Molar extinction coefficient calculation

Due to varying solvent systems, varying purities and water contents of purified pigments, different molar extinction coefficients have been reported." - - The most reliable ones commonly applied are 60,000 L/mol cm for betanin, 56,600 L/mol cm for amaranthin, and 48,000 L/mol cm for betaxanthins. ° Pigment contents may be calculated with the following formulae." - ... 

The electronic adsorption spectra for the complexes [Ir(OH)6]", where n = 0-2, have been resolved and peak maxima locations, molar extinction coefficients, oscillator strengths, and band half-widths calculated.44 Bands have been assigned in the main part to be one-electron MLCT transitions. Spectrophotometrically determined rate constants for the OH reduction of the IrVI and Irv complexes at 25 °C in 3M NaOH are (2.59 0.09) x 10—3 s—1 and (1.53 0.05) x 10 4 s 1 respectively. The activation energy for the reduction, Irv—>IrIV, is nAkcalmoC1. Cyclic voltammetry and potentiostatic coulometry of [Ir(OEI )r,]2 in 3M NaOH on a Pt electrode show that during the electro-oxidation compounds of Irv and IrVI are formed.45... 

The specific surface area of the fresh and used catalysts was measured by nitrogen adsorption method (Sorptometer 1900, Carlo Erba Instruments). The catalysts were outgassed at 473 K prior to the measurements and the Dubinin equation was used to calculate the specific surface area. The acidity of investigated samples was measured by infrared spectroscopy (ATI Mattson FTIR) by using pyridine (>99.5%, a.r.) as a probe molecule for qualitative and quantitative determination of both Bronstcd and Lewis acid sites (further denoted as BAS and LAS). The amounts of BAS and LAS were calculated from the intensities of corresponding spectral bands by using the molar extinction coefficients reported by Emeis (23). Full details of the acidity measurements are provided elsewhere (22). 

Normal incidence transmission IRLD measurements are used to study thin films (typically 100 pm thickness and less, depending on the molar extinction coefficient of the bands) with in-plane uniaxial orientation. Two spectra are recorded sequentially with the radiation polarized parallel (p) and perpendicular (s) to the principal (machine) direction of the sample. The order parameter of the transition moment of the studied vibration is calculated from either the dichroic ratio (R — Ap/As) or the dichroic difference (AA = Ap—As) as ... 

Hence the quantity of EA can be simply calculated from the corrected sensitized emission image and the acceptor only image provided the ratio of the molar extinction coefficients of the donor and acceptor at the donor excitation wavelength is known (ct). This quantity can be determined from absorption spectra of purified labeled components or can be experimentally determined as follows. First, let us define a factor v that relates the signal of N acceptors in the S channel to the signal of the same number of donors in the D channel ... 

A standard UV cell was filled with 3.5mL of a 3 X 10"4 M dichloromethane solution of polyether 2. The solution was then treated with 10 uL of trifluoromethanesulfon-ic acid and the changes in UV absorption of the mixture were monitored. Once the reaction was complete the molar extinction coefficient of the product at 276nm was identical to that of naphthalene, therefore conversions during acidolysis were calculated directly from absorption measurements (At/A ). 

Outlined below is the exact method of calculation of quantum yields of the disappearance of compound A and the formation of the compounds Bi to B , even if only their analytical concentrations at a few time intervals are known and their molar extinction coefficients are not known (for more details see Ref. 71). 

Assuming that the two carbonyl species have similar molar extinction coefficients, a simple calculation suggests that about half of the acyl radicals formed abstract hydrogen before decarbonylation. This process would thus be expected to reduce the efficiency of main-chain scission via the /3-scission mechanism. 

Calculate the decadic molar extinction coefficients of nitrobenzene for the wavelengths indicated above. 

From equation (73) it is possible to calculate V from the molar extinction coefficient at the absorption maximum (emax), the band width at half maximum (v,/2) and Eop if the interreactant separation is known. 

In this protocol, commercially purchased isoflavone standards (Table II. 6.3) are dissolved in a suitable solvent to prepare solutions in a series of decreasing concentrations. The absorbances are then measured using a UV spectrophotometer set at the isoflavone s maximum wavelength ( max), and the concentrations of isoflavone standard solutions are calculated using published molar extinction coefficients. The spectrum is also scanned in order to evaluate the fine structure (see Background Information, Spectral fine structure). 

This value was calculated using the molar extinction coefficients for the aromatic amino acids tyrosine and tryptophan given by T. W. Goodwin and R. A. Morton [BJ 40, 628 (1946)]. 

The absorbance at the band maximum for solutions of lithium, sodium, and barium in ND8 is a linear function of the concentration, and extrapolation of the linear function to zero concentration predicts zero absorbance (Figure 5 and Table II). The molar extinction coefficients as calculated by the least squares method for solutions of lithium, sodium, and barium in ND8 at —70° C. are given in Table II. If it is assumed that barium loses two electrons upon solvation, the molar extinction coefficients of lithium, sodium, and barium solutions are the same to within the estimated error of measurement (4%). The residual absorbance, as calculated from the least squares analysis, in each case is... 

The molar extinction coefficient a is calculated with the following formula ... 

At pH < 6 or at higher peroxide concentrations, other GSH adducts were also formed but have not yet been identified. Presumably they are formed by further oxidation of GS-CH2-AB and/or GSH adduct formation with other MAB oxidation products. Under optimal conditions in the H202 peroxidase system, 83% of the MAB could be recovered as GS-CH2 AB as calculated from a molar extinction coefficient for GS-CH2 AB of 22,600 M at 395 nm in methanol water 1 1. 

Glutathione-peroxidase activity was measured spectrophoto-metrically at 340nm by an enzyme coupled assay procedure of Paglia and Valentine (28) as modified by Reddy, et al. (26). A molar extinction coefficient of 6.2 x 103cm 1 was used in calculations. 

The ratio /spectrophotometric measurement, and the value of a is then calculated from eq. (3.5) to yield the desired absorption constant. The numerous absorption constants found in the literature arise from the choice of quantities incorporated in the constant b. Some of the terms most commonly used to express absorption in minerals are summarized in table 3.2. Note that optical densities (O.D.), representing the direct output from many spectrophotometers, lack specificity about sample thickness and element concentrations. Absorption coefficients (a) indicate that sample thicknesses have been measured or estimated. Molar extinction coefficients (e) require chemical analytical data as well as knowledge of sample thicknesses. 

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