Pressure and concentration dependent formation of oligomers of tetrakis(p-methylphenylisocyanide)rhodium(I)

The optical absorption of [Rh(tol)₄]PF₆ (tol p-methylphenylisocyanide) dissolved in acetonitrile has been measured as function of concentration (10⁻⁴ <= c(0) <= 1.5 X 10⁻² mol/l) and of applied pressure (0.1 <= p <= 400 MPa) at room temperature. Analysis of the spectra indicates the formation of oligomers [Rh(tol)₄]n“⁺, n = 2, 3 with increase of both the concentration and the pressure, respectively. Application of pressure increases the dimer-monomer equilibrium constant and yields a blue shift (ca.0.3 cm⁻¹/MPa) of the monomer absorption but a red shift ( ca. -0.6 cm⁻¹/MPa) of the dimer absorption

Properties of electronic spectra of antitumor-active dichlorobis(cycloalkylamine) platin(II) compounds

Complexes of PtCl₂(RNH₂)₂, with RNH, = cyclopropylamine, cyclobutylamine, cyclopentylamine, cyclohexylamine, cycloheptylamine and cyclooctylamine, are investigated as powder samples and in solution applying different spectroscopic methods (absorption, excitation, emission, emission lifetime). It is concluded that the involved low energy states are mainly of metal d character. All these complexes exhibit a similar spectroscopic behavior despite the strongly different properties of the PtCl₂(RNH₂)₂ compounds in tests against a cancer cell line. Moreover, crystallographic unit cells of the compounds are determined from powder diffraction measurements

Molecular mechanical and quantum chemical study on the species involved in the hydrolysis of cis-diaminedichloro-platinum(II) and substituted bis(ethylenediamine)dichloro-platinum(II) complexes. Part I. Reactans and products

Cisplatin and its substituted ethylenediamine derivatives, cis-PtCl₂(R₂en) (en = ethylenediamine, R = H, Ph (phenyl), 2-, 3- and 4-PhOH) have been studied with respect to the first step of their hydrolysis reaction. The geometry of the reactants and products was determined by molecular mechanics (MM). The MM optimized structures were used to calculate by the extended Huckel method the charge distribution and relative electronic energies. The MM and EH calculations were carried out with different ligand conformations. Due to increased non-bonded repulsion, with increasing ligand bulkiness, the square planar arrangement is the preferred geometry also by the MM results. This additlonal (to the electronic) stabilization of the square planar arrangement around Pt(II) is unfavorable for the aquation process. The thermodynamic stabilities correlate with the rate of hydrolysis of meso-, (+)- and (-)-[1,2-bis(2hydroxyphenyl)ethylenediamine]dichloroplatinum(II) (3-PtCI₂). The slower rate of hydrolysis of the meso diastereoisomer as compared with that of the d, I species of 3-PtCI₂ is explained by the presence of a 5th Pt-0 contact in the meso diastereoisomer which hinders the entrance of the water molecule and makes the hydrolysis slower

Molecular mechanical and quantum chemical study of the species involved in the hydrolysis of cis-diaminedichloroplatinum(II) and substituted bis(ethylenediamine)dichloroplatinum(II) complexes II, simulated transition states

Cis-diamminedichloroplatinum(II) (cisplatin) and its substituted ethylenediamine derivs. cis-PtCl2(R2en) (en = ethylenediamine, R = H, Ph, 2-, 3-, and 4-PhOH) were investigated with respect to the possible structures of the hypothetical transition state complexes (TSC) of the hydrolytic SN2 reaction in which 1 Cl is replaced by H2O. TSCs with trigonal bipyramid (TBP) and square pyramid (SP) geometry (coordination no. 5), were studied by mol. mechanics (MM) and extended Huckel (EH) methods. The EH and MM energies as well as the no. of occurrence (entropy factor) for the cisplatinum compd. point to a preferred TBP TSC geometry with NH3 and Cl in axial positions. However, for en and substituted en compds., TSCs with SP geometries (CI in apical position) are preferred. The calcd. EH and MM energies of the TBP and SP structures do not differ significantly and TBP .tautm. SP interconversions may play an essential role in TSC formation. To improve the discrimination, the MM-optimized geometries were treated in terms of displacement coordinates for D3h (TBP) and C4v (SP) by calcg. the total distortion vectors (DV). DV identified once again the TBP with NH3 and Cl in axial position as the least-distorted conformer, but it also revealed the combinations of displacement coordinates which shape the TSC geometry

Dichlorobis(cycloalkylamine)platinum(II) complexes. Structure activity relationship on the human MDA-MB-231 breast cancer cell line

The syntheses of dichlorobis(cycloalkylamine)platinum(II) complexes with cis and trans cycloalkylamine ligands [cis-PtCl2(C3H5NH2)2 to cis-PtCl2(C8H15NH2)2 and trans-PtCl2(C7H13NH2)2 and trans-PtCl2(C8H15NH2)2 are described. The distinction between cis and trans isomers was achieved by 1H-NMR spectroscopy. The antitumor activity was detd. on the cell proliferation of the human MDA-MB-231 breast cancer cell line during long-term drug exposure. The complexes with small cycloalkylamine ligands were inferior, those with large cycloalkylamine ligands were comparable or superior to cisplatin. All cycloalkylamine ligands were inactive. IR spectroscopic studies showed that the size of the cycloalkylamine ring does not lead to significant differences in the Pt-Cl binding strength. Therefore it is assumed that the markedly stronger antitumor activity of the higher homologs is not the result of a faster reaction with bionucleophiles such as DNA. A possible explanation of the high activity of some of the isomers is the strong lipophilicity of the complexes. This assumption was confirmed by toxicity tests against confluent cultures

High Field Cross Polarization NMR from Laser Polarized Xenon to a Polymer Surface

Surface-selective characterization of materials with NMR has been quite useful in the few cases where sufficient sensitivity and selectivity have been achieved.1 In this communication we report the use of laser-polarized xenon as the source of magnetization for a high-field cross polarization experiment, obtaining surfaceselective magnetization transfer. Gas-phase xenon with nuclear spin polarization several orders of magnitude higher than thermal Boltzmann levels in a high magnetic field can be produced using optically pumped rubidium vapor according to the pioneering work of Happer and co-workers.1 2 The angular momentum of circularly polarized laser light is transferred, via the rubidium electron spins, to the (slowly relaxing) xenon nuclear spin system. We have previously used xenon, with a large polarization enhancement («10 000), as a probe of low surface area materials.3 More recently, using thermal mixing in low field,4 polarization has been transferred between xenon isotopes5 and from xenon to 13C02 occluded in solid xenon.6 The approach of low-field mixing has the disadvantages of nonselective magnetization transfer, typically very short spin-lattice relaxation times in low field, and the necessity of rapid field switching or mechanical transport of the sample to high field for detection. High-field cross polarization methods should be advantageous in allowing nuclear spin selectivity in the transfer step as well as circumventing relaxation and transport problems. In the present work, contact between laser-polarized xenon and surface spins was achieved in high field by Hartmann-Hahn matching of the energy levels in the rotating frame with direct NMR detection of the polarized species.7-8 Proton spins are observed due to their abundance at the surface and the dominant dipolar interactions with adsorbed xenon