Franck-Condon Dominated Chemistry. Formation and Dissociations of the Dimethylhydroxysulfuranyl Radical

2000 ◽  
Vol 65 (4) ◽  
pp. 455-476 ◽  
Author(s):  
František Tureček
Keyword(s):  
Gas Phase ◽  
Density Functional ◽  
Dimethyl Sulfide ◽  
Vibrational Excitation ◽  
Single Point ◽  
Heat Of Formation ◽  
Isodesmic Reactions ◽  
Local Energy Minimum ◽  
A Charge ◽  
High Level

The structure and energetics of the hydroxyl radical adduct to dimethyl sulfide (DMS) was revisited using high level ab initio calculations. Density functional theory B3LYP/6-31++G(2d,p) and perturbational MP2(FULL)/6-31++G(2d,p) calculations found a weakly bound structure, (CH3)2SOH•, with a long S-O bond that was a local energy minimum. Single point calculations at the effective QCISD(T)/6-311++G(3df,2p) level of theory, denoted as G2++(MP2), found the (CH3)2S-OH• bonding energy to be 40 kJ mol-1 at 298 K. The standard heat of formation of (CH3)2SOH• was assessed from dissociation and isodesmic reactions as -45 ± 4 kJ mol-1. No other local minima corresponding to C2H7OS radicals were found at the present level of theory that could be derived from DMS or dimethyl sulfoxide (DMSO). A very weak complex, CH3S(H)-•OCH3, was found that was bound by mere 4 kJ mol-1 against dissociation to CH3SH and •OCH3. Vertical electron capture by (CH3)2SOH+ is predicted to form (CH3)2SOH• with a highly non-relaxed geometry corresponding to a vibrational excitation of 138 kJ mol-1 above the local minimum and 88 kJ mol-1 above the dissociation threshold to DMS and OH•. Unimolecular dissociation of (CH3)2SOH• to methanesulfenic acid (CH3SOH) and •OCH3 faces an energy barrier that diminishes at shorter S-O distances. The dipole-allowed electronic excitation in (CH3)2SOH• was calculated with CIS/6-311++G(2df,p) to have λmax = 248 nm in the gas phase. The resulting B state represents a charge-transfer complex of (CH3)2S+• and OH-. The present computational results allowed us to explain the existing controversy between the experimental results obtained by gas-phase flow kinetics, radiolysis in aqueous solution, and neutralization-reionization mass spectrometry.

A New Pathway for Activation of C - C and C - H Bonds by Transition Metals in the Gas Phase

2005 ◽  
Vol 58 (2) ◽  
pp. 82 ◽  
Author(s):  
Dongju Zhang ◽  
Ruoxi Wang ◽  
Rongxiu Zhu
Keyword(s):  
Transition Metals ◽  
Gas Phase ◽  
Density Functional Calculations ◽  
Density Functional ◽  
Bond Activation ◽  
Level Density ◽  
Elimination Mechanism ◽  
Activation Of Hydrocarbons ◽  
High Level ◽  
H2 Elimination

C–H and C–C bond activation of hydrocarbons at metal centres are of fundamental importance in biochemistry, organometallic chemistry, and catalysis. The present work aims to search for novel mechanisms for activation of C–C and C–H bonds by transition metals in the gas phase. Using high-level density functional calculations, we systemically studied the reactions of Ti+, V+, and Fe+ with ethane, and proposed new pathways of C–C and C–H bond activation—concerted activation of C–C and C–H bonds, and 1,2-H2 elimination. These two pathways clearly differ from the general addition–elimination mechanism.

scholarly journals Ability of B12N12 fullerènes like nano-cage for sensing and improving the antioxidant activity of juglone and its derivative: DFT investigation

2021 ◽  
Author(s):  
Vincent de Paul Zoua ◽  
Aymard Fouegue ◽  
Désiré Mama ◽  
Julius Ghogomu ◽  
Rahman Abdoul Ntieche
Keyword(s):  
Gas Phase ◽  
Density Functional ◽  
Nbo Analysis ◽  
Hydrogen Atom Transfer ◽  
Carbonyl Groups ◽  
Functional Theory ◽  
Non Covalent Interactions ◽  
A Charge ◽  
Covalent Interactions ◽  
Theoretical Results

Density functional theory (DFT) calculations were adopted in this work to investigate the ability of the B12N12 fullerene like nano-cage for sensing juglone (Jug) and one of its derivative (Jug-OH) using DFT based methods in gas phase, pentyl ethanoate (PE) and water. Results showed that B12N12 is able to adsorbed Jug preferentially by binding to one of the O-atom of its carbonyl groups. Based on NBO analysis, a charge transfer from the oxygen atoms of Jug and Jug-OH to the anti-bonding orbital of B was revealed. QTAIM analysis showed that the B12N12-Jug and B12N12-Jug-OH complexes are stabilized by a partially covalent B-O bond in addition to attractive non covalent interactions. The ability of Jug, Jug-OH as well as their complexes A and A-OH to scavenge radicals has been investigated via the usual hydrogen atom transfer (HAT) mechanism in the three media of study previously stated. Theoretical results revealed that in PE and water, the complexes are better antioxidant than Jug and Jug-OH. These results provide fundamental knowledge for the development of new antioxidant delivery careers.

Carbonate radical anion — Thermochemistry

2006 ◽  
Vol 84 (12) ◽  
pp. 1614-1619 ◽  
Author(s):  
D A Armstrong ◽  
W L Waltz ◽  
A Rauk
Keyword(s):  
Gas Phase ◽  
Radical Anion ◽  
Strong Acid ◽  
Free Energies ◽  
Isodesmic Reactions ◽  
Carbonate Radical ◽  
Reduction Potentials ◽  
High Level ◽  
Carbonate Radical Anion ◽  
Nitrate Species

High level ab initio calculations along with isodesmic reactions have been used to derive a set of self-consistent free energies of formation for carbonate and nitrate species in the gas phase and in aqueous solution. The results show that HCO3· is a strong acid, pKa = –4.1, and that E°(CO3·–/CO32) = 1.23 ± 0.15 V.Key words: carbonate radical anion, theoretical, thermochemistry, acidity, reduction potentials.

scholarly journals A Simple Computational Tool for Accurate, Quantitative Prediction of One–Electron Reduction Potentials of Hypoxia–Activated Tirapazamine Analogues

2020 ◽  
Vol 23 ◽  
pp. 231-242
Author(s):  
Hassan RH Elsaidi ◽  
Leonard I Wiebe ◽  
Piyush Kumar
Keyword(s):  
Gas Phase ◽  
Molecular Orbital ◽  
Density Functional ◽  
Polar Solvent ◽  
Single Point ◽  
Single Electron ◽  
Quantitative Prediction ◽  
Energy Calculation ◽  
Reduction Potentials ◽  
Electron Reduction

The reduction potentials of bioreductively-activated drugs represent an important design parameter to be accommodated in the course of creating lead compounds and improving the efficacy of older generation drugs.  Reduction potentials are traditionally reported as single–electron reduction potentials, E(1), measured against reference electrodes under strictly defined experimental conditions.  More recently, computational chemists have described redox properties in terms of a molecule’s highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO), in electron volts (eV).  The relative accessibility of HOMO/LUMO data through calculation using today’s computer infrastructure and simplified algorithms make the calculated value (LUMO) attractive in comparison to the accepted but rigorous experimental determination of E(1).  This paper describes the correlations of eV (LUMO) to E(1) for three series of bioreductively–activated benzotriazine di-N-oxides (BTDOs), ring-substituted BTDOs, ring-added BTDOs and a selection of aromatic nitro compounds. The current computational approach is a closed–shell calculation with a single optimization.  Gas phase geometry optimization was followed by a single–point DFT (Density Functional Theory) energy calculation in the gas phase or in the presence of polar solvent.  The resulting DFT–derived LUMO energies (eV) calculated for BTDO analogues in gas phase and in presence of polar solvent (water) exhibited very strong linear correlations with high computational efficiency (r2 = 0.9925) and a very high predictive ability (MAD = 7 mV and RMSD = 9 mV) when compared to reported experimentally determined single–electron reduction potentials.

scholarly journals Calculating Heat of Formation Values of Energetic Compounds: A Comparative Study

2016 ◽  
Vol 2016 ◽  
pp. 1-11 ◽  
Author(s):  
Michael S. Elioff ◽  
Jordan Hoy ◽  
John A. Bumpus
Keyword(s):  
Density Functional Theory ◽  
Gas Phase ◽  
Density Functional ◽  
Heat Of Formation ◽  
Semiempirical Methods ◽  
Group Contribution Method ◽  
Energetic Compounds ◽  
Functional Theory ◽  
Test Set ◽  
Experimental Reference

Heat of formation is one of several important parameters used to assess the performance of energetic compounds. We evaluated the ability of six different methods to accurately calculate gas-phase heat of formation (ΔfH298,go) values for a test set of 45 nitrogen-containing energetic compounds. Density functional theory coupled with the use of isodesmic or other balanced equations yielded calculated results in which 82% (37 of 45) of the ΔfH298,go values were within ±2.0 kcal/mol of the most recently recommended experimental/reference values available. This was compared to a procedure using density functional theory (DFT) coupled with an atom and group contribution method in which 51% (23 of 45) of the ΔfH298,go values were within ±2.0 kcal/mol of these values. The T1 procedure and Benson’s group additivity method yielded results in which 51% (23 of 45) and 64% (23 of 36) of the ΔfH298,go values, respectively, were within ±2.0 kcal/mol of these values. We also compared two relatively new semiempirical approaches (PM7 and RM1) with regard to their ability to accurately calculate ΔfH298,go. Although semiempirical methods continue to improve, they were found to be less accurate than the other approaches for the test set used in this investigation.

scholarly journals The Gas-Phase Heats of Formation ofn-Alkanes as a Function of the Electrostatic Potential Extrema on their Molecular Surfaces

2004 ◽  
Vol 1 (2) ◽  
pp. 81-86 ◽  
Author(s):  
Fakhr M. Abu-Awwad
Keyword(s):  
Gas Phase ◽  
Electrostatic Potential ◽  
Density Functional ◽  
Absolute Error ◽  
Heat Of Formation ◽  
Molecular Surface ◽  
Heats Of Formation ◽  
Normal Alkanes ◽  
Surface Electrostatic Potential ◽  
Hybrid Density Functional

The hybrid density functional B3LYP is employed to map the molecular electrostatic potentials on the surfaces of twenty normal alkanes, (CnH2n+2), n = 1-20. It is shown that gas-phase heats of formation of the alkanes can be represented quantitatively in terms of the potential, where a general equation of the heat of formation is introduced as a function of potentials' extrema, VS,minand VS,maxwith average absolute error of 0.028 kcal/mol and a standard deviation of 0.048 kcal/mol. This should be viewed as a success of the B3LYP functional and the molecular surface electrostatic potential as tools of chemistry. The predicted gas-phase heats of formation of thirty normal alkanes (n = 21-50) are reproduced and compared to their experimental counterparts when available.

Adsorption Forms of Water Molecules on Gas-Phase Platinum Clusters Pt3+ Studied by Vibrational Photodissociation Spectroscopy

2019 ◽  
Vol 233 (6) ◽  
pp. 881-894 ◽  
Author(s):  
Fumitaka Mafuné ◽  
Manami Abe ◽  
Satoshi Kudoh
Keyword(s):  
Density Functional Theory ◽  
Dft Calculations ◽  
Gas Phase ◽  
Vibrational Spectra ◽  
Density Functional ◽  
Molecular Form ◽  
Vibrational Excitation ◽  
Water Molecules ◽  
Functional Theory ◽  
Platinum Clusters

Abstract The vibrational spectra of Pt3(H2O)m+ (m = 1–4) cluster were measured in the 3000–3800 cm−1 range via infrared photodissociation (IRPD) spectroscopy. The IRPD spectra were recorded through the photodissociation of Pt3(H2O)m+-Ar (m = 1–3) complexes and Pt3(H2O)4+ cations upon vibrational excitation. The spectra were compared to the vibrational spectra of several stable isomers obtained by density functional theory (DFT) calculations and the adsorption forms of the water molecules were subsequently discussed. The IRPD spectra of all the studied Pt3(H2O)m+ cations exhibited intense peaks at ∼3600 and 3700 cm−1. This suggested that the water molecules mainly adsorb onto the Pt clusters in molecular form and that each molecule binds directly to a Pt atom via its O atom side. For the water-rich Pt3(H2O)4+ cations, all four water molecules were directly bound to the Pt atoms; however, according to the DFT calculations, the fourth H2O molecule could bind to a first-layer water molecule through hydrogen bonding.

Intrinsic Stacking Interactions of Natural and Artificial Nucleobases

2019 ◽  
Author(s):  
Drew P. Harding ◽  
Laura J. Kingsley ◽  
Glen Spraggon ◽  
Steven Wheeler
Keyword(s):  
Gas Phase ◽  
Electrostatic Interactions ◽  
Density Functional ◽  
Molecular Descriptors ◽  
Stacking Interactions ◽  
Interaction Energies ◽  
Functional Theory ◽  
Binding Partner ◽  
Heavy Atoms ◽  
Wide Range

The intrinsic (gas-phase) stacking energies of natural and artificial nucleobases were explored using density functional theory (DFT) and correlated ab initio methods. Ranking the stacking strength of natural nucleobase dimers revealed a preference in binding partner similar to that seen from experiments, namely G > C > A > T > U. Decomposition of these interaction energies using symmetry-adapted perturbation theory (SAPT) showed that these dispersion dominated interactions are modulated by electrostatics. Artificial nucleobases showed a similar stacking preference for natural nucleobases and were also modulated by electrostatic interactions. A robust predictive multivariate model was developed that quantitively predicts the maximum stacking interaction between natural and a wide range of artificial nucleobases using molecular descriptors based on computed electrostatic potentials (ESPs) and the number of heavy atoms. This model should find utility in designing artificial nucleobase analogs that exhibit stacking interactions comparable to those of natural nucleobases. Further analysis of the descriptors in this model unveil the origin of superior stacking abilities of certain nucleobases, including cytosine and guanine.

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