Kinetics and efficiency of chitosan reacetylation

Chitosan reacetylation kinetics and efficiency were studied in water-methanol (MeOH) mixtures. The polymer was dissolved using acetic acid and acetic anhydride was used for reacetylation. Combining second-order kinetics and acid-base dissociation equations of chitosan, and using acetic anhydride hydrolysis rates determined by conductivity measurements, reacetylation reaction rate constants of 187, 108, 46 min⁻¹ M⁻¹ were found in 0, 50 and 80% MeOH (v/v), respectively. Contrary to previous literature, it was found that improvement in reacetylation efficiency in the presence of MeOH is mainly due to an increase of acetic acid pK_a by MeOH that limits the ionization of the polymer in the course of the reaction rather than to a decreased acetic anhydride hydrolysis rate, as previously thought. Based on these insights, the model developed in this study was able to predict the significantly reduced efficiency of the reaction for a large extent of reacetylation, without requiring any steric hindrance from the acetyl group. Conditions to maximize the reaction efficiency for a large extent of reacetylation were identified.     

Polysaccharide peptide induces a tumor necrosis factor-α-dependent drop of body temperature in rats

Polysaccharide peptide (PSP) extracted from the Coriolus versicolor mushroom is frequently suggested as an adjunct to the chemo- or radiotherapy in cancer patients. It improves quality of the patients' life by decreasing pain, fatigue, loss of appetite, nausea, and vomiting. However, the effect of PSP on body temperature has not thus far been studied, although it is well known that treatment with other polysaccharide adjuvants, such as lipopolysaccharides, may induce fever. The aim of the present study, therefore, was to investigate the influence of PSP on temperature regulation in rats. We report that intraperitoneal injection of PSP provoked a dose-dependent decrease of temperature in male Wistar rats equipped with biotelemetry devices to monitor deep body temperature (T_b). The response was rapid (i.e., with latency of 15–20 min), transient (lasting up to 5 h post-injection), and accompanied by a significant elevation of the blood tumor necrosis factor-α (TNF-α) level. Pretreatment of the rats with anti-TNF-α antibody prevented the PSP-induced drop in T_b. Based on these data, we conclude that rats may develop an anapyrexia-like response to the injection of peptidopolysaccharide rather than fever, and the response was TNF-α-dependent.     

Genome diversity at the serA-linked capsule locus in Escherichia coli

Individual isolates of Escherichia coli synthesize one of more than 70 chemically distinct polysaccharides which form the capsule. In this article we review the genetics of capsule production in E. coli and highlight what this is beginning to reveal in terms of the genetic basis of the structural diversity of polysaccharides. The serA-linked capsule locus can take three different allelic forms. Two of these are associated with capsule genes and are themselves internally variant, whilst the third form has not so far been implicated in capsule biogenesis. Thus the serA-linked region of the E. coli genome is strikingly polymorphic.     

Preparation and characterization of fully deacetylated chitosan

A new method for N-deacetylation of chitosan is proposed in which a polymer free of N-acetyl groups is obtained without much decrease in molecular weight. Different methods for determining the degree of acetylation were used, mainly i.r. spectroscopy and conductimetry. Average molecular weights were determined by membrane osmometry and light scattering; a polydispersity <2 was found. This well defined amino-polymer can be used for investigation of chelating properties.