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

Abstract

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 R 1 ρ measurements using different pulse duration t p allows one to determine exchange rate, k ex, the product p a p b (Δ ω ab ) 2 involving populations of the exchanging species, p a and p b , together with chemical shift difference, Δ ω ab , and the strength of the spin-lock field, B 1. The interpretation is based on simple analytical expression for R 1 ρ 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 °C.