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  • 1
    Electronic Resource
    Electronic Resource
    Detection of photosynthetic energy storage in a photosystem I reaction center preparation by photoacoustic spectroscopy (1990)
    Springer
    Photosynthesis research 24 (1990), S. 201-208 
    Details
    ISSN: 1573-5079
    Keywords: photosynthesis ; thermal emission ; P700 ; quantum yield ; energy conversion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Thermal emission and photochemical energy storage were examined in photosystem I reaction center/core antenna complexes (about 40 Chl a/P700) using photoacoustic spectroscopy. Satisfactory signals could only be obtained from samples bound to hydroxyapatite and all samples had a low signal-to-noise ratio compared to either PS I or PS II in thylakoid membranes. The energy storage signal was saturated at low intensity (half saturation at 1.5 W m-2) and predicted a photochemical quantum yield of 〉90%. Exogenous donors and acceptors had no effect on the signal amplitudes indicating that energy storage is the result of charge separation between endogenous components. Fe(CN)6 -3 oxidation of P700 and dithionite-induced reduction of acceptors FA-FB inhibited energy storage. These data are compatible with the hypothesis that energy storage in PS I arises from charge separation between P700 and Fe-S centers FA-FB that is stable on the time scale of the photoacoustic modulation. High intensity background light (160 W m-2) caused an irreversible loss of energy storage and correlated with a decrease in oxidizable P700; both are probably the result of high light-induced photoinhibition. By analogy to the low fluorescence yield of PS I, the low signal-to-noise ratio in these preparations is attributed to the short lifetime of Chl singlet excited states in PS I-40 and its indirect effect on the yield of thermal emission.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00032307
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  • 2
    Electronic Resource
    Electronic Resource
    Calculation of absolute photosystem I absorption cross-sections from P700 photo-oxidation kinetics (1991)
    Springer
    Photosynthesis research 29 (1991), S. 23-35 
    Details
    ISSN: 1573-5079
    Keywords: absorption cross-section ; P700 ; antenna size ; photosystem I ; photosynthetic unit size ; cation effects
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A procedure is described which permits determination of the absolute absorption cross-section of a photosynthetic unit from the kinetics of reaction center photo-oxidation under weak, continuous actinic illumination. The method was first tested on a simple model compound of known absorption cross-section. We then applied the technique to absorption cross-section and functional antenna size measurements in photosystem I (PS I). A kinetic model is presented that can be used to fit P700 photo-oxidation measurements and extract the effective photochemical rate constant. The procedure is shown to properly correct for sample scattering and for the presence of heterogeneous absorbers (pigments not functionally coupled to P700). The relevance of these corrections to comparisons of antenna size using techniques that measure ‘relative’ absorption cross-sections is discussed. Measurements on pea thylakoids in the presence and absence of 5 mM MgCl2 show a 45% increase in PS I absorption cross-section in unstacked thylakoids. Analysis of detergent-isolated ‘native’ PS I preparations (200 chlorophyll a+b/P700) clearly indicate that the preparation contains a broad distribution of antenna sizes. Finally, we confirm that Chlamydomonas reinhardtii strain LM3-A4d contains a PS I core antenna complex which binds only ∼60 chlorophyll a/P700, about half the functional size of the wild type complex. Limitations associated with calculation of functional antenna size from cross-section measurements are also discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00035203
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  • 3
    Electronic Resource
    Electronic Resource
    Determination of the Enthalpies of Formation of DyI2 and DyI3 and estimation of the Dy3+/Dy2+ standard aqueous electrode potentialDedicated to Professor Rudolf Hoppe on his 70th Birthday (1992)
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 616 (1992), S. 162-168 
    Details
    ISSN: 0044-2313
    Keywords: Dysprosiumdiiodide ; dysprosium triiodide ; enthalpy ; electrode potential ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Bestimmung der Bildungsenthalpien von DyI2 und DyI3 sowie Abschätzung des Dy3+/Dy2+-Standardelektrodenpotentials in wäßrigem MediumDyI2 and DyI3 wurden nach Literaturmethoden hergestellt. Ihre Lösungsenthalpien wurden bestimmt und die Bildungsenthalpien zu ΔfH°(DyI3, s, 298 K) = -(394 ± 16) kJ · mol-1 und ΔfH°(DyI2, s, 298 K) = -(616 ± 10) kJ· mol-1 berechnet. Entsprechenden Literaturangaben sowie geschätzten Lösungsenthalpien und Standardentropien wurde E°(Dy3+/Dy2+, aq.) zu -(2.6 ± 0.2) V berechnet. Ein Vergleich der Enthalpien für die Reduktion von DyI3 zu DyI2 bzw. DyI zu DyI2 wird vorgenommen.
    Notes: DyI2 and Dy3I were synthesized by literature techniques. Their enthalpies of solution were determined and their enthalpies of formation calculated to be ΔfH°(DyI2, s, 298 K) = -(394 ± 16) kJ· mol-1 and ΔfH°(DyI3, s, 298 K) = -(616 ± 10) kJ· mol-1. With appropriate literature and estimated enthalpies of solution and standard entropies, the E°(Dy3+/Dy2+, aq) was calculated to be -(2.6 ± 0.2) V. A comparison is made of the enthalpies of reduction of DyI3 to DyI2 and of DyCl3 to DyCl2.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/zaac.19926161025
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  • 4
    Electronic Resource
    Electronic Resource
    Confusion between dimethyl selenenyl sulfide and dimethyl selenone released by bacteria (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Applied Organometallic Chemistry 7 (1993), S. 335-342 
    Details
    ISSN: 0268-2605
    Keywords: Bioremediation ; biodegradation ; dimethyl selenenyl sulfide ; biomethylation ; pathway ; chemiluminescence ; micro-organism ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Dimethyl selenone [(CH3)2SeO2] has been reported in the literature as a metabolite released by bacteria in contact with selenium metal or selenium salts. In this study, mass spectral, chromatographic, and boiling-point data are presented that show that dimethyl selenone has been confused with dimethyl selenenyl sulfide (CH3SeSCH3). In addition, the headspaces above monocultures of selenium-resistant bacteria were examined using gas chromatography followed by fluorine-induced chemiluminescence detection. A number of alkyl sulfur and selenium species were detected, along with dimethyl selenenyl sulfide. A pathway from oxidized selenium salts to reduced methylated selenides and dimethyl selenenyl sulfide is also presented.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aoc.590070507
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  • 5
    Electronic Resource
    Electronic Resource
    Amending cultures of selenium-resistant bacteria with dimethyl selenone (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Applied Organometallic Chemistry 8 (1994), S. 501-508 
    Details
    ISSN: 0268-2605
    Keywords: Amendment ; biomethylation ; bioremediation ; dimethyl selenone ; headspace analysis ; fluorine-induced chemiluminescence ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A possible biological intermediate in the reduction and methylation of selenium oxyanions, dimethyl selenone, was synthesized, and the first experiments involving the amendment of selenium resistant bacterial cultures with this compound are reported. The amount of volatile, reduced selenium-containing species released from these cultures into the headspace is significantly more than that produced in analogous experiments involving sodium selenate amended cultures. Dimethyl selenone is reduced in the presence of dimethyl sulfide and dimethyl disulfide in a complex growth medium, trypticase soy broth with 0.1% nitrate. This reduction occurs whether or not the reduced sulfur compounds are biologically produced.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aoc.590080602
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