4-Dimethylaminoazobenzene fluorescence

Thus, fluorescence may occur in aminoazobenzene-type compounds, but it is not prominent. Low-temperature, glassy solvents or other methods of external rigidification, such as adsorption to a surface at liquid nitrogen temperature, are necessary. For 4-dimethylaminoazobenzene, fluorescence in hydrocarbon solution at 77 K is on the red side of the n —> 7i band and assigned to n<—7t emission. With the high-power lasers available today, one would anticipate emission of many molecules of this class. 

Since BAs occurring in food do not exhibit satisfactory absorbance or fluorescence in the visible or ultraviolet range, chemical derivatization, either pre- (35-37) or postcolumn (38), is usually used for their detection in HPLC. The most frequently employed reagents for precolumn derivatization are fluorescamine, aminoquinolyl-lV-hydroxysuccinimidyl carbamate (AQC) (39, 40), 9-fluorenylmethyl chloroformate (FMOC) (41-43), 4-dimethylaminoazobenzene-4 -sul-fonyl chloride (dabsylchloride, DBS) (44), N-acetylcysteine (NAC) (45,46), and 5-dimethyl-amino-1-naphthalene-1-sulfonyl chloride (dansylchloride, DNS) (47,48), phthalaldehyde (PA), and orf/to-phthaldialdehyde (OPA) (49-51), together with thiols such as 3-mercaptopropionic acid (MPA) (37) and 2-mercaptoethanol (ME) (35,49). 

Acetoxymercuri-4 dimethylaminoazobenzene yields brick-red crystals having a violet reflex, M.pt. 215 C. Witli sulphuric acid it forms reddisli brown solutions having a green fluorescence, and with nitric and hydrochloric acids sparingly soluble salts are formed. 

Both dye solubilization and fluorescence probe methods have been used to study protein/ surfactant interaction. For example, data of Steinhardt et al. (137), who studied the solubilization of dimethylaminoazobenzene in ovalbumin-SDS mixtures, are shown in Figure 33. Solubilization occurs at concentrations of SDS well below the c.m.c., indicating that in the presence of ovalbumin the formation of nonpolar clusters is highly favorable. Unlike... 

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