William S. Sheldrick

The structures and ligand binding modes of polychalcogenide anions are reviewed in this article. Participation in hypervalent 3c‐4e bonds and/or weaker secondary np² → nσ^* bonds leads to a strikingly more diverse homopolytaomic anion chemistry for selenium and tellurium in comparison to sulfur, for which only unbranched chain anions S_n^2– with n = 2–9 have been reported. Trapped S₂^·– and S₃^·– radicals are responsible for the characteristic colours of the ultramarine pigments and S₃^·– is the dominant sulfur species at the high temperatures and pressures of deep metamorphic settings. Hypervalent linear TeTe₂^4–, T‐shaped TeTe₃^4– and square‐planar TeTe₄^6– units generate a remarkable variety of structural motifs and connectivity patterns for 1 to 3D polytelluride anions. Electron‐deficient polytelluride sheets are, however, prone to periodic spatial modifications of their charge density (CDWs) with a lower total free energy, whose formation is driven by nesting effects in the electronic band structure causing Fermi surface instabilities. Polychalcogenide ligands augment the typical terminal and bridging coordination modes of monoatomic chalcogenide anions through their ability to participate in chelation, side‐on and combination binding modes. In addition to the electrical conductivity and thermoelectric energy conversion properties of the polytellurides, potential applications of the polychalcogenides range from the manufacture of synthetic zeolite pigments and ion‐exchangeable polysulfide aerogels to NIR‐emissive lanthanide polyselenides with high quantum efficiency.

The DNA binding modes and cleavage properties of novel dinuclear Ir(III) polypyridyl (pp) complexes [{(η⁵-C₅Me₅)Ir(pp)}₂(μ-B)](CF₃SO₃)₄ depend on the lengths of their rigid bridging dipyridinyl ligands B. Mono-intercalation and strong DNA cleavage properties were observed for the dipyrido[2,3-a:2′,3′-c]phenazine (dppz) complexes 1 (B = 4-[(E)-2-(4-pyridinyl)ethenyl]pyridine) and 3 (B = 4-(2-pyridin-4-ylethynyl)pyridine), whose intracationic Ir⋯Ir′ distances are about 13.1 and 13.3 Å, respectively. In contrast, UV/Vis and CD spectra were in accordance with a stable intertwined bis-intercalation mode for pairs of cations of 5 (B = 1,4-di(2-pyridin-4-ylethynyl)benzene), whose much longer Ir⋯Ir′ distance of 20.6 Å allows a stack of five aromatic chromophores to be sandwiched between its effectively parallel dppz ligands. Whereas both 1 and 3 cleaved DNA in the dark, complex 5 exhibited only photoinduced nuclease activity. A significantly higher antiproliferative activity towards MCF-7 breast carcinoma cells was observed for the nucleases 1 and 3, whose IC₅₀ values of 0.61 and 0.49 were much lower than that of 2.2 μM for bis-intercalator 5. Values of 3.8 μM, only slightly higher than that of 5, were recorded for the 5,6-dimethylphenanthroline complexes 4 and 6, whose bridging ligands are identical to those of 3 and 5, respectively. Marked antileukemic activity (IC₅₀ = 6–7 μM) associated with increased levels of reactive oxygen species and apoptosis induction was recorded for both 3 and 5 towards Jurkat cells at concentrations of 5 μM and above. Online studies with a sensor chip system indicated that 5 μM solutions of these complexes invoke a rapid and massive reduction in MCF-7 cell respiration.

Solvothermal reaction of [MnCl₂(terpy)] with elemental As and Se at a 1:1:2 molar ratio in H₂O/trien (10:1) at 150 °C affords the linear trimanganese(II) complex [{Mn(terpy)}₃(μ‐AsSe₄)₂] (1). The tridentate [AsSe₂(Se₂)]³⁻ anions of 1 chelate the terminal {Mn(terpy)}²⁺ fragments and bridge these through their remaining Se atom to the central {Mn(terpy)}²⁺ moiety. Weak interactions of Mn1···Se and Mn3···Se bonds with length 2.914(7) and 3.000(7) Å link the molecules of 1 into infinite chains. Treatment of [MnCl₂(cyclam)]Cl with As and Se at a 1:1:2 molar ratio in superheated H₂O/CH₃OH (1:1) at 150 °C yields the dinuclear complex [{Mn(cyclam)}₂ (μ‐As₂Se₆)] (2), whose novel [(AsSe₂)₂(μ‐Se₂)]⁴⁻ ligands bridge the Mn^II atoms in a μ‐1κ²Se¹, Se²: 2κ²Se⁵,Se⁶ manner.

A simple route for renewable nano-sized arjunolic and asiatic acids and self-assembly of arjuna-bromolactone

The DNA binding of polypyridyl (pp) (η⁶‐hexamethylbenzene)ruthenium(II) complexes of the type [(η⁶‐C₆Me₆)RuCl(pp)](CF₃SO₃) (pp = phen, tap, dpq, dppz, dppn) 1–5 and [(η⁶‐C₆Me₆)Ru{(NH₂)₂CS}(pp)](CF₃SO₃)₂ (pp = dpq, dppz, dppn) 6–8 has been studied by UV/Vis spectroscopy, circular dichroism and viscosity measurements. Complexes 3–5, 7 and 8 are potent cytotoxic agents towards the human cancer cell lines MCF‐7 and HT‐29. Stable intercalative binding into CT DNA is indicated for the dpq and dppz complexes by large increases ΔT_m of 12–25 °C in the DNA thermal denaturation temperature for r = [complex]/[DNA] = 0.1. Large viscosity increases for DNA in the presence of 3 and 4 are also in accordance with this binding mode as are the pronounced hypochromic UV/Vis shifts for the π–π* transitions of the dppz ligands of 4 and 7 in the range 360–400 nm. A small ΔT_m value of 2 °C and effectively unchanged viscosity suggest that Ru–N (nucleobase) coordinative binding is thermodynamically preferred for the larger polypyridyl ligand of 5 under equilibrium conditions, as is also the case for the small ligands phen and tap in complexes 1 and 2. CD spectra indicate that the B DNA conformation is essentially retained for interaction with the chloro complexes 1–5 but that very significant distortions occur for the thiourea complexes 6–8. The in vitro cytotoxicities of the chloro complexes 3–5 are dependent on the size of the polypyridyl ligand with IC₅₀ values increasing in the order dppn < dppz < dpq: for instance IC₅₀ values of 11.1, 2.12, and 0.13 μM were determined for 3–5 towards MCF‐7. These values correlate well with the cellular uptake efficiency which increases from 1.1 over 146.6 to 906.7 ng(Ru)/mg (protein) within the series 3–5. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

An automated multidimensional protein identification technology, which combines biphasic liquid chromatography with electrospray ionisation tandem mass spectrometry (MS/MS), was employed to analyse tryptic peptides from Escherichia coli cells treated with the antiproliferation agent [(η⁶-p-cymene)RuCl₂(DMSO)], where DMSO is dimethyl sulfoxide. MS/MS spectra were recorded for molecular ions generated by neutral loss of p-cymene from intensive peptide ions coordinated by the (η⁶-p-cymene)Ru^II fragment. Matching of the MS/MS spectra of the ruthenated peptides to spectra of proteins in the E. coli database enabled the identification of five protein targets for [(η⁶-p-cymene)RuCl₂(DMSO)]. One of these is the constitutive cold-shock protein cspC, which regulates the expression of genes encoding stress-response proteins, and three of the other targets, ppiD, osmY and sucC, are proteins of the latter type. The DNA damage-inducible helicase dinG was likewise established as a protein target. Aspartate carboxylate functions were identified as the probable Ru binding sites in cspC, ppiD and dinG, and threonine and lysine side chains in osmY and sucC, respectively.