Molar absorptivity interaction

Fundamental Limitations to Beers Law Beer s law is a limiting law that is valid only for low concentrations of analyte. There are two contributions to this fundamental limitation to Beer s law. At higher concentrations the individual particles of analyte no longer behave independently of one another. The resulting interaction between particles of analyte may change the value of 8. A second contribution is that the absorptivity, a, and molar absorptivity, 8, depend on the sample s refractive index. Since the refractive index varies with the analyte s concentration, the values of a and 8 will change. For sufficiently low concentrations of analyte, the refractive index remains essentially constant, and the calibration curve is linear. 

The wavelength of maximum absorption and the molar absorptivity are very dependent on pH, buffer, temperature, solvent, and the presence of other materials that may interact with anthocyanins. In addition, anthocyanin absorption follows a linear relationship with concentration only when present at low levels therefore considerable dilution is usually necessary. Absorbance normally should vary from 0.2 to 1.0 unit in order to obey Lambert-Beer s law. However, absorbance values as high as 1.5 to 2.0 absorbance units may be valid for sophisticated new instruments. 

El-Ashry et al. [36] studied the complex formation between the bromophenol blue, primaquine, and other important aminoquinoline antimalarials. The colorimetric method used was described as simple and rapid and is based on the interaction of the drug base with bromophenol blue to give a stable ion-pair complex. The spectra of the complex show maxima at 415 420 nm with high apparent molar absorptivities. Beer s law was obeyed in the concentration range 1-8,2-10, and 2-12 pg/mL for amodiaquine hydrochloride, primaquine phosphate, and chloroquine phosphate, respectively. The method was applied to the determination of these drugs in certain formulations and the results were favorably comparable to the official methods. 

Brightness. Brighmess of a fluorophore is proportional to the product of the molar absorption coefficient at the excitation wavelength times its quantum yield. This is the theoretical value, but in practice it can be much reduced by fluorescent quenching on interaction with other labels on the protein or DNA surfaces. Sulfonic acid groups on the aromatic rings of cyanines reduce this interaction, giving very much improved protein fluorescence. 

The photometric estimation of protein concentration is subject to some special features Proteins interact with each other depending on their concentration and may change their secondary and/or tertiary structure in a concentration- dependent manner (especially denaturation in diluted solutions). These changes affect the absorption of light, i.e., concentration dependence of molar absorption coefficient e therefore, the Beer-Lambert law (eq. e) is not valid over a broad concentration range. 

When only polypyridine-type ligands are present, each mononuclear metal-based unit exhibits intense LC bands in the UV region and moderately intense MLCT bands in the visible. As it is shown by the electrochemical behavior vide supra), in the polymetallic species there is some interaction among the neighboring metal-based units. To a first approximation, however, each building block carries its own absorption properties in the polynuclear species so that the molar absorption coefficients exhibited by the compounds of higher nuclearity are huge, as it is clear by a cursory examination of the absorption data reported in Table 3. For example, the spectra of the decanuclear compounds lOB and lOC (Scheme 1 and Table 1)... 

In concentrated solutions, solute molecules influence one another as a result of their proximity. When solute molecules get close to one another, their properties (including molar absorptivity) change somewhat. At very high concentration, the solute becomes the solvent. Properties of a molecule are not exactly the same in different solvents. Nonabsorbing solutes in a solution can also interact with the absorbing species and alter the absorptivity. 

C34H40O3N2S X 0.5 H20) had a molar absorptivity of 13.8 0.4 X 104M 1 cm."1 at 542 n.m. at concentrations below 5 X 10"3M in water. At higher concentrations both Pseudocyanine and Astraphloxin failed to obey Beer s law, owing to dye-dye interaction leading to formation of new absorption bands (12). 

The plot in Figure 31 demonstrates a modest inverse correlation between absorptivity and frequency. The variation of molar absorptivity by a factor of 1.8 over this range of frequencies is striking, and suggests significant interaction between the C02 molecules and their environment. It is not clear if the extremely low intensities of the high frequency bands are due to... 

There is an inherent similarity between the spectrum and an electrochemical current-voltage curve that is important from the point of view of chemical selectivity. In both cases, the x-axis (voltage or wavelength) is directly related to the energy. In electrochemistry, this energy corresponds to the transfer of electrons between the analyte and the electrode. It is related to the standard electrochemical potential. In optical interactions, molar absorptivity is probabilistically related to the excitation energy of the molecule. 

Measurements on complexes formed with cyclic -diketones (fig. 43) demonstrated that for identical molar absorption coefficient values, higher luminescence intensities were observed for cyclic / -dikctonates compared to aliphatic ones. This indicates a more efficient energy transfer to the Ndm ion on account of the rigid structure of these cyclic /3-dikctonates in which the central ion is well shielded from interaction with water molecules. 

The solvent often exerts a profound influence on the quality and shape of the spectrum. For example, many aromatic chromophores display vibrational fine structure in non-polar solvents, whereas in more polar solvents this fine structure is absent due to solute-solvent interaction effects. A classic case is phenol and related compounds which have different spectra in cyclohexane and in neutral aqueous solution. In aqueous solutions, the pH exerts a profound effect on ionisable chromophores due to the differing extent of conjugation in the ionised and the non-ionised chromophore. In phenolic compounds, for example, addition of alkali to two pH units above the pKa leads to the classical red or bathochromic shift to longer wavelength, a loss of any fine structure, and an increase in molar absorptivity (hyper chromic... 

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