title: Combined effects of electrostatic and pi-pi stacking interactions: selective binding of nucleotides and aromatic carboxylates by platinum(II)-aromatic ligand complexes.
abstract: Adduct formations of Pt(II) complexes containing an aromatic diimine (DA) and an L-amino acid (A) with an aromatic carboxylate (AR) or a mononucleotide (NMP) has been studied by synthetic, structural, spectroscopic, and calorimetric methods. Several adducts between Pt(II) complexes, [Pt(DA)(L-A)] (charges are omitted; DA=2,2'-bipyrimidine (bpm); A=L-arginine (L-Arg), L-alaninate (L-Ala), and AR (=indole-3-acetate (IA), gentisate (GA)) or GMP were isolated as crystals and structurally characterized by the X-ray diffraction method. GMP in [Pt(bpm)(Arg)](GMP).5 H(2)O was revealed to be bound through the pi-pi stacking and guanidinium-phosphate hydrogen bonds. The [Pt(DA)(A)]-AR and -NMP systems in aqueous solution exhibited NMR upfield shifts of the aromatic ring proton signals due to stacking. The stability constants (K) for the adducts were determined by absorption and NMR spectra and calorimetric titrations. The log K values were found to be in the range 1.40-2.29 for AR and 1.8-3.3 for NMP, the order for NMP being GMP>AMP>CMP>UMP. The DeltaH degrees values were negative for all the systems studied, and the values for AR (=IA and GA) were more negative than those for NMP, indicating that ARs are stronger electron donors than NMPs. Comparison of the log K values for [Pt(bpm)(L-Arg)] and [Pt(bpm)(L-Ala)] (Ala=alaninate) indicated that the Arg moiety further stabilized the adducts by the guanidinium-carboxylate or -phosphate hydrogen bonds. The combined effects of weak interactions on the stability of the adducts in solution are discussed on the basis of the thermodynamic parameters and solid state structures.
authors.affiliation: Faculty of Engineering, Kansai University, Suita, Osaka 564-8680, Japan.
authors.forename: Tatsuo
authors.initials: T
authors.lastname: Yajima
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Maccarrone
authors.forename: Masako
authors.initials: M
authors.lastname: Takani
authors.forename: Annalinda
authors.initials: A
authors.lastname: Contino
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Arena
authors.forename: Reiko
authors.initials: R
authors.lastname: Takamido
authors.forename: Mieko
authors.initials: M
authors.lastname: Hanaki
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Funahashi
authors.forename: Akira
authors.initials: A
authors.lastname: Odani
authors.forename: Osamu
authors.initials: O
authors.lastname: Yamauchi