Tandem mass spectrometry investigation of ADP-ribosylated kemptide

Bacterial adenosine diphosphate-ribosyltransferases (ADPRTs) are toxins that play a significant role in pathogenicity by inactivating host proteins through covalent addition of ADP-ribose. In this study we used ADP-ribosylated Kemptide (LRRASLG) as a standard to examine the effectiveness of three common tandem mass spectrometry fragmentation methods for assignment of amino acid sequence and site of modification. Fragmentation mechanisms investigated include low-energy collision-induced dissociation (CID), infrared multiphoton dissociation (IRMPD), and electron-capture dissociation (ECD); all were performed on a hybrid linear ion trap Fourier transform ion cyclotron resonance mass spectrometer. We show that ECD, but neither CID nor IRMPD, of ADP-ribosylated Kemptide produces tandem mass spectra that are interpretable with regard to amino acid sequence assignment and site of modification. Examination of CID and IRMPD tandem mass spectra of ADP-ribosylated Kemptide revealed that fragmentation was primarily focused to the ADP-ribose region, generating several potential diagnostic ions for use in discovery of ADP-ribosylated proteins. Because of the lower relative sensitivity of ECD during data-dependent acquisition to CID, we suggest a 2-fold strategy where CID and IRMPD are first used to detect ADP-ribosylated peptides, followed by sequence assignment and location of modification by ECD analysis.     

Directional distance functions and slacks-based measures of efficiency

In this paper we introduce a SBM (slacks-based measure) of efficiency based on directional distance functions. This measure is contrasted with the SBM due to Professor Tone [Tone, K., 2001. A slacks-based measure of efficiency in data envelopment analysis. European Journal of Operational Research 130, 498–509].     

A comparison of shadow prices and reimbursement rates of hospital services

The purpose of this paper is to calculate shadow prices of hospital services and compare them to the reimbursement rates those hospitals receive. These shadow prices are calculated by estimating a multiple-output distance function and applying a dual Shephard's lemma, a technique suggested by Färe and Grosskopf [8]. In contrast to cost functions, distance functions require no price data and do not presume cost minimization. We apply this technique to a sample of California hospitals operating in 1986. We find that hospitals engaged in selective contracting for Medi-Cal patients exhibit closer agreement between relative shadow prices and relative reimbursement rates (Medi-Cal relative to private patients) than noncontracting hospitals.Contact author.     

Linear programming approaches to the measurement and analysis of productive efficiency

Invited by J. T. Pastor     

Olefin metathesis catalysts bearing a pH-responsive NHC ligand: a feasible approach to catalyst separation from RCM products

Two novel ruthenium-based olefin metathesis catalysts, H(2)ITap(PCy(3))Cl(2)Ru[double bond, length as m-dash]CH-Ph and H(2)ITapCl(2)Ru[double bond, length as m-dash]CH-(C(6)H(4)-O-iPr) (H(2)ITap = 1,3-bis(2',6'-dimethyl-4'-dimethylaminophenyl)-4,5-dihydroimidazol-2-ylidene), were synthesized bearing a pH-responsive NHC ligand with two aromatic NMe(2) groups. The crystal structures of complexes and were determined via X-ray crystallography. Both catalysts perform ring opening metathesis polymerization (ROMP) of cyclooctene (COE) at faster rates than their commercially available counterparts H(2)IMes(PCy(3))Cl(2)Ru[double bond, length as m-dash]CH-Ph and H(2)IMesCl(2)Ru[double bond, length as m-dash]CH-(C(6)H(4)-O-iPr) (H(2)IMes = 1,3-bis(2',4',6'-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene) and perform at similar rates during ring closing metathesis (RCM) of diethyldiallylmalonate (DEDAM). Upon addition of 2 equiv. of HCl, catalyst is converted into a mixture of several mono and diprotonated Ru-carbene species 12' which are soluble in methanol but degrade within a few hours at room temperature. Catalyst can be protonated with 2 equiv. of HCl and the resulting complex is moderately water-soluble. The complex is stable in aqueous solution in air for >4 h, but over prolonged periods of time shows degradation in acidic media due to hydrolysis of the NHC-Ru bond. Catalysts and perform RCM of diallylmalonic acid in acidic protic media with only moderate activity at 50 degrees C and do not produce polymer in the ROMP of cationic 7-oxanorbornene derivative under the same conditions. Catalyst was used for Ru-seperation studies when RCM of DEDAM or 3,3-diallypentadione (DAP) was conducted in low-polar organic solution and the Ru-species was subsequently precipitated by addition of strong acid. The Ru-species were removed by (1) filtration and (2) filtration and subsequent extraction with water. The residual Ru-levels could be reduced to as far as 11 ppm (method 2) and 24 ppm (method 1) without the use of chromatography or other scavenging methods.     

Zintl phases for thermoelectric devices

By converting waste heat into electricity and improving the efficiency of refrigeration systems, thermoelectric devices could play a significant role in solving today's energy problems. Increasing the thermoelectric efficiency (as measured by the thermoelectric material's figure-of-merit, zT) is critical to the development of this technology. Complex Zintl phases, in particular, make ideal candidates for thermoelectric materials because the necessary "electron-crystal, phonon-glass" properties can be engineered with an understanding of the Zintl chemistry. A recent example is the discovery that Yb(14)MnSb(11), a transition metal Zintl compound, has twice the zT as the material currently in use at NASA. This perspective outlines a strategy to discover new high zT materials in Zintl phases, and presents results pointing towards the success of this approach.     

Kinetics and mechanism of OH oxidation of small organic dicarboxylic acids in ice: comparison to behavior in aqueous solution

To better understand the oxidation of organic species by OH within frozen solutions, experiments were conducted with a simplified model system consisting of succinic acid (2.5, 5, and 10 mM), using H(2)O(2) (30 mM) as a condensed-phase OH precursor. Frozen (-20 °C) and aqueous (0 °C and room temperature) solutions were irradiated using a xenon arc lamp to study the differences between frozen and nonfrozen reaction media. Formation of products and decay of reactants were measured using ion chromatography (IC) and gas chromatography-mass spectrometry (GC-MS). Malonic acid was observed as the dominant product, with malic acid formed in significantly smaller amounts, in both frozen and unfrozen substrates, suggesting a common mechanism independent of phase. Notably, a large decrease was observed in the succinic acid first-order decay rate constant when moving from aqueous to frozen samples. This is due not to temperature-dependent second-order kinetics or different OH production rates between the samples, but instead probably arises from physical separation of the succinic acid and H(2)O(2) upon freezing or precipitation of succinic acid upon freeze concentration. The effect is not nearly as pronounced for the decay kinetics of a much more soluble species, namely, malonic acid. From an environmental perspective, this work is the first experimental demonstration that dicarboxylic acids present in the cryosphere might be subject to photochemical degradation into smaller organic acids and carbon dioxide.     

Measurement of radiative shock properties by x-ray Thomson scattering

X-ray Thomson scattering has enabled us to measure the temperature of a shocked layer, produced in the laboratory, that is relevant to shocks emerging from supernovas. High energy lasers are used to create a shock in argon gas which is probed by x-ray scattering. The scattered, inelastic Compton feature allows inference of the electron temperature. It is measured to be 34 eV in the radiative precursor and ～60 eV near the shock. Comparison of energy fluxes implied by the data demonstrates that the shock wave is strongly radiative.     

Increase of the density,temperature and velocity of plasma jets driven by a ring of high energy laser beams

Supersonic plasma outflows driven by multi-beam, high-energy lasers, such as Omega and NIF, have been and will be used as platforms for a variety of laboratory astrophysics experiments. Here we propose a new way of launching high density and high velocity, plasma jets using multiple intense laser beams in a hollow ring formation. We show that such jets provide a more flexible and versatile platform for future laboratory astrophysics experiments. Using high resolution hydrodynamic simulations, we demonstrate that the collimated jets can achieve much higher density, temperature and velocity when multiple laser beams are focused to form a hollow ring pattern at the target, instead of focused onto a single spot. We carried out simulations with different ring radii and studied their effects on the jet properties. Implications for laboratory collisionless shock experiments are discussed.