Quantum Chemical Quantities Research Articles

Using small database and energy descriptors to predict molecular thermodynamic energies through mediated learning models

Delta machine learning (DML) models have paved a new way to obtaining high fidelity ab initio simulation results of materials by using quantities with lower computational cost as learning materials. However, the low out-of-sample extrapolative ability and the requirement of large training sets have limited broader applications of conventional DML models. In this work, we proposed the concept of non-trivial electron energy, an intermediary energy quantity decoded from the electron total energy but exhibiting high Pearson's correlation with various thermodynamic energies, to build up mediated machine learning (MML) models. By hybridizing the intermediary non-trivial electron energy (N) with a bond descriptor (B) and a spatial matrix (S) of organic molecules, our integrated NBS descriptor shows excellent predictive power of thermodynamic energies with errors close to 1 kcal/mol for MML models when trained by a database with 100 entries and tested by a database with 500 entries. Moreover, adding supplemental sets with 10 ∼ 20 entries into the original training set could greatly improve the out-of-sample extendibility of NBS MML models, such as the molecules with obviously larger size, with disparate bond-type, and even with different elemental compositions. The method of mediated learning provides alternative ways to breakthrough limitations of traditional DML models and can be applied conveniently to study formation enthalpy, thermodynamic energy barriers, multi-dimensional Gibbs free energy surface, and other quantum chemical quantities related to materials' internal energy, enthalpy, and free energy under various conditions at tunable training cost, prediction efficiency, and accuracy.

Electrochemical investigations and theoretical studies of biocompatible niacin-modified carbon paste electrode interface for electrochemical sensing of folic acid

The modified electrode–analyte interaction is critical in establishing the sensing mechanism and in developing an electrochemical sensor. Here, the niacin-modified carbon paste electrode (NC/CPE) was fabricated for electrochemical sensing applications. The two stable structures of the niacin were optimized and confirmed by the absence of negative vibrational frequency, at B3LYP and B3LYP-GD3BJ level and 6–311 g** basis set. The physical and quantum chemical quantities were used to explain the molecular stability and electronic structure-related properties of the niacin. The natural bond orbital (NBO) analysis was performed to disclose the donor–acceptor interactions that were a critical role in explaining the modifier–analyte interaction. The fabricated NC/CPE was used for the determination of folic acid (FA) in physiological pH by cyclic voltammetry (CV) method. The limit of detection (LOD) for FA at NC/CPE was calculated to be 0.09 µM in the linear concentration range of 5.0 µM to 45.0 µM (0.2 M PBS, pH 7.4) by CV technique. The analytical applicability of the NC/CPE was evaluated in real samples, such as fruit juice and pharmaceutical sample, and the obtained results were acceptable. The HOMO and LUMO densities are used to identify the nucleophilic and electrophilic regions of niacin. The use of density functional theory-based quantum chemical simulations to understand the sensory performance of the modifier has laid a new foundation for fabricating electrochemical sensing platforms.

New Hybrid (E)‐4‐((pyren‐1‐ylmethylene)amino)‐N‐(thiazol‐2‐yl)benzenesulfonamide as a Potential Drug Candidate: Spectroscopy, TD‐DFT, NBO, FMO, and MEP Studies**

AbstractA novel pyrene‐sulfathiazole‐based potential drug candidate 3 was designed, successfully synthesized by a condensation reaction of pyrenecarboxaldehyde (1) with sulfathiazole (2) in good yield, and fully characterized by NMR, IR, UV‐Vis, and HRMS spectroscopic techniques. The TD‐DFT/B3LYP calculations displayed that the recorded peaks at 396, 377, 280, and 236 nm were due to the mainly n‐π* and partially π‐π* transitions that occurred on pyrene, azomethine, and sulfathiazole moieties. The NBO results disclosed that the electron delocalizations happened onto sulfathiazole, aromatic rings (pyrene and Ph‐), and azomethine groups had the main responsibility of the lowering stabilization energy of compound 3. The NMR shifts were calculated by using the GIAO approaches in the DMSO phase and compared with the relevant data recorded. The thermodynamic and quantum chemical quantities were used for elucidating the physicochemical properties and reactivity behavior, in THF, DMSO, and water simulation environments. Accordingly, the calculated DM (D) and α (au) order of compound 3 were calculated in the order of vacuum<THF<DMSO<water, which indicated that the stability and thus reactivity of the compound strongly depended on the solvent environment. The FMO studies implied that the electron‐donating possibility of compound 3 was dominant to the electron‐accepting potency. In this work, the SMD version of IEFPCM was used in solvent media simulations.

Estrogenic Active Stilbene Derivatives as Anti-Cancer Agents: A DFT and QSAR Study.

Exploring different quantum chemical quantities for lead compounds is an ongoing approach in identifying crucial structural activity related features that are contributing into their biological activities. Herein, activity-related quantum chemical calculations were performed for the selected estrogenic stilbene derivatives using density functional theory (DFT) with B3LYP functional and 6-311++G** basis set. In addition, specific activity-related geometry-independent drug-like properties are discussed for these derivatives. To obtain the mathematical model that correlates the chemical descriptors with their measured estrogenic activities, the quantitative structure activity relationship (QSAR) is established using multiple linear regression (MLR) and support vector regression (SVR) methods. Satisfactory fit with a reasonable regression correlation coefficient (${\rm{R}}^{2}= 0.78$R2=0.78) between predicted and experimental $pEC_{50}$pEC50 values is observed using MLR method. The present study identifies the essential physicochemical descriptors that effectively contribute in the estrogenic activity. The applied approach provides helpful insight into the designing novel estrogenic agents with improved anticancer activities.

Estimation of Lattice Enthalpies of Ionic Liquids Supported by Hirshfeld Analysis.

New measurements of vaporization enthalpies for 15 1:1 ionic liquids are performed by using a quartz-crystal microbalance. Collection and analysis of 33 available crystal structures of organic salts, which comprise 13 different cations and 12 anions, is performed. Their dissociation lattice enthalpies are calculated by a combination of experimental and quantum chemical quantities and are divided into the relaxation and Coulomb components to give an insight into elusive short-range interaction enthalpies. An empirical equation is developed, based on interaction-specific Hirshfeld surfaces and solvation enthalpies, which enables the estimation of the lattice enthalpy by using only the crystal-structure data.

Some beta-Aminoketone Derivatives as Corrosion Inhibitors for Nickel in Hydrochloric Acid Solution

The use of some β-aminoketone derivatives as corrosion inhibitors for nickel in 2 M acid chloride solution was investigated by gravimetric and galvanostatic polarization techniques. It was found that the investigated compounds behave as inhibitors for nickel dissolution and their inhibition efficiencies increase by the addition of iodide ions. Also, the adsorption isotherms were studied and it was found to follow the Frumkin's adsorption isotherm. By increasing the temperature of the corrosive medium containing different concentrations of the tested inhibitors, the corrosion rate of nickel increases, indicating that these inhibitors are physically adsorbed on the metal surface. Finally, some quantum chemical quantities such as HOMO, LUMO and dipole moment of the inhibitors were calculated and correlated with the rate of corrosion.

New Keys for Old Keywords. Case Studies within the Updated Paradigms of the Hybridization and Aromaticity

The recovery of the basic qualitative concepts of the chemical language into the quantum treatment is a rather challenging problem because the desirable simplicity is easily lost in the black box of technical mechanisms of computation, e.g. among the ingredients of post-orbital methods of correlation effects. We present here several clues for bringing the hybridization and aromaticity concepts in a nontrivial and non-redundant conjunction with both quantum chemical quantities and the chemists’ tools of intuition. A rather inedited structural correlation that works as an experimental proof of the hybridization is discussed. The main idea is to exploit the intermediate symmetries, where the hybridization is no longer tautological because of the symmetry. For instance in a MA2B2 tetrahedron, if the hybridization not existed as real engine of the stereochemistry, the AMA and BMB angles should be arbitrarily independent. In turn, if the hybridization acts, there is a certain trigonometric relationship between the two angles. The existence of this correlation is noticed and discussed in prototypic series. A new understanding and analysis of strain in cycles and clusters (with particular emphasis on organometallic structures) is constructed as continuation of discussed models. The problem of aromaticity in chelates, rings and clusters is approached by means of specific models. The careful attention devoted to the structural details rewards the theory with an extended understanding of various bonding regimes and at the same time enriches the experimentalists’ perspectives beyond the geometric description and taxonomic systematization of X-ray molecular structure and crystal packing data.

Polyamine류와 Imidazole 유도체가 배위된 Ni(Ⅱ) 착물의 저해 효과에 관한 분자궤도함수론적 해석

폴리아민과 이미다졸 유도체에 대해서 AM1, PM3, ZINDO/1법으로 형성엔탈피(<TEX>${\Delta}H_f$</TEX>), HOMO, LUMO에너지 및 쌍극자힘(<TEX>${\mu}_D$</TEX>) 값을 얻었다. 이들 리간드를 Ni(II)에 배위시킨 Ni(II)착물의 저해활성효과를 ZINDO/1(Zerner''s Intermediate Neglect of Differential Overlap No.1)법으로 조사하였다. Ni(II)착물의 중심금속의 알짜전하 값이 0.03 이상과 형성엔탈피가 음의 값으로 300 eV이상에서 실험적인 저해활성 값이 나타남을 보였다. 그 결과 Ni(II)착물은 불안정한 5배위 사각피라미드형인 [Ni(dpt)(tn)]<TEX>$^{2+}$</TEX>(dpt=3,3''-diaminodipropylamine)(tn=1,3-diaminopropane)와 일그러진 사면체인 [Ni(N-PropIm)<TEX>$_2$</TEX>(NCS))<TEX>$_2$</TEX>](N-PropIm=N-Propylimidazole)를 제외한 착물에서는 저해활성 값이 나타남을 알 수 있었다. Quantum chemical quantities, enthalpy of formation(<TEX>${\Delta}H_f$</TEX>), HOMO and LUMO energy, and dipole moment(<TEX>${\mu}_D$</TEX>) were acquired by AM1, PM3, and ZINDO/1 methods for polyamines and imidazole derivatives. The investigation of the inhibitory activity on some Ni(II) complexes with polyamines and imidazole derivatives is performed by ZINDO/1 calculations. It was found that experimental inhibitory activity(IA) appeared when the value of net charge and enthalpy of formation were over 0.03 and -300 eV, respectively for Ni(II) complexes. These results showed that the Ni(II) complexes have exception on the following very unstable compounds: square pyramidal [Ni(dpt)(tn)])]<TEX>$^{2+}$</TEX>(dpt=3,3'-diaminodipropylamine)(tn=1,3-diaminopropane) and distorted tetrahedral [Ni(N-PropIm))<TEX>$_2$</TEX>(NCS))<TEX>$_2$</TEX>](N-PropIm=N-Propylimidazole).

Topological Reference Systems for the Heterocyclic Conjugated Compound

General methods to get propagators under the Huckel approximation are presented for the topological reference systems of the heterocyclic conjugated molecules using the perturbation technique. We reinvestigate the off-diagonal elements of the propagators for the topological reference systems and define a new quantum chemical index for predicting the strength of a bond. Where the topological ref erence systems are the hypothetical reference systems for which construction of all substructural details of the systems, except the cycles, should be taken into account. This method enables us to discuss the influences of the heteroatom on the energy stabilization and chemical reactivity of the heterocyclic conjugated systems. Some quantum chemical quantities (such as the total π electron energy, the total π electron density, the index of the bond strength, the self-atom polarizability, and the frontier electron density)of some heterocyclic. conjugated molecules and its topological reference systems are obtained using the practical calculation method.

トポロジカル参照系の量子化学的諸量の実用的計算法

トポロジカル参照系の量子化学的諸量の実用的計算法

Pinnacle: An approach toward object oriented quantum chemistry

This article presents an object orientated approach to the calculation of quantum chemical quantities, specifically Moller-Plesset second- and third-order energies. Blocking and index symmetry is used to take advantage of the sparsity of the data structures. The two main classes, Arrays and BlockArrays, are presented along with a sample code segment. While this code has been specifically used to calculate quantum chemical quantities, the code has been made general enough to be of use in other computational settings. © 1995 John Wiley & Sons, Inc.

Simple theoretical models of elimination reactions on polar catalysts; Dehydration reactivity of secondary alcohols on acidic and basic catalysts

CNDO/2 calculations for simple models of adsorption and dehydration reactions of secondary aliphatic and aromatic alcohols on polar catalysts are presented. The models involve selected stages of elimination mechanisms of various types (E1, E2 and E1cB elimination). Calculated quantum chemical quantities were correlated with reported experimental data. It is shown that reactivities for the series of substituted phenylethanols correlate very well with the ease of carbonium ion formation. In the case of aliphatic alcohols, calculated quantities correlate generally with the reactivities on SiO2 and are in anticorrelation with the reactivities on Al2O3.NaOH.

Quantum Chemical Consideration of Substituent Effects on Tautomeric Properties of 2-Pyridones–2-Pyridinols

Abstract The tautomeric properties of 2-pyridones–2-pyridinols exerted by the substituent effect were discussed on the basis of quantum chemical quantities deduced from molecular orbital (MO) calculations. A substituent at the 6-position has the greatest stabilizing effect. The magnitude of this effect was greater on the 2-pyridinol form than the 2-pyridone form, irrespective of the nature of the substituent. This led to a large predominance of the 2-pyridinol form on the 6-polar-substituted derivatives to such an extent that it was observed by conventional UV measurements at ambient temperature. In the 6-methyl derivative, the 2-pyridinol form was not observed by a similar measurement due to the weak substituent effect. The association ability is still an important factor in determining tautomeric equilibrium in a solution, resulting in a strong lability to the molecular environment. The substituent effects on the stabilities of both tautomers were shown to be correlated with the N-atomic charges and ring structural modifications of the tautomers.

Simple theoretical models for elimination reactions on polar catalysts; Generalization of reactivities in series of chloroalkanes, alcohols, amines and thiols

CNDO/2 calculations have been made for simple models od adsorption of chloroalkane, alcohol, amine and thiol molecules on the surface of polar catalysts. The calculated values of selected quantum chemical quantities describing the properties of Cα-X and Cβ-HA bonds were correlated with reported experimental reactivities. Very good correlations with experimental data were obtained for quantum chemical quantities relating to the Cα-X bond. The results of calculations are discussed in relation to the reaction mechanism and the type of surface catalytic centres participating in the reaction.

Molecular orbital consideration of the cooperative effect of multiple substituents in some biologically active cinnamate derivatives.

Molecular orbital quantities of several cinnamate derivatives were calculated by the CNDO/2 method to evaluate the influence of the cooperative effect of multiple hydroxy substituents on their electronic features. The pathways undergone in TFA have been differentiated from each other by such substituents, which were totally consistent with the indices deduced from the calculated quantum chemical quantities.

Molecular Orbital Theory of Sulfur and Selenium Radicals

The electronic structures of various sulfur and selenium radicals were studied by semiempirical molecular orbital theory in the form of a parameter theory. The ESR data (g values) were used to determine the actual value of the parameter α, which is the coefficient of the s orbital in the bonding hybrid of the S(Se) atom in the radical. The physical significance of α so determined was studied by investigating some quantum chemical quantities such as valence state energies Ev and bond strengths B as functions of α. As a result, a criterion for the determination of the parameter value was deduced, namely, the selection of that value of α which maximizes B2 | Ev |. From theoretical considerations and experimental data in the literature, the relative signs of the principal values of the hyperfine-structure tensor of selenium were determined, and the magnitudes of the isotropic and anisotropic components were evaluated.