Water-Induced Chiral Separation on a Au(111) Surface

Tuning Surface Organic Structures by Small Gas Molecules through Catassembly and Coassembly

The field of molecular assembly has seen remarkable advancements across various domains, such as materials science, nanotechnology, and biomedicine. Small gas molecules serve as pivotal modulators, capable of altering the architecture of assemblies via tuning a spectrum of intermolecular forces including hydrogen bonding, dipole-dipole interactions, and metal coordination. Surface techniques, notably scanning tunneling microscopy and atomic force microscopy, have proven instrumental in dissecting the structural metamorphosis and characteristic features of these assemblies at an unparalleled single-molecule resolution. Recent research has spotlighted two innovative approaches for modulating surface molecular assemblies with the aid of small gas molecules: "catassembly" and "coassembly". This Perspective delves into these methodologies through the lens of varying molecular interaction types. The strategies discussed here for regulating molecular assembly structures using small gas molecules can aid in understanding various complex assembly processes and structures and provide guidance for the further fabrication of complex surface structures.

From Short- to Long-Range Chiral Recognition on Surfaces: Chiral Assembly and Synthesis

Research on chiral behaviors of small organic molecules at solid surfaces, including chiral assembly and synthesis, can not only help unravel the origin of the chiral phenomenon in biological/chemical systems but also provide promising strategies to build up unprecedented chiral surfaces or nanoarchitectures with advanced applications in novel nanomaterials/nanodevices. Understanding how molecular chirality is recognized is considered to be a mandatory basis for such studies. In this review, a series of recent studies in chiral assembly and synthesis at well-defined metal surfaces under ultra-high vacuum conditions are outlined. More importantly, the intrinsic mechanisms of chiral recognition are highlighted, including short/long-range chiral recognition in chiral assembly and two main strategies to steer the reaction pathways and modulate selective synthesis of specific chiral products on surfaces.

Stereoselective transport of 2-aryl propionic acid enantiomers in porous media subjected to chiral organic acids

The study examined the transport behavior of the 2-aryl propionic acid (2-APA) chiral pharmaceutical enantiomers by means of a laboratory-scale saturated quartz sand column experiment. Four typical of 2-APA and their enantiomers were selected for the study under different types of chiral organic acids (COAs)-mediated effects. Differences in the transport of the 2-APA enantiomeric pairs have been identified in response to various pH, types of COAs, and enantiomeric structures of COAs. Redundancy analysis identified the factors responsible for the largest differences in transport of 2-APA enantiomeric pairs, while spectroscopic characterization and density function theory (DFT) studies elucidated the underlying mechanisms contributing to the differences in transport of enantiomeric pairs. Obvious correlations among homochirality or heterochirality between COAs and 2-APA enantiomeric pairs were observed for changes in the mobility of 2-APA. The results indicate widespread COAs significantly affect the transport behavior of chiral man-made chemicals, suggesting more attention is needed to fill the gap in the perception of the transport behavior of chiral compounds.

Visualizing the Promoting Role of Interfacial Water in the Deprotonation of Formic Acid on Cu(111)

Water plays a crucial role in various heterogeneous catalytic reactions, but the atomic-scale characterization of how water participates in these chemical processes remains a significant challenge. Here we directly visualize the promoting role of interfacial water in the deprotonation of formic acid (FA) on a metal surface, using combined scanning tunneling microscopy and qPlus-based noncontact atomic force microscopy. We find the dissociation of FA when coadsorbed with water on the Cu(111) surface, resulting in the formation of hydronium and formate ions. Interestingly, most of the hydrated proton and formate ions exhibit a phase-separated behavior on Cu(111), in which Eigen and Zundel cations assemble into a monolayer hexagonal hydrogen-bonding (H-bonding) network, and bidentate formate ions are solvated with water and aggregate into one-dimensional chains or two-dimensional H-bonding networks. This phase-separated behavior is essential for preventing the proton transfer back from hydronium to formate and the reformation of FA. Density functional theory calculations reveal that the participation of water significantly reduces the deprotonation barrier of FA on Cu(111), in which water catalyzes the decomposition of FA through the Grotthuss proton transfer mechanism. In addition, the separate solvation of hydronium and bidentate formate ions is energetically preferred due to the enhanced interaction with the copper substrate. The promoting role of water in the deprotonation of FA is further confirmed by the temperature-programmed desorption experiment, which shows that the intensity of the H2 desorption peak significantly increases and the desorption of FA declines when water and FA coadsorbed on the Cu(111) surface.

Celebrating 20 Years of NCNST: Innovation in Nanoscience and Nanotechnology

With the development of nanoscience and technology, it has become an essential part of various research directions, changing our way of life, such as advanced accurate manufacturing in nanotechnology that facilitates reducing chip sizes, progress made in health care via nanoscience that provides hope to patients, and so on. As the nation's flagship institution of nanoscience and technology in China, the National Center for Nanoscience and Technology, China (NCNST), established in December 2003, has played a crucial role in promoting cutting-edge technologies in the field of nanoscience and expediting interdisciplinary fusion. With a strong research team and state-of-the-art research equipment, NCNST currently carries out frontier research and world-class technology innovation, including nanosystems and hierarchical fabrication, biological effects of nanomaterials and nanosafety, standardization and measurements for nanotechnology, as well as theoretical simulations. Serving as one of the most prestigious institutions in nanoscience and nanotechnology in China, NCNST will continue to foster impactful international cooperation, cultivate young talents, and boost inspiring innovation.

A cooperation tale of biomolecules and nanomaterials in nanoscale chiral sensing and separation

The cooperative relationship between biomolecules and nanomaterials makes up a beautiful tale about nanoscale chiral sensing and separation. Biomolecules are considered a fabulous chirality 'donor' to develop chiral sensors and separation systems. Nature has endowed biomolecules with mysterious chirality. Various nanomaterials with specific physicochemical attributes can realize the transmission and amplification of this chirality. We focus on highlighting the advantages of combining biomolecules and nanomaterials in nanoscale chirality. To enhance the sensors' detection sensitivity, novel cooperation approaches between nanomaterials and biomolecules have attracted tremendous attention. Moreover, innovative biomolecule-based nanocomposites possess great importance in developing chiral separation systems with improved assay performance. This review describes the formation of a network based on nanomaterials and biomolecules mainly including DNA, proteins, peptides, amino acids, and polysaccharides. We hope this tale will record the perpetual relation between biomolecules and nanomaterials in nanoscale chirality.

Insights into the Rearrangement of the Molecular Assembly Structure of 6-Aminonicotinic Acid in Its Hydrated Environment

Water, as a ubiquitous and essential component of life, is known to have a significant impact on the structure and function of organic molecules. In this study, we investigate the role of water in the phase transition of organic molecular assembly structures by scanning tunneling microscopy at room temperature. The results show that the -O-H···O hydrogen induced by water molecules can lead to a significant structural transition in the molecular assembly, specifically through selective weakening of -C-H···O between 6-aminonicotinic acid and the formation of new -O-H···O bonds between 6-aminonicotinic acid and water molecules. Subsequent thermal treatment of these molecular assembly structures reveals that the formation of -N-H···O hydrogen bonds induced by water molecules has created a different pathway for the phase transition of the molecular assembly structure. This knowledge has important implications for the design of organic molecules with specific nanostructures that can be controlled through hydration.

Construction of chiral capillary electrochromatography microsystems based on Aspergillus sp. CM96

Novel chiral capillary electrochromatography (CEC) microsystems were constructed based on Aspergillus sp. CM96. As a newly discovered intrinsic characteristic of the cell, cell chirality occupies an essential position in life evolution. Aspergillus sp. CM96 spore (CM96s) was chosen as a proof of concept to develop chiral capillary columns. Interestingly, various types of amino acid (AA) enantiomers were baseline separated under the optimized conditions. Furthermore, the time-dependent chiral interactions between AAs and CM96s were explored in a wider space. Pectinases generated from Aspergillus sp. CM96 fermentation were immobilized onto graphene oxide-functionalized capillary silica monoliths for separating AA enantiomers. Molecular docking simulations were performed to explore chiral separation mechanisms of pectinase for AA enantiomers. These results indicated that Aspergillus sp. CM96-based CEC microsystems have a significant advantage for chiral separation.

Structure transformation from Sierpiński triangles to chains assisted by gas molecules

Reversible transformations between fractals and periodic structures are of fundamental importance for understanding the formation mechanism of fractals. Currently, it is still a challenge to controllably achieve such a transformation. We investigate the effect of CO and CO2 molecules on Sierpiński triangles (STs) assembled from Fe atoms and 4,4″-dicyano-1,1':3',1″-terphenyl (C3PC) molecules on Au surfaces. Using scanning tunneling microscopy, we discover that the gas molecules induce a transition from STs into 1D chains. Based on density functional theory modeling, we propose that the atomistic mechanism involves the transformation of a stable 3-fold coordination Fe(C3PC)3 motif to Fe(C3PC)4 with an axially bonded CO molecule. CO2 causes the structural transformation through a molecular catassembly process.

Concentration-modulated global organizational chirality at the liquid/solid interface

Understanding the origin of homochirality in macroscopic assemblies and manipulating organizational chirality still remain a challenge. Herein, homochirality is achieved by combination of the majority-rules principle and concentration-dependent molecular assembly at the liquid/solid interface. A lower molecular concentration in solution facilitates more efficient amplification of chirality, which is formulated by a cooperative equilibrium model based on the Langmuir adsorption isotherm. Our results contribute to gain a new insight into chiral amplification in supramolecular assemblies. Particularly, a homochiral monolayer can be obtained just through modulating the molecular concentration in mixed enantiomer systems.

Surface Diffusion Aided by a Chirality Change of Self-Assembled Oligomers under 2D Confinement

Chirality switching of self-assembled molecular structures is of potential interest for designing functional materials but is restricted by the strong interaction between the embedded molecules. Here, we report on an unusual approach based on reversible chirality changes of self-assembled oligomers using variable-temperature scanning tunneling microscopy supported by quantum mechanical calculations. Six functionalized diazomethanes each self-assemble into chiral wheel-shaped oligomers on Ag(111). At 130 K, a temperature far lower than expected, the oligomers change their chirality even though the molecules reside in an embedded self-assembled structure. Each chirality change is accompanied by a slight center-of-mass shift. We show how the identical activation energies of the two processes result from the interplay of the chirality change with surface diffusion, findings that open the possibility of implementing various functional materials from self-assembled supramolecular structures.

High-Throughput Preparation of Supramolecular Nanostructures on Metal Surfaces

One of the contemporary challenges in materials science lies in the rapid materials screening and discovery. Experimental sample libraries can be generated by high-throughput parallel synthesis to map the composition space for rapid material discoveries. Molecular self-assembly on surfaces has proved a useful way to construct nanostructures with interesting topologies or properties. Despite the strong dependence of molecular stoichiometry on the structures, high-throughput preparations of supramolecular surface nanostructures have been far less explored. Here, by integrating a physical mask into the standard ultra-high-vacuum (UHV) molecular preparation system we show a high-throughput approach for preparing supramolecular nanostructures of continuous composition spreads on metal surfaces. The spatially addressable sample libraries of supramolecular self-assemblies are characterized by high-resolution scanning probe microscopy. We could explore different binary nanostructures of varying molecular ratios on one single substrate. Moreover, we use the minimum spanning tree approach to qualitatively and quantitatively study the structural properties of the formed nanostructures. This high-throughput approach may accelerate the screening and exploration of surface-supported, low-dimensional nanostructures not limited to supramolecular interactions.

Steering the Reaction Pathways of Terminal Alkynes by Introducing Oxygen Species: From C-C Coupling to C-H Activation

Selective regulation of chemical reactions is crucial in chemistry. Oxygen, as a key reagent in ubiquitous oxidative chemistry, exhibits great potential in regulating molecular assemblies, and more importantly, chemical reactions in molecular systems supported by metal surfaces. However, the unique catalytic performance and reaction mechanisms of oxygen species remain elusive, which are essential for understanding reaction selection and regulation. In this study, by a combination of scanning tunneling microscopy (STM) imaging/manipulations and density functional theory (DFT) calculations, we showed that the on-surface reaction pathways of terminal alkynes could be steered from C-C coupling to C-H activation with high selectivity by introducing O₂ into the molecular system. The catalytic performance and reaction mechanisms of oxygen species were explored in the C-H activation processes, and both molecular O₂ and atomic O could efficiently steer the reaction pathways. These results would provide a fundamental understanding of interfacial catalytic reaction processes.

Local Chiral Inversion of Thymine Dimers by Manipulating Single Water Molecules

Water, as one of the most important and indispensable small molecules in vivo, plays a crucial role in driving biological self-assembly processes. Real-space detection and identification of water-induced organic structures and further capture of dynamic dehydration processes are important yet challenging, which would help to reveal the cooperation and competition mechanisms among water-involved noncovalent interactions. Herein, introduction of water molecules onto the self-assembled thymine (T) structures under ultrahigh vacuum (UHV) conditions results in the hydration of hydrogen-bonded T dimers forming a well-ordered water-involved T structure. Reversibly, a local dehydration process is achieved by in situ scanning tunneling microscopy (STM) manipulation on single water molecules, where the adjacent T dimers connected with water molecules undergo a local chiral inversion process with the hydrogen-bonding configuration preserved. Such a strategy enables real-space identification and detection of the interactions between water and organic molecules, which may also shed light on the understanding of biologically relevant self-assembly processes driven by water.

Effect of an axial ligand on the self-assembly of molecular platforms

Sub-monolayer amounts of trioxatriangulenium (TOTA) molecules functionalized with biphenyl on Ag(111) were investigated with scanning tunnelling microscopy.