Measuring and Modeling Highly Accurate ¹⁵N Chemical Shift Tensors in a Peptide.

Abstract

NMR studies measuring chemical shift tensors are increasingly being employed to assign structure in difficult-to-crystallize solids. For small organic molecules, such studies usually focus on C sites, but proteins and peptides are more commonly described using N amide sites. An important and often neglected consideration when measuring shift tensors is the evaluation of their accuracy against benchmark standards, where available. Here we measure N tensors in the dipeptide glycylglycine at natural abundance using the slow-spinning FIREMAT method with SPINAL-64 decoupling. The accuracy of these N tensors is evaluated by comparing to benchmark single crystal NMR N measurements and found to be statistically indistinguishable. These FIREMAT experimental results are further used to evaluate the accuracy of theoretical predictions of tensors from four different density functional theory (DFT) methods that include lattice effects. The best theoretical approach provides a root mean square (rms) difference of ±3.9 ppm and is obtained from a fragment-based method and the PBE0 density functional.

Theoretical Investigations Into the Variability of the 15N Solid-State NMR Parameters Within an Antimicrobial Peptide Ampullosporin A

“…The conformation of the backbone is unaltered, and changes in the positions of side chain atoms are marginal. However, the geometrical optimization of an XRD structure is considered to be a crucial step in obtaining highly accurate 15 N CST data (Czernek et al 2013b, Kalakewich et al 2015, Soss et al 2017.…”

Modeling Small Structural and Environmental Differences in Solids with 15N NMR Chemical Shift Tensors

“…It is notable that the 15 N shift tensors of guanosine dihydrate have previously been reported using a slow spinning 1D experiment [50] . New data were acquired for the present study because the 2D FIREMAT provides superior resolution and has been demonstrated to provide highly accurate 15 N tensors [51] . A comparison of the FIREMAT shift tensors to the data obtained from the 1D analysis reveals an rms deviation of 3.4 ppm for data converted into the icosahedral representation.…”

Solid‐State 13C NMR Evidence for Long Multicenter Intradimer Bonding in Zwitterion‐like Structures

“…Tensors data were processed using procedures described elsewhere. [28] Prior studies on the accuracy of shift tensors obtained from FIREMATe stimate the error to range from AE 0.7 [36] to AE 0.9 ppm. [37] In order to assign chemical shifts in both phases of [TTF•••TCNE], lattice-including geometry refinements were performed using the program CASTEP [38][39][40][41][42][43] at the PW91-D2*/ultra-fine level with other modeling parameters set as recommended by Holmes and coworkers.…”

“…Tensors data were processed using procedures described elsewhere . Prior studies on the accuracy of shift tensors obtained from FIREMAT estimate the error to range from ±0.7 to ±0.9 ppm …”