Viologen, reduced

Materials and Methods section). To deactivate WT hydrogenases, a controlled amount of 02 was added to the anaerobic cell suspension in the sealed vial and incubated under vigorous mixing for 2 min. Anaerobic conditions were then rapidly re-established, and methyl viologen (reduced by addition of sodium dithionite) was added to serve as the electron donor to the hydrogenase. The mixture was then incubated in the dark for 15 min at 30°C, and the reaction was stopped by the addition of trichloroacetic acid. The amount of H2 produced was detected by gas chromatography. 

In contrast to viologens reduced anthraquinone-2,6-disulphonate formed by Reaction [31a] can be reoxidized in a non-enzymicly catalysed reaction with oxygen as final electron acceptor (Reaction [31b]). The formed hydrogen peroxide can be split by the extremely cheap catalase (Reaction [31c]). The stun of Reactions [31a]-[31c] leads to Reaction [31]. 

The methyl viologen-reducing activity of hydrogenase in crude extracts from the deep-sea thermophile Methanococcus jannaschii was assayed using the high-pressure, high-temperature reactor system shown in Fig. 1. The reaction vessel... 

A unit of activity is defined as I (xmol of methyl viologen reduced per min. 

Pt content of the solutions of different particle size, namely 3.5 mg Pt/25 cc. This figure also shows two extra points with 100 X particle size but with low Pt levels 0.35 mg Pt/25 cc solution, the upper one, and 0.25 mg Pt/25 cc solution, the lower one. Quantum yield measurements indicate a stoichiometric relation between the viologen reduced in the photoprocess and the amount of hydrogen produced. One might object to the high Pt levels (lUO mg/ltr) required to obtain these high yields. Such concentrations are intolerable for practical systems. However, reduction in particle size to a radius of only 15 A leads to a one himdred fold increase in the activity of the catalyst. Hence, the same hydrogen output can now be achieved with a Pt concentration of only l.U mg/ltr. 

The divalent cation methyl viologen is highly colored in reduced form and is used as an electrochromic in solution cells (Eig. 11). 

The added electron is delocalized on the monovalent radical ion to which it is reduced (3). There is no general agreement on the molecular representation of the reduced stmcture. Various other viologen compounds have been mentioned (9,12). Even a polymeric electrochromic device (15) has been made, though the penalty for polymerization is a loss in device speed. Methylviologen dichloride [1910-42-5] was dissolved in hydrated... 

The metal formed is deposited on the colloidal particles and causes the absorption of the solution to increase at all wavelengtlK. The depositel cadmium is very reactive. It is reoxidized when air is admitted to the illuminated solution. Addition of methyl viologen to the illuminated solution under the exclusion of air yields the blue colour of the semi-ceduced methyl viologen, MV". As the absorption coefficient of MV" is known, the concentration of reduced cadmium can be readily calculated. reoxidises cadmium atoms ... 

Gratzel and co-workers found in their first flash experiments that the luminescence of CdS decayed with a lifetime of 0.3 ns When methyl viologen was present, the signal of the half-reduced electron acceptor, MV, was present immediately after the laser flash. With increasing concentration, the amount of MV formed... 

Serpone et al. studied the fluorescence emitted from a CdS sol containing half-reduced methyl viologen, MV, and residual the MV being produced by... 

In the pulse radiolysis studies on the reaction of MV with TiOj, the sol contained propanol-2 or formate and methyl viologen, MV Ionizing radiation produces reducing organic radicals, i.e. (CH3)2COH or C02 , respectively, and these radicals react rapidly with MV to form MV. The reaction of MV with the colloidal particles was then followed by recording the 600 nm absorption of MV . The rate of reaction was found to be slower than predicted for a diffusion controlled reaction. 

Nitrate reductase ) Escherichia coli Reduced methyl viologen NO3 ... 

Indeed, the (200-fs) laser excitation of the EDA complexes of various benz-pinacols with methyl viologen (MV2+) confirms the formation of all the transient species in equation (59). A careful kinetic analysis of the decay rates of pinacol cation radical and reduced methyl viologen leads to the conclusion that the ultrafast C—C bond cleavage (kc c = 1010 to 1011 s- ) of the various pinacol cation radicals competes effectively with the back electron transfer in the reactive ion pair. 

Fig. 11 Transient spectra obtained upon the application of a 200-fs laser pulse to a solution of [Ph2C(0H)C02, MV2+] charge-transfer salt showing the simultaneous formation of benzophenone ketyl radical (dashed line) and the reduced methyl viologen (dotted line). The inset is the authentic spectrum of ketyl radical. Reproduced with permission from Ref. 92a.

Redox molecules are particularly interesting for an electrochemical approach, because they offer addressable (functional) energy states in an electrochemically accessible potential window, which can be tuned upon polarization between oxidized and reduced states. The difference in the junction conductance of the oxidized and the reduced forms of redox molecules may span several orders of magnitude. Examples of functional molecules used in these studies include porphyrins [31,153], viologens [33, 34,110,114,154,155], aniline and thiophene oligomers [113, 146, 156, 157], metal-organic terpyridine complexes [46, 158-163], carotenes [164], nitro derivatives of OPE (OPV) [165, 166], ferrocene [150, 167, 168], perylene tetracarboxylic bisimide [141, 169, 170], tetrathia-fulvalenes [155], fullerene derivatives [171], redox-active proteins [109, 172-174], and hydroxyquinones [175]. 

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