Oliveira Carla S, Bastos Erick L, Duarte Evandro L, Itri Rosangela, Baptista Mauricio S
Departamento de Bioquímica, IQ-USP, São Paulo-SP, C.P. 26077, 05599-970, Brazil.
Langmuir. 2006 Oct 10;22(21):8718-26. doi: 10.1021/la061117p.
The interfacial localization and the ion pair formation of the positively charged dye crystal violet (CV) in sodium bis(2-ethylhexyl)sulfosuccinate reverse micelles (AOT RMs) were studied by several structural and spectroscopic techniques and by quantum chemical calculations. The size and shape of the AOT RMs in the presence of CV were investigated by small-angle X-ray scattering, showing that CV does not significantly change the RM structure. CV localization as a function of the water to surfactant molar ratio (w(0)) was characterized by H(1) and (13)C NMR, indicating the close proximity of CV to the sulfosuccinate group of AOT at small and large w(0) values. These results were confirmed by calculation of magnetic shielding constants using the gauge-independent atomic orbital method with the HF/6-31G(d) basis set. Two different types of ion pairs between AOT and CV, i.e., contact ion pair (CIPs) and solvent-separated ion pair (SSIPs), were characterized by UV-vis spectroscopy and quantum chemical calculations using the semiempirical ZINDO-CI method. In nonpolar isotropic solvents CIPs are formed with an association constant (K(ASSOC)) of 2 x 10(4) mol(-1) L in isooctane and 750 mol(-1) L in chloroform. In AOT RMs at low w(0), CV-AOT CIPs are also formed. By increasing w(0), there is a sharp decrease in the CIP association free energy, and SSIPs are formed. (CV(+))(H(2)O)(AOT(-)) SSIPs are stable in the AOT RM up to the largest w(0) tested (w(0) = 33).
通过多种结构和光谱技术以及量子化学计算，研究了带正电荷的染料结晶紫（CV）在双（2-乙基己基）磺基琥珀酸钠反胶束（AOT RMs）中的界面定位和离子对形成。通过小角X射线散射研究了存在CV时AOT RMs的尺寸和形状，结果表明CV不会显著改变反胶束结构。通过H(1)和(13)C NMR表征了CV定位与水与表面活性剂摩尔比（w(0)）的关系，表明在小w(0)值和大w(0)值时CV都与AOT的磺基琥珀酸基团紧密相邻。使用HF/6-31G(d)基组的规范无关原子轨道方法计算磁屏蔽常数，证实了这些结果。通过紫外可见光谱和使用半经验ZINDO-CI方法的量子化学计算，表征了AOT和CV之间两种不同类型的离子对，即接触离子对（CIPs）和溶剂分隔离子对（SSIPs）。在非极性各向同性溶剂中，在异辛烷中形成的CIPs的缔合常数（K(ASSOC)）为2×10(4) mol(-1) L，在氯仿中为750 mol(-1) L。在低w(0)的AOT RMs中也形成了CV-AOT CIPs。随着w(0)的增加，CIP缔合自由能急剧下降，并形成了SSIPs。(CV(+))(H(2)O)(AOT(-)) SSIPs在AOT RM中一直稳定到测试的最大w(0)值（w(0) = 33）。
