Electron Affinities of Biological Molecules from Reduction Potentials

3 ELECTRON AFFINITIES OF BIOLOGICAL MOLECULES FROM REDUCTION POTENTIALS 

Absolute electron affinities can be obtained by classification of biological molecules to establish different values of AAG. This is illustrated for riboflavin, vitamin K, vitamin A, polyazines, and hydroxyprimidines. The Ea of these compounds are also predicted by substitution and replacement rules. Those for the dia-zines range from 0.2 eV to 0.4 eV. The values for 1,2,4 triazine and 1,2,4,5 tetrazine are 0.9 eV and 1.7 eV. The replacement of an additional CH by N increases the Ea by 0.6 eV. Therefore, the predicted values for pentazine and hexazine are 2.2 eV and 2.9 eV. The CURES-EC method gives better approximations to these Ea and can differentiate between isomers. 

The prototype molecule for vitamin A, a conjugated olefin, is decapentaene. The half-wave reduction potentials of the linear conjugated olefins can be converted to absolute Ea. The olefins are classified as A molecules, with AAG = 2.0 eV. The values calculated from the reduction potentials are the only absolute Ea of the 

TABLE 12.5 Electron Affinities of Biologically Related Compounds (in eV) 

The electron affinities of aromatic heterocyclic compounds have been measured by TCT and are included in the NIST tables [21]. At the same time the electron affinities of pyridine, the diazines, and aza-substituted phenanthrenes were 

---