Obtenção e caracterização de blendas colágeno-quitosana

Biodegradable polymer blends were obtained using collagen and chitosan. Membranes of collagen and chitosan in different proportions (3:1, 1:1 and 1:3) were prepared by mixing their acetate solutions (pH 3.5) at room temperature. The blends were characterized by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Fourier Transform infrared (FTIR) spectroscopy, specific viscosity, water absorption and stress-strain assays. The results showed that chitosan did not interfere in the structural arrangement of the collagen triple helix and the properties of the blends can be controlled by varing the proportion of the collagen and the chitosan.

The lipopolysaccharide of Aeromonas spp: structure-activity relationships

Marine microorganisms, including Aeromonas, are a source of compds. for drug development that have generated great expectations in the last decades. Aeromonas infections produce septicemia, and ulcerative and haemorrhagic diseases in fish. Among the pathogenic factors assocd. with Aeromonas, the lipopolysaccharides (LPS)​, a surface glyconconjugate unique to Gram-​neg. bacteria consisting of lipid A (lipid anchor of the mol.)​, core oligosaccharide and O-​specific polysaccharide (O antigen)​, are key elicitors of innate immune responses. The chem. structure of these three parts has been characterized in Aeromonas. Based on the high variability of repeated units of O-​polysaccharides, a total of 97 O-​serogroups have been described in Aeromonas species, of which four of them (O:11; O:16; O:18 and O:34) account for more than 60​% of the septicemia cases. The core of LPS is subdivided into two regions, the inner (highly conserved) and the outer core. The inner core of Aeromonas LPS is characterized by the presence of 3-​deoxy-​d-​manno-​oct-​2-​ulosonic (ketodeoxyoctonic) acid (Kdo) and l-​glycero-​d-​manno-​Heptoses (l,​d-​Hep)​, which are linked to the outer core, characterized by the presence of Glc, GlcN, Gal, and GalNAc (in Aeromonas salmonicida)​, d,​d-​Hep (in Aeromonas salmonicida)​, and l,​d-​Hep (in Aeromonas hydrophila)​. The biol. relevance of these differences in the distal part of the outer core among these species has not been fully assessed to date. The inner core is attached to the lipid A, a highly conserved structure that confers endotoxic properties to the LPS when the mol. is released in blood from lysed bacteria, thus inducing a major systemic inflammatory response known as septic or endotoxic shock. In Aeromonas salmonicida subsp. salmonicida the Lipid A components contain three major lipid A mols., differing in acylation patterns corresponding to tetra-​, penta- and hexa-​acylated lipid A species and comprising of 4'-​monophosphorylated β-​2-​amino-​2-​deoxy-​d-​glucopyranose-​(1→6)​-​2-​amino-​2-​deoxy-​d-​glucopyranose disaccharide. In the present review, we discuss the structure-​activity relationships of Aeromonas LPS, focusing on its role in bacterial pathogenesis and its possible applications.

The lipopolysaccharide of Aeromonas spp: structure-activity relationships

Marine microorganisms, including Aeromonas, are a source of compds. for drug development that have generated great expectations in the last decades. Aeromonas infections produce septicemia, and ulcerative and haemorrhagic diseases in fish. Among the pathogenic factors assocd. with Aeromonas, the lipopolysaccharides (LPS)​, a surface glyconconjugate unique to Gram-​neg. bacteria consisting of lipid A (lipid anchor of the mol.)​, core oligosaccharide and O-​specific polysaccharide (O antigen)​, are key elicitors of innate immune responses. The chem. structure of these three parts has been characterized in Aeromonas. Based on the high variability of repeated units of O-​polysaccharides, a total of 97 O-​serogroups have been described in Aeromonas species, of which four of them (O:11; O:16; O:18 and O:34) account for more than 60​% of the septicemia cases. The core of LPS is subdivided into two regions, the inner (highly conserved) and the outer core. The inner core of Aeromonas LPS is characterized by the presence of 3-​deoxy-​d-​manno-​oct-​2-​ulosonic (ketodeoxyoctonic) acid (Kdo) and l-​glycero-​d-​manno-​Heptoses (l,​d-​Hep)​, which are linked to the outer core, characterized by the presence of Glc, GlcN, Gal, and GalNAc (in Aeromonas salmonicida)​, d,​d-​Hep (in Aeromonas salmonicida)​, and l,​d-​Hep (in Aeromonas hydrophila)​. The biol. relevance of these differences in the distal part of the outer core among these species has not been fully assessed to date. The inner core is attached to the lipid A, a highly conserved structure that confers endotoxic properties to the LPS when the mol. is released in blood from lysed bacteria, thus inducing a major systemic inflammatory response known as septic or endotoxic shock. In Aeromonas salmonicida subsp. salmonicida the Lipid A components contain three major lipid A mols., differing in acylation patterns corresponding to tetra-​, penta- and hexa-​acylated lipid A species and comprising of 4'-​monophosphorylated β-​2-​amino-​2-​deoxy-​d-​glucopyranose-​(1→6)​-​2-​amino-​2-​deoxy-​d-​glucopyranose disaccharide. In the present review, we discuss the structure-​activity relationships of Aeromonas LPS, focusing on its role in bacterial pathogenesis and its possible applications.

Microesferas de quitosana reticuladas com tripolifosfato utilizadas para remoção da acidez, ferro(III) e manganês(II) de águas contaminadas pela mineração de carvão

Considerable attention has been paid to chitosan and derivatives as efficient adsorbents of pollutants such as metal ions and dyes in aqueous medium. Nevertheless, no report can be found on the remedial actions of chitosan microspheres crosslinked with tripolyphosphate to control acidity, iron (III) and manganese (II) contents in wastewaters from coal mining. In this work, chitosan microspheres crosslinked with tripolyphosphate were used for the neutralization of acidity and removal of Fe (III) and Mn (II) from coal mining wastewaters. The study involved static and dinamic methods. The neutralization capacity of the surface of the static system was 395 mmol of H3O+ per kilogram of microspheres, higher than that of the dynamic one (223 mmol kg-1). The removal of Fe(III) in wastewater was of 100% and that of Mn(II) was 90%.

O emprego de quitosana quimicamente modificada com anidrido succínico na adsorção de azul de metileno

The adsorption capacity of alpha-chitosan and its modified form with succinic anhydride was compared with the traditional adsorbent active carbon by using the dye methylene blue, employed in the textile industry. The isotherms for both biopolymers were classified as SSA systems in the Giles model, more specifically in L class and subgroup 3. The dye concentration in the supernatant in the adsorption assay was determined through electronic spectroscopy. By calorimetric titration thermodynamic data of the interaction between methyene blue and the chemically modified chitosan at the solid/liquid interface were obtained. The enthalpy of the dye/chitosan interaction gave 2.47 ± 0.02 kJ mol-1 with an equilibrium constant of 7350 ± 10 and for the carbon/dye interaction this constant gave 5951 ± 8. The spontaneity of these adsorptions are reflected by the free Gibbs energies of -22.1 ± 0.4 and -21.5 ± 0.2 kJ mol-1, respectively, found for these systems. This new adsorbent derived from a natural polysaccharide is as efficient as activated carbon. However 97% of the bonded dye can be eluted by sodium chloride solution, while this same operation elutes only 42% from carbon. Chitosan is efficient in dye removal with the additional advantage of being cheap, non-toxic, biocompatible and biodegradable.

Quitosana: derivados hidrossolúveis, aplicações farmacêuticas e avanços

Chitin and chitosan are copolymers build from N-acetyl-D-glucosamine and D-glucosamine. The former is widely found in nature and yields the latter on deacetylation. The copolymers are being used for several purposes. Since 1977, when the First International Conference on Chitin and Chitosan was held in Boston, USA, the interest on chitin and chitosan has remarkably increased. This review emphasizes pharmaceutical applications of chitosan and its derivatives, and presents recent advances. Some therapeutical applications of these polymers are also discussed.

Construção e aplicação de biossensores usando diferentes procedimentos de imobilização da peroxidase de vegetal em matriz de quitosana

Biosensors were developed by immobilization of gilo (Solanum gilo) enzymatic extract on chitosan biopolymers using three different procedures: glutaraldehyde, carbodiimide/glutaraldehyde and epichlorohydrin/glutaraldehyde. The best biosensor performance was obtained after the immobilization of peroxidase on chitosan with epichlorohydrin/glutaraldehyde. Linear analytical curves for hydroquinone concentrations from 2.5x10-4 to 4.5x10-3 mol L-1 with a detection limit of 2.0x10-6 mol L-1 and recovery of hydroquinone ranging from 95.1 to 105% were obtained. The relative standard deviation was < 1.0 % for a solution of 3.0x10-4 mol L-1 hydroquinone and 2.0x10-3 mol L-1 hydrogen peroxide in 0.1 mol L-1 phosphate buffer solution at pH 7.0 (n=8). The lifetime of this biosensor was 6 months (at least 300 determinations).

Extração, estruturas e propriedades de alfa- e beta-quitina

The fact that alpha- and beta-chitin adopt different arrays in the solid state is explored to emphasize their different properties and distinct spectral characteristics and X ray diffraction patterns. The methods for their extraction from the biomass in view of the preservation of their native structures and aiming to fulfill the claims of purity and uniformity for potential applications are discussed. The different arrays adopted by alpha- and beta-chitin also result in distinct reactivities toward the deacetylation reaction. Thus, the deacetylation of beta-chitin is more efficient owing to the better accessibility to amide groups due to the lower crystallinity of this polymorph.

Adsorção de íons cobre(II) pela quitosana usando coluna em sistema sob fluxo hidrodinâmico

The adsorption of Cu(II) ions from aqueous solution by chitosan using a column in a closed hydrodynamic flow system is described. The adsorption capacities as a function of contact time of copper(II) ions and chitosan were determined by varying the ionic strength, temperature and the flow of the metal solution. The Langmuir model reproduced the adsorption isothermal data better than the Freundlich model. The experimental kinetic data correlate properly with the second-order kinetic reaction for the whole set of experimental adsorption conditions. The rate constants exercise great influence on the time taken for equilibrium to be established by complexation or electrostatic interaction between the amino groups of chitosan and the metal.

Desenvolvimento de um método empregando quitosana para remoção de íons metálicos de águas residuárias

In this work a method was developed for removing metallic ions from wastewaters by co-precipitation of Cu2+, Pb2+, Cd2+, Cr3+ and Hg2+ with chitosan and sodium hydroxide solution. Solutions of these metallic ions in the range from 0.55 to 2160 mg L-1 were added to chitosan dissolved in 0.05 mol L-1 HCl. For the co-precipitation of metal-chitosan-hydroxide a 0.17 mol L-1 NaOH solution was added until pH 8.5-9.5. A parallel study was carried out applying a 0.17 mol L-1 NaOH solution to precipitate those metallic ions. Also, a chitosan solid phase column was used for removing those metallic ions from wastewaters.

Determinação voltamétrica por redissolução anódica de Cu(II) em águas residuárias empregando um eletrodo de pasta de carbono modificado com quitosana

The electrochemical applications of a CPE modified with chitosan for the determination of Cu(II) in wastewater samples using anodic stripping voltammetry are described. The best voltammetric response was observed for a paste containing 25% m/m of chitosan. A 0.10 mol L-1 NaNO3 solution (pH 6.5) as supporting electrolyte, a pre-concentration potential of -0.20 V, pre-concentration time of 270 s and a scan rate of 25 mV s-1 were selected. The calibration graph was linear in the Cu(II) concentration range from 2.0 x 10-7 to 7.4 x 10-6 mol L-1, with a detection limit of 8.3 x 10-8 mol L-1.

Um sistema simples para preparação de microesferas de quitosana

This article describes the construction and optimization of an inexpensive apparatus for the production of uniform and porous chitosan microspheres. It also describes the control of the main operational parameters and strategies for the production of uniform chitosan microspheres.

Avaliação de géis obtidos a partir da acetilação da quitosana em meio heterogêneo

Chitosan was acetylated during 2, 5 and 10h and physical gels were obtained at different polymer concentrations in N,N-dimethylacetamide containing 5% of LiCl. Acetylation was confirmed by infrared spectroscopy and 13C NMR, and degrees of acetylation in the range of 0.82-0.91 were determined by NMR. The O-acetylation degree (0.12-0.15) was exclusively determined by a volumetric method. Rheological studies showed that the storage modulus values were smaller for the more acetylated samples and increased with the temperature and the polymer concentration. All the gels presented storage modulus superior to loss modulus, evidencing more elastic than viscous characteristics. The results obtained in this work suggest a gelation process based on a balance between O and N-acetylation and intermolecular bonds.

Purificação e caracterização de uma gentioexaose obtida de botriosferana por hidrólise ácida parcial

A hexa-oligosaccharide was obtained by partial acid hydrolysis from botryosphaeran, an exopolysaccharide (EPS) β(1→3; 1→6)-D-glucan type, produced by the ascomyceteous fungus Botryosphaeria rhodina. The oligosaccharide was purified by gel filtration and charcoal-Celite column chromatography and the analysis was followed by HPAEC/PAD. The structure was determined by NMR spectroscopy and mass spectrometry, which showed that the oligosaccharide consists of six β-D-glucopiranosyl units O-6 substituted (gentiohexaose).

Adsorção de arsênio(V) pela quitosana ferro - III reticulada

The removal of As(V) by a crosslinked iron(III)-chitosan adsorbent was evaluated under various conditions. The adsorption capacity of CH-FeCL was around 54 mg/g of As(V). The kinetics of adsorption obeys a pseudo-first-order model with rate constants equal to 0.022, 0.028, and 0.033 min-1 at 15, 25 and 35 ºC respectively. Adsorption data were well described by the Langmuir model, although they could be modeled also by the Langmuir-Freundlich equation. The maximum adsorption capacity, calculated with the Langmuir model, was 127 mg g-1 of As(V). The inhibition by competing anions is dependant on their kind and valence.