Theoretical investigation of the molecular structure of the isoquercitrin molecule

Isoquercitrin is a glycosilated flavonoid that has received a great deal of attention because of its numerous biological effects. We present a theoret ical study on isoquercitrin using both empirical (Molecular Mechanics (MM), with MMX force field) and quantum chemical (AMI semiempirical method) tech niques. The most stable structures of the molecule obtained by MM calculati ons have been used as input data for the semiempirical treatment. The posit ion and orientation of the glucose moiety with regard to the remainder of t he molecule have been investigated. The flexibility of isoquercitrin princi pally lies in rotations around the inter-ring bond and the sugar link. In o rder to know the structural modifications generated by the substitution by a sugar, geometrical parameters of quercetin (aglycon) and isoquercitrin ha ve been compared. The good accordance between theoretical and experimental electronic spectra permits to confirm the reliability of the structural mod el. (C) 1999 Elsevier Science B.V. All rights reserved.