Simple Charge-Transfer Model for Metallic Complexes

Ionic liquids (ILs) hold great promise in many fields including energy storage and generation, mechanical, pharmaceutical, synthetic and separation applications to name just a few. For any given application, the desired physical properties of the ideal IL may differ substantially from others and no widely applicable patterns or trends to facilitate intuitive design. The origins of physical properties lie in the characteristics of the intermolecular energetics, which consist of a complex interplay between electrostatic and dispersion forces. This thesis investigates and develops computational methodologies for calculating a reliable description of the intermolecular interactions for this challenging class of solvents and electrolytes of the future. The electrostatic approximation used in classical molecular dynamics (MD) where atomic partial charges are assigned was investigated in terms of methods based on density matrix partitioning, and the restrained electrostatic potentials (RESP) approaches. It was found that the “geodesic” atomic partial charge scheme, part of the RESP family, produced the most accurate charges. This was measured in terms of (a) charge convergence with increasing basis set size; (b) charge invariance with changes to the coordinate system; (c) insensitivity to minor structural changes on the resulting charges; (d) adequate capture of charge transfer effects; and (e) the preservation of symmetric of charges in symmetric molecules. Although charges can vary dramatically depending on the scheme used, the careful use of atomic partial charge schemes may still produce reliable forcefields, or at least serve as a rapid diagnostic tool to quantify electrostatic interactions and charge transfer. In moving towards unbiased a priori descriptions of IL intermolecular interactions, second-order Moller-Plesset perturbation theory (MP2) was used with the linear-scaling fragment molecular orbital (FMO) framework to assess the extent to which dispersion forces play a role in the intermolecular energetics. ILs of increasing size were examined such that the many-body effects may be captured. The dispersion energy contribution formed up to 20% of the total interaction energy. Furthermore, the interaction energy as produced by FMO was within 1 kJ mol−1 of the full-wavefunction MP2 interaction energy when three-body effects were included. As the dispersion interaction is purely a quantum mechanical phenomenon, correlated quantum mechanical methods, such as MP2 or coupled-cluster approaches, are required to provide an unbiased account of these effects. Ab initio methods such as MP2 and CCSD(T) scale formally as N⁵ an N⁷, respectively, with chemical system size. While the FMO approach provides a marked improvement in efficiency, the counterpoise (CP) approach to correcting the basis set superposition error (BSSE) is not amenable to fragmented approaches and requires each ion in the cluster to be calculated in the basis set of the entire system. In order to remove this bottleneck, the spin-component scaled second-order Moller Plesset perturbation theory (SCS-MP2) methodology was refined by fitting 174 non-CP corrected interaction energies at the MP2/cc-pVTZ level of theory to CP corrected CCSD(T)/CBS benchmark energies. This has resulted in an implicit BSSE correction that may be used within the highly efficient FMO framework, and is shown to yield results on par with or exceeding the accuracy of MP2/cc-pVQZ for clusters of two and four ion pairs (IPs). This new approach as been termed SCS-IL-MP2. An alternative dispersion corrected density functional theory (DFT) approach, DFT- D3, was assessed and refined in view of producing accurate interaction energies at the same CCSD(T)/CBS quality. The same test set of 174 ILs was used to fit the SCS-IL-MP2 approach was used to refit the DFT-D3 approach for both the Hartree-Fock (HF) wavefunction and the PBE and BLYP density functionals (DFs). In most cases, the selection of the DF and associated DFT-D version 3 (DFT-D3) parameters differed negligibly with all reaching within 1 to 2 kJ mol−1 per IP. HF-D3 parameters, on the other hand, showed a substantial improvement, particularly when used with the Becke-Johnson (BJ) damping function. Refitted HF-D3 and the BJ damping function was able to consistently provide interaction energy errors below 5 kJ mol−1 per IP. It would be worthwhile further investigating the application of the refined HF-D3 in its ability to produce reliable energies and geometries over a more diverse set of ILs. Both the SCS-IL-MP2 and new DFT-D3 approaches may be applied to the highly scal- able FMO framework. These form the core elements of the quantum chemistry toolbox for the study and understanding of the physicochemical properties of ILs that have so far been only superficially characterised by electronic structure theory. From this starting point, a rigorous and unbiased a priori understanding of the intermolecular interactions and resulting physicochemical properties may be predicted by means of efficient ab initio molecular dynamics (AIMD) techniques.

ABSTRACTObjective: Pedestrian lower extremity represents the most frequently injured body region in car-to-pedestrian accidents. The European Directive concerning pedestrian safety was established in 2003 for evaluating pedestrian protection performance of car models. However, design changes have not been quantified since then. The goal of this study was to investigate front-end profiles of representative passenger car models and the potential influence on pedestrian lower extremity injury risk.Methods: The front-end styling of sedans and sport utility vehicles (SUV) released from 2008 to 2011 was characterized by the geometrical parameters related to pedestrian safety and compared to representative car models before 2003. The influence of geometrical design change on the resultant risk of injury to pedestrian lower extremity—that is, knee ligament rupture and long bone fracture—was estimated by a previously developed assessment tool assuming identical structural stiffness. Based on response surface generated from simulation results of a human body model (HBM), the tool provided kinematic and kinetic responses of pedestrian lower extremity resulted from a given car's front-end design.Results: Newer passenger cars exhibited a “flatter” front-end design. The median value of the sedan models provided 87.5 mm less bottom depth, and the SUV models exhibited 94.7 mm less bottom depth. In the lateral impact configuration similar to that in the regulatory test methods, these geometrical changes tend to reduce the injury risk of human knee ligament rupture by 36.6 and 39.6% based on computational approximation. The geometrical changes did not significantly influence the long bone fracture risk.Conclusions: The present study reviewed the geometrical changes in car front-ends along with regulatory concerns regarding pedestrian safety. A preliminary quantitative benefit of the lower extremity injury reduction was estimated based on these geometrical features. Further investigation is recommended on the structural changes and inclusion of more accident scenarios.

Interaction energies of halide-water dimers, X-(H2O), and trimers, X-(H2O)2, with X = F, Cl, Br, and I, are investigated using various many-body models and exchange correlation functionals selected across the hierarchy of density functional theory (DFT) approximations. Analysis of the results obtained with the many-body models demonstrates the need to capture important close-range interactions in the regime of large intermolecular orbital overlap, such as charge transfer and charge penetration. Failure to reproduce these effects can lead to large deviations relative to reference data calculated at the coupled cluster level of theory. Decompositions of interaction energies carried out with the absolutely localized molecular orbital energy decomposition analysis (ALMO-EDA) method demonstrate that permanent and inductive electrostatic energies are accurately reproduced by all classes of XC functionals (from generalized gradient corrected (GGA) to hybrid and range-separated hybrid functionals), while significant variance is found for charge transfer energies predicted by different XC functionals. Since GGA and hybrid XC functionals predict the most and least attractive charge transfer energies, respectively, the large variance is likely due to the delocalization error. In this scenario, the hybrid XC functionals are then expected to provide the most accurate charge transfer energies. The sum of Pauli repulsion and dispersion energies is the most varied among the XC functionals, but it is found that a correspondence between the interaction energy and the ALMO-EDA total frozen energy may be used to determine accurate estimates for these contributions.

Ab initio MP2/aug'-cc-pVTZ calculations have been carried out to determine the structures, binding energies, and bonding properties of complexes involving the cation (H2C═PH2)(+) and a set of sp-hybridized nitrogen bases including NCCH3, NP, NCCl, NCH, NCF, NCCN, and N2. On each (H2C═PH2)(+):N-base surface, four types of unique equilibrium structures exist: a complex with a P···N pnicogen bond formed through the π system of (H2C═PH2)(+) (ZB-π); a complex with a P···N pnicogen bond formed through the σ system of (H2C═PH2)(+) (ZB-σ); a hydrogen-bonded complex with a P-H···N hydrogen bond (HB); and a tetrel-bonded complex with a C···N bond (TB). Binding energies of complexes stabilized by the same type of intermolecular interaction decrease in the order NCCH3 > NP > NCCl > NCH > NCF > NCCN > N2. For a given base, binding energies decrease in the order ZB-π > HB > ZB-σ > TB, except for a reversal of HB and ZB-σ with the weakest base N2. Binding energies of ZB-π, HB, and ZB-σ complexes increase exponentially as the corresponding P-N distance decreases, but the correlation is not as good between the binding energies of TB complexes and the intermolecular C-N distance. Charge-transfer energies stabilize all complexes and also exhibit an exponential dependence on the corresponding intermolecular distances. EOM-CCSD spin-spin coupling constants (1p)J(P-N) for ZB-π and ZB-σ complexes, and (2h)J(P-N) for HB complexes increase quadratically as the corresponding P-N distance decreases. Values of (1t)J(C-N) for TB are small and show little dependence on the C-N distance. (1)J(P-H) values for the hydrogen-bonded P-H bond in HB complexes correlate with the corresponding P-H distance, whereas values of (1)J(P-H) for the non-hydrogen-bonded P-H correlate with the P-N distance.

Density functional theory assessed molecular insights into asphaltene interactions within silica and calcium carbonate surface with deep eutectic solvents

The intermolecular interaction energies for hydrogen-bonded complexes have been investigated using Hartree-Fock (HF), Møller-Plesset (MP2) and density functional theory (DFT). Interaction energies were computed for the following complexes: NH3--NH3, NH3--H2O, NH3--HF, H2O--H2O, H2O--HF, and HF--HF. Pople's split valence (6-31++G(2d,2p)) basis sets were employed throughout these calculations. The predicted interaction energies for these complexes using the B3-LYP hybrid method (without ZPE and BSSE) are: -4.02, -7.15, -14.26, -4.97, -9.30, and -4.73 kcal/mol, respectively. Charge transfer computed using the natural bond order (NBO) scheme suggests that the local density approximation tends to overestimate the amount of charge transferred between donor and acceptor when compared to MP2 results.

The present study is focused to cast light on the structural, electronic and energetic properties of isolated (G4)2 and (X4)2 DNA quadruplexes with transition metal cations which are investigated using ab initio and density functional theory (DFT). The geometrical analysis revealed that (G4)2 and (X4)2 with metal cation can adopt the normal tetraplex Hoogsteen hydrogen bond, and no bifurcated hydrogen bonds are occurred. The addition of metal cation in the central cavity of isolated (G4)2 and (X4)2 bases can affect the structural chirality and their charge distribution. Binding energy and metal ion affinity of (G4)2 and (X4)2 metal complexes follow the interaction energy order of (G4)2-Cu+ > (G4)2-Ag+ > (G4)2-Au+ > and (X4)2-Cu+ > (X4)2-Ag+ > (X4)2-Au+. The quantum theory of atoms in molecule (QTAIM) analysis revealed that the electrostatic interaction has occurred between carbonyl group oxygen atom and metal cation (O6⋯M+). The natural bonding orbital (NBO) analysis reveals that the N-H⋯O and N-H⋯N hydrogen bond strength and charge transfer have been calculated for both (G4)2 and (X4)2 metal complexes. The higher wavelength and lower excitation energies are observed for both (G4)2 and (X4)2 metal complexes which exhibit that the hyperchromic shift occurred during metal ion interaction. The obtained results showed that the transition metal cations are strongly interacted with (G4)2 and (X4)2 bases, and it controls the telomerase activity. While comparing (G4)2 and (X4)2 bases, the (X4)2 bases are having similar properties of (G4)2 bases. Thus, the xanthine and its derivatives are very auspicious candidates for artificial quadruplex DNA.

Computational quantum chemistry methods are used to study simultaneous cation-π and π–π stacking interactions with a graphene sheet and on the inner and outer faces of some bent graphenes as curved surfaces of carbon nanohorns (CNHs). Structural parameters and energy data of ternary benzene–graphene–Na+ and benzene-bent graphene–Na+ complexes are studied. Also, effects of charge transfer and aromaticity are estimated to determine how changes in the structure influences the above interactions. The results indicate that the graphene curvature leads to structural changes affecting simultaneous interactions of the Na+ cation and benzene with bent graphenes. Also, the results show that although π–π stacking is a weak interaction, it can manipulate the order of binding energies in complexes involving both mentioned interactions and affect drug delivery abilities of these systems.

ABSTRACTAb initio MP2/aug'-cc-pVTZ calculations have been carried out to investigate the pnicogen-bonded complexes F4-nHnP+:N-base, for n = 1–4, each with a linear or nearly linear Hax–P···N alignment. The sp3-hybridised nitrogen bases include NH3, NClH2, NFH2, NCl2H, NCl3, NFCl2, NF2H, NF2Cl, and NF3, and the sp bases are NCNH2, NCCH3, NP, NCOH, NCCl, NCH, NCF, NCCN, and N2. Binding energies increase as the P–N distance decreases, with an exponential curve showing this relationship when complexes with sp3 and sp hybridised bases are treated separately. However, the correlations are not as good as they are for the complexes F4-nHnP+:N-base for n = 0–3 with F–P···N linear. Different patterns are observed for the change in the binding energies of complexes with a particular base as the number of F atoms in the acid changes. Thus, the particular acid–base pair is a factor in determining the binding energies of these complexes.Three different charge-transfer interactions stabilise these complexes, namely Nlp→σ*P–Hax, Nlp→σ*P–Feq, and Nlp→σ*P–Heq. Unlike the corresponding complexes with F–P···N linear, Nlp→σ*P–Hax is not always the dominant charge-transfer interaction, since Nlp→σ*P–Feq is greater in some complexes. Nlp→σ*P–Heq makes the smallest contribution to the total charge-transfer energy. The total charge-transfer energies of all complexes increase exponentially as the P–N distance decreases in a manner very similar to that observed for the series of complexes with F–P···N linear.Equation-of-motion coupled cluster singles and doubles (EOM-CCSD) spin–spin coupling constants 1pJ(P–N) across the pnicogen bond vary with the P–N distance, but different patterns are observed which depend on the nature of the acid, and for some acids, on the hybridisation of the nitrogen base. 1pJ(P–N) values for complexes of F3HP+ initially increase as the P–N distance decreases, reach a maximum, and then decrease with decreasing P–N distance as the P···N bond acquires increased covalent character. 1pJ(P–N) for complexes with H–P···N linear and those with F–P···N linear exhibit similar distance dependencies depending on the number of F atoms in equatorial positions and the hybridisation of the base. Complexation may increase, decrease, or leave the P–Hax distance unchanged, but 1J(P–Hax) always decreases relative to the corresponding isolated ion. Decreasing 1J(P–Hax) can be related to decreasing intermolecular P–N distance.

To investigate the adsorption property of H2 and CO2 on the organic ligand of C-MOF-5 (H2BDC) and T-MOF-5 (ZnO-doped H2BDC (ZnO-H2BDC)), Density functional theory (DFT) method was performed. First, the adsorption of ZnO on H2BDC resulted in examining binding energies, the charge transfer, density of states, dipole moments and adsorption geometries were investigated. The binding properties have been calculated and investigated theoretically for ZnO-doped H2BDC in terms of binding energies, band structures, Mulliken charges, and density of states (DOSs). According to obtained results, the H2BDC was strongly doped with ZnO. H2 and CO2 adsorption capacities for ZnO-doped H2BDC are significantly enhanced while there are low adsorption capacities for H2BDC. According to results, at least in the organic ligand of the MOF-5, the highest and lowest adsorption of CO2 (or H2) is attributed to the T-MOF-5 and C-MOF-5 respectively. Our calculations reveal that ZnO-doped H2BDC system (T-MOF-5) has much higher adsorption energy and higher net charge transfer value than pristine H2BDC (C-MOF-5). Also by changing in structure from cubic to tetragonal, the main site for H2 and CO2 adsorption was changed.

Molecular pincers or tweezers are designed to hold and release the target molecule. Potential applications involve drug distribution in medicine, environment technologies, or microindustrial techniques. Typically, the binding is dominated by van der Waals forces. Modeling of such complexes can significantly enhance their design; yet obtaining accurate complexation energies by theory is difficult. In this study, density functional theory (DFT) computations combined with dielectric continuum solvent model are compared with the potential of mean force approach using umbrella sampling and the weighted histogram analysis method (WHAM) with molecular dynamics (MD) simulations. For DFT, functional and basis set effects are discussed. The computed results are compared to experimental data based on NMR spectroscopic measurements of five synthesized tweezers based on the Tröger's basis. Whereas the DFT computations correctly provided the observed trends in complex stability, they failed to produce realistic magnitudes of complexation energies. Typically, the binding was overestimated by DFT if compared to experiment. The simpler semiempirical PM6-DH2X scheme proposed lately yielded better magnitudes of the binding energies than DFT but not the right order. The MD-WHAM simulations provided the most realistic Gibbs binding energies, although the approximate MD force fields were not able to reproduce completely the ordering of relative stabilities of model complexes found by NMR. Yet the modeling provides interesting insight into the complex geometry and flexibility and appears as a useful tool in the tweezers' design.

Molecular interactions between uracil and nitrous acid (U–NA) [C4N2O2H4NO2H] have been studied using B3LYP, B3PW91, and MP2 methods with different basis sets. The optimized geometries, harmonic vibrational frequencies, charge transfer, topological properties of electron density, nucleus‐independent chemical shift (NICS), and nuclear magnetic resonance one‐ and two‐bonds spin–spin coupling constants were calculated for U–NA complexes. In interaction between U and NA, eight cyclic complexes were obtained with two intermolecular hydrogen bonds N(C)HU…N(O) and OHNA…OU. In these complexes, uracil (U) simultaneously acts as proton acceptor and proton donor. The most stable complexes labeled, UNA1 and UNA2, are formed via NH bond of U with highest acidity and CO group of U with lowest proton affinity. There is a relationship between hydrogen bond distances and the corresponding frequency shifts. The solvent effect on complexes stability was examined using B3LYP method with the aug‐cc‐pVDZ basis set by applying the polarizable continuum model (PCM). The binding energies in the gas phase have also been compared with solvation energies computed using the PCM. Natural bond orbital analysis shows that in all complexes, the charge transfer takes place from U to NA. The results predict that the Lone Pair (LP)(O)U → σ*(OH) and LP(N(O)NA → σ*(N(C)H)U donor–acceptor interactions are most important interactions in these complexes. Atom in molecule analysis confirms that hydrogen bond contacts are electrostatic in nature and covalent nature of proton donor groups decreases upon complexation. The relationship between spin–spin coupling constant (1hJH…Y and 2hJH…Y) with interaction energy and electronic density at corresponding hydrogen bond critical points and H‐bonds distances are investigated. NICS used for indicating of aromaticity of U ring upon complexation. © 2013 Wiley Periodicals, Inc.

Molecular interactions: a study of charge transfer effects

The ongoing quest for multifunctional organic molecules that exhibit both pharmaceutical and optoelectronic potential has intensified interest in heterocyclic compounds. Among them, hydrazone derivatives stand out for their diverse biological activities, including antimicrobial, antiviral, and anticancer properties, as well as their tunable electronic and optical properties. The presence of the –C N–NH– linkage enables effective conjugation and charge transfer, enhancing their chemical reactivity, stability, and nonlinear optical (NLO) behaviour. Owing to these versatile features, the design and synthesis of novel hydrazone-based heterocycles have gained prominence for potential applications in drug development and advanced material science. This study focuses on the design, synthesis, and characterization of a novel hydrazone derivative, N′-((2,3-dihydrobenzo[ b ][1,4]dioxin-6-yl)methylene)furan-2-carbohydrazide (DDMF). The compound combines furan and benzo dioxane moieties to enhance conjugation and biological activity. Its structural, electronic, and reactive properties were examined using FT-IR, ¹H NMR, ¹ ³C NMR, and DFT-based quantum chemical analyses. In addition, molecular docking and ADMET studies were performed to evaluate its binding affinity, drug-likeness, and pharmacokinetic behaviour, providing insight into its potential pharmaceutical and optoelectronic applications. The DDMF compound was synthesized and structurally confirmed using FT-IR, ¹H NMR, and ¹ ³C NMR spectroscopy. Theoretical investigations were carried out using Density Functional Theory (DFT) to study molecular geometry, electronic structure, and reactivity descriptors. Frontier Molecular Orbital (FMO), Natural Bond Orbital (NBO), and Molecular Electrostatic Potential (MEP) analyses were performed to assess charge distribution and reactive sites. In addition, UV-Vis, NLO, and molecular docking studies were conducted alongside ADMET and drug-likeness evaluations. The optimized geometry showed excellent correlation with experimental data, exhibiting minimal RMSD in bond lengths (0.020 Å) and bond angles (5.20°). FMO analysis revealed moderate reactivity and effective charge transfer, while NBO and MEP confirmed significant electron delocalization. The compound exhibited strong NLO activity and consistent NMR spectral agreement (¹H RMSD = 0.437 ppm; ¹³C RMSD = 1.24 ppm). UV-Vis spectra indicated distinct π→π* transitions at 275 and 350 nm. Docking studies showed stable interactions of DDMF with SARS-CoV-2 targets, supported by stable RMSD (∼1–2.5 Å) and low RMSF values. The compound demonstrated excellent intestinal absorption (94.63 %), favorable ADMET profiles, and high drug-likeness (MW 272.26 g/mol, LogP 1.84, TPSA 73.06 Ų). The combined experimental and theoretical investigations unequivocally confirm the successful synthesis, structural integrity, and stability of the DDMF molecule. The compound exhibits favorable electronic configuration, optical responsiveness, and pharmacological potential, as evidenced by its consistent spectroscopic characteristics, strong charge-transfer behaviour, and stable molecular interactions with biological targets. The integration of computational and spectroscopic analyses establishes DDMF as a structurally robust and functionally versatile molecule, making it a promising candidate for future advancements in both optoelectronic device fabrication and therapeutic drug development. • Synthesis of novel hydrazone derivative. • Investigation of electronic properties through DFT-based analysis. • Molecular docking analysis to evaluate the inhibitory potential of the synthesized compound. • Molecular dynamics simulation conducted over a 100 ns period to examine the dynamic interactions between the protein and ligand.

Intermolecular interaction network in liquid acetone