Calorimetric Study of Ligand Interactions with Protons and Metal Ions in the 100to 400 deg C Range

摘要

The thermodynamic quantities (log K, delta H, delta S, and delta Cp) associatedwith the interactions of protons and metal ions with ligands in aqueous solutions are strongly influenced by the structure and properties of water. These quantities, especially delta S and delta H, reflect the decrease in hydrogen bonding in water as temperature increases. The magnitude and the sign of delta S and delta H for proton interaction with amino acid and nucleotide anions are indicative of the interaction of charged species with water, the number of water molecules replaced upon complexation, and intra-molecular interactions. The interaction of l8-crown-6 with K(+), Sr(2+), and Ba(2+) produces delta S and delta H values of opposite sign to those expected from other neutral molecule-cation interactions. This result probably derives from the ability of l8-crown-6 to form a hydrophobic barrier to water molecules attracted by the metal cation. The resulting build-up of water molecules causes a more ordered system and the observed anomalous delta S and delta H values.