Rhenium fac-Tricarbonyl Bisimine Chalcogenide Complexes: Synthesis, Photophysical Studies, and Confocal and Time-Resolved Cell Microscopy.

We describe the preparation, characterization, and imaging studies of rhenium carbonyl complexes with a pyta (4-(2-pyridyl)-1,2,3-triazole) or tapy (1-(2-pyridyl)-1,2,3-triazole)-based heteroaromatic N∧N ligand and thiolate or selenoate X ligand. The stability and photophysical properties of the selenolate complexes are compared with parent chloride complexes and previously described analogues with benzenethiolate ligands. Two complexes were imaged in A549 cells upon excitation at 405 nm. Colocalization studies suggest a lysosomal accumulation, while one parent chloride complex was described to localize at the Golgi apparatus. Preliminary fluorescence lifetime measurements and imaging demonstrate potential for application in time-resolved microscopy techniques due to the long and variable lifetimes observed in cellular environments, including an increase in lifetime between the solution and solid state many times larger than previously reported.

Selective Transesterification to Control Copolymer Microstructure in the Ring-Opening Copolymerization of Lactide and ε-Caprolactone by Lanthanum Complexes.

A series of novel lanthanum amido complexes, supported by ligands designed around the salan framework (salan = N,N'-bis(o-hydroxy, m-di-tert-butylbenzyl)-1,2-diaminoethane) were synthesized and fully characterized in the solid and solution states. The ligands incorporate benzyl or 2-pyridyl substituents at each tertiary amine center. The complexes were investigated as catalysts in the ring-opening homopolymerization of lactide (LA) and ε-caprolactone (ε-CL) and copolymerization of equimolar amounts of LA and ε-CL at ambient temperature. Solvent (THF or toluene) and the number of 2-pyridyl groups in the complex were found to influence the reactivity of the catalysts in copolymerization reactions. In all cases, complete conversion of LA to PLA was observed. The use of THF, a coordinating solvent, suppressed ε-CL polymerization, while the presence of one or more 2-pyridyl groups promoted ε-CL polymerization. Each copolymer gave a monomodal trace in gel permeation chromatography-size-exclusion chromatography (GPC-SEC) experiments, indicative of copolymer formation over homopolymerization. Copolymer microstructure was found to be dependent on catalyst structure and reaction solvent, ranging from blocky to close to alternating. Experiments revealed rapid conversion of LA in the initial stages of the reaction, followed by incorporation of ε-CL into the copolymer by either transesterification or propagation reactions. Significantly, the mode of transesterification (TI or TII) that occurs is determined by the structure of the metal complex and the reaction solvent, leading to the possibility of controlling copolymer microstructure through catalyst design.

Tunable Emissive Ir(III) Benzimidazole-quinoline Hybrids as Promising Theranostic Lead Compounds.

Bioactive and luminescent cyclometallated Ir(III) complexes [Ir(ppy)2 L1]Cl (1) and [Ir(ppy)2 L2]Cl (2) containing a benzimidazole derivative (L1/L2) as auxiliary mimic of a nucleotide have been synthesised. The emissive properties of both complexes are conditioned by the nature of L1 and L2, rendering an orange and a green emitter respectively. Both are highly emissive with quantum yield increasing in absence of oxygen up to 0.26 (1) and 0.36 (2), suggesting their phosphorescent character. Antiproliferative activity against lung cancer A549 cells increased up to 15 times upon irradiation conditions, reaching IC50 values in the nanomolar range (0.3±0.09 µM (1) and 0.26±0.14 µM (2)) and pointing them as good PSs candidates for photodynamic therapy via 1 O2 generation. Cellular biodistribution analysis by fluorescence microscopy suggest the lysosomes as the preferential accumulation organelle. Time-resolved studies showed a greatly increased cellular emission lifetime compared to the solution values, indicating binding to macromolecules or cellular structures and restriction of collision and vibrational quenching.

Photochemical Oxidation of Pt(IV)Me3(1,2-diimine) Thiolates to Luminescent Pt(IV) Sulfinates.

We report the formation of dinuclear complexes from, and photochemical oxidation of, (CH3)3-Pt(IV)(N^N) (N^N = 1,2-diimine derivatives) complexes of thiophenolate ligands to the analogous sulfinates (CH3)3Pt(N^N)(SO2Ph) and structural, spectroscopic, and theoretical studies of the latter revealing tunable photophysics depending upon the 1,2-diimine ligands. Electron-rich thiolate and conjugated 1,2-diimines encourage formation of thiolate-bridged dinuclear complexes; smaller 1,2-diimines or electron-poor thiolates favor mononuclear complexes. Photooxidation of the thiolate ligand yields hitherto unreported Pt(IV)-SO2R complexes, promoted by electron-deficient thiolates such as 4-nitrothiophenol, which exclusively forms the sulfinate complex. Such complexes exhibit expected absorptions due to π-π* ligand transitions of the 1,2-diimines mixed with spin-allowed singlet MLCT (d-π*) at relatively high energy (270-290 nm), as well as unexpected broad, lower energy absorptions between 360 and 490 nm. DFT data indicate that these low energy absorption bands result from excitation of Pt-S and Pt-C σ-bonding electrons to π* orbitals on sulfinate and 1,2-diimine, the latter of which gives rise to emission in the visible range.

Silicon photosensitisation using molecular layers.

Silicon photosensitisation via energy transfer from molecular dye layers is a promising area of research for excitonic silicon photovoltaics. We present the synthesis and photophysical characterisation of vinyl and allyl terminated Si(111) surfaces decorated with perylene molecules. The functionalised silicon surfaces together with Langmuir-Blodgett (LB) films based on perylene derivatives were studied using a wide range of steady-state and time resolved spectroscopic techniques. Fluorescence lifetime quenching experiments performed on the perylene modified monolayers revealed energy transfer efficiencies to silicon of up to 90 per cent. We present a simple model to account for the near field interaction of a dipole emitter with the silicon surface and distinguish between the 'true' FRET region (<5 nm) and a different process, photon tunnelling, occurring for distances between 10-50 nm. The requirements for a future ultra-thin crystalline solar cell paradigm include efficient surface passivation and keeping a close distance between the emitter dipole and the surface. These are discussed in the context of existing limitations and questions raised about the finer details of the emitter-silicon interaction.

Average orientation of a fluoroaromatic molecule in lipid bilayers from DFT-informed NMR measurements of 1H-19F dipolar couplings.

Fluorine is often incorporated into the aromatic moieties of synthetic bioactive molecules such as pharmaceuticals and disease diagnostics in order to alter their physicochemical properties. Fluorine substitution may increase a molecule's lipophilicity, thereby enabling its diffusion across cell membranes to enhance bioavailability or to exert a direct physiological effect from within the lipid bilayer. Understanding the structure, dynamics and orientation of fluoroaromatic molecules in lipid bilayers can provide useful insight into the effect of fluorine on their mode of action, and their interactions with membrane-embedded targets or efflux proteins. Here we demonstrate that NMR measurements of 19F chemical shift anisotropy combined with 1H-19F dipolar coupling measurements together report on the average orientation of a lipophilic fluoroaromatic molecule, 4-(6-fluorobenzo[d]thiazol-2-yl)aniline (FBTA), rapidly rotating within a lipid bilayer. The 19F chemical shift tensor orientation in the molecular frame was calculated by density functional theory and corroborated by 1H-19F PISEMA NMR. It was then possible to analyse the line shapes of proton-coupled and proton-decoupled 19F spectra of FBTA in chain perdeuterated dimyristoylphosphatidylcholine (DMPC-d54) bilayers to restrict the average axis of molecular reorientation of FBTA in the bilayer to a limited range orientations. This approach, which exploits the high sensitivity and gyromagnetic ratios of 19F and 1H, will be useful for comparing the membrane properties of related bioactive fluoroaromatic compounds.

Stereoelectronic control of photophysics: red and yellow axial and equatorial anomers of a rhenium-quinoline complex.

A novel quinoline-substituted pyrimidine ligand forms two different coloured complexes upon reaction with Re(CO)5Br. These compounds display distinct photophysical properties that are dictated by their stereochemistry.

Platinum trimethyl bipyridyl thiolates--new, tunable, red- to near IR emitting luminophores for bioimaging applications.

Synthetic, spectroscopic, computational and biological imaging studies of platinum trimethyl bipyridyl thiolate complexes of the general formula [PtMe3(bpy)SR] reveal these to be easily accessed, tunable bioimaging agents which feature an unusual σ-π* Inter-Ligand Charge Transfer (ILCT) transition, and in some cases emit into the Near infra-red (NIR).

Single amino acid chelate complexes of the M(CO)3 (+) core for correlating fluorescence and radioimaging studies (M = (99m) Tc or Re).

Single amino acid chelates (SAACs) and SAAC-like bifunctional ligands can be exploited in the design of a variety of bioconjugates for facile metallation with the M(CO)3 (+) unit with M = (99m) Tc or Re. When the donor groups of the ligand are quinolone, thiazole or other similarly conjugated heterocycles, the rhenium complexes are fluorescent, affording complementary and isostructural fluorescent probes to the radioactive (99m) Tc analogues. The versatility of the approach has been demonstrated by the preparation of bioconjugates incorporating peptides, biotin, folic acid, thymidine and vitamin B12 . In addition, the unusual photophysical properties observed for rhenium of the [bisthiazole-diamino butane-Re(CO)3 (+) ] derivative [BTBA-Re(CO)3 ](+) are discussed.

Progress with, and prospects for, metal complexes in cell imaging.

This article summarises the state of the art of metal complexes in cell imaging, particularly fluorescence microscopy, and presents prospects for the future development of this area. This article combines discussion of, and examples from, both the d- and f-block which have traditionally been considered separately, presenting the important classes of agents in each case, with a general description of their photophysical and cellular behaviour, and comparing and contrasting their properties and applications.

Parasites pitched against nature: Pitch Lake water protects guppies (Poecilia reticulata) from microbial and gyrodactylid infections.

SUMMARY The enemy release hypothesis proposes that in parasite depleted habitats, populations will experience relaxed selection and become more susceptible (or less tolerant) to pathogenic infections. Here, we focus on a population of guppies (Poecilia reticulata) that are found in an extreme environment (the Pitch Lake, Trinidad) and examine whether this habitat represents a refuge from parasites. We investigated the efficacy of pitch in preventing microbial infections in Pitch Lake guppies, by exposing them to dechlorinated water, and reducing gyrodactylid infections on non-Pitch Lake guppies by transferring them to Pitch Lake water. We show that (i) natural prevalence of ectoparasites in the Pitch Lake is low compared to reference populations, (ii) Pitch Lake guppies transferred into aquarium water develop microbial infections, and (iii) experimentally infected guppies are cured of their gyrodactylid infections both by natural Pitch Lake water and by dechlorinated water containing solid pitch. These results indicate a role for Pitch Lake water in the defence of guppies from their parasites and suggest that Pitch Lake guppies might have undergone enemy release in this extreme environment. The Pitch Lake provides an ideal ecosystem for studies on immune gene evolution in the absence of parasites and long-term evolutionary implications of hydrocarbon pollution for vertebrates.

Biologically compatible, phosphorescent dimetallic rhenium complexes linked through functionalized alkyl chains: syntheses, spectroscopic properties, and applications in imaging microscopy.

A range of luminescent, dimetallic complexes based upon the rhenium fac-tricarbonyl diimine core, linked by aliphatic chains of varying lengths and functionality, have been synthesized and their photophysical properties examined. Each complex displays characteristic (3)M(Re)L(diimine)CT emission in aerated acetonitrile solution, with long lifetimes in the range of 129-248 ns and corresponding quantum yields in the range 3.2-8.0%. In aqueous solution, as opposed to acetonitrile, the complexes generally show a small hypsochromic shift in λ(em) and an extension of the (3)MLCT lifetime, attributed to a hydrophobically driven association of the alkyl chains with the rhenium-bound diimine units. In live cell imaging experiments using MCF7 cells the complexes all show good uptake by non-energy dependent mechanisms without endosomal entrainment, and with varying propensity to localize in organelles. The degrees of uptake and localization properties are discussed in terms of the length and chemical nature of the linkers, and in terms of the likely interactions between these and the various cellular components encountered.

Complexes in context: attempting to control the cellular uptake and localisation of rhenium fac-tricarbonyl polypyridyl complexes.

Transition metal lumophores are now well established as agents for cell imaging, but we are still not able to predict generally and with confidence their cellular localisation, or, for that matter, their uptake efficiencies. While many such complexes have been shown to illuminate cells, genuine applications in biomedical research will only be developed when their uptake and localisation are better understood. This perspective is not a comprehensive review of luminescence, but is an overview of attempts to control uptake and localisation, focussing on a personal account of this group's development of imaging agents based on the Re(CO)(3) bipyridine core, and our attempts to understand and control their cellular behaviour.

Carbohydrate and amino acid metabolism of Spironucleus vortens.

The metabolism of Spironucleus vortens, a parasitic, diplomonad flagellate related to Giardia intestinalis, was investigated using a combination of membrane inlet mass spectrometry, (1)H NMR, (13)C NMR, bioscreen continuous growth monitoring, and ion exchange chromatography. The products of glucose-fuelled and endogenous metabolism were identified by (1)H NMR and (13)C NMR as ethanol, acetate, alanine and lactate. Mass spectrometric monitoring of gas metabolism in buffered cell suspensions showed that glucose and ethanol could be used by S. vortens as energy-generating substrates, but bioscreen automated monitoring of growth in culture medium, as well as NMR analyses, suggested that neither of these compounds are the substrates of choice for this organism. Ion-exchange chromatographic analyses of free amino-acid and amino-acid hydrolysate of growth medium revealed that, despite the availability of large pools of free amino-acids in the medium, S. vortens hydrolysed large amounts of proteins during growth. The organism produced alanine and aspartate, and utilised lysine, arginine, leucine, cysteine and urea. However, mass spectrometric and bioscreen investigations showed that addition of the utilised amino acids to diluted culture medium did not induce any significant increase in metabolic or growth rates. Moreover, as no significant amounts of ornithine were produced, and addition of arginine under aerobic conditions did not generate NO production, there was no evidence of the presence of an energy-generating, arginine dihydrolase pathway in S. vortens under in vitro conditions.

A 'Sleeping Trojan Horse' which transports metal ions into cells, localises in nucleoli, and has potential for bimodal fluorescence/PET imaging.

A rhenium polypyridine-based molecular vessel is membrane impermeant when empty, but, upon loading with metal ions, the cationic form is taken up by MCF-7 cells, localising in nucleoli. The luminescence of the vessel and its copper binding ability suggest potential as a bimodal fluorescence/PET imaging agent.

Multimodal radio- (PET/SPECT) and fluorescence imaging agents based on metallo-radioisotopes: current applications and prospects for development of new agents.

This perspective focuses on complexes of radioactive metal ions applied in multimodal radio- and optical imaging. The application of metal ions in radioimaging techniques such as Positron Emission Tomography (PET) and Single Photon Emission Computed Tomography (SPECT) has advantages over lighter nuclei in terms of half-life, but there are particular issues related to their speciation (particularly leaching from complexes) and with the combination of certain ions with fluorescent systems. The basic coordination chemistry of the ions involved and issues relating to biological conditions and their compatibility with optical imaging techniques are reviewed, the current literature presented in context, and the prospect of exploiting the intrinsic luminescence of certain metal-ligand complexes is discussed.

Fluxionality and lability in rhenium 4'-hydroxyterpyridine complexes: evidence for an associative mechanism and correlated fluxionality and lability.

The complexes [ReX(CO)(3)(N,N-eta(2)-4'-hydroxy-2-2',6'-2''-terpyridine)] (X = Cl,Br,I) have been synthesised and their ligand exchange reactions and fluxionality of the terpyridine unit studied. The halides are far more labile in these species than in analogous bipyridines, and it is proposed that the ligand fluxionality is involved in this reactivity. Structural studies of the family are reported along with spectroscopic studies including variable temperature NMR which is used to demonstrate a negative entropy of activation for the fluxional process. Synthesis of an analogue which is incapable of fluxional behaviour confirms the link between fluxionality and lability in these complexes.

Uptake and localisation of rhenium fac-tricarbonyl polypyridyls in fluorescent cell imaging experiments.

The synthesis of a series of rhenium fac tricarbonyl bisimine complexes and their application as lumophores in fluorescence imaging of yeast and human adenocarcinoma cells is reported. A wide range of complexes are synthesised with varying charges and lipophilicities, all of which have photophysical properties which make them suitable as cell imaging agents. After attempts to apply these as imaging agents in various strains of yeast which showed limited uptake, an investigation was undertaken of their applications as imaging agents in mammalian cells. In general the uptake was high and short-term toxicity and photobleaching appear to be low. The patterns of uptake and localisation are correlated with structural and electronic features of the complexes in an attempt to establish ground-rules for the design and application of rhenium complexes in imaging of eukaryotes.

Functionalisation of terpyridine complexes containing the Re(CO)3(+) moiety.

The investigation into the substitution and addition chemistry of Re(sigma(2)-terpy)(CO)(3)Cl shows that the chloride in Re(sigma(2)-terpy)(CO)(3)Cl (1) may be substituted for acetonitrile to give [Re(sigma(2)-terpy)(CO)(3)(CH(3)CN)][PF(6)] (2), but in the cationic complex [Re(sigma(2)-terpyMe)(CO)(3)Cl][PF(6)] (4), where the pendant pyridine has been methylated, substitution of the chloride could not be achieved using standard conditions. However, use of [Re(sigma(2)-terpyMe)(CO)(3)I][PF(6)] (3) results in the formation of [Re(sigma(2)-terpyMe)(CO)(3)(CH(3)CN)][PF(6)](2) (5). The acetonitrile ligand in complex 2 was found to be labile and could be substituted by pyridine donors.

Probing intracellular oxygen by quenched phosphorescence lifetimes of nanoparticles containing polyacrylamide-embedded [Ru(dpp(SO3Na)2)3]Cl2.

Methods for measuring O(2) within living cells that rely on luminescent probes are hampered by several factors: local conditions of hydrophobicity, pH, ionic composition, dielectric constant, and photobleaching by free radical species. Use of a polymer-embedded luminophore should minimize these problems. Here we use a Ru(II) coordination complex embedded within 45 nm hydrodynamic diameter nanoparticles, and demonstrate that both phosphorescence intensity and lifetimes are O(2)-sensitive, both in aqueous suspensions and intracellularly (e.g. 4.06 versus 1.55 microseconds under anaerobic or aerobic conditions, respectively). Electroporation is necessary for incorporation of the nanoparticles into yeasts: it is more effective with the fission yeast, Schizosaccharomyces pombe, than for the budding yeast, Saccharomyces cerevisiae. However, electroporation was not required for particle uptake into a cultured human cell-line (mammary adenosarcoma MCF-7), although the intracellular distribution of the probe is more general to intracellular compartments when electroporation is employed. These procedures did not compromise vitality of cells over periods of 6 h, as judged by retention of structural characteristics evident in Nomarski interference or confocal microscopy images. Spatial resolution of intracellular structures defined by nanoparticle phosphorescence intensity imaging indicates potential usefulness of the application of lifetime imaging techniques for mapping of intracellular O(2) distributions.