Adsorption of the dye Acid Blue 158 premetalized with chromium on chitin/chitosan.

Removal of the premetalized dyes from the effluents of textile and leather industries is still open. The work aims to investigate functional groups taking part in the sorption of premetalized dye Acid Blue 158:Cr on chitin/chitosan and to investigate the mechanism of the sorption. The process was spontaneous (negative value of the Gibbs function), endothermic (ΔH = 0.2679 kJ/mol) with an affinity between the AB 158:Cr and chitin (ΔS = 1.315 J/mol*K). Langmuir, Freundlich, and Dubinin-Radushkevich isotherms were used to approximate experimental data giving a good correlation. Maximal capacity was evaluated as 46.1 mg/g and 370.4 mg/g for chitin and chitosan, respectively. Kinetics was described with a pseudo-second-order model. It was shown that physical sorption and chemisorption can occur parallelly: chemisorption on amine groups via interaction with chromium and physical sorption on amine group or hydroxyl group via interaction with the azo core of the dye.

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.

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.

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.

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.