No abstract

The phase compositions in liquid-liquid equilibria of aqueous two-phase systems (ATPS) composed of the poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymer L35 and various salt solutions (sodium carbonate, sodium succinate, sodium acetate, ammonium citrate, and ammonium sulfate) at several temperatures, (283.15, 298.15, and 313.15) K, are presented. The influence of temperature in the binodal position was pronounced for almost all of the ATPS's, with the phase-separation process being endothermic. Additionally, the slopes of the tie-lines (STL) tended to increase with increasing temperature. The capability of the various salts to induce formation of the biphasic system was evaluated and followed the order sodium carbonate > ammonium sulfate > sodium succinate > ammonium citrate > sodium acetate. The consistencies of the tie-line experimental compositions were confirmed by applying the Othmer-Tobias correlation, with excellent results, as shown by the regression coefficients acquired. The liquid-liquid equilibrium data of ternary systems have been correlated using the nonrandom twoliquid (NRTL) model for the activity coefficient. The results were considered very satisfactory with global root-mean-square deviations as low as 1.49 %.

Bovine serum albumin (BSA)/curcumin binding and dye photodegradation stability were evaluated. BSA/curcumin complex showed 1:1 stoichiometry, but the thermodynamic binding parameters depended on the technique used and BSA conformation. The binding constant was of the order of 10L·mol by fluorescence and microcalorimetric, and 10 and 10L·mol by surface plasmon resonance (steady-state equilibrium and kinetic experiments, respectively). For native BSA/curcumin, fluorescence indicated an enthalpic and entropic driven process based on the standard enthalpy change (ΔH=-8.67kJ·mol), while microcalorimetry showed an entropic driven binding process (ΔH=29.11kJ·mol). For the unfolded BSA/curcumin complex, it was found thatp ΔH=-16.12kJ·mol and ΔH=-42.63kJ·mol. BSA (mainly native) increased the curcumin photodegradation stability. This work proved the importance of using different techniques to characterize the protein-ligand binding.

Phase diagrams of aqueous two-phase systems (ATPS) composed of F68 triblock copolymer + salt + water were constructed at different temperatures. The ATPS composed of F68 + (NH 4 ) 3 C 6 H 5 O 7 + H 2 O was investigated at (278.15, 288.15, and 298.15) K, and the F68