Franco Delben

Structure of the oligomers obtained by enzymatic hydrolysis of the glucomannan produced by the plant Amorphophallus konjac.

Dimers and trimers obtained by enzymatic hydrolysis of the glucomannan produced by the plant Amorphophallus konjac were analysed in order to obtain information on the saccharidic sequences present in the polymer. The polysaccharide was digested with cellulase and beta-mannanase and the oligomers produced were isolated by means of size-exclusion chromatography. They were structurally characterised using electrospray mass spectrometry, capillary electrophoresis, and NMR. The investigation revealed that many possible sequences were present in the polymer backbone suggesting a Bernoulli-type chain.

Interaction of soluble chitosans with dyes in water. I. Optical evidence

Abstract The interaction of several cationic and anionic dyes with N -carboxymethyl chitosan (NCMCh), N -carboxybutyl chitosan (NCBCh), the reduction product of the aldimine obtained from chitosan and 5-hydroxymethyl-2-furaldehyde (NHMFCh) and the parent chitosan was studied in water with optical techniques. The interaction with cationic dyes was studied in the pH range of 5–6. No interaction was observed. The anionic dyes were able to modify the spectra of soluble chitosans in the pH range 2–5, the most remarkable alteration appearing at pH 3·5. For all the polysaccharide-dye systems studied, absorption and circular dichroism spectra were collected at different dye-to-polymer molar ratio values.

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.

Copper(II) binding by natural ionic polysaccharides: Part I. Potentiometric and spectroscopic data

Abstract The interaction between copper(II) ions and ionic polysaccharides of natural origin has been studied in 0.05 M NaClO4 aqueous solution at 25°C by means of ion-selective electrode potentiometry, spectrophotometry, and circular dichroism measurements. Many independent variables affect the Cu-polymer interaction: the chemical nature, composition and charge density of the polysaccharide, the copper to polymer ratio, the polymer concentration, and the ionic strength. Moreover, each technique employed seems to show specific features in the binding reaction. A parallel use of different techniques is therefore needed to discriminate between long-range electrostatic and short-range specific modes of interaction.

Interaction of food proteins with polysaccharides, I. Properties upon mixing

The interaction of ovalbumin and of β-casein with two carboxymethylcellulose samples and with glutamate glucan was studied in aqueous solution at different concentration, pH and ionic strength values. The techniques used were rheometry, optical and chiro-optical measurements and differential scanning calorimetry. In general, glutamate glucan is more effective in interacting with the protein than carboxymethylcellulose. Because of its disordered conformation, β-casein is strongly attracted at low pH values to the polysaccharides. When interaction occurs, soluble or insoluble complexes are formed. In the ovalbumin-glutamate glucan and β-casein-carboxymethyl cellulose systems the polysaccharide hinders the thermal or Ca(II)-induced aggregation of the protein.

Binding of metal cations by N-carboxymethyl chitosans in water

The binding of metal cations by N-carboxymethyl chitosan in dilute aqueous solution was studied as a function of charge density, temperature and pH. The techniques employed were absorption and circular dichroism measurements, potentiometric titration, dilatometry and isothermal microcalorimetry. The composition of the polymer significantly affected the binding of Ni(II), Co(II) and Pb(II), and had a small influence on the extent of binding of Cu(II). In any case, the density of glycine residues affected the binding constant with all the counterions studied, thus confirming that this residue is engaged in the complex formation. The whole of the optical, chirooptical and thermodynamic evidence showed that, at least in the case of Cu(II), the ions are bound by both carboxylic and amino groups. The temperature did not affect the extent of binding, at least in the case of Cu(II) and Pb(II) ions. Circular dichroism spectra, however, showed that these counterions are able to interact with NHCOgroups at high temperatures (61°C), very likely owing to the enhanced mobility of the polymer chain. Lowering pH depressed the binding ability of N-carboxymethyl chitosan towards Cu(II) and Pb(II) ions, the effect being much more pronounced in the case of Pb(II). Moreover, a refined method for collecting absorption spectra of the complex between the polymer and Cu(II) or Pb(II) ions, without interference with absorbance by undesired species, was tested and applied. The charge-transfer band exhibited by the N-carboxymethyl chitosan-Cu(II) system, recorded following this method, showed interesting features, on the basis of which the site of the binding of Cu(II) on to N-carboxymethyl chitosan was confirmed.

Thermodynamic study of the protonation and interaction with metal cations of three chitin derivatives

Abstract The chelating ability of N-carboxymethyl chitosan, chitosan and fully deacetylated chitosan was assessed for dilute solutions of Cu and Pb by means of potentiometry, calorimetry, dilatometry and circular dichroism measurements. N-Carboxymethyl chitosan, to which a significant freedom of the glycine residues imparts low conformational rigidity, was much more effective than chitosan and deacetylated chitosan in binding both Cu(II) and Pb(II). Dilatometry gave positive ΔV values for N-carboxymethyl chitosan only, as a consequence of the desolvation of the ionic species, mainly carboxyl groups, in the course of the binding reaction. The carboxyl group was not the only site of reaction, however, as indicated by the negative enthalpy variations. It is known that the reactions of metal ions with polycarboxylates as a rule are endothermic (positive ΔH) and those with polyamines are exothermic (negative ΔH); it is therefore concluded that the complexing ability of the amino group is corroborated by the presence of the carboxyl group in the glycine residue of N-carboxymethyl chitosan.

Thermodynamic study of the interaction of N-Carboxymethyl chitosan with divalent metal ions

Abstract Potentiometry and microcalorimetry indicate that calcium is not chelated by N-carboxymethyl chitosan and that the order of affinity of N-carboxymethyl chitosan for the other divalent metal ions studied is Cu > Cd ⪢ Pb, Ni > Co. For these metals the following binding constants were obtained, respectively: 7 × 10 5 ; 4 × 10 5 ; 3 × 10 3 and 1 × 10 3 . The number of water molecules liberated in the binding process by the solvated metal ions and by carboxylate were 25, 14 and 16 for Cu(II), Cd(II) and Pb(II), respectively. The binding was enthalpy driven and the negative ΔH values were thus attributed to the interaction of metal ions with nitrogen atoms. Cu(II) and Pb(II) introduced new bands in the CD and UV spectra, whilst the other metal ions did not: for Cu(II) they were a positive band at 237 nm and a negative one at 277 nm in the CD spectrum, and an absorption band at 246 nm in the UV spectrum; for Pb(II) they were a positive band at 229 nm and a negative one at 244 nm in the CD spectrum, and an absorption band at 231 nm in the UV spectrum.

Copper(II) binding by natural ionic polysaccharides: Part II. Polarographic data☆

Abstract Differential pulse polarography (d.p.p) was employed to study the interaction of copper(II) ions and carboxylic polysaccharides (pectate, P; algal alginate, AA; bacterial alginate, BA; gul(uronate)-rich oligomers, G; man(nuronate)-rich oligomers, M; alternating man-gul oligomers, MG; and polyacrylate, PAA — the last one for comparison) in 0.05 M NaClO 4 aqueous solution at 25°C. Three main reduction peaks appear in the range of potentials between +0.10 and −0.23 V versus s.c.e. The shapes, the positions of the maxima of the d.p. polarograms, and the areas of the integrated peaks vary with the nature of the polyelectrolyte and with the copper to polymer molar ratio. An attribution of the amount of non-reducible copper ions to a minimum value of bound species is tentatively performed and a comparison with ion selective electrode (i.s.e.) potentiometric results is done. The sequence of copper-binding affinity as determined by d.p.p. is PAA > P > BA ⋍ AA > G > MG > M and it parallels that found potentiometrically using copper ion selective electrodes.

Chelating ability and enzymatic hydrolysis of water-soluble chitosans

Abstract A novel water-soluble chitosan (NHMF-chitosan) was synthesized from crab chitosan and 5-hydroxymethyl-2-furfural, an amply available derivative of sucrose. The chelating ability of NHMF-chitosan and N-carboxybutyl chitosan in dilute aqueous solutions was studied by spectrophotometric and calorimetric methods. Both carbohydrate polymers were found to chelate Cu(II), the binding constants, KB, being 9 × 104 l.mol−1 for NHMF-chitosan and 2·2 × 103 for N-carboxybutyl chitosan; the latter was also able to chelate Pb(II), but no enthalpy variations were observed for other divalent cations. Chelation was strongly influenced by pH, and, to some extent, by temperature. Circular dichroism (cd) measurements revealed a positive rather than negative band at 225 nm, indicative of chirality change for NHMF-chitosan, which was found, however, to be a substrate for lysozyme.