Pulsed EPR Study of the Initial Steps of Radical-Scavenging Reactions of C70 with Diphenylphosphine Oxide, Hydroxycyclohexyl, and 2-Hydroxypropyl Radicals
Pulsed EPR Study of the Initial Steps of Radical-Scavenging Reactions of C70 with Diphenylphosphine Oxide, Hydroxycyclohexyl, and 2-Hydroxypropyl Radicals
复制标题
C70 与二苯基氧化膦、羟基环己基和 2-羟丙基自由基清除自由基反应初始步骤的脉冲 EPR 研究
DOI：
10.1021/acs.jpcb.2c03398
复制
发表时间：
2022
期刊：
影响因子：
--
通讯作者：
Akio Kawai
中科院分区：
文献类型：
--
作者：
Hiroki Hirano;Hirona Takahashi;Akio Kawai
采用时间分辨（TR-）和脉冲电子顺磁共振（EPR）方法研究了c70的自由基清除反应。在二苯基氧化膦（DPPO）自由基和c70体系中，由于磷原子的存在，c70加合自由基的结构异构体出现在TR-EPR光谱中，具有清晰的超精细结构。通过超精细耦合常数分析，确定了四种同分异构体。通过半经验计算生成各异构体的相对加成反应速率常数，确定了加合自由基的归属。采用脉冲电子自旋回波法测定了c70在甲苯中对DPPO、羟基环己基和2-羟丙基自由基的清除速率常数ksca。该数值接近109mol - 1dm3s - 1，几乎等于甲苯中扩散控制速率常数。这证明c70是一种优良的自由基清除剂。此外，通过考虑TR-EPR光谱中加合自由基的峰强度比，得到了c70对c70中不同碳原子的自由基加成速率常数kadd。在这项研究中，我们证明了五边形（五元环）中大量的碳原子是富勒烯高反应性的原因。
The radical scavenging reactions of C70were investigated using time-resolved (TR-) and pulsed electron paramagnetic resonance (EPR) methods. In the diphenylphosphine oxide (DPPO) radical and C70system, structural isomers of the adduct radicals of C70appeared in the TR-EPR spectrum with clear hyperfine structures due to the phosphorus atom. Four isomers were identified through the analysis of the hyperfine coupling constants. The assignment of the adduct radicals was confirmed by the semiempirical calculation of the relative addition reaction rate constants that produce each isomer. The radical scavenging rate constants,ksca, of C70in toluene were determined for DPPO, hydroxylcyclohexyl, and 2-hydroxypropyl radicals through electron spin echo observations using the pulsed-EPR method. Thekscavalues were nearly 109mol–1dm3s–1and were almost equal to the diffusion-controlled rate constant in toluene. This proves that C70acts as an excellent radical scavenger. In addition, the radical addition rate constants,kadd, of C70for varying carbon atoms in C70were obtained by considering the peak intensity ratio of the adduct radicals in the TR-EPR spectrum. In this study, we demonstrated that the large number of carbon atoms in pentagons (five-membered rings) is responsible for the high reactivity of fullerenes.