Proton-detected 3D 15N/1H/1H isotropic/anisotropic/isotropic chemical shift correlation solid-state NMR at 70 kHz MAS

Abstract

Chemical shift anisotropy (CSA) tensors offer a wealth of information for structural and dynamics studies of a variety of chemical and biological systems. In particular, CSA of amide protons can provide piercing insights into hydrogen-bonding interactions that vary with the backbone conformation of a protein and dynamics. However, the narrow span of amide proton resonances makes it very difficult to measure 1H CSAs of proteins even by using the recently proposed 2D 1H/1H anisotropic/isotropic chemical shift (CSA/CS) correlation technique. Such difficulties due to overlapping proton resonances can in general be overcome by utilizing the broad span of isotropic chemical shifts of low-gamma nuclei like 15N. In this context, we demonstrate a proton-detected 3D 15N/1H/1H CS/CSA/CS correlation experiment at fast MAS frequency (70kHz) to measure 1H CSA values of unresolved amide protons of N-acetyl-15N-l-valyl-15N-l-leucine (NAVL).