2- -1,8 -dihydroxynaphthalene-3 , 6-disulfonic acid

Unique methods based on new principles have been developed within the past 10 years. Threonine (27,28,249) is oxidized by lead tetraacetate or periodic acid to acetaldehyde, which is determined by photometric analysis of its p-hydroxydiphenyl complex or iodometric titration of its combined bisulfite. Serine is oxidized similarly to formaldehyde, which is determined gravimetrically (207) as its dimedon (5,5-dimethyldihydro-resorcinol) derivative or photometric analysis (31) of the complex formed with Eegriwe s reagent (l,8-dihydroxynaphthalene-3,5-disulfonic acid). It appears that the data obtained for threonine and serine in various proteins by these oxidation procedures are reasonably accurate. [Block and Bolling (26) have given data on the threonine and serine content of various proteins. ]... 

The rate constants in Figure 5-3 were measured by injecting the solution of the (E)-diazoate into a buffer solution that also contained a highly reactive coupling component (2-naphthol-3,6-disulfonic acid, except at pH values below 2.5, where l,8-dihydroxynaphthalene-3,6-disulfonic acid was used instead). The diazonium ion formed reacts rapidly with these naphthols, and the concentration of the corresponding azo compounds was determined spectrophotometrically. 

Technical Observations. The dyes described above have largely replaced the analogous dyes from chromotropic acid (l,8-dihydroxynaphthalene-3,6-disulfonic acid). They are cheaper and more stable to light. 

Dihydroxynaphthalenemono- and disulfonic acids couple so rapidly, even the second time, that the coupling is carried out in acetic acid solution containing sodium acetate, using diazotized p-aminoacetanilide. With many of the acids, the coupling requires several hours, as, for example, with chromotropic acid (l,8-dihydroxynaphthalene-3,6-di-sulfonic acid). In this case, also, the dye is highly soluble and separates slowly from the unreacted chromotropic acid so that considerable care must be exercised. 

The reaction of di- and polysulfonic acids can usually be carried out so that the replacement of the sulfo groups by hydroxyls takes place stepwise (partial alkali fusion). Thus, phenol-m-sulfonic acid is obtained from benzene-m-disulfonic acid under mild conditions, while resorcinol is formed under more vigorous conditions (see page 144) similarly, naphthalene-l,5-disulfonie acid yields, first, l-naphthol-5-sulfonic acid, then l,5 dihydroxynaphthalene, both valuable azo dye... 

Dihydroxynaphthalene-3,6-disulfonic acid (chromotropic acid) (Other values on Vol.3, p.235)... 

Bis(carboxymethyl)aminomethyl-l,8-dihydroxynaphthalene-3,6- 70EM disulfonic acid (C H O S )... 

The most commonly employed broad-spectrum PCR reagents are 4-(2-pyridylazo)resorcinol (PAR) and 2,7-bis(2-arsonophenylazo)-l,8-dihydroxynaphthalene-3,6-disulfonic acid (arsenazo III). The structures of these compounds are shown in Fig. 7. In general use, PAR is the preferred reagent for the PCR detection of transition metal ions, whereas arsenazo 111 is preferred for lanthanide ions. 

Phenyl-2,3-dimethyl-4-dimethylamino-l,2-diazol-5-one (pyramidone) 3,6-Bis(4-antipyrylazo)-4,5-dihydroxynaphthalene-2,7-disulfonic acid 2. 1,3-Diazoles ... 

The dyestuffs 3-( -nitrophenylazo)-4 -hydrox5maphthalene-l-sulfonic acid, l-(/)-nitrophenylazo)-2-hydroxy-3,6-disulfonic acid and 3-( -nitrophenyl-azo)-l,8-dihydroxynaphthalene-3,6-disulfonic acid (Chromotrope 2B, C.I. Acid Red 176) can be used as reagents for Mg. With these reagents, a spot test on filter paper is possible Idn. Limit 0.1 y Mg),... 

Nitroso-4-sulfo-l-naphthalenylazo)- N-00163 4,5-dihydroxynaphthalene-2,7-disulfonic acid... 

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