QSPR Analysis of Solvent Effect on Selectivity of 18-Crown-6 between Nd3+ and Eu3+ Ions: a Monte Carlo Simulation Study

Abstract

We have investigated the solvent effects on <TEX>$\Delta log\;K_s $</TEX>(the difference of stability constant of binding) and the different free energies of binding of <TEX>$Nd^{3+}$</TEX> and <TEX>$Eu^{3+}$</TEX> ions to 18-crown-6, i.e., the selectivity of <TEX>$Nd^{3+}$</TEX> and <TEX>$Eu^{3+}$</TEX> ions to 18-crown-6 using a Monte Carlo simulation of statistical perturbation theory (SPT) in diverse solvents. The stability constant (<TEX>$\Delta log\;K_s $</TEX>) of binding of <TEX>$Nd^{3+}$</TEX> and <TEX>$Eu^{3+}$</TEX> ions to 18-crown-6, in <TEX>$CH_3OH$</TEX> was calculated in this study as -1.06 agrees well with the different experimental results of -0.44~-0.6, respectively. We have reported here the quantitative solvent-polarity relationships (QSPR) studied on the solvent effects the relative free energies of binding of <TEX>$Nd^{3+}$</TEX> and <TEX>$Eu^{3+}$</TEX> ions to 18-crown-6. From the calculated coefficients of QSPR, we have noted that solvent polarity (ET) and Kamlet -Tafts solvatochromic parameters (b ) dominate the differences in relative solvation Gibbs free energies of <TEX>$Nd^{3+}$</TEX> and <TEX>$Eu^{3+}$</TEX> ions but basicity (Bj) dominates the negative values in differences in the stability constant (<TEX>$\Delta log\;K_s $</TEX>) as well as the relative free energies of binding of <TEX>$Nd^{3+}$</TEX> and <TEX>$Eu^{3+}$</TEX> ions to 18-crown-6 and acidity (Aj) dominates the positive values in differences in the stability constant (<TEX>$\Delta log\;K_s $</TEX>) as well as the relative free energies of binding of <TEX>$Nd^{3+}$</TEX> and <TEX>$Eu^{3+}$</TEX> ions to 18-crown-6.