Studies on Bioactive Metal Complex in Dynamic Processes

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Noncovalent interactions are important for molecular recognition, specificity of reactions, and biological activity. We have been studying ternary Cu (II) complex formation involving various weak interactions between two functional groups of coordinated ligands such as aromatic rings and charged groups.With a view to constructing molecular adducts and elucidating the factor affecting self-assembling, we studied weak intermolecular interactions between a small biomolecule as a guest and a planar Pt (L) (A) complex involving a coordinated aromatic ring (L) and a basic amino acid (A) by the thermodynamic, X-ray diffraction, and spectroscopic methods. The features of the adduct through aromatic ring stacking in a system involving a metal ion, such as Pt (phen) (en) ・・・indoleacetate, are (1) unusually high stability constants due to dominant -ΔH゜and (2) appearance of the charge transfer band and (3) Pt-195 NMR downfield shifts consistently proportional to the -ΔH゜ values. Some additional polar interactions have been indicated in the systems containing [Pt (L) (A)] and nucleotide monophosphates, DNA, or aromatic carboxylates as guests by further enhancement of ΔH゜, adduct formation constant K, and Pt-195 KMR shifts. The solid state structure of [Pt (phen) (en) ・・・indoleacetate]・ClOィイD24ィエD2, [Pt (2, 2'-bipyrimidine) (glycine and L-alanine)・・・indoleacetate] revealed aromatic ring stacking and intramolecular hydrogen bonding. Pt (2, 2'-bypyrimidine) (L-arginine) ・・・indoleacetate showed hydrogen bonding involving arginine guanidinium group. These findings clearly show that the metal ion regulates the interaction with the coordinating ligand to stabilizes the intermolecular interactions. Calorimetric results revealed these noncovalent interactions and were more informative.