Influence of cationic composition and pH on the formation of metal stearates at oil-water interfaces

We study the formation of layers of metal stearates at the interface between a decane solution of stearic acid and aqueous salt solutions of variable composition and pH by monitoring the evolution of their mechanical, optical, and chemical properties as a function of time after formation of the interface. For values of the pH below the pK(a) of stearic acid hardly any interfacial activity is observed. For pH > pK(a), stearic acid deprotonates at the interface and forms metal stearates, eventually leading to the formation of macroscopic solid layers. Dynamic interfacial tension measurements reveal that the process takes place in several stages, which we attribute to the successive formation of dilute and dense monolayers followed by three-dimensional growth. In the presence of divalent ions, the solid layers display a significant increase in the dilatational storage modulus. Experiments performed with an aqueous phase containing multiple cation species (artificial seawater) give rise to particularly pronounced growth of solid layers, which preferentially incorporate Ca(2+) as revealed by X-ray photoelectron and infrared spectroscopy. Our results highlight in particular the importance of the complex synergistic effects of simultaneously present monovalent and divalent cation species on the interfacial adsorption.     

Emerging Anticancer Therapeutic Modalities Brought by Gold Complexes: Overview and Perspectives

The medicinal chemistry of gold has experienced an exponential development since the 2000s. For long, the mechanisms of action of gold complexes have been limited to direct coordination of the gold ion or supramolecular interactions of the whole gold complex with biomolecules. In the recent years, other modes of action of gold-based drug candidates have emerged. Herein, we review these new modalities, including photo-induced cytotoxicity, selective protein modification and in cellulo catalysis.