Measurement of the shortest hetero-nuclear distances in multiple-spin systems using constant-time correlation NMR methods

Abstract

We demonstrate that the shortest hetero-nuclear distances in multiple-spin systems can be determined using Constant-Time Dipolar-mediated Hetero-nuclear Multiple-Quantum Correlation (CT-D-HMQC) two-dimensional NMR experiments. We show that this approach is applicable between two spin-1/2 isotopes, such as ¹³C and ¹⁵N, or between spin-1/2 and half-integer quadrupolar nuclei, such as ³¹P and ²⁷Al. Furthermore, numerical simulations of spin dynamics and experiments on L-histidine·HCl and microporous aluminophosphate VPI-5 prove that the delay between zero-crossings of CT-D-HMQC trajectories is a reliable estimator of the largest dipolar couplings when the distances with the second neighbors are at least 60% larger than with the first neighbor, and there exists a known number of first neighbors at similar distances with an angle between the inter-nuclear vectors ranging from 30° to 150°.