Thermodynamic Aspects of the Heterogeneous Deacetylation of β-Chitin: Reaction Mechanisms

Exploiting specific properties of squid pens for the preparation of oligochitosan hydrochloride

Herein, we describe in first the application of squid pens for the preparation of pharmaceutical-grade oligochitosan hydrochloride with the physicochemical characteristics corresponding with the requirements of the European Pharmacopoeia. It is shown that the use of specific properties of squid pens as a source of parent chitosan allows preparing the product with a high yield at relatively moderate process conditions used for squid pens treatments and chitosan depolymerization.

Alternative processes to produce chitin, chitosan, and their oligomers

Sustainable recovery of chitin and its derivatives from shellfish waste will be achieved when the industrial production of these polymers is achieved with a high control of their molecular structure, low costs, and acceptable levels of pollution. Therefore, the conventional chemical method for obtaining these biopolymers needs to be replaced or optimized. The goal of the present review is to ascertain what alternative methods are viable for the industrial-scale production of chitin, chitosan, and their oligomers. Therefore, a detailed review of recent literature was undertaken, focusing on the advantages and disadvantages of each method. The analysis of the existing data allows suggesting that combining conventional, biological, and alternative methods is the most efficient strategy to achieve sustainable production, preventing negative impacts and allowing for the recovery of high added-value compounds from shellfish waste. In conclusion, a new process for obtaining chitinous materials is suggested, with the potential of reducing the consumption of reagents, energy, and water by at least 1/10, 1/4, and 1/3 part with respect to the conventional process, respectively.

The source, activity influencing factors and biological activities for future development of chitin deacetylase

Chitin deacetylase (CDA), a prominent member of the carbohydrate esterase enzyme family 4 (CE4), is found ubiquitously in bacteria, fungi, insects, and crustaceans. This metalloenzyme plays a pivotal role in recognizing and selectively removing acetyl groups from chitin, thus offering an environmentally friendly and biologically-driven preparation method for chitosan with immense industrial potential. Due to its diverse origins, CDAs sourced from different organisms exhibit unique functions, optimal pH ranges, and temperature preferences. Furthermore, certain organic reagents can induce structural changes in CDAs, influencing their catalytic activity. Leveraging CDA's capabilities extends beyond chitosan biocatalysis, as it demonstrates promising application value in agricultural pest control. In this paper, the source, reaction mechanism, influencing factors, the fermentation methods and applications of CDA are reviewed, which provides theoretical help for the research and application of CDA.

Mechanism of Heterogeneous Alkaline Deacetylation of Chitin: A Review

This review provides an analysis of experimental results on the study of alkaline heterogeneous deacetylation of chitin obtained by the authors and also published in the literature. A detailed analysis of the reaction kinetics was carried out considering the influence of numerous factors: reaction reversibility, crystallinity and porosity of chitin, changes in chitin morphology during washing, alkali concentration, diffusion of hydroxide ions, and hydration of reacting particles. A mechanism for the chitin deacetylation reaction is proposed, taking into account its kinetic features in which the decisive role is assigned to the effects of hydration. It has been shown that the rate of chitin deacetylation increases with a decrease in the degree of hydration of hydroxide ions in a concentrated alkali solution. When the alkali concentration is less than the limit of complete hydration, the reaction practically does not occur. Hypotheses have been put forward to explain the decrease in the rate of the reaction in the second flat portion of the kinetic curve. The first hypothesis is the formation of “free” water, leading to the hydration of chitin molecules and a decrease in the reaction rate. The second hypothesis postulates the formation of a stable amide anion of chitosan, which prevents the nucleophilic attack of the chitin macromolecule by hydroxide ions.

Chemical and physical Chitosan modification for designing enzymatic industrial biocatalysts: How to choose the best strategy?

Chitosan is one of the most abundant natural polymer worldwide, and due to its inherent characteristics, its use in industrial processes has been extensively explored. Because it is biodegradable, biocompatible, non-toxic, hydrophilic, cheap, and has good physical-chemical stability, it is seen as an excellent alternative for the replacement of synthetic materials in the search for more sustainable production methodologies. Thus being, a possible biotechnological application of Chitosan is as a direct support for enzyme immobilization. However, its applicability is quite specific, and to overcome this issue, alternative pretreatments are required, such as chemical and physical modifications to its structure, enabling its use in a wider array of applications. This review aims to present the topic in detail, by exploring and discussing methods of employment of Chitosan in enzymatic immobilization processes with various enzymes, presenting its advantages and disadvantages, as well as listing possible chemical modifications and combinations with other compounds for formulating an ideal support for this purpose. First, we will present Chitosan emphasizing its characteristics that allow its use as enzyme support. Furthermore, we will discuss possible physicochemical modifications that can be made to Chitosan, mentioning the improvements obtained in each process. These discussions will enable a comprehensive comparison between, and an informed choice of, the best technologies concerning enzyme immobilization and the application conditions of the biocatalyst.

Effect of diffusional limitations on the kinetics of deacetylation of chitin/chitosan

A new model is proposed for the kinetics of the heterogeneous deacetylation of chitin/chitosan. This new model is able to represent the process over much broader ranges than the other kinetic models reported in the literature. The unreacted shrinking core model was modified with the inclusion of increasing diffusional effects as the reaction progresses, causing the rate to slow down and preventing the degree of deacetylation reaching 100 %, even in the presence of excess NaOH. The model was validated with data collected in experiments with different NaOH concentrations and temperatures. The proposed model was able to represent the experimental data correctly over the entire experiment span, resulting in a model with proven predictive ability, in contrast to existing kinetic models that have been applied in a piecewise fashion over a rather limited time range of the process. The proposed model represents an improvement in the understanding of the deacetylation process.

Chitosan: A review of sources and preparation methods

Chitosan, derived from chitin, has many desirable biomedical attributes. This review aims to explore different sources of chitin and methods of chitosan production with industrial consideration. This article first discussed different sources of chitin for industrial scale production, with considerations given to both their environmental impacts and commercialization potential. Secondly, this article reviews the two categories of chitosan preparation - chemical methods and biological methods - based on existing publications which used lobster by-products as a feedstock source. The mechanisms of the chemical methods are firstly summarized, and then the different chemical agents and reaction parameters used are discussed. Next, both enzymatic and fermentation-based approaches are reviewed under biological methods and compared with chemical methodologies, with lactic fermentation methods as the major focus. This article concludes that lobster cephalothorax could be an ideal source for chitosan preparation on an industrial scale; and chemical methods involve simpler processing overall, while producing chitosan with stronger bioactivities because of the lower molecular weight (MW) and higher degree of deacetylation (DD) achieved by the products. Moreover, due to biological methods inevitably necessitating further chemical processing, an approach involving some unconventional chemical methods has been regarded as a more suitable strategy for industrial scale chitosan production.

A Review on Chitosan's Uses as Biomaterial: Tissue Engineering, Drug Delivery Systems and Cancer Treatment

Chitosan, derived from chitin, is a biopolymer consisting of arbitrarily distributed β-(1-4)-linked D-glucosamine and N-acetyl-D-glucosamine that exhibits outstanding properties— biocompatibility, biodegradability, non-toxicity, antibacterial activity, the capacity to form films, and chelating of metal ions. Most of these peculiar properties are attributed to the presence of free protonable amino groups along the chitosan backbone, which also gives it solubility in acidic conditions. Moreover, this biopolymer can also be physically modified, thereby presenting a variety of forms to be developed. Consequently, this polysaccharide is used in various fields, such as tissue engineering, drug delivery systems, and cancer treatment. In this sense, this review aims to gather the state-of-the-art concerning this polysaccharide when used as a biomaterial, providing information about its characteristics, chemical modifications, and applications. We present the most relevant and new information about this polysaccharide-based biomaterial’s applications in distinct fields and also the ability of chitosan and its various derivatives to selectively permeate through the cancer cell membranes and exhibit anticancer activity, and the possibility of adding several therapeutic metal ions as a strategy to improve the therapeutic potential of this polymer.

Interaction Between Chitosan and Mucin: Fundamentals and Applications

The term chitosan (CS) refers to a family of aminopolysaccharides derived from chitin. Among other properties, CS is nontoxic, mucoadhesive and can be used for load and transport drugs. Given these and other physicochemical and biological properties, CS is an optimal biopolymer for the development of transmucosal drug delivery systems, as well as for the treatment of pathologies related to mucosal dysfunctions. Mucins are glycoprotein macromolecules that are the major components of mucus overlaying epithelia. CS interacts with mucin and adsorbs on and changes the rheology of mucus. However, CS and mucins denote families of polymers/macromolecules with highly variable chemical structure, properties, and behavior. To date, their interactions at the molecular level have not been completely unraveled. Also, the properties of complexes composed of CS and mucin vary as a function of the sources and preparation of the polymers. As a consequence, the mucoadhesion and drug delivery properties of such complexes vary as well. The breadth of this review is on the molecular interactions between CS and mucin. In particular, in vitro and ex vivo characterization methods to investigate both the interactions at play during the formation of CS-mucin complexes, and the advances on the use of CS for transmucosal drug delivery are addressed.

A reaction–diffusion kinetic model for the heterogeneous N-deacetylation step in chitin material conversion to chitosan in catalytic alkaline solutions

New mechanistic insight into the modelling of the heterogeneous N-deacetylation step of α-chitin, obtained from waste crustacean shells.

Alkali- or acid-induced changes in structure, moisture absorption ability and deacetylating reaction of β-chitin extracted from jumbo squid (Dosidicus gigas) pens

Alkali- or acid-induced structural modifications in β-chitin from squid (Dosidicus gigas, d'Orbigny, 1835) pens and their moisture absorption ability (MAA) and deacetylating reaction were investigated and compared with α-chitin from shrimp shells. β-Chitin was converted into the α-form after 3h in 40% NaOH or 1-3 h in 40% HCl solution, and α-chitin obtained from NaOH treatment had higher MAA than had native α-chitin, due to polymorphic destructions. In contrast, induced α-chitin from acid treatment of β-chitin had few polymorphic modifications, showing no significant change (P>0.05) in MAA. β-Chitin was more susceptible to alkali deacetylation than was α-chitin, and required a lower concentration of NaOH and shorter reaction time. These results demonstrate that alkali- or acid-treated β-chitin retained high susceptibility toward solvents, which in turn resulted in good biological activity of β-chitosan for use as a natural antioxidant and antimicrobial substance or application as edible coatings and films for various food applications.

Claw amphiphiles with a dendrimer core: nanoparticle stability and drug encapsulation are directly proportional to the number of digits

There are numerous pharmaceutical, food, and consumer product applications requiring the incorporation of hydrophobic solutes within aqueous media. Often amphiphiles and/or polymers are used to produce encapsulating nanostructures. Because the encapsulation efficiencies of these nanostructures directly impact on the process or product, it is often desirable to optimize this parameter. To produce these advanced functional materials, we hypothesized that an amphiphile with a claw shape would favor polymer aggregation into nanoparticles and hydrophobic compound encapsulation. Claw amphiphiles were prepared by attaching one end of comb-shaped chitosan amphiphile chains [N,N,N-trimethyl, N,N-dimethyl, N-monomethyl, N-palmitoyl, N-acetyl, 6-O-glycol chitosan (GCPQA)] to a central dendrimer core [generation 3 diaminobutane poly(propylenimine) dendrimer (DAB)] to give DAB-GCPQA. The linear chitosan amphiphile (GCPQA) forms the digits of the claw. These claw amphiphiles were very stable and had a high encapsulating efficiency. DAB-GCPQAs (Mn = 30 and 70 kDa) had extremely low critical micelle concentrations [CMCs = 0.43 μg mL(-1) (13 nM) and 0.093 μg mL(-1) (0.9 nM), respectively], and their CMCs were lower than that of linear GCPQA [Mn = 14 kDa, CMC = 0.77 μg mL(-1) (38 nM)]. The claw amphiphile CMCs decreased linearly with the number of digits (r(2) = 0.98), and drug encapsulation (hydrophobic drug propofol) in 4 mg mL(-1) dispersions of the amphiphiles increased linearly (r(2) = 0.94) with the number of digits. DAB-GCPQA70 (4 mg mL(-1), 0.058 mM) encapsulated propofol (7.3 mg mL(-1), 40 mM). Finally, despite their stability, claw amphiphile nanoparticles are able to release the encapsulated drug in vivo, as shown with the claw amphiphile-propofol formulations in a murine loss of righting reflex model.

An efficient method for 15N-labeling of chitin in fungi

To permit facile (15)N solid-state NMR (ssNMR) analysis of the degree of acetylation (DA) of chitinous materials in fungi a method for the introduction of a (15)N isotopic label has been developed. Using Penicillium chrysogenum as a model system, a series of (15)N-based media were surveyed for their abilities to support mycelial growth, and a rich medium supplemented with ((15)NH(4))(2)SO(4) supported good growth. Uptake of label into chitin extracted from mycelia grown in the rich ((15)NH(4))(2)SO(4)-based media was monitored by mass spectrometry, with approximately 1 g/L of ((15)NH(4))(2)SO(4) leading to approximately 65% incorporation. The labeled chitin was studied by ssNMR to determine its DA, and the (15)N label permitted measurement of DA to within 0.5% with acquisition times of on the order of half an hour. Similar studies validated the method for DA measurements on chitin from cultures of Aspergillus niger and Mucor rouxii.

A novel synthesis of chitosan nanoparticles in reverse emulsion

Physical hydrogels of chitosan in the colloidal domain were obtained in the absence of both cross-linker and toxic organic solvent. The approach was based on a reverse emulsion of a chitosan solution in a Miglyol/Span 80 mixture, generally regarded as safe. Temperature and surfactant concentration were optimized, and the impact of the degree of acetylation (DA) and the molar mass of chitosan was investigated. When chitosan had a DA above 30%, only macroscopic gels were obtained, because of the predominance of attractive Van der Waals forces. The lower the molar mass of chitosan, the better the control over particle size and size distribution, probably as a result of either a reduction in the viscosity of the internal aqueous phase or an increase in the disentanglement of the polymer chain during the process. After extraction and redispersion of the colloid in an ammonium acetate buffer, the composition of the particles was around 80% of pure chitosan corresponding to a recovery of 60% of the original input. These new and safe colloids offer wide perspectives of development in further applications.