In order to obtain a better understanding of the interaction between acetonitrile and secondary plant metabolites, partition behavior of quercetin as a biomolecule model was investigated in systems composed of acetonitrile, salt [NaCl/KCl/NaBr/KBr], and water at different temperatures. The salting-out ability of the constituent anions and cations of these salts followed the well-known Hofmeister series and the effect of anion was more pronounced than the effect of cation. The Setschenow-type equation is applied to study the slating-out effects on the selected systems. The effect of temperature on the cloud-points as a function of acetonitrile mole fraction was studied in the temperature range of 293.15–328.15 K at 5 K intervals in aqueous solution of acetonitrile. The results showed that the concentration of acetonitrile in equilibrium with a certain concentration of salts significantly increased by the increasing of temperature. The free energy, enthalpy and entropy changes of clouding point (CP) was estimated by using a simple method and the driving force of formation of two phases may be the decrease of enthalpy. Investigation of the distribution behavior of quercetin showed that with increasing the salting-out ability of salt, IC50 values (the concentration necessary for 50% reduction of DPPH) of bottom phases, partition coefficient and recovery of quercetin significantly increased. The effect of temperature on the recovery of quercetin showed that the recovery decreased with the increasing of temperature in total systems under investigation and the decrease more significantly for bromide salts. The change in Gibbs energy (ΔGt), enthalpy (ΔHt) and entropy (ΔSt) of quercetin transfer process was calculated from the partition data. The results confirmed that under the same conditions with increasing the salting-out ability of salt, the calculated ΔGt values were more negative.

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