title: Role of electrostatic interactions in two-dimensional self-assembly of tobacco mosaic viruses on cationic lipid monolayers.
abstract: We explore two-dimensional self-assembly of tobacco mosaic viruses (TMVs) on a substrate-supported, fluid lipid monolayer by manipulating the electrostatic interactions, with specific focus on the effects of the cationic lipid concentration in the monolayer and the presence of Ca(2+) ions in the surrounding bulk solution. The TMV assemblies were characterized by grazing-incidence X-ray scattering and atomic force microscopy, and the inter-particle interaction quantified through X-ray scattering data analysis. In the absence of Ca(2+) ions, we found that higher charge densities on the lipid monolayer led to poorer in-plane order, which may be attributed to faster adsorption kinetics, due to the surface potential that increases with charge density. At the same time, higher lipid-charge densities also resulted in weaker repulsion between TMVs, due to partial screening of Coulomb repulsion by mobile cationic lipids in the monolayer. The lipid-charge dependence was diminished with increasing concentration of Ca(2+) ions, which also led to tighter packing of TMVs. The results indicate that Ca(2+) ions strengthen the screening of Coulomb repulsion between TMVs and consequently enhance the role of attractive forces. Control experiments involving Na(+) ions suggest that the attractive inter-TMV interaction has contributions from both the van der Waals force and the counter-ion-induced attraction that depends on ion valence.
authors.affiliation: National Synchrotron Light Source, Photon Sciences Directorate, Brookhaven National Laboratory, Upton, NY 11973, USA.
authors.forename: Suntao
authors.initials: S
authors.lastname: Wang
authors.forename: Masafumi
authors.initials: M
authors.lastname: Fukuto
authors.forename: Antonio
authors.initials: A
authors.lastname: Checco
authors.forename: Zhongwei
authors.initials: Z
authors.lastname: Niu
authors.forename: Qian
authors.initials: Q
authors.lastname: Wang
authors.forename: Lin
authors.initials: L
authors.lastname: Yang
mesh_terms: D002118:Calcium / Q000737:chemistry; D002412:Cations; D008055:Lipids / Q000737:chemistry*; D018625:Microscopy, Atomic Force; D055672:Static Electricity; D014027:Tobacco Mosaic Virus / Q000737:chemistry*; D014961:X-Ray Diffraction
chemical_list: D002412:Cations; D008055:Lipids; D002118:Calcium