CHAPTER 5 



Ultraviolet Absorption Spectra 



Robert L. Sinsheimer 



Department of Physics, Iowa State College 

 Ames, Iowa 



Paravieters of absorption spectra: Position in the electromagnetic spectrum — Width of 

 absorption band — Intensity. Absorption and chemical constitution: Empirical correla- 

 tions — Theoretical developments. Specification of absorption: Intensity — Spectral posi- 

 tion — Band undth. Environmental factors influencing absorption: Solvent — pH value 

 — Concentration — -Temperature — Orientation — Scattering — Local concentrations. Ultra- 

 violet absorption spectra of important biological substances: Proteins and amino acids — 

 Nucleic acids and nucleotides — Steroids — Carotenoids — Porphyrins — Flavins — Pterins — 

 Vitamins — Plant pigments. References. 



The absorption of ultraviolet radiation by a molecule results in a change 

 in the electronic configuration of that molecule and therefore in a change, 

 usually transient and reductive, in the stability of the molecule. The 

 ability of any molecule to absorb ultraviolet radiation of a particular fre- 

 quency is dependent on the electronic configuration of the molecule and 

 the electronic configurations of the possible higher energy states of the 

 molecule. This absorptive ability is thus intimately related to the 

 detailed molecular structure (Lewis and Calvin, 1939; Ferguson, 1948; 

 Bowen, 1946, 1950; Maccoll, 1947). An absorption spectrum of any 

 substance is a quantitative description of the absorptive ability of 

 the molecules of that substance over some range of electromagnetic 

 frequencies. 



A knowledge of the absorption spectra of the major components of a 

 living organism makes it possible to limit the number of possible primary 

 receptors of radiation that are found to produce some biological effect. 

 Only those substances that absorb the radiation found to be responsible 

 for the effect need be considered. The correlation of the measured rela- 

 tive efficacy of radiations of various wave lengths in producing the effect, 

 with the variation of absorptive power with wave length of the substances 

 under consideration as primary receptors, can, under favorable circum- 

 stances, further limit the possibilities as to the nature of the receptor. 

 A knowledge of the influence of absorption on the stability of the 



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