Meldola blue

FIGURE 6-6 Chemical stmcture of some common redox mediators (a) dimethyl ferrocene (b) tetrathiafidvalene (c) tetracyanoquinodimethane (cl) Meldola Blue. 

NADH. Immobilized redox mediators, such as the phenoxazine Meldola Blue or phenothiazine compoimds, have been particularly useful for this purpose (20) (see also Figure 4-12). Such mediation should be useful for many other dehydrogenase-based biosensors. High sensitivity and speed are indicated from the flow-injection response of Figure 3-21. The challenges of NADH detection and the development of dehydrogenase biosensors have been reviewed (21). Alcohol biosensing can also be accomplished in the presence of alcohol oxidase, based on measurements of the liberated peroxide product. 

Macrocyclic compounds, 155 Magnesium, 155 Mass measurements, 52 Mass transport, 4, 5 Mechanism, 33, 36, 40 Mediator, 177, 178 Meldola Blue, 121, 179... 

An optode based on Meldola Blue immobilized in tetramethyl orthosUicate gel can be used to evaluate the concentration of H2O2 in the pH range from 5 to 12, in the dynamic... 

S. C. Litescu, L. Rotariu and C. Bala, Immobilisation of lactate dehydrogenase on electro-polymerised Meldola blue matrix, Rev. Chim., 56 (2005) 57-60. 

Oxidation of oxalic acid with dimethyl-V,V-dichlorohydantoin and dichloroisocya-nuric acid is of first order with respect to the oxidant. The order with respect to the reductant is fractional. The reactions are catalysed by Mn(II). Suitable mechanisms are proposed.129 A mechanism involving synchronous oxidative decarboxylation has been suggested for the oxidation of a-amino acids with l,3-dichloro-5,5-dimethylhydantoin.130 Kinetic parameters have been determined and a mechanism has been proposed for the oxidation of thiadiazole and oxadiazole with trichloroiso-cyanuric acid.131 Oxidation of two phenoxazine dyes, Nile Blue and Meldola Blue, with acidic chlorite and hypochlorous acid is of first order with respect to each of the reductant and chlorite anion. The rate constants and activation parameters for the oxidation have been determined.132... 

It should be mentioned in passing that the first oxazine to attain technical importance was Meldola blue (naphthol blue, Bengal blue), prepared from nitrosodimethylaniline hydrochloride and naphthol. It is a very fast dye but does not give pure shades. Furthermore, its dust irritates the mucuous membranes so severely that many persons cannot work with it. Despite these disadvantages, however, Meldola blue is still rather widely used. 

Fig. 2. Structural formulae of Meldola blue [top]., Nile blue (middle) and brilliant crysyl blue (bottom). All three compounds have been used in conjunction with chemically modified electrodes. (After Persson (89).)...

Note A, tetrathiafulalene (TTF) B, tecracyanoquinodimethane C, ferricinium D, N-methylphenazinium jNMP ) E, Meldola blue. 

Meldola Blue-Polysiloxane Graphite Dehydrogenase NADH 0.00 mV vs. SCE [151]... 

Modified electrodes for this analytical purpose have mostly been formed by electrode adsorption of the mediator systems on the electrode surface or by electropolymerization [24,116]. Recently, for example, NAD(P)H oxidations have been performed on platinum or gold electrodes modified with a monolayer of pyrroloquinoline quinone (PQQ) [117] or on poly(methylene blue)-modified electrodes with different dehydrogenases entrapped in a Nafion film for the amperometric detection of glucose, lactate, malate, or ethanol [118]. In another approach, carbon paste electrodes doped with methylene green or meldola blue together with diaphorase were used for the NADH oxidation [119]. A poly(3-methylthio-phene) conducting polymer electrode was efficient for the oxidation of NADH [120]. By electropolymerization of poly(aniline) in the presence of poly(vinylsulfonate) counterions. 

Basic dyes which contain the oxazine group of which Meldola Blue (5) was the first to be prepared ... 

Magenl 6, 593 Malachite Green, 368 Mauveine, 370 Meldola Blue, 369 Merantine Blue, 379 Methyl Green, 368, 369 Methyl Violet, 7 Methylene Blue, 369, 379 Methylene Violet, 370... 

Fig. 1. Chemical drawings of the most-commonly used intercalators in the development of electrochemical DNA biosensors (1) Cobalt(ll)-Tris-(1,10-phenanthroline), (2) Ruthenium(ll)-Tris-(1,10-bipyridine), (3) Methylene blue, (4) Meldola blue, (5) Ethidium bromide.

Coupling between a biologically catalyzed reaction and an electrochemical reaction, referred to as bioelectrocatalysis, is the constructional principle for enzyme-based electrochemical biosensors. This means that the flow of electrons from a donor through the enzyme to an acceptor must reach the electrode in order for the corresponding current to be detected. In case a direct electron transfer between the active site of an enzjane and an electrode is not possible, a small molecular redox active species, e.g. hydrophobic ferrocene, meldola blue and menadione as well as hydrophilic ferricyanide, can be used as an electron transfer mediator. This means that the electrons from the active site of the enzyme reduce the mediator molecule, which, in turn, can diffuse to the electrode, where it donates the electrons upon oxidation. When these mediator molecules are employed for coupling of an enzymatic redox reaction to an electrode at a constant potential, the resulting application can be referred to as mediated amperometry or mediated bioelectrocatalysis. 

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