Kalachand Mahali

Thermodynamics of DL-alanine solvation in water-dimethylsulfoxide mixtures at 298.15 K

In this study we mainly discuss the transfer Gibbs free energy ΔGt0(i) and ΔSt0(i)entropy of DL-alanine at 298.15 K and consequently the involved chemical transfer free energy (ΔGt,ch0(i)) and entropy (TΔSt,ch0(i)) in aqueous mixtures of dimethylsulfoxide are discussed to clarify the solvation chemistry of DL-alanine. For the evaluation of these energy terms, solubility of this amino acid has been measured by formol titrimetry at five equidistant temperatures i.e., from 288.15 to 308.15 K in different composition of this mixed solvent system. The various solvent parameters as well as thermodynamic parameters like molar volume, density, dipole moment and solvent diameter of this solvent system have also been reported here. The chemical effects of the transfer Gibbs energies (ΔGt,ch0(i)) and entropies of transfer (TΔSt,ch0(i)) have been obtained after elimination of cavity effect and dipole-dipole interaction effects from the total transfer energies. Here the chemical contribution of transfer energetics of DL-alanine is mainly guided by the composite effects of increased dispersion interaction, basicity effect and decreased acidity, hydrogen bonding effects, hydrophilic hydration and hydrophobic hydration of aqueous DMSO mixtures as compared to that of reference solvent, water.

Physico-chemical studies of DL-alanine in aqueous sodium nitrate solution

In this study solubility of DL-alanine is measured in aqueous solutions with various NaNO3 concentrations using the “formol titrimetry” method in the temperature range from 288.15 to 308.15 K. The standard transfer Gibbs energy and entropy have been evaluated for alanine. Chemical effects of the transfer Gibbs energy [ΔGi,ch0(i)], were obtained by subtracting theoretically computed ΔGt,cav0(i) and ΔGt,d-d0(i) from the total transfer free energy, ΔGt0(i). TΔSi,ch0(i) have been evaluated after elimination of cavity and dipole-dipole interaction effects from total transfer [TΔSt0(i)] entropy. Various solvents and thermodynamic parameters are presented in this manuscript. The data accumulated demonstrated that solubility was affected by the electrolyte.

Thermodynamics and mechanisms of glycine solvation in aqueous NaCl and KCl solutions at 298.15 K

In the present study the solubility of glycine in aqueous sodium chloride and potassium chloride solution was determined under different experimental conditions using ‘formol titrimetry’ method. The thermodynamic parameters like standard transfer Gibbs energies and entropies have been evaluated at 298.15 K. Other important parameters like molar volume, densities, solvent diameter, etc., of the experimental solutions have also been determined in this study. The above mentioned parameters have been used to determine ∆t,ch0(i)i.e., chemical effects of the transfer Gibbs energies and T∆t,ch0(i)i.e., chemical effects of the transfer entropy. The solvation of glycine is influenced by different factors such as nature of the solute, interactions between solute and solvents, etc., which has been explained by different physical and analytical approach.

Studies on the interaction of 2-amino-3-hydroxy-anthraquinone with surfactant micelles reveal its nucleation in human MDA-MB-231 breast adinocarcinoma cells

Structural and spectroscopic studies on 2-amino-3-hydroxy-anthraquinone (AQ), an analogue of anthracycline drugs, were carried out using computational methods. The interactions of AQ with anionic surfactant sodium dodecyl sulphate (SDS) and cationic surfactant cetyltrimethylammonium bromide (CTAB) were investigated in aqueous solution at physiological pH (7.4) by UV-Vis spectroscopy, and compared with the well-known anthracycline drugs. The affinity of such molecule to surfactant micelles may mean it can act as a model system for a biological membrane–drug interaction, which is important in determining the biological action of this molecule. The binding constant, partition coefficient and Gibbs free energy for the binding and distribution of AQ between the bulk aqueous solution and surfactant micelles were determined for AQ–surfactant interactions. It was observed that hydrophobic interaction plays a crucial role in the binding of AQ to SDS micelles, while the hydrophilic interaction plays an important role in its interaction with CTAB micelles. These interactions also have a vital role in the distribution of AQ between surfactant micelle–water phases. This study gives an idea that the present molecule may successfully permeate biological membranes, so AQ was allowed to interact with human breast adinocarcinoma cell MDA-MB-231. Experimental findings established that AQ induces apoptosis by means of nucleation into these cells.

Thermodynamics of DL-α-aminobutyric acid induced solvation mechanism in aqueous KCl solutions at 288.15–308.15 K

The solubilities of DL-α-aminobutyric acid in KCl solutions of different concentrations are measured at 288.15–308.15 K. Gibbs energies and entropies have been determined for transfer of α-aminobutyric acid form water to aqueous KCl solution at 298.15 K. The cavity, dipole-dipole and other interactions affecting the solubility, as well as stability of the amino acid in solution are also evaluated. Gibbs energy and entropy of transfer due to interactions are computed to create the model of the complex solute-solvent and solventsolvent interactions. Molar volume, densities, dipole moment of solvent and diameter of co-solvent in aqueous potassium chloride are also evaluated.

Employment of different spectroscopic tools for the investigation of chromium(VI) oxidation of acetaldehyde in aqueous micellar medium

Different spectroscopic methods have been applied to investigate the chromic acid oxidation of acetaldehyde in aqueous media, catalysed by surfactants. Three representative heteroaromatic nitrogen base promoters, 2-picolinic acid (PA), 2,2’-bipyridine (bpy) and 1,10-phenanthroline (phen), have been associated along with surfactants as promoters to the kinetic study. Comparative studies of unpromoted and promoted reactions invoked that 2,2’-bipyridine produced maximum rate enhancement. The mechanism of the reaction path has been proposed with the help of kinetic results and spectroscopic studies. The observed net enhancement of rate effects has been explained with scientific manipulations and data obtained. The combination of TX-100 and1,10-phenanthroline is found to be most effective for acetaldehyde oxidation.Graphical AbstractChromium(VI) oxidation of acetaldehyde in aqueous micellar media has been carried out. Micellar catalysis by TX-100 in association with a ‘phen’ promoter increases the rate of the reaction almost 60 fold. The combination of TX-100 and ‘phen’ is the most suitable one for chromic acid oxidation of acetaldehyde to acetic acid in aqueous media.

Picolinic Acid Promoted Permanganate Oxidation of D-Mannitol in Micellar Medium

Abstract Kinetics of permanganate oxidation of D-mannitol have been investigated spectrophotometrically under pseudo-first-order conditions in aqueous acidic media at 30 °C. The spectral analysis of hydrazone derivative of the product indicates the product to be an aldehyde. The observed rate constant value was found to be relatively slow in the uncatalyzed path, which increases by the presence of four isomeric promoters: 2-picolinic acid (2-PA), 4-picolinic acid (4-PA), 2,3-dipicolinic acid (2,3-diPA) and 2,6-dipicolinic acid (2,6-diPA). The catalytic effect of sodium dodecylbenzene sulfonate (SDBS) surfactant on the permanganate oxidation of D-mannitol has been also studied in the presence of the promoters. The critical micelle concentration (CMC) of SDBS alone and in presence of D-mannitol was determined by conductometry and spectrophotometry. The aggregation and morphological changes during reaction were studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The variation of the reaction rates for the different promoters in the presence and absence of SDBS micellar catalyst is discussed qualitatively in the terms of partitioning nature of substrate, charge of surfactant and reactants. 2,3-diPA in association with SDBS as micellar catalyst accelerated the reaction velocity compared to the uncatalyzed path.

A Co(II) complex of a vitamer of vitamin B6 acts as a sensor for Hg2+ and pH in aqueous media

A Co(II) complex of molecular formula C48H96.8N12O22.4Co2Cl2, 1, was synthesized from the Schiff base [H2pydmdp]Cl by a template reaction of pyridoxal (pyd), a vitamer of vitamin B6, N-methyl-1,3-diaminopropane (mdp) and cobalt(II) acetate. It was characterized by elemental analysis, 1H NMR, IR and UV-Vis spectroscopy, thermal analysis, electrochemistry and single crystal X-ray diffraction. The experimental results suggested that in complex 1, the central Co(II) is bonded to two phenolato-oxygens, two imine nitrogens and two amine nitrogens in an octahedral geometry. In aqueous media complex 1 exhibits an intense fluorescence emission peak at 506 nm when it was excited at 425 nm. The fluorescence behavior of complex 1 in aqueous media was employed to determine whether it acts as a chemosensor for some selective toxic metal ions. The studies showed that the present complex behaves as a promising sensor for Hg2+ even at the sub-micromolar level. In addition in aqueous solution, complex 1 acts as a sensor for the pH of the medium. A detailed study on the mechanism of sensing behavior established that Hg2+ interacts with complex 1 via weak non-covalent interaction with the N-atom of the pyridine moiety of the molecule. The pyridine nitrogen also plays a vital role in sensing the pH of the medium.

Solvation thermodynamics of L-cystine, L-tyrosine, and L-leucine in aqueous-electrolyte media

Solubilities of L-cystine, L-tyrosine, and L-leucine in aqueous NaCl media at 298.15 K have been studied. Indispensable and related solvent parameters such as molar mass, molar volume, etc., were also determined. The results are used to evaluate the standard transfer Gibbs free energy, cavity forming enthalpy of transfer, cavity forming transfer Gibbs free energy and dipole-dipole interaction effects during the course of solvation. Various weak interactions involving solute–solvent or solvent–solvent molecules were characterized in order to find their role on the solvation of these amino acids.