Computational study of elastic and electronically inelastic scattering of Br by ground state I atoms: Role of potential curve crossing

1976 ◽  
Vol 64 (7) ◽  
pp. 2971-2984 ◽  
Author(s):  
M. B. Faist ◽  
R. B. Bernstein
Keyword(s):  
Inelastic Scattering ◽  
Ground State ◽  
Computational Study ◽  
Potential Curve ◽  
Curve Crossing

scholarly journals Photoprotective Properties of Eumelanin: Computational Insights into the Photophysics of a Catechol:Quinone Heterodimer Model System

Photochem ◽  
2021 ◽  
Vol 1 (1) ◽  
pp. 26-37
Author(s):  
Victoria C. Frederick ◽  
Thomas A. Ashy ◽  
Barbara Marchetti ◽  
Michael N. R. Ashfold ◽  
Tolga N. V. Karsili
Keyword(s):  
Ground State ◽  
Sandwich Structure ◽  
Computational Study ◽  
Minimum Energy ◽  
Carbonyl Oxygen ◽  
Model System ◽  
Molecular Structures ◽  
Uv Damage ◽  
Chromosomal Dna ◽  
Relevant Model

Melanins are skin-centered molecular structures that block harmful UV radiation from the sun and help protect chromosomal DNA from UV damage. Understanding the photodynamics of the chromophores that make up eumelanin is therefore paramount. This manuscript presents a multi-reference computational study of the mechanisms responsible for the experimentally observed photostability of a melanin-relevant model heterodimer comprising a catechol (C)–benzoquinone (Q) pair. The present results validate a recently proposed photoinduced intermolecular transfer of an H atom from an OH moiety of C to a carbonyl-oxygen atom of the Q. Photoexcitation of the ground state C:Q heterodimer (which has a π-stacked “sandwich” structure) results in population of a locally excited ππ* state (on Q), which develops increasing charge-transfer (biradical) character as it evolves to a “hinged” minimum energy geometry and drives proton transfer (i.e., net H atom transfer) from C to Q. The study provides further insights into excited state decay mechanisms that could contribute to the photostability afforded by the bulk polymeric structure of eumelanin.

scholarly journals The Activating Effect of Strong Acid for Pd-Catalyzed Directed C–H Activation by Concerted Metalation-Deprotonation Mechanism

Molecules ◽  
2021 ◽  
Vol 26 (13) ◽  
pp. 4083
Author(s):  
Heming Jiang ◽  
Tian-Yu Sun
Keyword(s):  
Activation Energy ◽  
Dft Calculations ◽  
Energy Barrier ◽  
Computational Study ◽  
Strong Acid ◽  
Activation Energy Barrier ◽  
Pd Catalysts ◽  
Acid Ligand ◽  
Strong Acids

A computational study on the origin of the activating effect for Pd-catalyzed directed C–H activation by the concerted metalation-deprotonation (CMD) mechanism is conducted. DFT calculations indicate that strong acids can make Pd catalysts coordinate with directing groups (DGs) of the substrates more strongly and lower the C–H activation energy barrier. For the CMD mechanism, the electrophilicity of the Pd center and the basicity of the corresponding acid ligand for deprotonating the C–H bond are vital to the overall C–H activation energy barrier. Furthermore, this rule might disclose the role of some additives for C–H activation.

scholarly journals Antioxidant Properties of Ergosterol and Its Role in Yeast Resistance to Oxidation

Antioxidants ◽  
2021 ◽  
Vol 10 (7) ◽  
pp. 1024
Author(s):  
Sebastien Dupont ◽  
Paul Fleurat-Lessard ◽  
Richtier Gonçalves Cruz ◽  
Céline Lafarge ◽  
Cédric Grangeteau ◽  
...  
Keyword(s):  
Computational Study ◽  
Antioxidant Properties ◽  
Beneficial Effects ◽  
Tert Butyl Hydroperoxide ◽  
Resistance To Oxidation ◽  
Specific Accumulation ◽  
The Subject

Although the functions and structural roles of sterols have been the subject of numerous studies, the reasons for the diversity of sterols in the different eukaryotic kingdoms remain unclear. It is thought that the specificity of sterols is linked to unidentified supplementary functions that could enable organisms to be better adapted to their environment. Ergosterol is accumulated by late branching fungi that encounter oxidative perturbations in their interfacial habitats. Here, we investigated the antioxidant properties of ergosterol using in vivo, in vitro, and in silico approaches. The results showed that ergosterol is involved in yeast resistance to tert-butyl hydroperoxide and protects lipids against oxidation in liposomes. A computational study based on quantum chemistry revealed that this protection could be related to its antioxidant properties operating through an electron transfer followed by a proton transfer mechanism. This study demonstrates the antioxidant role of ergosterol and proposes knowledge elements to explain the specific accumulation of this sterol in late branching fungi. Ergosterol, as a natural antioxidant molecule, could also play a role in the incompletely understood beneficial effects of some mushrooms on health.

t+t clustering in He-isotopes

2006 ◽  
Vol 21 (31n33) ◽  
pp. 2499-2502
Author(s):  
S. Aoyama ◽  
N. Itagaki ◽  
K. Arai ◽  
K. Katō ◽  
M. Oi
Keyword(s):  
Configuration Space ◽  
Ground State ◽  
Cluster Component ◽  
Theoretical Approaches ◽  
He Isotopes

t+t clustering in He isotopes is investigated by using two theoretical approaches. A role of the t+t cluster component in the ground state is examined with AMD triple-S, allowing the wider configuration space containing simultaneously the "t+t+valence neutrons" structure and "4 He +valence neutrons" structure. We understand the importance of the t + t component even for the ground state. Further, t + t resonances are investigated with RGM type approach. We obtained many t + t states as resonances near to t + t threshold.

A meta-analysis and review examining a possible role for oxidative stress and singlet oxygen in diverse diseases

2017 ◽  
Vol 474 (16) ◽  
pp. 2713-2731 ◽  
Author(s):  
Athinoula L. Petrou ◽  
Athina Terzidaki
Keyword(s):  
Oxidative Stress ◽  
Excited State ◽  
Singlet Oxygen ◽  
Ground State ◽  
Meta Analysis ◽  
Common Mechanism ◽  
High Electron ◽  
A Value ◽  
First Excited State

From kinetic data (k, T) we calculated the thermodynamic parameters for various processes (nucleation, elongation, fibrillization, etc.) of proteinaceous diseases that are related to the β-amyloid protein (Alzheimer's), to tau protein (Alzheimer's, Pick's), to α-synuclein (Parkinson's), prion, amylin (type II diabetes), and to α-crystallin (cataract). Our calculations led to ΔG≠ values that vary in the range 92.8–127 kJ mol−1 at 310 K. A value of ∼10–30 kJ mol−1 is the activation energy for the diffusion of reactants, depending on the reaction and the medium. The energy needed for the excitation of O2 from the ground to the first excited state (1Δg, singlet oxygen) is equal to 92 kJ mol−1. So, the ΔG≠ is equal to the energy needed for the excitation of ground state oxygen to the singlet oxygen (1Δg first excited) state. The similarity of the ΔG≠ values is an indication that a common mechanism in the above disorders may be taking place. We attribute this common mechanism to the (same) role of the oxidative stress and specifically of singlet oxygen, (1Δg), to the above-mentioned processes: excitation of ground state oxygen to the singlet oxygen, 1Δg, state (92 kJ mol−1), and reaction of the empty π* orbital with high electron density regions of biomolecules (∼10–30 kJ mol−1 for their diffusion). The ΔG≠ for cases of heat-induced cell killing (cancer) lie also in the above range at 310 K. The present paper is a review and meta-analysis of literature data referring to neurodegenerative and other disorders.

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