Global Electronegativity Research Articles

Investigation of the Correlation between Geometrical Relationship and the Anomeric effect on Conformational Reactivities and Analyze the 1, 4-elimination

Abstract: Ab initio molecular orbital hybrid density functional theory (B3LYP/6-311++G**) based methods and natural bond orbital (NBO) interpretation were used to investigate the 1, 4- eliminations and the correlations between the global hardness, global electronegativity, anomeric effect, thermodynamic parameters of 3-chloro-8-methyl-8- azabicyclo[3.2.1]octane (1), 3-chloro-8-methyl-8- phosphabicyclo[3.2.1]octane (2) and 3-chloro-8-methyl-8- arsabicyclo [3.2.1]octane (3). The calculated global electronegativity (χ) differences between the axial- and equatorial-stereoisomers (Δ [χ (eq) - χ (ax)]) decreased from compound 1 to compound 3. This fact justifies that with the increase of the Lewis acid from the equatorial- stereoisomers of compound 1 to compound 3, the energy difference between the axial- and equatorial- stereoisomers decreases. NBO results showed that the anomeric effect is in benefit of the equatorial stereoisomers. The reactions shown in this work are illustrative of the power of anomeric effect and the geometrical relationship of the participating bonds. If the rC-Cl bond is axial, the 1, 4-elimination is avoided altogether. Whereas, if the rC-Cl bond is equatorial, the 1, 4-elimination is performed. These eliminations are rendered possible by the antiperiplanar relationship of the breaking central rC–C bond with the electron pair orbital on the heteroatom and the rC–X bond, X being a leaving group such as a halogen.

Phytochemical components of Allium Jesdianum flower as effective corrosion-resistant materials for Fe(1 1 0), Al(1 1 1), and Cu(1 1 1): DFT study

As anticorrosive materials, natural products such as flower extracts are widely used. In lieu of using the whole product, it is better to apply the isolated phytochemical active component among all existing components in the flower as anticorrosive. Therefore, identifying the component or components responsible for anticorrosion paves the road for its experimental synthesis and effective application. In the present investigation, a comprehensive investigation of three phytochemicals present in Allium Jesdianum (AJ) flower, namely Methyl heptadecanoate (Palmitic acid), Ethyl (9Z,12Z)-octadeca-9,12-dienoate (a-Linolenic acid), and Icosan-1-ol (1-Ecosanol) was characterized using computational methods (DMol3, and Monti Carlo (MC) simulations) to determine the inhibition potentials for corrosion, chemical reactivities, and adsorption behaviors. Isolated forms were characterized by local and global reactivity descriptors such as the energies and distributions of the highest occupied molecular orbitals (HOMOs), Lowest unoccupied molecular orbitals (LUMOs), their gaps, hardness (h), global softness (s), global electronegativity (χ), chemical potential (μ), electrophilicity (ω), nucleophilicity (ε), electron-accepting power (ω-), electron-donating power (ω+), and net electrophilicity (Δω±). A further investigation has been made into the adsorption of three types of industrial metals, namely Fe(110), Al(111), and Cu(111). Based on the most stable adsorption configurations, the three phytochemicals adsorbed parallel to all surfaces. Adsorbate and surfaces interact primarily via chemisorption. In line with this result, the radial distribution function (RDF) has been analyzed. Computed parameters illustrated 1-Ecosanol's superiority over other phytochemicals and justified the reason behind its efficiency.

Study of influence of anomeric effect on conformational preferences using hybrid density functional theory (DFT) and natural bond orbital (NBO) interpretation

For the relationship between thermodynamic parameters, global hardness, global electronegativity, anomeric effect, structural parameters, and structural properties of dodecahedro-spiro [isochromene-3,2'-pyran] (A), dodecahedro-spiro [isothiocromene-3,2'- thiopyran) (B), dodecahedro-spiro [isochroman-3,2'-thiopyran] (C) and dodecahedro-spiro [isothiochrome-3,2'-pyran] (D) computational methods (B3LYP / 6-311 ++ G **) were used. Results show that the calculated Gibbs free energy and enthalpy differences between the axial- and equatorial- stereoisomers [i.e. ΔG = Geq – Gax, ΔH = Heq- Hax] decrease from compound A to compound B and from compound C to compound D. NBO results show that the anomeric effect associated with the electron delocalization is in benefit of the axial-stereoisomers and with the decrease of the anomeric effect, the values of global hardness (η), and global electronegativity (χ), from compound A to compound B and from compound C to Composition D is also decrease. The correlations between the global hardness, global electronegativity, anomeric effect, structural parameters, and thermodynamic parameters [ΔH, ΔG, and ΔS] of compounds A-D have been investigated. Also, it can be concluded that the stability energy obtained from the numerical values of the anomeric effect and the values calculated theoretically (B3LYP / 6-311 ++ G **) confirmed each other.

Multiscale simulations of drug distributions in polymer dissolvable microneedles

Drug distribution in polymer dissolvable microneedles (MNs) is essential for enhancing the efficiency of drug delivery. In the present work, multiscale simulation was applied to study the interactions between polymer and drug molecules, which may influence the drug distribution in the MNs. In this study, Hyaluronic acid (HA) and Polyvinyl alcohol (PVA) were used to fabricate the MNs and sulfonhodamine B (SRB) was selected as the model drug. Firstly, from the quantum chemical calculations, the global electronegativity of HA (3.786 eV) is stronger than that of PVA (2.435 eV), which means that HA owns stronger electronegativity. The Flory-Huggins parameter of HA-SRB is -1.16 which is lower than that of PVA-SRB (53.51), indicating that HA has better compatibility with SRB molecules than PVA. From molecular dynamic simulations, the binding energy of HA-SRB is 93.52 kcal/mol which is much higher than that of PVA-SRB (-2.40 kcal/mol), meaning that HA is easier than PVA to combined with SRB. The mesoscale-based dissipative particle dynamics (DPD) simulations were applied to visualize the diffusion behavior of SRB and the swelling properties of the polymers. All the results indicated that SRB has a lower diffusion coefficient in PVA solution than that in HA solution, which may prevent the diffusion of drug from MN tips to the bases, facilitating the fabrication of MNs with drug concentrated MN tips. Finally, the SRB loaded PVA and HA MNs were prepared and the experimental results are consisted with the simulation results.

Understanding Inhibition of Steel Corrosion by Some Potent Triazole Derivatives of Pyrimidine through Density Functional Theory and Molecular Dynamics Simulation Studies

Density Functional Theory (DFT) calculation at B3LYP level of theory and 6-31G* basis set was applied on some triazole derivatives of pyrimidine which led to the optimization of their structures, generation of electronic and other important Quantum chemical descriptors such as the energy of the highest occupied molecular orbital (EHOMO), the energy of the lowest unoccupied molecular orbital (ELUMO), energy band gap (ΔE), Dipole Moment (μ), chemical hardness (η), chemical softness (σ), global electronegativity() and number of transferred electrons () using SPARTAN’14 Software. The obtained results shows a good correlation between the chemical structures of the inhibitors and their experimental inhibition efficiencies (%IEs). The ranking of these efficiencies (%IEs) nicely matched with the order of a good number of the generated descriptors but with a varying degree of correlation as majority of the descriptors indicates that I-4 is the best inhibitor among the data set. Furthermore, molecular dynamic (MD) simulations were carried out to search the best adsorption configuration of the inhibitor on the steel (1 1 0) surface using Material Studio 8.0. The obtained results of MD simulations suggest that the interaction was as a results of the chemical adsorption on the steel surface, since the binding energy > 100 Kcalmol-1 for all the inhibitors and the best adsorption energy was found to be -488.07 Kcalmol-1 (I-4). This observation are in good agreement with the DFT results and the experiment findings. Thus; this study provides a valuable approach and new direction to novel steel corrosion inhibitor discovery.

Correlations between hardness, electronegativity, anomeric effect associated with electron delocalizations and electrostatic interactions in 1,4,5,8-tetraoxadecalin and its analogs containing S and Se atoms

Hybrid density functional theory (B3LYP/6-311++G∗∗) based method and natural bond orbital (NBO) interpretation were used to investigate the correlations between the global hardness (η), global electronegativity (χ), anomeric effect associated with electron delocalization and electrostatic model associated with dipole–dipole interactions (four important conceptual descriptor in chemistry and physics) in 1,4,5,8-tetraoxadecalin (1), 1,4,5,8-tetrathiadecalin (2) and 1,4,5,8-tetraselenadecalin (3). B3LYP/6-311++G∗∗ results showed that the calculated Gibbs free energy and corrected electronic energy differences between the cis- and trans-stereoisomers [i.e. ΔG=Gtrans−Gcis, ΔEo=Eo(trans)−Eo(cis)] decrease from compound 1 to compound 3. On the other hand, the global hardness (η) differences between the cis- and trans-stereoisomers (i.e. Δ[η(cis)−η(trans)]) decrease from compound 1 to compound 2 but increase from compound 2 to compound 3. Accordingly, the variation of ΔG=Gtrans−Gcis, ΔEo=Eo(trans)−Eo(cis) parameters from compound 1 to compound 3 cannot be justified by the variation of their corresponding global hardness. Therefore, compounds 2 and 3 do not obey the maximum hardness principle. Interestingly, the calculated global electronegativity (χ) differences between the cis- and trans-stereoisomers (i.e. Δ[χ(cis)−χ(trans)]) decrease from compound 1 to compound 3. NBO results showed that the anomeric effect associated with the electron delocalization is in favor of the cis stereoisomers. Effectively, with the decrease of the anomeric effect, ΔG=Gtrans−Gcis, ΔEo=Eo(trans)−Eo(cis) parameters decrease from compound 1 to compound 3. Therefore, the variations of the anomeric effect and global electronegativity explain the variations of ΔG=Gtrans−Gcis, ΔEo=Eo(trans)−Eo(cis) parameters from compound 1 to compound 3. It should be noted that the variation of the calculated dipole moment differences between the cis and trans stereoisomers [i.e. Δ(μ(cis)−μ(trans)] does not justify the variation of ΔG=Gtrans−Gcis, ΔEo=Eo(trans)−Eo(cis) parameters from compound 1 to compound 3. The total steric exchange energy differences between the cis- and trans-stereoisomers (Δ[TSEEcis−TSEEtrans]) increase from compound 1 to compound 3 which in the trend observed for the anomeric effect and global electronegativity. The correlations between the global hardness, global electronegativity, anomeric effect, zero point energies, electrostatic model, structural parameters, corrected electronic energies (ΔEo), and thermodynamic parameters [ΔH, ΔG and ΔS] of compounds 1–3 have been investigated.

Electronic structure and reactivity in water splitting of the iron oxide dimers and their hexacarbonyls: A density functional study

The iron oxide dimers (FeO)2 and their peroxide isomers are studied with the B3LYP density functional as bare clusters and as hexacarbonyls. Among the bare clusters the planar four-member ring structures are more stable than the non-planar ones and the rhombic dioxide Fe2O2 with antiferromagnetically ordered electrons on iron centers is the global minimum. Water adsorption on the bare diiron dioxide is exothermic, but dissociation does not occur. Carbonylation favors a non-planar Fe2O2 ring for both the dioxides and the peroxides and high electron density at the Fe centers is induced, evidenced by the natural charge distribution, the high proton affinity, and the values of global electronegativity and hardness. The iron dioxide hexacarbonyl Fe2O2(CO)6 is diamagnetic in the state of the global minimum. It is separated from the next low-lying triplet state by a small energy gap of 0.22 eV. Time-dependent density functional theory methods were applied to examine electron excitations from the ground state to the low-lying triplet states in the hexacarbonyls and their adsorption complexes with water. Singlet-to-triplet state excitations occur via ligand-to-metal charge transfer in the hexacarbonyls; in the adsorption complexes excitations from the oxygen lone pairs to the adsorption center also occur and they appear in the IR-visible region. The lowest energy singlet and triplet state reaction paths for water splitting were followed. On the singlet potential energy surface (PES), water splitting is spontaneous, while for the triplet PES an activation barrier of 14.1 kJ mol(-1) was determined.

Molecular models of zinc phthalocyanines: semi-empirical molecular orbital computations and physicochemical properties studied by molecular mechanics simulations

A bstract To build 3D-molecular models of Zinc-phthalocyanines (ZnPc) and to study their diverse chemical and photosensitization properties, we performed quantum mechanical molecular orbital (MO) semi-empirical (AM1) computations of the ground, excited singlet and triplet states as well as free radical (ionic) species. RHF and UHF (open shell) geometry optimizations led to near-perfect symmetrical ZnPc. Predicted ionization potentials (IP), electron affinities (EA) and lowest electronic transitions of ZnPc are in good agreement with the published experimental and theoretical data. The computation-derived D4h/D2h-symmetry 3D-structures of ground and excited states and free radicals of ZnPc, together with the frontier orbital energies and Mulliken electron population analysis enabled us to build robust molecular models. These models were used to predict important chemical-reactivity entities such as global electronegativity ( χ ), hardness ( η ) and local softness based on Fukui-functions analysis. Examples of molecular mechanics (MM) applications of the 3D-molecular models are presented as approaches to evaluate solvation free energy (ΔG0)solv and to estimate ground- and excited- state oxidation/reduction potentials as well as intermolecular interactions and stability of ground and excited state dimers (exciplexes) and radical ion-pairs.

Comparing homogeneous and heterogeneous acid catalysts by a density-functional based sensitivity analysis of their interaction with carbenium ions

An attempt has been made to develop a quantitative comparison of the properties of homogeneous and heterogeneous catalyst systems. The bond formation, and its projected covalent character, of a carbenium ion with the surface of zeolites and with water molecules in solution served as a basis to collect quantitative data. These data are the global electronegativity and hardness and the local softness (reactivity parameter of atoms-in-molecules) as these can be calculated for solids and molecules in the EEM formalism. A consistent model could be developed for a quantitative and qualitative comparison. It shows that generally, hydrated carbenium ions remain more ionic than those interacting with the surface of silicates or zeolites.