Formation of Bioinorganic Complexes by the Corrosive Adsorption of (S)-Proline on Ni/Au(111)

Abstract

Nickel nanoparticles modified by the adsorption of chiral amino acids are known to be effective enantioselective heterogeneous catalysts. The leaching of nickel by amino acids has a number of potential effects including the induction of chirality in the nickel atoms left behind in the nanoparticle and the creation of catalytically active nickel complexes. The adsorption of (S)-proline onto Au(111) precovered by two dimensional nickel nanoclusters was investigated by scanning tunnelling microscopy, X-ray photoelectron spectroscopy and high resolution electron energy loss spectroscopy. Adsorption of (S)-proline at 300 K resulted in the corrosion of the nickel clusters, the oxidation of the leached nickel and the on-surface formation of bioinorganic complexes, which are concluded to contain three prolinate species in an 2 octahedral arrangement around the central Ni ion. Two distinguishable forms of nickel prolinate complexes were identified. One form self-assembles into 1-D chains and the other form gives rise to porous 2-D islands. Octahedral complexes of the type M(AB) 3 are intrinsically chiral resulting in two pairs of enantiomers. The mirror symmetry of each pair of enantiomers is broken when, as in this study, the bidentate ligand itself possesses a chiral center. DFT calculations are used to examine the relative energies of each Ni(prolinate) 3 complex as isolated gas phase species and isolated adsorbed species.

Constitutional Dynamics of Metal–Organic Motifs on a Au(111) Surface

“…The hybrid network structure is then formed by alternating arrangement of homochiral metal–organic trimers and hydrogen‐bonded T dimers linked together through two N−H⋅⋅⋅O hydrogen bonds as revealed by the optimized model which is overlaid on the STM image (Figure c). Such hybrid network structures look similar to the previously reported porous networks formed by the adsorption of ( S )‐proline on Ni/Au(111) . The remarkable difference is that the hybrid network is formed by two kinds of elementary structural motifs as shown in Figure a–c.…”

Structure and Reactivity of Cu-doped Au(111) Surfaces

“…Nucleation of guest metals on Au(111) generally occurs via the place-exchange mechanism [5], which was initially ruled out for the adsorption of copper; however, it was later reported that the onset of copper adsorption does occur via a place-exchange mechanism, at specific sites identified as the narrowed regions within the highly reactive elbows of the Au(111)-(22× √ 3), irrespective of hcp or fcc stacking [1]. Other than for copper [6][7][8], this is also the case for other transition metals such as nickel [9][10][11][12], iron [13,14], and chromium [15,16], to name a few. Added clusters are regarded as a source of reactive metal atoms, over a surface commonly considered as a 2D inert support, opening up the possibility of modifying the reactivity of the Au(111) surface itself, via the formation of surface alloys, whereby both the added metal and gold are present in the top layer.…”

Constitutional Dynamics of Metal–Organic Motifs on a Au(111) Surface

“…Such hybrid network structures look similar to the previously reported porous networks formed by the adsorption of (S)-proline on Ni/Au(111). [19] Ther emarkable difference is that the hybrid network is formed by two kinds of elementary structural motifs as shown in Figure 3a-c. It is noteworthy that the introduction of additional Tmolecules does not change the local stoichiometric ratio for the metal-organic motifs (i.e., T/ Ni ratio is kept as 3:1i nt he homochiral metal-organic trimer).…”