Photochemical reactions in organized assemblies. 40. Amylose and carboxymethylamylose inclusion complexes with photoreactive molecules

This paper focuses on a study of unimolecular and bimolecular photoreactions occurring with reactants which can be incorporated into the linear polysugars amylose and carboxymethylamylose. Hydrophobic and surfactant trans (E) stilbene derivatives form complexes in which the stilbene chromophore shows enhanced fluorescence and reduced trans → cis isomerization efficiencies. The reactivity of the excited surfactant–stilbene singlet towards the quencher iodide ion has been compared in water/dimethylsulfoxide in the presence and absence of amylose under conditions where complex formation is nearly complete. Some relatively hydrophobic viologen dications have also been found to form complexes with the water soluble carboxymethylamylose. Although the dications complex relatively weakly, the partially reduced monocations complex more strongly. This results in selective retardation of back electron transfer rates when the viologens are used as electron transfer quencher-oxidants for certain luminescent ruthenium polypyridine complexes.

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Ionic Liquid-Induced Local Charge Compensation: Effects on Back Electron-Transfer Rates in Dye-Sensitized TiO2Thin Films

The Journal of Physical Chemistry C ◽

10.1021/acs.jpcc.6b06088 ◽

2016 ◽

Vol 120 (36) ◽

pp. 20016-20023 ◽

Cited By ~ 7

Author(s):

Valeria Saavedra Becerril ◽

Daniele Franchi ◽

Maria Abrahamsson

Keyword(s):

Electron Transfer ◽

Ionic Liquid ◽

Charge Compensation ◽

Transfer Rates ◽

Dye Sensitized ◽

Local Charge ◽

Back Electron Transfer ◽

Local Charge Compensation

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ChemInform Abstract: Cyanoanthracene-Sensitized Photooxidations of N,N- Dibenzylhydroxylamine and Its Derivatives: Free-Energy Dependence of Back Electron-Transfer Rates within Geminate Radical Ion Pairs.

ChemInform ◽

10.1002/chin.199519027 ◽

2010 ◽

Vol 26 (19) ◽

pp. no-no

Author(s):

T. SAKURAI ◽

M. YOKONO ◽

K. KOMIYA ◽

Y. MASUDA ◽

H. INOUE

Keyword(s):

Electron Transfer ◽

Free Energy ◽

Energy Dependence ◽

Ion Pairs ◽

Transfer Rates ◽

Back Electron Transfer

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Cryo-EM structure and kinetics reveal electron transfer by 2D diffusion of cytochrome c in the yeast III-IV respiratory supercomplex

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.2021157118 ◽

2021 ◽

Vol 118 (11) ◽

pp. e2021157118

Author(s):

Agnes Moe ◽

Justin Di Trani ◽

John L. Rubinstein ◽

Peter Brzezinski

Keyword(s):

Electron Transfer ◽

Respiratory Chain ◽

Water Soluble ◽

Three Dimensions ◽

Oxidoreductase Activity ◽

Transfer Rates ◽

Cellular Processes ◽

Membrane Bound ◽

Kinetics Of ◽

Positively Charged

Energy conversion in aerobic organisms involves an electron current from low-potential donors, such as NADH and succinate, to dioxygen through the membrane-bound respiratory chain. Electron transfer is coupled to transmembrane proton transport, which maintains the electrochemical proton gradient used to produce ATP and drive other cellular processes. Electrons are transferred from respiratory complexes III to IV (CIII and CIV) by water-soluble cytochrome (cyt.) c. In Saccharomyces cerevisiae and some other organisms, these complexes assemble into larger CIII2CIV1/2 supercomplexes, the functional significance of which has remained enigmatic. In this work, we measured the kinetics of the S. cerevisiae supercomplex cyt. c-mediated QH2:O2 oxidoreductase activity under various conditions. The data indicate that the electronic link between CIII and CIV is confined to the surface of the supercomplex. Single-particle electron cryomicroscopy (cryo-EM) structures of the supercomplex with cyt. c show the positively charged cyt. c bound to either CIII or CIV or along a continuum of intermediate positions. Collectively, the structural and kinetic data indicate that cyt. c travels along a negatively charged patch on the supercomplex surface. Thus, rather than enhancing electron transfer rates by decreasing the distance that cyt. c must diffuse in three dimensions, formation of the CIII2CIV1/2 supercomplex facilitates electron transfer by two-dimensional (2D) diffusion of cyt. c. This mechanism enables the CIII2CIV1/2 supercomplex to increase QH2:O2 oxidoreductase activity and suggests a possible regulatory role for supercomplex formation in the respiratory chain.

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Bicarbonate Activation of Monomeric Photosystem II-PsbS/Psb27 Complex

10.1101/2022.01.13.476245 ◽

2022 ◽

Author(s):

A. William Rutherford ◽

Andrea Fantuzzi ◽

Dario Piano ◽

Patrycja Haniewicz ◽

Domenica Farci ◽

...

Keyword(s):

Electron Transfer ◽

Photosystem Ii ◽

Water Splitting ◽

Thylakoid Membranes ◽

Protective Mechanism ◽

Slow Electron ◽

Enhanced Fluorescence ◽

Transfer Rates ◽

Redox Tuning ◽

In Transit

In thylakoid membranes, Photosystem II monomers from the stromal lamellae contain the subunits PsbS and Psb27 (PSIIm-S/27), while Photosystem II monomers from granal regions (PSIIm) lack these subunits. Here, we have isolated and characterised these two types of Photosystem II complexes. The PSIIm-S/27 showed enhanced fluorescence, the near-absence of oxygen evolution, as well as limited and slow electron transfer from QA to QB compared to the near-normal activities in the granal PSIIm. However, when bicarbonate was added to the PSIIm-S/27, water splitting and QA to QB electron transfer rates were comparable to those in granal PSIIm. The findings suggest that the binding of PsbS and/or Psb27 inhibits forward electron transfer and lowers the binding affinity for the bicarbonate. This can be rationalized in terms of the recently discovered photoprotection role played by bicarbonate binding via the redox tuning of the QA/QA?- couple, which controls the charge recombination route, and this limits chlorophyll triplet mediated 1O2 formation (Brinkert K et al. (2016) Proc Natl Acad Sci U S A. 113(43):12144-12149). These findings suggest that PSIIm-S/27 is an intermediate in the assembly of PSII in which PsbS and/or Psb27 restrict PSII activity while in transit, by using a bicarbonate-mediated switch and protective mechanism.

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