Self-Assembly of Molecular Landers Equipped with Functional Moieties on the Surface: A Mini Review.

The bottom-up fabrication of supramolecular and self-assembly on various substrates has become an extremely relevant goal to achieve prospects in the development of nanodevices for electronic circuitry or sensors. One of the branches of this field is the self-assembly of functional molecular components driven through non-covalent interactions on the surfaces, such as van der Waals (vdW) interactions, hydrogen bonding (HB), electrostatic interactions, etc., allowing the controlled design of nanostructures that can satisfy the requirements of nanoengineering concepts. In this context, non-covalent interactions present opportunities that have been previously explored in several molecular systems adsorbed on surfaces, primarily due to their highly directional nature which facilitates the formation of well-ordered structures. Herein, we review a series of research works by combining STM (scanning tunneling microscopy) with theoretical calculations, to reveal the processes used in the area of self-assembly driven by molecule Landers equipped with functional groups on the metallic surfaces. Combining these processes is necessary for researchers to advance the self-assembly of supramolecular architectures driven by multiple non-covalent interactions on solid surfaces.

Strength of London Dispersion Forces in Organic Structure Directing Agent-Zeolite Assemblies.

Herein, we study the London dispersion forces between organic structure directing agents (OSDAs)-here tetraalkyl-ammonium or -phosphonium molecules-and silica zeolite frameworks (FWs). We demonstrate that the interaction energy for these dispersion forces is correlated to the number of H atoms in OSDAs, irrespective of the structures of OSDAs or FWs, and of variations in charges and thermal motions. All calculations considered-DFT-D3 and BOMD undertaken by us, and molecular mechanics from an accessible database-led to the same trend. The mean energy of these dispersion forces is ca. -2 kcal.mol-1 per H for efficient H-O contacts.

Advances and Prospects in Understanding London Dispersion Interactions in Molecular Chemistry.

London dispersion (LD) interactions are the main contribution of the attractive part of the van der Waals potential. Even though LD effects are the driving force for molecular aggregation and recognition, the role of these omnipresent interactions in structure and reactivity had been largely underappreciated over decades. However, in the recent years considerable efforts have been made to thoroughly study LD interactions and their potential as a chemical design element for structures and catalysis. This was made possible through a fruitful interplay of theory and experiment. This review highlights recent results and advances in utilizing LD interactions as a structural motif to understand and utilize intra- and intermolecularly LD-stabilized systems. Additionally, we focus on the quantification of LD interactions and their fundamental role in chemical reactions.

Stiff Shape Memory Polymers for High-Resolution Reconfigurable Nanophotonics.

Reconfigurable metamaterials require constituent nanostructures to demonstrate switching of shapes with external stimuli. Yet, a longstanding challenge is in overcoming stiction caused by van der Waals forces in the deformed configuration, which impedes shape recovery. Here, we introduce stiff shape memory polymers. This designer material has a storage modulus of ∼5.2 GPa at room temperature and ∼90 MPa in the rubbery state at 150 °C, 1 order of magnitude higher than those in previous reports. Nanopillars with diameters of ∼400 nm and an aspect ratio as high as ∼10 were printed by two-photon lithography. Experimentally, we observe shape recovery as collapsed and touching structures overcome stiction to stand back up. We develop a theoretical model to explain the recoverability of these sub-micrometer structures. Reconfigurable structural color prints with a resolution of 21150 dots per inch and holograms are demonstrated, indicating potential applications of the stiff shape memory polymers in high-resolution reconfigurable nanophotonics.

Chirality Inversion in Self-Assembled Nanocomposites Directed by Curvature-Mediated Interactions.

Nanoscale curvature-dependent interactions are of paramount importance in biological systems. Here, we report that nanoscale curvature plays an important role in regulating the chirality of self-assembled nanocomposites from chiral organic molecules and achiral nanoparticles. Specifically, we show that the supramolecular chirality of the nanocomposites markedly depends on the nanoparticle curvature, where small-sized nanoparticles of high curvature and large-sized nanoparticles of low curvature lead to nanocomposites with opposite chirality. Quantitative kinetic experiments and molecular dynamics simulations reveal that nanoparticle curvature plays a key role in promoting the pre-nucleation oligomerization of chiral molecules, which consequently regulates the supramolecular chirality of the nanocomposites. We anticipate that this study will aid in rational design of an artificial cooperative system giving rise to emergent assembling phenomena that can be surprisingly rich and often cannot be understood by studying the conventional noncooperative systems.

Be2 (BO3 )(IO3 ): The First Anion-mixed Van der Waals Member in the KBe2 BO3 F2 Family with a Very Strong Second Harmonic Generation Response.

To obtain new nonlinear optical (NLO) materials with a large second harmonic generation (SHG) effect has always been a great challenge. We have synthesized the first metal borate-iodate NLO crystal, Be2 (BO3 )(IO3 ) (BBIO), by multicomponent modification of KBe2 BO3 F2 (KBBF), in which the structural features of KBBF were maintained and (IO3 )- groups were connected to honeycomb [Be2 BO3 O2 ]∞ layers. As the first KBBF family member with mixed anionic groups, BBIO benefited from the synergistic effect of (IO3 )- , (BO3 )3- and (BeO4 )6- groups, and exhibited a very strong SHG response of ≈7.2×KH2 PO4 (KDP, @1064 nm) and a large birefringence (Δn) of 0.172 at 1064 nm. BBIO may, unexpectedly, optimize growth habits via van der Waals forces. This study presents borate-iodate as a new NLO material and it demonstrates opportunities in KBBF structural engineering.

Enhancing Van der Waals Interactions of Functionalized UiO-66 with Non-polar Adsorbates: The Unique Effect of para Hydroxyl Groups.

UiO-66 is a highly stable metal-organic framework (MOF) that has garnered interest for many adsorption applications. For small, nonpolar adsorbates, physisorption is dominated by weak Van der Waals interactions limiting the adsorption capacity. A common strategy to enhance the adsorption properties of isoreticular MOFs, such as UiO-66, is to add functional groups to the organic linker. Low and high pressure O2 isotherms were measured on UiO-66 MOFs functionalized with electron donating and withdrawing groups. It was found that the electron donating effects of -NH2 , -OH, and -OCF3 groups enhance the uptake of O2 . Interestingly, a significant enhancement in both the binding energy and adsorption capacity of O2 was observed for UiO-66-(OH)2 -p, which has two -OH groups para from one another. Density functional theory (DFT) simulations were used to calculate the binding energy of oxygen to each MOF, which trended with the adsorption capacity and agreed well with the heats of adsorption calculated from the Toth model fit to multi-temperature isotherms. DFT simulations also determined the highest energy binding site to be on top of the electron π-cloud of the aromatic ring of the ligand, with a direct trend of the binding energy with low pressure adsorption capacity. Uniquely, DFT found that oxygen molecules adsorbed to UiO-66-(OH)2 -p prefer to align parallel to the -OH groups on the aromatic ring. Similar effects for the electron donation of the functional groups were observed for the low pressure adsorption of N2 , CH4 , and CO2 .

Polyphenolic Compounds and Digestive Enzymes: In Vitro Non-Covalent Interactions.

The digestive enzymes-polyphenolic compounds (PCs) interactions behind the inhibition of these enzymes have not been completely studied. The existing studies have mainly analyzed polyphenolic extracts and reported inhibition percentages of catalytic activities determined by UV-Vis spectroscopy techniques. Recently, pure PCs and new methods such as isothermal titration calorimetry and circular dichroism have been applied to describe these interactions. The present review focuses on PCs structural characteristics behind the inhibition of digestive enzymes, and progress of the used methods. Some characteristics such as molecular weight, number and position of substitution, and glycosylation of flavonoids seem to be related to the inhibitory effect of PCs; also, this effect seems to be different for carbohydrate-hydrolyzing enzymes and proteases. The digestive enzyme-PCs molecular interactions have shown that non-covalent binding, mostly by van der Waals forces, hydrogen binding, hydrophobic binding, and other electrostatic forces regulate them. These interactions were mainly associated to non-competitive type inhibitions of the enzymatic activities. The present review emphasizes on the digestive enzymes such as α-glycosidase (AG), α-amylase (PA), lipase (PL), pepsin (PE), trypsin (TP), and chymotrypsin (CT). Existing studies conducted in vitro allow one to elucidate the characteristics of the structure-function relationships, where differences between the structures of PCs might be the reason for different in vivo effects.

Dynamics of Gold Nanoparticles on Carbon Nanostructures Driven by van der Waals and Electrostatic Interactions.

Transmission electron microscopy studies on the assembly and growth of gold nanoparticles on carbon nanotubes supported on few-layer graphene and amorphous carbon reveal a competition between van der Waals forces and electrostatic interactions, enabling controlled positioning and sizing of adsorbed nanoparticles at the nanochannels formed between the carbon nanotube and the few-layer graph-ene surface.

One-pot exfoliation of graphite and synthesis of nanographene/dimesitylporphyrin hybrids.

A simple one-pot process to exfoliate graphite and synthesize nanographene-dimesitylporphyrin hybrids has been developed. Despite the bulky mesityl groups, which are expected to hinder the efficient π-π stacking between the porphyrin core and graphene, the liquid-phase exfoliation of graphite is significantly favored by the presence of the porphyrins. Metallation of the porphyrin further enhances this effect. The resulting graphene/porphyrin hybrids were characterized by spectroscopy (UV-visible, fluorescence, and Raman) and microscopy (STEM, scanning transmission electron microscopy).

London dispersion in molecular chemistry--reconsidering steric effects.

London dispersion, which constitutes the attractive part of the famous van der Waals potential, has long been underappreciated in molecular chemistry as an important element of structural stability, and thus affects chemical reactivity and catalysis. This negligence is due to the common notion that dispersion is weak, which is only true for one pair of interacting atoms. For increasingly larger structures, the overall dispersion contribution grows rapidly and can amount to tens of kcal mol(-1) . This Review collects and emphasizes the importance of inter- and intramolecular dispersion for molecules consisting mostly of first row atoms. The synergy of experiment and theory has now reached a stage where dispersion effects can be examined in fine detail. This forces us to reconsider our perception of steric hindrance and stereoelectronic effects. The quantitation of dispersion energy donors will improve our ability to design sophisticated molecular structures and much better catalysts.

Dispersion interaction stabilizes sterically hindered double fullerenes.

By state-of-the-art quantum chemical methods, we show that for bulky functional groups like cyclohexane, [20]fullerene, dodecahedrane, and C60, the attractive dispersion interaction can have a greater impact on stereochemistry than the repulsive steric effect, making the compact isomer the more stable one. In particular, for the double C60 adduct of pentacene 1, the syn isomer should be the main product instead of the anti one inferred in the original synthesis experiment (Y. Murata et al., J. Org. Chem. 1999, 64, 3483). With and without dispersion interactions taken into account, the Gibbs energy difference ΔG(syn-anti) is -6.36 and +1.15 kcal mol(-1), respectively. This study reminds us that dispersion interactions as well as electrostatic or hyperconjugation effects, etc. can lead to some unusual stereochemical phenomena.

Van der Waals Colloidal Crystals.

A general guiding principle for colloidal crystallization is to tame the attractive enthalpy such that it slightly overwhelms the repulsive interaction. As-synthesized colloids are generally designed to retain a strong repulsive potential for the high stability of suspensions, encoding appropriate attractive potentials into colloids has been key to their crystallization. Despite the myriad of interparticle attractions for colloidal crystallization, the van der Waals (vdW) force remains unexplored. Here, it is shown that the implementation of gold cores into silica colloids and the resulting vdW force can reconfigure the pair potential well depth to the optimal range between -1 and -4 kBT at tens of nanometer-scale colloidal distances. As such, colloidal crystals with a distinct liquid gap can be formed, which is evidenced by photonic bandgap-based diffractive colorization.

Urea counteracts trimethylamine N-oxide (TMAO) compaction of lipid membranes by modifying van der Waals interactions.

To cope with stress induced by high salinity and hydrostatic pressure, some marine animals accumulate small organic solutes called osmolytes. Most notable among these osmolytes are the denaturant urea, and trimethylamine N-oxide (TMAO) that is known to stabilize proteins. Although their effects on proteins and nucleic acids have been extensively studied, osmolytes are less commonly studied in the context of lipids, which are a crucial component in many cellular processes. Here we resolve the mechanism for urea's action on the forces acting between lipid membranes, in the presence and absence of TMAO. We find that unlike the way urea denatures proteins, and by contrast to TMAO, urea does not preferentially interact with net-neutral lipid membranes. Instead, urea modulates the interactions between membranes mainly by weakening the van der Waals attraction between bilayers. Interestingly, regardless of concentration, the effects of urea and TMAO appear to be additive to a large extent, so that the presence of one osmolyte hardly changes the interaction of the other with lipid. Weak non-additive effects are likely due to structural changes in the lipid membrane induced by the osmolytes. Finally, we comment on the potential role of osmolytes acting together in the modification of lipid adhesion and fusion.

Effects of particle shape and surface roughness on van der Waals interactions and coupling to dynamics in nanocrystals.

The van der Waals interaction between colloids and nanoparticles is one of the key components to understanding particle aggregation, attachment, and assembly. While the ubiquity of anisotropic particle shapes and surface roughness is well-recognized in nanocrystalline materials, the effects of both on van der Waals forces and torques have not been adequately investigated. In this study, we develop a numerical scheme to determine the van der Waals forces and torques between cubic particles with multiple configurations and relative orientations. Our results show that the van der Waals torque due to anisotropic particle shapes is appreciable at nearly all configurations and mutual angles, outcompeting Brownian torque for various materials systems and conditions. Surface roughness enhances this particle shape effect, resulting in stronger van der Waals interactions ascribed to protrusions on the surfaces. Moreover, a scaling analysis indicates that the surface roughness alters the separation dependence of the van der Waals force and, more importantly, significantly influences the dynamics of two approaching particles. Our results clearly demonstrate that surface roughness and anisotropic shape play a crucial role in the energetics and kinetics of various particle-scale and emergent phenomena, such as crystal growth by oriented attachment, nanomaterials synthesis and assembly, mud flow rheology, as well as the deposition of natural nanocrystals within the subsurface.

Synthesis, crystal structure and Hirshfeld surface analysis of tert-butyl 4-[4-(di-fluoro-meth-oxy)phen-yl]-2,7,7-trimethyl-5-oxo-1,4,5,6,7,8-hexa-hydro-quinoline-3-carboxyl-ate.

The 1,4-di-hydro-pyridine ring of the title compound, C24H29F2NO4, adopts a distorted boat conformation, while the cyclo-hexene ring is in an almost twist-boat conformation. In the crystal, N-H⋯O and C-H⋯O hydrogen bonds as well as C-H⋯π inter-actions connect mol-ecules, forming layers parallel to the (100) plane. These layers are linked by van der Waals forces and C-H⋯F inter-actions, which consolidate the crystal structure. Hirshfeld surface analysis shows the major contributions to the crystal packing are from H⋯H (54.1%), F⋯H/H⋯F (16.9%), O⋯H/H⋯O (15.4%) and C⋯H/H⋯C (12.6%) contacts.

Interaction mechanism of carotenoids and polyphenols in mango peels.

In this study, carotenoids and polyphenols were demonstrated to be the major active substances in the crude pigment extracts (CPE) of mango peels, accounting for 0.26 mg/g and 0.15 mg/g, respectively. The interactions between carotenoids and polyphenols in CPE was observed, as evidenced by that polyphenols significantly improved the antioxidant activity and storage stability of carotenoids in the CPE. Meanwhile, scanning electron microscopy showed that polyphenols are tightly bound to carotenoids. To further elucidate the interaction mechanism, the monomers of carotenoids and polyphenols were identified by HPLC and LC-MS analysis. Lutein (203.85 µg/g), ß-carotene (41.40 µg/g), zeaxanthin (4.20 µg/g) and α-carotene (1.50 µg/g) were authenticated as the primary monomers of carotenoids. Polyphenols were mainly consisted of gallic acid (95.10 µg/g), quercetin-3-ß-glucoside (29.10 µg/g), catechin (11.85 µg/g) and quercetin (11.55 µg/g). The interaction indexes between carotenoid and polyphenol monomer of CPE were calculated. The result indicated that lutein and gallic acid showed the greatest synergistic effect on the scavenging of DPPH and ABTS radical, suggesting the interaction between carotenoids and polyphenols in CPE was mainly caused by lutein and gallic acid. Molecular dynamics simulations and thermodynamic parameters analysis demonstrated that hydrogen bonding, electrostatic interactions, and van der Waals forces played dominant roles in the interaction between lutein and gallic acid, which was confirmed by Raman and X-ray diffraction. These results provided a new perspective on the interaction mechanism between carotenoids and polyphenols, which offered a novel strategy for the enhancement of the activities and stability of bioactive substances.

Analytical theory for the crossover from retarded to non-retarded interactions between metal plates.

The van der Waals force established between two surfaces plays a central role in many phenomena, such as adhesion or friction. However, the dependence of this forces on the distance of separation between plates is very complex. Two widely different non-retarded and retarded regimes are well known, but these have been traditionally studied separately. Much less is known about the important experimentally accessible cross-over regime. In this study, we provide analytical approximations for the van der Waals forces between two plates that interpolates exactly between the short distance and long distance behavior, and provides new insight into the crossover from London to Casimir forces at finite temperature. At short distance, where the behavior is dominated by non-retarded interactions, we work out a very accurate simplified approximation for the Hamaker constant which adopts analytical form for both the Drude and Lorentz models of dielectric response. We apply our analytical expressions for the study of forces between metallic plates, and observe very good agreement with exact results from numerical calculations. Our results show that contributions of interband transitions remain important in the experimentally accessible regime of decades nm for several metals, including gold.

Hybrid Swarming Algorithm With Van Der Waals Force.

This paper proposes a hybrid swarming algorithm based on Ant Colony Optimization and Physarum Polycephalum Algorithm. And the Van Der Waals force is first applied to the pheromone update mechanism of the hybrid algorithm. The improved method can prevent premature convergence into the local optimal solution. Simulation results show the proposed approach has excellent in solving accuracy and convergence time. We also compare the improved algorithm with other advanced algorithms and the results show that our algorithm is more accurate than the literature algorithms. In addition, we use the capitals of 35 Asian countries as an example to verify the robustness and versatility of the hybrid algorithm.

Disjoining pressure analysis of the lubricant nanofilm stability of liquid-infused surface upon lubricant depletion.

HYPOTHESIS: The structure of the slippery layer and the evolution of functional properties of a lubricant infused substrate (LIS) is determined by the isotherm of disjoining pressure in the lubricant film. METHODS: The macroscopic theory of van der Waals forces was applied to the layered system used to model the structure and properties of LIS. For a lubricant layer sandwiched between the flat substrate and air or water, the isotherms of disjoining pressure were calculated and their analysis was used to conclude about stability of LIS. FINDINGS: The results obtained for silicone oil and perfluorodecalin on smooth and porous hydrophilic and hydrophobic solids allow selecting the LIS components corresponding to stability of lubricant films in air and water. It was found that for hydrophilic substrates in conditions of lubricant depletion, silicone oil and perfluorodecalin show lubricant film stability in both air and water. On flat or post microtexture hydrophobic substrate with flat tops, the perfluorodecalin lubricating layer is typically stable in air and unstable in water. In contrast, silicone oil lubricating layer demonstrates the stability in a wide range of lubricant film thicknesses for the hydrophobic substrate with flat-top textures in water, however, it can be unstable in air.