NMR studies of chitin and chitin derivatives

Abstract

The l3C NMR spectra of N-acetyl-D-glucosamine (1) and chitobiose (2), monomer and dimer of chitin, were assigned and used to assign the I3C NMR spectra of chitin in lithium thiocyanate and in LiCl/dimethylacetamide solutions. The dissolution of chitin in formic acid was studied.IR, I3C and 'H NMR spectra show that dissolution occurs by a reaction of formic acid with chitin with the formation of formyl chitin as a statistical derivative of chitin. I3C NMR spectra of diformyl-and diacetylchitin were also assigned to characterize these regular polymers.

Solubility of Cellulose Acetate Prepared by Different Methods and Its Correlationships with Average Acetyl Group Distribution on Glucopyranose Units

“…As was also the solubility of CA against DMAC and DMSO. The results are compiled in the last columns of Tables I and II. RESULTS AND DISCUSSION Figure 1 shows the 13 CC H} NMR spectra in 0-acetyl carbonyl carbon region of CT A = 2. 92) and CA (one-step method, sample code I-1-1-5).…”

“…It should be noted again here that the spectra patterns between 169.0 and 169.7 ppm are very complicated especially for CA with 0.68 and 0.80. Assuming that the peak positions of the carbonyl carbon peaks due to disubstituted glucopyranose units are not far from the corresponding peaks of mono-and tri-substituted glucopyranose units, we can divide roughly the whole spectra in a carbonyl carbon region into three regions: the region between 170-169.6 ppm for C 6 , 169.6-168.9 ppm for C 3 , and 168.9-168.3 ppm for C 2 • It should be remembered that this technique might give a convenient basis for estimating from 13 C NMR spectra, but it is not so rigorous. For example, two peaks groups assigned for c3 and c2 positions have an innegligible possibility of mutual overlapping, which can be realized, for example, by noting that at least more than 6 peaks are observed experimentally in the above defined carbonyl carbon region at the so-called c3 position, although the maximum number of corresponding peaks, theoretically expected, is only four (one for mono-, for tri-, and two for disubstituted glucopyranose units).…”

“…In contrast to this, the carbonyl carbon peak group at c6 position is absolutely separated from those at other positions. Then, and ( + can be accurately estimated, regardless of its from 13 C NMR carbonyl carbon region spectra of CA with help of (by the titration method).…”

“…'s claim 13 that the intramolecular hydrogen bonding between the hydroxyl group at c3 position and a heterocyclic oxygen atom in neighbouring glucopyranose unit of cellulose may exist even in the solution. Note that Gagnaire et al's assertion was formed only indirectly by observing the constancy of 1 H NMR spectra peak position of hydroxyl proton at c3 position ( 4.6 ppm) of cellobiose (not cellulose!)…”

“…In this article we clarify the effects of the preparing conditions on and the relative ratio of various substituted glucopyranose units of CA and to obtain the relations between (k = 2, 3, and 6) and the solubility of CA, discussing the dissolution mechanism of cellulose derivatives in solvents. For this purpose, we prepared nine CA samples by (1) a direct acetylation method of cellulose solution (one-step method) and (2) the acidhydrolysis of cellulose triacetate with = 2.92 (two-step method), as described in the previous paper, 7 and measured 13 vacuo again. The five samples prepared in this way were subjected to further NMR measurements.…”