An X-ray evidence for the ring-stacking interaction between indole ring and the pyrimidine moiety of thiamin: Crystal structure of thiamin indole-3-propionate

Abstract

The crystal structure of thiamin indole-3-propionate was determined by X-ray diffraction as a model for the possible thiamin coenzyme-tryptophan residue interaction at the binding site of thiamin pyrophosphate dependent enzymes. There is an intermolecular stacking interaction of the indole ring with the pyrimidine ring, but not with the positively charged thiazolium ring, of thiamin retaining the characteristic F-conformation. Although this association is due to dipole-dipole interaction between both aromatic rings, charge-transfer interaction cannot be ruled out in solution state because the absorption spectrum shows the characteristic charge-transfer band.