Application of pyridine-modified chitosan derivative for simultaneous adsorption of Cu(II) and oxyanions of Cr(VI) from aqueous solution.

The bioadsorbent C1, which is a chitosan derivative prepared in a one-step synthesis, was successfully used to adsorb Cr(VI) and Cu(II) simultaneously. Here, for the first time the simultaneous adsorption of a cation and an anion was modeled using the Corsel model for kinetics and the Real Adsorbed Solution Theory model for equilibrium data. Batch studies of the adsorption of Cu(II) and Cr(VI) in single and binary aqueous solutions were performed as a function of initial solute concentration, contact time, and solution pH. The maximum adsorption capacities of C1 in single and binary aqueous solutions were 1.84 and 1.13 mmol g-1 for Cu(II) and 3.86 and 0.98 mmol g-1 for Cr(VI), respectively. The reuse of C1 was investigated, with Cu(II) ions being almost completely desorbed and fully re-adsorbed. For Cr(VI), the desorption was incomplete resulting in a lower re-adsorption. Energy-dispersive X-ray spectroscopy was used for mapping the distributions of Cr(VI) and Cu(II) adsorbed on the C1 surface in single and binary adsorption systems. Isothermal titration calorimetry experiments were performed for Cr(VI) and Cu(II) adsorption in single solutions. The thermodynamic parameters of adsorption showed that the adsorption of both metal ions was enthalpically driven, but entropically unfavorable.

Thermodynamics of Aggregation between the Cationic Surfactant and Polymer Based on Biodegradable Poly(vinyl Alcohol).

The formation of aggregates between carboxylated (PVCOOH) or neutral hydrolyzed (PVOH) poly(vinyl alcohol) and hexadecylpyridinium chloride (C16PyCl) was examined by conductimetry, turbidimetry, and isothermal titration calorimetry (ITC) in the presence of different NaCl concentrations. The interaction between the polymers and C16PyCl in pure water showed a critical aggregation concentration (cac = 0.8 mmol L-1) only for the neutral polymer. PVCOOH interacted with the surfactant through electrostatic attraction, forming macroscopic aggregates. Integral enthalpy changes for aggregate formation (ΔHagg) obtained from ITC curves varied from -0.61 (for the PVOH system in pure water) to -4.14 kJ mol-1 (for PVOH in the presence of 10.0 mmol L-1 NaCl), indicating that the formation of the aggregates was enthalpically favored. However, hydrophobic interactions drove the process for low surfactant concentration for both polymers. Saturation concentrations (C2) obtained from conductimetry were smaller than those from ITC, revealing that the binding of C16PyCl on the chain of the polymers at higher surfactant concentrations shows the same electric properties as that of free micelles on the solution. Increase of the ionic strength favored the aggregation and decreased the complexity of the ITC curves, suggesting that the reorganization of the surfactant monomers on the polymeric chain with the increase in their concentration was suppressed.

The kinetics of formation of resveratrol-ß-cyclodextrin-NH2 and resveratrol analog-ß-cyclodextrin-NH2 supramolecular complexes.

The determination of the kinetics of inclusion processes is significant for the application of inclusion complexes as carriers for bioactive molecules. We determined the kinetic parameters of inclusion between modified ß-cyclodextrin (ß-CD-NH2) and the polyphenols resveratrol (RES) and its structural analog (RESAn1), using the real-time analysis of surface plasmon resonance. The association and dissociation rate constants (ka and kd) showed that RESAn1 inclusion and its dissociation from ß-CD-NH2 were faster than a similar process for RES ( [Formula: see text]  = 3.10∙104 ± 0.14 M-1s-1, [Formula: see text] =1.87∙103 ± 0.11 M-1s-1; [Formula: see text] =0.39 ± 0.02 s-1, [Formula: see text] =0.30 ± 0.02 s-1, at 25 °C). The activated complex formation was also affected by the structural differences between the polyphenols, as showed by the activation energies of the association step ( [Formula: see text] 14.81 ± 0.64 kJ∙mol-1, [Formula: see text] -15.01 ± 0.75 to 82.35 ± 4.47 kJ∙mol-1). These effects of polyphenol structural differences are due to the desolvation process of interacting molecules. These results elucidate the role of small group to the dynamics of the molecular inclusion of ß-CD.

Dynamics and energetics of bovine lactoferrin and phenylmethane dyes interaction followed by surface plasmon resonance.

Although toxic and dangerous, Phenylmethane (PhM) dyes have a variety of medicinal functions. To optimize the use of these dyes, it is essential to understand their interaction mechanism with proteins. Through surface plasmon resonance, we investigated the kinetics and thermodynamics of interaction between bovine lactoferrin (BLF) and PhM dyes at pH 7.4, which allowed elucidate the effect of the dyes' functional groups on the binding process. Negative ΔG° revealed that at thermodynamic equilibrium the formed [BLF-PhM]° complex was more stable than the free BLF and PhM molecules. The increase in the number of methyl groups in the PhM structure led to an increase in the rates of association (ka) and dissociation (kd) and the binding constant (Kb). A similar effect was observed when comparing methyl violet B (MVB) and methyl violet 6 B (MV6B), in which the charged MV6B structure promoted an increase in the ka, kd, and Kb values. By contrast, an increase in the number of phenyl groups (2-3 rings) led to a decrease in the Kb values. The [BLF-PhM]° formation was entropically driven, indicating that hydrophobic interactions are critical for stabilizing these complexes These results are beneficial for understanding the molecular dynamics of protein-dye interactions.