Heteronuclear Correlation Spectroscopy with RF Gradients

Abstract

The applicability of RF gradients for suppressing the resonances of uncoupled spins in inverse-detected heteronuclear spectroscopy has been investigated. Pulse sequences were designed which incorporate RF gradients in heteronuclear single-quantum-correlation experiments (HSQC), and they can be divided into three categories based on how the RF gradients are used. In the first type of experiment, the desired coherences are spin locked in the RF-gradient held, while unwanted terms, placed perpendicular to the direction of the RF-gradient held, are dephased. In a second type of experiment, the dephasing action of the gradient and the coherence-transfer RF pulses are combined into a single RF-gradient pulse. A second RF-gradient pulse is then used to rephase the desired spin terms. The third type of experiment uses a period of longitudinal storage of the heteronuclear magnetization, during which time the magnetization of the uncoupled spins is destroyed by an RF-gradient pulse. Experimental results are shown from all three techniques, and the techniques are compared.