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Showing papers in "Dalton Transactions in 2009"


Journal ArticleDOI
TL;DR: A comprehensive understanding of 8 different methods reported so far to achieve high phosphorescence quantum efficiency from Ir(III) complexes leads to conclude that the modulation in ligand structures has a profound effect on both the phosphorescence colour and phosphorescence Quantum efficiency.
Abstract: Phosphorescent Ir(III) complexes attract enormous attention because they allow highly efficient electrophosphorescence. In pursuing the development of Ir(III) complexes during the last decade, significant progress has been made in terms of the colour-tunability, thermal- and photo-stability, phase homogeneity, and phosphorescence efficiency. By far, extensive synthetic efforts have been focused on the molecular design of ligands to achieve a wide range of phosphorescence colour that is compatible with organic light-emitting device (OLED) applications. In contrast, less has been known about a collective structure–property relationship for phosphorescence quantum efficiency. In fact, a few rule-of-thumbs for high phosphorescence quantum efficiency have been occasionally reported, but a collective rationale is yet to be investigated. In this article, we provide a comprehensive review of 8 different methods reported so far to achieve high phosphorescence quantum efficiency from Ir(III) complexes. The methods included herein are limited to the cases of intramolecular controls, and thus are discussed in terms of variations in ligand structures: (1) geometric isomer control, (2) rigid structure and restricted intramolecular motion, (3) larger mixing of 1MLCT and 3LC states, (4) de-stabilizing a thermally accessible non-emissive state, (5) introducing dendrimer structures, (6) control in substituents of ligands, (7) confining the phosphorescent region of a mixed ligand Ir(III) complex and (8) sensitized phosphorescence by using attached energy donors. Each method is closely related to intramolecular excited state interactions, which strongly affect radiative or non-radiative transitions. A comprehensive understanding of these methods leads us to conclude that the modulation in ligand structures has a profound effect on both the phosphorescence colour and phosphorescence quantum efficiency. Thus, the judicious selection of ligand structures and their chelate disposition should be considered before synthesis. We expect that the guidelines for attaining a high phosphorescence efficiency, summarized in this Perspective, would be helpful in developing highly phosphorescent Ir(III) complexes.

593 citations


Journal ArticleDOI
TL;DR: The reactivity of alcohols can be enhanced by the temporary removal of hydrogen using a transition metal catalyst to generate an intermediate aldehyde or ketone, which has a greater reactivity towards nucleophilic addition accommodating the in situ formation of imines or alkenes.
Abstract: The reactivity of alcohols can be enhanced by the temporary removal of hydrogen using a transition metal catalyst to generate an intermediate aldehyde or ketone. The so-formed carbonyl compound has a greater reactivity towards nucleophilic addition accommodating the in situ formation of imines or alkenes. The return of hydrogen from the catalyst leads to the formation of new C-N and C-C bonds, often with water as the only reaction by-product.

568 citations


Journal ArticleDOI
TL;DR: The combination of Lewis acids and bases that are sterically precluded from forming Lewis acid-base adducts, termed Frustrated Lewis pairs provide a unique route to the activation of small molecules and applications in catalysis.
Abstract: The combination of Lewis acids and bases that are sterically precluded from forming Lewis acid–base adducts, termed Frustrated Lewis pairs provide a unique route to the activation of small molecules and applications in catalysis.

496 citations


Journal ArticleDOI
TL;DR: A critical review on the coordination chemistry of the metal ions copper and zinc to the amyloid-beta (Abeta) peptide and the affinity of these metal ions towards the peptide, which has been linked to Alzheimer's disease.
Abstract: In the present perspective, we give a critical review on the coordination chemistry of the metal ions copper and zinc to the amyloid-β (Aβ) peptide; such complexes have been linked to Alzheimer's disease. We focus on two main issues: the identification of the coordination sphere of the Cu(II) and Zn(II) ions and the affinity of these metal ions towards the peptide. With the aim to come up with as few as possible valuable structural models and binding affinity values, we critically review the divergent propositions reported in the literature and take into account the experimental differences and the limits of the methods used in the published studies. We propose that: (i) the conditional dissociation constant of the Cu(Aβ) complexes lies in the range of 10 pM to 100 nM, with a preference for the region between 100 pM to 1 nM. (ii) Two most likely coordination modes for the predominant form of the Cu(Aβ) complexes at physiological pH can be retained, both being 3N1O distorted square planar. In the first model, the Cu(II) ion is coordinated by the Nτ atoms of the three His residues and the carboxylate of the Asp1. In the second model, both the N-terminus and the carboxylate functions of Asp1 are ligated together with the Nτ of His6 and of His13 (or His14). An equilibrium between these two forms at room temperature, and a preferentially freezing out of the second one would explain most of the divergences in the published results (in particular, between those obtained by EPR and NMR). (iii) The apparent dissociation constants of Zn(Aβ) in various buffers are in the range of 1 to 20 μM (a 10 times lower conditional dissociation constant can be estimated. (iv) For the Zn(II) coordination, the implication of the three His and the Asp1 residues is consensual. The Asp1 can be coordinated by the carboxylate and/or the N-terminus functions. Additional ligands are possible, such as Glu11 or H2O.

457 citations


Journal ArticleDOI
TL;DR: A comprehensive overview of PACT developments for complexes of the different d-block metals for the treatment of cancer is provided, detailing the more established areas concerning Ti, V, Cr, Mn, Re, Fe, Ru, Os, Co, Rh, Pt, and Cu and also highlighting areas where there is potential for greater exploration.
Abstract: The fields of phototherapy and of inorganic chemotherapy both have long histories. Inorganic photoactivated chemotherapy (PACT) offers both temporal and spatial control over drug activation and has remarkable potential for the treatment of cancer. Following photoexcitation, a number of different decay pathways (both photophysical and photochemical) are available to a metal complex. These pathways can result in radiative energy release, loss of ligands or transfer of energy to another species, such as triplet oxygen. We discuss the features which need to be considered when developing a metal-based anticancer drug, and the common mechanisms by which the current complexes are believed to operate. We then provide a comprehensive overview of PACT developments for complexes of the different d-block metals for the treatment of cancer, detailing the more established areas concerning Ti, V, Cr, Mn, Re, Fe, Ru, Os, Co, Rh, Pt, and Cu and also highlighting areas where there is potential for greater exploration. Nanoparticles (Ag, Au) and quantum dots (Cd) are also discussed for their photothermal destructive potential. We also discuss the potential held in particular by mixed-metal systems and Ru complexes.

408 citations


Journal ArticleDOI
TL;DR: This Perspective is not intended as a comprehensive review, but rather a systematic highlight of key contributions, which have served to extend the forefront of this exciting field.
Abstract: Interest in the utility of polylactide as a commodity polymer has increased significantly in recent years due to numerous environmental advantages over conventional petrochemically derived plastics. As such, the development of novel catalyst systems for the ring opening polymerization of lactide has seen tremendous progress in the past decade. In particular, divalent metals (i.e.Mg, Ca and Zn) supported by monoanionic ancillary scaffolds are appealing because of their low toxicity and cost. A much less common approach involves the use of neutral ligands in combination with the aforementioned divalent metal centres. The additional valence thus renders it possible, upon reaction with traditional Lewis or Bronsted acid activators, to generate sterically and electronically unsaturated species, akin to the most widely employed olefin polymerization catalysts. This Perspective is not intended as a comprehensive review, but rather a systematic highlight of key contributions, which have served to extend the forefront of this exciting field.

406 citations


Journal ArticleDOI
TL;DR: The term 'ambiphilic metal ligand activation' (AMLA) is introduced to describe reactions where lone pair assistance via heteroatom co-ligands or carboxylates are highlighted as a particularly promising means of cleaving C-H bonds.
Abstract: Recent computational studies of C–H bond activation at late transition metal systems are discussed and processes where lone pair assistance via heteroatom co-ligands or carboxylates are highlighted as a particularly promising means of cleaving C–H bonds. The term ‘ambiphilic metal ligand activation’ (AMLA) is introduced to describe such reactions.

380 citations


Journal ArticleDOI
TL;DR: Most of the metal-N-Heterocyclic Carbenes considered display higher cytotoxicities than the reference metallo-drug cisplatin, and their mechanisms of action at the cellular level are discussed, showing that the nature of themetal is of great importance.
Abstract: New weapons to fight cancer are constantly needed. Among chemotherapeutics, anti-cancer metal-drugs have enjoyed a long and successful history since the discovery of the benchmark cisplatin. Advances in metal-drug discovery have motivated chemists to build plethora of complex structures. Among them, a novel area is emerging. This article presents a survey of the metal-N-Heterocyclic Carbenes (Ag(I), Au(I), Pd(II) and Cu(I)-NHCs) as potential anti-cancer agents. Most of the metal-NHCs considered display higher cytotoxicities than the reference metallo-drug cisplatin. Some of them are even selective for particular cell lines. Their mechanisms of action at the cellular level are further discussed, showing that the nature of the metal is of great importance. All these promising results demonstrate that this approach deserves more attention and work.

332 citations


Journal ArticleDOI
TL;DR: This perspective gives an introduction into the design of luminescent lanthanide(iii)-containing complexes possessing chiral properties and used to probe biological materials and used as potential probes of biomolecular substrates.
Abstract: This perspective gives an introduction into the design of luminescent lanthanide(III)-containing complexes possessing chiral properties and used to probe biological materials. The first part briefly describes general principles, focusing on the optical aspect (i.e. lanthanide luminescence, sensitization processes) of the most emissive trivalent lanthanide ions, europium and terbium, incorporated into molecular luminescent edifices. This is followed by a short discussion on the importance of chirality in the biological and pharmaceutical fields. The second part is devoted to the assessment of the chiroptical spectroscopic tools available (typically circular dichroism and circularly polarized luminescence) and the strategies used to introduce a chiral feature into luminescent lanthanide(III) complexes (chiral structure resulting from a chiral arrangement of the ligand molecules surrounding the luminescent center or presence of chiral centers in the ligand molecules). Finally, the last part illustrates these fundamental principles with recent selected examples of such chiral luminescent lanthanide-based compounds used as potential probes of biomolecular substrates.

287 citations


Journal ArticleDOI
TL;DR: The chemistry of the pyrazole ring is summarized, and the metal coordination modes adopted by 1H-pyrazoles and their anions are reviewed, highlighting the wide structural diversity in apparently simple main group pyrazolides.
Abstract: This Perspective summarises the chemistry of the pyrazole ring, and reviews the metal coordination modes adopted by 1H-pyrazoles and their anions. Pyrazolide anions are probably the most versatile ligands in coordination chemistry, with 20 different terminal or bridging coordination modes having been identified so far. Metal cluster compounds supported by pyrazolido ligation are surveyed, concentrating on those reported during the past ten years. Highlights include the wide structural diversity in apparently simple main group pyrazolides; luminescence and charge-transfer complexes in coinage metal pyrazolide clusters; the use of robust metal pyrazolide clusters to construct liquid crystals, supramolecular materials and metal–organic frameworks; and supramolecular complexes formed by pyrazolide-supported metallacrowns.

285 citations


Journal ArticleDOI
TL;DR: A categorization of metal anticancer compounds into five classes based on their mode of action is suggested, that is clearly focused on the metal compound and is independent from the nature of its bio-target(s)-most often still unknown-has the purpose of providing an intellectual tool that might be helpful in the rational development of new drugs.
Abstract: The development of new metal anticancer compounds is a challenge for inorganic chemists. We have to face the fact that four decades of research in this field have only produced a small number of clinically used compounds, most often developed through serendipity rather than through rational chemical design. Nevertheless, by virtue of the wealth of knowledge acquired in these years, medicinal inorganic chemistry is probably mature for making significant steps forward and there are great expectations for future developments. With the aim of contributing to the rationalization of this field, we suggest here a categorization of metal anticancer compounds into five classes based on their mode of action: (i) the metal has a functional role, i.e. it must bind to the biological target; (ii) the metal has a structural role, i.e. it is instrumental in determining the shape of the compound and binding to the biological target occurs through non-covalent interactions; (iii) the metal is a carrier for active ligands that are delivered in vivo; (iv) the metal compound is a catalyst; and (v) the metal compound is photoactive and behaves as a photo-sensitizer. Selected examples for each category are given. The few metal anticancer drugs that are in clinical use are all believed to be functional compounds. Our classification, that is clearly focused on the metal compound and is independent from the nature of its bio-target(s)—most often still unknown—has the purpose of providing an intellectual tool that might be helpful in the rational development of new drugs.

Journal ArticleDOI
TL;DR: The current methods envisaged for increasing adsorption at higher temperatures involve modification of the surface chemistry, in particular, the inclusion of open metal centres to increase hydrogen surface site interactions, and utilisation of the framework flexibility are discussed.
Abstract: Hydrogen adsorption on porous materials is one of the possible methods proposed for hydrogen storage for transport applications. High pressure experimental studies of a wide range of porous materials have obtained maximum hydrogen excess capacities of 6–8 wt% at 77 K for metal–organic frameworks (MOFs) and porous carbon materials. Grand canonical Monte Carlo (GCMC) simulation studies indicate that higher hydrogen capacities are possible for covalent organic frameworks (COFs). Currently, the maximum isosteric enthalpies of adsorption of ∼13 kJ mol−1 at 77 K have been observed experimentally for metal–organic framework materials and this is higher than for COFs, where the maximum predicted from GCMC simulations is ∼8 kJ mol−1. Metal–organic framework materials have structural diversity and scope for modification of surface chemistry to enhance hydrogen surface interactions. The synthesis of MOFs with stronger H2–surface interactions to give similar hydrogen capacities at much higher temperatures than 77 K is required and eventually, materials that have these high capacities at ambient temperatures with rapid adsorption/desorption characteristics are necessary for applications as hydrogen storage materials for transport applications. The current methods envisaged for increasing adsorption at higher temperatures involve modification of the surface chemistry, in particular, the inclusion of open metal centres to increase hydrogen surface site interactions, and utilisation of the framework flexibility are discussed.

Journal ArticleDOI
TL;DR: This compound is isostructural to the MIL-53 type, previously observed with the trivalent cations Cr, Fe, Al, In and exhibits a three-dimensional metal-organic framework built up from infinite chains of trans corner-sharing GaO(4)(OH)(2) octahedra (viamu(2)-hydroxo bonds) linked to each other through the terephthalate linkers.
Abstract: The gallium terephthalate Ga(OH)[O2C-C6H4-CO2]·xA (A = HO2C–C6H4–CO2H) was hydrothermally synthesized in water under mild conditions (210 °C, 3½ h) in the presence of terephthalic acid. The compound was characterized by powder X-ray diffraction, TGA, IR and BET method. This compound is isostructural to the MIL-53 type, previously observed with the trivalent cations Cr, Fe, Al, In. It exhibits a three-dimensional metal–organic framework built up from infinite chains of trans corner-sharing GaO4(OH)2 octahedra (viaμ2-hydroxo bonds) linked to each other through the terephthalate linkers. It results in the formation of lozenge-shape channels structure running parallel to the infinite files of gallium-centered octahedra. After activation, the compound is able to adsorb one molar equivalent of water at room temperature under ambient air (MIL-53(Ga){H2O}). Different hydrogen bond interactions are observed for the encapsulated water within the channels. In one tunnel, pairs of water species with strong hydrogen-bond interactions were observed whereas in the adjacent tunnel, only a continuous linear and weakly hydrogen bonded network occurs. The dehydrated form is obtained upon heating the MIL-53(Ga) solid at 80 °C together with the shrinkage of the channels (MIL-53(Ga)_lt. This form is stable up to 220 °C and then the open structure MIL-53(Ga)_ht is visible, but starts to decompose from 350 °C. Such a breathing effect was previously reported with cations such as Cr or Al but in the case of Ga, the stability domain of the narrow pore structure MIL-53(Ga)_lt is larger (160 °C instead of 20–30 °C for Al, for instance). The BET surface area was 1140 ± 114 m2.g−1. The phase transitions were characterized by IR spectroscopy at different temperatures, which confirms the stability domain of the narrow close form (specific band at 1016 cm−1) of MIL-53(Ga) and then the pore opening (shifted band toward 1024 cm−1) together with the structure collapse. An identical behaviour is also discussed for the aluminum MIL-53 analogue. A comparison between the behaviour of the Al, Ga and Fe samples is presented.

Journal ArticleDOI
TL;DR: Recent progresses in the synthesis, properties and application of metal-based molecular catalysts for photoinduced hydrogen evolution in homogeneous systems are summarized.
Abstract: The development of heterogeneous catalytic systems for hydrogen production from water under light irradiation has been investigated during last three decades Homogeneous photocatalysts, however, are very attractive in sense that their chemical and photochemical properties can be understood and tuned on molecular level Moreover, in homogeneous systems catalysts may be covalently bound to photosensitizers, which leads to more efficient electron transfer Molecular devices for water splitting based on such a systems are of great interest In this review, we summarize recent progresses in the synthesis, properties and application of metal-based molecular catalysts for photoinduced hydrogen evolution in homogeneous systems

Journal ArticleDOI
TL;DR: Five illustrative examples of SCO systems, published during the past twelve months, showing new aspects of the unique and very appealing behaviour of these molecular switches, which may find interesting applications in the near future.
Abstract: Over the past five years, the spin-crossover (SCO) phenomenon has experienced a clear new lease of interest from the scientific community coinciding with the recent publication of remarkable new advances. This perspective paper describes five illustrative examples of SCO systems, published during the past twelve months, showing new aspects of the unique and very appealing behaviour of these molecular switches, which may find interesting applications in the near future.

Journal ArticleDOI
TL;DR: Advances in the synthesis and evaluation of such non-traditional platinum compounds, including cationic and tumor-targeting constructs, are discussed.
Abstract: The five platinum anticancer compounds currently in clinical use conform to structure-activity relationships formulated (M. J. Cleare and J. D. Hoeschele, Bioinorg. Chem., 1973, 2, 187-210) shortly after the discovery that cis-diamminedichloroplatinum(II), cisplatin, has antitumor activity in mice. These compounds are neutral platinum(II) species with two am(m)ine ligands or one bidentate chelating diamine and two additional ligands that can be replaced by water through aquation reactions. The resulting cations ultimately form bifunctional adducts on DNA. Information about the chemistry of these platinum compounds and correlations of their structures with anticancer activity have provided guidance for the design of novel anticancer drug candidates based on the proposed mechanisms of action. This article discusses advances in the synthesis and evaluation of such non-traditional platinum compounds, including cationic and tumor-targeting constructs.

Journal ArticleDOI
TL;DR: The aqueous speciation of ferric citrate has been investigated by mass spectrometry and EPR spectroscopy and the most relevant species are a monoiron dicitrate species and dinuclear and trinuclear oligomeric complexes, the relative concentration of which depends on the solution pH value and the iron : citric acid molar ratio.
Abstract: Citrate is an iron chelator and it has been shown to be the major iron ligand in the xylem sap of plants. Furthermore, citrate has been demonstrated to be an important ligand for the non-transferrin bound iron (NTBI) pool occurring in the plasma of individuals suffering from iron-overload. However, ferric citrate chemistry is complicated and a definitive description of its aqueous speciation at neutral pH remains elusive. X-Ray crystallography data indicates that the alcohol function of citrate (Cit4−) is involved in Fe(III) coordination and that deprotonation of this functional group occurs upon complex formation. The inability to include this deprotonation in the affinity constant calculations has been a major source of divergence between various reports of iron(III)–citrate affinity constants. However the recent determination of the alcoholic pKa of citric acid (H4Cit) renders the reassessment of the ferric citrate system possible. The aqueous speciation of ferric citrate has been investigated by mass spectrometry and EPR spectroscopy. It was observed that the most relevant species are a monoiron dicitrate species and dinuclear and trinuclear oligomeric complexes, the relative concentration of which depends on the solution pH value and the iron : citric acid molar ratio. Spectrophotometric titration was utilized for affinity constant determination and the formation constant for the biologically relevant [Fe(Cit)2]5− is reported for the first time.

Journal ArticleDOI
TL;DR: The zinc and cadmium coordination polymers show a strong bluish fluorescence upon excitation with UV light (the free btre ligand is non-luminescent).
Abstract: The hydrothermal reaction of M(NO3)2·4H2O (M = Zn and Cd) with benzene-1,4-dicarboxylic acid (H2bdc) or benzene-1,3-dicarboxylic acid (H2ip) and 1,2-bis(1,2,4-triazol-4-yl)ethane (btre) produced the mixed-ligand coordination polymers (MOFs) 3∞{[Zn2(μ2-bdc)2(μ4-btre)]} (1), 3∞{[Cd2(μ4-bdc)(μ4-btre)2](NO3)2·H2O} (2) and 2∞{[Zn2(μ3-ip)2(μ2-btre)(H2O)2]·2H2O} (3). The compounds, characterized by single-crystal X-ray diffraction, X-ray powder diffraction, solid-state cross-polarization (CP) magic-angle-spinning (MAS) 13C NMR and thermoanalysis, feature 3D metal–organic frameworks for 1 and 2 and 2D double layers which are connected through hydrogen bonds from the aqua ligands for 3. The CPMAS 13C NMR spectra picture the symmetry-independent (unique) C atoms and the bdc/ip-to-btre ligand ratio in agreement with the crystal structures. The zinc and cadmium coordination polymers 1–3 show a strong bluish fluorescence upon excitation with UV light (the free btre ligand is non-luminescent).

Journal ArticleDOI
TL;DR: A new heteroleptic ethyl-zinc complex stabilized by a chelating bis(morpholinomethyl)phenoxy ligand has been synthesised and shown to be a highly potent initiator for the immortal ring-opening polymerisation (ROP) of lactide and beta-butyrolactone.
Abstract: A new heteroleptic ethyl-zinc complex stabilized by a chelating bis(morpholinomethyl)phenoxy ligand has been synthesised and shown to be a highly potent initiator for the immortal ring-opening polymerisation (ROP) of lactide and β-butyrolactone, being able to convert up to 50 000 equiv. of monomer in the presence of up to 1000 equiv. of an alcohol as transfer agent. Two related heteroleptic complexes of magnesium and calcium have also been prepared. These complexes are stable in solution, even in the presence of large amounts of alcohol, and constitute effective catalysts for the immortal ROP of lactide under mild conditions.

Journal ArticleDOI
TL;DR: In this paper, mixed-phase TiO2 nanocomposites consisting of anatase and rutile nanoparticles (NPs) were used as photoanodes in dye-sensitized solar cells (DSSCs) and were characterized by using UV-vis spectroscopy, powder X-ray diffraction and scanning electron microscopy.
Abstract: A synergistic effect between anatase and rutile TiO2 is known, in which the addition of rutile can remarkably enhance the photocatalytic activity of anatase in the degradation of organic contaminants. In this study, mixed-phase TiO2 nanocomposites consisting of anatase and rutile nanoparticles (NPs) were prepared for use as photoanodes in dye-sensitized solar cells (DSSCs) and were characterized by using UV-vis spectroscopy, powder X-ray diffraction and scanning electron microscopy. The addition of 10–15% rutile significantly improved light harvesting and the overall solar conversion efficiency of anatase NPs in DSSCs. The underlying mechanism for the synergistic effect in DSSCs is now explored by using time-resolved terahertz spectroscopy. It is clearly demonstrated that photo-excited electrons injected into the rutile NPs can migrate to the conduction band of anatase NPs, enhancing the photocurrent and efficiency. Interfacial electron transfer from rutile to anatase, similar to that in heterogeneous photocatalysis, is proposed to account for the synergistic effect in DSSCs. Our results further suggest that the synergistic effect can be used to explain the beneficial effect of TiCl4 treatment on DSSC efficiency.

Journal ArticleDOI
TL;DR: This perspective highlights important recent developments in the construction of complex molecular architectures using reversible condensation reactions from simple starting materials.
Abstract: Boronic acids are versatile building blocks for the construction of complex molecular architectures. Using reversible condensation reactions, it is possible to obtain macrocycles, cages, dendritic structures, and rotaxanes, as well as 1-, 2-, and 3-dimensional polymers in one-pot reactions from simple starting materials. This perspective highlights important recent developments in this area.

Journal ArticleDOI
TL;DR: A selection of recent advances in metal complexes bearing terminal phosphido or phosphinidene ligands in the stoichiometric and catalytic preparation of phosphorus-element bonds are described.
Abstract: Metal complexes bearing terminal phosphido or phosphinidene ligands have become versatile tools in the stoichiometric and catalytic preparation of phosphorus–element bonds. This Perspective describes a selection of recent advances in this field, and certain emphasis has been placed on reactions that vary from what has been previously observed. Some of the general reactivity trends and mechanistic understanding in these metal-mediated reactions that has emerged are also described. Much of what is chronicled herein comes from a flux of reports over the last decade describing unique metal-mediated phosphorus–element bond formation reactions that are likely to stimulate further discoveries.

Journal ArticleDOI
TL;DR: A water-soluble Ni-Ru complex has been synthesized as a functional model for the [NiFe] hydrogenases and revealed a rather unique structure of the hetero-bimetallic Ni-Fe active site.
Abstract: [NiFe] hydrogenases catalyze the reversible oxidation of dihydrogen. For this simple reaction the molecule has developed a complex catalytic mechanism, during which the enzyme passes through various redox states. The [NiFe] hydrogenase contains several metal centres, including the bimetallic Ni–Fe active site, iron–sulfur clusters and a Mg2+ ion. The Ni–Fe active site is located in the inner part of the protein molecule, therefore a number of pathways are involved in the catalytic reaction route. These consist of an electron transfer pathway, a proton transfer pathway and a gas-access channel. Over the last 10–15 years we have been investigating the crystal structures of the [NiFe] hydrogenase from Desulfovibrio vulgaris Miyazaki F, which is a sulfate-reducing anaerobic bacterium. So far the crystal structures of the oxidized, H2-reduced and carbon monoxide inhibited states have been determined at high resolution and have revealed a rather unique structure of the hetero-bimetallic Ni–Fe active site. Furthermore, intensive spectroscopic studies have been performed on the enzyme. Based on the crystal structure, a water-soluble Ni–Ru complex has been synthesized as a functional model for the [NiFe] hydrogenases. The present review gives an overview of the catalytic reaction mechanism of the [NiFe] hydrogenases.

Journal ArticleDOI
TL;DR: This paper looks at different perspectives offered in several ways by the outstanding properties of porous hybrid frameworks and suggested orientations concern all the aspects of the field: syntheses, structures and the dedicated potential applications related to energy, energy savings, sustainable development and health.
Abstract: From the current state-of-the-art, this paper looks at different perspectives offered in several ways by the outstanding properties of porous hybrid frameworks. These suggested orientations concern all the aspects of the field: syntheses, structures and the dedicated potential applications related to energy, energy savings, sustainable development and health.

Journal ArticleDOI
TL;DR: Investigations focused on photochemical methodologies to deliver therapeutic doses of NO to such targets utilizing transition metal complexes that are nitric oxide precursors are described.
Abstract: The bioregulatory molecule NO plays key roles in cancer biology and has been implicated in both tumor growth and suppression. Furthermore, it is a γ-radiation sensitizer that may enhance selective killing of neoplastic tissues. For these reasons, there is considerable interest in developing methods for NO delivery to specific physiological targets. In this Perspective, we describe ongoing investigations focused on photochemical methodologies to deliver therapeutic doses of NO to such targets utilizing transition metal complexes that are nitric oxide precursors. The photochemical strategy has the advantages that it allows for precise control of the timing, location, and dosage for the targeted delivery of a bioactive agent.

Journal ArticleDOI
TL;DR: An overview of the X-ray crystallography data for representative members of the three enzyme families is given here, focusing on the mechanistic implications drawn from the structural data.
Abstract: Molybdenum and tungsten enzymes which contain the pyranopterin cofactor are ubiquitous in Nature and perform a wide variety of biological functions. They catalyze a diversity of mostly two-electron oxidation–reduction reactions crucial in the metabolism of nitrogen, sulfur and carbon. These enzymes share common structural features, but reveal different polypeptide folding topologies and different active site coordination geometries, which, in part, dictate their function and specificity. On the basis of structural, spectroscopic and biochemical characteristics, they have been classified into three broad families named according to well-studied enzymes of each family: xanthine oxidase, sulfite oxidase and DMSO reductase. An overview of the X-ray crystallography data for representative members of the three enzyme families is given here, focusing on the mechanistic implications drawn from the structural data.

Journal ArticleDOI
TL;DR: The routes by which lanthanide arrays and polymetallic d-f hybrids can be prepared by conventional synthesis and self-assembly are discussed and the possibilities for exploiting and evaluating the intermediates in the sensitisation process are evaluated, with particular emphasis on the mechanisms of energy transfer.
Abstract: Sensitised luminescence from lanthanide complexes offers many potential advantages in imaging and assay, particularly when coupled with time-gating protocols that can be used to gate out background signal. In this perspective, we discuss the routes by which lanthanide arrays and polymetallic d–f hybrids can be prepared by conventional synthesis and self-assembly, and discuss and evaluate the possibilities for exploiting and evaluating the intermediates in the sensitisation process, with particular emphasis on the mechanisms of energy transfer.

Journal ArticleDOI
TL;DR: This review describes the design and synthesis of hosts based on salen or related N( 2)O(2) ligands, which are useful for the development of cooperative metal complexation systems.
Abstract: This review describes the design and synthesis of hosts based on salen or related N2O2 ligands, which are useful for the development of cooperative metal complexation systems. A key to the design of the N2O2-based metallohosts is the negative charges of the phenoxo groups, which further coordinate to metal ions in a bridging fashion. In particular, the integration of two or more N2O2 coordination sites is effective for the construction of metallohosts. A variety of cyclic and acyclic oligo(N2O2) compounds were designed and synthesized. They show unique complexation behavior due to the integrated coordination sites. For examples, cyclic tris(N2O2) ligands formed novel cluster complexes and acyclic bis(N2O2) ligands bind alkaline earth and rare earth metal ions in the central recognition site via metal exchange. The suitable arrangement of the phenoxo moieties contributes to the preorganization for the cooperative metal complexation, producing metallocyclic or metallohelical structures.

Journal ArticleDOI
TL;DR: The main intention is to call upon researchers in the field to re-examine the working hypotheses that may have been formulated on the basis of outdated methodologies for cisplatin anticancer research.
Abstract: Although 40 years have passed since the discovery of the anticancer activity of cisplatin, the mechanism of action of the drug is unclear. There are several working hypotheses that guide the researchers in this field. Unexpected results that we obtained cannot be reconciled with some of those assumptions. Our main intention is to call upon researchers in the field to re-examine the working hypotheses that may have been formulated on the basis of outdated methodologies.

Journal ArticleDOI
TL;DR: A recently identified photoactivatable CO releasing molecule (CORM) based on [Mn(CO)(3)(tpm)](+) was conjugated to functionalized amino acids and model peptides using the Pd-catalyzed Sonogashira cross-coupling and the alkyne-azide 1,3-dipolar cycloaddition ("Click reaction").
Abstract: A recently identified photoactivatable CO releasing molecule (CORM) based on [Mn(CO)3(tpm)]+ was conjugated to functionalized amino acids and model peptides using the Pd-catalyzed Sonogashira cross-coupling and the alkyne–azide 1,3-dipolar cycloaddition (“Click reaction”). Both were found to be fully compatible with all functional groups present. The CORM–peptide conjugates were isolated in reasonable yield and high purity, as indicated by IR spectroscopy, ESI mass spectrometry and RP-HPLC. The myoglobin assay was used to demonstrate that they have CO release properties identical those of the parent compound. This work thus opens the way for a targeted delivery of CORMs to cellular systems.