Synthesis and Molecular Structures of Carboxylic Acid Group Bearing Two Ketoimines that Exist in Enaminone Form

Condensation reaction involving substituted aminobenzoic acids (2-aminobenzoic acid and 4-aminobenzoic acid) and acetylacetone results in the formation of ketoimines [CH3C(= O)CH2C(CH3)(= NAr)] (Ar = C6H4COOH-4; 1 and C6H4COOH-2 2). Compounds 1 and 2 have been characterized by spectroscopic techniques and by single crystal X-ray diffraction studies. The absorption, emission and lifetime measurement studies have also been performed for the new compounds. While compound 1 forms a linear chain type of aggregation though intermolecular hydrogen bonding, compound 2 forms a discrete dimer in the solid state.

Synthesis and characterization of cobalt(II), nickel(II), copper(II) and zinc(II) complexes of 2-nitrobenzoic acid with methyl carbazate as ancillary ligand. Crystal structure of the copper(II) complex

Divalent metal complexes of general formula M(2-nb)(2)(mc)(2)].2(2-nbH), where M = Co(II), Ni(II), Cu(II) or Zn(II), 2-nbH = 2-nitrobenzoic acid and mc = methyl carbazate (NH2NHCOOCH3), have been prepared and characterized by physicochemical and spectroscopic methods. Single-crystal X-ray study of the Cu(II) complex revealed that the molecule is centrosymmetric, with two N,O-chelating mc ligands in equatorial positions and a pair of monodentate 2-nb anions in the axial positions. The lattice 2-nbH molecules help to establish the packing of monomers through hydrogen-bonding interactions. Thermal stability and reactivity of the complexes were studied by TG-DTA. Emission studies show that these complexes are fluorescent.

Probing acid-amide intermolecular hydrogen bonding by NMR spectroscopy and DFT calculations

Benzene carboxylic acids and Benzamide act as their self-complement in molecular recognition to form inter-molecular hydrogen bonded dimers between amide and carboxylic acid groups, which have been investigated by H-1, C-13 and N-15 NMR spectroscopy. Extensive NMR studies using diffusion ordered spectroscopy (DOSY), variable temperature 1D, 2D NMR, established the formation of heterodimers of benzamide with benzoic acid, salicylic acid and phenyl acetic acid in deuterated chloroform solution. Association constants for the complex formation in the solution state have been determined. The results are ascertained by X-ray diffraction in the solid state. Intermolecular interactions in solution and in solid state were found to be similar. The structural parameters obtained by X-ray diffraction studies are compared with those obtained by DFT calculations. (C) 2012 Elsevier B.V. All rights reserved.

Raman spectroscopic characterization of different regioisomers of monoacyl and diacyl chlorogenic acid

We have investigated the Raman spectra of different regioisomeric forms of monoacyl and diacyl chlorogenic acids. Raman spectra of 3-caffeoylquinic acid, 4-caffeoylquinic acid, 5-caffeoylquinic, 3,4-di-O-caffeoylquinic acid, 3,5-di-O-caffeoylquinic acid, 4,5-di-O-caffeoylquinic acid, and a synthetic derivative of 3-feruloylqunic acid were recorded using visible Raman spectroscopic technique and vibrational bands are assigned. Additionally, a theoretical study of 5-caffeoylquinic acid was performed using Gaussian 03. (C) 2012 Elsevier B.V. All rights reserved.

Distinct mechanisms of DNA repair in mycobacteria and their implications in attenuation of the pathogen growth

About a third of the human population is estimated to be infected with Mycobacterium tuberculosis. Emergence of drug resistant strains and the protracted treatment strategies have compelled the scientific community to identify newer drug targets, and to develop newer vaccines. In the host macrophages, the bacterium survives within an environment rich in reactive nitrogen and oxygen species capable of damaging its genome. Therefore, for its successful persistence in the host, the pathogen must need robust DNA repair mechanisms. Analysis of M. tuberculosis genome sequence revealed that it lacks mismatch repair pathway suggesting a greater role for other DNA repair pathways such as the nucleotide excision repair, and base excision repair pathways. In this article, we summarize the outcome of research involving these two repair pathways in mycobacteria focusing primarily on our own efforts. Our findings, using Mycobacterium smegmatis model, suggest that deficiency of various DNA repair functions in single or in combinations severely compromises their DNA repair capacity and attenuates their growth under conditions typically encountered in macrophages. (C) 2011 Elsevier Ireland Ltd. All rights reserved.

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.

Crystal Structures and Physicochemical Properties of Four New Lamotrigine Multicomponent Forms

In the present study, four new multicomponent forms of lamotrigine (LTG) with selected carboxylic acids, viz. acetic acid, propionic acid, sorbic acid, and glutaric acid, have been identified. Preliminary solid-state characterization was done by differential scanning calorimetry/thermogravimetric, infrared, and powder X-ray diffraction techniques. X-ray single-crystal structure analysis confirmed the proton transfer, stoichiometry, and the molecular composition, revealing all of these to be a new salt/salt-cocrystal/salt monosolvate monohydrate of LTG. All four compounds exhibited both the aminopyridine dimer of LTG (motif 4) and cation-anion dimers between protonated LTG and the carboxylate anion in their crystal structures. Further, these new crystal forms were subjected to solubility studies in water, powder dissolution studies in 0.1 N HCl, and stability studies under humid conditions in comparison with pure LTG base. The solubility of these compounds in water is significantly enhanced compared with that of pure base, which is attributed to the type of packing motifs present in their crystal structures as well as to the lowering of the pH by the acidic coformers. Solid residues of all forms remaining after solubility and dissolution experiments were also assessed for any transformation in water and acidic medium.

Advances in base- and mobile-station aided cooperative wireless communications : An overview

In recent years, there has been an upsurge of research interest in cooperative wireless communications in both academia and industry. This article presents a simple overview of the pivotal topics in both mobile station (MS)- and base station (BS)- assisted cooperation in the context of cellular radio systems. Owing to the ever-increasing amount of literature in this particular field, this article is by no means exhaustive, but is intended to serve as a roadmap by assembling a representative sample of recent results and to stimulate further research. The emphasis is initially on relay-base cooperation, relying on network coding, followed by the design of cross-layer cooperative protocols conceived for MS cooperation and the concept of coalition network element (CNE)-assisted BS cooperation. Then, a range of complexity and backhaul traffic reduction techniques that have been proposed for BS cooperation are reviewed. A more detailed discussion is provided in the context of MS cooperation concerning the pros and cons of dispensing with high-complexity, power-hungry channel estimation. Finally, generalized design guidelines, conceived for cooperative wireless communications, are presented.

Ternary ion-pair complexation: a protocol for chiral discrimination and the assignment of absolute configuration of chiral hydroxy acids

The study demonstrates the utility of ternary ion-pair complex formed among BINOL (1,1'-Bi-2-naphthol), a carboxylic acid and an organic base, such as, dimethylpyridine (DMAP), 1,4-diazabicyclo2.2.2]octane (DABCO), as a versatile chiral solvating agent (CSA) for the enantiodiscrimination of carboxylic acids, measurement of enantiomeric excess (ee) and the assignment of absolute configuration of hydroxy acids. The proposed mechanism of ternary complex has wider application for testing the enantiopurity owing to the fact that the binary mixture using BINOL alone does not serve as a solvating agent for their discrimination. In addition, the developed protocol has an excellent utility for the assignment of the absolute configurations of hydroxy acids.

Sr2+ and Cd2+ coordination polymers: the effect of the different coordinating behaviour of a newly designed tricarboxylic acid

This article presents the investigation of the coordination behavior of a newly synthesized tricarboxylate ligand, obtained by joining imidazole dicarboxylic acid and 4-carboxybenzyl moieties cbimdaH(3), 1-(4-carboxybenzyl)-1H-imidazole-4,5-dicarboxylic acid]. Two novel coordination polymers were obtained through solvothermal reactions under similar conditions namely Sr(cbimdaH)(H2O)](n) (1) and Cd-2(cbimdaH)(2)(H2O)(6)](n)center dot(DMF)(3n)(H2O)(3n) (2), with the ligand behaving as a dianionic tricarboxylate linker. The single crystal X-ray structures show that while 1 forms a 3D coordination polymer, 2 forms a 1D polymer which is further assembled in three dimensions through supramolecular interactions (H-bonding). Complex 1 consists of Sr2+ ions in a distorted dodecahedral coordination geometry, while 2 consists of Cd2+ ions in distorted pentagonal bipyramidal geometries. A topology study reveals that 1 has a new topology based on the 5,6-coordinated 3D net architecture. The luminescence properties of the complexes in the solid state and their thermal stabilities were studied.

Amide Functionalized Microporous Organic Polymer (Am-MOP) for Selective CO2 Sorption and Catalysis

We report the design and synthesis of an amide functionalized microporous organic polymer (Am-MOP) prepared from trimesic acid and p-phenylenediamine using thionyl chloride as a reagent. Polar amide (CONH) functional groups act as a linking unit between the node and spacer and constitute the pore wall of the continuous polymeric network. The strong covalent bonds between the building blocks (trimesic acid and p-phenylenediamine) through amide bond linkages provide high thermal and chemical stability to Am-MOP. The presence of a highly polar pore surface allows selective CO2 uptake at 195 K over other gases such as N-2, Ar, and O-2. The CO2 molecule interacts with amide functional groups via Lewis acid base type interactions as demonstrated through DFT calculations. Furthermore, for the first time Am-MOP with basic functional groups has been exploited for the Knoevenagel condensation reaction between aldehydes and active methylene compounds. Availability of a large number of catalytic sites per volume and confined microporosity gives enhanced catalytic efficiency and high selectivity for small substrate molecules.

Using heat treatment effects and EBSD analysis to tailor microstructure of hybrid Mg nanocomposite for enhanced overall mechanical response

In this study, a detailed investigation on the effect of heat treatment on the microstructural characteristics, texture evolution and mechanical properties of Mg-(5.6Ti+2.5B(4)C)(BM) hybrid nanocomposite is presented. Optimised heat treatment parameters, namely, heat treatment temperature and heat treatment time, were first identified through grain size and microhardness measurements. Initially, heat treatment of composites was conducted at temperature range between 100 and 300 degrees C for 1 h. Based on optical microscopic analysis and microhardness measurements, it was evident that significant grain growth and reduction in microhardness occurred for temperatures > 200 degrees C. The cutoff temperature that caused significant grain growth/matrix softening was thus identified. Second, at constant temperature (200 degrees C), the effect of variation of heat treatment time was carried out (ranging between 1 and 5 h) so as to identify the range wherein increase in average grain size and reduction in microhardness occurred. Furthering the study, the effect of optimised heat treatment parameters (200 degrees C, 5 h) on the microstructural texture evolution and hence, on the tensile and compressive properties of the Mg-(5.6Ti+2.5B(4)C)(BM) hybrid nanocomposite was carried out. From electron backscattered diffraction (EBSD) analysis, it was identified that the optimised heat treatment resulted in recrystallisation and residual stress relaxation, as evident from the presence of similar to 87% strain free grains, when compared to that observed in the non-heat treated/as extruded condition (i.e. 2.2 times greater than in the as extruded condition). For the heat treated composite, under both tensile and compressive loads, a significant improvement in fracture strain values (similar to 60% increase) was observed when compared to that of the non-heat treated counterpart, with similar to 20% reduction in yield strength. Based on structure-property correlation, the change in mechanical characteristics is identified to be due to: (1) the presence of less stressed matrix/reinforcement interface due to the relief of residual stresses and (2) texture weakening due to matrix recrystallisation effects, both arising due to heat treatment.

Boron and Nitrogen Co-doped Carbon Nanoparticles as Photoluminescent Probes for Selective and Sensitive Detection of Picric Acid

Here, we report the synthesis of boron and nitrogen Co-doped carbon nanoparticles (BN-CNPs) by a hydrothermal method using sucrose, boric acid, and urea as the precursors. The BN-CNPs show excellent photoluminescence with a quantum yield of similar to 14.2% in aqueous solution and can be used as photoluminescent probes for selective and sensitive detection of picric acid (PA). PA quenches the photoluminescence signal remarkably, while other explosives cause a little quenching confirming the high selectivity of BN-CNPs. The sensitivity toward PA sensing is high at pH 7 and increases with temperature. The detection limit as well as the sensitivity are shown to improve by adding NaCl to the PA. The low detection limit can be as low as 10 nM at room temperature and pH 7, which indicates the BN-CNPs are superior as compared to other luminescent probes reported in the literature.

Physical insights into salicylic acid release from poly(anhydrides)

Salicylic acid (SA) based biodegradable polyanhydrides (PAHs) are of great interest for drug delivery in a variety of diseases and disorders owing to the multi-utility of SA. There is a need for the design of SA-based PAHs for tunable drug release, optimized for the treatment of different diseases. In this study, we devised a simple strategy for tuning the release properties and erosion kinetics of a family of PAHs. PAHs incorporating SA were derived from related aliphatic diacids, varying only in the chain length, and prepared by simple melt condensation polymerization. Upon hydrolysis induced erosion, the polymer degrades into cytocompatible products, including the incorporated bioactive SA and diacid. The degradation follows first order kinetics with the rate constant varying by nearly 25 times between the PAH obtained with adipic acid and that with dodecanedioic acid. The release profiles have been tailored from 100% to 50% SA release in 7 days across the different PAHs. The release rate constants of these semi-crystalline, surface eroding PAHs decreased almost linearly with an increase in the diacid chain length, and varied by nearly 40 times between adipic acid and dodecanedioic acid PAH. The degradation products with SA concentration in the range of 30-350 ppm were used to assess cytocompatibility and showed no cytotoxicity to HeLa cells. This particular strategy is expected to (a) enable synthesis of application specific PAHs with tunable erosion and release profiles; (b) encompass a large number of drugs that may be incorporated into the PAH matrix. Such a strategy can potentially be extended to the controlled release of other drugs that may be incorporated into the PAH backbone and has important implications for the rational design of drug eluting bioactive polymers.