Improved NMR transfer of magnetization from protons to half-integer spin quadrupolar nuclei at moderate and high MAS frequencies

Half-integer spin quadrupolar nuclei are the only magnetic isotopes for the majority of the chemical elements. Therefore, the transfer of polarization from protons to these isotopes under magic-angle spinning (MAS) can provide precious insights into the interatomic proximities in hydrogen-containing solids, including organic, hybrid, nanostructured and biological solids. Furthermore, this transfer has recently been combined with dynamic nuclear polarization (DNP) in order to enhance the NMR signal of half-integer quadrupolar isotope. Nevertheless, the cross-polarization transfer lacks of robustness in the case of quadrupolar nuclei and we have recently introduced as an alternative technique a through-space refocused insensitive nuclei enhancement by polarization transfer (D-RINEPT) scheme combining hetero-nuclear dipolar recoupling built from adiabatic pulses and continuous wave decoupling. This technique has been demonstrated at 9.4 T with moderate MAS frequencies, νR ≈ 10-15 kHz, in order to transfer the DNP-enhanced 1H polarization to quadrupolar nuclei. Nevertheless, polarization transfers from protons to quadrupolar nuclei are also required at higher MAS frequencies in order to improve the resolution of 1H spectra. We investigate how this transfer can be achieved at νR ≈ 20 and 60 kHz. We demonstrate that the D-RINEPT sequence using adiabatic pulses still produces efficient and robust transfer but requires large rf-fields, which may not be compatible with the specifications of commonly employed MAS NMR probes. As an alternative, we introduce robust and efficient variants of D-RINEPT and PRESTO (phase-shifted recoupling effects a smooth transfer of order) sequences using symmetry-based recoupling schemes built from single and composite π-pulses. Their performances are compared using the average Hamiltonians and experiments at B0 = 18.8 T on γ-alumina and isopropylamine templated microporous aluminophosphate AlPO4-14, featuring low and significant 1H-1H dipolar interactions, respectively. These experiments demonstrate that the 1H magnetization can be efficiently transferred to 27Al nuclei using D-RINEPT with SR412(270090180) recoupling, and PRESTO with R2227(1800) or R1672(270090180) schemes at νR = 20 or 62.5 kHz, respectively. The D-RINEPT and PRESTO recouplings complement each other since the latter is affected by dipolar truncation, whereas the former is not.

Expanding the NMR Toolkit for Biological Solids: Oxygen-17 Enriched Fmoc-Amino Acids

We report the solid-state 17O NMR parameters for five previously uncharacterized N-α-fluoren-9-yl-methoxycarbonyl-O-t-butyl (Fmoc) protected amino acids. These molecules are critical to constructing synthetic biological systems, like peptides, and provide an...

Nutritional Value of Black Soldier Fly Grown on Abattoir Waste

Meat processing plants generate a range of solid and liquid wastes, including manure, paunch solids, and biological solids from wastewater treatment. There is growing interest in alternative technologies for treating abattoir waste, including using insects to transform waste into high-value products. Black Soldier Fly (BSF) larvae may be a competitive source of digestible amino acids and, depending on the protein digestibility, can be used as a replacement for fish meal, soybean meal or cottonseed meal in livestock and aquaculture rations. The objective of this study was to evaluate the effect of using different substrates and substrate mixes from abattoir waste streams on the nutritional quality of BSF harvested at two growth stages (larvae and prepupae). Protein digestibility was evaluated using an adapted pepsin digestion. Averaged across all substrates, there was no difference between growth stages in total protein content (43.7%). However, protein digestibility was higher for larvae (86.5%) than for prepupae (65.1%). The substrate used greatly influenced the nutritional composition of BSF. Prepupae protein content varied from 42 to 48% and protein digestibility varied from 42 to 80%, according to the substrate. Variation in larvae across substrates was greater than prepupae for protein content (34% to 53%) but much lower for digestibility (80% to 91%). Both substrate and growth stage altered the mineral composition of BSF prepupae and larvae. Iron levels varied from 79 (paunch) to 453 mg/kg DM (substrate containing blood), illustrating the plasticity of BSF. In conclusion, BSF can be used to transform abattoir waste into high-value products.