Hydrophobic Interaction of mer-Tris(α-amino acidato)cobalt(III) with Tetrabutylammonium Ion

An interaction of NaBr, NH4Br, Me4NBr, Et4NBr, Pr4NBr, Bu4NBr, and NaBPh4 with mer-(+)-tris(L-alaninato)cobalt(III) (mer-(+)-[Co(L-ala)3]) was examined by estimating the standard enthalpy (ΔHtr°) and entropy of transfer (ΔStr°) of mer-(+)-[Co(L-ala)3] from water to the salt solutions on the basis of the temperature dependence of solubility. A difference in correlation between ΔHtr° and TΔStr° demonstrated that while NaBr and NH4NBr increase the solubility of mer-(+)-[Co(L-ala)3] by hydrophilic interaction, Pr4NBr, Bu4NBr, and NaBPh4 increase the solubility of mer-(+)-[Co(L-ala)3] by hydrophobic interaction. On the basis of this finding, ΔHtr° and TΔStr° of the transfer from water to aqueous Bu4NBr solution for the mer-tris(aniono)cobalt(III) of glycine (glyH), L-alanine (alaH), L-serine (serH), DL-2-aminobutylic acid (abaH), DL-norvaline (nvalH), L-valine (valH), and L-leucine (leuH) led to the conclusion that hydrophobicity of the amino acids increases in the order of glyH < serH < alaH < abaH < nvalH < ...