scholarly journals Structure and Stability of Chemically Modified DNA Bases: Quantum Chemical Calculations on 16 Isomers of Diphosphocytosine

2013 ◽  
Vol 2013 ◽  
pp. 1-10 ◽  
Author(s):  
Abdullah G. Al-Sehemi ◽  
Tarek M. El-Gogary ◽  
Karl Peter Wolschann ◽  
Gottfried Koehler
Keyword(s):  
Relative Stability ◽  
Density Functional ◽  
Chemically Modified ◽  
Functional Methods ◽  
Modified Dna ◽  
Polarized Continuum Model ◽  
Stability Order ◽  
High Dielectric ◽  
High Level ◽  
First Time

We studied for the first time 16 tautomers/rotamers of diphosphocytosine by four computational methods. Some of these tautomers/rotamers are isoenergetic although they have different structures. High-level electron correlation MP2 and MP4(SDQ) ab initio methods and density functional methods employing a B3LYP and the new M06-2X functional were used to study the structure and relative stability of 16 tautomers/rotamers of diphosphocytosine. The dienol tautomers of diphosphocytosine are shown to be much more stable than the keto-enol and diketo forms. The tautomers/rotamers stability could be ranked as PC3 = PC12 < PC2 = PC11 < PC1 < PC10 < PC8 < PC9 < PC15 < PC16 < PC6 ~ PC7 < PC13 < PC4 ~ PC14 < PC5. This stability order was discussed in the light of stereo and electronic factors. Solvation effect has been modeled in a high dielectric solvent, water using the polarized continuum model (PCM). Consideration of the solvent causes some reordering of the relative stability of diphosphocytosine tautomers: PC3 ~ PC12 ~ PC2 ~ PC11 < PC1 < PC10 < PC8 < PC9 < PC15 ~ PC16 < PC13 < PC6 ~ PC7 ~ PC14 < PC4 ~ PC5.

scholarly journals Adsorption and sensing of CO and NH3 on chemically modified graphene surfaces

RSC Advances ◽  
2020 ◽  
Vol 10 (69) ◽  
pp. 42318-42326
Author(s):  
A. Sahithi ◽  
K. Sumithra
Keyword(s):  
Carbon Monoxide ◽  
Electronic Structure ◽  
Ab Initio ◽  
Density Functional ◽  
Chemically Modified ◽  
Density Functional Methods ◽  
Functional Methods ◽  
Chemically Modified Surfaces ◽  
Modified Surfaces ◽  
Modified Graphene

We have studied the electronic structure and adsorption characteristics of environmentally potent gaseous molecules like carbon monoxide (CO) and ammonia (NH3) on chemically modified surfaces of graphene, employing ab initio density functional methods.

scholarly journals Tautomeric Equilibrium Revisited: proton-tautomerism in solvent and the fundamentals of molecular stability prediction.

2019 ◽  
Author(s):  
Andre Ricardo Carvalho
Keyword(s):  
Gas Phase ◽  
Relative Stability ◽  
Density Functional ◽  
Software Tool ◽  
Tautomeric Equilibrium ◽  
Consistent Estimate ◽  
Methods Development ◽  
Functional Methods ◽  
Molecular Stability ◽  
Molecular Orbital Analysis

Understanding the molecular stability is important for predicting the relative reactivity of chemical agents and the relative yields of desirable products. However, over decades, a consistent estimate of a particular chemical equilibrium (proton-tautomerism) has proven challenging. We revisit the molecular orbital analysis in the classic tautomeric oxo-hydroxy case, i.e., 2-pyridone/2-hydroxypyridine in gas-phase and solution, (Wong et al. 1992). Our results indicate the possibility of tuning the tautomeric equilibrium through directing groups. Our findings also reveal the lack of <a></a>reproducibility of orbital energies as responsible for the remarkable contrast between the results of the wavefunction and density functional methods. Our proposal leads the correction in the estimation of relative stability in excellent agreement with experiments in gas-phase and solution. The analogous approach for different compounds corroborates the reliability of our description on the molecular stability and its potential application, e.g., a guide to estimate the relative stability of molecules, to measure the confidence of the proposed reaction mechanisms by different theoretical methods, development of the molecular switches and computer-aided drug design. A software tool for Gaussian 09 package, in the support information, is available on the author's ORCiD page.<br>

Prototype of the Heteroaromatic Tautomers: 2-Pyridone / 2-Hydroxypyridine

2019 ◽  
Author(s):  
Andre Ricardo Carvalho
Keyword(s):  
Relative Stability ◽  
Density Functional ◽  
Molecular Switches ◽  
Tautomeric Equilibrium ◽  
Original Research ◽  
Dft Methods ◽  
Computer Aided Drug Design ◽  
Hartree Fock ◽  
Koopmans Theorem ◽  
Stability Order

In this work, we review the theoretical/experimental study progress in the classic case of a tautomeric equilibrium, 2-pyridone/2-hydroxypyridine (2-PY/2-HY), as well as original research on tautomerization reaction energetics. Our work sheds light on a matter of investigation which lasts more than a century, a challenge to the reliability of the quantum methods, especially to DFT. Our results reveal the responsible for the notable contrast between the relative stability order estimation by wavefunction (WF) and density functional (DFT) methods: The Koopmans’ theorem. Among the results by Hartree-Fock, QCISD and 127 DFT functionals, our work extends on one LC functional. The estimation of the relative stability is in excellent agreement with experiments. The analogous approach for other tautomeric compounds corroborates the reliability of our description and its potential application, e.g., on the development of the molecular switches, computer-aided drug design, and new DFT functionals. <br>

Investigation of Structural Properties of Heteropropellane Compounds by ab initio methods

2000 ◽  
Vol 2000 (2) ◽  
pp. 93-95 ◽  
Author(s):  
Ali Ebrahimi ◽  
Farzad Deyhimi ◽  
Hosein Roohi
Keyword(s):  
Molecular Structure ◽  
Ab Initio ◽  
Ground State ◽  
Relative Stability ◽  
Density Functional ◽  
Ab Initio Methods ◽  
Inversion Barrier ◽  
Barrier Energy ◽  
Density Functional Methods ◽  
Functional Methods

Molecular structure and relative stability of the ground state of [1.1.1] propellane, various [1.1.1] heteropropellane compounds and also their respective hydrogenated bicyclo compounds along with inversion barrier energy of nitrogen and its corresponding transition state in some of these compounds have been determined using ab initio molecular orbital and hybrid HF-density functional methods.

Assessment of DFT methods for studying acid gas capture by ionic liquids

2015 ◽  
Vol 17 (40) ◽  
pp. 26875-26891 ◽  
Author(s):  
Gregorio García ◽  
Mert Atilhan ◽  
Santiago Aparicio
Keyword(s):  
Ionic Liquids ◽  
Density Functional ◽  
Dft Methods ◽  
Acid Gas ◽  
Density Functional Methods ◽  
Functional Methods ◽  
First Time

For the first time, this work reports an analysis of the performance of Density Functional methods for studying acid gas capture (CO2 and SO2) by ionic liquids (ILs).

Preparation of flexible microwave interactive fabric for 8.2 to 18.0 GHz frequency: Functional evaluation and validation

2019 ◽  
Vol 50 (6) ◽  
pp. 847-869
Author(s):  
Krishna Kumar Gupta ◽  
Ashutosh C Abhyankar ◽  
Anurag Srivastava ◽  
Sayad Mohammed Abbas
Keyword(s):  
Carbon Fibre ◽  
Cotton Fabric ◽  
Microwave Properties ◽  
Functional Evaluation ◽  
Scattering Parameters ◽  
Coated Fabric ◽  
High Dielectric ◽  
High Level ◽  
Coating Formulation ◽  
First Time

In this study, for the first time, coating formulation based on milled carbon fibre has been applied on textile substrate to prepare flexible covering material for microwave protection. Cotton fabric with its inherent high dielectric property and finite length with close network of carbon milled fibre has synergised to generate highly conducting surface (σ = 96.22 S/m). The samples are prepared by coating of milled carbon fibre in various concentrations with polyurethane as binder on cotton fabric. Polyurethane contains hydroxyl and hexamethylene diisocynate groups which are polar under external electric field (dielectric constant 3.2–6.5) and also contribute high dielectric properties in coated fabric. Samples were evaluated for surface resistivity and microwave properties, i.e. permittivity, scattering parameters, reflection, transmission, absorption and reflection loss. Permittivity of high level (ɛ′: 21–31, ɛ″: 60–84) and attenuation of high order (α = 1971–2354 Np/m) are achieved. The sample coated with milled carbon fibre and polyurethane in ratio of 1: 1.67 on weight basis has shown 67–70% reflection, 28–30% absorption, 0.1–0.5% transmission, and EMI shielding of 28–30 dB in X (8.2–12.4 GHz) and Ku (12.4–8 GHz) frequency band. The results were further analysed theoretically and correlated with the scattering parameters and other microwave properties.

scholarly journals Interaction of Several Toxic Heterocarbonyl Gases with Polypyrrole as a Potential Gas Sensor

Chemosensors ◽  
2020 ◽  
Vol 8 (3) ◽  
pp. 84
Author(s):  
Francisco C. Franco
Keyword(s):  
Gas Sensor ◽  
Density Functional ◽  
Energy Gap ◽  
Carbonyl Sulfide ◽  
High Sensitivity ◽  
Basis Sets ◽  
Dft Methods ◽  
Functional Methods ◽  
Sensitivity And Selectivity ◽  
High Level

The interactions of the toxic heterocarbonyl gases phosgene, carbonyl fluoride, formaldehyde, carbonyl sulfide, and acetone with polypyrrole as a toxic heterocarbonyl gas sensor, were extensively studied by density functional theory (DFT). The Becke 3-parameter, Lee-Yang-Parr (B3LYP) exchange-correlation functional methods were first tested against several high-level DFT methods employing the Dunning’s double-ζ and triple-ζ basis sets and were found to be sufficient in describing the non-covalent interactions involved in this study. The interaction of pyrrole with the heterocarbonyl gases resulted in changes in the structure and optoelectronic properties of the polymer and it was observed that acetone and formaldehyde had the strongest H-bonding interaction with polypyrrole, while the interaction of phosgene and formaldehyde resulted in the lowest energy gap and may result in its high sensitivity towards these gases. The UV-Vis absorption revealed significant red-shifted first singlet excited states (Eexcited, 1st) of the complexes and follows the same trend as the EGap values. It is shown that the Eexcited, 1st was due to the π(HOMOPy) ⟶ π*(LUMOHC) transitions and the excited state at maximum absorption (Eexcited, max) was due to the π(HOMOPy) ⟶ π*(LUMOPy) transitions. This study demonstrates the potential sensitivity and selectivity of polypyrrole as a toxic heterocarbonyl sensor.

scholarly journals Tautomeric Equilibrium Revisited: proton-tautomerism in solvent and the fundamentals of molecular stability prediction.

2019 ◽  
Author(s):  
Andre Ricardo Carvalho
Keyword(s):  
Gas Phase ◽  
Relative Stability ◽  
Density Functional ◽  
Software Tool ◽  
Tautomeric Equilibrium ◽  
Consistent Estimate ◽  
Methods Development ◽  
Functional Methods ◽  
Molecular Stability ◽  
Molecular Orbital Analysis

Understanding the molecular stability is important for predicting the relative reactivity of chemical agents and the relative yields of desirable products. However, over decades, a consistent estimate of a particular chemical equilibrium (proton-tautomerism) has proven challenging. We revisit the molecular orbital analysis in the classic tautomeric oxo-hydroxy case, i.e., 2-pyridone/2-hydroxypyridine in gas-phase and solution, (Wong et al. 1992). Our results indicate the possibility of tuning the tautomeric equilibrium through directing groups. Our findings also reveal the lack of <a></a>reproducibility of orbital energies as responsible for the remarkable contrast between the results of the wavefunction and density functional methods. Our proposal leads the correction in the estimation of relative stability in excellent agreement with experiments in gas-phase and solution. The analogous approach for different compounds corroborates the reliability of our description on the molecular stability and its potential application, e.g., a guide to estimate the relative stability of molecules, to measure the confidence of the proposed reaction mechanisms by different theoretical methods, development of the molecular switches and computer-aided drug design. A software tool for Gaussian 09 package, in the support information, is available on the author's ORCiD page.<br>

A Confrontation between Two Doctrines: The Birth of Struggle for Hegemony in Hebrew Children's Literature during the 1930s and 1940s

2008 ◽  
Vol 1 (2) ◽  
pp. 139-155 ◽  
Author(s):  
YAEL DARR
Keyword(s):  
Children's Literature ◽  
Educational System ◽  
Single Channel ◽  
Children’S Literature ◽  
The Political ◽  
Literary Creation ◽  
History Of ◽  
High Level ◽  
First Time ◽  
Literary Quality

This article describes a crucial and fundamental stage in the transformation of Hebrew children's literature, during the late 1930s and 1940s, from a single channel of expression to a multi-layered polyphony of models and voices. It claims that for the first time in the history of Hebrew children's literature there took place a doctrinal confrontation between two groups of taste-makers. The article outlines the pedagogical and ideological designs of traditionalist Zionist educators, and suggests how these were challenged by a group of prominent writers of adult poetry, members of the Modernist movement. These writers, it is argued, advocated autonomous literary creation, and insisted on a high level of literary quality. Their intervention not only dramatically changed the repertoire of Hebrew children's literature, but also the rules of literary discourse. The article suggests that, through the Modernists’ polemical efforts, Hebrew children's literature was able to free itself from its position as an apparatus controlled by the political-educational system and to become a dynamic and multi-layered field.

Sign in / Sign up

Export Citation Format

Share Document