Birte Varnholt

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.

On the incorporation of functionalities into hydroxyapatite capsules

Nature is capable of building materials with tailor-made properties under ambient conditions for specific applications. We apply some of the basic building principles of biomineralization in this paper: we stabilize an oil/water emulsion with the protein hydrophobin and mineralize this emulsion, resulting in hollow mineral capsules. The use of an emulsion as a liquid template enables precise size control over the final capsules. We mimic nature by using complexing agents and surfactants as additives to alter the properties of the growing mineral. We also modify the mineral itself by addition of different cations. Furthermore, we show the inclusion of silver into the capsules. This should add antibacterial properties to the capsules and shows exemplarily that catalytically active metals can be included. While the manual process needs numerous working steps and long waiting times, we ease the whole process by automation and use phosphatases to shorten synthesis time. Our experiments show the flexibility and adaptability of our system, making it an ideal platform for various possible applications such as drug transport and especially as microreactors.

Symmetry Breaking in Chiral Ionic Liquids Evidenced by Vibrational Optical Activity

Ionic liquids (ILs) are receiving increasing interest for their use in synthetic laboratories and industry. Being composed of charged entities, they show a complex and widely unexplored dynamic behavior. Chiral ionic liquids (CILs) have a high potential as solvents for use in asymmetric synthesis. Chiroptical methods, owing to their sensitivity towards molecular conformation, offer unique possibilities to study the structure of these chiral ionic liquids. Raman optical activity proved particularly useful to study ionic liquids composed of amino acids and the achiral 1-ethyl-3-methylimidazolium counterion. We could substantiate, supported by selected theoretical methods, that the achiral counterion adopts an overall chiral conformation in the presence of chiral amino acid ions. These findings suggest that in the design of chiral ionic liquids for asymmetric synthesis, the structure of the achiral counter ion also has to be carefully considered.