Design of artificial membrane transporters from gold nanoparticles with controllable hydrophobicity

Abstract

Gold nanoparticles with variable hydrophobicity have been prepared in three different size regimes following established methods. The control of hydrophobicity was achieved by complexation of the 18-crown-6-CH-thiolate ligand shell with potassium ions. Potassium dependent phase transfer of these particles from dispersion in water to chloroform was demonstrated, and the equilibrium partitioning of the particles in water-chloroform liquid/liquid systems was quantified by optical spectroscopy. The gradual complexation of the ligand shell with potassium ions was further monitored by zeta potential measurements. Potassium dependent insertion of nanoparticles into the phospholipid bilayer membrane of vesicles in aqueous dispersion has been demonstrated by cryogenic transmission electron microscopy (cryo-TEM). Nanoparticle-dependent potassium ion transport across the vesicle membrane has been established by monitoring the membrane potential with fluorescence spectroscopy using a potential sensitive dye.

Ion Transport across Biological Membranes by Carborane-Capped Gold Nanoparticles

“…The fluorescence intensity of safranin O was calibrated against the membrane potential values calculated from the Nernst equation ( Figure S2 ). 20 , 23 If, instead of valinomycin, the nanoparticles are added, a rapid polarization of the membrane in the same direction (inside negative) is also observed, but the final value does not depend on the potassium concentrations on both sides of the membrane but only on the amount of nanoparticles added.…”

Entropy‐Driven Reversible Agglomeration of Crown Ether Capped Gold Nanoparticles

“…We have recently shown that the use of thiolated crown ethers (18‐C‐6‐CH 2 ‐SH) as capping agents for gold nanoparticles allowed us to control the hydrophilicity via complexation of K + cations to the crown ether, resulting in phase transfer between aqueous and organic solvents . Here we demonstrate that this ligand can also be used to prepare thermoresponsive particles that show entropy driven reversible agglomeration with controllable transition temperatures directly related to the degree of cation complexation of the crown ether moiety (Scheme ).…”

Ion shuttling between emulsion droplets by crown ether modified gold nanoparticles

“…40 nm in size and to modulate their dispersibility and phase transfer between water and oil. [28][29][30][31][32][33][34][35] When shaking the emulsion, the chloroform sublayers immediately adopted a reddish brown (4 nm GNPs) or pink (7 nm GNPs) color, which we attribute to the transfer of some GNPs to the chloroform phase (see Fig. ESI1 †).…”

“…We have previously reported the transfer of a number of different GNPs across phospholipid mono-and bilayer membranes and also noted their ability to carry across ionic charge. [35][36][37][38] Drawing on this experience, we have conducted an electrochemical experiment that independently conrms barium ion transport across such a hydrophobic boundary between two aqueous compartments.…”

“…Notably, under the conditions of the emulsion experiments, the GNPs always carry a signicant amount of net charge (positive zeta potential), which helps to retain them within the water droplet phase of the emulsion. In a separate experiment, using a two-phase water/chloroform system, it is shown that complexation of cations, which makes the crown-ether more hydrophobic, 34,35,41 causes the GNPs to partition between both phases and also to settle at the phase boundary (Fig. ESI11 †).…”