Determination of transverse relaxation rates of individual spins while quenching echo modulations due to homonuclear scalar couplings

The envelopes of spin-echo amplitudes obtained with trains of multiple refocusing pulses are normally modulated by homonuclear scalar couplings. Echo modulations make it difficult to determine transverse relaxation rate constants R-2. Provided that the pulses are of moderate amplitude so that spins at different offsets experience different tilted effective fields, and provided one avoids recoupling conditions, it is possible to quench the modulations of spin echoes. When the modulations are quenched, apparent transverse relaxation rate constants R2(I) can be determined for individual spins I. The principle is demonstrated for solutions of glycine with single or double carbon-13 enrichment. (C) 2008 Elsevier B. V. All rights reserved.