Separation of quadrupolar and chemical/paramagnetic shift interactions in two-dimensional ~2H (l=1)nuclear magnetic resonance spectroscopy

摘要

A novel two-dimensional ~2H (spin 7= 1) nuclear magnetic resonance technique is introduced for determination of both quadrupole and chemical/paramagnetic shift tensors and their relative orientation.The new method is based upon the well-known quadrupolar-echo experiment and is designed to refocus the quadrupolar interaction at the end of the t_1 evolution period while retaining the modulation introduced by the shift interaction.As a result,a projection of the resulting two-dimensional spectrum onto its F_1 dimension yields a shift anisotropy powder lineshape free from any quadrupolar broadening.The chemical/paramagnetic shifts appear in both F_1 and F_2 dimensions and are thus spread along a +1 frequency gradient;hence,a projection orthogonal to this gradient yields the pure quadrupolar powder lineshape,free from all shift interaction effects.The relative orientation of the quadrupole and shift tensors can be obtained by analysis of the full two-dimensional correlation lineshape.Unlike the well-known double-quantum experiment,the new method is,in principle,equally effective for all values of the quadrupolar splitting,including zero.The properties of the new technique are demonstrated using computer simulation and methods for the extraction of quadrupole and shift tensor parameters are described.The new technique is applied to (diamagnetic) benzoic acid-d_1 (C_6H_5CO_2D) and (paramagnetic) copper(II) chloride dihydrate-d_4(CuCl_2-2D_2O).