Publications (17)83.9 Total impact
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Article: Following the energy transfer in and out of a polyproline-peptide.
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ABSTRACT: The intramolecular and intermolecular vibrational energy flow in a polyproline peptide with a total number of nine amino acids in the solvent dimethyl sulfoxide is investigated using time-resolved infrared (IR) spectroscopy. Azobenzene covalently bound to a proline sequence containing nitrophenylalanine as a local sensor for vibrational excess energy serves as a heat source. Information on through-space distances in the polyproline peptides is obtained by independent Förster resonance energy transfer measurements. Photoexcitation of the azobenzene and subsequent internal conversion yield strong vibrational excitation of the molecule acting as a local heat source. The relaxation of excess heat, its transfer along the peptide and to the solvent is monitored by the response of the nitro-group in nitrophenylalanine acting as internal thermometer. After optical excitation, vibrational excess energy is observed via changes in the IR absorption spectra of the peptide. The nitrophenylalanine bands reveal that the vibrational excess energy flows in the peptide over distances of more than 20 Å and arrives delayed by up to 7 ps at the outer positions of the peptide. The vibrational excess energy is transferred to the surrounding solvent on a time scale of 10-20 ps. The experimental observations are analyzed by different heat conduction models. Isotropic heat conduction in three dimensions away from the azobenzene heat source is not able to describe the observations. One-dimensional heat dissipation along the polyproline peptide combined with a slower transversal heat transfer to the solvent surrounding well reproduces the observations. © 2012 Wiley Periodicals, Inc. Biopolymers (Pept Sci) 100: 38-50, 2013.Biopolymers 01/2013; 100(1):38-50. · 2.87 Impact Factor -
Article: Vibrational Spectra of the Ground and the Singlet Excited ππ* State of 6,7-Dimethyl-8-ribityllumazine
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ABSTRACT: 6,7-Dimethyl-8-ribityllumazine serves as fluorophore in lumazine proteins (LumP) of luminescent bacteria. The molecule exhibits several characteristic vibrational absorption bands between 1300 and 1750 cm−1 in its electronic ground state. The IR-absorption pattern of the singlet excited ππ* state was monitored via ultrafast infrared spectroscopy after photoexcitation at 404 nm. The comparison of experimentally observed band shifts for a number of isotopologues allows for a clear assignment of several absorption bands—most importantly the two carbonyl bands. This assignment is confirmed by normal-mode calculations by means of either density functional theory (DFT) calculations for the ground state or the configuration interaction singles (CIS) method for the excited singlet state. A good agreement between experiment and calculation is obtained for models including explicitly a first solvation shell. The results provide a basis for further investigations of lumazine protein and demonstrate the necessity of proper accounting for explicit hydrogen bonding in case of strongly polar molecular systems.03/2011; -
Article: Nitro-phenylalanine: a novel sensor for heat transfer in peptides.
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ABSTRACT: Femtosecond IR-pump-IR-probe experiments with independently tunable pulses are used to monitor the ultrafast response of selected IR absorption bands to vibrational excitation of other modes of Fmoc-nitrophenylalanine. The absorptions of both NO(2)-bands change rapidly within <2 ps upon excitation of other vibrational modes. The results point to considerable coupling between the monitored NO(2) modes and the initially excited modes or low-frequency modes. The latter are populated by a rapid energy redistribution process. The strong IR absorption of the NO(2) stretching bands and the intense coupling to other modes makes the nitro group of nitrophenylalanine a sensitive monitor for vibrational energy arriving at this amino acid.The Journal of Physical Chemistry A 03/2011; 115(11):2169-75. · 2.95 Impact Factor -
Article: Vibrational spectra of the ground and the singlet excited ππ* state of 6,7-dimethyl-8-ribityllumazine.
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ABSTRACT: 6,7-Dimethyl-8-ribityllumazine serves as fluorophore in lumazine proteins (LumP) of luminescent bacteria. The molecule exhibits several characteristic vibrational absorption bands between 1300 and 1750 cm(-1) in its electronic ground state. The IR-absorption pattern of the singlet excited ππ* state was monitored via ultrafast infrared spectroscopy after photoexcitation at 404 nm. The comparison of experimentally observed band shifts for a number of isotopologues allows for a clear assignment of several absorption bands--most importantly the two carbonyl bands. This assignment is confirmed by normal-mode calculations by means of either density functional theory (DFT) calculations for the ground state or the configuration interaction singles (CIS) method for the excited singlet state. A good agreement between experiment and calculation is obtained for models including explicitly a first solvation shell. The results provide a basis for further investigations of lumazine protein and demonstrate the necessity of proper accounting for explicit hydrogen bonding in case of strongly polar molecular systems.The Journal of Physical Chemistry B 03/2011; 115(13):3689-97. · 3.70 Impact Factor -
Article: Folding and unfolding of light-triggered β-hairpin model peptides.
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ABSTRACT: Ultrafast spectroscopy in the visible and mid-infrared is used to study the reaction dynamics of two light-triggered model peptides containing an azobenzene derivative as a switching element. One model peptide, the AzoTrpZip2, forms a β-hairpin structure in the cis form of the chromophore. This peptide is compared to the core structure consisting of the chromophore and the two flanking amino acid residues, used as a minimal model. This combination of experiments performed in different spectral ranges on peptides of different sizes allows for improved insight into light triggered reaction dynamics. The kinetics observed for the core structure are directly connected to the switching process of the chromophore and are finished on the 10 ps time scale. The trans-to-cis reaction of AzoTrpZip2, leading to the formation of the β-hairpin structure involves ultrafast processes on the 100 ps time scale, which are directly related to the relaxation of the strain between the isomerized molecular switch and the two peptide strands. IR-signatures characteristic for changes in interstrand interactions are absent on the <1 ns time scale. Thus folding into the β-hairpin structure occurs on a much longer time scale. In the cis-to-trans unfolding reaction, all IR signatures related to changes in interstrand interactions occur within 1 ns, in a time range where visible spectroscopy reveals the final decay of the intramolecular strain. Apparently unfolding of AzoTrpZip2 is to a large extent a fast, driven process.The Journal of Physical Chemistry B 12/2010; 115(18):5219-26. · 3.70 Impact Factor -
Article: Relaxation time prediction for a light switchable peptide by molecular dynamics.
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ABSTRACT: We study a monocyclic peptide called cAPB, whose conformations are light switchable due to the covalent integration of an azobenzene dye. Molecular dynamics (MD) simulations using the CHARMM22 force field and its CMAP extension serve us to sample the two distinct conformational ensembles of cAPB, which belong to the cis and trans isomers of the dye, at room temperature. For gaining sufficient statistics we apply a novel replica exchange technique. We find that the well-known NMR distance restraints are much better described by CMAP than by CHARMM22. In cAPB, the ultrafast cis/trans photoisomerization of the dye elicits a relaxation dynamics of the peptide backbone. Experimentally, we probe this relaxation at picosecond time resolution by IR spectroscopy in the amide I range up to 3 ns after the UV/vis pump flash. We interpret the spectroscopically identified decay kinetics using ensembles of non-equilibrium MD simulations, which provide kinetic data on conformational transitions well matching the observed kinetics. Whereas spectroscopy solely indicates that the relaxation toward the equilibrium trans ensemble is by no means complete after 3 ns, the 20 ns MD simulations of the process predict, independently of the applied force field, that the final relaxation into the trans-ensemble proceeds on a time scale of 23 ns. Overall our explicit solvent simulations cover more than 6 micros.Physical Chemistry Chemical Physics 04/2010; 12(23):6204-18. · 3.57 Impact Factor -
Article: Impact of vibrational excitation on the kinetics of a nascent ketene.
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ABSTRACT: The formation and decay of a ketene intermediate photochemically formed from o-nitrobenzaldehyde has been studied by femtosecond UV/Vis and IR spectroscopy. The ketene is formed predominantly within a few 100 fs and to a minor extent within approximately 200 ps via the recombination of a triplet phased bi-radical. In tetrahydrofuran solution the ketene intermediate is seen to form a secondary intermediate with biphasic kinetics. The first phase of this decay occurs within a few picoseconds. It can be attributed to the reaction of vibrationally excited ketenes. The second phase characterized by a time constant of 2 ns is due to the reaction of thermalized molecules. In 2-butanol solution the lifetime of the thermalized ketene is only approximately 60 ps and the rapid and the slow phases of the decay start to merge.Physical Chemistry Chemical Physics 12/2009; 11(48):11596-607. · 3.57 Impact Factor -
Chapter: Energy transfer along a poly(Pro) - peptide
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ABSTRACT: Using a novel molecular thermometer, p-nitro-phenylalanine, we investigate the transport of vibrational excess energy along a poly(Pro) sequence. Time resolved IRspectroscopy reveals that heat transfer proceeds at a speed of several Å per picosecond.12/2008: pages 529-531; -
Chapter: Assignment of the Excited-State Infrared-Spectra in the Course of the Ring Opening Reaction of a Photochromic Dihydroazulene
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ABSTRACT: With femtosecond infrared spectroscopy and ab initio calculations we could assign the transient spectrum at 1 ps to the ring opened product of the dihydroazulene photo induced reaction. Thus, ring-opening proceeds within 1 ps.12/2008: pages 355-357; -
Article: Ultrafast ring-closure reaction of photochromic indolylfulgimides studied with UV-pump-IR-probe spectroscopy.
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ABSTRACT: The ring-opening and ring-closure reactions of a photochromic indolylfulgimide are investigated with femtosecond vibrational spectroscopy. Spectral signatures due to excited-state decay and vibrational cooling are seen in the mid-IR region. For the ring-opening reaction triggered with visible pulses, a lifetime of the excited electronic state of 4 ps was obtained in polar solution. In a nonpolar solvent, this time constant is reduced to 2 ps. The ring-closure reaction induced with UV pulses displays an excited-state lifetime and thus a building of the photoproduct of roughly 0.5 ps. For all processes, the subsequent cooling occurs on a 15-ps time scale lasting up to approximately 50 ps. The time-resolved IR measurements do not support the existence of any long-living intermediate states.The Journal of Physical Chemistry A 02/2008; 112(2):210-4. · 2.95 Impact Factor -
Article: Generation of narrowband subpicosecond mid-infrared pulses via difference frequency mixing of chirped near-infrared pulses.
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ABSTRACT: The widely used setup for the generation of femtosecond infrared (IR) pulses based on parametric amplifiers (OPAs) and difference frequency mixing (DFM) is extended to produce tunable narrowband mid-IR pulses. The insertion of pairs of silicon prisms after the OPA induces adjustable chirp, which leads to the generation of narrowband pulses in the DFM stage. Rapid tunability of the mid-IR wavelength via a computer-controllable actuator can be achieved in a range of approximately 200 cm(-1) at a bandwidth of the IR-pulses between approximately 15 and approximately 50 cm(-1) and pulse energies up to 0.4 microJ. The narrowband mid-IR pulses are well suited for 2D IR spectroscopy.Optics Letters 12/2007; 32(22):3339-41. · 3.40 Impact Factor -
Article: Light-triggered beta-hairpin folding and unfolding.
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ABSTRACT: A light-switchable peptide is transformed with ultrashort pulses from a beta-hairpin to an unfolded hydrophobic cluster and vice versa. The structural changes are monitored by mid-IR probing. Instantaneous normal mode analysis with a Hamiltonian combining density functional theory with molecular mechanics is used to interpret the absorption transients. Illumination of the beta-hairpin state triggers an unfolding reaction that visits several intermediates and reaches the unfolded state within a few nanoseconds. In this unfolding reaction to the equilibrium hydrophobic cluster conformation, the system does not meet significant barriers on the free-energy surface. The reverse folding process takes much longer because it occurs on the time scale of 30 micros. The folded state has a defined structure, and its formation requires an extended search for the correct hydrogen-bond pattern of the beta-strand.Proceedings of the National Academy of Sciences 11/2007; 104(40):15729-34. · 9.68 Impact Factor -
Article: Light-triggered β-hairpin folding and unfolding
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ABSTRACT: A light-switchable peptide is transformed with ultrashort pulses from a β-hairpin to an unfolded hydrophobic cluster and vice versa. The structural changes are monitored by mid-IR probing. Instantaneous normal mode analysis with a Hamiltonian combining density functional theory with molecular mechanics is used to interpret the absorption transients. Illumination of the β-hairpin state triggers an unfolding reaction that visits several intermediates and reaches the unfolded state within a few nanoseconds. In this unfolding reaction to the equilibrium hydrophobic cluster conformation, the system does not meet significant barriers on the free-energy surface. The reverse folding process takes much longer because it occurs on the time scale of 30 μs. The folded state has a defined structure, and its formation requires an extended search for the correct hydrogen-bond pattern of the β-strand.Proceedings of the National Academy of Sciences 10/2007; 104(40):15729-15734. · 9.68 Impact Factor -
Article: Infrared studies of small azobenzene peptides: unexpectedly slow reactions on the time range of minutes.
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ABSTRACT: Infrared absorption experiments on light-triggered azobenzene peptides have been performed below and above the freezing point of the solvent dimethyl sulfoxide (DMSO). Even 20 K below the freezing point, illumination of the azobenzene chromophore resulted in IR absorption changes indicative of light-induced structural rearrangements of the peptide. In addition, new conformational states could be found at low temperature, which involve the formation of additional hydrogen bonds. In one sample the new low-temperature state survived melting and reheating and disappeared at 298 K only on the time scale of 10 min. The observations indicate that at low temperatures the peptide, together with traces of water present in the sample, forms a shell in the vicinity of the chromophore that facilitates internal motion even in the rigid cage of frozen DMSO.The Journal of Physical Chemistry B 10/2007; 111(35):10481-6. · 3.70 Impact Factor -
Article: Thymine dimerization in DNA is an ultrafast photoreaction.
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ABSTRACT: Femtosecond time-resolved infrared spectroscopy was used to study the formation of cyclobutane dimers in the all-thymine oligodeoxynucleotide (dT)18 by ultraviolet light at 272 nanometers. The appearance of marker bands in the time-resolved spectra indicates that the dimers are fully formed approximately 1 picosecond after ultraviolet excitation. The ultrafast appearance of this mutagenic photolesion points to an excited-state reaction that is approximately barrierless for bases that are properly oriented at the instant of light absorption. The low quantum yield of this photoreaction is proposed to result from infrequent conformational states in the unexcited polymer, revealing a strong link between conformation before light absorption and photodamage.Science 03/2007; 315(5812):625-9. · 31.20 Impact Factor -
Article: Ultrafast structural dynamics of photochromic indolylfulgimides studied by vibrational spectroscopy and DFT calculations.
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ABSTRACT: The structural dynamics of the ring-opening reaction in a photochromic indolylfulgimide, a reversible, ultrafast photoswitch, is investigated by ultra-broadband time-resolved vibrational spectroscopy. The experimentally observed vibrational modes of the indolylfulgimide photoisomers C and E are assigned to normal modes with the help of DFT calculations. A complete evaluation of the observed vibrational dynamics including excited-state vibrational modes is used to characterize the reaction path and the cooling behavior of the photoswitch.The Journal of Physical Chemistry A 12/2006; 110(47):12769-76. · 2.95 Impact Factor -
Article: Ultrafast vibrational excitation transfer and vibrational cooling of propionic acid dimers investigated with IR-pump IR-probe spectroscopy
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ABSTRACT: Ultrafast IR-pump IR-probe spectroscopy is used to study the relaxation dynamics of propionic acid dimers. The spectral changes in the regions of CO-stretching at ∼1700 cm−1, OH and CH-bending modes around 1400 cm−1 are investigated after excitation in the range of the CH- and CO-stretching modes. A strong coupling of the OH-stretch vibration to CO-stretching and OH/CH-bending modes is found. The intramolecular redistribution of vibrational energy takes place on a 1 ps time-scale. A further cooling process and energy transfer to the surrounding occur with ∼12 ps. The dynamics depend on the wavelength of the IR-excitation and point to a transient breaking of one of the two H-bonds of the propionic acid dimers.Chemical Physics.
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Institutions
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2006–2013
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Ludwig-Maximilian-University of Munich
- Faculty of Physics
München, Bavaria, Germany
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