van der Waals Radii of Pt(II) and Pd(II) in Molecular Mechanics Models and an Analysis of Their Relevance to the Description of Axial M.H(-C), M.H(-N), M.S, and M.M (M = Pd(II) or Pt(II)) Interactions

Hydrocarbyl Ligand “Tuning” of the PtII/IV Redox Potential

The potentially tridentate macrocycle [2.1.1]-(2,6)-pyridinophane (L) enables the transient LPt(II)(CH(3))(+) to cleave the C-H bond of two molecules of C(6)F(5)H. The resulting product has two aryl groups on Pt but, in contrast to nonfluorinated analogue, varies in its location of the cleaved H, as is evident from the two products (HL(+))Pt(II)R(2) and (eta(3)-L)Pt(IV)H(R)(2)(+). At equilibrium, the related example where R = CH(3) is purely the Pt(IV) redox isomer, which with R = C(6)H(5) shows detectable populations of both isomers, and with R = C(6)F(5) is purely the pyridine-protonated (HL(+))Pt(II) redox isomer. All species show a hydrogen bond from the pyridinium proton to Pt(II). Consistent with the idea that electron-withdrawing R makes platinum(II) more resistant to oxidation (i.e., a proton on Pt), and thus less Brønsted basic, the (1)J(PtH) coupling constant falls in the series R = Me (90 Hz), R = C(6)H(5) (86 Hz), and R = C(6)F(5) (63 Hz).

Investigations into the interactions between DNA and conformationally constrained pyridylamineplatinum(II) analogues of AMD473

The syntheses of [PtCl(2)(amp)] (amp = 2-pyridylmethylamine) and enantiomerically pure [PtCl(2)(R-pea)] and [PtCl(2)(S-pea)] (pea = 1-(2-pyridyl)ethylamine) and the crystal structure of [PtCl(2)(R-pea)] are reported. The reactions of [PtCl(2)(amp)] and of the enantiomers of [PtCl(2)(pea)] with d(GpG) and with a 52-base-pair oligonucleotide were investigated. Each of the reactions with d(GpG) resulted in the formation of three platinated bifunctional d(GpG) species in a ratio of 1:2:1. These species were shown to be a pair of isomers, one of which exists as a pair of slowly interconverting rotamers that can be separated by HPLC but reequilibrate after 5 days at 37 degrees C. The pyridyl moieties of the pyridylalkylamine ligands are constrained to lie in the coordination plane, and as a consequence, the rotation about the Pt-N7 bond of the adjacent guanine is highly restricted. 2D NMR investigations were carried out on the isomer of [Ptd(GpG)(amp)] that did not form separable rotamers and identified it as the isomer having the pyridine adjacent to the 5'-guanine of the d(GpG). The reaction of each of the three [PtCl(2)(py-R)] complexes (py-R = amp or pea) with a 52-base-pair oligonucleotide resulted in the formation of the same three bifunctional d(GpG) adducts in approximately the same ratios as the reactions with d(GpG), indicating that negligible stereoselectivity results from interactions between the complexes and duplex DNA.

Synthesis and structural studies of binuclear platinum(II) complexes with a novel phosphorus-nitrogen-phosphorus ligand

The new pyridinediphosphinite ligand PONOP (1) was synthesized in one step from 2,6-pyridinedimethanol and diphenylchlorophosphane. Reaction of 1 with PtCl(2)(PhCN)(2) led to the neutral homobimetallic complex [Pt(2)Cl(4)(PONOP)(2)] (2), where the benzonitriles have been substituted by the phosphorus atoms of 1. The X-ray structure of 2 revealed a metallamacrocycle where the pyridines remained free. Addition of 2 equiv of [Cu(MeCN)(4)](BF(4)) to 2 led to CuCl and to the binuclear dicationic complex [Pt(2)Cl(2)(PONOP)(2)](BF(4))(2) (3), where chloro ligands have been substituted by pyridine groups. Conversely, reaction of 3 with chloride anions gave back complex 2. Solid-state (X-ray) and solution (NMR) studies indicated that after the transformation of 2 into 3, the platinum centers were brought much closer and the pyridinediphosphinite ligand was stiffened. The methylene NMR protons of 3 were strongly deshielded, and the corresponding proton-phosphorus coupling constants followed a Karplus-type relationship.

Examination of the effects of oxidation and ring closure on the cytotoxicities of the platinum complexes of N-(2-hydroxyethyl)ethane-1,2-diamine and ethane-1,2-diamine-N,N'-diacetic acid

The crystal structures, electrochemical properties and cytotoxicities of platinum(II) and platinum(IV) complexes of the multidentate ligands N-(2-hydroxyethyl)ethane-1,2-diamine (NNOH) and ethane-1,2-diamine-N,N'-diacetic acid (H(2)enda) are reported. In the platinum(II) state the NNOH and H(2)enda ligands act as bidentate ligands, coordinating through the two amine groups with the hydroxyethyl and carboxylate groups remaining uncoordinated. Oxidation with hydrogen peroxide followed by refluxing yields the ring closed Pt(IV) complexes in which the NNOH and H(2)enda ligands are deprotonated and coordinate via the two amine groups and either the deprotonated alcohol group in the case of NNO or both carboxylato groups in the case of enda. The platinum(IV) complex of NNO is 2- to 5-fold more active against a panel of cisplatin sensitive and resistant human tumour cell lines than is the platinum(II) complex, whereas in the case of enda, the reverse is true. Ring closure to occupy both axial sites apparently leads to deactivation of platinum(IV) complexes, but a single closure does not necessarily do so.

Modeling platinum group metal complexes in aqueous solution

We construct force fields suited for the study of three platinum group metals (PGM) as chloranions in aqueous solution from quantum chemical computations and report experimental data. Density functional theory (DFT) using the local density approximation (LDA), as well as extended basis sets that incorporate relativistic corrections for the transition metal atoms, has been used to obtain equilibrium geometries, harmonic vibrational frequencies, and atomic charges for the complexes. We found that DFT calculations of [PtCl(6)](2-).3H(2)O, [PdCl(4)](2-).2H(2)O, and [RhCl(6)](3-).3H(2)O water clusters compared well with molecular mechanics (MM) calculations using the specific force field developed here. The force field performed equally well in condensed phase simulations. A 500 ps molecular dynamics (MD) simulation of [PtCl(6)](2-) in water was used to study the structure of the solvation shell around the anion. The resulting data were compared to an experimental radial distribution function derived from X-ray diffraction experiments. We found the calculated pair correlation functions (PCF) for hexachloroplatinate to be in good agreement with experiment and were able to use the simulation results to identify and resolve two water-anion peaks in the experimental spectrum.