Relaxation of longitudinal three-spin order

Abstract

Nuclear magnetic resonance relaxation studies are an important tool for the study of mo lecular dynamics in liquids. Recent advances in both NMR theory and experimental techniques have substantially increased the level of information of mo lecular dynamics in liquids. The development of mu ltiple-quantum relaxation (MQR) ( I ) has paved new ways to study the mo lecular dynamics in liquids. The advent of the MQR experiment opens the possibility of selecting the appropriate spin interaction which generates only a certain order of MQR. Mu ltiple-quantum relaxation via transverse relaxation for degenerate spin systems has been applied to the study of slow mo lecular motion in macromolecules and mo lecular aggregates (2,3). For longitudinal relaxation, several authors have demonstrated that dipole-dipole cross-relaxation may lead to the conversion of Zeeman order into three-spin order (4). Particularly in the work of Bijhlen et al., a so-called “pseudo-two-dimensional” spectrum has been obtained to demonstrate the effect of dipole-dipole cross-relaxation (4). In the present work, we report the result of a study which utilizes the one-dimensional analog of the triple-quantum 2D experiment via longitudinal relaxation to determine the relaxation behavior of three-spin order for the methyl protons in the deoxycholate (DOC) m icelle system. The pulse sequence used for measur ing the relaxation of three-spin order is basically a mu ltiple-quantum-filter pulse sequence as depicted in F ig. 1. The phases of the receiver and of the various pulses in the phase-cycl ing scheme were reported earlier (3, 57) for a tr iple-quantum filter. In order to eliminate the transverse contribu-