Efficient deuterium-carbon REDOR NMR spectroscopy

Phase modulated pulses for deuterium recoupling in H-2-C-13 REDOR NMR spect roscopy have been introduced to improve dephasing of the detected C-13 nucl ei. The deuterium inversion properties of phase modulated recoupling pulses have been studied experimentally on L-alanine-2-d(1) and theoretically usi ng average Hamiltonian theory and exact simulations of the equation of moti on of the density matrix. The best C-13 dephasing was observed when XYXYX ( PM5) deuterium recoupling pulses were applied. A comparison to the 900-180 degrees-90 degrees (CPL) composite pulse scheme revealed an improvement of recoupling on the order of 2.5. Simple CW recoupling pulses of the same len gth of PM5 and CPL pulses showed the weakest C-13 dephasing. Simulations ha ve shown that the H-2 recoupling efficiency of PM5 REDOR experiments approa ch the very efficient REAPDOR results. However, in our case a REAPDOR study of L-alanine-2-d(1) resulted in a significant decrease of the C-13 signal intensity due to pulse imperfections of C-13 pi-pulses. The new PM5-REDOR t echnique has been employed to study the torsion angle between C1/2 and C5 i n ethylmalonic acid-4-d(2). (C) 2000 Academic Press.