title: Stability and electrostatics of mercaptoundecanoic acid-capped gold nanoparticles with varying counterion size.
abstract: The solubility of charged nanoparticles is critically dependent on pH. However, the concentration range available with bases such as NaOH is quite narrow, since the particles precipitate due to compression of the electric double layer when the ionic strength is increased. The stability of mercaptoundecanoic acid-capped Au nanoparticles is studied at a set pH using the hydroxide as base and different cations of various sizes. The counterions used are sodium (Na(+)), tetramethylammonium (TMA(+)), tetraethylammonium (TEA(+)), and tetrabutylammonium (TBA(+)). The particles precipitate in the 70-90 mM range with Na(+) as the counterion, but with quaternary ammonium hydroxides the particles are stable even in concentrations exceeding 1 M. The change in solubility is linked to a strongly adsorbed layer on the surface of the ligand shell of the nanoparticles. The increased concentration range obtained with TEAOH is further used to facilitate thiol exchange which occurs at a greater extent than would be achieved in NaOH solution.
authors.affiliation: Laboratory of Physical Chemistry and Electrochemistry Helsinki University of Technology, P.O. Box 6100, 02015 HUT, Finland.
authors.forename: Timo
authors.initials: T
authors.lastname: Laaksonen
authors.forename: Päivi
authors.initials: P
authors.lastname: Ahonen
authors.forename: Christoffer
authors.initials: C
authors.lastname: Johans
authors.forename: Kyösti
authors.initials: K
authors.lastname: Kontturi
mesh_terms: D002412:Cations; D004355:Drug Stability; D005227:Fatty Acids / Q000737:chemistry*; D006046:Gold / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D053768:Metal Nanoparticles / Q000737:chemistry*; D010316:Particle Size; D000644:Quaternary Ammonium Compounds / Q000737:chemistry*; D012995:Solubility; D055672:Static Electricity; D013438:Sulfhydryl Compounds / Q000737:chemistry*; D013499:Surface Properties
chemical_list: C505222:11-mercaptoundecanoic acid; D002412:Cations; D005227:Fatty Acids; D000644:Quaternary Ammonium Compounds; D013438:Sulfhydryl Compounds; D006046:Gold