Chiral Electrokinetic Phenomena in Single Nanopores

The arrangement of solvent molecules and ions at solid–liquid interfaces determines electrochemical properties that are important in separations platforms, sensing technologies, and energy-storage systems. Here we show that single glass and polymer pores in contact with propylene carbonate (PC) solutions of LiClO₄ exhibit an effective surface potential that is modulated by the enantiomeric excess of the solvent. In particular, electrochemical and electrokinetic measurements of ionic transport through glass pipettes and polymer pores reveal that the effective surface potential is significantly lower in solutions prepared using enantiomerically pure PC than in solutions prepared using racemic PC. Both pore systems became positively charged in all racemic solutions examined in the range of LiClO₄ concentrations between 1 mM and 100 mM, whereas solutions in (R)-(+)-PC induced a positive surface potential only at concentrations above ~5 mM. The effective surface potential is quantified through asymmetry in current–voltage curves and zeta-potential measurements. Vibrational sum-frequency-generation experiments on LiClO₄ solutions in racemic and enantiomerically pure PC indicate that the surface lipid-bilayer-like region in the former is more strongly organized than in the latter, dictating the favorable positions for lithium and perchlorate ions in each case. The more ordered molecular packing in the racemic liquid leads to accumulation of lithium ions on the outside of the bilayer, creating a higher effective positive charge. Our results highlight the extreme sensitivity of the interfacial potential on molecular organization of the solvent, and the relatively unexplored role that chirality can play in electrokinetic phenomena.