Department of Biochemistry, Agricultural University, Wageningen, The Netherlands.
Proc Natl Acad Sci U S A. 1981 Oct;78(10):5928-32. doi: 10.1073/pnas.78.10.5928.
The effectiveness of negatively charged colloidal SiO(2) particles in controlling photosensitized electron transfer reactions has been studied and compared with that of the negatively charged sodium lauryl sulfate (NaLauSO(4)) micellar system. In particular, the photosensitized reduction of the zwitterionic electron acceptor propylviologen sulfonate (PVS(0)) with tris(2,2'-bipyridinium)ruthenium(II) [Ru(bipy)(3) (2+)] as the sensitizer and triethanolamine as the electron donor is found to have a quantum yield of 0.033 for formation of the radical anion (PVS([unk])) in the SiO(2) colloid compared with 0.005 in the homogeneous system and 0.0086 in a NaLauSO(4) micellar solution. The higher quantum yields obtained with the SiO(2) colloidal system are attributed to substantial stabilization against back reaction of the intermediate photoproducts-i.e., Ru(bipy)(3) (3+) and PVS([unk])-by electrostatic repulsion of the reduced electron acceptor from the negatively charged particle surface. The binding properties of the SiO(2) particles and NaLauSO(4) micelles were investigated by flow dialysis. The results show that the sensitizer binds to both interfaces and that the SiO(2) interface is characterized by a much higher surface potential than the micellar interface ( approximately -170 mV vs. -85 mV). The effect of ionic strength on the surface potential was estimated from the Gouy-Chapman theory, and the measured quantum yields of photosensitized electron transfer were correlated with surface potential at different ionic strengths. This correlation shows that the quantum yield is not affected by surface potentials smaller than approximately -40 mV. At larger potentials, the quantum yield increases rapidly. The quantum yield obtained in the micellar system at different strengths fits nicely on the correlation curve for the colloid SiO(2) system. These results indicate that the surface potential is the dominant factor in the quantum yield improvement for PVS(0) reduction.
已研究并比较了带负电荷的胶体二氧化硅 (SiO2) 颗粒在控制光敏电子转移反应中的效果，其效果与带负电荷的十二烷基硫酸钠 (NaLauSO4) 胶束系统相比较。特别是，用三(2,2'-联吡啶)钌(II) [Ru(bipy)3(2+)] 作为敏化剂和三乙醇胺作为电子供体，对两性离子电子受体丙基紫精磺酸盐 (PVS(0)) 的光致还原反应发现，在 SiO2 胶体中形成自由基阴离子 (PVS([unk])) 的量子产率为 0.033，而在均相体系和 NaLauSO4 胶束溶液中的量子产率分别为 0.005 和 0.0086。SiO2 胶体体系获得的更高量子产率归因于静电排斥作用使中间光产物 - 即 Ru(bipy)3(3+) 和 PVS([unk])- 远离带负电荷的粒子表面，从而阻止了它们的反向反应。通过流动透析法研究了 SiO2 粒子和 NaLauSO4 胶束的结合特性。结果表明，敏化剂与两个界面结合，SiO2 界面的表面电势比胶束界面高得多（约为-170 mV 对-85 mV）。根据古依-查普曼理论估算了离子强度对表面电势的影响，并用不同离子强度下光致电子转移的量子产率与表面电势相关联。该相关性表明，当表面电势小于约-40 mV 时，量子产率不受影响。在更大的电势下，量子产率迅速增加。在不同强度下的胶束体系中获得的量子产率很好地符合胶体 SiO2 体系的相关曲线。这些结果表明，表面电势是提高 PVS(0)还原量子产率的主要因素。
