REACTIVITY OF EXCITED STATES OF FLAVIN AND 5-DEAZAFLAVIN IN ELECTRON TRANSFER REACTIONS

Abstract— Quenching of the excited states of lumiflavin and 3-methyl-5-deazalumiflavin by methyl-and methoxy-substituted benzenes and naphthalenes in methanol was investigated. The observed difference in the reactivity of acid and neutral lumiflavin triplets is explained thermodynamically by applying the Michaelis cycle, as being due to the higher reduction potential of the acid triplet. In this connection the p K values of lumiflavin triplet (p K ^M= 6.5) and semiquinone (p K ^M= 11.3) have also been determined in methanol. The difference in the reactivity between the singlet and triplet states of lumiflavin is found to be greater as predicted by the difference in excitation energy. The reactivities of the excited states of flavin and 5-deazaflavin differ only slightly in contrast to the marked difference in the ground state reactivities of electron transfer reactions. This is explained in terms of the model of Rehm and Weller. The pH dependence of the electron transfer quenching of 5-deazaflavin triplet was investigated in water, yielding a triplet p K of 2.5. In contrast to the flavin, this triplet p K does not significantly differ from the p K of the 5-deazaflavin ground state. From this, different sites of protonation are deduced for the photoexcited triplet states of flavin and 5-deazaflavin.     

Ein Vergleichssatz für komplexe lineare Differentialgleichungen

Ohne Zusammenfassung     

Optimal cocircuits in regular matroids and applications

Let M = (E, C) be a regular matroid with circuit set H and cocircuit set H and let $\text{(}\text{H}\text{, +, ?)}$ be an ordered group. To given partitions D = D⁺ ∈ D^? for all D ?H and weighting functions ?,k: E → H optimale ê-cocircuits are defined by having a minimal value $\text{K}\text{(}\text{D}{}^{\mathrm{+}}\text{) ? ol(}\text{D}{}^{\mathrm{?}}\text{ø 1^e1}$.It is shown that P as well as NP problems can be formulated by means of optimal cocircuits. We discuss a class of optimal cocircuit problems which can be solved using flow theory in regular matroids. Applications of the derived theory and algorithms to graphic and cographic matroids and to special ordered groups yield polynomial algorithms for some new minimal cut and shortest path problems which are useful in combinatorial and integer optimization problems.