Electrostatic Solvent Effects Research Articles

The Structure of Carbon Dioxide at the Air-Water Interface and its Chemical Implications.

The efficient reduction of CO2 into valuable products is a challenging task in an international context marked by the climate change crisis and the need to move away from fossil fuels. Recently, the use of water microdroplets has emerged as an interesting reaction media where many redox processes which do not occur in conventional solutions take place spontaneously. Indeed, several experimental studies in microdroplets have already been devoted to study the reduction of CO2 with promising results. The increased reactivity in microdroplets is thought to be linked to unique electrostatic solvation effects at the air-water interface. In the present work, we report a theoretical investigation on this issue for CO2 using first-principles molecular dynamics simulations. We show that CO2 is stabilized at the interface, where it can accumulate, and that compared to bulk water solution, its electron capture ability is larger. Our results suggest that reduction of CO2 might be easier in interface-rich systems such as water microdroplets, which is in line with early experimental data and indicate directions for future laboratory studies. The effect of other relevant factors which could play a role in CO2 reduction potential is discussed.

Formic acid stability in different solvents by DFT calculations.

New technologies have been developed toward the use of green energies. The production of formic acid (FA) from carbon dioxide (CO[Formula: see text]) hydrogenation with H[Formula: see text] is a sustainable process for H[Formula: see text] storage. However, the FA adduct stabilization is thermodynamically dependent on the type of solvent and thermodynamic conditions. The results suggest a wide range of dielectric permittivity values between the dimethyl sulfoxide (DMSO) and water solvents to stabilize the FA in the absence of base. The thermodynamics analysis and the infrared and charge density difference results show that the formation of the FA complex with H[Formula: see text]O is temperature dependent and has a major influence on aqueous solvents compared to the FA adduct with amine, in good agreement with the experiment. In these conditions, the stability thermodynamic of the FA molecule may be favorable at non-organic solvents and dielectric permittivity values closer to water. Therefore, a mixture of aqueous solvents with possible ionic composition could be used to increase the thermodynamic stability of H[Formula: see text] storage in CO[Formula: see text] conversion processes. Using the Quantum ESPRESSO package, density functional theory (DFT) calculations were performed with periodic boundary conditions, and the electronic wave functions were expanded in plane waves. For the exchange-correlation functional, we use the vdW-DF functional with the inclusion of van der Waals (vdW) forces. Electron-ion interactions are treated by the projector augmented wave (PAW) method with pseudopotentials available in the PSlibrary repository. The wave functions and the electronic densities were expanded employing accurate cut-off energies of 6.80[Formula: see text]10[Formula: see text] and 5.44[Formula: see text]10[Formula: see text] eV, respectively. The electronic density was computed from the wave functions calculated at the [Formula: see text]-point in the first Brillouin-zone. Each structural optimization was minimized according to the Broyden-Fletcher-Goldfarb-Shanno (BFGS) algorithm, with force and energy convergence criteria of 25 meV[Formula: see text]Å[Formula: see text] and 1.36 meV, respectively. The electrostatic solvation effects were performed by the [Formula: see text] package with the Self-Consistent Continuum Solvation (SCCS) approach.

Porous ionic liquids for oxidative desulfurization influenced by electrostatic solvent effect

Developing a highly efficient strategy for the stabilization of the solid-liquid interface is a persistent pursuit for researchers. Herein, porous ionic liquids based on UiO-66 (Zr) porous materials were synthesized and applied to the selective desulfurization catalysis, which integrates the permanent pores of porous solids with the exceptional properties of ionic liquids. Results show that porous ionic liquids possess high activity and selectivity for dibenzothiophene. Experimental analysis and density functional theory calculations revealed that the ionic liquids moiety served as an extractant to enrich dibenzothiophene into the porous ionic liquids phase through the π···π and CH···π interactions. Additionally, the electrostatic solvent effect in the porous ionic liquids contributes to the stabilization solid-liquid interface, which was favorable for UiO-66 moiety to catalytically activate hydrogen peroxide (H2O2) to generate ·OH radicals, and subsequently oxidized dibenzothiophene to the corresponding sulfone. It is hoped that the development of porous ionic liquids could pave a new route to the stabilization of the solid-liquid interface for catalytic oxidation.

Atomic-Level Investigation of Reactant Recognition Mechanism and Thermodynamic Property in Glucosamine 6-Phosphate Deaminase Catalysis.

Glucosamine 6-phosphate deaminase (NagB) influences the direction of N-acetylglucosamine (GlcNAc) metabolism, facilitating the conversion of D-glucosamine 6-phosphate (GlcN6P) to D-fructose 6-phosphate (Fru6P) with the release of ammonia. Here, extensive molecular dynamics simulations combined with various techniques were performed to study the recognition and delivery process of GlcN6P by SmuNagB, due to its guidance of subsequent enzymatic reaction. The key residues Lys194, His130, Arg127, Thr38, and Ser37 stabilize GlcN6P in the active site by hydrogen bond interactions, therein electrostatic and polar solvent effects provide the primary traction. Four delivery channels were identified, with GlcN6P most likely to enter the active site of NagB through a “door” comprising residues 6–10, 122–136, and 222–233. The corresponding mechanism and thermodynamic properties were investigated. An exothermic recognition and delivery process were detected, accompanied by the flipping of GlcN6P and changes in key direct and indirect hydrogen bond interactions, which provide the driving force for the chemical reaction to occur. Furthermore, “the lid motif” was identified that remain open in alkaline condition with different extent of opening at each stage of transfer that induced GlcN6P to move the active site of NagB. The work will assist in the elucidation of the catalytic mechanism of action of NagB, allowing inhibitors to be designed with superior dynamic behavior.

Interacting Quantum Atoms Approach and Electrostatic Solvation Energy: Assessing Atomic and Group Solvation Contributions.

The interacting quantum atoms (IQA) method decomposes the total energy of a molecular system in terms of one- and two-center (atomic) contributions within the context of the quantum theory of atoms in molecules. Here we incorporate electrostatic continuum solvent effects into the IQA energy decomposition. To this end, the interaction between the solute electrostatic potential and the solvent screening charges as defined within the COSMO solvation model is now included in a new version of the PROMOLDEN code, allowing thus to apply IQA in combination with COSMO-quantum chemical methods as well as to partition the electrostatic solvation energy into effective atomic and group contributions. To test the robustness of this approach, we carry out COSMO-HF/aug-cc-pVTZ calculations followed by IQA calculations on more than 400 neutral and ionic solutes extracted from the MNSol database. The computational results reveal a detailed atomic mapping of the electrostatic solvation energy that is useful to assess to what extent the solvation energy can be decomposed into atomic and group contributions of various parts of a solute molecule, as generally assumed by empirical methodologies that estimate solvation energy and/or logP values.

Electrostatic Estimation of Intercalant Jump-Diffusion Barriers Using Finite-Size Ion Models.

We report on a scheme for estimating intercalant jump-diffusion barriers that are typically obtained from demanding density functional theory-nudged elastic band calculations. The key idea is to relax a chain of states in the field of the electrostatic potential that is averaged over a spherical volume using different finite-size ion models. For magnesium migrating in typical intercalation materials such as transition-metal oxides, we find that the optimal model is a relatively large shell. This data-driven result parallels typical assumptions made in models based on Onsager's reaction field theory to quantitatively estimate electrostatic solvent effects. Because of its efficiency, our potential of electrostatics-finite ion size (PfEFIS) barrier estimation scheme will enable rapid identification of materials with good ionic mobility.

Partial atomic multipoles for internally consistent microelectrostatic calculations

An extension of the extant microelectrostatic methodologies, based on the concept of distributed generalized polarizability matrix derived from the Coupled Perturbed Hartree-Fock (CPHF) equations, is proposed for self-consistent calculation of charge carrier and charge-transfer (CT) state electrostatic energies in molecular solids, including the doped, defected and disordered ones. The CPHF equations are solved only once and the generalized molecular polarizability they yield enables low cost iterations that mutually adjust the molecular electronic distributions and the local electric field in which the molecules are immersed. The approach offers a precise picture of molecular charge densities, accounting for atomic partial multipoles up to order 2, which allows one to reproduce the recently reported large charge-quadrupole contributions to CT state energies in low-symmetry local environments. It is particularly well suited for repetitive calculations for large clusters (up to 300,000 atoms), and may potentially be useful for describing electrostatic solvent effects. © 2017 Wiley Periodicals, Inc.

Polyoxometalate/Polyethylene Glycol Interactions in Water: From Nanoassemblies in Water to Crystal Formation by Electrostatic Screening.

In the last decade organic-inorganic hybrid materials have become essential in materials science as they combine properties of both building blocks. Nowadays the main routes for their synthesis involve electrostatic coupling, covalent grafting, and/or solvent effects. In this field, polyoxometalates (POMs) have emerged as interesting inorganic functional building blocks due to their outstanding properties. In the present work the well-known α-Keggin polyoxometalate, α-PW12 O403- (PW), is shown to form hybrid crystalline materials with industrial (neutral) polyethylene glycol oligomers (PEG) under mild conditions, that is, in aqueous medium and at room temperature. The formation of these materials originates from the spontaneous self-assembly of PW with EOx , (EO=ethylene oxide) with at least four EO units (x>4). The PW-PEG nanoassemblies, made of a POM surrounded by about two PEG oligomers, are stabilized by electrostatic repulsions between the negatively charged PW anions. Addition of NaCl, aimed at screening the inter-nanoassembly repulsions, induces aggregation and formation of hybrid crystalline materials. Single-crystal analysis showed a high selectivity of PW towards EO5 -EO6 oligomers from PEG200, which is made of a mixture of EO3-8 . Therefore, a general "soft" route to produce POM-organic composites is proposed here through the control of electrostatic repulsions between spontaneously formed nanoassemblies in water. However, this rational design of new POM hybrid (crystalline) materials with hydrophilic blocks, using such a simple mixing procedure of the components, requires a deep understanding of the molecular interactions.

The divide-and-conquer second-order proton propagator method based on nuclear orbital plus molecular orbital theory for the efficient computation of proton binding energies.

An efficient computational method to evaluate the binding energies of many protons in large systems was developed. Proton binding energy is calculated as a corrected nuclear orbital energy using the second-order proton propagator method, which is based on nuclear orbital plus molecular orbital theory. In the present scheme, the divide-and-conquer technique was applied to utilize local molecular orbitals. This use relies on the locality of electronic relaxation after deprotonation and the electron-nucleus correlation. Numerical assessment showed reduction in computational cost without the loss of accuracy. An initial application to model a protein resulted in reasonable binding energies that were in accordance with the electrostatic environment and solvent effects.

Sodium affinity of caffeine and adenine: the effect of microsolvation and electrostatic field of solvent on the sodium affinity

ABSTRACTThe sodium affinity (SA) of caffeine (CAF), adenine (AD) and their microsolvated clusters containing one X molecule (CAF-X and AD-X; X = H2O, NH3, H2S and HF) has been calculated in the gas phase and water, separately. The density functional theory (DFT) employing CAM-B3LYP functional has been used for all of the calculations in this work. The solvent was modelled by the polarised continuum model (PCM) which considers the electrostatic field of solvent on solute. The calculated SA of [CAF-X] and [AD-X] was higher than that of CAF and AD in the gas phase, respectively, which showed that the microsolvation of molecules in the gas phase could be used for changing the tendency of molecules for binding to Na+. Also, it was observed that the electrostatic effect of solvent decreases the SA of the species compared to the gas phase, considerably. The symmetry adapted perturbation theory (SAPT) calculations were also used to interpret the change in the SA of CAF and AD due to the clustering with one X molecule in the gas phase. In addition, there is a detailed study on the position of Na+ relative to AD and CAF structures in different conditions including gas phase, microsolvation and electrostatic field of solvent in this work.

DFT-Based Simulations of Amide I′ IR Spectra of a Small Protein in Solution Using Empirical Electrostatic Map with a Continuum Solvent Model

A continuum solvent model was tested for simulations of amide I' IR spectra for a 40-residue subdomain of P22 viral coat protein in aqueous solution. Spectra obtained using DFT (BPW91/6-31G**) parameters for a reduced all-Ala representation of the protein were corrected by an electrostatic potential map obtained from the solvent cavity surface and AMBER99 side-chain atom partial charges. Various cavity sizes derived from van der Waals atomic radii with an added effective solvent radius up to 2.0 Å were tested. The interplay of the side-chain and solvent electrostatic effects was investigated by considering the side chains and solvent separately as well as together. The sensitivity to side-chain conformational fluctuations and to the parametrization of C(β) group partial charges was also tested. Simulation results were compared to the experimental amide I' spectra of P22 subdomain, including two (13)C isotopically edited variants, as well as to the previous simulations based on the molecular dynamics trajectory in explicit solvent. For small cavity sizes, between van der Waals and that with added solvent radius of 0.5 Å, better qualitative agreement with experiment was obtained than with the explicit solvent representation, in particular for the (13)C-labeled spectra. Larger protein cavities led to progressively worse predictions due to increasingly stronger electrostatic effects of side chains, which could no longer be well compensated for by the solvent potential. Balance between side-chain and solvent electrostatic effects is important in determining the width and shape of the simulated amide I', which is also virtually unaffected by side-chain-geometry fluctuations. The continuum solvent model combined with the electrostatic map is a computationally efficient and potentially robust approach for the simulations of IR spectra of proteins in solution.

Magnetic exchange coupling in bis-nitroxides: a theoretical analysis of the solvent effects

Magnetic properties of nitroxide radicals can be greatly affected by solvent effects. In this study, the change of the magnetic exchange interaction J, coupling the two unpaired electrons of a model solvated antiferromagnetic bis-iminyl-nitroxide molecule (2IN), is rationalized thanks to different geometric and electronic criteria provided by density functional theory calculations. It is shown that for a given geometry, simple tools can be used to analyze with good accuracy the dependence of J with the solvent polarity. Estimates of two important magnetic parameters are given: the magnetic orbitals exchange and the in-site energy gap between ionic and neutral configurations. 2IN can be engaged in different hydrogen-bonds with first shell water molecules, modifying both the 2IN geometry and the electrostatic potential felt by the molecule. In all, the additivity of electrostatic and hydrogen-bond solvent effects is found to be responsible for J variations as large as 50%.

The dielectric continuum solvent model adapted for treating preferential solvation effects

Theoretical investigation of electrostatic solvation effects in binary solvent mixtures composed of non-polar and polar ingredients require the elaboration of advanced continuum solvent models in order to treat explicitly the non-uniformity of the dielectric medium, which is an inherent feature of such complicated systems. The present article gives a concise account of the appropriate continuum-level theory developed recently and tested on the solutions of spherical Born ions in the mixtures of benzene and dimethylsulfoxide (DMSO). Its further application for studies of the interaction of ion pairs in the same solvent mixtures with the DMSO contents varying in a wide range is reported. The results are compared with the MD simulations of the same systems which allows for the proper calibration of the parameters of the continuum solvent model.

A Theoretical Investigation on N7(H)→N9(H) Tautomerization of Isolated and Monohydrated 2,6‐Dithiopurine Combined with IPCM Solvent Model

AbstractThe tautomerization reaction mechanism has been reported between N7(H) and N9(H) of isolated and monohydrated 2,6‐dithiopurine using B3LYP/6‐311+G(d,p). The isodensity polarized continuum model (IPCM) in the self‐consistent reaction field (SCRF) method is employed to account for the solvent effect of water on the tautomerization reaction activation energies. The results show that the two pathways P(1) (via the carbene intermediate I1) and P(2) (via the sp3‐hybrid intermediate I2) are found in intramolecular proton transfer, and each pathway is composed by two primary steps. The calculated activation energy barriers of the rate‐determining steps in isolated 2,6‐dithiopurine N7(H)→N9(H) tautomerism are 308.2 and 220.0 kJ·mol−1 in the two pathways, respectively. Interestingly, in one‐water molecule catalyst, it dramatically lowers the N7(H)→N9(H) energy barriers by the concerted double proton transfer mechanism in P(1), favoring the formation of 2,6‐dithiopurine N9(H). However, the single proton transfer mechanism assisted with out‐of‐plane water in the first step of P(2) increases the activation energy barrier from 220.0 to 232.3 kJ·mol−1, while the second step is the out‐of‐plane concerted double proton transfer mechanism, indicating that they will be less preferable for proton transfer. Additionally, the results also show that all the pathways are put into the aqueous solution, and the activation energy barriers have no significant changes. Therefore, the long‐range electrostatic effect of bulk solvent has no significant impact on proton transfer reactions and the interaction with explicit water molecules will significantly influence proton transfer reactions.

Association Thermodynamics and Conformational Stability of β-Sheet Amyloid β(17-42) Oligomers: Effects of E22Q (Dutch) Mutation and Charge Neutralization

Amyloid fibrils are associated with many neurodegenerative diseases. It was found that amyloidogenic oligomers, not mature fibrils, are neurotoxic agents related to these diseases. Molecular mechanisms of infectivity, pathways of aggregation, and molecular structure of these oligomers remain elusive. Here, we use all-atom molecular dynamics, molecular mechanics combined with solvation analysis by statistical-mechanical, three-dimensional molecular theory of solvation (also known as 3D-RISM-KH) in a new MM-3D-RISM-KH method to study conformational stability, and association thermodynamics of small wild-type A β 17–42 oligomers with different protonation states of Glu 22, as well the E22Q (Dutch) mutants. The association free energy of small β-sheet oligomers shows near-linear trend with the dimers being thermodynamically more stable relative to the larger constructs. The linear (within statistical uncertainty) dependence of the association free energy on complex size is a consequence of the unilateral stacking of monomers in the β-sheet oligomers. The charge reduction of the wild-type A β 17–42 oligomers upon protonation of the solvent-exposed Glu 22 at acidic conditions results in lowering the association free energy compared to the wild-type oligomers at neutral pH and the E22Q mutants. The neutralization of the peptides because of the E22Q mutation only marginally affects the association free energy, with the reduction of the direct electrostatic interactions mostly compensated by the unfavorable electrostatic solvation effects. For the wild-type oligomers at acidic conditions such compensation is not complete, and the electrostatic interactions, along with the gas-phase nonpolar energetic and the overall entropic effects, contribute to the lowering of the association free energy. The differences in the association thermodynamics between the wild-type A β 17–42 oligomers at neutral pH and the Dutch mutants, on the one hand, and the A β 17–42 oligomers with protonated Glu 22, on the other, may be explained by destabilization of the inter- and intrapeptide salt bridges between Asp 23 and Lys 28. Peculiarities in the conformational stability and the association thermodynamics for the different models of the A β 17–42 oligomers are rationalized based on the analysis of the local physical interactions and the microscopic solvation structure.

Metal−Phosphine Bond Strengths of the Transition Metals: A Challenge for DFT

Previous promising tests of the new M06 family of functionals in predicting ruthenium-metal phosphine bond dissociation energies (Zhao, Y.; Truhlar, D. G. Acc. Chem. Res. 2008, 41, 157) have been extended to a series of phosphine complexes of chromium, molybdenum, nickel, and ruthenium for which relevant experimental data are available. In addition to the M06 family of functionals, bond dissociation enthalpies have been calculated using a selection of density functionals and hybrid functionals based on the generalized gradient approximation (GGA), and with or without an empirical term (i.e., DFT-D) accounting for long-range dispersion. For the ruthenium complexes, second-order Møller-Plesset perturbation theory (MP2) has also been applied. Electrostatic and nonelectrostatic solvent effects have been estimated using the polarizable continuum model (PCM), allowing for comparison with experimental data obtained for dissociation reactions in organic solvents. Whereas the GGA and hybrid-GGA functionals grossly underestimate the absolute metal-phosphine bond enthalpies, with mean unsigned errors (MUEs) for a set of 10 phosphine dissociation reactions in the range 13-27 kcal/mol, the recently developed DFT-based methods for inclusion of attractive noncovalent interactions and dispersion (the DFT-D and M06 functionals) dramatically improve upon the situation. The best agreement with experiment is observed for BLYP-D (MUE = 2.2 kcal/mol), and with the exception for M06-2X, all these methods provide MUEs well below 5 kcal/mol, which should be sufficient for a broad range of applications. The improvements in predicted relative bond enthalpies are less convincing, however. In several cases the GGA and hybrid-GGA functionals are better at reproducing substitution effects than the DFT-D and M06 methods.

Theoretical study of solvent effects in the 1,3 rearrangement in the allyl-fluoride system in polar media

The influence of electrostatic solvent effects on the barrier for the internal return rearrangement in the allyl–fluoride model system has been analyzed. The solvent was modeled through the self-consistent reaction field (SCRF) theory. It is shown that there exists a significant solvent effect operating in favor of the 1,3 fluoride migration. The results are compared with previous theoretical studies based on a supermolecule scheme of calculation, which reported no solvent influence on the barrier for the internal return process in this system. Finally, the effect of acid catalysis is reinterpreted on the basis of the results obtained and discussed in connection with experimental data in related systems.

An Adaptive Fast Multipole Boundary Element Method for Poisson−Boltzmann Electrostatics

The numerical solution of the Poisson−Boltzmann (PB) equation is a useful but a computationally demanding tool for studying electrostatic solvation effects in chemical and biomolecular systems. Recently, we have described a boundary integral equation-based PB solver accelerated by a new version of the fast multipole method (FMM). The overall algorithm shows an order N complexity in both the computational cost and memory usage. Here, we present an updated version of the solver by using an adaptive FMM for accelerating the convolution type matrix-vector multiplications. The adaptive algorithm, when compared to our previous nonadaptive one, not only significantly improves the performance of the overall memory usage but also remarkably speeds the calculation because of an improved load balancing between the local- and far-field calculations. We have also implemented a node-patch discretization scheme that leads to a reduction of unknowns by a factor of 2 relative to the constant element method without sacrificing accuracy. As a result of these improvements, the new solver makes the PB calculation truly feasible for large-scale biomolecular systems such as a 30S ribosome molecule even on a typical 2008 desktop computer.

Formation of a Rotaxane from the End-Capping Process of a Pseudorotaxane. Effects of the Solvent

The effects that the solvent exerts on the end-capping process of a pseudorotaxane formed by the [Ru(NH 3) 5(4,4'-bpy)]2+ complex and beta-cyclodextrin were studied. In this process the 4,4'-bpy ligand acts as rigid axle and the cyclodextrin as ring or macrocycle. The stopper used was the [Fe(CN) 5 H2O]3(-) complex. The solvents used were mixtures of ethyleneglycol-water and tert-butyl alcohol-water. Results showed similar, although strange, behavior in both media studied. Thus, a decrease of the observed rate constant was obtained when the concentration of cyclodextrin increases for all the media studied. However, at fixed cyclodextrin concentrations, an increase of k obs was obtained when small quantities of the cosolvent were added to the medium and, further, a decrease of k obs for the higher quantities of the organic solvents. This strange behavior could be explained by taking into account electrostatic and specific solvent (solvent-solvent and solvent-solute) effects.

DFT computational studies on rotation barriers, tautomerism, intramolecular hydrogen bond, and solvent effects in 8‐hydroxyquinoline

AbstractIntramolecular hydrogen binding interactions in 8‐hydroxyquinoline, both in its zwitterionic tautomer and in the rotamer without the intramolecular hydrogen bond (IHB), have been computed using the B3LYP and MPW1K density functionals. The rotation of the OH bond and intramolecular proton transfer reactions were studied theoretically. The following theory levels have been applied: B3LYP/6‐31G(d,p), B3LYP/6‐311++G(d,p), MPW1K/6‐311++G(d,p), and MPW1K/6‐311++G(2d,3p)//MPW1K/6‐311++G(d,p). Natural bond orbital (NBO) analysis has also been carried out. The effect of medium (benzene, chloroform, tetrahydrofuran, 1,2‐dichloroethane, acetone, water) was simulated using the self‐consistent reaction field (SCRF) method within the framework of the polarizable continuum model (PCM), at the MPW1K/6‐311++G(d,p) level. The evolution of geometry, relative energies, heights of rotation (around the OH bond) and tautomerization barriers, IHB energies, and ΔG(solv) have been systematically investigated. The results obtained have shown the failure to neglect some changes of the above characteristics in polar media with respect to the gaseous phase. The series of stability of the forms under study in the gaseous phase remains the same in solution. Thus, in spite of the important role of the solvent electrostatic effects, the intrinsic stability of those species overcomes the solvent effects. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006