EFFECT OF HYDROPHOBIC AND HYDROPHILIC INTERACTIONS ON THE STABILITY OF DIASTEREOISOMERS OF DELTA-[RU(S-AM)(BPY)2]+ AND LAMBDA-[RU(S-AM)(BPY)2]+ COMPLEXES (AM = ALA, PHG, LEU, PHE OR TYR LIGAND) IN AQUEOUS-SOLUTIONS

The equilibrium constant (K) of photochemical inversion between DELTA- and LAMBDA-[Ru(S-am)(bpy)2]+ (bpy=2,2'-bipyridine (bpy); S-am=(S)-alaninato (S-Ala), (S)-phenylglycinato (S-Phg), (S)-leucinato (S-Leu), (S)-phenyl-alaninato (S-Phe) or (S)-tyrosinato (S-Tyr) ligand) was obtained in H2O, D2O, CH3OH and CH3CN-H2O (1:1 in molar ratio) solutions at temperatures of 0 to 100-degrees-C, and DELTAH-degrees and DELTAS-degrees were estimated. The hydrophilic solvation favored the DELTA isomer in water, appearing on the enthalpy difference, and the hydrophobic solvation preferred the LAMBDA isomer, controlling the entropy difference. These opposite effects dominated the stability of the two isomers of the complex containing the S-Leu, S-Phe or S-Tyr ligand in water. The results suggested the importance of intramolecular hydrophobic bonding. The photochemical inversion hardly occurred in pure acetonitrile.