N - 乙酰 - L - 半胱氨酸辐照晶体中³³S的核耦合及自由基的性质
Nuclear coupling of 33S and the nature of free radicals in irradiated crystals of N-acetyl-L-cysteine.
作者信息
Hadley J H, Gordy W
出版信息
Proc Natl Acad Sci U S A. 1977 Jan;74(1):216-20. doi: 10.1073/pnas.74.1.216.
Hyperfine structure due to 33S in its natural abundance of 0.76% has been measured in the electron spin resonance of free radicals produced by x-irradiation of single crystals of N-acetyl-L-cysteine at 77 K. These measurements proved that the radicals produced at 77 K with principal g values of 1.990, 2.006, and 2.214 are monosulfide radicals with the 3p unpaired electron density of 0.70 on the S. They are believed to be negatively charged molecules RCH2S-H or neutral RCH2SH2 radicals in which 90% of the spin density of the captured electron is concentrated in a d-p hybrid orbital on the S. As the temperature is raised to 300 K, these, as well as the carbon-centered radicals produced at the lower temperature, are mostly converted to neutral disulfide radicals RCH2SS like those observed in irradiated cystine.
在77K下，对经X射线辐照的N-乙酰-L-半胱氨酸单晶产生的自由基进行电子自旋共振测量，测定了天然丰度为0.76%的³³S所引起的超精细结构。这些测量结果证明，在77K下产生的、主g值为1.990、2.006和2.214的自由基是单硫化物自由基，其硫原子上3p未配对电子密度为0.70。它们被认为是带负电荷的分子RCH₂S⁻H或中性的RCH₂SH₂自由基，其中捕获电子的自旋密度90%集中在硫原子上的d-p杂化轨道中。当温度升至300K时，这些自由基以及在较低温度下产生的碳中心自由基，大多会转化为中性二硫化物自由基RCH₂SS，就像在辐照胱氨酸中观察到的那样。
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