Angeles Heras

Functional Characterization of Chitin and Chitosan

Chitin and its deacetylated derivative chitosan are natural polymers composed of randomly distributed � -(1-4)- linked D-glucosamine (deacetylated unit) and N-acetyl-D-glucosamine (acetylated unit). Chitin is insoluble in aqueous media while chitosan is soluble in acidic conditions due to the free protonable amino groups present in the D-glucosamine units. Due to their natural origin, both chitin and chitosan can not be defined as a unique chemical structure but as a fam- ily of polymers which present a high variability in their chemical and physical properties. This variability is related not only to the origin of the samples but also to their method of preparation. Chitin and chitosan are used in fields as different as food, biomedicine and agriculture, among others. The success of chitin and chitosan in each of these specific applica- tions is directly related to deep research into their physicochemical properties. In recent years, several reviews covering different aspects of the applications of chitin and chitosan have been published. However, these reviews have not taken into account the key role of the physicochemical properties of chitin and chitosan in their possible applications. The aim of this review is to highlight the relationship between the physicochemical properties of the polymers and their behaviour. A functional characterization of chitin and chitosan regarding some biological properties and some specific applications (drug delivery, tissue engineering, functional food, food preservative, biocatalyst immobilization, wastewater treatment, molecular imprinting and metal nanocomposites) is presented. The molecular mechanism of the biological properties such as biocompatibility, mucoadhesion, permeation enhancing effect, anticholesterolemic, and antimicrobial has been up- dated.

N-methylene phosphonic chitosan : a novel soluble derivative

Abstract A novel water-soluble chitosan derivative carrying phosphonic groups was synthesized using a one-step reaction that allowed homogeneous modifications without any sharp decrease in its properties, such as filmogenic capacity (this compound and its synthesis have been protected with a patent). The 1 H NMR, 13 C NMR assignments and 1 H– 13 C NMR correlation permitted the identification of the structure by the subtituent distribution of the product, which is partly N -monophosphonomethylated (0.24) and N , N -diphosphonomethylated (0.14) and N -acetylated (0.16) without modification of the initial degree of acetylation. The identity of the N -methylene phosphonic chitosan was confirmed by FT-IR spectrometry, X-ray diffraction and elemental analysis.Taking advantage of the known chelating ability of the phosphonic groups, especially for calcium, this new derivative opens new perspectives as biomedical material.

Chitosan Amphiphilic Derivatives. Chemistry and Applications

Chitosan is a natural polymer composed of randomly distributed -(1-4)-linked D-glucosamine (deacetylated unit) and Nacetyl-D-glucosamine (acetylated unit). It has been described as a non-toxic, biodegradable and biocompatible polymer with very interesting biological properties, such as permeation-enhancing and mucoadhesive properties, anticoagulant and antimicrobial activity and so on. Chitosan has been used in several areas such as biomedical, pharmaceutical and biotechnological fields as well as in the food industry. Recently, there has been a growing interest in the modification of chitosan to improve its solubility in physiological conditions, to introduce new applications or to improve chitosan biological properties. Research and development on a variety of amphiphilic copolymers containing hydrophobic and hydrophilic segments, have been very active due to their spontaneous self-assembly behaviour in aqueous media These smart transitions often lead to diverse functional compartment structures like micelles, vesicles and gels, which represent promising applications in the field of biotechnology and pharmaceutics. The aim of the present paper is to review the latest advances in the synthesis of chitosan amphiphilic derivatives with a special emphasis in their applications.

Tight junction modulation by chitosan nanoparticles: Comparison with chitosan solution

Present work investigates the potential of chitosan nanoparticles, formulated by the ionic gelation with tripolyphosphate (TPP), to open the cellular tight junctions and in doing so, improve the permeability of model macromolecules. A comparison is made with chitosan solution at equivalent concentrations. Initial work assessed cytotoxicity (through MTS and LDH assays) of chitosan nanoparticles and solutions on Calu-3 cells. Subsequently, a concentration of chitosan nanoparticles and solution exhibiting minimal toxicity was used to investigate the effect on TEER and macromolecular permeability across filter-cultured Calu-3 monolayer. Chitosan nanoparticles and solution were also tested for their effect on the distribution of the tight junction protein, zonnula occludens-1 (ZO-1). Chitosan nanoparticles produced a sharp and reversible decrease in TEER and increased the permeability of two FITC-dextrans (FDs), FD4 (MW 4 kDa) and FD10 (MW 10 kDa), with effects of a similar magnitude to chitosan solution. Chitosan nanoparticles produced changes in ZO-1 distribution similar to chitosan solution, indicating a tight junction effect. While there was no improvement in permeability with chitosan nanoparticles compared to solution, nanoparticles provide the potential for drug incorporation, and hence the possibility for providing controlled drug release and protection from enzymatic degradation.

Modified chitosan carrying phosphonic and alkyl groups

Abstract The introduction of an alkyl chain onto a water soluble modified chitosan (N-methylene phosphonic chitosan) offer the presence of hydrophobic and hydrophilic branched for controlling solubility properties. A simple methodology for the preparation of a new chitosan derivative surfactant, N-lauryl-N-methylene phosphonic chitosan, has been developed. Its chemical identity was determined by FTIR and confirmed by 1H and 13C NMR. The degree of lauryl substitution was estimated to be 0.33. As a result of the amphiphilic properties, like surface activity typical for surfactants, this derivative opens new perspectives in pharmaceutical and cosmetic field.

N-methylene phosphonic chitosan. Effect of preparation methods on its properties

Abstract N-methylene phosphonic chitosan is prepared from chitosan with different acetylation degrees and sources using three reaction times. The degree of substitution is not dependent on chitosans source and degree of deacetylation but it depends on reaction time. Data are confirmed by 1H NMR and FT-IR. A significant decrease of viscosity and molecular weight is observed due to derivatization. It is demonstrated that N-methylene phosphonate chitosan is a powerful chelating agent of transition metal and calcium ions.

Chitosan-genipin microspheres for the controlled release of drugs: clarithromycin, tramadol and heparin.

The aim of this study was to first evaluate whether the chitosan hydrochloride-genipin crosslinking reaction is influenced by factors such as time, and polymer/genipin concentration, and second, to develop crosslinked drug loaded microspheres to improve the control over drug release. Once the crosslinking process was characterized as a function of the factors mentioned above, drug loaded hydrochloride chitosan microspheres with different degrees of crosslinking were obtained. Microspheres were characterized in terms of size, morphology, drug content, surface charge and capacity to control in vitro drug release. Clarithromycin, tramadol hydrochloride, and low molecular weight heparin (LMWH) were used as model drugs. The obtained particles were spherical, positively charged, with a diameter of 1–10 μm. X-Ray diffraction showed that there was an interaction of genipin and each drug with chitosan in the microspheres. In relation to the release profiles, a higher degree of crosslinking led to more control of drug release in the case of clarithromycin and tramadol. For these drugs, optimal release profiles were obtained for microspheres crosslinked with 1 mM genipin at 50 ºC for 5 h and with 5 mM genipin at 50 ºC for 5 h, respectively. In LMWH microspheres, the best release profile corresponded to 0.5 mM genipin, 50 ºC, 5 h. In conclusion, genipin showed to be eligible as a chemical-crosslinking agent delaying the outflow of drugs from the microspheres. However, more studies in vitro and in vivo must be carried out to determine adequate crosslinking conditions for different drugs.

Nano and microparticulate chitosan-based systems for antiviral topical delivery

Acyclovir (ACV) is one of the drugs of choice for the treatment of epidermal, ocular or systemic herpetic infections. Nevertheless, its trans-mucosal limited absorption and the scarce contact time of the formulation with the mucosal surface - especially in the ocular mucosa - constitute a big limitation of the antiviral efficiency. The most effective way to solve these problems is to increase the quantity and the residence time of the drug over the ocular surface. In order to cope with all these requirements, micro-particles (MPs) and nano-particles (NPs) containing ACV have been developed using cross-linked chitosan with tripolyphosphate (TPP) due to the biocompatibility, bio-adhesion ability and the potential power as penetration enhancer of this polymer. Particles were characterized by Fourier-transformed infrared (FTIR) spectroscopy, X-ray diffraction, SEM, Zeta potential and particle size. Encapsulation efficiency and release profiles in flow through diffusion cells were also determined. Besides the Slug Mucosal Irritation (SMI) assay has been applied as an alternative to the Draize test to predict the mucosal irritation of the selected formulation. FTIR and X-ray results suggested an electrostatic interaction ACV-Chitosan that made ACV be molecularly dispersed within the polymer matrix. Encapsulation efficiency was 75% for MP and 16% for NP. Release profiles in flow through diffusion cells were also determined. From the diffusion profiles, it was found that the amounts of ACV effectively diffused in 24h were 30, 430 and 80 μg for the ACV solution, MP and NP respectively. SMI results showed that chitosan-based particles induced moderate irritation and mild tissue damage, what supposes that ACV-MP constitute a promising alternative for further development of an antiviral formulation.

Poly(styrenesulphonic) acid: an active and reusable acid catalyst soluble in polar solvents

This article reports on the catalytic activity of soluble poly(styrenesulphonic) acid (PSSA) in three different reactions driven by acidic sites: tributyrin methanolysis, biodiesel synthesis and xylose dehydration to furfural. The PSSA catalyst, soluble in the polar media used in these reactions, displayed larger catalytic activity than other non-soluble sulphonic solid catalysts studied (Amberlyst 36, Amberlyst 70 and Nafion®-SAC13). The ultrafiltration of the used PSSA catalyst allowed retention and reutilisation of the catalyst for several runs. No significant decay in catalytic activity was observed for the three reaction repeats investigated. All these results demonstrated that PSSA, a material that can be obtained from polystyrene waste, is an excellent reusable catalyst for conducting reactions demanding acidic sites.

Influence of the physico-chemical characteristics of chito-oligosaccharides (COS) on antioxidant activity

Chito-oligosaccharides (COS) are being used as important functional materials for many applications due to their bioactivities. The aim of this research has been to assess the relationship between the physico-chemical characteristics, average molecular weight (Mw), acetylation degree (DA), polymerization degree (DP) and specially sequence composition determined by MALDI-TOF MS and the antioxidant properties of COS. These oligosaccharides were obtained by enzymatic depolymerization with chitosanase and lysozyme using a specific chitosan and its reacetylated product. The COS fraction below 5 kDa obtained from chitosanase depolymerization showed the highest capacity to scavenge DPPH radicals and to reduce Fe(3+). A correlation was found between the relative amount of molecules with a given A/D (acetylated vs deacetylated units) ratio within the COS and their antioxidant activity, which could be used to predict the antioxidant behavior of a fraction of chito-oligosaccharides.