scholarly journals Electron transfer quenching in light adapted and mutant forms of the AppA BLUF domain

2015 ◽  
Vol 177 ◽  
pp. 293-311 ◽  
Author(s):  
Sergey P. Laptenok ◽  
Andras Lukacs ◽  
Richard Brust ◽  
Allison Haigney ◽  
Agnieszka Gil ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Electron Donor ◽  
Ground State ◽  
Structural Changes ◽  
Structure Change ◽  
Radical Intermediate ◽  
Time Resolved ◽  
Radical Intermediates ◽  
Bluf Domain ◽  
A Charge

The Blue Light Using Flavin (BLUF) domain proteins are an important family of photoreceptors controlling a range of responses in a wide variety of organisms. The details of the primary photochemical mechanism, by which light absorption in the isoalloxazine ring of the flavin is converted into a structure change to form the signalling state of the protein, is unresolved. In this work we apply ultrafast time resolved infra-red (TRIR) spectroscopy to investigate the primary photophysics of the BLUF domain of the protein AppA (AppABLUF) a light activated antirepressor. Here a number of mutations at Y21 and W104 in AppABLUF are investigated. The Y21 mutants are known to be photoinactive, while W104 mutants show the characteristic spectral red-shift associated with BLUF domain activity. Using TRIR we observed separately the decay of the excited state and the recovery of the ground state. In both cases the kinetics are found to be non-single exponential for all the proteins studied, suggesting a range of ground state structures. In the Y21 mutants an intermediate state was also observed, assigned to formation of the radical of the isoalloxazine (flavin) ring. The electron donor is the W104 residue. In contrast, no radical intermediates were detected in the studies of the photoactive dark adapted proteins, dAppABLUF and the dW104 mutants, suggesting a structure change in the Y21 mutants which favours W104 to isoalloxazine electron transfer. In contrast, in the light adapted form of the proteins (lAppABLUF, lW104) a radical intermediate was detected and the kinetics were greatly accelerated. In this case the electron donor was Y21 and major structural changes are associated with the enhanced quenching. In AppABLUF and the seven mutants studied radical intermediates are readily observed by TRIR spectroscopy, but there is no correlation with photoactivity. This suggests that if a charge separated state has a role in the BLUF photocycle it is only as a very short lived intermediate.

A new ground state single electron donor for excess electron transfer studies in DNA

2009 ◽  
pp. 3583 ◽  
Author(s):  
Christian Trindler ◽  
Antonio Manetto ◽  
Jürgen Eirich ◽  
Thomas Carell
Keyword(s):  
Electron Transfer ◽  
Electron Donor ◽  
Ground State ◽  
Excess Electron ◽  
Single Electron

The Generation of Aryl Anions by Double Electron Transfer to Aryl Iodides from a Neutral Ground-State Organic Super-Electron Donor

2007 ◽  
Vol 46 (27) ◽  
pp. 5178-5183 ◽  
Author(s):  
John A. Murphy ◽  
Sheng-ze Zhou ◽  
Douglas W. Thomson ◽  
Franziska Schoenebeck ◽  
Mohan Mahesh ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Electron Donor ◽  
Ground State ◽  
Aryl Iodides ◽  
Double Electron ◽  
Neutral Ground

REVERSIBLE, METASTABLE, ULTRAFAST PHOTOINDUCED ELECTRON TRANSFER FROM SEMICONDUCTING POLYMERS TO BUCKMINSTERFULLERENE AND IN THE CORRESPONDING DONOR/ACCEPTOR HETEROJUNCTIONS

1994 ◽  
Vol 08 (03) ◽  
pp. 237-274 ◽  
Author(s):  
N. S. SARICIFTCI ◽  
A. J. HEBGER
Keyword(s):  
Electron Transfer ◽  
Steady State ◽  
Ground State ◽  
Charge Separation ◽  
Photoinduced Electron Transfer ◽  
Semiconducting Polymers ◽  
Time Resolved ◽  
Degenerate Ground State ◽  
Photoinduced Charge Separation ◽  
Donor Acceptor

The results of comprehensive studies of photoinduced electron transfer from semiconducting (conjugated) polymers to buckminsterfullerene are reviewed. Steady state and femtosecond time-resolved photoinduced absorption (photoexcitation spectroscopy), steady state and picosecond time-resolved photoluminescence, steady state and picosecond photoconductivity, and steady state light-induced electron spin resonance measurements are summarized as experimental evidence which demonstrates ultrafast, long lived photoinduced electron transfer. Comparative studies with different semiconducting polymers as donors demonstrate that in degenerate ground state polymers, soliton excitations form before the electron transfer can occur; thereby inhibiting charge transfer and charge separation. In non-degenerate ground state systems, photoinduced electron transfer occurs in less than 10−12 s , quenching the photoluminescence as well as the intersystem crossing into the triplet manifold. The importance of electron–phonon coupling and structural relaxation following photoexcitation in these quasi-one-dimensional semiconducting polymers is proposed as a principal contribution to the stabilization of the charge separated state. Utilizing thin films of the semiconducting polymer (donor) and buckminsterfullerene (acceptor) to form a heterojunction interface, we have fabricated bilayers which functioned as photodiodes and as photovoltaic cells. The results are discussed in terms of opportunities for solar energy conversion, for photodiode detector devices, and for a variety of other applications which use photoinduced charge separation.

Photophysical properties of Sn(IV)tetraphenylporphyrin-pyrene dyad with a β-vinyl linker

2015 ◽  
Vol 19 (01-03) ◽  
pp. 288-300 ◽  
Author(s):  
P. Silviya Reeta ◽  
Adis Khetubol ◽  
Tejaswi Jella ◽  
Vladimir Chukharev ◽  
Fawzi Abou-Chahine ◽  
...  
Keyword(s):  
Excited State ◽  
Ground State ◽  
Transient Absorption ◽  
Photophysical Properties ◽  
Intermediate Species ◽  
Broad Absorption ◽  
Time Resolved ◽  
Near Ir ◽  
A Charge ◽  
Porphyrin Moiety

A Sn (IV)tetraphenylporphyrin (T) has been functionalized with a β-vinyl pyrene (P) and the photophysical properties of the formed dyad (T-P) with its corresponding precursors were studied in three solvents with different polarities using steady-state and time-resolved measurements in ps and fs timescales. When the pyrene moiety is excited at λex = 340 nm, the fluorescence spectroscopy experiments indicate in all the studied solvents, an efficient quenching of the pyrene emission. When excited at either λex = 340 nm or λex = 405 nm, where porphyrin absorbs, a new emissive excited state complex (T-P)* is observed at wavelenghts close to the parent porphyrin emission. The emission is more pronounced in nonpolar hexane showing a mono-exponential decay, but bi-exponential decays are observed in more polar dicloromethane and acetonitrile. When the porphyrin moiety is excited at λex = 425 nm, the fs transient absorption analysis shows two different intermediate species (~ 7–11 ps and 80–100 ps) with broad absorption in the near-IR region. This implies either the existence of two different excited conformers (T-P)*, which decay to the ground state via a charge separated state (CSS), or the formation of the (T-P)* state via the second excited state of the porphyrin moiety, yielding first an excited emissive v(T-P)* state, with a lifetime of 80–100 ps.

scholarly journals Ultrafast Dynamical Study Using Time-resolved Laue Diffraction

2014 ◽  
Vol 70 (a1) ◽  
pp. C766-C766
Author(s):  
Sreevidya Thekku Veedu
Keyword(s):  
Electron Transfer ◽  
Time Scales ◽  
Structural Changes ◽  
Reaction Centre ◽  
Dynamical Study ◽  
Light Harvesting Complexes ◽  
Time Resolved ◽  
Wide Range ◽  
Donor Acceptor ◽  
Excitation Processes

Electron transfer reactions are fundamental processes in chemistry and also in biology [1-3]. Light harvesting complexes are functional centers in plants where sunlight is converted into chemical energy. In this, optical excitation in a chromophore unit leads to the transfer of electrons within the system. However, due to the complexity of the biological photo-reaction centre, recent spectroscopic efforts have concentrated on a smaller chemical model which share characteristic with their biological counter parts. A promising model is the so-called D-A (donor-acceptor) systems, which are chemically synthetic molecules with electron transfer capabilities. The electrical conductivity is a function of the optical state of the system. An optically switching diode is an interesting application of donor-acceptor molecules. We aimed to determine photo-induced structural changes in Pyrene-N,N-dimethylaniline (PyDMA). Static structures for many molecules are available at high resolution but the mechanism by which these molecules function and the structures of intermediate states often remain elusive. Knowledge of the geometry of molecular excited states at atomic resolution is crucial for a full understanding of photo-induced chemical processes. Time-resolved X-ray diffraction (TR-XRD) using polychromatic synchrotron radiation allows a detailed study of the time evolution of structural intermediates and short living states of chemical systems at wide range of time-scales, drawing a complete picture of the photo-induced charge transfer process. Investigation of photo-excitation processes in molecular single crystals, where the initial photo-excitation processes occur on extremely short time-scales (femto-/picosecond time domain) and have been in the focus of scientific investigations due to their possible applications, e.g. as optical switches.

scholarly journals Electron transfer reactions in sub-porphyrin–naphthyldiimide dyads

2019 ◽  
Vol 21 (30) ◽  
pp. 16477-16485 ◽  
Author(s):  
Betül Küçüköz ◽  
B. Adinarayana ◽  
Atsuhiro Osuka ◽  
Bo Albinsson
Keyword(s):  
Electron Transfer ◽  
Electron Donor ◽  
Transient Absorption ◽  
Transfer Reactions ◽  
Time Resolved ◽  
Electron Transfer Reactions ◽  
Donor Acceptor ◽  
Absorption Measurements

A series of donor–acceptor compounds based on a sub-porphyrin (SubP) as an electron donor and naphthyldiimide (NDI) as an acceptor has been designed, synthesized and investigated by time-resolved emission and transient absorption measurements.

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