206 results on '"Robert Bittl"'
Search Results
2. Selective 13C labelling reveals the electronic structure of flavocoenzyme radicals
- Author
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Erik Schleicher, Stephan Rein, Boris Illarionov, Ariane Lehmann, Tarek Al Said, Sylwia Kacprzak, Robert Bittl, Adelbert Bacher, Markus Fischer, and Stefan Weber
- Subjects
Medicine ,Science - Abstract
Abstract Flavocoenzymes are nearly ubiquitous cofactors that are involved in the catalysis and regulation of a wide range of biological processes including some light-induced ones, such as the photolyase-mediated DNA repair, magnetoreception of migratory birds, and the blue-light driven phototropism in plants. One of the factors that enable versatile flavin-coenzyme biochemistry and biophysics is the fine-tuning of the cofactor’s frontier orbital by interactions with the protein environment. Probing the singly-occupied molecular orbital (SOMO) of the intermediate radical state of flavins is therefore a prerequisite for a thorough understanding of the diverse functions of the flavoprotein family. This may be ultimately achieved by unravelling the hyperfine structure of a flavin by electron paramagnetic resonance. In this contribution we present a rigorous approach to obtaining a hyperfine map of the flavin’s chromophoric 7,8-dimethyl isoalloxazine unit at an as yet unprecedented level of resolution and accuracy. We combine powerful high-microwave-frequency/high-magnetic-field electron–nuclear double resonance (ENDOR) with 13C isotopologue editing as well as spectral simulations and density functional theory calculations to measure and analyse 13C hyperfine couplings of the flavin cofactor in DNA photolyase. Our data will provide the basis for electronic structure considerations for a number of flavin radical intermediates occurring in blue-light photoreceptor proteins.
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- 2021
- Full Text
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3. Blue-light reception through quaternary transitions
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Christopher Engelhard, Ralph P. Diensthuber, Andreas Möglich, and Robert Bittl
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Medicine ,Science - Abstract
Abstract Sensory photoreceptors absorb light via their photosensor modules and trigger downstream physiological adaptations via their effector modules. Light reception accordingly depends on precisely orchestrated interactions between these modules, the molecular details of which often remain elusive. Using electron-electron double resonance (ELDOR) spectroscopy and site-directed spin labelling, we chart the structural transitions facilitating blue-light reception in the engineered light-oxygen-voltage (LOV) histidine kinase YF1 which represents a paradigm for numerous natural signal receptors. Structural modelling based on pair-wise distance constraints derived from ELDOR pinpoint light-induced rotation and splaying apart of the two LOV photosensors in the dimeric photoreceptor. Resultant molecular strain likely relaxes as left-handed supercoiling of the coiled-coil linker connecting sensor and effector units. ELDOR data on a photoreceptor variant with an inverted signal response indicate a drastically altered dimer interface but light-induced structural transitions in the linker that are similar to those in YF1. Taken together, we provide mechanistic insight into the signal trajectories of LOV photoreceptors and histidine kinases that inform molecular simulations and the engineering of novel receptors.
- Published
- 2017
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4. Nanocrystals for Improved Drug Delivery of Dexamethasone in Skin Investigated by EPR Spectroscopy
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Silke B. Lohan, Siavash Saeidpour, Miriam Colombo, Sven Staufenbiel, Michael Unbehauen, Amanuel Wolde-Kidan, Roland R. Netz, Roland Bodmeier, Rainer Haag, Christian Teutloff, Robert Bittl, and Martina C. Meinke
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skin penetration ,nanocarriers ,nanocrystals ,penetration kinetics ,1D general diffusion equation ,electron paramagnetic resonance (EPR) spectroscopy ,Pharmacy and materia medica ,RS1-441 - Abstract
Nanocrystals represent an improvement over the traditional nanocarriers for dermal application, providing the advantages of 100% drug loading, a large surface area, increased adhesion, and the potential for hair follicle targeting. To investigate their advantage for drug delivery, compared to a base cream formulation, dexamethasone (Dx), a synthetic glucocorticoid frequently used for the treatment of inflammatory skin diseases, was covalently linked with the paramagnetic probe 3-(carboxy)-2,2,5,5-tetramethyl-1-pyrrolidinyloxy (PCA) to DxPCA. To investigate the penetration efficiency between these two vehicles, electron paramagnetic resonance (EPR) spectroscopy was used, which allows the quantification of a spin-labeled drug in different skin layers and the monitoring of the drug release. The penetration behavior in excised healthy and barrier-disrupted porcine skin was monitored by EPR, and subsequently analyzed using a numerical diffusion model. As a result, diffusion constants and free energy values in the different layers of the skin were identified for both formulations. Dx-nanocrystals showed a significantly increased drug amount that penetrated into viable epidermis and dermis of intact (factor 3) and barrier-disrupted skin (factor 2.1) compared to the base cream formulation. Furthermore, the observed fast delivery of the spin-labeled drug into the skin (80% DxPCA within 30 min) and a successive release from the aggregate unit into the viable tissue makes these nanocrystals very attractive for clinical applications.
- Published
- 2020
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5. Correction: Human and Drosophila Cryptochromes Are Light Activated by Flavin Photoreduction in Living Cells.
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Nathalie Hoang, Erik Schleicher, Sylwia Kacprzak, Jean-Pierre Bouly, Marie Picot, William Wu, Alex Berndt, Eva Wolf, Robert Bittl, and Margaret Ahmad
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Biology (General) ,QH301-705.5 - Published
- 2008
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6. Human and Drosophila cryptochromes are light activated by flavin photoreduction in living cells.
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Nathalie Hoang, Erik Schleicher, Sylwia Kacprzak, Jean-Pierre Bouly, Marie Picot, William Wu, Albrecht Berndt, Eva Wolf, Robert Bittl, and Margaret Ahmad
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Biology (General) ,QH301-705.5 - Abstract
Cryptochromes are a class of flavoprotein blue-light signaling receptors found in plants, animals, and humans that control plant development and the entrainment of circadian rhythms. In plant cryptochromes, light activation is proposed to result from photoreduction of a protein-bound flavin chromophore through intramolecular electron transfer. However, although similar in structure to plant cryptochromes, the light-response mechanism of animal cryptochromes remains entirely unknown. To complicate matters further, there is currently a debate on whether mammalian cryptochromes respond to light at all or are instead activated by non-light-dependent mechanisms. To resolve these questions, we have expressed both human and Drosophila cryptochrome proteins to high levels in living Sf21 insect cells using a baculovirus-derived expression system. Intact cells are irradiated with blue light, and the resulting cryptochrome photoconversion is monitored by fluorescence and electron paramagnetic resonance spectroscopic techniques. We demonstrate that light induces a change in the redox state of flavin bound to the receptor in both human and Drosophila cryptochromes. Photoreduction from oxidized flavin and subsequent accumulation of a semiquinone intermediate signaling state occurs by a conserved mechanism that has been previously identified for plant cryptochromes. These results provide the first evidence of how animal-type cryptochromes are activated by light in living cells. Furthermore, human cryptochrome is also shown to undergo this light response. Therefore, human cryptochromes in exposed peripheral and/or visual tissues may have novel light-sensing roles that remain to be elucidated.
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- 2008
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7. Does Tyrosine Protect S. coelicolor Laccase from Oxidative Degradation or Act as an Extended Catalytic Site?
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Patrycja J. Kielb, Christian Teutloff, Robert Bittl, Harry B. Gray, and Jay R. Winkler
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Materials Chemistry ,Physical and Theoretical Chemistry ,Surfaces, Coatings and Films - Published
- 2022
8. Chirality‐Induced Spin Selectivity: An Enabling Technology for Quantum Applications
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Alessandro Chiesa, Alberto Privitera, Emilio Macaluso, Matteo Mannini, Robert Bittl, Ron Naaman, Michael R. Wasielewski, Roberta Sessoli, and Stefano Carretta
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Mechanics of Materials ,Mechanical Engineering ,General Materials Science - Published
- 2023
9. Ein m ‐Terphenylisocyanid stabilisiert 17‐Elektronen‐Monoradikale von drei Elementen der Gruppe 7
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Federico Salsi, Shuai Wang, Christian Teutloff, Marvin Busse, Michael L. Neville, Adelheid Hagenbach, Robert Bittl, Joshua S. Figueroa, and Ulrich Abram
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General Medicine - Published
- 2023
10. A Complete Triad of Zero-Valent 17-Electron Monoradicals of Group 7 Elements Stabilized by m-Terphenyl Isocyanides
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Federico Salsi, Shuai Wang, Christian Teutloff, Marvin Busse, Michael L. Neville, Adelheid Hagenbach, Robert Bittl, Joshua S. Figueroa, and Ulrich Abram
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m-terphenyl isocyanides ,group 7 elements ,metalloradicals ,General Chemistry ,high-field EPR ,500 Naturwissenschaften und Mathematik::540 Chemie::540 Chemie und zugeordnete Wissenschaften ,Catalysis ,17-electron compounds - Abstract
The first consistent series of mononuclear 17-electron complexes of three Group 7 elements has been isolated in crystalline form and studied by X-ray diffraction and spectroscopic methods. The paramagnetic compounds have a composition of [M0(CO)(CNp-F-ArDarF2)4] (M = Mn (1), Tc (3), Re (6); ArDArF2 = 2,6-(3,5-(CF3)2C6H3)2C6H3)) and are stabilized by four sterically encumbering isocyanides, which prevent the metalloradicals from dimerization. They have a square pyramidal structure with the carbonyl ligands as apexes. The frozen-solution EPR spectra of the rhenium and technetium compounds are clearly anisotropic with large 99Tc and 185,187Re hyperfine interactions for one component. High-field EPR (Q band and W band) has been applied for the elucidation of the EPR parameters of the manganese(0) complex.
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- 2023
11. Does Tyrosine Protect
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Patrycja J, Kielb, Christian, Teutloff, Robert, Bittl, Harry B, Gray, and Jay R, Winkler
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Oxygen ,Oxidative Stress ,Catalytic Domain ,Laccase ,Tryptophan ,Tyrosine ,Streptomyces coelicolor ,Oxidation-Reduction ,Copper - Abstract
We have investigated the roles of tyrosine (Tyr) and tryptophan (Trp) residues in the four-electron reduction of oxygen catalyzed by
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- 2022
12. Spin–spin interactions and spin delocalisation in a doped organic semiconductor probed by EPR spectroscopy
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Claudia E. Tait, Jan Behrends, Robert Bittl, Dieter Neher, Anna Reckwitz, and Malavika Arvind
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Materials science ,General Physics and Astronomy ,spin delocalisation ,02 engineering and technology ,010402 general chemistry ,01 natural sciences ,law.invention ,Condensed Matter::Materials Science ,Electron transfer ,law ,Physical and Theoretical Chemistry ,Electron paramagnetic resonance ,Hyperfine structure ,Dopant ,organic semiconductor ,Pulsed EPR ,500 Naturwissenschaften und Mathematik::530 Physik::530 Physik ,Doping ,spin–spin interactions ,021001 nanoscience & nanotechnology ,0104 chemical sciences ,Organic semiconductor ,Crystallography ,Radical ion ,Condensed Matter::Strongly Correlated Electrons ,0210 nano-technology - Abstract
The enhancement and control of the electrical conductivity of organic semiconductors is fundamental for their use in optoelectronic applications and can be achieved by molecular doping, which introduces additional charge carriers through electron transfer between a dopant molecule and the organic semiconductor. Here, we use Electron Paramagnetic Resonance (EPR) spectroscopy to characterise the unpaired spins associated with the charges generated by molecular doping of the prototypical organic semiconductor poly(3-hexylthiophene) (P3HT) with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) and tris(pentafluorophenyl)borane (BCF). The EPR results reveal the P3HT radical cation as the only paramagnetic species in BCF-doped P3HT films and show evidence for increased mobility of the detected spins at high doping concentrations as well as formation of antiferromagnetically coupled spin pairs leading to decreased spin concentrations at low temperatures. The EPR signature for F4TCNQ-doped P3HT is found to be determined by spin exchange between P3HT radical cations and F4TCNQ radical anions. Results from continuous-wave and pulse EPR measurements suggest the presence of the unpaired spin on P3HT in a multitude of environments, ranging from free P3HT radical cations with similar properties to those observed in BCF-doped P3HT, to pairs of dipolar and exchange-coupled spins on P3HT and the dopant anion. Characterisation of the proton hyperfine interactions by ENDOR allowed quantification of the extent of spin delocalisation and revealed reduced delocalisation in the F4TCNQ-doped P3HT films.
- Published
- 2021
13. Pigmentierungschemie und radikalbasierter Kollagenabbau bei Alkaptonurie und Arthrose
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Robert Bittl, Hartmut Oschkinat, Christian Teutloff, Norman B. Roberts, Brendan P. Norman, Wing Ying Chow, Melinda J. Duer, Lakshminarayan R. Ranganath, and James A. Gallagher
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Chemistry ,General Medicine - Published
- 2020
14. Assessing the Nature of Chiral-Induced Spin Selectivity by Magnetic Resonance
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Stefano Carretta, Mario Chiesa, Enrico Salvadori, Francesco Tacchino, Robert Bittl, Alessandro Chiesa, Paolo Santini, E. Garlatti, Ivano Tavernelli, M Chizzini, and Roberta Sessoli
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DYNAMICS ,Letter ,CORRELATED RADICAL PAIRS, PHOTOSYNTHETIC REACTION CENTERS, TRANSIENT EPR, ELECTRON-TRANSFER, QUANTUM COHERENCE, DYNAMICS, POLARIZATION, QUBITS, MOLECULES, TRANSPORT ,POLARIZATION ,FOS: Physical sciences ,02 engineering and technology ,010402 general chemistry ,01 natural sciences ,law.invention ,Electron transfer ,CORRELATED RADICAL PAIRS ,MOLECULES ,Charge transfer ,law ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,General Materials Science ,ELECTRON-TRANSFER ,Physical and Theoretical Chemistry ,Electron paramagnetic resonance ,Spin (physics) ,Quantum computer ,Physics ,Quantum Physics ,Condensed Matter - Mesoscale and Nanoscale Physics ,PHOTOSYNTHETIC REACTION CENTERS ,QUANTUM COHERENCE ,Charge (physics) ,021001 nanoscience & nanotechnology ,Polarization (waves) ,Acceptor ,TRANSPORT ,0104 chemical sciences ,3. Good health ,QUBITS ,Chemical physics ,Qubit ,TRANSIENT EPR ,0210 nano-technology ,Quantum Physics (quant-ph) ,Electron paramagnetic resonance spectroscopy - Abstract
Understanding chiral-induced spin selectivity (CISS), resulting from chargetransport through helical systems, has recently inspired many experimental and theoreticalefforts but is still the object of intense debate. In order to assess the nature of CISS, wepropose to focus on electron-transfer processes occurring at the single-molecule level. Wedesign simple magnetic resonance experiments, exploiting a qubit as a highly sensitive andcoherent magnetic sensor, to provide clear signatures of the acceptor polarization. Moreover,we show that information could even be obtained from time-resolved electron paramagnetic resonance experiments on a randomly oriented solution of molecules. The proposedexperiments will unveil the role of chiral linkers in electron transfer and could also beexploited for quantum computing applications.
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- 2021
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15. Reply to comments referee 2
- Author
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Robert Bittl
- Published
- 2020
16. Pigmentation Chemistry and Radical-Based Collagen Degradation in Alkaptonuria and Osteoarthritic Cartilage
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Lakshminarayan R. Ranganath, James A. Gallagher, Robert Bittl, Christian Teutloff, Melinda J. Duer, Hartmut Oschkinat, Brendan P. Norman, Wing Ying Chow, and Norman B. Roberts
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Cartilage, Articular ,Magnetic Resonance Spectroscopy ,Collagen helix ,Osteoarthritis ,Alkaptonuria ,Catalysis ,fibrous proteins ,chemistry.chemical_compound ,Pigment ,NMR spectroscopy ,Spinal osteoarthropathy ,Fibrous Proteins | Hot Paper ,medicine ,Humans ,Homogentisic acid ,Homogentisic Acid ,Ochronosis ,Pigmentation ,Cartilage ,Communication ,500 Naturwissenschaften und Mathematik::530 Physik::530 Physik ,Electron Spin Resonance Spectroscopy ,General Chemistry ,Pigments, Biological ,medicine.disease ,radicals ,Communications ,medicine.anatomical_structure ,chemistry ,Biochemistry ,visual_art ,visual_art.visual_art_medium ,sense organs ,600 Technik, Medizin, angewandte Wissenschaften::610 Medizin und Gesundheit::615 Pharmakologie, Therapeutik ,Oxidation-Reduction ,metabolism ,EPR spectroscopy - Abstract
Alkaptonuria (AKU) is a rare disease characterized by high levels of homogentisic acid (HGA); patients suffer from tissue ochronosis: dark brown pigmentation, especially of joint cartilage, leading to severe early osteoarthropathy. No molecular mechanism links elevated HGA to ochronosis; the pigment's chemical identity is still not known, nor how it induces joint cartilage degradation. Here we give key insight on HGA‐derived pigment composition and collagen disruption in AKU cartilage. Synthetic pigment and pigmented human cartilage tissue both showed hydroquinone‐resembling NMR signals. EPR spectroscopy showed that the synthetic pigment contains radicals. Moreover, we observed intrastrand disruption of collagen triple helix in pigmented AKU human cartilage, and in cartilage from patients with osteoarthritis. We propose that collagen degradation can occur via transient glycyl radicals, the formation of which is enhanced in AKU due to the redox environment generated by pigmentation., Alkaptonuria is a rare disease that leads to striking pigmentation and mechanical failure of cartilage tissue. DNP‐enhanced solid‐state NMR enabled us to observe disruption of interstrand hydrogen bonding in collagen proteins from alkaptonuria patient tissue. A mechanism involving transient glycyl radicals is proposed as basis of the degradation and pigmentation of cartilage tissue in alkaptonuria.
- Published
- 2020
17. Probing the Wave Function and Dynamics of the Quintet Multiexciton State with Coherent Control in a Singlet Fission Material
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John E. Anthony, Leah R. Weiss, Jan Behrends, Robert Bittl, Felix Kraffert, D. B. Granger, and Sam L. Bayliss
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Physics ,excitons ,QC1-999 ,Dynamics (mechanics) ,500 Naturwissenschaften und Mathematik::530 Physik::530 Physik ,electron spin resonance ,General Physics and Astronomy ,State (functional analysis) ,Function (mathematics) ,01 natural sciences ,010305 fluids & plasmas ,organic electronics ,Coherent control ,Quantum mechanics ,0103 physical sciences ,Singlet fission ,Condensed Matter::Strongly Correlated Electrons ,010306 general physics ,organic semiconductors ,Spin-½ - Abstract
High-spin states play a key role in chemical reactions found in nature. In artificial molecular systems, singlet fission produces a correlated triplet-pair state, a spin-bearing excited state that can be harnessed for more efficient solar-energy conversion and photocatalysis. In particular, triplet-pair states with overall quintet character (total spin \ud S\ud =\ud 2\ud ) have been discovered, but many of the fundamental properties of these biexciton states remain unexplored. The net spin of these pair states makes spin-sensitive probes attractive for their characterization. Combined with their surprisingly long spin coherence (of order microseconds), this opens up techniques relying on coherent spin control. Here we apply coherent manipulation of triplet-pair states to (i) isolate their spectral signatures from coexisting free triplets and (ii) selectively couple quintet and triplet states to specific nuclear spins. Using this approach, we separate quintet and triplet transitions and extract the relaxation dynamics and hyperfine couplings of the fission-borne spin states. Our results highlight the distinct properties of correlated and free triplet excitons and demonstrate optically induced nuclear spin polarization by singlet fission.
- Published
- 2020
18. EPR Study of NO radicals encased in modified open C60 Fullerenes
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Klaus-Peter Dinse, Tatsuhisa Kato, Shota Hasegawa, Yoshifumi Hashikawa, Yasujiro Murata, and Robert Bittl
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Electricity and magnetism ,C60 ,QC501-766 ,500 Naturwissenschaften und Mathematik::530 Physik::539 Moderne Physik ,open-cage fullerene ,encapsulation ,Magnetic Resonance ,g matrix ,EPR spectroscopy ,NO - Abstract
Using pulsed electron paramagnetic resonance (EPR) techniques, the low-temperature magnetic properties of the NO radical being confined in two different modified open C60-derived cages are determined. It is found that the smallest principal g value g3, being assigned to the axis of the radical, deviates strongly from the free electron value. This behaviour results from partial compensation of the spin and orbital contributions to the g3 value. The measured g3 values in the range of 0.7 yield information about the deviation of the locking potential for the encaged NO from axial symmetry. The estimated 17 meV asymmetry is quite small compared to the situation found for the same radical in polycrystalline or amorphous matrices ranging from 300 to 500 meV. The analysis of the temperature dependence of spin relaxation times resulted in an activation temperature of about 3 K, assigned to temperature-activated motion of the NO within the modified open C60-derived cages with coupled rotational and translational degrees of freedom in a complicated three-dimensional locking potential.
- Published
- 2020
19. Coupled Methyl Group Rotation in FMN Radicals Revealed by Selective Deuterium Labeling
- Author
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Richard Brosi, Ryu-Ryun Kim, Lorenz Heidinger, Robert Bittl, Adelbert Bacher, Stefan Weber, Boris Illarionov, Markus Fischer, and Erik Schleicher
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Proton ,Rotation ,Flavin Mononucleotide ,Radical ,Flavoprotein ,Flavin mononucleotide ,Flavin group ,Methylation ,chemistry.chemical_compound ,Flavins ,Magnetic properties ,Organic compounds ,Materials Chemistry ,Physical and Theoretical Chemistry ,Hyperfine structure ,500 Naturwissenschaften und Mathematik::530 Physik::539 Moderne Physik ,biology ,Deuterium ,Alkyls ,Surfaces, Coatings and Films ,Crystallography ,chemistry ,Isotope Labeling ,biology.protein ,Protons ,Oxidation-Reduction ,Electron paramagnetic resonance spectroscopy ,Methyl group - Abstract
Flavin semiquinones are common intermediate redox states in flavoproteins, and thus, knowledge of their electronic structure is essential for fully understanding their chemistry and chemical versatility. In this contribution, we use a combination of high-field electron nuclear double resonance spectroscopy and selective deuterium labeling of flavin mononucleotide (FMN) with subsequent incorporation as cofactor into a variant Avena sativa LOV domain to extract missing traits of the electronic structure of a protein-bound FMN radical. From these experiments, precise values of small proton hyperfine and deuterium nuclear quadrupole couplings could be extracted. Specifically, isotropic hyperfine couplings of ���3.34, ���0.11, and +0.91 MHz were obtained for the protons H(6), H(9), and H(7��), respectively. These values are discussed in the light of specific protein���cofactor interactions. Furthermore, the temperature behavior of the H(7��) methyl-group rotation elicited by its energy landscape was analyzed in greater detail. Pronounced interplay between the two methyl groups at C(7) and C(8) of FMN could be revealed. Most strikingly, this rotational behavior could be modulated by selective deuterium editing.
- Published
- 2020
20. Cobalt‐exchanged poly(heptazine imides) as transition Metal–Nx electrocatalysts for the oxygen evolution reaction
- Author
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Meng-Yang Ye, Robert Bittl, Arne Thomas, Shuang Li, Christian Teutloff, Xiaojia Zhao, Wing Ying Chow, and Nadezda V. Tarakina
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Materials science ,Heptazine ,Inorganic chemistry ,chemistry.chemical_element ,M–Nx–C ,02 engineering and technology ,poly(heptazine imides) ,Overpotential ,010402 general chemistry ,Electrocatalyst ,01 natural sciences ,chemistry.chemical_compound ,Transition metal ,electrocatalysis ,General Materials Science ,carbon nitride ,Carbon nitride ,Tafel equation ,500 Naturwissenschaften und Mathematik::530 Physik::539 Moderne Physik ,Mechanical Engineering ,Oxygen evolution ,021001 nanoscience & nanotechnology ,0104 chemical sciences ,chemistry ,Mechanics of Materials ,oxygen evolution reaction ,ddc:540 ,ddc:660 ,0210 nano-technology ,500 Naturwissenschaften und Mathematik::540 Chemie::540 Chemie und zugeordnete Wissenschaften ,600 Technik, Medizin, angewandte Wissenschaften::610 Medizin und Gesundheit::615 Pharmakologie, Therapeutik ,Cobalt - Abstract
Poly(heptazine imides) hosting cobalt ions as countercations are presented as promising electrocatalysts for the oxygen evolution reaction (OER). A facile mixed-salt melt-assisted condensation is developed to prepare such cobalt poly(heptazine imides) (PHI-Co). The Co ions can be introduced in well-controlled amounts using this method, and are shown to be atomically dispersed within the imide-linked heptazine matrix. When applied to electrocatalytic OER, PHI-Co shows a remarkable activity with an overpotential of 324 mV and Tafel slope of 44 mV dec?1 in 1 m KOH.
- Published
- 2020
- Full Text
- View/download PDF
21. Localization of dexamethasone within dendritic core-multishell (CMS) nanoparticles and skin penetration properties studied by multi-frequency electron paramagnetic resonance (EPR) spectroscopy
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Siavash Saeidpour, Silke B. Lohan, Christian Teutloff, Michael Unbehauen, Robert Bittl, Emanuel Fleige, M. Anske, Martina C. Meinke, and Rainer Haag
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Materials science ,Polymers ,Swine ,Skin Absorption ,Pharmaceutical Science ,Nanoparticle ,02 engineering and technology ,skin penetration ,Administration, Cutaneous ,Dexamethasone ,law.invention ,030207 dermatology & venereal diseases ,03 medical and health sciences ,Drug Delivery Systems ,0302 clinical medicine ,Nuclear magnetic resonance ,law ,dendritic core-multishell systems ,Stratum corneum ,medicine ,drug delivery system ,Animals ,Penetration depth ,Electron paramagnetic resonance ,Rotational correlation time ,Skin ,solvent polarity ,Drug Carriers ,integumentary system ,500 Naturwissenschaften und Mathematik::530 Physik::530 Physik ,Electron Spin Resonance Spectroscopy ,General Medicine ,Penetration (firestop) ,021001 nanoscience & nanotechnology ,dual-frequency EPR ,mobility ,medicine.anatomical_structure ,Drug delivery ,Nanoparticles ,Spin Labels ,Nanocarriers ,0210 nano-technology ,Biotechnology - Abstract
The skin and especially the stratum corneum (SC) act as a barrier and protect epidermal cells and thus the whole body against xenobiotica of the external environment. Topical skin treatment requires an efficient drug delivery system (DDS). Polymer-based nanocarriers represent novel transport vehicles for dermal application of drugs. In this study dendritic core-multishell (CMS) nanoparticles were investigated as promising candidates. CMS nanoparticles were loaded with a drug (analogue) and were applied to penetration studies of skin. We determined by dual-frequency electron paramagnetic resonance (EPR) how dexamethasone (Dx) labelled with 3-carboxy-2,2,5,5-tetramethyl-1-pyrrolidinyloxy (PCA) is associated with the CMS. The micro-environment of the drug loaded to CMS nanoparticles was investigated by pulsed high-field EPR at cryogenic temperature, making use of the fact that magnetic parameters (g-, A-matrices, and spin-lattice relaxation time) represent specific probes for the micro-environment. Additionally, the rotational correlation time of spin-labelled Dx was probed by continuous wave EPR at ambient temperature, which provides independent information on the drug environment. Furthermore, the penetration depth of Dx into the stratum corneum of porcine skin after different topical applications was investigated. The location of Dx in the CMS nanoparticles is revealed and the function of CMS as penetration enhancers for topical application is shown.
- Published
- 2017
22. Bestimmung des Radikal-Radikal-Abstands in lichtaktiven Proteinen im angeregten Zustand und dessen Bedeutung für die biologische Magnetorezeption
- Author
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Robert Bittl, Erik Schleicher, Asako Okafuji, Daniel Nohr, Bernd Paulus, Ryan Rodriguez, and Stefan Weber
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0301 basic medicine ,03 medical and health sciences ,030104 developmental biology ,General Medicine - Abstract
Durch Licht erzeugte, kurzlebige Radikalpaare sind Reaktionsintermediate in Photolyasen und Cryptochromen. Cryptochrome spielen wahrscheinlich bei der Magnetfeldwahrnehmung durch Zugvogel und beim magnetfeldabhangigen Verhalten von Insekten eine Rolle. Wir haben transiente Zustande im Cryptochrom aus Drosophila melanogaster und im strukturverwandten DNA-Reparaturenzym DNA-Photolyase aus Escherichia coli untersucht. Mithilfe eines Puls-EPR-Verfahrens konnten die beiden Beitrage zur Spin-Spin-Wechselwirkung, die Austauschwechselwirkung und die magnetische Dipol-Dipol-Kopplung, direkt bestimmt werden. Anhand dieser Grosen wurden in beiden Proteinen die Radikalpaarpartner identifiziert, und es konnten Aussagen uber die potenzielle Effizienz des Radikalpaars im Drosophila-Cryptochrom als Magnetorezeptor getroffen werden. Weiterhin wurden Beweise fur eine erweiterte Elektrontransferkaskade in diesem Protein erbracht: Der Tryptophanrest W394 ist ein essentieller Bestandteil fur die Photoreduktion des Flavin-Kofaktors und fur die Bildung eines Radikalpaars mit einer fur eine Magnetfeldsensibilitat ausreichend langen Lebenszeit.
- Published
- 2017
23. Cobalt-Exchanged Poly(Heptazine Imides) as Transition Metal-N
- Author
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Meng-Yang, Ye, Shuang, Li, Xiaojia, Zhao, Nadezda V, Tarakina, Christian, Teutloff, Wing Ying, Chow, Robert, Bittl, and Arne, Thomas
- Abstract
Poly(heptazine imides) hosting cobalt ions as countercations are presented as promising electrocatalysts for the oxygen evolution reaction (OER). A facile mixed-salt melt-assisted condensation is developed to prepare such cobalt poly(heptazine imides) (PHI-Co). The Co ions can be introduced in well-controlled amounts using this method, and are shown to be atomically dispersed within the imide-linked heptazine matrix. When applied to electrocatalytic OER, PHI-Co shows a remarkable activity with an overpotential of 324 mV and Tafel slope of 44 mV dec
- Published
- 2019
24. A blue light receptor that mediates RNA binding and translational regulation
- Author
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Laura Lledo Bryant, Marc Juraschitz, Stefanie Schrottke, Andreas Möglich, Günter Mayer, Thea Ziegler, Ankana Kakoti, Lisa Sixt, Christian Renzl, Georg Pietruschka, Sebastian Pilsl, Robert Bittl, Clemens Steegborn, Sébastien Moniot, Jennifer Kaiser, and Anna Weber
- Subjects
Light ,RNA-binding protein ,RNA-binding proteins ,Article ,03 medical and health sciences ,Bacterial Proteins ,Gene expression ,Translational regulation ,Protein biosynthesis ,Molecular Biology ,030304 developmental biology ,X-ray crystallography ,0303 health sciences ,Chemistry ,Effector ,030302 biochemistry & molecular biology ,500 Naturwissenschaften und Mathematik::530 Physik::530 Physik ,RNA ,Photoreceptor protein ,Cell Biology ,Cell biology ,Protein Biosynthesis ,Signal transduction ,Protein Binding ,Signal Transduction - Abstract
Sensory photoreceptor proteins underpin light-dependent adaptations in nature and enable the optogenetic control of organismal behavior and physiology. We identified the bacterial light-oxygen-voltage (LOV) photoreceptor PAL that sequence-specifically binds short RNA stem loops with around 20 nM affinity in blue light and weaker than 1 µM in darkness. A crystal structure rationalizes the unusual receptor architecture of PAL with C-terminal LOV photosensor and N-terminal effector units. The light-activated PAL–RNA interaction can be harnessed to regulate gene expression at the RNA level as a function of light in both bacteria and mammalian cells. The present results elucidate a new signal-transduction paradigm in LOV receptors and conjoin RNA biology with optogenetic regulation, thereby paving the way toward hitherto inaccessible optoribogenetic modalities. A light-oxygen-voltage photoreceptor was found to bind short RNA stem loops in a light-dependent manner, which can be harnessed to regulate gene expression in bacteria and mammalian cells.
- Published
- 2019
- Full Text
- View/download PDF
25. Tuning spin dynamics in crystalline tetracene
- Author
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Rui Wang, Jan Behrends, Robert Bittl, Chunfeng Zhang, Sam L. Bayliss, and Felix Kraffert
- Subjects
Materials science ,Dephasing ,Exciton ,02 engineering and technology ,010402 general chemistry ,01 natural sciences ,Molecular physics ,Crystals ,Quantum mechanics ,law.invention ,chemistry.chemical_compound ,law ,General Materials Science ,Singlet state ,Physical and Theoretical Chemistry ,Electron paramagnetic resonance ,500 Naturwissenschaften und Mathematik::530 Physik::539 Moderne Physik ,Spin polarization ,Crystal structure ,Nuclear fission ,021001 nanoscience & nanotechnology ,0104 chemical sciences ,Tetracene ,Intersystem crossing ,chemistry ,Singlet fission ,Condensed Matter::Strongly Correlated Electrons ,0210 nano-technology ,Electron paramagnetic resonance spectroscopy - Abstract
Tetracene is an archetypal material undergoing singlet fission—the generation of a pair of triplet excitons from one singlet exciton. Here, using time-resolved electron spin resonance, we show how the spin dynamics in tetracene crystals are influenced by temperature and morphology. Upon cooling from 300 to 200 K, we observe a switch between singlet fission and intersystem crossing generated triplets, manifesting as an inversion in transient spin polarization. We extract a spin dephasing time of approximately 40 ns for fission-generated triplets at room temperature, nearly 100 times shorter than the dephasing time that we measure for triplets localized on isolated tetracene molecules. These results highlight the importance of morphology and thermal activation in singlet fission systems.
- Published
- 2019
26. Investigation of cutaneous penetration properties of stearic acid loaded to dendritic core-multi-shell (CMS) nanocarriers
- Author
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Emanuel Fleige, N. Icken, Stefan F. Haag, Rainer Haag, Martina C. Meinke, Silke B. Lohan, Christian Teutloff, Robert Bittl, Siavash Saeidpour, and Juergen Lademann
- Subjects
Glycerol ,Dendrimers ,Polymers ,Swine ,Skin Absorption ,Analytical chemistry ,Pharmaceutical Science ,02 engineering and technology ,Polyethylene glycol ,In Vitro Techniques ,Administration, Cutaneous ,Fluorescence spectroscopy ,Polyethylene Glycols ,law.invention ,030207 dermatology & venereal diseases ,03 medical and health sciences ,chemistry.chemical_compound ,0302 clinical medicine ,law ,Stratum corneum ,medicine ,Fluorescence microscope ,Animals ,Electron paramagnetic resonance ,Fluorescent Dyes ,Skin ,Drug Carriers ,integumentary system ,Chemistry ,Electron Spin Resonance Spectroscopy ,Penetration (firestop) ,Carbocyanines ,021001 nanoscience & nanotechnology ,Nanostructures ,medicine.anatomical_structure ,Microscopy, Fluorescence ,Chemical engineering ,Stearic acid ,Nanocarriers ,0210 nano-technology ,Hair Follicle ,Stearic Acids - Abstract
Dendritic core-multi shell (CMS) particles are polymer based systems consisting of a dendritic polar polyglycerol polymer core surrounded by a two-layer shell of nonpolar C18 alkyl chains and hydrophilic polyethylene glycol. Belonging to nanotransport systems (NTS) they allow the transport and storage of molecules with different chemical characters. Their amphipihilic character CMS-NTS permits good solubility in aqueous and organic solutions. We showed by multifrequency electron paramagnetic resonance (EPR) spectroscopy that spin-labeled 5-doxyl stearic acid (5DSA) can be loaded into the CMS-NTS. Furthermore, the release of 5DSA from the carrier into the stratum corneum of porcine skin was monitored ex vivo by EPR spectroscopy. Additionally, the penetration of the CMS-NTS into the skin was analyzed by fluorescence microscopy using indocarbocyanine (ICC) covalently bound to the nanocarrier. Thereby, no transport into the viable skin was observed, whereas the CMS-NTS had penetrated into the hair follicles down to a depth of 340 μm ± 82 μm. Thus, it could be shown that the combined application of fluorescence microscopy and multi-frequency EPR spectroscopy can be an efficient tool for investigating the loading of spin labeled drugs to nanocarrier systems, drug release and penetration into the skin as well as the localization of the NTS in the skin.
- Published
- 2016
27. Innentitelbild: Pigmentierungschemie und radikalbasierter Kollagenabbau bei Alkaptonurie und Arthrose (Angew. Chem. 29/2020)
- Author
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Wing Ying Chow, Christian Teutloff, Norman B. Roberts, James A. Gallagher, Robert Bittl, Lakshminarayan R. Ranganath, Brendan P. Norman, Melinda J. Duer, and Hartmut Oschkinat
- Subjects
General Medicine - Published
- 2020
28. Inside Cover: Pigmentation Chemistry and Radical‐Based Collagen Degradation in Alkaptonuria and Osteoarthritic Cartilage (Angew. Chem. Int. Ed. 29/2020)
- Author
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Robert Bittl, Hartmut Oschkinat, Wing Ying Chow, Norman B. Roberts, Lakshminarayan R. Ranganath, James A. Gallagher, Christian Teutloff, Brendan P. Norman, and Melinda J. Duer
- Subjects
Collagen degradation ,Chemistry ,Radical ,INT ,General Chemistry ,Nuclear magnetic resonance spectroscopy ,Photochemistry ,medicine.disease ,Catalysis ,Alkaptonuria ,law.invention ,law ,medicine ,Cover (algebra) ,Electron paramagnetic resonance ,Osteoarthritic cartilage - Published
- 2020
29. Site-selective measurement of coupled spin pairs in an organic semiconductor
- Author
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Sam L. Bayliss, P. Plochocka, Karl J. Thorley, Neil C. Greenham, Richard H. Friend, Alexei D. Chepelianskii, John E. Anthony, K. M. Yunusova, Akshay Rao, Krzysztof Galkowski, Jan Behrends, Anatolie A. Mitioglu, Robert Bittl, Alessandro Surrente, Leah R. Weiss, Zhuo Yang, Peter C. M. Christianen, Surrente, A [0000-0003-4078-4965], Apollo - University of Cambridge Repository, Laboratoire national des champs magnétiques intenses - Toulouse (LNCMI-T), Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes [2016-2019] (UGA [2016-2019])-Institut National des Sciences Appliquées - Toulouse (INSA Toulouse), Institut National des Sciences Appliquées (INSA)-Institut National des Sciences Appliquées (INSA), Institut National des Sciences Appliquées - Toulouse (INSA Toulouse), Institut National des Sciences Appliquées (INSA)-Université de Toulouse (UT)-Institut National des Sciences Appliquées (INSA)-Université de Toulouse (UT)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes [2016-2019] (UGA [2016-2019]), ANR-16-CE30-0013,SPINEX_1,Spintronique des exitons triplets dans la limite quantique(2016), Institut National des Sciences Appliquées (INSA)-Institut National des Sciences Appliquées (INSA)-Université Toulouse III - Paul Sabatier (UT3), and Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes [2016-2019] (UGA [2016-2019])
- Subjects
Coupled spin pairs ,organic ,biological systems ,FOS: Physical sciences ,exchange coupling ,02 engineering and technology ,triplet excitons ,01 natural sciences ,Molecular physics ,Soft Condensed Matter and Nanomaterials ,Physics - Chemical Physics ,0103 physical sciences ,Singlet state ,010306 general physics ,Spin (physics) ,organic semiconductors ,ComputingMilieux_MISCELLANEOUS ,Physics ,Organic electronics ,Chemical Physics (physics.chem-ph) ,spintronics ,Condensed Matter - Materials Science ,Multidisciplinary ,Spintronics ,physics ,Intermolecular force ,singlet fission ,500 Naturwissenschaften und Mathematik::530 Physik::530 Physik ,Materials Science (cond-mat.mtrl-sci) ,021001 nanoscience & nanotechnology ,Organic semiconductor ,[PHYS.COND.CM-S]Physics [physics]/Condensed Matter [cond-mat]/Superconductivity [cond-mat.supr-con] ,organic spintronics ,Singlet fission ,Physical Sciences ,0210 nano-technology ,Luminescence - Abstract
From organic electronics to biological systems, understanding the role of intermolecular interactions between spin pairs is a key challenge. Here we show how such pairs can be selectively addressed with combined spin and optical sensitivity. We demonstrate this for bound pairs of spin-triplet excitations formed by singlet fission, with direct applicability across a wide range of synthetic and biological systems. We show that the site sensitivity of exchange coupling allows distinct triplet pairs to be resonantly addressed at different magnetic fields, tuning them between optically bright singlet ([Formula: see text]) and dark triplet quintet ([Formula: see text]) configurations: This induces narrow holes in a broad optical emission spectrum, uncovering exchange-specific luminescence. Using fields up to 60 T, we identify three distinct triplet-pair sites, with exchange couplings varying over an order of magnitude (0.3-5 meV), each with its own luminescence spectrum, coexisting in a single material. Our results reveal how site selectivity can be achieved for organic spin pairs in a broad range of systems., This work was supported by HFMLRU/ FOM and LNCMI-CNRS, members of the European Magnetic Field Laboratory (EMFL) and by EPSRC (UK) via its membership to the EMFL (grant no. EP/N01085X/1 and NS/A000060/1) and through grant no. EP/M005143/1. L.R.W. acknowledges support of the Gates-Cambridge and Winton Scholarships. We acknowledge support from Labex ANR-10-LABX-0039-PALM, ANR SPINEX, and DFG SPP-1601 (Bi-464/10-2).
- Published
- 2018
- Full Text
- View/download PDF
30. Strukturelle Einblicke in den Mo-Cofaktor-Einbau in Sulfitoxidase durch ortsspezifische Spinmarkierung
- Author
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Silke Leimkühler, Christopher Engelhard, Christian Teutloff, Stefan Reschke, Robert Bittl, Aaron Hahn, and Thomas Risse
- Subjects
Chemistry ,General Medicine - Published
- 2015
31. Active Site of the NAD+-Reducing Hydrogenase from Ralstonia eutropha Studied by EPR Spectroscopy
- Author
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Robert Bittl, Lars Lauterbach, Christian Teutloff, Julia Löwenstein, and Oliver Lenz
- Subjects
Hydrogenase ,Stereochemistry ,chemistry.chemical_element ,Photochemistry ,law.invention ,Ralstonia ,law ,Catalytic Domain ,Materials Chemistry ,Physical and Theoretical Chemistry ,Electron paramagnetic resonance ,Histidine ,biology ,Hydride ,Electron Spin Resonance Spectroscopy ,Active site ,NAD ,biology.organism_classification ,Surfaces, Coatings and Films ,Nickel ,chemistry ,biology.protein ,Cupriavidus necator ,NAD+ kinase ,Oxidation-Reduction - Abstract
Pulsed ENDOR and HYSCORE measurements were carried out to characterize the active site of the oxygen-tolerant NAD(+)-reducing hydrogenase of Ralstonia eutropha. The catalytically active Nia-C state exhibits a bridging hydride between iron and nickel in the active site, which is photodissociated upon illumination. Its hyperfine coupling is comparable to that of standard hydrogenases. In addition, a histidine residue could be identified, which shows hyperfine and nuclear quadrupole parameters in significant variance from comparable histidine residues that are conserved in standard [NiFe] hydrogenases, and might be related to the O2 tolerance of the enzyme.
- Published
- 2015
32. Protein Dynamics in the Reductive Activation of a B12-Containing Enzyme
- Author
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Sebastian Goetzl, Holger Dobbek, Sandra E. Hennig, Robert Bittl, Jae-Hun Jeoung, Christian Teutloff, and Tobias Werther
- Subjects
0301 basic medicine ,Iron-Sulfur Proteins ,Models, Molecular ,Conformational change ,crystal structure ,conformational transitions ,Stereochemistry ,Protein Conformation ,Coenzymes ,Enzyme Activators ,Firmicutes ,Crystallography, X-Ray ,Biochemistry ,03 medical and health sciences ,Electron transfer ,chemistry.chemical_compound ,Protein structure ,Corrinoid ,Bacterial Proteins ,Multienzyme Complexes ,Protein Interaction Domains and Motifs ,Databases, Protein ,Chemistry ,Protein dynamics ,kinetic parameters ,500 Naturwissenschaften und Mathematik::530 Physik::530 Physik ,monomers ,Aldehyde Oxidoreductases ,proteins ,Recombinant Proteins ,Kinetics ,Protein Subunits ,Vitamin B 12 ,030104 developmental biology ,Förster resonance energy transfer ,Catalytic cycle ,Amino Acid Substitution ,Solubility ,Mutation ,peptides ,Mutagenesis, Site-Directed ,Anaerobic bacteria ,Protein Multimerization ,Dimerization ,Oxidation-Reduction - Abstract
B12-dependent proteins are involved in methyl transfer reactions ranging from the biosynthesis of methionine in humans to the formation of acetyl-CoA in anaerobic bacteria. During their catalytic cycle, they undergo large conformational changes to interact with various proteins. Recently, the crystal structure of the B12-containing corrinoid iron–sulfur protein (CoFeSP) in complex with its reductive activator (RACo) was determined, providing a first glimpse of how energy is transduced in the ATP-dependent reductive activation of corrinoid-containing methyltransferases. The thermodynamically uphill electron transfer from RACo to CoFeSP is accompanied by large movements of the cofactor-binding domains of CoFeSP. To refine the structure-based mechanism, we analyzed the conformational change of the B12-binding domain of CoFeSP by pulsed electron–electron double resonance and Förster resonance energy transfer spectroscopy. We show that the site-specific labels on the flexible B12-binding domain and the small subunit of CoFeSP move within 11 Å in the RACo:CoFeSP complex, consistent with the recent crystal structures. By analyzing the transient kinetics of formation and dissociation of the RACo:CoFeSP complex, we determined values of 0.75 μM–1 s–1 and 0.33 s–1 for rate constants kon and koff, respectively. Our results indicate that the large movement observed in crystals also occurs in solution and that neither the formation of the protein encounter complex nor the large movement of the B12-binding domain is rate-limiting for the ATP-dependent reductive activation of CoFeSP by RACo.
- Published
- 2017
33. Determination of Radical-Radical Distances in Light-Active Proteins and Their Implication for Biological Magnetoreception
- Author
-
Stefan Weber, Bernd Paulus, Asako Okafuji, Daniel Nohr, Robert Bittl, Erik Schleicher, and Ryan Rodriguez
- Subjects
0301 basic medicine ,Free Radicals ,Light-Harvesting Protein Complexes ,Flavin group ,010402 general chemistry ,Photochemistry ,01 natural sciences ,Catalysis ,law.invention ,Electron Transport ,03 medical and health sciences ,Cryptochrome ,law ,Flavins ,Escherichia coli ,Animals ,Photolyase ,Electron paramagnetic resonance ,biology ,Pulsed EPR ,Chemistry ,Electron Spin Resonance Spectroscopy ,Magnetoreception ,General Chemistry ,DNA photolyase ,biology.organism_classification ,0104 chemical sciences ,Cryptochromes ,030104 developmental biology ,Drosophila melanogaster ,Magnetic Fields ,Deoxyribodipyrimidine Photo-Lyase - Abstract
Light-generated short-lived radial pairs have been suggested to play pivotal roles in cryptochromes and photolyases. Chryptochromes are very probably involved in magnetic compass sensing in migratory birds and the magnetic-field-dependent behavior of insects. We examined photo-generated transient states in the cryptochrome of Drosophila melanogaster and in the structurally related DNA-repair enzyme Escherichia coli DNA photolyase. Using pulsed EPR spectroscopy, the exchange and dipolar contributions to the electron spin–spin interaction were determined in a straightforward and direct way. With these parameters, radical-pair partners may be identified and the magnetoreceptor efficiency of chryptochromes can be evaluated. We present compelling evidence for an extended electron-transfer cascade in the Drosophila cryptochrome, and identified W394 as a key residue for flavin photoreduction and formation of a spin-correlated radical pair with a sufficient lifetime for high-sensitivity magnetic-field sensing.
- Published
- 2017
34. Recent progress in synchrotron-based frequency-domain Fourier-transform THz-EPR
- Author
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Joscha Nehrkorn, Karsten Holldack, Robert Bittl, and Alexander Schnegg
- Subjects
Nuclear and High Energy Physics ,Terahertz radiation ,Biophysics ,Analytical chemistry ,02 engineering and technology ,Zero field splitting ,010402 general chemistry ,01 natural sciences ,Biochemistry ,law.invention ,symbols.namesake ,law ,Electron paramagnetic resonance ,frequency-domain EPR spectroscopy ,Chemistry ,500 Naturwissenschaften und Mathematik::530 Physik::530 Physik ,high-spin transition-metal ion ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,zero-field splitting ,Synchrotron ,0104 chemical sciences ,Computational physics ,Fourier transform ,Frequency domain ,symbols ,0210 nano-technology - Abstract
We describe frequency-domain Fourier-transform THz-EPR as a method to assign spin-coupling parameters of high-spin ( S > 1/2) systems with very large zero-field splittings. The instrumental foundations of synchrotron-based FD-FT THz-EPR are presented, alongside with a discussion of frequency-domain EPR simulation routines. The capabilities of this approach is demonstrated for selected mono- and multinuclear HS systems. Finally, we discuss remaining challenges and give an outlook on the future prospects of the technique.
- Published
- 2017
35. Drug distribution in nanostructured lipid particles
- Author
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Agnieszka Solik, Victoria Paul, Rainer Haag, Michael Unbehauen, Robert Bittl, Christian Teutloff, Roland Bodmeier, Siavash Saeidpour, Gaith Zoubari, Silke B. Lohan, and Martina C. Meinke
- Subjects
Polymers ,Analytical chemistry ,Pharmaceutical Science ,Nanoparticle ,02 engineering and technology ,030226 pharmacology & pharmacy ,law.invention ,Spin probe ,Fats ,Colloid ,0302 clinical medicine ,law ,drug delivery system ,Electron paramagnetic resonance ,media_common ,Drug Carriers ,Aqueous solution ,Chemistry ,500 Naturwissenschaften und Mathematik::530 Physik::530 Physik ,General Medicine ,021001 nanoscience & nanotechnology ,Dilution ,Cold Temperature ,0210 nano-technology ,Biotechnology ,Drug ,Surface Properties ,media_common.quotation_subject ,dexamethasone ,lipids ,03 medical and health sciences ,Distribution (pharmacology) ,Colloids ,Particle Size ,Glucocorticoids ,Triglycerides ,dermal drug delivery ,Electron Spin Resonance Spectroscopy ,electron paramagnetic resonance spectroscopy ,Chemical engineering ,Solubility ,Propylene Glycols ,Drug Design ,Spin Labels ,nanoparticles ,500 Naturwissenschaften und Mathematik::570 Biowissenschaften ,Biologie::572 Biochemie ,Oils ,spinlabel - Abstract
The targeted design of nanoparticles for efficient drug loading and defined release profiles is even after 25 years of research on lipid-based nanoparticles still no routine procedure. It requires detailed knowledge about the interaction of the drug with the lipid compounds and about its localisation and distribution in the nanoparticle. We present here an investigation on nano-sized lipid particles (NLP) composed of Gelucire and Witepsol as solid lipids, and Capryol as liquid lipid, loaded with Dexamethasone, a glucocorticoid used in topical treatment of inflammatory dermal diseases. The interactions of Dexamethasone, which was spin-labelled by 3-(Carboxy)-2,2,5,5-tetramethyl-1-pyrrolidinyloxy (DxPCA), with its microenvironment are monitored by EPR spectroscopy at 94 GHz at low temperatures. The mobility of the spin-labelled drug was probed by X-band EPR at room temperature. In order to relate the magnetic and dynamic parameters deduced from EPR to the local environment of the spin probe in the NLP, investigations of DxPCA in the individual lipid compounds were carried out. The magnetic parameters reflecting the polarity of DxPCA’s environment as well as the parameters describing the mobility of the drug reveal that in the case of colloidal dispersions of the lipids and also the NLP DxPCA is attached to the surface of the nanoparticles. Although the lipophilic drug is almost exclusively associated with the NLP in aqueous solution, dilution experiments show, that it can be easily released from the nanoparticle.
- Published
- 2017
36. Impact of morphology on polaron delocalization in a semicrystalline conjugated polymer
- Author
-
Robert Steyrleuthner, Jan Behrends, Felix Kraffert, Alejandro L. Briseno, Robert Bittl, Benjamin P. Cherniawski, Yuexing Zhang, Jean-Luc Brédas, and Lei Zhang
- Subjects
chemistry.chemical_classification ,Materials science ,Spins ,General Physics and Astronomy ,02 engineering and technology ,Polymer ,Conjugated system ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Polaron ,01 natural sciences ,Oligomer ,0104 chemical sciences ,Delocalized electron ,chemistry.chemical_compound ,chemistry ,Computational chemistry ,Chemical physics ,Density functional theory ,Physical and Theoretical Chemistry ,0210 nano-technology ,Hyperfine structure - Abstract
We investigate the delocalization of holes in the semicrystalline conjugated polymer poly(2,5-bis(3-alkylthiophene-2-yl)thieno[3,2-b]thiophene) (PBTTT) by directly measuring the hyperfine coupling between photogenerated polarons and bound nuclear spins using electron nuclear double resonance spectroscopy. An extrapolation of the corresponding oligomer spectra reveals that charges tend to delocalize over 4.0-4.8 nm with delocalization strongly dependent on molecular order and crystallinity of the PBTTT polymer thin films. Density functional theory calculations of hyperfine couplings confirm that long-range corrected functionals appropriately describe the change in coupling strength with increasing oligomer size and agree well with the experimentally measured polymer limit. Our discussion presents general guidelines illustrating the various pitfalls and opportunities when deducing polaron localization lengths from hyperfine coupling spectra of conjugated polymers.
- Published
- 2017
37. Strongly exchange-coupled triplet pairs in an organic semiconductor
- Author
-
John E. Anthony, Richard H. Friend, Sam L. Bayliss, Jan Behrends, Neil C. Greenham, Karl J. Thorley, Leah R. Weiss, Felix Kraffert, Robert Bittl, Akshay Rao, Rao, A [0000-0003-0320-2962], and Apollo - University of Cambridge Repository
- Subjects
Physics ,Foundation (engineering) ,General Physics and Astronomy ,Nanotechnology ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,language.human_language ,Engineering and Physical Sciences ,5108 Quantum Physics ,0104 chemical sciences ,German ,Research council ,Sustainability ,language ,Engineering ethics ,0210 nano-technology ,51 Physical Sciences ,Excellence initiative - Abstract
From biological complexes to devices based on organic semiconductors, spin interactions play a key role in the function of molecular systems. For instance, triplet-pair reactions impact operation of organic light-emitting diodes as well as photovoltaic devices. Conventional models for triplet pairs assume they interact only weakly. Here, using electron spin resonance, we observe long-lived, strongly-interacting triplet pairs in an organic semiconductor, generated via singlet fission. Using coherent spin-manipulation of these two-triplet states, we identify exchange-coupled (spin-2) quintet complexes co-existing with weakly coupled (spin-1) triplets. We measure strongly coupled pairs with a lifetime approaching 3 µs and a spin coherence time approaching 1 µs, at 10 K. Our results pave the way for the utilization of high-spin systems in organic semiconductors.
- Published
- 2017
38. Electrically Detected HYSCORE on Conduction Band Tail States in $$^{29}$$ 29 Si-Enriched Microcrystalline Silicon
- Author
-
Robert Bittl, Oleksandr Astakhov, Christoph Meier, Friedhelm Finger, Jan Behrends, and Christian Teutloff
- Subjects
Paramagnetism ,Solid-state physics ,Chemistry ,Microcrystalline silicon ,Isotropy ,Atomic physics ,Spectroscopy ,Anisotropy ,Hyperfine structure ,Conduction band ,Atomic and Molecular Physics, and Optics - Abstract
Electrically detected hyperfine sublevel correlation (ED-HYSCORE) measurements are presented and employed to study spin-dependent transport in thin-film microcrystalline silicon solar cells. We explore the hyperfine coupling between paramagnetic conduction band tail states involved in hopping transport and neighboring 29Si nuclei at low temperature ( $$T = 5$$ K). ED-HYSCORE measurements performed on solar cells with 29Si-enriched absorber layers reveal that the hyperfine interaction between these current-influencing centers and 29Si nuclei in the surroundings is dominated by isotropic couplings up to $$\sim$$ 4 MHz, whereas the anisotropic contributions are small. This indicates that the wave function of the conduction band tail states is distributed over several nuclei. Our results demonstrate that the ED-HYSCORE technique can provide helpful insight into the microscopic structure of transport-relevant paramagnetic states and thus usefully complement the toolbox of electrically detected magnetic resonance spectroscopy.
- Published
- 2014
39. Effect of TMAO and betaine on the energy landscape of photosystem I
- Author
-
Robert Bittl, Martin Hussels, Marc Brecht, and Jana B. Nieder
- Subjects
Photosystem I ,Single-molecule spectroscopy ,Energy landscape ,Osmolyte ,Biophysics ,TMAO ,Biochemistry ,Methylamines ,chemistry.chemical_compound ,Betaine ,Native state ,Extreme environment ,Spectroscopy ,Synechococcus ,Photosystem I Protein Complex ,Cell Biology ,Small molecule ,Kinetics ,Crystallography ,Spectrometry, Fluorescence ,chemistry - Abstract
The accumulation of organic co-solvents in cells is a basic strategy for organisms from various species to increase stress tolerance in extreme environments. Widespread representatives of this class of co-solvents are trimethylamine-N-oxide (TMAO) and betaine; these small molecules are able to stabilize the native conformation of proteins and prevent their aggregation. Despite their importance, detailed experimental studies on the impact of these co-solvents on the energy landscape of proteins have not yet been carried out. We use single-molecule spectroscopy at cryogenic temperatures to examine the influence of these physiological relevant co-solvents on photosystem I (PSI) from Thermosynechococcus elongatus. In contrast to PSI ensemble spectra, which are almost unaffected by the addition of TMAO and betaine, statistical analysis of the fluorescence emission from individual PSI trimers yields insight into the interaction of the co-solvents with PSI. The results show an increased homogeneity upon addition of TMAO or betaine. The number of detectable zero-phonon lines (ZPLs) is reduced, indicating spectral diffusion processes with faster rates. In the framework of energy landscape model these findings indicate that co-solvents lead to reduced barrier heights between energy valleys, and thus efficient screening of protein conformations can take place.
- Published
- 2014
40. Reversible [4Fe-3S] cluster morphing in an O2-tolerant [NiFe] hydrogenase
- Author
-
Stefan Frielingsdorf, Yvonne Rippers, Martin Kaupp, Friedhelm Lendzian, Christian Teutloff, Julia Löwenstein, Mathias Hammer, Robert Bittl, Patrick Scheerer, Johannes Fritsch, Tina Jaenicke, Bärbel Friedrich, Vladimir Pelmenschikov, Jacqueline Kalms, Oliver Lenz, Andrea Schmidt, Peter Hildebrandt, Ingo Zebger, and Elisabeth Siebert
- Subjects
Iron-Sulfur Proteins ,Models, Molecular ,Hydrogenase ,biology ,010405 organic chemistry ,Stereochemistry ,Chemistry ,Cell Biology ,Ligands ,010402 general chemistry ,01 natural sciences ,Catalysis ,Cofactor ,3. Good health ,0104 chemical sciences ,Oxygen ,Morphing ,Crystallography ,Cluster (physics) ,biology.protein ,NiFe hydrogenase ,Oxidation-Reduction ,Molecular Biology ,Hydrogen - Abstract
Hydrogenases catalyze the reversible oxidation of H(2) into protons and electrons and are usually readily inactivated by O(2). However, a subgroup of the [NiFe] hydrogenases, including the membrane-bound [NiFe] hydrogenase from Ralstonia eutropha, has evolved remarkable tolerance toward O(2) that enables their host organisms to utilize H(2) as an energy source at high O(2). This feature is crucially based on a unique six cysteine-coordinated [4Fe-3S] cluster located close to the catalytic center, whose properties were investigated in this study using a multidisciplinary approach. The [4Fe-3S] cluster undergoes redox-dependent reversible transformations, namely iron swapping between a sulfide and a peptide amide N. Moreover, our investigations unraveled the redox-dependent and reversible occurence of an oxygen ligand located at a different iron. This ligand is hydrogen bonded to a conserved histidine that is essential for H(2) oxidation at high O(2). We propose that these transformations, reminiscent of those of the P-cluster of nitrogenase, enable the consecutive transfer of two electrons within a physiological potential range.
- Published
- 2014
41. A structural model for the full-length blue light-sensing protein YtvA from Bacillus subtilis, based on EPR spectroscopy
- Author
-
Yifen Tang, Robert Bittl, Ralph P. Diensthuber, Aba Losi, Andreas Möglich, Christopher Engelhard, Sarah Raffelberg, and Wolfgang Gärtner
- Subjects
Models, Molecular ,Light ,Dimer ,Spin labelling ,Crystal structure ,Bacillus subtilis ,Crystallography, X-Ray ,law.invention ,chemistry.chemical_compound ,Bacterial Proteins ,law ,Physical and Theoretical Chemistry ,Electron paramagnetic resonance ,Blue light ,chemistry.chemical_classification ,biology ,Electron Spin Resonance Spectroscopy ,biology.organism_classification ,Protein Structure, Tertiary ,Amino acid ,Crystallography ,chemistry ,Mutagenesis, Site-Directed ,Spin Labels - Abstract
A model for the full-length structure of the blue light-sensing protein YtvA from Bacillus subtilis has been determined by EPR spectroscopy, performed on spin labels selectively inserted at amino acid positions 54, 80, 117 and 179. Our data indicate that YtvA forms a dimer in solution and enable us, based on the known structures of the individual domains and modelling, to propose a three-dimensional model for the full length protein. Most importantly, this includes the YtvA N-terminus that has so far not been identified in any structural model. We show that our data are in agreement with the crystal structure of an engineered LOV-domain protein, YF1, that shows the N-terminus of the protein to be helical and to fold back in between the β-sheets of the two LOV domains, and argue for an identical arrangement in YtvA. While we could not detect any structural changes upon blue-light activation of the protein, this structural model now forms an ideal basis for identifying residues as targets for further spin labelling studies to detect potential conformational changes upon irradiation of the protein.
- Published
- 2013
42. Multi-frequency EDMR applied to microcrystalline thin-film silicon solar cells
- Author
-
Oleksandr Astakhov, Alexander Schnegg, Klaus Lips, Christoph Meier, Robert Bittl, Christian Teutloff, and Jan Behrends
- Subjects
Solar cells ,Nuclear and High Energy Physics ,Materials science ,Silicon ,Electrically detected magnetic resonance ,Biophysics ,Analytical chemistry ,Resonance ,chemistry.chemical_element ,Condensed Matter Physics ,Biochemistry ,Molecular physics ,Spectral line ,Multi-frequency EDMR ,Amorphous solid ,law.invention ,Paramagnetism ,Microcrystalline ,chemistry ,law ,Electron spin resonance ,Microcrystalline silicon ,Thin film ,Electron paramagnetic resonance - Abstract
Pulsed multi-frequency electrically detected magnetic resonance (EDMR) at X-, Q- and W-Band (9.7, 34, and 94 GHz) was applied to investigate paramagnetic centers in microcrystalline silicon thin-film solar cells under illumination. The EDMR spectra are decomposed into resonances of conduction band tail states (e states) and phosphorus donor states (P states) from the amorphous layer and localized states near the conduction band (CE states) in the microcrystalline layer. The e resonance has a symmetric profile at all three frequencies, whereas the CE resonance reveals an asymmetry especially at W-band. This is suggested to be due to a size distribution of Si crystallites in the microcrystalline material. A gain in spectral resolution for the e and CE resonances at high fields and frequencies demonstrates the advantages of high-field EDMR for investigating devices of disordered Si. The microwave frequency independence of the EDMR spectra indicates that a spin-dependent process independent of thermal spin-polarization is responsible for the EDMR signals observed at X-, Q- and W-band.
- Published
- 2013
43. Electrical detection of Rabi oscillations in microcrystalline silicon thin-film solar cells
- Author
-
Robert Bittl, Jan Behrends, and Christoph Meier
- Subjects
Rabi cycle ,Chemistry ,Biophysics ,Condensed Matter Physics ,law.invention ,Paramagnetism ,Microcrystalline silicon ,law ,Solar cell ,Thin film solar cell ,Physical and Theoretical Chemistry ,Atomic physics ,Spin (physics) ,Molecular Biology ,Microwave ,Rabi frequency - Abstract
The microscopic structure of light-activated paramagnetic conduction band tail states and their participation in spin-dependent hopping transport is studied in a microcrystalline silicon thin-film solar cell. Application of X- and S-band electrically detected magnetic resonance (EDMR) experiments in combination with numerical simulations of Rabi oscillations indicates that the spin-dependent process takes place between two neighbouring band tail states. For sufficiently high microwave (mw) power, two Rabi frequencies Ω1 and Ω2 = 2Ω1 show up in the coherent EDMR signals. An analysis of their relative contributions to the Rabi traces suggests that the g-values of both spin partners are not correlated for the majority of the EDMR-active pairs. A small fraction of doublet pairs with similar g-values may explain the appearance of a larger Ω2 contribution than predicted by the simulations.
- Published
- 2013
44. Zero-field splittings in metHb and metMb with aquo and fluoro ligands: a FD-FT THz-EPR study
- Author
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Berta M. Martins, Holger Dobbek, Karsten Holldack, Robert Bittl, Alexander Schnegg, Stefan Stoll, and Joscha Nehrkorn
- Subjects
Spectrometer ,Field (physics) ,Chemistry ,Biophysics ,Analytical chemistry ,Zero field splitting ,zero-field splitting ,Condensed Matter Physics ,haemoglobin ,Synchrotron ,Spectral line ,law.invention ,chemistry.chemical_compound ,Myoglobin ,law ,myoglobin ,Physical and Theoretical Chemistry ,Electron paramagnetic resonance ,Spin (physics) ,Molecular Biology ,EPR spectroscopy - Abstract
A combined X-band and frequency-domain Fourier-transform THz electron paramagnetic resonance (FD-FT THz-EPR) approach has been employed to determine heme Fe(III) S = 5/2 zero-field splitting (ZFS) parameters of frozen metHb and metMb solutions, both with fluoro and aquo ligands. Frequency-domain EPR measurements have been carried out by an improved synchrotron-based FD-FT THz- EPR spectrometer. ZFS has been determined by field dependence of spin transitions within the mS = ±1/2 manifold, for all four protein systems, and by zero-field spin transitions between mS = ±1/2 and mS = ±3/2 levels, for metHb and metMb flouro-states. FD-FT THz-EPR data were simulated with a novel numerical routine based on Easyspin, which allows now for direct comparison of EPR spectra in field and frequency domain. We found purely axial ZFSs of D = 5.0(1) cm−1 (flouro-metMb), D = 9.2(4) cm−1 (aquo-metMb), D = 5.1(1) cm−1 (flouro-metHB) and D = 10.4(2) cm−1 (aquo-metHb).
- Published
- 2013
45. 95 GHz ESEEM of radical pairs: a source of radical separations and relative orientations
- Author
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Robert Bittl, C.E. Fursman, Stephan G. Zech, and P. J. Hore
- Subjects
Modulation ,Chemistry ,Analytical chemistry ,Solid-state ,General Physics and Astronomy ,Energy transformation ,Physical and Theoretical Chemistry ,Molecular physics ,Envelope (waves) - Abstract
W-band (95 GHz) electron spin echo envelope modulation (ESEEM) is proposed as a method for simultaneously determining the relative orientation and separation of the constituents of spin-correlated radical pairs in the solid state. The discussion focuses on the transient secondary radical pair in bacterial photosynthetic energy conversion. © 2001 Elsevier Science B.V.
- Published
- 2016
46. Triplet excitons as sensitive spin probes for structure analysis of extended defects in microcrystalline silicon
- Author
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Klaus Lips, Christian Teutloff, Jan Behrends, Robert Bittl, Oleksandr Astakhov, and Christoph Meier
- Subjects
Materials science ,Spins ,Condensed matter physics ,Band gap ,Exciton ,02 engineering and technology ,Electron ,021001 nanoscience & nanotechnology ,01 natural sciences ,Delocalized electron ,0103 physical sciences ,ddc:530 ,Charge carrier ,Grain boundary ,010306 general physics ,0210 nano-technology ,Spectroscopy - Abstract
Electrically detected magnetic resonance (EDMR) spectroscopy is employed to study the influence of triplet excitons on the photocurrent in state-of-the-art microcrystalline silicon thin-film solar cells. These triplet excitons are used as sensitive spin probes for the investigation of their electronic and nuclear environment in this mixed-phase material. According to low-temperature EDMR results obtained from solar cells with different Si29 isotope concentrations between 0.01% and 50%, the triplet excitons reside at extended defects in the crystallites of microcrystalline silicon that give rise to shallow states in the silicon band gap. The excitons possess a rather delocalized wave function, couple to electron spins in conduction band tail states nearby, and take part in a spin-dependent recombination process. Our study shows that extended defects such as grain boundaries or stacking faults in the crystalline part of the material act as charge carrier traps that can influence the material conductivity. © 2016 American Physical Society.
- Published
- 2016
47. Investigation of the cutaneous penetration behavior of dexamethasone loaded to nano-sized lipid particles by EPR spectroscopy, and confocal Raman and laser scanning microscopy
- Author
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Michael Unbehauen, Pin Dong, Robert Bittl, Gaith Zoubari, Silke B. Lohan, Jürgen Lademann, Roland Bodmeier, Alexa Patzelt, Christian Teutloff, Siavash Saeidpour, Maxim E. Darvin, Martina C. Meinke, Rainer Haag, Heike Richter, Agnieszka Solik, and Sabine Schanzer
- Subjects
Curcumin ,Swine ,Confocal ,Skin Absorption ,Analytical chemistry ,Pharmaceutical Science ,02 engineering and technology ,Dexamethasone ,Spin probe ,Excipients ,030207 dermatology & venereal diseases ,03 medical and health sciences ,symbols.namesake ,0302 clinical medicine ,Microscopy ,Fluorescence microscope ,Stratum corneum ,medicine ,Animals ,Particle Size ,Glucocorticoids ,Skin ,Drug Carriers ,Microscopy, Confocal ,integumentary system ,Chemistry ,Electron Spin Resonance Spectroscopy ,Ear ,General Medicine ,Penetration (firestop) ,021001 nanoscience & nanotechnology ,Controlled release ,Lipids ,medicine.anatomical_structure ,Biophysics ,symbols ,Nanoparticles ,Epidermis ,0210 nano-technology ,Raman spectroscopy ,Hair Follicle ,Biotechnology - Abstract
An improvement of the penetration efficiency combined with the controlled release of actives in the skin can facilitate the medical treatment of skin diseases immensely. Dexamethasone (Dx), a synthetic glucocorticoid, is frequently used for the treatment of inflammatory skin diseases. To investigate the penetration of nano-sized lipid particles (NLP) loaded with Dx in comparison to a commercially available base cream, different techniques were applied. Electron paramagnetic resonance (EPR) spectroscopy was used to monitor the penetration of Dx, which was covalently labeled with the spin probe 3-(Carboxy)-2,2,5,5-tetramethyl-1-pyrrolidinyloxy (PCA). The penetration into hair follicles was studied using confocal laser scanning microscopy (CLSM) with curcumin-loaded NLP. The penetration of the vehicle was followed by confocal Raman microscopy (CRM). Penetration studies using excised porcine skin revealed a more than twofold higher penetration efficiency for DxPCA into the stratum corneum (SC) after 24h incubation compared to 4h incubation when loaded to the NLP, whereas when applied in the base cream, almost no further penetration was observed beyond 4h. The distribution of DxPCA within the SC was investigated by consecutive tape stripping. The release of DxPCA from the base cream after 24h in deeper SC layers and the viable epidermis was shown by EPR. For NLP, no release from the carrier was observed, although DxPCA was detectable in the skin after the complete SC was removed. This phenomenon can be explained by the penetration of the NLP into the hair follicles. However, penetration profiles measured by CRM indicate that NLP did not penetrate as deeply into the SC as the base cream formulation. In conclusion, NLP can improve the accumulation of Dx in the skin and provide a reservoir within the SC and in the follicular infundibula.
- Published
- 2016
48. Dangling bonds in amorphous silicon investigated by multifrequency EPR
- Author
-
Christoph Freysoldt, Robert Bittl, Klaus Lips, Alexander Schnegg, Christian Teutloff, Matthias Fehr, Bernd Rech, Oleksandr Astakhov, and Friedhelm Finger
- Subjects
Amorphous silicon ,Materials science ,Dangling bond ,Analytical chemistry ,Resonance ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,law.invention ,chemistry.chemical_compound ,Paramagnetism ,chemistry ,law ,Materials Chemistry ,Ceramics and Composites ,Tensor ,Spectroscopy ,Electron paramagnetic resonance ,Hyperfine structure - Abstract
Paramagnetic coordination defects in undoped hydrogenated amorphous silicon (a-Si:H) are studied using multifrequency pulsed electron-paramagnetic resonance (EPR) spectroscopy at S-, X-, Q- and W-band microwave frequencies (3.6, 9.7, 34, and 94 GHz, respectively). The improved spectral information extractable from a multifrequency fitting procedure allows us to conclude that the g tensor exhibits a rhombic splitting instead of axial symmetry. Our methods allow for precise and accurate determination of the g tensor principal values g x = 2.0079(2), g y = 2.0061(2) and g z = 2.0034(2) and their distribution parameters ( g strain).
- Published
- 2012
49. Light-generated Paramagnetic Intermediates in BLUF Domains†
- Author
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Peter Hegemann, Robert Bittl, Stefan Weber, Lars-Oliver Essen, Claudia Schroeder, Sylwia Kacprzak, Radoslaw M. Kowalczyk, Tilo Mathes, and Erik Schleicher
- Subjects
Free Radicals ,Light ,Stereochemistry ,Flavoprotein ,Electrons ,Rhodobacter sphaeroides ,Flavin group ,Photoreceptors, Microbial ,Photochemistry ,Biochemistry ,Cofactor ,chemistry.chemical_compound ,Protein structure ,Bacterial Proteins ,Flavins ,Escherichia coli ,Physical and Theoretical Chemistry ,BLUF domain ,Flavin adenine dinucleotide ,Cofactor binding ,Binding Sites ,Flavoproteins ,biology ,Electron Spin Resonance Spectroscopy ,Synechocystis ,General Medicine ,Photochemical Processes ,biology.organism_classification ,Protein Structure, Tertiary ,chemistry ,Flavin-Adenine Dinucleotide ,biology.protein ,Tyrosine ,Protein Binding - Abstract
Blue-light sensitive photoreceptory BLUF domains are flavoproteins, which regulate various, mostly stress-related processes in bacteria and eukaryotes. The photoreactivity of the flavin adenine dinucleotide (FAD) cofactor in three BLUF domains from Rhodobacter sphaeroides, Synechocystis sp. PCC 6803 and Escherichia coli have been studied at low temperature using time-resolved electron paramagnetic resonance. Photoinduced flavin triplet states and radical-pair species have been detected on a microsecond time scale. Differences in the electronic structures of the FAD cofactors as reflected by altered zero-field splitting parameters of the triplet states could be correlated with changes in the amino-acid composition of the various BLUF domains' cofactor binding pockets. For the generation of the light-induced, spin-correlated radical-pair species in the BLUF domain from Synechocystis sp. PCC 6803, a tyrosine residue near the flavin's isoalloxazine moiety plays a critical role.
- Published
- 2011
50. Contents Vol. 24, 2011
- Author
-
Druck Reinhardt Druck Basel, Bernhard Lange-Asschenfeldt, Axel Kramer, Maria Claudia Gross, Dorothea Terhorst, Juergen Lademann, J.L. Du Preez, Lizelle T. Fox, Torsten Koburger, J. du Plessis, Robert Bittl, Martina Ulrich, Ringo Wenzel, Minja Gerber, Mei-Ling Chen, Marty O. Visscher, Anil Jain, Namrata D. Barai, D. Marenbach, T. Kirkbride, Robin M. Warren, P.W. Wertz, Satz Mengensatzproduktion, Christin Lang, Martina C. Meinke, Steven B. Hoath, W. Gehring, Alexa Patzelt, Monika Schäfer-Korting, M. Ebert, N.-O. Hübner, Ojan Assadian, William L. Pickens, Christian Teutloff, Alfred Fahr, Vivek Narendran, Ute Wölfle, Stefan F. Haag, Mathias Rohr, Anne Grobler, A. Maltusch, B. Taskoparan, Federica Casetti, Eggert Stockfleth, Angela A. LaRuffa, Andreas Schrader, Christoph M. Schempp, Ingrid Rieger, Wolfram Sterry, and M. Brunner
- Subjects
Pharmacology ,Toxicology ,Traditional medicine ,Physiology ,Dermatology ,General Medicine ,Biology - Published
- 2011
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