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 Synthesis, Characterization, Catalytic Activity, and DFT Calculations of Zn(II) Hydrazone Complexes

Molecules ◽  
2020 ◽  
Vol 25 (18) ◽  
pp. 4043 ◽  
Author(s):  
Temiloluwa T. Adejumo ◽  
Nikolaos V. Tzouras ◽  
Leandros P. Zorba ◽  
Dušanka Radanović ◽  
Andrej Pevec ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Gas Phase ◽  
Molecular Orbital ◽  
Density Functional ◽  
Chemical Potential ◽  
Chemical Reactivity ◽  
Geometry Optimization ◽  
Coupling Reaction ◽  
Functional Theory ◽  
Reactivity Descriptors

Two new Zn(II) complexes with tridentate hydrazone-based ligands (condensation products of 2-acetylthiazole) were synthesized and characterized by infrared (IR) and nuclear magnetic resonance (NMR) spectroscopy and single crystal X-ray diffraction methods. The complexes 1, 2 and recently synthesized [ZnL3(NCS)2] (L3 = (E)-N,N,N-trimethyl-2-oxo-2-(2-(1-(pyridin-2-yl)ethylidene)hydrazinyl)ethan-1-aminium) complex 3 were tested as potential catalysts for the ketone-amine-alkyne (KA2) coupling reaction. The gas-phase geometry optimization of newly synthesized and characterized Zn(II) complexes has been computed at the density functional theory (DFT)/B3LYP/6–31G level of theory, while the highest occupied molecular orbital and lowest unoccupied molecular orbital (HOMO and LUMO) energies were calculated within the time-dependent density functional theory (TD-DFT) at B3LYP/6-31G and B3LYP/6-311G(d,p) levels of theory. From the energies of frontier molecular orbitals (HOMO–LUMO), the reactivity descriptors, such as chemical potential (μ), hardness (η), softness (S), electronegativity (χ) and electrophilicity index (ω) have been calculated. The energetic behavior of the investigated compounds (1 and 2) has been examined in gas phase and solvent media using the polarizable continuum model. For comparison reasons, the same calculations have been performed for recently synthesized [ZnL3(NCS)2] complex 3. DFT results show that compound 1 has the smaller frontier orbital gap so, it is more polarizable and is associated with a higher chemical reactivity, low kinetic stability and is termed as soft molecule.

scholarly journals Theoretical Study on the Extraction of Alkaline Earth Salts by 18-Crown-6: Roles of Counterions, Solvent Types and Extraction Temperatures

2014 ◽  
Vol 14 (2) ◽  
pp. 199-208 ◽  
Author(s):  
Saprizal Hadisaputra ◽  
Lorenz R Canaval ◽  
Harno Dwi Pranowo ◽  
Ria Armunanto
Keyword(s):  
Gas Phase ◽  
Density Functional ◽  
Alkaline Earth ◽  
Theoretical Study ◽  
Polar Solvent ◽  
Density Functional Method ◽  
Nitrate Anion ◽  
Interaction Energies ◽  
Free Energies ◽  
Solvent Phase

The roles of counterions, solvent types and extraction temperatures on the selectivity of 18-crown-6 (L) toward alkaline earth salts MX2 (M = Ca, Sr, Ba; X = Cl-, NO3-) have been studied by density functional method at B3LYP level of theory in gas and solvent phase. In gas phase, the chloride anion Cl- is the preference counterion than nitrate anion NO3-. This result is confirmed by the interaction energies, the second order interaction energies, charge transfers, energy difference between HOMO-LUMO and electrostatic potential maps. The presence of solvent reversed the gas phase trend. It is found that NO3- is the preference counterion in solvent phase. The calculated free energies demonstrate that the solvent types strongly change the strength of the complex formation. The free energies are exothermic in polar solvent while for the non polar solvent the free energies are endothermic. As the temperature changes the free energies also vary where the higher the temperatures the lower the free energy values. The calculated free energies are correlated well with the experimental stability constants. This theoretical study would have a strong contribution in planning the experimental conditions in terms of the preference counterions, solvent types and optimum extraction temperatures.

scholarly journals Mechanistic Insights on Hypervalent Iodine-Mediated Styrene Hetero- and Homodimerization

2020 ◽  
Author(s):  
Aqeel A. Hussein ◽  
Ahmed Al-Yasari ◽  
Yumiao Ma
Keyword(s):  
Density Functional ◽  
Energy Gap ◽  
Single Electron ◽  
Hypervalent Iodine ◽  
Functional Theory ◽  
Rate Determining Step ◽  
Before And After ◽  
Electron Reduction ◽  
Dynamics Simulations ◽  
Insight Into

A mechanistic insight into the hetero- and homodimerizations (HETD and HOMD) of styrenes promoted by hypervalent iodine reagents (HVIRs; DMP and PIDA) and facilitated by HFIP to yield all trans cyclobutanes is reported using density functional theory (DFT) calculations. The HFIP molecules lower the energy of the single electron oxidation (SEO) or initiation as a result of strong hydrogen bonding interactions that substantially stabilize the frontier orbitals before and after electron addition. The HETD or HOMD is a radically-characterized π-π stacked head-to-head stepwise [2+2] cycloaddition initiated via SEO by DMP or PIDA, respectively. DFT results supported by quasiclassical molecular dynamics simulations show that HOMD is a competing pathway to HETD although the latter is relatively faster, in accordance with experimental observations. The initiation is a rate-determining step as a thermodynamically endergonic and propagation is accomplished by radically-cationic hetero- and homodimerized intermediate as propagation is faster than single electron reduction (SER) or termination by radically-anionic HVIRs. Initiation by DMP found to be faster and less endergonic than by PIDA due to (1) the energy gap of electron transfer in a SEO step by I(V) is lower than I(III) and (2) the SOMO energy of the radical anion I(V) is lower than I(III). Furthermore, the presence of p-methoxy group is essential to underpin the SEO by which the more thermodynamically favorable SEO leads to a successful cycloaddition as the thermodynamic term represents a major contribution in the initiative barrier.

scholarly journals Thermodynamics Control Reactivity of Hypervalent Iodine-Mediated Styrene Hetero- and Homodimerization: Mechanistic Insights

2020 ◽  
Author(s):  
Aqeel A. Hussein ◽  
Ahmed Al-Yasari ◽  
Yumiao Ma
Keyword(s):  
Density Functional ◽  
Energy Gap ◽  
Single Electron ◽  
Hypervalent Iodine ◽  
Functional Theory ◽  
Rate Determining Step ◽  
Before And After ◽  
Electron Reduction ◽  
Dynamics Simulations ◽  
Insight Into

A mechanistic insight into the hetero- and homodimerizations (HETD and HOMD) of styrenes promoted by hypervalent iodine reagents (HVIRs; DMP and PIDA) and facilitated by HFIP to yield all trans cyclobutanes is reported using density functional theory (DFT) calculations. The HFIP molecules lower the energy of the single electron oxidation (SEO) or initiation as a result of strong hydrogen bonding interactions that substantially stabilize the frontier orbitals before and after electron addition. The HETD or HOMD is a radically-characterized π-π stacked head-to-head stepwise [2+2] cycloaddition initiated via SEO by DMP or PIDA, respectively. DFT results supported by quasiclassical molecular dynamics simulations show that HOMD is a competing pathway to HETD although the latter is relatively faster, in accordance with experimental observations. The initiation is a rate-determining step as a thermodynamically endergonic and propagation is accomplished by radically-cationic hetero- and homodimerized intermediate as propagation is faster than single electron reduction (SER) or termination by radically-anionic HVIRs. Initiation by DMP found to be faster and less endergonic than by PIDA due to (1) the energy gap of electron transfer in a SEO step by I(V) is lower than I(III) and (2) the SOMO energy of the radical anion I(V) is lower than I(III). Furthermore, the presence of p-methoxy group is essential to underpin the SEO by which the more thermodynamically favorable SEO leads to a successful cycloaddition as the thermodynamic term represents a major contribution in the initiative barrier.

Mechanistic Insights on Hypervalent Iodine-Mediated Styrene Hetero- and Homodimerization

2020 ◽  
Author(s):  
Aqeel A. Hussein ◽  
Ahmed Al-Yasari ◽  
Yumiao Ma
Keyword(s):  
Density Functional ◽  
Energy Gap ◽  
Single Electron ◽  
Hypervalent Iodine ◽  
Functional Theory ◽  
Rate Determining Step ◽  
Before And After ◽  
Electron Reduction ◽  
Dynamics Simulations ◽  
Insight Into

A mechanistic insight into the hetero- and homodimerizations (HETD and HOMD) of styrenes promoted by hypervalent iodine reagents (HVIRs; DMP and PIDA) and facilitated by HFIP to yield all trans cyclobutanes is reported using density functional theory (DFT) calculations. The HFIP molecules lower the energy of the single electron oxidation (SEO) or initiation as a result of strong hydrogen bonding interactions that substantially stabilize the frontier orbitals before and after electron addition. The HETD or HOMD is a radically-characterized π-π stacked head-to-head stepwise [2+2] cycloaddition initiated via SEO by DMP or PIDA, respectively. DFT results supported by quasiclassical molecular dynamics simulations show that HOMD is a competing pathway to HETD although the latter is relatively faster, in accordance with experimental observations. The initiation is a rate-determining step as a thermodynamically endergonic and propagation is accomplished by radically-cationic hetero- and homodimerized intermediate as propagation is faster than single electron reduction (SER) or termination by radically-anionic HVIRs. Initiation by DMP found to be faster and less endergonic than by PIDA due to (1) the energy gap of electron transfer in a SEO step by I(V) is lower than I(III) and (2) the SOMO energy of the radical anion I(V) is lower than I(III). Furthermore, the presence of p-methoxy group is essential to underpin the SEO by which the more thermodynamically favorable SEO leads to a successful cycloaddition as the thermodynamic term represents a major contribution in the initiative barrier.

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.

Fast and accurate prediction of proton affinities: revisiting the extended Koopmans' theorem for protons

2017 ◽  
Vol 19 (37) ◽  
pp. 25324-25333 ◽  
Author(s):  
Laura Pedraza-González ◽  
Jorge Charry ◽  
William Quintero ◽  
Jorge Alí-Torres ◽  
Andrés Reyes
Keyword(s):  
Gas Phase ◽  
Molecular Orbital ◽  
Accurate Prediction ◽  
Quantitative Prediction ◽  
Proton Affinities ◽  
Koopmans Theorem

In this work we propose schemes based on the extended Koopmans' theorem for quantum nuclei (eKT), in the framework of the any particle molecular orbital approach (APMO/KT), for the quantitative prediction of gas phase proton affinities (PAs).

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