Bonifacić M, Asmus K D
Int J Radiat Biol Relat Stud Phys Chem Med. 1984 Jul;46(1):35-45. doi: 10.1080/09553008414551041.
Absolute rate constants have been measured for the reaction of (CH3SSCH3)+. and sulphur centred radical cations of lipoic acid, lip (SS)+., with various thiols including penicillamine, cysteamine and cysteine. Under pulse radiolysis conditions no reactions was observed between the disulphide radical cations and the neutral thiols, RSH, i.e. kappa less than or equal to 10(7) M-1 s-1. Rate constants in the order of 10(9) M-1 s-1, i.e. close to the diffusion controlled limit, were, however, found for the corresponding reactions with the thiolates, RS-. In systems containing lipoate and cysteamine the lip (S therefore S)+. induced oxidation of CyaS- proceeds via CyaS., (CyaS therefore SCya)- and lip (S S)- as intermediates, i.e. results in a cysteamine mediated conversion of an oxidizing lip (S therefore S)+. radical cation to a reducing lip (S S)- radical anion along the reaction route. In other cases the reaction of disulphide radical cations with thiolate anions was found to proceed via an optically absorbing transient (lambda max approximately 380 nm) which is suggested to be an adduct radical. The mechanism of the (RSSR)+. induced oxidation of thiolate appears to depend on the stability of the 3-electron bonded disulphide radical anion.
已测定了(CH3SSCH3)+与硫辛酸的硫中心自由基阳离子lip(SS)+与包括青霉胺、半胱胺和半胱氨酸在内的各种硫醇反应的绝对速率常数。在脉冲辐解条件下，未观察到二硫化物自由基阳离子与中性硫醇RSH之间的反应，即κ小于或等于10(7) M-1 s-1。然而，发现与硫醇盐RS-的相应反应的速率常数约为10(9) M-1 s-1，即接近扩散控制极限。在含有硫辛酸和半胱胺的体系中，lip(S所以S)+诱导的CyaS-氧化通过CyaS.、(CyaS所以SCya)-和lip(S S)-作为中间体进行，即沿着反应路线导致半胱胺介导的氧化性lip(S所以S)+自由基阳离子向还原性lip(S S)-自由基阴离子的转化。在其他情况下，发现二硫化物自由基阳离子与硫醇盐阴离子的反应通过一个光吸收瞬态（λmax约为380 nm）进行，该瞬态被认为是一个加合自由基。(RSSR)+诱导的硫醇盐氧化机制似乎取决于三电子键合二硫化物自由基阴离子的稳定性。
