Bordi F, Cametti C, Sennato S, Viscomi D
Dipartimento di Fisica, Università di Roma La Sapienza, Piazzale A. Moro 2, I-00185 Rome, Italy.
J Chem Phys. 2007 Jan 14;126(2):024902. doi: 10.1063/1.2423028.
The radiowave dielectric properties of aqueous heterogeneous systems during the complexation of charged polyions and oppositely charged liposomal particles have been measured in a wide frequency range, between 100 Hz and 2 GHz. The formation of a polyion-liposome complex driven by the correlated polyion adsorption at the particle surface implies two concomitant effects referred to as reentrant condensation and charge inversion. Both of them are governed by electrostatic interactions and there is now strong evidence, based on experiments and simulations, that counterion release is the driving force of the aggregation process. From this point of view, dielectric technique may offer a suitable tool in the investigation of the structural properties of these aggregates. In spite of the fact that interaction of polyions with oppositely charged surfaces was extensively experimentally investigated, there are no papers concerning the dielectric properties during the polyion-induced aggregation. To get an insight into this important topic, the authors present here an extensive set of radiowave dielectric measurements of liposomal vesicle aqueous suspensions where the liposome aggregation was induced by an oppositely charged polyion. The aggregation was followed from the beginning, when most of the isolated liposomes predominate, up to the formation of polyion-coated liposomes of inverted charge, crossing the isoelectric condition, where large, almost neutral, aggregates appear. The authors describe the observed dielectric dispersions as due to counterion polarization in the adjacency of the liposome and liposome aggregate surface, primarily governed by the zeta potential, according to the standard electrokinetic model.
在100Hz至2GHz的宽频率范围内，测量了带电聚离子与带相反电荷的脂质体颗粒络合过程中水性多相体系的射频介电特性。由颗粒表面相关的聚离子吸附驱动的聚离子-脂质体复合物的形成意味着两种伴随效应，即折返凝聚和电荷反转。它们都受静电相互作用的支配，现在基于实验和模拟有强有力的证据表明，抗衡离子的释放是聚集过程的驱动力。从这个角度来看，介电技术可能为研究这些聚集体的结构特性提供一个合适的工具。尽管对聚离子与带相反电荷表面的相互作用进行了广泛的实验研究，但尚无关于聚离子诱导聚集过程中介电特性的论文。为了深入了解这个重要课题，作者在此展示了一组广泛的射频介电测量结果，这些测量针对的是脂质体囊泡水悬浮液，其中脂质体聚集是由带相反电荷的聚离子诱导的。从一开始，当大多数孤立的脂质体占主导时，就跟踪聚集过程，直至形成带相反电荷的聚离子包被脂质体，跨越等电条件，此时会出现大的、几乎呈中性的聚集体。作者将观察到的介电色散描述为主要由ζ电位控制的、脂质体和脂质体聚集体表面附近的抗衡离子极化所致，这符合标准的电动模型。
