Absorbance coefficients

Chlorophyll a and chlorophyll b are distinguishable by their typical spectral properties (Figure 6.1.lA). Each one shows a specific absorbance coefficient and E... 

Amotf was the first to develop a set of equations for acetone to simultaneously calculate chlorophyll a and chlorophyll b in 1949. Several authors later proposed different new equations based on more adjusted and accurate extinction coefficients due to the development of higher resolution spectrophotometers adapted to each special condition. Moreover, besides 80% acetone, coefficients for diethyl ether and ethanol were also established and their respective equations developed, as reviewed by Schwartz and Lorenzo and Eder. Solvents chosen should be those for which specific absorbance coefficients have been published to derive equations and updates should be carefully tracked for new values. 

Although these equations are still frequently used, Porra and co-workers in 1989 recognized that the absorbance coefficients published by Mackinney ° were low and proposed new values for chlorophyll a 85.95 e -j = 20.79) and for... 

VCD and FTIR spectra should always be obtained on the same samples, the FTIR at higher resolution and optimized S/N to permit computation of deconvolved (resolution-enhanced) spectra (Kauppinen etal., 1981). VCD spectra of biomolecules are often normalized to the absorbance, since concentration and path lengths are rarely known to good accuracy. Because the absorbance coefficients for different molecules will vary, this is only an approximate correction for concentration variation. 

For fixed time assays this most frequently involves the use of standards and a calibration graph. Some methods, e.g. the use of the molar absorbance coefficient in spectrophotometry, do not requite standards and giiNometric methods permit the calculation of molar concentration from the volume of gas (1 gram mole of gas occupies 22.4 litres at standard temperature and pressure, STP). 

Fig. 1.3 Second-order kinetic plot for decay of RefCO) obtained by flash photolysis of 120 pM RejlCOlm with 10 mM CO in isooctane. (CO slows further reactions of RelCO) ) At X = 535 nm, the molar absorbance coefficient, 8m of Re(CO)5 is 1.0 x lO lVf cm". Since therefore from Beer-Lambert law (Df-Df) = [A]e ,l, where D s are optical absorbances and 1 is the path length (10 cm), the slope of Fig. 1.3 is 2k/s and 2k therefore equals (5.3 x lO KlO lflO) = 5.3 x lO M- s". Ref. 25. Reproduced with permission of the Journal of the American Chemical Society. 1982, American Chemical Society.

This treatment yields the time course of the relaxation which is of most concern to us, but ignores the relative magnitudes of the relaxations (contained in the X and Y terms in (1.163)). These latter are complex functions of reaction enthalpies and absorbance coefficients, but can yield equilibrium constants for the two steps.However, relaxation data are much less used for thermodynamic than kinetic information. 

Concentration (mg/ml) = (1.55 x A280) — 0.76 x A260) or Concentration = A280nm divided by absorbance coefficient... 

Table F4.3.1 Wavelength Maxima (Amax) and Specific Absorbance Coefficients (a)a of Chi a and bfor Extracts in Different Organic Solvents...

This original Lambert-Beer law can only be applied for one isolated pigment. Absorbance coefficients taken from the literature (Table F4.3.1) are valid only for one substance (e.g., Chi a) using one solvent (e.g., 100% acetone) and one wavelength (e.g., 661.6 nm). Changes in substance, solvent, or wavelength lead to changes in the absorbance coefficient. 

The relationship between the molar absorbance coefficient (e) and the specific absorbance coefficient A %cm) is... 

Given that the molar absorbance coefficient of tyrosine in water is 1,420 L mol 1 cm-1 at 275 nm. what is the concentration of tyrosine in a solution of path length 1 cm for which the absorbance is 0.71 ... 

A suspension of mitochondria was incubated under anaerobic conditions in the presence of NADH. Oxidative phosphorylation was initiated by a pulse of oxygen, and it was found that the ATP concentration in the suspension increased by 1.5 X 10 4mol L-1, with a corresponding decrease in the absorbance of the suspension of 0.30 at 340 nm, when using a 1-cm path length in a spectrophotometer. Given that the absorbance coefficient of NADH at 340 nm is 6.2 x 103 L mol-1 cm-1, calculate the number of ATP molecules produced per molecule of NADH oxidized. 

Chirality is the origin of the spectroscopic property optical activity. The interaction of light and matter is characterized by the refractive index and the absorption coefficient. For chiral molecules, both the refractive index and the absorbance coefficient of one enantiomer differ for right and left circularly polarized light (r-cpl and 1-cpl). 

The amount of commercial alkaline phosphatase was estimated by monitoring the change in absorbance at 405 nm of approximately 0.01 units of enzyme in 1.5 ml of 1 M diethanolamine (pH 9.8) containing 0.5 mM MgCl2 and 10 mM p-nitrophenylphosphate. The absorbance coefficient of p-nitrophenol at this wavelength is 18450 Lmol cm. A molecular weight of 140 kDa and a specific activity of 2000 u/mg under these conditions (Life Technologies, data sheet) were used to calculate enzyme concentration. 

The radiation dose absorbed by the water is the water s UV demand, which is analogous to chlorine demand and is quantified as the absorption of UV energy (at a wavelength of 253.7 nm) in a given depth of water. The measurement is most commonly expressed by the UV absorbance coefficient alpha ... 

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