Swelling of polyelectrolyte multilayers with aqueous solution of ionic liquid (IL) is examined with a dissipative quartz crystal microbalance. Multilayers are prepared with different combinations of polyelectrolyte, employing PEI(PSS/ PAH) 4 PSS and PEI(PSS/PDADMAC) 4 PSS. An enhancement of mass coverage and dissipation is found for films in contact with aqueous solution of IL, i.e., 1-hexyl-3-methylimidazolium chloride and 1-methyl-3-methylimidazolium chloride, suggesting incorporation of IL, accompanied by film swelling. Swelling increases with increasing IL concentration. It is strictly reversible up to a stability limit of IL concentration, above which irreversible layer decomposition starts. Each swelling step can be divided into a fast and a slow process, resulting from IL uptake and chain reorganization or layer decomposition, respectively. While absolute IL uptake and swelling limits differ, the concentration dependence is similar in all systems investigated. The swelling is attributed to hydrophobic interactions, since we find a correlation of the swelling with hydrophobicity of IL.

Multivalent receptor-mediated interactions between virions and a lipid membrane can be weakened using competitive nonpathogenic ligand binding. In particular, the subsequent binding of such ligands can induce detachment of bound virions, a phenomenon of crucial relevance for the development of new antiviral drugs. Focusing on the simian virus 40 (SV40) and recombinant cholera toxin B subunit (rCTB), and using (monosialotetrahexosyl)ganglioside (GM1) as their common receptor in a supported lipid bilayer (SLB), we present the first detailed investigation of this phenomenon by employing the quartz crystal microbalance with dissipation (QCM-D) and total internal reflection fluorescence (TIRF) microscopy assisted 2D single particle tracking (SPT) techniques. Analysis of the QCM-D-measured release kinetics made it possible to determine the binding strength of a single SV40-GM1 pair. The release dynamics of SV40, monitored by SPT, revealed that a notable fraction of SV40 becomes mobile just before the release, allowing to estimate the distribution of SV40-bound GM1 receptors just prior to release.

A longstanding question exists on the impact of the HIV-1 integration site on viral gene expression. This unsolved question has significant implications for the search toward an HIV-1 cure, as eradication strategies set up to reactivate and eliminate HIV-1 depend on the site where the provirus is integrated.

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Virus internalization into the host cells occurs via multivalent interactions, in which a single virus binds to multiple receptors in parallel. Because of analytical and experimental limitations this complex type of interaction is still poorly understood and quantified. Herein, the multivalent interaction of norovirus-like particles (noroVLPs) with H or B type 1 glycosphingolipids (GSLs), embedded in a supported phospholipid bilayer, is investigated by following the competition between noroVLPs and a lectin (from Ralstonia solanacearum) upon binding to these GSLs. Changes in noroVLP and lectin coverage, caused by competition, were monitored for both GSLs and at different GSL concentrations using quartz crystal microbalance with dissipation monitoring. The study yields information about the minimum GSL concentration needed for i) noroVLPs to achieve firm attachment to the bilayer prior to competition, and to ii) remain firmly attached to the bilayer during competition. We show that these two concentrations are almost identical for the H type 1-noroVLP interaction, but differ for B type 1, indicating an accumulation of B type 1 GSLs in the noroVLP-bilayer interaction area. Furthermore, the GSL concentration required for firm attachment is significantly larger for H type 1 than for B type 1, indicating a higher affinity of noroVLP towards B type 1. This finding is supported by extracting the energy of single noroVLP-H type 1 and noroVLP-B type 1 bonds from the competition kinetics, which were estimated to be 5 and 6 kcal/mol, respectively. This demonstrates the potential of utilizing competitive binding kinetics to analyse multivalent interactions, which has remained difficult to quantify using conventional approaches.