Dynamics and local environment of an aromatic counterion bound to di-chain cationic surfactant bilayers studied by avoided level crossing muon spin resonance: evidence for counterion condensation

Avoided level crossing muon spin resonance (ALC-μSR) was used to study the dynamics of muon-spin-labelled 2,4,6-trimethylbenzoate counterions and their interaction with DODMAC (dioctadecyldimethylammonium chloride) bilayers in the Lα and Lβ states.

Fracto-eutectogels: SDS dendritic fractals via counterion condensation in a deep eutectic solvent

Glyceline, a deep eutectic solvent comprising glycerol and choline chloride, is a green nonaqueous solvent with potential industrial applications. Molecular mechanisms of surfactant self-assembly in deep eutectic solvents are expected...

Differences of the tumour cell glycocalyx affect binding of capsaicin-loaded chitosan nanocapsules

The glycocalyx regulates the interaction of mammalian cells with extracellular molecules, such as cytokines. However, it is unknown to which extend the glycocalyx of distinct cancer cells control the binding and uptake of nanoparticles. In the present study, exome sequencing data of cancer patients and analysis of distinct melanoma and bladder cancer cell lines suggested differences in cancer cell-exposed glycocalyx components such as heparan sulphate. Our data indicate that glycocalyx differences affected the binding of cationic chitosan nanocapsules (Chi-NCs). The pronounced glycocalyx of bladder cancer cells enhanced the internalisation of nanoencapsulated capsaicin. Consequently, capsaicin induced apoptosis in the cancer cells, but not in the less glycosylated benign urothelial cells. Moreover, we measured counterion condensation on highly negatively charged heparan sulphate chains. Counterion condensation triggered a cooperative binding of Chi-NCs, characterised by a weak binding rate at low Chi-NC doses and a strongly increased binding rate at high Chi-NC concentrations. Our results indicate that the glycocalyx of tumour cells controls the binding and biological activity of nanoparticles. This has to be considered for the design of tumour cell directed nanocarriers to improve the delivery of cytotoxic drugs. Differential nanoparticle binding may also be useful to discriminate tumour cells from healthy cells.

Contributions and competition of Mg2+ and K+ in folding and stabilization of the Twister Ribozyme

Native folded and compact intermediate states of RNA typically involve tertiary structures in the presence of divalent ions such as Mg2+ in a background of monovalent ions. In a recent study we showed how the presence of Mg2+ impacts the transition from partially unfolded to folded states through a “push-pull” mechanism where the ion both favors and disfavors the sampling of specific phosphate-phosphate interactions. To better understand the ion atmosphere of RNA in folded and partially folded states results from atomistic Umbrella Sampling and oscillating chemical potential Grand Canonical Monte Carlo/Molecular Dynamics (GCMC/MD) simulations are used to obtain atomic-level details of the distributions of Mg2+ and K+ ions around Twister RNA. Results show the presence of 100 mM Mg2+ to lead to increased charge neutralization over that predicted by counterion condensation theory. Upon going from partially unfolded to folded states overall charge neutralization increases at all studied ion concentrations that, while associated with an increase in the number of direct ion-phosphate interactions, is fully accounted for by the monovalent K+ ions. Furthermore, K+ preferentially interacts with purine N7 atoms of helical regions in partially unfolded states thereby potentially stabilizing them. Thus, both secondary helical structures and formation of tertiary structures leads to increased counterion condensation, thereby stabilizing those structural features of Twister. Notably, it is shown that K+ can act as a surrogate for Mg2+ by participating in specific interactions with non-sequential phosphate pairs that occur in the folded state, explaining the ability of Twister to self-cleave at sub-millimolar Mg2+ concentrations.

Volume transition effects on the correlations and effective interactions among highly charged microgels

Microgels shrinkage promotes counterion condensation, which in the highly charged regime markedly inhibits the effective interaction and induces strong counterion–counterion correlations that deviate this potential from the traditional Yukawa shape.

Counterion condensation or lack of solvation? Understanding the activity of ions in thin film block copolymer electrolytes

Dissociation of ion charge pairs in block copolymer electrolytes and its relation to activity coefficients and normalized ionic conductivity.

Ionic conductivity and counterion condensation in nanoconfined polycation and polyanion brushes prepared from block copolymer templates

Counterion condensation sensed in nano-confined and non-confined polymer electrolyte brushes with 2D force mapping AFM.