Figure: The proton
NMR spectrum originating from the ligand layer of the Au102 nanoparticle
in water (left).
The spectrum has been fully interpreted by assigning the observed signals
(peaks)
to all of the 22
symmetry-unique thiol ligands numbered in the solid state structure of the
Au102 particle
(right). From ref. 1.
(January 21, 2016) Researchers
at the University of Jyväskylä, Finland, and Colorado State University, USA,
have for the first time ever determined the dynamical behaviour of the ligand
layer of a water-soluble gold nanocluster in solution. The breakthrough opens a
way towards controllable strategies for the functionalisation of ligated
nanoparticles for applications. The work at the University of Jyväskylä was
supported by the Academy of Finland. The research was published in Nature
Communications on 21 January 2016. (1)
Nanometre-scale gold particles are intensively investigated
for applications as catalysts, sensors, drug delivery devices and biological
contrast agents and as components in photonics and molecular electronics. The
smallest particles have metal cores of only 1–2 nm with a few tens to a couple
of hundred gold atoms. Their metal cores are covered by a stabilising organic
ligand layer. The molecular formulas and solid-state atomic structure of many
of these compounds, called “clusters”, have been resolved during the past few
years. Still, it is a considerable challenge to understand their atomic-scale
structure and dynamical behaviour in the solution phase. This is crucial
information that can help researchers understand how nanoclusters interact with
the environment.
The researchers studied a previously identified molecularly
precise nanocluster that has 102 gold atoms and 44 thiol ligands (Figure 1,
right). The solid-state structure of this cluster was resolved from
single-crystal X-ray diffraction experiments in 2007 (2). The ligand shell has
a low symmetry and produces a large number of signals in conventional
proton-NMR measurement (Figure 1, left). The researchers achieved a full assignment
of all signals to specific thiol ligands by using a combination of correlated
nuclear magnetic resonance (NMR) experiments, density functional theory
computations and molecular dynamics simulations.