Sando Gerald M, Dahl Kevin, Owrutsky Jeffrey C
Code 6111, U.S. Naval Research Laboratory, Washington, D.C. 20375-5342, USA.
J Phys Chem B. 2005 Mar 10;109(9):4084-95. doi: 10.1021/jp045287r.
Ultrafast infrared spectroscopy has been used to measure vibrational energy relaxation (VER) and reorientation (Tr) times for the high frequency CN stretches of potassium ferrocyanide and ferricyanide and the NO stretch of sodium nitroprusside (SNP) in several reverse micelle (RM) systems using cationic, anionic, and nonionic surfactants. The confinement effects on anion vibrational spectra and dynamics in aqueous RMs depend on the charge of the surfactant that is used to form the RMs. Spectra and VER dynamics of ferrocyanide are not significantly altered in the limited number of RMs in which it could be solubilized. The static spectra of ferricyanide suggest an environment that is most bulklike in anionic RMs and least bulklike in cationic RMs. The dynamics of ferricyanide are slower in cationic RMs and indistinguishable from the bulk in nonionic RMs. The VER dynamics and static spectra of SNP are indistinguishable from the bulk in anionic RMs, but much slower in cationic RMs. This suggests a strong surfactant-solute repulsion in the former and an attraction in the latter. Broad static spectra and probe frequency dependent dynamics are seen for SNP in nonionic RMs, indicating an inhomogeneous distribution of environments. Similar measurements were carried out for SNP in mixtures of water and a model compound containing only the hydrophilic portion of the nonionic surfactants in which RMs are not formed. The results closely resemble those observed for SNP in nonionic RMs and provide evidence that in the latter water penetrates the interface and hydrates the ethylene oxide groups before forming a water pool. The results are consistent with the explanation that Coulombic forces determine the anion location. The anions are repelled to the interior of the water pool, which has a bulklike environment in anionic RMs, and are attracted to the interface in cationic RMs, resulting in a strong interaction with the surfactant. The solute location in the nonionic RMs depends on the hydrophilic nature of the probe, with ferrocyanide and ferricyanide being more hydrophilic than SNP. These results and the dependence on surfactant charge are similar to those reported for azide.
利用阳离子、阴离子和非离子表面活性剂，在多个反胶束（RM）体系中，采用超快红外光谱法测量了亚铁氰化钾和铁氰化钾高频CN伸缩振动以及硝普钠（SNP）的NO伸缩振动的振动能量弛豫（VER）和重取向（Tr）时间。水相RM中阴离子振动光谱和动力学的限制效应取决于用于形成RM的表面活性剂的电荷。在有限数量的可溶解亚铁氰化物的RM中，其光谱和VER动力学没有显著变化。铁氰化物的静态光谱表明，在阴离子RM中其环境最接近本体，而在阳离子RM中最不像本体。铁氰化物在阳离子RM中的动力学较慢，在非离子RM中与本体无法区分。SNP的VER动力学和静态光谱在阴离子RM中与本体无法区分，但在阳离子RM中要慢得多。这表明在前者中表面活性剂与溶质存在强烈排斥，而在后者中存在吸引。在非离子RM中，SNP呈现出较宽的静态光谱和与探针频率相关的动力学，表明环境分布不均匀。对SNP在水与仅含非离子表面活性剂亲水性部分的模型化合物的混合物中进行了类似测量，其中不会形成RM。结果与在非离子RM中观察到的SNP的结果非常相似，并提供了证据表明，在后者中，水在形成水池之前会穿透界面并使环氧乙烷基团水合。结果与库仑力决定阴离子位置的解释一致。阴离子被排斥到水池内部，在阴离子RM中水池内部具有类似本体的环境，而在阳离子RM中阴离子被吸引到界面，导致与表面活性剂发生强烈相互作用。溶质在非离子RM中的位置取决于探针的亲水性，亚铁氰化物和铁氰化物比SNP更亲水。这些结果以及对表面活性剂电荷的依赖性与报道的叠氮化物的结果相似。
