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  • 1
    Online Resource
    Online Resource
    Ultrafast photodriven intramolecular electron transfer from an iridium-based water-oxidation catalyst to perylene diimide derivatives
    Proceedings of the National Academy of Sciences ; 2012
    In:  Proceedings of the National Academy of Sciences Vol. 109, No. 39 ( 2012-09-25), p. 15651-15656
    Details
    In: Proceedings of the National Academy of Sciences, Proceedings of the National Academy of Sciences, Vol. 109, No. 39 ( 2012-09-25), p. 15651-15656
    Abstract: Photodriving the activity of water-oxidation catalysts is a critical step toward generating fuel from sunlight. The design of a system with optimal energetics and kinetics requires a mechanistic understanding of the single-electron transfer events in catalyst activation. To this end, we report here the synthesis and photophysical characterization of two covalently bound chromophore-catalyst electron transfer dyads, in which the dyes are derivatives of the strong photooxidant perylene-3,4:9,10-bis(dicarboximide) (PDI) and the molecular catalyst is the Cp ∗ Ir(ppy)Cl metal complex, where ppy = 2-phenylpyridine. Photoexcitation of the PDI in each dyad results in reduction of the chromophore to PDI •- in less than 10 ps, a process that outcompetes any generation of 3∗ PDI by spin-orbit-induced intersystem crossing. Biexponential charge recombination largely to the PDI-Ir(III) ground state is suggestive of multiple populations of the PDI •- -Ir(IV) ion-pair, whose relative abundance varies with solvent polarity. Electrochemical studies of the dyads show strong irreversible oxidation current similar to that seen for model catalysts, indicating that the catalytic integrity of the metal complex is maintained upon attachment to the high molecular weight photosensitizer.
    Type of Medium: Online Resource
    ISSN: 0027-8424 , 1091-6490
    URL: Article
    DOI: 10.1073/pnas.1202075109
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    Language: English
    Publisher: Proceedings of the National Academy of Sciences
    Publication Date: 2012
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  • 2
    Online Resource
    Online Resource
    Determination of the primary charge separation rate in isolated photosystem II reaction centers with 500-fs time resolution
    Proceedings of the National Academy of Sciences ; 1989
    In:  Proceedings of the National Academy of Sciences Vol. 86, No. 2 ( 1989-01), p. 524-528
    Details
    In: Proceedings of the National Academy of Sciences, Proceedings of the National Academy of Sciences, Vol. 86, No. 2 ( 1989-01), p. 524-528
    Abstract: We have measured directly the rate of formation of the oxidized chlorophyll a electron donor (P680 + ) and the reduced electron acceptor pheophytin a - (Pheo a - ) following excitation of isolated spinach photosystem II reaction centers at 4°C. The reaction-center complex consists of D 1 , D 2 , and cytochrome b -559 proteins and was prepared by a procedure that stabilizes the protein complex. Transient absorption difference spectra were measured from 440 to 850 nm as a function of time with 500-fs resolution following 610-nm laser excitation. The formation of P680 + -Pheo a - is indicated by the appearance of a band due to P680 + at 820 nm and corresponding absorbance changes at 505 and 540 nm due to formation of Pheo a - . The appearance of the 820-nm band is monoexponential with τ = 3.0 ± 0.6 ps. The time constant for decay of 1* P680, the lowest excited singlet state of P680, monitored at 650 nm, is τ = 2.6 ± 0.6 ps and agrees with that of the appearance of P680 + within experimental error. Treatment of the photosystem II reaction centers with sodium dithionite and methyl viologen followed by exposure to laser excitation, conditions known to result in accumulation of Pheo a - , results in formation of a transient absorption spectrum due to 1* P680. We find no evidence for an electron acceptor that precedes the formation of Pheo a - .
    Type of Medium: Online Resource
    ISSN: 0027-8424 , 1091-6490
    URL: Article
    DOI: 10.1073/pnas.86.2.524
    RVK:
    TA 1000
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    WA 15000
    Language: English
    Publisher: Proceedings of the National Academy of Sciences
    Publication Date: 1989
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  • 3
    Online Resource
    Online Resource
    Picosecond Optical Switching Based on Biphotonic Excitation of an Electron Donor-Acceptor-Donor Molecule
    American Association for the Advancement of Science (AAAS) ; 1992
    In:  Science Vol. 257, No. 5066 ( 1992-07-03), p. 63-65
    Details
    In: Science, American Association for the Advancement of Science (AAAS), Vol. 257, No. 5066 ( 1992-07-03), p. 63-65
    Type of Medium: Online Resource
    ISSN: 0036-8075 , 1095-9203
    URL: Article
    DOI: 10.1126/science.257.5066.63
    RVK:
    TA 1000
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    WA 15000
    Language: English
    Publisher: American Association for the Advancement of Science (AAAS)
    Publication Date: 1992
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  • 4
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    Online Resource
    Functional asymmetry of photosystem II D1 and D2 peripheral chlorophyll mutants of Chlamydomonas reinhardtii
    Proceedings of the National Academy of Sciences ; 2002
    In:  Proceedings of the National Academy of Sciences Vol. 99, No. 6 ( 2002-03-19), p. 4091-4096
    Details
    In: Proceedings of the National Academy of Sciences, Proceedings of the National Academy of Sciences, Vol. 99, No. 6 ( 2002-03-19), p. 4091-4096
    Abstract: The peripheral accessory chlorophylls (Chls) of the photosystem II (PSII) reaction center (RC) are coordinated by a pair of symmetry-related histidine residues (D1-H118 and D2-H117). These Chls participate in energy transfer from the proximal antennae complexes (CP43 and CP47) to the RC core chromophores. In addition, one or both of the peripheral Chls are redox-active and participate in a low-quantum-yield electron transfer cycle around PSII. We demonstrate that conservative mutations of the D2-H117 residue result in decreased Chl fluorescence quenching efficiency attributed to reduced accumulation of the peripheral accessory Chl cation, Chl \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} \begin{equation*}{\mathrm{_{Z}^{+}}}\end{equation*}\end{document} . In contrast, identical symmetry-related mutations at residue D1-H118 had no effect on Chl fluorescence yield or quenching kinetics. Mutagenesis of the D2-H117 residue also altered the line width of the Chl \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} \begin{equation*}{\mathrm{_{Z}^{+}}}\end{equation*}\end{document} EPR signal, but the line shape of the D1-H118Q mutant remained unchanged. The D1-H118 and D2-H117 mutations also altered energy transfer properties in PSII RCs. Unlike wild type or the D1-H118Q mutant, D2-H117N RCs exhibited a reduced CD doublet in the red region of Chl absorbance band, indicative of reduced energetic coupling between P680 and the peripheral accessory Chl. In addition, transient absorption measurements of D2-H117N RCs, excited on the blue side of the Chl absorbance band, exhibited a (≈400 fs) pheophytin Q X band bleach lifetime component not seen in wild-type or D1-H118Q RCs. The origin of this component may be related to delayed fast-energy equilibration of the excited state between the core pigments of this mutant.
    Type of Medium: Online Resource
    ISSN: 0027-8424 , 1091-6490
    URL: Article
    DOI: 10.1073/pnas.062056899
    RVK:
    TA 1000
    RVK:
    WA 15000
    Language: English
    Publisher: Proceedings of the National Academy of Sciences
    Publication Date: 2002
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  • 5
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    Online Resource
    Distance-Dependent Electron Transfer in DNA Hairpins
    American Association for the Advancement of Science (AAAS) ; 1997
    In:  Science Vol. 277, No. 5326 ( 1997-08), p. 673-676
    Details
    In: Science, American Association for the Advancement of Science (AAAS), Vol. 277, No. 5326 ( 1997-08), p. 673-676
    Abstract: The distance dependence of photoinduced electron transfer in duplex DNA was determined for a family of synthetic DNA hairpins in which a stilbene dicarboxamide forms a bridge connecting two oligonucleotide arms. Investigation of the fluorescence and transient absorption spectra of these hairpins established that no photoinduced electron transfer occurs for a hairpin that has six deoxyadenosine-deoxythymidine base pairs. However, the introduction of a single deoxyguanosine-deoxycytidine base pair resulted in distance-dependent fluorescence quenching and the formation of the stilbene anion radical. Kinetic analysis suggests that duplex DNA is somewhat more effective than proteins as a medium for electron transfer but that it does not function as a molecular wire.
    Type of Medium: Online Resource
    ISSN: 0036-8075 , 1095-9203
    URL: Article
    DOI: 10.1126/science.277.5326.673
    RVK:
    TA 1000
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    WA 15000
    Language: English
    Publisher: American Association for the Advancement of Science (AAAS)
    Publication Date: 1997
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  • 6
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    Online Resource
    Electrochemically addressable trisradical rotaxanes organized within a metal–organic framework
    Proceedings of the National Academy of Sciences ; 2015
    In:  Proceedings of the National Academy of Sciences Vol. 112, No. 36 ( 2015-09-08), p. 11161-11168
    Details
    In: Proceedings of the National Academy of Sciences, Proceedings of the National Academy of Sciences, Vol. 112, No. 36 ( 2015-09-08), p. 11161-11168
    Abstract: The organization of trisradical rotaxanes within the channels of a Zr 6 -based metal–organic framework (NU-1000) has been achieved postsynthetically by solvent-assisted ligand incorporation. Robust Zr IV –carboxylate bonds are forged between the Zr clusters of NU-1000 and carboxylic acid groups of rotaxane precursors (semirotaxanes) as part of this building block replacement strategy. Ultraviolet–visible–near-infrared (UV-Vis-NIR), electron paramagnetic resonance (EPR), and 1 H nuclear magnetic resonance (NMR) spectroscopies all confirm the capture of redox-active rotaxanes within the mesoscale hexagonal channels of NU-1000. Cyclic voltammetry measurements performed on electroactive thin films of the resulting material indicate that redox-active viologen subunits located on the rotaxane components can be accessed electrochemically in the solid state. In contradistinction to previous methods, this strategy for the incorporation of mechanically interlocked molecules within porous materials circumvents the need for de novo synthesis of a metal–organic framework, making it a particularly convenient approach for the design and creation of solid-state molecular switches and machines. The results presented here provide proof-of-concept for the application of postsynthetic transformations in the integration of dynamic molecular machines with robust porous frameworks.
    Type of Medium: Online Resource
    ISSN: 0027-8424 , 1091-6490
    URL: Article
    DOI: 10.1073/pnas.1514485112
    RVK:
    TA 1000
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    WA 15000
    Language: English
    Publisher: Proceedings of the National Academy of Sciences
    Publication Date: 2015
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  • 7
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    Online Resource
    Monomeric chlorophyll a enol : Evidence for its possible role as the primary electron donor in photosystem I of plant photosynthesis
    Proceedings of the National Academy of Sciences ; 1981
    In:  Proceedings of the National Academy of Sciences Vol. 78, No. 5 ( 1981-05), p. 2957-2961
    Details
    In: Proceedings of the National Academy of Sciences, Proceedings of the National Academy of Sciences, Vol. 78, No. 5 ( 1981-05), p. 2957-2961
    Abstract: The chlorophyll a (Chl a ) special-pair model of the primary donor of photosystem I (P700) does not account in a completely adequate fashion for the magnetic resonance properties observed for P700 + . Moreover, P700 is at least 420 mV easier to oxidize than is Chl a in vitro . Neither Chl a dimer formation nor selective ligation of Chl a can account for this potential difference. Enolization of the Chl a ring V β-keto ester results in a very different π electronic structure. The Chl a enol can be trapped as a silyl enol ether. In addition, the enol analog 9-desoxo-9,10-dehydro-Chl a can be prepared. Both the trapped enol and its 9-H analog are ≈350 mV easier to oxidize than Chl a . The ESR spectrum of the cation radical consists of a single 6.1-G gaussian line that is line narrowed relative to that of Chl a + in a manner similar to P700 + . Electron-nuclear double resonance (ENDOR) spectroscopy resolves only a 3.5-MHz hyperfine splitting for the 3-methyl-group. The remaining splittings are all less than 3.5 MHz. The second moment of the ESR line of fully 13 C-enriched 9-desoxo-9,10-dehydro-Chl a + agrees with that of [ 13 C] P700 + to within 10%. Application of the special-pair model to the [ 13 C]P700 + second-moment data yields a 100% error. Ab initio molecular orbital calculations on ethyl chlorophyllide a enol cation bear out the ESR and ENDOR data. We conclude that a monomeric Chl a enol model provides a better description of the magnetic resonance parameters and oxidation potential of P700 than a Chl a special-pair model.
    Type of Medium: Online Resource
    ISSN: 0027-8424 , 1091-6490
    URL: Article
    DOI: 10.1073/pnas.78.5.2957
    RVK:
    TA 1000
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    Language: English
    Publisher: Proceedings of the National Academy of Sciences
    Publication Date: 1981
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  • 8
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    Online Resource
    A Radically Configurable Six-State Compound
    American Association for the Advancement of Science (AAAS) ; 2013
    In:  Science Vol. 339, No. 6118 ( 2013-01-25), p. 429-433
    Details
    In: Science, American Association for the Advancement of Science (AAAS), Vol. 339, No. 6118 ( 2013-01-25), p. 429-433
    Abstract: Most organic radicals possess short lifetimes and quickly undergo dimerization or oxidation. Here, we report on the synthesis by radical templation of a class of air- and water-stable organic radicals, trapped within a homo[2]catenane composed of two rigid and fixed cyclobis(paraquat- p -phenylene) rings. The highly energetic octacationic homo[2]catenane, which is capable of accepting up to eight electrons, can be configured reversibly, both chemically and electrochemically, between each one of six experimentally accessible redox states (0, 2+, 4+, 6+, 7+, and 8+) from within the total of nine states evaluated by quantum mechanical methods. All six of the observable redox states have been identified by electrochemical techniques, three (4+, 6+, and 7+) have been characterized by x-ray crystallography, four (4+, 6+, 7+, and 8+) by electron paramagnetic resonance spectroscopy, one (7+) by superconducting quantum interference device magnetometry, and one (8+) by nuclear magnetic resonance spectroscopy.
    Type of Medium: Online Resource
    ISSN: 0036-8075 , 1095-9203
    URL: Article
    DOI: 10.1126/science.1228429
    RVK:
    TA 1000
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    WA 15000
    Language: English
    Publisher: American Association for the Advancement of Science (AAAS)
    Publication Date: 2013
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  • 9
    Online Resource
    Online Resource
    Mechanically induced intramolecular electron transfer in a mixed-valence molecular shuttle
    Proceedings of the National Academy of Sciences ; 2012
    In:  Proceedings of the National Academy of Sciences Vol. 109, No. 29 ( 2012-07-17), p. 11546-11551
    Details
    In: Proceedings of the National Academy of Sciences, Proceedings of the National Academy of Sciences, Vol. 109, No. 29 ( 2012-07-17), p. 11546-11551
    Abstract: The kinetics and thermodynamics of intramolecular electron transfer (IET) can be subjected to redox control in a bistable [2]rotaxane comprised of a dumbbell component containing an electron-rich 1,5-dioxynaphthalene (DNP) unit and an electron-poor phenylene-bridged bipyridinium (P-BIPY 2+ ) unit and a cyclobis (paraquat- p -phenylene) (CBPQT 4+ ) ring component. The [2]rotaxane exists in the ground-state co-conformation (GSCC) wherein the CBPQT 4+ ring encircles the DNP unit. Reduction of the CBPQT 4+ leads to the CBPQT 2(•+) diradical dication while the P-BIPY 2+ unit is reduced to its P-BIPY •+ radical cation. A radical-state co-conformation (RSCC) results from movement of the CBPQT 2(•+) ring along the dumbbell to surround the P-BIPY •+ unit. This shuttling event induces IET to occur between the pyridinium redox centers of the P-BIPY •+ unit, a property which is absent between these redox centers in the free dumbbell and in the 1∶1 complex formed between the CBPQT 2(•+) ring and the radical cation of methyl-phenylene-viologen (MPV •+ ). Using electron paramagnetic resonance (EPR) spectroscopy, the process of IET was investigated by monitoring the line broadening at varying temperatures and determining the rate constant ( k ET  = 1.33 × 10 7  s -1 ) and activation energy (Δ G ‡  = 1.01 kcal mol -1 ) for electron transfer. These values were compared to the corresponding values predicted, using the optical absorption spectra and Marcus–Hush theory.
    Type of Medium: Online Resource
    ISSN: 0027-8424 , 1091-6490
    URL: Article
    DOI: 10.1073/pnas.1201561109
    RVK:
    TA 1000
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    Language: English
    Publisher: Proceedings of the National Academy of Sciences
    Publication Date: 2012
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  • 10
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    Optical Control of Photogenerated Ion Pair Lifetimes: An Approach to a Molecular Switch
    American Association for the Advancement of Science (AAAS) ; 1996
    In:  Science Vol. 274, No. 5287 ( 1996-10-25), p. 584-587
    Details
    In: Science, American Association for the Advancement of Science (AAAS), Vol. 274, No. 5287 ( 1996-10-25), p. 584-587
    Abstract: A prototype molecular switch is demonstrated that works on the principle that the local electric field produced by one photogenerated ion pair (D 1 + -A 1 − ) can influence the rate constants for photoinduced electron transfer and recombination in a second donor-acceptor pair (A 2 -D 2 ). Two ultrafast laser pulses were used to control the rate of a photoinduced electron transfer reaction within a molecule that consists of two covalently linked electron donor-acceptor pairs fixed in a linear structure, D 1 -A 1 -A 2 -D 2 . This type of molecular architecture may lead to the development of electronic devices that function on the molecular length scale.
    Type of Medium: Online Resource
    ISSN: 0036-8075 , 1095-9203
    URL: Article
    DOI: 10.1126/science.274.5287.584
    RVK:
    TA 1000
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    WA 15000
    Language: English
    Publisher: American Association for the Advancement of Science (AAAS)
    Publication Date: 1996
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    detail.hit.zdb_id: 2060783-0
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