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15 pages, 521 KB

Open AccessReview

Atoms-In-Molecules’ Faces of Chemical Hardness by Conceptual Density Functional Theory

by Savas Kaya and Mihai V. Putz

Molecules 2022, 27(24), 8825; https://doi.org/10.3390/molecules27248825 - 12 Dec 2022

Cited by 58 | Viewed by 4983

The chemical hardness concept and its realization within the conceptual density functional theory is approached with innovative perspectives, such as the electronegativity and hardness equalization of atoms in molecules connected with the softness kernel, in order to examine the structure–reactivity equalization ansatz between the electronic sharing index and the charge transfer either in the additive or geometrical mean picture of bonding. On the other hand, the maximum hardness principle presents a relation with the chemical stability of the hardness concept. In light of the inverse relation between hardness and polarizability, the minimum polarizability principle has been proposed. Additionally, this review includes important applications of the chemical hardness concept to solid-state chemistry. The mentioned applications support the validity of the electronic structure principles regarding chemical hardness and polarizability in solid-state chemistry. Full article

(This article belongs to the Special Issue Density Functional Theory in the Age of Chemical Intelligence)

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56 pages, 1641 KB

Open AccessArticle

Determining Chemical Reactivity Driving Biological Activity from SMILES Transformations: The Bonding Mechanism of Anti-HIV Pyrimidines

by Mihai V. Putz and Nicoleta A. Dudaş

Molecules 2013, 18(8), 9061-9116; https://doi.org/10.3390/molecules18089061 - 30 Jul 2013

Cited by 31 | Viewed by 8062

Abstract

Assessing the molecular mechanism of a chemical-biological interaction and bonding stands as the ultimate goal of any modern quantitative structure-activity relationship (QSAR) study. To this end the present work employs the main chemical reactivity structural descriptors (electronegativity, chemical hardness, chemical power, electrophilicity) to unfold the variational QSAR though their min-max correspondence principles as applied to the Simplified Molecular Input Line Entry System (SMILES) transformation of selected uracil derivatives with anti-HIV potential with the aim of establishing the main stages whereby the given compounds may inhibit HIV infection. The bonding can be completely described by explicitly considering by means of basic indices and chemical reactivity principles two forms of SMILES structures of the pyrimidines, the Longest SMILES Molecular Chain (LoSMoC) and the Branching SMILES (BraS), respectively, as the effective forms involved in the anti-HIV activity mechanism and according to the present work, also necessary intermediates in molecular pathways targeting/docking biological sites of interest. Full article

(This article belongs to the Special Issue Computational Chemistry)

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37 pages, 490 KB

Open AccessArticle

Alert-QSAR. Implications for Electrophilic Theory of Chemical Carcinogenesis

by Mihai V. Putz, Cosmin Ionaşcu, Ana-Maria Putz and Vasile Ostafe

Int. J. Mol. Sci. 2011, 12(8), 5098-5134; https://doi.org/10.3390/ijms12085098 - 11 Aug 2011

Cited by 43 | Viewed by 11345

Abstract

Given the modeling and predictive abilities of quantitative structure activity relationships (QSARs) for genotoxic carcinogens or mutagens that directly affect DNA, the present research investigates structural alert (SA) intermediate-predicted correlations A^SA of electrophilic molecular structures with observed carcinogenic potencies in rats (observed activity, A = Log[1/TD₅₀], i.e., A^SA=f(X₁^SA,X₂^SA,...)). The present method includes calculation of the recently developed residual correlation of the structural alert models, i.e., ARA^SA=f(A-A^SA,X₁^SA,X₂^SA,...) . We propose a specific electrophilic ligand-receptor mechanism that combines electronegativity with chemical hardness-associated frontier principles, equality of ligand-reagent electronegativities and ligand maximum chemical hardness for highly diverse toxic molecules against specific receptors in rats. The observed carcinogenic activity is influenced by the induced SA-mutagenic intermediate effect, alongside Hansch indices such as hydrophobicity (LogP), polarizability (POL) and total energy (Etot), which account for molecular membrane diffusion, ionic deformation, and stericity, respectively. A possible QSAR mechanistic interpretation of mutagenicity as the first step in genotoxic carcinogenesis development is discussed using the structural alert chemoinformation and in full accordance with the Organization for Economic Co-operation and Development QSAR guidance principles. Full article

(This article belongs to the Special Issue Recent Advances in QSAR/QSPR Theory)

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42 pages, 567 KB

Open AccessArticle

Compactness Aromaticity of Atoms in Molecules

by Mihai V. Putz

Int. J. Mol. Sci. 2010, 11(4), 1269-1310; https://doi.org/10.3390/ijms11041269 - 26 Mar 2010

Cited by 22 | Viewed by 12116

Abstract

A new aromaticity definition is advanced as the compactness formulation through the ratio between atoms-in-molecule and orbital molecular facets of the same chemical reactivity property around the pre- and post-bonding stabilization limit, respectively. Geometrical reactivity index of polarizability was assumed as providing the benchmark aromaticity scale, since due to its observable character; with this occasion new Hydrogenic polarizability quantum formula that recovers the exact value of 4.5 a₀³ for Hydrogen is provided, where a₀ is the Bohr radius; a polarizability based–aromaticity scale enables the introduction of five referential aromatic rules (Aroma 1 to 5 Rules). With the help of these aromatic rules, the aromaticity scales based on energetic reactivity indices of electronegativity and chemical hardness were computed and analyzed within the major semi-empirical and ab initio quantum chemical methods. Results show that chemical hardness based-aromaticity is in better agreement with polarizability based-aromaticity than the electronegativity-based aromaticity scale, while the most favorable computational environment appears to be the quantum semi-empirical for the first and quantum ab initio for the last of them, respectively. Full article

(This article belongs to the Special Issue Atoms in Molecules and in Nanostructures)

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22 pages, 269 KB

Open AccessArticle

Lubrication Chemistry Viewed from DFT-Based Concepts and Electronic Structural Principles

by Li Shenghua, Yang He and Jin Yuansheng

Int. J. Mol. Sci. 2004, 5(1), 13-34; https://doi.org/10.3390/i5010013 - 26 Dec 2003

Cited by 33 | Viewed by 11796

Abstract

Fundamental molecular issues in lubrication chemistry were reviewed under categories of solution chemistry, contact chemistry and tribochemistry. By introducing the Density Functional Theory(DFT)-derived chemical reactivity parameters (chemical potential, electronegativity, hardness, softness and Fukui function) and related electronic structural principles (electronegativity equalization principle, hard-soft acid-base principle, and maximum hardness principle), their relevancy to lubrication chemistry was explored. It was suggested that DFT, theoretical, conceptual and computational, represents a useful enabling tool to understand lubrication chemistry issues prior to experimentation and the approach may form a key step in the rational design of lubrication chemistry via computational methods. It can also be optimistically anticipated that these considerations will gestate unique DFT-based strategies to understand sophisticated tribology themes, such as origin of friction, essence of wear, adhesion in MEMS/NEMS, chemical mechanical polishing in wafer manufacturing, stress corrosion, chemical control of friction and wear, and construction of designer tribochemical systems. Full article

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22 pages, 293 KB

Open AccessArticle

Chemical Reactivity Dynamics and Quantum Chaos in Highly Excited Hydrogen Atoms in an External Field: A Quantum Potential Approach

by P. K. Chattaraj and B. Maiti

Int. J. Mol. Sci. 2002, 3(4), 338-359; https://doi.org/10.3390/i3040338 - 25 Apr 2002

Cited by 17 | Viewed by 10067

Abstract

Dynamical behavior of chemical reactivity indices like electronegativity, hardness, polarizability, electrophilicity and nucleophilicity indices is studied within a quantum fluid density functional framework for the interactions of a hydrogen atom in its ground electronic state (n = 1) and an excited electronic state (n = 20) with monochromatic and bichromatic laser pulses. Time dependent analogues of various electronic structure principles like the principles of electronegativity equalization, maximum hardness, minimum polarizability and maximum entropy have been found to be operative. Insights into the variation of intensities of the generated higher order harmonics on the color of the external laser field are obtained. The quantum signature of chaos in hydrogen atom has been studied using a quantum theory of motion and quantum fluid dynamics. A hydrogen atom in the electronic ground state (n = 1) and in an excited electronic state ( n = 20) behaves differently when placed in external oscillating monochromatic and bichromatic electric fields. Temporal evolutions of Shannon entropy, quantum Lyapunov exponent and Kolmogorov – Sinai entropy defined in terms of the distance between two initially close Bohmian trajectories for these two cases show marked differences. It appears that a larger uncertainty product and a smaller hardness value signal a chaotic behavior. Full article

(This article belongs to the Special Issue Application of Density Functional Theory)

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