Spektren und Strukturen der am Flavin‐Redoxsystem beteiligten Partikeln. Studien in der Flavinreihe IX [1

Abstract

AbstractFor a better understanding of structure and properties of heteroaromatic species involved in flavin catalysed electron transfer, an investigation has been made with suitable isoalloxazine models of flavo‐coenzymes, e. g. 2‐ and 4‐thio‐ and ‐iminoflavins, N‐ and O‐alkylated flavins as well as N,N‐, N,O‐, O,O‐dialkylated and unsubstituted leucoflavins and flavinium salts. From analyses of UV.‐, visible, IR.‐ and ESR.‐spectra at different redox‐states, pH's and solvent polarities, the following conclusions can be drawn: In the oxidised state (“flavoquinonc”) flavin appears in the “diketo” form only. It is protonated at N(1). Its two “iminol‐esters” (term to be preferred over “enolethers”) do not differ markedly in the visible and UV. absorption from the parent compound, but can be differentiated by their basicities. Both are “high energy” forms of flavin, the 2‐isomers being more stable than the 4‐isomers. In the reduced state (“flavohydroquinone”) concentrated flavin solutions are, by long wave end‐absorption, rendered more deeply coloured than in the oxidized state. The intensity of this absorption in the 500–700 mμ range appears to be a measure of molecular planarity.