The Experts below are selected from a list of 12270 Experts worldwide ranked by ideXlab platform
Rienk Van Grondelle - One of the best experts on this subject based on the ideXlab platform.
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reaction pathways of photoexcited retinal in proteorhodopsin studied by pump dump probe spectroscopy
2009Co-Authors: Alisa Rupenyan, Rienk Van Grondelle, Ivo H M Van Stokkum, Klaas J. Hellingwerf, Jos C Arents, Marie Louise GrootAbstract:Proteorhodopsin (pR) is a membrane-embedded proton pump from the microbial rhodopsin family. Light absorption by its retinal chromophore initiates a photocycle, driven by trans/cis isomerization on the femtosecond to picosecond time scales. Here, we report a study on the photoisomerization dynamics of the retinal chromophore of pR, using dispersed ultrafast pump−dump−probe spectroscopy. The application of a pump pulse initiates the photocycle, and with an appropriately tuned dump pulse applied at a time delay after the dump, the molecules in the initial stages of the photochemical process can be de-excited and driven back to the ground state. In this way, we were able to resolve an intermediate on the electronic ground state that represents chromophores that are unsuccessful in isomerization. In particular, the fractions of molecules that undergo slow isomerization (20 ps) have a high probability to enter this state rather than the isomerized K-state. On the ground state reaction surface, return to the st...
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use of ultrafast dispersed pump dump probe and pump repump probe spectroscopies to explore the light induced dynamics of peridinin in solution
2006Co-Authors: Emmanouil Papagiannakis, Ivo H M Van Stokkum, Delmar S Larsen, Mikas Vengris, Roger G Hiller, Rienk Van GrondelleAbstract:Optical pump-induced dynamics of the highly asymmetric carotenoid peridinin in methanol was studied by dispersed pump−probe, pump−dump−probe, and pump−repump−probe transient absorption spectroscopy in the visible region. Dispersed pump−probe measurements show that the decay of the initially excited S2 state populates two excited states, the S1 and the intramolecular charge-transfer (ICT) state, at a ratio determined by the excitation wavelength. The ensuing spectral evolution occurs on the time scale of a few picoseconds and suggests the equilibration of these states. Dumping the stimulated emission of the ICT state with an additional 800-nm pulse after 400- and 530-nm excitation preferentially removes the ICT state contribution from the broad excited-state absorption, allowing for its spectral characterization. At the same time, an unrelaxed ground-state species, which has a subpicosecond lifetime, is populated. The application of the 800-nm pulse at early times, when the S2 state is still populated, led...
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Ultrafast dynamics of isolated model photoactive yellow protein chromophores: "Chemical perturbation theory" in the laboratory
2005Co-Authors: Mikas Vengris, Michael A. Van Der Horst, Olaf F.a. Larsen, Delmar S Larsen, Klaas J. Hellingwerf, Rienk Van GrondelleAbstract:Pump-probe and pump-dump probe experiments have been performed on several isolated model chromophores of the photoactive yellow protein (PYP). The observed transient absorption spectra are discussed in terms of the spectral signatures ascribed to solvation, excited-state twisting, and vibrational relaxation. It is observed that the protonation state has a profound effect on the excited-state lifetime of p-coumaric acid. Pigments with ester groups on the coumaryl tail end and charged phenolic moieties show dynamics that are significantly different from those of other pigments. Here, an unrelaxed ground-state intermediate could be observed in pump-probe signals. A similar intermediate could be identified in the sinapinic acid and in isomerization-locked chromophores by means of pump-dump probe spectroscopy; however, in these compounds it is less pronounced and could be due to ground-state solvation and/or vibrational relaxation. Because of strong protonation-state dependencies and the effect of electron donor groups, it is argued that charge redistribution upon excitation determines the twisting reaction pathway, possibly through interaction with the environment. It is suggested that the same pathway may be responsible for the initiation of the photocycle in native PYP.
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Photoisomerization and Photoionization of the Photoactive Yellow Protein Chromophore in Solution
2004Co-Authors: Delmar S Larsen, Michael A. Van Der Horst, Ivo H M Van Stokkum, Frank L De Weerd, Mikas Vengris, Klaas J. Hellingwerf, Rienk Van GrondelleAbstract:Dispersed pump-dump-probe spectroscopy has the ability to characterize and identify the underlying ultrafast dynamical processes in complicated chemical and biological systems. This technique builds on traditional pump-probe techniques by exploring both ground- and excited-state dynamics and characterizing the connectivity between constituent transient states. We have used the dispersed pump-dump-probe technique to investigate the ground-state dynamics and competing excited-state processes in the excitation-induced ultrafast dynamics of thiomethyl p-coumaric acid, a model chromophore for the photoreceptor photoactive yellow protein. Our results demonstrate the parallel formation of two relaxation pathways (with multiple transient states) that jointly lead to two different types of photochemistry: cis-trans isomerization and detachment of a hydrated electron. The relative transition rates and quantum yields of both pathways have been determined. We find that the relaxation of the photoexcited chromophores involves multiple, transient ground-state intermediates and the chromophore in solution does not generate persistent photoisomerized products, but instead undergoes photoionization resulting in the generation of detached electrons and radicals. These results are of great value in interpreting the more complex dynamical changes in the optical properties of the photoactive yellow protein.
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excited state dynamics of β carotene explored with dispersed multi pulse transient absorption
2003Co-Authors: Delmar S Larsen, Ivo H M Van Stokkum, Mikas Vengris, Emmanouil Papagiannakis, John T M Kennis, Rienk Van GrondelleAbstract:Abstract The excited-state dynamics of β-carotene in hexane was studied with dispersed ultrafast transient absorption techniques. A new excited state is produced after blue-edge excitation. Pump–repump–probe and pump–dump–probe measurements identified and characterized this state, termed S ‡ , which exhibits a blue-shifted spectrum with a longer lifetime than S1. We establish the independent co-existence of the S ‡ and S1 states following the relaxation of S2 and demonstrate that S ‡ is an electronically excited state and not a vibrationally excited ground-state species. Our data support the premise that S ‡ is formed directly from S2 and not via preferential excitation of ground-state sub-populations.
Delmar S Larsen - One of the best experts on this subject based on the ideXlab platform.
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second chance forward isomerization dynamics of the red green cyanobacteriochrome npr6012g4 from nostoc punctiforme
2012Co-Authors: Lucy H Freer, Nathan C Rockwell, Shelley S Martin, Clark J Lagarias, Delmar S LarsenAbstract:The primary ultrafast Z-to-E isomerization photodynamics of the phytochrome-related cyanobacteriochrome NpR6012g4 from Nostoc punctiforme was studied by transient absorption pump–dump–probe spectroscopy. A 2 ps dump pulse resonant with the stimulated emission band depleted 21% of the excited-state population, while the initial photoproduct Lumi-R was depleted by only 11%. We observed a red-shifted ground-state intermediate (GSI) that we assign to a metastable state that failed to isomerize fully. Multicomponent global analysis implicates the generation of additional Lumi-R from the GSI via crossing over the ground-state thermal barrier for full isomerization, explaining the discrepancy between excited-state and Lumi-R depletion by the dump pulse. This second-chance ground-state dynamics provides a plausible explanation for the unusually high quantum yield of 40% for the primary isomerization step in the forward reaction of NpR6012g4.
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excited state self trapping and ground state relaxation dynamics in poly 3 hexylthiophene resolved with broadband pump dump probe spectroscopy
2011Co-Authors: Erik Busby, Elizabeth C Carroll, Erin M Chinn, Lilian Chang, Adam J Moule, Delmar S LarsenAbstract:Broadband femtosecond transient absorption spectroscopy is used to explore the mechanisms underlying excited-state and ground-state exciton relaxation in poly(3-hexylthiophene) (P3HT) solution. We focus on the picosecond spectral shifts in the ground and excited states of P3HT, using pump–probe (PP) and pump–dump–probe (PDP) techniques to investigate exciton relaxation mechanisms. Excited-state PP signals resolved a dynamic stimulated emission Stokes shift and ground-state reorganization; PDP signals resolved a blue-shifting nonequilibrium ground-state bleach. Initial structural reorganization is shown to be faster in the excited state. Ground-state reorganization is shown to be dependent on dump time, with later times resulting in relatively more population undergoing slow (∼20 ps) reorganization. These observations are discussed in the context of structural relaxation involving small-scale ( 1 ps) planarization of thiophene groups following photoexcitation. Excited-state and grou...
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use of ultrafast dispersed pump dump probe and pump repump probe spectroscopies to explore the light induced dynamics of peridinin in solution
2006Co-Authors: Emmanouil Papagiannakis, Ivo H M Van Stokkum, Delmar S Larsen, Mikas Vengris, Roger G Hiller, Rienk Van GrondelleAbstract:Optical pump-induced dynamics of the highly asymmetric carotenoid peridinin in methanol was studied by dispersed pump−probe, pump−dump−probe, and pump−repump−probe transient absorption spectroscopy in the visible region. Dispersed pump−probe measurements show that the decay of the initially excited S2 state populates two excited states, the S1 and the intramolecular charge-transfer (ICT) state, at a ratio determined by the excitation wavelength. The ensuing spectral evolution occurs on the time scale of a few picoseconds and suggests the equilibration of these states. Dumping the stimulated emission of the ICT state with an additional 800-nm pulse after 400- and 530-nm excitation preferentially removes the ICT state contribution from the broad excited-state absorption, allowing for its spectral characterization. At the same time, an unrelaxed ground-state species, which has a subpicosecond lifetime, is populated. The application of the 800-nm pulse at early times, when the S2 state is still populated, led...
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Ultrafast dynamics of isolated model photoactive yellow protein chromophores: "Chemical perturbation theory" in the laboratory
2005Co-Authors: Mikas Vengris, Michael A. Van Der Horst, Olaf F.a. Larsen, Delmar S Larsen, Klaas J. Hellingwerf, Rienk Van GrondelleAbstract:Pump-probe and pump-dump probe experiments have been performed on several isolated model chromophores of the photoactive yellow protein (PYP). The observed transient absorption spectra are discussed in terms of the spectral signatures ascribed to solvation, excited-state twisting, and vibrational relaxation. It is observed that the protonation state has a profound effect on the excited-state lifetime of p-coumaric acid. Pigments with ester groups on the coumaryl tail end and charged phenolic moieties show dynamics that are significantly different from those of other pigments. Here, an unrelaxed ground-state intermediate could be observed in pump-probe signals. A similar intermediate could be identified in the sinapinic acid and in isomerization-locked chromophores by means of pump-dump probe spectroscopy; however, in these compounds it is less pronounced and could be due to ground-state solvation and/or vibrational relaxation. Because of strong protonation-state dependencies and the effect of electron donor groups, it is argued that charge redistribution upon excitation determines the twisting reaction pathway, possibly through interaction with the environment. It is suggested that the same pathway may be responsible for the initiation of the photocycle in native PYP.
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Photoisomerization and Photoionization of the Photoactive Yellow Protein Chromophore in Solution
2004Co-Authors: Delmar S Larsen, Michael A. Van Der Horst, Ivo H M Van Stokkum, Frank L De Weerd, Mikas Vengris, Klaas J. Hellingwerf, Rienk Van GrondelleAbstract:Dispersed pump-dump-probe spectroscopy has the ability to characterize and identify the underlying ultrafast dynamical processes in complicated chemical and biological systems. This technique builds on traditional pump-probe techniques by exploring both ground- and excited-state dynamics and characterizing the connectivity between constituent transient states. We have used the dispersed pump-dump-probe technique to investigate the ground-state dynamics and competing excited-state processes in the excitation-induced ultrafast dynamics of thiomethyl p-coumaric acid, a model chromophore for the photoreceptor photoactive yellow protein. Our results demonstrate the parallel formation of two relaxation pathways (with multiple transient states) that jointly lead to two different types of photochemistry: cis-trans isomerization and detachment of a hydrated electron. The relative transition rates and quantum yields of both pathways have been determined. We find that the relaxation of the photoexcited chromophores involves multiple, transient ground-state intermediates and the chromophore in solution does not generate persistent photoisomerized products, but instead undergoes photoionization resulting in the generation of detached electrons and radicals. These results are of great value in interpreting the more complex dynamical changes in the optical properties of the photoactive yellow protein.
Kavitha Muthiah - One of the best experts on this subject based on the ideXlab platform.
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effect of exercise and pump speed modulation on invasive hemodynamics in patients with centrifugal continuous flow left ventricular assist devices
2015Co-Authors: Robertw. Prichard, Anne Keogh, Desiree Robson, Kavitha Muthiah, S. Gupta, R WalkerAbstract:Background Continuous-flow left ventricular assist devices (CF-LVADs) improve functional capacity in patients with end-stage heart failure. Pump output can be increased by increased pump speed as well as changes in loading conditions. Methods The effect of exercise on invasive hemodynamics was studied in two study protocols. The first examined exercise at fixed pump speed ( n = 8) and the second with progressive pump speed increase ( n = 11). Patients underwent simultaneous right-heart catheterization, mixed venous saturation, echocardiography and mean arterial pressure monitoring. Before exercise, a ramp speed study was performed in all patients. Patients then undertook symptom-limited supine bicycle exercise. Results Upward titration of pump speed at rest (by 11.6 ± 8.6% from baseline) increased pump flow from 5.3 ± 1.0 to 6.3 ± 1.0 liters/min (18.9% increase, p p p p p p p = 0.07; PCWP: 26.8 ± 12.7 mm Hg; p = 0.47). Serum lactate and NT-proBNP levels increased significantly with exercise. Conclusions Pump flow increases with up-titration of pump speed and with exercise. Although increased pump speed decreases filling pressures at rest, the benefit is not seen with exercise despite concurrent up-titration of pump speed.
Anne Keogh - One of the best experts on this subject based on the ideXlab platform.
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effect of exercise and pump speed modulation on invasive hemodynamics in patients with centrifugal continuous flow left ventricular assist devices
2015Co-Authors: Robertw. Prichard, Anne Keogh, Desiree Robson, Kavitha Muthiah, S. Gupta, R WalkerAbstract:Background Continuous-flow left ventricular assist devices (CF-LVADs) improve functional capacity in patients with end-stage heart failure. Pump output can be increased by increased pump speed as well as changes in loading conditions. Methods The effect of exercise on invasive hemodynamics was studied in two study protocols. The first examined exercise at fixed pump speed ( n = 8) and the second with progressive pump speed increase ( n = 11). Patients underwent simultaneous right-heart catheterization, mixed venous saturation, echocardiography and mean arterial pressure monitoring. Before exercise, a ramp speed study was performed in all patients. Patients then undertook symptom-limited supine bicycle exercise. Results Upward titration of pump speed at rest (by 11.6 ± 8.6% from baseline) increased pump flow from 5.3 ± 1.0 to 6.3 ± 1.0 liters/min (18.9% increase, p p p p p p p = 0.07; PCWP: 26.8 ± 12.7 mm Hg; p = 0.47). Serum lactate and NT-proBNP levels increased significantly with exercise. Conclusions Pump flow increases with up-titration of pump speed and with exercise. Although increased pump speed decreases filling pressures at rest, the benefit is not seen with exercise despite concurrent up-titration of pump speed.
Mikas Vengris - One of the best experts on this subject based on the ideXlab platform.
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use of ultrafast dispersed pump dump probe and pump repump probe spectroscopies to explore the light induced dynamics of peridinin in solution
2006Co-Authors: Emmanouil Papagiannakis, Ivo H M Van Stokkum, Delmar S Larsen, Mikas Vengris, Roger G Hiller, Rienk Van GrondelleAbstract:Optical pump-induced dynamics of the highly asymmetric carotenoid peridinin in methanol was studied by dispersed pump−probe, pump−dump−probe, and pump−repump−probe transient absorption spectroscopy in the visible region. Dispersed pump−probe measurements show that the decay of the initially excited S2 state populates two excited states, the S1 and the intramolecular charge-transfer (ICT) state, at a ratio determined by the excitation wavelength. The ensuing spectral evolution occurs on the time scale of a few picoseconds and suggests the equilibration of these states. Dumping the stimulated emission of the ICT state with an additional 800-nm pulse after 400- and 530-nm excitation preferentially removes the ICT state contribution from the broad excited-state absorption, allowing for its spectral characterization. At the same time, an unrelaxed ground-state species, which has a subpicosecond lifetime, is populated. The application of the 800-nm pulse at early times, when the S2 state is still populated, led...
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Ultrafast dynamics of isolated model photoactive yellow protein chromophores: "Chemical perturbation theory" in the laboratory
2005Co-Authors: Mikas Vengris, Michael A. Van Der Horst, Olaf F.a. Larsen, Delmar S Larsen, Klaas J. Hellingwerf, Rienk Van GrondelleAbstract:Pump-probe and pump-dump probe experiments have been performed on several isolated model chromophores of the photoactive yellow protein (PYP). The observed transient absorption spectra are discussed in terms of the spectral signatures ascribed to solvation, excited-state twisting, and vibrational relaxation. It is observed that the protonation state has a profound effect on the excited-state lifetime of p-coumaric acid. Pigments with ester groups on the coumaryl tail end and charged phenolic moieties show dynamics that are significantly different from those of other pigments. Here, an unrelaxed ground-state intermediate could be observed in pump-probe signals. A similar intermediate could be identified in the sinapinic acid and in isomerization-locked chromophores by means of pump-dump probe spectroscopy; however, in these compounds it is less pronounced and could be due to ground-state solvation and/or vibrational relaxation. Because of strong protonation-state dependencies and the effect of electron donor groups, it is argued that charge redistribution upon excitation determines the twisting reaction pathway, possibly through interaction with the environment. It is suggested that the same pathway may be responsible for the initiation of the photocycle in native PYP.
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Photoisomerization and Photoionization of the Photoactive Yellow Protein Chromophore in Solution
2004Co-Authors: Delmar S Larsen, Michael A. Van Der Horst, Ivo H M Van Stokkum, Frank L De Weerd, Mikas Vengris, Klaas J. Hellingwerf, Rienk Van GrondelleAbstract:Dispersed pump-dump-probe spectroscopy has the ability to characterize and identify the underlying ultrafast dynamical processes in complicated chemical and biological systems. This technique builds on traditional pump-probe techniques by exploring both ground- and excited-state dynamics and characterizing the connectivity between constituent transient states. We have used the dispersed pump-dump-probe technique to investigate the ground-state dynamics and competing excited-state processes in the excitation-induced ultrafast dynamics of thiomethyl p-coumaric acid, a model chromophore for the photoreceptor photoactive yellow protein. Our results demonstrate the parallel formation of two relaxation pathways (with multiple transient states) that jointly lead to two different types of photochemistry: cis-trans isomerization and detachment of a hydrated electron. The relative transition rates and quantum yields of both pathways have been determined. We find that the relaxation of the photoexcited chromophores involves multiple, transient ground-state intermediates and the chromophore in solution does not generate persistent photoisomerized products, but instead undergoes photoionization resulting in the generation of detached electrons and radicals. These results are of great value in interpreting the more complex dynamical changes in the optical properties of the photoactive yellow protein.
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excited state dynamics of β carotene explored with dispersed multi pulse transient absorption
2003Co-Authors: Delmar S Larsen, Ivo H M Van Stokkum, Mikas Vengris, Emmanouil Papagiannakis, John T M Kennis, Rienk Van GrondelleAbstract:Abstract The excited-state dynamics of β-carotene in hexane was studied with dispersed ultrafast transient absorption techniques. A new excited state is produced after blue-edge excitation. Pump–repump–probe and pump–dump–probe measurements identified and characterized this state, termed S ‡ , which exhibits a blue-shifted spectrum with a longer lifetime than S1. We establish the independent co-existence of the S ‡ and S1 states following the relaxation of S2 and demonstrate that S ‡ is an electronically excited state and not a vibrationally excited ground-state species. Our data support the premise that S ‡ is formed directly from S2 and not via preferential excitation of ground-state sub-populations.
