Chiral Gold Nanoparticles

Abstract

Monolayer-protected gold nanoparticles have many appealing physical and chemical properties such as quantum size effects, surface plasmon resonance, and catalytic activity. These hybrid organic-inorganic nanomaterials have promising potential applications as building blocks for nanotechnology, as catalysts, and as sensors. Recently, the chirality of these materials has attracted attention, and application to chiral technologies is an interesting perspective. This minireview deals with the preparation of chiral gold nanoparticles and their chiroptical properties. On the basis of the latter, together with predictions from quantum chemical calculations, we discuss different models that were put forward in the past to rationalize the observed optical activity in metal-based electronic transitions. We furthermore critically discuss these models in view of recent results on the structure determination of some gold clusters as well as ligand-exchange experiments examined by circular dichroism spectroscopy. It is also demonstrated that vibrational circular dichroism can be used to determine the structure of a chiral adsorbate and the way it interacts with the metal. Finally, possible applications of these new chiral materials are discussed.

Fluxionality of gold nanoparticles investigated by Born-Oppenheimer molecular dynamics

“…This has indeed been experimentally observed by Gautier and Bürgi who were able to detect a VCD adsorption in the region of the gold metal vibrations, when they bound chiral ligands to gold nanoparticles [88][89][90]. The chiral ligand seemed to be able to preferentially stabilize one of the enantiomeric forms.…”

“…Also this topology is cage-like as the previous one, but it loses symmetry and drops to point group C 1 being therefore chiral. Chirality seems a frequently occurring phenomenon for gold clusters and has been observed by several researchers [82][83][84][85][86][87][88][89][90]. (Table I).…”

Asymmetric Synthesis of Chiral Bimetallic [Ag28Cu12(SR)24]4– Nanoclusters via Ion Pairing

“…Based on the increased CD and the decreased UV-vis absorption, the anisotropy factor of the chiral cluster estimated to be ~110 -3 at 465 nm ( Figure S9b). Though quite stable in solid-state in months ( Figure S10) and reasonably stable in solution in hours ( Figure S11) at room temperature, [Ag28Cu12(SR) 24] 4-in solutions was degraded in a rather fast rate by air in the presence of halides even at 0C ( Figure S12). Indeed, the timedependent ESI-MS ( Figure S8) showed gradually diminishing signals of the parent peaks [Ag28Cu12(SR)24] 4-(1) and [Ag28Cu12(SR)24H] 3-when BCNC was introduced.…”

“…Inspired by this observation, the as-prepared racemic mixture was separated into enantiomers by employing chiral quaternary ammonium salts as chiral resolution agents. Subsequently, direct asymmetric synthesis of optically pure enantiomers of [Ag28Cu12(SR) 24] 4-was achieved by using appropriate chiral ammonium cations (such as Nbenzylcinchoninium vs N-benzylcinchonidinium) in the cluster synthesis.…”

“…Transmission electron microscopic (TEM) analyses revealed that the as-prepared AgCu nanoparticles had a uniform size of 2.06 0.22 nm ( Figure S1). Single-crystal X-ray structure determination revealed that the formulation of [Ag28Cu12(SR) 24] 4-(1) (Figure 1a), as the n Bu4N + salt, which crystallizes in a monoclinic cell of P21/n space group. The unit cell comprises two pairs (Z = 4) of enantiomeric nanoclusters 1 and four cations ( Figure S2).…”