Two-Dimensional Coordination Networks from Cyclic Dipeptides.

Peptide-based biomimetic nanostructures and metal-organic coordination networks on surfaces are two promising classes of hybrid materials which have been explored recently. However, despite the great versatility and structural variability of natural and synthetic peptides, the two directions have so far not been merged in fabrication of metal-organic coordination networks using peptides as building blocks. Here we demonstrate that cyclic peptides can be used as ligands to form highly ordered, two-dimensional, peptide-based metal-organic coordination networks.

Three-dimensional hydrogen bonding between Landers and planar molecules facilitated by electrostatic interactions with Ni adatoms.

Using a combination of UHV-STM and molecular mechanics calculations, we investigate the surface self-assembly of a complex multi-component metal-molecule system with synergistic non-covalent interactions. Hydrogen bonding between three-dimensional Lander-DAT molecules and planar PTCDI molecules, adsorbed closer to the surface, is found to be facilitated by electrostatic interactions between co-adsorbed Ni adatoms and the flexible molecular DAT groups.

Influence of CH···N Interaction in the Self-Assembly of an Oligo(isoquinolyne-ethynylyne) Molecule with Distinct Conformational States.

Molecular conformational flexibility can play an important role in supramolecular self-assembly on surfaces, affecting not least chiral molecular assemblies. To explicitly and systematically investigate the role of molecular conformational flexibility in surface self-assembly, we synthesized a three-bit conformational switch where each of three switching units on the molecules can assume one of two distinct binary positions on the surface. The molecules are designed to promote C-H···N type hydrogen bonds between the switching units.

Steering Surface Reaction at Specific Sites with Self-Assembly Strategy.

To discern the catalytic activity of different active sites, a self-assembly strategy is applied to confine the involved species that are "attached" to specific surface sites. The employed probe reaction system is the Ullmann coupling of 4-bromobiphenyl, CHCHBr, on an atomically flat Ag(111) surface, which is explored by combined scanning tunneling microscopy, synchrotron X-ray photoelectron spectroscopy, and density functional theory calculations. The catalytic cycle involves the detachment of the Br atom from the initial reactant to form an organometallic intermediate, CHCHAgCHCH, which subsequently self-assembles with its central Ag atom residing either on 2-fold bridge or 3-fold hollow sites at full coverage.

Supramolecular Corrals on Surfaces Resulting from Aromatic Interactions of Nonplanar Triazoles.

Interaction forces between aromatic moieties, often referred to as π-π interactions, are an important element in stabilizing complex supramolecular structures. For supramolecular self-assembly occurring on surfaces, where aromatic moieties are typically forced to adsorb coplanar with the surface, the possible role of intermolecular aromatic interactions is much less explored. Here, we report on unusual, ring-shaped supramolecular corral surface structures resulting from adsorption of a molecule with nonplanar structure, allowing for intermolecular aromatic interactions.

Revealing the structural detail of individual polymers using a combination of electrospray deposition and UHV-STM.

A phenylene vinylene polymer derivative is deposited onto a Au(111) surface under Ultra-High Vacuum (UHV) conditions using electrospray ionisation deposition and characterised using Scanning Tunnelling Microscopy (STM). High resolution STM images reveal the polymer structure on the monomeric scale, allowing the identification of regioisomerism, the intricate isomerisations of the polymer side-chains, as well as the larger-scale topologies of the polymer strands.

A surface coordination network based on copper adatom trimers.

Surface coordination networks formed by co-adsorption of metal atoms and organic ligands have interesting properties, for example regarding catalysis and data storage. Surface coordination networks studied to date have typically been based on single metal atom centers. The formation of a novel surface coordination network is now demonstrated that is based on network nodes in the form of clusters consisting of three Cu adatoms.

Chiral induction with chiral conformational switches in the limit of low "sergeants to soldiers" ratio.

Molecular-level insights into chiral adsorption phenomena are highly relevant within the fields of asymmetric heterogeneous catalysis or chiral separation and may contribute to understand the origins of homochirality in nature. Here, we investigate chiral induction by the "sergeants and soldiers" mechanism for an oligo(phenylene ethynylene) based chiral conformational switch by coadsorbing it with an intrinsically chiral seed on Au(111). Through statistical analysis of scanning tunneling microscopy (STM) data, we demonstrate successful chiral induction with a very low concentration of seeding molecules down to 3%.

Adsorption of the organic salt TAB(HCl)4 on Cu(111) studied using STM and XPS.

Sublimation of Tetra-Amino Benzene (TAB) in its tetrahydrochlorinated form onto Cu(111) leads to the formation of long range ordered structures consisting of TAB molecules with partially protonated amino groups interspersed with Cl species.

On-surface azide-alkyne cycloaddition on Cu(111): does it "click" in ultrahigh vacuum?

Using scanning tunneling microscopy, we demonstrate that the 1,3-dipolar cycloaddition between a terminal alkyne and an azide can be performed under solvent-free ultrahigh vacuum conditions with reactants adsorbed on a Cu(111) surface. XPS shows significant degradation of the azide upon adsorption, which is found to be the limiting factor for the reaction.

Scanning tunneling microscopy reveals single-molecule insights into the self-assembly of amyloid fibrils.

Many severe diseases are associated with amyloid fibril deposits in the body caused by protein misfolding. Structural information on amyloid fibrils is accumulating rapidly, but little is known about the assembly of peptides into fibrils at the level of individual molecules. Here we investigate self-assembly of the fibril-forming tetrapeptides KFFE and KVVE on a gold surface under ultraclean vacuum conditions using scanning tunneling microscopy.

Chiral induction by seeding surface assemblies of chiral switches.

It is demonstrated by scanning tunneling microscopy that coadsorption of a molecular chiral switch with a complementary, intrinsically chiral induction seed on the Au(111) surface leads to the formation of globally homochiral molecular assemblies.

Homochiral xanthine quintet networks self-assembled on Au(111) surfaces.

Xanthine molecule is an intermediate in nucleic acid degradation from the deamination of guanine and is also a compound present in the ancient solar system that is found in high concentrations in extraterrestrial meteorites. The self-assembly of xanthine molecules on inorganic surfaces is therefore of interest for the study of biochemical processes, and it may also be relevant to the fundamental understanding of prebiotic biosynthesis. Using a combination of high-resolution scanning tunneling microscopy (STM) and density functional theory (DFT) calculations, two new homochiral xanthine structures have been found on Au(111) under ultrahigh vacuum conditions.

Controlling chiral organization of molecular rods on Au(111) by molecular design.

Chiral self-assembled structures formed from organic molecules adsorbed on surfaces have been the subject of intense investigation in the recent decade, owing both to relevance in applications such as enantiospecific heterogeneous catalysis or chiral separation as well as to fundamental interest, for example, in relation to the origin of biomolecular homochirality. A central target is rational design of molecular building blocks allowing transfer of chirality from the molecular to the supramolecular level. We previously studied the surface self-assembly of a class of linear compounds based on an oligo(phenylene ethynylene) backbone, which were shown to form a characteristic windmill adsorption pattern on the Au(111) surface.

Global and local expression of chirality in serine on the Cu{110} surface.

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.

Guanine- and potassium-based two-dimensional coordination network self-assembled on Au(111).

In this study, through the choice of the well-known G-K biological coordination system, bioligand-alkali metal coordination has for the first time been brought onto an inert Au(111) surface. Using the interplay between high-resolution scanning tunneling microscopy and density functional theory calculations, we show that the mobile G molecules on Au(111) can effectively coordinate with the K atoms, resulting in a metallosupramolecular porous network that is stabilized by a delicate balance between hydrogen bonding and metal-organic coordination.

Self-assembly of hydrogen-bonded chains of molecular landers.

One-dimensional chains of a specially designed lander molecule with di-carboxyl imide functional moieties, enabling complementary intermolecular hydrogen bonding, have been self-assembled under ultra high vacuum conditions on a Au(111) surface and characterized by scanning tunneling microscopy.

Supramolecular architectures on surfaces formed through hydrogen bonding optimized in three dimensions.

Supramolecular self-assembly on surfaces, guided by hydrogen bonding interactions, has been widely studied, most often involving planar compounds confined directly onto surfaces in a planar two-dimensional (2-D) geometry and equipped with structurally rigid chemical functionalities to direct the self-assembly. In contrast, so-called molecular Landers are a class of compounds that exhibit a pronounced three-dimensional (3-D) structure once adsorbed on surfaces, arising from a molecular backboard equipped with bulky groups which act as spacer legs. Here we demonstrate the first examples of extended, hydrogen-bonded surface architectures formed from molecular Landers.

Steering organizational and conformational surface chirality by controlling molecular chemical functionality.

Molecular chirality on surfaces has been widely explored, both for intrinsically chiral molecules and for prochiral molecules that become chiral upon adsorption due to the reduced symmetry which follows from surface confinement. However, little attention has been devoted to chiral effects that originate from conformational degrees of freedom for adsorbed molecules. Here we have used scanning tunneling microscopy to investigate the self-assembled structures formed when a class of six linear, organic molecules (oligo-phenylene-ethynylenes) are adsorbed on a Au(111) surface under ultrahigh vacuum conditions.

Hydrogen-bonded molecular networks of melamine and cyanuric acid on thin films of NaCl on Au(111).

Self-assembly of organized molecular structures on insulators is technologically very relevant, but in general rather challenging to achieve due to the comparatively weak molecule-substrate interactions. Here the self-assembly of a bimolecular hydrogen-bonded network formed by melamine (M) and cyanuric acid (CA) on ultrathin NaCl films grown on a Au(111) surface is reported. Using scanning tunneling microscopy under ultrahigh-vacuum conditions it is demonstrated that it is possible to exploit strong intermolecular forces in the M-CA system, resulting from complementary triple hydrogen bonds, to grow 2D bimolecular networks on an ultrathin NaCl film that are stable at a relatively high temperature of approximately 160 K and at a coverage below saturation of the first molecular monolayer.

Molecular self-assembly from building blocks synthesized on a surface in ultrahigh vacuum: kinetic control and topo-chemical reactions.

Self-assembly of organic molecules on solid surfaces under ultrahigh vacuum conditions has been the focus of intense study, in particular utilizing the technique of scanning tunneling microscopy. The size and complexity of the organic compounds used in such studies are in general limited by thermal decomposition in the necessary vacuum sublimation step. An interesting alternative approach is to deposit smaller molecular precursors, which react with each other on the surface and form the building blocks for the subsequent self-assembly.