Direct Determination of ¹⁵N- and ¹⁹F-NMR Correlation Times from Spin−Lattice and Spin−Spin Relaxation Times

Abstract

The NMR rotational correlation equations for dipolar relaxation between 1 H and the nuclei 15 N and 19 F have been solved for viscous solutions using the R 2 / R 1 dipolar ratio. The rotational correlation times have been determined over the dipolar R 2 / R 1 range 1.1−1200 at field strengths of 4.7, 6.35, 7.05, 9.4, 11.75, and 14.1 T. The calculated correlation times at each field strength have been fitted to pairs of polynomials that reproduce the correlation times from R 2 / R 1 values at a given temperature. These polynomials are used to determine correlation times in two studies where molecular rotation is slow (ωτ > 1). The studies include (1) where the 15 N− 1 H correlation-time polynomial equations are used to determine the correlation times of the enzyme 4-oxalocrotonate tautomerase and the backbone correlation time of the intestinal fatty acid binding protein and (2) where the 19 F− 1 H polynomial equations are used to characterize the rotational mobility of 5-fluorouracil-substituted Escherichia coli tRNA 1 Val and to establish the existence of scalar relaxation in the case of an isomer of the peptide complex [Co(benzyloxycarbonyl-cys-pro-leu-cys-gly-NHC 6 H 4 - m -F) 2 ] 2- .