Abstract
In this work, a theoretical model describing the interaction between a positively or negatively charged nanoparticle and neutral zwitterionic lipid bilayers is presented. It is shown that in the close vicinity of the positively charged nanoparticle, the zwitterionic lipid headgroups are less extended in the direction perpendicular to the membrane surface, while in the vicinity of the negatively charged nanoparticle, the headgroups are more extended. This result coincides with the calculated increase in the osmotic pressure between the zwitterionic lipid surface and positively charged nanoparticle and the decrease of osmotic pressure between the zwitterionic lipid surface and the negatively charged nanoparticle. Our theoretical predictions agree well with the experimentally determined fluidity of a lipid bilayer membrane in contact with positively or negatively charged nanoparticles. The prospective significance of the present work is mainly to contribute to better understanding of the interactions of charged nanoparticles with a zwitterionic lipid bilayer, which may be important in the efficient design of the lipid/nanoparticle nanostructures (like liposomes with encapsulated nanoparticles), which have diverse biomedical applications, including targeted therapy (drug delivery) and imaging of cancer cells.
Highlights
The basic building block of a cell membrane is a bilayer of lipid molecules with embedded carbohydrates and proteins [1,2,3,4,5,6]
Membrane fluidity denotes the viscosity of the phospholipid bilayer of a cell, and fluidity enables the free mobility of the lipids and protein molecules in a cell membrane [47]
The fluidity of the lipid bilayer membrane of small unilamellar vesicles was determined by measuring the fluorescence anisotropy, which is directly proportional to the lipid ordering in the membrane and inversely proportional to the membrane fluidity
Summary
The basic building block of a cell membrane is a bilayer of lipid molecules with embedded carbohydrates and proteins [1,2,3,4,5,6]. In the high electric field of dipolar lipid headgroups (see [13] and the references therein), the water dipoles are oriented towards the negatively charged plane (see, for example, [23,26,27,28,29,30,31,32]). It was shown that within a simple mean-field approach, due to the saturation effect in the orientational ordering of water dipoles, the relative permittivity in the zwitterionic headgroup region is decreased, while the corresponding electric potential becomes more negative [26]. In this paper, the interaction between a negatively charged or dipolar flat lipid layer and positively or negatively charged nanoparticles (Figure 1) mediated by water dipoles and ions is studied within the mean-field approach using the modified Langevin-Poisson-Boltzmann (LPB) model [26,30]. Through experimental study of the nanoparticle-induced changes in lipid bilayer fluidity, we intend to establish a correlation between the theoretical calculations and experimental results
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