The μ3-cyclopentadienylidene ligand: X-ray structure of [Ru4(CO)5 {P(OMe)3}(μ3-C5H4)2(η-C5H5)2]

UV irradiation of [Ru₂(CO)₄(η-C₅H₅)₂] yields the tri- and tetra-ruthenium complexes [Ru₂(CO)₄(η-C₅H₅){η-C₅H₄Ru(CO)₂(η-C₅H₅)}] and [Ru₄(CO)₆(μ₃-C₅H₄)₂(η-C₅H₅)₂]. The μ₃-C₅H₄ ligand in the latter has been characterised through an X-ray diffraction study on [Ru₄(CO)₅{P(OMe)₃}(μ₃-C₅H₄)₂(η-C₅H₅)₂].     

C-C bond formation at polynuclear metal centers

Studies on C-C bond formation between simple hydrocarbon species such as CH₂, C=CH₂, CH=CH₂, CH₂=CH₂, CH₂=C=CH₂ and CHCH at a diruthenium center suggest that the process is promoted when the dimetal center can readily compensate for the two electrons lost in the formation of the new C-C bond. Thus, whereas -CH₂ and ethene combine only under forcing conditions, the combination of -CH₂ with allene or ethyne, which have additional -electrons available for coordination, occurs readily at room temperature. Likewise, the availability of uncoordinated -electrons in -C=CH₂ allows vinylidene to link rapidly with ethene at room temperature. Alkyne complexes [Ru₂(CO)(-RCCR)(-C₅H₅)₂] (R=CF₃ or Ph) react only under vigorous conditions with additional alkyne to give [Ru₂(CO)(-C₄R₄) (-C₅H₅)₂], but give these same species at room temperature in the presence of acid, shown to be due to the intermediacy of highly reactive 30-electron -vinyl cations. Thermally, alkyne linking proceedsvia three-alkyne species [Ru₂(-C₆R₆)(-C₅H₅)₂] to a four-alkyne complex [Ru₂(-C₈R₈)(-C₅H₅)₂], containing an unprecedented C₈ ligand composed of a C₆ ring with a C₂ tail. Treatment of [Ru₂(CO)(-RCCR)(-C₅H₅)₂] with unsaturated metal fragments gives trimetal complexes such as [Ru₃(CO)₅(₃-CF₃CCCF₃) (-C₅H₅)₂]. The MeCN derivative of this species undergoes unusual linking processes on reaction with additional alkyne to giveinter alia [Ru₃(CO)₃(₃-CCF₃){₃-C₃(CF₃)₃}(-C₅H₅)₂], arising from alkyne cleavage, and [Ru₃(CO)₃{₃-C₄(CF₃)₂(CO₂Me)₂}(-C₅H₅)₂], a closo-pentagonal bipyramidal Ru₃C₄ cluster.     

The inverse hull of the free semigroup on a set X

In this paper the inverse hull of the free semigroup on a non-empty set X is characterized. It is shown that if F^O is a certain semilattice and (G,*) is the free group on X, then is isomorphic to a Rees factor semigroup of a subsemigroup of (F^O x G, #), where (A,w)#(B,u) = ((A*w B)*w^–1, w*u). Several properties of , including Green's relations on are also determined.     

Inhibition of class A beta-lactamases by carbapenems: crystallographic observation of two conformations of meropenem in SHV-1

Carbapenem antibiotics are often the "last resort" in the treatment of infections caused by bacteria resistant to penicillins and cephalosporins. To understand why meropenem is resistant to hydrolysis by the SHV-1 class A beta-lactamase, the atomic structure of meropenem inactivated SHV-1 was solved to 1.05 A resolution. Two conformations of the Ser70 acylated intermediate are observed in the SHV-1-meropenem complex; the meropenem carbonyl oxygen atom of the acyl-enzyme is in the oxyanion hole in one conformation, while in the other conformation it is not. Although the structures of the SHV-1 apoenzyme and the SHV-1-meropenem complex are very similar (0.29 A rmsd for Calpha atoms), the orientation of the conserved Ser130 is different. Notably, the Ser130-OH group of the SHV-1-meropenem complex is directed toward Lys234Nz, while the Ser130-OH of the apo enzyme is oriented toward the Lys73 amino group. This altered position may affect proton transfer via Ser130 and the rate of hydrolysis. A most intriguing finding is the crystallographic detection of protonation of the Glu166 known to be involved in the deacylation mechanism. The critical deacylation water molecule has an additional hydrogen-bonding interaction with the OH group of meropenem's 6alpha-1 R-hydroxyethyl substituent. This interaction may weaken the nucleophilicity and/or change the direction of the lone pair of electrons of the water molecule and result in poor turnover of meropenem by the SHV-1 beta-lactamase. Using timed mass spectrometry, we further show that meropenem is covalently attached to SHV-1 beta-lactamase for at least 60 min. These observations explain key properties of meropenem's ability to resist hydrolysis by SHV-1 and lead to important insights regarding future carbapenem and beta-lactamase inhibitor design.     

Functionalised cyclopentadienyl zirconium compounds as potential anticancer drugs

New neutral and ionic functionalised zirconocene dichloride compounds have been isolated and characterised. The ionic zirconocene exhibits excellent cytotoxicity against a range of human tumour cell lines, which represents the first active anticancer zirconocene dichloride compound.     

Broadly tunable femtosecond parametric oscillator using a photonic crystal fiber

Pulses as short as 460 fs and a tuning range as wide as 200 nm around 1 microm have been achieved from a photonic-crystal-fiber-based parametric oscillator. The ring cavity with only 65 cm of photonic crystal fiber is synchronously pumped with a tunable passively mode-locked Yb-doped fiber laser. Widely extended tunability is achieved by using the modulation instability gain in normal dispersion as the result of high-order dispersion in the photonic crystal fiber.     

Luminol-dependent chemiluminescence analysis of human platelets

We describe a simple, sensitive, and reproducible assay system to measure the chemiluminescence (CL) produced by injecting arachidonic acid (AA) into a preparation of human platelets containing luminol.The CL appears to result from the metabolism of the AA by enzymes in human platelets, namely, cyclooxygenase, lipoxygenase, and possibly peroxidases. It is believed that when the AA is injected, free radicals and/or oxidizing agents are formed that react with the luminol producing an excited state and emitting blue light (425 nm).The enzymes can be inhibited by drugs to varying degrees. BW755C inhibits all CL at micromolar doses and it is known to inhibit both lipoxygenase and cyclooxygenase. Aspirin, indomethacin, and sulindac sulfide inhibit only cyclooxygenase and inhibit 35–65% of the light from an individual. This assay system can be used to screen certain drugs that are effective in inflammatory diseases. It could be used to determine whether the drugs would be effective in a given individual and also whether drugs have a long-term toxic effect in vivo on platelets. Further the assay is practical with a few milliters of blood.     

True fundamental solitons in a passively mode-locked short-cavity Cr(4+):YAG laser

We demonstrate a self-starting, passively mode-locked short-cavity Cr(4+):YAG laser that supports fundamental intracavity solitons over wide ranges of cavity group-velocity dispersion and pulse energies. The total dispersion and nonlinear effects are small enough that stable, N=1 soliton pulses are generated. Equally spaced multiple pulsing is also observed, with fundamental soliton behavior preserved. Regions of bistability exist where, at a constant cavity dispersion, the laser can produce transform-limited pulses of a different width and energy. The laser produces 200-fs pulses at approximately 0.9-, 1.8-, and 2.7-GHz repetition rates with a total of 82 mW of average output power.     

Phase locking and periodic evolution of solitons in passively mode-locked fiber lasers with a semiconductor saturable absorber

Passively mode-locked lasers with intracavity weakly birefringent fiber are theoretically analyzed based on two coupled complex one-dimensional Ginzburg-Landau equations. The model includes fiber birefringence, spectral filtering, saturable gain, and saturable loss. Phase-locked soliton solutions are found for small amounts of birefringence and several types of soliton with periodic polarization evolution for higher amounts of birefringence. Numerical simulations show qualitative agreement with experimental results.