α-Chitin dissolution, N-deacetylation and valorization in deep eutectic solvents.

Area of Science:

• Biopolymer Chemistry
• Green Chemistry
• Materials Science

Background:

• Chitin's rigid structure, due to extensive hydrogen bonding, limits its solubility and deacetylation.
• Deep eutectic solvents (DESs), formed from hydrogen bond donors and acceptors, can disrupt chitin's hydrogen bonds, enhancing its solubility.
• Conventional chitin deacetylation requires harsh conditions (high NaOH concentration and temperature), posing environmental and biocompatibility concerns.

Purpose of the Study:

• To investigate the efficacy of four distinct DESs in dissolving chitin.
• To evaluate the application of the most effective DESs in the homogeneous N-deacetylation of chitin under milder conditions.
• To establish a proof of concept for a greener approach to chitin modification.

Main Methods:

• Four DESs (choline chloride-lactic acid, choline chloride:oxalic acid, choline chloride:urea, and betaine-glycerol) were employed for chitin dissolution.
• The most effective DESs were used for homogeneous N-deacetylation of chitin using 30 wt% NaOH at 80°C for 18 hours.
• Attenuated Total Reflectance Fourier-Transform Infrared Spectroscopy (ATR-FTIR) was utilized for reaction analysis.

Main Results:

• DESs successfully dissolved chitin by disrupting its hydrogen bonding network.
• Chitin was converted to chitosan with a 70-80% degree of deacetylation (DDA) under the optimized, milder conditions.
• Betaine-glycerol (Bet:G) and choline chloride-lactic acid ([Ch]Cl:LA) based DESs demonstrated significant potential for greener chitin deacetylation.

Conclusions:

• Bet:G and [Ch]Cl:LA based DESs offer a promising, environmentally friendly alternative for homogeneous chitin N-deacetylation.
• The developed method utilizes milder reaction conditions compared to traditional approaches.
• This study provides the first evidence for the use of these specific DESs in a sustainable chitin modification process.