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

Office: Physics (221), Room B352

Mail Stop 8380

Tel: (301)975-8768

FAX: (301)869-4020

denis.bergeron@nist.gov

Not a Sigma Xi member

 

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, AuP and PPh (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.