Behavior of rifampicin in association with<Emphasis Type="Italic"> β</Emphasis>-cyclodextrin in aqueous media: a spectroscopic and conductometric study

The behavior of rifampicin (D) with -cyclodextrin (-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 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 occurs. The standard free energy change, of aggregation was also calculated from the critical concentration data. An attempt has also been made to estimate the stoichiometry of -cyclodextrin:rifampicin association.     

Determination of Aggregation Parameters of Hexadecyltrimethylammonium Bromide from Probe Absorption

The mean aggregation number (n) and the critical micelle concentrations (CMC) of reverse micelles formed by hexadecyltrimethylammonium bromide have been determined by means of an optical absorption probe (acridine orange). The procedure to obtain these quantities from absorption spectrophotometric measurements is described. The CMC and mean aggregation number are in satisfactory agreement with published results obtained from more sophisticated methods.     

The aggregation of sodium dehydrocholate in water

 We used a battery of different methods to study the association in aqueous sodium dehydrocholate (NaDHC) solutions. This salt associates by a stepwise mechanism. Below (9.6 ± 4.2) × 10⁻⁴ mol dm⁻³ there is a molecular solution with some strongly insoluble dehydrocholic acid produced by hydrolysis. Between (9.6 ± 4.2) × 10⁻⁴ and (5.2 ± 2.2) × 10⁻³ mol dm⁻³, an aggregate similar to acid soap (NaDHC.HDHC) appears and its amount and the aggregate's size increase with concentration. At =(2.20 ± 0.85) × 10⁻² mol dm⁻³ the aggregates formed have properties usually associated with true micelles, such as solubilisation of water-insoluble dyes. These aggregates increase in size with concentration and change their shape at 8 × 10⁻² mol dm⁻³, giving nonsymmetrical aggregates. The changes in the solution physicochemical properties at these concentrations may be misinterpreted and this explains the different values of the critical micelle concentration reported in the literature for substances with similar structure, such as bile salts. Received: 14 May 2001 Accepted: 10 August 2001     

A temperature study on critical micellization concentration (CMC), solubility, and degree of counterion binding of α-sulfonatomyristic acid methyl ester in water by electroconductivity measurements

 For a sodium salt of α-sulfonatomyristic acid methyl ester (14SFNa), one of the α-SFMe series surfactants, critical micellization concentration (CMC), solubility and degree of counterion binding (β) were determined by means of electrocon-ductivity measurements at different temperatures (at every 5 °C) ranging from 15 to 50 °C. The phase diagram of 14SFNa in pure water was constructed from the CMC- and solubility-temperature data, in which the Krafft temperature (critical solution temperature) was found around 0 °C. The changes in the Gibbs energy, ΔG ⁰ _m, enthalpy, ΔH ⁰ _m, and entropy, ΔS ⁰ _m, upon micelle formation as a function of temperature were evaluated taking βvalues into calculation. Received: 28 August 1996 Accepted: 5 November 1996     

Optimization strategies in micellar electrokinetic capillary chromatography

Summary Computer-assisted procedures for the one-parameter optimization of the surfactant concentration and the concentration of urea or D-glucose as modifiers in micellar electrokinetic capillary chromatography have been developed. These procedures permit a rapid optimization of one parameter on the basis of only two experiments. Predicted values are compared to empirically obtained optimum values. The influence of the modifier concentration on the critical micelle concentration of sodium dodecyl sulfate was experimentally determined in buffers commonly employed in micellar electrokinetic chromatography. The alteration of retention factors of solutes caused by the influence of urea addition on the critical micelle concentration of sodium dodecyl sulfate was calculated under the assumption of constant distribution coefficients and compared to experimentally obtained values. It was demonstrated that the addition of urea or of D-glucose does not alter the phase ratio substantially.     

离子液体[BMim]BF4对SDS水溶液表面活性和聚集能力的促进

采用表面张力测定法和核磁共振谱等方法研究了阴离子表面活性剂十二烷基硫酸钠(SDS)在水溶性室温离子液体[BMim]BF4/水混合溶剂中的表面性质及聚集行为, 发现极少量[BMim]BF4的介入就可以显著降低SDS的临界胶束浓度, 提高体系的表面活性; 且[BMim]BF4在混合溶剂中所占的摩尔分数(x1)在一定范围内(0相似文献   

分子内环化对聚乙烯醇交联体系的影响

以聚乙烯醇(PVA)-戊二醛(GA)体系作为研究对象, 系统地研究了分子内环化对凝胶体系的影响, 为水凝胶体系的网络结构评价奠定了一定的实验基础.     

无机盐对正负表面活性剂混合体系性质的影响

用滴体积法测定了四种离子强度下(μ=0.02, 0.05, 0.1, 0.2 mol·kg~(-1), 支持电解质为NaBr)C_(12)H_(25)SO_4Na/C_6H_(13)(NC_5H_5)Br混合体系在五种比例(10:1, 3:1, 1:1, 1:3, 1:10)时的临界胶团活度cma(25 ℃). 提出了无机盐对正负表面活性剂混合体系临界胶团活度的影响程度的计算式.     

吸附伏安法测定表面活性剂的临界胶束浓度

以易溶于有机溶剂，微溶于水的氧化－还原指示剂中性红为探针，用吸附伏安法测定了阴离子表面活性剂的临界胶束浓度。测量的基本原理是：存在于表面活性剂溶液中的微量中性红在悬汞电极上的吸附伏安峰电流对表面活性剂浓度的曲线在临界胶束浓度处有一拐点。