Fabio Tanfani

N-(carboxymethylidene)chitosans and N-(carboxymethyl)chitosans: Novel chelating polyampholytes obtained from chitosan glyoxylate

Abstract Glyoxylic acid, added to aqueous suspensions of chitosan, causes immediate dissolution of chitosan and gel formation within 3–4 h if the pH is 4.5–5.5. Solutions at lower pH values gel after 2 min of warming at 60–80°. Chitosan glyoxylate solutions brought to alkaline pH with sodium hydroxide do not precipitate chitosan. Evidence is given that a Schiff base, namely N -(carboxymethylidene)chitosan, is formed. N -(Carboxymethylidene)chitosans are reduced by sodium cyanoborohydride at room temperature to give N -(carboxymethyl)chitosans, obtained as white, free-flowing powders, soluble in water at all pH values. A series of N -(carboxymethyl)chitosans having various degrees of acetylation and N -carboxymethylation was obtained, and characterized by viscometry, elemental analysis, and i.r. spectrometry. For the fully substituted N -(carboxymethyl)chitosans, the pK′ is 2.3, the pK″ is 6.6, and the isoelectric point is 4.1. The addition of N -(carboxymethyl)chitosan to solutions (0.2–0.5m m ) of transition-metal ions produces immediate insolubilization of N -(carboxymethyl)chitosan-metal ion chelates.

The N-permethylation of chitosan and the preparation of N-trimethyl chitosan iodide

Abstract Chitosan was N-permethylated by reaction with formaldehyde and sodium borohydride under controlled conditions (pH 4·0, 15°C, reaction times 12 and 8 h, respectively). The N-permethylated chitosan was reacted with methyl iodide at 35°C and N-trimethyl chitosan iodide with a quaternary nitrogen degree of 60% was obtained. This material may have uses as an antibiotic and an ion exchange material.

Sulfated N-(carboxymethyl)chitosans: Novel blood anticoagulants

N-(Carboxymethyl)chitosan was subjected to sulfation in a mixture of concentrated sulfuric acid (oleum) and N,N-dimethylformamide, under anhydrous conditions. The resulting product contained 11% of sulfur and degree of substitution: N-acetyl, 42%; N-carboxymethyl, 58%; and sulfate, 100%. Sonication of the sulfated N-(carboxymethyl)chitosan gave two main fractions whose molecular weights were 39,000 and 80,000. In human blood, complexes of sulfated N-(carboxymethyl)chitosan and antithrombin inhibited both thrombin and factor Xa, and produced neither hemolysis nor alterations in erythrocytes and lymphocytes. Sulfated N-(carboxymethyl)chitosan is therefore proposed as a blood anticoagulant.

The characterization of N-methyl, N-ethyl, N-propyl, N-butyl and N-hexyl chitosans, novel film-forming polymers

Abstract The N -alkyl chitosans in the title were prepared from chitosan ( Euphausia superba ) by aldimine formation and hydrogenation at room temperature in aqueous media. They are white powders with a certain degree of crystallinity; their substitution degrees are: acetamido 36%, secondary amine 23-33%, primary amine 31-41%. The chelating ability of N -alkyl chitosans is specific for certain cations such as Cu 2+ , Hg 2+ and Pb 2+ for which the capacities are in the range 2-6% by weight, depending on conditions and choice of N -alkyl chitosan. In the N-alkyl chitosans, the hydrogen bonds are weakened by the presence of substituents and therefore they swell in water. Membranes are easily cast from acetic acid solutions. Circular dichroism and ultraviolet spectrometry measurements indicate that the chelation of metal ions depresses the acetamido group bands and introduces new spectral bands due to the chelates. Circular dichroism spectra also reveal the hydration state of the membranes. Applications are foreseen in the pharmaceutical, cosmetic and textile industries

N-(o-carboxybenzyl) chitosans: Novel chelating polyampholytes

Abstract The imine formed by chitosan with phthalaldehydic acid was reduced with sodium cyanoborohydride and the resulting N -( o -carboxybenzyl) chitosan (NCBC) was insolubilised with ethanol and acetone and obtained as a white, free-flowing powder, soluble in both acidic and alkaline solutions. A sample of NCBC with the following degrees of substitution: acetamido 42%±4%, N -( o -carboxybenzyl) amine 43%±3%, free amine 15%±1% and containing 16%±1% moisture, was characterised by IR and UV-Vis. spectrometry, titration and viscometry. The isoelectric point was 6·8; the pK a values were 5·7 and 8·0. NCBC could be determined by UV-Vis. spectrophotometry in aqueous solutions at 274 nm; maximum viscosity of the solutions was observed at pH 4. Upon addition of NCBC to transition metal ion solutions (0·1–0·5 m m ) chelation and insolubilisation took place immediately. The dependence of the collection percentage on pH, NCBC and metal ion concentrations was studied for nine metal ions.

Chelating derivatives of chitosan obtained by reaction with ascorbic acid

Abstract Ascorbic acid immediately dissolves Euphausia superba chitosan upon mixing and forms chitosan ascorbate; during the 6-h period after dissolution in water at pH 5–7, ascorbate is oxidized to dehydroascorbate which undergoes Schiff reaction with the amino groups of chitosan, thus yielding a viscous solution of a polymeric ketimine. The latter is characterized by infrared spectrometry, circular dichroism spectropolarimetry, viscometry and alkalimetry. When brought into contact with transition metal ions, the chitosan ascorbate ketimine yields insoluble metal chelates. Upon reduction with sodium cyanoborohydride, the water-insoluble N-[2-(1,2-dihydroxyethyl)tetrahydrofuryl] chitosan (NDTC) is obtained, which shows enhanced capacity for uranium, up to 800 mg U/g from solutions at pH 4·5.

The degree of acetylation of chitins by gas chromatography and infrared spectroscopy

Gas chromatography of a number of amines, alcohols and sulfur derivatives was carried out on chitin and partially deacetylated chitins as well as on chitosan. The retention time of methanol is proportional to the degree of acetylation, and therefore a method is proposed for the gas-chromatographic determination of the degree of acetylation of chitin/chitosan. The analysis of the infrared spectra of chitin/chitosan also permits one to determine the degree of acetylation by using the ratio of the bands 1550 and 2878 cm-1.

Preparation and characteristic properties of dithiocarbamate chitosan, a chelating polymer

Abstract Dithiocarbamate chitosan was obtained by treating chitosan with carbon disulfide in a mixture of ammonia and methanol, and was studied by infrared spectrometry. Dithiocarbamate chitosan having a sulfur content of 7.8% was used to extract metal ions in high yield from acc, neutral, and alkaline solutions.

ESR characterization of chitins and chitosans

Abstract Chitins and chitosans from crabs and shrimps as well as the chitosan-glucan complex from Aspergillus niger show an ESR singlet at 3387–3391 G and g values 2.00117-200354; this signal is altered by the action of oxygen from the atmosphere and from hydrogen peroxide, and by hot water.

Ligand-Exchange Chromatography of Amino Acids on Copper-Loaded Chitosan

Abstract Amino acids are retained on the copper form and on the amino copper form of chitosan, especially aspartic acid, glutamic acid, tryptophan, and cysteine. The best conditions for collection and for elution are in phosphate buffers at pH 7 and 12, respectively. No leakage of copper occurs; the amino acids are recovered as copper complexes with a ratio of 1:2 copper: amino acid. Several advantages of chitosan over the resin Chelex are pointed out; namely, absence of swelling, great copper capacity. hydrophilicity, and porous structure.