Powerful first-order analysis of intraprotein electron transfer is developed from electron-transfer measurements both in biological and in chemical systems. A variation of 20 A in the distance between donors and acceptors in protein changes the electron-transfer rate by 10(12)-fold. Protein presents a uniform electronic barrier to electron tunnelling and a uniform nuclear characteristic frequency, properties similar to an organic glass. Selection of distance, free energy and reorganization energy are sufficient to define rate and directional specificity of biological electron transfer, meeting physiological requirements in diverse systems.

Nature of biological electron transfer

Photophysical, Photochemical and Photokinetic Properties of Photochromic Systems, G. Gauglitz. Photochromism Based on "E-Z" Isomerization of Double Bonds: CIS-trans isomerization of C=C double bonds, J. Saltiel, Y.-P. Sun Azo compounds, H. Rau. Photochromism Based on Pericyclic Reactions: Electrocyclization Reactions: 4n systems based on l,3-electrocyclization, C. Schulz, H. Durr 4n+2 systems based on 1,5-electrocyclization, H. Durr 4n+2 systems - molecules derived from Z-Hexa-1,3,5-Triene/ Cyclohexa- 1,3-Diene, W.H. Laarhoven 4n+2 systems - spiropyrans, R. Guglielmetti 4n+2 systems - fulgides, J. Whittal 4n+2 systems - spirooxazines, N.Y.C. Chu 4n and 4n+2 systems (n>2) based on 1,7- and l,10-electrocyclization, H. Durr. Photochromism Based on Pericyclic Reactions - Cycloaddition Reactions: Cycloaddition reactions involving 4n electrons - (2+2) cycloaddition - photochemical energy storage systems based on reversible valence photoi somerization, G. Jones II Cycloaddition reactions involving 4n electrons - (2+2) cycloaddition - molecules with multiple bonds ingorporated in or linked 10 aromatic systems, J-P. Desvergne, H. Bouas-Laurent Cycloaddition reactions involving 4n electrons - (4+4) cycloaddition reactions between unsaturated conjugated systems, H. Bouas-Laurent, J-P. Desvergne Cycloaddition reactions involving 4n+2 electrons - photochromism based on the reversible reagtion of singlet oxygen with aromatic compounds, H.-D. Brauer, R. Schmidt. Photochromism Based on Tautomerism (Hydrogen Transfer): Tautomerism by hydrogen transfer in salicylates, triazoles and oxazoles, H.E.A. Kramer Tautomerism by hydrogen transfer in anils, aci-nitro and related compounds, E. Hadjoudis. Photochromism Based of Dissociation Processes: Photochromism based on dissociation processes, R. Aldag. Photochromism in Biological Systems: Phytochrome, S.E. Braslavsky Retinal proteins, F. Siebert. Environmental Effects on Organic Photochromic Systems, V.A. Krongauz. The Use of Silver Salts for Photochromic Glasses: The use of silver salts for photochromic glasses, H.J. Hoffmann Applications Spiropyrans and related compounds, R. Guglielmetti Spirooxazines, N.Y.C. Chu Actinometry, G. Gauglitz Photochromic materials and photoresists, K. Ichimura. New Developments Highly Promising for Applications: Photochromism by orientation, J. Michl S Pectral hole - burning, U.P. Wild, A. Renn Bacteriorhodopsin and its functional variants - potential applications in modern optics, N. Hampp, C. Brauchle.

Photochromism : molecules and systems

Energy is the most important issue of the 21st century. About 85 % of our energy comes from fossil fuels, a finite resource unevenly distributed beneath the Earth’s surface. Reserves of fossil fuels are progressively decreasing, and their continued use produces harmful effects such as pollution that threatens human health and greenhouse gases associated with global warming. Prompt global action to solve the energy crisis is therefore needed. To pursue such an action, we are urged to save energy and to use energy in more efficient ways, but we are also forced to find alternative energy sources, the most convenient of which is solar energy for several reasons. The sun continuously provides the Earth with a huge amount of energy, fairly distributed all over the world. Its enormous potential as a clean, abundant, and economical energy source, however, cannot be exploited unless it is converted into useful forms of energy. This Review starts with a brief description of the mechanism at the basis of the natural photosynthesis and, then, reports the results obtained so far in the field of photochemical conversion of solar energy. The “grand challenge” for chemists is to find a convenient means for artificial conversion of solar energy into fuels. If chemists succeed to create an artificial photosynthetic process, “… life and civilization will continue as long as the sun shines!”, as the Italian scientist Giacomo Ciamician forecast almost one hundred years ago.

Photochemical Conversion of Solar Energy

Electron Transfer Past and Future (R Marcus) Electron Transfer Reactions in Solution: A Historical Perspective (N Sutin) Electron Transfer--From Isolated Molecules to Biomolecules (M Bixon & J Jortner) Charge Transfer in Bichromophoric Molecules in the Gas Phase (D Levy) Long--Range Charge Separation in Solvent--Free Donor--Bridge--Acceptor Systems (B Wegewijs & J Verhoeven) Electron Transfer and Charge Separation in Clusters (C Dessent, et al) Control of Electron Transfer Kinetics: Models for Medium Reorganization and Donor--Acceptor Coupling (M Newton) Theories of Structure--Function Relationships for Bridge--Mediated Electron Transfer Reactions (S Skourtis & D Beratan) Fluctuations and Coherence in Long--Range and Multicenter Electron Transfer (G Iversen, et al) Lanczos Algorithm for Electron Transfer Rates in Solvents with Complex Spectral Densities (A Okada, et al) Spectroscopic Determination of Electron Transfer Barriers and Rate Constants (K Omberg, et al) Photoinduced Electron Transfer Within Donor--Spacer--Acceptor Molecular Assemblies Studied by Time--Resolved Microwave Conductivity (J Warman, et al) From Close Contact to Long--Range Intramolecular Electron Transfer (J Verhoeven) Photoinduced Electron Transfers Through sigma Bonds in Solution (N--C Yang, et al) Indexes

Electron transfer : from isolated molecules to biomolecules

https://www.cell.com/article/S0969212694000948/pdf

Structure of the photosynthetic reaction centre from Rhodobacter sphaeroides at 2.65 A resolution: cofactors and protein-cofactor interactions

https://epub.ub.uni-muenchen.de/2301/1/158.pdf

Observation of a bacteriochlorophyll anion radical during the primary charge separation in a reaction center

The initial electron transfer steps in the photosynthetic reaction center of the purple bacterium Rhodobacter sphaeroides have been investigated by femtosecond time-resolved spectroscopy. The experimental data taken at various wavelengths demonstrate the existence of at least four intermediate states within the first nanosecond. The difference spectra of the intermediates and transient photodichroism data are fully consistent with a sequential four-step model of the primary electron transfer: Light absorption by the special pair P leads to the state P*. From the excited primary donor P*, the electron is transferred within 3.5 +/- 0.4 ps to the accessory bacteriochlorophyll B. State P+B- decays with a time constant of 0.9 +/- 0.3 ps passing the electron to the bacteriopheophytin H. Finally, the electron is transferred from H- to the quinone QA within 220 +/- 40 ps.

https://www.pnas.org/content/pnas/87/13/5168.full.pdf

Initial electron-transfer in the reaction center from Rhodobacter sphaeroides.

Terahertz quantum beats in molecular liquids

Synchronous pumping of a femtosecond and a tunable picosecond dye laser provides synchronized trains of ultrashort pulses at variable frequency difference. The system allows the authors to study coherently excited Raman transitions with femtosecond time resolution. Fast dephasing processing with decay times of a few hundred femtosecond are measured. >

Fast dephasing processes studied with a femtosecond coherent Raman system

A recently developed femtosecond coherent Raman technique allows the measurement of Fourier transform coherent Raman spectra with high-frequency differences. The simultaneous excitation of different vibrational modes with a broad-band tunable driving force leads to a strong beating of the coherent Raman probe scattering. The high time resolution of the experimental set-up allows one to measure beat frequencies of more than 10 THz with high precision Mesure des spectres Raman coherent a transformee de Fourier avec des differences haute-frequence. L'excitation simultanee de differents modes de vibration conduit a un fort battement de la diffusion Raman coherent de la sonde. La haute resolution temporelle du montage experimental permet des mesures precises des battements de frequence de plus de 10 THz

https://hal.archives-ouvertes.fr/jpa-00245733/document

Wolfgang Holzapfel

Papers

Observation of a bacteriochlorophyll anion radical during the primary charge separation in a reaction center

Initial electron-transfer in the reaction center from Rhodobacter sphaeroides.

Terahertz quantum beats in molecular liquids

Fast dephasing processes studied with a femtosecond coherent Raman system

Terahertz beats of vibrational modes studied by femtosecond coherent Raman spectroscopy