Global and Local Expression of Chirality in Serine on the Cu{110} Surface

Abstract

Establishing a molecular-level understanding of enantioselectivity and chiral resolution at the organic-inorganic interfaces is a key challenge in the field of heterogeneous catalysis. As a model system, we investigate the adsorption geometry of serine on Cu{110} using a combination of low-energy electron diffraction (LEED), scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. The chirality of enantiopure chemisorbed layers, where serine is in its deprotonated (anionic) state, is expressed at three levels: (i) the molecules form dimers whose orientation with respect to the substrate depends on the molecular chirality, (ii) dimers of L- and D-enantiomers aggregate into superstructures with chiral (-1 ∓2; 4 0) lattices, respectively, which are mirror images of each other, and (iii) small islands have elongated shapes with the dominant direction depending on the chirality of the molecules. Dimer and superlattice formation can be explained in terms of intra- and interdimer bonds involving carboxylate, amino, and β-OH groups. The stability of the layers increases with the size of ordered islands. In racemic mixtures, we observe chiral resolution into small ordered enantiopure islands, which appears to be driven by the formation of homochiral dimer subunits and the directionality of interdimer hydrogen bonds. These islands show the same enantiospecific elongated shapes those as in low-coverage enantiopure layers.

Adsorption and self-assembly of bio-organic molecules at model surfaces: A route towards increased complexity

“…On the contrary, the thermodynamically stable thin lines grow along the <-310> direction suggestan adsorption structure similar to that of Ala/Cu(001) [136]. On Cu(110) dimer formation is observed by STM, but a different organization is proposed [43]. Indeed, the combination of LEED and STM data demonstrate that, at full monolayer coverage and after annealing to 420 K, D/L-serine overlayers on Cu(110) form well-ordered superstructures with (-1 ±2; 4 0) periodicity after annealing.…”

“…The multiple desorption peaks correspond to adsorbates in different chemical states (physisorbed, chemisorbed, dissociated, in single-or in multi-layer etc…) and hence characterised by different adsorption energies. Due to the relatively simple setup required by this technique, it is among the most common from the early days of surface science and has been employed quite extensively also for the characterisation of AA and peptides adsorption at surfaces [38][39][40][41][42][43].…”

“…The authors propose that intermolecular H-bonding involving the β-OH groups affects the ordering of the molecules on the surface. More recent studies suggest that both on Cu(110) [43] and on Cu(001) [160] adsorption occurs with the formation of Ser-dimers which are, however, stabilised by different H-bonds on the two surfaces. Serine interaction with Cu(001) was investigated first and it was found that, at 310 K, a domain of thick lines with a 2 −1 2 4 periodicity initially appears along the <-130> direction regardless of serine exposure (see Figure 21a).…”

Bicomponent Supramolecular Architectures at the Vacuum–Solid Interface

“…312,313,314,315,134,135 For instance, the four nucleobases cytosine (C), 316 guanine (G), 317 adenine (Ad), 103 and thymine (T) 318 form well-organized 1D and 2D structures on Cu, Ag and Au surfaces. The H-bonding in these homomolecular systems is sufficiently strong that the role of the surface can be idealized as a simple support with minimal influence over the self-assembly process.…”

Quantitative local structure determination of R,R-tartaric acid on Cu(110): Monotartrate and bitartrate phases

“…One surprising feature of the C 1s spectra is that the peak at lower kinetic energy appears to be consistently weaker than the peak at higher kinetic energy, although according to this assignment, both peaks arise from 2 C atoms in the tartrate species. This effect has also been observed in C 1s spectra in many other adsorbed (deprotonated) species produced by reaction with carboxylic acids, notably acetic acid on Cu(110) [15], glycine on Cu(111) [22] and Pd(111) [23], serine on Cu(110) [24], and alanine on Cu(110) [25,26 ], and must be attributed to loss of intensity in one of the peaks to shake-up satellites; the shoulder visible in the spectra at lower kinetic energy is consistent with this interpretation. (2)), these four O atoms may be expected to lead to peaks at the same energies as the two peaks in the bitartrate spectrum.…”