Harasit Kumar Mandal

Kinetic investigation on the oxidation of tris(1,10-phenanthroline)iron(II) by oxone: the effect of BSA-SDS interaction.

The kinetic investigations of oxidation of tris(1,10-phenanthroline)iron(II) by oxone have been studied spectrophotometrically in phosphate buffer medium of pH 6.8, temperature 308 K, and ionic strength 0.25 mol L(-1). The reactions were also carried out in presence of globular transport protein, bovine serum albumin (BSA) having isoelectric point 4.9, anionic surfactant sodium dodecyl sulfate (SDS), and their mixtures. The critical aggregation concentration (CAC) and critical micelle concentration (CMC) of SDS in presence of BSA have been determined using conductivity and kinetic measurement techniques. The secondary structure of BSA was examined by Circular Dichroism (CD) measurement at 308 K. The helix nature of BSA decreases with increase of SDS concentration. The effect of pH on rate in presence of BSA is opposite to its absence, and the effect of urea on rate in presence of BSA indicates the denaturation of BSA. The results depict that amphiphile SDS interacts with BSA and different molecular events, for example, specific binding, cooperative binding, protein unfolding, and micelle formation act. Activation parameters of the reaction in different environments have been determined.

Influence of polymer–surfactant interactions on the reactivity of the CoIII–FeII redox couple

In continuation of our recent study on the inner sphere electron transfer reduction of the cobalt(III) complex, [Co(III)(NH(3))(5)N(3)]Cl(2) by Mohrs salt (Fe(II)), we have investigated the effect of neutral polymer (poly(ethylene glycol) with relative molecular mass 200, PEG 200)-surfactant (both cationic and non-ionic) mixture on the kinetics of the same reaction using spectrophotometric and conductometric techniques at 298 K. Both the cationic and non-ionic surfactants have undergone interaction with polymer. Experimental consequences reveal that the catalytic effect imposed by the polymer-surfactant complexes causes significant change of the kinetic activities of the reaction. The gradual enhancement and retardation of the rate have been found with gradual addition of PEG 200 and cationic surfactant respectively. An attempt has been taken to rationalize the experimental findings with proper correlation of the reported literature.

Kinetic exploration supplemented by spectroscopic and molecular docking analysis in search of the optimal conditions for effective degradation of malachite green

The degradation of malachite green (MG) by an alkaline hydrolytic process has been explored spectrophotometrically. The kinetics of the reaction have been meticulously studied under the influence of cationic alkyltrimethylammonium bromide (DTAB, TTAB and CTAB) surfactants, α-, β- and γ-cyclodextrins (CDs) and surfactant–β-CD mixed systems applying pseudo-first order conditions at 298 K. The surfactants and cyclodextrins individually catalyze the hydrolytic rate, whereas surfactant–β-CD mixed systems exhibit both an inhibiting and catalytic influence depending on the surfactant concentrations. The kinetic results have been explained precisely based on the pseudo-phase ion exchange (PIE) model of micelles and CD-catalyzed model of CD systems. The surfactants exhibit micellar surface catalysis, while CDs accelerate the rate by forming MG–CD inclusion complexes, thereby facilitating nucleophilic attack of its ionized secondary hydroxyl group on the carbocation center of MG. The encapsulation of MG within the supramolecular host cavity of the CDs has been investigated diligently using a steady-state absorption spectroscopic technique. The result shows 1 : 1 host–guest complexation with different relative orientations of the guest (MG) inside the hosts. Studies employing density functional theory (DFT) as well as molecular docking analysis provide valuable insight on the insertion mechanism. The results reveal that quantitative analysis can be utilized to predict the optimum conditions for the fastest degradation of MG in ambient environments.

Micellar and Mixed-Micellar Effects on Alkaline Hydrolysis of tris(1,10–phenanthroline)iron(II): Kinetic Exploration

The kinetics of alkaline hydrolysis of tris(1,10–phenanthroline)iron(II) has been studied in the presence of nonionic and mixed nonionic–ionic micellar media at 308 K. The effects of mixed-micellar environments of nonionic with ionic surfactants (C12E23/ATABs and C12E23/SDS) on the hydrolytic rate have been studied. The rate decreases monotonically with an increment of [C12E23]T (total Brij 35 concentration) at constant [−OH]0 and has been discussed with the pseudo-phase micellar model. The rate also decreases with [C12E23]T at a continuous addition of ionic surfactants (ATABs and SDS). The observed rate constant kobs follows the empirical relation: kobs = (k0 + θK [C12E23]T)/(1 + K [C12E23]T) (where θ and K are empirical constants). The values of θ remain unaffected, whereas K decreases nonlinearly with [ATABs]T in a mixed C12E23−ATAB micellar system. But the kobs in a mixed C12E23–SDS micellar system is much lower than that of the C12E23–ATAB system and do not comply with any micellar kinetic models. GRAPHICAL ABSTRACT

Kinetic investigations on the alkaline hydrolysis of tris-(1,10-phenenthroline)Fe(II) with guar gum–surfactant interactions

ABSTRACT The kinetic investigations on the alkaline hydrolysis of tris-(1,10–phenanthroline)iron(II) has been explored spectrophotometrically in microheterogeneous environment at 301 K and ionic strength of 0.13 mol L−1. Guar gum, cationic amphiphiles, and their mixtures are used as the reaction environments to carry out the reaction. Guar gum decreases the rate of reaction, which indicates that Fe(II) complex may be trapped in the hydrophobic region of gum. Cationic amphiphile decreases the rate in the presence of guar gum. The extent of interaction between guar gum and amphiphile increases with the hydrophobic carbon chain length. The critical aggregation concentration (CAC) and critical micelle concentration (CMC) of the amphiphiles (cetyl trimenthyl ammonium bromide (CTAB), tetradecyl trimenthyl ammonium bromide (TTAB), dodecyl trimenthyl ammonium bromide (DTAB)) in the presence of guar gum have been determined with conductometry and tensiometry. All observations support either weak or strong interaction of cationic amphiphiles with guar gum. Activation parameters of the reaction in different environments have been determined which corroborate the rate data. GRAPHICAL ABSTRACT