Intermolecular multiple quantum coherences in liquids

Abstract

In the early 1990s, the traditional framework of NMR spectroscopy was challenged through a series of simple experiments. The pulse sequences used consisted of a few RF pulses and a few gradient pulses, and the samples were mixtures of simple molecules. The spectra showed unexpected cross peaks between spins in different molecules. () In order to explain these results, two basic assumptions had to be revisited: 1 the () high-temperature approximation to the Boltzmann distribution at equilibrium, and 2 the cancellation of dipolar couplings in solution. A close look at the physics involved showed that correlations between spins in separate molecules exist even after a single pulse, and that dipolar couplings can make these correlations visible in the presence of gradient pulses. A comprehensive description of the effect is given here, and some present and future applications are discussed. 2000 John Wiley & Sons, Inc. Concepts Magn Reson 12: 396409, 2000