Fluorinated models of the iron-only hydrogenase: An electrochemical study of the influence of an electron-withdrawing bridge on the proton reduction overpotential and catalyst stability

AbstractHere we report the synthesis, electrochemistry and electrocatalytic activity of Fe2(CO)6(μ-SC6F5)2 (1) where the highly fluorinated bridge is electron-withdrawing, resulting in decreased electron-density at the iron–iron bond. Additionally we discuss the related substituted complexes Fe2(CO)5(PPh3)(μ-SC6F5)2 (2) and Fe2(CO)4(μ-Ph2PCH2PPh2)(μ-SC6F5)2 (3). As none of the complexes could be protonated in their neutral form it was found that proton reduction catalysis in the presence of strong acid (HBF4) took place at the potential of the first reduction of complex 1 and 3, following an EC mechanism. Complex 2 was unstable in the presence of strong acid. For 1 the potential at which proton reduction took place represented a relatively mild reduction potential (−1.15V vs. Fc/Fc+ in acetonitrile) that was comparable to examples of similar complexes in the literature. Complex 1 generated a small concentration of a highly catalytic species after electrochemical reduction, which we attribute to cleavage of the Fe–Fe bond and formation of a mono-nuclear iron species or to Fe–S bond breakage generating a vacant coordination site. The contributions to the catalytic currents were simulated using DigiSim, where it was found that the rate limiting step for 3 was the elimination of H2. It was also found that the highly catalytic species generated after reduction of 1 was more basic than 1− and also that protonation of this species was faster

A Consistency Test of Spectroscopic Gravities for Late-Type Stars

Chemical analyses of late-type stars are usually carried out following the classical recipe: LTE line formation and homogeneous, plane-parallel, flux-constant, and LTE model atmospheres. We review different results in the literature that have suggested significant inconsistencies in the spectroscopic analyses, pointing out the difficulties in deriving independent estimates of the stellar fundamental parameters and hence,detecting systematic errors. The trigonometric parallaxes measured by the HIPPARCOS mission provide accurate appraisals of the stellar surface gravity for nearby stars, which are used here to check the gravities obtained from the photospheric iron ionization balance. We find an approximate agreement for stars in the metallicity range -1 <= [Fe/H] <= 0, but the comparison shows that the differences between the spectroscopic and trigonometric gravities decrease towards lower metallicities for more metal-deficient dwarfs (-2.5 <= [Fe/H] <= -1.0), which casts a shadow upon the abundance analyses for extreme metal-poor stars that make use of the ionization equilibrium to constrain the gravity. The comparison with the strong-line gravities derived by Edvardsson (1988) and Fuhrmann (1998a) confirms that this method provides systematically larger gravities than the ionization balance. The strong-line gravities get closer to the physical ones for the stars analyzed by Fuhrmann, but they are even further away than the iron ionization gravities for the stars of lower gravities in Edvardsson's sample. The confrontation of the deviations of the iron ionization gravities in metal-poor stars reported here with departures from the excitation balance found in the literature, show that they are likely to be induced by the same physical mechanism(s).Comment: AAS LaTeX v4.0, 35 pages, 10 PostScript files; to appear in The Astrophysical Journa

Taking the Measure of the Universe: Precision Astrometry with SIM PlanetQuest

Precision astrometry at microarcsecond accuracy has application to a wide range of astrophysical problems. This paper is a study of the science questions that can be addressed using an instrument that delivers parallaxes at about 4 microarcsec on targets as faint as V = 20, differential accuracy of 0.6 microarcsec on bright targets, and with flexible scheduling. The science topics are drawn primarily from the Team Key Projects, selected in 2000, for the Space Interferometry Mission PlanetQuest (SIM PlanetQuest). We use the capabilities of this mission to illustrate the importance of the next level of astrometric precision in modern astrophysics. SIM PlanetQuest is currently in the detailed design phase, having completed all of the enabling technologies needed for the flight instrument in 2005. It will be the first space-based long baseline Michelson interferometer designed for precision astrometry. SIM will contribute strongly to many astronomical fields including stellar and galactic astrophysics, planetary systems around nearby stars, and the study of quasar and AGN nuclei. SIM will search for planets with masses as small as an Earth orbiting in the `habitable zone' around the nearest stars using differential astrometry, and could discover many dozen if Earth-like planets are common. It will be the most capable instrument for detecting planets around young stars, thereby providing insights into how planetary systems are born and how they evolve with time. SIM will observe significant numbers of very high- and low-mass stars, providing stellar masses to 1%, the accuracy needed to challenge physical models. Using precision proper motion measurements, SIM will probe the galactic mass distribution and the formation and evolution of the Galactic halo. (abridged)Comment: 54 pages, 28 figures, uses emulateapj. Submitted to PAS

The Mass and Structure of the Pleiades Star Cluster from 2MASS

We present the results of a large scale search for new members of the Pleiades star cluster using 2MASS near-infrared photometry and proper motions derived from POSS plates digitized by the USNO PMM program. The search extends to a 10 degree radius around the cluster, well beyond the presumed tidal radius, to a limiting magnitude of R ~ 20, corresponding to ~ 0.07 M_sun at the distance and age of the Pleiades. Multi-object spectroscopy for 528 candidates verifies that the search was extremely effective at detecting cluster stars in the 1 - 0.1 M_sun mass range using the distribution of H_alpha emission strengths as an estimate of sample contamination by field stars. When combined with previously identified, higher mass stars, this search provides a sensitive measurement of the stellar mass function and dynamical structure of the Pleiades. The degree of tidal elongation of the halo agrees well with current N body simulation results. Tidal truncation affects masses below ~ 1 M_sun. The cluster contains a total mass ~ 800 M_sun. Evidence for a flatter mass function in the core than in the halo indicates the depletion of stars in the core with mass less than ~ 0.5 M_sun, relative to stars with mass \~1 - 0.5 M_sun, and implies a preference for very low mass objects to populate the halo or escape. The overall mass function is best fitted with a lognormal form that becomes flat at ~ 0.1 M_sun. Whether sufficient dynamical evaporation has occurred to detectably flatten the initial mass function, via preferential escape of very low mass stars and brown dwarfs, is undetermined, pending better membership information for stars at large radial distances.Comment: 19 pages, 14 figures, 2 tables, accepted by AJ, to appear April 200

Negatively-stained polysomes on rough microsome vesicles viewed by electron microscopy: further evidence regarding the orientation of attached ribosomes

Rough microsomes, derived from rough endoplasmic reticulum of rat liver, were studied by electron microscopy after negative staining, to seek further information about the orientation of ribosomal small and large subunits in bound polysomes. Rough microsomal vesicles were fixed with 2% formaldehyde, centrifuged onto electron-microscopic grid membranes, and were then negatively-stained with 2% phosphotungstic acid. In these preparations, viewed with the electron microscope, flattened rough microsomal vesicles with bound polysomes were sometimes discernible, and the individual ribosomes in the polysomes occasionally showed small and large subunits. The small subunits were uniformly oriented toward the inside of the polysomal curve. The large and small subunits appeared to be alongside one another on the membrane, consistent with the orientation that has been described by Unwin and his co-workers. The boundary between the small and large subunits occurred at approximately the same level in the ribosome where inter-ribosomal strands have been described previously in surface views of bound polysomes in positively-stained electron-microscopic tissue sections. This further confirms the identity of the strands as messenger RNA.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47690/1/441_2004_Article_BF00343942.pd

High precision astrometry mission for the detection and characterization of nearby habitable planetary systems with the Nearby Earth Astrometric Telescope (NEAT)

(abridged) A complete census of planetary systems around a volume-limited sample of solar-type stars (FGK dwarfs) in the Solar neighborhood with uniform sensitivity down to Earth-mass planets within their Habitable Zones out to several AUs would be a major milestone in extrasolar planets astrophysics. This fundamental goal can be achieved with a mission concept such as NEAT - the Nearby Earth Astrometric Telescope. NEAT is designed to carry out space-borne extremely-high-precision astrometric measurements sufficient to detect dynamical effects due to orbiting planets of mass even lower than Earth's around the nearest stars. Such a survey mission would provide the actual planetary masses and the full orbital geometry for all the components of the detected planetary systems down to the Earth-mass limit. The NEAT performance limits can be achieved by carrying out differential astrometry between the targets and a set of suitable reference stars in the field. The NEAT instrument design consists of an off-axis parabola single-mirror telescope, a detector with a large field of view made of small movable CCDs located around a fixed central CCD, and an interferometric calibration system originating from metrology fibers located at the primary mirror. The proposed mission architecture relies on the use of two satellites operating at L2 for 5 years, flying in formation and offering a capability of more than 20,000 reconfigurations (alternative option uses deployable boom). The NEAT primary science program will encompass an astrometric survey of our 200 closest F-, G- and K-type stellar neighbors, with an average of 50 visits. The remaining time might be allocated to improve the characterization of the architecture of selected planetary systems around nearby targets of specific interest (low-mass stars, young stars, etc.) discovered by Gaia, ground-based high-precision radial-velocity surveys.Comment: Accepted for publication in Experimental Astronomy. The full member list of the NEAT proposal and the news about the project are available at http://neat.obs.ujf-grenoble.fr. The final publication is available at http://www.springerlink.co

A randomised controlled trial of a lengthened and multi-disciplinary consultation model in a socially deprived community: a study protocol

<p>Abstract</p> <p>Background</p> <p>There has been little development of the general practice consultation over the years, and many aspects of the present consultation do not serve communities with multiple health and social problems well. Many of the problems presenting to general practitioners in socio-economically disadvantaged areas are not amenable to a purely medical solution, and would particularly benefit from a multidisciplinary approach. Socio-economic deprivation is also associated with those very factors (more psychosocial problems, greater need for health promotion, more chronic diseases, more need for patient enablement) that longer consultations have been shown to address. This paper describes our study protocol, which aims to evaluate whether a lengthened multidisciplinary primary care team consultation with families in a socially deprived area can improve the psychological health of mothers in the families.</p> <p>Methods/Design</p> <p>In a randomised controlled trial, families with a history of social problems, substance misuse or depression are randomly allocated to an intervention or control group. The study is based in three general practices in a highly deprived area of North Dublin. Primary health care teams will be trained in conducting a multidisciplinary lengthened consultation. Families in the intervention group will participate in the new style multidisciplinary consultation. Outcomes of families receiving the intervention will be compared to the control group who will receive only usual general practitioner care. The primary outcome is the psychological health of mothers of the families and secondary outcomes include general health status, quality of life measures and health service usage.</p> <p>Discussion</p> <p>The main aim of this study is to evaluate the effectiveness of a lengthened multidisciplinary team consultation in primary care. The embedded nature of this study in general practices in a highly deprived area ensures generalisability to other deprived communities, but more particularly it promises relevance to primary care.</p> <p>Trial registration</p> <p>Current Controlled Trials ISRCTN70578736</p

Clinical trials in a remote Aboriginal setting: lessons from the BOABS smoking cessation study

Background: There is limited evidence regarding the best approaches to helping Indigenous Australians to stop smoking. The composite analysis of the only two smoking cessation randomised controlled trials (RCTs)investigating this suggests that one-on-one extra support delivered by and provided to Indigenous Australians in a primary health care setting appears to be more effective than usual care in encouraging smoking cessation. This paper describes the lessons learnt from one of these studies, the Be Our Ally Beat Smoking (BOABS) Study, and how to develop and implement an integrated smoking cessation program. Methods: Qualitative study using data collected from multiple documentary sources related to the BOABS Study. As the project neared completion the research team participated in four workshops to review and conduct thematic analyses of these documents. Results: Challenges we encountered during the relatively complex BOABS Study included recruiting sufficient number of participants; managing the project in two distant locations and ensuring high quality work across both sites; providing appropriate training and support to Aboriginal researchers; significant staff absences, staff shortages and high workforce turnover; determining where and how the project fitted in the clinics and consequent siloing of the Aboriginal researchers relating to the requirements of RCTs; resistance to change, and maintaining organisational commitment and priority for the project.The results of this study also demonstrated the importance of local Aboriginal ownership, commitment, participation and control. This included knowledge of local communities, the flexibility to adapt interventions to local settings and circumstances, and taking sufficient time to allow this to occur. Conclusions: The keys to the success of the BOABS Study were local development, ownership and participation, worker professional development and support, and operating within a framework of cultural safety. There were difficulties associated with the BOABS Study being an RCT, and many of these are shared with stand-alone programs. Interventions targeted at particular health problems are best integrated with usual primary health care. Research to investigate complex interventions in Indigenous health should not be limited to randomised clinical trials and funding needs to reflect the additional, but necessary, cost of providing for local control of planning and implementation