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  • 1
    Language: English
    In: Analytical chemistry, 04 August 2015, Vol.87(15), pp.7803-9
    Description: We report on improvements made on our previously introduced technique of cavity-enhanced Raman spectroscopy (CERS) with optical feedback cw-diode lasers in the gas phase, including a new mode-matching procedure which keeps the laser in resonance with the optical cavity without inducing long-term frequency shifts of the laser, and using a new CCD camera with improved noise performance. With 10 mW of 636.2 nm diode laser excitation and 30 s integration time, cavity enhancement achieves noise-equivalent detection limits below 1 mbar at 1 bar total pressure, depending on Raman cross sections. Detection limits can be easily improved using higher power diodes. We further demonstrate a relevant analytical application of CERS, the multicomponent analysis of natural gas samples. Several spectroscopic features have been identified and characterized. CERS with low power diode lasers is suitable for online monitoring of natural gas mixtures with sensitivity and spectroscopic selectivity, including monitoring H2, H2S, N2, CO2, and alkanes.
    Keywords: Alkanes ; Integration ; Raman Spectroscopy ; Cavities ; Cameras ; Feedback ; Lasers ; Pressure ; Internet ; Radioactive Materials;
    ISSN: 00032700
    E-ISSN: 1520-6882
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  • 2
    Language: English
    In: The journal of physical chemistry. A, 01 September 2016, Vol.120(34), pp.6677-87
    Description: The stereochemistry and dynamics of MoO2(acac)2 in benzene, chloroform, and toluene were investigated by variable temperature (1)H NMR, density functional theory (SOGGA11-X, B3LYP), and ab initio (MP2) methods. In solution, an equilibrium between two chiral enantiomers with C2 symmetry was identified, Λ-cis-MoO2(acac)2 and Δ-cis-MoO2(acac)2. The two enantiomers are connected via achiral cis transition states that switch the enantiomeric conformations via a Ray-Dutt, Bailar, and a newly described racemization twisting mechanism. All three mechanisms have similar calculated activation energies. Activation parameters Ea, ΔH(‡), and ΔS(‡) were experimentally determined for the exchange process, with a small, negative ΔS(‡), and a positive ΔH(‡) of 68.1 kJ mol(-1) in benzene, 54.9 kJ mol(-1) in chloroform, and 60.6 kJ mol(-1) in toluene, in reasonable general agreement with the calculations. Trans configurations of MoO2(acac)2 are very much higher in energy than cis and are not relevant in the temperature range experimentally studied, 243-340 K. The enantiomers interconvert within seconds near room temperature and much faster at elevated temperatures. Racemization will thus prevent the use of enantiomerically pure MoO2(acac)2 for chiral catalysis under practical conditions.
    Keywords: Chemistry;
    ISSN: 10895639
    E-ISSN: 1520-5215
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  • 3
    Language: English
    In: Analytical Chemistry, Feb 7, 2017, Vol.89(3), p.2147(8)
    Description: The article reports improvements made on the technique and its first application in the biosciences for in situ, multicomponent, and isotope selective gas measurements to study hydrogen production and consumption by Escherichia coli. Different phases with distinctly different kinetic regimes of H2 and CO2 production and D2 consumption are identified. Addition of CO is found to completely inhibit H2 production and significantly reduce D2 oxidation, indicating at least some role for O2-tolerant Hyd-1 in D2 consumption.
    Keywords: Raman Spectroscopy – Usage ; Escherichia Coli – Research ; Hydrogen – Chemical Properties
    ISSN: 0003-2700
    Source: Cengage Learning, Inc.
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  • 4
    Language: English
    In: Analytical chemistry, 07 February 2017, Vol.89(3), pp.2147-2154
    Description: Recently we introduced cavity-enhanced Raman spectroscopy (CERS) with optical feedback cw-diode lasers as a sensitive analytical tool. Here we report improvements made on the technique and its first application in the biosciences for in situ, multicomponent, and isotope selective gas measurements to study hydrogen production and consumption by Escherichia coli. Under anaerobic conditions, cultures grown on rich media supplemented with d-glucose or glycerol produce H and simultaneously consume some of it. By introducing D in the headspace, hydrogen production and consumption could be separated due to the distinct spectroscopic signatures of isotopomers. Different phases with distinctly different kinetic regimes of H and CO production and D consumption were identified. Some of the D consumed is converted back to H via H/D exchange with the solvent. HD was formed only as a minor component. This reflects either that H/D exchange at hydrogenase active sites is rapid compared to the rate of recombination, rapid recapture of HD occurs after the molecule is formed, or that the active sites where D oxidation and proton reduction occur are physically separated. Whereas in glucose supplemented cultures, addition of D led to an increase in H produced, while the yield of CO remained unchanged; with glycerol, addition of D led not only to increased yields of H, but also significantly increased CO production, reflecting an impact on fermentation pathways. Addition of CO was found to completely inhibit H production and significantly reduce D oxidation, indicating at least some role for O-tolerant Hyd-1 in D consumption.
    Keywords: Engineering ; Chemistry;
    ISSN: 00032700
    E-ISSN: 1520-6882
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  • 5
    Language: English
    In: BBA - Bioenergetics, 2011, Vol.1807(8), pp.864-877
    Description: Eukaryotic photosystem I consists of two functional moieties: the photosystem I core, harboring the components for the light-driven charge separation and the subsequent electron transfer, and the peripheral light-harvesting complex (LHCI). While the photosystem I-core remained highly conserved throughout the evolution, with the exception of the oxidizing side of photosystem I, the LHCI complex shows a high degree of variability in size, subunits composition and bound pigments, which is due to the large variety of different habitats photosynthetic organisms dwell in. Besides summarizing the most current knowledge on the photosystem I-core structure, we will discuss the composition and structure of the LHCI complex from different eukaryotic organisms, both from the red and the green clade. Furthermore, mechanistic insights into electron transfer between the donor and acceptor side of photosystem I and its soluble electron transfer carrier proteins will be given. This article is part of a Special Issue entitled: Regulation of Electron Transport in Chloroplasts. ►Structure and function of Photosystem I ►Structure and function of light-harvesting complexes ►Electron transfer from plastocyanin to PSI ►Electron transfer from PSI to ferredoxin
    Keywords: Photosystem I ; Light Harvesting ; Lhci ; Red Algae ; Green Algae ; Plastocyanin ; Ferredoxin ; Electron Transfer ; Chemistry
    ISSN: 0005-2728
    E-ISSN: 1879-2650
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  • 6
    Language: English
    In: Proceedings of the National Academy of Sciences of the United States of America, 23 October 2012, Vol.109(43), pp.17717-22
    Description: Cyclic photosynthetic electron flow (CEF) is crucial to photosynthesis because it participates in the control of chloroplast energy and redox metabolism, and it is particularly induced under adverse environmental conditions. Here we report that down-regulation of the chloroplast localized Ca(2+) sensor (CAS) protein by an RNAi approach in Chlamydomonas reinhardtii results in strong inhibition of CEF under anoxia. Importantly, this inhibition is rescued by an increase in the extracellular Ca(2+) concentration, inferring that CEF is Ca(2+)-dependent. Furthermore, we identified a protein, anaerobic response 1 (ANR1), that is also required for effective acclimation to anaerobiosis. Depletion of ANR1 by artificial microRNA expression mimics the CAS-depletion phenotype, and under anaerobic conditions the two proteins coexist within a large active photosystem I-cytochrome b(6)/f complex. Moreover, we provide evidence that CAS and ANR1 interact with each other as well as with PGR5-Like 1 (PGRL1) in vivo. Overall our data establish a Ca(2+)-dependent regulation of CEF via the combined function of ANR1, CAS, and PGRL1, associated with each other in a multiprotein complex.
    Keywords: Photosynthesis ; Caenorhabditis Elegans Proteins -- Physiology
    ISSN: 00278424
    E-ISSN: 1091-6490
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  • 7
    Language: English
    In: Journal of Chemical Education, March 2010, Vol.87(3), p.326
    Description: We describe the construction and performance of an inexpensive modular Raman spectrometer that has been assembled in the framework of a fourth-year undergraduate project (costs below $5000). The spectrometer is based on a 4 mW 532 nm green laser pointer and a compact monochromator equipped...
    Keywords: Spectroscopy ; Chemistry ; Science Experiments ; Measurement Equipment ; Undergraduate Study ; Graduate Study ; College Science ; Demonstrations (Educational) ; Science Instruction ; Education ; Chemistry
    ISSN: 0021-9584
    E-ISSN: 1938-1328
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  • 8
    Language: English
    In: Biochemistry, 18 September 2012, Vol.51(37), pp.7297-303
    Description: The binding and electron transfer between plastocyanin (pc) or cytochrome c(6) (cyt c(6)) and photosystem I (PSI) can be described by hydrophobic as well as electrostatic interactions. The two α helices, l and l' in PsaB and PsaA, respectively, are involved in forming the hydrophobic interaction site at the oxidizing site of PSI. To obtain mechanistic insights into the function of the two negatively charged residues D612 and E613, present in α helix l of PsaB, we exchanged both residues by site-directed mutagenesis with His and transformed a PsaB deficient mutant of Chlamydomonas reinhardtii. Flash-induced absorption spectroscopy revealed that PSI harboring the changes D612H and E613H had a high affinity toward binding of the electron donors and possessed an altered pH dependence of electron transfer with pc and cyt c(6). Despite optimized binding and electron transfer between the altered PSI and its electron donors, the mutant strain PsaB-D612H/E613H exhibited a strong light sensitive growth phenotype, indicating that decelerated turnover between pc/cyt c(6) and PSI with respect to electron transfer is deleterious to the cells.
    Keywords: Chlamydomonas Reinhardtii -- Enzymology ; Cytochromes C6 -- Chemistry ; Photosystem I Protein Complex -- Chemistry ; Plastocyanin -- Chemistry
    ISSN: 00062960
    E-ISSN: 1520-4995
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  • 9
    Language: English
    In: The Journal of biological chemistry, 13 May 2016, Vol.291(20), pp.10602-14
    Description: N-Glycosylation is a post-translational modification common to all three domains of life. In many archaea, the oligosacharyltransferase (AglB)-dependent N-glycosylation of flagellins is required for flagella assembly. However, whether N-glycosylation is required for the assembly and/or function of the structurally related archaeal type IV pili is unknown. Here, we show that of six Haloferax volcanii adhesion pilins, PilA1 and PilA2, the most abundant pilins in pili of wild-type and ΔaglB strains, are modified under planktonic conditions in an AglB-dependent manner by the same pentasaccharide detected on H. volcanii flagellins. However, unlike wild-type cells, which have surfaces decorated with discrete pili and form a dispersed layer of cells on a plastic surface, ΔaglB cells have thick pili bundles and form microcolonies. Moreover, expressing PilA1, PilA2, or PilA6 in ΔpilA[1-6]ΔaglB stimulates microcolony formation compared with their expression in ΔpilA[1-6]. Conversely, expressing PilA3 or PilA4 in ΔpilA[1-6] cells results in strong surface adhesion, but not microcolony formation, and neither pilin stimulates surface adhesion in ΔpilA[1-6]ΔaglB cells. Although PilA4 assembles into pili in the ΔpilA[1-6]ΔaglB cells, these pili are, unlike wild-type pili, curled, perhaps rendering them non-functional. To our knowledge, this is the first demonstration of a differential effect of glycosylation on pilus assembly and function of paralogous pilins. The growth of wild-type cells in low salt media, a condition that decreases AglB glycosylation, also stimulates microcolony formation and inhibits motility, supporting our hypothesis that N-glycosylation plays an important role in regulating the transition between planktonic to sessile cell states as a response to stress.
    Keywords: Haloferax Volcanii ; N-Linked Glycosylation ; Adhesion ; Archaea ; Biofilm ; Flagella ; Flagellin ; Pili ; Pilin ; Type IV Pili ; Archaeal Proteins -- Metabolism ; Fimbriae Proteins -- Metabolism ; Haloferax Volcanii -- Metabolism
    E-ISSN: 1083-351X
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  • 10
    Language: English
    In: The Journal of biological chemistry, 09 November 2018, Vol.293(45), pp.17559-17573
    Description: The supramolecular organization of membrane proteins (MPs) is sensitive to environmental changes in photosynthetic organisms. Isolation of MP supercomplexes from the green algae , which are believed to contribute to cyclic electron flow (CEF) between the cytochrome complex (Cyt- ) and photosystem...
    Keywords: Chlamydomonas ; Cytochrome B6f Complex ; Electron Transfer Complex ; Membrane Protein ; Photosynthesis ; Protein Cross-Linking ; Chlamydomonas Reinhardtii -- Enzymology ; Cytochrome B6f Complex -- Metabolism ; Photosystem I Protein Complex -- Metabolism
    E-ISSN: 1083-351X
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