Visible chromophores

The purple acid phosphatases can occur in two diferric forms—one as the tightly bound phosphate complex (characterized for the bovine and porcine enzymes) (45, 171, 203) and the other derived from peroxide or ferricyanide oxidation of the reduced enzyme (thus far accessible for only the porcine enzyme) (206). These oxidized forms are catalytically inactive. They are EPR silent because of antiferromagnetic coupling of the two Fe(IIl) ions and exhibit visible absorption maxima near 550-570 nm associated with the tyrosinate-to-Fe(III) charge-transfer transition. The unchanging value of the molar extinction coefficient between the oxidized and reduced enzymes indicates that the redox-active iron does not contribute to the visible chromophore and that tyrosine is coordinated only to the iron that remains ferric in agreement with the NMR spectrum of Uf, (45). 

A. In vitro Metallothionein/Na AuTM Reactions. Highly purified equine renal MT was allowed—to react with various amounts of Na2AuTM and then fractionated on Sephadex 6-50 to separate the protefn-bound and free metals. Because the protein does not have any UV-visible chromophores independent of the metal mercaptide linkages, the protein was "quantitated" by its cadmium content (measured by atomic absorption spectroscopy) and results are reported for various Au/Cd ratios of the reactants. Aliquots of a reaction mixture having a 10/1 Au/Cd ratio were fractionated after 2, 24 and 48 hours incubation time to insure complete reaction. 

Prior to the introduction of commercially available tuneable UV lasers, the major constraint for exploitation of RRS in industry has been the restricted number of systems which exhibited visible chromophores and could be conveniently probed. Clearly a more widespread use of visible resonance Raman spectroscopy would be possible except that in practice (i) only a few chromophores absorb in the visible region and (ii) fluorescence interference is nearly ubiquitous in real life samples. 

Segall J, Zare R N, Dubai H R, Lewerenz M and Quack M 1987 Tridiagonal Fermi resonance structure in the vibrational spectrum of the CM chromophore in CHFg. II. Visible spectra J. Chem. Phys. 86 634-46... 

Chromophore (Section 13 21) The structural unit of a mole cule principally responsible for absorption of radiation of a particular frequency a term usually applied to ultraviolet visible spectroscopy... 

Table 7.9 Electronic Absorption Bands for Representative Chromophores Table 7.10 Ultraviolet Cutoffs of Spectrograde Solvents Table 7.11 Absorption Wavelength of Dienes Table 7.12 Absorption Wavelength of Enones and Dienones Table 7.13 Solvent Correction for Ultraviolet-Visible Spectroscopy Table 7.14 Primary Bands of Substituted Benzene and Heteroaromatics Table 7.15 Wavelength Calculation of the Principal Band of Substituted Benzene Derivatives...

The concept of a chromophore is analogous to that of a group vibration, discussed in Section 6.2.1. Just as the wavenumber of a group vibration is treated as transferable from one molecule to another so is the wavenumber, or wavelength, at which an electronic transition occurs in a particular group. Such a group is called a chromophore since it results in a characteristic colour of the compound due to absorption of visible or, broadening the use of the word colour , ultraviolet radiation. 

Hydantoin derivatives show weak absorption in the uv-visible region, unless a part of the molecule other than the imidazohdinedione ring behaves as a chromophore (13) however, piC values have been determined by spectrophotometry in favorable cases (14). Absorption of uvby thiohydantoins is more intense, and the two bands observed have been attributed to n — tt and n — tr transitions of the thiocarbonyl group (15,16). Several piC values of thiohydantoins have been determined by uv-visible spectrophotometry (16). 

Phosphazene polymers are inherently good electrical insulators unless side-group stmctures allow ionic conduction in the presence of salts. This insulating property forms the basis for appHcations as wire and cable jackets and coatings. Polyphosphazenes also exhibit excellent visible and uv radiation transparency when chromophoric substituents are absent. 

In view of the chromophoric character of the elemental iodine itself, many colorimetric methods have been proposed for the deterrnination of inorganic iodine (88—92). These methods use the visible portion of the spectmm in reading iodine concentrations. In the visible range the extinction coefficient for iodine is not high enough to be used for minute quantities of iodine in water and other solvents (93). Higher sensitivities have been reported for elemental iodine in potassium iodide solutions in the ultraviolet (93,94). 

Many spectral-sensitizing dyes can be classified according to molecular stmctures (228). The stmctural part of a dye molecule that enables the molecule to absorb visible or infrared radiation is called a chromophore. The resonance stmcture for three common chromophores is shown. 

Dyestuff organic chemistry is concerned with designing molecules that can selectively absorb visible electromagnetic radiation and have affinity for the specified fiber, and balancing these requirements to achieve optimum performance. To be colored the dyestuff molecule must contain unsaturated chromophore groups, such as a2o, nitro, nitroso, carbonyl, etc. In addition, the molecule can contain auxochromes, groups that supplement the chromophore. Typical auxochromes are amino, substituted amino, hydroxyl, sulfonic, and carboxyl groups. 

The optical properties can be tuned by variations of the chromophores (e.g. type of side-chains or length of chromophorc). The alkyl- and alkoxy-substituted polymers emit in the bluc-gnecn range of the visible spectrum with high photolu-inincsccncc quantum yields (0.4-0.8 in solution), while yellow or red emission is obtained by a further modification of the chemical structure of the chromophores. For example, cyano substitution on the vinylene moiety yields an orange emitter. 

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