3D ¹⁴N/¹H Double Quantum/¹H Single Quantum Correlation Solid‐State NMR for Probing the Parallel and Anti‐Parallel Beta‐Sheet Arrangement of Oligo‐Peptides at Natural Abundance

Abstract

The beta (β)-sheet structures of oligopeptides and polypeptides can be formed in anti-parallel (AP) and parallel (P) forms, which is an important feature to understand such structures. In principle, P- and AP-β-sheet structures can be identified by the presence (AP) or absence (P) of inter-strand H / H correlations on a diagonal in the corresponding 2D H double quantum (DQ)/ H single quantum (SQ) spectrum due to the different inter-strand H / H distances between the two arrangements. However, the H / H peaks overlap with the H / H peaks, which always give cross-peaks regardless of the β-sheet arrangement. The H / H peaks disturb the observation of the presence/absence of H / H correlations and the assignment of H and H is not always available. Here, 3D N/ H DQ/ H SQ correlation solid-state NMR experiments at fast magic angle spinning (70 kHz) are introduced to distinguish AP- and P-β-sheet structures. The N dimension allows the distinction of H / H peaks from H / H peaks with clear assignments of H and H . In addition, the high natural abundance of H and N enables 3D N/ H DQ/ H SQ experiments of oligo-alanines (Ala ) in four hours without isotope labelling.

14N1H HMQC Solid-State NMR as a Powerful Tool to Study Amorphous Formulations – an Exemplary Study of Paclitaxel Loaded Polymer Micelles

“…For example, this has been observed for small di-and oligopeptides, where nitrogen atoms with three bonds and thus a less tetrahedral environment due to the lone pair showed high second order quadrupolar shifts, while in the case of zwitterionic 3 + environments (proton transfer being the extreme case of hydrogen bonding interaction) only a very small shift was observed. 28,36 Finally, the formulation with medium loading gives further insights into the drug-polymer assembly. While the amount of PTX in POL-2-PTX is very low and the 14 25 the NH group and all three OH-groups act as hydrogen bond donor to adjacent PTX and water molecules suggesting that this would also be the case for PTX -polymer interactions.…”

“…29 So far, the majority of 14 N-1 H HMQC experiments was acquired for highly ordered, crystalline compounds. 28,[30][31][32][33][34][35][36][37][38][39] In contrast, disordered systems with significant differential dynamics are more challenging systems and there are thus very seldom reports employing the 14 N-1 H HMQC experiment for their characterization. However, the characterization of disordered and amorphous materials could substantially benefit from the additional 14 N second-order isotropic quadrupolar shifts (see SI for detailed equations) as opposed to the 15 N isotropic chemical shifts alone.…”

Quantitative analysis of14N quadrupolar coupling using1H detected14N solid-state NMR

“…Despite the large variation in d iso Q reported for proteins, for larger biomolecules its application will remain challenging due to the limited chemical shift dispersion in the amide protons. Although further enhancements in resolution and sensitivity can be realised through the application of faster MAS and higher 14 N rf fields, 26,32 for larger biomolecules it is clear that higher-dimensionality spectra will be required to aid resolution and assignment. In Fig.…”

“…Alternatively, polarisation transfer can be driven by the recoupling of the 1 H/ 14 N dipolar coupling using rotary resonance (R 3 ), REDOR or symmetry based recoupling sequences, in sequences that have been generally termed D-HMQC experiments. 19,26,27 Similarly, double cross-polarization schemes have also been proposed for indirect detection which function well at higher spinning speeds. 28 These indirect techniques benefit from the sensitivity and resolution that are afforded by the 'spy' nuclei and do not require excitation or detection of the entire first-order broadened 14 N spectrum.…”

Self‐Assembly of DNA and RNA Building Blocks Explored by Nitrogen‐14 NMR Crystallography: Structure and Dynamics

“…In contrast to nuclei with half‐integer spins I =3/2, 5/2, etc., that have a central transition m 1 =±1/2↔∓1/2 which is not affected by the quadrupolar interaction to first order, nuclei with integer spins I =1 only have two allowed single‐quantum transitions m 1 =±1↔ m 1 that are displaced by ± ω Q with respect to the center of the spectrum, which is itself affected by a second‐order quadrupolar term. Nonetheless, NMR methodologies for the acquisition of 14 N spectra in the solid state have been developed over the past 15 years for both static and spinning samples . Techniques involving overtone irradiation have been explored .…”