碱溶液中DMPO-OH加合物EPR信号形成研究

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

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 paramagneticresonance,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.

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.