Chemical preparation and structural characterization of a homogeneous series of chitin/chitosan oligomers.
The preparation of a homogeneous series of chitin/chitosan oligomers (chito-oligomers) with the same distribution of degrees of polymerization (DP) ranging from 2 to 12, but with various average degrees of N-acetylation (DA) from 0 to 90% is described. This DA-series was obtained according to a two-step chemical process involving (i) the production of a well-defined mixture of glucosamine (GlcN) oligomers obtained by acid hydrolysis of a fully N-deacetylated chitosan and after selective precipitations of the hydrolysis products, and (ii) the partial N-acetylation of the GlcN units of these oligomers from a hydro-alcoholic solution of acetic anhydride in a controlled manner. The characterization of this series of samples with different DAs by proton nuclear magnetic resonance (1H NMR) spectroscopy and matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) allowed us to determine their average DA and identify the main oligomer structures constituting each mixture. Furthermore, MALDI-TOF MS was particularly helpful to study the distribution evolution of the diverse oligomers as a function of DA for the main DPs from 3 to 7. The modeling of these distributions by means of a binomial law displayed that the chemical N-acetylation of low DP GlcN oligomers, produced in a homogeneous medium, occurs randomly along the oligosaccharide chains in accordance with a statistical (Bernoullian) arrangement. In this case, the relative proportion of each chito-oligomer present in the mixture can be estimated precisely as a function of DA considering oligomers of same DP.
Laboratoire des Matériaux Polymères et des Biomatériaux, UMR CNRS 5223 Ingénierie des Matériaux Polymères, Université Claude Bernard Lyon 1, Domaine scientifique de La Doua, Bâtiment ISTIL, Villeurbanne Cedex, France. stephane.trombotto@univ-lyon1.fr
Stéphane
S
Trombotto
Catherine
C
Ladavière
Frédéric
F
Delolme
Alain
A
Domard
D000107:Acetylation; D002236:Carbohydrate Conformation; D002686:Chitin / Q000138:chemical synthesis / Q000737:chemistry*; D048271:Chitosan / Q000138:chemical synthesis / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D009844:Oligosaccharides / Q000138:chemical synthesis / Q000737:chemistry*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
D009844:Oligosaccharides; D002686:Chitin; D048271:Chitosan