Combined Effects of Electrostatic and π–π 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.

Measuring Self‐Association of Pt Complexes by 195Pt NMR

“…We consider that the deshielding may be the consequence of a small charge delocalization from the Pt atom due to the action of the large dipole of the Pt-halogen moiety of the partner molecule in aggregate located directly above (see Figure 2). Similar deshielding of 195 Pt nucleus was reported previously for stacking of Pt-containing heterocyclic compounds with nucleotides that were also explained by charge delocalization in Pt atom [8] . Another possibility is the presence of metallophilic interactions corresponding to 'short' Pt...Pt distance of typically 3.45 Å.…”

π–π Stacking assisted binding of aromatic amino acids by copper(ii)–aromatic diimine complexes. Effects of ring substituents on ternary complex stability

“…11,12 While 2N1O-donor tripod-like ligands containing one pyridine and one phenol ring and a pendent indole ring were found to undergo only weak intramolecular indole-pyridine interactions in CH 3 CN, their Pd(II) complexes exhibited much stronger interactions as evidenced by the 1 H NMR upfield shifts due to the ring current effect and the methylene proton signals showing a fixed side chain conformation. 13 The adduct formation between planar Pt(II) complexes, Pt(DA)(L') (L' = ethylenediamine or amino acids), and mononucleotides was revealed to be enthalpically driven mainly through stacking interactions by the relevant thermodynamic parameters 14 and decrease the electron density of the Pt(II) center as seen from and the downfield shift of the 195 Pt NMR signal. 15 The adduct stability sequence due to DA,3,4,7,10-phenanthroline > 1,10-phenanthroline ≈ 5-nitro-1,10-phenanthroline, reflected the effects of the DA substituents on stacking.…”

Studies of lysozyme binding to histamine as a ligand for hydrophobic charge induction chromatography

“…22 In brief, drained Sepharose gel (2.0 g), sodium hydroxide (0.8 mol/L, 3.0 mL), ECH (1.0 mL), and dimethyl sulfoxide (4.0 mL) were mixed in a 50-mL Erlenmeyer flask and incubated in a water bath with an orbital shaker at 40 C for 3 h. ECH-activated Sepharose was collected by draining and washed with excess distilled water until no ECH was detected in the washing waste by sodium thiosulfate. 23 After 0.5 g of the activated gel was suspended in 3.0 mL of 1.3 mol/L sodium thiosulfate at room temperature for 1 h, the mixture was neutralized by titration with 0.1 mol/L HCl and the volume of HCl used was recorded.…”