An Efficient, Robust New Scheme for Establishing Broadband Homonuclear Correlations in Biomolecular Solid State NMR

Abstract

An efficient mixing scheme is introduced for establishing two‐dimensional (2D) homonuclear correlations based on dipolar couplings. This mixing scheme achieves broadband dipolar recoupling using remarkably low powers even under ultrafast magic‐angle spinning (MAS) rates. This Adiabatic Linearly FREquency Swept reCOupling (AL FRESCO) method applies a series of weak frequency‐chirped pluses on the 1H channel, for performing efficient 13C−13C magnetization transfers leading to cross peaks between sites separated over small or large chemical shift differences. The mixing scheme is nearly free from dipolar truncation effects, and thanks to the low RF powers it involves it can act over long mixing times (≥1.5 sec). Key considerations required for optimizing this chirped pulse mixing scheme are discussed, and the new kind of correlations that can emerge from this method are demonstrated using uniformly 13C‐labeled Barstar as test protein sample.

Selective One-Dimensional 13C–13C Spin-Diffusion Solid-State Nuclear Magnetic Resonance Methods to Probe Spatial Arrangements in Biopolymers Including Plant Cell Walls, Peptides, and Spider Silk

“…6 For example, the newly developed adiabatic frequency-swept recoupling scheme AL FRESCO might be an excellent candidate for implementation at moderate and fast spinning speeds. 56 Moreover, we have demonstrated that 1D DARR difference can be used to quickly obtain detailed performance metrics of various recoupling methods and the effect of spinning speed, which should prove valuable to researchers developing new schemes or choosing between existing ones.…”

“…Alternatively, if no RF power is applied during the mixing period, the experiment becomes the selective 1D equivalent to the 2D PDSD method. If higher MAS spinning speeds are used, the DARR recoupling scheme could be easily replaced by recoupling programs better suited for higher MAS frequencies (CORD, AL FRESCO, and PARIS). − ,, A 13 C hard pulse is then used to read out chemical shift-selected spin-diffusion edited 13 C magnetization. Importantly, the receiver phase is alternated every other scan by 180°, matched with on- and off-power selective pulses.…”

Solid-State NMR Dipolar and Chemical Shift Anisotropy Recoupling Techniques for Structural and Dynamical Studies in Biological Systems

“…However, both PDSD and DARR sequences are most efficient for correlating spin pairs with small ΔΩ ij and around R 2 conditions. , The effective recoupling bandwidth would be insufficient at faster MAS rates (>22 kHz) for correlating the surrounding homonuclear spins with a wide range of chemical shifts, as required in NCACX and NCOCX types of experiments. In this sense, many kinds of broadband SD-based sequences with (phase-, amplitude-, and/or resonance frequency)-modulated RF irradiation (Figure ), such as PARISxy, SHA+, CORDxy, AM-MIRROR (Amplitude-Modulated MIRROR), and AL FRESCO (Adiabatic Linearly FREquency Swept reCOupling), have been developed for improving the effective recoupling bandwidth at faster MAS rates. Nowadays, some of these broadband SD-based sequences have already been used in NCACX and NCOCX type experiments of practical biological systems for homonuclear correlations at moderate and fast MAS rates (see Table ).…”

Solid-State NMR: Methods for Biological Solids

“…Copyright 2013 Elsevier. Parts of (D) (variants of AL-FRESCO) have been reproduced with permission from ref . Copyright 2019 Wiley, respectively.…”