Structural, thermal and quantum chemical studies of p-coumaric and caffeic acids

Two hydroxycinnamic acids viz., p-coumaric, and caffeic acids have been extracted and purified from Parthenium hysterophorus, subsequently characterized by elemental analysis, FT-IR, NMR, single crystal X-ray crystallography. The optimized structures of these acids were calculated in terms of density functional theory by Gaussian 09. The validation of experimental and theoretically obtained data for structural parameters such as bond lengths and bond angles has have been carried out to analyze the statistical significance by curve fitting analysis and the values of correlation coefficient found to be 0.985, 0.992, and 0.984, 0.975 in p-coumaric, and caffeic acids, respectively. The calculated HOMO and LUMO energies show the eventual charge transfer interaction within the molecule. Thermal studies were also carried out by thermogravimetry (TG), differential thermogravimetric analysis (DTA), and derivative thermogravimetry (DTG). (C) 2014 Elsevier B.V. All rights reserved.

Structural studies on Mycobacterium tuberculosis RecA: Molecular plasticity and interspecies variability

Structures of crystals of Mycobacterium tuberculosis RecA, grown and analysed under different conditions, provide insights into hitherto underappreciated details of molecular structure and plasticity. In particular, they yield information on the invariant and variable features of the geometry of the P-loop, whose binding to ATP is central for all the biochemical activities of RecA. The strengths of interaction of the ligands with the P-loop reveal significant differences. This in turn affects the magnitude of the motion of the `switch' residue, Gln195 in M. tuberculosis RecA, which triggers the transmission of ATP-mediated allosteric information to the DNA binding region. M. tuberculosis RecA is substantially rigid compared with its counterparts from M smegmatis and E. coli, which exhibit concerted internal molecular mobility. The interspecies variability in the plasticity of the two mycobacterial proteins is particularly surprising as they have similar sequence and 3D structure. Details of the interactions of ligands with the protein, characterized in the structures reported here, could be useful for design of inhibitors against M. tuberculosis RecA.

Structural and functional analysis of two universal stress proteins YdaA and YnaF from Salmonella typhimurium: possible roles in microbial stress tolerance

In many organisms ``Universal Stress Proteins'' CUSPS) are induced in response to a variety of environmental stresses. Here we report the structures of two USPs, YnaF and YdaA from Salmonella typhimurium determined at 1.8 angstrom and 2.4 angstrom resolutions, respectively. YnaF consists of a single USP domain and forms a tetrameric organization stabilized by interactions mediated through chloride ions. YdaA is a larger protein consisting of two tandem USP domains. Two protomers of YdaA associate to form a structure similar to the YnaF tetramer. YdaA showed ATPase activity and an ATP binding motif G-2X-G-9X-G(S/T/N) was found in its C-terminal domain. The residues corresponding to this motif were not conserved in YnaF although YnaF could bind ATP. However, unlike YdaA, YnaF did not hydrolyse ATP in vitro. Disruption of interactions mediated through chloride ions by selected mutations converted YnaF into an ATPase. Residues that might be important for ATP hydrolysis could be identified by comparing the active sites of native and mutant structures. Only the C-terminal domain of YdaA appears to be involved in ATP hydrolysis. The structurally similar N-terminal domain was found to bind a zinc ion near the segment equivalent to the phosphate binding loop of the C-terminal domain. Mass spectrometric analysis showed that YdaA might bind a ligand of approximate molecular weight 800 daltons. Structural comparisons suggest that the ligand, probably related to an intermediate in lipid A biosynthesis, might bind at a site close to the zinc ion. Therefore, the N-terminal domain of YdaA binds zinc and might play a role in lipid metabolism. Thus, USPs appear to perform several distinct functions such as ATP hydrolysis, altering membrane properties and chloride sensing. (C) 2015 Elsevier Inc. All rights reserved.

A Gaussian network model study suggests that structural fluctuations are higher for inactive states than active states of protein kinases

We performed Gaussian network model based normal mode analysis of 3-dimensional structures of multiple active and inactive forms of protein kinases. In 14 different kinases, a more number of residues (1095) show higher structural fluctuations in inactive states than those in active states (525), suggesting that, in general, mobility of inactive states is higher than active states. This statistically significant difference is consistent with higher crystallographic B-factors and conformational energies for inactive than active states, suggesting lower stability of inactive forms. Only a small number of inactive conformations with the DFG motif in the ``in'' state were found to have fluctuation magnitudes comparable to the active conformation. Therefore our study reports for the first time, intrinsic higher structural fluctuation for almost all inactive conformations compared to the active forms. Regions with higher fluctuations in the inactive states are often localized to the aC-helix, aG-helix and activation loop which are involved in the regulation and/or in structural transitions between active and inactive states. Further analysis of 476 kinase structures involved in interactions with another domain/protein showed that many of the regions with higher inactive-state fluctuation correspond to contact interfaces. We also performed extensive GNM analysis of (i) insulin receptor kinase bound to another protein and (ii) holo and apo forms of active and inactive conformations followed by multi-factor analysis of variance. We conclude that binding of small molecules or other domains/proteins reduce the extent of fluctuation irrespective of active or inactive forms. Finally, we show that the perceived fluctuations serve as a useful input to predict the functional state of a kinase.

Importance of structural distortions in enhancement of transition temperature in FeSe1-xTex superconductors

Temperature (12 K <= T <= 300 K) dependent extended x-ray absorption fine structure (EXAFS) studies at the Fe K edge in FeSe1-xTex (x = 0, 0.5 and 1.0) compounds have been carried out to understand the reasons for the increase in T-C upon Te doping in FeSe. While local distortions are present near superconducting onset in FeSe and FeSe0.5Te0.5, they seem to be absent in non superconducting FeTe. Of crucial importance is the variation of anion height. In FeSe0.5Te0.5, near the superconducting onset, the two heights, h(Fe-Se) and h(Fe-Te) show a nearly opposite behaviour. These changes indicate a possible correlation between Fe-chalcogen hybridization and the superconducting transition temperature in these Fe-chalcogenides.

Hybrid Elements for Modelling Squeeze Film Effects Coupled with Structural Interactions in Vibratory MEMS Devices

We present a hybrid finite element based methodology to solve the coupled fluid structure problem of squeeze film effects in vibratory MEMS devices, such as gyroscopes, RF switches, and 2D resonators. The aforementioned devices often have a thin plate like structure vibrating normally to a fixed substrate, and are generally not perfectly vacuum packed. This results in a thin air film being trapped between the vibrating plate and the fixed substrate which behaves like a squeeze film offering both stiffness and damping. For accurate modelling of such devices the squeeze film effects must be incorporated. Extensive literature is available on squeeze film modelling, however only a few studies address the coupled fluid elasticity problem. The majority of the studies that account for the plate elasticity coupled with the fluid equation, either use approximate mode shapes for the plate or use iterative solution strategies. In an earlier work we presented a single step coupled methodology using only one type of displacement based element to solve the coupled problem. The displacement based finite element models suffer from locking issues when it comes to modelling very thin structures with the lateral dimensions much larger than the plate thickness as is typical in MEMS devices with squeeze film effects. In this work we present another coupled formulation where we have used hybrid elements to model the structural domain. The numerical results show a huge improvement in convergence and accuracy with coarse hybrid mesh as compared to displacement based formulations. We further compare our numerical results with experimental data from literature and find them to be in good accordance.

Eu3+-activated SrMoO4 phosphors for white LEDs applications: Synthesis and structural characterization

We report the synthesis of Eu3+-activated SrMoO4 phosphors by the facile nitrate-citrate gel combustion method. Powder XRD and Rietveld refinement data confirmed that these phosphors have a monophasic scheelite-type tetragonal structure with space group I4(1)/a (No. 88). FESEM micrographs indicate the agglomerated spherical particles. FTIR spectra showed four stretching and bending vibrational modes (2A(u) and 2E(u)). UV-Visible absorption spectroscopy illustrated that the optical band gap energy (E-g) values increase with increase in Eu3+ concentration. The host SrMoO4 phosphor exhibited an intense blue emission under UV excitation (368 nm). The Eu3+-activated SrMoO4 phosphors revealed characteristic luminescence due to Eu3+ ion corresponding to D-5(1) -> F-7(J) (J = 1,2) and D-5(0) -> F-7(J) (J = 1,2,3,4) transitions upon 465 nm excitation. The electric dipole transition located at 615 nm (D-5(0) -> F-7(2)) was stronger than the magnetic dipole transition located at 592 nm (D-5(0) -> F-7(1)). Intensity parameters (Omega(2), Omega(4)) and radiative properties such as transition probabilities (A(T)), radiative lifetime (tau(rad)) and branching ratio (beta) of Eu3+-activated SrMoO4 phosphors were calculated using the Judd-Ofelt theory. Based on the CIE chromaticity diagram, these phosphors can be promising materials for the development of blue and orange-red component in white LEDs. (C) 2015 Elsevier B.V. All rights reserved.

Structural variations in aromatic 2 pi-electron three-membered rings of the main group elements

Structural variations of different Z pi-aromatic three-membered ring systems of main group elements, especially group 14 and 13 elements as compared to the classical description of cyclopropenyl cation has been reviewed in this article. The structures of heavier analogues as well as group 13 analogues of cyclopropenyl cation showed an emergence of dramatic structural patterns which do not conform, to the general norms of carbon chemistry. Isolobal analogies between the main group fragments have been efficiently used to explain the peculiarities observed in these three-membered ring systems.

First principles study of structural stability and site preference in Co-3 (W,X)

Since the discovery 1] of gamma' precipitate (L1(2) - Co-3 (Al, W)) in the Co-Al-W ternary system, there has been an increased interest in Co-based superalloys. Since these alloys have two phase microstructures (gamma + gamma') similar to Ni-based superalloys 2], they are viable candidates in high temperature applications, particularly in land-based turbines. The role of alloying on stability of the gamma' phase has been an active area of research. In this study, electronic structure calculations were done to probe the effect of alloying in Co3W with L1(2) structure. Compositions of type Co-3(W, X), (where X/Y = Mn, Fe, Ni, Pt, Cr, Al, Si, V, W, Ta, Ti, Nb, Hf, Zr and Mo) were studied. Effect of alloying on equilibrium lattice parameters and ground state energies was used to calculate Vegard's coefficients and site preference related data. The effect of alloying on the stability of the L1(2) structure vis a vis other geometrically close packed ordered structures was also studied for a range of Co3X compounds. Results suggest that the penchant of element for the W sublattice can be predicted by comparing heats of formation of Co3X in different structures.

Metallophosphoesterases: structural fidelity with functional promiscuity

Calcineurin-like metallophosphoesterases (MPEs) form a large superfamily of binuclear metal-ion-centre-containing enzymes that hydrolyse phosphomono-, phosphodi-or phosphotri-esters in a metal-dependent manner. The MPE domain is found in Mre11/SbcD DNA-repair enzymes, mammalian phosphoprotein phosphatases, acid sphingomyelinases, purple acid phosphatases, nucleotidases and bacterial cyclic nucleotide phosphodiesterases. Despite this functional diversity, MPEs show a remarkably similar structural fold and active-site architecture. In the present review, we summarize the available structural, biochemical and functional information on these proteins. We also describe how diversification and specialization of the core MPE fold in various MPEs is achieved by amino acid substitution in their active sites, metal ions and regulatory effects of accessory domains. Finally, we discuss emerging roles of these proteins as non-catalytic protein-interaction scaffolds. Thus we view the MPE superfamily as a set of proteins with a highly conserved structural core that allows embellishment to result in dramatic and niche-specific diversification of function.

Structural and Magnetic Phase Transformations of Hydroxyapatite-Magnetite Composites under Inert and Ambient Sintering Atmospheres

The present work reports the impact of sintering conditions on the phase stability in hydroxyapatite (HA) magnetite (Fe3O4) bulk composites, which were densified using either pressureless sintering in air or by rapid densification via hot pressing in inert atmosphere. In particular, the phase abundances, structural and magnetic properties of the (1-x)HA-xFe(3)O(4) (x = 5, 10, 20, and 40 wt %) composites were quantified by corroborating results obtained from Rietveld refinement of the X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Mossbauer spectroscopy. Post heat treatment phase analysis revealed a major retention of Fe3O4 in argon atmosphere, while it was partially/completely oxidized to hematite (alpha-Fe2O3) in air. Mossbauer results suggest the high-temperature diffusion of Fe3+ into hydroxyapatite lattice, leading to the formation of Fe-doped HA. A preferential occupancy of Fe3+ at the Ca(1) and Ca(2) sites under hot-pressing and conventional sintering conditions, respectively, was observed. The lattice expansion in HA from Rietveld analysis correlated well with the amounts of Fe-doped HA determined from the Mossbauer spectra. Furthermore, hydroxyapatite in the monoliths and composites was delineated to exist in the monoclinic (P2(1)/b) structure as against the widely reported hexagonal (P6(3)/m) crystal lattice. The compositional similarity of iron doping in hydroxyapatite to that of tooth enamel and bone presents HA-Fe3O4 composites as potential orthopedic and dental implant materials.

Doping effect of Ag+, Mn2+ ions on Structural and Optical Properties of ZnO nanoparticles

Pure ZnO and co-doped (Mn, Ag) ZnO nanoparticles have been successfully prepared by chemical co-precipitation method without using a capping agent. X-ray diffraction (XRD) studies confirms the presence of wurtzite (hexagonal) crystal structure similar to undoped ZnO, suggesting that doped Mn, Ag ions are substituted to the regular Zn sites. The morphology of the samples were studied by scanning electron microscopy (SEM). The chemical composition of pure and co-doped ZnO nanoparticles were characterized by energy dispersive X-ray analysis spectroscopy (EDAX). Optical absorption properties were determined by UV-vis Diffuse Reflectance Spectrophotometer. The incorporation of Ag+, Mn2+ in the place of Zn2+ provoked to decrease the size of nanocrystals as compared to pure ZnO. Optical absorption measurements indicates blue shift in the absorption band edge upon Ag, Mn ions doped ZnO nanoparticles.

Structural and magnetic properties of Dy3+ doped Y3Fe5O12 for microwave devices

The Dy3+ doped Y3-xDyxFe5O12 (x=0-3) nanopowders were prepared using microwave hydrothermal route. The structural and morphological studies were analyzed using transmission electron microscope, X-ray diffractometer and field emission scanning electron microscope. The nanopowders were sintered at 900 degrees C/90 min using microwave furnace. Dense ceramics with theoretical density of around 95% was obtained. Ferro magnetic resonance (FMR) spectrum and microwave absorption spectrum of Dy3+ doped YIG were studied, the signal exhibits a resonance character for all Dy3+ variations. It was observed that the location of the FMR signal peak at the field axes monotonically shifts to higher field with increasing Dy3+ content. The dielectric and magnetic properties (epsilon', epsilon `', mu' and mu `') of Dy3+ doped YIG were studied over a wide range of frequency (1-50 GHz). With increase of Dy3+ both epsilon' and mu' decreased. The low values of dielectric, magnetic properties and broad distribution of FMR line width of these ceramics are opening the real opportunity to use them for microwave devices above K- band frequency. (C) 2015 Elsevier Ltd. All rights reserved.

Cyclic nucleotide binding and structural changes in the isolated GAF domain of Anabaena adenylyl cyclase, CyaB2

GAF domains are a large family of regulatory domains, and a subset are found associated with enzymes involved in cyclic nucleotide (cNMP) metabolism such as adenylyl cyclases and phosphodiesterases. CyaB2, an adenylyl cyclase from Anabaena, contains two GAF domains in tandem at the N-terminus and an adenylyl cyclase domain at the C-terminus. Cyclic AMP, but not cGMP, binding to the GAF domains of CyaB2 increases the activity of the cyclase domain leading to enhanced synthesis of cAMP. Here we show that the isolated GAFb domain of CyaB2 can bind both cAMP and cGMP, and enhanced specificity for cAMP is observed only when both the GAFa and the GAFb domains are present in tandem(GAFab domain). In silico docking and mutational analysis identified distinct residues important for interaction with either cAMP or cGMP in the GAFb domain. Structural changes associated with ligand binding to the GAF domains could not be detected by bioluminescence resonance energy transfer (BRET) experiments. However, amide hydrogen-deuterium exchange mass spectrometry (HDXMS) experiments provided insights into the structural basis for cAMP-induced allosteric regulation of the GAF domains, and differences in the changes induced by cAMP and cGMP binding to the GAF domain. Thus, our findings could allow the development of molecules that modulate the allosteric regulation by GAF domains present in pharmacologically relevant proteins.

Structural basis for the catalytic mechanism of homoserine dehydrogenase

Homoserine dehydrogenase (HSD) is an oxidoreductase in the aspartic acid pathway. This enzyme coordinates a critical branch point of the metabolic pathway that leads to the synthesis of bacterial cell-wall components such as L-lysine and m-DAP in addition to other amino acids such as L-threonine, L-methionine and L-isoleucine. Here, a structural rationale for the hydride-transfer step in the reaction mechanism of HSD is reported. The structure of Staphylococcus aureus HSD was determined at different pH conditions to understand the basis for the enhanced enzymatic activity at basic pH. An analysis of the crystal structure revealed that Lys105, which is located at the interface of the catalytic and cofactor-binding sites, could mediate the hydride-transfer step of the reaction mechanism. The role of Lys105 was subsequently confirmed by mutational analysis. Put together, these studies reveal the role of conserved water molecules and a lysine residue in hydride transfer between the substrate and the cofactor.