Molecular interaction studies on the binding ability of hydrated zinc sulphate with aqueous solution of ascorbic acid at different temperatures

The ternary systems containing Water, Ascorbic acid (AA) and ZnSO4·7H2O were investigated using three approaches namely volumetric studies, viscosity studies and conductance studies. The solvent systems used were 2, 4 and 6% (by weight) of AA in water. The studies were conducted at four temperatures (303.15–318.15 K with an interval of 5 K) and pressure 0.1 MPa with concentration of ZnSO4·7H2O in the solution ranging from 0.01 to 0.12 m. Various parameters like partial molar volume (ϕ v), apparent molar volume ( ϕ v o ) $({\phi }_{\text{v}}^{\text{o}})$ , Hepler’s constant ( ( d 2 ϕ v o / d T 2 ) p ) $({({d}^{2}{\phi }_{\text{v}}^{\text{o}}/d{T}^{2})}_{p})$ , partial molar expansibility ( ϕ E o ) $({\phi }_{\text{E}}^{\text{o}})$ and transfer volume ( Δ t r ϕ v o ) $({{\Delta}}_{tr}{\phi }_{\text{v}}^{\text{o}})$ have been evaluated from volumetric studies. The viscosity studies have yielded Jones-Dole parameters (A and B) and free energy of activation per mole for solvent ( Δ μ 1 0 ‡ ) $({\Delta}{\mu }_{1}^{0{\ddagger}})$ and solute ( Δ μ 2 0 ‡ ) $({\Delta}{\mu }_{2}^{0{\ddagger}})$ . The conductance data has been used to calculate molar conductance (Λm), limiting molar conductance ( Λ m o ) $({{\Lambda}}_{\text{m}}^{\text{o}})$ and Walden product ( Λ m o η o ) $({{\Lambda}}_{\text{m}}^{\text{o}}{\eta }_{\text{o}})$ . The results of these studies agree with each other and have concluded the structure breaker behavior of ZnSO4·7H2O in the solvent system containing AA and water.

Molecular interaction investigation of some alkaline earth metal salts in aqueous citric acid at various temperatures by physiochemical studies

Densities, ultrasonic velocity, conductance and viscosity of some alkaline earth metal chlorides such as magnesium chloride (MgCl2) and calcium chloride (CaCl2) were calculated in the concentration range (0.01–0.12 mol kg−1) in 0.01 mol kg−1 aqueous solution of citric acid (CA + H2O) at four varying temperatures T 1 = 303.15 K, T 2 = 308.15 K, T 3 = 313.15 K and T 4 = 318.15 K. The parameters like apparent molar volume (ϕ v ), limiting apparent molar volume ( ϕ v o ${\phi }_{v}^{o}$ ) and transfer volume (Δtr ϕ v o ${\phi }_{v}^{o}$ ) were calculated from density data. Viscosity data have been employed to calculate Falkenhagen coefficient (A), Jone–Dole’s coefficient (B), relative viscosity (η r ), and relaxation time (τ) whereas limiting molar conductance ( Λ m o ${{\Lambda}}_{m}^{o}$ ) has been evaluated from conductance studies. Using these parameters, various type of interactions occurred in the molecules have been discussed. Values of Hepler’s constant (d 2 ϕ v o ${\phi }_{v}^{o}$ /dT 2) p , (dB/dT) and d( Λ m o ${{\Lambda}}_{m}^{o}$ η o )/dT suggests that both MgCl2 and CaCl2 behave as structure breaker in (CA + H2O) system. The positive value of transfer volume exclusively tells about solute–solvent interactions which further indicate that both metal chlorides distort the structure of water and act as structure breaker. These studies are helpful in understanding the nature of interactions occurs in biological systems as CA and metal salts are essential for normal functioning of body.

Thermodynamics and acoustic effects of quercetin on micellization and interaction behaviour of CTAB in different hydroethanol solvent systems

Flavonoids amongst the class of secondary metabolites possess numerous health benefits, are known for its use in pharmaceutical industry. Quercetin, a flavonoid has more prominent medical advantages however its utilization is constrained because of various instability and insolubility issues and therefore, taken into consideration for studying its physico-chemical properties. In view of that, the thermodynamic and thermoacoustic properties of quercetin were examined in presence of cationic surfactant cetyltrimethylammonium bromide (CTAB) at different hydroethanolic concentrations and temperatures. The conductivity studies were used to calculate change in enthalpy (∆H o m ), change in entropy (∆S o m ) and change in Gibbs free Energy (∆G o m ) of micellization. The interactions between quercetin and CTAB were found to be endothermic, entropically controlled and spontaneous. Further, ultrasonic sound velocity and density studies were carried out and utilized for the calculation of thermoacoustic parameters i.e. apparent molar volume and apparent molar compressibility. Thermoacoustic properties revealed that at higher surfactant concentration, hydrophobic interactions are dominant. The results suggested that the flavonoid-surfactant interactions in hydroethanolic solutions is more favourable as compared with aqueous solution. Overall, the data is favourable for the framework to be used for detailing advancement, drug development, drug industry, pharmaceutical industry, medical administration and formulation development studies.

On the Thermodynamics of Micellizationof Oppositely Charged Surfactants in the Presence of Organic Additives in the Aqueous Medium

To investigate the effect of additives urea and thiourea, on the micellization behavior of sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB), detailed conductance measurements were carried out in aqueous media at different temperatures. The critical micelle concentration (CMC), determined from the discontinuity in the plots of molar conductance versus square root of concentration, indicated an inhibitory effect of urea and thiourea on micelle forming ability of the surfactants SDS and CTAB in the range of composition studied. The demicellizing effect of urea has been found to be more pronounced in SDS than CTAB. These observations are further augmented by the evaluation of thermodynamic parameters of micellization. A negative change in enthalpy of micellization ( Δ H m ∘ $\Delta{\text{H}}_{\text{m}}^{\circ}$ ) indicates a strong interaction between water and the additives and a positive change observed in entropy of micellization ( Δ S m ∘ $\Delta{\text{S}}_{\text{m}}^{\circ}$ ) manifest, that the micellization is an entropy-driven process. Further Δ H m ∘ $\Delta{\text{H}}_{\text{m}}^{\circ}$ and Δ S m ∘ $\Delta{\text{S}}_{\text{m}}^{\circ}$ change in mutually compensating manner, so that Δ G m ∘ < 0 $\Delta{\text{G}}_{\text{m}}^{\circ} < 0$ is not significantly affected. Finally, the counterion binding values (β) obtained for SDS and CTAB remain practically constant from 0.6 to 0.8 between 25 °C and 45 °C indicate that the size and shape of micelle remain essentially constant. Moreover, the increase in Δ G II ∘ $\Delta{\text{G}}_{{\text{II}}}^{\circ}$ values, which represent the effect of co-solvent or additive on micellization, substantiates the above observations. Many early works has investigated the micellization behavior of surfactants using a fixed additive composition. However, in this study, variable aqueous compositions of urea (0.30–1.78 wt%) and thiourea (0.24–1.41 wt%) have been considered.

Decomposition Kinetics of Levofloxacin: Drug-Excipient Interaction

The present study is focused on the thermal decomposition of Levofloxacin in the absence and presence of different excipients (sodium starch glycolate, magnesium stearate, microcrystalline cellulose and lactose using Thermogravimetry (TG). Fourier Transform Infra Red Spectroscopy (FTIR) and Differential Scanning Calorimetry (DSC) were used to study the possible drug – excipient interaction. It has been shown that the interaction of the first three excipients (sodium starch glycolate, magnesium stearate, and microcrystalline cellulose) with Levofloxacin is physical in nature. Lactose was shown to decrease the degradation temperature to a maximum extent. This indicates a strong chemical interaction between the drug and lactose. The activation energies in the former case were found almost similar but deviated considerably in the latter case.

Effect of Maltodextrin and Temperature on Micellar Behavior of Bile Salts in Aqueous Medium: Conductometric and Spectrofluorimetric Studies

Conductivity and fluorescence probe techniques have been employed to study the micellar behavior of bile salts i.e. sodium cholate (1–20 mmol⋅kg−1) and sodium deoxycholate (0.5–10.0 mmol⋅kg−1) in aqueous solutions of maltodextrin (0.0, 0.5, 1.1, and 1.6 mmol⋅kg−1) at different temperatures. The influence of maltodextrin on the micellization behavior of bile salts has been determined in terms of critical micelle concentration (CMC) values obtained from conductivity measurement. The variation in CMC values has been discussed by considering the alteration in the hydrophobic environment of maltodextrin-sodium cholate/sodium deoxycholate complex imparted by the carbohydrate molecules. In order to substantiate the CMC values determined from conductivity method, the fluorescence probe study of aqueous sodium cholate and sodium deoxycholate solutions in presence of fluorescent, pyrene has also been carried. The CMC values obtained from both techniques are in full agreement with each other. Moreover, application of charged pseudo-phase separation model has been made to discuss the thermodynamics of the system.