Extinction coefficient chromophores

Many of the physical properties are not affected by the optical composition, with the important exception of the melting poiat of the crystalline acid, which is estimated to be 52.7—52.8°C for either optically pure isomer, whereas the reported melting poiat of the racemic mixture ranges from 17 to 33°C (6). The boiling poiat of anhydrous lactic acid has been reported by several authors it was primarily obtained duriag fractionation of lactic acid from its self-esterification product, the dimer lactoyUactic acid [26811-96-1]. The difference between the boiling poiats of racemic and optically active isomers of lactic acid is probably very small (6). The uv spectra of lactic acid and dilactide [95-96-5] which is the cycHc anhydride from two lactic acid molecules, as expected show no chromophores at wavelengths above 250 nm, and lactic acid and dilactide have extinction coefficients of 28 and 111 at 215 nm and 225 nm, respectively (9,10). The iafrared spectra of lactic acid and its derivatives have been extensively studied and a summary is available (6). 

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). 

The reduced symmetry of the chromophore, which still contains 187t-electrons and is therefore an aromatic system, influences the electronic spectrum which shows a bathochromic shift and a higher molar extinction coefficient of the long-wavelength absorption bands compared to the porphyrin, so that the photophysical properties of the chlorins resulting from this structural alteration render them naturally suitable as pigments for photosynthesis and also make them of interest in medical applications, e.g. photodynamic tumor therapy (PDT).2... 

In colorants, the spectral absorption pattern and the extinction coefficient are determined by the chromophore and rarely by side groups of the molecule, p-carotene and zeaxanthin contain the same chromophore but their molecular masses... 

Fig. 6. Difference spectra between xanthine oxidase inactivated with various pyra-zolo [3, 4-d] pyrimidines and the native enzyme. The spectra are believed to represent the increase in absorption occurring when Mo(VI) of native enzyme is converted to Mo(IV) complexed with the inhibitors. Spectra were obtained by treating the enzyme with inhibitors in the presence of xanthine, then admitting air, so as to re-oxidize the iron and flavin chromophores. The extinction coefficients, de, are expressed per mole of enzyme flavin. Since some inactivated enzyme was present, extinction coefficients per atom of molybdenum of active enzyme will be about 30% higher than these values. (Reproduced from Ref. 33, with the permission of Dr. V. Massey.)...

Phthalocyanine-based dyes are especially useful for CD-R, as the chromophore absorption band falls in the desirable spectral range, and they are noted for excellent photostability. Unlike cyanine dyes, phthalocyanines tend to have very poor solubility, particularly in solvents such as alcohols and aliphatic hydrocarbons (which do not attack polycarbonate and are therefore used for spin coating). Therefore, the main barrier to the wider use of these dyes is the relatively high cost of synthesizing soluble derivatives. Suitable modifications to the Pc core which have been developed, notably by Mitsui Toatsu, are shown in Scheme 7. The bulky R groups reduce undesirable molecular association (which in turn lower the extinction coefficient and hence reflectivity), whereas partial bromination allows fine-tuning of the film absorbance and reflectivity. The metal atom influences the position of the absorption band, the photostability, and the efficiency of the radiationless transition from the excited state.199 This material is marketed by Ciba as Supergreen.204... 

This is a tiny value, and reveals how a small amount of beetroot dye will stain a standard aluminosilicate plate in other words, it demonstrates how large is the extinction coefficient e of the beetroot juice chromophore. 

Molar Extinction Coefficients of the TBA Chromophore (4) in Different Solvents... 

Charon and Szabo17 demonstrated that chromophore 4 may be produced to a significant extent from a 5-O-substituted derivative of KDO (which does not contain a free diol grouping at C-4-C-5). These authors synthesized 3-deoxy-5-0-methyl-2-octulosonic acid (7 configuration at C-5-C-7, arabino at C-4, unknown) by the Comforth reaction18,19 from 4-0-formyl-2-0-methyl-D-arabinose (see Scheme 4 and Section IV,1). Compound 7 gave a millimolar extinction coefficient of 13 in the TBA assay (as compared to 92 5 for KDO). Based on this result, Charon and Szabo17 formulated for the TBA reaction of 5-0-... 

Assuming that no other strongly absorbing chromophores are present, then the organic C60 adducts tend to be intensely red, whereas the organometallic adducts tend to be intensely green or red. The extinction coefficients (e) have values comparable to those of uncomplexed, with the more intense color arising because of small shifts in the 450-600 nm band. 

The synthetic GFP chromophore analogue (2-(4-nitrophenyl)-5-(4-cyanophenyl methylidene) imidazol-4-one ), was synthetized according to ref [6]. It was recrystallized from ethanol and characterized by 1H-NMR through their typical proton signal at 7.1 2 ppm. High concentrated solutions of approximately 3.10 3M were prepared by dissolution in dioxan. The photophysical characteristics of this analogue were determined from the UV absorption spectra and from steady-state fluorescence. An extinction coefficient of 20700 M cm 1 was determined at the maximum absorption wavelength at 406 nm. The fluorescence emission peaks at 508 nm. 

The electronic spectra of square pyramidal chromophores are characterized by a band in the near IR region from 4000 to 9000cm-1 (3BX- 3E) with molar extinction coefficient M near 10-20, a more intense transition at 12 000-18 000 cm-1 (3BX —> 3E, M 20-100) with a shoulder on the low frequency side due to 3B1- 3B2 transitions, a weak band at 17000-25 000cm-1 (3BX—>3A2 (P)) and the most intense transition at 19000-29000cm-1 (3BX— 3E (P), eM 100-800). 

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