Two‐dimensional magic angle spinning NMR investigation of naturally occurring chitins: Precise ¹H and ¹³C resonance assignment of α‐ and β‐chitin

Abstract

13C homonuclear through-bond correlations of alpha- and beta-chitin were determined by using two-dimensional (2D) INADEQUATE spectra of these allomorphs purified from crab shell and squid pen, respectively. The 2D (13)C-(13)C correlation spectra where two directly bonded carbons share a common double-quantum frequency (DQ) enabled us to precisely assign all (13)C resonances of the chitin allomorphs for the first time. Following the complete (13)C assignment, (1)H chemical shifts of protons attached to each carbon nuclei were assigned by 2D frequency-switched Lee-Goldberg (FSLG) (1)H-(13)C heteronuclear correlation (HETCOR) spectra of the chitin allomorphs, recorded with a short mixing time (60 micros) to provide isotropic (1)H-(13)C chemical shift correlations between bonded pairs proton and carbon nuclei. From the (13)C and (1)H chemical shifts of chitin allomorphs, all 2-deoxy-2-acetamide-D-glucose (N-acetyl-D-glucosamine) monomer units in each allomorph were revealed to be an identical (13)C-(13)C backbone conformation and magnetically equivalent. In addition, it was strongly suggested that there are two different hydrogen-bonding patterns at the hydroxyl groups of alpha-chitin by comparing (1)H chemical shifts at the C6 site of alpha-chitin with those at the same site of beta-chitin.

Characterization of dissolved and particulate natural organic matter (NOM) in Neversink Reservoir, New York

“…The anomeric band in the FPO fraction occurs at about 104 ppm. This is in the same region as the anomeric carbon atoms of chitin and cellulose, and the bands at 23.6, 58.1, 61.8, 72.5, 103.7, and 173.4 ppm are within 1 or 2 ppm of the bands that have been observed by Heux and others (2000) and Kono (2004) for chitin. The infrared spectrum of the fraction ( fig.…”

Contrasts between organic participation in apatite biomineralization in brachiopod shell and vertebrate bone identified by nuclear magnetic resonance spectroscopy

“…The 13 C SSNMR spectra of L. anatina and D. tenuis shells ( figure 1) show prominent signals from chitin [17], a homopolymer of b-(1 -4) glycosidically linked 2-deoxy-2-N-acetylaminoglucose sugars, assignments of which following Kono [18] are shown in figure 1, although it is possible that other structurally similar aminosugars such as N-acetylgalactosamine contribute to these signals. There are other signals consistent with proteins; wherever possible these are assigned in figure 1 to specific amino acid residues or types, or the more prominent are asterisked where this is not possible.…”

The refocused INADEQUATE MAS NMR experiment in multiple spin-systems: Interpreting observed correlation peaks and optimising lineshapes

“…These include the solid-state INADEQUATE [7,8] and INADEQUATE-CR [9], the refocused INADEQUATE [10], the UC2QF-COSY [11][12][13], spin-state selective experiments [14], and the recently introduced J-mediated triple-quantum (TQ) experiment [15]. In this paper, we focus on the refocused INADEQUATE experiment, whose robustness has been repeatedly demonstrated in a wide range of 13 C-enriched [16][17][18][19][20] or 15 N-enriched [21,22] and 13 C natural abundance [23][24][25][26][27][28] polycrystalline organic systems, as well as in disordered [29][30][31] organic systems and in crystalline and disordered inorganic solids [32][33][34][35][36].…”