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Polyelectrolyte complexes formed between DNA and chitosan present different and interesting physicochemical properties combined with high biocompatibility; they are very useful for biomedical applications. DNA in its double helical structure is a semi-rigid polyelectrolyte chain. Chitosan, an abundant polysaccharide in nature, is considered as one of the most attractive vectors due to its biocompatibility and biodegradability. Here we study chitosan/DNA polyelectrolyte complex formation mechanism and the key factors of their stability. Compaction process of DNA with chitosan was monitored in terms of the ζ-potential and hydrodynamic radius variation as a function of charge ratios between chitosan and DNA. The influence of chitosan degree of acetylation (DA) and its molecular weight on the stoichiometry of chitosan/DNA complexes characteristics was also studied. It is shown that the isoelectric point of chitosan/DNA complexes, as well as their stability, is directly related to the degree of protonation of chitosan (depending on pH), to the DA and to the external salt concentration. It is demonstrated that DNA compaction process corresponds to an all or nothing like-process. Finally, since an important factor in cell travelling is the buffering effect of the vector used, we demonstrated the essential role of free chitosan on the proton-sponge effect., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Up to now, chitosan and DNA have been investigated for gene delivery due to chitosan advantages. It is recognized that chitosan is a biocompatible and biodegradable non-viral vector that does not produce immunological reactions, contrary to viral vectors. Chitosan has also been used and studied for its ability to protect DNA against nuclease degradation and to transfect DNA into several kinds of cells. In this work, high molecular weight DNA is compacted with chitosan. DNA-chitosan complex stoichiometry, net charge, dimensions, conformation and thermal stability are determined and discussed. The influence of external salt and chitosan molecular weight on the stoichiometry is also discussed. The isoelectric point of the complexes was found to be directly related to the protonation degree of chitosan. It is clearly demonstrated that the net charge of DNA-chitosan complex can be expressed in terms of the ratio [NH3(+)]/[P(-)], showing that the electrostatic interactions between DNA and chitosan are the main phenomena taking place in the solution. Compaction of DNA long chain complexed with low molar mass chitosan gives nanoparticles with an average radius around 150nm. Stable nanoparticles are obtained for a partial neutralization of phosphate ionic sites (i.e.: [NH3(+)]/[P(-)] fraction between 0.35 and 0.80)., (Copyright © 2016 Elsevier B.V. All rights reserved.)

The purpose of this research was to evaluate the cytotoxicity of chitosans with different degrees of acetylation (DA) and molecular weights (MW), as well as the effect of their positive ionic charges controlled by pH on bladder carcinoma cells (RT112 and RT112cp) using the tetrazolium salt colorimetric (MTT) assay. Our data showed that all chitosan samples were cytotoxic on RT112 and RT112cp cells with a higher cytotoxicity obtained at lower pH. Further, it was found that the toxicity increased with increasing DA. However, no significant difference in cytotoxicity between chitosans with different molecular weights was observed. Annexin V-FITC staining test was then used to study and quantify the induction of apoptosis. Data shows that chitosans induce apoptosis of RT112 and RT112cp cells with the same dependence with DA., (Copyright © 2015. Published by Elsevier B.V.)

Chitin and derivatives used for biomedical or pharmaceutical applications require a high level of purity and quality that are difficult to achieve. In this study, we propose to optimize the extraction of chitin in order to obtain pure product keeping a structure as close as possible to the native form. Thus, demineralization step was firstly optimized using response surface methodology. In the optimized conditions predicted by the model, the obtained chitin has an acetylation degree (DA) and a demineralization degree (DM) equal to 99% and 100%, respectively. Then, different microbial and fish crude alkaline proteases were tested for their efficiency in deproteinization. Crude alkaline proteases giving the highest deproteinization degrees (DP), Bacillus mojavensis A21 and Scorpaena scrofa, were selected for chitin extraction. The obtained DP was 88±2% and 83±1%, respectively. At the end, effect of the use of mixed enzymatic treatment with the two selected crude enzymes and the order of demineralization/deproteinization steps were tested. The results demonstrated that two separated steps in enzymatic treatments realized on demineralized sample give the best DP (96%) preserving the DA (99%)., (Copyright © 2015. Published by Elsevier B.V.)

An original sodium alginate from Tunisian seaweed (Cystoseira barbata) was purified and characterized by circular dichroism (CD) and ATR-FTIR spectroscopies. ATR-FTIR spectrum of C. barbata sodium alginate (CBSA) showed the characteristic bands of mannuronic (M) and guluronic acids (G). The M/G ratio was estimated by CD (M/G = 0.59) indicating that CBSA was composed of 37% mannuronic acid and 63% guluronic acid. The analysis of viscosity of CBSA showed evidence of pseudoplastic fluid behaviour. The emulsifying capacity of CBSA was evaluated at different concentrations (0.25-3%), temperatures (25-100 °C) and pH (3.0-11.0). Compared to most commercial emulsifiers, the emulsion formulated by CBSA was found to be less sensitive to temperature changes and more stable at acidic pH. CBSA was examined for antioxidant properties using various antioxidant assays. CBSA exhibited important DPPH radical-scavenging activity (74% inhibition at a concentration of 0.5 mg/ml) and considerable ferric reducing potential. Effective hydroxyl-radical scavenging activity (82% at a concentration of 5 mg/ml) and potent protection activity against DNA breakage were also recorded for CBSA. However, in the linoleate-β-carotene system, CBSA exerted moderate antioxidant activity (60% at a concentration of 1.5 mg/ml). Therefore, CBSA can be used as a natural ingredient in food industry or in the pharmaceutical field., (Copyright © 2014 Elsevier B.V. All rights reserved.)

Chitosan is obtained by deacetylation of chitin. Chitosan versatility is directly related to the polymer's characteristics depending on the deacetylation process. The aim of this research was to study the parameters influencing deacetylation and to elucidate their effect on acetylation degree (DA) and molecular weight (MW). The effect on chitosan DA was investigated using a fractional factorial design 2(7-3) with seven factors and two variation levels. The tested factors were: X1=number of successive baths, X2=reaction time, X3=temperature, X4=alkali reagent, X5=sodium borohydride, X6=the atmospheric conditions and X7=alkali concentration. A mathematical model was investigated corresponding to the following relation ŷ=7.469-1.344X1-1.094X2-3.094X3+1.906X4+0.656X5+0.906X6-1.031X7+0.469X1X2-0.781X3X4+0.906X1X3X4 with R2=0.99. This model allows fixing experimental conditions for each desired DA. To study the effect on chitosan MW, only atmospheric conditions and use of sodium borohydride as an oxygen scavenger were investigated. The use of sodium borohydride and nitrogen atmosphere was found to have a protective effect against chitosan degradation during deacetylation., (Copyright © 2014 Elsevier B.V. All rights reserved.)

Chitin was recovered through enzymatic deproteinization of the shrimp processing by-products. Different microbial and fish viscera proteases were tested for their deproteinization efficiency. High levels of protein removal of about 77±3% and 78±2% were recorded using Bacillus mojavensis A21 and Balistes capriscus proteases, respectively, after 3h of hydrolysis at 45°C using an enzyme/substrate ratio of 20U/mg. Therefore, these two crude proteases were used separately for chitin extraction and then chitosan preparation by N-deacetylation. Chitin and chitosan samples were then characterized by 13 Cross polarization magic angle spinning nuclear magnetic resonance (CP/MAS)-NMR spectroscopy and compared to samples prepared through chemical deproteinization. All chitins and chitosans showed identical spectra. Chitosans prepared through enzymatic deproteinization have practically the same acetylation degree but higher molecular weights compared to that obtained through chemical process. Antimicobial, antioxidant and antitumoral activitities of chitosan-M obtained by treatment with A21 proteases and chitosan-C obtained by alkaline treatment were investigated. Results showed that both chitosans inhibited the growth of most Gram-negative, Gram-positive bacteria and fungi tested. Furthermore, both chitosans exhibited antioxidant and antitumor activities which was dependent on the molecular weight., (Copyright © 2014 Elsevier B.V. All rights reserved.)

Three marine sources of chitin from Tunisia were investigated. Structural differences between α-chitin from shrimp (Penaeus kerathurus) waste, crab (Carcinus mediterraneus) shells, and β-chitin from cuttlefish (Sepia officinalis) bones were studied by the (13)C NMR, FTIR, and XRD diffractograms. The (13)C NMR analysis showed a splitting of the C3 and C5 carbon signals for α-chitin, while that of β-chitin was merged into a single resonance. The bands contour of deconvoluted and curve-fit FTIR spectra showed a more detailed structure of α-chitin in the region of O-H, N-H and CO stretching regions. IR and (13)C NMR were used to determine the chitin degree of acetylation (DA). XRD analysis indicated that α-chitins were more crystalline polymorph than β-chitin. Shrimp chitin was obtained with a good yield (20% on raw material dry weight) and no residual protein and salts. Chitosans, with a DA lower than 20% and relatively low molecular masses were prepared from the wet chitins in the same experimental conditions. They were perfectly soluble in acidic medium. Nevertheless, chitin and chitosan characteristics were depending upon the chitin source., (Copyright © 2014 Elsevier B.V. All rights reserved.)

In this work, three methods (ethanol, HCl, and CaCl(2) routes) of sodium alginate extraction-purification from brown seaweeds (Macrocystis pyrifera) were used in order to study the influence of process conditions on final properties of the polymer. In the CaCl(2) route, was found that the precipitation step in presence of calcium ions followed by proton-exchange in acid medium clearly gives alginates with the lowest molecular weight and poor mechanical properties. It is well known that the acid treatment degrade the ether bonds on the polymeric chain. Ethanol route displayed the best performance, where the highest yield and rheological properties were attained with the lowest number of steps. Although the polymer I.1 showed a molar mass and polydispersity index (M(w)/M(n)) similar to those of commercial sample, its mechanical properties were lower. This performance is related to the higher content of guluronic acid in the commercial alginate, which promotes a more successful calcium chelation. Moreover, the employment of pH 4 in the acid pre-treatment improved the yield of the ethanol route, avoiding the ether linkage hydrolysis. Therefore, samples I.2 and I.3 displayed a higher M(w) and a narrower distribution of molecular weights than commercial sample, which gave a higher viscosity and better viscoelastic properties.

This paper concerns the interaction between hyaluronan and fibrinogen as model for protein-polysaccharide interaction. From rheological investigation, it is shown that a 3D physical network is promoted by mixing the two components; the mechanism is attributed to electrostatic interactions. The influences of the molecular weight and of the hyaluronan concentration are examined; the loose interaction obtained for addition of small amount of soluble protein induces a non-Newtonian behaviour which may be in direct relation with the behaviour observed previously on synovial fluids.

A new route to starch derivatives bearing hydrolyzable cationic groups was developed. This was based on reacting starch compounds with betaine derivatives in the presence of diisopropylcarbodiimide and 4-dimethylaminopyridine as coupling reagents in an aprotic polar solvent. Water-soluble starches with a perfectly controlled degree of substitution were thus obtained which were fully characterized by infrared, 1H and 13C spectroscopy and viscosity measurements. The cationic groups grafted on the polysaccharides are shown to hydrolyze slowly upon storage at room temperature.

A new bacterial polysaccharide '1644' is studied in aqueous solutions and in the gel state. The viscometric measurements for dilute and semi-dilute solutions in presence of monovalent salts are usual; however, in presence of divalent cations like Ca2+ an original behaviour is observed, related to intermolecular bonds. For larger polymer concentrations a clear gel is obtained with divalent counterions. This gel exhibits unusual properties compared to other gelling polysaccharides: it is very elastic and resistant because of low crosslinking. The mechanical properties of this gel depend closely on the fraction of divalent ions linked to the polymer and so on thermodynamic parameters.

The use of the n.m.r. method in the investigation of chitosan carboxymethylation was evaluated. It seems to be the most effective technique to determine concurrently the degree and the position of substitution of the carboxymethylated chitosan derivatives. The 13C-n.m.r., by the DEPT method, 1H-1H and 1H-13C-n.m.r. correlations give much valuable information from the chemical shifts of the complex carboxymethylchitosan spectra. The relative reactivity of the functional groups of chitosan towards carboxymethylation was also determined assuming a higher reactivity of the C-6 position.

We report the rheological behaviour of a succinoglycan polysaccharide in dilute and semi-dilute solutions as a function of temperature, ionic strength and the nature of counterion. We have examined the viscosity dependence as a function of molecular weight using samples obtained by ultrasonication. We have also prepared samples lacking succinate substitutes and compared their behaviour with that of the native polymer. In both cases, we observed that, after heating a polymer solution for the first time above the conformational transition temperature, a different ordered state was obtained on cooling. This state had a lower molecular weight and intrinsic viscosity but identical chemical structure and local properties. A role for the side chain in the stabilization of breaks in the backbone is suggested. Nevertheless, a unique curve is obtained for the specific viscosity as a function of the overlap parameter c[eta] for different polymer concentrations of both the native and heated forms. However, different curves are obtained for normal and succinate-free polymers, and the succinate-free polymer is characterized by a lower Huggins constant.

We report the chemical characterization and the relationship between the physicochemical properties and conformational change of a succinoglycan polysaccharide produced by Pseudomonas sp, NCIB 11592. The expected chemical structure is confirmed, with a ratio of D-glucose: D-galactose: pyruvate: succinate of 7:1:1:1. The molecular weight of the native form is 4.2 x 10(6) but after a single heating cycle through the disordered state the molecular weight is reduced to 3.0 x 10(6). The polymer has a polymolecularity index of 1.3 in both cases. The conformational change was studied by different methods which enabled us to define the exact nature of the ordered and disordered states. The conformational transition depends on the temperature, the ionic strength and the nature of the counterion. The polyelectrolyte behaviour is in favour of a single chain conformation with an intramolecular helix-coil transition. The enthalpy change during this transition is greater than that expected solely on the basis of the polyelectrolyte contribution. It may be associated with changes in solvation or a rearrangement of water molecules in close association with the polymer.