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The conformational mobility of peptide molecules plays a significant role in peptide-receptor interactions and quantitative structure-activity relationships. As a receptor mimetic system, bis(2-ethylhexyl) sodium succinate (AOT) reversed micelles containing an aqueous solution of one of the melanotrophine inhibiting factor analogues prolyltyrosyl-glycinamide hydrochloride in the inner cavity have been used. Two-dimensional nuclear magnetic resonance spectroscopy (NOESY) and 13C spin-lattice relaxation time measurements have been used to establish that the peptide molecule assumes the biologically active beta II turn conformation when it is adsorbed at the surfactant-water border. This conformation is stabilized by intramolecular H-bonding between the proline carbonyl oxygen atom and amide protons. Moreover, it has been shown that the phenyl ring of tyrosine was inserted into the AOT intermolecular cavity, which is located between the polar AOT groups and the branches of iso-octane fragments. By and large, the phenyl ring acts as a hydrophobic anchor. Reversed micelles can be regarded as providing a realistic model of the receptor.

Understanding the mechanisms of mutual recognition and complementary binding of molecules in guest-The boom development of cyclodextrin (CD) chemistry is explained by the unique ability of these compounds to form guest-host complexes with many organic and inorganic molecules [1], which belong to virtual-topological isomers, and is related with the evolution of a new field of chemistry -supramolecular chemistry [2]. This ability makes it possible to use CD as enzyme models or, in general, as molecular sensors modeling receptor binding [3, 4], as catalysts for chemical reactions [5], modifiers for pharmaceuticals [6][7][8], etc.A rather promising technique for raising the solubility and biological accessibility of drugs is synthesis of their inclusion complexes with cyclodextrins or their derivatives. In these complexes, volatile and liquid substances are available in the solid phase, their odor and taste may be modified, and incompatible drugs may be combined within one drug form [6]. These possibilities are realized best if the host molecule is a cavitand. Cyclodextrius are just cavitands. For example, the fl-CD molecule (cyclic heptamer of glucose) has the form of a truncated cone (bracelet), which is A. V. Bogatskii Physicochemical Institute, Ukrainian National Academy of Sciences.

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