Investigation of proton-proton short-range correlations via the 12C(e,e'pp) reaction

We investigated simultaneously the 12C(e,e'p) and 12C(e,e'pp) reactions at Q2=2 (GeV/c)2, xB=1.2, and in an (e, e'p) missing-momentum range from 300 to 600 MeV/c. At these kinematics, with a missing momentum greater than the Fermi momentum of nucleons in a nucleus and far from the delta excitation, short-range nucleon-nucleon correlations are predicted to dominate the reaction. For (9.5+/-2)% of the 12C(e,e'p) events, a recoiling partner proton was observed back-to-back to the 12C(e,e'p) missing-momentum vector, an experimental signature of correlations.     

An investigation into the one-pot Heck olefination-hydrogenation reaction

Herein is described an operationally simple process concerning the observation that, following either inter-, or intramolecular Heck olefination, stirring of the so formed substituted alkenyl product under an atmosphere of hydrogen efficiently effects alkene hydrogenation. Overall this two-operation, one-pot "reductive Heck" sequence is notable since direct reductive Heck processes, using additives such as formate salts, are restricted to a limited range of substrates. In total 25 examples are reported (yields ranging from 0 to 95%), which were selected in order to probe the scope and limitations of this method. Finally, the utility of this sequence was demonstrated in a short synthesis of the calcimimetic agent, cinacalcet.     

Stark broadening of visible neutral helium lines in a plasma

Side-on observations of the visible spectrum emitted by a helium plasma generated in a wall-stabilized arc are reported. Electron densities range from 0.2 to 1.3 × 10²²m^-3 and electron temperatures vary from 10,000 to 20,000 K. Most of the seventeen measured lines are “isolated” at the conditions of the experiment. Here, “isolated” refers to quantum levels which are non-degenerate even in the presence of perturbing fields. Electron densities derived from the Stark-widths of the isolated lines agree to within 15% of the values determined from Hβ and from the quasi-degenerate He(I) lines at 4471 and 4921 Å. Similar agreement is observed for the static-ion Stark broadening parameters. However, at the conditions of this experiment, the static-ion approximation is not valid near the center of some of the isolated lines. The observation of ion-dynamic effects in neutral isolated lines is reported here for the first time. In the isolated lines, the measured ion-dynamic effects are reasonably consistent with calculations based on an adiabatic “unified” theory for the ion perturbers. A simple parametric expression closely approximates the ion-dynamic contribution to the half-width of isolated lines. Hydrogenic (non-isolated) neutral helium lines exhibit a large discrepancy with theoretical profiles near the line center, where ion-dynamic effects are important.     

Characterization of a new tailoring domain in polyketide biogenesis: the amine transferase domain of MycA in the mycosubtilin gene cluster

We report the expression and characterization of a truncated form of MycA from the Mycosubtilin gene cluster from Bacillus subtilis. The MycA fragment contains a new amino transferase (AMT) tailoring domain, allowing the first detailed study of a PLP-dependent enzyme operating in cis within the PKS and NRPS biosynthetic paradigm. As the AMT domain acts on covalently bound beta-ketothioesters, and is therefore a single-turnover system, electrospray ionization-Fourier transform mass spectrometry (ESI-FTMS) was used to observe the amine-transfer reaction both for amine donor substrate specificity and to regiospecifically determine enzyme-bound intermediates. We confirm the function of the AMT domain, dissect the mechanistic steps of amine transfer, identify the preferred amine source, and localize the beta-ketothioester substrate during amine transfer.     

Stability properties of current-profiled quantum dot lasers

The stability properties of injection-current profiled quantum dot lasers are analyzed for broad area devices of different length. In general, devices demonstrate stable output at low to moderate injection levels before the onset of filamentary dynamics at higher injection levels. By comparing devices of different lengths, the onset of filamentary dynamics is shown to coincide in each case with the onset of excited state lasing and so the loss in stability may be linked to the increased low frequency noise and phase-amplitude coupling that occurs in this regime.     

Quark-hadron duality in neutron (3He) spin structure

We present experimental results of the first high-precision test of quark-hadron duality in the spin-structure function g_{1} of the neutron and 3He using a polarized 3He target in the four-momentum-transfer-squared range from 0.7 to 4.0 (GeV/c);{2}. Global duality is observed for the spin-structure function g_{1} down to at least Q;{2}=1.8 (GeV/c);{2} in both targets. We have also formed the photon-nucleon asymmetry A1 in the resonance region for 3He and found no strong Q2 dependence above 2.2 (GeV/c);{2}.     

Top-down proteomics reveals novel protein forms expressed in methanosarcina acetivorans

Combining our previous work with current platforms presented here that identified 99 new proteins (Supplemental Table 1), a total of 200 protein identities in M. acetivorans have been confirmed. Of these, five proteins were unannotated, 15 were mispredicted, two exhibited variable removal of the start methionine, and one was a proteolysis fragment from the identical C-terminus of two possible proteins. The incorporation of LC-MS/MS and offline automation speeds up the processing of samples through automation of the top-down process. For five data files that were automatically processed and iteratively searched, 2 h were required to complete analysis. In these, a total of 835 identifications were detected by the search algorithm in this time period. The expanded use of top-down will use both online and offline strategies, with increasingly sophisticated data acquisition strategies tailored for the challenges of top-down fragmentation [[16], [18], [19], [32] and [33]].     

Dissecting non-ribosomal and polyketide biosynthetic machineries using electrospray ionization Fourier-Transform mass spectrometry

Many virulence factors and bioactive compounds with antifungal, antimicrobial, and antitumor properties are produced via the non-ribosomal peptide synthetase (NRPS) or polyketide synthase(PKS) paradigm. During the biosynthesis of these natural products, substrates, intermediates and side products are covalently tethered to the NRPS or PKS catalyst, introducing mass changes, making these biosynthetic systems ideal candidates for interrogation by large molecule mass spectrometry. This review serves as an introduction into the application of electrospray ionization Fourier-Transform massspectrometry (ESI-FTMS) to investigate NRPS and PKS systems. ESI-FTMS can be used to understand substrate tolerance, timing of covalent linkages, timing of tailoring reactions and the transfer of substrates and biosynthetic intermediates from domain to domain. Therefore we not only highlight key mechanistic insights for thiotemplate systems as found on the enterobactin,yersiniabactin, epothilone, clorobiocin, coumermycin, pyoluteorin, gramicidin, mycosubtilin, C-1027,6-deoxyerythronolide B and FK520 biosynthetic pathways, but we also explain the approaches taken to identify active sites from complex digests and compare the FTMS based assay to traditional assays and other mass spectrometric techniques. Although mass spectrometry was introduced over two decades ago to investigate NRPS and PKS biosynthetic systems, this is the first review devoted to this methodology.