Degradation pathway of bisphenol A: Does ipso substitution apply to phenols containing a quaternary alpha-carbon structure in the para position?

The degradation of bisphenol A and nonylphenol involves the unusual rearrangement of stable carboncarbon bonds. Some nonylphenol isomers and bisphenol A possess a quaternary alpha-carbon atom as a common structural feature. The degradation of nonylphenol in Sphingomonas sp. strain TTNP3 occurs via a type II ipso substitution with the presence of a quaternary alpha-carbon as a prerequisite. We report here a new degradation pathway of bisphenol A. Consequent to the hydroxylation at position C-4, according to a type 11 ipso substitution mechanism, the C-C bond between the phenolic moiety and the isopropyl group of bisphenol A is broken. Besides the formation of hydroquinone and 4-(2-hydroxypropan-2-yl) phenol as the main metabolites, further compounds resulting from molecular rearrangements consistent with a carbocationic intermediate were identified. Assays with resting cells or cell extracts of Sphingomonas sp. strain TTNP3 under an 18 02 atmosphere were performed. One atom of 180, was present in hydroquinone, resulting from the monooxygenation of bisphenol A and nonylphenol. The monooxygenase activity was dependent on both NADPH and flavin adenine dinucleotide. Various cytochrome P450 inhibitors had identical inhibition effects on the conversion of both xenobiotics. Using a mutant of Sphingomonas sp. strain TTNP3, which is defective for growth on nonylphenol, we demonstrated that the reaction is catalyzed by the same enzymatic system. In conclusion, the degradation of bisphenol A and nonylphenol is initiated by the same monooxygenase, which may also lead to ipso substitution in other xenobiotics containing phenol with a quaternary a-carbon.

Synthesis, structure and solution chemistry of quaternary oxovanadium(V) complexes incorporating hydrazone ligands

[VIVO(acac)(2)] reacts with an equimolar amount of benzoyl hydrazone of 2-hydroxyacetophenone (H2L1) or 5-chloro-2-hydroxyacetophenone (H2L2) in the presence of excess pyridine (py) in methanol to produce the quaternary [(VO)-O-V(L-1)(OCH3)(py)] (1) and [(VO)-O-V(L-2)(OCH3)(py)] (2) complexes, respectively, while under similar condition, the benzoyl hydrazones of 2-hydroxy-5-methylacetophenone (H2L3) and 2-hydroxy-5-methoxyacetophenone (H2L4) afforded only the methoxy bridged dimeric [(VO)-O-V(L-3/L-4)(OCH3)](2) complexes. The X-ray structural analysis of 1 and 2 indicates that the geometry around the metal is distorted octahedral where the three equatorial positions are occupied by the phenolate-O, enolate-O and the imine-N of the fully deprotonated hydrazone ligand in its enolic form and the fourth one by a methoxide-O atom. An oxo-O and a pyridine-N atom occupy two axial positions. Quaternary complexes exhibit one quasi-reversible one-electron reduction peak near 0.25 V versus SCE in CH2Cl2 and they decompose appreciably to the corresponding methoxy bridged dimeric complex in CDCl3 solution as indicated by their H-1 NMR spectra. These quaternary VO3+ complexes are converted to the corresponding V2O34+-complexes simply on refluxing them in acetone and to the VO2+-complexes on reaction with KOH in methanol. An equimolar amount of 8-hydroxyquinoline (Hhq) converts these quaternary complexes to the ternary [(VO)-O-V(L)(hq)] complexes in CHCl3. (C) 2009 Elsevier B. V. All rights reserved.

Structure-Activity Relationship for Quaternary Ammonium Compounds Hybridized with Poly(methyl methacrylate)

Hybrid films from poly (methylmethacrylate) (PMMA) and dioctadecyldimethylammonium bromide (DODAB), cetyltrimethylammonium bromide (CTAB), or tetrapropylammonium bromide (TPAB) were characterized by determination of wettability, ellipsometry, atomic force microscopy, active compounds diffusion to water, X-ray photoelectron spectroscopy (XPS) with determination of atomic composition on the films surface, and biocidal activity against Pseudomonas aeruginosa or Staphylococcus aureus. QAC mobility in the films increased from DODAB to CTAB to TPAB. Diffusion and optimal hydrophobic hydrophilic balance imparted the highest bioactivity to CTAB. DODAB sustained immobilization at the film surface killed bacteria upon contact. TPAB ability to diffuse was useless because of its unfavorable hydrophobic hydrophilic balance for bioactivity.

Structure and properties of quaternary and tetragonal Heusler compounds for spintronics and spin transfer torque applications

Diese Dissertation ist in zwei Teile aufgeteilt: Teil 1 befasst sich mit der Vorhersage von Halb-Metallizität in quarternären Heuslerverbindungen und deren Potential für Spintronik-Anwendungen. Teil 2 befasst sich mit den strukturellen Eigenschaften der Mn2-basierenden Heuslerverbindungen und dem Tuning von ihrer magnetischen Eigenschaften bzgl. Koerzitivfeldstärke und Remanenz. Diese Verbindungen sind geeignet für Spin-Transfer Torque-Anwendungen.rnrnIn Teil 1 wurden die folgenden drei Probenserien quarternärer Heuslerverbindungen untersucht: XX´MnGa (X = Cu, Ni und X´ = Fe, Co), CoFeMnZ (Z = Al, Ga, Si, Ge) und Co2−xRhxMnZ (Z = Ga, Sn, Sb). Abgesehen von CuCoMnGa wurden alle diese Verbindungen mittels ab-initio Bandstrukturrechnungen als halbmetallische Ferromagnete prognostiziert. In der XX´MnGa-Verbindungsklasse besitzt NiFeMnGa zwar eine zu niedrige Curie-Temperatur für technologische Anwendungen, jedoch NiCoMnGa mit seiner hohen Spinpolarisation, einem hohen magnetischen Moment und einer hohen Curie-Temperatur stellt ein neues Material für Spintronik-Anwendungen dar. Alle CoFeMnZ-Verbindungen kristallisieren in der kubischen Heuslerstruktur und ihre magnetischen Momente folgen der Slater-Pauling-Regel, was Halbmetalizität und eine hohe Spinpolarisation impliziert. Die ebenfalls hohen Curie-Temperaturen ermöglichen einen Einsatz weit über Raumtemperatur hinaus. In der strukturellen Charakterisierung wurde festgestellt, dass sämtliche Co2−xRhxMnZ abgesehen von CoRhMnSn verschiedene Typen von Unordnung aufweisen; daher war die ermittelte Abweichung von der Slater-Pauling-Regel sowie von der 100%-igen Spinpolarisation dieser Verbindungen zu erwarten. Die Halbmetallizität der geordneten CoRhMnSn-Verbindung sollte nach den durchgeführten magnetischen Messungen vorhanden sein.rnrnIm zweiten Teil wurden Mn3−xCoxGa und Mn2−xRh1+xSn synthetisiert und charakterisiert. Es wurde gezeigt, dass Mn3−xCoxGa im Bereich x = 0.1 − 0.4 in einer tetragonal verzerrten inversen Heuslerstruktur kristallisiert und im Bereich x = 0.6−1 in einer kubisch inversen Heuslerstruktur. Während die tetragonalen Materialien hartmagnetisch sind und Charakeristika aufweisen, die typischerweise für Spin-Transfer Torque-Anwengungen attraktiv sind, repräsentieren die weichmagnetischen kubischen Vertreter die 100% spinpolarisierten Materialien, die der Slater-Pauling-Regel folgen. Mn2RhSn kristallisiert in der inversen tetragonal verzerrten Heuslerstruktur, weist einernhartmagnetische Hystereseschleife auf und folgt nicht der Slater-Pauling-Regel. Bei hohen Rh-Gehalt wird die kubische inverse Heuslerstruktur gebildet. Alle kubischen Proben sind weichmagnetisch und folgen der Slater-Pauling-Regel.

Intra and Inter-Molecular Communications Through Protein Structure Network

Communication within and across proteins is crucial for the biological functioning of proteins. Experiments such as mutational studies on proteins provide important information on the amino acids, which are crucial for their function. However, the protein structures are complex and it is unlikely that the entire responsibility of the function rests on only a few amino acids. A large fraction of the protein is expected to participate in its function at some level or other. Thus, it is relevant to consider the protein structures as a completely connected network and then deduce the properties, which are related to the global network features. In this direction, our laboratory has been engaged in representing the protein structure as a network of non-covalent connections and we have investigated a variety of problems in structural biology, such as the identification of functional and folding clusters, determinants of quaternary association and characterization of the network properties of protein structures. We have also addressed a few important issues related to protein dynamics, such as the process of oligomerization in multimers, mechanism on protein folding, and ligand induced communications (allosteric effect). In this review we highlight some of the investigations which we have carried out in the recent past. A review on protein structure graphs was presented earlier, in which the focus was on the graphs and graph spectral properties and their implementation in the study of protein structure graphs/networks (PSN). In this article, we briefly summarize the relevant parts of the methodology and the focus is on the advancement brought out in the understanding of protein structure-function relationships through structure networks. The investigations of structural/biological problems are divided into two parts, in which the first part deals with the analysis of PSNs based on static structures obtained from x-ray crystallography. The second part highlights the changes in the network, associated with biological functions, which are deduced from the network analysis on the structures obtained from molecular dynamics simulations.

Preparation, structure, and magnetic properties of isostructural La3MAlS7 and La3MFeS7 (M = Mg, Mn, Fe, Co, Ni, or Zn)

A series of quaternary metal sulfides of the general formula La3MM′S7 (M = Mn, Fe, Co; M′ = Al and M = Mg, Mn, Fe, Co, Ni; M′ = Fe) consisting of linear chains of face shared MS6 octahedra and isolated M′S4 tetrahedra has been prepared and studied. The aluminium compounds La3MAlS7 (M = Mn, Fe, Co) exhibit linear chain antiferromagnetism. Magnetic behavior of other La3MFeS7 sulfides has been examined in detail. The magnetic susceptibility of La3MgFeS7 shows that tetrahedral site Fe3+ undergoes a transition from Image to S = 2 spin state around 150 K.

Structure-Based Phylogeny as a Diagnostic for Functional Characterization of Proteins with a Cupin Fold

Background: The members of cupin superfamily exhibit large variations in their sequences, functions, organization of domains, quaternary associations and the nature of bound metal ion, despite having a conserved beta-barrel structural scaffold. Here, an attempt has been made to understand structure-function relationships among the members of this diverse superfamily and identify the principles governing functional diversity. The cupin superfamily also contains proteins for which the structures are available through world-wide structural genomics initiatives but characterized as ``hypothetical''. We have explored the feasibility of obtaining clues to functions of such proteins by means of comparative analysis with cupins of known structure and function. Methodology/Principal Findings: A 3-D structure-based phylogenetic approach was undertaken. Interestingly, a dendrogram generated solely on the basis of structural dissimilarity measure at the level of domain folds was found to cluster functionally similar members. This clustering also reflects an independent evolution of the two domains in bicupins. Close examination of structural superposition of members across various functional clusters reveals structural variations in regions that not only form the active site pocket but are also involved in interaction with another domain in the same polypeptide or in the oligomer. Conclusions/Significance: Structure-based phylogeny of cupins can influence identification of functions of proteins of yet unknown function with cupin fold. This approach can be extended to other proteins with a common fold that show high evolutionary divergence. This approach is expected to have an influence on the function annotation in structural genomics initiatives.

Structure-function relationships of icosahedral plant

X-ray diffraction studies on single crystals of a few viruses have led to the elucidation of their three dimensional structure at near atomic resolution. Both the tertiary structure of the coat protein subunit and the quaternary organization of the icosahedral capsid in these viruses are remarkably similar. These studies have led to a critical re-examination of the structural principles in the architecture of isometric viruses and suggestions of alternative mechanisms of assembly. Apart from their role in the assembly of the virus particle, the coat proteins of certian viruses have been shown to inhibit the replication of the cognate RNA leading to cross-protection. The coat protein amino acid sequence and the genomic sequence of several spherical plant RNA viruses have been determined in the last decade. Experimental data on the mechanisms of uncoating, gene expression and replication of several classes of viruses have also become available. The function of the non-structural proteins of some viruses have been determined. This rapid progress has provided a wealth of information on several key steps in the life cycle of RNA viruses. The function of the viral coat protein, capsid architecture, assembly and disassembly and replication of isometric RNA plant viruses are discussed in the light of this accumulated knowledge.

Structure-function relationships of icosahedral plant viruses

X-ray diffraction studies on single crystals of a few viruses have led to the elucidation of their three dimensional structure at near atomic resolution. Both the tertiary structure of the coat protein subunit and the quaternary morganization of the icosahedral capsid in these viruses are remarkably similar. These studies have led to a critical re-examination of the structural principles in the architecture of isometric viruses and suggestions of alternative mechanisms of assembly. Apart from their role in the assembly of the virus particle, the coat proteins of certian viruses have been shown to inhibit the replication of the cognate RNA leading to cross-protection. The coat protein amino acid sequence and the genomic sequence of several spherical plant RNA viruses have been determined in the last decade. Experimental data on the mechanisms of uncoating, gene expression and replication of several classes of viruses have also become available. The function of the non-structural proteins of some viruses have been determined. This rapid progress has provided a wealth of information on several key steps in the life cycle of RNA viruses. The function of the viral coat protein, capsid architecture, assembly and disassembly and replication of isometric RNA plant viruses are discussed in the light of this accumulated knowledge.

Phase equilibria in the system CaO-CoO-SiO2 and Gibbs energies of formation of the quaternary oxides CaCoSi2O6, Ca2CoSi2O7, and CaCoSiO4

Phase relations in the pseudoternary system CaO-CoO-SiO2 have been established at 1323 K. Three quaternary oxides were found to be stable: CaCoSi2O6 with clinopyroxene (Cpx), Ca2CoSi2O7 with melilite (Mel), and CaCoSiO4 with olivine (Ol) structures. The Gibbs energies of formation of the quaternary oxides from their component binary oxides were measured using solid-state galvanic cells incorporating yttria-stabilized zirconia as the solid electrolyte in the temperature range of 1000-1324 K. The results can be summarized as follows: CoO (rs) + CaO (rs) + 2SiO(2) (Qtz) --> CaCoSi2O6 (Cpx), Delta G(f)(0) = -117920 + 11.26T (+/-150) J/mol CoO (rs) + 2CaO (rs) + 2SiO(2) (Qtz) --> Ca2CoSi2O7 (Mel), Delta G(f)(0) = -192690 + 2.38T (+/-130) J/mol CoO (rs) + CaO (rs) + SiO2 (Qtz) --> CaCoSiO2 (Ol), Delta G(f)(0) = -100325 + 2.55T (+/-100) J/mol where rs = rock salt (NaCl) structure and Qtz = quartz. The uncertainty limits correspond to twice the standard error estimate. The experimentally observed miscibility gaps along the joins CaO-CoO and CaCoSiO4-Co2SiO4 were used to calculate the excess free energies of mixing for the solid solutions CaxCo1-xO and (CayCo1-y)CoSiO4:Delta G(E) = X(1 - X)[31975X + 26736 (1 - X)] J/mol and Delta G(E) = 23100 (+/-250) Y(1 - Y) J/mol. A T-X phase diagram for the binary CaO-CoO was computed from the thermodynamic information; the diagram agrees with information available in the literature. The computed miscibility gap along the CaCoSiO4-Co2SiO4 join is associated with a critical temperature of 1389 (+/-15) K. Stability fields for the various solid solutions and the quaternary compounds are depicted on chemical-potential diagrams for SiO2, CaO, and CoO at 1323 K.

Structure of sesbania mosaic virus at 3 å resolution

Background: Sobemoviruses are a group of RNA plant viruses that have a narrow host range. They are characterized in vitro by their stability, high thermal inactivation point and longevity. The three-dimensional structure of only one virus belonging to this group, southern bean mosaic virus (SBMV), is known. Structural studies on sesbania mosaic virus (SMV), which is closely related to SBMV, will provide details of the molecular interactions that are likely to be important in the stability and assembly of sobemoviruses. Results: We have determined the three-dimensional structure of SMV at 3 Angstrom resolution. The polypeptide fold and quaternary organization are very similar to those of SBMV. The capsid consists of sixty icosahedral asymmetric units, each comprising three copies of a chemically identical coat protein subunit, which are designated as A, B and C and are in structurally different environments. Four cation-binding sites have been located in the icosahedral asymmetric unit. Of these, the site at the quasi-threefold axis is not found in SBMV. Structural differences are observed in loops and regions close to this cation-binding site. Preliminary studies on ethylene diamine tetra acetic acid (EDTA) treated crystals suggest asymmetry in removal of the quasi-equivalent cations at the AB, BC, and AC subunit interfaces. Conclusions: Despite the overall similarity between SMV and SBMV in the nature of the polypeptide fold, these viruses show a number of differences in intermolecular interactions. The polar interactions at the quasi-threefold axis are substantially less in SMV and positively charged residues on the RNA-facing side of the protein and in the N-terminal arm are not particularly well conserved. This suggests that protein-RNA interactions are likely to be different between the two viruses.

Quaternary association in beta-prism I fold plant lectins: Insights from X-ray crystallography, modelling and molecular dynamics

Dimeric banana lectin and calsepa, tetrameric artocarpin and octameric heltuba are mannose-specific beta-prism I fold lectins of nearly the same tertiary structure. MD simulations on individual subunits and the oligomers provide insights into the changes in the structure brought about in the protomers on oligomerization, including swapping of the N-terminal stretch in one instance. The regions that undergo changes also tend to exhibit dynamic flexibility during MD simulations. The internal symmetries of individual oligomers are substantially retained during the calculations. Energy minimization and simulations were also carried out on models using all possible oligomers by employing the four different protomers. The unique dimerization pattern observed in calsepa could be traced to unique substitutions in a peptide stretch involved in dimerization. The impossibility of a specific mode of oligomerization involving a particular protomer is often expressed in terms of unacceptable steric contacts or dissociation of the oligomer during simulations. The calculations also led to a rationale for the observation of a heltuba tetramer in solution although the lectin exists as an octamer in the crystal, in addition to providing insights into relations among evolution, oligomerization and ligand binding.

Mesoporous bioactive glass and glass-ceramics: Influence of the local structure on in vitro bioactivity

Mesoporous quaternary bioactive glasses and glass-ceramic with alkali-alkaline-earth oxide were successfully synthesized by using non-ionic block copolymer P123 and evaporation induced self assembly (EISA) process followed by acid treatment assisted sal-gel method. As prepared samples has been characterized for the structural, morphological and textural properties with the various analytical techniques. Glass dissolution/ion release rate in simulated body fluid (SBF) was monitored by inductively coupled plasma (ICP) emission spectroscopy, whereas the formation of apatite phase and its crystallization at the glass and glass-ceramic surface was examined by structural, textural and microscopic probes. The influence of alkaline-earth oxide content on the glass structure followed by textural property has become more evident. The pristine glass samples exhibit a wormhole-like mesoporous structure, whereas the glass-ceramic composition is found to be in three different phases, namely crystalline hydroxyapatite, wollastonite and a residual glassy phase as observed in Cerabone (R) A/W. The existence of calcium orthophosphate phase is closely associated with the pore walls comprising nanometric-sized ``inclusions''. The observed high surface area in conjunction with the structural features provides the possible explanation for experimentally observed enhanced bioactivity through the easy access of ions to the fluid. On the other hand, presence of multiple phases in glass-ceramic sample inhibits or delays the kinetics of apatite formation. (C) 2013 Elsevier Inc. All rights reserved.

Raman signatures of intermediate phase in quaternary Ge15Te80 (-) xIn5Agx glasses

Micro-Raman studies are conducted on as-quenched and annealed Ge15Te80 -_xIn5Agx glasses to probe the structural network and its evolution with composition. These studies reveal the presence of tetrahedral GeTe4 structural units in as-quenched samples. Specific signatures of the intermediate phase (IP) are observed in the composition dependence of Raman frequencies and corresponding intensities of different modes in the composition range, 8 <= x <= 16. In addition, the Raman peak positions are found to shift with silver doping. Apart from the Raman results, the compositional dependence of density, molar volume and thermal diffusivity, observed in the present study, confirms the presence of the intermediate phase. In thermally annealed samples, a unique variation of Raman wave-numbers in the intermediate region is observed due to the retention of some of the local structure even after the sample is crystallized. The observed Raman peaks are attributed to crystalline tellurium and silver lattice vibrational modes. Based on our present and earlier studies, we propose the occurrence of three thresholds in Ge15Te80 - xIn5Agx glasses, namely percolation of rigidity, percolation of stress and the onset of chemical phase separation on a nanoscale at 8%, 16% and 20% of silver concentration respectively. (C) 2014 Elsevier B.V. All rights reserved.

The structure and petrology of the Johnny Lyon Hills area, Cochise County, Arizona

The Johnny Lyon Hills area is located in Cochise County in southeastern Arizona. The rocks of the area include a central core of Lower pre-Cambrian igneous and metamorphic rocks surrounded by a complexly faulted and tilted section of Upper pre-Cambrian and Paleozoic strata. Limited exposures of Mesozoic and Tertiary sedimentary and volcanic rocks are present at the north end of the map area. Late Tertiary and Quaternary alluvium almost completely surrounds and overlaps upon the older rocks.

The older pre-Cambrian rocks include a section of more than 9000 feet of generally moderately metamorphosed graywackes, slates and conglomerates of the Pinal schist injected in zones by somewhat younger rnyolite sheets. The original sediments were deposited in a geosyncline whose extent probably included large parts of Arizona, New Mexico and west Texas. During the Mazatzal Revolution the Pinal schist was deformed into northeast-trending, steeply dipping and plunging structures and the entire local section was overturned steeply toward the northwest. The pre-Cambrian Johnny Lyon granodiorite was emplaced as a large epi-tectonic pluton which modified the metamorphic character of part of the Pinal schist. Larsen method determinations indicate an age of about 715 million years for this rock, which is about the minimum age compatible with the geologic relations.

The Laramide orogeny produced numerous major thrust faults in the area involving all rocks older than and including the Lower Cretaceous Bisbee group. Major compression from the southwest and subsequent superimposed thrusting from the southeast and east are indicated. Minimum thrust displacements of more than a mile are clear and the probable displacements are of much greater magnitude. The crystalline core behaved as a single structural unit and probably caused important local divergences from the regional pattern of northeast-trending compressive forces. The massif was rotated as a unit 40 degrees or more about a northwest-trending axis overturning the pre-Cambrian fold axes in the Pinal schist.

Swarms of Late Cretaceous(?) or Early Tertiary(?) lamprophyric dikes cross the Laramide structures and are probably related to the large Texas Canyon stock several miles southeast of the map area. Intermittent high angle faulting, both older and younger than the dikes, has continued since the Laramide orogeny and has been superimposed on the older structures. This steep faulting combined with the fundamental northwesterly Laramide structural grain to produce the northwesterly trends characteristic of the mountain ridges and valleys of the area.