engleski

A fast MAS 1H NMR study of amino acids and proteins

Fast sample spinning (up to 32kHz) in tandem with delayed acquisition enabled resolved 1H NMR spectra of solid amino acids to be recorded. The resulting spectra are, however, significantly dependent on sample crystallinity and on sample preparation conditions, e.g. sample drying. Sample heating leads to a marked increase in signal to noise ratio and enables groups with different dynamic properties to be identified. In addition, the observation of peak shifts as a function of heating allows the identification of hydrogen bonded sites. Spectral assignment of the 1H MAS spectra is proposed for some examples based on relaxation properties, study of deuteriated samples and 2D NMR. The effects of molecular weight and sample complexity on the 1H MAS spectra were investigated using tetraglycine, polyglycine and two proteins: a small protein (lysozyme) and a much larger protein (a cereal storage protein named high molecular weight subunit 1Dx5). Moderate spectral resolution was achieved for the peptides and lysozyme, but for 1Dx5, significant resolution enhancement was obtained enabling the identification of resonances in all regions of the spectra including the alpha region, the aromatic region and the NH backbone region.

1H NMR; MAS; Amino acid; Protein; Solid state

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