Methylene blue reduction

Kinetics of Methylene Blue Reduction by Ascorbic Acid 233... 

ScHRAuzER GN and Rhead WJ (1971) Interpretation of the methylene blue reduction test of human plasma and the possible cancer preventing effect of selenium. Experientia 27 1069—1071. 

Several workers (28-29) reported an increase in the methylene blue reduction time when 0.05-0.5 lU Penicillin were present per milliliter of milk. Similarly, Manokidis et al. (30) noted that Penicillin and Oxytetracycline were responsible for a false positive phosphatase test in pasteurized or partially pasteurized milk while Streptomycin, Erythromycin and Neomycin inhibited the phosphatase test to some extent in partially pasteurized milk, but not in raw milk. Although raw milk containing antibiotic residues was never mistakenly identified as pasteurized, these authors suggested that as a "precaution" antibiotic assays be run in conjunction with the phosphatase test. 

Methylene blue reduction test This test is used to estimate the keeping quality of pasteurized milk. In principle, a measured quantity of methylene blue solution is added to 10 ml of milk in a tube. This is mixed by slow inversion, then the tube is sealed and incubated in a water bath at 37°C. A satisfactory test is given when there is no decoloration in 30 min. 

The methylene blue and resazurin reduction methods indirectly measure bacterial densities in milk and cream in terms of the time interval required, after starting incubation, for a dye—milk mixture to change color (methylene blue, from blue to white resazurin, from blue through purple and mauve to... 

Thus, the presence of a thiamine ring in Cl Sulfur Blue 9 was conclusively proved. The thiamine ring is the fundamental chromophore that accounts for the high color value of both the sulfur dye and Methylene Blue [61-73-4] including their abiUty to form pale yeUow leuco forms on reduction. Methylene Violet (15) is obtained from Methylene Blue (16) by hydrolysis in boiling alkah. 

This enzyme is of wide occurrence in bacteria where it is concerned with the reduction of nitrate and CO2 as well as sulphur. Methods for its estimation depend on measuring some activity of hydrogenase by (a) dye reduction (benzyl viologen or methylene blue), (b) isotopic exchange and (c) evolution of molecular hydrogen. Interpretation of quantitative results is difficult due to the complex relationship between the enzyme cell structure and the particular method selected. ... 

Fig. 3.12 The dependence on pH of the oxidation-reduction potential for c0x = cRcd (1) 6-dibromphenol indophenol, (2) Lauth s violet, (3) methylene blue, (4) ferricytochrome c/ferrocytochrome c, (5) indigo-carmine... 

J. Ye and R.P. Baldwin, Catalytic reduction of myoglobin and haemoglobin at chemically modified electrodes containing methylene blue. Anal. Chem. 60, 2263—2268 (1988). 

Pt-catalysed reduction of methylene blue and 10-methyl-5-deazoisoalloxazine -3-propanesulfonic acid Polymerized surfactant vesicles. Catalytic efficiencies high in these systems Kurihara and Fendler, 1983... 

Where the reduction potentials of two analytes are sufficiently different a mixture may be analysed. Titanium(III), = 0-lOV may be titrated with cerium(IV) in the presence of iron(II), =0.77 V usjng methylene blue as indicator. Subsequently the total, iron plus titanium, may be determined using ferroin as indicator. The determination of iron is illustrative of some practical problems which are encountered in direct titration procedures. 

The stimulating action of methylene blue and other reducible dyes on MHb reduction has long been established. However, this function is not constant, and may even be absent (H22, H23). In beef erythrocytes, and in MHbR prepared from yeast, no stimulating effect of methylene blue could be observed (A6, H22). When beef blood enzyme was boiled, a substance was obtained which activates the human MHbR without... 

These findings lead to (he conclusion that the reduction of MHb by its reductase requires a natural cofactor, which is abolished during the purification procedure and can be replaced by methylene blue (G5, H22, H23, K8, K14). Since methylene blue and the other effective dyes are redox intermediates, it is obvious that the postulated cofactor interacts in the electron transport sequence of the MHbR reaction (H23). This is confirmed by the finding that oxygen and cytochrome c serve as well as terminal electron acceptor as does MHb (H22, H23, K14). Nevertheless, it had been possible to separate a cytochrome c reductase from MHbR in yeast extracts (A6). 

It was shown that trivalent iron was able to provide the electronic linkage and to produce a 4-fold stimulation of MHbR activity in the absence of any dye (H23). Furthermore, it has been found that the addition of methylene blue to crude enzyme preparations was necessary for reducing MHb but not for using oxygen as a terminal electron acceptor (H23). The enhancement of MHb reduction in methemoglobinemia by ascorbic acid (e.g., B14) also indicates the implication of reduction-oxidation mechanisms in MHbR activity. 

The differences between the enzyme preparations with respect to the requirement of added methylene blue are in good agreement with the finding of varying amounts of MHb in the normal blood of several species (H7) and variable, but species-linked abilities to reduce MHb (K9, Kll, S17). Furthermore, an age variation in MHb reduction of rabbit erythrocytes has been observed (S17). 

Finally, the methemoglobin reduction test may be briefly mentioned. The test has been developed for the detection of primaquine sensitivity and depends on the function of the G-6-PDH system. Its principle consists in the oxidation of Hb to MHb by sodium nitrite and the subsequent enzymatic reduction to Hb in presence of methylene blue. The activity of this system can be followed easily by observation of alterations in color after an incubation period or by means of MHb determinations before and after this period (B18). 

Methylene blue and other reducible dyes were shown to enhance the activity of NADPHa-linked MHbR (K8, K9). This is confirmed by the finding that intravenous injections of methylene blue in methemo-globinemic patients result in a striking decrease of MHb levels (e.g., B14, K9, K10). This seems to be paradoxical, since methylene blue is capable of reacting with Hb with formation of MHb, but the dye reacts much more effectively as an artificial electron carrier in the NADPH2-MHbR Systran (B14). It has been stated (K10) that methemoglobin reduction is associated with the formation of pyruvate in equivalent amounts, but that in reactions accelerated by reducible dyes no correlation between pyruvate formation and MHb reduction could be found. 

A further spectrophotometric method [3, 4] for water soluble boron in soil, boron is extracted from soil with boiling water. Borate in the extract is converted to fluoroborate by the action of orthophosphoric acid and sodium fluoride. The concentration of fluoroborate is measured spectrophotometrically as the blue complex formed with methylene blue and which is extracted into 1, 2-dichloroethane. Nitrates and nitrites interfere they are removed by reduction with zinc powder and orthophosphoric acid. 

Fresh cows milk contains an enzyme which very greatly accelerates the reduction by aldehyde of methylene blue to its leuco-compound. This reduction does not show itself if the enzyme is absent. Two H-... 

Xanthine oxidase (XO) was the first enzyme studied from the family of enzymes now known as the molybdenum hydroxylases (HiUe 1999). XO, which catalyzes the hydroxylation of xanthine to uric acid is abundant in cow s milk and contains several cofactors, including FAD, two Fe-S centers, and a molybdenum cofactor, all of which are required for activity (Massey and Harris 1997). Purified XO has been shown to use xanthine, hypoxan-thine, and several aldehydes as substrates in the reduction of methylene blue (Booth 1938), used as an electron acceptor. Early studies also noted that cyanide was inhibitory but could only inactivate XO during preincubation, not during the reaction with xanthine (Dixon 1927). The target of cyanide inactivation was identified to be a labile sulfur atom, termed the cyanolyzable sulfur (Wahl and Rajagopalan 1982), which is also required for enzyme activity. 

Numerous experimental systems verified the theory of surface electrode reactions. Reductions of methylene blue [92], azobenzene [79, 82] alizarine red S [93], probucol [94], molybdenum(V)-fulvic acid complex [95], molybdeniun(VI)-1,10 phenanthroline-fulvic acid complex [96], indigo [97], and reduction of vana-dium(V) [98] at a mercury electrode are some of the examples for surface electrode... 

There are numerous analytically oriented studies developed upon adsorption coupled electrode reactions (2.144) and (2.146), which are summarized in the Sect. 3.1. For the purpose of verification of the theory, electrode mechanisms including reductions of a series of metallic ions in the presence of anion-induced adsorption [110], as well as electrode mechanisms at a mercury electrode of methylene blue [92], azobenzene [79], midazolam [115], berberine [111], jatrorubine [121], Cn(lI)-sulfoxine and ferron complexes [122], Cd(II)- and Cu(II)-8-hydoxy-qninoline... 

The theory for the reaction of an adsorbed redox couple (2.146) has been exemplified by experiments with methylene blue [92], and azobenzene [79], Both redox couples, methylene blue/leucomethylene, and azobenzene/hydrazobenzene adsorb strongly on the mercury electrode surface. The reduction of methlylene blue involves a very fast two-step redox reaction with a standard rate constants of 3000 s and 6000 s for the first and second step, respectively. Thus, for / < 50 Hz, the kinetic parameter for the first electron transfer is log(m) > 1.8, implying that the reaction appears reversible. Therefore, regardless of the adsorptive accumulation, the net response of methylene blue is a small peak, the peak current of which depends linearly on /J. Increasing the frequency above 50 Hz, the electrochemical... 

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