A thermodynamic study of alpha-, beta-, and gamma-cyclodextrin-complexed m-methyl red in alkaline solutions

作者：Khouri Sa'ib J^*; Abdel Rahim Ibrahim A; Shamaileh Ehab M

来源：Journal of Inclusion Phenomena and Macrocyclic Chemistry, 2013, 77(1-4): 105-112.

DOI：10.1007/s10847-012-0221-x

• Inclusion complexes
• Cyclodextrins
• Formation constant
• m-methyl red
• alpha- beta- and gamma-Cyclodextrin

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 (K-f) for the inclusion of basic form of m-MR with alpha-, Beta-, and gamma-Cyclodextrin (alpha-, beta- and gamma-CD) was evaluated at different temperatures using Benesi-Hildebrand method. The values of K-f at 25 A degrees C were found to be 8.70 x 10(3), 4.93 x 10(3) mol(-1) dm(3) and 2.95 x 10(7) mol(-2) dm(6) basis on the inclusion complex ratios (m-MR:CD) of 1:1, 1:1, and 2:1 respectively. The values of the thermodynamic quantities Delta HA degrees, Delta SA degrees, Delta GA degrees 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.

• 出版日期2013-12