The interaction of two flavonoid species (resorcinolic and fluoroglucinolic) with the 20 essential amino acids was studied by the multiple minima hypersurface (MMH) procedures, through the AM1 and PM3 semiempirical methods. Remarkable thermodynamic data related to the properties of the molecular association of these compounds were obtained, which will be of great utility for future investigations concerning the interaction of flavonoids with proteins. These results are compared with experimental and classical force field results reported in the available literature, and new evidences and criteria are shown. The hydrophilic amino acids demonstrated high affinity in the interaction with flavonoid molecules; the complexes with lysine are especially extremely stable. An affinity order for the interaction of both flavonoid species with the essential amino acids is suggested. Our theoretical results are compared with experimental evidence on flavonoid interactions with proteins of biomedical interest. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005

In order to reproduce the solvation effects on the monomers and dimers of naturally occurring flavonoid structures, a complete screening of their multiple minima hypersurfaces (MMH) was done by a semiempirical Hamiltonian. Such hypersurfaces corresponded to several solute–solvent supermolecules. This searching confirms some NMR results reported in the available literature and provides new theoretical evidences of these structures. The reaction energy of the flavonoid dimerization was calculated in this study, adding the corresponding terms related with the association process due to the presence of different solvents in the system. We are reporting the energetic and conformational analysis of all the possibilities of dimeric structures in different phases. The most important results of this work are related with the structural changes suffered by the monomeric and dimeric structures due to the presence of water and/or acetone molecules, the preferential position of interactions between solvent molecules and monomeric and dimeric structures, and the thermodynamic stability of dimeric structures in these phases.

Flavonoids are polyphenolic compounds found in all land plants and in plant-related foods. These compounds have many positive effects, and the interaction with proline aminoacid is one of the most important characteristics. The present work shows the results of the application of the multiple minima hypersurfaces procedures, in the study of the interactions of flavonoid monomers (catechin and robinetinidin) with proline. These results are compared with experimental and classical theoretical results reported in the available literature. The most important results of this work are related with the conformations of monomers in these interactions, the preferential position of interactions and the thermodynamic stability of these complexes. All the results are successfully compared in both, gas and aqueous phases.

Vegetable tannins are polyphenolic plants secondary metabolites, widely distributed in all parts of trees and herbs. The role of these substances in many metabolic processes is very important. Vegetable tannins have been implicated as probable antinutritional factors, decreasing the assimilation of diet protein assimilation by cattle. On the other hand, protective antioxidant and antimutagenic properties have been ascribed for these compounds. Characterization of vegetable tannins is important in order to find new sources of natural raw materials with medical and pharmaceutical applications. Protein precipitation capacity as a function of pH, competitive protein and ADN binding assays and the determination of tannins concentration are described. Radioisotope labeled protein and tannins were used in all of the determinations.