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Berlin Brandenburg

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  • 1
    Language: English
    In: Journal of the American Chemical Society, 07 March 2012, Vol.134(9), pp.4169-76
    Description: Electron transport (ETp) across bacteriorhodopsin (bR), a natural proton pump protein, in the solid state (dry) monolayer configuration, was studied as a function of temperature. Transport changes from thermally activated at T 〉 200 K to temperature independent at 〈130 K, similar to what we have observed earlier for BSA and apo-azurin. The relatively large activation energy and high temperature stability leads to conditions where bR transports remarkably high current densities above room temperature. Severing the chemical bond between the protein and the retinal polyene only slightly affected the main electron transport via bR. Another thermally activated transport path opens upon retinal oxime production, instead of or in addition to the natural retinal. Transport through either or both of these paths occurs on a background of a general temperature-independent transport. These results lead us to propose a generalized mechanism for ETp across proteins, in which tunneling and hopping coexist and dominate in different temperature regimes.
    Keywords: Temperature ; Bacteriorhodopsins -- Chemistry
    ISSN: 00027863
    E-ISSN: 1520-5126
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  • 2
    Language: English
    In: Journal of the American Chemical Society, 16 February 2011, Vol.133(6), pp.1626-9
    Description: A VIS pump/hyperspectral NIR probe study of all-trans-retinal protonated Schiff base (RPSB) in ethanol is presented. Upon irradiation, a short-lived absorption band covers the recorded range of λ = 1-2 μm. It decays to reveal the tail of S(1) emission at λ 〈 1.3 μm, along with a residual absorption at longer wavelengths, both of which decay with the known kinetics of internal conversion to S(0). The existence of this hitherto unrecorded excited-state absorption deep in the NIR will require a revision of current models for RPSB electronic structure. The phenomenological similarity of these observations with ultrafast NIR studies of carotenoids raises the question of whether three, and not two, electronic states participate in RPSB photochemistry as well. The relevance of these observations to retinal protein photochemistry is discussed.
    Keywords: Photochemical Processes ; Spectrum Analysis ; Eye Proteins -- Chemistry ; Retina -- Chemistry
    ISSN: 00027863
    E-ISSN: 1520-5126
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  • 3
    Language: English
    In: The journal of physical chemistry. B, 06 September 2012, Vol.116(35), pp.10444-52
    Description: Femtosecond spectroscopy is used to compare photochemical dynamics in light-adapted and dark-adapted bacteriorhodopsin (BR). The retinal prosthetic group is initially all-trans in the former, while it is nearly a 1:1 mixture with 13-cis in the latter. Comparing photochemistry in both serves to assess how the initial retinal configuration influences internal conversion and photoisomerization dynamics. Contrary to an earlier study, our results show that after excitation of the 13-cis form it crosses back to the ground state much more rapidly than the biologically active all-trans reactant. A similar result was recently obtained for another microbial retinal protein, Anabaena Sensory Rhodospin (ASR), which can be toggled by light between two analogous ground state configurations. Together, these studies suggest that this disparity in rates may be a general trend in the photochemistry of microbial retinal proteins. This may bear as well on the well-known enhancement in photoisomerization rates going from microbial retinal proteins to the visual pigments, as the latter also start the course of photoreception in a cis retinal configuration, in that case 11-cis. In lieu of indications for pretwisting or straining of the 13-cis retinal forms of BR and ASR, akin to those reported for rhodopsin, current results challenge many of the mechanisms held responsible for the ballistic photochemical dynamics observed in visual pigment.
    Keywords: Bacteriorhodopsins -- Metabolism ; Retinaldehyde -- Chemistry
    ISSN: 15206106
    E-ISSN: 1520-5207
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  • 4
    Language: English
    In: The journal of physical chemistry. B, 25 April 2013, Vol.117(16), pp.4670-9
    Description: Photochemistry of bacteriorhodopsin (bR), anabaena sensory rhodopsin (ASR), and all-trans retinal protonated Schiff base (RPSB) in ethanol is followed with femtosecond pump-hyperspectral near-IR (NIR) probe spectroscopy. This is the first systematic probing of retinal protein photochemistry in this spectral range. Stimulated emission of the proteins is demonstrated to extend deep into the NIR, and to decay on the same characteristic time scales previously determined by visible probing. No signs of a transient NIR absorption band above λpr 〉 1.3 μm, which was recently reported and is verified here for the RPSB in solution, is observed in either protein. This discrepancy demonstrates that the protein surroundings change photochemical traits of the chromophore significantly, inducing changes either in the energies or couplings of photochemically relevant electronic excited states. In addition, low-frequency and heavily damped spectral modulations are observed in the NIR signals of all three systems up to 1.4 μm. By background subtraction and Fourier analysis they are shown to resemble wave packet signatures in the visible, stemming from multiple vibrational modes and by analogy are assigned to torsional wave packets in the excited state of the retinal chromophore. Differences in the vibrational frequencies between the three samples and the said discrepancy in transient spectra are discussed in terms of opsin effects on the RPSB electronic structure.
    Keywords: Anabaena -- Metabolism ; Bacteriorhodopsins -- Chemistry ; Eye Proteins -- Chemistry ; Schiff Bases -- Chemistry ; Sensory Rhodopsins -- Chemistry
    ISSN: 15206106
    E-ISSN: 1520-5207
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  • 5
    Language: English
    In: Proceedings of the National Academy of Sciences of the United States of America, 10 September 2013, Vol.110(37), pp.14872-6
    Description: Spin-dependent photoelectron transmission and spin-dependent electrochemical studies were conducted on purple membrane containing bacteriorhodopsin (bR) deposited on gold, aluminum/aluminum-oxide, and nickel substrates. The result indicates spin selectivity in electron transmission through the membrane. Although the chiral bR occupies only about 10% of the volume of the membrane, the spin polarization found is on the order of 15%. The electrochemical studies indicate a strong dependence of the conduction on the protein's structure. Denaturation of the protein causes a sharp drop in the conduction through the membrane.
    Keywords: Chirality ; Electrochemistry ; Electron Transfer ; Magnetic Effect ; Bacteriorhodopsins -- Chemistry ; Purple Membrane -- Chemistry
    ISSN: 00278424
    E-ISSN: 1091-6490
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  • 6
    Language: English
    In: Journal of the American Chemical Society, 31 March 2010, Vol.132(12), pp.4131-40
    Description: Electron transfer (ET) through proteins, a fundamental element of many biochemical reactions, is studied intensively in aqueous solutions. Over the past decade, attempts were made to integrate proteins into solid-state junctions in order to study their electronic conductance properties. Most such studies to date were conducted with one or very few molecules in the junction, using scanning probe techniques. Here we present the high-yield, reproducible preparation of large-area monolayer junctions, assembled on a Si platform, of proteins of three different families: azurin (Az), a blue-copper ET protein, bacteriorhodopsin (bR), a membrane protein-chromophore complex with a proton pumping function, and bovine serum albumin (BSA). We achieve highly reproducible electrical current measurements with these three types of monolayers using appropriate top electrodes. Notably, the current-voltage (I-V) measurements on such junctions show relatively minor differences between Az and bR, even though the latter lacks any known ET function. Electron Transport (ETp) across both Az and bR is much more efficient than across BSA, but even for the latter the measured currents are higher than those through a monolayer of organic, C18 alkyl chains that is about half as wide, therefore suggesting transport mechanism(s) different from the often considered coherent mechanism. Our results show that the employed proteins maintain their conformation under these conditions. The relatively efficient ETp through these proteins opens up possibilities for using such biomolecules as current-carrying elements in solid-state electronic devices.
    Keywords: Electron Transport ; Proteins -- Chemistry
    ISSN: 00027863
    E-ISSN: 1520-5126
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  • 7
    Language: English
    In: The journal of physical chemistry. B, 15 January 2015, Vol.119(2), pp.456-64
    Description: Xanthorhodopsin (xR) is a retinal protein that contains, in addition to the retinal moiety, a salinixanthin chromophore absorbing at 456, 486, and 520 nm [Balashov, S. P.; Science 2005, 309, 2061]. The CD spectrum of xR is very unique with a "conservative" character, containing negative and positive lobes and resembling the first derivative of the absorption spectrum [Balashov, S. P.; Biochemistry 2006, 45, 10998]. It was suggested that the CD spectrum is likely to be composed of several components and that the salinixanthin interacts closely with the retinal chromophore [Balashov, S. P.; Biochemistry 2006, 45, 10998; Imasheva, E. S.; Photochem. Photobiol. 2008, 84, 977; Lanyi, J. K.; Acta Bioenerg. 2008, 1777, 684; Smolensky, E.; Biochemistry 2009, 48, 8179; Smolensky Koganov, E.; Biochemistry 2013, 52, 1290]. In this work, we aim to further explore the nature and origin of the unique CD spectrum of xR. We follow the absorption and CD spectra at different pHs of wild-type (wt) xR and of artificial xR pigments, characterized by a shifted absorption maximum of the retinal chromophore, as well as their corresponding reduced retinal protonated Schiff base pigments. Our results revealed a protein residue (other than the protonated Schiff base counterion), for which protonation affects the CD spectrum by decreasing the negative lobe at ∼530 nm and the positive lobes at 478 and 455 nm, which might be due to elimination of excitonic coupling between the salinixanthin chromophores, although other possibilities cannot be completely excluded. This spectrum change occurs by the pH decreasing, even in artificial pigment where the absorption of the retinal pigment is significantly shifted from 570 to about 450 nm. The possible excitonic coupling between the salinixanthin chromophores and its contribution to the CD spectrum of xR were supported by a good fitting of the CD spectrum to conservative (excitonic) bands [Zsila, F.; Tetrahedron: Asymmetry 2001, 12, 3125; Zsila, F.; Tetrahedron: Asymmetry 2002, 13, 273]. We propose that the CD spectrum of xR consists of contributions from an excitonic coupling interaction between the salinixanthins chromophores located in different subunits of the 3D structure of xR, the chiral conformation of the salinixanthin within its binding site, and the contribution of the retinal chromophore to the negative lobe at around 550 nm.
    Keywords: Circular Dichroism ; Bacterial Proteins -- Chemistry ; Retinaldehyde -- Chemistry ; Rhodopsins, Microbial -- Chemistry
    ISSN: 15206106
    E-ISSN: 1520-5207
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  • 8
    Language: English
    In: Journal of the American Chemical Society, 31 August 2005, Vol.127(34), pp.11902-3
    Description: Because of the localized field amplification that occurs, excitation of surface plasmons (SPs) in metal nanoparticle-based current-carrying nanoelectronic devices is expected to lead to new and interesting applications. We report a simple way to prepare surface plasmon resonance (SPR)-mediated colloid Au monolayer junctions by a wet chemistry and soft top electrode deposition. The SPR-enhanced junction current is observed upon illumination with light of energies close to the nanoparticle plasmon resonance wavelengths. This current is superimposed on tunneling current observed in the absence of surface plasmons.
    Keywords: Chemistry;
    ISSN: 0002-7863
    E-ISSN: 15205126
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  • 9
    Language: English
    In: Journal of Colloid And Interface Science, 15 December 2012, Vol.388(1), pp.300-305
    Description: ► Lipid bilayers are tethered specifically with [metal: chelator] complexes. ► Tethered bilayers are stable for months when kept at 19 °C. ► The functional state of the membrane protein bacteriorhodopsin is preserved. ► The process is potentially general. A strategy for clustering of native lipid membranes is presented. It relies on the formation of complexes between hydrophobic chelators embedded within the lipid bilayer and metal cations in the aqueous phase, capable of binding two (or more) chelators simultaneously . We used this approach with purple membranes containing the light driven proton pump protein bacteriorhodopsin (bR) and showed that patches of purple membranes cluster into mm sized aggregates and that these are stable for months when incubated at 19 °C in the dark. The strategy may be general since four different hydrophobic chelators (1,10-phenanthroline, bathophenanthroline, Phen-C10, and 8-hydroxyquinoline) and various divalent cations (Ni , Zn , Cd , Mn , and Cu ) induced formation of membrane clusters. Moreover, the absolute requirement for a hydrophobic chelator and the appropriate metal cations was demonstrated with light and atomic force microscopy (AFM); the presence of the metal does not appear to affect the functional state of the protein. The potential utility of the approach as an alternative to assembled lipid bilayers is suggested.
    Keywords: Lipid Bilayer ; Membrane Protein ; Specific Conjugation ; Hydrophobic Chelator ; Bathophenanthroline ; Engineering ; Chemistry
    ISSN: 0021-9797
    E-ISSN: 1095-7103
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  • 10
    Language: English
    In: The journal of physical chemistry. B, 04 March 2010, Vol.114(8), pp.3038-45
    Description: Excited-state dynamics of xanthorhodopsin (XR) and of salinixanthin (SX) in ethanol were investigated by ultrafast pump-hyperspectral probe spectroscopy. Following excitation to the strongly allowed S(2) state of the SX chromophore, transient spectra were recorded photoselectively in the range 430-850 nm. Global kinetic analysis of these data shows the following. (1) Efficient energy transfer from S(2) of the SX in XR to its retinal moiety is verified here. The lifetime of S(2) in SX is, however, determined to be approximately 20 fs, much shorter than previously reported. (2) Branching ratios of excitation transfer from S(2) to S(1), to S*, and to retinal in XR are measured leading to species associated difference spectra (SADS) for all the states involved. Strong protein effects are detected on these branching probabilities. (3) S(1) and S* absorption bands in both systems exhibit anisotropy well below the expected r = 0.4, indicating an angle of approximately 25 degrees between the S(0) --〉 S(2) and S(1) --〉 S(n)/S* --〉 S(n) transition dipoles. The latter allows confident assignment of the debated S* absorption band to an excited state of SX, and not to "hot" S(0). In light of the extremely fast IC from S(2) to lower excited singlets, possible involvement of ballistic IC in SX, and of coherent energy transfer in XR, are discussed.
    Keywords: Bacterial Proteins -- Chemistry ; Carotenoids -- Chemistry ; Glycosides -- Chemistry ; Rhodopsins, Microbial -- Chemistry
    ISSN: 15206106
    E-ISSN: 1520-5207
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