Leucomethylene blue

Pharmacokinetics Erratic absorpf ion. Protein binding unknown. Metabolized in tissues to leucomethylene blue. Excreted unchanged in urine and feces. Unknown if removed by hemodialysis. Half-iife Unknown. 

Residues of methylene blue in edible animal tissues are of public health concern because tliis dye and its metabolites are mutagenic (74). Metabolism studies in cattle have indicated that methylene blue can be eliminated in urine partly unchanged, partly metabolized to leucomethylene blue, or demethylated to N-methyl homologues of thionin, the completely demethylated metabolite of methylene blue, or reduced in vivo and subsequently eliminated in its leuco-form or in one or more chromogenic substances (75). 

Electrochemical indicator methods are based on the application of redox probe that undergoes oxidation and reduction transition due to electron transfer from electrode surface to a probe. In 2005, several studies that used methylene blue (MB) as an electrochemical indicator were published. MB is positively charged low-molecular-weight compound that can be reduced by two electrons to a leucomethylene blue (LB). The reduction process can be effectively monitored, e.g., by differential pulse voltammetry or coulometry. In presence of redox probe Fe(CN)6, the LB is oxidized to MB and the system is regenerated [44,45]. In papers by Hianik et al. [31,46], MB was used as the indicator of detection of interaction of human thrombin with DNA aptamer. The method of detection is schematically shown in Fig. 33.3B. MB binds both to DNA and to the protein. For charge transfer from electrode to MB, i.e., for MB reduction, it is important that MB should be close to the electrode surface. Therefore, the charge transfer from the electrode... 

Extraction (1,2-dichloroethane) using leucomethylene blue was applied to determine... 

HCOO + Methylene Blue + H O ----------HCOp + leucoMethylene Blue... 

R Sevick and B. Dunford [7nf. J. Chem. Kinet., 27, 925-928 (1995)] indicated that at 25°C, k = 4.21 M"Vs and K = 3.53 X 10 M at the pH of the buffered solution (9.0) which will result from blending the two hquid streams. Furthermore, the level of dissolved oxygen in the blended stream is sufficient to ensure rapid reoxidation of the product leucomethylene blue (MBH) back to MB" " so that the concentration of MBT in this stream will be essentially invariant (i.e., the MB" " can be regarded as a catalyst for the oxidation of NADH by dissolved oxygen). This blended stream is available at a rate of 6 L/min. 

Chipault et d. (1945) determined the tocopherol content of mixtures of a- and 7-tocopherol by reducing the orthoquinone (a- and 7-tocopherol give the same orthoquinone) with leucomethylene blue. This colorimetric determination is specific and sensitive. 

FefCN] ] " by methylene blue (MB] at a DNA-modified electrode. LB+ is leucomethylene blue, the product of the electrochemical reduction, (b] Cyclic voltammetry at a gold electrode modified with DNA of 2 mM [Fe(CN]6] (curve 1], 2 p.M MB (curve 2], and 2 mM [FefCNJe] and 2 p.M MB (curve 3]. Reproduced from S. 0. Kelly, E. M. Boon, J. K. Barton, N. M. Jackson, and M. G. Hill, Single-base mismatch detection based on charge transduction through DNA, Nucleic Acids Research, 1999, 27(24], 4830-4837, by permission of Oxford University Press. 

Hydrogen sulphide and dimethyl-p-phenylenediamine form a sulphurous intermediate compound (intermediate stage), which changes into leucomethylene blue. The leucomethylene blue is oxidized by iron (III) ions to methylene blue. The methylene blue is measured photometrically at 670 nm. 

Wang and Yuan [13] applied leucomethylene blue reagent for the determination of chlorine dioxide disinfectant residues in drinking water and wastewater samples. In their method, the sample is mixed with 3 cm reagent solution (20 mg/dm ), filled up to 20 cm, and extracted with 1,2-dichloroethane at pH 1.3. After a reaction time of 10 min the absorbance is measured at 658 nm. The interfering chlorine and h5q30chlorite ions can be masked by adding oxalic acid. 

MB were mercaptoethanol (RSH) and dithioerythritol (R(SH)2) which were oxidized to the corresponding disulfides (RSSR and RS2, respectively) with concurrent reduction of MB to leucomethylene blue (LMB). 

To carry out a similar reaction, leucomethylene blue or the more stable benzoyl-leucomethylene blue can also be used. The first reagent is oxidized by peroxides to a blue dye (47) and the second to the cation of methylene blue. 

Leucomethylene blue is regenerated again from the deprotonated form of methylene blue (MB ) by electrochemical reduction ... 

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