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1.
Dey A Peng Y Broderick WE Hedman B Hodgson KO Broderick JB Solomon EI 《Journal of the American Chemical Society》2011,133(46):18656-18662
S K-edge X-ray absorption spectroscopy on the resting oxidized and the S-adenosyl-l-methionine (SAM) bound forms of pyruvate formate-lyase activating enzyme are reported. The data show an increase in pre-edge intensity, which is due to additional contributions from sulfide and thiolate of the Fe(4)S(4) cluster into the C-S σ* orbital. This experimentally demonstrates that there is a backbonding interaction between the Fe(4)S(4) cluster and C-S σ* orbitals of SAM in this inner sphere complex. DFT calculations that reproduce the data indicate that this backbonding is enhanced in the reduced form and that this configurational interaction between the donor and acceptor orbitals facilitates the electron transfer from the cluster to the SAM, which otherwise has a large outer sphere electron transfer barrier. The energy of the reductive cleavage of the C-S bond is sensitive to the dielectric of the protein in the immediate vicinity of the site as a high dielectric stabilizes the more charge separated reactant increasing the reaction barrier. This may provide a mechanism for generation of the 5'-deoxyadenosyl radical upon substrate binding. 相似文献
2.
K. Andersen O. P. Anderson T. Miller N. S. Mani T. F. Baumann M. Anderson W. E. Broderick D. M. Eichhorn D. Goldberg W. Jarrell S. J. Lange S. Lee H. Nie M. Sabat J. W. Sibert C. Stern B. M. Hoffman S. Baum L. S. Beall A. S. Cook Q. J. Mccubbin A. Garrido Montalban M. S. Rodriguez-Morgade A. J. P. White D. B. G. Williams D. J. Williams A. G. M. Barrett H. Hope M. M. Olmstead 《Journal of heterocyclic chemistry》1998,35(5):1013-1042
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We report an approach to the in situ synthesis of oligonucleotide arrays on surfaces coated with crosslinked polymer multilayers. Our approach makes use of methods for the 'reactive' layer-by-layer assembly of thin, amine-reactive multilayers using branched polyethyleneimine (PEI) and the azlactone-functionalized polymer poly(2-vinyl-4,4'-dimethylazlactone) (PVDMA). Post-fabrication treatment of film-coated glass substrates with d-glucamine or 4-amino-1-butanol yielded hydroxyl-functionalized films suitable for the Maskless Array Synthesis (MAS) of oligonucleotide arrays. Glucamine-functionalized films yielded arrays of oligonucleotides with fluorescence intensities and signal-to-noise ratios (after hybridization with fluorescently labeled complementary strands) comparable to those of arrays fabricated on conventional silanized glass substrates. These arrays could be exposed to multiple hybridization-dehybridization cycles with only moderate loss of hybridization density. The versatility of the layer-by-layer approach also permitted synthesis directly on thin sheets of film-coated poly(ethylene terephthalate) (PET) to yield flexible oligonucleotide arrays that could be readily manipulated (e.g., bent) and cut into smaller arrays. To our knowledge, this work presents the first use of polymer multilayers as a substrate for the multi-step synthesis of complex molecules. Our results demonstrate that these films are robust and able to withstand the ~450 individual chemical processing steps associated with MAS (as well as manipulations required to hybridize, image, and dehybridize the arrays) without large-scale cracking, peeling, or delamination of the thin films. The combination of layer-by-layer assembly and MAS provides a means of fabricating functional oligonucleotide arrays on a range of different materials and substrates. This approach may also prove useful for the fabrication of supports for the solid-phase synthesis and screening of other macromolecular or small-molecule agents. 相似文献
4.
Ionic liquids (ILs) are considered to be one of the steppingstones to fabricate next generation electrochemical devices given their unique physical and chemical properties. The addition of water to ILs significantly impact electrochemical related properties including viscosity, density, conductivity, and electrochemical window. Herein we utilize ambient pressure X-ray photoelectron spectroscopy (APXPS) to examine the impact of water on values of the electrochemical shift (S), which is determined by measuring changes in binding energy shifts as a function of an external bias. APXPS spectra of C 1s, O 1s and N 1s regions are examined for the IL 1-butyl-3-methylimidazolium acetate, [C4mim][OAc], at the IL/gas interface as a function of both water vapor pressure and external bias. Results reveal that in the absence of water vapor there is an IL ohmic drop between the working electrode and quasi reference electrode, giving rise to chemical specific S values of less than one. Upon introducing water vapor, S values approach one as a function of increasing water vapor pressure, indicating a decrease in the IL ohmic drop as the IL/water mixture becomes more conductive and the potential drop is driven by the electric double layer at the electrode/IL interface. 相似文献
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6.
Greater than 20%-efficient frequency doubling of 1532-nm nanosecond pulses in quasi-phase-matched germanosilicate optical fibers 总被引:2,自引:0,他引:2
Pruneri V Bonfrate G Kazansky PG Richardson DJ Broderick NG de Sandro JP Simonneau C Vidakovic P Levenson JA 《Optics letters》1999,24(4):208-210
We fabricated second-order nonlinear gratings in D-shaped germanosilicate fibers, using thermal poling and periodic electrodes defined by standard photolithography. These gratings, which are up to 75 mm long, were used for efficient quasi-phase-matched frequency doubling of 1.532-mum nanosecond pulses from a high-power erbium-doped fiber amplifier. Average second-harmonic powers as high as 6.8 mW and peak powers greater than 1.2 kW at 766 nm were generated, with average and peak conversion efficiencies as high as 21% and 30%, respectively. 相似文献
7.
Spore photoproduct (SP) lyase, which catalyzes the direct reversal of SP (5-thyminyl-5,6-dihydrothymine) to thymine monomers, is the only identified nonphotoactivatable pyrimidine dimer lyase. Unlike DNA photolyase, SP lyase does not contain a flavin cofactor and does not require light for activation. Instead, preliminary studies point to the presence of an iron-sulfur cluster in SP lyase and the requirement for S-adenosylmethionine (AdoMet) for catalytic activity, suggesting that SP lyase belongs to the growing group of iron-sulfur cluster and AdoMet-dependent radical enzymes. Here we provide evidence for the role of AdoMet as a reversible deoxyadenosyl radical generator, which initiates repair by hydrogen atom abstraction from C-6 of SP. Reaction of 6-(3)H-SP, but not methyl-(3)H-SP, with SP lyase and AdoMet results in transfer of (3)H to AdoMet, while no tritiated 5'-deoxyadenosine is observed. When 5'-tritiated AdoMet is used in the reaction with unlabeled SP, transfer of (3)H into the repaired thymine monomers is observed. These results point to the reversible generation of a 5'-deoxyadenosyl radical intermediate, which reacts directly with the DNA lesion to initiate a radical-mediated beta-scission. We also demonstrate that AdoMet is a catalytic cofactor that is not consumed during turnover. Together, these results support a novel radical-based mechanism for the repair of UV-induced DNA damage. 相似文献
8.
Neville F Broderick MJ Gibson T Millner PA 《Langmuir : the ACS journal of surfaces and colloids》2011,27(1):279-285
In nature, some peptides induce precipitation of silicic acid into silica nanoparticles such as is found in marine algae called diatoms. However, polybasic polymers can act as peptide mimics; one such polymer, polyethyleneimine (PEI), has the advantage that it is stable at room temperature and is inexpensive, in comparison with synthetic peptides. We describe the fabrication and characterization of biosilicate nanoparticles formed by mimicking the peptides using PEI. Brownian motion nanoparticle tracking analysis and field emission gun scanning electron microscopy have been used for the first time to characterize nanoparticles made with tetramethyl orthosilicate (TMOS) and PEI to investigate the fundamental factors that affect particle properties. These factors include the effect of phosphate concentration, PEI molecular weight, TMOS concentration, and species of alkoxy-silane used. The properties of the particles are compared with other particles made with polymers that induce silication. Our results show that using PEI gives differences in particle size compared with previous work using other polymers that induce silication. The entrapment of enzymes during the silication process, rationale for using nonphosphate and phosphate buffers during enzyme entrapment, and the analysis of enzyme activity are also presented. Because enzymes can be entrapped during fabrication, it means that there are many future possibilities for the use of silicate nanoparticles containing enzymes, such as biosensors and biocatalytic reactors. 相似文献
9.
Brian E. Broderick Wim P. Cofino Rita Cornelis Kaj Heydorn William Horwitz David T. E. Hunt Robert C. Hutton Howard M. Kingston Herbert Muntau Renato Baudo Daria Rossi Jacobus G. van Raaphorst Tjip T. Lub Peter Schramel Frank T. Smyth David E. Wells Allan G. Kelly 《Mikrochimica acta》1991,104(1-6):523-542
The Euroanalysis VII conference in Vienna included a two-day session: Quality Assurance in Analytical Chemistry. The contributions comprised 15 lectures devoted to: intra-laboratory quality measures, inter-laboratory control, formal aspects and accreditation and implementation. The paper presents an overview of the main items developed by the contributors.A survey on the session on Quality Assurance in Analytical Chemistry of Euroanalysis VIIThe authors thank the organizers of EUROANALYSIS VII and in particular Dr. B. Griepink and Dr. E. Maier of the Community Bureau of Reference (BCR) of the CEC for their support and considerable contributions. 相似文献
10.
In the paper “The Photon Momentum” [1], Dr. Umul makes the erroneous assumption that a photon can be absorbed by a free electron and then discusses the paradoxical consequences of this assumption. In this comment the correct physics is discussed (i.e. Compton scattering [2]). 相似文献