Neutron reflectometry has been used to study the adsorption of the anionic surfactant bis(2-ethylhexyl) sulfosuccinate cesium salt on the anionic surface of mica. Evidence of significant adsorption is reported. The adsorption is reversible and changes little with pH. This unexpected adsorption behavior of an anionic molecule on an anionic surface is discussed in terms of recent models for surfactant adsorption such as cation bridging, where adsorption has been reported with the divalent ion calcium but not previously observed with monovalent ions.

The adsorption and desorption of a cationic surfactant, didodecyldimethylammonium bromide, from water onto a mica surface has been investigated using neutron reflectivity. The surfactant was observed to adsorb strongly as a bilayer that was tenacious to a sustained water wash, but on the addition of an anionic surfactant, sodium dodecyl sulfate, at its critical micelle concentration complete desorption was observed.

Molecular-dynamics simulations are used to explore bilayers formed by simple ionic surfactants at the mica–water interface, and to shed light on experimental observations.

The bridging eect of a series of common cations between the anionic mica surface and the AOT anion has been studied in a condition of constant ionic strength and surfactant concentration. It was found that sodium ions did not show any bridging eect in this system; however, calcium, magnesium, and potassium all caused adsorption of the organic to the mica surface. The concentrations at which bridging occurred was probed, revealing that only a very low bridging cation concentration was required for binding. The bridged layer stability was also investigated and the interaction was shown to be a weak one, with the bound layer in equilibrium with the species in the bulk and easily removed. Even maintaining ionic strength and bridging ion concentration was not sucient to retain the layer when the free organic in solution was removed.

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Summary The ability of human induced pluripotent stem cells (hiPSCs) to differentiate in vitro to each of the three germ layer lineages has made them an important model of early human development and a tool for tissue engineering. However, the factors that disturb the intricate transcriptional choreography of differentiation remain incompletely understood. Here, we uncover a critical time window during which DNA damage significantly reduces the efficiency and fidelity with which hiPSCs differentiate to definitive endoderm. DNA damage prevents the normal reduction of p53 levels as cells pass through the epithelial-to-mesenchymal transition, diverting the transcriptional program toward mesoderm without induction of an apoptotic response. In contrast, TP53 -deficient cells differentiate to endoderm with high efficiency after DNA damage, suggesting that p53 enforces a “differentiation checkpoint” in early endoderm differentiation that alters cell fate in response to DNA damage.

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