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Tezpur, India

Satapathy S.S.,Tezpur University | Powdel B.R.,Darrang College | Dutta M.,Tezpur University | Buragohain A.K.,Tezpur University | And 2 more authors.
Journal of Molecular Evolution | Year: 2014

The fourfold degenerate site (FDS) in coding sequences is important for studying the effect of any selection pressure on codon usage bias (CUB) because nucleotide substitution per se is not under any such pressure at the site due to the unaltered amino acid sequence in a protein. We estimated the frequency variation of nucleotides at the FDS across the eight family boxes (FBs) defined as Um(g), the unevenness measure of a gene g. The study was made in 545 species of bacteria. In many bacteria, the Um(g) correlated strongly with Nc′ - a measure of the CUB. Analysis of the strongly correlated bacteria revealed that the U-ending codons (GGU, CGU) were preferred to the G-ending codons (GGG, CGG) in Gly and Arg FBs even in the genomes with G+C % higher than 65.0. Further evidence suggested that these codons can be used as a good indicator of selection pressure on CUB in genomes with higher G+C %. © 2013 Springer Science+Business Media New York.

Boruah B.,Tezpur University | Saikia P.M.,Darrang College | Gohain B.,Tezpur University | Dutta R.K.,Tezpur University
Journal of Molecular Liquids | Year: 2010

Acid-base equilibrium of phenol red (PR), a sulphonephthalein dye, was studied spectrophotometrically in aqueous media containing water soluble nonionic polymers viz., polyvinyl alcohol (PVA) and polyethylene glycol (PEG) in the presence of an anionic surfactant, sodium dodecyl sulfate (SDS). A partition equilibrium method was utilized to determine the equilibrium constant of partition of the PR between micellar pseudo phase and aqueous phase and the critical aggregation concentration (CAC) of SDS in buffered aqueous systems containing the neutral polymers. The pH dependent association constants, Kass of PR with SDS-PVA, and SDS-PEG system increase in the order PEG 200 < PEG 400 < PEG 600 < PVA. The value of Kass was found to be greater in Tris buffer system than in phosphate buffer system of same pH. Interaction of the dye with the aqueous SDS-PVA and SDS-PEG systems is found to be endothermic and entropy oriented. © 2009 Elsevier B.V. All rights reserved.

Gohain B.,Tezpur University | Boruah B.,Tezpur University | Saikia P.M.,Darrang College | Dutta R.K.,Tezpur University
Journal of Physical Organic Chemistry | Year: 2010

The premicellar and micelle formation behaviors of four cationic triphenylmethane dyes, viz, Pararosaniline (RN), Crystal violet (CV), Ethyl violet (EV), and Malachite green (MG), in aqueous anionic surfactant solutions of sodium dodecyl sulfate (SDS), sodium dodecyl benzene sulfonate (SDBS), and sodium dodecyl sulfonate (SDSN) have been studied by spectral and surface tension measurements. The study was carried out within a pH range where the dyes are stable in their quinoid forms. The dyes have been found to form dye-surfactant ion pairs (DSIPs) with the surfactants, at the surfactant concentrations well below their critical micelle concentration, CMC*. The DSIPs behave like nonionic surfactants and form an air-water interfacial monolayer. The DSIPs have a lower critical micelle concentration (CMC IP), greater efficiency, and lower effectiveness than the corresponding pure surfactants. As the surfactant concentration is increased below the CMC*, the DSIPs start forming micelles of their own where the dye gets protonated and exists as a protonated dye-surfactant ion pair (PDSIP) in the ion pair micelles. As the concentration of the surfactant exceeds the CMC* of the pure surfactant, the protonation reverses gradually with the dye remaining in the micelles in solubilized form and the DSIPs in the air-water interfacial monolayer are replaced by pure surfactants. The distorted helical isomeric form (isomer B) of the dyes is favored in the PDSIPs. Copyright © 2009 John Wiley & Sons, Ltd.

Dutta A.,Tezpur University | Boruah B.,Tezpur University | Saikia P.M.,Darrang College | Dutta R.K.,Tezpur University
Journal of Molecular Liquids | Year: 2013

The interaction of aqueous curcumin with cationic surfactants of varying chain lengths and head group, stabilizing its β-diketo tautomer and exhibiting an UV band around 355 nm, has been studied in buffered aqueous solutions in the pH range of 2.00-7.00 by UV-visible and fluorescence spectroscopy, and surface tensiometry under optimal experimental conditions of submicellar concentration of the surfactants. Time Dependent Density Functional Theory (TD-DFT) has also been used to predict the molecular structure and excitation energies of the interaction product in the ground state and the nature of the interaction. As the surfactant concentration increases, the curcumin-cationic complex forms premicellar aggregates where the curcumin exists in a highly polar microenvironment before shifting its location to the nonpolar core of the surfactant micelles. The strength of the interaction increases with the chain length of the surfactant and also changes on changing the head group of the surfactant. An observed secondary salt effect on the interaction indicates an unusual involvement of a proton in the interaction. Based on the experimental and theoretical evidences the following mechanism has been proposed for the stabilization of the β-diketo form: on the approach of the cationic surfactant, a protonation of the methylenic central carbon atom of curcumin takes place simultaneously breaking the π-conjugation and facilitating the detachment of the enolic proton paving the way for an ion dipole binding between the cationic head group and the electron-rich β-diketo oxygen atoms. Hydrophobic interaction between the tail of the surfactant and the nonionic curcumin molecule assists the electrostatic interaction. © 2013 Elsevier B.V.

Dutta A.,Tezpur University | Boruah B.,Tezpur University | Manna A.K.,Jawaharlal Nehru Centre for Advanced Scientific Research | Gohain B.,Tezpur University | And 2 more authors.
Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy | Year: 2013

A newly observed UV band of aqueous curcumin, a biologically important molecule, in presence of anionic surfactants, viz., sodium dodecylsulfate (SDS), sodium dodecylbenzenesulfonate (SDBS), and sodium dodecylsulfonate (SDSN) in buffered aqueous solutions has been studied experimentally and theoretically. The 425 nm absorption band of curcumin disappears and a new UV-band is observed at 355 nm on addition of the surfactants in the submicellar concentration range which is reversed as the surfactant concentration approaches the critical micelle concentration (CMC). The observed spectral absorption, fluorescence intensity and surface tension behavior, under optimal experimental conditions of submicellar concentration ranges of the surfactants in the pH range of 2.00-7.00, indicate that the new band is due to the β-diketo tautomer of curcumin stabilized by interactions between curcumin and the anionic surfactants. The stabilization of the diketo tautomer by submicellar anionic surfactants described here as well as by submicellar cationic surfactant, reported recently, is unique as this is the only such behavior observed in presence of submicellar surfactants of both charge types. The experimental results are in good agreement with the theoretical calculations using ab initio density functional theory combined with time dependent density functional theory (TD-DFT) calculations. © 2012 Elsevier B.V. All rights reserved.

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