Kooperativer Bibliotheksverbund

Berlin Brandenburg

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  • 1
    Language: English
    In: Journal of the American Chemical Society, 03 July 2013, Vol.135(26), pp.9624-7
    Description: The spectral tuning of halorhodopsin from Halobacterium salinarum (shR) during anion transport was analyzed at the molecular level using DFT-QM/MM [SORCI+Q//B3LYP/6-31G(d):Amber96] hybrid methods. Insights into the influence of Cl(-) depletion, Cl(-) substitution by N3(-) or NO3(-), and mutation of key amino acid residues along the ion translocation pathway (H95A, H95R, Q105E, R108H, R108I, R108K, R108Q, T111V, R200A, R200H, R200K, R200Q, and T203V) were analyzed for the first time in a fully atomistic model of the shR photoreceptor. We found evidence that structural rearrangements mediated by specific hydrogen bonds of internal water molecules and counterions (D238 and Cl(-)) in the active site induce changes in the bond-length alternation of the all-trans retinyl chromophore and affect the wavelength of maximal absorption in shR.
    Keywords: Quantum Theory ; Halorhodopsins -- Chemistry
    ISSN: 00027863
    E-ISSN: 1520-5126
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  • 2
    Language: English
    In: Journal of the American Chemical Society, 05 December 2012, Vol.134(48), pp.19536-9
    Description: The nonvisual ocular photoreceptor melanopsin, found in the neurons of vertebrate inner retina, absorbs blue light and triggers the "biological clock" of mammals by activating the suprachiasmatic nuclei (a small region of the brain that regulates the circadian rhythms of neuronal and hormonal activities over 24 h cycles). The structure of melanopsin, however, has yet to be established. Here, we propose for the first time a structural model of the active site of mouse melanopsin. The homology model is based on the crystal structure of squid rhodopsin (λ(max) = 490 nm) and shows a maximal absorbance (λ(max) = 447 nm) consistent with the observed absorption of the photoreceptor. The 43 nm spectral shift is due to an increased bond-length alternation of the protonated Schiff base of 11-cis-retinal chromophore, induced by N87Q mutation and water-mediated H-bonding interactions with the Schiff base linkage. These findings, analogous to spectral changes observed in the G89Q bovine rhodopsin mutant, suggest that single site mutations can convert photopigments into visual light sensors or nonvisual sensory photoreceptors.
    Keywords: Models, Biological ; Biological Clocks -- Physiology ; Photoreceptor Cells -- Chemistry ; Rod Opsins -- Chemistry
    ISSN: 00027863
    E-ISSN: 1520-5126
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  • 3
    Language: English
    In: The journal of physical chemistry. B, 12 May 2011, Vol.115(18), pp.5234-42
    Description: A general coherent control scenario to suppress or accelerate tunneling of quantum states decaying into a continuum is investigated. The method is based on deterministic, or stochastic, sequences of unitary pulses that affect the underlying interference phenomena responsible for quantum dynamics, without inducing decoherence, or collapsing the coherent evolution of the system. The influence of control sequences on the ensuing quantum dynamics is analyzed by using perturbation theory to first order in the control pulse fields and compared to dynamical decoupling protocols and to sequences of pulses that collapse the coherent evolution and induce quantum Zeno (QZE) or quantum anti-Zeno effects (AZE). The analysis reveals a subtle interplay between coherent and incoherent phenomena and demonstrates that dynamics analogous to the evolution due to QZE or AZE can be generated from stochastic sequences of unitary pulses when averaged over all possible realizations.
    Keywords: Chemistry;
    ISSN: 15206106
    E-ISSN: 1520-5207
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  • 4
    Language: English
    In: Journal of the American Chemical Society, 15 June 2011, Vol.133
    Description: An inverse design methodology suitable to assist the synthesis and optimization of molecular sensitizers for dye-sensitized solar cells is introduced. The method searches for molecular adsorbates with suitable photoabsorption properties through continuous optimization of "alchemical" structures in the vicinity of a reference molecular framework. The approach is illustrated as applied to the design and optimization of linker chromophores for TiO(2) sensitization, using the recently developed phenyl-acetylacetonate (i.e., phenyl-acac) anchor [McNamara et al. J. Am. Chem. Soc.2008, 130, 14329-14338] as a reference framework. A novel anchor (3-acac-pyran-2-one) is found to be a local optimum, with improved sensitization properties when compared to phenyl-acac. Its molecular structure is related to known coumarin dyes that could be used as lead chromophore anchors for practical applications in dye-sensitized solar cells. Synthesis and spectroscopic characterization confirms that the linker provides robust attachment to TiO(2), even in aqueous conditions, yielding improved sensitization to solar light and ultrafast interfacial electron injection. The findings are particularly relevant to the design of sensitizers for dye-sensitized solar cells because of the wide variety of structures that are possible but they should be equally useful for other applications such as ligand design for homogeneous catalysis.
    Keywords: Catalysis (Homogeneous), Catalysis (Heterogeneous), Solar (Photovoltaic), Solar (Fuels), Photosynthesis (Natural and Artificial), Bio-Inspired, Hydrogen and Fuel Cells, Electrodes - Solar, Defects, Charge Transport, Spin Dynamics, Membrane, Materials and Chemistry By Design, Optics, Synthesis (Novel Materials), Synthesis (Self-Assembly)
    ISSN: 00027863
    E-ISSN: 15205126
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  • 5
    Language: English
    In: Journal of the American Chemical Society, 10 June 2015, Vol.137(22)
    Description: The preparation of the facial and meridional isomers of [Ir(pyalk)3] (pyalk = 2-(2-pyridyl)isopropanoate), as model complexes for a powerful water oxidation catalyst, is reported. The strongly donating N3O3 ligand set is very oxidation-resistant, yet promotes facile metal-centered oxidation to form stable Ir(IV) compounds. The Ir(III/IV) reduction potentials of the two isomers differ by 340 mV despite the identical ligand set. A ligand field rationalization is advanced and supported by DFT calculations.
    Keywords: Catalysis (Homogeneous), Catalysis (Heterogeneous), Solar (Photovoltaic), Solar (Fuels), Photosynthesis (Natural and Artificial), Bio-Inspired, Hydrogen and Fuel Cells, Electrodes - Solar, Defects, Charge Transport, Spin Dynamics, Membrane, Materials and Chemistry By Design, Optics, Synthesis (Novel Materials), Synthesis (Self-Assembly) ; Chemistry
    ISSN: 0002-7863
    E-ISSN: 1520-5126
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  • 6
    Language: English
    In: Journal of the American Chemical Society, 12 August 2015, Vol.137(33)
    Description: We introduce a new family of complexes with the general formula [Ru(n)(tda)(py)2](m+) (n = 2, m = 0, 1; n = 3, m = 1, 2(+); n = 4, m = 2, 3(2+)), with tda(2-) being [2,2':6',2″-terpyridine]-6,6″-dicarboxylate, including complex [Ru(IV)(OH)(tda-κ-N(3)O)(py)2](+), 4H(+), which we find to be an impressive water oxidation catalyst, formed by hydroxo coordination to 3(2+) under basic conditions. The complexes are synthesized, isolated, and thoroughly characterized by analytical, spectroscopic (UV-vis, nuclear magnetic resonance, electron paramagnetic resonance), computational, and electrochemical techniques (cyclic voltammetry, differential pulse voltammetry, coulometry), including solid-state monocrystal X-ray diffraction analysis. In oxidation state IV, the Ru center is seven-coordinated and diamagnetic, whereas in oxidation state II, the complex has an unbonded dangling carboxylate and is six-coordinated while still diamagnetic. With oxidation state III, the coordination number is halfway between the coordination of oxidation states II and IV. Species generated in situ have also been characterized by spectroscopic, computational, and electrochemical techniques, together with the related species derived from a different degree of protonation and oxidation states. 4H(+) can be generated potentiometrically, or voltammetrically, from 3(2+), and both coexist in solution. While complex 3(2+) is not catalytically active, the catalytic performance of complex 4H(+) is characterized by the foot of the wave analysis, giving an impressive turnover frequency record of 8000 s(-1) at pH 7.0 and 50 000 s(-1) at pH 10.0. Density functional theory calculations provide a complete description of the water oxidation catalytic cycle of 4H(+), manifesting the key functional role of the dangling carboxylate in lowering the activation free energies that lead to O-O bond formation.
    Keywords: Catalysis (Homogeneous), Catalysis (Heterogeneous), Solar (Photovoltaic), Solar (Fuels), Photosynthesis (Natural and Artificial), Bio-Inspired, Hydrogen and Fuel Cells, Electrodes - Solar, Defects, Charge Transport, Spin Dynamics, Membrane, Materials and Chemistry By Design, Optics, Synthesis (Novel Materials), Synthesis (Self-Assembly) ; Chemistry
    ISSN: 0002-7863
    E-ISSN: 1520-5126
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  • 7
    Language: English
    In: Proceedings of the National Academy of Sciences of the United States of America, 23 June 2015, Vol.112(25), pp.E3155
    Description: Author contributions: E.B., S.J., H.M., V.S.B., and H.Z. wrote the paper.
    Keywords: Models, Biological ; Odorants ; Receptors, Odorant -- Metabolism ; Smell -- Physiology
    ISSN: 00278424
    E-ISSN: 1091-6490
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  • 8
    Language: English
    In: Journal of the American Chemical Society, 06 March 2013, Vol.135(9), pp.3592-8
    Description: Studying hydrogen/deuterium (H/D) exchange in proteins can provide valuable insight on protein structure and dynamics. Several techniques are available for probing H/D exchange in the bulk solution, including NMR, mass spectroscopy, and Fourier transform infrared spectroscopy. However, probing H/D exchange at interfaces is challenging because it requires surface-selective methods. Here, we introduce the combination of in situ chiral sum frequency generation (cSFG) spectroscopy and ab initio simulations of cSFG spectra as a powerful methodology to probe the dynamics of H/D exchange at interfaces. This method is applied to characterize H/D exchange in the antiparallel β-sheet peptide LK7β. We report here for the first time that the rate of D-to-H exchange is about 1 order of magnitude faster than H-to-D exchange in the antiparallel structure at the air/water interface, which is consistent with the existing knowledge that O-H/D dissociation in water is the rate-limiting step, and breaking the O-D bond is slower than breaking the O-H bond. The reported analysis also provides fundamental understanding of several vibrational modes and their couplings in peptide backbones that have been difficult to characterize by conventional methods, including Fermi resonances of various combinations of peptide vibrational modes such as amide I and amide II, C-N stretch, and N-H/N-D bending. These results demonstrate cSFG as a sensitive technique for probing the kinetics of H/D exchange in proteins at interfaces, with high signal-to-noise N-H/N-D stretch bands that are free of background from the water O-H/O-D stretch.
    Keywords: Protons ; Peptides -- Chemistry
    ISSN: 00027863
    E-ISSN: 1520-5126
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  • 9
    Language: English
    In: Journal of the American Chemical Society, 11 May 2011, Vol.133(18), pp.6922-5
    Description: We have characterized the covalent binding of the CO(2) reduction electrocatalyst ReC0A (Re(CO)(3)Cl(dcbpy) (dcbpy =4,4'-dicarboxy-2,2'-bipyridine)) to the TiO(2) rutile (001) surface. The analysis based on sum frequency generation (SFG) spectroscopy and density functional theory (DFT) calculations indicates that ReC0A binds to TiO(2) through the carboxylate groups in bidentate or tridentate linkage motifs. The adsorbed complex has the dcbpy moiety nearly perpendicular to the TiO(2) surface and the Re exposed to the solution in a configuration suitable for catalysis.
    Keywords: Rhenium -- Chemical Properties ; Titanium -- Chemical Properties ; Rutile -- Chemical Properties;
    ISSN: 00027863
    E-ISSN: 1520-5126
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  • 10
    Language: English
    In: Journal of Physical Chemistry A, Sept 29, 2011, Vol.115(38), p.10511-10516
    Keywords: Density Functional Theory -- Usage ; Infrared Spectroscopy -- Usage ; Naphtha -- Spectra ; Naphtha -- Electric Properties ; Vibrational Spectra -- Research
    ISSN: 1089-5639
    Source: Cengage Learning, Inc.
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