Interstellar molecule CCCN may be formed by charge-stripping of [CCCN]- in the gas phase, and when energized, undergoes loss of C with partial carbon scrambling

Deprotonation of CH2=CHCN with HO- in the chemical ionization source of a VG ZAB 2HF mass spectrometer gives CH2=-CCN which fragments through [H- (HCCCN)] to give [CCCN]-. Similar reactions with 13CH2CHCN and CH2CH13CN give [13CCCN]- and [CC13CN]-. Collision induced dissociations of these anions, together with calculations at the CCSD(T)/aug-cc-pVDZ//B3LYP/6-31+G(d) level of theory indicate that the anions do not rearrange under conditions used to charge strip them to their neutrals. A comparison of the charge reversal (-CR+) and neutralization/reionization (-NR+) mass spectra of [CCCN]- indicate that neutral C3N species (formed by charge stripping of the anion) decompose by loss of C. Experimental studies with the 13C labeled analogues indicate that the loss of C occurs subsequent to or accompanying partial carbon scrambling of the CCCN backbone. Theoretical studies suggest that this scrambling may occur during equilibration of CCCN and CCNC via a decomposing "rhombic" C3N intermediate.     

Proposed reaction mechanisms for selenium UV photolysis vapor generation by computational methods

The production of volatile analyte species by UV photolysis in the presence of low-molecular-weight organic acids as an alternative to chemical vapor generation has been of recent interest. The mechanism of this process is not well understood. Proposed mechanisms often involve photolytic cleavage of the organic acid as the initial step. Evidence suggests that this may not be the dominant route for UV photolysis vapor generation. In this work computational methods were applied to determine a possible alternative mechanism in the absence of free-radical production. The proposed mechanism specifically focused on selenium vapor generation. An energetically favored mechanism was found for UV photolysis of inorganic selenium in the presence of formic and acetic acids which is consistent with previously reported experimental results.     

Interaction of a diaphragm pressure gage with a viscoelastic halfspace

The results of an analysis to determine the interaction between a diaphragm pressure transducer and a solid propellant grain are presented. The solutions to a clamped circular plate and a halfspace are superposed to yield the desired solution. The boundary conditions on the halfspace are shown to be such that the solution to an internally pressurized Sneddon “penny-shaped” crack is applicable for an incompressible material. The problem is first solved elastically, in terms of a material-stiffness parameter which relates the diaphragm stiffness to the propellant stiffness. The solution is then extended to viscoelastic behavior through parameterization of the stiffness parameter. The electrical output of the diaphragm gage is determined and compared with the output from hydrostatic calibration, in order to determine the error or loss in gage sensitivity based on hydrostatic calibration, due to the interaction between the gage and the propellant.     

False-Positive Rate Determination of Protein Target Discovery using a Covalent Modification- and Mass Spectrometry-Based Proteomics Platform

Detection and quantitation of protein–ligand binding interactions is important in many areas of biological research. Stability of proteins from rates of oxidation (SPROX) is an energetics-based technique for identifying the proteins targets of ligands in complex biological mixtures. Knowing the false-positive rate of protein target discovery in proteome-wide SPROX experiments is important for the correct interpretation of results. Reported here are the results of a control SPROX experiment in which chemical denaturation data is obtained on the proteins in two samples that originated from the same yeast lysate, as would be done in a typical SPROX experiment except that one sample would be spiked with the test ligand. False-positive rates of 1.2-2.2 % and <0.8 % are calculated for SPROX experiments using Q-TOF and Orbitrap mass spectrometer systems, respectively. Our results indicate that the false-positive rate is largely determined by random errors associated with the mass spectral analysis of the isobaric mass tag (e.g., iTRAQ®) reporter ions used for peptide quantitation. Our results also suggest that technical replicates can be used to effectively eliminate such false positives that result from this random error, as is demonstrated in a SPROX experiment to identify yeast protein targets of the drug, manassantin A. The impact of ion purity in the tandem mass spectral analyses and of background oxidation on the false-positive rate of protein target discovery using SPROX is also discussed.

Study of the Interface Microstructures of CVD Diamond Films by TEM

 The characteristics of the interface microstructures between a CVD diamond film and the silicon substrate have been studied by transmission electron microscopy and electron energy loss spectroscopy. The investigations are performed on plan-view TEM specimens which were intentionally thinned only from the film surface side allowing the overall microstructural features of the interface to be studied. A prominent interfacial layer with amorphous-like features has been directly observed for CVD diamond films that shows a highly twinned defective diamond surface morphology. Similar interfacial layers have also been observed on films with a <100> growth texture but having the {100} crystal faces randomly oriented on the silicon substrate. These interfacial layers have been unambiguously identified as diamond phase carbon by both electron diffraction and electron energy loss spectroscopy. For the CVD diamond films that exhibit heteroepitaxial growth features, with the {100} crystal faces aligned crystallographically on the silicon substrate, such an interfacial layer was not observed. This is consistent with the expectation that the epitaxial growth of CVD diamond films requires diamond crystals to directly nucleate and grow on the substrate surface or on an epitaxial interface layer that has a small lattice misfit to both the substrate and the thin film material.