4- Hydroxy azobenzene

Trinitro-3-hydroxy-azobenzene, H0.C6H2(N02)2N N.C6H4.N02 red ndls (from acet ac + w), mp 179° was prepd by heating benzoquinone-( 1,4)-oxime-4,6-dinitro-3-hy droxy-phenylhydrazone with nitric acid (d 1.39) acetic acid (Refs 1 3). No expl props are reported... 

Spectral Transparence Starting from 230 nm 4-Hydroxy-Azobenzene Presence of a Thermally and Photochemically Isomerizable Azo Group Trans-Cis Photoisomerization Photochromism ... 

Prepd by reacting 5 -chloro-2,4,-dinitro-4-hydroxy-azobenzene hydrazine hydrate in hot alcohol. Decomposes 178—80°... 

Nitro-2-hydroxy-azobenzene, H0.C6H3(N02)N N.C6H5, orn-red pltlts (from dil acetic acid), mp 150—51° (Ref 1) 3-Nitro-4-hydroxy-azobenzene, lt-yel pltlts (from benz), mp 128° (Ref 2)... 

Nitro-4-hydroxy-azobenzene, H0.C6H4.N N.C6H4.N02 dk-red ndls (from dil MeOH), mp 162-63° (Ref 3)... 

Nitro-4-hydroxy-azobenzene, crysts (from ale or xylol), mp 219-219.5° (Ref 5)... 

Dinitro-4-hydroxy-azobenzene, H0.C6H4J N.C6H3(>I02)2 crysts (from MeOH), mp 185-86° (Ref 2)... 

Trini tro-4-hydroxy-azobenzene, H0.C6H4.N N.C6H2(N02)3 dk-red, blue colored ndls (from dd acetic acid), mp 194—... 

NOTE No higher nitrated derivs of Hydroxy-azobenzene were found in the literature... 

H0.C6H4.N N.C6H2(N02)2NH.NH2 mw 318.25, N 26.41% red-brown crystals si sol in boiling ale sol in boiling nitro-benzene. Prepd by reacting 5,-chloro-2,4,-dinitro-4-hydroxy-azobenzene hydrazine hydrate in hot alcohol. Decomposes 178—80°... 

Sodium - 3 - chloromercuri - 4 - hydroxy - azobenzene - 4 -sulphonate is formed by diazotising sulphanilic acid and adding the diazotised solution to a cold solution of o-chloromercuriphenol in sodium hydroxide. The coupling requires about four hours for completion. The mixture is then acidified with acetic acid, when the sodium salt of the azo compound separates as a heavy, orange-yellow precipitate. The product is recrystallised from hot water, air-dried, and then dried in a vacuum dryer at 50" C. Since the C -Ilg linkage is easily split it is impossible to obtain the free acid. The reaction is represented as follows —-... 

ITC). Unfortunately, these data are still sparse and are difficult to interpret.27 Existing thermodynamic data indicate that there is always a substantial compensation between enthalpic and entropic contributions.28-30 The data also show that the binding may be enthalpy-driven (e.g., streptatividin-biotin, AG = — 76.5kJ/mol, AH = 134kJ/mol) or entropy-driven (e.g., streptavi-din-2-(4 -hydroxy-azobenzene)benzoic acid (HABA), AG = 22.0kJ/mol,... 

Fig. 5 MALDI MS spectra of Au25(SCH2CH2Ph)ig using different matrices. The matrices are universal maldi matrix (UMM -1 1 mixture of dihydroxybenzoic acid and a-cyano-4-hydroxycinnamic acid), 4 -hydroxy-azobenzene-2-carboxylic acid (HABA), sinapinic acid (SA) and DCTB. Their structures are shown above the traces. ACS Publishing. Reproduced with permission. ...

Simple chemical laboratory procedures for biotin are restricted to pure materials as described in pharmacopeia monographs using alkaline titration. Similarly, spectral methods for determining native biotin are unknown in most samples except for highly purified materials as it has no useful absorption above 210 nm. To obtain suitable sensitivity and selectivity, biotin must first be derivatized. For example, the disruption of a / -hydroxy-azobenzene-2 -carboxylic acid (HABA) avidin complex by biotin, which binds to avidin with higher affinity, can be followed titrimetrically or spectroscopically to give useful determinations of biotin. 

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