Analysis of¹H–¹⁴N polarization transfer experiments in molecular crystals

Abstract

A general theoretical description of polarization transfer processes in multi-spin systems containing dipole as well as quadrupole spins is formulated on the background of the Liouville–von Neumann equation. The density operator formalism is used to describe the evolution of an arbitrary spin system due to quadrupole, Zeeman and dipole–dipole interactions. This approach is applied to interpret previously published 1H–14N cross-relaxation NMR experiments for measuring the 14N quadrupole coupling constants of paranitrotoluene (PNT) and trinitrotoluene (TNT) (Nolte et al 2002 J. Phys. D: Appl. Phys. 35 939) and new experiments on urea and urotropine. It is demonstrated that according to the complexity of the analysed spin system an appropriate number of spins has to be taken into consideration for a correct description of the cross-relaxation spectra. The work is a part of an extended project aiming for a method which should permit detection of TNT explosive in anti-personnel landmines.

Thermodynamic properties and molecular motions in ferroelectric (C3N2H5)5Sb2Br11

“…One of them is related to polarization transfer effects [24][25][26][27] between protons and Br nuclei. Polarization transfer can occur in systems containing nuclei of the spin quantum number 1/2 mutually coupled to nuclei possessing quadrupole moments.…”

Predicting quadrupole relaxation enhancement peaks in proton R1-NMRD profiles in solid Bi-aryl compounds from NQR parameters

“…One of the first articles demonstrating this effect is dealing with powdery polyvinylchloride containing 35 Cl and 37 Cl nuclei (I = 3/2) [12]. Also, studies on solids containing 14 N [16,17] were reported. Cases were presented, where 14 N (I = 1) nuclei produce QRE peaks in the NMRD profile of biological systems, e.g.…”

Dynamics of Molecular Crystals by Means of 1H NMR Relaxometry: Dynamical Heterogeneity versus Homogenous Motion

“…The contributions to the 1 H spin-lattice relaxation caused by 1 H-X (X = 14 N, Bi, Br) dipoledipole interactions can lead to an effect referred to as quadrupole relaxation enhancement ("quadrupole peaks"). [31][32][33][34][35] H-X contribution to the overall relaxation is almost negligible, except for the frequencies at which the "quadrupole peaks" appear. [10,36] This effect is as ource of information on the timescale of molecular dynamics and molecular arrangement (structure) around the quadrupole nucleus, as the positions of the peaks depend on the electric field gradient at the position of this nucleus.…”