Attilio Cesàro

Chitosan nanoparticles: preparation, size evolution and stability.

PURPOSE Characterisation of chitosan-tripolyphosphate nanoparticles is presented with the aim of correlating particle shape and morphology, size distribution, surface chemistry, and production automatisation with preparation procedure, chitosan molecular weight and loaded protein. METHODS Nanoparticles were prepared by adding drop wise a tripolyphosphate-pentasodium solution to chitosan solutions under stirring. Trehalose, mannitol and polyethylene-glycol as bioprotectants were used to prevent particle aggregation and to reduce mechanical stress during freezing and drying processes. RESULTS As a novel result, time evolution of the particle size distribution curve showed the presence of a bimodal population composed of a fraction of small particles and of a second fraction of larger particles attributed to the rearrangement of particles after the addition of tripolyphosphate. Storage for 4 weeks resulted in a slight increase in average size, due to the continuous rearrangement of small particles. Improvement of nanoparticle stability after lyophilisation and spray-drying was observed in the presence of all bioprotectants. Trehalose was the best protectant for both methods. Finally, in vivo tests using chick embryos assessed the biocompatibility of chitosan, tripolyphosphate and the nanoparticles. CONCLUSION The simple ionotropic gelation method with low-MW chitosan was effective in achieving reproducible nanoparticles with the desired physico-chemical and safety characteristics.

Polysaccharides from cyanobacteria

Abstract This review deals with the different glycans produced by cyanobacteria such as reserve polymers, polysaccharides from the cell envelope and exocellular polysaccharides. For each group a description of previous work is reported, quoting all different strains tested, methods of polysaccharide extraction and chemical and physical characterization. In particular, chemical composition and sequence (when known) are reported although inhomogeneity of results reveals that sometimes methods used are outdated. Emphasis is put on exocellular polysaccharides, the most interesting type of polymers from the technological point of view.

Reversible dehydration of trehalose and anhydrobiosis: from solution state to an exotic crystal?

Abstract Physico-chemical properties of the trehalose–water system are reviewed with special reference to the transformations that may shed light on the mechanism of trehalose bio-protection. Critical analysis of solution thermodynamics is made in order to scrutinize trehalose properties often called ‘anomalous’ and to check the consistency of literature results. Discussion on the conversion between the solid state polymorphic forms is given, with a special emphasis of the transformations involving the newly identified anhydrous crystalline form of α,α-trehalose, TREα. This exotic crystal is almost ‘isomorphous’ with the dihydrate crystal structure, and possesses the unique feature of reversibly absorbing water to produce the dihydrate, without changing the main structural features. The reversible process could play a functional role in the well-known ability of this sugar to protect biological structures from damage during desiccation. The final aim of the paper is to add some new insights into and to reconcile previous hypotheses for the peculiar ‘in vivo’ action of trehalose.

New glucuronoglucans obtained by oxidation of amylose at position 6

Abstract By adding finely powdered sodium nitrite to solutions of amylose in 85% (w/w) orthophosphoric acid, a series of d -glucurono- d -glucans was prepared, having number-average molecular weights of ∼104 and GlcA/Glc ratios varying from 0.5 to 3.0. The products were soluble in water, both as sodium salts and free acids, formed complexes with iodine having λmax in the range of 508–574 nm, and exhibited strongly pH-dependent chiroptical properties.

Molecular Dynamics Simulation Studies of Caffeine Aggregation in Aqueous Solution

Molecular dynamics simulations were carried out on a system of eight independent caffeine molecules in a periodic box of water at 300 K, representing a solution near the solubility limit for caffeine at room temperature, using a newly developed CHARMM-type force field for caffeine in water. Simulations were also conducted for single caffeine molecules in water using two different water models (TIP3P and TIP4P). Water was found to structure in a complex fashion around the planar caffeine molecules, which was not sensitive to the water model used. As expected, extensive aggregation of the caffeine molecules was observed, with the molecules stacking their flat faces against one another like coins, with their methylene groups staggered to avoid steric clashes. A dynamic equilibrum was observed between large n-mers, including stacks with all eight solute molecules, and smaller clusters, with the calculated osmotic coefficient being in acceptable agreement with the experimental value. The insensitivity of the results to water model and the congruence with experimental thermodynamic data suggest that the observed stacking interactions are a realistic representation of the actual association mechanism in aqueous caffeine solutions.

Viscoelastic and thermal properties of bacterial poly(d-(−)-β-hydroxybutyrate)

Abstract Three poly( d -(-)-β-hydroxybutyrate) (PHB) samples from Rhbizobium spp. have been characterized in order to evaluate the effects of different extraction procedures of the polymer. Only the molecular weight is found to change, being 6 × 10 4 for the sample extracted with HCl (1 m and of the order of 10 6 for the samples extracted with acetone. Thermogravimetric results on PHB with different molecular weights, indicate that the temperature at which weight loss becomes significant is lower than 230°C only for the lowest molecular weight examined (6 × 10 4 ). The calorimetric properties strongly depend on thermal history. The d.s.c. curves of ‘room stored’ samples show only a melting endotherm at 177°C, whose area increases with annealing. Quenching from the melt shows evidence an intense glass transition (ΔCp = 0.43 J/g deg) in the vicinity of 0°C, followed by a ‘cold crystallization’ peak preceding melting. The viscoelastic spectrum shows three relaxations: a water-related low temperature relaxation (−80°C), the glass transition (apparent activation energy ΔH a = 356 KJ/mol) and a broad relaxation in the temperature range between T g and T m due to motions in the crystalline phase.

Physicochemical properties of the exocellular polysaccharide from Cyanospira capsulata

This paper reports on the chemical structure and on some physicochemical properties of a new exopolysaccharide, CC-EPS, secreted by a filamentous nitrogen-fixing cyanobacterium, Cyanospira capsulata. Solution properties of CC-EPS were studied with the aim of characterizing the conformational state of the polysaccharide in water and in aqueous salt solution, in view of the peculiar rheological properties. Because the molecule has two different uronic acid residues, a variation of pH and/or ionic strength was considered to be the best perturbation to disclose any possible ordered structures. We found no evidence for a cooperative conformational transition from the change of the chiro-optical properties or from the smooth increase of pKa as a function of the degree of ionization, alpha, of the polyacid. The same conclusion was drawn from the study of the temperature dependence and ionic strength dependence (in the range up to 0.1 M NaCl) of solution properties. The data suggest that the solution conformation of CC-EPS is a random coil with a chain flexibility comparable to that of alginate.

Enthalpy relaxation and glass transition behaviour of sucrose by static and dynamic DSC

Abstract The relaxation process of the sucrose in the glassy state and its glass transition are studied by differential scanning calorimetry in both the conventional and the dynamic mode. The data on the kinetics of glassy relaxation are experimentally evaluated by measuring the enthalpy relaxation peaks as a function of the ageing times at three different ageing temperatures, namely 45, 55 and 60°C. It is shown that the ageing process is a complex phenomenon with a rather large distribution of relaxation times. The value of the breath of the distribution of relaxation processes, β, is 0.32 and it is in the lower range of the distributions commonly observed. The dynamic components of the heat capacity ( C ′ p and C ″ p ) have been obtained from the experiments carried out at different frequency of temperature modulation ( ν =8.3−83 mHz). These components are unaffected by the ageing process and therefore are more reliable for the correct T g determination. The activation energies for the relaxation process and for the glass transition process are also evaluated.

Supramolecular structure of microbial polysaccharides in solution : from chain conformation to rheological properties

Abstract Literature data and unpublished results have been used to correlate the primary and secondary structures of gellan, welan, rhamsan, succinoglycan and galactoglucan in solution with their rheological properties. In dilute solution the chain conformation ranges from that of the random coil of galactoglucan to that of the stiffer double helix of gellan, and possibly a similar conformation exists for welan and rhamsan. In semidilute solution the rheological behaviour of the above microbial polysaccharides is mainly determined by their conformation in solution. Ordered regions along the polysaccharide chains seem to be the prerequisite to establish intermolecular interactions which lead to non-transient polymer networks. The lack of ordered secondary structure leads to entangled networks in which the topological constraints govern the rheological behaviour. Experimental evidence is reported to support the hypothesis that the chain conformation and rigidity can be qualitatively predicted on the basis of rheological measurements.

“The Good, the Bad and the Ugly” of Chitosans

The objective of this paper is to emphasize the fact that while consistent interest has been paid to the industrial use of chitosan, minor attention has been devoted to spread the knowledge of a good characterization of its physico-chemical properties. Therefore, the paper attempts to critically comment on the conflicting experimental results, highlighting the facts, the myths and the controversies. The goal is to indicate how to take advantage of chitosan versatility, to learn how to manage its variability and show how to properly tackle some unexpected undesirable features. In the sections of the paper various issues that relate chitosan properties to some basic features and to advanced solutions and applications are presented. The introduction outlines some historical pioneering works, where the chemistry of chitosan was originally explored. Thereafter, particular reference is made to analytical purity, characterization and chain modifications. The macromolecular characterization is mostly related to molecular weight and to degree of acetylation, but also refers to the conformational and rheological properties and solution stability. Then, the antimicrobial activity of chitosan in relation with its solubility is reviewed. A section is dedicated to the formulation of chitosan biomaterials, from gel to nanobeads, exploring their innovative application as active carrier nanoparticles. Finally, the toxicity issue of chitosan as a polymer and as a constructed nanomaterial is briefly commented in the conclusions.