Excited-state processes in protochlorophyllide a – a femtosecond time-resolved absorption study

Dietzek, Benjamin; Maksimenka, Raman; Siebert, Thorsten; Birckner, Eckhard; Kiefer, W.; Popp, Jürgen; Hermann, Gudrun; Schmitt, Michael

doi:10.1016/j.cplett.2004.08.075

Cited by 31 publications

(103 citation statements)

References 19 publications

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“…In the present paper we review our recent work on femtosecond time-resolved spectroscopy to investigate the light-induced ultrafast excited-state processes of two very important biological photoreceptor chromophores, phycocyanobilin (PCB) [20] and protochlorophyllide a (PChla) [21][22][23][24]. The spectroscopic techniques employed to interrogate the light-induced processes in these systems are femtosecond time-resolved transient absorption and transient-grating spectroscopy, the latter being a special case of four-wave-mixing spectroscopy.…”

Section: Introductionmentioning

confidence: 99%

“…Briefly, the excited-state relaxation processes in PCB [20] are investigated using pump-energy-dependent transient-grating spectroscopy. Furthermore, experiments on photoexcited PChla [21,23,24] and magnesium octaethyl porphyrin [22] are presented. With the knowledge gained from these experiments, the light-induced excited-state processes in PChla are investigated using femtosecond transient absorption and picosecond time-resolved fluorescence spectroscopy.…”

Section: Introductionmentioning

confidence: 99%

“…The Nobel Prize to Ahmed H. Zewail stimulated even more this active research area. Even complex processes such as photosynthesis [13,14] or the initial ultrafast steps in vision [15], are well characterized and a quite detailed understanding of light-induced reactions on model systems now exists [13,[16][17][18][19][20][21][22][23][24].…”

Section: Introductionmentioning

confidence: 99%

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Femtosecond time‐resolved spectroscopy on biological photoreceptor chromophores

Schmitt¹,

Dietzek

Hermann

et al. 2007

Laser & Photonics Reviews

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This paper reviews our results on femtosecond timeresolved spectroscopy (transient absorption, transient-grating and fluorescence spectroscopy) to study the photophysics and photochemistry of the two very important biological photoreceptor chromophores phycocyanobilin (PCB) and protochlorophyllide a (PChla). The compound PCB serves as a model chromophore for the photoreceptor phytochrome. By means of transient-grating spectroscopy where the excitation wavelength was varied over the spectral region of the S0 → S1-absorption the ultrafast processes were studied upon excitation with varying excess energy delivered to the system. On the basis of the results obtained, both the rate of the photoreaction in PCB and the rate of the decay of different excited-state species via different decay channels depend on the excitation wavelength. Furthermore, transient absorption experiments illuminating the excited-state dynamics of PChla, a porphyrin-like compound and, as substrate of the NADPH/protochlorophyllide oxidoreductase (POR), a precursor of the chlorophyll biosynthesis are presented. In addition to pump-energy-dependent measurements performed with PChla dissolved in methanol, the excited-state dynamics of PChla was interrogated in different solvents that were chosen to mimic different environmental conditions. In addition to the femtosecond time-resolved absorption experiments the picosecond time-resolved fluorescence of the system was studied. The transient absorption and time-resolved fluorescence data allow suggesting a detailed model for the excited-state relaxation of PChla describing the excited-state processes in terms of The model suggested to account for the excited-state relaxation processes in protochlorophyllide a upon photoexcitation is presented a branching of the initially excited state population into a reactive and nonreactive path. Thus, the excited-state potential energy surface exhibits two distinct S1 and Sx minima separated from the Franck-Condon region along two most likely orthogonal reaction coordinates. Finally, the model derived is related to models suggested to account for the reduction of PChla to chlorophyllide a within the natural enzymatic environment of POR.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Femtosecond time‐resolved spectroscopy on biological photoreceptor chromophores

Schmitt¹,

Dietzek

Hermann

et al. 2007

Laser & Photonics Reviews

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“…This is accompanied by the appearance of broad excited-state absorption (ESA) bands on either side of the ground state bleach (GSB) band. The initial femtosecond-picosecondd ynamics,w hich represent the S2!S1 transition, vibrational relaxation, and formation of an ICT state,h ave been described previously [11][12][13][14][15] and are not the main focus of the current study.T he subsequent excited-state dynamics could be fitted to three sequentially evolving exponential functions with time constants of 390 ps, 3.2 ns,a nd 2.7 ms, confirming the model proposed previously. [11][12][13][14]15] The3 90 ps component is likely to represent the solvation of the ICT state.…”

mentioning

confidence: 99%

“…[3] An umber of time-resolved transient spectroscopy studies have identified different short-lived Pchlide* species,both in the isolated pigment [11][12][13][14][15] and in the ternary enzyme-substrate complex. [16][17][18][19][20] TheP chlide molecule is intrinsically very reactive with multi-exponential excited-state dynamics [11][12][13][14][15][16] and the formation of an umber of Pchlide excited-state species within afew nanoseconds,including an intramolecular charge-transfer (ICT) complex [11][12][13][14][15] and atriplet state. [13,15] A detailed understanding of the initial ultrafast steps in the ternary enzyme-substrate (POR-Pchlide-NADPH) complex that lead directly to the chemistry of Pchlide photoreduction has proved more challenging.…”

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confidence: 99%

Excited‐State Charge Separation in the Photochemical Mechanism of the Light‐Driven Enzyme Protochlorophyllide Oxidoreductase

et al. 2014

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The unique light-driven enzyme protochlorophyllide oxidoreductase (POR) is an important model system for understanding how light energy can be harnessed to power enzyme reactions.T he ultrafast photochemical processes, essential for capturing the excitation energy to drive the subsequent hydride-and proton-transfer chemistry,h ave so far proven difficult to detect. We have used ac ombination of time-resolved visible and IR spectroscopy, providing complete temporal resolution over the picosecond-microsecond time range,t op ropose an ew mechanism for the photochemistry. Excited-state interactions between active site residues and acarboxyl group on the Pchlide molecule result in apolarized and highly reactive double bond. This so-called "reactive" intramolecular charge-transfer state creates an electron-deficient site across the double bond to trigger the subsequent nucleophilic attacko fN ADPH, by the negatively charged hydride from nicotinamide adenine dinucleotide phosphate. This work provides the crucial, missing link between excitedstate processes and chemistry in POR. Moreover,i tp rovides important insight into how light energy can be harnessed to drive enzyme catalysis with implications for the design of lightactivated chemical and biological catalysts.

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Excited State Dynamics in the Light‐Driven Enzyme Protochlorophyllide Oxidoreductase (POR)

Groot

Heyes

2010

Hydrogen Bonding and Transfer in the Excited State

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Excited-state processes in protochlorophyllide a – a femtosecond time-resolved absorption study

Cited by 31 publications

References 19 publications

Femtosecond time‐resolved spectroscopy on biological photoreceptor chromophores

Femtosecond time‐resolved spectroscopy on biological photoreceptor chromophores

Excited‐State Charge Separation in the Photochemical Mechanism of the Light‐Driven Enzyme Protochlorophyllide Oxidoreductase

Excited State Dynamics in the Light‐Driven Enzyme Protochlorophyllide Oxidoreductase (POR)

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