Abstracts Chemistry

Establishing the Relative Composition of Functionalized Thiols in Mixed Ligand Gold Nanoparticles by 1H-NMR Spectroscopy

by Matthias Carroll

Functionalized gold nanoparticles (AuNPs) are of interest for their optical and electrical properties, specifically the surface plasmon resonance phenomenon and potential applications for medicine and nano-circuitry. In this study, the ligand composition of small (~5 nm diameter) thiol functionalized AuNPs with mixed ligand monolayers was investigated to better understand how the molar feed ratio of ligands used during their synthesis influences the composition of ligands on the particle’s surface. The system under study was a combination of two ω-functionalized thiols, mercapto ethoxy ethoxy ethanol (MEEE) and mercapto pentyl trimethyl ammonium chloride (MPTMA). UV/Visible spectrophotometry, dynamic light scattering, and electron microscopy were utilized to determine particle size, while ¹H-NMR and FTIR spectroscopy were used to characterize monolayer composition and surface chemistry. Alkyl halide ligand precursors were analyzed via ¹H-NMR to generate a signal response factor. Furthermore, the gold cores were digested with iodine to better elucidate the ligand composition without baseline broadening which accompanies metal nanoparticles. ¹H-NMR data suggests that the distribution of functionalized thiols on the AuNP surface is not indicative of ligand feed ratio stoichiometry, that 10 mole % MEEE reagent is over-represented and comprises 63.66 ± 0.45% (0.71% RSD) of the mixed ligand monolayer.