Microsecond time-scale dynamics from relaxation in the rotating frame: experiments using spin lock with alternating phase.

A spin lock comprised of radiofrequency pulses with alternating phase, (x) (-x)(x) (-x) , is proposed as a new technique to probe microsecond time-scale dynamics. A series of R1rho measurements using different pulse duration tp allows one to determine exchange rate, kex, the product p(a)p(b)(Delta omega(ab))2 involving populations of the exchanging species, p(a) and p(b), together with chemical shift difference, (Delta omega(ab)), and the strength of the spin-lock field, B1. The interpretation is based on simple analytical expression for R1rho derived on the basis of Redfield theory. The application of the method is demonstrated for partially deuterated molecule of cyclohexane undergoing chair-to-chair interconversion at -9 degrees C.