Rotating-Frame Overhauser Transfer via Long-Lived Coherences

Solution-state distance restraints for protein structure determination with Ångström-level resolution rely on through-space transfer of magnetization between nuclear spins. Such magnetization transfers, named Overhauser effects, occur via dipolar magnetic couplings. We demonstrate improvements in magnetization transfer using long-lived coherences (LLCs)—singlet-triplet superpositions that are antisymmetric with respect to spin-permutation within pairs of coupled magnetic nuclei—as the magnetization source. Magnetization transfers in the presence of radio-frequency irradiation, known as ‘rotating-frame’ Overhauser effects (ROEs), are predicted by theory to improve by the use of LLCs; calculations are matched by preliminary experiments herein. The LLC-ROE transfers were compared to the transmission of magnetization via classical transverse routes. Long-lived coherences accumulate magnetization on an external third proton, K, with transfer rates that depended on the tumbling regime. I,S →K transfers in the LLC configuration for (I,S) are anticipated to match, and then overcome, the same transfer rates in the classical configuration as the molecular rotational correlation times increase. Experimentally, we measured the LLC-ROE transfer in dipeptide AlaGly between aliphatic protons in different residues K = Ala − Hα and (I,S) = Gly − Hα1,2 over a distance dK,I,S = 2.3 Å. Based on spin dynamics calculations, we anticipate that, for such distances, a superior transfer of magnetization occurs using LLC-ROE compared to classical ROE at correlation times above τC=10 ns. The LLC-ROE effect shows potential for improving structural studies of large proteins and offering constraints of increased precision for high-affinity protein-ligand complexes in slow tumbling in the liquid state.

An algebraic solution for determining overall rotational correlation times from cross-correlated relaxation rates

SummaryAn accurate rotational correlation time is critical for quantitative analysis of fast timescale NMR dynamics. As molecular weights increase, the classic derivation using transverse and longitudinal relaxation rates becomes increasingly unsuitable due to the non-trivial contribution of dipole-dipole and chemical exchange processes. Derivation using cross-correlated relaxation experiments, such as TRACT, overcome these limitations but are erroneously calculated in at approximately 50% of the citing literature. The goals of this study are to 1) investigate the potential sources of the error, 2) provide an algebraic solution, and 3) highlight that future inaccuracies can be minimized by requiring publication of sufficient raw data and computational routes for re-evaluation.

Simultaneous determination of deuteron quadrupole coupling constants and rotational correlation times: the model case of hydrogen bonded ionic liquids

We show that deuteron quadrupole coupling constants, and reorientational correlation times of molecular bonds N–D that are involved in hydrogen bonding, can be determined from NMR T1 relaxation time experiments simultaneously by assuming anisotropic motion.

The influence of like-charge attraction on the structure and dynamics of ionic liquids: NMR chemical shifts, quadrupole coupling constants, rotational correlation times and failure of Stokes–Einstein–Debye

The formation of clusters of like-charge influences the structure and dynamics of ionic liquids.