Electron capture dissociation implementation progress in fourier transform ion cyclotron resonance mass spectrometry

Successful electron capture dissociation (ECD) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) applications to peptide and protein structural analysis have been enabled by constant progress in implementation of improved electron injection techniques. The rate of ECD product ion formation has been increased to match the liquid chromatography and capillary electrophoresis timescales, and ECD has been combined with infrared multiphoton dissociation in a single experimental configuration to provide simultaneous irradiation, fast switching between the two techniques, and good spatial overlap between ion, photon, and electron beams. Here we begin by describing advantages and disadvantages of the various existing electron injection techniques for ECD in FT-ICR MS. We next compare multiple-pass and single-pass ECD to provide better understanding of ECD efficiency at low and high negative cathode potentials. We introduce compressed hollow electron beam injection to optimize the overlap of ion, photon, and electron beams in the ICR ion trap. Finally, to overcome significant outgassing during operation of a powerful thermal cathode, we introduce nonthermal electron emitter-based electron injection. We describe the first results obtained with cold cathode ECD, and demonstrate a general way to obtain low-energy electrons in FT-ICR MS by use of multiple-pass ECD.     

Industrial scale-up of pH-controlled liquid hot water pretreatment of corn fiber for fuel ethanol production

The pretreatment of cellulose in corn fiber by liquid hot water at 160°C and a pH above 4.0 dissolved 50% of the fiber in 20 min. The pretreatment also enabled the subsequent complete enzymatic hydrolysis of the remaining polysaccharides to monosaccharides. The carbohydrates dissolved by the pretreatment were 80% soluble oligosaccharides and 20% monosaccharides with o1% of the carbohydrates lost to degradation products. Only a minimal amount of protein was dissolved, thus enriching the protein content of the un dissolved material. Replication of laboratory results in an industrial trial at 43 gallons per minute (163 L/min) of fiber slurry with a residence time of 20 min illustrates the utility and practicality of this approach for pretreating corn fiber. The added costs owing to pretreatment, fiber, and hydrolysis are equivalent to less than $0.84/gal of ethanol produced from the fiber. Minimizing monosaccharide formation during pretreatment minimized the formation of degradation products; hence, the resulting sugars were readily fermentable to ethanol by the recombinant hexose and by pentose-fermenting Saccharomyces cerevisiae 424A (LNH-ST) and ethanologenic Escherichia coli at yields >90% of theoretical based on the starting fiber. this cooperative effort and first successful trial opens the door for examining the robustness of the pretreatment system under extended run conditions as well as pretreatment of other cellulose-containing materials using water at controlled pH.     

Sorptive recovery of dilute ethanol from distillation column bottoms stream

Applied Biochemistry and Biotechnology - Modern ethanol distillation processes are designed to ensure removal of all ethanol from the column bottoms, i.e., to levels <100 ppm ethanol, and...     

Wideband perfect light absorber at midwave infrared using multiplexed metal structures

We experimentally demonstrate a wideband near-perfect light absorber in the midwave IR region using a multiplexed plasmonic metal structure. The wideband near-perfect light absorber is made of two different size gold metal squares multiplexed on a thin dielectric spacing layer on top of a thick metal layer in each unit cell. We also fabricate regular nonmultiplexed structure perfect light absorbers. The multiplexed structure IR absorber absorbs more than 98% of the incident light over a much wider spectral band than regular nonmultiplexed structure perfect light absorbers in the midwave IR region.     

Supercharacters,symmetric functions in noncommuting variables,and related Hopf algebras

We identify two seemingly disparate structures: supercharacters, a useful way of doing Fourier analysis on the group of unipotent uppertriangular matrices with coefficients in a finite field, and the ring of symmetric functions in noncommuting variables. Each is a Hopf algebra and the two are isomorphic as such. This allows developments in each to be transferred. The identification suggests a rich class of examples for the emerging field of combinatorial Hopf algebras.     

Observation of two-photon absorption at low power levels using tapered optical fibers in rubidium vapor

Nonlinear optical effects can be enhanced in tapered optical fibers with diameters less than the wavelength of the propagating light. Here we report on the observation of two-photon absorption using tapered fibers in rubidium vapor at power levels of less than 150 nW. Transit-time broadening produces two-photon absorption spectra with sharp peaks that are very different from conventional line shapes.     

Molecular insight into γ–γ tubulin lateral interactions within the γ-tubulin ring complex (γ-TuRC)

γ-tubulin is essential for the nucleation and organization of mitotic microtubules in dividing cells. It is localized at the microtubule organizing centers and mitotic spindle fibres. The most well accepted hypothesis for the initiation of microtubule polymerization is that α/β-tubulin dimers add onto a γ-tubulin ring complex (γTuRC), in which adjacent γ-tubulin subunits bind to the underlying non-tubulin components of the γTuRC. This template thus determines the resulting microtubule lattice. In this study we use molecular modelling and molecular dynamics simulations, combined with computational MM-PBSA/MM-GBSA methods, to determine the extent of the lateral atomic interaction between two adjacent γ-tubulins within the γTuRC. To do this we simulated a γ–γ homodimer for 10 ns and calculated the ensemble average of binding free energies of ?107.76 kcal/mol by the MM-PBSA method and of ?87.12 kcal/mol by the MM-GBSA method. These highly favourable binding free energy values imply robust lateral interactions between adjacent γ-tubulin subunits in addition to their end-interactions longitudinally with other proteins of γTuRC. Although the functional reconstitution of γ-TuRC subunits and their stepwise in vitro assembly from purified components is not yet feasible, we nevertheless wanted to recognize hotspot amino acids responsible for key γ–γ interactions. Our free energy decomposition data from converting a compendium of amino acid residues identified an array of hotspot amino acids. A subset of such mutants can be expressed in vivo in living yeast. Because γTuRC is important for the growth of yeast, we could test whether this subset of the hotspot mutations support growth of yeast. Consistent with our model, γ-tubulin mutants that fall into our identified hotspot do not support yeast growth.