Collision complexes between purines and phenylalanine: a 1H NMR study.

Abstract

Addition of increasing amounts of phenylalanine in dilute aqueous solutions of adenine, theophilline, theobromine, caffeine and tetramethyluric acid induces proton chemical shift changes that can be interpreted on the basis of the existence of 1:1 complexes. Their formation quotients are comparable to those of the analogous complexes formed by purines with benzene in apolar solvents. Differences among formation quotients of a given complex, extracted from different nuclei of the purine, hint that 1:2 or higher complexes may be present, but the extremely narrow concentration range accessible for the donor compound prevents an accurate numerical analysis of these equilibria.