Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2012 Apr 24:3:798.
doi: 10.1038/ncomms1802.

First enantioseparation and circular dichroism spectra of Au38 clusters protected by achiral ligands

Igor Dolamic  1 , Stefan Knoppe, Amala Dass, Thomas Bürgi
Affiliations
Free PMC article

First enantioseparation and circular dichroism spectra of Au38 clusters protected by achiral ligands

Igor Dolamic et al. Nat Commun. .
Free PMC article

Abstract

Bestowing chirality to metals is central in fields such as heterogeneous catalysis and modern optics. Although the bulk phase of metals is symmetric, their surfaces can become chiral through adsorption of molecules. Interestingly, even achiral molecules can lead to locally chiral, though globally racemic, surfaces. A similar situation can be obtained for metal particles or clusters. Here we report the first separation of the enantiomers of a gold cluster protected by achiral thiolates, Au(38)(SCH(2)CH(2)Ph)(24), achieved by chiral high-performance liquid chromatography. The chirality of the nanocluster arises from the chiral arrangement of the thiolates on its surface, forming 'staple motifs'. The enantiomers show mirror-image circular dichroism responses and large anisotropy factors of up to 4×10(-3). Comparison with reported circular dichroism spectra of other Au(38) clusters reveals that the influence of the ligand on the chiroptical properties is minor.

PubMed Disclaimer

Figures

Figure 1
Figure 1. Crystal structure of the left-handed enantiomer of Au38(SCH2CH2Ph)24.
For clarity, the -CH2CH2Ph units were removed; yellow, gold adatoms; green, core atoms (Au); orange, sulphur. (a) Top view of the cluster; (b) side-view; (c) schematic representation highlighting the handedness of the cluster. The inner triangle represents the top three core atoms binding to the long staples. The arrows represent long staples and the outer triangle represent the core Au atoms binding to the 'end' of the staple. This representation is a top view along the C3 axis, and the two triangles are not in one plane. (d) Top-view in space-filling representation mode; (e) side-view in space-filling representation mode. The structures were created using the crystallographic data provided in ref. .
Figure 2
Figure 2. Characterization of rac-Au38(SCH2CH2Ph)24.
(a) MALDI mass spectra of Au38(SCH2CH2Ph)24 before (black) and after (red) size selection. The signals for Au40(SCH2CH2Ph)24 (11,173 Da) and Au25(SCH2CH2Ph)18 (7,391 Da) disappeared from the spectrum, indicating successful size exclusion. For a detailed description of this process, see ref. . (b) Ultraviolet-visible spectra of Au38(SCH2CH2Ph)24 before (black) and after (red) size selection. The absorption features of Au38 are drastically enhanced.
Figure 3
Figure 3. HPLC-separation of rac-Au38(SCH2CH2Ph)24.
(a) HPLC-chromatogram of the enantioseparation of rac-Au38(SCH2CH2Ph)24 with the ultraviolet-visible detector at 380 nm. The peak at 8.45 min corresponds to enantiomer 1; the second peak at 17.45 corresponds to enantiomer 2. (b) Ultraviolet-visible spectra of enantiomers 1 (black) and 2 (red) and of the racemate (blue). The spectra were normalized at 300 nm and off-set for clarity. The well-known ultraviolet-visible signature of Au38 is perfectly reproduced in all spectra, showing that the two collected fractions are composed of Au38(SCH2CH2Ph)24.
Figure 4
Figure 4. CD spectra and anisotropy factors of Au38(SCH2CH2Ph)24.
(a) CD spectra of isolated enantiomers 1 (black) and 2 (red) and the racemic Au38(SCH2CH2Ph)24 (blue) before separation; (b) corresponding anisotropy factors of enantiomers 1 and 2 and of the racemate. The spectra exhibit excellent mirror-image relationships and anisotropy factors g=ΔA/A of up to 4×10−3.
See this image and copyright information in PMC

References

    1. Böhringer M., Morgenstern K., Schneider W.- D. & Berndt R. Separation of a Racemic Mixture of Two-Dimensional Molecular Clusters by Scanning Tunneling Microscopy. Angew. Chem. Int. Ed. 38, 821–823 (1999). - PubMed
    1. Chen Q., Frankel D. J. & Richardson N. V. Chemisorption induced chirality: glycine on Cu{110}. Surf. Sci. 497, 37–46 (2002).
    1. Parschau M., Romer S. & Ernst K. H. Induction of homochirality in achiral enantiomorphous monolayers. J. Am. Chem. Soc. 126, 15398–15399 (2004). - PubMed
    1. Lorenzo M. O., Baddeley C. J., Muryn C. & Raval R. Extended surface chirality from supramolecular assemblies of adsorbed chiral molecules. Nature 404, 376–379 (2000). - PubMed
    1. Jadzinsky P. D., Calero G., Ackerson C. J., Bushnell D. A. & Kornberg R. D. Structure of a thiol monolayer-protected gold nanoparticle at 1.1 A resolution. Science 318, 430–433 (2007). - PubMed

Publication types