Towards Structure Determination of Self‐Assembled Peptides Using Dynamic Nuclear Polarization Enhanced Solid‐State NMR Spectroscopy

Abstract

Supra‐sensitivity: Dynamic nuclear polarization (DNP) enhanced solid‐state NMR spectroscopy was performed on self‐assembled peptide nanotubes. This approach yields significant experimental time savings (about five orders of magnitude; see picture) and was used to exemplify the feasibility of supramolecular structural studies of organic nanoassemblies at an atomic scale using DNP‐enhanced solid‐state NMR spectroscopy.

Is solid-state NMR enhanced by dynamic nuclear polarization?

“…Furthermore, as highlighted by the inset in Fig. 4, there appears to be larger residual signals from the reception of FM broadcasting around the 13 C resonant frequency at 9.4 T for the probe at 100 K than stemming from thermal noise in the probe at 300 K. This then leads to more "noise" in 13 C (or 27 Al) spectra recorded at 100 K. This was noted in our laboratory by observing S/N fluctuations for experiments with extremely low sensitivity [25, 44,45]. However, sufficient grounding of the probe can alleviate this problem.…”

“…Fig. 7 illustrates a method introduced by Takahashi et al [25,44,45] whereby one could alleviate the requirement of an excess of a DNP matrix, while avoiding detrimental radical exclusion and aggregation that would cause extremely fast T 1e and result in very poor DNP. This method, termed the Matrix-Free (MF) approach, relies on either a direct or indirect non-covalent interaction between the polarizing agent and the analyte, suppressing the "desire" of the polarizing agents to aggregate upon the removal of the solvent.…”

“…Amorphous materials such as silicas (SiO 2 ) can exhibit inhomogeneous broadening at RT to such an extent that the DNP conditions make little difference, and have thus already been extensively studied with this technique [29,46,[59][60][61][62]. Furthermore, extremely rigid systems [44] and systems with nuclei of interest with a relatively large quadrupolar coupling, such as 27 Al [36][37][38] and 17 O [6], will also experience little change in resolution upon addition of DNP matrices and polarizing agents and are therefore also highly pertinent for MAS-DNP studies. 17 O is a particularly interesting, yet difficult, nucleus for NMR studies and should be distinctly suitable for future DNP-enhanced studies.…”

Ultra-Low Temperature Nuclear Magnetic Resonance

“…8. For this organic semiconductor system under structural study in our laboratory [30], performing an experiment at ~50 K results in a sensitivity increase of a factor of 5.6 compared to the same experiment recorded at ~110 K and corresponds to a 30-fold reduction in required experimental time. Fig.…”

Developments in Solid-State NMR Spectroscopy of Polymer Systems

“…Peptide nanoassemblies have been studied by solid-state NMR. Using the recent development of high-field MAS dynamic nuclear polarization (MAS-DNP), an increase in sensitivity for the peaks of crystalline components of the polymer system can be achieved [14]. Using this approach, self-assembled structures of systems based on diphenylalanine dipeptide (FF) have been studied.…”