Showing papers in "Dalton Transactions in 2005"

Thermal, pressure and light switchable spin-crossover materials

Abstract: This article reviews the most relevant chemical and structural aspects that influence the spin-crossover phenomenon (SCO). Special attention is focussed on the recent development of SCO coordination polymers. The different approaches currently being explored in order to achieve multifunctionality in SCO materials are discussed.

Tris(pentafluorophenyl)borane: a special boron Lewis acid for special reactions

Abstract: Tris(pentafluorophenyl)borane is best known for its role as an excellent activator component in homogeneous Ziegler–Natta chemistry. However, the special properties of B(C6F5)3 have made this strong boron Lewis acid an increasingly used catalyst or stoichiometric reagent in organic and organometallic chemistry. This includes catalytic hydrometallation reactions, alkylations and catalyzed aldol-type reactions. B(C6F5)3 catalyzes tautomerizations and can sometimes stabilize less favoured tautomeric forms by adduct formation. It induces some rather unusual reactions of early metal acetylide complexes and can help in stabilizing uncommon coordination geometries of carbon. The growing number of such examples indicates an increasing application potential of the useful Lewis acid B(C6F5)3 aside from its established role in olefin polymerization catalysis.

New C–N and C–C bond forming reactions catalyzed by titanium complexes

Abstract: Titanium(IV) complexes with two basic dimethylamido ligands can be efficient catalysts for alkyne hydroamination by primary amines. Readily prepared pyrrolyl ligands have proven to be especially useful in generating active catalysts for hydroamination and hydrohydrazination. From these reactions, new methodologies for the synthesis of imines, hydrazones, α,β-unsaturated imines, pyridines, indoles, and pyrroles have developed. In addition, a new reaction that is mechanistically related to hydroamination, alkyne iminoamination, has been discovered. Iminoamination, which is a multicomponent coupling between an amine, alkyne, and isonitrile, provides unsymmetrical α,β-unsaturated β-iminoamines in a single, titanium-catalyzed step.

Metal complexes in molecular electronics: progress and possibilities.

Abstract: A selective summary of some of the issues surrounding the development of a molecular-based electronics technology is presented, highlighting the characteristics of metal complexes that make these species particularly attractive for the construction of highly integrated, functional molecular components.

Coordination, organometallic and related chemistry of tris(pyrazolyl)methane ligands

Abstract: Tris(pyrazolyl)methanes are the neutral analogues of the widely exploited and highly useful tris(pyrazolyl)hydroborates, yet by comparison with their boron based counterparts their chemistry is underdeveloped. Recent breakthroughs in the synthesis of ring-substituted tris(pyrazolyl)methanes offer the opportunity for the development of this useful and promising class of ligand. This review summarises the current state of the coordination and organometallic chemistry of tris(pyrazolyl)methanes and highlights areas in which development is likely to occur.

U2af-homology-motifs: protein recognition in the rrm world

Abstract: Recent structures of the heterodimeric splicing factor U2 snRNP auxiliary factor (U2AF) have revealed two unexpected examples of RNA recognition motif (RRM)-like domains with specialized features for protein recognition. These unusual RRMs, called U2AF homology motifs (UHMs), represent a novel class of protein recognition motifs. Defining a set of rules to distinguish traditional RRMs from UHMs is key to identifying novel UHM family members. Here we review the critical sequence features necessary to mediate protein-UHM interactions, and perform comprehensive database searches to identify new members of the UHM family. The resulting implications for the functional and evolutionary relationships among candidate UHM family members are discussed.

Identical extraction behavior and coordination of trivalent or hexavalent f-element cations using ionic liquid and molecular solvents

Abstract: The extraction of both UO22+ and trivalent lanthanide and actinide ions (Am3+, Nd3+, Eu3+) by dialkylphosphoric or dialkylphosphinic acids from aqueous solutions into the ionic liquid, 1-decyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide has been studied and compared to extractions into dodecane. Radiotracer partitioning measurements show comparable patterns of distribution ratios for both the ionic liquid/aqueous and dodecane/aqueous systems, and the limiting slopes at low acidity indicate the partitioning of neutral complexes in both solvent systems. The metal ion coordination environment, elucidated from EXAFS and UV-visible spectroscopy measurements, is equivalent in the ionic liquid and dodecane solutions with coordination of the uranyl cation by two hydrogen-bonded extractant dimers, and of the trivalent cations by three extractant dimers. This is the first definitive report of a system where both the biphasic extraction equilibria and metal coordination environment are the same in an ionic liquid and a molecular organic solvent.

Substituent effects of iridium complexes for highly efficient red OLEDs.

Abstract: This study reports substituent effects of iridium complexes with 1-phenylisoquinoline ligands. The emission spectra and phosphorescence quantum yields of the complexes differ from that of tris(1-phenylisoquinolinato-C2,N)iridium(III) (Irpiq) depending on the substituents. The maximum emission peak, quantum yield and lifetime of those complexes ranged from 598–635 nm, 0.17–0.32 and 1.07–2.34 µs, respectively. This indicates the nature of the substituents has a significant influence on the kinetics of the excited-state decay. The substituents attached to phenyl ring have an influence on a stability of the HOMO. Furthermore, those substituents have effect on the contribution to a mixing between 3π–π* and 3MLCT for the lowest excited states. Some of the complexes display the larger quantum yield than Irpiq, which has the quantum yield of 0.22. The organic light emitting diode (OLED) device based on tris [1-(4-fluoro-5-methylphenyl)isoquinolinato-C2,N]iridium(III) (Ir4F5Mpiq) yielded high external quantum efficiency of 15.5% and a power efficiency of 12.4 lm W−1 at a luminance of 218 cd m−2. An emission color of the device was close to an NTSC specification with CIE chromaticity characteristics of (0.66, 0.34).

Syntheses, structures and fluorescent properties of two novel coordination polymers in the U-Cu-H3pdc system.

Abstract: Two novel coordination polymers, UO2(C5H2N2O4)(H2O) (1) and (UO2)Cu(C5H2N2O4)2(H2O)2 (2), have been prepared by the hydrothermal reaction of uranyl nitrate hexahydrate [(UO2(NO3)2·6H2O], 3,5-pyrazoledicarboxylic acid (H3pdc) and copper(II) nitrate hemipentahydrate (Cu(NO3)2·2.5H2O) and characterized by single-crystal X-ray diffraction, thermogravimetric analyses (TGA) and fluorescence spectroscopy. Compound 1 (monoclinic, P21/c, a = 6.9556(6) A, b = 11.302(1) A, c = 10.5288(9) A, β = 90.057(2)° and Z = 4) consists of a two-dimensional sheet containing uranyl hexagonal bipyramids. Compound 2 (triclinic, P-1, a = 5.1014(7) A, b = 7.6067(11) A, c = 10.2910(15) A, α = 72.380(3)°, β = 86.796(3)°, γ = 84.447(3)° and Z = 1) consists of two-dimensional sheets. Both structures contain the linear UO22+ moiety and have extended networks built up from the H3pdc ligand. Compound 1 exhibits the characteristic UO22+ emission spectra when it is excited at the ligand or uranium excitation wavelength. With the addition of the copper metal center in compound 2, the uranium emission is absent regardless of the excitation wavelength.

From model compounds to protein binding: syntheses, characterizations and fluorescence studies of [RuII(bipy)(terpy)L]2+ complexes (bipy = 2,2'-bipyridine; terpy = 2,2':6',2''-terpyridine; L = imidazole, pyrazole and derivatives, cytochrome c).

Abstract: Compounds [RuII(bipy)(terpy)L](PF6)2 with bipy = 2,2′-bipyridine, terpy = 2,2′:6′,2″-terpyridine, L = H2O, imidazole (imi), 4-methylimidazole, 2-methylimidazole, benzimidazole, 4,5-diphenylimidazole, indazole, pyrazole, 3-methylpyrazole have been synthesized and characterized by 1H NMR, ESI-MS and UV/Vis (in CH3CN and H2O). For L = H2O, imidazole, 4,5-diphenylimidazole and indazole the X-ray structures of the complexes have been determined with the crystal packing featuring only few intermolecular C–H⋯π or π–π interactions due to the separating action of the PF6-anions. Complexes with L = imidazole and 4-methylimidazole exhibit a fluorescence emission with a maximum at 662 and 667 nm, respectively (λexc = 475 nm, solvent CH3CN or H2O). The substitution of the aqua ligand in [Ru(bipy)(terpy)(H2O)]2+ in aqueous solution by imidazole to give [Ru(bipy)(terpy)(imi)]2+ is fastest at a pH of 8.5 (as followed by the increase in emission intensity). Coupling of the [Ru(bipy)(terpy)]2+ fragment to cytochrome c (Yeast iso-1) starting from the Ru-aqua complex was successful at 35 °C and pH 7.0 after 5 d under argon in the dark. The [Ru(bipy)(terpy)(cyt c)]-product was characterized by UV/Vis, emission and mass spectrometry. The location where the [Ru(bipy)(terpy)] complex was coupled to the protein was identified as His44 (corresponding to His39 in other numbering schemes) using digestion of the Ru-coupled protein by trypsin and analysis of the tryptic peptides by HPLC-high resolution MS.

Molecular and multidimensional polyoxotungstates functionalized by {Cu(bpy)}2+ groups

Abstract: Five new materials built from polyoxotungstates and Cu(II) ions as linkers have been synthesized by hydrothermal reactions from a mixture of sodium tungstate, copper chloride and bipyridine. The value of the initial pH, the nature of the heteroelement (P or Si) and of the ligand (2,2′- and/or 4,4′-bipyridine) permit the control of the nature of the polyoxotungstate clusters and their connectivity via the copper ions, and hence the dimensionality of the framework. A single phase has been obtained with silicon as heteroelement at an initial pH of 5, namely the 2D material [SiW12O40][Cu(2,2′-bpy)2]2·10H2O (1) with saturated Keggin polyoxotungstates linked by {Cu(2,2′-bpy)2}2+ groups. With phosphorous as heteroelement and at the same initial pH, three different structures have been isolated according to the nature of the ligand. Indeed, the two 1D materials [{Cu5(2,2′-bpy)5(H2O)(HPO4)(PO4)}PW11CuO39]·6H2O (2) with 2,2′-bpy and [4,4′-Hbpy][{Cu2(2,2′-bpy)2(4,4′-bpy)2.5}PW11CuO39]·16H2O (3) with a mixture of 2,2′- and 4,4′-bpy have been characterized, and a coordination polymer with polyoxometalate guests Na3[4,4′-Hbpy]{Cu4(4,4′-bpy)8(H2O)8}[PW11CuO39(H2O)][PW10Cu2O38(H2O)2]·38H2O (4) with 4,4′-bpy has been obtained. Finally, in basic medium (pH = 10) the unprecedented molecular cluster Na2[{Cu8(2,2′-bpy)8}(PW8O31)2]·15H2O (5) has been evidenced. Magnetic studies of compound 2 revealed that the predominant interactions involve only 4 paramagnetic centers, which are interacting within pairs, among the 6 Cu(II) centers. The χMT = f(T) curve can be fitted using the dinuclear expression appropriate to the HDVV isotropic exchange Hamiltonian H = −JS1×S2, with S1 = S2 = ½ and J = −105.4 cm−1, showing strong antiferromagnetic interactions within the two Cu(II) pairs.

Organorhenium(VII) and organomolybdenum(VI) oxides: syntheses and application in olefin epoxidation

Abstract: The first members of the classes of the organorhenium(VII) oxides and organomolybdenum(VI) oxides were described during the 1960s and 1970s. However, despite the fact that methyltrioxorhenium(VII) (MTO) is probably the best examined organometallic oxide known, many of its derivatives as well as the Mo congeners were not tested for any application. Nevertheless, it is known that several organomolybdenum oxides, particularly those of formula η5-(C5R5)MoO2Cl and η5-(C5R5)MoO2R′ are powerful epoxidation catalysts if applied together with tert-butylhydroperoxide (TBHP). MTO catalyzes a broad variety of organic reactions, among them being olefin epoxidation – in this case with the “green” oxidant H2O2 – the most thoroughly examined. The heterogenization of the molybdenum compounds as well as of MTO both on carrier materials and in ionic liquids has already been achieved and it is to be expected that a suitable modification of the organic ligands will lead to applications in chiral catalysis in the near future.

Dioxygen Reduction by Multi-Copper Oxidases; a Structural Perspective.

Abstract: The multi-copper oxidases oxidise substrate molecules by accepting electrons at a mononuclear copper centre and transferring them to a trinuclear centre. Dioxygen binds to the trinuclear centre and, following the transfer of four electrons, is reduced to two molecules of water. The precise mechanism of this reduction has been unclear, but recent X-ray structural studies using the CotA endospore coat protein from Bacillus subtilis have given further insights into the principal stages. It is proposed that the mechanism involves binding of the dioxygen into the trinuclear centre so that it is sited approximately symmetrically between the two type 3 copper ions with one oxygen atom close to the type 2 copper ion. Further stages involve the formation of a peroxide intermediate and following the splitting of this intermediate, the migration of the hydroxide moieties towards the solvent exit channel. The migration steps are likely to involve a movement of the type 2 copper ion and its environment. Details of a putative mechanism are described herein based both on structures already reported in the literature and on structures of the CotA protein in the oxidised and reduced states and with the addition of peroxide and the inhibitor, azide.

The mineral phase in the cuticles of two species of Crustacea consists of magnesium calcite, amorphous calcium carbonate, and amorphous calcium phosphate.

Abstract: The cuticules (shells) of the woodlice Porcellio scaber and Armadillidium vulgare were analysed with respect to their content of inorganic material. It was found that the cuticles consist of crystalline magnesium calcite, amorphous calcium carbonate (ACC), and amorphous calcium phosphate (ACP), besides small amounts of water and an organic matrix. It is concluded that the cuticle, which constitutes a mineralized protective organ, is chemically adapted to the biological requirements by this combination of different materials.

Rational design and construction of the first tetrahedral net with photoluminescent Cu4I4 cubane cluster as the tetrahedral node

Abstract: Solvothermal reaction of CuI with flexible 1,3-bis(4-pyridyl)propane generated the first three-dimensional coordination polymer constructed with the rigid tetrahedrally connected Cu4I4 cluster unit. The net is a rare chiral triple-interpenetrated, quartz net with of vertex symbol 64.82. The solid-state luminescence spectrum displays a strong red emission band at room temperature (λmax = 601 nm), characteristic of the Cu4I4 cluster centers.

Polyhedra in (inorganic) chemistry.

Abstract: A systematic description of polyhedra with varying degrees of regularity is illustrated with examples of chemical structures, mostly from different fields of Inorganic Chemistry. Also the geometrical relationships between different polyhedra are highlighted and their application to the analysis of complex structures is discussed.

Metal-assisted red light-induced DNA cleavage by ternary L-methionine copper(II) complexes of planar heterocyclic bases

Abstract: Ternary copper(II) complexes [Cu(L-met)B(Solv)](ClO4) (1–4), where B is a N,N-donor heterocyclic base like 2,2′–bipyridine (bpy, 1), 1,10-phenanthroline (phen, 2), dipyrido[3,2-d:2′,3′-f]quinoxaline (dpq, 3) and dipyrido[3,2-a:2′,3′-c]phenazene (dppz, 4), are prepared and their DNA binding and photo-induced DNA cleavage activity studied (L-Hmet = L-methionine). Complex 2, structurally characterized by X-ray crystallography, shows a square pyramidal (4 + 1) coordination geometry in which the N,O-donor L-methionine and N,N-donor heterocyclic base bind at the basal plane and a solvent molecule is coordinated at the axial site. The complexes display a d–d band at ∼600 nm in DMF and exhibit a cyclic voltammetric response due to the Cu(II)/Cu(I) couple near −0.1 V in DMF–Tris-HCl buffer. The complexes display significant binding propensity to the calf thymus DNA in the order: 4 (dppz) > 3 (dpq) > 2 (phen) ≫ 1 (bpy). Control cleavage experiments using pUC19 supercoiled DNA and distamycin suggest major groove binding for the dppz and minor groove binding for the other complexes. Complexes 2–4 show efficient DNA cleavage activity on UV (365 nm) or red light (632.8 nm) irradiation via a mechanistic pathway involving formation of singlet oxygen as the reactive species. The DNA cleavage activity of the dpq complex 3 is found to be significantly more than its dppz and phen analogues.

Synthesis, characterisation and catalytic potential of hydrazonato-vanadium(V) model complexes with [VO]3+ and [VO2]+ cores.

Abstract: Reaction between [VO(acac)2] and H2L (H2L are the hydrazones H2sal-nah I or H2sal-fah II; sal = salicylaldehyde, nah = nicotinic acid hydrazide and fah = 2-furoic acid hydrazide) in methanol leads to the formation of oxovanadium(IV) complexes [VOL·H2O] (H2L = I: 1, H2L = II: 4). Aerial oxidation of the methanolic solutions of 1 and 4 yields the dinuclear oxo-bridged monooxovanadium(V) complexes [{VOL}2µ-O] (H2L = I: 2, H2L = II: 5). These dinuclear complexes slowly convert, in excess methanol, to [VO(OMe)(MeOH)L] (H2L = I: 9, H2L = II: 10), the crystal and molecular structures of which have been determined, confirming the ONO binding mode of the dianionic ligands in their enolate form. Reaction of aqueous K[VO3] with the ligands at pH ca. 7.5 results in the formation of [K(H2O)][VO2L] (H2L = I: 3, H2L = II: 6). Treatment of 3 and 6 with H2O2 yields (unstable) oxoperoxovanadium(V) complexes K[VO(O2)L], the formation of which has been monitored spectrophotometrically. Acidification of methanolic solutions of 3 and 6 with HCl affords oxohydroxo complexes, while the neutral complexes [VO2(Hsal-nah)] 7 and [VO2(Hsal-fah)] 8 were isolated on treatment of aqueous solutions of 3 and 6 with HClO4. These complexes slowly transform into 9 and 10 in methanol, as confirmed by 1H, 13C and 51V NMR. The anionic complexes 3 and 6 catalyse the oxidative bromination of salicylaldehyde in water in the presence of H2O2/KBr to 5-bromosalicylaldehyde and 3,5-dibromosalicylaldehyde, a reaction similar to that exhibited by vanadate-dependent haloperoxidases. They are also catalytically active for the oxidation of benzene to phenol and phenol to catechol and p-hydroquinone.

Homochiral crystallization of helical coordination chains bridged by achiral ligands: can it be controlled by the ligand structure?

Abstract: Homochiral/heterochiral crystallizations of helical chiral polymer chains bridged by achiral poly-pyridyl ligands dependent on the structures of the bridging ligands and independent on the solvent are described, implying a possible strategy to design achiral crystals of helical chains using chiral bridging ligands.

Synthesis, characterization, in vitro antitumor activity, DNA-binding properties and electronic structure (DFT) of the new complex cis-(Cl,Cl)[RuIICl2(NO+)(terpy)]Cl.

Abstract: The complex cis-(Cl,Cl)-[RuCl2(terpy)(NO)]Cl (1) has been synthesized by the reaction of [RuCl3(H2O)2(NO)] with terpyridine (terpy) and characterized by various spectroscopic, analytical techniques and using electronic structure calculation (DFT) methods. The cytotoxic activity and the DNA-binding properties of 1 have also been studied using biochemical techniques. The results establish unequivocally that 1 corresponds to a so-called [RuNO]6 species, which readily releases the nitrosyl ligand upon irradiation with a mercury lamp in acetonitrile solution. DFT calculations provided a satisfactory description of structural, bonding, electronic and related properties of the new compound and throw light on the mechanism of the photo-induced NO release. Screening on A2780 (human ovarian carcinoma) cell lines showed significant cytotoxicity with an IC50 value of 0.49 µM. 31P and 23Na NMR spectroscopy along with electrophoretic mobility studies illustrated that complex 1 primarily binds by coordination to DNA without any π-interaction between the planar terpy ligand and the DNA bases, while weak electrostatic interactions could not be excluded. Studies on the inhibition of the restriction enzymes DraI and SmaI revealed that 1 prefers the guanine and cytosine bases of DNA.

Non-trivial behavior of palladium(II) acetate.

Abstract: Reaction of activated palladium metal with a HNO3/acetic acid mixture produces both orange Pd3(OAc)6, 1, and purple Pd3(OAc)5(NO2), 2. Compound 2 has a trinuclear structure derived from that of the well-known triangular complex 1 in which one acetate group has been replaced by a nitrite group which is bonded to one palladium atom by the nitrogen atom and to another Pd atom using one of the oxygen atoms. Highly pure 1 can be made by continuous removal of the nitric oxides from the reaction mixture using a flow of N2. 1H NMR spectra of solutions of 1 in CDCl3 and C6D6 show several signals of various intensities when a small amount of water is present in the deuterated solvents but only one signal when the solvents are thoroughly dried. These results are consistent with the occurrence of one or more hydrolysis processes when the solvents contain water and suggest that hypotheses about various [Pd(OAc)2]n aggregates that have previously been brought forward in the literature to explain the complexity of the spectrum of 1 are unnecessary, especially for nonpolar solvents. Compound 2 does not hydrolyze, and in wet or dried solvents shows a 1H NMR spectrum that consists of five equal-intensity signals due to the five nonequivalent acetate groups.

Coordination chemistry of buckybowls: from corannulene to a hemifullerene

Abstract: This work highlights the progress made in coordination chemistry of transition-metal centers to open geodesic polyaromatic hydrocarbons that map onto the surface of C60, the family of compounds known as buckybowls or ‘fullerene fragments’. In particular, an overview of our recent gas-phase coordination studies of several bowl-shaped polyarenes toward the dinuclear metal complex, [Rh2(O2CCF3)4], is given. Selected buckybowls include corannulene (C20H10) and two of its derivatives, namely dibenzo[a,g]corannulene (C28H14) and 1,3,5,7,9-penta-tert-butylcorannulene (C40H50), as well as a hemifullerene (C30H12). This study has resulted in the first X-ray structural characterization of buckybowl coordination complexes and has revealed η2-rim coordination preferences of open geodesic polyarenes in rhodium(II) binding reactions.

Metalloid Al- and Ga-clusters: a novel dimension in organometallic chemistry linking the molecular and the solid-state areas?

Abstract: Formation and fragmentation of metal–metal bonds on the way between stable metal compounds in which the metal atoms are oxidised (e.g. isolated species in solution or metal salts in bulk) and the bulk metal are the fundamental steps to understand this process in which formation and chemical behaviour of metalloid Al and Ga clusters as intermediates are essential. Many examples of metalloid Al and Ga clusters show that their formation reflects a high degree of complexity like that of the simple seeming formation of the bulk metal itself: starting from metastable Al(I) and Ga(I) solutions containing small molecular entities, metalloid clusters grow during many self-organization steps including aggregation as well as irreversible redox cascades. This novel class of clusters seems to open a new dimension in chemistry between the molecular and the solid-state area, because, for the first time, it is shown that under well selected conditions definite molecular species, i.e. metalloid clusters, grow via the formation of additional metal–metal bonds and that the solid metal represents the final step.

Molybdenum: biological activity and metabolism

Abstract: Molybdenum and tungsten are available to all organisms, with molybdenum having the far greater abundance and availability. Molybdenum occurs in a wide range of metalloenzymes in bacteria, fungi, algae, plants and animals, while tungsten was found to be essential only for a limited range of bacteria. In order to gain biological activity, molybdenum has to be complexed by a pterin compound, thus forming a molybdenum cofactor. In this article I will review the way that molybdenum takes from uptake into the cell, via formation of the molybdenum cofactor and its storage, to the final modification of molybdenum cofactor and its insertion into apo-metalloenzymes.

Synthetic, structural and spectroscopic studies of (pseudo)halo(1,3-di-tert-butylimidazol-2-ylidine)gold complexes.

Abstract: A series of (pseudo)halo(1,3-di-tert-butylimidazol-2-ylidine)gold complexes [(But2Im)AuX] (X = Cl, Br, I, CN, N3, NCO, SCN, SeCN, ONO2, OCOCH3, CH3) have been synthesized and characterised spectroscopically and structurally. 13C NMR chemical shifts for the carbene carbon vary widely with differing ancillary anion, correlating well with the σ-donor ability of the latter and with the M–C(carbene) bond distance. These results reinforce the notion that N-heterocyclic carbene ligands are primarily σ-donor ligands with little π-acceptor ability.

Formation of protein-coated iron minerals.

Abstract: The ability of iron to cycle between Fe2+ and Fe3+ forms has led to the evolution, in different forms, of several iron-containing protein cofactors that are essential for a wide variety of cellular processes, to the extent that virtually all cells require iron for survival and prosperity. The redox properties of iron, however, also mean that this metal is potentially highly toxic and this, coupled with the extreme insolubility of Fe3+, presents the cell with the significant problem of how to maintain this essential metal in a safe and bioavailable form. This has been overcome through the evolution of proteins capable of reversibly storing iron in the form of a Fe3+ mineral. For several decades the ferritins have been synonymous with the function of iron storage. Within this family are subfamilies of mammalian, plant and bacterial ferritins which are all composed of 24 subunits assembled to form an essentially spherical protein with a central cavity in which the mineral is laid down. In the past few years it has become clear that other proteins, belonging to the family of DNA-binding proteins from starved cells (the Dps family), which are oligomers of 12 subunits, and to the frataxin family, which may contain up to 48 subunits, are also able to lay down a Fe3+ mineral core. Here we present an overview of the formation of protein-coated iron minerals, with particular emphasis on the structures of the protein coats and the mechanisms by which they promote core formation. We show on the one hand that significant mechanistic similarities exist between structurally dissimilar proteins, while on the other that relatively small structural differences between otherwise similar proteins result in quite dramatic mechanistic differences.

A quarter of a century of explorations in organozirconium chemistry.

Abstract: Systematic explorations of organozirconium chemistry over the past quarter of a century have led to the discoveries and development as well as structural and mechanistic clarifications of novel Zr-catalyzed and -promoted carbon-carbon bond-forming reactions including (i) Ni- or Pd-catalyzed cross-coupling reaction of organozirconiums, (ii) Zr-catalyzed carboalumination of alkynes, (iii) Zr-catalyzed asymmetric carboalumination of alkenes, (iv) generation and carbometallative ring expansion of zirconacyclopropanes and zirconacyclopropenes and a myriad of their transformations and (v) various organozirconium migratory insertion reactions.

Substituent effects and the mechanism of alkene metathesis catalyzed by ruthenium dichloride catalysts

Abstract: Density functional theory calculations are reported concerning the dissociative mechanism for alkene metathesis by ruthenium dichloride catalysts, including both bisphosphine and diaminocarbene/phosphine complexes. The calculations use a hierarchy of models, ranging from [(L)(PH3)Ru(Cl)2(CH2)] (L = PH3 or diaminocarbene) through the larger [(L)(PMe3)Ru(Cl)2(CHPh)] to the “real” [(L)(PCy3)Ru(Cl)2(CHPh)]. Calculations show that the rate-limiting step for metathesis is either ring closing from an alkene complex to form a ruthena-cyclobutane, or ring-opening of the latter intermediate to form an isomeric alkene complex. The higher efficiency of the diaminocarbene based catalysts is due to the stabilization of the formal +IV oxidation state of the ruthenium centre in the metallacycle. This effect is partly masked in the smaller model systems due to a previously unnoticed stereoelectronic effect. The calculations do not reproduce the experimental observation whereby the initiation step, phosphine dissociation, is more energetically demanding and hence slower for the diaminocarbene-containing catalyst system than for the bisphosphine. Further calculations on the corresponding bond energies using a variety of DFT and hybrid DFT/molecular mechanics methods all find instead a larger phosphine dissociation energy for the bisphosphine catalyst. This reversed order of binding energies would in fact be the one expected based on the stronger trans influence of the diaminocarbene ligand. The discrepancy with experiment is small and could have a number of causes which are discussed here.

Tetrakis(2-quinolinylmethyl)ethylenediamine (TQEN) as a new fluorescent sensor for zinc

Abstract: A new fluorescent sensor for zinc that binds 1 equivalent of zinc ion, N,N,N′,N′-tetrakis(2-quinolylmethyl)ethylenediamine (TQEN), has been prepared and characterized. Zinc-bound TQEN exhibits fluorescence around 383 nm upon excitation at 317 nm, while free TQEN emits very weak fluorescence. UV-Vis and 1H NMR spectral changes also detected the binding of TQEN with zinc ion. The crystal structure of zinc complex with TQEN was determined by X-ray crystallography and compared with that of the TPEN–Zn complex (TPEN = N,N,N′,N′-tetrakis(2-pyridylmethyl)ethylenediamine). The binding affinity of TQEN with zinc ion is very high (Kd < 1 µM in aqueous dmf solution). Competition experiments reveal that the zinc-binding affinity of TQEN is lower than the parent, strong metal ion chelator TPEN, and comparable to EGTA (EGTA = ethylene glycol-bis(2-aminomethyl)-N,N,N′,N′-tetraacetic acid).

Synthesis of iron(II), manganese(II) cobalt(II) and ruthenium(II) complexes containing tridentate nitrogen ligands and their application in the catalytic oxidation of alkanes.

Abstract: A series of Fe(II), Mn(II), Co(II) and Ru(II) complexes containing bis(imino)pyridine or bis(amino)pyridine ligands and weakly coordinating triflate (OTf−) or non-coordinating SbF6− anions have been prepared. The complexes have been fully characterized including several solid-state structure analyses. Two unusual mono-chelate six-coordinate bis(imino)pyridine Fe(II) and Mn(II) complexes have been observed. The catalytic properties of the complexes for the oxidation of cyclohexane with H2O2 have been evaluated. Only the Fe(II) complexes have shown catalytic activity, which is mainly due to Fenton-type free radical auto-oxidation.