[Show abstract][Hide abstract] ABSTRACT: The effect of the addition of cyclodextrins (CD) viz., alpha-, beta-, HPbeta- and gamma-CD to the aqueous solutions of the most widely prescribed anti-inflammatory drug, diclofenac sodium (DS), has been fully investigated by means of spectroscopic (UV-vis, steady-state fluorescence, (1)H NMR and ROESY) and thermodynamic (conductivity) techniques. The global picture of the results indicates that diclofenac sodium penetrates the CD cavity. The apparent association constants for all the inclusion complexes were estimated from fluorescence data. Conductivity measurements of aqueous solutions of diclofenac sodium were performed both as a function of DS concentration and CD concentration, at different temperatures ranging from 15 to 40 degrees C. Results suggested the existence of 1:1 complex between DS and CD. The thermodynamics of the system was discussed in terms of change in Gibbs free energy. Free energy of the DS/W system was found to decrease on addition of cyclodextrin, which points towards the energetically favorable interactions between drug and cyclodextrin molecules in solution phase. (1)H NMR chemical shift changes and ROESY spectra provide powerful means for probing CD:DS interactions.
Full-text · Article · Oct 2008 · Journal of Colloid and Interface Science
[Show abstract][Hide abstract] ABSTRACT: Conductivity, static fluorescence and 1H NMR measurements have been carried out to study the micellar behavior of aqueous solutions of dodecyldimethylethylammonium bromide (DDAB), dodecyltrimethylammonium chloride (DTAC) and tetradecyltrimethylammonium chloride (TDAC) in absence and presence of α-cyclodextrin (α-CD), β-cyclodextrin (β-CD), hydroxypropyl-β-cyclodextrin (HPβ-CD) and γ-cyclodextrin (γ-CD). The conductivity measurements were carried out at 298.15 K. The influence of cyclodextrins on the micellar parameters, such as cmc∗ (apparent critical micellar concentration), β (degree of ionization) have been analyzed. Thermodynamics of the systems was discussed in terms of the change in standard free energy of micellization, ΔGm0. Micellization was found to be less spontaneous in presence of cyclodextrins. The fluorescence intensity of the surfactant solutions is enhanced by the addition of cyclodextrins. The association constants obtained from conductivity and fluorescence data suggest the binding of γ-CD with the surfactants to be strongest among all the cyclodextrins used. 1H NMR chemical shift changes provide powerful means for probing the cyclodextrin–micellar interactions and inclusion of surfactant is shown by the change in the chemical shift of some of the guest and host protons in comparison with the chemical shifts of the same protons in the free compounds.
No preview · Article · May 2008 · Journal of Colloid and Interface Science
[Show abstract][Hide abstract] ABSTRACT: The micellar properties of cationic surfactants (S) viz. dodecyldimethylethyl ammonium bromide (DDAB) and dodecyltrimethylammonium chloride (DTAC) in aqueous media in the presence of diclofenac sodium (D) have been investigated by spectroscopic and conductivity measurements. The UV–vis and 1H NMR studies suggest possible packing of diclofenac sodium molecules in the micelles. The conductivity studies were carried out over the temperature range 288.15–308.15K. The critical micelle concentration (cmc) and degree of counterion binding (β) of the micelles were determined at different temperatures. Delay in micellisation was observed for both DDAB and DTAC. Thermodynamic parameters (ΔGm0, ΔHm0 and ΔSm0) for the micelle system were estimated by applying the charged pseudo-phase separation model. The results of the ternary S/D/W system were analysed in comparison with the reported results of binary S/W system. The ΔGm0 values for the ternary S/D/W system in both the cases show an increase in comparison to the respective binary S/W system. However, ΔSm0 decreased with temperature and remained positive in both the systems. At lower temperatures, the micellisation was found to be entropy-driven while at higher temperatures it was enthalpy-driven.
Full-text · Article · Apr 2006 · Colloids and Surfaces A Physicochemical and Engineering Aspects
[Show abstract][Hide abstract] ABSTRACT: Micellar behavior of cationic surfactants, dodecyldimethylethylammonium bromide (DDAB) and dodecyltrimethylammonium chloride (DTAC) in aqueous media has been investigated over the temperature range 288.15–308.15 K. The critical micelle concentration (cmc) and degree of ionization (β) of the micelles were determined from the conductivity measurements at different temperatures. The cmc behavior of DDAB and DTAC was analyzed in comparison with the results of DTAB in terms of effect of counter ion and increase in alkyl chain. Thermodynamic parameters (, and ) for the micelle system were estimated by applying the charged pseudo-phase separation model. At lower temperatures, the micellization in case of DDAB was found to be entropy-driven while at higher temperatures it was enthalpy-driven. In case of DTAC only entropic effect dominates over the entire temperature range.
No preview · Article · Mar 2005 · Colloids and Surfaces A Physicochemical and Engineering Aspects
[Show abstract][Hide abstract] ABSTRACT: The behavior of rifampicin (D) with β-cyclodextrin (β-CyD) in aqueous media (W) has been examined by means of UV-vis spectroscopy and conductivity measurements over the temperature range 15-30 °C. The UV-vis study has been used to characterize the systems. The estimated molar absorption coefficient ε for D/CyD/W system was 10757±280 M-1 cm-1 in comparison to the value of 6133±99 M-1 cm-1 for D/W system. The conductivity was measured (i) as a function of [D] for binary D/W systems, (ii) as a function of [CyD], keeping the concentration of drug constant, for D/CyD/W system, and (iii) as a function of [D] in the presence of a constant cyclodextrin concentration. Two transition points were observed for D/CyD/W system at constant [CyD], which were assigned as cac-1 and cac-2. The stoichiometry of the association was estimated from the conductivity data. This was obtained from [drug] value at which the change in slope of K occurs. The standard free energy change, ΔGao of aggregation was also calculated from the critical concentration data. An attempt has also been made to estimate the stoichiometry of β-cyclodextrin:rifampicin association.
No preview · Article · Feb 2005 · Colloid and Polymer Science