A thermodynamic study of α-, β-, and γ-cyclodextrin-complexed m-methyl red in alkaline solutions
作者:Sa’ib J. Khouri、Ibrahim A. Abdel-Rahim、Ehab M. Shamaileh
DOI:10.1007/s10847-012-0221-x
日期:2013.12
The UV/Visible spectra of m-methyl red (m-MR) (3-[4-(dimethyl-amino) phenylazo] benzoic acid}) were examined in basic, acidic and strongly acidic aqueous solutions. The observed spectra of m-MR were analyzed and compared with the tautomeric and resonance structures that suggested theoretically. Three isosbestic points in the spectra were observed around 508, 464 and 443 nm representing three different equilibriums between four different species of m-MR. The inclusion constant (Kf) for the inclusion of basic form of m-MR with alpha-, Beta-, and gamma-Cyclodextrin (α-, β- and γ-CD) was evaluated at different temperatures using Benesi-Hildebrand method. The values of Kf at 25 °C were found to be 8.70 × 103, 4.93 × 103 mol−1 dm3 and 2.95 × 107 mol−2 dm6 basis on the inclusion complex ratios (m-MR:CD) of 1:1, 1:1, and 2:1 respectively. The values of the thermodynamic quantities ΔH°, ΔS°, ΔG° for the different inclusion processes were calculated by using Van’t Hoff plot. For all cases of the studied inclusion processes, these inclusions were favored through entropy and enthalpy changes.
在碱性、酸性和强酸性水溶液中检查了间甲基红 (m-MR)(3-[4-(二甲基氨基)苯基偶氮]苯甲酸})的紫外/可见光谱。对观察到的 m-MR 光谱进行了分析,并与理论上提出的互变异构和共振结构进行了比较。在 508、464 和 443 nm 附近观察到光谱中的三个等吸光点,代表四种不同 m-MR 物种之间的三种不同平衡。使用 Benesi-Hildebrand 方法在不同温度下评估 m-MR 基本形式与 α-、Beta- 和 γ-环糊精(α-、β- 和 γ-CD)的包合常数 (Kf)。根据 1:1、1 的包合物比 (m-MR:CD),25 °C 时的 Kf 值为 8.70 × 103、4.93 × 103 mol−1 dm3 和 2.95 × 107 mol−2 dm6分别为 :1 和 2:1。利用 Van’t Hoff 图计算了不同夹杂过程的热力学量 ΔH°、ΔS°、ΔG° 的值。对于所研究的夹杂物过程的所有情况,这些夹杂物通过熵和焓变化而受到青睐。