%0 Journal Article %1 Varum2001 %A Varum, K. M. %A Ottoy, M. H. %A Smidsrod, O. %C THE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD OX5 1GB, OXON, ENGLAND %D 2001 %I ELSEVIER SCI LTD %J Carbohydr. Polym. %K ; ;; [ISI:] activation chitins chitosan; chitosans; de-N-acetylation; deacetylated degradation; depolymerization; energies field lysozyme mechanisms; n-acetylated nmr-spectroscopy; reaction specificity; %N 1 %P 89 -- 98 %T Acid hydrolysis of chitosans %V 46 %X The hydrolysis of the O-glycosidic linkages (depolymerization) and the N-acetyl linkage (de-N-acetylation) of partially N-acetylated chitosans were studied in dilute and concentrated HCl. The rate of hydrolysis of the glycosidic linkages was found to be equal to the rate of de-N-acetylation in dilute acid, while the glycosidic linkages was hydrolysed more than 10 times faster than the N-acetyl linkage in concentrated HCl. This can be explained by assuming that the hydrolysis of the N-acetyl Linkage is a S(N)2 reaction Gate-Limiting step: addition of water to the carbonium ion) while the hydrolysis of the glycosidic linkages is a S(N)1 reaction where the rate-limiting step is the formation of the carbonium ion. The specificity of the acid-catalysed cleavage of the different chitosan glycosidic linkages in concentrated HCl was such that the linkages between two acetylated units (A-A) and between an acetylated and a deacetylated unit (A-D) was cleaved with about equal rate and three orders of magnitude faster than the other two linkages (D-A and D-D). The activation energies for acid hydrolysis of two almost fully de-N-acetylated chitosans (F-A = 0.002 and F-A < 0.0003) were determined to be 152.2 +/- 8.1 and 158.1 +/- 9.8 kJ mol(-1), respectively, representing the activation energy for hydrolysis of the D-D glycosidic linkage in chitosans. The activation energies for acid hydrolysis of two partially N-acetylated chitosans (F-A = 0.47 and F-A = 0.62) were determined to be 130.4 +/- 2.5 and 134.3 +/- 3.1 kJ mol(-1), respectively, representing the activation energy for hydrolysis of the A-A and A-D glycosidic linkage in chitosans. (C) 2001 Elsevier Science Ltd. All rights reserved.

@article{Varum2001, __markedentry = {[phpts:6]}, abstract = {The hydrolysis of the O-glycosidic linkages (depolymerization) and the N-acetyl linkage (de-N-acetylation) of partially N-acetylated chitosans were studied in dilute and concentrated HCl. The rate of hydrolysis of the glycosidic linkages was found to be equal to the rate of de-N-acetylation in dilute acid, while the glycosidic linkages was hydrolysed more than 10 times faster than the N-acetyl linkage in concentrated HCl. This can be explained by assuming that the hydrolysis of the N-acetyl Linkage is a S(N)2 reaction Gate-Limiting step: addition of water to the carbonium ion) while the hydrolysis of the glycosidic linkages is a S(N)1 reaction where the rate-limiting step is the formation of the carbonium ion. The specificity of the acid-catalysed cleavage of the different chitosan glycosidic linkages in concentrated HCl was such that the linkages between two acetylated units (A-A) and between an acetylated and a deacetylated unit (A-D) was cleaved with about equal rate and three orders of magnitude faster than the other two linkages (D-A and D-D). The activation energies for acid hydrolysis of two almost fully de-N-acetylated chitosans (F-A = 0.002 and F-A < 0.0003) were determined to be 152.2 +/- 8.1 and 158.1 +/- 9.8 kJ mol(-1), respectively, representing the activation energy for hydrolysis of the D-D glycosidic linkage in chitosans. The activation energies for acid hydrolysis of two partially N-acetylated chitosans (F-A = 0.47 and F-A = 0.62) were determined to be 130.4 +/- 2.5 and 134.3 +/- 3.1 kJ mol(-1), respectively, representing the activation energy for hydrolysis of the A-A and A-D glycosidic linkage in chitosans. (C) 2001 Elsevier Science Ltd. All rights reserved.}, added-at = {2011-11-04T13:47:04.000+0100}, address = {THE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD OX5 1GB, OXON, ENGLAND}, author = {Varum, K. M. and Ottoy, M. H. and Smidsrod, O.}, authoraddress = {Norwegian Univ Sci & Technol, Dept Biotechnol, NOBIPOL, Norwegian Biopolymer Lab, N-7491 Trondheim, Norway. ; Norsk Hydro AS, Res Ctr, Div Biotechnol, N-3901 Porsgrunn, Norway.}, biburl = {https://www.bibsonomy.org/bibtex/26f484d8c801c1f044e799a82340a2da6/pawelsikorski}, citedref = {ANTHONSEN MW, 1993, CARBOHYD POLYM, V22, P193 ; DRAGET KI, 1992, BIOMATERIALS, V13, P635 ; HOLME HK, 2000, IN PRESS THERMAL DEP ; ISHIGURO K, 1992, CARBOHYD RES, V237, P333 ; MEYER KH, 1937, HELV CHIM ACTA, V20, P353 ; MOGGRIDGE RCG, 1938, J CHEM SOC 1, P745 ; NORDTVEIT RJ, 1994, CARBOHYD POLYM, V23, P253 ; RUPLEY JA, 1964, BIOCHIM BIOPHYS ACTA, V83, P245 ; SANNAN T, 1976, MAKROMOL CHEM, V177, P3589 ; TANFORD C, 1961, PHYSICAL CHEM MACROM ; TSUKADA S, 1981, CARBOHYD RES, V88, P19 ; VARUM KM, 1991, CARBOHYD RES, V211, P17 ; VARUM KM, 1991, CARBOHYD RES, V217, P19 ; VARUM KM, 1996, ADV CHITIN SCI, V1, P173 ; VARUM KM, 1996, BBA-GEN SUBJECTS, V1291, P5 ; VARUM KM, 1997, ADV CHITIN SCI, V2, P168}, interhash = {4fa8a83e015e6e0921f32f0b60689620}, intrahash = {6f484d8c801c1f044e799a82340a2da6}, isifile-dt = {Article}, isifile-ga = {444HZ}, isifile-j9 = {CARBOHYD POLYM}, isifile-nr = {16}, isifile-pi = {OXFORD}, isifile-rp = {Varum, KM, Norwegian Univ Sci & Technol, Dept Biotechnol, NOBIPOL, ; Norwegian Biopolymer Lab, N-7491 Trondheim, Norway.}, isifile-sc = {Chemistry, Applied; Chemistry, Organic; Polymer Science}, isifile-tc = {27}, issn = {0144-8617}, journal = {Carbohydr. Polym.}, keywords = {; ;; [ISI:] activation chitins chitosan; chitosans; de-N-acetylation; deacetylated degradation; depolymerization; energies field lysozyme mechanisms; n-acetylated nmr-spectroscopy; reaction specificity;}, language = {English}, month = SEP, number = 1, owner = {phpts}, pages = {89 -- 98}, publisher = {ELSEVIER SCI LTD}, size = {10 p.}, sourceid = {ISI:000169395200010}, timestamp = {2011-11-04T13:47:27.000+0100}, title = {Acid hydrolysis of chitosans}, volume = 46, year = 2001 }