The aqueous radiation chemistry of cysteamine and some related compounds

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The radiation churistqy of c y s t e m b e and o f cysteamlne-S- phosphoric acid in oxygen-free

ma

oxygen~.ted solution has been studies a t acidic and near-neukal p'IL

I n oxyger,-free solution and i n oqyeenated solution above pH

5

the mechanism of cysteamine radiolysis appears similar t o t h a t of

cysteine. From measurenents of the dependmce of G(-RSH),

G(RSSR),

aria G(?T2o2) cpon pX and cys teamine conce~tratior., suggestions regar&_lg t l x s t o i c h i m e t r y of the

chain

reaction occurring a t higher pH and

the

mechanistic implications have been made.

The

dependame o f the rate o f oxicbtion of cysteamine by hy6rogen peroxit% upon pH has been studied, second-order

kinetics

be* observed over the pH range

6.5

t o 40.9, and the r a t e has been found t o

depend in

a simple manner upon ionisation cf the thiol.

The r a t e constant of the reaction of aquatea electrons with cystearnine-S-phosphoric acid has been measured as about 5x1

o9

hf-' secl by competition d t h cysteamine a t pII lc.2, and

measurements have indicated the

formation

of orthophosphate,

inorganic

phosphorothiozte, and an aldehyde as pro&.cts of the reaction of

h y c ' i o ~ l m a i c e l s w i t h cystearnine-S-phosphoric

acid

a t pH 8.6.