scholarly journals Efficiency of ferredoxins and flavodoxins as mediators in systems for hydrogen evolution

1980 ◽  
Vol 192 (2) ◽  
pp. 665-672 ◽  
Author(s):  
M P Fitzgerald ◽  
L J Rogers ◽  
K K Rao ◽  
D O Hall
Keyword(s):  
Electron Transfer ◽  
Hydrogen Evolution ◽  
Tertiary Structure ◽  
Red Alga ◽  
Anacystis Nidulans ◽  
Clostridium Pasteurianum ◽  
Hydrogenase Activity ◽  
Higher Plant ◽  
Porphyra Umbilicalis ◽  
Nostoc Strain

1. The efficiencies of ferredoxins and flavodoxins from a range of sources as mediators in systems for hydrogen evolution were assessed. 2. In supporting electron transfer from dithionite to hydrogenase of the bacterium Clostridium pasteurianum, highest activity was shown by the ferredoxin from the cyanobacterium Chlorogloeopsis fritschii and flavodoxin from the bacterium Megasphaera elsdenii. The latter was some twenty times as active as comparable concentrations of Methyl Viologen. Ferredoxins from the cyanobacterium Anacystis nidulans and the red alga Porphyra umbilicalis also showed high activity. 3. In mediating electron transfer from chloroplast membranes to Clostridium pasteurianum hydrogenase the flavodoxin from Anacystis nidulans proved the most active with Nostoc strain MAC flavodoxin and Porphyra umbilicalis ferredoxin also being appreciably more active than other cyanobacterial and higher plant ferredoxins. 4. In both hydrogenase systems the ferredoxin and flavodoxin from the red alga Chondrus crispus and the ferredoxin from another red alga Gigartina stellata showed very low activity. 5. There appeared to be no apparent correlation of efficiency in supporting hydrogenase activity with midpoint redox potential (Em) of the mediators, though some correlation of Em with the efficiency of the mediators in supporting NADP+ photoreduction by chloroplasts, or pyruvate oxidation by a Clostridium pasteurianum system, was evident. 6. Activity of the mediators in the hydrogenase systems therefore primarily reflects differences in tertiary structure conferring differing affinities for the other components of the systems.

scholarly journals Redox potentials of algal and cyanobacterial flavodoxins

1984 ◽  
Vol 217 (3) ◽  
pp. 845-850 ◽  
Author(s):  
G A Sykes ◽  
L J Rogers
Keyword(s):  
Potentiometric Titration ◽  
Red Alga ◽  
Anacystis Nidulans ◽  
Chondrus Crispus ◽  
Redox Potentials ◽  
Ph Dependent ◽  
Nostoc Strain ◽  
Synechococcus Pcc 6301

The redox potentials of flavodoxins from the cyanobacteria Synechococcus PCC 6301 (formerly Anacystis nidulans) and Nostoc strain MAC, and from the red alga Chondrus crispus, were determined by potentiometric titration. For the oxidized-semiquinone interconversion the potentials at pH 7.0 of the three flavodoxins were between −210 and −235 mV, and these were pH-dependent over the range pH 6.9-8.2. For the semiquinone-reduced interconversion the potentials of the cyanobacterial flavodoxins were close to −414 mV, and that for the algal flavodoxin, −370 mV, is the highest reported in this group of flavoproteins.

Modulating photogenerated electron transfer with selectively exposed Co–Mo facets on a novel amorphous g-C3N4/CoxMo1−xS2 photocatalyst

RSC Advances ◽  
2016 ◽  
Vol 6 (28) ◽  
pp. 23709-23717 ◽  
Author(s):  
Xuqiang Hao ◽  
Zhiliang Jin ◽  
Shixiong Min ◽  
Gongxuan Lu
Keyword(s):  
Electron Transfer ◽  
Catalytic Activity ◽  
Hydrogen Evolution ◽  
Photogenerated Electron ◽  
Photocatalytic Hydrogen Evolution ◽  
Exposed Facets

Novel photocatalysts, g-C3N4/Co0.04Mo0.96S2 with different exposed facets of Co–Mo, were employed as catalysts for the examination of facet-dependent catalytic activity toward photocatalytic hydrogen evolution.

scholarly journals Ferredoxin from a Red Alga, Porphyra umbilicalis

1976 ◽  
Vol 69 (1) ◽  
pp. 243-248 ◽  
Author(s):  
Peter W. ANDREW ◽  
Lyndon J. ROGERS ◽  
Donald BOULTER ◽  
Barry G. HASLETT
Keyword(s):  
Red Alga ◽  
Porphyra Umbilicalis

scholarly journals Atoms vs. Ions: Intermediates in Reversible Electrochemical Hydrogen Evolution Reaction

Catalysts ◽  
2021 ◽  
Vol 11 (9) ◽  
pp. 1135
Author(s):  
Jurga Juodkazytė ◽  
Kȩstutis Juodkazis ◽  
Saulius Juodkazis
Keyword(s):  
Electron Transfer ◽  
Hydrogen Evolution ◽  
Hydrogen Evolution Reaction ◽  
Ionic Species ◽  
Absolute Temperature ◽  
Main Reaction ◽  
Adsorbed Hydrogen ◽  
H2 Evolution ◽  
Hydrogen Electrode ◽  
Reported Data

We present a critical analysis of the mechanism of reversible hydrogen evolution reaction based on thermodynamics of hydrogen processes considering atomic and ionic species as intermediates. Clear distinction between molecular hydrogen evolution/oxidation (H2ER and H2OR) and atomic hydrogen evolution/oxidation (HER and HOR) reactions is made. It is suggested that the main reaction describing reversible H2ER and H2OR in acidic and basic solutions is: H3O++2e−⇌(H2+)adH2+OH− and its standard potential is E0 = −0.413 V (vs. standard hydrogen electrode, SHE). We analyse experimentally reported data with models which provide a quantitative match (R.J.Kriek et al., Electrochem. Sci. Adv. e2100041 (2021)). Presented analysis implies that reversible H2 evolution is a two-electron transfer process which proceeds via the stage of adsorbed hydrogen molecular ion H2+ as intermediate, rather than Had as postulated in the Volmer-Heyrovsky-Tafel mechanism. We demonstrate that in theory, two slopes of potential vs. lg(current) plots are feasible in the discussed reversible region of H2 evolution: 2.3RT/F≈60 mV and 2.3RT/2F≈30 mV, which is corroborated by the results of electrocatalytic hydrogen evolution studies reported in the literature. Upon transition to irreversible H2ER, slowdown of H2+ formation in the first electron transfer stage manifests, and the slope increases to 2.3RT/0.5F≈120 mV; R,F,T are the universal gas, Faraday constants and absolute temperature, respectively.

Sign in / Sign up

Export Citation Format

Share Document