Livshits, V.A. and Maksimova, O.V. and Rudyak , V.Y. (2007) Guest/host complexes of spin-labeled stearic acids with cyclodextrins. Nanotechnologies in Russia, Volume 2 (9-10).
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Guest/host complexes of spin-labeled stearic acids with cyclodextrins Guest/host complexes of hydroxypropyl-?-cyclodextrin (hpbCD) and methyl- ?-cyclodextrin (mbCD) with spin-labeled stearic acids in which the doxyl ring is covalently attached to the 5-th and 16-th positions on the acyl chain (5-dsa, 16-dsa) were prepared and studied by ESR. Interaction of dsa with CD results in an increase in rotational correlation time (?R) due to uncoiling of the coiled conformations of free dsa and in an increase in hydrophobicity of the NO group local environment (h) because of its contact with CD cavity. Dependences of ?R and h on the hpbCD concentration consist of two regions both for 5-dsa and 16-dsa: there is an initial sharp rise in h and ?R which is followed by a gradual increase in both parameters. These dependences are interpreted to be due to successive binding to dsa of two (pH 7.9) or three (pH 3.5) hpbCD molecules. Binding constants determined with non-linear fitting procedure were shown to differ by more than 1.5 orders of magnitude (1.6-5? 104 è ? 9? 102 Ì-1, respectively) for the first and second regions of these dependences. It was concluded that the first hpbCD molecule is put on through acyl chain of dsa and is in contact with doxyl group. For higher hpbCD concentrations and protonated COOH group, two additional hpbCD molecules are bound to two regions: hydrocarbon tail and a polar head including COOH group. For the deprotonated carboxyl group only one additional hpbCD molecule is bound to the hydrocarbon tail. The quantum-chemical PM3 method was used to calculate the initial conformations of hpbCD, 5-dsa and 16-dsa, and the energies and conformations of both 1:1 and 2hpbCD:1dsa complexes for different positions of hpbCD molecules on the acyl chains of dsa. The calculations are in general in good agreement with experimental data and the outlined binding model.
|Subjects:||Material Science > Nanochemistry|
Material Science > Nanostructured materials
|Deposited By:||Prof. Alexey Ivanov|
|Deposited On:||19 Dec 2008 13:14|
|Last Modified:||16 Feb 2009 20:36|
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