碱溶液中DMPO-OH加合物EPR信号形成研究

为考察碱溶液中DMPO-OH加合物的形成情况及其影响因素，以NaOH溶液为对象，利用EPR（electron paramagnetic resonance，电子顺磁共振）技术，通过DMPO（5，5-二甲基-1-吡咯啉-N-氧化物）自旋捕获，对不同条件下NaOH溶液中DMPO-OH加合物的形成及变化规律进行研究，探讨DMPO-OH加合物的生成过程及降解过程反应机制.结果表明:①将DMPO添加到碱溶液中后，在EPR内检测到典型的DMPO-OH四重特征峰（1:2:2:1），说明碱溶液中形成了DMPO-OH加合物.②紫外光激发下，碱溶液体系能产生更强的DMPO-OH加合物特征信号，暗反应体系次之，可见光条件下最弱.③体系中DMPO-OH加合物的生成与碱溶液浓度密切相关，当c（NaOH）由0.001 mol/L增至2 mol/L时，DMPO-OH加合物的EPR信号峰呈先增后减最终几乎消失的变化趋势.④紫外光照时间对体系中DMPO-OH加合物的存在影响显著，随着光照时间的延长，DMPO-OH加合物的浓度并没有逐渐增高，而是更加倾向于逐渐降低的趋势，这可能是由于形成的DMPO-OH加合物在短时间内被淬灭或分解.⑤碱溶液中DMPO-OH加合物的生成过程为瞬态过程，降解过程占主导，并且紫外光在其生成及降解过程中发挥了重要作用.研究显示，当c（DMPO）为350 mmol/L、c（NaOH）为0.1 mol/L、紫外光照时间为15 min时，碱溶液中DMPO-OH加合物的EPR信号最佳. 

Study on EPR Signal Formation of DMPO-OH Adduct in Alkali Solution

To investigate the DMPO-OH adduct formation condition and its influencing factors in alkali solution, the DMPO-OH adducts in NaOH solution under different conditions were measured by an electron paramagnetic resonance (EPR), and 5,5-dimethyl-1-pyrroline N-oxide (DMPO) was used as the spin trapping compound. The results showed that:(1) The typical quadruple peak of the DMPO-OH (1:2:2:1) could be detected by EPR after adding DMPO to the alkali solution, indicating the formation of DMPO-OH adduct would take place in the alkali solution. (2) For the alkali solution system, a stronger characteristic signal of DMPO-OH adducts could be observed under UV-irradiation, followed by the dark reactions and the weakest under the visible light. (3) The formation of DMPO-OH adduct was closely related to the c(NaOH). When the c(NaOH) increased from 0.001 mol/L to 2 mol/L, the EPR signal peak of DMPO-OH adduct was firstly strengthened and then weakened, and eventually disappeared. (4) The presence of DMPO-OH adduct in the system was affected prominently by the UV-irradiation time. It did not increase gradually, but tended to decrease gradually with the increase of UV-irradiation time, which could be attributed to the quenching or degradation of the formed DMPO-OH adduct. (5) The degradation process of DMPO-OH adduct in alkali solution was dominant and its generation process was a transient response, UV light played a significant role in its formation and degradation processes. The optimum formation conditions of the DMPO-OH adduct in alkali solution were determined as c(DMPO) 350 mmol/L, c(NaOH) 0.1 mol/L and UV-irradiation time 15 min via the univariate experiments.