• J Santhanalakshmi

      Articles written in Journal of Chemical Sciences

    • Solvent effects on reverse micellisation of Tween 80 and Span 80 in pure and mixed organic solvents

      J Santhanalakshmi S I Maya

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      Reverse micellisations of nonionic surfactants (Tween 80 and Span 80) in various pure nonaqueous solvents like carbontetrachloride, benzene, toluene, chloroform, cyclohexane and xylene, and in mixed solvent systems like CCl4-DMF and CCl4-DMSO covering the low dielectric range, are studied by UV electronic spectroscopy at 25°C. Micellar aggregation number (ns) in various solvents is evaluated using the hydrophobic dye, Oil Red. 0. The critical micellar concentration (cmc) andns) dependencies on the solvent dielectric, solvent ionization potential, solvent-surfactant interaction potentials, mole fractions of solvents in mixtures and internal pressures are studied. The CCl4-DMSO system shows acmc increase effect, while the CCl4-DMF system shows acmc decrease effect and the excess functions of CCl4-DMSO and CCl4-DMF show increase and decrease effects respectively. Rationalisations of the results and the role of the solvent cage effect have been discussed.

    • Surfactant-induced stabilization of four-coordinated hemes in reconstituted hemoglobins

      B Venkatesh S Ramasamy V Swarnalatha J Santhanalakshmi R Asokan J M Rifkind P T Manoharan

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      A transition from 5-coordination to 4-coordination metal centres of porphyrins in carbonmonoxy Fe(II), Cu(II) and Ni(II) hemoglobins is observed as a consequence of ionic surfactant interactions with metalloproteins through UV-Vis studies. SDS (anionic) and CTAB (cationic) surfactants are used. Values of heme partition coefficient (K) between globin and surfactant show that, in both CTAB and SDS, partitioning increases proportionately with surfactant concentration for a fixed concentration of hemoglobin. The interactions seem to be mainly hydrophobic in nature with metalloproteins, though coordination and coulombic interactions may also play a minor role in CTAB and SDS respectively. The present study provides new insight into reconstituted hemoglobin-surfactant interaction.

    • Small-angle neutron scattering study of the effect ofn-alkanols on interacting micelles

      J Santhanalakshmi P S Goyal V K Aswal G Vijayalakshmi

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      Small-angle neutron scattering cross-section distributions of sodium dodecyl sulphate (SDS) and dodecyl trimethyl ammonium bromide (DTAB), each 0·3 M in D2O were obtained in the absence and presence of 0·1 M 1-pentanol, 1-hexanol, and 1-octanol at 25°C. The Hayter-Penfold type analysis was adopted. An ellipsoidal model with semiminor axis (a=16·5 Å) and semimajor axes (b=40·7 Å and 29·8 Å) for pure SDS and DTAB micelles has produced best fits. On increasing alkanol chain lengths an increase inb values was found. Micellar parameters like effective radius (R), (a, b), fraction of counterions per micelle, and intermicellar distances were obtained. Surfactant aggregation number, additive aggregation number intermicellar interaction potentials and values of Debye screening length were obtained for SDS and DTAB in the presence of alkanols. Implications of partitioning effect, surfactant ionicity and intermicellar potentials on the microstructures are rationalised.

    • Small-angle neutron scattering study of sodium cholate and sodium deoxycholate interacting micelles in aqueous medium

      J Santhanalakshmi G Shantha Lakshmi V K Aswal P S Goyal

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      Small angle neutron scattering (SANS) measurements of D2O solutions (0.1 M) of sodium cholate (NaC) and sodium deoxycholate (NaDC) were carried out atT= 298 K. Under compositions very much above the critical micelle concentration (CMC), the bile salt micelle size growths were monitored by adopting Hayter-Penfold type analysis of the scattering data. NaC and NaDC solutions show presence of correlation peaks atQ = 0.12 and 0.1 å-1 respectively. Monodisperse ellipsoids of the micelles produce best fits. For NaC and NaDC systems, aggregation number (9.0, 16.0), fraction of the free counterions per micelle (0.79, 0.62), semi-minor (8.0 å) and semi-major axes (18.4, 31.7 å) values for the micelles were deduced. Extent of micellar growth was studied using ESR correlation time measurements on a suitable probe incorporating NaC and NaDC micelles. The growth parameter (axial ratio) values were found to be 2.3 and 4.0 for NaC and NaDC systems respectively. The values agree with those of SANS.

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