Host-guest interaction between cyclen based macrotricyclic ligands and phosphate anions. A potentiometric investigation

The host-guest interaction between orthophosphate, pyrophosphate and triphosphate anions and three cyclen based macrotricyclic ligands possessing ortho- (TOC), meta- (TMC) and para-xylenyl (TPC) linkers was investigated by potentiometric measurements. The ternary species present in solution and their stability constants have been determined. The different behaviours are explained in terms of hydrogen bond formation and coulombic attraction between the organic host and the inorganic guest. The selectivity, illustrated with species distribution diagrams, is discussed. The results unambiguously showed the importance of the distance between the two cyclen cores and emphasized the increasing of the triphosphate species selectivity together with the cavity size of the ligand. A comparison of the present results with those obtained with their mono-bridged homologues is also discussed.     

The co-ordination chemistry of tris(3,5-dimethylpyrazolyl)methane manganese carbonyl complexes: synthetic, electrochemical and DFT studies

The tricarbonyl [Mn(CO)(3){HC(pz')(3)}][PF(6)] 1(+)[PF(6)](-) (pz' = 3,5-dimethylpyrazolyl) reacts with a range of P-, N- and C-donor ligands, L, in the presence of trimethylamine oxide to give [Mn(CO)(2)L{HC(pz')(3)}](+) {L = PEt(3)3(+), P(OEt)(3)4(+), P(OCH(2))(3)CEt 5(+), py 6(+), MeCN 7(+), CNBu(t)8(+) and CNXyl 9(+)}. The complex [Mn(CO)(2)(PMe(3)){HC(pz')(3)}](+)2(+) is formed by reaction of 7(+) with PMe(3). Complexes 2(+) and 6(+) were structurally characterised by X-ray diffraction methods. Reaction of 7(+) with half a molar equivalent of 4,4'-bipyridine gives a purple compound assumed to be the bridged dimer [{HC(pz')(3)}Mn(CO)(2)(μ-4,4'-bipy)Mn(CO)(2){HC(pz')(3)}](2+)10(2+). The relative electron donating ability of HC(pz')(3) has been established by comparison with the cyclopentadienyl and tris(pyrazolyl)borate analogues. Cyclic voltammetry shows that each of the complexes undergoes an irreversible oxidation. The correlation between the average carbonyl stretching frequency and the oxidation potential for complexes of P- and C-donor ligands is coincident with the correlation observed for [Mn(CO)(3-m)L(m)(η-C(5)H(5-n)Me(n))]. The data for complexes of N-donor ligands, however, are not coincident due to the presence of a node (and phase change) between the metal and the N-donor in the HOMO of the complex as suggested by preliminary DFT calculations.     

Structure-activity relationships for organometallic osmium arene phenylazopyridine complexes with potent anticancer activity

We report the synthesis and characterisation of 32 half sandwich phenylazopyridine Os(II) arene complexes [Os(η(6)-arene)(phenylazopyridine)X](+) in which X is chloride or iodide, the arene is p-cymene or biphenyl and the pyridine and phenyl rings contain a variety of substituents (F, Cl, Br, I, CF(3), OH or NO(2)). Ten X-ray crystal structures have been determined. Cytotoxicity towards A2780 human ovarian cancer cells ranges from high potency at nanomolar concentrations to inactivity. In general the introduction of an electron-withdrawing group (e.g. F, Cl, Br or I) at specific positions on the pyridine ring significantly increases cytotoxic activity and aqueous solubility. Changing the arene from p-cymene to biphenyl and the monodentate ligand X from chloride to iodide also increases the activity significantly. Activation by hydrolysis and DNA binding appears not to be the major mechanism of action since both the highly active complex [Os(η(6)-bip)(2-F-azpy)I]PF(6) (9) and the moderately active complex [Os(η(6)-bip)(3-Cl-azpy)I]PF(6) (23) are very stable and inert towards aquation. Studies of octanol-water partition coefficients (log P) and subcellular distributions of osmium in A2780 human ovarian cancer cells suggested that cell uptake and targeting to cellular organelles play important roles in determining activity. Although complex 9 induced the production of reactive oxygen species (ROS) in A2780 cells, the ROS level did not appear to play a role in the mechanism of anticancer activity. This class of organometallic osmium complexes has new and unusual features worthy of further exploration for the design of novel anticancer drugs.     

Photochromic and redox properties of bisterpyridine ruthenium complexes based on dimethyldihydropyrene units as bridging ligands

We report herein the synthesis and characterization of four new bisterpyridine dinuclear ruthenium complexes containing the dimethyldihydropyrene (DHP) photochrome as bridging ligand. A synthetic strategy has been developed based on a Suzuki coupling reaction to synthesize these novel terpyridine-DHPs. The reactivity of these different ligands and dinuclear ruthenium complexes with light was examined by (1)H NMR and monitoring the changes in their absorption spectra upon irradiation at controlled wavelengths. The free ligands and their corresponding ruthenium complexes all displayed photochromic properties with highly efficient conversion between the closed stable isomers (DHP) and their open forms (CPD). The properties of the compounds in their closed and open forms were investigated by cyclic voltammetry, spectroscopy, and luminescence measurements.     

Convenient synthesis of water-soluble nitrilotriacetic acid (NTA) BODIPY dyes

Mono- and bis-NTA-BODIPY dyes have been efficiently synthesized by amide bond formation between hepta-alkylated meso-aryl-BODIPY derivatives and the free amine of mono- and bis-NTA binder surrogates. These new fluorescent hybrids exhibited valuable photophysical properties under buffered aqueous conditions, thus expanding the arsenal of water-soluble BODIPY dyes for potential labeling and monitoring of biological systems and processes.     

Palladium‐Mediated Cleavage of Proteins with Thiazolidine‐Modified Backbone in Live Cells

Chemical protein synthesis and biorthogonal modification chemistries allow production of unique proteins for a range of biological studies. Bond‐forming reactions for site‐selective protein labeling are commonly used in these endeavors. Selective bond‐cleavage reactions, however, are much less explored and still pose a great challenge. In addition, most of studies with modified proteins prepared by either total synthesis or semisynthesis have been applied mainly for in vitro experiments with very limited extension to live cells. Reported here is an approach for studying uniquely modified proteins containing a traceless cell delivery unit and palladium‐based cleavable element for chemical activation, and monitoring the effect of these proteins in live cells. This approach is demonstrated for the synthesis of a caged ubiquitin‐aldehyde, which was decaged for the inhibition of deubiquitinases in live cells.     

Chiral semiconductor phases: the optically pure D3[M(III)(S,S-EDDS)]2 (D=TTF, TSF) family

A new family of optically pure tetrathiafulvalenium and tetraselenafulvalenium salts, D(3)[M(III)(S,S-EDDS)](2)·nH(2)O (where D = TTF, TSF; M = Co, Fe, Cr; EDDS = ethylenediaminedisuccinato), were synthesized electrochemically. These phases are semiconductors with conductivities between 6.9 × 10(-6) and 1.3 × 10(-5) S·cm(-1) (E(a)ca. 0.3 eV) for TTF and 2.8 × 10(-4) to 2.8 × 10(-5) S·cm(-1) (E(a)ca. 0.1 eV) for TSF compounds. While some crystals suffer from twinning, other well resolved structures consist of TTF/TSF stacks which, under the influence of the chiral anion, exhibit a periodic undulation described by an elliptical helix. The crystallographic data, along with computational work, indicate charge localization in the semiconducting motifs.     

Pd‐Catalyzed Reaction of Allyl Carbonate with Polyols: The Role of CO2 in Transesterification versus Etherification of Glycerol

An intermolecular Pd/PPh₃‐catalyzed transesterification of diallyl carbonate with glycerol to generate glycerol carbonate has been developed. Analysis of the reaction kinetics in THF indicates a first‐order dependence on Pd and diallyl carbonate, that the Pd bears two phosphines during the turnover limiting event, and that increasing the glycerol concentration inhibits reaction, possibly via change in the polarity of the medium. ¹³C isotopic labeling studies demonstrate that the Pd‐catalyzed transesterification requires at least one allyl carbonate moiety and that there is rapid equilibrium of the allyl carbonate with CO₂ in solution, even when present only at low concentrations. A mechanism that is consistent with these results involves oxidative addition of the allyl carbonate to Pd followed by reversible decarboxylation, with the intermediate η¹‐ and η³‐allyl Pd alkoxides mediating direct and indirect transesterification reactions with the glycerol. Using this model, successful simulations of the kinetics of reactions conducted under atmospheres of N₂ or CO₂ could be achieved, including switching in selectivity between etherification and transesterification in the early stages of reaction. Reactions with the higher polyols threitol and erythritol are also efficient, generating the terminal (1,2) monocarbonates with high selectivity.