Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas (INIFTA), Facultad de Ciencias Exactas, Universidad Nacional de la Plata, C.C. 16, suc. 4, (1900) La Plata, Argentina.
Langmuir. 2011 May 3;27(9):5304-9. doi: 10.1021/la2005997. Epub 2011 Apr 8.
A series of photoinduced H-atom abstraction reactions between anthraquinone-2,6,-disulfonate, disodium salt (AQDS) and differently charged micellar substrates is presented. After a 248 nm excimer laser flash, the first excited triplet state of AQDS is rapidly formed and then quenched by abstraction of a hydrogen atom from the alkyl chain of the micelle surfactant, leading to a spin-correlated radical pair (SCRP). The SCRP is detected 500 ns after the laser flash using time-resolved (direct detection) electron paramagnetic resonance (TREPR) spectroscopy at X-band (9.5 GHz). By changing the charge on the surfactant headgroup from negative (sodium dodecyl sulfate, SDS) to positive (dodecyltrimethylammonium chloride, DTAC), TREPR spectra with different degrees of antiphase structure (APS) in their line shape were observed. The first derivative-like APS line shape is the signature of an SCRP experiencing an electron spin exchange interaction between the radical centers, which was clearly observable in DTAC micelles and absent in SDS micellar solutions. Solutions with surfactant concentrations well below the critical micelle concentration (cmc) or solutions where micellar formation had been disrupted (1:1 v/v CH(3)CN/H(2)O) also showed no APS line shapes in their TREPR spectra. These results support the conclusion that electrostatic forces between the sensitizer (AQDS) charge and the substrate (surfactant) headgroup charge are responsible for the observed effects. The results represent a new example of electrostatic control of a spin exchange interaction in mobile radical pairs.
本文介绍了蒽醌-2,6-二磺酸钠（AQDS）与带不同电荷的胶束底物之间的一系列光诱导 H 原子攫取反应。在 248nm 准分子激光闪光后，AQDS 的第一激发三重态迅速形成，然后通过从胶束表面活性剂的烷基链上攫取氢原子而猝灭，导致自旋相关自由基对（SCRP）。在激光闪光后 500ns，使用 X 波段（9.5GHz）的时间分辨（直接检测）电子顺磁共振（TREPR）光谱检测到 SCRP。通过改变表面活性剂头基的电荷从负（十二烷基硫酸钠，SDS）变为正（十二烷基三甲基氯化铵，DTAC），观察到具有不同程度反相结构（APS）的 TREPR 光谱。具有一阶导数样 APS 线形状的特征是自由基中心之间经历电子自旋交换相互作用的 SCRP，在 DTAC 胶束中可以明显观察到，而在 SDS 胶束溶液中则不存在。表面活性剂浓度远低于临界胶束浓度（cmc）的溶液或胶束形成被破坏的溶液（1：1v/v CH 3 CN/H 2 O）的 TREPR 光谱中也没有 APS 线形状。这些结果支持了这样的结论，即敏化剂（AQDS）电荷和底物（表面活性剂）头基电荷之间的静电力是观察到的效应的原因。这些结果代表了在可移动自由基对中静电控制自旋交换相互作用的新实例。
