Building up PtII -Thiosemicarbazone-Lysine-sC18 Conjugates

Three chiral tridentate N^N^S coordinating pyridine-carbaldehyde (S)-N4-(α-methylbenzyl)thiosemicarbazones (HTSCmB) were synthesised along with lysine-modified derivatives. One of them was selected and covalently conjugated to the cell-penetrating peptide sC18 by solid-phase peptide synthesis. The HTSCmB model ligands, the HTSCLp derivatives and the peptide conjugate rapidly and quantitatively form very stable PtII chlorido complexes [Pt(TSC)Cl] when treated with K2 PtCl4 in solution. The Pt(CN) derivatives were obtained from one TSCmB model complex and the peptide conjugate complex through Cl- →CN- exchange. Ligands and complexes were characterised by NMR, IR spectroscopy, HR-ESI-MS and single-crystal XRD. Intriguingly, no decrease in cell viability was observed when testing the biological activity of the lysine-tagged HdpyTSCLp, its sC18 conjugate HdpyTSCL-sC18 or the PtCl and Pt(CN) conjugate complexes in three different cell lines. Thus, given the facile and effective preparation of such Pt-TSC-peptide conjugates, these systems might pave the way for future use in late-stage labelling with Pt radionuclides and application in nuclear medicine.

Vibrational Spectroscopy of Reduced Re(I) Complexes of 1,10-Phenanthroline and Substituted Analogues

IR spectroscopy in concert with DFT calculations and resonance Raman spectroelectrochemistry has been used to identify the molecular orbital nature of the singly occupied molecular orbital (SOMO) in reduced [Re(CO)(3)Cl(L)] and [Re(CO)(3)(4-Mepy)(L)](+) complexes, where L = 1,10-phenanthroline and its 4,7-diphenyl- and 3,4,7,8-tetramethyl-substituted analogues. The SOMO of each reduced species considered was found to be of b(1) symmetry, rather than the close lying orbital of a(2) symmetry (within a C(2)(v)() symmetry description of the phenanthroline moiety). This was deduced in a number of ways. First, the average carbonyl band force constants (Deltak(av) = k(av){reduced complex} - k(av){parent complex}) range from -57 to -41 N m(-1) for the series of compounds studied. The value of Deltak(av) relates to the extent of orbital overlap between the ligand MO and the metal dpi MO. These values are consistent with population of a b(1) MO because the wave function amplitude at the chelating nitrogens for this MO is significantly greater than that for a(2) MO. Second, calculations on singly reduced [Re(CO)(3)(4-Mepy)(phen)](+) and [Re(CO)(3)(4-Mepy)(tem)](+) predict population of a b(2) SOMO. The spectra predicted for these species are in close agreement with the vibrational spectroscopic data; for the IR data the shifts in the CO bands are predicted to 6 cm(-1) and the mean absolute deviation between calculated and measured Raman bands was found to be 10 cm(-1).

Participation of co-ligands in electronic transitions of platinum(II) diazabutadiene complexes

The low-lying electronic transitions and photochemical reactions of a series of [((i)Pr-DAB)Pt(R)(2)] (where the co-ligand R = CH(3), CD(3), adme, neop, neoSi, C(triple bond)C(t)Bu, C(triple bond)CPh, Ph, Mes) compounds were studied using both experimental (electronic absorption and resonance Raman spectroscopy) and theoretical (density functional theory, DFT) techniques. The high-lying filled orbitals were revealed to have a significant co-ligand contribution in the case of alkyl complexes, while this contribution is predominant for the complexes with unsaturated co-ligands. Because the electronic transition removes electron density from the sigma(Pt-C) bond in the former complexes, it is best described as a metal-to-ligand charge transfer transition (MLCT) with partial sigma-bond-to-ligand charge transfer (SBLCT) character. Because the sigma(Pt-C) orbital is not involved in the HOMOs of the latter complexes, the low-lying transitions were characterized as mixed MLCT/L'LCT, where L'LCT stands for ligand-to-ligand charge transfer from the pi system of the unsaturated co-ligand to the pi((i)Pr-DAB) orbital. The alkyl complexes are photoreactive on visible light irradiation with Pt-C bond homolysis as the primary step. The efficiency of the photoreaction increases with increasing sigma donor strength of the alkyl ligand. The absolute quantum yield is quite low. The other complexes are virtually photostable, except when irradiated at relatively high energies.