Two types of tetrathiolated surface passivants were synthesized in order to explore the effect of S-functional groups (disulfide vs. S-thioester) to control the size of gold nanoparticles prepared by a simple one-pot reduction of tetrachloroaurate with sodium tetrahydroborate. Both the passivants have four thiolated arms in the same direction perpendicular to a porphyrin plane, and produced small porphyrin-coated gold nanoparticles 2 to 4 nm in size by one-pot reduction of AuIII ions at S/Au from 1 to 16. The constancy in particle size at S/Au ratio less than 4 was greater with use of tetradentate disulfide passivant compared with use of tetradentate S-thioester ligand, which should be attributed to faster adsorption of disulfide groups with gold than that of S-thioester groups. The results described here suggest that passivants having multivalent disulfide bonds should be promising candidates for constructing monolayer-protected gold nanoparticles of well-defined size.
2010 The Chemical Society of Japan