Spin Topology from "Taylored" TOCSY

A new method is introduced which makes it possible to determine the number of successive couplings through which the magnetization giving rise to a particular TOCSY cross peak has been transferred. The method is based on two properties of the period of isotropic mixing used in TOCSY sequences: (i) the intensity variation of the in-phase part of a cross peak can be represented as an even-order power series in the mixing time, and (ii) if the cross peak is the result of magnetization having been transferred through n successive couplings, the lowest order term in this expansion is the one in which the mixing time is raised to the 2nth power. Proofs of both these theorems are described. A practical 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.