Nanoscale insights into the creation of chiral surfaces

Interaction of chiral L-dialanine with Cu(100)

We report on the properties of the thin films of the short peptide L-dialanine grown on Cu(100) surfaces and compare them to those of L-alanine by using surface techniques like XPS, IRRAS and STM. The first dialanine monolayer, in contact with the metallic substrate, is found to consist of whole neutral molecules in the non-zwitterionic state forming a c(2 × 4) pattern with quasi-hexagonal symmetry. The peptide bond of dialanine is preserved in the adsorption state. The ordering of the L-dialanine overlayer is shown to replicate rearrangements of the atoms of the substrate around dislocations of the latter indicating a strong molecule-surface interaction. In the multilayer regime, molecules of the second and further layers are found to be in a zwitterionic state, readily desorbing even at room temperature. The first dialanine layer is tightly bound to the substrate, begins to desorb at temperatures higher than 390 K and cracks down at the surface, transforming into a new moiety, beyond 435 K.

Spectroscopy for model heterogeneous asymmetric catalysis

Heterogeneous catalysis has vastly benefited from investigations performed on model systems under well-controlled conditions. The application of most of the techniques utilized for such studies is not feasible for asymmetric reactions as enantiomers possess identical physical and chemical properties unless while interacting with polarized light and other chiral entities. A thorough investigation of a heterogeneous asymmetric catalytic process should include probing the catalyst prior to, during, and after the reaction as well as the analysis of reaction products to evaluate the achieved enantiomeric excess. I present recent studies that demonstrate the strength of chiroptical spectroscopic methods to tackle the challenges in investigating model heterogeneous asymmetric catalysis covering all the abovementioned aspects.

Surface-site reactivity in small-molecule adsorption: A theoretical study of thiol binding on multi-coordinated gold clusters

BACKGROUND

The adsorption of organic molecules on metal surfaces has a broad array of applications, from device engineering to medical diagnosis. The most extensively investigated class of metal-molecule complexes is the adsorption of thiols on gold.

RESULTS

In the present manuscript, we investigate the dependence of methylthiol adsorption structures and energies on the degree of unsaturation at the metal binding site. We designed an Au20 cluster with a broad range of metal site coordination numbers, from 3 to 9, and examined the binding conditions of methylthiol at the various sites.

CONCLUSION

We found that despite the small molecular size, the dispersive interactions of the backbone are a determining factor in the molecular affinity for various sites. Kink sites were preferred binding locations due to the availability of multiple surface atoms for dispersive interactions with the methyl groups, whereas tip sites experienced low affinity, despite having low coordination numbers.

Interfacial chiral selection by bulk species

A chiral selection process in a self-assembled soft monolayer of an achiral amphiphile as a consequence of its interaction with chiral species dissolved in the aqueous subphase, is reported. The extent of the chiral selection is statistically measured in terms of the enantiomorphic excess of self-assembled submillimeter domains endowed with well-defined orientational chirality that is unambiguously resolved using optical microscopy. Our results show that the emergence of chirality is mediated by electrostatic interactions and significantly enhanced by hydrophobic effects. This chiral chemical effect can be suppressed and even reversed by opposing a macroscopic physical influence, such as vortical stirring. This result gives evidence for the crucial role of hydrodynamic effects in supramolecular aggregation.

A tale of tails: alkyl chain directed formation of 2D porous networks reveals odd-even effects and unexpected bicomponent phase behavior

Supramolecular self-assembly of suitably functionalized building blocks on surfaces can serve as an excellent test-bed to gain understanding and control over multicomponent self-assembly in more complex matter. Here we employ a powerful combination of scanning tunnelling microscopy (STM) and molecular modeling to uncover two-dimensional (2D) crystallization and mixing behavior of a series of alkylated building blocks based on dehydrobenzo[12]annulene, forming arrays of nanowells. Thorough STM investigation employing high-resolution spatial imaging, use of specially designed marker molecules, statistical analysis and thermal stability measurements revealed rich and complex supramolecular chemistry, highlighting the impact of odd-even effects on the phase behavior. The methodology and analysis presented in this work can be easily adapted to the self-assembly of other alkylated building blocks.