Experimental and Molecular Mechanical Studies of Complexation of Some 2H- and 3H- Indole Derivatives with Aqueous β-Cyclodextrin

Author： Al-Sou’od Khaldoun Zughul Mohammad Badwan Adnan

Publisher： Springer Publishing Company

ISSN： 0095-9782

Source： Journal of Solution Chemistry, Vol.35, Iss.10, 2006-10, pp. : 1377-1388

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Abstract

Phase solubility diagrams (PSDs) at 25 ^∘C and molecular mechanical (MM) modeling were used to study the aqueous complexation of some 2H- and 3H-indole derivatives with β-cyclodextrin (β-CD). Among the 3H-indole derivatives investigated in this work, indole-3H-butyric acid forms the most stable 1:1 complex of the B_s-type PSD, whereas shorter chain derivatives form soluble 1:1 complexes (A_L-type PSDs) with their stability increasing as the chain length increases. Indole-2 carboxylic acid forms highly stable 1:1 and 1:2 complexes, with the lower-order complex reaching saturation first (B_s-type PSD). MM modeling indicates that the stability of the complex is highly correlated with the flexibility of the 3H-indole hydrocarbon chain, which yields a better geometrical fit within the β-CD cavity resulting from different hydrophilic interactions. These interactions are represented in the H-bonding of the carboxyl group with the primary hydroxyl group network that is situated at the narrow rim of the cavity, and also by a favorable interaction of the aromatic ring with the hydroxyl group network at the other rim.