Molecular Self-assembly Process Research Articles

Optimizing Double-Fibril Network Morphology via Solid Additive Strategy Enables Binary All-Polymer Solar Cells with 19.50% Efficiency.

Double-fibril network morphology (DFNM), in which the donor and the acceptor can self-assemble into a double-fibril structure, is beneficial for exciton dissociation and charge transport in organic solar cells. Herein, it is demonstrated that such DFNM can be constructed and optimized in all-polymer solar cells (all-PSCs) with the assistance of 2-alkoxynaphthalene volatile solid additives. It is revealed that the incorporation of 2-alkoxynaphthalene can induce a stepwise regulation in the aggregation of donor and acceptor molecules during film casting and thermal annealing processes. Through altering the alkoxy of 2-alkoxynaphthalene solid additives, both the intermolecular interactions and molecular miscibility with the host materials can be precisely tuned, which allows for the optimization of the molecular aggregation process and facilitation of molecular self-assembly, and thus leading to reinforced molecular packing and optimized DFNM. As a result, an unprecedented efficiency of 19.50% (certified as 19.1%) is obtained for 2-ethoxynaphthalene-processed PM6:PY-DT-X all-PSCs with excellent photostability (T80=1750h). This work reveals that the optimization of DFNM via solid additive strategy is a promising avenue to boosting the performance of all-PSCs.

Chemical reaction steers spatiotemporal self-assembly of supramolecular hydrogels.

Supramolecular structures are widespread in living system, which are usually spatiotemporally regulated by sophisticated metabolic processes to enable vital biological functions. Inspired by living system, tremendous efforts have been made to realize spatiotemporal control over the self-assembly of supramolecular materials in synthetic scenario by coupling chemical reaction with molecular self-assembly process. In this review, we focused on the works related to supramolecular hydrogels that are regulated in space and time using chemical reaction. Firstly, we summarized how spatially controlled self-assembly of supramolecular hydrogels can be achieved via chemical reaction-instructed self-assembly, and the application of such a self-assembly methodology in biotherapy was discussed as well. Second, we reviewed dynamic supramolecular hydrogels dictated by chemical reaction networks that can evolve their structures and properties against time. Third, we discussed the recent progresses in the control of the self-assembly of supramolecular hydrogels in both space and time though a reaction-diffusion-coupled self-assembly approach. Finally, we provided a perspective on the further development of spatiotemporally controlled supramolecular hydrogels using chemical reaction in the future.

Self-assembled peptide nanotubes (SPNTs)/SnO2 nanocomposites for high-performance NO2 sensing at room temperature

Nitrogen dioxide (NO2) is a major pollutant that poses significant risks to sustainable human life. As a result, a growing focus has been placed on the development of highly selective and sensitive gas sensors for NO2. Traditional cutting-edge non-organic NO2 gas detectors often necessitate stringent production conditions and potentially harmful materials, which are not environmentally friendly, and these shortcomings have limited their widespread practical use. To overcome these challenges, we synthesized self-assembled peptide nanotubes (SPNTs) through a molecular self-assembly process. The SPNTs were then combined with SnO2 in varying proportions to construct NO2 gas sensors. The design of this sensor ensured efficient electron transfer and leverage the extensive surface area of the SPNTs for enhanced gas adsorption and the effective dispersion of SnO2 nanoparticles. Notably, the performance of the sensor, including its sensitivity, response time, and recovery rate, along with a lower detection threshold, could be finely tuned by varying the SPNTs content. This approach illustrated the potential of bioinspired methodologies, using peptide self-assemblies, to develop integrated sensors for pollutant detection, providing a significant development in environmentally conscious sensor technology.

Functionalized Nanoporous Ceramic Membranes for Electrodialysis Treatment of Harsh Wastewater

INTRODUCTION Electrodialysis (ED) is a well-developed technology for electrochemical desalination. However, many industries generate harsh wastewater streams that are incompatible with traditional ion exchange membranes and thus limit the use of ED. Membrion® has developed novel ceramic-based ion exchange membranes which offer a number of advantages over traditional polymer membranes: high performance in low pH, chemical resistance to oxidizers, and a rigid structure which minimizes membrane swelling. This presentation will discuss these novel membranes and their performance in electrodialysis stacks. EXPERIMENTAL Novel ceramic ion exchange membranes (IEM) are synthesized with patented silane-based sol-gel techniques. These ceramic membranes have covalently bound charged moieties similar to polymer IEMs; however, they are attached to a tunable nanoporous structure. The pore size, shape, and network structure are engineered through a molecular self-assembly process where thermodynamic driving forces are used to direct where and how pores form. Either cation (e.g., SO3 -) or anion (e.g., NH4 +) groups can be added within the membrane nanopore structure to enhance ion selectivity. The ceramic IEMs are produced on a roll-to-roll manufacturing line with low temperature processing. Membrane performance is assessed by measuring permselectivity (PS), area-specific resistance (ASR), and batch electrodialysis tests. RESULTS Figure 1 shows that both cation exchange membranes (CEM) and anion exchange membranes (AEM) show a decreased ASR compared to traditional polymer membranes, while maintaining comparable PS (i.e., the ability to separate cations and anions). The lower ASR of ceramic membranes is advantageous, as this can improve the overall energy efficiency of electrodialysis desalination. We maintain good performance (i.e., comparable current efficiency and water recovery) when integrated into a 10-cell pair stack. Most significantly, the right plot of Figure 1 shows a stable dilute water recovery of ~90% achieved with ceramic membranes after being stored in solutions ranging from pH 3 to pH 0 for 30 days. We have also demonstrated this technology in the field with copper wastewater generated at a microelectronics manufacturing facility. On site bench and pilot testing showed that our membranes could be used to nearly eliminate the copper sent to single-use IEX resin. DISCUSSION Ceramic-based ion exchange membranes are able to achieve comparable performance to traditional polymer membranes and offer some unique advantages. Long exposure to very low pH has negligible impact on ceramic ED stack performance. Additionally, we have observed stable performance in the presence of strong oxidizing agents such as hydrogen peroxide. This stability is expected, as the silica backbone of these materials is already in a fully oxidized state, as opposed to traditional polystyrene-based membranes. This data suggests ceramic membranes could be an ideal solution for acidic and/or oxidizing wastewater streams found in industries such as semiconductor manufacturing and mining. In addition to offering chemical stability in harsh environments, the patented silica sol-gel process used to cast these membranes is extremely tunable. Through incorporating commercially available functionalized silanes, the pore size and chemical make-up can be easily altered to target specific waste streams. CONCLUSIONS Ceramic ion exchange membranes are shown to have similar performance attributes to traditional polymer IEMs when evaluated for electrodialysis water purification applications. The good stack-level performance combined with stability in harsh environments have the potential to dramatically broaden the use of ED/EDR for industrial wastewater treatment. Figure 1

Size Control of On-Surface Self-Assembled Nanochains Using Soft Building Blocks.

Owing to their conformational flexibility, soft molecules with side chains play a crucial role in molecular self-assembly or self-organization processes toward bottom-up building of supramolecular nanostructures. However, the influence of the rotating side chains in the confined space and subsequent surface-confined supramolecular self-assembly remains rarely explored. Herein, using the spatial confinement effect between soft building blocks, we realized size control on surface-confined supramolecular coordination self-assembly through the synergy between the repulsive steric hindrance and the attractive chemical interactions. Combining scanning tunneling microscopy with density functional theory calculations and Monte Carlo simulations, we elucidated the effective repulsive force generated by the thermal wiggling motions of the soft building blocks, allowing length tuning of the self-assembled chain structures. Through a delicate balance between the repulsive interaction induced by the spatial confinement effect and the coordinate chemical interaction, we provide a new strategy for controlling the geometry of the on-surface supramolecular nanostructures.

Synthesis and Structural Studies of Nucleobase Functionalized Hydrogels for Controlled Release of Vitamins.

The development of biomolecule-derived biocompatible scaffolds for drug delivery applications is an emerging research area. Herein, we have synthesized a series of nucleobase guanine (G) functionalized amino acid conjugates having different chain lengths to study their molecular self-assembly in the hydrogel state. The gelation properties have been induced by the correct choice of chain lengths of fatty acids present in nucleobase functionalized molecules. The effect of alkali metal cations, pH, and the concentration of nucleobase functionalized amino acid conjugates in the molecular self-assembly process has been explored. The presence of Hoogsteen hydrogen bonding interaction drives the formation of a G-quadruplex functionalized hydrogel. The DOSY nuclear magnetic resonance is also performed to evaluate the self-assembling behavior of the newly formed nucleobase functionalized hydrogel. The nanofibrillar morphology is responsible for the formation of a hydrogel, which has been confirmed by various microscopic experiments. The mechanical behaviors of the hydrogel were evaluated by rheological experiments. The in vitro biostability of the synthesized nucleobase amino acid conjugate is also investigated in the presence of hydrolytic enzymes proteinase K and chymotrypsin. Finally, the nucleobase functionalized hydrogel has been used as a drug delivery platform for the control and sustained pH-responsive release of vitamins B2 and B12. This synthesized nucleobase functionalized hydrogel also exhibits noncytotoxic behavior, which has been evaluated by their in vitro cell viability experiment using HEK 293 and MCF-7 cell lines.

Manipulating Molecular Self-Assembly Process at the Solid-Liquid Interface Probed by Scanning Tunneling Microscopy.

The phenomenon of ordered self-assembly on solid substrates is a topic of interest in both fundamental surface science research and its applications in nanotechnology. The regulation and control of two-dimensional (2D) self-assembled supra-molecular structures on surfaces have been realized through applying external stimuli. By utilizing scanning tunneling microscopy (STM), researchers can investigate the detailed phase transition process of self-assembled monolayers (SAMs), providing insight into the interplay between intermolecular weak interactions and substrate-molecule interactions, which govern the formation of molecular self-assembly. This review will discuss the structural transition of self-assembly probed by STM in response to external stimuli and provide state-of-the-art methods such as tip-induced confinement for the alignment of SAM domains and selective chirality. Finally, we discuss the challenges and opportunities in the field of self-assembly and STM.

Achieving Greener, Super-Robust Performance Water-Based Lubrication: Obtained by a Multifunctional Ionic Liquid Aqueous System and Formation of Unique Interfacial Interactions

Owing to the green, high-performance, and application-specific work conditions, water-based lubricating systems show unlimited potential for chemical engineering development. The interfacial behavior of functional additives in aqueous systems is complex and variable due to polarity and interfacial activity, thus showing important research significance. Herein, five novel ionic liquids were synthesized; their unique interfacial behavior in the polar water system contributes a lot to the advanced corrosion resistance and the improved extreme pressure-bearing capacity. The polar groups in the molecular structure of ionic liquids can adsorb preferentially in competition with water molecules, resulting in the formation of an adsorption layer with a high elastic modulus on the metal surface. Benefiting from the tribochemical reaction and the strong polar adsorption effect, the tribofilm at the sliding asperity exhibited effective antiscuffing and antiwear performance. Moreover, their characteristic cationic groups enrich the driving force of the molecular self-assembly process and enhance the ability to form ordered molecular aggregates, whose behavior in an aqueous system facilitates super-robust lubricity. This work can promote the in-depth understanding, future design, and optimization of the aqueous lubricating system, providing content enrichment and expansion for the lubrication technology for harsh service conditions.

Quantifying the Cooperative Process of Molecular Self-Assembly on Surfaces: A Case Study of Isophthalic Acids

Molecular self-assembly, a promising strategy for modifying surfaces on the nanometer scale, is essential for developing functional materials in electronics, catalysis, or two-dimensional (2D) crystal engineering. In this work, we are shifting attention to the physical chemistry of the process at a molecular level through a study of the effect of concentration on the overall process of self-assembled molecular network formation using scanning tunneling microscopy. The overarching idea is to correlate experimental results with analytical thermodynamic models to improve the understanding of supramolecular chemistry in two dimensions by obtaining quantitative data. For this purpose, a series of isophthalic acids have been chosen as a model system. The effect of the concentration on the adsorption behavior, focusing on the surface coverage, has been evaluated at the nanoscale. Our results confirm the existence of a critical concentration above which self-assembly occurs and that a change in the molecular structure (the length of the alkyl chain) has a remarkable impact on the value of this critical threshold. Finally, we report highly cooperative behavior in studied systems, which presents one of the rare examples of quantitative measurement of cooperative phenomena at the liquid/solid interface.

Fluorescence correlation spectroscopy and fluorescence lifetime imaging microscopy for deciphering the morphological evolution of supramolecular self-assembly.

The properties and functions of non-covalent interaction-driven fluorescent supramolecular self-assembly depend greatly on their evolution dynamics. Electron microscopy, atomic force microscopy, and confocal laser scanning microscopy have been used to elucidate the formation of molecular self-assembly. However, some pertinent issues, such as the drying or freezing of the sample for electron microscopy, the influence of the interactions between the tip and the sample in atomic force microscopy imaging, and the low spatial resolution of confocal laser scanning microscopy images, often impede the real-time analysis and exploration of the dynamics of molecular self-assembly processes. In this context, fluorescence correlation spectroscopy and fluorescence lifetime imaging microscopy have recently been explored to unravel the physical picture of the in situ growth dynamics and stimuli-induced morphological transformation of luminescent self-assembled structures. The current highlight article demonstrates the need for fluorescence correlation spectroscopy and fluorescence lifetime imaging microscopy to acquire precise information on the dynamics and morphological evolution of fluorescent self-assembled architectures using a few remarkable recent studies. In addition to the current status and challenges, the future directions for the further exploration of dynamic self-assembly processes towards developing next-generation functional materials have been delineated.

Theoretical and computational methodologies for understanding coordination self-assembly complexes.

This perspective highlights three theoretical and computational methods to capture the coordination self-assembly processes at the molecular level: quantum chemical modeling, molecular dynamics, and reaction network analysis. These methods cover the different scales from the metal-ligand bond to a more global aspect, and approaches that are best suited to understand the coordination self-assembly from different perspectives are introduced. Theoretical and numerical researches based on these methods are not merely ways of interpreting the experimental studies but complementary to them.

Unraveling Molecular Assembly and Tracking Lipid Droplet Dynamics Using Fluorescent Phenanthroimidazole Derivatives

Small strategic perturbations of the molecular structures impart significant variation in the evolution dynamics and properties of supramolecular self-assembled architectures. However, probing the in situ evolution dynamics of molecular assembly remains a challenge. Herein, we unraveled the real-time, early stage environment-sensitive dynamic molecular self-assembly processes and stimuli-induced reversible morphological transformation between supramolecular fibers and spherical nanoaggregates of alkyl chain-substituted phenanthroimidazole-based luminogen (BPIB1) through fluorescence lifetime imaging microscopy (FLIM). The presence of an octyl chain and basic nitrogen centers in BPIB1 led to a distinct self-assembly pattern. The gradual progression in the fluorescence lifetime provides a unique strategy for elucidating the dynamics of the self-assembly process leading to distinct nano/microarchitectures. Among the varied self-assembled structures, the smaller-sized (diameter ∼ 20–30 nm), highly photostable, water-dispersible, and biocompatible fluorescent nanoaggregates of BPIB1 were employed for tracking the dynamics of lipid droplets in live cells and a model organism, C. elegans, using fluorescence correlation spectroscopy and FLIM. Thus, a combined microscopic and spectroscopic approach demonstrated in the present study opens up new avenues to explore the formation pathways of diverse molecular aggregates and their use to decipher complex organelle dynamics.

Building block 3D printing based on molecular self-assembly monolayer with self-healing properties

The spontaneous formation of biological substances, such as human organs, are governed by different stimuli driven by complex 3D self-organization protocols at the molecular level. The fundamentals of such molecular self-assembly processes are critical for fabrication of advanced technological components in nature. We propose and experimentally demonstrate a promising 3D printing method with self-healing property based on molecular self-assembly-monolayer principles, which is conceptually different than the existing 3D printing protocols. The proposed molecular building-block approach uses metal ion-mediated continuous self-assembly of organic molecular at liquid–liquid interfaces to create 2D and 3D structures. Using this technique, we directly printed nanosheets and 3D rods using dithiol molecules as building block units.

Effective dye degradation by an environment-friendly porous few-layered carbon nitride photocatalyst developed using sequential molecule self-assembly

Two-dimensional (2D) g-C3N4 (CN) has garnered massive interest for photocatalytic applications owing to its excellent photon contact area, visible-light absorption, and easy transport of photogenerated charge carriers to the surface. However, bulk CN suffers from intrinsically poor charge separation, limited specific surface area, and insufficient visible-light absorption, significantly limiting its photocatalytic efficiency. Exfoliation of bulk crystals into nanosheets with few layers has proven to be an effective and widely used strategy to enhance photocatalytic performance; however, this process is quite complicated, requiring longer times and external energy. Here, a few-layered porous g-C3N4 (PCN) was synthesized using the molecular self-assembly process. This prepared PCN exposes more active sites, leading to enhanced separation of charge carriers, resulting in a higher photocatalytic activity than regular CN. PCN achieved the best photocatalytic degradation (97.46%) of Rhodamine B (RhB) dye in 1 h, which is three times higher than that by CN (32.57%) because of enhanced porosity of the photocatalyst with few layers. This enhanced degradation performance of PCN was caused by increased visible-light absorption and charge separation along with higher number exposed active sites triggered by the high porosity under visible light, which is greater than those of other metal-free photocatalysts reported thus far.

Optomechanical controlling of intermolecular interaction and the application in molecular self-assembly.

In this paper, we combined cavity optomechanics and quantum mechanical mechanism of van der Waals force to study the dynamic behavior of interacting bimolecules in the plasmonic localized field, and extend it to the interacting multi-molecular system. We explored how plasmonic optomechanical coupling affects the strength of intermolecular interactions. Based on our results, we propose to use optical field to modulate the intermolecular interaction potential in plasmonic cavity, which can be utilized in the enhancement of the efficiency of the molecular self-assembly process and controlling the yield of the reaction in an optical environment. This research extends molecular optomechanics from intramolecular interactions to intermolecular interactions and may has high application potential in some nanostructure synthesis.

A rapid and effective synthetic route to functional cuboctahedron nanospheres

Multiferrocenyl and multiadamantyl cuboctahedron nanospheres were synthesized via rapid self-assembly reactions of twelve 90° PdII-containing compounds and twenty-four 120° organic bidentate N-ligands in acetone solution. The selected self-assembly reaction and corresponding solvent were demonstrated to be effective and simple in the preparation of self-assembled nanospheres. DOSY NMR spectroscopy, AFM images and theoretical calculations confirmed the formation of cuboctahedron complexes with the size of 4–5 ​nm. Multifunctional molecular self-assembly processes offer considerable synthetic advantages including significantly fewer steps, fast and facile formation of final desirable products, and will lead to a new multifunctionality platform for cuboctahedron complexes.

Self-Organizing Microdroplet Protocells Displaying Light-Driven Oscillatory and Morphological Evolution.

The development of synthetic systems that enable the sustained active self-assembly of molecular blocks to mimic the complexity and dynamic behavior of living systems is of great interest in elucidating the origins of life, understanding the basic principles behind biological organization, and designing active materials. However, it remains a challenge to construct microsystems with dynamic behaviors and functions that are connected to molecular self-assembly processes driven by external energy. Here, an active self-assembly of microdroplet protocells with dynamic structure and high structural complexity through living radical polymerization under constant energy flux is reported. The active microdroplet protocells exhibit nonlinear behaviors including oscillatory growth and shrinkage. This relies on the transient stabilization of molecular assembly, which can channel the inflow of energy through noncovalent interactions of pure synthetic components. The intercommunication of microdroplet protocells through stochastic fusion leads to the formation of a variety of dynamic and higher-order biomimetic microstructures. This work constitutes an important step toward the realization of autonomous and dynamic microsystems and active materials with life-like properties.

The retinal toxicity profile towards assemblies of Amyloid-\u03b2 indicate the predominant pathophysiological activity of oligomeric species

Amyloid-β (Aβ), reported as a significant constituent of drusen, was implicated in the pathophysiology of age-related macular degeneration (AMD), yet the identity of the major pathogenic Aβ species in the retina has remained hitherto unclear. Here, we examined the in-vivo retinal impact of distinct supramolecular assemblies of Aβ. Fibrillar (Aβ40, Aβ42) and oligomeric (Aβ42) preparations showed clear biophysical hallmarks of amyloid assemblies. Measures of retinal structure and function were studied longitudinally following intravitreal administration of the various Aβ assemblies in rats. Electroretinography (ERG) delineated differential retinal neurotoxicity of Aβ species. Oligomeric Aβ42 inflicted the major toxic effect, exerting diminished ERG responses through 30 days post injection. A lesser degree of retinal dysfunction was noted following treatment with fibrillar Aβ42, whereas no retinal compromise was recorded in response to Aβ40 fibrils. The toxic effect of Aβ42 architectures was further reflected by retinal glial response. Fluorescence labelling of Aβ42 species was used to detect their accumulation into the retinal tissue. These results provide conceptual evidence of the differential toxicity of particular Aβ species in-vivo, and promote the mechanistic understanding of their retinal pathogenicity. Stratifying the impact of pathological Aβ aggregation in the retina may merit further investigation to decipher the pathophysiological relevance of processes of molecular self-assembly in retinal disorders.

Coordination Self-Assembly Processes Revealed by Collaboration of Experiment and Theory: Toward Kinetic Control of Molecular Self-Assembly.

The importance of the collaboration of experiment and theory has been proven in many examples in science and technology. Here, such a new example is shown in the investigation of molecular self-assembly process, which is a complicated multi-step chemical reaction occurring in the reaction network composed of a huge number of intermediates. An experimental method, QASAP (quantitative analysis of self-assembly process), developed by us and a numerical approach, NASAP (numerical analysis of self-assembly process), that analyzes the experimental data obtained by QASAP to draw detail molecular self-assembly pathways, which was also developed by us, are introduced, and their application to the investigation of Pd(II)-mediated coordination assemblies are presented. Further, the possibility of the prediction of the outcomes of molecular self-assembly by varying the reaction conditions is also demonstrated. Finally, a future direction in the field of artificial molecular self-assembly based on pathway-dependent self-assembly, that is, kinetic control of molecular self-assembly is discussed.

Li+ storage properties of SiO2@C core-shell submicrosphere and its hollow counterpart synthesized by molecular self-assembly in wet-chemistry condition as anodes for LIBs

SiO2@C core-shell submicrospheres (SiO2@C) were fabricated via molecular self-assembly process in wet-chemistry condition and followed by post-calcination. SEM and TEM indicated the outer diameter of SiO2@C is ∼300–400 nm. The diameter of inner SiO2 core can be controlled from maximum size to zero by NaOH solution etching. XRD, TG-DSC, BET, Raman and XPS were adopted to reveal its microstructure and elemental composition. Systematic electrochemical tests manifested that the specific capacity of SiO2@C reduces at the beginning then increases with the decrease of SiO2 core diameter. The underlying Li+ storage mechanism is discussed and analyzed, which illustrates that the effective utilization of active sites is the key for electrochemical performance when SiO2@C used as anode material for LIBs. And the completely etched hollow mesoporous carbon sphere without SiO2 core (HMCS, SiO2@C-12 h) exhibited the highest capacity and rate capability (349.2 mA h/g at 100 mA/g after 200 cycles; 316.0 mA h/g at 400 mA/g), which is due to the effective Li+ active sites benefitted from its conductive and porous carbon network.