J.L.C. Fonseca

Determination of deacetylation degree of chitosan: a comparison between conductometric titration and CHN elemental analysis

Chitosan is a polysaccharide used in a broad range of applications. Many of its unique properties come from the presence of amino groups in its structure. A proper quantification of these amino groups is very important, in order to specify if a given chitosan sample can be used in a particular application. In this work, a comparison between the determination of chitosan degree of deacetylation by conductometry and CHN elemental analysis was carried out, using a rigorous error analysis. Accurate expressions relating CHN composition, conductometric titration, and degree of deacetylation, in conjunction with their associated errors, were developed and reported in this note. Error analysis showed conductometric analysis as an inexpensive and secure method for the determination of the degree of deacetylation of chitosan.

Equilibrium and kinetic analysis of methyl orange sorption on chitosan spheres.

Chitosan can be used as adsorbent in the treatment of effluents from the textile industry, especially for negatively charged dyes, due to its cationic polyelectrolyte nature. In this work, the sorption of a model dye, methyl orange, on chitosan hydrobeads is analyzed in terms of equilibrium and kinetic approaches. Equilibrium studies showed that dye adsorption had a mixed Freundlich-Langmuir behavior that had its Langmuir character increased as the pH was increased. In terms of adsorption kinetics, it was found to be of nth-pseudo-order, with fractional n increasing from approximately 2 to approximately 2.5 as pH and initial dye concentration in the continuous phase were increased. The increase in the apparent pseudo-order was related to changes in mathematical approximation for the solution of the sorption rate equation, which were the result of the decrease in the ratio (number of active sites for adsorption)/(number of adsorbate molecules).

Surface charging and dimensions of chitosan coacervated nanoparticles.

Chitosan nanoparticles have been used in several systems destined to controlled release of active agents. In this manuscript the process of formation of chitosan nanoparticles, obtained employing the coacervation method with sodium sulfate is analyzed using zeta potential and small angle X-ray scattering (SAXS) measurements. Dispersions were obtained at pH=1 and pH=3 and presented a behavior, in terms of surface charging, that was independent of pH. However, SAXS results indicated a dependence of size-related behavior on pH. The difference in terms of behavior was explained through the influence of enthalpic and entropically driven components.

Polyelectrolytes in solution and the stabilization of colloids

Polyelectrolytes are very versatile macromolecular materials that have found more and more applications in several technologies. In this article applications related to their use as (de)stabilizers for colloids are reviewed. Additionally, some theories that deal with colloid stabilization are described. Finally, the rheology of the disperser phase as well as the relationship between the rheology of the whole colloidal system and polyelectrolyte stabilization are discussed.

Chitosan membranes modified by contact with poly(acrylic acid)

In this work chitosan membranes modified by contact with poly(acrylic acid) (PAA) aqueous solution at two different temperatures (25 degrees C and 60 degrees C) were obtained. The pure chitosan (CS) membranes, as well as those treated with PAA (CSPAA_25 and CSPAA_60) were characterized by FTIR-ATR, water sorption capacity, thermal analysis (TG/DTG), and scanning electron microscopy (SEM). In addition, in vitro permeation experiments were carried out using metronidazol and sodium sulfamerazine aqueous solutions at 0.1% and 0.2% as model drugs. FTIR-ATR results showed the presence of absorption bands of NH3+ and COO(-) indicating the formation of a polyelectrolyte complex between chitosan and poly(acrylic acid). The results also indicated that PAA penetrates deeper into the membrane at higher temperature (60 degrees C), forming a thicker complex layer. Polyelectrolyte complex formation as well as the influence of treatment temperature was confirmed by lower hydrophilicity, higher thermal stability, and lower permeability of the treated membranes. The results show that the methodology used is a simple and very efficient way to drastically change some membrane properties, especially their permeability.

Viscometric monitoring of poly(ethylene oxide) degradation

The degradation of poly(ethylene oxide) was carried out using viscometry as a way of quantifying it in situ. The method was adequate to follow the kinetics of degradation, the main advantadge being that, for high polymer molecular weights and low concentration of persulfate, the kinetics are simplified by reduction to a simple linear function for any order. Deviations from these functions were corretated to disentanglement kinetics being important in the viscometric monitoring and/or higher occurrence of end groups for long degradation times.

Rheology and dynamic light scattering of octa-ethyleneglycol-monododecylether/chitosan solutions

In this work we used rheometry and DLS to probe relaxation phenomena in solutions of chitosan and octa-ethyleneglycol-monododecylether. The dispersions had a marked pseudoplastic behavior, which became less evident, as surfactant concentration was increased. Arrhenius plots showed that systems with surfactant presented a characteristic temperature at which apparent enthalpy of activation (varying from 3 to 40 kJ mol(-1)) changed: this change was correlated to a possible transition of colloidal aggregates to a wormlike configuration. DLS intensity correlation functions were described by KWW equation: pure chitosan solutions had relaxation rate distributions centered at a characteristic relaxation rate around 4.6×10(-6) μS(-1); as surfactant was added, a new component, with a faster characteristic relaxation rate with a magnitude order of 10(-3) μs(-1), appeared. It was shown that the dependence between these relaxation rates and surfactant concentration could be used to describe DLS-related relaxation phenomena as an Arrhenius-activated process, agreeing with results obtained using rheometry.

Serum production against Tityus serrulatus scorpion venom using cross-linked chitosan nanoparticles as immunoadjuvant.

Several species of scorpions are known to cause accidents which can lead to death, most of them belonging to the genus Tityus. Tityus serrulatus is considered the most dangerous scorpion in South America. In Brazil, T. serrulatus is responsible for serious accidents, including deaths, which occur mainly with children and elderly people. Anti-scorpion sera are routinely produced by various institutions, and suitable technologies have been investigated for encapsulation and release recombinant or native proteins capable of inducing antibody production. In this context, biocompatible and biodegradable polymers, such as chitosan, have been employed for this purpose. This study aimed to obtain a protein release system for the peptides or proteins from T. serrulatus, based on cross-linked chitosan nanoparticles (CN) in order to generate a new model of immunization in animals, and consequently a potentially novel polyclonal serum, namely an anti-T. serrulatus venom. CN were successfully obtained by ionic gelation using the polyanion tripolyphosphate (TPP), which demonstrated a suitable particle size of about 200 nm, with maximum encapsulation efficiency (100%) and enhanced antigen-specific antibody titers of 72%. The serum production data revealed that CN were equipotent to aluminum hydroxide, the traditional adjuvant for immunization. This study demonstrates that chitosan nanoparticles are a promising and safe system for peptide/protein delivery for T. serrulatus scorpion.

Viscosity–temperature behavior of chitin solutions using lithium chloride/DMA as solvent

Solutions of chitin in Li(+)/N,N-dimethylacetamide systems were studied via viscometry, using LiCl concentrations of 3% and 5% (m/v) and chitin concentrations ranging from 0.075 to 0.375 gL(-1). The reduced viscosity number versus concentration plot showed a minimum that was related to the formation of Li(+)-OC complex moieties along chitin macromolecular chains. Viscosity behavior was affected by temperature according to the Eyring model: concentration dependence of flow enthalpy of activation was correlated to polymer-polymer interactions and flow entropy of activation to the stiffness of the complexed chitosan macromolecular chain.

Equilibrium and kinetic aspects of sodium cromoglycate adsorption on chitosan: Mass uptake and surface charging considerations

Chitosan has more and more been suggested as a material for use as adsorbent in the treatment of effluents as well as in the synthesis of drug-loaded nanoparticles for controlled release. In both cases, a good understanding of the process of adsorption, both kinetically and in terms of equilibrium, has an importance of its own. In this manuscript we study the interaction between sodium cromoglycate, a drug used in asthma treatment, and chitosan. Equilibrium experiments showed that Sips (or Freundlich-Langmuir) isotherm described well the resultant data and adsorption possibly occurred as in multilayers. A model based on ordinary reaction-rate theory, compounded of two processes, each one with a correlated velocity constant, described the kinetics of sorption. Kinetic and equilibrium data suggested the possibility of surface rearrangement, favored by the increase of temperature.