Synthesis, growth and characterization of bis (glycine) lithium molybdate—A semi-organic NLO material

Single crystals of bis (glycine) lithium molybdate [BGLM] with dimensions 20 mm × 10 mm × 5 mm were grown by slow evaporation technique. The grown crystals were subjected to powder X-ray diffraction studies. Functional groups of the crystallized molecules were confirmed by FTIR analyses. Transmission range of the crystal was determined by UV–vis–NIR spectra. Vickers microhardness test was performed on the prominent plane (0 1 1) of the grown crystal. The NLO property of the crystal was confirmed by Kurtz SHG test and compared with NLO efficiency of KDP crystal.     

High-resolution terahertz spectroscopy of crystalline trialanine: extreme sensitivity to beta-sheet structure and cocrystallized water

High-resolution terahertz absorption spectra (0.06-3 THz) have been obtained at 4.2 K for three crystalline forms of trialanine [H2+-(Ala)3-O-]. The crystal structures differ in their beta-sheet forms (parallel vs antiparallel) and in their water composition (hydrated vs dehydrated antiparallel beta-sheet). The spectra are nearly vibrationally resolved, with little absorption below 1 THz. In sharp contrast to observations made in the mid-IR region, the spectral patterns of all three forms are qualitatively different, illustrating the extreme sensitivity to changes in the intermolecular hydrogen-bonding networks that stabilize peptide crystals. Predictions obtained from a classical force field model (CHARMM) and density functional theory (DFT/PW91) for periodic solids are compared with the X-ray structural data and the terahertz absorption spectra. In general, the results for the parallel beta-sheet are in better agreement with experiment than those for the antiparallel beta-sheet. For all three structures, however, most hydrogen bond distances are underestimated at both levels of theory, and the predicted absorption features are significantly red-shifted for the two antiparallel beta-sheet structures. Moreover, the nuclear motions predicted at the two levels of theory are qualitatively different. These results indicate that the PW91 functional is not sufficient to treat the weak intersheet hydrogen bonding present in the different beta-sheet forms and strongly suggest the need for improved force field models that include three-atom hydrogen-bonding terms for periodic solids.     

An X-band time domain electron paramagnetic resonance spectrometer

A computer-controlled X-band time domain electron paramagnetic resonance (EPR) spectrometer, with a time resolution of the order of 0.5μsec, has been constructed with many of the crucial microwave components designed and fabricated by the Microwave Engineering Group of TIFR. The spectrometer operates either in a microwave power pulsed mode for determination of spin-lattice relaxation times by the saturation recovery technique or in the kinetic mode for determination of the time dependence of EPR signal after laser excitation. It has an automatic frequency control, an automatic phase control and, most importantly, a field-frequency lock which ensures good stability of the EPR line positions enabling signal averaging for extended periods. The constructional details of the spectrometer and its performance in both the modes are described here by reporting results on certain typical systems.     

Spin-lattice relaxation studies on semiquinone ions

Electron spin-lattice relaxation times ofp-benzosemiquinone, durosemiquinone and 2, 5 ditertiary butyl-p-benzosemiquinone ions have been measured by the pulsed saturation recovery technique. The relaxation times of the different hyperfine components of a semiquinone ion are the same within the limits of experimental error in disagreement with the findings of Schreurs and Fraenkel. The dependence of T₁ on viscosity does not follow the BPP’s theory.     

Comparative neuroprotective effects of native curcumin and its galactomannoside formulation in carbofuran-induced neurotoxicity model

Abstract

Toxicity of the pesticide carbofuran (CF) can be alleviated by curcumin, if not for its poor bioavailability. Hence, we investigated the effect of a bioavailable curcumin-galactomannan complex (CGM) on CF-induced neurotoxicity in rats in comparison to that of unformulated standard curcumin (CS). The CF (5?mg/kg b.wt/day) treatment for 90?days produced chronicity model which were treated with either CS or CGM (100?mg/kg b.wt and 250?mg/kg b.wt/day) for another 30?days. Improvement in CF-induced behaviour was evident in endurance, motor co-ordination and pain response on both CS (p?<?0.01) and CGM (p?<?0.001) supplementation. Amelioration of CF-induced toxicity parameters, oxidative stress, and mitochondrial dysfunction on CS (p?<?0.01) and CGM (p?<?0.001) supplementation was further confirmed by histopathology of brain and liver tissues. But, CGM was more effective in mitigating CF toxicity, with results comparable to that of normal. Hence, CGM might be superior in toxicity management against CF.     

A synthesis of N-bridged 5,6-bicylic pyridines via a mild cyclodehydration using the burgess reagent and discovery of a novel carbamylsulfonylation reaction

Cyclodehydration using the Burgess reagent provided a novel approach toward the synthesis of N-bridged 5,6-bicylic pyridines including pyrolo-, imidazo-, and triazolopyridines under mild and neutral conditions. The methodology tolerates acid-sensitive functional groups. A novel addition product was observed between the resulting pyrrolo- or imidazopyridine and an additional equivalent of the Burgess reagent, producing the corresponding sulfonylcarbamate adduct.     

UV resonance raman investigation of electronic transitions in alpha-helical and polyproline II-like conformations

UV resonance Raman (UVRR) excitation profiles and Raman depolarization ratios were measured for a 21-residue predominantly alanine peptide, AAAAA(AAARA) 3A (AP), excited between 194 and 218 nm. Excitation within the pi-->pi* electronic transitions of the amide group results in UVRR spectra dominated by amide vibrations. The Raman cross sections and excitation profiles provide information about the nature of the electronic transitions of the alpha-helix and polyproline II (PPII)-like peptide conformations. AP is known to be predominantly alpha-helical at low temperatures and to take on a PPII helix-like conformation at high temperatures. The PPII-like and alpha-helix conformations show distinctly different Raman excitation profiles. The PPII-like conformation cross sections are approximately twice those of the alpha-helix. This is due to hypochromism that results from excitonic interactions between the NV 1 transition of one amide group with higher energy electronic transitions of other amide groups, which decreases the alpha-helical NV 1 (pi-->pi*) oscillator strengths. Excitation profiles of the alpha-helix and PPII-like conformations indicate that the highest signal-to-noise Raman spectra of alpha-helix and PPII-like conformations are obtained at excitation wavelengths of 194 and 198 nm, respectively. We also see evidence of at least two electronic transitions underlying the Raman excitation profiles of both the alpha-helical and the PPII-like conformations. In addition to the well-known approximately 190 nm pi-->pi* transitions, the Raman excitation profiles and Raman depolarization ratio measurements show features between 205-207 nm, which in the alpha-helix likely results from the parallel excitonic component. The PPII-like helix appears to also undergo excitonic splitting of its pi-->pi* transition which leads to a 207 nm feature.     

A validated high-performance thin-layer chromatography method for quantification of echioidin from Andrographis echioides plant

JPC – Journal of Planar Chromatography – Modern TLC - A simple, reliable and reproducible high-performance thin-layer chromatography (HPTLC) method was established for determining...     

Antibiofilm Activity of α-Amylase from Bacillus subtilis S8-18 Against Biofilm Forming Human Bacterial Pathogens

The extracellular α-amylase enzyme from Bacillus subtilis S8-18 of marine origin was proved as an antibiofilm agent against methicillin-resistant Staphylococcus aureus (MRSA), a clinical strain isolated from pharyngitis patient, Vibrio cholerae also a clinical isolate from cholera patient and Pseudomonas aeruginosa ATCC10145. The spectrophotometric and microscopic investigations revealed the potential of α-amylase to inhibit biofilm formation in these pathogens. At its BIC level, the crude enzyme caused 51.81–73.07% of biofilm inhibition. Beyond the inhibition, the enzyme was also effective in degradation of preformed mature biofilm by disrupting the exopolysaccharide (EPS), an essential component in biofilm architecture. Furthermore, the enzyme purified to its homogeneity by chromatographic techniques was also effective in biofilm inhibition (43.83–61.68%) as well as in degradation of EPS. A commercial α-amylase enzyme from B. subtilis was also used for comparative purpose. Besides, the effect of various enzymes and temperature on the antibiofilm activity of amylase enzymes was also investigated. This study, for the first time, proved that α-amylase enzyme alone can be used to inhibit/disrupt the biofilms of V. cholerae and MRSA strains and beholds much promise in clinical applications.