On-Surface Dual-Response Structural Transformations of Guanine Molecules and Fe Atoms

Directing Organometallic Ring-Chain Equilibrium by Electrostatic Interactions

Dynamic chemistry, which falls into the realm of both supramolecular and covalent chemistry, enables intriguing properties, such as structural diversity, self-healing, and adaptability. Due to robustness of covalent bonds compared to noncovalent ones, dynamic covalent chemistry has been exploited to synthesize complex molecular nanostructures at solid/liquid interfaces under ambient conditions, generally responsive to internal factors that directly regulate intermolecular covalent bonds. However, directing dynamics of covalent nanostructures, e.g., the typical ring-chain equilibria, on surface by extrinsic interactions remains elusive and challenging. Herein, we have controllably directed the ring-chain equilibrium of covalent organometallic structures by regulating intermolecular electrostatic interactions, thus achieving on-surface dynamic covalent chemistry under ultrahigh vacuum conditions. Our findings unravel the dynamic mechanism of covalent polymers governed by weak intermolecular interactions at the submolecular level, which not only bridges the gap between supramolecular and covalent chemistry but also offers great opportunities for the fabrication of adaptive polymeric nanostructures that respond to different conditions.

Modulation on the Iron Centers by Selective Synthesis of Organic Ligands with Stereo-Specific Conformations

Advanced fabrication of surface metal-organic complexes with specific coordination configuration and metal centers will facilitate to exploit novel nanomaterials with attractive electronic/magnetic properties. The precise on-surface synthesis provides an appealing strategy for in situ construction of complex organic ligands from simple precursors autonomously. In this paper, distinct organic ligands with stereo-specific conformation are separately synthesized through the well-known dehalogenative coupling. More interestingly, the exo-bent ligands promote the mono-iron chelated complexes with the Fe center significantly decoupled from the surface and of high spin, while the endo-bent ligands lead to bi-iron chelated ones instead with ferromagnetic properties.

Linear array of cesium atoms assisted by uracil molecules on Au(111)

A series of metal–organic U + Cs structures are achieved in which the Cs cations tend to form linear arrays.

Two-dimensional self-assembled nanostructures of nucleobases and their related derivatives on Au(111)

The construction of two-dimensional (2D) self-assembled nanostructures has been one of the considerably interesting areas of on-surface chemistry in the past few decades, and has benefited from the rapid development and improvement of scanning probe microscopy techniques. In this research field, many attempts have been made in the controllable fabrication of well-ordered and multifunctional surface nanostructures, which attracted interest because of the prospect for artificial design of functional molecular nanodevices. DNA and RNA are considered to be programmable self-assembly systems and it is possible to use their base sequences to encode instructions for assembly in a predetermined fashion at the nanometer scale. As important constituents of nucleic acids, nucleobases, with intrinsic functional groups for hydrogen bonding, coordination bonding, and electrostatic interactions, can be employed as a potential system for the versatile construction of various biomolecular nanostructures, which may be used to structure the self-assembly of DNA-based artificial molecular constructions and play an important role in novel biosensors based on surface functionalization. In this article, we will review the recent progress of on-surface self-assembly of nucleobases and their derivatives together with different reactants (e.g., metals, halogens, salts and water), and as a result, various 2D surface nanostructures are summarized.

Structural Transformation of Guanine Coordination Motifs in Water Induced by Metal Ions and Temperature

The transformation effects of metal ions and temperature on the DNA base guanine (G) metal-organic coordination motifs in water have been investigated by scanning tunneling microcopy (STM). The G molecules form an ordered hydrogen-bonded structure at the water-highly oriented pyrolytic graphite interface. The STM observations reveal that the canonical G/9H form can be transformed into the G/(3H,7H) tautomer by increasing the temperature of the G solution to 38.6 °C. Moreover, metal ions bind with G molecules to form G₄Fe₁³⁺, G₃Fe₃²⁺, and the heterochiral intermixed G₄Na₁⁺ metal-organic networks after the introduction of alkali-metal ions in cellular environment.

Tuning the ease of formation of on-surface metal-adatom coordination polymers featuring diketones

We use pyrene-4,5,9,10-tetraketone molecules with substituents of varying bulkiness in the 2,7 positions to probe the generality and versatility of the previously reported on-surface coordination of two diketones with a single metal atom, leading to one-dimensional coordination polymers. Three different low index surfaces of group 11 metals (Cu, Ag and Au) are used to provide both the support and the metal atoms for metal-organic coordination. By real space visualisation with single molecule resolution employing scanning tunnelling microscopy we investigate the molecular self-assembly and show how this can be substantiated with the formation of metal-organic linear and cyclic oligomers, depending on the employed substrate.

Hierarchical formation of Fe-9eG supramolecular networks via flexible coordination bonds

From the interplay between high-resolution scanning tunneling microscopy imaging/manipulations and density functional theory calculations, we display the hierarchical formation of supramolecular networks by codeposition of 9eG molecules and Fe atoms on Au(111) based on the flexible coordination bonds (the adaptability and versatility in the coordination modes). In the first step, homochiral islands composed of homochiral G₄Fe₂ motifs are formed; and then in the second step, thermal treatment results in the transformation into the porous networks composed of heterochiral G₄Fe₂ motifs with the ratio of the components being constant. In situ STM manipulations and the coexistence of some other heterochiral G₄Fe₂ motifs and clusters also show the flexibility of the coordination bonds involved. These studies may provide a fundamental understanding of the regulations of multilevel supramolecular structures and shed light on the formation of designed supramolecular nanostructures.

On-Surface Synthesis of Adenine Oligomers via Ullmann Reaction

Despite the fact that DNA bases have been well-studied on surface, the on-surface synthesis of one-dimensional DNA analogs through in situ reactions is still an interesting topic to be investigated. Herein, from the interplay of high-resolution scanning tunneling microscopy (STM) imaging and density functional theory (DFT) calculations, we have delicately designed a halogenated derivative of adenine as precursor to realize the combination of DNA bases and Ullmann reaction, and then successfully synthesized adenine oligomers on Au(111) via Ullmann coupling. This model system provides a possible bottom-up strategy of fabricating adenine oligomers on surface, which may further give access to man-made DNA strands with multiple bases.

Real-space evidence of the formation of the GCGC tetrad and its competition with the G-quartet on the Au(111) surface

From the interplay of high-resolution scanning tunneling microscopy (STM) imaging and density functional theory (DFT) calculations, we show the first real-space evidence of the formation of GCGC tetrad on an Au(111) surface, and further investigate its competition with the well-known G-quartet with the aid of NaCl under ultrahigh vacuum (UHV) conditions.

Structural diversity of metal-organic self-assembly assisted by chlorine

From the combination of STM imaging and DFT calculations, we show that both alkali metal and halogens interact with different sites of the target molecules resulting in structural formation in a synergistic way. The elementary metal-organic motifs are connected by Cl in a variety of fashions demonstrating structural diversity.