Dept. of Chemistry, University of Coimbra, 3004-535 Coimbra, Portugal.
J Colloid Interface Sci. 2011 Feb 15;354(2):670-6. doi: 10.1016/j.jcis.2010.10.063. Epub 2010 Nov 3.
The interaction between aqueous solutions of trivalent lanthanide ions (M(3+): La(III) and Gd(III) and Tb (III)) at fixed (1mM) concentrations and various concentrations of sodium dodecyl sulfate (SDS), ranging from pre- to post-micellar, has been investigated by ICP-AES (La(III) and Gd(III)), luminescence spectra (Gd(III)) and lifetimes (Tb(III)) and (139)La NMR spectroscopy. It has been found that at concentration ratios, r=[SDS]/[M(3+)], around the charge neutralization value (ca. 3), dodecyl sulfate (DS(-)) anion interacts with the metal ions to form insoluble aggregates. The metal ion-DS(-) complexes remain flocculated for r values below 5-6 (Gd(III) and La(III), respectively), while at higher r values, re-dissolution takes place. The flocculated aggregates have been characterized by X-ray powder diffraction, and show a lamellar structure. Job plot method indicates that a complex with a 1:3 (M(3+):DS(-)) stoichiometry is formed. From ICP-AES analysis, a model based on a three-step mechanism has been developed and association constants calculated. For all systems the interaction between DS(-) and metal ions follows an associative process with K values ranging between K(1)=10 and K(3)=10(4). These data are discussed on the basis of the physical-chemical characteristics of the metal ions. Re-dissolution with increasing surfactant concentration is attributed to formation of mixed lanthanide/sodium dodecyl sulfate aggregates, with the relative lanthanide fraction in these species decreasing with increasing SDS concentration.
三价镧系离子（M(3+)：La(III)和 Gd(III)以及 Tb(III)）在固定（1mM）浓度和不同浓度的十二烷基硫酸钠（SDS）水溶液之间的相互作用，从预胶束到胶束后，已经通过 ICP-AES（La(III)和 Gd(III)）、发光光谱（Gd(III)）和寿命（Tb(III)）和（139）La NMR 光谱进行了研究。已经发现，在浓度比，r=[SDS]/[M(3+)],接近电荷中和值（约 3）时，十二烷基硫酸盐（DS(-)）阴离子与金属离子相互作用形成不溶性聚集体。对于 r 值低于 5-6（Gd(III)和 La(III)，分别）的金属离子-DS(-)复合物仍然絮凝，而在较高的 r 值下，重新溶解发生。絮凝聚集体已通过 X 射线粉末衍射进行了表征，并显示出层状结构。工作图法表明形成了具有 1:3（M(3+):DS(-)）化学计量比的复合物。从 ICP-AES 分析中，已经开发了基于三步机制的模型并计算了缔合常数。对于所有体系，DS(-)与金属离子之间的相互作用遵循缔合过程，K 值在 K(1)=10 和 K(3)=10(4)之间。这些数据是基于金属离子的物理化学特性进行讨论的。随着表面活性剂浓度的增加而重新溶解归因于形成混合镧系元素/十二烷基硫酸钠聚集体，这些物种中的相对镧系元素分数随着 SDS 浓度的增加而降低。
