MAKING AND BREAKING DIPHOSPHINE PROTECTED GOLD CLUSTERS: SYNTHESIS AND COLLISION INDUCED DISSOCIATION
Denis E. Bergeron
Mentor: Jeffrey W. Hudgens
Physical and Chemical Properties Division (838)
Chemical Science and Technology Laboratory
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Chemistry
The precise synthesis of nanoparticles of specific sizes is in principle possible via manipulation of reaction conditions. We found that highly monodisperse samples of diphosphine ligand (1,3-Bis(diphenylphosphino)propane or 1,5-Bis(diphenylphosphino)pentane) protected gold nanoparticles form much more rapidly (minutes) in a mixed methanol/chloroform solvent environment than in pure chloroform (~ eight hours). Methanol soluble octagold, decagold, and undecagold monolayer protected clusters yield very stable ion currents when introduced into a mass spectrometer via electrospray ionization. In addition to neutral ligand loss pathways, collision induced dissociation generates [AuL]+ and [Au3L]+ (L = diphosphine ligand) as particularly stable product ions from all clusters considered. These core fission products are indicate the absolute necessity of a full complement of ligands for the stabilization of very small nanoparticles. Furthermore, deca- and undecagold clusters are found to be more resistant to collision induced dissociation, and more susceptible to partial ligand losses than octagold clusters. This suggests that for the deca- and undecagold species, Au—P and P—Ph (Ph = phenyl) bonds within the ligand-protected clusters are of comparable strength. By studying the fragmentation patterns of species like these, we elucidate basic structural and chemical properties, thus establishing a foundation for the development of nanoparticles with tailored properties.