Aromatic amine chromophore

Sulfur Bake. The yellow, orange, and brown sulfur dyes belong to this group. The dyes are usually made from aromatic amines, diamines, and their acyl and nuclear alkyl derivatives. These may be used in admixture with nitroanilines and nitrophenols or aminophenols to give the desired shade. The color formed is said to be the result of the formation of the thiazole chromophore, evident in dye structure (1). 

In the application of oxidation dyes, aromatic amines form insoluble polyazine derivatives in the fiber (azine dyes [81]). Synthesis proceeds in several steps in a hydrochloric acid medium by oxidation (e.g., with dichromate). For the chief representative of this group, aniline black, the chromophore consists of dibenzo-pyran rings. Oxidation dyes are rapidly decreasing in importance because aniline and other aromatic amines as well as the bichromate used for oxidation are toxic. The colors produced by aniline black are characterized by a full bluish black shade and excellent fastness. Since they are easily reserved, they are still used occasionally for printing grounds. For individual processes, see [82],... 

Recently, many aromatic ligands derived from amines have been synthesized and the luminescence properties of their lanthanide complexes have been investigated. The ligand which is composed of an aromatic amine as a chromophore and tetra(acetic acid) as a chelation... 

The blue or hypsochromic shift to shorter wavelengths is shown by aromatic amines. On acidifica-tion, the protonated quaternary ammonium group no longer participates in the chromophore so... 

A kinetic method for determination of aromatic amines was proposed, based on measuring the development of azo dyes (134) resulting from coupling a diazonium ion derived from a PAA analyte and the chromophoric substrate 1 -(4-hydroxy-6-methylpyrimidin-2-yl)-3-methylpyrazolin-5-one (133), as shown in equation 22. After a short induction period initial rate kinetics can be measured when the process is quite advanced, absorbance reaches a maximum and starts to recede due to oxidation of the azo dye by excess nitrous acid. Each PAA has to be calibrated for its molar absorption coefficient and reaction rate, for optimal measurement. A tenfold excess of 133 over the analytes ensures a pseudo... 

A shift in A,max to shorter wavelength is called a hypsochromic effect, or blue shift, and usually occurs when compounds with a basic auxochrome ionise and the lone pair is no longer able to interact with the electrons of the chromophore. Hypsochromic effects can also be seen when spectra are run in different solvents or at elevated temperatures. Spectral shifts of this type can be used to identify drugs that contain an aromatic amine functional group, e.g. the local anaesthetic benzocaine (see Figure 7.9). 

As has already been mentioned, the most important chromophore system is that based on the azo group. This group is nearly always introduced into colorants via aromatic amines. Certain aromatic amines which were available (and frequently used) from the beginning of the synthetic dye era were later realised to entail considerable hazards and potential impacts. The acute toxicity of a few of these compounds was identified at a relatively early stage the clinical symptoms that they gave rise to were called anilism. It has also been shown that, for example, benzidine-based azo dyes can be reduced to the free benzidine based diamine by intestinal bacteria-- and also by UV light (see Fig. 10.2). 

A recent LFP, electron spin resonance, and product study on the photodissociation of 7/-(triphenylmethyl)anilines concludes that the primary photochemical event is homolytic cleavage [72]. However, the chromophore in these molecules is the aromatic amine. Triphenylmethyl cations were observed when the excitation wavelength was 248 nm but these were apparently formed by a biphotonic process of electron photoejection from the triphenylmethyl radical. 

An additional type of derivative that is often used for glycan profiling and analysis is the modification of the reducing end with a chromophore, usually achieved by the formation of a Schiff base with an aromatic amine, and subsequent reduction with sodium borohydride to stabilize the initially formed product by its conversion to a saturated amine. This procedure was initially developed for HPLC analysis with ultraviolet detection, but it is also appropriate for MS analysis because the substituted amino group represents a site for charge localization that simplifies the fragmentation pattern and also provides the opportunity to introduce a stable isotope label for quantitative purposes (54). 

EKC methodologies for aromatic amines are based on electrolytes containing SDS, " mixtures of SDS and nonionic surfactants, and bile salts as well as modifiers (tetraalkyl-ammonium salts, urea, " organic solvents, " - " - and CDs ). Combinations of anionic soluble polymers or crown ether and CDs have also been reported. Despite being chromophoric, alternative detectors for aromatic amines have been proposed (CE-ESI-MS, electrochemical, and fluorescence detection). 

Because azo dyes, as amaranth, are the most widely used food colorants and are water soluble, they were bonded to selected polymers via a sulfonamide linkage. However, the azo linkages in the dyes themselves were unstable to intestinal microbial action and do not meet the requirements of biological stability because they are cleaved in the gut to yield absorbable aromatic amines. Hence a variety range of chromophore classes have been reported to be incorporated into polymers. For the anthraquinone class of chromophores, the basic water insolubility was changed by converting a portion of the backbone to sulfonic acids that impart anionic solubilizing functions. However, this meant that fewer chromophores could be attached and less intense colors would result. 

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