Molecular extinction coefficient

The absolute intensity of an absorption band may be expressed by giving the value of em x., the molecular extinction coefficient at the wave... 

The molecular extinction coefficients (at various wavelengths) of the four main components of the irradiation are shown in Table 5. The absorption of light above 300 nm is favored by tachysterol. A yield of 83% of the previtamin at 95% conversion of 7-dehydrocholesterol can be obtained by irradiation first at 254 nm, followed by reirradiation at 350 nm with a yttrium aluminum garnet (YAG) laser to convert tachysterol to previtamin D. A similar approach with laser irradiation at 248 nm (KrF) and 337 nm (N2) has also been described (76). 

Table 5. Molecular Extinction Coefficients of Irradiation Products ...

Provitamin D. The molecular extinction coefficient of 7-dehydrocholesterol at 282 nm is 11,300 and is used as a measure of 7-dehydro isomer... 

Mercaptoquinolines of this type exist in the zwitterion or the zwitterion-extended quinone form to a greater extent than do the analogous hydroxy compounds ° (see Table V and Section II,R), and the color of 8-mercaptoquinoline has been attributed to the zwitterion structure.The concentration of the zwitterion decreases as the dielectric constant of the solvent decreases in the order H2O > MeOH > EtOH > Bu OH as indicated by the change in the molecular extinction coefficient. ... 

K Fe(CN)6 oxidation Compound F is stoichiometrically inactivated by oxidation with K.3Fe(CN)6 (Shimomura and Johnson, 1967) thus, it is possible to estimate the molecular extinction coefficient (e) of the 388-390 nm absorption peak by titrating F with K.3Fe(CN)6- The e value obtained by the titration in 50% ethanol was 15,400 (assuming the reaction to be one-electron oxidation) or 30,800 (assuming two-electron oxidation). Two other methods of lesser precision were used to determine the true s value 1) the dry weight of the ethyl acetate extract of an acidified solution of F gave an e value of 14,100 2) the comparison of NMR signal intensities gave a value of 11,400 2,000 in water (H. Nakamura, Y. Oba, and A. Murai, 1995, personal... 

Starch D. P. Xmax (A.) Molecular extinction coefficient References... 

In Fig. 14, the UV spectra of the domino oxidation products are shown. As the number of oxatetrasilacyclopentane rings increases, the lowest energy absorption maximum shifts bathochromically, and the molecular extinction coefficient becomes far larger (10 270 nm (s 3200), 11 273 nm (s 7600), 12 292 nm (s 25000), 13 297 nm (s 51900). The intense absorption of the order 104 is remarkable because these molecules contain no obvious chromo-phores which should give such intense absorption. Since the intense absorption is not observed in the ladder polysilanes, it is apparently due to the electronic effect of the oxygen atoms on the Si-Si a conjugation systems. 

An automated method can be run after validation using multiparametric open analysers [1, 11, 17], For example, KONELAB 30 (Thermo Fisher Scientific, Waltham, USA). There is no standard for pyruvate, ACAC or . The results are calculated taking into account the molecular extinction coefficient of NADH (6.3 mmol 1 cm 1). A lactate standard is provided in the kit. 

Figure 5 (a)-(c) shows the absorption spectra of some halogenated ketones in the near ultraviolet. In the case of acetone itself the absorption may be attributed to an n - tt transition associated with the carbonyl group. The substitution of halogen atoms leads to an increase in the molecular extinction coefficient and a shift of the absorption maximum toward the red. The ketones containing both chlorine and fluorine atoms show absorption curves with some fine structure but it is not possible to find any correlation between the structure and the shape of the absorption curve. 

Equation (2) also shows how the intensity of fluorescence varies when the frequency of the exciting light varies. For a given solution the fluorescence intensity is proportional to 7oe0 and for many substances in solution the fluorescence efficiency () is approximately independent of the excitation frequency. Thus, if the intensity of exciting light is kept constant as the frequency is varied, the fluorescence intensity will be proportional to e, the molecular extinction coefficient of the solute. Hence the true excitation spectrum frequently corresponds closely to the absorption spectrum of the compound (see Fig. 2). Spectrofluorimetry can thus be used to measure the absorption spectra of fluorescent solutes, but at concentrations far lower than could be measured directly with an absorption spectrophotometer. It has the further advantage that the... 

The electronic transitions which produce spectra in the visible and ultraviolet are accompanied by vibrational and rotational transitions. In the condensed state, however, rotation is hindered by solvent molecules, and stray electrical fields affect the vibrational frequencies. For these reasons, electronic bands are very broad. An electronic band is characterised by the wave length and molecular extinction coefficient at the position of maximum intensity (Xmax. and emax ). 

Molecular extinction coefficients, 1135 Molecular weight, by Rast camphor method, 1037 Molisch test, 453 ... 

C. Klein, R. Humphry-Baker, S. M. Zakeeruddln, ana M. Grdtzel, A High Molecular Extinction Coefficient Sensitizer for Stable DyeSensItlzed Solar Cells," J. Am. Chem. Soc. 2005, 127, SOB.]... 

The specific refraction 8 is 0-2732 and the refraction equivalent 49-50. The absorption of light by a 0-0lN-solution of arsenic trichloride in N-hydrochiorie acid has been examined,9 and it has been observed that the molecular extinction coefficient varies from 5 to 30 as the wavelength of the incident light decreases from 3570 to 2270 A. 

A good absolute theoretical comparison of strength is represented by the area under the absorption bands in the visible spectrum, or less accurately by the molecular extinction coefficients at the maximum wavelength of absorption. 

Wilkinson and Johnston record intensities in terms of the atmospheric absorption coefficient at 30° c. Their values have been multiplied by (22 4 x 3O3)/(2 30 x 273) in order to obtain molecular extinction coefficients. The present discussion assumes that the bands observed by them in the continuum are not due to impulines. There is some doubt of this, however, since Rathenau s findings arc not entirely in agreement with those of Wilkinson and Johnston. 

Fio. 1.—Molecular Extinction Coefficients of Cyclic Tellurium Compounds. 

The 5-nitrotetrazole ring has a max in the ultraviolet at 257mM, which can be used for analysis. The molecular extinction coefficient is 5.4 x 103... 

A colorimetric assay involves the oxidative cleavage of proanthocyanidins with ferrous sulfate. To 0.5 mL of aqueous plant extract is added a 5-mL portion of an acidic solution of ferrous sulfate (77 mg of FeS04.7H20 dissolved in 500 mL of 2 3 HCl/ -butanol). The tubes are loosely covered and placed in a water bath at 95°C for 15 min. The absorbance is read at 530 nm. The concentration of proanthocyanidins is expressed as cyanidin equivalents (used for the standard curve). The molecular extinction coefficient emoi that can be used to convert the absorbance values to a concentration is equal to 34700 L mol cm 1. 

The quaternary carbon at C 12a separates the chromophores of the tetracyclines into two relatively distinct regions. The B-tricarbo-nyl system of ring A contributes a strong absorption band at about 260 nm while the aromatic ring D conjugates with the B-diketone moiety in rings B and C to produce a visible band at about 360 nm (21). the molecular extinction coefficients and Alj of TC-HC1 in different solvents are reported to be (22) ... 

The ultraviolet spectra 27,28 exhibit, in agreement with the general postulate of Braude et al.2%-30 a bathoehromic shift to 225-235 m/j. caused by the auxochromic action of the nitrogen-free electron pair. This shift is approximately the same as that caused by introduction of a conjugated double bond, and is increased by further conjugation with other multiple bonds, e.g. in diene-amines prepared from A -3-oxosteroids.31,32 Spectral maxima (at 280-285 mfi, e 19,000-26,000) point to the conjugation of three mobile electron pairs but cannot decide the position of the double bonds the molecular extinction coefficient indicates a transoid (5) rather than cisoid arrangement (e.g. 6).33... 

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