M. H. Frey

Complete Solid State 13C NMR Chemical Shift Assignments for α-D-Glucose, α-D-Glucose-H2O and β-D-Glucose

Abstract NMR spectra of crystalline α-D-glucose DH2O (1), α-D-glucose (2), and β-D-glucose (3) were examined by 13C cross polarization magic angle spinning (CPMAS) methods. Each of the three forms of glucose exhibited a distinctly different spectrum. Chemical interconversion of 2 and 3 as well as the in situ dehydration of 1 during the course of the CPMAS NMR experiment was monitored in the 13C spectra. Samples of 1, 2, and 3 specifically enriched at C-1 and C-6 with 13C yielded 13C spectra in which the resonances corresponding to the adjacent C-2 and C-5 carbons were not visible due to strong homonuclear 13C dipolar interactions with the high abundance label. Spectra of these analogues as well as the C-2 and C-3 labeled materials provided the complete 13C chemical shift assignments of crystalline 1 2, and 3. A comparison of the solid state and solution 13C spectra revealed substantial resonance shifts for each of the three structures examined.

13C solid-state NMR chromatography by magic angle spinning 1H T1 relaxation ordered spectroscopy

An efficient method to separate the (13)C NMR spectra of solid mixtures is introduced. The (1)H longitudinal (T(1)) relaxation time is used to separate the overlapping (13)C chemical shift spectra of solid mixtures via an inverse Laplace transform (ILT) of the relaxation dimension. The resulting 2D spectrum of the mixture contains separate (13)C spectra for each component of the mixture that are identical to (13)C spectra of the isolated materials. The separation is based on the equalization of (1)H T(1) values in a single domain by rapid (1)H spin diffusion and on the (1)H T(1) value differences between different domains. The introduction of a general ILT scheme enables efficient and reduced data acquisition time. The method is demonstrated on a mixture of two disaccharides and on a commercial drug containing several compounds.

The Effect of pH on solid-state 13C NMR spectra of histidine

Abstract High-resolution solid-state 13C NMR spectra of histidine powder samples prepared from solutions at several pH values near the pKa of the imidazole group are presented. These spectra demonstrate several effects due to the titration of the imidazole group. The chemical shifts for all of the carbon sites change upon titration. They are in “slow exchange” in the solid state in contrast to the “fast exchange” behavior seen in solution. Changes in the quadrupole interactions in the 14N sites occur upon titration and are observed by their effects on the resonance lineshapes of the 13C sites to which they are bonded.

High-resolution features of the 13C n.m.r. spectra of solid amino acids and peptides

13 C N.m.r. spectra of solid amino acids and peptides display resonance shifts and splittings not seen in solution; these solid state effects are illustrated with Tyr, Leu, and the mixed peptides Tyr-Leu and Leu-Tyr.