Separation of quadrupolar and chemical/paramagnetic shift interactions in two-dimensional H2 (I=1) nuclear magnetic resonance spectroscopy

Abstract

A novel two-dimensional (2)H (spin I=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(6)H(5)CO(2)D) and (paramagnetic) copper(II) chloride dihydrate-d(4) (CuCl(2).2D(2)O).

Two-dimensional NMR measurement and point dipole model prediction of paramagnetic shift tensors in solids

“…Discernible in this 2D spectrum is a pair of overlapping triangles, similar to the simulated spectrum in the lower left corner of spectra in Fig. 3, as other studies have analyzed [32,71].…”

“…Together, the two 1D projections only lack information about the relative orientations of the two tensors, which can then be determined from the full 2D correlation spectrum if desired [32,71]. Discernible in this 2D spectrum is a pair of overlapping triangles, similar to the simulated spectrum in the lower left corner of spectra in Fig.…”

“…Antonijevic and Wimperis [32] proposed a shifted-echo solution [70] for obtaining a pure 2D absorption mode lineshapes in the solid-echo experiment with an additional π/2 pulse as …”

“…First, we describe two-pulse strategies for generating echoes in terms of the recently proposed symmetry pathway formalism [33], a framework that provides a simple picture for understanding many correlation experiments, a framework that provides a simple picture for understanding many correlation experiments. We then proceed to analyze the sequence of Antonijevic and Wimperis [32] in this context, from which we propose a modification that provides a two-fold sensitivity enhancement and eliminates a substantial spectral artifact. We demonstrate the utility of these sequences in obtaining accurate parameters for the 2 H paramagnetic shift and quadrupolar coupling tensors for the model compound CuCl 2 · 2D 2 O, modulated by the rapid flipping of the heavy water ligands about their C 2 axes.…”

“…These experiments, however, suffer from severe non-uniform lineshape excitation. To remedy this problem, Antonijevic and Wimperis [32] recently proposed a three-pulse solid-echo sequence for correlating first-order quadrupolar and shift interactions in stationary samples.…”