1. Precursor Ion–Ion Aggregation in the Brust–Schiffrin Synthesis
of Alkanethiol Nanoparticles
Introduction
Acknowledgements
• The Voiland School of Chemical Engineering and Bioengineering provided
a research assistantship and laboratory funding.
• Partially supported by the Microbes in Transition (MinT) Initiative, a
Laboratory Directed Research and Development Program at Pacific
Northwest National Laboratory. PNNL is a multiprogram national
laboratory operated by Battelle for the U.S. Department of Energy under
Contract DE-AC06-76RL01830.
Supramolecular Structure
• 1H Nuclear Magnetic Resonance
spectroscopy (NMR) quantified the
concentration and chemical environment of
water.
• Validated with Density Functional Theory
(DFT) 1H chemical shift calculations
• Diffusion ordered NMR (DOSY-NMR)
determined extent of self assembly
• Two chemicals known to form reverse
micelle (AOT and CTA-X) were controls
Methodology
Larger ion aggregates in TOA-AuBr4/Br increase NP size
Influence on Nanoparticle Size
• The Brust-Schiffrin Synthesis creates gold nanoparticles (NPs) using
tetraoctylammonium bromide, a phase transfer catalyst (PTC).
• Chloroaurate (AuCl4
-) is phase transferred to the organic phase
• The PTC then self-assembles into either ion-ion aggregates or
reverse micelles.
• Understanding precursor self assembly will improve models
predicting the nucleation and growth of gold NPs.
• The hydration of the quaternary ammonium anion increases the
water concentration in the organic phase
• TOA-X PTC anions deshield both water and chloroform
• Anion electronegativity governs ion-ion aggregation
• Ion-Ion aggregation influences NP size
Full publication:
http://pubs.acs.org/doi/abs/10.1021/acs.jpcc.6b06155
• Water and chloroform are de-
shielded for TOA-X dispersions
• Only water is deshielded for
reverse micelles
• TOA-X anion is not sequestered in
an aqueous core
• Anion nucleophilicity increases aggregation.
• The transfer of AuBr4 forms larger aggregates than AuCl4
-
Species
𝐾𝟐
[mol-1 L]
∆𝐺 𝟐
[kJ mol-1]
𝐾
[mol-1 L]
∆G
[kJ mol-1]
TOA-AuCl4-xBrx
50.6 ± 3.8 -9.7 ± 0.2 56.2 ± 4.2 -9.9 ± 0.2
TOA-Br 4.9 ± 0.3 -4.0 ± 0.1 4.5 ± 0.2 -3.7 ± 0.1
TOA-Cl 17.0 ± 0.1 -7.0 ± 0.02 11.0 ± 0.1 -5.9 ± 0.02
TOA-AuBr4/Cl/Br (Brust) 24.2 ± 1.9 -7.9 ± 0.2 13.2 ± 1.0 -6.4 ± 0.2
TOA-AuBr4/Br (Brust) 18.2 ± 1.3 -7.2 ± 0.2 18.2 ± 1.3 -7.2 ± 0.2
Species Experimental
𝑁 𝐻 𝛿 𝐻 [ppm]
DFT
𝛿 𝐻
𝐷𝐹𝑇
[ppm]
TOA-AuCl4-xBrx
0.16 ± 0.03 2.39 ± 0.12 < 2.40
TOA-Br 0.54 ± 0.02 2.87 ± 0.02 2.88
TOA-Cl 0.88 ± 0.05 3.25 ± 0.01 2.96
TOA-AuBr4/Cl/Br (Brust) 0.59 ± 0.02 3.09 ± 0.01 n/a
TOA-AuBr4/Br (Brust) 0.42 ± 0.03 2.85 ± 0.02 n/a
Trent Graham1 Ryan Renslow2,1 Niranjan Govind2 and Steven Saunders1
(1) The Voiland College of Engineering & Architecture, Washington State University, Pullman WA
(2) Earth and Biological Sciences Directorate, Pacific Northwest National Laboratory, Richland, WA
Aggregation Thermodynamics
Anion electronegativity:
Cl > Br > AuBr4/Br/Cl > AuBr4/Br > AuBr4-xClx
𝑁 𝐻 = Number of hydrating water molecules
𝛿 𝐻 = 1H chemical shift of hydrating water
• Reverse micelle dispersions can
hold almost 10x more water at
saturation
• Swollen reverse micelles are
smaller than water saturated
TOA-X solutions Conclusions
Pulsed Field Gradient
DOSY-NMR
Indefinite
Association Models
Evidence is consistent with ion-ion aggregations
Lines are hydration model fits
Line is to guide the eye
Lines are aggregation model fits