L-Tryptophan-Modified-Beta-Cyclodextrin as Molecular and Enantiomeric Selector: Semiempirical Calculations

E.N. COSCARELLO; D.A. BARBIRIC; E.A. CASTRO

Global J. Mol. Sci.

Año: 2006 vol. 1 p. 1 - 8

Semiempirical treatment -molecular mechanics and PM3- of the complexation of L-tryptophan-modified-b-cyclodextrin with cyclic alcohols from pentanol to octanol, (+)-menthol and (-)-menthol and 1- and 2-adamantanol was carried out.  The purpose was to rationalize through energies and structures, the proven capability of the substituted cyclodextrin for molecular recognition and selectivity.   Molecular recognition of cycloalcohols appeared guided by size and shape rigidity, deduced from intermolecular hydrogen-bonding viability, and increasing energies of stabilization, intermolecular interaction and driving force towards complex formation with molecular size.  The better fitted complexation of (-)-menthol as compared to (+)-menthol was observed for two different host conformers and the guest insertion by the methyl extreme appeared as more efficient.  Results did not support the experimental evidence that 2-adamantanol forms more stable complexes than 1-adamantanol, so a treatment at a higher level of theory was initiated. Theoretical results support the experimental evidence that the indolyl moiety tends to locate within the cyclodextrin cavity.