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Ultrafast time-resolved infrared (TRIR) is used to report on the binding site of the [Ru(phen)2 (dppz)]2+ "light-switch" complex with both bimolecular (Oxytricha nova telomere) and intramolecular (human telomere) guanine-quadruplex structures in both K+ and Na+ containing solutions. TRIR permits the simultaneous monitoring both of the "dark" and "bright" states of the complex and of the quadruplex nucleobase bases, the latter via a Stark effect induced by the excited state of the complex. These data are used to establish the contribution of guanine base stacking and loop interactions to the binding site of this biologically relevant DNA structure in solution. A particularly striking observation is the strong thymine signal observed for the Na+ form of the human telomere sequence, which is expected to be in the anti-parallel conformation.

We have previously described a number of lipophilic conformationally constrained spiro carbocyclic 2,6-diketopiperazine (2,6-DKP)-1-acetohydroxamic acids as potent anti-trypanosomal agents. In this report, we extend the SAR analysis in this class of compounds with respect to in vitro growth inhibition of Trypanosoma and Leishmania parasites. Introduction of bulky hydrophobic substituents at the vicinal position of the basic nitrogen atom in the spiro carbocyclic 2,6-DKP ring system can provide analogues which are potently active against bloodstream-form T. brucei and exhibit significant activities towards T. cruzi epimastogotes and L. infantum promastogotes and intracellular amastigotes. In particular, compounds possessing a benzyl or 4-chlorobenzyl substituent were found to be the most active growth inhibitors, with activities in the low nanomolar and low micromolar ranges for T. brucei and L. infantum, respectively. The benzyl substituted (S)-enantiomer was the most potent derivative against T. brucei (IC50 =6.8 nM), T. cruzi (IC50 =0.21 μΜ) and L. infantum promastigotes (IC50 =2.67 μM) and intracellular amastigotes (IC50 =2.60 μM). Moreover, the (R)-chiral benzyl substituted derivative and its racemic counterpart displayed significant activities against L. donovani. Importantly, the active compounds show high selectivity in comparison with two mammalian cell lines. This article is protected by copyright. All rights reserved.

Weinheim Key to the development of DNA-targeting phototherapeutic drugs is determining the interplay between the photoactivity of the drug and its binding preference for a target sequence. For the photo-oxidising lambda-[Ru(TAP)2(dppz)]2+ (Λ-1) (dppz=dipyridophenazine) complex bound to either d{T1C2G3G4C5G6C7C8G9A10}2 (G9) or d{TCGGCGCCIA}2 (I9), the X-ray crystal structures show the dppz intercalated at the terminal T1C2;G9A10 step or T1C2;I9A10 step. Thus substitution of the G9 nucleobase by inosine does not affect intercalation in the solid state although with I9 the dppz is more deeply inserted. In solution it is found that the extent of guanine photo-oxidation, and the rate of back electron-transfer, as determined by pico- and nanosecond time-resolved infrared and transient visible absorption spectroscopy, is enhanced in I9, despite it containing the less oxidisable inosine. This is attributed to the nature of the binding in the minor groove due to the absence of an NH2 group. Similar behaviour and the same binding site in the crystal are found for d{TTGGCGCCAA}2 (A9). In solution, we propose that intercalation occurs at the C2G3;C8I9 or T2G3;C8A9 steps, respectively, with G3 the likely target for photo-oxidation. This demonstrates how changes in the minor groove (in this case removal of an NH2 group) can facilitate binding of RuIIdppz complexes and hence influence any sensitised reactions occurring at these sites. No similar enhancement of photooxidation on binding to I9 is found for the delta enantiomer. Irish Research Council Science Foundation Ireland University College Dublin Biotechnology and Biological Sciences Research Council Royal Irish Academy/Royal Society

Trimethylsilyl chloride is an efficient activating agent for azines in isocyanide-based reactions, which then proceed through a key insertion of the isocyanide into a N-Si bond. The reaction is initiated by N activation of the azine, followed by nucleophilic attack of an isocyanide in a Reissert-type process. Finally, a second equivalent of the same or a different isocyanide inserts into the N-Si bond leading to the final adduct. The use of distinct nucleophiles leads to a variety of α-substituted dihydroazines after a selective cascade process. Based on computational studies, a mechanistic hypothesis for the course of these reactions was proposed. The resulting products exhibit significant activity against Trypanosoma brucei and T. cruzi, featuring favorable drug-like properties and safety profiles.

The first example of a one-component room temperature curing redox cationic polymerization for metal surfaces is described. A weak Lewis acid (Ag+) is used as a latent catalyst to likely generate a much stronger one (Fe2+/Fe3+ or Cu2+) at the bond line interface. Such a process has been demonstrated for 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate using [Ag(1,5-cyclooctadiene)2]SbF6 with the polymerization monitored most conveniently by fourier transform infrared spectroscopy (FTIR). This system, however, demonstrates a relatively low adhesive strength even following curing for 24 h. Higher bond strengths were achieved using mixtures with other cationically polymerizable monomers (vinyl ethers, tetrahydrofuran (THF), oxetanes). Factors considered for optimization of the rates and extent of reaction were the concentrations of a vinyl ether comonomer and [AgLn]X, the nature of the counterion (X), and of the ligand (L). The performance of the Ag(I) system was compared to that of Cu(I) and various organic cations and the activity of the redox cationic polymerizations on a range of metallic (iron, copper, and aluminium) and nonmetallic (glass and various plastics) substrates was studied. A relatively high glass transition temperature was recorded for the optimized model system and the bonding strength at elevated temperature (150–200 °C) following a room temperature cure was found to be attractive compared to selected model anaerobic acrylate compositions. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

The photochemistry of Ru-tris-(1,4,5,8-tetraazaphenanthrene) (Ru(tap)32+) in the absence and in the presence of adenosine-5′-monophosphate (AMP) and guanosine-5′-monophosphate (GMP) has been studied by flash photolysis and by steady state illumination. Laser pulsed irradiation of Ru(tap)32+ in the presence of AMP produces, with a rather low yield, the transient reduced complex, Ru(tap)31+, by electron transfer from AMP to the excited complex. The flash photolysis of the same solution, after pre-illumination, shows that a new photoactive compound absorbs at = 500 nm and its efficiency of production decreases at lower temperature and pH. Comparison with the photodechelation of Ru(tap)32+ in the absence of mononucleotide, and with the photoadduct formation between Ru(tap)32+ and GMP/AMP, leads to the conclusion that this photoactive species could correspond to [Ru(tap)2AMP, X]n+ formed by photosubstitution of a tap ligand in the presence of AMP.

In recent years, galvanic replacement reactions have been successfully employed to produce hollow bimetallic nanostructures of a range of shapes, yet to date there has been no example of the formation of hollow triangular AuAg nanostructures from a Ag nanoprism template. In this manuscript the first example of the synthesis of enclosed triangular AuAg nanostructures (triangular nanoboxes) via galvanic replacement reactions from Ag nanoprisms is reported. These triangular nanoboxes are studied by TEM and HAADF-STEM imaging to elucidate their structure. These studies show that the nanostructures are hollow and do not consist of a Ag core surrounded by a Au shell. Discrete dipole approximation calculations for the extinction spectra are carried out and provide additional evidence that the nanostructures are hollow. These new triangular nanoboxes are very attractive candidates for encapsulation and transport of materials of interest such as drugs, radioisotopes, or magnetic materials.

Aiming at the development of new adamantano building blocks for treating African trypanosomiasis, we report on the synthesis of spiro adamantane 2-imidazolines 8a-f and 9a-c, and their congeneric 5-(1-adamantyl)imidazolines 14 and 15. The potency of these compounds against Trypanosoma brucei was compared to that of rimantadine and found, in the case of compound 14e, to be three fold higher. Together with the other active compounds, 14b and 15b, which were equipotent to rimantadine, the new molecules illustrate the synergistic effect of the lipophilic character of adamantane and the C1 amidine functionality on trypanocidal activity.

A rapid and readily reproducible seed-based method for the production of high quality silver nanoprisms in high yield is presented. The edge-length and the position of the main plasmon resonance of the nanoprisms can be readily controlled through adjustment of reaction conditions. From UV-vis spectra of solutions of the nanoprisms, the inhomogeneously broadened line width of the in-plane dipole plasmon resonance is measured and trends in the extent of plasmon damping as a function of plasmon resonance energy and nanoprism size have been elucidated. In addition, an in-depth analysis of the lamellar defect structure of silver nanoprisms is provided that confirms that the defects can lead to a transformation of the crystal structure in the vicinity of the defects. These defects can combine give rise to lamellar regions, thicker than 1 nm, that extend across the crystal, where the silver atoms are arranged in a continuous hexagonal-close-packed (hcp) structure. This hcp structure has a periodicity of 2.50 A, thus explaining the 2.50 A lattice fringes that are commonly observed in 〈111〉 oriented flat-lying nanoprisms. A new understanding of the mechanisms behind anisotropic growth in silver nanoprisms is presented.

Transient species formed by photoexcitation (400 nm) of [Ru(dppz)(tap)2]2+ (1) (dppz = dipyrido[3,2-a:2',3'-c]phenazine; tap=1,4,5,8-tetraazaphenanthrene) in aqueous solution and when intercalated into a double-stranded synthetic polynucleotide, [poly(dG-dC)]2, have been observed on a picosecond timescale by both visible transient absorption (allowing monitoring of the metal complex intermediates) and transient infrared (IR) absorption spectroscopy (allowing direct study of the DNA nucleobases). By contrast with its behavior when free in aqueous solution, excitation of 1 when bound to [poly(dG-dC)]2 causes a strong increase in absorbance at 515 nm due to formation of the reduced complex [Ru(dppz)(tap)2]+ (rate constant=(2.0+/-0.2) x 10(9) s(-1)). The subsequent reformation of 1 proceeds with a rate constant of (1.1+/-0.2) x 10(8) s(-1). When the process is carried out in D2O, the rates of formation and removal of [Ru(dppz)(tap)2]+ are reduced (rate constants (1.5+/-0.3) x 10(9) and (0.7+/-0.2) x 10(8) s(-1) respectively) consistent with proton-coupled electron transfer processes. Picosecond transient IR measurements in the 1540-1720 cm(-1) region in D2O solution confirm that the reduction of 1 intercalated into [poly(dG-dC)]2 is accompanied by bleaching of IR ground-state bands of guanine (1690 cm(-1)) and cytosine (1656 cm(-1)), each with similar rate constants.

Summary Cells respond to signals of both environmental and biological origin. Responses are often receptor mediated and result in the synthesis of so-called second messengers that then provide a link between extracellular signals and downstream events, including changes in gene expression. Cyclic nucleotides (cAMP and cGMP) are among the most widely studied of this class of molecule. Research on their function and mode of action has been a paradigm for signal transduction systems and has shaped our understanding of this important area of biology. Cyclic nucleotides have diverse regulatory roles in both unicellular and multicellular organisms, highlighting the utility and success of this system of molecular communication. This review will examine the structural diversity of microbial adenylyl and guanylyl cyclases, the enzymes that synthesize cAMP and cGMP respectively. We will address the relationship of structure to biological function and speculate on the complex origin of these crucial regulatory molecules. A review is timely because the explosion of data from the various genome projects is providing new and exciting insights into protein function and evolution.

Sex is an obligate step in the life cycle of the malaria parasite and occurs in the midgut of the mosquito vector. With both Plasmodium falciparum and Plasmodium berghei, the tryptophan metabolite xanthurenic acid induces the release of motile male gametes from red blood cells (exflagellation), a prerequisite for fertilization. The addition of cGMP or phosphodiesterase inhibitors to cultures of mature gametocytes has also been shown to stimulate exflagellation. Here, we demonstrate that there is a guanylyl cyclase activity associated with mature P. falciparum gametocyte membrane preparations, which is dependent on the presence of Mg(2+)/Mn(2+) but is inhibited by Ca(2+). Significantly, this activity is increased on addition of xanthurenic acid. In contrast, a xanthurenic acid precursor (3-hydroxykynurenine), which is not an inducer of exflagellation, does not induce this guanylyl cyclase activity. These results therefore suggest that xanthurenic acid-induced exflagellation may be mediated by activation of the parasite cGMP signalling pathway.

The development of functional 1,8-naphthalimide derivatives as DNA targeting, anticancer and cellular imaging agents is a fast growing area and has resulted in several such derivatives entering into clinical trials. This review gives an overview of the many discoveries and the progression of the use of 1,8-naphthalimides as such agents and their applications to date; focusing mainly on mono-, bis-naphthalimide based structures, and their various derivatives (e.g. amines, polyamine conjugates, heterocyclic, oligonucleotide and peptide based, and those based on metal complexes). Their cytotoxicity, mode of action and cell-selectivity are discussed and compared. The rich photophysical properties of the naphthalimides (which are highly dependent on the nature and the substitution pattern of the aryl ring) make them prime candidates as probes as the changes in spectroscopic properties such as absorption, dichroism, and fluorescence can all be used to monitor their binding to biomolecules. This also makes them useful species for monitoring their uptake and location within cells without the use of co-staining. The photochemical properties of the compounds have also been exploited, for example, for photocleavage of nucleic acids and for the destruction of tumour cells.

Bloodstream-form Trypanosoma brucei acquire iron by receptor-mediated endocytosis of host transferrin. However, the mechanism(s) by which iron is then transferred from the lysosome to the cytosol are unresolved. Here, we provide evidence for the involvement of a protein (TbMLP) orthologous to the mammalian endolysosomal cation channel Mucolipin 1. In T. brucei, we show that this protein is localized to the single parasite lysosome. TbMLP null mutants could only be generated in the presence of an expressed ectopic copy, suggesting that the protein is essential. RNAi-mediated ablation resulted in a growth defect in vitro and led to a sevenfold increase in susceptibility to the iron-chelators deferoxamine and salicylhydroxamic acid. Conditional null mutants remained viable when the ectopic copy was repressed, but were hypersensitive to deferoxamine and displayed a growth defect similar to that observed following RNAi. The conditional nulls also retained virulence in vivo in the absence of the doxycycline inducer. These data provide strong evidence that TbMLP has a role in import of iron into the cytosol of African trypanosomes. They also indicate that even when expression is greatly reduced, there is sufficient protein, or an alternative mechanism, to provide the parasite with an adequate supply of cytosolic iron.

The luminescence quenching of ruthenium-tris-1,4,5,8-tetraazaphenanthrene [Ru(tap)3(2+)] by nucleotides approaches the diffusion rate only with guanosine-5'-monophosphate (GMP), the most reducing nucleotide, and leads to an electron transfer with the production of the monoreduced complex and the oxidized base. The resulting deprotonated GMP(-H).radical recombines with the monoreduced complex according to a bimolecular equimolar process. The pH dependence of the decay of the transient reduced complex, in the presence of an oxidant (oxygen or benzoquinone) indicates the formation of Ru(tap)2(tapH)2+, i.e. the reduced protonated species, subsequent to the electron transfer, with a pKa of 7.6 as confirmed from pulse radiolysis experiments. As the non-protonated reduced complex, Ru(tap)2(tap-.)+, has a higher reducing power than the protonated one, oxygen is able to reoxidize only the non-protonated species, whereas benzoquinone reoxidizes both species but with different rate constants. The flash photolysis of Ru(tap)3(2+) in the presence of DNA and the effect of Mg2+ ions and GMP as supplementary additives also show the existence of a photo-induced electron transfer with the nucleic acid, which can be correlated to the photosensitized cleavage of DNA by this complex.

Aiming at the development of new adamantano building blocks for treating African trypanosomiasis, we report on the synthesis of spiro adamantane 2-imidazolines 8a-f and 9a-c, and their congeneric 5-(1-adamantyl)imidazolines 14 and 15. The potency of these compounds against Trypanosoma brucei was compared to that of rimantadine and found, in the case of compound 14e, to be three fold higher. Together with the other active compounds, 14b and 15b, which were equipotent to rimantadine, the new molecules illustrate the synergistic effect of the lipophilic character of adamantane and the C1 amidine functionality on trypanocidal activity.

New conformationally constrained adamantane 2-oxazoline building blocks 1-4 were synthesized and their antimicrotubule and anti trypanosomal potency was investigated. Although most of the new compounds affect tubulin polymerization, this does not make a major contribution to trypanocidal activity.

A Leishmania donovani promastigote cDNA library was screened with serum obtained from a patient infected with visceral leishmaniasis. Sequence analysis of a clone obtained from this library revealed that the 600-bp insert corresponded to the carboxy-terminal region of an antigen related to the 70-kDa heat-shock protein family. The full-length sequence of the corresponding gene (1959 nucleotides) was determined after isolation of genomic clones. Genes encoding the antigen are present on a single chromosome as a series of approximately twelve 3.7-kb direct tandem repeats. The antigen can be identified as a 70-kDa heat-shock cognate protein by virtue of its molecular mass, sequence and constitutive expression during heat shock. It is expressed at all stages of the parasite life-cycle. Antibodies against the lambda gt11 fusion protein were detected in more than 50% of serum samples obtained from patients with visceral leishmaniasis, but were not detected in sera from patients with cutaneous leishmaniasis or Chagas' disease.

Spiro[aziridine-2,2'-adamantanes] 1 and 2, spiro[azetidine-2,2'-adamantanes] 3 and 5, spiro[azetidine-3,2'-adamantane] 13, spiro[piperidine-4,2'-adamantanes] 25 and 27, and spiro barbituric analog 18 were synthesized and tested for their anti-influenza A virus properties and for trypanocidal activity. The effect of ring size on potency was investigated. Piperidine 25 showed significant anti-influenza A virus activity, being 12-fold more active than amantadine, about 2-fold more active than rimantadine, and 54-fold more potent than ribavirin. It also proved to be the most active of the compounds tested against bloodstream forms of the African trypanosome, Trypanosoma brucei, being 1.5 times more potent than rimantadine and at least 25 times more active than amantadine.

A method for the preparation of anatase TiO2, which is stable to a temperature as high as 900 °C, without using any complex cationic dopants is presented. The synthetic procedure involves the reaction of titanium tetraisopropoxide (TTIP) with trifluoroacetic acid (TFA) followed by hydrolysis and sol−gel conversion to the xerogel and further calcination. The retention of the anatase phase to high temperatures can be attributed to the presence of small amounts of fluorine in the lattice, which is gradually removed between 500 and 900 °C as confirmed by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopic analysis. Samples prepared with a 1:16 TTIP/TFA composition calcined at 900 °C showed significantly higher photocatalytic activity compared to the control sample, standard commercial photocatalyst Degussa P25, and samples prepared using acetic acid and oxalic acid. The high-temperature anatase phase stability, determined by X-ray diffraction and Raman spectroscopy, coupled with its ...

The synthesis of 3-phenylindenone (la), 6-methoxy-3-phenylindenone (1b), 2-bromo-6-methoxy-3-phenylindenone (1c) and 2-ethoxycarbonyl-6-methoxy-3-phenylindenone (1d) is described using two methods - synthesis via indanoneprecursors and synthesis via propanedione precursors. Crystal structures of 2-bromo-6-methoxy-3-phenylindanone, the synthetic precursor to 1b and 2-bromo-6-methoxy-3-phenylindenone were obtained. Preliminary photochemical studies showed that 1b dimerizes readily, but no transient species were detectable using ns-flash photolysis.

The nature of the binding of several ruthenium polypyridyl complexes containing 2,2'-bipyridine (bipy), 4,4'-dimethyl-2,2'-bipyridine (DMB), 1,10-phenanthroline (phen), 4,7-diphenyl-1,10-phenanthroline (DPP), 2,2',2"-terpyridine (terpy), 2,2'-biquinoline (biq), 1,4,5,8-tetraazaphenanthrene (TAP) and 1,4,5,8,9,12-hexaazatriphenylene (HAT), with calf thymus DNA, poly[d(A-T)] and poly[d(G-C)] were studied by absorption and emission spectroscopy, DNA melting techniques, and emission lifetime measurements. In low ionic strength phosphate buffer, spectroscopic changes and DNA stabilization depended on the polypyridyl ligands present, and indicated binding that varied from substantially electrostatic to intercalative. Ru(bipy)2(HAT)2+ and Ru(phen)3(2+), which bind by partial intercalation, also show a strong preference for poly[d(A-T)]. The emission quantum yields for most complexes were increased in the presence of DNA. An exception was Ru(TAP)3(2+) which has a markedly reduced emission quantum yield and lifetime in the presence of poly[d(G-C)] or CT-DNA, due to photoredox interaction with quanines. Emission decays of the complexes generally showed multiexponential behaviour. The ability of the ruthenium complexes to sensitise DNA cleavage was determined using pBR322 plasmid DNA. Ru(TAP)3(2+) is the most efficient sensitiser while uncharged complexes and complexes with very short-lived excited states do not cleave DNA.

An intact interferon-inducible gene has been isolated from a cosmid library of human genomic DNA. The gene (designated 6-16) encodes a mRNA of approximately 1 kb which is induced well by alpha- and beta- but poorly by gamma-interferons. Genomic and cDNA sequences indicate that the gene contains five exons, and that the mRNA encodes a hydrophobic polypeptide of 130 amino acids with a putative NH2-terminal signal sequence. The 5' end has been identified by primer extension. The corresponding genomic DNA contains a TATA box 20 nucleotides upstream of the putative transcription initiation site. After transfection of the human genomic cosmid into mouse Ltk- cells, human 6-16 mRNA is expressed in response to mouse alpha- and beta- but not gamma-interferons with the same kinetics and dose-response as in the human cells. No such expression is observed in response to human interferons. It can be concluded that the human cosmid DNA contains all of the sequences necessary for alpha- and beta-interferon-induced gene expression and that the mechanisms governing such expression are conserved between murine and human cells.

The world's peoples are demanding: who should be the Lords of the Land or—should anyone be? By what right does anyone acquire the privilege of monopolizing that which should be the heritage of all? A century ago Henry George saw the nature of this question, the land question, outlined the solution and foresaw the consequences if we failed to address it. The rioting in the slums, the looting and other crime in the cities and rural areas, the tension of our time, the rising fears, paranoia and greed bear testimony to the legacy George foresaw. Against monopoly and privilege, George raised the banner of Justice and Liberty, achievable only by taxing the land and untaxing labor and its products. The failure to act upon the land question is at the bottom of the threat of a new barbarism. But the Intellectual Revolution fostered by the new computer technology promises to undermine myths that have enslaved the human mind.

A direct comparison of the photochemical interconversions between red (Pr-) and far-red (Pfr-) absorbing forms of highly-purified 124 kDa oat and rye phytochromes under identical experimental conditions was performed. In two different buffer systems at 5°C, the quantum yields for the Pr to Ptr and Pfr to Pr phototransformations under constant red and far-red illumination, φr and φfr respectively, were determined to be 0.152-0.154 and 0.060-0.065 for oat preparations and 0.172-0.174 and 0.074-0.078 for rye preparations. These values as well as the wavelength dependence of the photoequilibrium produced under continuous illumination throughout the visible and near-ultraviolet spectrum were based on the absorption spectra of the two phytochrome preparations and revised molar absorption coefficients. The molar absorption coefficients were estimated by quantitative amino acid analysis and shown to be identical for the two monocot phytochromes (i.e. 132 mM−1 cm−1 at the red absorption maximum for the Pr form). Because these measurements were performed under identical experimental conditions, including buffer, temperature, light fluence rate, and instrumentation, the differences observed must reflect structural features inherent to the two different monocotyledonous phytochromes.

Absorption spectra, fluorescence spectra and quantum yields, triplet state absorption spectra, yields and rates of decay have been obtained for methylene blue (MB+), MB+/CT-DNA complexes and complexes of MB+ with the synthetic polynucleotides poly[d(G-C)] and poly[d(A-T)]. Strong fluorescence quenching is observed in the complexes of the dye with CT-DNA and poly[d(G-C)] concomitant with a decrease in the triplet yield. The fluorescence and triplet yield of MB+ with poly[d(A-T)] are similar to those of the free dye. The triplet decay times are increased in all three polymer/dye complexes and show a decreased sensitivity to oxygen quenching. These results are interpreted in terms of the binding of the dye to these polymers and the implications of polymer binding on the photosensitizing properties of the dye are discussed.

The rates of reaction of Cr(CO) 5 with several solvents L(L = acetone, acetonitrile, benzene, diethyl ether, ethyl acetate and methanol) and of the decay of the Cr(CO) 5 L in CO-saturated cyclohexane solutions have been measured by both conventional and laser flash photolysis. The rate constants for formation and the stability constants of Cr(CO) 5 L have been deduced, and both sets of values are suggested as possible solvent parameters for organometallic reactions [e.g. for the catalytic oligomerisation of butadiene by dibutadieneiron monocarbonyl].

The preparation of a series of cis-[RuII(L–L)2(CO)L]n+ complexes [L–L-2,2′-bipyridyl (bipy), n= 1, L = H, Cl, or NCS; n= 2, L = H2O, MeCN, CO, pyridine (py), 4-vinylpyridine (vpy), or 4-methylpyridine (Mepy); L–L = 4,4′-dimethyl-2,2′-bipyridyl (Me2bipy), n= 1, L = H or Cl; n= 2, L = H2O or CO] is reported. The CO stretching frequency, the energy of the d–π* metal to ligand charge-transfer absorption bands, and the oxidation and reduction potentials of the complexes are found to depend markedly on the σ- and the π-donor abilities of the ligands. In complexes [Ru(L–L)2(CO)(H2O)]2+ and [Ru(L–L)2(CO)Cl]+ the water and Cl– ligands are thermally substitution labile. On u.v. irradiation all complexes except [Ru(L–L)2(CO)H]+ are efficiently decarbonylated.

Reaction of Li(CPhCMe2) with SnCl4 or CrCl3·3thf (thf = tetrahydrofuran) affords the isoleptic compounds Sn(CPhCMe2)4 or [Cr(CPhCMe2)4] respectively. The mode of formation and chemical properties are reported for the chromium species, and the structures of the new compounds, both of which have been determined by single-crystal X-ray analysis, are described.

Complexes [Ru(bipy)2H(L)]X (bipy = 2,2′-bipyridyl; L = CO or PPh3, X = PF6; L = AsPh3, X = ClO4) and [Ru(Me2bipy)H(CO)]PF6(Me2bipy = 4,4′-dimethyl-2,2′-bipyridyl) have been synthesised by the reaction of the corresponding [Ru(bipy)2Cl(L)]+ complex or [Ru(Me2bipy)Cl(CO)]+ respectively with sodium tetrahydroborate in aqueous ethanol. In dilute acid [Ru(bipy)2H(CO)]+ yields [Ru(bipy)2(OH2)(CO)]2+ and hydrogen gas. [Ru(bipy)2H(CO)]+ is relatively photostable compared with [Ru(bipy)2H(PPh3)]+. The phosphine and arsine complexes show, in general, an increased reactivity compared to the carbonyl complexes.