Gandini Shirley C M, Itri Rosangela, de Sousa Neto Diógenes, Tabak Marcel
Instituto de Química de São Carlos, Universidade de São Paulo, Cx. Postal 780, CEP 13560-970, São Carlos, SP, Brazil.
J Phys Chem B. 2005 Dec 1;109(47):22264-72. doi: 10.1021/jp052657i.
In this work, small-angle X-ray scattering (SAXS) and electron paramagnetic resonance (EPR) studies on the interaction of three anionic mesotetrakis (4-sulfonatophenyl) porphyrins, TPPS4, FeTPPS4, and ZnTPPS4, at concentrations in the 2-10 mM range, with micelles of the zwitterionic surfactant 3-(N-hexadecyl-N,N-dimethylammonium) propane sulfonate (HPS, 30 mM) at pH 4.0 and 9.0 are reported. The SAXS results demonstrate that, upon addition of all species of porphyrins, the HPS micelle of prolate shape reduces its axial ratio from 1.8 +/- 0.2 (in the absence of porphyrin) to 1.5 +/- 0.1. Such an effect is accompanied by a shrinking of the paraffinic shortest semiaxis from 22.5 +/- 0.5 A to 18.0 +/- 0.2 A. This shows that the micellar hydrophobic core is affected by porphyrin incorporation, independent of the type of porphyrin and pH. Concurrently, EPR results demonstrate an increase in the micellar packing as noticed from the increase in motional restriction for both nitroxides. Furthermore, increase of the porphyrin concentration induces the appearance of a repulsive interference function over the SAXS curve of zwitterionic micelles, which is typical of an interaction between surface-charged micelles. Such a finding gives strong evidence that the negatively charged porphyrin molecule must accommodate in the HPS micelle dipole layer close to the inner positive charges (near the hydrophobic core), inducing a surface charge (probably a negative one associated with the HPS sulfonate external groups) in the original zwitterionic (overall neutral) micelle. Such a porphyrin location is favored by both electrostatic and hydrophobic contributions, giving rise to binding constant values that are quite large compared to the binding of cationic drugs to HPS micelles (Caetano, W.; Barbosa, L. R. S.; Itri, R.; Tabak, M. J. Coll. Int. Sci. 2003, 260, 414).
本文报道了在pH值为4.0和9.0时，对三种阴离子型中位四（4 - 磺酸苯基）卟啉（TPPS4、FeTPPS4和ZnTPPS4）在2 - 10 mM浓度范围内与两性离子表面活性剂3 - （N - 十六烷基 - N，N - 二甲基铵）丙烷磺酸盐（HPS，30 mM）胶束相互作用的小角X射线散射（SAXS）和电子顺磁共振（EPR）研究。SAXS结果表明，加入所有种类的卟啉后，长形的HPS胶束的轴比从1.8±0.2（无卟啉时）降低到1.5±0.1。这种效应伴随着石蜡最短半轴从22.5±0.5 Å收缩到18.0±0.2 Å。这表明胶束疏水核心受到卟啉掺入的影响，与卟啉类型和pH无关。同时，EPR结果表明，从两种氮氧化物的运动受限增加可以看出胶束堆积增加。此外，卟啉浓度的增加导致两性离子胶束的SAXS曲线上出现排斥干涉函数，这是表面带电胶束之间相互作用的典型特征。这一发现有力地证明，带负电荷的卟啉分子必须容纳在HPS胶束偶极层中靠近内部正电荷（靠近疏水核心）的位置，在原始两性离子（总体呈中性）胶束中诱导出表面电荷（可能是与HPS磺酸盐外部基团相关的负电荷）。这种卟啉位置受到静电和疏水作用的共同支持，产生的结合常数与阳离子药物与HPS胶束的结合相比相当大（Caetano，W.；Barbosa，L. R. S.；Itri，R.；Tabak，M. J. Coll. Int. Sci. 2003，260，414）。
