Determination of the degree of acetylation of chitin materials by 13C CP/MAS NMR spectroscopy.
13C CP/MAS NMR spectroscopy has been shown to be a powerful tool to quantify the degree of acetylation of chitin and chitosan. In order to optimise the parameters which afford quantitative 13C cross-polarisation magic-angle spinning NMR spectra, a detailed relaxation study has been carried out on selected chitin and deacetylated chitin samples. A relaxation delay of 5 s and a contact time of 1 ms have been found to yield quantitative NMR spectra of samples with deacetylation degree values of 0.68 and 0.16. The measured spin-lattice relaxation times in the rotating frame, T(1rhoH), are in the range 6.4-8.9 ms for chitin and 4.3-7.3 ms for deacetylated chitin, while TCH values for both samples are very similar and range from 0.03 to 0.19 ms. Spin-counting experiments indicate that, within experimental error, all carbon is detected by NMR indicating that the samples studied contain no (or very few) paramagnetic centres.
Duarte
M L
ML
Department of Chemistry and Biochemistry, CECUL, University of Lisbon, 1749-016, Lisbon, Portugal. joduarte@mail.telepac.pt
Ferreira
M C
MC
Marvão
M R
MR
Rocha
J
J
D000107:Acetylation; D000818:Animals; D003386:Brachyura / Q000737:chemistry*; D002247:Carbon Isotopes; D002686:Chitin / Q000032:analysis* / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy; D019906:Nuclear Magnetic Resonance, Biomolecular
D002247:Carbon Isotopes; D002686:Chitin