Hello,
The reaction I am evaluating is the following:
Cystine + Hydrogen peroxide ---> Cysteic acid
I have evaluated my results and I have obtained a pseudo second order rate constant in respect of Cystine. So this indicates that the stoichiometry of the reaction is the following:
2 Cystine + 6 H2O2 ----> 4 Cysteic acid + (either 8H+ or 4H2 not sure which.)
From the literature it is noted that the rate for this reaction is increased in the presence of paramagnetic Cu 2+ ions. It is also noted that the rate for this reaction is not increased when there are diamagnetic Fe 3+ ions in solution.
An explanation to this is that interaction between Cu 2+ ions and hydrogen peroxide in the presence of base (the pH of the reaction conditions were 10) forms Cu + cations and super oxide anion radical: O2 - (radical)
This indicated to me that the reaction is following a radical anion mechanism for the oxidation of a disulphide bridge involving the superoxide. (I have assumed this because Fe 3+ when reacting with peroxide will not form this superoxide, it may form a hydroxyl radical however, but as the reaction was not faster I assumed this was not the correct reaction path)
So I have got to the stage where I think there is a radical anion mechanism involved and I also think a cyclic formation of of 2 cystines are involved (due to the second order rate)
However I am completely stuck as to proposing a mechanism. If anyone has any ideas as to how this reaction proceeds please let me know!