title: The influence of chitosans with defined degrees of acetylation on the thermodynamic data for copper coordination.
abstract: The interaction of copper with three different chitosans having degrees of deacetylation of 77.5, 81.5, and 86.1%, named C, A, and F, respectively, was followed by the batch method at 298+/-1 K and the values obtained were fitted to a modified Langmuir equation. These interactions were also obtained by calorimetric titration. Experimentally, 50.0 mg of each chitosan was suspended in doubly distilled water at 298.15+/-0.02 K under mechanical turbine stirring. The titration was performed by adding increments of 10 microl of a 0.10 mol dm3 Cu(NO3)2 aqueous solution and the calorimetric isotherms obtained were adjusted to a modified Langmuir equation. From the net thermal effects K and DeltaH values were calculated, also permitting the acquisition of other thermodynamic data for the chitosan-copper interaction at the solid/liquid interface. The exothermic enthalpic values of -45.65+/-1.97, -49.91+/-1.57, and -48.64+/-0.82 kJ mol(-1), for chitosans C, A, and F, respectively, reflect the degree of deacetylation. The spontaneity of the systems is shown by the negative DeltaG values, -36.1+/-0.2, 36.8+/-0.1, and -38.1+/-0.3 kJ mol(-1) for the same sequence of chitosans. The negative entropic values, -34, -44, and -35 J mol(-1) K(-1), are in agreement with an ordering of solvent as the complexation occurred. The intensity of the thermal effects and the thermodynamic data obtained from the copper/chitosan interactions can be associated with the ability of these biopolymers to extract copper from aqueous solutions.
authors.affiliation: Universidade de Fortaleza, CCT, Avenida Washington Soares 1321, Edson Queiroz, 60811-341 Fortaleza, Ceará, Brazil.
authors.forename: Oyrton A C
authors.initials: OA
authors.lastname: Monteiro
authors.forename: Claudio
authors.initials: C
authors.lastname: Airoldi
mesh_terms: D000107:Acetylation; D002151:Calorimetry; D048271:Chitosan / Q000737:chemistry*; D003300:Copper / Q000737:chemistry*; D012996:Solutions; D013816:Thermodynamics; D017186:Titrimetry
chemical_list: D012996:Solutions; D003300:Copper; D048271:Chitosan