Phase transfer of hydrophilic, cyclodextrin-modified gold nanoparticles tochloroform solutions

The preparation and characterization of gold nanoparticles (similar to3 nm in diameter) capped with thiolated alpha- and beta -cyclodextrins (alpha an d beta -CD) is described. The CD-capped nanoparticles are hydrophilic and b ind ferrocene derivatives as evidenced by electrochemical and H-1 NMR spect roscopic measurements. The binding interactions of the CD-capped nanopartic les with a series of five alkyldimethyl(ferrocenylmethyl)ammonium ions (the alkyl group is propyl for compound 1, heptyl for 2, dodecyl for 3, hexadec yl for 4, and docosyl for 5) can be utilized for the phase transfer of the hydrophilic, CD-capped nanoparticles into a nonpolar chloroform phase. Only 3, 4, and 5 act as effective phase transfer agents, since 1 and 2 do not h ave enough amphiphilic character. The structure of the aggregates formed up on transfer of the CD-capped nanoparticles to the chloroform solution is po stulated to resemble that of reverse micelles, as the nanoparticles templat e the peripheral arrangement of the cationic ferrocene amphiphiles, counter ions and water molecules around their surfaces.