Bipransh Kumar Tiwary

Spectroscopic and theoretical characterization of 2-(4-methoxyphenyl)-4,5-dimethyl-1H-imidazole 3-oxide.

The optimized molecular structure, vibrational frequencies, corresponding vibrational assignments of 2-(4-methoxyphenyl)-4,5-dimethyl-1H-imidazole 3-oxide have been investigated experimentally and theoretically. Gauge-including atomic orbital (1)H NMR chemical shifts calculations were carried out and compared with experimental data. The HOMO and LUMO analysis is used to determine the charge transfer within the molecule. The stability of the molecule arising from hyper-conjugative interaction and charge delocalization has been analyzed using NBO analysis. The calculated geometrical parameters are in agreement with that of similar derivatives. Molecular electrostatic potential was performed by the DFT method. Mullikens net charges have been calculated and compared with the atomic natural charges. First and second hyperpolarizability are calculated in order to find its role in non-linear optics. Molecular docking is also reported.

Guava Leaf Extract Inhibits Quorum-Sensing and Chromobacterium violaceum Induced Lysis of Human Hepatoma Cells: Whole Transcriptome Analysis Reveals Differential Gene Expression

Quorum sensing (QS) is a process mediated via small molecules termed autoinducers (AI) that allow bacteria to respond and adjust according to the cell population density by altering the expression of multitudinous genes. Since QS governs numerous bioprocesses in bacteria, including virulence, its inhibition promises to be an ideal target for the development of novel therapeutics. We found that the aqueous leaf extract of Psidium guajava (GLE) exhibited anti-QS properties as evidenced by inhibition of violacein production in Chromobacterium violaceum and swarming motility of Pseudomonas aeruginosa. The gram-negative bacterium, C. violaceum is a rare pathogen with high mortality rate. In this study, perhaps for the first time, we identified the target genes of GLE in C. violaceum MTCC 2656 by whole transcriptome analysis on Ion Torrent. Our data revealed that GLE significantly down-regulated 816 genes at least three fold, with p value≤0.01, which comprises 19% of the C. violaceum MTCC 2656 genome. These genes were distributed throughout the genome and were associated with virulence, motility and other cellular processes, many of which have been described as quorum regulated in C. violaceum and other gram negative bacteria. Interestingly, GLE did not affect the growth of the bacteria. However, consistent with the gene expression pattern, GLE treated C. violaceum cells were restrained from causing lysis of human hepatoma cell line, HepG2, indicating a positive relationship between the QS-regulated genes and pathogenicity. Overall, our study proposes GLE as a QS inhibitor (QSI) with the ability to attenuate virulence without affecting growth. To the best of our knowledge, this is the first report which provides with a plausible set of candidate genes regulated by the QS system in the neglected pathogen C. violaceum.

Diverse Gene Cassettes in Class 1 Integrons of Facultative Oligotrophic Bacteria of River Mahananda, West Bengal, India

Background In this study a large random collection (n = 2188) of facultative oligotrophic bacteria, from 90 water samples gathered in three consecutive years (2007–2009) from three different sampling sites of River Mahananda in Siliguri, West Bengal, India, were investigated for the presence of class 1 integrons and sequences of the amplification products. Methodology/Principal Findings Replica plating method was employed for determining the antibiotic resistance profile of the randomly assorted facultative oligotrophic isolates. Genomic DNA from each isolate was analyzed by PCR for the presence of class 1 integron. Amplicons were cloned and sequenced. Numerical taxonomy and 16S rRNA gene sequence analyses were done to ascertain putative genera of the class 1 integron bearing isolates. Out of 2188 isolates, 1667 (76.19%) were antibiotic-resistant comprising of both single-antibiotic resistance (SAR) and multiple-antibiotic resistant (MAR), and 521 (23.81%) were sensitive to all twelve different antibiotics used in this study. Ninety out of 2188 isolates produced amplicon(s) of varying sizes from 0.15 to 3.45 KB. Chi-square (χ2) test revealed that the possession of class 1 integron in sensitive, SAR and MAR is not equally probable at the 1% level of significance. Diverse antibiotic-resistance gene cassettes, aadA1, aadA2, aadA4, aadA5, dfrA1, dfrA5, dfrA7, dfrA12, dfrA16, dfrA17, dfrA28, dfrA30, dfr-IIe, blaIMP-9, aacA4, Ac-6′-Ib, oxa1, oxa10 and arr2 were detected in 64 isolates. The novel cassettes encoding proteins unrelated to any known antibiotic resistance gene function were identified in 26 isolates. Antibiotic-sensitive isolates have a greater propensity to carry gene cassettes unrelated to known antibiotic-resistance genes. The integron-positive isolates under the class Betaproteobacteria comprised of only two genera, Comamonas and Acidovorax of family Comamonadaceae, while isolates under class Gammaproteobacteria fell under the families, Moraxellaceae, Pseudomonadaceae, Aeromonadaceae and Enterobacteriaceae. Conclusions Oligotrophic bacteria are good sources of novel genes as well as potential reservoirs of antibiotic resistance gene casettes.

A mechanistic study of carbonyl activation under solvent-free conditions: evidence drawn from the synthesis of imidazoles

Syntheses of various imidazoles and their derivatives, imidazole N-oxides and 1-hydroxyimidazole 3-oxides, from sterically different dicarbonyl moieties provided insights into the self-catalytic effect of the condensed phase reactions of carbonyl compounds. The self-catalytic activity in solvent-free multi-component syntheses was investigated using a combination of methods viz., reactivity, spectroscopy and theory. While IR spectroscopic studies revealed that reacting molecules were polarised in bulk, quantum mechanical calculations of associated HCHO monomers suggest an increase in the average dipole moment of each monomer and provide evidence for the presence of cooperative effects. A comparative study of the kinetics of un-catalysed and catalysed reactions with the help of HPLC provided insights into the mechanism.

Implication of Quinazoline-4(3H)-ones in Medicinal Chemistry: A Brief Review

Quinazoline, a heterocyclic compound, has been extensively studied and used in certain specific biological activities. The quinazoline-4(3H)-one and its derivatives constitute an important class of fused heterocycles that are found in more than 200 naturally occurring alkaloids. With passage of time, newer and more complex variants of the quinazolinone structures are being discovered. The stability of the quinazolinone nucleus has inspired researchers to introduce many bioactive moieties to this nucleus to create new potential medicinal agents. With a view to explore the versatile lead molecule 4(3H)-quinazolinones, a series of novel 2-methyl-3-(1’3’4-thiadiazole-2- yl)-4-(3H) quinazolinones have been synthesized by reacting 2-amino-5-aryl/alkyl-1’3’4’-thiadiazoyl with 2-substituted benzoxazin-2-one. The designed compounds have shown antibacterial activity on Staphylococcus aureus, Bacillus subtilis and Escherichia coli. In the journey of a compound to be established as a lead and finally to a drug, the problem of solubility is a major challenge for medicinal chemists and formulation scientists. The present review has touched all these issues with a hope that some of the quinazoline derivative with sufficient bioavailability could help us to counter the menace of antibiotic resistance.

An Escherichia coli Strain, PGB01, Isolated from Feral Pigeon Faeces, Thermally Fit to Survive in Pigeon, Shows High Level Resistance to Trimethoprim

In this study, of the hundred Escherichia coli strains isolated from feral Pigeon faeces, eighty five strains were resistant to one or more antibiotics and fifteen sensitive to all the antibiotics tested. The only strain (among all antibiotic-resistant E. coli isolates) that possessed class 1 integron was PGB01. The dihydrofolate reductase gene of the said integron was cloned, sequenced and expressed in E. coli JM109. Since PGB01 was native to pigeon’s gut, we have compared the growth of PGB01 at two different temperatures, 42°C (normal body temperature of pigeon) and 37°C (optimal growth temperature of E. coli; also the human body temperature), with E. coli K12. It was found that PGB01 grew better than the laboratory strain E. coli K12 at 37°C as well as at 42°C. In the thermal fitness assay, it was observed that the cells of PGB01 were better adapted to 42°C, resembling the average body temperature of pigeon. The strain PGB01 also sustained more microwave mediated thermal stress than E. coli K12 cells. The NMR spectra of the whole cells of PGB01 varied from E. coli K12 in several spectral peaks relating some metabolic adaptation to thermotolerance. On elevating the growth temperature from 37°C to 42°C, susceptibility to kanamycin (both strains were sensitive to it) of E. coli K12 was increased, but in case of PGB01 no change in susceptibility took place. We have also attempted to reveal the basis of trimethoprim resistance phenotype conferred by the dfrA7 gene homologue of PGB01. Molecular Dynamics (MD) simulation study of docked complexes, PGB01-DfrA7 and E. coli TMP-sensitive-Dfr with trimethoprim (TMP) showed loss of some of the hydrogen and hydrophobic interaction between TMP and mutated residues in PGB01-DfrA7-TMP complex compared to TMP-sensitive-Dfr-TMP complex. This loss of interaction entails decrease in affinity of TMP for PGB01-DfrA7 compared to TMP-sensitive-Dfr.

A study on optimization of marigold petal yield, pure lutein, and formulation of free-flowing lutein esters

The present study was conducted with the main objective to optimize petal yield from important marigold cultivars in West Bengal, and to standardize isolation of lutein from petals because these dietary xanthophylls are known to reduce the risks of agerelated macular degeneration (AMD) and cataracts. Six cultivars were studied viz. African marigold-Double (AFM-D), African marigold-Single (AFM-S), African marigold-Orange (AFM-O), French marigold-Orange (FRM-O), French marigold-Double (FRMD), and LC (Local type), which withstand typical environmental conditions of northern West Bengal and produce flowers that do not vary in color and are relatively unaffected by pests and diseases. Lutein esters were extracted from milled marigold petals using nhexane. However, overall performance showed that LC is superior to the other cultivars. Pure lutein was obtained after saponification with 50% KOH. The re-crystallized lutein was characterized by UV-VIS, IR spectroscopy, and HPLC. A free-flowing lutein ester was also formulated. This free-flowing lutein ester was found to be suitable to undergo commercialization or subsequent processing. An economic method for petal yield and isolation of lutein was thus standardized.