INFLUENCE OF CHEMICAL-EXCHANGE AMONG HOMONUCLEAR SPINS IN HETERONUCLEAR COHERENCE-TRANSFER EXPERIMENTS IN LIQUIDS

An analysis is presented of the effects of chemical exchange on the co herence-transfer efficiencies of two different types of solution-state NMR methodologies, represented by the heteronuclear single-quantum co herence (HSQC) experiment and the heteronuclear cross-polarization tec hnique. The cross-polarization experiment is demonstrated both experim entally and theoretically to have significant advantages over the free -precession-type sequences such as HSQC in the presence of chemical re organization processes. Special emphasis is given to a I(1)I(2)ZS spin system in which the two I spins are undergoing mutual exchange. (C) 1 995 Academic Press, Inc.