Biological substances, reactions hydrated electron with

Reactions of the Hydrated Electron with Substances of Biological Importance... 

As well as for substances of exclusively biological importance, it is necessary, for a full understanding, to know the reactivity of hydrated electrons with substances such as H+, 02, CO, water, etc. which are equally present in biological systems. Many of these rate constants are known, but unfortunately the rate constant for reaction with water itself is still not entirely certain, although it has been investigated recently by two independent groups (4, 14). 

Reactions of the hydrated electron possibly may be somewhat relevant to the action of dose-modifying agents such as 02, NO, C02, and sulfhydryl compounds. It can safely be assumed that these exert their influence at the radiation-chemical level, and it is notable that many of them react rapidly with hydrated electrons. Table II, taken from a paper by Braams (6), compares the rate constant for reaction with the hydrated electron with the concentration at which certain compounds have been used as protective agents. It can be seen that, at the concentrations used in biological systems, those substances which are effective as protectors can compete favorably with oxygen for hydrated electrons. Penicillamine was not a good protector at the concentration used and did not compete as favorably as the other substances for hydrated electrons. Higher concentrations of penicillamine could not be... 

Among other reactions of the hydrated electron may be mentioned the reaction with methylene blue. Methylene blue may be regarded as the prototype of easily reducible biological substances such as NAD, cytochrome-c, etc. The preliminary value for the rate constant for reaction with the hydrated electron (5) has now been shown to be too high, and the more reasonable value of 2.5 X 1010 M-1 sec.-1 has been obtained (19). It is thus no longer necessary to attribute special properties to methylene blue. 

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