High-resolution magic angle spinning NMR for intact biological specimen analysis: Initial discovery, recent developments, and future directions

High-resolution magic angle spinning (HRMAS) NMR, an approach for intact biological material analysis discovered more than 25 years ago, has been advanced by many technical developments and applied to many biomedical uses. This article provides a history of its discovery, first by explaining the key scientific advances that paved the way for HRMAS NMR's invention, and then by turning to recent developments that have profited from applying and advancing the technique during the last 5 years. Developments aimed at directly impacting healthcare include HRMAS NMR metabolomics applications within studies of human disease states such as cancers, brain diseases, metabolic diseases, transplantation medicine, and adiposity. Here, the discussion describes recent HRMAS NMR metabolomics studies of breast cancer and prostate cancer, as well as of matching tissues with biofluids, multimodality studies, and mechanistic investigations, all conducted to better understand disease metabolic characteristics for diagnosis, opportune windows for treatment, and prognostication. In addition, HRMAS NMR metabolomics studies of plants, foods, and cell structures, along with longitudinal cell studies, are reviewed and discussed. Finally, inspired by the technique's history of discoveries and recent successes, future biomedical arenas that stand to benefit from HRMAS NMR-initiated scientific investigations are presented.

Unusual temperature-sensitive protonation behaviour of 4-(dimethylamino)pyridine

An unusually strong impact of temperature on the protonation degree of DMAP in strong acid solutions has been found.

Chirality dependent inverse-melting and re-entrant gelation in α-cyclodextrin/1-phenylethylamine mixtures

Solutions of cyclohexakis-(1→4)-α-d-glucopyranosyl, α-cyclodextrin, αCD, in R-(+)-1-phenylethylamine, αCD/R-PEA, and S-(−)-1-phenylethylamine, αCD/S-PEA, display abnormal phase transitions that strongly depend on supramolecular diastereomeric interactions. While αCD/R-PEA mixtures show one sol–gel inverse-melting phase transition, αCD/S-PEA mixtures show temperature dependent gel–sol–gel re-entrant behavior. NMR, Raman spectroscopy, microscopy and X-ray scattering measurements reveal that hydrogen bond weakening in solution, as well as changes in crystal composition are responsible for entropy increase and gel formation upon heating.

Solutions of α-cyclodextrin in chiral 1-phenylethylamine display abnormal phase transitions. Depending on supramolecular diastereomeric interactions, inverse-melting and re-entrant gels are formed.

Smart control of guest inclusion by α-cyclodextrin using its hydration history

Hydration history was found to control the inclusion capacity of α-cyclodextrin (aCD) for volatile organic guests, so that its level may be switched from zero to the stoichiometric value and back by the variation of aCD hydration/dehydration order and direction. Such variation of the inclusion capacity is caused by the balance of two water roles: the activation of guest inclusion and guest/water competition. These observed concurrent roles and the cooperativity of guest inclusion and hydration make possible the smart tuning of the guest inclusion by the subtle change of preparation procedure. Depending on the hydration history, aCD was shown to form hydrates with the same water contents but different packing types and different kinetics of dehydration, which correlates with their different inclusion capacities for organic guests. This correlation reveals how the “high-energy” and “low-energy” water works in the guest inclusion by aCD, which may be relevant for other cyclodextrins and hydrophilic receptors of biomimetic and biological natures. The results can help to rationalize the technologies of producing various inclusion compounds of cyclodextrins.

The hydration level and hydration history of alpha-cyclodextrin significantly affects its structure and inclusion capacity for organic guests.