Malgorzata M. Jaworska

Review of the application of ionic liquids as solvents for chitin

Abstract Chitin is one of the most abundant biopolymers, but due to its high crystallinity, it is completely insoluble in most organic and inorganic solvents. Chitin is soluble only in solvents that can destroy intersheet and intrasheet H-bonds, and many of these solvents are toxic, corrosive, nondegradable, or mutagenic. Because of these drawbacks, there is a search for more environmentally friendly solvents for chitin. It has been shown that ionic liquids (ILs) can dissolve chitin at elevated temperatures (80°–110°C) or with application of microwave irradiation. The highest solubility of chitin in an IL was about 20% (1-ethyl-3-methylimidazolium acetate), whereas chitin was shown to be insoluble in 1-allyl-3-methylimidazolium chloride and 1-butyl-3-methylimidazolium formate. Dissolved chitin can be regenerated by mixing with water or methanol, where the polymer precipitates from the solution. X-ray diffraction patterns of native polymer and precipitates have been compared and only small changes in crystallinity have been observed. In addition, Fourier transform infrared spectra remained similar for both forms of chitin, native and regenerated. Presented data hold great promise for the improvement of the chemistry of chitin and open new routes for chemical and enzymatic modifications of this polymer.

Kinetics of enzymatic deacetylation of chitosan

The current paper reports on an investigation of the kinetics of chitosan deacetylation by chitin deacetylase isolated from Absidia orchidis vel coerulea. The reaction rate was correlated with the concentration of GlcNHAc units of the polymer. It is shown that the process follows the Michaelis–Menten mechanism. Modification of the Michaelis–Menten equation by introducing the activity of the enzyme instead of its concentration was tested and found to give a better approximation to the experimental data than the original Michaelis–Menten model. Parameters for both the original and the modified Michaelis–Menten equations are also proposed.

Water leaching of titanium from ore flotation residue.

Copper ore tailings were tested for the stability of titanium submitted to water leaching in three different reactor systems (agitated vessel, bioreactor and percolated fixed-bed column). For each of these systems, titanium extraction did not exceed 1% of the available metal. Biomass removed from ore residue adsorbed a small part of the titanium with sorption capacities below 20-30 mg g(-1), but most of this biomass was sequestered in the ore residue. Oxygen and carbon dioxide concentrations were monitored and changes in concentration correlated with bacteria development at the initial stage of the process and to fungal development in the latter stages.

Kinetics of chitin deacetylase activation by the ionic liquid [Bmim][Br]

Chitin deacetylase is the only known enzyme that can deacetylate the N-acetyl-d-glucosamine units in chitin and chitosan to D-glucosamine. Unfortunately, this enzyme, originally obtained from fungi, usually has low activity. Here, we present that it is possible to enhance the activity of chitin deacetylase using the ionic liquid [Bmim][Br]. An increase in activity of up to 160% from the basal chitin deacetylase activity was observed. Kinetic investigations suggest that [Bmim][Br] is a non-essential activator.

Modification of Chitin Particles with Ionic Liquids Containing Ethyl Substituent in a Cation

Chitin cannot be dissolved in conventional solvents due to the strong inter- and intrasheet network of hydrogen bonds and the large number of crystalline regions. Some ionic liquids (ILs) have been suggested in the literature as possible solvents for chitin. Seven of them, all having an ethyl group as substituent in the cationic ring, have been tested in this work: [Emim][Cl], [Emim][Br], [Emim][I], [Emim][OAc], [Emim][Lact], [Epyr][I], and [EMS][BFSI]. Chitin was insoluble in [EMS][BFSI] while for all other ILs solubility was limited due to high viscosity of solutions and equilibria have not been reached. Changes in physical structure, particle size distribution, and crystallinity of recovered chitin depended on ionic liquid used. Increase in porosity was observed for chitin treated with [Emim][Cl], [Emim][I], [Emim][Br], and [Emim][Lact]; changes in particle size distribution were observed for [Emim][AcOH] and [EMS][BFSI]; increase in crystallinity was noticed for chitin treated with [Epyr][I] while decrease in crystallinity for [Emim][I] was noticed. All tested ionic liquids were reused four times and changes in FTIR spectra could be observed for each IL.

Chitin deacetylase product inhibition

Chitin deacetylase is the only known enzyme catalyzing the hydrolysis of the acetamino linkage in the N-acetylglucosamine units of chitin and chitosan. This reaction can play an important role in enzymatic production of chitosan from chitin, or in enzymatic modification of chitosan, which has applications in medicine, pharmacy or plant protection. It was previously shown that acetic acid, a product of the deacetylation process, may act as an inhibitor of chitin deacetylase. Here we show the mechanism of inhibition of chitin deacetylase isolated from Absidia orchidis vel coerulea by acetic acid released during the deacetylation process. The process follows competitive inhibition with respect to acetic acid with an inhibition constant of K(i) = 0.286 mmol/L. These results will help to find the optimal system to carry out the enzymatic deacetylation process for industrial applications.

New ionic liquids for modification of chitin particles

Chitin particles are chemically and mechanically stable due to the strong inter- and intra-sheet network of hydrogen bonds and the large number of crystalline regions. Thus, it is difficult to make any modification of the chitin particles themselves. Therefore, new solvents which can modify the structure of chitin particles are being sought. This work presents the influence of unreported ionic liquids (ILs) containing the TCB anion on chitin: three of them contained the imidazolium ring, ([Im], [Dmim], [EOHmim]) and another three contained the pyridinum ring ([Pyr], [EOHpyr], [POHpyr]). Chitin did not dissolve in any of the tested ILs but the ILs were able to modify the structure (porosity and corrugation) of chitin particles. It has also been shown that [EOHpyr][TCB] caused the degradation of chitin particles. The degradation process strongly depends on temperature and the time of interaction; choosing proper conditions, particles with a narrow particle size distribution could be obtained.

Modification of chitin structure with tailored ionic liquids

Chitin, poly N-acetylglucosamine, has a great potential for use on an industrial scale as an enzyme carrier but it has an unfavorable particle structure that can be modified using ionic liquids (ILs). Several ionic liquids were investigated that have the same substituents on the ring (methyl- and propyl-) but differed in the type of cationic ring (pyrrolidinium, piperidinium, and piperazinium). Organic acid ions (acetic and lactic) were used as counter ions. 1-ethyl-3-methyl-imidazolium acetate and 1-ethyl-3-methyl-imidazolium lactate were used as a reference. The results confirm that the chitin particle structure or size, or both, simultaneously changes if chitin is dissolved in an IL and then precipitated. Organic acid anions and short substituents on the cationic ring of ILs influenced particle modification substantially, whereas the type of ring played a minor role. Additionally, the ionic liquids [MPpyrr][OAc], [MPpip][OAc] and [DMPpz][OAc] could be reused up to at least 4 times without losing their ability to dissolve chitin.