Optical properties specific extinction coefficient

Hubert Tschamler They were derived either from mean values observed for model compounds of known structure or from the properties of solvent extracts of coals. In the latter case an accurate value for %H i can be derived by measuring proton spin resonance in solution and this, combined with the optical densities observed in the infrared spectra, gives the specific extinction coefficients. (See J. F. M. Oth, E. de Ruiter and H. Tschamler, Brennstoff-Chem. 42, 378 (1961) also Ref. 7). 

Fairly wide use has been made of preparative gel electrophoresis in protein chemistry, and in principle there is no reason why the same procedures should not be adopted for use with nucleic acids which have the advantage that much may be accomplished with very small quantities of purified material. Thus, it is relatively easy in many situations to introduce radioactive label at very high levels and specific activity, and the use of for this purpose offers a degree of sensitivity that cannot be matched in work on proteins. The extinction coefficients of nucleic acids are also very high in the ultraviolet, so that with say 20 pg in 1 ml or less it is possible to measure optical properties, thermal melting profiles, sedimentation coefficients, and even molecular weights by sedimentation equilibrium in an instrument equipped with scanner optics. Consequently, the sacrifice of resolution that, by a malign law of nature, always accompanies any attempt to scale up an analytical fractionation method is often at least partly avoided. 

It is useful to collect here a few more definitions normally used in the discussion of optical properties. One is the molar extinction coefficient Gm = g/c, where c is the concentration in moles/liter of the absorbing material which implies the assumption that the absorption of light is due to specific light absorbing species. Absorbance (A) and optical density (D) are the other two quantities. They are related as follows ... 

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