J. Santhanalakshmi

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

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.

Selective N-methylation of aniline by calcined MgIIAlIII layered double hydroxides

Abstract Gas phase N-methylation of aniline with methanol was carried out in a fixed bed flow reactor over the calcined Mg II Al III layered double hydroxides (LDH) with various atomic ratios of Mg:Al from 3 to 10. Only a single product (N-methylaniline) was formed. The catalytic activity, selectivity, longevity, time on stream and reactivations are investigated based on the extent of mono-alkylated product formations. All calcined LDHs were more active than the physical mixtures of MgO Al 2 O 3 . A higher surface area and lattice parameter of 4:1 mole ratio of calcined LDHs effectively produced a maximum conversion of 68% at 425°C at a feed mixture mole ratio of 1:7 (aniline to methanol) when the flow rate was 5 ml/h over all other catalysis.

Au–ZnO bullet-like heterodimer nanoparticles: synthesis and use for enhanced nonenzymatic electrochemical determination of glucose

In this work, the gold nanoseed mediated growth of bullet-like gold–zinc oxide (Au–ZnO) heterodimer nanoparticles has been reported. A formation pathway for the bullet-like morphology has been proposed. The heterojunction effect of the Au–ZnO nanoparticles was studied using UV-vis spectroscopy, X-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy (HRTEM) and electrochemical impedance spectroscopy (EIS). The bullet-like Au–ZnO heterodimer nanoparticles were effectively employed as a sensor for the nonenzymatic determination of glucose (GLU) in a Au–ZnO/MWCNTs/GC modified electrode. This showed good sensitivity and a wide linear range of 19–291 μM with a sensitivity of 0.0447 μA μM−1 and a limit of detection of 0.19 μM. The resulting sensor displayed excellent repeatability and long-term stability.

Antipyrilquinoneimine dye formation by coupling aniline derivatives with 4-aminoantipyrine in the presence of ruthenium nanoparticles

The coupling of 4-aminoantipyrine (4-AAP) with aniline derivatives catalyzed by ruthenium nanoparticles (Rnp) has been studied by UV-Vis spectroscopy in aqueous medium. The rate constant for antipyrilquinoneimine dye formation depends on the nature of the aniline substituent and the pH, ionic strength and temperature of the reaction medium. The maximum rate constant of the dye formation reaction is observed at pH 3.6. Aniline derivatives with electron donating substituents show higher rate constant values than those with electron withdrawing substituents, with increasing rate constant values in the order: N,N-dimethyl aniline > o-toluidine > o-chloroaniline > m-chloroaniline. With pseudo first order kinetics, the total order is 1.0 + 1.0 + 1.0 = 3.0, which includes the orders with respect to amine, 4-AAP and Rnp. Studies on these effects help to complete the kinetic analysis as well as propose the reaction pathway. Furthermore, TEM measurement confirms that the nanoscalar size of the Rnp is 7 nm.

Electrostatic fabrication of oleylamine capped nickel oxide nanoparticles anchored multiwall carbon nanotube nanocomposite: A robust electrochemical determination of riboflavin at nanomolar levels

A simple and strong electrostatic adsorption of oleylamine (OLA) capped nickel oxide (NiO) nanoparticles (oleylamine–amine group) onto the acid functionalized multiwalled carbon nanotubes (MWCNTs) (–COOH group) through coulombic interaction, leads to the construction of OLA–NiO/MWCNTs nanocomposite. The optimum loading of OLA–NiO nanoparticles on to the acid functionalized MWCNTs is investigated by Fourier transform infrared spectroscopy. Moreover, the optimum amount of loading and stability of the modified electrodes were studied by using linear sweep voltammetry and conductivity of optimum loadings are also studied by electrochemical impedance spectroscopy. OLA–NiO/MWCNTs nanocomposite was fabricated on glassy carbon electrode for the electrochemical determination of riboflavin (RF) at nanomolar levels. The results show a dynamic linear range of 0.009–55.9 μM with excellent sensitivity of 0.489 μA μM−1 and the limit of detection was found to be 1 nM (S/N = 3). The developed OLA–NiO/MWCNTs composite decorated GC exhibited good sensitivity, stability, and reproducibility for the determination of RF in differential pulse voltammetry. The OLA–NiO/MWCNTs/GC modified electrode was applied for the determination of RF in pharmaceutical formulation tablet and syrup samples.

Interaction of sulfur dioxide with zinc(II) tetrasulfo phthalocyanine in aqueous medium: steady state fluorescence quenching studies

Abstract A sensitive fluorimetric method of determination of SO 2 dissolved in solvents using the steady state fluorescence of tetrasulfonated zinc(II) phthalocyanine and SO 2 in the concentration range (0.1–1.0 mM) was carried out. Effects of various solvents, pH, and salt on the interaction properties of ZnPcTsSO 2 are determined, based on the quenchings by SO 2 . Linear and non-linear Stern–Volmer plots have been analysed. Modified non-linear Stern–Volmer analysis produced best fits for a 1:2 stoichiometry. The association constant values of the ZnPcTsSO 2 complex in various environments have been determined adopting single stage and two step equilibria processes. Stern–Volmer deviations are attributed to solvent extraplanar coordinations, a 20% DMSO–water mixture seems to produce a stability constant value higher than the other effects. A cyclic voltammogram in DMSO–water medium shows significantly suppressed redox processes of the central Zinc metal ion in ZnPcTs in the presence of SO 2 (1×10 −3 M). Axial coordination leading to the formation of bis sulfonato ZnPcTs is envisaged.

Insights into the catalytic reduction of organic dyes and antibacterial activity of graphene oxide supported mono and bimetallic nanocomposites

Graphene oxide (GO) supported mono (GO/Ru, GO/Ag and GO/Pd) and bimetallic (GO/Ru–Ag and GO/Ru–Pd) nanocomposites (NCs) were prepared via a simple chemical reduction method. The newly designed GO-supported mono and bimetallic NCs were characterized using various techniques, such as Fourier transform-infrared spectroscopy (FT-IR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDAX) and high resolution transmission electron microscopy (HR-TEM). Furthermore, the GO-supported mono and bimetallic NCs were utilized for the reduction of two organic dyes, crystal violet (CV) and malachite green (MG), using NaBH4 in an aqueous medium at 25 °C. The catalytic reaction followed pseudo-first-order reaction kinetics, as monitored using UV-visible spectroscopy. In addition to this, the antibacterial activity of these prepared mono and bimetallic NCs was studied against two Gram (+ve), Staphylococcus aureus (S. aureus) and Bacillus subtilis (B. subtilis), and two Gram (−ve) bacteria, Salmonella typhi (S. typhi) and Escherichia coli (E. coli). The bimetallic NCs exhibited excellent catalytic and antibacterial activity as compared to the monometallic NCs.

Synthesis, H2PO4− and Pd2+ ion sensing and gold nanoparticle encapsulation of ferrocenyldendrimers by a green chemistry approach

A green chemistry approach for the synthesis of three novel ferrocenyldendrimers containing a triazolyl ferrocenyl group at the periphery under microwave conditions using an ionic liquid (IL) mediated click reaction is described. The application of such ferrocenyldendrimers as sensors for H2PO4− and Pd2+ is also discussed. The ferrocenyldendrimers which are used for the synthesis of Au nanoparticles were characterized using UV-Vis, spectroscopy and high resolution transmission electron microscopy (HRTEM). From the HRTEM images it is shown that dendrimer 1 stabilizes the gold nanoparticle, whereas dendrimers 2 and 3 encapsulate the gold nanoparticle.

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

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.

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

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.