Sudip Choudhury

Synthesis, Characterization, and Mesogenic Properties of Anisotropic Imines

Two homologous series of highly anisotropic diimines containing five and six aromatic rings in the mesogenic core derived from 1,4-terephthaldehyde and 4-formylphenyl-4-formylbenzoate have been synthesized and characterized by spectroscopic methods. The liquid-crystalline phases and the phase-transition temperatures are investigated using a polarizing microscope attached to a hot stage and differential scanning calorimetry. Most of the compounds are thermally stable and exhibit smectic and nematic phases over a large thermal range. In the majority of the compounds studied, a SmC phase exists over a very broad temperature range. The importance of the alkyl chain length in competing with the size of the aromatic core in determining the phase variant and in the increase of thermal range of the mesomorphism in a homologous series is described.

Computational analysis of the activity of pongachalcone I against highly resistant bacteria Pseudomonas putida.

TtgR is a multidrug binding protein in the gram negative bacteria Pseudomonas putida (DOTT1E strain) and regulates one of the key mechanisms of its antibiotic resistance by active extrusion of toxic compounds through the membranebound efflux pumps. The paper reports the molecular docking studies of Pongachalcone I, a natural pyranochalcone and reported potent inhibitor of the bacteria, on the transcriptional regulator (TtgR) enzyme (PDB Code: 2UXI) which is a key efflux pump TtgABC operon repressor. Although the bacterium is capable to expel antibiotics like Chloramphenicol, Tetracycline and Naringenin, yet Pongachalcone I has potent activity against it. The work unveils the key roles played by the residues ASN 110 and CYS 137 in the active site of the enzyme, which would be highly beneficial in providing insight into the molecular mechanism of multiple drug recognition and in designing drugs for antibiotic resistance bacteria.

Sulphonate anchored hemicyanine dyes for dye solar cell: A study on dipole moment and polarity

The effect of the molecular architecture of dye on the performance of a hemicyanine based dye sensitized solar cell (DSSC) has been studied using theoretical and experimental tools. These dyes were utilized as sensitizers in DSSC and then later were characterized using various techniques like I-V, impedance, electron transfer kinetics, dielectrics, and Tafel polarization in order to study the photovoltaic performance. The dye having a p-OH group (INS 1) exhibited very good photon to electricity conversion efficiency (3%) along with good fill factor while the dye having a p-OMe group (INS 2) lagged behind in performance. The substituent effect was studied theoretically as well as experimentally emphasizing the dipole moment of the dye in various directions. Theoretical investigation reveals that the presence of a p–OH group in the donor unit enhances the dipole moment of the molecule in comparison to a p-OMe group, thereby imparting longer lifetime of excited state leading to better charge transfer at the ...

Synthesis, X-ray Diffraction Study and Antimicrobial Activity of Calcium Sulphate Nanocomposites from Plant Charcoal

Calcium sulphate nanocomposite materials (CB) have been synthesised from plant charcoal. Crushed charcoal powder was heated to red hot over a Bunsen burner flame and produced a white material which has been isolated. The surface morphology of the material has been studied by Scanning Electron Microscopy (SEM) and the elements were analyzed by Energy Dispersion Spectroscopy (EDS). To explore the structural features of the materials X-Ray Diffraction (XRD) patterns were recorded. The material showed pronounced inhibitory effects against Streptococcus faecaelis, Bacillus subtilis, Klebsilla pneumoni, E. coli, Proteus vulgaris and Pseudomonas aeruginosa.

Molecular and in silico analysis of a new plasmid-mediated AmpC β-lactamase (CMH-2) in clinical isolates of Klebsiella pneumoniae.

Two Klebsiella strains isolated from urine samples were positive for blaAmpC by PCR and showed sequence similarity with CMH-1 (98.6%) after sequencing. It also shares 82% similarity with ACT-1, 85% with MIR-1 and 81% with the chromosomal AmpC gene of Enterobacter cloacae. This gene was associated with the plasmid of IncK type. It has an open reading frame of 381 amino acid with four amino acid substitutions at position D144A, C189R, Q192E, and A195T as compared to CMH-1. When expressed in E.coli DH5α and E.coli strain B, this β-lactamase conferred resistance to cefotaxime, ceftriaxone and ceftazidime. In addition, both in vitro and in silico analysis revealed that this cephalosporinase was inhibited by cefepime and carbapenem group of drugs. Therefore, this new plasmid-encoded AmpC type β-lactamase gene was designated as CMH-2.

Grafting a mesomorphic Schiff base onto gold nanoparticle via ester link – photoluminescence, mesomorphism, electrical conductivity and antioxidant activity

ABSTRACT Liquid crystal-gold nanoparticle (GNP-LC) composite were accessed via covalent coupling of 4-mercaptophenol capped gold nanoparticles (GNP) and a carboxylic acid functionalised rod shaped mesomorphic Schiff base (LC). The Schiff base ligand and the composite both showed schlieren texture with distinct difference in phase transition temperature. The X-ray diffraction study suggested a smectic C mesophase for the compounds. The LC and GNP-LC, both exhibited room temperature photoluminescence when excited at 264nm.The transmission electron micrography revealed the composite to be nearly monodisphersed having almost spherical shape of ~ 2nm size. The composite material in addition to being mesomorphic exhibited pronounced AC conductivity in the semiconductor domain and antioxidant activity. Graphical Abstract

Aggregation dependent fluorescence switching in benzothiazole derivative based H-bonded mesogen

ABSTRACT In this work, hydrogen-bonded liquid crystal exhibiting phase dependent fluorescence has been reported. The H-bonded materials were prepared using pyridenyl benzothiazole and alkoxy benzoic acid as H-bond acceptor and donor respectively. The formation of the target materials was confirmed via different spectroscopic technique and their mesogenic behaviour has been studied through polarising optical microscope, differential scanning calorimetry and 2D-X-ray diffraction. The H-bonded mesogenic material showed aggregation dependent fluorescence switching when subjected to transformation from isotropic-nematic-crystalline phase sequence. Computational studies were performed to probe into fluorescence switching behaviour of the mesogenic material. GRAPHICAL ABSTRACT

Green, One-Pot, Multicomponent Synthesis of Fused-Ring 2-Aminothiazoles

Abstract A facile, green, and efficient Fe(III) chloride, one-pot, multicomponent reaction (MCR) for synthesis of 2-aminothiazole-based compounds is reported. Considering the medicinal importance of fused ring 2-aminothiazoles, this process provides an easy route to the synthesis of this class of compound. Detailed mechanism of the reaction has been discussed. GRAPHICAL ABSTRACT