Repulsive Intermolecular Interactions Research Articles

Charge induced frustration in C60 monolayers on h-BN/Ni(111)

Frustration in a system occurs when all interacting components cannot reach their minimum energy simultaneously. We report on the development of a frustrated adsorption configuration of a C60 monolayer on epitaxial hexagonal boron nitride (h-BN) grown on Ni(111). In the low-temperature adsorption configuration, we discover non-periodic patterns with striped and zigzag elements, which are characteristic of frustrated systems, formed by molceules with different orientational alignement. Using scanning probe techniques, we investigate these complex patterns' structural and electronic properties. We find two distinct C60 species, one of which is neutral, and the other is charged due to a locally preferred energy level alignment that favors an electron transfer from the Ni(111). Discharging single or multiple intrinsically charged C60 molecules creates local changes in the electrostatic potential, shifting the energy of surrounding molecular orbitals. This allows us to measure the inter-fullerene Coulomb interactions, which plays a crucial role in the formation of the frustrated structure. Monte Carlo simulations derived from the antiferromagnetic Ising model replicate the experimentally observed frustration pattern by considering competing attractive and repulsive intermolecular interactions. As such, the C60 h-BN/Ni(111) system opens a window for essential insights into charge-induced frustration and intermolecular interactions.

A dissipative particle dynamics simulation of controlled loading and responsive release of theranostic agents from reversible crosslinked triblock copolymer vesicles.

To control the transport stability and release efficiency of loaded theranostic drugs in triblock copolymer carriers, the reversible crosslinking ability is of great significance. A molecular level exploration of such a function is needed to extend existing stabilizing and responsive dissociation mechanisms of carriers. Here, dissipative particle dynamics simulations were used to first demonstrate the formation of triblock copolymer vesicular carriers. Chemical crosslinking was used to strengthen the structural stability of the vesicle shell to avoid drug leakage. Reversible decrosslinking along with dissociation of the vesicle and release of loaded drugs were then explored. The structural, energetic and dynamical properties of the system were discussed at the molecular level. The regulation mechanism of drug release patterns was revealed by systematically exploring the effect of intra and intermolecular repulsive interactions. The results indicate that the chemical crosslinking of copolymers enhanced the compactness of the vesicle shell with a strengthened microstructure, increased binding energy, and limited chain migration, thus achieving more stable delivery of drugs. In terms of drug release, we clarified how the pairwise interactions of beads in the solution system affect the responsive dissociation of the vesicle and associated release patterns (speed and amount) of drugs. More efficient delivery and smart release of theranostic drugs are achieved using such reversible crosslinked triblock copolymer vesicles.

A comprehensive study on the inhibition behaviour of four carboxylate-based corrosion inhibitors focusing on efficiency drop after the optimum concentration for carbon steel in the simulated concrete pore solution

In this research, the inhibition action of four carboxylate derivatives with different numbers of functional carboxylate groups on carbon steel in 0.5 M NaCl simulating concrete pore solution was investigated using electrochemical measurements in conjunction with the XPS technique. Quantum chemical calculations were also applied to discuss the EIS data and the inhibitor's adsorption behaviour. This paper focuses on the inhibitive action of carboxylate derivates after optimal concentration. The results show that after a critical concentration, the corrosion inhibition efficiency drops to lower values, which the reasons for this matter are still uncertain. We suggest that the adsorption process is directly affected by the number of attractive and repulsive intermolecular interactions. At higher concentrations, electrostatic forces cause the local molecular clusters on the surface, which results in an imperfect layer of molecules that is vulnerable to aggressive agents such as chloride ions. Although with increasing the number of carboxylate groups, the corrosion inhibition efficiency decreases by 35%. However, quantitative XPS results reveal no noticeable reduction in the oxide layer thickness, which indicates that localized attacks lead the corrosion.

Structural Distortion and Bandgap Increase of Two-Dimensional Perovskites Induced by Trifluoromethyl Substitution on Spacer Cations.

In further advancing display technologies, especially for improved blue emitters, to engineer the bandgap of promising semiconductors such as hybrid perovskites is important. Present-day methods for tuning the bandgaps of perovskites, such as the incorporation of mixed halide anions, suffer drawbacks such as phase separation and difficulty in synthesis. Here we report a new 2D lead iodide perovskite that emits in the blue spectral region. We exploit an increased angular distortion of PbI42- octahedra to widen the bandgap of 2D metal halide perovskites. We synthesized 2D lead iodide perovskites based on (4-Y-C6H4CH2NH3)2PbI4 (Y = H, F, Cl, Br, I) and substituted the halogen atoms with a -CF3 group to create (4-CF3-C6H4CH2NH3)2PbI4 compounds. We observed that the CF3-substituted material exhibited a ∼0.16 eV larger bandgap than did the halogen-substituted materials. We used X-ray diffraction and density functional theory simulations and found that the blue shift can be assigned to the angular distortion of the PbI42- lattice, a distortion traceable to repulsive intermolecular interactions between the trifluoromethyl groups on oppositely-arranged spacers. These results add a degree of freedom in tuning 2D perovskites to selected bandgaps for optoelectronic applications.

Synthesis, structural and computational studies of new tetrazole derivatives

Herein, we report a synthesis of two new disubstituted tetrazoles, 2-(2,4-dinitrophenyl)-5-methyl-2H-tetrazole (2) and 1-(2,4-dinitrophenyl)-5-methyl-1H-tetrazole (3). The products were characterized by 1H and 13C NMR spectroscopy, as well as single-crystal X-ray diffraction. The intermolecular interactions in the crystals were investigated by Hirshfeld surface analysis, 2D fingerprint plots, and noncovalent interaction analysis (NCI). Tetrazole rings of both compounds were found to be involved in both strongest attractive and repulsive intermolecular interactions. DFT calculations were performed using the PW6B95-D3(BJ)/def2-TZVP level of theory in order to obtain information about the molecular electrostatic potential (MEP), and global and local reactivity (dual descriptor) indices of the studied tetrazoles. The calculated molecular electrostatic potentials correlated well with the Hirshfeld surface and NCI plots. The 1,5-disubstituted tetrazole exhibited lower kinetic stability and was slightly more electrophilic than the 2,5-regioisomer. The dual descriptor index was used to reveal electrophilic and nucleophilic sites for both molecules.

Thermodynamic geometry for binary mixtures: A constrained approach

Thermodynamic geometry for binary mixtures is explored in a constrained version. In order to have an insight into the interpretation of the scalar curvature (R) for mixtures, we develop and discuss the thermodynamic geometry for binary mixtures of hard spheres and van der Waals fluids with a restriction in the total particle number. For the case of hard spheres we have an interaction which is exclusively repulsive and van der Waals fluids account for repulsive and attractive interactions, which is a more realistic model. From our analysis, it is seen that the physical interpretation of R given for monocomponent systems, is no longer satisfied for the case of mixture of ideal gases and hard spheres. For the constrained version of the mixture of van der Waals fluids, we have that the scalar curvature nicely reproduces the behavior observed for the monocomponent fluid, including the interpretation of R as an indicator of repulsive or attractive intermolecular interactions and phase transitions.

Artificial Intracellular Filaments

Intracellular protein filaments are ubiquitous for cellular functions, but forming bona fide biomimetic intracellular filaments of small molecules in living cells remains elusive. Here, we report the in situ formation of self-limiting intracellular filaments of a small peptide via enzymatic morphological transition of a phosphorylated and trimethylated heterochiral tetrapeptide. Enzymatic dephosphorylation reduces repulsive intermolecular electrostatic interactions and converts the peptidic nanoparticles into filaments, which exhibit distinct types of cross-β structures with either C7 or C2 symmetries, with the hydrophilic C-terminal residues at the periphery of the helix. Macromolecular crowding promotes the peptide filaments to form bundles, which extend from the plasma membrane to nuclear membrane and hardly interact with endogenous components, including cytoskeletons. Stereochemistry and post-translational modification (PTM) of peptides are critical for generating the intracellular bundles. This work may offer a way to gain lost functions or to provide molecular insights for understanding normal and aberrant intracellular filaments.

Short-Distance Intermolecular Correlations of Mono- and Disaccharides in Condensed Solutions: Bulky Character of Trehalose.

Organisms with tolerance to extreme environmental conditions (cryptobiosis) such as desiccation and freezing are known to accumulate stress proteins and/or sugars. Trehalose, a disaccharide, has received considerable attention in the context of cryptobiosis. It has already been shown to have the highest glass-transition temperature and different hydration properties from other mono- and disaccharides. In spite of the importance of understanding cryptobiosis by experimentally clarifying sugar–sugar interactions such as the clustering in concentrated sugar solutions, there is little direct experimental evidence of sugar solution structures formed by intermolecular interactions and/or correlation. Using a wide-angle X-ray scattering method with the real-space resolution from ∼3 to 120 Å, we clarified the characteristics of the structures of sugar solutions (glucose, fructose, mannose, sucrose, and trehalose), over a wide concentration range of 0.05–0.65 g/mL. At low concentrations, the second virial coefficients obtained indicated the repulsive intermolecular interactions for all sugars and also the differences among them depending on the type of sugar. In spite of the presence of such repulsive force, a short-range intermolecular correlation was found to appear at high concentrations for every sugar. The concentration dependence of the observed scattering data and p(r) functions clearly showed that trehalose prefers a more disordered arrangement in solution compared to other sugars, that is, bulky arrangement. The present findings will afford a new insight into the molecular mechanism of the protective functions of the sugars relevant to cryptobiosis, particularly that of trehalose.

A TPD and RAIRS comparison of the low temperature surface behavior of benzene, toluene, and xylene on graphite.

The first comparative study of the surface behavior of four small aromatic molecules, benzene, toluene, p-xylene, and o-xylene, adsorbed on graphite at temperatures ≤30 K, is presented. Intermolecular interactions are shown to be important in determining the growth of the molecules on the graphite surface at low (monolayer) exposures. Repulsive intermolecular interactions dominate the behavior of benzene and toluene. By contrast, stronger interactions with the graphite surface are observed for the xylene isomers, with islanding observed for o-xylene. Multilayer desorption temperatures and energies increase with the size of the molecule, ranging from 45.5 to 59.5 kJ mol-1 for benzene and p-xylene, respectively. Reflection absorption infrared spectroscopy gives insight into the effects of thermal processing on the ordering of the molecules. Multilayer benzene, p-xylene, and o-xylene form crystalline structures following annealing of the ice. However, we do not observe an ordered structure for toluene in this study. The ordering of p-xylene shows a complex relationship dependent on both the annealing temperature and exposure.

Macromolecular crowding effects in flexible polymer solutions

Biological environments are often “crowded” due to high concentrations (300–400[Formula: see text]g/L) of macromolecules. Computational modeling approaches like Molecular Dynamics (MD), rigid-body Brownian Dynamics and Monte Carlo simulations have recently emerged, which allow to study the effects macromolecular crowding at a microscopic level and to provide complementary information to experiments. Here, we use a recently introduced multiple-conformation Monte Carlo (mcMC) approach in order to study the influence of intermolecular interactions on the structural equilibrium of flexible polyethylene glycol (PEG) polymers under self-crowding conditions. The large conformational space accessible to PEG polymers allows us to evaluate the general applicability of the mcMC approach, which describes the intramolecular degrees of freedom by a finite-size ensemble of discrete conformations. Despite the simplicity of the approach, we show that influences of intermolecular interactions on the intramolecular free energy surface can be described qualitatively using mcMC. By varying the magnitude of distinct terms in the intermolecular potential, we can further study the compensating effects of repulsive and nonspecific attractive intermolecular interactions, which favor compact and extended polymer states, respectively. We use our simulation results to derive an analytical model that describes the effects of intermolecular interactions on the stability of PEG polymer conformations as a function of the radius of gyration and the corresponding solvent accessible surface. We use this model to confirm the role of molecular surfaces for attractive interactions that can counteract excluded volume effects. Extrapolation of the model further allows for the analysis of scenarios that are not easily accessible to direct simulations as described here.

NH3 adsorption on anatase-TiO2(101).

The adsorption of ammonia on anatase TiO2 is of fundamental importance for several catalytic applications of TiO2 and for probing acid-base interactions. Utilizing high-resolution scanning tunneling microscopy (STM), synchrotron X-ray photoelectron spectroscopy, temperature-programmed desorption (TPD), and density functional theory (DFT), we identify the adsorption mode and quantify the adsorption strength on the anatase TiO2(101) surface. It was found that ammonia adsorbs non-dissociatively as NH3 on regular five-fold coordinated titanium surface sites (5f-Ti) with an estimated exothermic adsorption energy of 1.2 eV for an isolated ammonia molecule. For higher adsorbate coverages, the adsorption energy progressively shifts to smaller values, due to repulsive intermolecular interactions. The repulsive adsorbate-adsorbate interactions are quantified using DFT and autocorrelation analysis of STM images, which both showed a repulsive energy of ∼50 meV for nearest neighbor sites and a lowering in binding energy for an ammonia molecule in a full monolayer of 0.28 eV, which is in agreement with TPD spectra.

Quaterrylene molecules on Ag(111): self-assembly behavior and voltage pulse induced trimer formation.

The self-assembly behavior of quaterrylene (QR) molecules on Ag(111) surfaces has been investigated by scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. It is found that the QR molecules are highly mobile on the Ag(111) surface at 78 K. No ordered assembled structure is formed on the surface with a sub-monolayer coverage up to 0.8 monolayer due to the intermolecular repulsive interactions, whereas ordered molecular structures are observed at one monolayer coverage. According to our DFT calculations, charge transfer occurs between the substrate and the adsorbed QR molecule. As a result, out-of-plane dipoles appear at the interface, which are ascribed to the repulsive dipole-dipole interactions between the QR molecules. Furthermore, due to the planar geometry, the QR molecules exhibit relatively low diffusion barriers on Ag(111). By applying a voltage pulse between the tunneling gap, immobilization and aggregation of QR molecules take place, resulting in the formation of a triangle-shaped trimer. Our work demonstrates the ability of manipulating intermolecular repulsive and attractive interactions at the single molecular level.

Hydrogen bond and surface stress relaxation by aldehydic and formic acidic molecular solvation

Solvation of aldehydes and formic acids has an important impact to health care because these additives can damage DNA and denature proteins causing cancers with the mechanism behind remaining great challenge. From the perspective of solvent hydrogen bond (O:HO or HB with “:” being the electron lone pair of oxygen) transition from the mode of the ordinary water to the hydrating states, we examined the solvation bonding dynamics and the solute capabilities of O:HO bond and surface stress transition using differential Raman spectroscopy and contact angle detection. Results suggest that besides the short-range O:H van der Waals (vdW) bond, the H↔H and O:⇔:O repulsive intermolecular interactions, and the molecular dipolar polarization play important roles in disrupting the solution network and surface stress. Observations may infer the manner of DNA fragmentation by aldehyde and formic acid disruption.

Behavior of the Enthalpy of Adsorption in Nanoporous Materials Close to Saturation Conditions.

Many important industrial separation processes based on adsorption operate close to saturation. In this regime, the underlying adsorption processes are mostly driven by entropic forces. At equilibrium, the entropy of adsorption is closely related to the enthalpy of adsorption. Thus, studying the behavior of the enthalpy of adsorption as a function of loading is fundamental to understanding separation processes. Unfortunately, close to saturation, the enthalpy of adsorption is hard to measure experimentally and hard to compute in simulations. In simulations, the enthalpy of adsorption is usually obtained from energy/particle fluctuations in the grand-canonical ensemble, but this methodology is hampered by vanishing insertions/deletions at high loading. To investigate the fundamental behavior of the enthalpy and entropy of adsorption at high loading, we develop a simplistic model of adsorption in a channel and show that at saturation the enthalpy of adsorption diverges to large positive values due to repulsive intermolecular interactions. However, there are many systems that can avoid repulsive intermolecular interactions and hence do not show this drastic increase in enthalpy of adsorption close to saturation. We find that the conventional grand-canonical Monte Carlo method is incapable of determining the enthalpy of adsorption from energy/particle fluctuations at high loading. Here, we show that by using the continuous fractional component Monte Carlo, the enthalpy of adsorption close to saturation conditions can be reliably obtained from the energy/particle fluctuations in the grand-canonical ensemble. The best method to study properties at saturation is the NVT energy (local-) slope methodology.

Direct observation of the conformational transitions of single pyridine molecules on a Ag(110) surface induced by long-range repulsive intermolecular interactions

The transition between two conformations of pyridine molecules adsorbed on a Ag(110) surface at 13 K was investigated by performing single-molecule manipulation at a very low coverage and the track-imaging of pyridines for various surface coverages using a variable low-temperature scanning tunneling microscope. A single tilted conformer was converted to an upright conformer when another coadsorbed tilted pyridine molecule approached to within ∼2 nm. The conversion probability depends on the molecular separation. The tilted conformers that are prevalent at a very low coverage were converted to upright conformers with an increasing surface coverage. The minimum molecular separation before this transition is induced was determined to be 2.2 nm using molecular track-imaging and statistical analysis of the pyridine separation as a function of the molecular coverage. The conformation transition was attributed to substrate-mediated long-range repulsive interactions between the pyridine molecules, which are produced by charge redistribution that occurs upon pyridine adsorption on the silver surface.

A Multitechnique Study of CO Adsorption on the TiO2 Anatase (101) Surface

The adsorption of carbon monoxide on the anatase TiO2 (101) surface was studied with infrared reflection absorption spectroscopy (IRRAS), temperature-programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS), scanning tunneling microscopy (STM), and density functional theory (DFT). The IRRAS data reveal only one CO band at ∼2181 cm–1 for both stoichiometric and reduced TiO2 (101) surfaces. From TPD, an adsorption energy of 0.37 ± 0.03 eV is estimated for the isolated molecule, which shifts to slightly smaller values at higher coverages. Combining STM imaging and controlled annealing of the sample confirms the adsorption energies estimated from TPD and the slight repulsive intermolecular interaction. CO molecules desorb from electron-rich, extrinsic donor defect sites at somewhat higher temperatures. Confronting the experimental results with DFT calculations indicates that the anatase (101) surface does not contain any significant concentration of subsurface oxygen vacancies in the near-surface r...

Charged supramolecular assemblies of surfactant molecules in gas phase

The aim of this review is to critically analyze recent literature on charged supramolecular assemblies formed by surfactant molecules in gas phase. Apart our specific interest on this research area, the stimuli to undertake the task arise from the widespread theoretical and applicative benefits emerging from a comprehensive view of this topic. In fact, the study of the formation, stability, and physicochemical peculiarities of non-covalent assemblies of surfactant molecules in gas phase allows to unveil interesting aspects such as the role of attractive, repulsive, and steric intermolecular interactions as driving force of supramolecular organization in absence of interactions with surrounding medium and the size and charge state dependence of aggregate structural and dynamical properties. Other interesting aspects worth to be investigated are joined to the ability of these assemblies to incorporate selected solubilizates molecules as well as to give rise to chemical reactions within a single organized structure. In particular, the incorporation of large molecules such as proteins has been of recent interest with the objective to protect their structure and functionality during the transition from solution to gas phase. Exciting fall-out of the study of gas phase surfactant aggregates includes mass and energy transport in the atmosphere, origin of life and simulation of supramolecular aggregation in the interstellar space. Moreover, supramolecular assemblies of amphiphilic molecules in gas phase could find remarkable applications as atmospheric cleaning agents, nanosolvents and nanoreactors for specialized chemical processes in confined space. Mass spectrometry techniques have proven to be particularly suitable to generate these assemblies and to furnish useful information on their size, size polydispersity, stability, and structural organization. On the other hand molecular dynamics simulations have been very useful to rationalize many experimental findings and to furnish a vivid picture of the structural and dynamic features of these aggregates. Thus, in this review, we will focus on the most important achievements gained in recent years by both these investigative tools.

Intermolecular Interactions in Mixed Self‐Assembled Monolayers of Ferrocene

AbstractElectrochemical characterization of mixed self‐assembled monolayers (SAMs) of 6‐ferrocenyl‐1‐hexanethiol (FcH) and mercaptoundecanoic acid tyrosinamide (MUATyr) on gold is reported. Single‐component SAMs of FcH presented repulsive intermolecular interactions (vGθT=−1.12), while mixed SAMs of FcH/MUATyr (1 : 1) exhibited attractive interactions (vGθT=+0.20), with a homogeneous distribution of both components. Electrochemical kinetic determinations on mixed SAMs of FcH/MUATyr, indicated a secondary electron transfer pathway between the redox centers of both components. Higher amounts of FcH in the mixed SAMs lowered the observed rate of electron transfer of MUATyr. The oxidation of FcH caused an anodic shift of 160 mV in the voltammetric wave of MUATyr.

Analysis of antibody aggregate content at extremely high concentrations using sedimentation velocity with a novel interference optics.

Monoclonal antibodies represent the most important group of protein-based biopharmaceuticals. During formulation, manufacturing, or storage, antibodies may suffer post-translational modifications altering their physical and chemical properties. Such induced conformational changes may lead to the formation of aggregates, which can not only reduce their efficiency but also be immunogenic. Therefore, it is essential to monitor the amount of size variants to ensure consistency and quality of pharmaceutical antibodies. In many cases, antibodies are formulated at very high concentrations > 50 g/L, mostly along with high amounts of sugar-based excipients. As a consequence, all routine aggregation analysis methods, such as size-exclusion chromatography, cannot monitor the size distribution at those original conditions, but only after dilution and usually under completely different solvent conditions. In contrast, sedimentation velocity (SV) allows to analyze samples directly in the product formulation, both with limited sample-matrix interactions and minimal dilution. One prerequisite for the analysis of highly concentrated samples is the detection of steep concentration gradients with sufficient resolution: Commercially available ultracentrifuges are not able to resolve such steep interference profiles. With the development of our Advanced Interference Detection Array (AIDA), it has become possible to register interferograms of solutions as highly concentrated as 150 g/L. The other major difficulty encountered at high protein concentrations is the pronounced non-ideal sedimentation behavior resulting from repulsive intermolecular interactions, for which a comprehensive theoretical modelling has not yet been achieved. Here, we report the first SV analysis of highly concentrated antibodies up to 147 g/L employing the unique AIDA ultracentrifuge. By developing a consistent experimental design and data fit approach, we were able to provide a reliable estimation of the minimum content of soluble aggregates in the original formulations of two antibodies. Limitations of the procedure are discussed.

Amorphous supramolecular structure of carboxymethyl cellulose in aqueous solution at different pH values as determined by rheology, small angle X-ray and light scattering

Carboxymethyl cellulose (CMC) is one of the most widely used thickening agents in industry. The combination of small-angle X-ray scattering (SAXS), static and dynamic light scattering, as well as viscosity measurements and microscopy at different pH values was utilized to explore the physicochemical properties of CMC on a scale ranging from individual macromolecules to supramolecular assemblies. The supramolecular structure of CMC was represented as a set of characteristic sample subspaces based on SAXS data utilizing the string-of-beads model. The results indicate that at pH 7.0 individual CMC molecules are approximately uniformly distributed in a supramolecular structure owing to strong intra- and intermolecular repulsive interactions. The structure of CMC is most expanded at the value of pKa, where it has the largest radius of gyration, persistence length, and size of heterogeneous regions. Below pKa the majority of the CMC sample volume belongs to the low density subspaces. Most of CMC molecules, however, reside in a few high density subspaces. Dynamically, supramolecular structure of CMC is composed of fast diffusive relaxation processes embedded in a background of non-diffusive slow relaxation process at high pH and mostly slow relaxation processes at low pH. The rheological properties of CMC at different pH values were directly related to the CMC supramolecular structure in the aqueous environment.