Chemistry

Two manganese(II) carbodithioates, i.e. [Mn(4-MPipzcdtH) 2 ](X) 2 and two manganese(III) carbodithioates of the type [Mn 2 (4-MPipzcdtH) 6 (O 2) 2 ](X) 4 (4-MPipzcdtH = 4-methylpipearzine-1-carbodithioic acid and X = ClO 4 , Cl) have been prepared. These have been characterized by elemental analyses, conductance, infrared and electronic absorption spectral and room temperature as well as variable temperature magnetic susceptibility measurements. Manganese(II) complexes exhibit antiferromagnetic behavior. Antiferromagnetic interactions through superoxo bridge have been proposed for temperature dependent magnetic behaviour of manganese(III) complexes.

The apparent molar volume of ammonium bromide and ammonium nitrate has been determined in various solutions of ammonium chloride at 30~ from density measurements using an hydrostatic balance. The molar volumes show a linear function of concentration. The values of NH~Br, NH,NOs are larger in NH,CI solutions than in pure water and this has been attributed to the increase in the interactions of NH,Br and NH4NOs with NH,CI. The mean apparent molar volume of NH4Br-NH,CI and NH~NOs-NH,CI solutions have also been estimated directly from density measurements as well as from pure water data using Young's rule. The deviations are approximately studied as excess volume of mixing of NH,Br and NH4NOs with NH4CI. I~yword& Molar volumes; Young's rule; solute-solvent interactions; ammonium chloride ; ammonium salt.

Using the WIEN2K code, the hydrogen storage capabilities of lithium-based KXH3 (X = Zn, Co) hydrides perovskites are examined. To verify the stability of these hydrides, first-principles simulations are employed to examine their structural, electronic, and hydrogen storage capabilities. These compositions' structural investigation shows that the hydrides are stable and part of the cubic space group (221 Pm-3m). We have examined several aspects of these composition's features throughout, using the Perdew-Burke-Ernzerhof generalized gradient approximation. The study identifies stable phases and structural parameters of hydrides using BE equations, assessing thermodynamic stability in terms of hydrogen storage capacities. The metallic nature of these hydrides is confirmed through band structure and density calculations using WIEN2K.

Using the WIEN2K code, the hydrogen storage capabilities of lithium compositions like LiXH 3 (X = Pd, Ag, Cd) hydrides are examined. Structural, electrical, mechanical, thermoelectric, and hydrogen storage properties of these hydrides are analyzed using first-principles simulations to verify their stability. Structural analysis of these compositions reveals that the hydrides are stable and belong to the cubic space group number (221 Pm-3m). The thermodynamic stability of these hydrides are given in term of gravimetric hydrogen storage capacities. The purpose of the study is to calculate calefaction of formation and breakdown temperature to determine stability of these hydrides. The metallic nature of all compositions are confirmed by band plots and density of states. The elastic properties such as elastic constant, Pugh's ratio, bulk modulus, Poisson's ratio and anisotropy factor are calculated to check the applicability of these compositions for applications involving hydrogen storage. The present paper represents the initial theoretical approach toward the future exploration of these material for hydrogen storage applications.

Apparent molar volumes (/ v), apparent molar adiabatic compressions (/ j) and thermodynamic parameters of cetyltrimethyl ammonium bromide (CTAB) in 0.001, 0.01, 0.05 and 0.1 molÁdm-3 aqueous solution of glycine in the temperature range 25–40 °C (at an interval of 5 °C) have been determined from density, speed of sound and conductometric measurements, respectively. The above calculated parameters were found to be sensitive to the interactions prevailing in the glycine–CTAB–water system. The analysis of the data was found to suggest that the / v and / j values decrease sharply in the pre-micellar region and thereafter the decrease is almost linear at all concentrations of glycine, showing the dominance of hydrophobic interactions and facilitating the process of micellization. The / v and / j values of these surfactants are found to be completely consistent with temperature over the entire concentration range. From conductance studies, the value of critical micelle concentration has been calculated, which shows dependence on the concentration of glycine as well as on temperature. A reasonably good qualitative correlation is found to exist with regard to CTAB–glycine interactions obtained from the conductance measurements and those from density and sound velocity measurements. All these observations demonstrate that this amino acid–surfactant system behaves in a different manner as compared to amino acid–electrolyte systems.

In the present studies, micellization behavior of cetyltrimethylammonium bromide, CTAB (cationic surfactant) has been studied in the aqueous solution, containing 0.001, 0.005, 0.01, 0.025, 0.05, 0.075 and 0.1 M leucine as a solvent, using specific conductances (κ), densities (d) and velocities of sound (v), in the temperature range 25–40 °C at an interval of 5 °C. The cmc of CTAB was determined from the plots of specific conductance (κ) of CTAB in aqueous leucine solution. The cmc values of surfactant increase with increase in temperature but they decrease linearly with increase in the concentration of the leucine. By using cmc data various thermodynamic parameters have also been evaluated. The apparent molar volume (ϕ v) and apparent molar adiabatic compressibil-ity (ϕ κ) have been computed using densities and velocities of sound data. The above calculated parameters were found to be sensitive towards the interactions prevailing in the leucine–CTAB–water systems. The analysis of the data is found to suggest that ϕ v and ϕ κ values in general are positive at all temperatures and increase with rise in temperature while decrease sharply to about 0.8 mM [CTAB] at all concentrations of leucine. Thereafter, the decrease is almost linear. The cmc as determined from the fluorescence measurements indicating a transition point of I 1 /I 3 plot which shows that the cmc lies at ≈0.8 mM, the results of which are consistent with the other physico-chemical studies. A reasonably good qualitative correlation is found to exist with regard to CTAB–leucine interactions obtained from the different measurements.

Densities (d) and sound velocities (v) of an ethoxylated alkyl phenol surfactant in aqueous solutions of two amino acids, namely glycine and leucine, have been measured over a temperature range of 25–40 °C at intervals of 5 °C by using density and sound analyzers. Experimental data have been used to calculate the isen-tropic compressibilities (j s), apparent molar volumes (/ v) and apparent molar adiabatic compressions (/ j) in order to explain amino acid–surfactant interactions. The results have been discussed in terms of the effect of amino acids on the micellization behavior of the surfactant. A comparative study of both the amino acids has been carried out and is found that both amino acids produce a decrease in the CMC value of nonionic surfactant but to different extents.

Volumetric and viscometric properties of glycine and methionine (amino acids) in a 0.2 vol. % amikacin sulphate (antibiotic drug) aqueous solution with the molality range of 0.025 mol kg −1 – 0.25 mol kg −1 were measured over the temperature range of 20 • C – 40 • C at the interval of 5 • C. Different parameters like apparent molar volume (φV), apparent molar adiabatic compression (φκ), isentropic compression (κS) along with other acoustical parameters were calculated. Parameters like viscous relaxation time (τ), free volume (VF), internal pressure (ΠI), and molar cohesive energy (MCE) were calculated from dynamic viscosity measurements. The φV values are positive in both cases, but with higher magnitude observed in methionine. These positive values of φV are indicative of strong solute–solvent interactions at all temperatures. In case of methionine there is a sharp initial increase in the φV values which become almost constant with further additions of the amino acid. Structural differences in the two amino acids studied are clearly reflected in the different nature of the plots of different parameters. In case of an amino acid–drug system, dynamic viscosity increase has been attributed to the increase in the hydrophilic–ionic and hydrophilic–hydrophilic interactions with the increase in the amino acid concentration which in turn may cause more frictional resistance to the flow of the solution. All other parameters are discussed in terms of solute–solvent and solvent– solvent interactions.

Carbohydrate–surfactant interactions and micellization behavior of anionic surfactant (sodium dodecyl sulfate, SDS) in aqueous solution of (0, 0.5, 1.0 and 1.5% w/v) maltodextrin have been studied using density, sound velocity, viscosity and surface tension in the temperature range of 20–40 • C at an interval of 5 • C. Density and speed of sound data have been used to derive parameters like isentropic compressibility (Ä s), apparent molar volume (˚ v) and apparent molar isentropic compression (˚ k). Surface tension has been used to calculate surface excess concentration (max), minimum area occupied by the surfactant (A min) and surface film pressure (cmc) whereas relaxation time () is calculated using viscosity data. Volumetric measurements indicate that˚v values are positive and generally increase with rise in temperature as well as with increase in percentage of maltodextrin (0.5–1.5%). Viscous relaxation time () and surface tension () have been found to decrease with rise in temperature.

Specific conductance of (0.3 to 3.0) mmol Á kg À1 sodium dodecyl benzene sulfonate (SDBS) and (3.0 to 30.0) mmol Á kg À1 dodecyltrimethylammonium bromide (DTAB) has been determined in water and in the presence of (0.01, 0.05 and 0.10) mol Á kg À1 aqueous solution of glutamine/histidine/methionine at T = (293.15, 298.15, 303.15, 308.15 and 313.15) K. From the conductivity data, the critical micellar concentration (CMC) and thermodynamic parameters of micellization (DG o m ; DH o m and DS o m) have been computed by applying the mass action model. Enthalpy–entropy compensation effect has also been observed. The effect of amino acid on the micellar properties of SDBS and DTAB depends upon their nature , concentration, as well as on temperature and has been used to study the interactions present in the micellar systems. There occurs a gradual increase in the value of CMC with temperature in case of SDBS while in case of DTAB, it passes through a broad minimum and then tends to increase with increase in temperature. Increase of amino acid concentration is found to decrease CMC in both the surfactants. The DG o m values are negative and the feasibility of the micellization is found to increase with rise in temperature. The magnitude of hydrophilic and hydrophobic dehydration determines whether the CMC values increase or decrease with rise in temperature.

In this paper, we examine density (d), ultrasonic velocity (u) and viscosity studies of SDBS and DTAB in water and in aqueous solutions of 0.01, 0.05, 0.10 mol kg −1 l-glutamine, l-histidine and l-methionine at T = 293. 15, 298.15, 303.15, 308.15, 313.15 K. The apparent molar volume ( v ) dependence on SDBS and DTAB concentration reflects the modification of water-water interactions described as hydrophobic hydration of the surfactant molecules in the presence of amino acid. The trends of apparent molar adiabatic compression ( k ) values of DTAB with surfactant concentration appear reasonable to suggest that hydrophilic hydration of DTAB-amino acid complex occurs at low surfactant concentration region rendering it to be negative. The gradual increase in viscous relaxation time ( ) with rise in concentration of surfactant and decrease with temperature seem to be happen due to the structural relaxation processes occurring as a result of re-arrangement of molecules.

The surface tension and fluorescence measurements have been carried out to study the interactions
present between anionic surfactant, sodium dodecyl benzene sulfonate (SDBS) and cationic surfactant,
dodecyltrimethylammonium bromide (DTAB), in aqueous solution, in presence and absence of additives
(glutamine, histidine and methionine) at different composition and temperature. Critical micelle concentrations
(CMCs) have been determined using surface tension measurement. In case of SDBS, the CMC
value increases with rise in temperature while in case of DTAB, it shows a U-type behavior, meaning
thereby, both hydrophobic and hydrophilic dehydration becomes prominent in case of DTAB while only
hydrophilic dehydration plays decisive role for the micellization to take place in case of SDBS. From
surface tension data, the surface excess concentration at air/water interface ( max), minimum area per
surfactant molecule (Amin) and the surface pressure at CMC (CMC) have been evaluated. Thermodynamic
parameters of transfer, adsorption and micellization have also been evaluated and discussed in detail.
Fluorescence probe study has been carried out to outline the results stated above. The CMC values calculated
using pyrene as a fluorescent probe at room temperature resembles well with the micellar values
determined using surface tension measurement.

In this paper, micelle formation of a well known anionic surfactant, sodium dodecyl sulfate (SDS) in aqueous solutions of four structurally different sugars viz. ribose, glucose, sucrose and raffinose at wide temperature range T = (293.15–318.15) K has been studied. From specific conductance data, the value of CMC and X CMC have been calculated whose dependence on sugar concentration correlates well with the hydrophobic nature of sugar molecule. A non-linear trend in CMC values is attributed to the presence of both hydrophilic and hydrophobic dehydrations. From X CMC values, thermodynamic parameters such as standard enthalpy (H m •), standard entropy (S m •), and standard free energy of micellization (G m •) have also been evaluated. The results of these thermodynamic parameters have been discussed in terms of the structural consequences of the intermolecular interactions. Enthalpy–entropy compensation gave linear dependence, thus suggesting that micellization of SDS is governed by the delicate balance of sugar–water interactions by changing the structural property of water in the presence of sugars. The effect of organic solvents such as dimethyl sulfoxide (DMSO), methanol (MeOH) and dioxane has also been discussed in detail.

In the present study, we have investigated in detail the interactions of the anionic surfactant sodium dodecyl sulfate (SDS) with aqueous polyethylene glycol (PEG), polyvinyl pyrrolidone (PVP) and various PEG ? PVP mixtures at 293.15, 303.15 and 313.15 K by applying conductivity , density and speed of sound techniques. From experimentally measured data, the critical micelle concentration (CMC) values, standard free energy of micellization (DG m o), standard enthalpy of micellization (DH m o), standard entropy of micellization (DS m o), isentropic compressibilities (j s), apparent molar volumes (/ v) and apparent molar isen-tropic compressions (/ k) of SDS in aqueous polymer mixtures have been calculated. The nature of the process of micellization has been evidenced from the magnitude of DG m o , DH m o and DS m o values. The trends of variations obtained in the various parameters have been explained in terms of the electrostatic as well as hydrophobic interactions pertaining in SDS-PEG/PVP-water systems.

The volumetric properties for this mixture of amino acid–surfactant system have already been discussed in an earlier published article, but to go further into the details on molecular interactions, different acoustical parameters viz. relative association (RA), intermolecular free length (L f), molar sound number ([U]), specific acoustic impedance (Z), free volume (V f), molar volume (V m), internal pressure (π i) and molar cohesive energy (MCE) have been evaluated from the parent data of density, speed of sound and viscosity. The variation of these parameters with concentration of surfactant helps us in understanding the nature and extent of interactions present among the molecules in the mixture. The effect of amino acid concentrations on the micellization behavior of these surfactants has also been discussed through these parameters.