Local Ionization Potential Research Articles

Comparative catalytic approach of Ag doped ZnO with various nanocarbon materials toward CO2 reduction with magnetic field and carbon form dependence

Graphene oxide (GO) is a compromising catalyst material with a two-dimensional layer of carbon atoms having sp2 hybridization bonded in a hexagonal lattice structure. The gCN is a member of 2D-structured metal-free carbon materials. In this study, GO, gCN, fluorine, and nitrogen treated GO and ZnO-Ag (Ag doped ZnO) loaded carbon nanocomposites were studied. Fluorine and nitrogen treated GO is an up-rising carbon member. It has high stability. Its layer structure possess unique properties due to its C-F (covalent and semi -ionic) and C-N bonds. The computer simulations of all molecules were conducted using the Hartree-Fock function with a 6–311 G* mode on Spartan’14 software. A number of properties like molecule structure, electrostatic potential, local ionization potential, density, HOMO, and LUMO level of the molecules were obtained from computer simulations. Electrochemical CO2 reduction to CH3OH on catalysts was investigated in different electrolysis conditions, such as different electrolytes with UV-light and 0.07 T magnetic core treatment. Results showed that the introduction of ZnO-Ag on carbon nanocomposites improved properties of carbon nanocomposites, leading to a high conversion of CO2 to CH3OH. Methanol production rate was improved by five-times after UV-light (λ = 254 nm) and 0.07 T magnetic core treatment. Faradaic efficiencies of carbon nanocomposites for methanol production through electrochemical reduction of CO2 in bicarbonate buffer and electrolytes were found to be 67.48% and 58.93% (compared to Ag/AgCl) at − 2.7 V, respectively. Charge carrier properties and morphology profile of these nanocomposites were also analyzed.

An interesting possibility of forming special hole stepping stones with high-stacking aromatic rings in proteins: three-π five-electron and four-π seven-electron resonance bindings.

Long-range hole transfer of proteins plays an important role in many biological processes of living organisms. Therefore, it is highly useful to examine the possible hole stepping stones, which can facilitate hole transfer in proteins. However, the structures of stepping stones are diverse because of the complexity of the protein structures. In the present work, we proposed a series of special stepping stones, which are instantaneously formed by three and four packing aromatic side chains of amino acids to capture a hole, corresponding to three-π five-electron (π:π∴π↔π∴π:π) and four-π seven-electron (π:π∴π:π↔π:π:π∴π) resonance bindings with appropriate binding energies. The aromatic amino acids include histidine (His), phenylalanine (Phe), tyrosine (Tyr) and tryptophan (Trp). The formations of these special stepping stones can effectively reduce the local ionization potential of the high π-stacking region to efficiently capture the migration hole. The quick formations and separations of them promote the efficient hole transfer in proteins. More interestingly, we revealed that a hole cannot delocalize over infinite aromatic rings along the high π–π packing structure at the same time and the micro-surroundings of proteins can modulate the formations of π:π∴π↔π∴π:π and π:π∴π:π↔π:π:π∴π bindings. These results may contribute a new avenue to better understand the potential hole transfer pathway in proteins.

Substituted naphthalene reaction rates with peroxy-acid treatment: prediction of reactivity using PEST

ABSTRACTPersistent organic contaminants in the environment pose an environmental risk due to widespread occurrence and toxic properties. Advanced oxidation processes (AOPs) are treatment methods that have been used to successfully degrade organic contaminants in water, soil, sediments and sludge. Reaction rate constants (k) for peroxy acid treatment of 10 substituted naphthalene compounds were determined. The treatment method utilized acetic acid, hydrogen peroxide and a sulphuric acid catalyst to degrade the polyaromatic structures found in the compounds. Molecular structures of the selected compounds were derived at the B3LYP/6-31G* level of theory. Property-encoded surface translator (PEST) descriptors were calculated from B3LYP/6-31G* optimized structures and were found to have significant levels of correlation with k. Models using minimum local ionization potential (PIP.MIN) and a histogram [bin] of the gradient of the K electronic kinetic energy normal to the isosurface (DKN) were evaluated and found to agree within 10% of experimentally derived values of k in most instances. Results show that a combination of PEST descriptors could be used to predict reactivity by the peroxy-acid process. The PEST technology could prove to be a valuable asset for effective remediation design by predicting reaction outcomes for substituted naphthalene compounds and possibly other hydrophobic organic compounds (HOCs).

A theoretical investigation of sugar and phosphate contributions to the activation barriers of guanine methylation by carcinogenic methane diazonium ion

Feedback from electrostatic potential and local ionization potential maps provides evidence that in the gas phase electrostatic interactions cause the activation barriers of guanine methylation by methane diazonium ion at the N7 site to increase upon addition of sugar and phosphate moieties, from 24.6 kcal/mol with the 6–31 + G∗ basis set to 29.87 kcal/mol with the 6–311 + G (2df, 2p) basis set at the DFT/B3LYP-D3 level of theory. Aqueous activation barriers strongly depend on the interaction of guanine with discrete number of water molecules and, in implicit water, they lie between 4.37 for free guanine to 5.39 kcal/mol for syn-dGMP−

Application of Hirshfeld surfaces, semiempirical calculations and molecular dynamics analysis to study the intermolecular interactions, reactivity and dynamics of two polyoxometalate compounds

A large study of the theoretical properties was reported in this work. The Hirshfeld surfaces analysis has confirmed that the intermolecular interactions in the crystal packing of K5[HP2Mo5O23]·10H2O (1) and [C7H7N2]2[H2P2Mo5O23]0.5·3.5H2O (2) compounds has been dominated by hydrogen bonding which makes the hydrogen atoms of polyanions, water molecules and organic cations play the most important role in the stability of crystal structures. Applying semiempirical calculations on the compounds, we get information about their reactivity. In this context, several discussions concerning the frontier molecular orbital, electron density, molecular electrostatic potential, thermodynamic properties and local ionization potential have been mentioned. Also, the molecular dynamics analysis performed on the compounds structures allows us to study the dynamics of this type of compounds.

Exploration of selected electronic characteristics of half-sandwich organoruthenium(II) β-diketonate complexes.

Based on experimental work, 12 half-sandwich organoruthenium(II) complexes with p-cymene and various substituted β-diketonates (acac) modified by several functional groups were explored. These complexes were optimized at the B3PW91/6-31 + G(d)/PCM/UFF computational level with the Ru atom described by Stuttgart pseudopotentials. The electron density analysis was performed using the B3LYP/ 6-311++G(2df,2pd)/DPCM/scaled-UAKS model. Electrostatic and averaged local ionization potential were explored and extremes on 0.001 e/a.u.3 isodensity surfaces discussed. Natural population analysis partial charges and electron densities in bond critical point of the key Ru(II) coordination bonds were determined. There was a clear correlation between the results obtained and experimentally known anticancer descriptors. Graphical abstract Top Average local ionization potential (ALIP) of half-sandwich organoruthenium(II) β-diketonate complex, bottom IC 50 of b-series for ovarian cancer and Ru-P distances (in Å).

Structures, electronic properties, reactivity and dynamic studies of three new polyoxometalate compounds.

We report a complex study on the crystal structures, electronic properties, reactivity and dynamics of three polyoxometalate compounds (C6NH8)4[H2P2Mo5O23]·5H2O (1), (C2H8N)5[HP2Mo5O23]·(C3H9NO2)0.5·(H2O)1.5 (2) and (C2H8N)3[PMo12O40]·(H2O)0.34 (3). These compounds were synthesized using a solution method and characterized by single-crystal X-ray diffraction. Crystallography confirmed three distinct symmetries P1[combining macron], P21/c and R3[combining macron]c for 1, 2, and 3, respectively, and unit cell constants a = 12.5609(2) Å, b = 13.2470(2) Å, c = 14.0353(2) Å, α = 107.1568(14)°, β = 101.2854(13)°, γ = 92.1445(14)° for 1, a = 15.8583(6) Å, b = 17.3578(5) Å, c = 14.8499 (4) Å, β = 114.933(3)° for 2, and a = 16.3798(3) Å, c = 50.2781(5) Å for 3. Semi-empirical calculations applied on the compounds provided information about their reactivity and electronic structures. In this context, several discussions concerning the frontier molecular orbitals, molecular electrostatic potential, thermodynamic properties and local ionization potential were mentioned. We also conducted molecular dynamics analysis in order to elucidate the dynamics of cations and anions and their energy variation.

Hirshfeld surfaces analysis and Theoretical calculations of β-Octamolybdate compound

ABSTRACTThe nature of [(C7H7N2)3(NH4)]2[Mo8O26]2·4H2O intermolecular interactions has been analysed through Hirshfeld surfaces and 2D fingerprint plots. So it is explicit that presence of amine groups and water molecules reveals that O···H/H···O intermolecular interactions are the most abundant contacts in the crystal packing. Semi-empirical calculation has been done to study the theoretical properties of this polyoxometalate compound. In this study, we have investigated several properties such as frontier molecular orbital, molecular electrostatic potential, electron density, thermodynamic properties, dipole moment, QSAR properties and local ionization potential. This work provided helpful information for the study of electronic structure and molecular properties.

Polycyclic aromatic hydrocarbon reaction rates with peroxy-acid treatment: prediction of reactivity using local ionization potential

Property-Encoded Surface Translator (PEST) descriptors were found to be correlated with the degradation rates of polycyclic aromatic hydrocarbons (PAHs) by the peroxy-acid process. Reaction rate constants (k) in hr-1 for nine PAHs (acenaphthene, anthracene, benzo[a]pyrene, benzo[k]fluoranthene, fluoranthene, fluorene, naphthalene, phenanthrene, and pyrene) were determined by a peroxy-acid treatment method that utilized acetic acid, hydrogen peroxide, and a sulphuric acid catalyst to degrade the polyaromatic structures. Molecular properties of the selected nine PAHs were derived from structures optimized at B3LYP/6-31G(d) and HF/6-31G(d) levels of theory. Properties of adiabatic and vertical ionization potential (IP), highest occupied molecular orbitals (HOMO), HOMO/lowest unoccupied molecular orbital (LUMO) gap energies and HOMO/singly occupied molecular orbital (SOMO) gap energies were not correlated with rates of peroxy-acid reaction. PEST descriptors were calculated from B3LYP/6-31G(d) optimized structures and found to have significant levels of correlation with k. PIP Min described the minimum local IP on the surface of the molecule and was found to be related to k. PEST technology appears to be an accurate method in predicting reactivity and could prove to be a valuable asset in building treatment models and in remediation design for PAHs and other organic contaminants in the environment.

Charge-Transfer Localization in Molecularly Doped Thiophene-Based Donor Polymers

We provide evidence for highly localized charge-transfer complex formation between a series of thiophenetetrafluorobenzene donor copolymers and the molecular acceptor tetrafluorotetracyanoquinodimethane (F4TCNQ). Infrared absorption spectra of diagnostic vibrational bands in conjunction with theoretical modeling show that one acceptor molecule undergoes charge transfer with a quaterthiophene segment of the polymers, irrespective of the macroscopic polymer ionization energy and acceptor concentration in thin films. The interaction is thus determined by the “local ionization potential” of quaterthiophene. Consequently, using materials parameters determined on a macroscopic length scale as a guideline for making new charge-transfer complex materials for high electrical conductivity turns out to be oversimplified, and a reliable material design must take into account property variations on the nm scale as well.

Photoemission Spectroscopy of Tethered CdSe Nanocrystals: Shifts in Ionization Potential and Local Vacuum Level As a Function of Nanocrystal Capping Ligand

We report the characterization of the frontier orbital energies and interface dipole effects for bare and ligand-capped 3.6 and 6.0 nm diameter CdSe nanocrystals (NC) tethered to smooth gold substrates, using He(I) and He(II) UV photoemission spectroscopy. Changes in the ionization potential (IP) of the NCs and local effective work function of the films were explored as a function of the dipolar nature of the NC capping ligands. The addition of thiol-capping ligands 1-hexanethiol, 1-benzenethiol, and 4-fluorothiophenol to both sizes of NCs produces negligible shifts in energy offset between the high kinetic energy edge of the CdSe NCs and the gold substrate Fermi energy. However, the local vacuum level and IP of the nanocrystal layer are altered by as much as 0.3 eV. We demonstrate the importance of determining both the local vacuum level and the high kinetic energy edge of a tethered NC sample. These studies demonstrate a method that can be used in the future to characterize the frontier orbital energy offsets for modified or unmodified nanocrystalline films, in which the NCs are incorporated into host materials, for applications ranging from photovoltaics to light-emitting diodes.

The time scale for electronic reorganization upon sudden ionization of the water and water-methanol hydrogen bonded dimers and of the weakly bound NO dimer

When the valence molecular orbital is localized sudden ionization can cause the nascent hole to move rapidly even before any relaxation of the geometry occurs. Hydrogen bonded clusters offer suitable test systems where the hole is initially localized on one moiety. Computational studies are reported for the water dimer and water-methanol bimer. The local ionization potential of water is different in the methanol-water and water-methanol conformers and this difference is very clearly reflected in the dynamics of charge migration. For the NO dimer the results are that its structure is symmetric so that the two NO molecules are equivalent and do not exhibit the required localization. The role of symmetry is also evident in the charge propagation for holes created in different orbitals. Localization of the initial hole distribution even if absent in the bare molecule can still be induced by the intense electric field of a sudden photoionization. This effect is computationally studied for the NO dimer in the presence of a static electric field.

New molecular descriptors based on local properties at the molecular surface and a boiling-point model derived from them.

New molecular descriptors based on statistical descriptions of the local ionization potential, local electron affinity, and the local polarizability at the surface of the molecule are proposed. The significance of these descriptors has been tested by calculating them for the Maybridge database in addition to our set of 26 descriptors reported previously. The new descriptors show little correlation with those already in use. Furthermore, the principal components of the extended set of descriptors for the Maybridge data show that especially the descriptors based on the local electron affinity extend the variance in our set of descriptors, which we have previously shown to be relevant to physical properties. The first nine principal components are shown to be most significant. As an example of the usefulness of the new descriptors, we have set up a QSPR model for boiling points using both the old and new descriptors.

On the band gap in peptide ?-helices

The variation in the band gap of a (Gly)30 α-helix with position in the peptide sequence has been investigated using AM1 semiempirical molecular orbital (MO) theory within an extensive singles configuration interaction (CI) treatment. The dipole-charge interaction along the length of the helix results in the highest local electron affinity near the N-terminus and the lowest local ionization potential near the C-terminus. The calculations suggest that the band gap, measured as the difference between the local ionization potential and electron affinity, decreases from the C-terminus to the N-terminus for the model (Gly)30 α-helix in vacuo. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 79: 120–124, 2000

Charge migration and control of site selective reactivity: The role of covalent and ionic states

A many-electron description of charge migration along a molecular backbone is discussed. Reference is made to site selective reactivity and the recent experiments of Weinkauf and Schlag on the dissociation of peptide ions following a localized ionization. The use of many-electron states allows a classification of the charge migration pathways through either covalent or ionic states. Electron correlation is introduced via Coulomb repulsion of electrons of opposite spins à-la Hubbard. Complete configuration interaction is implemented using the unitary group basis of Paldus. The primary factor determining charge migration is found to be the local ionization potential. It is shown that, at lower levels of excitation, the majority of possible initial states which describe localized ionization at one end of the chain lead to a preferential dissociation at the other end of the chain.

QSPR analysis of HPLC column capacity factors for a set of high-energy materials using electronic van der waals surface property descriptors computed by transferable atom equivalent method

The new transferable atom equivalent (TAE) method for rapid molecular electron density reconstruction was used to compute a set of molecular surface property descriptors. These descriptors were then used to construct HPLC column capacity factor PLS models for a series of high-energy materials. The new TAE-derived surface property indices are also available from ab initio or semiempirical wave functions, but the speed and accuracy of TAE reconstruction make it the method of choice for obtaining these indices. The new QSPR indices are based upon the extrema, distributions, and surface integrals of the electronic kinetic energy density, the Politzer average local ionization potential (pip), and the electrostatic potential, as well as the rates at which these properties change normal to the 0.002-e/au3 molecular surface. The distribution of the properties were recorded as surface histograms. While property extrema and surface integral averages proved to be descriptive, the most useful new indices were found to correspond to histogram bin data computed for K and G surface kinetic energy densities. All-subsets-regression modeling showed that when mixtures of traditional connectivity indices, theoretical linear solvation energy relations (TLSERs), and generalized interaction properties functions (GIPFs) were included with the new indices in the variable sets, the new indices were consistently involved in the best 2% of the capacity factor models. Peak retention time data from two different columns were examined (a Hypersil “CPS” cyanoalkylated column and a standard reverse-phase Hypersil “ODS” column) using a phosphate buffer mobile phase at pH 3.0. The result were compared to an earlier TLSER correlation analysis of the same data by Lowrey and Famini. The TAE-generated surface property descriptors were shown to provide superior PLS models for both sets of columns and conditions. © 1997 by John Wiley & Sons, Inc.