Water-Soluble 2,5-Anhydro-d-mannofuranose Chain End Chitosan Oligomers of a Very Low Molecular Weight: Synthesis and Characterization

Abstract

Five chitosan with different acetylation degree (DA), molar masses and origin were depolymerized by nitrous acid treatment in acidic media leading to water soluble 2,5 anhydro-Dmannose end chain oligomers with DPn<20. The kinetics of the reaction was studied and the best work conditions were found to be 3h reaction at 50°C. It was shown that the DPn of oligomers only depends on the quantity of NaNO2 involved. Molar masses or DA do not have an impact on the depolymerization process when targeting oligomers with less than 20 units. This depolymerization process also leads to free AMF that might react with the free amines of obtained oligomers to form imines. This reaction is pH dependant and in acidic condition, leads to the formation of 5-hydromethyl-2-furfural (HMF). At the end, the oligomers were purified with dialysis to get rid of most free AMF (<5%) and other residual salts, and appeared to have no acute toxicity.

Diels-Alder-Chitosan based dissociative covalent adaptable networks

“…Synthesis of chitosan oligomers functionalised with furfuryl glycidyl ether (FGO) The depolymerization of 30,000 g/mol chitosan was performed by nitrous deamination involving NaNO 2 as previously described (Chapelle et al, 2019). Briefly, 1g (w/w) of chitosan was dissolved in 90 mL of AcOH (350µL in 90 mL of deionized water) solution overnight (pH 4.5).…”

Advances in chitooligosaccharides chemical modifications

“…This method has been widely described for being efficient and reproducible to obtain COS. Yet, this reaction leads to the formation of side reaction when the aldehyde reacts with the free amines of chitosan to form imines, thus leading to branched structures and in acidic condition, and to the formation of free 5‐hydroxymethyl‐2‐furfural with additional breakage of the glycosidic bond [47] . This is why some teams tried to block the aldehyde moieties.…”

“…The chemical depolymerizations consists of acid hydrolysis, [41,42] the use of oxidative agent such as hydrogen peroxide [43,44] or even the action of nitrous acid [45,46] . This last method was shown to be applicable and reproducible for any kind of crude chitosan leading to low‐molecular‐weight oligomers [47] . It leads to a 2,5‐anhydro‐ d ‐mannose (AMF) chain end, which is electrophilic and reactive for further reactions.…”

Surfactant properties of chemically modified chitooligosaccharides and their potential application in bitumen emulsions

“…COS of DP5 DP10 and DP15 were obtained according to precedent work [24] and functionalized with butyl glycidyl ether (C4), octyl/decyl glycidyl ether (C9), hexadecyl glycidyl ether (C16), and epoxidized cardanol according to reaction conditions established in a previous work [27].…”

“…Nevertheless, high molar masses chitosan shows high viscosity in solution and low reactivity. When reducing the molar mass, chitooligosaccharides (COS) can be obtained [24]. COS are easier to functionalize in order to obtain amphiphilic structures.…”