Selective measurements of long-range homonuclear J-couplings in solid-state NMR.

Abstract: We demonstrate here that the principle of frequency-selective spin-echoes can be extended to the measurements of long-range homonuclear scalar J-couplings in the solid-state. Singly or doubly frequency-selective pulses were used to generate either a J-modulated experiment (S) or a reference experiment (S 0). The combination of these two distinct experiments provides experimental data that, in favorable cases, are insensitive to incoherent relaxation effects, and which can be used to estimate long-range homonuclear J-couplings in multiple spin-systems. The concept is illustrated in the case of a uniformly 13C and 15N labeled sample of l-histidine, where the absolute value of homonuclear J-couplings between two spins separated by one, two or three covalent bonds are measured. Moreover, we show that a 2 J(15N–C–15N) coupling as small as 0.9Hz can be precisely measured with the method presented here. [Copyright &y& Elsevier]