Combined Effects of Electrostatic and π–π Stacking Interactions: Selective Binding of Nucleotides and Aromatic Carboxylates by Platinum(II)–Aromatic Ligand Complexes

Autor: Yajima, Tatsuo, Maccarrone, Giuseppe, Takani, Masako, Contino, Annalinda, Arena, Giuseppe, Takamido, Reiko, Hanaki, Mieko, Funahashi, Yasuhiro, Odani, Akira, Yamauchi, Osamu
Zdroj: Chemistry - A European Journal; July 2003, Vol. 9 Issue: 14 p3341-3352, 12p
Abstrakt: Adduct formations of PtII 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 PtII 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 H2O was revealed to be bound through the π–π 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 ΔH ° 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.
Databáze: Supplemental Index
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