Dispersion Interactions Research Articles

Uniform doping of onion-like carbon nanofillers in carbon nanofibers via functionalization and in-situ polymerization for improved fiber graphitic structure and mechanical properties

Carbonaceous nanofillers have been widely used as template additives to strengthen carbon nanofibers (CNFs), while their poor dispersion and insufficient interaction with fiber matrix often limit their optimization roles. Herein, this paper takes functionalized onion-like carbon (fOLC) as an improved nanofiller and provides a bottom-up solution to prepare fOLC-reinforced CNFs. The in-situ polymerization technique is developed to introduce fOLC in polyacrylonitrile (PAN) precursors. Meanwhile, moderate functionalization of the nanofiller is applied to further promote their dispersion and interaction with PAN. On this bases, the nanoscale spherical fOLC can achieve uniform distribution in the fiber matrix without the trouble of shape control, thus having more comprehensive impacts on fiber structures. It is shown that the added fOLC can organize the PAN molecular chains into crystalline nanofibrils in as-spun nanofibers and further promote their graphitization through nucleating and templating effects during annealing. In this case, the dispersed fOLC not only increases nucleation sites to cause grain refinement, but these rigid nanoparticles with well-developed interaction with the fiber matrix can further impede crack propagation through dispersion strengthening. As a result, the tensile strength and elongation at break of CNFs simultaneously increase by up to 65.15 % and 41.25 %, respectively.

The Realm of Unconventional Noncovalent Interactions in Proteins: Their Significance in Structure and Function.

Proteins and their assemblies are fundamental for living cells to function. Their complex three-dimensional architecture and its stability are attributed to the combined effect of various noncovalent interactions. It is critical to scrutinize these noncovalent interactions to understand their role in the energy landscape in folding, catalysis, and molecular recognition. This Review presents a comprehensive summary of unconventional noncovalent interactions, beyond conventional hydrogen bonds and hydrophobic interactions, which have gained prominence over the past decade. The noncovalent interactions discussed include low-barrier hydrogen bonds, C5 hydrogen bonds, C-H···π interactions, sulfur-mediated hydrogen bonds, n → π* interactions, London dispersion interactions, halogen bonds, chalcogen bonds, and tetrel bonds. This Review focuses on their chemical nature, interaction strength, and geometrical parameters obtained from X-ray crystallography, spectroscopy, bioinformatics, and computational chemistry. Also highlighted are their occurrence in proteins or their complexes and recent advances made toward understanding their role in biomolecular structure and function. Probing the chemical diversity of these interactions, we determined that the variable frequency of occurrence in proteins and the ability to synergize with one another are important not only for ab initio structure prediction but also to design proteins with new functionalities. A better understanding of these interactions will promote their utilization in designing and engineering ligands with potential therapeutic value.

Preparation of dual-use GPTES@ZnO photocatalyst from waste warm filter cake and evaluation of its synergic photocatalytic degradation for air-water purification

Organic pollutants are the most critical threats to the health of air and water resources. On this basis, fabricating a photocatalytic acrylic film with dual-use (i.e. removing benzene from air and MB/MO dyes from water) was aimed in this research. For this purpose, waste warm filter cake (WWFC) was used to extract zinc from it. Zinc element was separated from WWFC by a basic leaching method and acidified to prepare zinc oxide nanoparticles. In the following, a simple hydrothermal method was used to increase the surface functionality of the extracted ZnO nanoparticles in order to establish active reaction sites for reaction to silane coupling agent and increase in the holes that were prepared during photo-excitation. Thereafter, the nanoparticles were modified with 3-glycidoxypropyltriethoxysilane (GPTES) at different concentrations. The band gap of the modified nanoparticles decreased from 3.25 to 3.1 eV by surface modification. The photocatalytic performance of ZnO nanoparticles was assessed by degradation of MB and MO aqueous solution (50 ppm) under simulated UV/Visible irradiations. MB and MO were degraded 91 and 60% under UV light and 65 and 50% under visible light after 150 min of irradiation. The photo degradation rate increased after adding carboxy methyl cellulose (CMC) surfactant to methylene blue and adding cocamide-dea (CDE-G) surfactant to methyl orange. The results confirmed that the green surfactants improve the dispersion and surface interaction of the modified nanoparticles in the dyes solution and cause more electron charge transfer which creates effective photocatalytic sites. The prepared nanocomposite films were placed in a photo-reactor to remove gaseous benzene from air under UV/visible irradiation. Gas chromatography (GC) results showed that the modified nanoparticles removed up to 35.25 and 20.34% of benzene from air. Colorimetric analysis (ΔE*) showed that the acrylic film contained modified nanoparticles degraded 91 and 82% of MB, and 85 and 76% of MO under UV/visible lights, respectively. In the end, it can be said that these photocatalytic films are able to remove environmental pollution in air and water.

Role of Preaggregation in Single-Molecule Photoredox Catalysis

We investigate the role of preaggregation among photocatalyst and substrate in the paradigmatic molecular dye rhodamine 6G by means of fluorescence correlation experiments and quantum-mechanical modeling. By varying the substrate concentration, we experimentally confirm earlier conclusions that consecutive photoelectron transfer between rhodamine 6G and a model substrate molecule is not diffusion limited, raising puzzling questions regarding the mechanisms underlying its established photocatalytic activity. By theoretically exploring alternative explanations for ultrafast excited-state charge transfer, it is indeed found that preaggregation between photocatalyst and substrate is required to reach charge-transfer rates similar to those experimentally observed. Electrostatic as well as dispersive interactions are found to be most important for the molecular attraction involved in preaggregation. We show that tuning these contributions by chemical design alters the binding energies of photocatalyst–substrate assemblies. This suggests that reaction rates can be adjusted by adapting the composition of the species involved in preaggregation, which appears as an appealing concept in photocatalysis.

Solvent Polarity under Vibrational Strong Coupling.

Vibrational strong coupling (VSC) occurs when molecular vibrations hybridize with the modes of an optical cavity, an interaction mediated by vacuum fluctuations. VSC has been shown to influence the rates and selectivity of chemical reactions. However, a clear understanding of the mechanism at play remains elusive. Here, we show that VSC affects the polarity of solvents, which is a parameter well-known to influence reactivity. The strong solvatochromic response of Reichardt's dye (RD) was used to quantify the polarity of a series of alcohol solvents at visible wavelengths. We observed that, by simultaneously coupling the OH and CH vibrational bands of the alcohols, the absorption maximum of Reichardt's dye redshifted by up to ∼15.1 nm, corresponding to an energy change of 5.1 kJ·mol-1. With aliphatic alcohols, the magnitude of the absorption change of RD was observed to be related to the length of the alkyl chain, the molecular surface area, and the polarizability, indicating that dispersion forces are impacted by strong coupling. Therefore, we propose that dispersion interactions, which themselves originate from vacuum fluctuations, are impacted under strong coupling and are therefore critical to understanding how VSC influences chemistry.

Rotational Spectroscopy Probes Lone Pair···π-Hole Interactions in Hexafluorobenzene-Tertiary Alkylamines Complexes.

We employed microwave spectroscopy to investigate the 1:1 complexes of hexafluorobenzene with trimethylamine and quinuclidine, respectively. These complexes exhibit a C3v symmetry and are stabilized by nitrogen lone pair···π-hole interactions along the C3 axes. The N···π-center distances were determined to be 3.110(1) and 3.040(2) Å, respectively, which are shorter than that of hexafluorobenzene-ammonia at 3.2685(3) Å. Additionally, the strength of the intermolecular interaction increases with cluster size. While it was initially expected that the electron-donating effect of alkyl groups was responsible for changing the N···π interaction, the symmetry-adapted perturbation theory analysis revealed that, from hexafluorobenzene-ammonia to both hexafluorobenzene-alkylamines, electrostatic interaction actually decreases while dispersion interaction increases and becomes dominant. Interestingly, dispersion interaction decreases while electrostatic interaction increases from C6F6-N(CH3)3 to C6F6-NC7H13. The splitting pattern of the spectra indicates hexafluorobenzene rotates freely relative to its partners along the axis of the N···π-hole interactions.

Dispersion interactions with analytes at the center of graphene nanoflakes turn into electrostatic at the edge

Adsorption of small gaseous molecules on the center and edges of polycyclic aromatic hydrocarbons is studied through density functional theory calculations. The choice of selected functional for the study is based on a benchmarking, where 37 functionals are evaluated at low cost basis set against high level DFT SAPT calculations for adsorption of water molecule on coronene and hexabenzocoronene. After benchmarking, the detailed analysis is performed for the adsorption of H2S, H2O, NH3, CH3OH, HCN, H2O2 and NH2NH2 on coronene at its center and edges. The coronene is chosen to better elucidate the edge effect on the adsorption of analytes. All of the studied analytes are physiosorbed on coronene with adsorption energies ranging from 1 to 6 kcal mol−1. These complexes are stabilized by X-H---π interactions between analytes and coronene surface. The SAPT0 analysis reveals that the X-H---π interactions at the center (non-edge) position of coronene are dominated by dispersion interaction whereas the similar interactions at the edges are dominated by electrostatic interactions. The change from dispersion to electrostatic on edges is attributed to polarization of the systems by C–H polarity differences. The complexes having lone pair---π interactions have unexpectedly repulsive electrostatic interactions in H2S@GNF and NH3@GNF complexes. Electronic properties reveal that coronene surface is highly selective for hydrazine whereas adsorption of other analytes does not bring any significant changes in the electronic structure of coronene. The high selectivity of coronene for NH2NH2 is also evident from the redistribution of densities in frontier molecular orbitals. For NH2NH2@GNF complexes, the HOMOs are present on hydrazine whereas LUMOs are present in coronene. For other analytes, HOMOs and LUMOs are present merely on graphene nanoflake. This high sensitivity of coronene for hydrazine is due to better overlap of frontier molecular orbitals of analyte with coronene.

Linear Dispersion and Nonlinear Interactions in 2.5D Particle-in-Cell Simulations of Kinetic Alfvén Waves

Linear Dispersion and Nonlinear Interactions in 2.5D Particle-in-Cell Simulations of Kinetic Alfvén Waves

Highly Enantio- and Diastereoselective Hydrogenation of Cyclic Tetra-Substituted β-Enamido Phosphorus Derivatives.

Catalytic asymmetric hydrogenation of enamido phosphorus derivatives is one of the most efficient methods for the construction of chiral amino phosphorus products, among which the congested tetra-substituted substrates remains an unaddressed challenge. In this study, we utilize a commercially available Rh-Josiphos system for the efficient and stereoselective hydrogenation of a wide set of tetra-substituted cyclic β-enamido phosphonates/phosphine oxides, thus enabling access to chiral β-amino phosphorus compounds featuring two vicinal stereocenters. This protocol was broadly applicable to different ring systems possessing various phosphonate/phosphine oxide groups and further applied in the preparation of amino-phosphine ligands. DFT mechanistic explorations indicate that the C=C migratory insertion into RhIII -H bond could be the rate- and stereo-determining step. The origins of stereoselectivity are revealed through distortion/interaction analysis, which is primarily regulated by distinguished dispersion interactions and steric repulsions.

Highly Enantio‐ and Diastereoselective Hydrogenation of Cyclic Tetra‐Substituted β‐Enamido Phosphorus Derivatives

AbstractCatalytic asymmetric hydrogenation of enamido phosphorus derivatives is one of the most efficient methods for the construction of chiral amino phosphorus products, among which the congested tetra‐substituted substrates remains an unaddressed challenge. In this study, we utilize a commercially available Rh‐Josiphos system for the efficient and stereoselective hydrogenation of a wide set of tetra‐substituted cyclic β‐enamido phosphonates/phosphine oxides, thus enabling access to chiral β‐amino phosphorus compounds featuring two vicinal stereocenters. This protocol was broadly applicable to different ring systems possessing various phosphonate/phosphine oxide groups and further applied in the preparation of amino‐phosphine ligands. DFT mechanistic explorations indicate that the C=C migratory insertion into RhIII−H bond could be the rate‐ and stereo‐determining step. The origins of stereoselectivity are revealed through distortion/interaction analysis, which is primarily regulated by distinguished dispersion interactions and steric repulsions.

Hyperbolic resonant radiation of concomitant microcombs induced by cross-phase modulation

A high-quality optical microcavity can enhance optical nonlinear effects by resonant recirculation, which provides a reliable platform for nonlinear optics research. When a soliton microcomb and a probe optical field are coexisting in a micro-resonator, a concomitant microcomb (CMC) induced by cross-phase modulation (XPM) will be formed synchronously. Here, we characterize the CMC comprehensively in a micro-resonator through theory, numerical simulation, and experimental verification. It is found that the CMCs spectra are modulated due to resonant radiation (RR) resulting from the interaction of dispersion and XPM effects. The group velocity dispersion induces symmetric RRs on the CMC, which leads to a symmetric spectral envelope and a dual-peak pulse in frequency and temporal domains, respectively, while the group velocity mismatch breaks the symmetry of RRs and leads to asymmetric spectral and temporal profiles. When the group velocity is linearly varying with frequency, two RR frequencies are hyperbolically distributed about the pump, and the probe light acts as one of the asymptotic lines. Our results enrich the CMC dynamics and guide microcomb design and applications such as spectral extension and dark pulse generation.

Defect-Rich and Boron-Doped Al2O3-Supported Ru Nanocatalyst for Enhanced CO2 Methanation Activity

Presently, fabricating a stable and high-performance noble metal catalyst is still a challenging task due to the easy aggregation and growth of metal particles during heterogeneous catalysis reactions. In this regard, catalyst supports always can profoundly impact the metal dispersion and electronic interaction with active metal species, thereby significantly regulating the catalytic performance of catalysts. Herein, a new strategy for fabricating boron-doped alumina support with coordinatively unsaturated penta-coordinated Al3+ (Alpenta3+) sites via a micro-liquid-film reactor-assisted coprecipitation approach was developed. Accordingly, as-formed alumina could efficiently immobilize Ru atoms via the anchoring effect of the Alpenta3+ site to construct a supported Ru catalyst for CO2 methanation. An as-constructed Alpenta3+ site-rich and boron-doped Al2O3-supported Ru nanocatalyst exhibited a better catalytic performance in CO2 methanation along with a higher methane yield of 81.2% under reaction conditions (i.e., 350 °C, 0.1 MPa pressure, and gas hourly space velocity of 6000 mL·gcat–1·h–1), compared to other supported Ru ones over commercial alumina and defect-free alumina. It was demonstrated that the high catalytic performance was closely associated with the coexistence of surface-defective Alpenta3+ sites and B–O species, thereby facilitating the accommodation of active hydrogen species on the support during CO2 hydrogenation as well as the activation adsorption of CO2 at the medium-strength basic sites originating from surface B–O–Al structures. This work provides a new strategy to construct high-performance and stable supported noble metal catalysts through engineering alumina support with special defective structures and surface modification for the applications in advanced heterogeneous catalytic systems.

An U.V visible absorption study of the preferential solvation of 4-nitropyridine N-oxide in alcohol-water binary mixture

The influence of solute–solvent and solvent–solvent interaction on the preferential solvation of 4-Nitropyridine N-oxide (PNO) in alcohol-water binary mixture has been studied, from the absorption energy changes of π→π∗ transition with respect to mole-fraction of alcohol. The non-linear profile is fitted to the model developed by Bosch and Rosés. It shows that, the affinity to get solvated by alcohol increases as the length of the alkyl group of alcohol increases. This leads to the preferential solvation of 1-propanol with respect to water. Studies show that this originates from greater stability imparted by 1-propanol due to dispersion and induction interaction.

Benchmarking Aspects of Ab Initio Fragment Models for Accurate Excimer Potential Energy Surfaces.

While Coupled-Cluster methods have been proven to provide an accurate description of excited electronic states, the scaling of the computational costs with the system size limits the degree for which these methods can be applied. In this work different aspects of fragment-based approaches are studied on noncovalently bound molecular complexes with interacting chromophores of the fragments, such as π-stacked nucleobases. The interaction of the fragments is considered at two distinct steps. First, the states localized on the fragments are described in the presence of the other fragment(s); for this we test two approaches. One method is founded on QM/MM principles, only including the electrostatic interaction between the fragments in the electronic structure calculation with Pauli repulsion and dispersion effects added separately. The other model, a Projection-based Embedding (PbE) using the Huzinaga equation, includes both electrostatic and Pauli repulsion and only needs to be augmented by dispersion interactions. In both schemes the extended Effective Fragment Potential (EFP2) method of Gordon et al. was found to provide an adequate correction for the missing terms. In the second step, the interaction of the localized chromophores is modeled for a proper description of the excitonic coupling. Here the inclusion of purely electrostatic contributions appears to be sufficient: it is found that the Coulomb part of the coupling provides accurate splitting of the energies of interacting chromophores that are separated by more than 4 Å.

Anisotropic Phonon Bands in H-Bonded Molecular Crystals: The Instructive Case of α-Quinacridone

Phonons play a crucial role in the thermodynamic and transport properties of solid materials. Nevertheless, rather little is known about phonons in organic semiconductors. Thus, we employ highly reliable quantum mechanical calculations for studying the phonons in the α-polymorph of quinacridone. This material is particularly interesting, as it has highly anisotropic properties with distinctly different bonding types (H-bonding, π-stacking, and dispersion interactions) in different spatial directions. By calculating the overlaps of modes in molecular quinacridone and the α-polymorph, we associate Γ-point phonons with molecular vibrations to get a first impression of the impact of the crystalline environment. The situation becomes considerably more complex when analyzing phonons in the entire 1st Brillouin zone, where, due to the low symmetry of α-quinacridone, a multitude of avoided band crossings occur. At these, the character of the phonon modes typically switches, as can be inferred from mode participation ratios and mode longitudinalities. Notably, avoided crossings are observed not only as a function of the length but also as a function of the direction of the phonon wave vector. Analyzing these avoided crossings reveals how it is possible that the highest frequency acoustic band is always the one with the largest longitudinality, although longitudinal phonons in different crystalline directions are characterized by fundamentally different molecular displacements. The multiple avoided crossings also give rise to a particularly complex angular dependence of the group velocities, but combining the insights from the various studied quantities still allows drawing general conclusions, e.g., on the relative energetics of longitudinal vs transverse deformations (i.e., compressions and expansions vs slips of neighboring molecules). They also reveal how phonon transport in α-quinacridone is impacted by the reinforcing H-bonds and by π-stacking interactions (resulting from a complex superposition of van der Waals, charge penetration, and exchange repulsion).

Influence of Dispersion Interactions on the Polymorphic Stability of Crystalline Oxides.

The accurate determination of relative phase stabilities using DFT methods is a significant challenge when some of these can vary by only a few kJ/mol. Here, we demonstrate that for a selection of oxides (TiO2, MnO2, and ZnO) the inclusion of dispersion interactions, accomplished using the DFT-D3 correction scheme, allows for the correct ordering and an improved calculation of the energy differences between polymorphic phases. The energetic correction provided is of the same order of magnitude as the energy difference between phases. D3-corrected hybrid functionals systematically yield results closest to experiment. We propose that the inclusion of dispersion interactions makes a significant contribution to the relative energetics of polymorphic phases, especially those with different densities, and should therefore be included for calculations of relative energies using DFT methods.

Nonlinear Sideband Cooling to a Cat State of Motion.

The ability to prepare a macroscopic mechanical resonator into a quantum superposition state is an outstanding goal of cavity optomechanics. Here, we propose a technique to generate cat states of motion using the intrinsic nonlinearity of a dispersive optomechanical interaction. By applying a bichromatic drive to an optomechanical cavity, our protocol enhances the inherent second-order processes of the system, inducing the requisite two-phonon dissipation. We show that this nonlinear sideband cooling technique can dissipatively engineer a mechanical resonator into a cat state, which we verify using the full Hamiltonian and an adiabatically reduced model. While the fidelity of the cat state is maximized in the single-photon, strong-coupling regime, we demonstrate that Wigner negativity persists even for weak coupling. Finally, we show that our cat state generation protocol is robust to significant thermal decoherence of the mechanical mode, indicating that such a procedure may be feasible for near-term experimental systems.

Synthesis and mechanism of porous molecular sieves

Porous molecular sieve was a kind of material with different pore structure. Porous molecular sieve had molecular sieve separation ability and rapid mass transfer ability. These materials effectively solved the mass transmission problem of traditional molecular sieve. And allowed substrate molecules to enter the active site located in the micropore, thus improving the reaction rate and lifetime. In addition, the secondary porosity of the porous zeolite created an ideal space for the deposition of the products, controlling their size and allowing high dispersion and strong interactions between the zeolite and the medium. In this paper, the synthesis and mechanism of porous molecular sieve were summarized and summarized, which laid a theoretical foundation for the synthesis of porous molecular sieve.

Robust orientation-3D conductive network enabled high-performance flexible sensor for traffic monitoring: Role of surface functionalization on self-assembled microspheres arrays

Flexible strain sensors prepared by self-sensing nanocomposites using polydimethylsiloxane (PDMS) as the matrix material and carbon nanotubes (CNTs) as the conductive filler have received widespread attention due to their structural flexibility, outstanding weatherability and biocompatibility. Nevertheless, the high sensitivity, stable signal output, and durability are still limited by the uniform dispersion of the CNTs inside. In this paper, a novel preparation method different from direct dispersion was explored, in which CNTs were assembled on the surface of polystyrene (PS) microspheres to assist in CNT dispersion during the self-deployment of microspheres arrays. The free CNTs acted as a bridge to connect the conductive microspheres in the orientation-3D conductive network, which were essential for forming abundant conductive pathways. As numerous conductive fillers were added to the system to enhance conductivity, the self-alignment effect of the microsphere arrays was significantly inhibited, and it failed to assist well in the dispersion. Therefore, the covalent bonding strategy was employed to improve the dispersion and construct strong interfacial interaction, providing impressive electrical conductivity, structural stability, and outstanding durability and thermal stability. The PDMS/PS-C/CNT-N composites prepared with aminated CNT (CNT-N) and carboxylated PS microspheres (PS-C) showed better performance in sensitivity, achieving a gauge factor of over 70, a wide sensing range of 0–124%, and fast response of 330 ms and fast recovery of 190 ms. The developed sensory film was used as an intelligent sensor to monitor traffic flow information. It has been proved that not only the vehicle configuration can be accurately identified, but also the speed can be precisely back-calculated. It opens up new territory to develop high-performance flexible strain sensors for accurate, long-term, and stable acquisition of traffic flow information.

Extra-ductile and strong tin bronze alloy via high-density intragranular ultra-nano precipitation with minimal lattice misfit

Here we report an “intragranular ultra-nano precipitation” strategy to strongly plasticizing and simultaneously strengthen polycrystalline Cu alloys. Our strategy relies on a high density (more than 1023 m−3) and uniform dispersion of extremely fine Fe nanoprecipitates (5.0 ± 2.7 nm) with minimal lattice misfit (theoretically 0.69%) inside Cu grains. The intragranular dispersion of ultra-nano particles not only considerably enhance tensile ductility of a plasticity-poor tin bronze alloy more than 2 times, but also elevate tensile strength above 20% in the meantime, arising from more stable and greater work hardening. The superb plasticizing and hardening of this class of Cu alloy are based on minimal lattice misfit to achieve maximal precipitate dispersion and durable intragranular nanoprecipitation-dislocation interactions (i.e., dislocations cut through fully-coherent Fe nanoprecipitates and hence produce plastic deformation), and we envisage that this intragranular ultra-nano precipitation strategy may be applied to many other metallic alloys.