Detailed analysis of ligands on gold nanoparticles

Gold nanoparticles are utilized in several fields including sensing, biological therapies, and catalysis due to their relatively inert surfaces, tunable optical properties, and light-to-heat conversion. The surfaces of these nanoparticles are frequently coated with organic ligands to impart colloidal stability and engineer functionality, serving as the face of the nanoparticle to the environment. This dissertation seeks to further our current understanding of how organic ligands bind to, arrange on, and protect gold nanoparticle surfaces. In Chapter 1, the current state of the literature on gold nanocrystal surface chemistry is reviewed. Background on the properties of gold nanoparticles and how surface chemistry affects their eventual application is mentioned. Finally, some recent literature examples of ligand environment analysis on gold nanoparticles using state-of-the-art methods are presented and discussed. The work described in Chapter 2 presents a systematic investigation into how ligand length and size of gold nanoparticles affect ligand structure, dynamics, and mobility using 1H solution NMR, cyanide etching experiments, and molecular dynamics simulations. A library of gold nanoparticles with 4 average diameters (2, 4, 9, and 12 nm) and appended with 4 different mercapto-(X-alkyl)-N,N,N-trimethylammonium bromide (MxTAB) ligands (X= 11, 16, 18, 20) was synthesized, and patterns in NMR peak shift, ligand density quantification, and T2 relaxation constants were used to draw conclusions about the bifactorial effects of gold nanoparticle diameter and ligand length. Additionally, cyanide etching experiments and molecular dynamics simulations gave additional clues to the overall structure and character of the ligand shell on each gold nanoparticle type. In Chapter 3, the impact of the synthesis and functionalization method, and the intermediates used therein, on the resulting character of the ligand shell are investigated. Nominally similar 5 nm diameter gold nanospheres coated with identical cationic ligands were synthesized and functionalized through 3 methods, their ligand shells characterized, and the nanoparticles’ resistance to cyanide etching and morphology change with thermal annealing were investigated. Future experiments were proposed to further investigate how intermediates used in processing of the nanoparticles could affect the character of the ligand shell. Finally, in Chapter 4, N-heterocyclic carbenes (NHCs) were investigated through density functional theory and spectroscopy methods to determine the kinetics and thermodynamics of ligand binding and etching to gold nanoparticle surfaces. We discovered a negative correlation between gold-NHC binding energy and extent of gold nanoparticle etching, which is opposite of conventional thinking about surface etching. We proposed a ligand pKa-related model to corroborate these surprising findings.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Chemistry

Grantor

University of Illinois Urbana-Champaign

Year dc:date

2025

Author dc:creator

• Hatzis, Katherine M.

Contributors dc:contributor

• Murphy, Catherine J.
• Murphy, Catherine J
• Gruebele, Martin H. W.
• Girolami, Gregory S
• Jain, Prashant K.

• Nanoparticles
• Gold
• Organic-inorganic Hybrids
• Surface Ligands
• Surface Characterization

Statement dc:rights

• Copyright 2025 Katherine Hatzis

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/129849

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F129849