Oxidation of formate

Shilov et al studied the rate of oxidation of formate ions in phosphate and carbonate buffers, and showed that the reaction with molecular chlorine is negligible in solutions of pH 6. At 20 °C the rate of reaction with hypochlorous acid is constant in the range pH 5.5-7, then it decreases with increase of pH, and becomes negligible at pH 13. The kinetics are second-order with respect to hypochlorous acid, and first with respect to formate ions. In alkaline solution hydroxide ion catalysis is apparent viz. 

Lister and Rosenblum suggest that the rate-determining step is the attack of HCIO on HCOO-, viz. 

From rale measurements at 60 and 70 °C, the activation energy for reaction (6) is 6.7 kcal.mole S and the. 4-factor is 3.4 x 10 l.mole sec The latter is unusually small, but Lister and Rosenblum point out that similar low values have been obtained for the oxidations of bromide and nitrite ions by hypochlorous acid. They suggest that the formation of the transition state requires a special orientation of the reactant molecules. 

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Formate is one of the most representative hydrogen sources for the biocatalytic reduction because CO2 formed by the oxidation of formate is released easily from the reaction system [4]. For example, for the reduction of aromatic ketones by the... 

The oxidation of formate bound to cobalt(lll) ( captive formate ) has been examined by Candlin and Halpern . The kinetics are... 

Reductive dechlorination in combination with the elimination of chloride has been demonstrated in a strain of Clostridium rectum (Ohisa et al. 1982) y-hexachlorocyclohexene formed 1,2,4-trichlorobenzene and y-l,3,4,5,6-pentachlorocyclohexene formed 1,4-dichlorobenzene (Figure 7.69). It was suggested that this reductive dechlorination is coupled to the synthesis of ATP, and this possibility has been clearly demonstrated during the dehalogenation of 3-chlorobenzoate coupled to the oxidation of formate in Desulfomonile tiedjei (Mohn and Tiedje 1991). Combined reduction and elimination has also been demonstrated in methanogenic cultures that transform 1,2-dibromoethane to ethene and 1,2-dibromoethene to ethyne (Belay and Daniels 1987). 

Photocatalytic oxidation of ethanol on Pt/ri02 and Nafion coated Ti02 catalysts were studied using in situ infrared IR techniques. Infrared studies show that the reaction produced acetaldehyde, acetic acid, acetate, formic acid, formate, and CO2/H2O. Modification of the Ti02 catalyst by Pt and Nafion slowed down the oxidation reaction through site blocking. Incorporation of Pt was found to favor formation of formate (HCOO ), indicating Pt decreases the rate of oxidation of formate more than that of its formation. 

It is possible that colloidal photochemistry will provide a new approach to prebiotic syntheses. The work described previously on redox reactions at colloidal ZnS semiconductor particles has been carried on successfully by S. T. Martin and co-workers, who studied reduction of CO2 to formate under UV irradiation in the aqueous phase. ZnS acts as a photocatalyst in the presence of a sulphur hole scavenger oxidation of formate to CO2 occurs in the absence of a hole scavenger. The quantum efficiency for the formate synthesis is 10% at pH 6.3 acetate and propionate were also formed. The authors assume that the primeval ocean contained semiconducting particles, at the surface of which photochemical syntheses could take place (Zhang et al 2007). 

As a consequence of the previous considerations Kieber et al. [75] have developed an enzymic method to quantify formic acid in non-saline water samples at sub-micromolar concentrations. The method is based on the oxidation of formate by formate dehydrogenase with corresponding reduction of /3-nicotinamide adenine dinucleotide (j6-NAD+) to reduced -NAD+(/3-NADH) jS-NADH is quantified by reversed-phase high performance liquid chromatography with fluorimetric detection. An important feature of this method is that the enzymic reaction occurs directly in aqueous media, even seawater, and does not require sample pre-treatment other than simple filtration. The reaction proceeds at room temperature at a slightly alkaline pH (7.5-8.5), and is specific for formate with a detection limit of 0.5 im (SIN = 4) for a 200 xl injection. The precision of the method was 4.6% relative standard deviation (n = 6) for a 0.6 xM standard addition of formate to Sargasso seawater. Average re-... 

Yeast alcohol dehydrogenase (YADH), catalysis of reduction by NADH of acetone formate dehydrogenase (FDH), oxidation by NAD of formate horse-liver alcohol dehydrogenase (HLAD), catalysis of reduction by NADH of cyclohexanone With label in NADH, the secondary KIE is 1.38 for reduction of acetone (YADH) with label in NAD, the secondary KIE is 1.22 for oxidation of formate (FDH) with label in NADH, the secondary KIE is 1.50 for reduction of cyclohexanone (HLAD). The exalted secondary isotope effects were suggested to originate in reaction-coordinate motion of the secondary center. 

In the following year, Cleland and his coworkers reported further and more emphatic examples of the phenomenon of exaltation of the a-secondary isotope effects in enzymic hydride-transfer reactions. The cases shown in Table 1 for their studies of yeast alcohol dehydrogenase and horse-liver alcohol dehydrogenase would have been expected on traditional grounds to show kinetic isotope effects between 1.00 and 1.13 but in fact values of 1.38 and 1.50 were found. Even more impressively, the oxidation of formate by NAD was expected to exhibit an isotope effect between 1.00 and 1/1.13 = 0.89 - an inverse isotope effect because NAD" was being converted to NADH. The observed value was 1.22, normal rather than inverse. Again the model of coupled motion, with a citation to Kurz and Frieden, was invoked to interpret the findings. 

Thymidine-specific depyrimidination of DNA by this and other Ru(lV) 0x0 complexes, e.g. electrocatalytically by [Ru(0)(py)(bpy)2] Vaq. formate buffer was studied and related to their Ru(IV)/Ru(ll) redox potentiis [664]. Oxidation of formate and of formic acid to CO by stoich. aT-[Ru(0)(py)(bpy)2] Vwater was studied kinetically, and a two-electron hydride transfer mechanism proposed [665]. 

Formate dehydrogenases from many bacteria contain molybdopterin and also often selenium (Table 15-4).664/665 A membrane-bound Mo-containing formate dehydrogenase is produced by E. coli grown anaerobically in the presence of nitrate. Under these circumstances it is coupled to nitrate reductase via an electron-transport chain in the membranes which permits oxidation of formate by nitrate (Eq. 18-26). This enzyme is also a multisubunit protein.665 666 Two other Mo- and Se- containing formate dehydrogenases are produced... 

If possible, the cell should be undivided to minimize the construction cost and also the energy consumption (see goal 1). The application of a controlled reaction at the auxiliary electrode taking place at low potential allows for the use of undivided cells in many cases. For oxidations, the cathodic process at the auxiliary electrode may be a proton reduction under formation of hydrogen. For reductions, the anodic process may be the oxidation of formate or oxalate under production of carbon dioxide [68] or the dissolution of sacrificial anodes [69] (see also Sec. V.B). 

The half reactions for the oxidation of formate, sulfate, and xanthine the reduction of nitrate and the reduction of C02 via the carbamate of methanofuran are listed in Table 3b. The potentials for several relevant redox partners are listed in Table 4. On the basis of the respective E° values for the substrate reactions and their physiological redox partners, it is clear that most (if not all) reactions... 

Figure 23 Possible Se-cys assisted oxidation of formate by the (MPTpG)2Mo(Se-cys)(OH) site of formate dehydrogenase.

The procedure involves precolumn oxidation of formate with formate dehydrogenase which is accompanied by a corresponding reduction of p-nicotinamideadenine dinucleotide (P(NAD)+) to reduced P-nicotinamide dinucleotide (ie P NADH). The latter is quantified by high performance liquid chromatography. See also Table 4.1. 

Formate dehydrogenase (FDH, EC 1.2.1.2) catalyzes the oxidation of formate to carbon dioxide while NAD+ is reduced to NADH. A major advantage is the... 

Administration of diphenylhydantoin leads to decreased activity of methylene tetrahydrofolate reductase and an increased rate of oxidation of formyl tetrahydrofolate (increased oxidation of formate and histidine), with a fall in methylene- and methyl-tetrahydrofolate - the reverse of the effect of the methyl folate trap (Billings, 1984a, 1984b). 

FIGURE 1. Examples of reactions catalyzed by molybdenum containing enzymes. From top to bottom, hydroxylation of xanthine, hydroxylation of acetaldehyde, dehydrogenation of carbon monoxide, transhydroxylation of pyrogallol, oxidation of sulfite, reduction of nitrate, reduction of dimethylsulfoxide, oxidation of formate, reduction of polysulfide and formation of formylmethanofuran. 

As for the reactions catalyzed by members of this third family of molybdenum enzymes, there are several variations from the principal theme of oxygen atom transfer. Formate dehydrogenase from E. coli catalyzes the oxidation of formate to CO2, a reaction that isotope studies have shown does not pass through a bicarbonate intermediate (Khangulov et al., 1998). Instead, it appears likely that C02is formed by direct hydride transfer from substrate to the molybdenum center. Polysulfide reductase is another molybdenum enzyme that catalyzes a non-canonical reaction the... 

Norbomanone is a useful starting material for various bicyclic derivatives of theoretical interest. The present procedure provides a convenient method for its preparation and illustrates a general method for the oxidation of formate esters to ketones. 

About 50% of these species can use formate as substrate. Formate conversion to CH4 (Reaction 2) involves the oxidation of formate to CO2 by formate dehydrogenase, generating reducing equivalents which are subsequently used to reduce CO2 to CH4 ... 

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