Accurate determination of frequency dependent cross-relaxation terms in homonuclear and heteronuclear two spin-1/2 systems

Abstract

One-dimensional N.M.R. methods are proposed for accurately determining homo- and heteronuclear longitudinal cross-relaxation terms. These sequences employ exclusively hard pulses and do not require critical adjustments of the instrument even in the case of selective perturbation (inversion) of one magnetization in a homonuclear two-spin system. Emphasis is put on the initial conditions which prevail at the beginning of the relaxation interval; they are determined by means of adequate experimental or numerical procedures. An algorithm, based on analytical solutions of Solomon equations, is described; it allows to analyse as many sets of data as desired for arbitrary initial conditions. These methods have been applied to the 1H-1H spin system of ortho protons in an aromatic ring, which bears in para positions the polar head and the aliphatic chain of benzene-sulphonate surfactants. Proton homonuclear cross-relaxation parameters are complemented by heteronuclear carbon-proton parameters and classical carbon-...