Structural and conformational studies on bio-active flavonoids. Crystal and molecular structure of a complex formed...

In order to investigate mechanisms of action of flavones at the molecular level, we have prepared a complex between a flavone and orthophosphoric acid which can be considered as a simplest model of interaction between a flavone and a more complex biological phosphate such as nucleotide, coenzyme or DNA. With orthophosphoric acid, the title flavone forms crystals which have 1:2 stoichiometry (C17H14O4.2H3PO4). This compound was found to be the 1:1 salt co-crystallized with the unionized molecular acid C17H15O4+.H2PO4-.H3PO4. The symmetry is monoclinic, space group P2(1)/n and unit cell dimensions a = 15.571(2), b = 7.369(1), c = 17.837(2) A, beta = 100.84(1) degrees. One molecule of phosphoric acid is present as a solvate molecule of crystallization, but the other is ionized and protonates the carbonyl oxygen, introducing conformational and bond distance changes in the flavone. The dihedral angle between the benzopyrone and phenyl rings is 47 degrees. Complexes with phosphate groups involve strong hydrogen bonds and are expected to play important roles in biomolecular structures.