyridine rings within the same molecule. These two forms of the same moiety had not only different geometries but different electronic structures as well. One of the imidazopyridine rings was in the ionic form, while the other was in the meso-ionic form. DFT calculations provided an explanation for such an observed phenomena. The averaging of ionic and meso-ionic forms of imidazopyridine rings within the same molecule is hindered because of an attractive interaction between them. Analysis of electronic density revealed that, indeed, a new type of bonding is formed as the result of an overlap between pi aromatic and pi C=O molecular orbitals. This bonding, like the hydrogen bond, is primarily of electrostatic character, and its energy was estimated at 3.5 kcal/mol.

Thermodynamic and kinetic characterization of polycyclic aromatic hydrocarbons in reversed-phase liquid chromatography.

PubMed

Howerton, Samuel B; McGuffin, Victoria L

2003-07-15

The retention of six polycyclic aromatic hydrocarbons (PAHs) was characterized by reversed-phase liquid chromatography. The PAHs were detected by laser-induced fluorescence at four points along an optically transparent capillary column. The profiles were characterized in space and time using an exponentially modified Gaussian equation. The resulting parameters were used to calculate the retention factors, as well as the concomitant changes in molar enthalpy and molar volume, for each PAH on monomeric (2.7 micromol/m2) and polymeric (5.4 micromol/m2) octadecylsilica. The changes in molar enthalpy become more exothermic as ring number increases and as annelation structure becomes less condensed. The changes in molar volume become more negative as ring number increases for the planar PAHs, but are positive for the nonplanar solutes. In addition, the rate constants, as well as the concomitant activation enthalpy and activation volume, are calculated for the first time. The kinetic data demonstrate that many of the PAHs exhibit very fast transitions between the mobile and stationary phases. The transition state is very high in energy, and the activation enthalpies and volumes become greater as ring number increases and as annelation structure becomes less condensed. The changes in thermodynamic and kinetic behavior are much more pronounced for the polymeric phase than for the monomeric phase.

Reaction of nitrosonium cation with resorc[4]arenes activated by supramolecular control: covalent bond formation.

PubMed

Ghirga, Francesca; D'Acquarica, Ilaria; Delle Monache, Giuliano; Mannina, Luisa; Molinaro, Carmela; Nevola, Laura; Sobolev, Anatoly P; Pierini, Marco; Botta, Bruno

2013-07-19

Resorc[4]arenes 1 and 2, which previously proved to entrap NO(+) cation within their cavities under conditions of host-to-guest excess, were treated with a 10-fold excess of NOBF4 salt in chloroform. Kinetic and spectral UV-visible analyses revealed the formation of isomeric 1:2 complexes as a direct evolution of the previously observed event. Accordingly, three-body 1-(NO(+))2 and 2-(NO(+))2 adducts were built by MM and fully optimized by DFT calculations at the B3LYP/6-31G(d) level of theory. Notably, covalent nitration products 4, 5 and 6, 7 were obtained by reaction of NOBF4 salt with host 1 and 2, respectively, involving macrocycle ring-opening and insertion of a nitro group in one of the four aromatic rings. In particular, compounds 4 and 6, both containing a trans-double bond in the place of the methine bridge, were oxidized to aldehydes 5 and 7, respectively, after addition of water to the reaction mixture. Calculation of the charge and frontier orbitals of the aromatic donor (HOMO) and the NO(+) acceptor (LUMO) clearly suggests an ipso electrophilic attack by a first NO(+) unit on the resorcinol ring, mediated by the second NO(+) unit.

Lubricating oil dominates primary organic aerosol emissions from motor vehicles.

PubMed

Worton, David R; Isaacman, Gabriel; Gentner, Drew R; Dallmann, Timothy R; Chan, Arthur W H; Ruehl, Christopher; Kirchstetter, Thomas W; Wilson, Kevin R; Harley, Robert A; Goldstein, Allen H

2014-04-01

Motor vehicles are major sources of primary organic aerosol (POA), which is a mixture of a large number of organic compounds that have not been comprehensively characterized. In this work, we apply a recently developed gas chromatography mass spectrometry approach utilizing "soft" vacuum ultraviolet photoionization to achieve unprecedented chemical characterization of motor vehicle POA emissions in a roadway tunnel with a mass closure of >60%. The observed POA was characterized by number of carbon atoms (NC), number of double bond equivalents (NDBE) and degree of molecular branching. Vehicular POA was observed to predominantly contain cycloalkanes with one or more rings and one or more branched alkyl side chains (≥80%) with low abundances of n-alkanes and aromatics (<5%), similar to "fresh" lubricating oil. The gas chromatography retention time data indicates that the cycloalkane ring structures are most likely dominated by cyclohexane and cyclopentane rings and not larger cycloalkanes. High molecular weight combustion byproducts, that is, alkenes, oxygenates, and aromatics, were not present in significant amounts. The observed carbon number and chemical composition of motor vehicle POA was consistent with lubricating oil being the dominant source from both gasoline and diesel-powered vehicles, with an additional smaller contribution from unburned diesel fuel and a negligible contribution from unburned gasoline.

Evidence for the Presence of Hn-PAHs in Post AGB Stars

NASA Technical Reports Server (NTRS)

Materese, Christopher K.; Bregman, Jesse D.; Sandford, Scott A.

2017-01-01

Polycyclic aromatic hydrocarbons (PAHs) are believed to be ubiquitous in space therefore represent an important class of molecules for the field of astrochemistry. PAHs are relatively stable under interstellar conditions, account for a significant fraction of the known Universe's molecular carbon inventory, and are believed responsible for numerous telltale interstellar infrared emission bands. PAHs can be subdivided into numerous classes, one of which is Hydrogenated PAHs (Hn-PAHs). Hn-PAHs are multi-ringed partially aromatic compounds with excess hydrogenation, leading to a partial disruption of the aromatic system. The infrared spectra of these compounds produce telltale signatures that make them distinct from ordinary aromatic or aliphatic molecules (or a mixture of both). Hn-PAHs may be an important subclass of PAHs that could explain the spectra of some astronomical objects with anomalously large 3.4 micron features. The 3.4 micron feature observed in these objects may be associated with the aliphatic C-H stretching vibrations of the excess hydrogen. If this presumption is correct, we also expect to observe methylene scissoring modes at 6.9 microns. We have recently conducted a series of follow-up observations to compliment our laboratory experiments into the properties of Hn-PAHs. Here we present our laboratory and observational results in support of the hypothesis that Hn-PAHs are a viable candidate molecule as the emission source for numerous post-asymptotic giant branch objects with abnormally large 3.4 micron features.

Extension of the SAFT-VR Mie EoS To Model Homonuclear Rings and Its Parametrization Based on the Principle of Corresponding States.

PubMed

Müller, Erich A; Mejía, Andrés

2017-10-24

The statistical associating fluid theory of variable range employing a Mie potential (SAFT-VR-Mie) proposed by Lafitte et al. (J. Chem Phys. 2013, 139, 154504) is one of the latest versions of the SAFT family. This particular version has been shown to have a remarkable capability to connect experimental determinations, theoretical calculations, and molecular simulations results. However, the theoretical development restricts the model to chains of beads connected in a linear fashion. In this work, the capabilities of the SAFT-VR Mie equation of state for modeling phase equilibria are extended for the case of planar ring compounds. This modification proposed replaces the Helmholtz energy of chain formation by an empirical contribution based on a parallelism to the second-order thermodynamic perturbation theory for hard sphere trimers. The proposed expression is given in terms of an extra parameter, χ, that depends on the number of beads, m s , and the geometry of the ring. The model is used to describe the phase equilibrium for planar ring compounds formed of Mie isotropic segments for the cases of m s equals to 3, 4, 5 (two configurations), and 7 (two configurations). The resulting molecular model is further parametrized, invoking a corresponding states principle resulting in sets of parameters that can be used indistinctively in theoretical calculations or in molecular simulations without any further refinements. The extent and performance of the methodology has been exemplified by predicting the phase equilibria and vapor pressure curves for aromatic hydrocarbons (benzene, hexafluorobenzene, toluene), heterocyclic molecules (2,5-dimethylfuran, sulfolane, tetrahydro-2H-pyran, tetrahydrofuran), and polycyclic aromatic hydrocarbons (naphthalene, pyrene, anthracene, pentacene, and coronene). An important aspect of the theory is that the parameters of the model can be used directly in molecular dynamics (MD) simulations to calculate equilibrium phase properties and interfacial tensions with an accuracy that rivals other coarse grained and united atom models, for example, liquid densities, are predicted, with a maximum absolute average deviation of 3% from both the theory and the MD simulations, while the interfacial tension is predicted, with a maximum absolute average of 8%. The extension to mixtures is exemplified by considering a binary system of hexane (chain fluid) and tetrahydro-2H-pyran (ring fluid).

Crystal structure of azilsartan methyl ester ethyl acetate hemisolvate.

PubMed

Li, Zhengyi; Liu, Rong; Zhu, Meilan; Chen, Liang; Sun, Xiaoqiang

2015-02-01

The title compound, C26H22N4O5 (systematic name: methyl 2-eth-oxy-1-{4-[2-(5-oxo-4,5-di-hydro-1,2,4-oxa-diazol-3-yl)phenyl]benz-yl}-1H-1,3-benzo-diazole-7-carboxyl-ate ethyl acetate hemisolvate), was obtained via cyclization of methyl (Z)-2-eth-oxy-1-{(2'-(N'-hy-droxy-carbamimido-yl)-[1,1'-biphen-yl]-4-yl)meth-yl}-1H-benzo[d]imidazole-7-carboxyl-ate with diphen-yl carbonate. There are two independent mol-ecules (A and B) with different conformations and an ethyl acetate solvent mol-ecule in the asymmetric unit. In mol-ecule A, the dihedral angle between the benzene ring and its attached oxa-diazole ring is 59.36 (17); the dihedral angle between the benzene rings is 43.89 (15) and that between the benzene ring and its attached imidazole ring system is 80.06 (11)°. The corres-ponding dihedral angles in mol-ecule B are 58.45 (18), 50.73 (16) and 85.37 (10)°, respectively. The C-O-C-Cm (m = meth-yl) torsion angles for the eth-oxy side chains attached to the imidazole rings in mol-ecules A and B are 93.9 (3) and -174.6 (3)°, respectively. In the crystal, the components are linked by N-H⋯N and C-H⋯O hydrogen bonds, generating a three-dimensional network. Aromatic π-π stacking inter-actions [shortest centroid-centroid separation = 3.536 (3)Å] are also observed.

The Effect of K and Acidity of NiW-Loaded HY Zeolite Catalyst for Selective Ring Opening of 1-Methylnaphthalene.

PubMed

Lee, You-Jin; Kim, Eun-Sang; Kim, Jeong-Rang; Kim, Joo-Wan; Kim, Tae-Wan; Chae, Ho-Jeong; Kim, Chul-Ung; Lee, Chang-Ha; Jeong, Soon-Yong

2016-05-01

Bi-functional catalysts were prepared using HY zeolites with various SiO2/Al2O3 ratios for acidic function, NiW for metallic function, and K for acidity control. 1-Methylnaphthalene was selected as a model compound for multi-ring aromatics in heavy oil, and its selective ring opening reaction was investigated using the prepared bi-functional catalysts with different levels of acidity in a fixed bed reactor system. In NiW/HY catalysts without K addition, the acidity decreased with the SiO2/Al2O3 mole ratio of the HY zeolite. Ni1.1W1.1/HY(12) catalyst showed the highest acidity but slightly lower yields for the selective ring opening than Ni1.1W1.1/HY(30) catalyst. The acidity of the catalyst seemed to play an important role as the active site for the selective ring opening of 1-methylnaphthalene but there should be some optimum catalyst acidity for the reaction. Catalyst acidity could be controlled between Ni1.1W1.1/HY(12) and Ni1.1W1.1/HY(30) by adding a moderate amount of K to Ni1.1W1.1/HY(12) catalyst. K0.3Ni1.1W1.1/HY(12) catalyst should have the optimum acidity for the selective ring opening. The addition of a moderate amount of K to the NiW/HY catalyst must improve the catalytic performance due to the optimization of catalyst acidity.

1-(2,4-Dinitro­phen­yl)-2-(1,2,3,4-tetra­hydro­naphthalen-1-yl­idene)hydrazine

PubMed Central

Danish, M.; Hamid, Masood; Tahir, M. Nawaz; Ahmad, Nazir; Ghafoor, Sabiha

2010-01-01

In the title compound, C14H14N4O4, the dihedral angle between the benzene rings is 10.42 (8)°. The nitro groups make dihedral angles of 5.3 (2) and 6.47 (15)° with their parent ring and are oriented at 11.2 (3)° with respect to each other. An intra­molecular N—H⋯O hydrogen bond completes an S(6) ring motif. In the crystal, mol­ecules are linked by C—H⋯O inter­actions, thus forming (010) chains in which R 2 2(13) ring motifs are present. There also exist aromatic π–π stacking inter­actions [centroid–centroid separation = 3.7046 (9) Å]. PMID:21588393

Thiophene/thiazole-benzene replacement on guanidine derivatives targeting α2-Adrenoceptors.

PubMed

Flood, Aoife; Trujillo, Cristina; Sanchez-Sanz, Goar; Kelly, Brendan; Muguruza, Carolina; Callado, Luis F; Rozas, Isabel

2017-09-29

Searching for improved antagonists of α 2 -adrenoceptors, a thorough theoretical study comparing the aromaticity of phenyl-, pyridinyl-, thiophenyl- and thiazolylguanidinium derivatives has been carried out [at M06-2X/6-311++G(p,d) computational level] confirming that thiophene and thiazole will be good 'ring equivalents' to benzene in these guanidinium systems. Based on these results, a small but chemically diverse library of guanidine derivatives (15 thiophenes and 2 thiazoles) were synthesised to explore the effect that the bioisosteric change has on affinity and activity at α 2 -adrenoceptors in comparison with our previously studied phenyl derivatives. All compounds were tested for their α 2 -adrenoceptor affinity and unsubstituted guanidinothiophenes displayed the strongest affinities in the same range as the phenyl analogues. In the case of cycloakyl systems, thiophenes with 6-membered rings showed the largest affinities, while for the thiazoles the 5-membered analogue presented the strongest affinity. From all the compounds tested for noradrenergic activity, only one compound exhibited agonistic activity, while two compounds showed very promising antagonism of α 2 -adrenoceptors. Copyright © 2017 Elsevier Masson SAS. All rights reserved.

[4-(All­yloxy)phen­yl](phen­yl)methanone

PubMed Central

D’Vries, Richard F.; Grande, Carlos D.; Chaur, Manuel N.; Ellena, Javier A.; Advincula, Rigoberto C.

2014-01-01

The structure of the title compound, C16H14O2, features a dihedral angle of 54.4 (3)° between the aromatic rings. The allyl group is rotated by 37.4 (4)° relative to the adjacent benzene ring. The crystal packing is characterized by numerous C—H⋯O and C—H⋯π inter­actions. Most of these inter­actions occur in layers along (011). The layers are linked by C—H⋯π inter­actions along [100], forming a three-dimensional network. PMID:25161593

2-Nitro­benzyl 2-chloro­acetate

PubMed Central

Zhu, Kai; Liu, Hui; Wang, Yan-Hua; Han, Ping-Fang; Wei, Ping

2009-01-01

In the mol­ecule of the title compound, C9H8ClNO4, an intra­molecular C—H⋯O inter­action results in the formation of a near-planar (r.m.s. deviation 0.002 Å) five-membered ring, which is oriented at a dihedral angle of 4.07 (4)° with respect to the adjacent aromatic ring. In the crystal structure, inter­molecular C—H⋯O inter­actions link the mol­ecules into a two-dimensional network. PMID:21577790

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

Lee, Jongbok; Li, Huanbin; Kalin, Alexander J.

Well-defined, fused-ring aromatic oligomers represent promising candidates for the fundamental understanding and application of advanced carbon-rich materials, though bottom-up synthesis and structure–property correlation of these compounds remain challenging. In this work, an efficient synthetic route was employed to construct extended benzo[k]tetraphene-derived oligomers with up to 13 fused rings. The molecular and electronic structures of these compounds were clearly elucidated. Precise correlation of molecular sizes and crystallization dynamics was established, thus demonstrating the pivotal balance between intermolecular interaction and molecular mobility for optimized processing of highly ordered solids of these extended conjugated molecules.

Isomer effects on polyimide properties

NASA Technical Reports Server (NTRS)

Stump, B. L.

1975-01-01

The effect of structure variation on the solubility and glass-transition temperature of polyimide polymers is investigated. The addition of alkyl substituents to an aromatic ring in the polymer molecule, the reduction in the number of imide rings per average polymer chain-length, and a variation in the symmetry of the polymer molecule are studied. The synthesis of key intermediates for the preparation of the monomers required in this investigation is reported along with progress made in the synthesis of polyimide-precursor amines that contain functional groups to allow for post-cure cross-linking.

2,6-Bis[1-(2-isopropyl­phenyl­imino)­ethyl]­pyridine

PubMed Central

Agrifoglio, Giuseppe; Reyes, Julian; Atencio, Reinaldo; Briceño, Alexander

2008-01-01

The title compound, C27H31N3, has E substitution at each imine double bond where the two N atoms adopt a trans–trans relationship. The benzene rings are twisted out of the mean plane of the pyridine ring; the mean planes of the aromatic groups are rotated by 63.0 (1) and 72.58 (8)°. The crystal structure is sustained mainly by C—H⋯π and hydro­phobic methyl–methyl inter­actions. PMID:21200845

Tough, high performance, addition-type thermoplastic polymers

NASA Technical Reports Server (NTRS)

Pater, Ruth H. (Inventor)

1992-01-01

A tough, high performance polyimide is provided by reacting a triple bond conjugated with an aromatic ring in a bisethynyl compound with the active double bond in a compound containing a double bond activated toward the formation of a Diels-Adler type adduct, especially a bismaleimide, a biscitraconimide, or a benzoquinone, or mixtures thereof. Addition curing of this product produces a high linear polymeric structure and heat treating the highly linear polymeric structure produces a thermally stable aromatic addition-type thermoplastic polyimide, which finds utility in the preparation of molding compounds, adhesive compositions, and polymer matrix composites.

Total synthesis of the cyclopeptide alkaloid abyssenine A. Application of inter- and intramolecular copper-mediated coupling reactions in organic synthesis.

PubMed

Toumi, Mathieu; Couty, François; Evano, Gwilherm

2007-11-23

The first total synthesis of the 15-membered ring cyclopeptide alkaloid abyssenine A 1 has been achieved with a longest linear sequence of 15 steps. Central to the synthetic approach was an efficient copper-mediated Ullmann coupling/Claisen rearrangement sequence allowing for both ipso and ortho functionalization of aromatic iodide 4. This sequence was used for the synthesis of the aromatic core. The synthetic utility of copper-catalyzed coupling reactions was further demonstrated to install the enamide with a concomitant straightforward macrocyclization starting from acyclic alpha-amido-omega-vinyl iodide 13.

Bench-scale evaluation of in situ bioremediation strategies for soil at a former manufactured gas plant site.

PubMed

Li, Jun; Pignatello, Joseph J; Smets, Barth F; Grasso, Domenico; Monserrate, Esteban

2005-03-01

We examined the biodegradation and desorption of a set of 15 polycyclic aromatic hydrocarbon (PAH) compounds in coal tar-contaminated soil at a former manufactured gas plant site to evaluate the feasibility of in situ bioremediation. Experiments were conducted in well-mixed aerobic soil suspensions containing various additives over a 93- to 106-d period. In general, both biotransformation and desorption decreased with PAH ring size, becoming negligible for the six-ring PAH compounds. Biodegradation by indigenous microorganisms was strongly accelerated by addition of inorganic nutrients (N, P, K, and trace metals). The rates of biotransformation of PAH compounds by indigenous microorganisms in nutrient-amended flasks outpaced their maximum (i.e., chelate-enhanced) rates of desorption to an infinite sink (Tenax) in sterilized systems run in parallel, suggesting that indigenous organisms facilitated desorption. Biodegradation by indigenous organisms in nutrient-amended flasks appeared to be unaffected by the addition of a site-derived bacterial enrichment culture, resulting in approximately 100-fold higher aromatic dioxygenase levels, and by the addition of 0.01 M chelating agent (citrate or pyrophosphate), although such chelating agents greatly enhanced desorption in microbially inactivated flasks. The strong ability of nutrients to enhance degradation of the bioavailable PAHs indicates that their persistence for many decades at this site likely results from nutrient-limited natural biodegradation, and it also suggests that an effective strategy for their bioremediation could consist simply of adding inorganic nutrients.

Surfactant-Enhanced Desorption and Biodegradation of Polycyclic Aromatic Hydrocarbons in Contaminated Soil

PubMed Central

Zhu, Hongbo; Aitken, Michael D.

2010-01-01

We evaluated two nonionic surfactants, one hydrophobic (Brij 30) and one hydrophilic (C12E8), for their ability to enhance the biodegradation of polycyclic aromatic hydrocarbons (PAHs) in contaminated soil after it had been treated in an aerobic bioreactor. The effects of each surfactant were evaluated at doses corresponding to equilibrium aqueous-phase concentrations well above the surfactant’s critical micelle concentration (CMC), slightly above the CMC, and below the CMC. The concentrations of all 3- and 4-ring PAHs were significantly lower in the soil amended with Brij 30 at the two lower doses compared to controls, whereas removal of only the 3-ring PAHs was significantly enhanced at the highest Brij 30 dose. In contrast, C12E8 did not enhance PAH removal at any dose. In the absence of surfactant, <5% of any PAH desorbed from the soil over an 18-d period. Brij 30 addition at the lowest dose significantly increased the desorption of most PAHs, whereas the addition of C12E8 at the lowest dose actually decreased the desorption of all PAHs. These findings suggest that the effects of the two surfactants on PAH biodegradation could be explained by their effects on PAH bioavailability. Overall, this study demonstrates that the properties of the surfactant and its dose relative to the corresponding aqueous-phase concentration are important factors in designing systems for surfactant-enhanced bioremediation of PAH-contaminated soils in which PAH bioavailability is limited. PMID:20586488

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

Lee, B.D.; Apel, W.A.; Walton, M.R.

Conceptually, biofilters are vapor phase bioreactors that rely on microorganisms in the bed medium to oxidize contaminants in off-gases flowing through the bed to less hazardous compounds. In the most studied and utilized systems reduced compounds such as fuel hydrocarbons are enzymatically oxidized to compounds such as carbon dioxide and water. In these types of reactions the microorganisms in the bed oxidize the contaminant and transfer the electrons to oxygen which is the terminal electron acceptor in the process. In essence the contaminant is the carbon and energy source for the microorganisms in the bed medium and through this catabolicmore » process oxygen is reduced to water. An example of this oxidation process can be seen during the degradation of benzene and similar aromatic compounds. Aromatics are initially attacked by a dioxygenase enzyme which oxidizes the compounds to a labile dihydrodiole which is spontaneously converted to a catechol. The dihydroxylated aromatic rings is then opened by oxidative {open_quotes}ortho{close_quotes} or {open_quotes}meta{close_quotes} cleavage yielding cis, cis-muconic acid or 2-hydroxy-cis, cis-muconic semialdehyde, respectively. These organic compounds are further oxidized to carbon dioxide or are assimilated for cellular material. This paper describes the conversion of carbon tetrachloride using methanol as the primary carbon and energy source.« less

Suspended particulate matter collection methods influence the quantification of polycyclic aromatic compounds in the river system.

PubMed

Abuhelou, Fayez; Mansuy-Huault, Laurence; Lorgeoux, Catherine; Catteloin, Delphine; Collin, Valéry; Bauer, Allan; Kanbar, Hussein Jaafar; Gley, Renaud; Manceau, Luc; Thomas, Fabien; Montargès-Pelletier, Emmanuelle

2017-10-01

In this study, we compared the influence of two different collection methods, filtration (FT) and continuous flow field centrifugation (CFC), on the concentration and the distribution of polycyclic aromatic compounds (PACs) in suspended particulate matter (SPM) occurring in river waters. SPM samples were collected simultaneously with FT and CFC from a river during six sampling campaigns over 2 years, covering different hydrological contexts. SPM samples were analyzed to determine the concentration of PACs including 16 polycyclic aromatic hydrocarbons (PAHs), 11 oxygenated PACs (O-PACs), and 5 nitrogen PACs (N-PACs). Results showed significant differences between the two separation methods. In half of the sampling campaigns, PAC concentrations differed from a factor 2 to 30 comparing FT and CFC-collected SPMs. The PAC distributions were also affected by the separation method. FT-collected SPM were enriched in 2-3 ring PACs whereas CFC-collected SPM had PAC distributions dominated by medium to high molecular weight compounds typical of combustion processes. This could be explained by distinct cut-off threshold of the two separation methods and strongly suggested the retention of colloidal and/or fine matter on glass-fiber filters particularly enriched in low molecular PACs. These differences between FT and CFC were not systematic but rather enhanced by high water flow rates.

A detailed kinetic modeling study of aromatics formation in laminar premixed acetylene and ethylene flames

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

Wang, H.; Frenklach, M.

1997-07-01

A computational study was performed for the formation and growth of polycyclic aromatic hydrocarbons (PAHs) in laminar premixed acetylene and ethylene flames. A new detailed reaction mechanism describing fuel pyrolysis and oxidation, benzene formation, and PAH mass growth and oxidation is presented and critically tested. It is shown that the reaction model predicts reasonably well the concentration profiles of major and intermediate species and aromatic molecules in a number of acetylene and ethylene flames reported in the literature. It is demonstrated that reactions of n-C{sub 4}H{sub x} + C{sub 2}H{sub 2} leading to the formation of one-ring aromatics are asmore » important as the propargyl recombination, and hence must be included in kinetic modeling of PAH formation in hydrocarbon flames. It is further demonstrated that the mass growth of PAHs can be accounted for by the previously proposed H-abstraction-C{sub 2}H{sub 2}-addiction mechanism.« less

Irradiated Benzene Ice Provides Clues to Meteoritic Organic Chemistry

NASA Technical Reports Server (NTRS)

Callahan, Michael Patrick; Gerakines, Perry Alexander; Martin, Mildred G.; Hudson, Reggie L.; Peeters, Zan

2013-01-01

Aromatic hydrocarbons account for a significant portion of the organic matter in carbonaceous chondrite meteorites, as a component of both the low molecular weight, solvent-extractable compounds and the insoluble organic macromolecular material. Previous work has suggested that the aromatic compounds in carbonaceous chondrites may have originated in the radiation-processed icy mantles of interstellar dust grains. Here we report new studies of the organic residue made from benzene irradiated at 19 K by 0.8 MeV protons. Polyphenyls with up to four rings were unambiguously identified in the residue by gas chromatography-mass spectrometry. Atmospheric pressure photoionization Fourier transform mass spectrometry was used to determine molecular composition, and accurate mass measurements suggested the presence of polyphenyls, partially hydrogenated polyphenyls, and other complex aromatic compounds. The profile of low molecular weight compounds in the residue compared well with extracts from the Murchison and Orgueil meteorites. These results are consistent with the possibility that solid phase radiation chemistry of benzene produced some of the complex aromatics found in meteorites.

Refining of fossil resin flotation concentrates from Western coal. Final fifth quarterly report, January 1, 1994--March 31, 1994

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

Jensen, G.F.; Miller, J.D.

1994-05-07

Fossil resins occurring in the Wasatch Plateau coal field are composed mainly of aliphatic components, partially aromatized multi-cyclic terpenoids and a few oxygen functional groups (such as {minus}OH and {minus}COOH). The solvent extracted resins show the presence of a relatively large number of methyl groups when compared to the methylene groups, and this indicates the presence of extensive tertiary carbon and/or highly branching chains. In contrast coal consists primarily of aromatic ring structures, various oxygen functional groups ({minus}OH, >C=O, {minus}C{minus}O) and few aliphatic chains. The color difference observed among the four resin types is explained by the presence of chromophoresmore » (aromatized polyterpenoid) and also by the presence of finely dispersed coal particle inclusions in the resin matrix. The hexane soluble resin fraction has few aromatic compounds when compared to the hexane insoluble but toluene soluble resin fraction.« less

Formation of highly oxygenated organic molecules from aromatic compounds

NASA Astrophysics Data System (ADS)

Molteni, Ugo; Bianchi, Federico; Klein, Felix; El Haddad, Imad; Frege, Carla; Rossi, Michel J.; Dommen, Josef; Baltensperger, Urs

2018-02-01

Anthropogenic volatile organic compounds (AVOCs) often dominate the urban atmosphere and consist to a large degree of aromatic hydrocarbons (ArHCs), such as benzene, toluene, xylenes, and trimethylbenzenes, e.g., from the handling and combustion of fuels. These compounds are important precursors for the formation of secondary organic aerosol. Here we show that the oxidation of aromatics with OH leads to a subsequent autoxidation chain reaction forming highly oxygenated molecules (HOMs) with an O : C ratio of up to 1.09. This is exemplified for five single-ring ArHCs (benzene, toluene, o-/m-/p-xylene, mesitylene (1,3,5-trimethylbenzene) and ethylbenzene), as well as two conjugated polycyclic ArHCs (naphthalene and biphenyl). We report the elemental composition of the HOMs and show the differences in the oxidation patterns of these ArHCs. A potential pathway for the formation of these HOMs from aromatics is presented and discussed. We hypothesize that AVOCs may contribute substantially to new particle formation events that have been detected in urban areas.

Bio-Based Aromatic Epoxy Monomers for Thermoset Materials.

PubMed

Ng, Feifei; Couture, Guillaume; Philippe, Coralie; Boutevin, Bernard; Caillol, Sylvain

2017-01-18

The synthesis of polymers from renewable resources is a burning issue that is actively investigated. Polyepoxide networks constitute a major class of thermosetting polymers and are extensively used as coatings, electronic materials, adhesives. Owing to their outstanding mechanical and electrical properties, chemical resistance, adhesion, and minimal shrinkage after curing, they are used in structural applications as well. Most of these thermosets are industrially manufactured from bisphenol A (BPA), a substance that was initially synthesized as a chemical estrogen. The awareness on BPA toxicity combined with the limited availability and volatile cost of fossil resources and the non-recyclability of thermosets implies necessary changes in the field of epoxy networks. Thus, substitution of BPA has witnessed an increasing number of studies both from the academic and industrial sides. This review proposes to give an overview of the reported aromatic multifunctional epoxide building blocks synthesized from biomass or from molecules that could be obtained from transformed biomass. After a reminder of the main glycidylation routes and mechanisms and the recent knowledge on BPA toxicity and legal issues, this review will provide a brief description of the main natural sources of aromatic molecules. The different epoxy prepolymers will then be organized from simple, mono-aromatic di-epoxy, to mono-aromatic poly-epoxy, to di-aromatic di-epoxy compounds, and finally to derivatives possessing numerous aromatic rings and epoxy groups.

Deciphering Stability of Five-Membered Heterocyclic Radicals: Balancing Act Between Delocalization and Ring Strain.

PubMed

Sah, Chitranjan; Yadav, Ajit Kumar; Venkataramani, Sugumar

2018-06-21

Computational studies on five-membered heterocycles with single heteroatom and their isomeric dehydro-borole 1a-1c, cyclopentadiene 2a-2c, pyrrole 3a-3c, furan 4b-4c, phosphole 5a-5c, and thiophene 6b-6c radicals have been carried out. Geometrical aspects through ground state electronic structures and stability aspects using bond dissociation energies (BDE) and radical stabilization energies (RSE) have been envisaged in this regard. Spin densities, electrostatic potentials (ESP), and natural bond orbital (NBO) analysis unveiled the extent of spin delocalization. The estimated nucleus-independent chemical shifts (NICS) values revealed the difference in aromaticity characteristics of radicals. Particularly the heteroatom centered radicals exhibit odd electron π-delocalized systems with a quasi-antiaromatic character. Various factors such as, the relative position of the radical center with respect to heteroatoms, resonance, ring strain and orbital interactions influence the stability that follows the order: heteroatom centered > β-centered > α-centered radicals. Among the influences of various factors, we confirmed the existence of a competition between delocalization and the ring strain, and the interplay of both decides the overall stability order.

Specificity of the Antibody Receptor Site to D-Lysergamide: Model of a Physiological Receptor for Lysergic Acid Diethylamide

PubMed Central

Vunakis, Helen Van; Farrow, John T.; Gjika, Hilda B.; Levine, Lawrence

1971-01-01

Antibodies to D-lysergic acid have been produced in rabbits and guinea pigs and a radioimmunoassay for the hapten was developed. The specificity of this lysergamide-antilysergamide reaction was determined by competitive binding with unlabeled lysergic acid diethylamide (LSD), psychotomimetic drugs, neurotransmitters, and other compounds with diverse structures. LSD and several related ergot alkaloids were potent competitors, three to seven times more potent than lysergic acid itself. The N,N-dimethyl derivatives of several compounds, including tryptamine, 5-hydroxytryptamine, 4-hydroxytryptamine, 5-methoxytryptamine, tyramine, and mescaline, were only about ten times less effective than lysergic acid, even though these compounds lack some of the ring systems of lysergic acid. The pattern of inhibition by related compounds with various substituents suggests that the antibody receptor site recognizes structural features resembling the LSD molecule. In particular, the aromatic nucleus and the dimethylated ethylamine side chain in phenylethylamine and tryptamine derivatives may assume in solution a conformation resembling ring A and the methylated nitrogen in ring C of LSD. Among the tryptamine derivatives, a large percentage of the most potent competitors are also psychotomimetic compounds. PMID:5283939

The leap-frog effect of ring currents in benzene.

PubMed

Ligabue, Andrea; Soncini, Alessandro; Lazzeretti, Paolo

2002-03-06

Symmetry arguments show that the ring-current model proposed by Pauling, Lonsdale, and London to explain the enhanced diamagnetism of benzene is flawed by an intrinsic drawback. The minimal basis set of six atomic 2p orbitals taken into account to develop such a model is inherently insufficient to predict a paramagnetic contribution to the perpendicular component of magnetic susceptibility in planar ring systems such as benzene. Analogous considerations can be made for the hypothetical H(6) cyclic molecule. A model allowing for extended basis sets is necessary to rationalize the magnetism of aromatics. According to high-quality coupled Hartree-Fock calculations, the trajectories of the current density vector field induced by a magnetic field perpendicular to the skeletal plane of benzene in the pi electrons are noticeably different from those typical of a Larmor diamagnetic circulation, in that (i) significant deformation of the orbits from circular to hexagonal symmetry occurs, which is responsible for a paramagnetic contribution of pi electrons to the out-of-plane component of susceptibility, and (ii) a sizable component of the pi current density vector parallel to the inducing field is predicted. This causes a waving motion of pi electrons; streamlines are characterized by a "leap-frog effect".

Recognition of extended linear and cyclised polyketide mimics by a type II acyl carrier protein† †Electronic supplementary information (ESI) available: Detailed experimental procedures and characterisation data for all new compounds, additional spectra and structural statistics for derivatised ACP three-dimensional structures. See DOI: 10.1039/c5sc03864b Click here for additional data file.

PubMed Central

Dong, Xu; Bailey, Christopher D.; Williams, Christopher; Crosby, John; Simpson, Thomas J.

2016-01-01

Polyketides are secondary metabolites which display both valuable pharmaceutical and agrochemical properties. Biosynthesis is performed by polyketide synthases (PKSs), and the acyl carrier protein (ACP), a small acidic protein, that transports the growing polyketide chain and is essential for activity. Here we report the synthesis of two aromatic probes and a linear octaketide mimic that have been tethered to actinorhodin ACP. These experiments were aimed at probing the ACP's capacity to sequester a non-polar versus a phenolic aromatic ring (that more closely mimics a polyketide intermediate) as well as investigations with extended polyketide chain surrogates. The binding of these mimics has been assessed using high-resolution solution NMR studies and high-resolution structure determination. These results reveal that surprisingly a PKS ACP is able to bind and sequester a bulky non-polar substrate containing an aromatic ring in a fatty acid type binding mode, but the introduction of even a small degree of polarity favours a markedly different association at a surface site that is distinct from that employed by fatty acid ACPs. PMID:28936328

Aryl sulfate formation in sea urchins (Strongylocentrotus droebachiensis) ingesting marine algae (Fucus distichus) containing 2,6-dimethylnapthalene

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

Malins, D.C.; Roubal, W.T.

1982-04-01

The metabolism of tritiated 2,6-dimethylnapthalene (2,6-DMN) was studied in sea urchins (Strongylocentrotus droebachiensis) feeding on marine algae (Fucus distichus). The Fucus accumulated this hydrocarbon from sea water without converting it to metabolites. Most of the tritium accumulated by the sea urchins (e.g., 70.8% after 3 days) from feeding on 2,6-DMN-exposed Fucus was present in the exoskeleton (shell and spines). Moreover, after 3 days feeding, about 90% of the tritium in the total metabolite fraction of the gonads and digestive tract of the sea urchin was present as sulfate derivatives. These metabolites were identified through hydrolysis with aryl sulfatase, followed bymore » thin-layer chromatography of the products. After 14 days of feeding, the tritium associated with the sulfate derivatives decreased in the gonads and digestive tract to 61 and 65%, respectively, of the total metabolite fraction. Hydroxy compounds from sulfatase hydrolysis were chromatographed using multiple elutions with toluene. The hydroxy isomers were separated and the R/sub f/ values were compared to those of pure reference compounds. The data indicated that 80% of the 2,6-dimethylnaphtyl sulfate contained the sulfate on the 1 and/or 3 position of the aromatic ring. Moreover, 6-methyl-2-naphthalenemethanol was not detected, which implies that sea urchins, unlike fish, metabolize alkyl-substituted aromatic hydrocarbons primarily through aromatic ring oxidations.« less

Complexation facilitated reduction of aromatic N-oxides by aqueous Fe(II)-tiron complex: reaction kinetics and mechanisms.

PubMed

Chen, Yiling; Zhang, Huichun

2013-10-01

Rapid reduction of carbadox (CDX), olaquindox and several other aromatic N-oxides were investigated in aqueous solution containing Fe(II) and tiron. Consistent with previous work, the 1:2 Fe(II)-tiron complex, FeL2(6-), is the dominant reactive species as its concentration linearly correlates with the observed rate constant kobs under various conditions. The N-oxides without any side chains were much less reactive, suggesting direct reduction of the N-oxides is slow. UV-vis spectra suggest FeL2(6-) likely forms 5- or 7-membered rings with CDX and olaquindox through the N and O atoms on the side chain. The formed inner-sphere complexes significantly facilitated electron transfer from FeL2(6-) to the N-oxides. Reduction products of the N-oxides were identified by HPLC/QToF-MS to be the deoxygenated analogs. QSAR analysis indicated neither the first electron transfer nor N-O bond cleavage is the rate-limiting step. Calculations of the atomic spin densities of the anionic N-oxides confirmed the extensive delocalization between the aromatic ring and the side chain, suggesting complex formation can significantly affect the reduction kinetics. Our results suggest the complexation facilitated N-oxide reduction by Fe(II)-tiron involves a free radical mechanism, and the subsequent deoxygenation might also benefit from the weak complexation of Fe(II) with the N-oxide O atom.

Monocyclic aromatic amines as potential human carcinogens: old is new again

PubMed Central

Skipper, Paul L.; Kim, Min Young; Sun, H.-L. Patty; Wogan, Gerald N.; Tannenbaum, Steven R.

2010-01-01

Alkylanilines are a group of chemicals whose ubiquitous presence in the environment is a result of the multitude of sources from which they originate. Exposure assessments indicate that most individuals experience lifelong exposure to these compounds. Many alkylanilines have biological activity similar to that of the carcinogenic multi-ring aromatic amines. This review provides an overview of human exposure and biological effects. It also describes recent investigations into the biochemical mechanisms of action that lead to the assessment that they are most probably more complex than those of the more extensively investigated multi-ring aromatic amines. Not only is nitrenium ion chemistry implicated in DNA damage by alkylanilines but also reactions involving quinone imines and perhaps reactive oxygen species. Recent results described here indicate that alkylanilines can be potent genotoxins for cultured mammalian cells when activated by exogenous or endogenous phase I and phase II xenobiotic-metabolizing enzymes. The nature of specific DNA damage products responsible for mutagenicity remains to be identified but evidence to date supports mechanisms of activation through obligatory N-hydroxylation as well as subsequent conjugation by sulfation and/or acetylation. A fuller understanding of the mechanisms of alkylaniline genotoxicity is expected to provide important insights into the environmental and genetic origins of one or more human cancers and may reveal a substantial role for this group of compounds as potential human chemical carcinogens. PMID:19887514

Identification and Quantification of Six-Ring C26H16 Cata-Condensed Polycyclic Aromatic Hydrocarbons in a Complex Mixture of Polycyclic Aromatic Hydrocarbons from Coal Tar

PubMed Central

Oña-Ruales, Jorge O.; Sharma, Arun K.; Wise, Stephen A.

2015-01-01

We applied a combination of normal-phase liquid chromatography (NPLC) with ultraviolet-visible spectroscopy and gas chromatography with mass spectrometry (GC/MS) for the fractionation, identification, and quantification of six ring C26H16 cata-condensed polycyclic aromatic hydrocarbons, PAHs, in the Standard Reference Material 1597a, Complex Mixture of PAHs from Coal Tar. For the characterization analysis, we calculated the GC retention indices of 17 C26H16 PAH authentic reference standards using the Rxi-PAH and DB-5 GC columns. Then, we used NPLC with ultraviolet-visible spectroscopy to isolate the fractions containing the C26H16 PAHs, and subsequently, we used GC/MS to establish the identity and quantity of the C26H16 PAHs using authentic reference standards. Following this procedure, 12 C26H16 cata-condensed PAHs benzo[c]pentaphene, dibenzo[f,k]tetraphene, benzo[h]pentaphene, dibenzo[a,l]tetracene, dibenzo[c,k]tetraphene, naphtho[2,3-c]tetraphene, dibenzo[a,c]tetracene, benzo[b]picene, dibenzo[a,j]tetracene, naphtho[2,1-a]tetracene, dibenzo[c,p]chrysene, and dibenzo[a,f]tetraphene were identified and quantified for the first time, and benzo[c]picene was quantified for the first time in an environmental combustion sample. PMID:26449848

Dechlorination of chlorinated phenols by subnanoscale Pd 0 /Fe 0 intercalated in smectite: pathway, reactivity, and selectivity.

PubMed

Jia, Hanzhong; Wang, Chuanyi

2015-12-30

Smectite clay was employed as templated matrix to prepare subnanoscale Pd(0)/Fe(0) particles, and their components as well as intercalated architectures were well characterized by X-ray energy dispersive spectroscopy (X-EDS) and X-ray diffraction (XRD). Furthermore, as-prepared Pd(0)/Fe(0) subnanoscale nanoparticles were evaluated for their dechlorination effect using chlorinated phenols as model molecules. As a result, pentachlorophenol (PCP) is selectively transformed to phenol in a stepwise dechlorination pathway within 6h, and the dechlorination rate constants show linearly relationship with contents of Pd as its loadings <0.065%. Comparing with PCP, other chlorinated phenols display similar degradation pattern but within much shorter time frame. The dechlorination rate of chlorinated phenols increases with decreasing in number of -Cl attached to aromatic ring, which can be predicted by the total charge of the aromatic ring, exhibiting an inversely linear relationship with the dechlorination rates. While the selectivity of dechlorination depends on the charges associated with the individual aromatic carbon. Chloro-functional groups at the ortho-position are easier to be dechlorinated than that at meta- and para- positions yielding primarily 3,4,5-TCP as intermediate from PCP, further to phenol. The effective dechlorination warrants their potential utilizations in development of in-situ remediation technologies for organic pollutants in contaminated water. Copyright © 2015 Elsevier B.V. All rights reserved.

Enhancement of the orientational order parameter of nematic liquid crystals in thin cells.

PubMed

Dhara, Surajit; Madhusudana, N V

2004-04-01

Abstract. We report measurements of birefringence (Delta n) of several nematic liquid crystals having transverse as well as longitudinal dipole moments in thin (1.4 to 2.3 microm) and thick (7 to 16 microm) cells. Rubbed polyimide-coated glass plates are used to get planar alignment of the nematic director in these cells. We find significant enhancement (6 to 18%) of Delta n (proportional to S, where S is the orientational order parameter) in thin cells in all compounds with aromatic cores even at temperatures far approximately 20 degrees C) below the nematic-isotropic transition point. The enhancement is larger in compounds having several phenyl rings and lower if the number of phenyl rings is reduced. In a compound that does not have an aromatic core no significant enhancement is observed, implying that the strength of the surface potential depends on the aromaticity of the cores. Assuming a perfect orientational order at the surface, calculations based on the Landau-de Gennes theory show that the thickness averaged enhancement of S is sharply reduced as the temperature is lowered in the nematic phase. The measured order parameter S is further enhanced in thin cells because of the stiffening of the elastic constant which reduces the thermal fluctuations of the nematic director. The combined effect is however too small at low temperatures to account for the experimental data.

Solvated Electrons in Organic Chemistry Laboratory

ERIC Educational Resources Information Center

Ilich, Predrag-Peter; McCormick, Kathleen R.; Atkins, Adam D.; Mell, Geoffrey J.; Flaherty, Timothy J.; Bruck, Martin J.; Goodrich, Heather A.; Hefel, Aaron L.; Juranic, Nenad; Seleem, Suzanne

2010-01-01

A novel experiment is described in which solvated electrons in liquid ammonia reduce a benzyl alcohol carbon without affecting the aromatic ring. The reductive activity of solvated electrons can be partially or completely quenched through the addition of electron scavengers to the reaction mixture. The effectiveness of these scavengers was found…

INTERACTION OF PAH-RELATED COMPOUNDS WITH THE ALPHA AND BETA ISOFORMS OF ESTROGEN RECEPTOR. (R826192)

EPA Science Inventory

The ability of several 4- and 5-ring polycyclic aromatic hydrocarbons (PAHs), heterocyclic PAHs, and their monohydroxy derivatives to interact with the estrogen receptor (ER) alpha and beta isoforms was examined. Only compounds possessing a hydroxyl group were able to compete wit...

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

Wear, Jr., John Edmund

The objective of this study was to examine the hypothesis that select functional groups of bacteria from pristine sites have an innate ability to degrade synthetic aromatics that often contaminate groundwater environments,due to exposure to naturally occurring recalcitrant aromatics in their environment. This study demonstrates that subsurface microbial communities are capable of utilizing lignin and humic acid breakdown products. Utilizers of these compounds were found to be present in most all the wells tested. Even the deepest aquifer tested had utilizers present for all six of the aromatics tested. Highest counts for the aromatics tested were observed with the naturallymore » occurring breakdown products of either lignin or humic acid. Carboxylic acids were found to be an important sole carbon source for groundwater bacteria possibly explained by the fact that they are produced by the oxidative cleavage of aromatic ring structures. The carbohydrate sole carbon sources that demonstrated the greatest densities were ones commonly associated with humics. This study indicates that utilization of naturally occurring aromatic compounds in the subsurface is an important nutritional source for groundwater bacteria. In addition, it suggests that adaptation to naturally occurring recalcitrant substrates is the origin of degradative pathways for xenobiotic compounds with analogous structure. This work has important implications for in situ bioremediation as a method of environmental cleanup.« less

Effects of sugar functional groups, hydrophobicity, and fluorination on carbohydrate-DNA stacking interactions in water.

PubMed

Lucas, Ricardo; Peñalver, Pablo; Gómez-Pinto, Irene; Vengut-Climent, Empar; Mtashobya, Lewis; Cousin, Jonathan; Maldonado, Olivia S; Perez, Violaine; Reynes, Virginie; Aviñó, Anna; Eritja, Ramón; González, Carlos; Linclau, Bruno; Morales, Juan C

2014-03-21

Carbohydrate-aromatic interactions are highly relevant for many biological processes. Nevertheless, experimental data in aqueous solution relating structure and energetics for sugar-arene stacking interactions are very scarce. Here, we evaluate how structural variations in a monosaccharide including carboxyl, N-acetyl, fluorine, and methyl groups affect stacking interactions with aromatic DNA bases. We find small differences on stacking interaction among the natural carbohydrates examined. The presence of fluorine atoms within the pyranose ring slightly increases the interaction with the C-G DNA base pair. Carbohydrate hydrophobicity is the most determinant factor. However, gradual increase in hydrophobicity of the carbohydrate does not translate directly into a steady growth in stacking interaction. The energetics correlates better with the amount of apolar surface buried upon sugar stacking on top of the aromatic DNA base pair.

Synthesis and Late-Stage Functionalization of Complex Molecules through C–H Fluorination and Nucleophilic Aromatic Substitution

PubMed Central

2015-01-01

We report the late-stage functionalization of multisubstituted pyridines and diazines at the position α to nitrogen. By this process, a series of functional groups and substituents bound to the ring through nitrogen, oxygen, sulfur, or carbon are installed. This functionalization is accomplished by a combination of fluorination and nucleophilic aromatic substitution of the installed fluoride. A diverse array of functionalities can be installed because of the mild reaction conditions revealed for nucleophilic aromatic substitutions (SNAr) of the 2-fluoroheteroarenes. An evaluation of the rates for substitution versus the rates for competitive processes provides a framework for planning this functionalization sequence. This process is illustrated by the modification of a series of medicinally important compounds, as well as the increase in efficiency of synthesis of several existing pharmaceuticals. PMID:24918484

Nucleophilic fluorination of aromatic compounds

DOEpatents

Satyamurthy, Nagichettiar; Barrio, Jorge R

2014-03-18

Iodylbenzene derivatives substituted with electron donating as well as electron withdrawing groups on the aromatic ring are used as precursors in aromatic nucleophilic substitution reactions. The iodyl group (IO.sub.2) is regiospecifically substituted by nucleophilic fluoride to provide the corresponding fluoroaryl derivatives. No-carrier-added [F-18]fluoride ion derived from anhydrous [F-18](F/Kryptofix, [F-18]CsF or a quaternary ammonium fluoride (e.g., Me.sub.4NF, Et.sub.4NF, n-Bu.sub.4NF, (PhCH.sub.2).sub.4NF) exclusively substitutes the iodyl moiety in these derivatives and provides high specific activity F-18 labeled fluoroaryl analogs. Iodyl derivatives of a benzothiazole analog and 6-iodyl-L-dopa derivatives have been synthesized as precursors and have been used in the preparation of no-carrier-added [F-18]fluorobenzothiazole as well as 6-[F-18]fluoro-L-dopa.

Occurrence and source apportionment of polycyclic aromatic hydrocarbons in soils and sediment from Hanfeng Lake, Three Gorges, China.

PubMed

Cai, Jing; Gao, Shutao; Zhu, Like; Jia, Xuwei; Zeng, Xiangying; Yu, Zhiqiang

2017-11-10

This study was conducted to investigate the pollutant status and the retention mechanism of polycyclic aromatic hydrocarbons (PAHs) in soils and sediment from bank-water-level-fluctuating zone (WLFZ)-water systems in Hanfeng Lake, Three Gorges, China. The concentrations of the 16 PAHs ranged from 21.8 to 1324 ng g -1 dry wt for all 20 soil and sediment samples. These concentration levels were remarkably lower than those in soils and sediment collected domestically and worldwide. PAHs with two and three rings were found to be dominant in all the samples, with phenanthrene being most abundant. The spatial distribution of PAHs in bank soil, WLFZ soil, and sediment implied that the transfer and fate of PAHs in the bank soil-WLFZ soil-sediment systems were influenced by both water dynamic factors and physicochemical properties of PAHs. Diagnostic ratio analysis and principal component analysis suggested that the PAHs in the areas of Hanfeng Lake were primarily (>75%) derived from coal combustion and vehicle emissions . Use of natural gas, improving gasoline/diesel quality and phasing out old and nonstandard vehicles and ships are proposed to control PAH contamination and protect drinking water safety in the region.

Infrared spectroscopy of hydrated polycyclic aromatic hydrocarbon cations: naphthalene+-water.

PubMed

Chatterjee, Kuntal; Dopfer, Otto

2017-12-13

Polycyclic aromatic hydrocarbons (PAHs) are suggested to occur in interstellar media and ice grains. It is important to characterize hydrated PAHs and their cations to explore their stability in interstellar and biological media. Herein, the infrared photodissociation (IRPD) spectrum of the naphthalene + -H 2 O radical cation (Np + -H 2 O) recorded in the O-H and C-H stretch range is analysed by dispersion-corrected density functional theory calculations at the B3LYP-D3/aug-cc-pVTZ level to determine its structure and intermolecular bonding. Monohydration of Np + in its 2 A u ground electronic state leads to the formation of a bifurcated CHO ionic hydrogen bond (H-bond), in which the lone pairs of H 2 O bind to two adjacent CH proton donors of the two aromatic rings. The frequency-dependent branching ratios observed for IRPD of cold Np + -H 2 O-Ar clusters allows the estimation of the dissociation energy of Np + -H 2 O as D 0 ∼ 2800 ± 300 cm -1 . The monohydration motif of Np + differs qualitatively from that of the benzene cation in both structure and binding energy, indicating the strong influence of the multiple aromatic rings on the hydration of PAH + cations. This difference is rationalized by natural bond orbital analysis of the ionic H-bond motif. Comparison with neutral Np-H 2 O reveals the large change in structure and bond strength of the hydrated PAHs upon ionization. While neutral Np-H 2 O is stabilized by weak π H-bonds (OHπ, π-stacking), strong cation-dipole forces favour a planar bifurcated CHO ionic H-bond in Np + -H 2 O.

Extending Halogen-based Medicinal Chemistry to Proteins

PubMed Central

El Hage, Krystel; Pandyarajan, Vijay; Phillips, Nelson B.; Smith, Brian J.; Menting, John G.; Whittaker, Jonathan; Lawrence, Michael C.; Meuwly, Markus; Weiss, Michael A.

2016-01-01

Insulin, a protein critical for metabolic homeostasis, provides a classical model for protein design with application to human health. Recent efforts to improve its pharmaceutical formulation demonstrated that iodination of a conserved tyrosine (TyrB26) enhances key properties of a rapid-acting clinical analog. Moreover, the broad utility of halogens in medicinal chemistry has motivated the use of hybrid quantum- and molecular-mechanical methods to study proteins. Here, we (i) undertook quantitative atomistic simulations of 3-[iodo-TyrB26]insulin to predict its structural features, and (ii) tested these predictions by X-ray crystallography. Using an electrostatic model of the modified aromatic ring based on quantum chemistry, the calculations suggested that the analog, as a dimer and hexamer, exhibits subtle differences in aromatic-aromatic interactions at the dimer interface. Aromatic rings (TyrB16, PheB24, PheB25, 3-I-TyrB26, and their symmetry-related mates) at this interface adjust to enable packing of the hydrophobic iodine atoms within the core of each monomer. Strikingly, these features were observed in the crystal structure of a 3-[iodo-TyrB26]insulin analog (determined as an R6 zinc hexamer). Given that residues B24–B30 detach from the core on receptor binding, the environment of 3-I-TyrB26 in a receptor complex must differ from that in the free hormone. Based on the recent structure of a “micro-receptor” complex, we predict that 3-I-TyrB26 engages the receptor via directional halogen bonding and halogen-directed hydrogen bonding as follows: favorable electrostatic interactions exploiting, respectively, the halogen's electron-deficient σ-hole and electronegative equatorial band. Inspired by quantum chemistry and molecular dynamics, such “halogen engineering” promises to extend principles of medicinal chemistry to proteins. PMID:27875310

Dispersion Forces and the Molecular Origin of Internal Friction in Protein.

PubMed

Sashi, Pulikallu; Ramakrishna, Dasari; Bhuyan, Abani K

2016-08-23

Internal friction in macromolecules is one of the curious phenomena that control conformational changes and reaction rates. It is held here that dispersion interactions and London-van der Waals forces between nonbonded atoms are major contributors to internal friction. To demonstrate this, the flipping motion of aromatic rings of F10 and Y97 amino acid residues of cytochrome c has been studied in glycerol/water mixtures by cross relaxation-suppressed exchange nuclear magnetic resonance spectroscopy. The ring-flip rate is highly overdamped by glycerol, but this is not due to the effect of protein-solvent interactions on the Brownian dynamics of the protein, because glycerol cannot penetrate into the protein to slow the internal collective motions. Sound velocity in the protein under matching solvent conditions shows that glycerol exerts its effect by rather smothering the protein interior to produce reduced molecular compressibility and root-mean-square volume fluctuation (δVRMS), implying an increased number of dispersion interactions of nonbonded atoms. Hence, δVRMS can be used as a proxy for internal friction. By using the ansatz that internal friction is related to nonbonded interactions by the equation f(n) = f0 + f1n + f2n(2) + ..., where the variable n is the extent of nonbonded interactions with fi coefficients, the barrier to aromatic ring rotation is found to be flat. Also interesting is the appearance of a turnover region in the δVRMS dependence of the ring-flip rate, suggesting anomalous internal diffusion. We conclude that cohesive forces among nonbonded atoms are major contributors to the molecular origin of internal friction.

Phosphorescence Tuning through Heavy Atom Placement in Unsymmetrical Difluoroboron β-Diketonate Materials.

PubMed

Liu, Tiandong; Zhang, Guoqing; Evans, Ruffin E; Trindle, Carl O; Altun, Zikri; DeRosa, Christopher A; Wang, Fang; Zhuang, Meng; Fraser, Cassandra L

2018-02-06

Difluoroboron β-diketonates (BF 2 bdks) show both fluorescence (F) and room-temperature phosphorescence (RTP) when confined to a rigid matrix, such as poly(lactic acid). These materials have been utilized as optical oxygen sensors (e.g., in tumors, wounds, and cells). Spectral features include charge transfer (CT) from the major aromatic donor to the dioxaborine acceptor. A series of naphthyl-phenyl dyes (BF 2 nbm) (1-6) were prepared to test heavy-atom placement effects. The BF 2 nbm dye (1) was substituted with Br on naphthyl (2), phenyl (3), or both rings (4) to tailor the fluorescence/phosphorescence ratio and RTP lifetime-important features for designing O 2 sensing dyes by means of the heavy atom effect. Computational studies identify the naphthyl ring as the major donor. Thus, Br substitution on the naphthyl ring produced greater effects on the optical properties, such as increased RTP intensity and decreased RTP lifetime compared to phenyl substitution. However, for electron-donating piperidyl-phenyl dyes (5), the phenyl aromatic is the major donor. As a result, Br substitution on the naphthyl ring (6) did not alter the optical properties significantly. Experimental data and computational modeling show the importance of Br position. The S 1 and T 1 states are described by two singly occupied MOs (SOMOs). When both of these SOMOs have substantial amplitude on the heavy atom, passage from S 1 to T 1 and emission from T 1 to S 0 are both favored. This shortens the excited-state lifetimes and enhances phosphorescence. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

From Quasi-Planar B56 to Penta-Ring Tubular Ca©B56: Prediction of Metal-Stabilized Ca©B56 as the Embryo of Metal-Doped Boron α-Nanotubes

NASA Astrophysics Data System (ADS)

Tian, Wen-Juan; Chen, Qiang; Tian, Xin-Xin; Mu, Yue-Wen; Lu, Hai-Gang; Li, Si-Dian

2016-11-01

Motifs of planar metalloborophenes, cage-like metalloborospherenes, and metal-centered double-ring tubular boron species have been reported. Based on extensive first-principles theory calculations, we present herein the possibility of doping the quasi-planar C2v B56 (A-1) with an alkaline-earth metal to produce the penta-ring tubular Ca©B56 (B-1) which is the most stable isomer of the system obtained and can be viewed as the embryo of metal-doped (4,0) boron α-nanotube Ca©BNT(4,0) (C-1). Ca©BNT(4,0) (C-1) can be constructed by rolling up the most stable boron α-sheet and is predicted to be metallic in nature. Detailed bonding analyses show that the highly stable planar C2v B56 (A-1) is the boron analog of circumbiphenyl (C38H16) in π-bonding, while the 3D aromatic C4v Ca©B56 (B-1) possesses a perfect delocalized π system over the σ-skeleton on the tube surface. The IR and Raman spectra of C4v Ca©B56 (B-1) and photoelectron spectrum of its monoanion C4v Ca©B56- are computationally simulated to facilitate their spectroscopic characterizations.

The adsorption of biogenic amines on carbon nanotubes

NASA Astrophysics Data System (ADS)

Sidorenko, I. G.; Markitan, O. V.; Vlasova, N. N.; Zagorovskii, G. M.; Lobanov, V. V.

2009-06-01

The adsorption of phenylethylamine, tryptamine, and tyramine on carbon nanotubes from aqueous solutions (pH 7.4) was studied depending on time and sorbate concentration. The suggestion was made that their interaction with electrodes was determined by electrostatic attraction between protonated amino groups and oxygen-containing functional groups of the surface of carbon. An increase in the adsorption of biological amines was caused by the interaction of the π systems of their aromatic rings with carbon surface hexagons. The adsorption of biogenic amines on carbon nanotubes was necessary for their possible electrooxidation and analytic determination by electrochemical methods with the use of carbon electrodes.

Development of a Paper Strip Test for Detection of Niacin Produced by Mycobacteria

PubMed Central

Young, William D.; Maslansky, Alvin; Lefar, Morton S.; Kronish, Donald P.

1970-01-01

The development of a reagent-impregnated paper strip test for niacin is described. The test system is based on the formation of cyanogen chloride by the reaction of chloramine-T and potassium thiocyanate in the presence of citric acid. Rupture of the pyridine ring of niacin by cyanogen chloride yields γ-carboxy glutaconic aldehyde and coupling with a primary aromatic amine produces a yellow color. Sensitivity to niacin, both in known solutions and from extracts of 378 clinical mycobacteria isolates, equalled or exceeded that of other methods for detection of niacin. Correlation with other tests for mycobacterial niacin was excellent. PMID:4321713

Low-Q peak in X-ray patterns of choline-phenylalanine and -homophenylalanine: A combined effect of chain and stacking

NASA Astrophysics Data System (ADS)

Campetella, Marco; Martino, Delia Chillura; Scarpellini, Eleonora; Gontrani, Lorenzo

2016-09-01

In this contribution we report for the first time the X-ray patterns of choline-phenylalanine and choline-homophenylalanine ionic liquids. The presence of a low Q peak in both systems is another evidence that a long alkyl chain is not always needed to establish a nanodomain segregation in the liquid sufficient to be revealed by the diffraction experiment. These new data are compared with the diffraction patterns and the theoretical calculations of other choline-aminoacid ionic liquids recently reported. A significant role might be played by the stacking interactions between aromatic rings.

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

Custelcean, Radu; Bartsch, Richard A.

Two series of novel mono-ionizable calix[4]arene-benzocrown-6 ligands in 1,3-alternate conformations are synthesized. In one series, the proton-ionizable group (PIG) is attached to the para position of one aromatic ring in the calixarene framework, thereby positioning it over the polyether ring cavity. In the other series, the PIG is a substituent on the benzo group in the polyether ring. This orients the PIG away from the crown ether cavity. In addition to carboxylic acid functions, the PIGs include N-(X)sulfonyl carboxamide groups. With X group variation from methyl to phenyl to 4-nitrophenyl to trifluoromethyl, the acidity of the PIG is 'tuned'. Solventmore » extraction of Ag{sup +} from aqueous solutions into chloroform is used to probe the influence of structural variation within the mono-ionizable calixcrown ligand on metal ion extraction efficiency, including the identity and acidity of the PIG and its orientation with respect to the polyether ring.« less

Formation of Benzene in the Interstellar Medium

NASA Technical Reports Server (NTRS)

Jones, Brant M.; Zhang, Fangtong; Kaiser, Ralf I.; Jamal, Adeel; Mebel, Alexander M.; Cordiner, Martin A.; Charnley, Steven B.; Crim, F. Fleming (Editor)

2010-01-01

Polycyclic aromatic hydrocarbons and related species have been suggested to play a key role in the astrochemical evolution of the interstellar medium, but the formation mechanism of even their simplest building block-the aromatic benzene molecule-has remained elusive for decades. Here we demonstrate in crossed molecular beam experiments combined with electronic structure and statistical calculations that benzene (C6H6) can be synthesized via the barrierless, exoergic reaction of the ethynyl radical and 1,3- butadiene, C2H + H2CCHCHCH2 --> C6H6, + H, under single collision conditions. This reaction portrays the simplest representative of a reaction class in which aromatic molecules with a benzene core can be formed from acyclic precursors via barrierless reactions of ethynyl radicals with substituted 1,3-butadlene molecules. Unique gas-grain astrochemical models imply that this low-temperature route controls the synthesis of the very first aromatic ring from acyclic precursors in cold molecular clouds, such as in the Taurus Molecular Cloud. Rapid, subsequent barrierless reactions of benzene with ethynyl radicals can lead to naphthalene-like structures thus effectively propagating the ethynyl-radical mediated formation of aromatic molecules in the interstellar medium.

Formation of benzene in the interstellar medium

PubMed Central

Jones, Brant M.; Zhang, Fangtong; Kaiser, Ralf I.; Jamal, Adeel; Mebel, Alexander M.; Cordiner, Martin A.; Charnley, Steven B.

2011-01-01

Polycyclic aromatic hydrocarbons and related species have been suggested to play a key role in the astrochemical evolution of the interstellar medium, but the formation mechanism of even their simplest building block—the aromatic benzene molecule—has remained elusive for decades. Here we demonstrate in crossed molecular beam experiments combined with electronic structure and statistical calculations that benzene (C6H6) can be synthesized via the barrierless, exoergic reaction of the ethynyl radical and 1,3-butadiene, C2H + H2CCHCHCH2 → C6H6 + H, under single collision conditions. This reaction portrays the simplest representative of a reaction class in which aromatic molecules with a benzene core can be formed from acyclic precursors via barrierless reactions of ethynyl radicals with substituted 1,3-butadiene molecules. Unique gas-grain astrochemical models imply that this low-temperature route controls the synthesis of the very first aromatic ring from acyclic precursors in cold molecular clouds, such as in the Taurus Molecular Cloud. Rapid, subsequent barrierless reactions of benzene with ethynyl radicals can lead to naphthalene-like structures thus effectively propagating the ethynyl-radical mediated formation of aromatic molecules in the interstellar medium. PMID:21187430

Removal of antibiotic cloxacillin by means of electrochemical oxidation, TiO2 photocatalysis, and photo-Fenton processes: analysis of degradation pathways and effect of the water matrix on the elimination of antimicrobial activity.

PubMed

Serna-Galvis, Efraim A; Giraldo-Aguirre, Ana L; Silva-Agredo, Javier; Flórez-Acosta, Oscar A; Torres-Palma, Ricardo A

2017-03-01

This study evaluates the treatment of the antibiotic cloxacillin (CLX) in water by means of electrochemical oxidation, TiO 2 photocatalysis, and the photo-Fenton system. The three treatments completely removed cloxacillin and eliminated the residual antimicrobial activity from synthetic pharmaceutical wastewater containing the antibiotic, commercial excipients, and inorganic ions. However, significant differences in the degradation routes were found. In the photo-Fenton process, the hydroxyl radical was involved in the antibiotic removal, while in the TiO 2 photocatalysis process, the action of both the holes and the adsorbed hydroxyl radicals degraded the pollutant. In the electrochemical treatment (using a Ti/IrO 2 anode in sodium chloride as supporting electrolyte), oxidation via HClO played the main role in the removal of CLX. The analysis of initial by-products showed five different mechanistic pathways: oxidation of the thioether group, opening of the central β-lactam ring, breakdown of the secondary amide, hydroxylation of the aromatic ring, and decarboxylation. All the oxidation processes exhibited the three first pathways. Moreover, the aromatic ring hydroxylation was found in both photochemical treatments, while the decarboxylation of the pollutant was only observed in the TiO 2 photocatalysis process. As a consequence of the degradation routes and mechanistic pathways, the elimination of organic carbon was different. After 480 and 240 min, the TiO 2 photocatalysis and photo-Fenton processes achieved ∼45 and ∼15 % of mineralization, respectively. During the electrochemical treatment, 100 % of the organic carbon remained even after the antibiotic was treated four times the time needed to degrade it. In contrast, in all processes, a natural matrix (mineral water) did not considerably inhibit pollutant elimination. However, the presence of glucose in the water significantly affected the degradation of CLX by means of TiO 2 photocatalysis.

Polycyclic aromatic hydrocarbons in surface waters and riverine sediments of the Hooghly and Brahmaputra Rivers in the Eastern and Northeastern India.

PubMed

Khuman, Sanjenbam Nirmala; Chakraborty, Paromita; Cincinelli, Alessandra; Snow, Daniel; Kumar, Bhupander

2018-04-30

Sixteen priority polycyclic aromatic hydrocarbons (PAHs) regulated by the United States Environmental Protection Agency (USEPA) were analyzed in surface waters and riverine sediments of Brahmaputra and Hooghly Rivers, along urban-suburban-rural transects. ∑ 16 PAHs concentrations were higher in Hooghly riverine sediment (HRS) (Avg, 445 ng g -1 ) than Brahmaputra riverine sediment (BRS) (Avg, 169 ng g -1 ) dominated by 4-ring PAHs. In contrast, PAHs concentrations in surface water of Brahmaputra River (BRW) (Avg, 4.04 μg L -1 ) were comparable with Hooghly River (HRW) (Avg, 4.8 μg L -1 ), with dominance by 3-ring PAHs. Toxic PAHs (BaA, Chr, BbF, BkF, BaP, InP and DBA) were dominant in sub-urban transect of HRS (Avg, 387 ng g -1 ) and BRS (Avg, 14 ng g -1 ). Diagnostic ratios, principal component analysis (PCA) and ring wise composition suggested combustion as the main PAHs source in these riverine belts. In BRS, higher PAHs in suburban and rural transects were attributed to incomplete combustion of fossil fuel and biomass burning. In HRS, >85% of high molecular weight PAHs were found in the industrial areas of the suburban transect possibly associated with the discharge of industrial effluents. Harbor and port activities were other major contributors of HMW-PAHs in Hooghly riverine system. Carcinogenic potency estimated in terms of toxic equivalent (TEQ) was several folds higher in HRS (Avg, 106 ng TEQ g -1 ) compared with BRS (Avg, 2.5 ng TEQ g -1 ). Mostly low molecular weight PAHs are likely posing a risk to fishes in both the rivers. Risk on edible fish species may be a matter of concern considering the regular consumption of fishes in this region. Copyright © 2018 Elsevier B.V. All rights reserved.

Second-Generation Phenylthiazole Antibiotics with Enhanced Pharmacokinetic Properties.

PubMed

Seleem, Mohammed A; Disouky, Ahmed M; Mohammad, Haroon; Abdelghany, Tamer M; Mancy, Ahmed S; Bayoumi, Sammar A; Elshafeey, Ahmed; El-Morsy, Ahmed; Seleem, Mohamed N; Mayhoub, Abdelrahman S

2016-05-26

A series of second-generation analogues for 2-(1-(2-(4-butylphenyl)-4-methylthiazol-5-yl)ethylidene)aminoguanidine (1) have been synthesized and tested against methicillin-resistant Staphylococcus aureus (MRSA). The compounds were designed with the objective of improving pharmacokinetic properties. This main aim has been accomplished by replacing the rapidly hydrolyzable Schiff-base moiety of first-generation members with a cyclic, unhydrolyzable pyrimidine ring. The hydrazide-containing analogue 17 was identified as the most potent analogue constructed thus far. The corresponding amine 8 was 8 times less active. Finally, incorporating the nitrogenous side chain within an aromatic system completely abolished the antibacterial character. Replacement of the n-butyl group with cyclic bioisosteres revealed cyclohexenyl analogue 29, which showed significant improvement in in vitro anti-MRSA potency. Increasing or decreasing the ring size deteriorated the antibacterial activity. Compound 17 demonstrated a superior in vitro and in vivo pharmacokinetic profile, providing compelling evidence that this particular analogue is a good drug candidate worthy of further analysis.

Substitution and solvent effects in the chalcones isomerization barrier of flavylium photochromic systems.

PubMed

Roque, Ana; Lima, João Carlos; Parola, A Jorge; Pina, Fernando

2007-04-01

Useful application of photochromic compounds as optical memories implies the existence of a large kinetic barrier between the forms interconverted by light. In the case of flavylium salts, the ground state isomerization barrier between the photoisomerizable chalcone isomers is shown to correlate with the electron donating ability of the substituents, measured by their effects in the (1)H NMR chemical shifts of the aromatic protons. Substitution with electron donating groups in ring A lowers the barrier while substitution at ring B has the opposite effect. However, in water, the observed increase is higher than expected in the case of compound 4',9-dihydroxychalcone when compared with the analogous 4'-dimethylamino-9-hydroxychalcone, containing a better electron donating group in the same position. Our interpretation is that the water network is providing an efficient pathway to form tautomers. In acetonitrile, unlike water, the expected order is indeed observed: E(a)(4',9-dihydroxychalcone) = 60 kJ mol(-1) < E(a) (4'-dimethylamino-9-hydroxychalcone) = 69 kJ mol(-1).

Heterologous Expression of Polycyclic Aromatic Hydrocarbon Ring-Hydroxylating Dioxygenase Genes from a Novel Pyrene-Degrading Betaproteobacterium

PubMed Central

Hu, Jing; Aitken, Michael D.

2012-01-01

A betaproteobacterium within the family Rhodocyclaceae previously identified as a pyrene degrader via stable-isotope probing (SIP) of contaminated soil (designated pyrene group 1 or PG1) was cultivated as the dominant member of a mixed bacterial culture. A metagenomic library was constructed, and the largest contigs were analyzed for genes associated with polycyclic aromatic hydrocarbon (PAH) metabolism. Eight pairs of genes with similarity to the α- and β-subunits of ring-hydroxylating dioxygenases (RHDs) associated with aerobic bacterial PAH degradation were identified and linked to PG1 through PCR analyses of a simplified enrichment culture. In tandem with a ferredoxin and reductase found in close proximity to one pair of RHD genes, six of the RHDs were cloned and expressed in Escherichia coli. Each cloned RHD was tested for activity against nine PAHs ranging in size from two to five rings. Despite differences in their predicted protein sequences, each of the six RHDs was capable of transforming phenanthrene and pyrene. Three RHDs could additionally transform naphthalene and fluorene, and these genotypes were also associated with the ability of the E. coli constructs to convert indole to indigo. Only one of the six cloned RHDs was capable of transforming anthracene and benz[a]anthracene. None of the tested RHDs were capable of significantly transforming fluoranthene, chrysene, or benzo[a]pyrene. PMID:22427500

Characterization of polycyclic aromatic hydrocarbons in fugitive PM10 emissions from an integrated iron and steel plant.

PubMed

Khaparde, V V; Bhanarkar, A D; Majumdar, Deepanjan; Rao, C V Chalapati

2016-08-15

Fugitive emissions of PM10 (particles <10μm in diameter) and associated polycyclic aromatic hydrocarbons (PAHs) were monitored in the vicinity of coking unit, sintering unit, blast furnace and steel manufacturing unit in an integrated iron and steel plant situated in India. Concentrations of PM10, PM10-bound total PAHs, benzo (a) pyrene, carcinogenic PAHs and combustion PAHs were found to be highest around the sintering unit. Concentrations of 3-ring and 4-ring PAHs were recorded to be highest in the coking unit whereas 5-and 6-ring PAHs were found to be highest in other units. The following indicatory PAHs were identified: indeno (1,2,3-cd) pyrene, dibenzo (a,h) anthracene, benzo (k) fluoranthene in blast furnace unit; indeno (1,2,3-cd) pyrene, dibenzo (a,h) anthracene, chrysene in sintering unit; Anthracene, fluoranthene, chrysene in coking unit and acenaphthene, fluoranthene, fluorene in steel making unit. Total-BaP-TEQ (Total BaP toxic equivalent quotient) and BaP-MEQ (Total BaP mutagenic equivalent quotient) concentration levels ranged from 2.4 to 231.7ng/m(3) and 1.9 to 175.8ng/m(3), respectively. BaP and DbA (dibenzo (a,h) anthracene) contribution to total-BaP-TEQ was found to be the highest. Copyright © 2016 Elsevier B.V. All rights reserved.

Two unprecedented aromatic guanidines supramolecular chains self-assembled by hydrogen bonding interaction

NASA Astrophysics Data System (ADS)

Zhang, Yunshen; Huang, Yichao; Zhang, Jiangwei; Zhu, Li; Chen, Kun; Hao, Jian

2015-10-01

Two aromatic guanidine derivatives, C6H5N = C(NHCy)2 (1), (n-TBA)C6H5NHC(NHCy)2Mo2O7 (2) (Cy = cyclohexyl), were synthetized with high yields. Both of them self-assembled into supramolecules via H-bond interactions. Single crystal XRD indicated that crystal 1 showed helix chains combining pseudo four-fold and pseudo six-fold symmetries, while crystal 2 presented ladder chains with alternate ring structures. In this paper, a novel way to design ladder-like supramolecular chains from helix chains was presented, using POMs (polyoxometalates) to provide protons to help assembly.

Luminescent Li-based metal-organic framework tailored for the selective detection of explosive nitroaromatic compounds: direct observation of interaction sites.

PubMed

Kim, Tae Kyung; Lee, Jae Hwa; Moon, Dohyun; Moon, Hoi Ri

2013-01-18

A luminescent lithium metal-organic framework (MOF) is constructed from the solvothermal reaction of Li(+) and a well-designed organic ligand, bis(4-carboxyphenyl)-N-methylamine (H(2)CPMA). A Li-based MOF can detect an explosive aromatic compound containing nitro groups as an explosophore, by showing a dramatic color change with concurrent luminescence quenching in the solid state. The detection sites are proven directly through single-crystal-to-single-crystal transformations, which show strong interactions between the aromatic rings of the electron-rich CPMA(2-) molecules and the electron-deficient nitrobenzene.

Mechanochemical synthesis and structural characterization of three novel cocrystals of dimethylglyoxime with N-heterocyclic aromatic compounds and acetamide

NASA Astrophysics Data System (ADS)

Abidi, Syed Sibte Asghar; Azim, Yasser; Gupta, Abhishek Kumar; Pradeep, Chullikkattil P.

2017-12-01

With an aim to explore the interactions of (RR'Cdbnd Nsbnd OH) oxime moiety of dimethylglyoxime (DMG) with pyridyl ring of N-heterocyclic aromatic compounds and acetamide, three novel cocrystals of dimethylglyoxime with acridine (ACR), 1,10-phenanthroline monohydrate (PT) and acetamide (ACT) are reported. These three cocrystals were obtained with a mechanochemical synthesis approach and were characterized by single crystal X-ray diffraction (SCXRD), powder X-ray diffraction (PXRD), fourier transform-infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Additionally, Hirshfeld surface analysis is used to investigate the intermolecular interaction and the crystal packing of cocrystals.

Development of high temperature liquid lubricants for low-heat rejection heavy duty diesel engines

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

Wiczynski, T.A.; Marolewski, T.A.

1993-03-01

Objective was to develop a liquid lubricant that will allow advanced diesel engines to operate at top ring reversal temperatures approaching 500 C and lubricant sump temperatures approaching 250 C. Base stock screening showed that aromatic esters and diesters has the lowest deposit level, compared to polyol esters, poly-alpha-olefins, or refined mineral oil of comparable viscosity. Classical aryl and alkyl ZDP antiwear additives are ineffective in reducing wear with aromatic esters; the phosphate ester was a much better antiwear additive, and polyol esters are more amenable to ZDP treatment. Zeolites and clays were evaluated for filtration.

Electrolyte salts for nonaqueous electrolytes

DOEpatents

Amine, Khalil; Zhang, Zhengcheng; Chen, Zonghai

2012-10-09

Metal complex salts may be used in lithium ion batteries. Such metal complex salts not only perform as an electrolyte salt in a lithium ion batteries with high solubility and conductivity, but also can act as redox shuttles that provide overcharge protection of individual cells in a battery pack and/or as electrolyte additives to provide other mechanisms to provide overcharge protection to lithium ion batteries. The metal complex salts have at least one aromatic ring. The aromatic moiety may be reversibly oxidized/reduced at a potential slightly higher than the working potential of the positive electrode in the lithium ion battery. The metal complex salts may also be known as overcharge protection salts.

N-[4-Cyano-3-(trifluoro­meth­yl)phen­yl]-2-eth­oxy­benzamide

PubMed Central

Naveen, S.; Basappa; Manjunath, H. R.; Sridhar, M. A.; Shashidhara Prasad, J.; Rangappa, K. S.

2010-01-01

In the title compound, C17H13F3N2O2, the two aromatic rings are essentially coplanar, forming a dihedral angle of 2.78 (12)°. The non-H atoms of the eth­oxy group are coplanar with the attached ring [maximum deviation = 0.271 (3) Å]. An intra­molecular N—H⋯O hydrogen bond occurs. In the crystal structure, mol­ecules are linked by inter­molecular C—H⋯N and C—H⋯F hydrogen bonds. PMID:21587782

Arctigenin: a lignan from Arctium lappa.

PubMed

Gao, Haiyan; Li, Guanglei; Zhang, Junhe; Zeng, Jie

2008-07-19

The title compound {systematic name: (3R-trans)-4-[(3,4-dimethoxy-phen-yl)meth-yl]-3-[(4-hydr-oxy-3-methoxy-phen-yl)meth-yl]-4,5-dihydrofuran-2(3H)-one}, C(21)H(24)O(6), has a dibenz-yl-butyrolactone skeleton. The two aromatic rings are inclined at a dihedral angle of 68.75 (7)° with respect to each other. The lactone ring adopts an envelope conformation. A series of O-H⋯O and C-H⋯O hydrogen bonds contribute to the stabilization of the crystal packing. The absolute configuration was assigned on the basis of the published literature.

The sensitive and selective adsorption of aromatic compounds with highly crosslinked polymer nanoparticles

NASA Astrophysics Data System (ADS)

Liu, Shuqin; Chen, Darui; Zheng, Juan; Zeng, Lewei; Jiang, Jijun; Jiang, Ruifeng; Zhu, Fang; Shen, Yong; Wu, Dingcai; Ouyang, Gangfeng

2015-10-01

This study presents the preparation and characterization of a nanoscale Davankov-type hyper-crosslinked-polymer (HCP) as an adsorbent of benzene-ring-containing dyes and organic pollutants. HCP nanoparticles post-crosslinked from a poly(DVB-co-VBC) precursor were synthesized in this study, possessing ultrahigh surface area, hydrophobicity and stability. The as-synthesized Davankov-type HCP exhibited a rapid and selective adsorption ability towards the benzene-ring-containing dyes due to its highly conjugated structure. Besides, for the first time, the prepared HCP nanoparticles were adopted for the adsorption of nonpolar organic pollutants by means of solid-phase microextraction (SPME). Owing to its high hydrophobicity, diverse pore size distribution and highly conjugated structure, a 10 μm HCP coating exhibited excellent adsorption abilities towards benzene-ring-containing polycyclic aromatic hydrocarbons (PAHs) and benzene series compounds (benzene, toluene, ethylbenzene and o-xylene; abbreviated to BTEX) and to highly hydrophobic long-chain n-alkanes. Finally, the HCP-nanoparticles-coated SPME fiber was applied to the simultaneous analysis of five PAHs in environmental water samples and satisfactory recoveries were achieved. The findings could provide a new benchmark for the exploitation of superb HCPs as effective adsorbents for SPME or other adsorption applications.This study presents the preparation and characterization of a nanoscale Davankov-type hyper-crosslinked-polymer (HCP) as an adsorbent of benzene-ring-containing dyes and organic pollutants. HCP nanoparticles post-crosslinked from a poly(DVB-co-VBC) precursor were synthesized in this study, possessing ultrahigh surface area, hydrophobicity and stability. The as-synthesized Davankov-type HCP exhibited a rapid and selective adsorption ability towards the benzene-ring-containing dyes due to its highly conjugated structure. Besides, for the first time, the prepared HCP nanoparticles were adopted for the adsorption of nonpolar organic pollutants by means of solid-phase microextraction (SPME). Owing to its high hydrophobicity, diverse pore size distribution and highly conjugated structure, a 10 μm HCP coating exhibited excellent adsorption abilities towards benzene-ring-containing polycyclic aromatic hydrocarbons (PAHs) and benzene series compounds (benzene, toluene, ethylbenzene and o-xylene; abbreviated to BTEX) and to highly hydrophobic long-chain n-alkanes. Finally, the HCP-nanoparticles-coated SPME fiber was applied to the simultaneous analysis of five PAHs in environmental water samples and satisfactory recoveries were achieved. The findings could provide a new benchmark for the exploitation of superb HCPs as effective adsorbents for SPME or other adsorption applications. Electronic supplementary information (ESI) available: Fig. S1-S8, details of optimization of the SPME condition, Tables S1-S5. See DOI: 10.1039/c5nr04624f

N-(1,3-Thia­zol-2-yl)benzamide

PubMed Central

Zonouzi, Afsaneh; Mirzazadeh, Roghieh; Rahmani, Hossein; Ng, Seik Weng

2009-01-01

The title compound, C10H8N2OS, features a nonplanar mol­ecule [dihedral angle between the two aromatic rings = 43.6 (1)°]. Two mol­ecules are linked by N—H⋯N hydrogen bonds about a centre of inversion, giving rise to a hydrogen-bonded dimer. PMID:21582538

1-(4-Chloro­benzyl­ideneamino)pyridinum iodide

PubMed Central

Cui, Yong-Tao; Wang, Jian-Qiang; Ji, Chun-Xiang; Wang, Hai-Bo; Cheng, Guo

2009-01-01

In the title compound, C12H10ClN2 +·I−, the aromatic rings are oriented at a dihedral angle of 54.55 (3)°. In the crystal structure, inter­molecular C—H⋯I and C—H⋯Cl hydrogen bonds link the mol­ecules. PMID:21581845

4-[(3-Chloro-2-methyl-phen-yl)imino-meth-yl]phenol.

PubMed

Manjunath, B C; Abdoh, M M M; Mallesha, L; Mohana, K N; Lokanath, N K

2012-11-01

In the title compound, C(14)H(12)ClNO, the dihedral angle between the aromatic rings is 39.84 (7)°. In th crystal, mol-ecules are connected by O-H⋯N hydrogen bonds into chains parallel to [001]. In addition, a C-H⋯π contact occurs.

Association of (+)-catechin and catechin-(4a-8)-catechin with oligopeptides

Treesearch

Tsutomu Hatano; Richard W. Hemingway

1996-01-01

NOE studies on the complexation of (poly)flavanoids with peptides containing proline residues in aqueous solutions reveal site specific approach directed by hydrophobic interaction of the aromatic rings of catechin and its dimer, catechin-(4α→8)-catechin, to conformationally accessible regions of peptides without strong preferencef or interaction...

CLONING AND CHARACTERIZATION OF THE PHTHALATE CATABOLISM REGION OF PRE1 OF ARTHROBACTER KEYSERI 12B

EPA Science Inventory

o-Phthalate (benzene-1,2-dicarboxylate) is a central intermediate in the bacterial degradation of phthalate ester plasticizers as well as of a number of fused-ring polycyclic aromatic hydrocarbons found in fossil fuels. In Arthrobacter keyseri 12B, the genes encoding catabolism o...

Process for reducing aromatic compounds in ethylenediamine with calcium

DOEpatents

Benkeser, Robert A.; Laugal, James A.; Rappa, Angela

1985-01-01

Olefins are produced by containing an organic compound having at least one benzene ring with ethylenediamine and calcium metal, the calcium metal being used in large excess or alternatively in conjunction with an inert abrasive particulate substance. Substantially all of the organic compounds are converted to corresponding cyclic olefins, largely mono-olefins.

Process for reducing aromatic compounds in ethylenediamine with calcium

DOEpatents

Benkeser, R.A.; Laugal, J.A.; Rappa, A.

1985-08-06

Olefins are produced by containing an organic compound having at least one benzene ring with ethylenediamine and calcium metal, the calcium metal being used in large excess or alternatively in conjunction with an inert abrasive particulate substance. Substantially all of the organic compounds are converted to corresponding cyclic olefins, largely mono-olefins.

Synthesis of a Near-Infrared Emitting Squaraine Dye in an Undergraduate Organic Laboratory

ERIC Educational Resources Information Center

Marks, Patrick; Levine, Mindy

2012-01-01

Squaraines are a class of organic fluorophores that possess unique photophysical properties, including strong near-infrared absorption and emission. The synthesis of many squaraines involves the condensation of an electron-rich aromatic ring with squaric acid. These reactions are generally refluxed overnight in a benzene-butanol solvent mixture.…