Some thermodynamic data on copper-chitin and copper-chitosan biopolymer interactions

Chitin and chitosan are good removers of cations from aqueous solution and wastewater. The interactive effect of cation with both biopolymers in aqueous medium was studied by the batch method at 298 +/- 1 K. The results were fitted to the modified Langmuir equation. The same adsorption was followed by calorimetric titration. In this process, 50.0 mg of each polymer was suspended in 19.0 cm(3) of bidistilled water at 298.15 +/- 0.02 K, maintained under mechanical turbine stirring. The titration was performed by adding increments of 10 mu L of 0.10 mol dm(-3) Cu(NO3)(2) aqueous solution to the system. The resulting isotherm was also adjusted to a modified Langmuir equation. From the thermal effects K and Delta H values were determined, enabling the calculation of Delta G and Delta S for the interaction of copper cations with chitin and chitosan, giving the enthalpic values of -19.85 +/- 0.34 and -41.27 +/- 1.57 kJ mol(-1), respectively. The spontaneity of this interaction is shown from Delta G values of -35.9 +/- 0.1 and -36.8 +/- 0.1 kJ mol(-1), which are followed by Delta S values of +54 and of -15 J mol(-1) K-1, respectively. The complexation is probably associated with the lack of order of the chitin polymeric chain or with the freedom of water molecules initially bonded to cations. The copper ion is coordinated to the pendant groups of the polymeric chain to form stable complexes. (C) 1999 Academic Press.212221221

The influence of chitosans with defined degrees of acetylation on the thermodynamic data for copper coordination

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 mul of a 0.10 mol dm(3) 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. (C) 2004 Elsevier Inc. All rights reserved.2821323

Copper adsorption and enzyme immobilization on organosilane-glutaraldehyde hybrids as support

New hybrids SiglutX (X=1 to 3) were synthesized from silylant agents: (CH3O)(3)Si-R-NH2 [R = -(CH2)(2)-, -(CH2)(2)NH(CH2)(2)- and -(CH2)(2)NH(CH2)(2)NH(CH2)(2)-]. The primary amine groups crosslinked with linear glutaraldehyde in two stages: crosslinking and sol-gel processes. The resulting polymers are amorphous, insoluble in organic as well as in acidic or alkaline aqueous media. The hybrids have a large capacity for copper adsorption with very similar kinetic behaviors, defining a plateau after I h. The adsorption increases with the increase of nitrogen atoms attached to the organic chain length of the precursor silylant, being 0.25 0.01, 0.37+/-0.01 and 0.50+/-0.01 mmol g(-1) for X = I to 3, respectively. These hybrids also presented a good ability for immobilizing enzymes with distinguishable affinities. The amount of catalase and urease immobilization increased significantly from Siglut1 to Siglut2, while the amount of glucose oxidase and invertase anchored decreased from Siglut1 to Siglut2. Undefined amounts of enzyme immobilized for Siglut3 could be related to possible difficulties arising from its degradation during the interactive process.5041671616