Chirality is one of the most-studied phenomena in chemical sciences. Its ubiquitous presence in biological systems leads to strong demand for development of asymmetric drugs, sensors, and catalysts. It is also expected to play an important role in the development of metamaterials. Chirality on the nanoscale has become an intensively investigated field in modern material sciences. Intrinsically chiral thiolate-protected gold clusters showed to possess a peculiar type of chirality where the distribution of the thiolate ligands on the surface create an asymmetric environment. These systems have risen a lot of attention due to their potential applications as chiral smart materials.
The main objective of this project is creating a new class of enantiodiscriminating sensors based on intrinsically chiral Au38(SR)24 nanoclusters (Figure). To achieve such goal, we focused our attention towards two main topics:
- Investigation of the chiral properties of Au38(SR)24 nanoclusters. In particular, we studied in detail the “transfer of chirality” occurring from the chiral surface of the cluster to the achiral ligand attached to it. This phenomenon holds great potential for the development of novel sensors since it allows to bestow transient chirality to the molecules attached at the surface of the cluster.
- Design of new thiolate ligands bearing functional groups able to establish specific interactions with the target molecules (methamphetamine derivatives).
Conclusion:
- We show that the transfer of chirality for the intrinsically chiral gold cluster Au38(SR)24 is site dependent, i.e. it differs depending on the ligand binding sites. This is closely related to the dynamic nature of the ligands on the cluster surface. Using a combination of NMR techniques and molecular dynamics simulations, we could reveal the largely different conformational dynamics of the bound ligands, explaining the diverse diastereotopicities observed for the CH2 protons of the ligands. Although chirality is a structural property, our study reveals the importance of dynamics for the transfer of chirality (Figure).
- We synthesized a small library of different thiols with similar structure as 2PET (2-phenyl ethane thiol). Different functionalities were inserted in the phenyl ring of the 2PET moiety. These functionalized thiols were employed in the synthesis of Au38(SR)24. Unfortunately, it was not possible to obtain stable Au38(SR)24 clusters protected with such thiolate. We obtained clusters of different sizes and/or large undefined nanoparticles. In order to solve this problem two strategies were adopted: 1) The desired thiol is inserted via thiol exchange reaction on preformed Au38(SR)24 (where SR are alkyl thiols). 2) Dynamic covalent chemistry for the thiol functionalization directly on the cluster monolayer. Among the two new approaches, the dynamic covalent chemistry showed some interesting preliminary results, that will require future investigation.
