Study of molecular structure and vibrational spectra of poly (beta,-1-malic acid) PMLA] using DFT approach

Poly (beta-L-malic acid) (PMLA) is a biodegradable polymer and it has various important applications in the biomedical field. In the present work the structural and spectral characteristics of PMLA have been studied by methods of infrared. Raman spectroscopy and quantum chemistry. Electrostatic potential surface, optimized geometry, harmonic vibrational frequencies, infrared intensities and activities of Raman scattering were calculated by density functional theory (DFT) using oligomeric approach employing B3LYP with complete relaxation in the potential energy surface using 6-311++G (d, p) basis set. Based on results, we have discussed the correlation between the vibrational modes and the structure of the PMLA. A complete analysis of the experimental infrared and Raman spectra has been reported on the basis of wavenumber of the vibrational bands and potential energy distribution. The calculated HOMO and LUMO energies shows that charge transfer occur within the molecule. The calculated infrared and the Raman spectra of the polymer based on DFT calculations show reasonable agreement with the experimental results. (c) 2012 Elsevier Ltd. All rights reserved.

Catalytic Asymmetric Synthesis of alpha,beta-Disubstituted alpha,gamma-Diaminophosphonic Acid Precursors by Michael Addition of alpha-Substituted Nitrophosphonates to Nitroolefins

Michael additions of alpha-substituted nitrophosphonates to various nitroolefins are shown to proceed with high diastereo- and enantioselectivity when catalyzed by a quinine-derived thiourea-tertiary amine bifunctional catalyst and generate alpha,gamma-diaminophosphonic acid precursors with contiguous quaternary and tertiary stereocenters.

Kinetics of adsorption of methylene blue and rhodamine 6G on acrylic acid-based superabsorbents

Superabsorbent polymers (SAPs) of acrylic acid, sodium acrylate, and acrylamide (AM), crosslinked with ethylene glycol dimethacrylate, were synthesized by inverse suspension polymerization. The equilibrium swelling capacities of the SAPs were determined and these decreased with increasing AM content. The adsorption of the two cationic dyes, methylene blue and rhodamine 6G, on the dry as well as equilibrium swollen SAPs was investigated. The amount of the dye adsorbed at equilibrium per unit weight of the SAPs and the rate constants of adsorption were determined. The amount of the dye adsorbed at equilibrium by the SAPs decreased with increasing mol % of AM in the SAPs. The amount of the dye adsorbed at equilibrium was almost equal for the dry and equilibrium swollen SAPs. However, the equilibrium swollen SAPs adsorbed dyes at a higher rate than the dry SAPs. The higher rate of adsorption was attributed to the availability of all the anionic groups present in the fully elongated conformation of the SAPs in the equilibrium swollen state. The effect of initial dye concentration on the adsorption was also investigated and the adsorption was described by Langmuir adsorption isotherms. (C) 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Determination of C-13 Chemical Shift Anisotropy Tensors and Molecular Order of 4-Hexyloxybenzoic Acid

4-Alkoxy benzoic acids belong to an important class of thermotropic liquid crystals that are structurally simple and often used as starting materials for many novel mesogens. 4-Hexyloxybenzoic acid (HBA) is a homologue of the same series and exhibits an enantiotropic nematic phase. As this molecule could serve as an ideal model compound, high resolution C-13 NMR studies of HEA in solution, solid, and liquid crystalline phases have been undertaken. In the solid state, two-dimensional separation of undistorted powder patterns by effortless recoupling (2D SUPER) experiments have been carried out to estimate the magnitude of the components of the chemical shift anisotropy (GSA) tensor of all the aromatic carbons. These values have been used subsequently for calculating the orientational order parameters in the liquid crystalline phase. The GSA values computed by density functional theory (DFT) calculations showed good agreement with the 2D SUPER values. Additionally, C-13-H-1 dipolar couplings in the nematic phase have been determined by separated local field (SLF) spectroscopy at various temperatures and were used for computing the order parameters, which compared well with those calculated by using the chemical shifts. It is anticipated that the CSA values determined for MBA would be useful for the assignment of carbon chemical shifts and for the study of order and dynamics of structurally similar novel mesogens in their nematic phases.

Surface Modified CaTiO3 Loaded in Polyaniline by Sodium Dodecyl Benzene Sulphonic Acid for Humidity Sensor

Polyaniline-CaTiO3 nanocomposites with their various weight percentages were prepared by chemical oxidative in situ polymerization technique. The prepared composites were characterized by Fourier transform infrared spectroscopy, scanning electronic microscope, and X-ray diffraction. The temperature-dependent dc conductivity of polyaniline-CaTiO3 nanocomposite was studied within the range of 40-200 degrees C and found that 50 wt% shows high conductivity compared to other composites. Humidity sensor properties of polyaniline-CaTiO3 nanocomposite show better sensing properties and exhibit good linearity in sensing response curve, which discuss the implications of distortions and nonstoichiometry on their physical properties. Among all composites, 50 wt% of polyaniline-CaTiO3 nanocomposites show high sensitivity up to similar to 90% and their response-recovery times are 500 and 453 s, respectively.

The fifth solvatomorph of gallic acid with a supramolecular channel structure: Structural complexity and phase transitions

A new solvatomorph of gallic acid was generated using chiral additive technique and characterized by single crystal and powder X-ray diffraction, C-13 NMR, IR spectroscopic techniques and thermal analysis. The supramolecular channels formed by hexameric motifs of gallic acid and solvent molecules contain highly disordered solvent molecules with fractional occupancies. © 2012 Elsevier B.V.

Structural landscape of benzoic acid: using experimental crystal structures of fluorobenzoic acids as a probe

Experimental crystal structures of mono and polyfluorinated benzoic acids correspond to high energy computed crystal structures of benzoic acid itself, thereby permitting access to its structural landscape.

Conformational Polymorphism in a Non-steroidal Anti-inflammatory Drug, Mefenamic Acid

For several years, the non-steroidal anti-inflammatory drug mefenamic acid, MA, has been known to exist as dimorphs (I and II). We report a new metastable polymorph (III) of MA obtained during attempted co-crystallization experiments and establish its stability relationship with existing forms. At elevated temperatures I and III convert to II, as evident from DSC experiments. On the basis of the lattice energy calculations in conjunction with thermal analysis, the stability order is proposed to be I > II > III at ambient conditions, whereas at elevated temperature the order is II > I > III. In either condition III is a metastable form and hence transforms to I at ambient conditions and to II at higher temperatures. Also we report the structural studies of a DMF solvate and a cytosine complex.

Mixture solubilities of nitrobenzoic acid isomers in supercritical carbon dioxide

The ternary solubilities of solid isomers of nitrobenzoic acid (NBA) were experimentally determined at 308, 318 and 328K over a pressure range of 12-18 MPa in supercritical carbon dioxide (SCCO2). Compared to its binary solubility, the ternary solubilities of m-NBA increased at 308 K while it decreased at 328 K. However, the ternary solubilities of p-NBA increased at all temperatures and pressures except at 13 MPa and 328K. A new model was developed by applying solution model and activity coefficient model for the ternary solubilities of pharmaceutical and non-pharmaceutical solid mixtures in terms of temperature, density and cosolute composition. The model equation involves four temperature independent constraint-free parameters. The model equation correlates the ternary solubilities of seven pharmaceutical solid mixtures along with current data with an average AARD around 9.5% and sixteen non-pharmaceutical solid mixtures with 9% AARD. (C) 2012 Elsevier B.V. All rights reserved.

Charge-transfer interaction mediated organogels from bile acid appended anthracenes: rheological and microscopic studies

In this article we present dual-component charge-transfer interaction (CT) induced organogel formation with bile acid anthracene conjugates as donors and 2,4,7-trinitrofluorenone (TNF) as the acceptor. The use of TNF (1) as a versatile electron acceptor in the formation of gels is demonstrated through the formation of gels with different steroidal groups on the anthracene moiety in a variety of solvents ranging from aromatic hydrocarbons to long chain alcohols. Thermal stability and variable temperature fluorescence experiments were performed on these CT gels. Dynamic rheological experiments conducted on these gels suggest that these are viscoelastic soft materials and with the gel strength can be modulated by varying the donor/acceptor ratios.

Mechanistic Aspects for the Formation of Copper Dimer Bridged by Phosphonic Acid and Extending Its Dimensionality by Organic and Inorganic Linkers: Synthesis, Structural Characterization, Magnetic Properties, and Theoretical Studies

Six new copper metal complexes with formulas Cu(H2O)(2,2'-bpy) (H2L)](2) center dot H4L center dot 4 H2O (1), {Cu(H2O)(2,2'-bpy)-(H3L)}(2)(H2L)]center dot 2H(2)O (2), Cu(H2O)(1,10-phen)(H2L)](2)center dot 6H(2)O (3), Cu(2,2'-bpy)(H2L)](n)center dot nH(2)O (4), Cu(1,10-phen)(H2L)](n)center dot 3nH(2)O (5), and {Cu(2,2'-bpy)(MoO3)}(2)(L)](n)center dot 2nH(2)O (6) have been synthesized starting from p-xylylenediphosphonic acid (H4L) and 2,2'-bipyridine (2,2'-bpy) or 1,10-phenanthroline (1,10-phen) as secondary linkers and characterized by single crystal X-ray diffraction analysis, IR spectroscopy, and thermogravimetric (TG) analysis. All the complexes were synthesized by hydrothermal methods. A dinuclear motif (Cu-dimer) bridged by phosphonic acid represents a new class of simple building unit (SBU) in the construction of coordination architectures in metal phosphonate chemistry. The initial pH of the reaction mixture induced by the secondary linker plays an important role in the formation of the molecular phosphonates 1, 2, and 3. Temperature dependent hydrothermal synthesis of the compounds 1, 2, and 3 reveals the mechanism of the self assembly of the compounds based on the solubility of the phosphonic acid H4L. Two-dimensional coordination polymers 4, 5, and 6, which are formed by increasing the pH of the reaction mixture, comprise Cu-dimers as nodes, organic (H2L) and inorganic (Mo4O12) ligands as linkers. The void space-areas, created by the (4,4) connected nets in compounds 4 and 5, are occupied by lattice water molecules. Thus compounds 4 and 5 have the potential to accommodate guest species/molecules. Variable temperature magnetic studies of the compounds 3, 4, 5, and 6 reveal the antiferromagnetic interactions between the two Cu(II) ions in the eight membered ring, observed in their crystal structures. A density functional theory (DFT) calculation correlates the conformation of the Cu-dimer ring with the magnitude of the exchange parameter based on the torsion angle of the conformation.

Synthesis and supramolecular assembly of the bifunctional borinic acid 1,2-fcB(OH)](2)

Treatment of the chloro-substituted diboradiferrocene derivative 1 with Me3SiOMe and subsequent hydrolysis resulted in formation of the novel organometallic bis(borinic acid) derivative 3. The assembly of 3 into supramolecular structures via hydrogen bonding and reversible covalent boron-oxygen bond formation was explored. Upon crystallization from acetone or THF one-dimensional chains form in which molecules of 3 alternately serve as hydrogen bond donors and acceptors. The additional OH hydrogens that are not involved in hydrogen bonding within the polymeric chains undergo hydrogen bonding to the solvent molecules. Removal of the solvent was achieved at moderate temperature under high vacuum. While the polymeric chains remain intact, in the absence of the solvent as a hydrogen bond acceptor, short contacts to the Cp rings of neighboring polymer strands lead to a network-like structure. At higher temperatures, further dehydration occurs with formation of B-O-B linkages as confirmed by MALDI-TOF mass spectrometry. Oligomers with up to 15 repeating units (30 ferrocenes) were detected.

The Structural Characterization of Folded Peptides Containing the Conformationally Constrained beta-Amino Acid Residue beta(2,2)Ac(6)c

Backbone alkylation has been shown to result in a dramatic reduction in the conformational space that is sterically accessible to a-amino acid residues in peptides. By extension, the presence of geminal dialkyl substituents at backbone atoms also restricts available conformational space for beta and ? residues. Five peptides containing the achiral beta 2,2-disubstituted beta-amino acid residue, 1-(aminomethyl)cyclohexanecarboxylic acid (beta 2,2Ac6c), have been structurally characterized in crystals by X-ray diffraction. The tripeptide Boc-Aib-beta 2,2Ac6c-Aib-OMe (1) adopts a novel fold stabilized by two intramolecular H-bonds (C11 and C9) of opposite directionality. The tetrapeptide Boc-Aib-beta 2,2Ac6c]2-OMe (2) and pentapeptide Boc-Aib-beta 2,2Ac6c]2-Aib-OMe (3) form short stretches of a hybrid a beta C11 helix stabilized by two and three intramolecular H-bonds, respectively. The structure of the dipeptide Boc-Aib-beta 2,2Ac6c-OMe (5) does not reveal any intramolecular H-bond. The aggregation pattern in the crystal provides an example of an extended conformation of the beta 2,2Ac6c residue, forming a polar sheet like H-bond. The protected derivative Ac-beta 2,2Ac6c-NHMe (4) adopts a locally folded gauche conformation about the C beta?Ca bonds (?=-55.7 degrees). Of the seven examples of beta 2,2Ac6c residues reported here, six adopt gauche conformations, a feature which promotes local folding when incorporated into peptides. A comparison between the conformational properties of beta 2,2Ac6c and beta 3,3Ac6c residues, in peptides, is presented. Backbone torsional parameters of H-bonded a beta/beta a turns are derived from the structures presented in this study and earlier reports.

Charge Density Analysis of Ferulic Acid: Robustness of a Trifurcated C-H center dot center dot center dot O Hydrogen Bond

The toplogical features of a sporadic trifurcated C-H center dot center dot center dot O interaction region, where an oxygen atom acts as an acceptor of three weak hydrogen bonds, has been investigated by experimental and theoretical charge density analysis of ferulic acid. The interaction energy of the asymmetric molecular dimer formed by the trifurcated C-H center dot center dot center dot O motif, based on the multipolar model, is shown to be greater than the corresponding asymmetric O-H center dot center dot center dot O dimer in this crystal structure. Further, the hydrogen bond energies associated with these interaction motifs have been estimated from the local kinetic and potential energy densities at the bond critical points. The trends suggest that the interaction energy of the trifurcated C-H center dot center dot center dot O region is comparable to that of a single O-H center dot center dot center dot O hydrogen bond.