Contribution Of Dispersion Forces Research Articles

Unravelling dispersion forces in liquid-phase enantioseparation. Part II: Planar chiral 1-(iodoethynyl)-3-arylferrocenes

BackgroundIn the first part of our study on possible contribution of dispersion forces in liquid-phase enantioseparations, the enantioseparation of the axially chiral 3,3′-dibromo-5,5′-bis-ferrocenylethynyl-4,4′-bipyridine with an amylose tris(3,5-dimethylphenylcarbamate)-based chiral column appeared reasonably consistent with a picture of the enantioselective recognition based on the interplay between hydrogen bond (HB), π-π stacking and dispersion interactions. ResultsIn the second part of this study, we evaluated the impact of analyte and chiral stationary phase (CSP) structure, mobile phase and temperature on the enantioseparations of planar chiral 1-(iodoethynyl)-3-arylferrocenes (3-aryl = phenyl, 2-naphthyl, 4-methylphenyl, 4-t-butylphenyl) with polysaccharide-based chiral columns. The main aim of the present study was to understand the molecular bases of the high affinity observed for the second eluted (Rp)-enantiomer of some of these analytes toward amylose phenylcarbamate-based selectors when methanol-containing mixtures were used as mobile phases. Significantly, higher affinity of the second eluted (Rp)-enantiomer toward the selector could be also observed for the sterically hindered 1-(iodoethynyl)-3-(4-t-butylphenyl)ferrocene (k2 = 6.21) compared to the smaller 1-(iodoethynyl)-3-(4-methylphenyl)ferrocenes (k2 = 4.07) as 2.5% methanol was added to the n-hexane-based mobile phase. SignificanceThis study reasonably showed that the contribution of dispersion forces may explain the unusually large retention of the second eluted enantiomers observed for the enantioseparation of some planar chiral 1-(iodoethynyl)-3-arylferrocenes with amylose-based selectors. Based on the obtained results, we can conclude that in liquid-phase enantioseparation steric repulsion can be turned into attraction depending on the features of analyte, selector, and mobile phase.

Unravelling dispersion forces in liquid-phase enantioseparation. Part I: Impact of ferrocenyl versus phenyl groups

BackgroundHighly ordered chiral secondary structures as well as multiple (tunable) recognition sites are the keys to success of polysaccharide carbamate-based chiral selectors in enantioseparation science. Hydrogen bonds (HBs), dipole-dipole, and π-π interactions are classically considered the most frequent noncovalent interactions underlying enantioselective recognition with these chiral selectors. Very recently, halogen, chalcogen and π-hole bonds were also identified as interactions working in polysaccharide carbamate-based selectors to promote enantiomer distinction. On the contrary, the function of dispersion interactions in this field was not explored so far. ResultsThe enantioseparation of chiral ferrocenes featuring chiral axis or chiral plane as stereogenic elements was performed by comparing five polysaccharide carbamate-based chiral columns, with the aim to identify enantioseparation outcomes that could be reasonably determined by dispersion forces, making available a reliable experimental data set for future theoretical studies to confirm the heuristic hypothesis. The effects of mobile phase polarity and temperature on the enantioseparation were considered, and potential recognition sites on analytes and selectors were evaluated by electrostatic potential (V) analysis and molecular dynamics (MD). In this first part, the enantioseparation of 3,3′-dibromo-5,5′-bis-ferrocenylethynyl-4,4′-bipyridine bearing two ferrocenylethynyl units linked to an axially chiral core was performed and compared to that of the analyte featuring the same structural motif with two phenyl groups in place of the ferrocenyl moieties. The results of this study showed the superiority of the ferrocenyl compared to the phenyl group, as a structural element favouring enantiodifferentiation. Significance and noveltyEven if dispersion (London) forces have been envisaged acting in liquid-phase enantioseparations, focused studies to explore possible contributions of dispersion forces with polysaccharide carbamate-based selectors are practically missing. This study allowed us to collect experimental information that support the involvement of dispersion forces as contributors to liquid-phase enantioseparation, paving the way to a new picture in this field.

Influence of the molecular structure of compounds with terminal isothiocyanate group on the induction of the smectic A phase: Part II

ABSTRACT The influence of the structure of compounds having terminal isothiocyanate group in binary mixtures with compounds having terminal alkyl chains on the induction of the smectic A phase is shown. Compounds with a triple bond in the molecular core exhibit a weaker induction of a SmA phase than compounds without it. Molecular lengths, dipole moments and polarisabilities of investigated compounds were calculated. Dielectric spectroscopy studies were done for the chosen system to show that single compounds have the opposite signs of the dielectric anisotropy, while the mixture with maximum temperature of SmA-N phase transition in the nematic phase has a positive dielectric anisotropy. In addition, the dielectric spectroscopy results confirm that the SmA phase is indeed nucleated in the mixture. It has been concluded that there is a competition of different factors, like the shape of molecules, their polarity and polarisability affecting the induction of SmA phase. The shape of a molecule appears to be a crucial factor here since it determines the distance between molecules and influences the contribution of dispersion forces.

A supramolecular self-assembly of peptide-derived compounds via 1,5-disubstituted tetrazole-based supramolecular synthons: An experimental and computational study

The tetrazole moiety is a versatile scaffold in medicinal chemistry due to its specific structure and essential roles in biosciences. Here, a supramolecular behavior of newly synthesized benzyl 2-[5-(benzyloxycarbonylaminomethyl)tetrazol-1-yl)-3-phenyl-propanoate, 1, was studied by single-crystal X-ray crystallography and computational techniques, and compared with 21 structurally diversified 1,5-disubsituted tetrazole-containing peptide-derived structures, retrieved from the Cambridge Structure Database, providing a library of tetrazole-based H-bonding synthons reported for the first time. Hirshfeld surface analysis, followed by the enrichment ratios, demonstrates that the supramolecular assembly of this class of compounds was controlled mainly by O…H, N…H, C…H and π-stacking interactions. Synergy of π…π and X-Y…π (X=C, N; Y=H, F) inter-contacts leads to diverse supramolecular patterns. The 3D topologies of the supramolecular architectures were visualised via energy frameworks, revealing a high contribution of dispersion forces. Using a quantum-chemical treatment, the molecular electrostatic potential and the HOMO and LUMO levels designated the chemical activity and stability of the compound. The compilation of these findings provides valuable information that may eventually form the basis of the design of more effective therapeutic agents containing tetrazole motifs.

Influence of Particle Geometry on Dispersion Forces

Dispersion forces (van der Waals force and Casimir force) originating from quantum fluctuations are crucial in the cohesion of microscale and nanoscale particles. The nonadditivity of these forces and the complex geometry of realistic particles make conventional additive algorithms produce unacceptable errors, and it is experimentally challenging to identify the contribution of dispersion forces from the many forces that constitute the cohesion. In this study, we use the fluctuating surface current technique, an exact scattering theory-based nonadditive algorithm, to accurately quantify the influence of geometry on dispersion forces. To characterize the complex geometries, we employ a data-adaptive spatial filtering method and three-level descriptors. Our results determine the influence of multiscale surface fluctuations on dispersion forces. Additionally, we establish a convenient formula for predicting the dispersion forces between realistic particles with complex shapes from the exact Lifshitz solution via multistage corrections.

The influence of N⋯π pnicogen bonding in π-stacked parallel displaced geometry of nitrobenzene dimers: Evidence using matrix isolation infrared spectroscopy and ab initio computations

The present study elucidates the preferential stabilization of parallel displaced geometry of nitrobenzene dimers by co-operative action of π…π interactions and ON⋯π pnicogen bonding. The homodimers have also been synthesized within Ne and Ar matrixes at cryogenic temperatures followed by their characterization using infrared spectroscopy. The significant contribution of short-range dispersion forces in stabilization of parallel-displaced geometries causes a concomitant rise in Pauli repulsion effects, owing to increased electron correlation. This destabilization is efficiently compensated for, by the added electrostatic effects due to the π-hole facilitated ON⋯π pnicogen bond. The directional determinism of the pnicogen bond proves pivotal in facilitating this co-operation with π…π interactions. These inferences have been obtained by a comparative computational analysis of the parallel displaced and ‘T-shaped’ geometries of the benzene homodimer, with their nitrobenzene analogues.

The interaction mechanism of polystyrene microplastics with pharmaceuticals and personal care products

Microplastics (MPs) have been detected in the hydrosphere, with hazardous implications in transporting coexisting water pollutants. Our knowledge about the interaction mechanisms that MPs establish with organic pollutants are still growing, which is essential to understand the adsorption properties of MPs and their relative stability with adsorbates. Here, we used classical (force field methods) and ab-initio (density functional theory) computational chemistry tools to characterize the interaction mechanisms between Polystyrene-MPs (PS-MPs) and pharmaceuticals/personal care products (PPCPs). Adsorption conformations and energies, thermochemistry, binding, and energy decomposition analyses were performed to obtain the quantitative mechanistic information. Our results show that PS-MPs have permanent dipoles, increasing the interaction with neutral PPCPs while repelling the charged pollutants; in all cases, a stable physisorption takes place. Moreover, PS-MPs increase their solubility upon pollutant adsorption due to an increase in the dipole moment, increasing their co-transport ability in aqueous environments. The stability of the PS-MPs/PPCPs complexes is further confirmed by thermochemical and molecular dynamics trajectory analysis as a function of temperature and pressure. The interaction mechanism of high pKa pollutants (pKa > 5) is due to a balanced contribution of electrostatic and dispersion forces, while the adsorption of low pKa pollutants (pKa < 5) maximizes the electrostatic forces, and steric repulsion effects explain their relative lower adsorption stability. In this regard, several pairwise intermolecular interactions are recognized as a source of stabilization in the PS-MPs/PPCPs binding: hydrogen bonding, π-π, OH⋯π, and CH⋯π, CCl⋯CH and CH⋯CH interactions. The ionic strength in solution slightly affects the adsorption stability of neutral PPCPs, while the sorption of charged pollutants is enhanced. This mechanistic information provides quantitative data for a better understanding of the interactions between organic pollutants and MPs, serving as valuable information for sorption/kinetic studies.

R•-hole interactions of group IV-VII radical-containing molecules: A comparative study

For the first time, the potentiality of the sp2-hybridized group IV-VII radical (R•)-containing molecules to participate in R•-hole interactions was comparatively assessed using •SiF3,•POF2, •SO2F, and •ClO3 models in the trigonal pyramidal geometry. In that spirit, a plethora of quantum mechanical calculations was performed at the MP2/aug-cc-pVTZ level of theory. According to the results, all the investigated R•-containing molecules exhibited potent versatility to engage in R•-hole … Lewis base interactions with significant negative binding energies for the NCH-based complexes. The strength of R•-hole interactions was perceived to obey the •ClO3 … > •SO2F … > •POF2 … > •SiF3 … Lewis base order, outlining an inverse correlation between the binding energy and the atomic size of the R•-hole donor. Benchmarking of the binding energy at the CCSD/CBS(T) computational level was executed for all the explored interactions and addressed an obvious similarity between the MP2 and CCSD energetic findings. QTAIM analysis critically unveiled the closed-shell nature of the explored R•-hole interactions. SAPT-EDA proclaimed the reciprocal contributions of electrostatic and dispersion forces to the total binding energy. These observations demonstrate in better detail the nature of R•-hole interactions, leading to a convincing amelioration for versatile fields relevant to materials science and drug design.

RETRACTED ARTICLE: A novel biosensor for gabapentin drug detection based on the Pd-decorated aluminum nitride nanotube

Density functional theory calculations were performed to inspect the potential application of pristine AlN nanotube (AlNNT) as well as Pd-decorated AlNNT (Pd@AlNNT) in recognition of gabapentin (GB) drug. The sensing response of AlNNT to the GB drug is very small (~ 5.2 at 298 K) attributed to the small adsorption energy (AE) of −0.16 eV. Molecular orbital energy decomposition method (EDA) showed that the contributions of electrostatic attraction, Pauli repulsion, orbital relations, and dispersion forces in the AE are about −0.21, 0.19, −0.11, and −0.09 eV, respectively. A Pd atom preferentially adsorbed over an Al–N bond of the AlNNT, releasing the energy of 2.93 eV. We found that the GB strongly adsorbed on the Pd@AlNNT with AE of −1.29 eV and the sensing response increased to 524.6 by the Pd decoration. Based on the results, the main stabilization contribution to the AE of GB on the Pd@AlNNT comes from the electrostatic attraction based on the EDA analysis. The recovery time was achieved to be 1.8 s for the GB desorption from the Pd@AlNNT surface. Finally, we concluded that the Pd@AlNNT can transform the presence of GB molecules into electrical signal, and it may potentially be applied as an electronic sensor for GB drug detection.

DFT study of the hydrogen adsorption and storage on Ni4 cluster embedded in multivacancy graphene

Hydrogen adsorption stability, geometry, electronic structure and mechanism has been investigated on Ni4 cluster embedded in graphene with three, four and six vacancies by density functional theory (DFT) calculations. An energetic analysis of hydrogen adsorption by addition of one to four H2 molecules was performed for each system in order to determine their hydrogen storage capacity. Dispersion force contribution to the adsorption energy is quantitative evaluated to know whether H2 molecules adsorption behavior is dominated by chemical or van der Waals interactions. A further analysis of this type of interactions is also addressed by total and partial density of states. Bonding and charge transfer characteristics for the different steps involved in the adsorption mechanism are also included. Special attention is given to the effects caused by this new Ni/graphene interface to the hydrogen adsorption behavior.

To Distinguish Electrostatic, Coordination Bond, Nonclassical Polarization, and Dispersion Forces on Cation–Clay Interactions

Recent research has suggested that inorganic ions give rise to complex interfacial adsorption effects, but people do not fully understand the mechanisms at present. In this study, the interface adsorption energies of H+ (without extranuclear electron), Li+, and Cs+ (with extranuclear electrons but possessing a large difference in ionic radius) on montmorillonite surface were estimated to elucidate the contribution of electrostatic, coordination bond, nonclassical polarization, and dispersion forces to interface adsorption energies. The results showed that under given cationic concentrations, the equilibrium adsorption energies followed the sequence of Cs+ > H+ > Li+. Moreover, the adsorption energies of H+ (with minimum ion radius) were close to Cs+ (with largest ion radius) but much larger than that of Li+ under relative low cationic concentrations, whereas the adsorption energies of Cs+, H+, and Li+ approached each other under the highest cationic concentration of 0.1 mol L–1, although their ionic sizes...

On the Contribution of Dispersion Forces to the Linear and Point Energies of Graphene

For two-dimensional structures, the linear and point energies are physical parameters of the same significance as the surface and linear energies, respectively, for three-dimensional bodies. The theory presented in this communication enables one to calculate the contribution of dispersion forces to the local cohesion energy, local linear energy, and point energy of graphene from its microscopic parameters, namely, the lattice spacing, two-dimensional atomic density, and pair interaction potential. The local values are calculated on the basis of the Irving–Kirkwood pressure tensor inside of a plane-parallel empty two-dimensional slit with a finite size extension between two rectangular pieces of graphene lying in the same plane. The calculation is performed for the absolute zero of temperature (when the energy is equivalent to the free energy). The structure of graphene is assumed to be rigid, which entails ignorance of the effect of relaxation upon the separation of the two graphene pieces. The calculation result depends on the direction of graphene boundary line. The line normal to the σ-bonds has been selected for the calculations, with this line corresponding to the natural boundary of graphene. The linear and point energies of graphene are calculated within the model of rigid spheres with dispersion forces and the Lennard—Jones model. It has been found that, near a corner of a rectangular graphene piece, the linear energy becomes a value variable within five distances between atoms in the lattice, thereby making it possible to evaluate the contribution of the dispersion forces to the point energy of graphene.

Effect of the Molecular Weight of Polyarylene Ether Ketones on the Tribological Properties

The effect of the molecular weights of amorphous polyarylene ether ketone (PAEK) synthesized by the reaction of 4,4'-difluorobenzophenone with 2,2-bis (4'-hydroxyphenyl) propane (bisphenol A) potassium diphenolate on its tribological characteristics has been studied. In the case of the friction of a sample with M w < 200 × 103 Da, its high wear resistance and the coefficient of friction decreased to 0.4, even at high pressures of up to 10 MPa. These properties of high-molecular-weight PAEK are due to the high contribution of the weak dispersion forces into the intermolecular interaction energy of the polymer. Low wear determines the nature of tribodestruction, which, during the process of self-organization, leads to the appearance of a positive gradient in the physicomechanical properties in the surface layers. The XPS study shows that, during PAEK pressing at 260°C, the intensive oxidation of a thin surface layer occurs.

Computational molecular perspectives on the interaction of propranolol with β-cyclodextrin in solution: Towards the drug-receptor mechanism of interaction

Abstract Elucidating the mechanism of interaction between a drug molecule and its corresponding receptors is of great importance. It had been demonstrated that Propranolol as a β-blocker interacts with β-adrenoreceptors through three different binding sites, including the aromatic group (naphthalene) and the secondary amine and hydroxyl groups of the side chain. In this work we exploited selected computational methods for mimicking such kind of interaction via examining computationally the supramolecular interaction of β-cyclodextrin with Propranolol in Solution. We examined and compared the performances of selected computational approaches, namely SQM(PM3 and PM7), DFT(631G), and ONIOM(DFT,SQM(PM3)) for studying such supramolecular interaction, emphasizing the importance of the contribution of dispersion forces and hydrogen bonding in the mechanism of interaction. The stability of the optimized geometries was evaluated using Atom Centered Density Matrix propagation-Dynamic Simulation (ADMP-DS) method. The appropriateness of the examined methods was validated based on comparison with reported experimental results gathered from the literature. In terms of accuracy, the computational methods employed in this work exhibited notable similarities regarding all molecular and geometrical properties, however, great discrepancy was noted regarding the binding thermodynamic quantities, namely ΔG°, ΔH° and TΔS, as well as the driving forces responsible for the formation and stabilization of the PPL-β-CD inclusion complexes. Interestingly, employing the MOPAC-SQM-PM7 method yielded good agreement with the experimental values of ΔG°, ΔH° and TΔS, with absolute deviations of 1.4, 3.3, and 1.5 kcal.mol-1, respectively, for the β-CD wide-rim inclusion of PPL with substantial reduced computational cost. Utilizing the ADMP-MD method confirmed the stability of the optimized geometries of the inclusion complexes within a time frame of 100 fs with average variations in the total energy and length of selected hydrogen bonds of

Contact Forces between TiO2 Nanoparticles Governed by an Interplay of Adsorbed Water Layers and Roughness

Interparticle forces govern the mechanical behavior of granular matter and direct the hierarchical assembling of nanoparticles into supramolecular structures. Understanding how these forces change under different ambient conditions would directly benefit industrial-scale nanoparticle processing units such as filtering and fluidization. Here we rationalize and quantify the contributions of dispersion, capillary, and solvation forces between hydrophilic TiO2 nanoparticles with sub-10 nm diameter and show that the humidity dependence of the interparticle forces is governed by a delicate interplay between the structure of adsorbed water layers and the surface roughness. All-atom molecular dynamics modeling supported by force-spectroscopy experiments reveals an unexpected decrease in the contact forces at increasing humidity for nearly spherical particles, while the forces between rough particles are insensitive to strong humidity changes. Our results also frame the limits of applicability of discrete solvation and continuum capillary theories in a regime where interparticle forces are dominated by the molecular nature of surface adsorbates.

Adsorption enthalpies of alkyl halides in a FAU acidic zeolite investigated by the ONIOM2 method

The adsorption of a series of alkyl halides, RX ( X = Cl , Br , I ) over acidic zeolite has been investigated by the ONIOM2 method. A 56T model cluster constructed from 55 Si atoms and one tetrahedral Al atom with one Brönsted acid site, has been used to represent the zeolite catalyst. Density functional theory (DFT) and specifically, the two layered schemes B3LYP/6-31+G(d,p)genECP:UFF and M06-2X/6-31+G(d,p)genECP:UFF have been employed, augmented with the addition of extra polarization functions for the proper treatment of the halogen atoms. Examination of selective structural changes and the computed adsorption enthalpies, ΔH ad , of the van der Waals 1:1 adsorption complexes assumingly formed, shows a strong dependence both on the theoretical method and the alkyl radical structure. A modest influence of the halogen atom involved is also observed. The comparison of the performance of the two functionals underlines the higher capacity of the M06-2X functional to provide a more satisfactory description of the adsorption process and the contribution of the van der Waals dispersion forces.

The effect of N-methylation of amino acids (Ac-X-OMe) on solubility and conformation: a DFT study.

N-Methylation has a significant impact on improving the oral bioavailability, lipophilicity and aqueous solubility of peptide-based lead drug structures. The selected mono-amino acid derivatives Ac-X-OMe, where X = Gly, Val, Leu, Ile, Phe, Met, Cys, Ser, Asp and His as well as their corresponding N-methylated analogues were studied. The clog P values of all N-methylated peptides are greater than those of native compounds. Quantum chemical calculations were performed to estimate the aqueous solubility of these lipophilic compounds using density functional theory (DFT). To confirm the contribution of dispersion forces on quantum chemical data, the long-range corrected (LC) hybrid density functional (ωB97X-D) was also probed for some amino acid derivatives. The ωB97X functional gave similar results. Our results reveal that after mono N-methylation of the peptide backbone, ΔGsolv becomes more negative (more water soluble) while polarizability and dipole moment are also increased. Natural atomic charges derived by natural bond orbital (NBO) analysis of N, C, and O atoms involved in amide functional group become more positive/(less negative) after N-methylation. All N-methylated amino acids have higher EHOMO (less negative) in comparison with the amino acid analogues, and in all cases N-methylation decreases EHOMO-LUMO. The calculated amide cis/trans activation energies (EA) of all the N-methylated amino acid derivatives were lower than that of native species. N-methylation of these compounds leads to an increase in lipophilicity, aqueous solubility, polarization, dipole moment and lowering of the cis/trans amide energy barrier (EA).

Contributions of dispersion forces to R-3-methylcyclohexanone physisorption on low and high Miller index Cu surfaces

The physisorption of R-3-methylcyclohexanone on low and high Miller index Cu surfaces is studied with temperature programmed desorption (TPD) and density functional theory (DFT). The DFT calculations are performed with D2, vdW-optB86b, and vdW-optB88 dispersion corrected methods. The adsorption energies calculated by the dispersion corrected methods are more comparable to the TPD results than those calculated without dispersion corrections, although, the former methods have a tendency to overbind the surface adsorbates. The implementation of dispersion corrected methods also indicates a possible adsorbate induced surface reconstruction on Cu(110).

The role of the Lewis acid−base properties in the supramolecular association of 1,2,5-chalcogenadiazoles

The secondary bonding interactions that link the supramolecular structures assembled by 1,2,5-chalcogenadiazoles were analyzed through explicit orthogonalization of molecular orbitals (NBO), topological analysis of the electron density (AIM), and the electron localization function (ELF). The results of these analyses are consistent with a bonding description that attributes important covalent and electrostatic character to these interactions. Application of these analyses to the individual molecules highlighted the structural features from which each of those contributions originates, namely the polarity and modest strength of the E–N bond. Both of these effects increase along the series S, Se, Te. Perturbations to the heterocycle electronic structure that result in a weaker and more polar E–N bond cause an increase in the Lewis acidity at the chalcogen centre, which in turn leads to stronger secondary bonding interactions with Lewis bases. Additionally, the contribution of dispersion forces is not negligible and is most important in the case of sulfur.

On the Adsorption of Formaldehyde and Methanol on a Water-Covered Pt(111): a DFT-D Study

The interaction of a single formaldehyde or methanol molecule with a bare and a water-covered Pt(111) surface has been investigated using density-functional calculations, including the contribution of dispersion forces. van der Waals (vdW) terms are found to be essential to obtain the adsorption energies of both isolated molecules to the Pt(111) surface and the water wetting layer in agreement with experimental data. Moreover, the vdW correction changes completely the view on the mixed molecule–water–surface adsorption profile. In turn, the change induced by the vdW-forces on the geometric properties is very small for the minima found. For the water-covered surface, pure density-functional calculations underestimate the binding energy of a wetting-layer on Pt(111) by about 140 meV/H2O molecule. The dispersion corrected calculations reveal a binding energy of 0.61 eV/H2O molecule of a water bilayer at the platinum (111) surface, which is in perfect agreement with the experimental lattice energy of bulk ice...