Molecular Ionization Potentials Research Articles

A theoretical and experimental study: the influence of different standards on the determination of total phenol content in the Folin–Ciocalteu assay

With the aim of choosing an appropriate standard for determining total phenol content (TPC) in food extracts, a theoretical study was done to demonstrate the electronic properties of nine phenolic compounds. Besides, TPC of three different tea extracts was determined by the Folin–Ciocalteu (F–C) assay with nine phenolic compounds as the standards. The frontier molecular orbitals (FMO), molecular electrostatic potential (MEP) and ionization potential (IP) of these standards were calculated with density functional theory. Results indicated the active sites of the nine standards by FMO and MEP. Moreover, the IP value of epigallocatechin gallate was about 15% lower than that of epigallocatechin, indicating that the 3-galloy group at C ring rendered a higher reactivity in the F–C assay. TPC of green tea measured by epicatechin was about 19% lower than that of gallic acid, suggesting that epicatechin was not an appropriate standard for tea extracts. It is deduced that gallic acid is a comparably good standard among commercial standards (relative standards). However, it is recommended that researchers should not choose a universal standard for all food extracts considering the heterogeneity and diversity of polyphenols in food extracts.

Improved density matrices for accurate molecular ionization potentials

The ionization potential and the other quasiparticle energies of electrons in molecules or solids are often evaluated within the $GW$ approximation. Though this approximation can be considered as a fantastic tradeoff between accuracy and simplicity, there exist ionization potentials of simple molecules that are unacceptably wrong. We derive here a working approximation to the density matrix that we name the $GW$ density matrix. This relatively light approximation improves several physical properties and, in particular, it yields excellent electronic dipoles for the examined molecules. As a direct consequence, the ionization potentials are affected through the change in the electrostatic potential and in the exchange operator. Benchmarking on a set of 34 molecules, we demonstrate that most of the error in the $GW$ ionization potentials is indeed eliminated thanks to this simple addition. This contribution is not a vertex correction, but nevertheless it is crucial when going beyond the standard $GW$.

Prediction of structural, vibrational and nonlinear optical properties of small organic conjugated molecules derived from pyridine

Nonlinear optical (NLO) effects of organic materials are caused by delocalized electrons and large polarization in molecules. In the present work, theoretical study by using the Density Functional Theory (DFT) at B3LYP/6-311G(d,p) level of theory on three types of pyridine derivates 2,6-dimethoxy-3,5-dinitropyridine (M1), 2-methoxy-3-nitropyridine (M2) and 2-methoxy-5-nitropyridine (M3) is reported. The nuclear magnetic resonance (1H and 13C NMR) chemical shifts of the title compounds were calculated using the Gauge Independent Atomic Orbital (GIAO) method and compared to the observed results. Both infrared absorption and Raman are complementary to provide characteristic fundamental vibrations that are necessary for the identification of the molecular structures. Electronic properties such as frontier molecular orbital (HOMO, LUMO), ionization potential (IPad) and electronic affinity (EAad) were determined to get better insight into the molecular properties. Using the Time-Dependent Density Functional Theory (TD-DFT), electronic absorption spectra have been predicted and closely matching the experimental findings. The natural bonding orbital (NBO) calculations were performed in order to elucidate various second order interactions in between the filled and vacant orbitals which are a measure of the intermolecular as well as the delocalization within the molecule. In addition, we have demonstrated that these molecular systems have large first static hyperpolarizabilities and may have potential applications in the development of NLO materials.

Toward of Safer Phenylbutazone Derivatives by Exploration of Toxicity Mechanism.

A drug design for safer phenylbutazone was been explored by reactivity and docking studies involving single electron transfer mechanism, as well as toxicological predictions. Several approaches about its structural properties were performed through quantum chemistry calculations at the B3LYP level of theory, together with the 6-31+G(d,p) basis sets. Molecular orbital and ionization potential were associated to electron donation capacity. The spin densities contribution showed a preferential hydroxylation at the para-positions of phenyl ring when compared to other positions. In addition, on electron abstractions the aromatic hydroxylation has more impact than alkyl hydroxylation. Docking studies indicate that six structures 1, 7, 8 and 13–15 have potential for inhibiting human as well as murine COX-2, due to regions showing similar intermolecular interactions to the observed for the control compounds (indomethacin and refecoxib). Toxicity can be related to aromatic hydroxylation. In accordance to our calculations, the derivatives here proposed are potentially more active as well safer than phenylbutazone and only structures 8 and 13–15 were the most promising. Such results can explain the biological properties of phenylbutazone and support the design of potentially safer candidates.

Technological Characteristics of Ga4 In4 B4 P12 Nanotube for Drugs Carrier

The interaction of drug 5-fluorouracil with (4, 0) single wall Ga4 In4 B4 P12 nanotube with H8 as a carrier have been studied by using quantum mechanics. All of the calculations have been performed using a hybrid density functional theory (DFT) at B3LYP level and 3-21G standard basis set. The optimized structures, total energies, energy gaps, highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO) energy, ionization potentials, electron affinities, chemical potential, global hardness, softness, and electrophilicity index have been investigated. Vibration properties such as reduced mass, force constant, IR and Raman spectra are study.Radial breathing modes (RBM) at vibration is (296.16) cm-1 for carrier nanotube, while for the complex (carrier/5-FU) is (57.10 and 273.23) cm-1. The vibration at (770.99 cm−1) it denote to vibration (movement) drug only without vibration of nanotube. Our results show that the carrier SWNT can act as a suitable drug delivery vehicle for 5-fluorouracil within biological systems.

Combined Experimental and Quantum Chemistry Studies on the pH Dependence of the Adsorption Efficiency of Uranium(VI): Lewis Theory of Acid–Base Reactions in Adsorption Processes

The pH dependence of the adsorption efficiency of uranium(VI) ions by adsorbents was investigated experimentally. Moreover, quantum chemistry calculations were subsequently performed to reveal the vague adsorption mechanisms not clarified experimentally in detail. The highest uptake of uranium(VI) on alginate acid was commonly observed at pH 5 and all the adsorption efficiencies decreased with decreasing pH, whereby uranium(VI) species took on a variety of chemical forms. The tendency was reasonably predicted from the calculations of the highest occupied molecular orbital energy, lowest unoccupied molecular orbital energy, energy gap, ionization potential, electron affinity, absolute electronegativity, hardness, softness, dipole moment, principal polarizabilities, isotropic polarizability, molecular volume, and dielectric constant of uranium(VI) species found in solution with a specific pH. This implies that the speciation of the adsorbate dominates greatly, whereas the adsorbent only plays a minor role i...

Theoretical study on the grafting reaction of maleimide and its derivatives to polyethylene in the UV radiation cross-linking process

Theoretical investigation on the reactions of the maleimide and its derivatives in the UV radiation cross-linking of polyethylene is accomplished by density functional theory. The reaction potential energy surface information of 12 reaction channels is determined at the B3LYP/6-311+G(d,p) level. The highest occupied molecular orbital-lowest unoccupied molecular orbital energy gaps, ionization potentials, and electron affinities of the maleimide and its derivatives are obtained. The calculated results show that the maleimide and its derivatives can be grafted to polyethylene chain during the UV radiation process. In addition, the calculated results also show that the reaction energy barrier of 1,8-bismaleimidotriethylene glycol grafted to polyethylene is lower than that of N-phenylmaleimide, and 1,8-bismaleimidotriethylene glycol can be used as cross-linking agent. The bismaleimide grafted to polyethylene can also be used as space charge inhibitor. This survey for dual function additive is expected to provide reliable information for the development of UV radiation cross-linking polyethylene process and high-voltage insulation cables exceed 500 kV in real application.

The impact of diperfluorophenyl and thienyl substituents on the electronic structures and charge transport properties of the fused thiophene semiconductors

AbstractThe charge transport properties of 3 fused thiophene semiconductors, end‐capped with diperfluorophenylthien‐2‐yl (DFPT) groups (DFPT‐thieno[2′, 3′:4, 5]thieno[3, 2‐b]thieno[2, 3‐d]thiophene (TTA), DFPT‐dithieno[2, 3‐b:3′, 2′‐d]thiophenes (DTT), and DFPT‐thieno[3, 2‐b]thiophene (TT)), are explored via density functional theory (DFT). To gain a better understanding of the impact of diperfluorophenyl and thienyl substituents on the electronic structures and charge transport properties of these molecules, the geometric structures, reorganization energy, frontier molecular orbitals, molecular ionization potentials and electron affinities, absorption spectra of the corresponding molecules including diperfluorophenyl (DFP)‐TTA, DFP‐DTT, DFP‐TT, dithienyl (DT)‐TTA, DT‐DTT, DT‐TT as well as their parent molecules (TTA, DTT and TT) are investigated for comparison. The calculated results show that introducing perfluorophenyl groups to the fused thiophenes could be a good strategy to promote electron transport, while the insertion of additional thiophene rings to DFP‐end‐capped derivatives could further extend the π‐conjugation and enhance the charge transport properties of DFPT‐end‐capped analogs.

The influence of the type of substituents and the solvent on the interactions between different coumarins and selected TEMPO analogues – Fluorescence quenching studies

The interactions between a group of different coumarins {7-hydroxycoumarin, 7-methoxycoumarin, 7-hydroxy-6-methoxycoumarin, 7-amino-4-methylcoumarin, 7-hydroxy-4-methylcoumarin, 7-hydroxy-4-(trifluoromethyl)coumarin} and 2,2,6,6-tetramethylpiperidinyl-N-oxyl (TEMPO) and its C4-substituted derivatives (4-hydroxy-TEMPO, 4-methoxy-TEMPO, 4-carboxy-TEMPO, 4-acetamido-TEMPO, 4-oxo-TEMPO) have been studied mainly in aqueous solutions with the use of spectroscopic techniques – namely UV-Vis absorption as well as steady-state and time-resolved fluorescence spectroscopy – and supported by theoretical calculations of molecular radii and ionization potentials. Since it has been found that the fluorescence intensity of the chosen coumarins is efficiently decreased by the nitroxides, the mechanism of fluorescence quenching has been determined. The work constitutes a continuation of our previous experiments on the interactions between different coumarin derivatives and 4-hydroxy-TEMPO (J Fluoresc 24, 713–718, 2014). The biological significance of this work is proven by the fact that TEMPO nitroxides have already many applications and their detection and quantitative determination under physiological conditions might help to understand the mechanism of an oxidative stress.

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.

On the [2+2] cycloaddition reaction of configurationally locked polyenes – An experimental and theoretical study

This paper provides experimental and theoretical study of reaction of [2 + 2] cycloaddition of substituted α–unsaturated isophorone dyes, involving high resolution electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) tandem mass spectrometric (MS/MS) analysis in solution and in gas–phase (GP) of substituted 3-[2-(X-substituted-phenyl)-vinyl]-5,5-dimethyl-cyclohex-2-enone and configurationally locked polyenes (CLP). The ab initio and density functional theoretical (DFT) examining provides information about molecular geometry, thermodynamics, kinetics and ionization potentials of sixty six isomers of dimeric dyes, including corresponding cis-anti-cis and cis-syn-cis head-to-tail and head-to-head forms. The comparative collision induced dissociation (CID) or collision activated MS and theoretical analyses carried out bring light into the mechanisms of competitive dimerization within the frame of 3-[2-(X-substituted-phenyl)-vinyl]-5,5-dimethyl-cyclohex-2-enone; molecular and environmental factors governing regioselectivity of reaction. The analyses involve both qualitative and quantitative kinetics and thermodynamics of experimental MS data along with corresponding theoretical examining of CLP dimers. As far as 3-[2-(X-substituted-phenyl)-vinyl]-5,5-dimethyl-cyclohex-2-enone and CLP dyes have already found an industrial scale application as non-linear optical materials (NLO) for THz wave generation and detection as well as pharmaceutics for treatment of and preventing of neurodegenerative diseases, this study has a strong transdisciplinary impact to many research fields as well as to still not well understood, but crucial to fields of organic synthesis and catalysis, molecular level fundamentals of chemical reactivity in gas– and condense phases. Following the latter lines of contributions of the work, we might hopefully expect that the prospective highlighted in this study should inspired further research effort devoted to correlative quantitative thermodynamic and kinetic CID mass spectrometric and quantum chemical analyses, which allow to improve the reaction effectiveness depending on the complexity of the wanted CLP scaffolds.

Role of Electron-Donating and Electron-Withdrawing Groups in Tuning the Optoelectronic Properties of Difluoroboron-Napthyridine Analogues.

Five napthyridine-based fluorine-boron (BF2-napthyridine) conjugated compounds have been theoretically designed, and subsequently, their photophysical properties are investigated. The influence of electron-donating and electron-withdrawing groups attached with the N∧C∧O moiety of BF2-napthyridine molecule has been interpreted. The optoelectronic properties, including absorption spectra and emission spectra of the BF2-napthyridine derivatives are studied using density functional theory (DFT) and time-dependent density functional theory (TD-DFT) based methods. Different characteristics, such as HOMO-LUMO gap, molecular orbital density, ionization potential, electron affinity, and reorganization energy for hole and electron, are calculated. All these molecules show excellent π-electron delocalization. TD-DFT results illustrate that the amine-substituted BF2-napthyridine derivative has the highest absorption and emission maxima; it also shows a maximum Stoke shift. These results are well-correlated with the structural parameters and calculated HOMO-LUMO gap. Moreover, it is found that introduction of an electron-donating group into the BF2-napthyridine complex improves the hole transport properties and provides useful clues in designing new materials for organic light emitting diodes (OLED). As a whole, this work demonstrates that electron-donating and electron-withdrawing groups in BF2 derivatives can extend their effectiveness toward designing of OLED materials, vitro cellular studies, ex vivo assays, and in vivo imaging agents.

A thermo-electrodynamic electric field dependent molecular ionization model to design electrical insulation system of HVDC wet-mate connectors under transient conditions

A powerful engineering software tool is elaborated to design proper dimensions/ systems/materials in a wet-mate DC connector under transient conditions. By using this tool, designers can examine various preventive measures to avoid streamer growth or limit it to only glow discharge in the oil portion of a wet-mate DC connector. In this regard, for a compact design of a wet-mate DC connector envisaged in this paper four mitigation methods including 1) using a dielectric solid covering the front portion of the moving contact, 2) increasing the relative permittivity of the dielectric solid, 3) using the dielectric oil with molecular constituents having high molecular ionization potentials, and 4) increasing the radius of curvature of the edge are evaluated.

A rigid planar low band gap polymer PTTDPP-DT-DTT for heterojunction solar cell: a study of density functional theory

A low band gap polymer, PTTDPP-DT-DTT, was studied using density functional theory and time-dependent density functional theory to obtain geometric structures, frontier molecular orbitals, ionization potentials, electron affinities, optical absorption and charge transfer properties in the application of solar cells. Marcus theory was used to calculate the charge separation and recombination rates of the donor and acceptor (D/A) interfaces [(PTTDPP-DT-DTT)2/PC61BM and (PTTDPP-DT-DTT)2/PC71BM]. It was found that with the increase of the conjugated unit of the polymer, the reorganization energies of holes and electrons are both decreased, indicating that the ability for charge transport is enhanced. For D/A interfaces, (PTTDPP-DT-DTT)2/PC61BM and (PTTDPP-DT-DTT)2/PC71BM have appropriate exciton binding energies, and the rate of charge separation is much faster than the rate of charge recombination. The performance of (PTTDPP-DT-DTT)2/PC61BM is better than that of (PTTDPP-DT-DTT)2/PC71BM in the charge transfer process. Simulation of polymer/fullerene solar cells provides a deep understanding of the relationship between structure and performance.

Factors Influencing the Potency of Alzheimer Inhibitors: Computational and Docking Studies.

Density functional theory (B3LYP/6-31G [d]) is performed to study the effect of molecular and electronic structures of the investigated β-secretase 1 (BACE1) Alzheimer's inhibitors on their biological activities and discuss the correlation between their inhibition efficiencies and quantum chemical descriptors. IC50 values of the investigated compounds are mostly affected by the substituted R2 phenyl moiety. The calculations show that the presence of electron withdrawing group increases the half maximal inhibitory concentration (IC50). Structure-activity relationship studies show that the electronic descriptors, energy of high occupied molecular orbital, ΔE, lipophilicity, hardness, and ionization potential index, are the most significant descriptors for the correlation with IC50. Molecular docking simulation is performed to explain the mode of interaction between the most potent drug and the binding sites of the BACE1 target. A good correlation between the experimental and the theoretical data confirms that the quantum chemical methods are successful tools for the discovery of novel BACE1 drugs.

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.

Structure, electronic properties, NBO, NLO and chemi-cal reactivity of bis (1, 4-dithiafulvalene) derivatives: functional density theory study

In this work, through computational study based on density functional theory (DFT/B3LYP) using basis set 6-31G (d,p) a number of global and local reactivity descriptors for a series of molecules containing a TTF function which are bis (1,4-dithiafulvalene) derivatives. They were computed to predict the reactivity and the reactive sites on the molecules. The molecular geometry and the electronic properties in the ground state such as frontier molecular orbital (HOMO and LUMO), ionization potential (I) and electron affinity (A) were investigated to get a better insight of the molecular properties. Molecular electrostatic potential (MEP) for all compounds were determined to check their electrophilic or nucleophilic reactivity. Fukui index, polarizability, hyperpolarizability, second order NLO property and natural bond orbital (NBO) analyses have also employed to determine the reactivity of bis (1,4-dithiafulvalene) derivatives.

Modeling molecular boiling points using computed interaction energies.

The noncovalent van der Waals interactions between molecules in liquids are typically described in textbooks as occurring between the total molecular dipoles (permanent, induced, or transient) of the molecules. This notion was tested by examining the boiling points of 67 halogenated hydrocarbon liquids using quantum chemically calculated molecular dipole moments, ionization potentials, and polarizabilities obtained from semi-empirical (AM1 and PM3) and ab initio Hartree-Fock [HF 6-31G(d), HF 6-311G(d,p)], and density functional theory [B3LYP/6-311G(d,p)] methods. The calculated interaction energies and an empirical measure of hydrogen bonding were employed to model the boiling points of the halocarbons. It was found that only terms related to London dispersion energies and hydrogen bonding proved significant in the regression analyses, and the performances of the models generally improved at higher levels of quantum chemical computation. An empirical estimate for the molecular polarizabilities was also tested, and the best models for the boiling points were obtained using either this empirical polarizability itself or the polarizabilities calculated at the B3LYP/6-311G(d,p) level, along with the hydrogen-bonding parameter. The results suggest that the cohesive forces are more appropriately described as resulting from highly localized interactions rather than interactions between the global molecular dipoles.

Quantitative Structure-Cytotoxicity Relationship of Newly Synthesized Piperic Acid Esters.

Eleven piperic acid esters were subjected to quantitative structure-activity relationship (QSAR) analysis based on their cytotoxicity and tumor-specificity, in order to find their new biological activities. Cytotoxicity against four human oral squamous cell carcinoma cell lines and three oral normal mesenchymal cells was determined by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) method. Tumor specificity (TS) was evaluated by the ratio of the mean 50% cytotoxic concentration (CC50) against normal cells to that against tumor cell lines. Potency-selectivity expression (PSE) value was calculated by dividing the TS value by CC50 against tumor cells. Apoptosis markers were detected by western blot analysis. Physicochemical, structural and quantum-chemical parameters were calculated based on the conformations optimized by force-field minimization. One phenylmethyl ester and five phenylethyl esters showed relatively higher cytotoxicity and tumor specificity, that were significantly modified by introduction of hydroxyl and methoxy groups. On the other hand, phenylpropyl ester, phenylbutyl ester and decyl ester were essentially inactive. (2E,4E)-5-(3,4-methylenedioxyphenyl)-2,4-pentadienoic acid 2-(3,4-dihydroxyphenyl)ethyl ester [4] had the highest TS and PSE values. This compound also stimulated the cleavage of caspase-3, suggesting the induction of apoptosis. TS values were correlated with molecular size, ionization potential, molecular shape, ionization potential and electronegativity. None of the compounds had any anti-HIV activity. Chemical modification of the lead compound may be a potential choice for designing a new type of anticancer drugs.

Accurate Valence Ionization Energies from Kohn-Sham Eigenvalues with the Help of Potential Adjustors.

An accurate yet computationally very efficient and formally well justified approach to calculate molecular ionization potentials is presented and tested. The first as well as higher ionization potentials are obtained as the negatives of the Kohn-Sham eigenvalues of the neutral molecule after adjusting the eigenvalues by a recently [ Görling Phys. Rev. B 2015 , 91 , 245120 ] introduced potential adjustor for exchange-correlation potentials. Technically the method is very simple. Besides a Kohn-Sham calculation of the neutral molecule, only a second Kohn-Sham calculation of the cation is required. The eigenvalue spectrum of the neutral molecule is shifted such that the negative of the eigenvalue of the highest occupied molecular orbital equals the energy difference of the total electronic energies of the cation minus the neutral molecule. For the first ionization potential this simply amounts to a ΔSCF calculation. Then, the higher ionization potentials are obtained as the negatives of the correspondingly shifted Kohn-Sham eigenvalues. Importantly, this shift of the Kohn-Sham eigenvalue spectrum is not just ad hoc. In fact, it is formally necessary for the physically correct energetic adjustment of the eigenvalue spectrum as it results from ensemble density-functional theory. An analogous approach for electron affinities is equally well obtained and justified. To illustrate the practical benefits of the approach, we calculate the valence ionization energies of test sets of small- and medium-sized molecules and photoelectron spectra of medium-sized electron acceptor molecules using a typical semilocal (PBE) and two typical global hybrid functionals (B3LYP and PBE0). The potential adjusted B3LYP and PBE0 eigenvalues yield valence ionization potentials that are in very good agreement with experimental values, reaching an accuracy that is as good as the best G0W0 methods, however, at much lower computational costs. The potential adjusted PBE eigenvalues result in somewhat less accurate ionization energies, which, however, are almost as accurate as those obtained from the most commonly used G0W0 variants.