SPIN TOPOLOGY FROM TAYLORED TOCSY

A new method is introduced which makes it possible to determine the nu mber of successive couplings through which the magnetization giving ri se to a particular TOCSY cross peak has been transferred. The method i s based on two properties of the period of isotropic mixing used in TO CSY sequences: (i) the intensity variation of the in-phase part of a c ross peak can be represented as an even-order power series in the mixi ng time, and (ii) if the cross peak is the result of magnetization hav ing been transferred through n successive couplings, the lowest order term in this expansion is the one in which the mixing time is raised t o the 2nth power, Proofs of both these theorems are described, A pract ical implementation of an algorithm which exploits these properties is given and its effectiveness in the presence of noise and experimental imperfections is assessed, An experimental example of the use of the procedure is described. (C) 1995 Academic Press. Inc.