Utilisation of an eta(3)-allyl hydride complex, formed by UV irradiation, as a controlled source of 16-electron (eta(5)-C(5)Me(5))Rh(CH(2)[double bond, length as m-dash]CHMe)

Low temperature UV irradiation of solutions of (eta(5)-C(5)Me(5))Rh(CH(2)[double bond, length as m-dash]CHMe)(2) yields (eta(5)-C(5)Me(5))Rh(eta(3)-CH(2)CHCH(2))(H), which provides controlled access to the 16-electron fragment (eta(5)-C(5)Me(5))Rh(CH(2)[double bond, length as m-dash]CHMe).     

Unoriented two-stage DEA: The case of the oscillating intermediate products

Data envelopment analysis (DEA) allows us to evaluate the relative efficiency of each of a set of decision-making units (DMUs). However, the methodology does not permit us to identify specific sources of inefficiency because DEA views the DMU as a “black box” that consumes a mix of inputs and produces a mix of outputs. Thus, DEA does not provide a DMU manager with insight regarding the internal source of the organization’s inefficiency.     

A spectroscopic study of the adsorption and reactions of methanol,formaldehyde and methyl formate on clean and oxygenated Cu(110) surfaces

The adsorption and reaction of methanoi (CH₃OH), methyl formate (CH₃OCHO) and formaldehyde (H₂CO) on clean and oxygen-covered Cu(110) surfaces has been studied with EELS, UPS and thermal desorption spectroscopy (TDS). The clean surface is relatively unreactive but adsorbed oxygen readily attacks the hydroxyl proton and formyl carbon atoms to generate the intermediate methoxy (CH₃O) and formate (HCOO). Methyl formate is split into two intermediates, methoxy and formate. By correlating the three techniques we analyse (a) the condensed multilayer at 90 K; (b) the weakly bound molecular monolayer states prior to dissociation or reaction and (c) the reactive intermediates at higher temperatures. Formaldehyde forms the surface polymer polyoxymethylene [(CH₂O)_n] in the monolayer on Cu(110) which subsequently reacts with oxygen to generate formate. No molecular formaldehyde was observed above 120 K. Correlation of the EELS and UPS results for polyoxymethylene shows that an earlier interpretation by Rubloff et al. [Phys. Rev. B14 (1976) 1450] of anomalous shifts in the formaldehyde UPS spectrum on surfaces is incorrect, and due simply to the new polymeric structure of surface formaldehyde. Methyl formate coordinates to copper via the carbonyl lone pair orbital and methanol via the oxygen lone pair orbital. No evidence was found for methyl formate synthesis by dimerization of formaldehyde (the Tischenko reaction) or dehydrogenation of methanol on the clean Cu(110) surface. These latter reactions are facile over copper catalysts at atmospheric pressure. The success of the oxidation experiments and the failure of the synthesis reactions in UHV is a consequence of the pressure dependence of the equilibrium constants for the different reactions. As found previously in Fischer-Tropsch studies, condensation reaction equilibria are pressure dependent and product formation is considerably suppressed at UHV pressures.     

57Fe Mössbauer Spectroscopy Studies of Meteorites: Implications for Weathering Rates,Meteorite Flux,and Early Solar System Processes

Ordinary chondrite finds, terrestrial age dated using ¹⁴C analyses, from different meteorite accumulation sites, have been examined by Mössbauer spectroscopy to quantitatively determine terrestrial oxidation. We observe differences in weathering rates between sites, and also between different chondrite groups. A comparison of weathering over time, and its effect in eroding meteorites, together with the number and mass distribution of meteorites in each region, enables us to derive estimates of the number of meteorite falls over a given mass per year. Studies of how the oxygen isotopic composition of samples varies with weathering indicate that incipient alteration may occur without a pronounced isotopic effect, possibly due to weathering of silicates to topotactically oriented smectite confined spaces where the water volume is limited. This finding has profound implications for the use of oxygen isotopes as a tool in understanding water–rock interaction. It also may reconcile previously contradictory data regarding the nebular or asteroidal location of pre-terrestrial aqueous alteration. Finally, Mössbauer spectroscopy is also found to be a useful tool in determining mineral abundance in carbonaceous chondrites, where a fine-grained matrix makes traditional approaches inapplicable. Again, the results have implications for the modification of chondritic materials in the early solar system.     

Refractive microlens array for wave-front analysis in the medium to hard x-ray range

We report an alternative approach to x-ray wave-front analysis that uses a refractive microlens array as a Shack-Hartmann sensor. The sensor was manufactured by self-assembly and electroplating techniques and is suitable for high-resolution wave-front analysis of medium to hard x rays. We demonstrate its effectiveness at an x-ray energy of 3 keV for analysis of x-ray wave-front perturbations caused by microscopic objects. The sensor has potential advantages over other methods for x-ray phase imaging and will also be useful for the characterization of x-ray beams and optics.     

Resistive-pulse studies of proteins and protein/antibody complexes using a conical nanotube sensor

There is increasing interest in using nanopores in synthetic membranes as resistive-pulse sensors for molecular and macromolecule analytes. In general, this method entails measuring current pulses associated with translocation of the analyte through the nanopore sensor element. A key challenge for this sensing paradigm is building selectivity into the protocol so that the current pulses for the target analyte can be distinguished from current pulses for other species that might be present in the sample. We show here that this can be accomplished with a protein analyte by adding to the solution an antibody that selectively binds the protein. We demonstrate this concept using bovine serum albumin (BSA) and a Fab fragment from a BSA-binding polyclonal antibody. Because the complex formed upon binding of the Fab to BSA is larger than the free BSA molecule, the current-pulse signature for the BSA/Fab complex can be easily distinguished from the free BSA. Furthermore, the BSA/Fab pulses can be easily distinguished from the pulses obtained for the free Fab and from pulses obtained for a control protein that does not bind to the Fab. Finally, we also show that the current-pulse signature for the BSA/Fab complex can provide information about the size and stoichiometry of the complex.     

Determination of Rigidity of Protein Bound Au(144) Clusters by Electron Cryomicroscopy

A method for estimating the positional displacement of protein bound gold nanoparticles is presented and used to estimate the rigidity of linkage of Au(144) nanoparticles bound to a tetrameric model protein. We observe a distribution of displacement values where most Au(144) clusters are immobilized to within 3? relative to the protein center of mass. The shape of the distribution suggests two physical processes of thermal motion and protein deformation. The application of this and similar rigid gold nanoparticle/protein conjugates in high resolution single particle electron cryo-microscopy is discussed.     

Synthesis,properties and X‐ray structure of 5‐azido‐2‐methoxy‐1,3‐xylyl‐18‐crown‐5

5‐Azido‐2‐methoxy‐1,3‐xylyl‐18‐crown‐5 has been prepared by reacting p‐toluenesulfonyl azide with the carbanion generated from the reaction of 5‐bromo‐2‐methoxy‐1,3‐xylyl‐18‐crown‐5 with n‐butyl lithium. The asymmetric N₃ stretch of this product has been observed as a single band at 2110 cm^?1 in dichloromethane solution. Addition of solid NaSCN, KSCN and CsSCN shifts this band to 2115, 2113 and 2112 cm^?1, respectively. Computational studies of this azide at the B3LYP‐6‐31G* level in the presence and absence of Na⁺ predicted these bands to be at 2173 cm^?1 and 2184 cm^?1. For the salt‐containing solutions, additional bands were observed at 2066 cm^?1, 2056 cm^?1 and 2055 cm^?1, respectively, which are in the range expected for CN stretches. The X‐ray structure of this azide has been determined. The terminal and internal N? N bond lengths were found to be 1.127(2) and 1.245(2) Δ, respectively, which is the usual pattern for aromatic azides. The crown ether is looped over the face of the aromatic ring resulting in an angle of 38.94° between the plane defined by the aromatic ring and that defined by the five ring oxygen atoms. In addition, the CH₃ group is rotated out of the plane of the phenyl ring with C1‐C18‐O181‐C182 and C17‐C18‐O181‐C182 dihedral angles of 93.81(14)° and ‐90.54(14)°, respectively.