Igor Dolamic

Size exclusion chromatography for semipreparative scale separation of Au38(SR)24 and Au40(SR)24 and larger clusters.

Size exclusion chromatography (SEC) on a semipreparative scale (10 mg and more) was used to size-select ultrasmall gold nanoclusters (<2 nm) from polydisperse mixtures. In particular, the ubiquitous byproducts of the etching process toward Au(38)(SR)(24) (SR, thiolate) clusters were separated and gained in high monodispersity (based on mass spectrometry). The isolated fractions were characterized by UV-vis spectroscopy, MALDI mass spectrometry, HPLC, and electron microscopy. Most notably, the separation of Au(38)(SR)(24) and Au(40)(SR)(24) clusters is demonstrated.

Separation of Enantiomers and CD Spectra of Au40(SCH2CH2Ph)24: Spectroscopic Evidence for Intrinsic Chirality

Chirality unveiled: Thiolate-protected Au40(SR)24 clusters were enantioenriched using an HPLC approach. CD spectra show strong mirror-image responses, indicating the intrinsic chirality of a cluster of unknown structure protected with achiral ligands.

Racemization of a Chiral Nanoparticle Evidences the Flexibility of the Gold–Thiolate Interface

Thiolate-protected gold nanoparticles and clusters combine size-dependent physical properties with the ability to introduce (bio)chemical functionality within their ligand shell. The engineering of the latter with molecular precision is an important prerequisite for future applications. A key question in this respect concerns the flexibility of the gold-sulfur interface. Here we report the first study on racemization of an intrinsically chiral gold nanocluster, Au38(SCH2CH2Ph)24, which goes along with a drastic rearrangement of its surface involving place exchange of several thiolates. This racemization takes place at modest temperatures (40-80 °C) without significant decomposition. The experimentally determined activation energy for the inversion reaction is ca. 28 kcal/mol, which is surprisingly low considering the large rearrangement. The activation parameters furthermore indicate that the process occurs without complete Au-S bond breaking.

Chirality transfer from gold nanocluster to adsorbate evidenced by vibrational circular dichroism

The transfer of chirality from one set of molecules to another is fundamental for applications in chiral technology and has likely played a crucial role for establishing homochirality on earth. Here we show that an intrinsically chiral gold cluster can transfer its handedness to an achiral molecule adsorbed on its surface. Solutions of chiral Au38(2-PET)24 (2-PET=2-phenylethylthiolate) cluster enantiomers show strong vibrational circular dichroism (VCD) signals in vibrations of the achiral adsorbate. Density functional theory (DFT) calculations reveal that 2-PET molecules adopt a chiral conformation. Chirality transfer from the cluster to the achiral adsorbate is responsible for the preference of one of the two mirror images. Intermolecular interactions between the adsorbed molecules on the crowded cluster surface seem to play a dominant role for the phenomena. Such chirality transfer from metals to adsorbates likely plays an important role in heterogeneous enantioselective catalysis.

Pd2Au36(SR)24 cluster: structure studies

The location of the Pd atoms in Pd2Au36(SC2H4Ph)24, is studied both experimentally and theoretically. X-ray photoelectron spectroscopy (XPS) indicates oxidized Pd atoms. Palladium K-edge extended X-ray absorption fine-structure (EXAFS) data clearly show Pd-S bonds, which is supported by far infrared spectroscopy and by comparing theoretical EXAFS spectra in R space and circular dichroism spectra of the staple, surface and core doped structures with experimental spectra.

Probing chiral nanoparticles and surfaces by infrared spectroscopy

Chiral metal surfaces and nanoparticles have the potential to be used for the selective production, the resolution and the detection of enantiomers of a chiral compound, which renders them highly attractive in view of the tremendous consequences of homochirality on earth. Their capability to distinguish between enantiomers of a chemical compound relies on their structure and the ability to form intermolecular interactions. However, molecular-level understanding of the interactions that are at the origin of enantiodiscrimination is lagging behind due to the lack of powerful experimental techniques that are able to spot these interactions selectively with high sensitivity. In this article two techniques based on infrared spectroscopy are presented that are able to selectively target the chiral properties of nanoparticles and interfaces. These are the combination of attenuated total reflection infrared (ATR-IR) with modulation excitation spectroscopy (MES) to probe enantiodiscriminating interactions at chiral solid-liquid interfaces and vibrational circular dichroism (VCD), which is used to probe the structure of chirally modified metal nanoparticles.