Chromogen, chromophore

Figure 2.3 Ninhydrin Test. Ninhydrin combines with a-iV-primary amine functional groups to form primary amine product that combines with a second molecule of ninhydrin to generate a chromogenic chromophore.

Theoretically, the dye or chromogen can be any colored species. Of course, requirements for fastness, solubiUty, tinctorial value, ecology, and economy must be met. Most commonly used chromophores parallel those of other dye classes. Azo dyes (qv) represent the largest number with anthraquiaone and phthalocyanine making up most of the difference. Metallized azo and formazan dyes are important and have gained ia importance as a chromophore for blue dyes duriag receat years (6) (see Dyes and dye intermediates). 

Chemical classification is based on chromogen. For example, nitro dyes have the chromophore -NOj. The Color Index (C.I.), published by the Society of Dyers... 

The colorimetric methods depend on a chemical reaction or interaction between the protein and the colorimetric reagent. The resulting generation of a chro-mophore, whose intensity is protein-concentration dependent, can be quantified using a spectrophotometer. Beer s Law is employed to derive the protein concentration from a standard curve of absorbances. Direct interaction of the protein with a chromogenic molecule (dye) or protein-mediated oxidation of the reporter molecule generates a new chromophore that can be readily measured in the presence of excess reagent dye. 

The assay involves a chromogenic tag such as pNA linked to a specific peptide corresponding to the cleavage site of the respective caspase. Proteolysis of this peptide releases the chromogenic tag, thereby increasing the chromophore intensity. 

Enzymic hydrolysis (25-40°C) at the heterosidic bond of the chromogenic substrates was followed either continuously (via formation of 2 -chloro,4 -nitrophenol) at pH 5.5 (O.D. 405 nm) or discontinuously (4-methylumbel-liferone fluorescence at pH 10, emission at A > 435, excitation at A366 nm). Reaction rates were calculated from the linear increase of O.D. (em = 9000 M-1cm-1) or fluorescence (standardization with 4-methylumbelliferone) versus time. Alternatively, an HPLC method was used to follow the formation of chromophoric reaction products, phenols and glycosides (1). Concentrations were calculated from peak heights after appropriate standardization. 

These chromophores have declined significantly in importance as textile dyes bnt have remained of interest becanse of their fluorescent behaviour, as discussed in Chapter 3, section 3.5.1.5. One exception is the triphenodioxazine ring system, which is used to produce valuable blue dyes in the Direct (2.19) and Reactive dye classes (2.20) as well as pigments (see section 2.4.1.7). The dyes from this chromogen have a very high molar absorption coefficient (ca. 80 000) versus typical anthraquinone dyes (ca. 15 000) and have therefore replaced some of the dyes from this latter chromogen in the reactive dyeing of cotton. ... 

Chromogen is the coloured molecular structure (often used synonymously with the term chromophore). 

Chromophore - the unsaturated building blocks of colour, i.e. -N=N-, carbonyl and nitro groups etc. (see also chromogen). 

Chromophores (or oxochromes) are small groups of atoms responsible for characteristic absorptions. By extension, the chromophore in a molecule corresponds to the site responsible for the electronic transition. A chromogene is a species formed by a skeleton on which many chromophores can be found. For a series of molecules containing the same chromophore, the position and intensity of the absorption bands are constant (Table 11.1). When a molecule contains several isolated chromophores separated by at least two single bonds, the overlapping of individual effects is observed. If the chromophores are adjacent to one another, a different situation results. 

Capacity factor, 14 Capillary column, 4, 26 Carbowax, 33 Carrier gas, 23 CEC, 119 Cell constant, 70 Channeltron, 314 Chemical ionisation, 308 Chemical quenching, 224 Chemical shift, 138 Chemical vaporisation, 262 Chemiluminescence, 231 Chopper, 203 Chromatogram, 6 Chromogene, 194 Chromophore, 194 Cl, 308 CID, 200 Cliff-Lorimer, 248 Coefficient of variation, 387 Column (chromatographic), 28 Column 530 , 30 ... 

The study indicated that the ground state of the molecule should be regarded as a resonance hybrid of (1) and (118) and that the basic chromogen is the H- chromophore... 

The question of the contribution of the benzene rings to the indigo chromogen led to a search for the basic chromophore. Consecutively removing parts of the mesomeric system leaves a cross-conjugated structure 7 that, as the basic chromophore, still exhibits the typical deep color and redox properties of indigo. 

These hosts include simple anion sensor systems containing urea, thiourea, amine, amide, alcohol, and pyrrole groups linked to chromophores. Chro-mophores used in this type of chromogenic anion sensors are mainly organic dyes such as azobenzene, nitrobenzene, indoaniline, and anthraquinone or... 

Besides the covalent attachment of the chromophore to the receptor units or displacement of a chromogenic guest, one can employ the advantages of the selective reactivity between a particular anion and chromogenic hosts, which will display dramatic color changes. There have been at least nine examples of these chromoreactands published recently. 

Since the time of Wald s demonstration that rhodopsin, the conceptual chromophore of vision relied upon retinol as a chromogen and Hubbard s contemporary proposal that photodetection involved an isomerism of the chromophore, the conventional wisdom has adopted that position. To support these proposals, Collins proposed that a Shiff-base was... 

---