13C NMR investigations on the stacking of 5'-AMP with tryptamine

Complex formation between 5'-adenosine monophosphate (5'-AMP) and tryptamine was investigated by measuring 13C chemical shifts and spin-lattice relaxation times. The chemical shift changes observed were attributed to ring current effects originating in the stacking of the two respective aromatic moieties and to puckering changes of the AMP ribose. Differences in the magnitude of the shifts of the aromatic carbons were related to the geometry of the complex and compared with those found for AMP selfassociation. Upon complex formation the relaxation times of especially the tryptamine indole carbons were greatly reduced, this was explained by an increase in the particle size. Small changes found for the AMP carbons in solutions without tryptamine result from AMP selfassociation. Deviations from isotropic motion observed for the non-aromatic moieties are discussed.