Impact of selective excitation on carbon longitudinal relaxation: Towards fast solid-state NMR techniques

The effect of selective pulses on the apparent carbon longitudinal relaxation is investigated in three fully ¹³C-labeled systems, histidine as a model system and two proteins MerP and YajG. It is shown that the longitudinal relaxation of a selectively excited carbon spin is greatly enhanced, mainly because of fast spin-diffusion. This relaxation enhancement allows reducing the time necessary for polarization recovery between two experiments. This effect can be exploited either to improve the sensitivity of NMR experiments or to reduce the experimental time. Using selective carbon excitation combined with fast pulsing on fully ¹³C-labeled proteins, a sensitivity improvement of 20–45% over standard cross-polarization methods is predicted from the measured relaxation times.     

Hadamard frequency-encoded SOFAST-HMQC for ultrafast two-dimensional protein NMR

We demonstrate the feasibility of recording (1)H-(15)N correlation spectra of proteins in only one second of acquisition time. The experiment combines recently proposed SOFAST-HMQC with Hadamard-type (15)N frequency encoding. This allows site-resolved real-time NMR studies of kinetic processes in proteins with an increased time resolution. The sensitivity of the experiment is sufficient to be applicable to a wide range of molecular systems available at millimolar concentration on a high magnetic field spectrometer.     

Sensitivity-enhanced 2D IPAP,TROSY-anti-TROSY,and E.COSY experiments: alternatives for measuring dipolar 15N-1HN couplings

Sensitivity-enhanced versions of the IPAP, TROSY-anti-TROSY, and E.COSY experiments for measuring one-bond 15N-1HN couplings are presented. Together with the previously developed sensitivity-enhanced E.COSY-type HSQC experiment they comprise a suite of sensitivity-enhanced experiments that allows one to chose the optimal spectrum for accurate measurement of one-bond 15N-1HN residual dipolar couplings in proteins. Since one-bond 15N-1HN residual dipolar couplings play uniquely important roles in structural NMR, these additional methods provide further tools for improving structure determination of proteins and other biological macromolecules.     

A new method for suppressing the central transition in I=3/2 NMR spectra with a demonstration for 23Na in bovine articular cartilage

The splitting and the lineshape of the satellite transitions of 23Na are measures of the residual quadrupolar interaction and its distribution, which are related to the degrees of order and binding of sodium in biological tissues. However, these transitions are often masked by the stronger signals of the central transition and the isotropic sodium ions. A way to suppress the central signals, while preserving the lineshape and the intensity of the satellites, is suggested and tested on a liquid crystal and on bovine articular cartilage.