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Bayat A, Fattahi A. A quantum chemical study on the OH radical quenching by natural antioxidant fisetin. J PHYS ORG CHEM 2017. [DOI: 10.1002/poc.3692] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Affiliation(s)
- Ahmad Bayat
- Department of Chemistry; Sharif University of Technology; Tehran Iran
| | - Alireza Fattahi
- Department of Chemistry; Sharif University of Technology; Tehran Iran
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Nalawade P, Naumov S, Kapoor S. Hidden chemistry of substituted aniline radical cations in water: a mechanistic study. J PHYS ORG CHEM 2014. [DOI: 10.1002/poc.3386] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Affiliation(s)
- Pradnya Nalawade
- Radiation & Photochemistry Division; Bhabha Atomic Research Centre; Trombay Mumbai 400 085 India
| | - Sergej Naumov
- Leibniz-Institut für Oberflächenmodifizierung; Permoserstrasse 15 D-04318 Leipzig Germany
| | - Sudhir Kapoor
- Radiation & Photochemistry Division; Bhabha Atomic Research Centre; Trombay Mumbai 400 085 India
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Anouar EH, Raweh S, Bayach I, Taha M, Baharudin MS, Di Meo F, Hasan MH, Adam A, Ismail NH, Weber JFF, Trouillas P. Antioxidant properties of phenolic Schiff bases: structure-activity relationship and mechanism of action. J Comput Aided Mol Des 2013; 27:951-64. [PMID: 24243063 DOI: 10.1007/s10822-013-9692-0] [Citation(s) in RCA: 65] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2013] [Accepted: 11/09/2013] [Indexed: 11/27/2022]
Abstract
Phenolic Schiff bases are known for their diverse biological activities and ability to scavenge free radicals. To elucidate (1) the structure-antioxidant activity relationship of a series of thirty synthetic derivatives of 2-methoxybezohydrazide phenolic Schiff bases and (2) to determine the major mechanism involved in free radical scavenging, we used density functional theory calculations (B3P86/6-31+(d,p)) within polarizable continuum model. The results showed the importance of the bond dissociation enthalpies (BDEs) related to the first and second (BDEd) hydrogen atom transfer (intrinsic parameters) for rationalizing the antioxidant activity. In addition to the number of OH groups, the presence of a bromine substituent plays an interesting role in modulating the antioxidant activity. Theoretical thermodynamic and kinetic studies demonstrated that the free radical scavenging by these Schiff bases mainly proceeds through proton-coupled electron transfer rather than sequential proton loss electron transfer, the latter mechanism being only feasible at relatively high pH.
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Affiliation(s)
- El Hassane Anouar
- Atta-ur-Rahman Institute for Natural Product Discovery (RiND), Universiti Teknologi MARA, Kampus Puncak Alam, 42300 Bandar Puncak Alam, Shah Alam, Selangor DE, Malaysia,
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Nalawade P, Naumov S, Kapoor S. Comparative study of p-amino benzhydrazide and m-amino benzhydrazide by free radicals and free electron transfer. J PHYS ORG CHEM 2013. [DOI: 10.1002/poc.3182] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Affiliation(s)
- Pradnya Nalawade
- Radiation & Photochemistry Division; Bhabha Atomic Research Centre; Trombay Mumbai 400 085 India
| | - Sergej Naumov
- Leibniz-Institut für Oberflächenmodifizierung; Permoserstrasse 15 D-04318 Leipzig Germany
| | - Sudhir Kapoor
- Radiation & Photochemistry Division; Bhabha Atomic Research Centre; Trombay Mumbai 400 085 India
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Di Meo F, Lemaur V, Cornil J, Lazzaroni R, Duroux JL, Olivier Y, Trouillas P. Free radical scavenging by natural polyphenols: atom versus electron transfer. J Phys Chem A 2013; 117:2082-92. [PMID: 23418927 DOI: 10.1021/jp3116319] [Citation(s) in RCA: 176] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Polyphenols (synthetically modified or directly provided by human diet) scavenge free radicals by H-atom transfer and may thus decrease noxious effects due to oxidative stress. Free radical scavenging by polyphenols has been widely theoretically studied from the thermodynamic point of view whereas the kinetic point of view has been much less addressed. The present study describes kinetic-based structure-activity relationship for quercetin. This compound is very characteristic of the wide flavonoid subclass of polyphenols. H-atom transfer is a mechanism based on either atom or electron transfer. This is analyzed here by quantum chemical calculations, which support the knowledge acquired from experimental studies. The competition between the different processes is discussed in terms of the nature of the prereaction complexes, the pH, the formation of activated-deprotonated forms, and the atom- and electron-transfer efficiency. The role of the catechol moiety and the 3-OH group of quercetin as scavengers of different types of free radicals (CH3OO(•), CH3O(•), (•)OH, and (•)CH2OH) is rationalized. Identifying the exact mechanism and accurately evaluating kinetics is of fundamental importance to understand antioxidant behavior in physiological environments.
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Affiliation(s)
- Florent Di Meo
- Laboratoire de Chimie des Substances Naturelles EA-1069, Faculté de Pharmacie, Université de Limoges, 2 rue du Docteur Marcland, Limoges Cedex, France
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Brede O, Naumov S. Free electron transfer--relations between molecule dynamics and reaction kinetics. Chem Soc Rev 2010; 39:3057-71. [PMID: 20523928 DOI: 10.1039/b917327g] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Electron transfer in non-polar media (alkanes, alkyl chlorides) exhibits some essential peculiarities. For instance the reaction of hetero-substituted aromatics with parent solvent radical cations results in the parallel formation of metastable donor radical cations and fragmentation products, in comparable amounts. The fragmentation products originate from a dissociative donor radical cation which decays extremely rapidly, i.e., in a few femtoseconds. This phenomenon is explained in terms of intramolecular dynamic motions which cause changes of the electron density (pi- and n-orbitals) in dependence on the deformation angle between the substituents and the aromatic ring. Hence femtosecond dynamics is reflected in the nanosecond time range and can be observed with real-time spectroscopy. Therefore, the process is named free electron transfer (FET) which corresponds to an unhindered electron jump occurring in the first approach of the reactants. This dynamic controlled process is compared with the classical electron transfer theories which are based on equilibrium kinetics. From the FET mechanism some new aspects for chemical reaction kinetics can be derived (critical review, 69 references).
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Affiliation(s)
- Ortwin Brede
- University of Leipzig, Wilhelm Ostwald Institute of Physical and Theoretical Chemistry, Linnestr. 2, 04103 Leipzig, Germany.
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Karakostas N, Naumov S, Brede O. Free Electron Transfer with Bifunctional Donors: p-Aminotritylsilanes. J Phys Chem A 2009; 113:14087-94. [DOI: 10.1021/jp9073569] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Nikolaos Karakostas
- University of Leipzig, Wilhelm Ostwald Institute of Physical and Theoretical Chemistry, Linne’strasse 2, 04103 Leipzig, Germany, and Leibniz Institute of Surface Modification, Permoserstrasse 15, 04318 Leipzig, Germany
| | - Sergej Naumov
- University of Leipzig, Wilhelm Ostwald Institute of Physical and Theoretical Chemistry, Linne’strasse 2, 04103 Leipzig, Germany, and Leibniz Institute of Surface Modification, Permoserstrasse 15, 04318 Leipzig, Germany
| | - Ortwin Brede
- University of Leipzig, Wilhelm Ostwald Institute of Physical and Theoretical Chemistry, Linne’strasse 2, 04103 Leipzig, Germany, and Leibniz Institute of Surface Modification, Permoserstrasse 15, 04318 Leipzig, Germany
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Chadha R, Mahal HS, Mukherjee T, Kapoor S. Evidence for a possible role of 3-hydroxyanthranilic acid as an antioxidant. J PHYS ORG CHEM 2009. [DOI: 10.1002/poc.1485] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
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Karakostas N, Naumov S, Brede O. Ionization of Aromatic Sulfides in Nonpolar Media: Free vs Reaction-Controlled Electron Transfer. J Phys Chem A 2006; 111:71-8. [PMID: 17201390 DOI: 10.1021/jp066619q] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The primary products of the bimolecular free electron transfer (FET) from aromatic sulfides (PhSCH2Ph, PhSCHPh2, PhSCPh3) to n-butyl chloride radical cations are two radical cation conformers: a dissociative and a metastable one. In analogy with formerly studied donor systems, this result seems to reflect femtosecond oscillations in the ground state of the sulfides such as torsion motions around the Ar-S bond. This motion is accompanied by a marked electron fluctuation within the HOMO (or the n) orbitals. The FET products observed in the nanosecond time scale such as the metastable sulfide radical cations (Ar-S-CR3*+), the dissociation products R3C+; and R3C*, and their (experimentally) nondetectable counterparts Ar-S* as well as Ar-S+ can be understood with the simplified assumption of two extreme conformations, namely a planar and a twisted donor molecule. Using mediator radical cations (benzene, butylbenzene, biphenyl), the stepwise reduction of the free energy of the electron transfer from -DeltaH = 2.5 to <or=0.5 eV changes the dissociation pattern of the sulfide radical cations toward a uniform product such as the metastable sulfide radical cation. From that, we tentatively interpret the mechanism of the studied electron transfer as diffusion-controlled (collision-determined FET) at higher -DeltaH values and as reaction-controlled at -DeltaH below 0.5 eV.
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Affiliation(s)
- Nikolaos Karakostas
- Interdisciplinary Group for Time-Resolved Spectroscopy, University of Leipzig, Permoserstrasse 15, 04303 Leipzig, Germany
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Brede O, Naumov S. Femtodynamics Reflected in Nanoseconds: Bimolecular Free Electron Transfer in Nonpolar Media. J Phys Chem A 2006; 110:11906-18. [PMID: 17064178 DOI: 10.1021/jp063489c] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The (free) electron transfer (FET) from electron donor molecules to parent solvent radical cations of alkanes and alkyl chlorides exhibits mechanistic peculiarities that are conditioned by the low polarity of these solvents. Because of the negligible solvation of ions in such systems and the almost complete lack of an activation barrier, the electron jump takes place at the very first encounter of the reactants and, as such, in extremely short times of <or=10(-15) s. Molecular oscillations (deformation, bending) occurring within the femtosecond time domain result directly in significant changes of the pi- or n-electron distribution in the HOMO ground state of the donor molecule, thereby generating a distribution of conformers. This is considered to be a rationale for a possible generation of different product radical cations in the free electron transfer, which exhibit different spin and charge distribution and, consequently different stability. Experimentally, the latter has been verified for aromatic donors, substituted with mobile, i.e., not rigidly fixed heteroatom-centered groups (various phenol type compounds, thiophenols, aromatic amines, benzyltrimethylsilanes etc.). The individually characteristic product distribution could be visualized and quantified by time-resolved spectroscopy in the nanosecond time domain. On the basis of a manifold of experimental data and supported by quantum-chemical calculations, the free electron transfer phenomenon is analyzed and discussed in detail in this summarizing report. The results presented here stand also for a, seemingly paradox, situation in which the products of a diffusion-controlled bimolecular reaction are governed by femtosecond events.
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Affiliation(s)
- Ortwin Brede
- Interdisciplinary Group Time-Resolved Spectroscopy, University of Leipzig, Permoserstrasse 15, 04303 Leipzig, Germany.
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Karakostas N, Naumov S, Siskos MG, Zarkadis AK, Hermann R, Brede O. Free Electron Transfer from Xanthenyl- and Fluorenylsilanes (Me3 or Ph3) to Parent Solvent Radical Cations: Effects of Molecule Dynamics. J Phys Chem A 2005; 109:11679-86. [PMID: 16366617 DOI: 10.1021/jp055028h] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Parent radical cations of nonpolar solvents (alkanes and alkyl chlorides) ionize 9-(trimethylsilyl)xanthenes and 9-(trimethylsilyl)fluorenes in a diffusion-controlled electron transfer. The actual electron jump as the deciding part of the process does not require a defined encounter complex, and therefore the reactants are not subjected to any geometry optimization. Considering the molecule dynamics of the donors, bending motions of the silyl group are concerted with fluctuations of the highest occupied molecular orbital electrons. Ionizing such a standing conformer mixture creates metastable (microsecond) as well as dissociative donor radical cations. A mobility restriction of the benzylic silane group in positions vertical to the phenyl plane stabilizes the radical cations and accounts for a declining amount of dissociative radical cations, which undergo C-Si bond fragmentation in the order benzylsilane > xanthenylsilane > fluorenylsilane.
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Affiliation(s)
- Nikolaos Karakostas
- Interdisciplinary Group for Time-Resolved Spectroscopy, University of Leipzig, Permoserstrasse 15, D-04303 Leipzig, Germany
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Brede O, Naumov S, Hermann R. Monitoring molecule dynamics by free electron transfer. Radiat Phys Chem Oxf Engl 1993 2003. [DOI: 10.1016/s0969-806x(03)00041-0] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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Milosavljevic BH, Thomas JK. The photophysics of 1-hydroxypyrene, the acidity of its singlet excited state, and the nature of its photoionization process in polar media. Photochem Photobiol Sci 2002; 1:100-4. [PMID: 12659124 DOI: 10.1039/b107925e] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The photophysics of 1-hydroxypyrene, Py-OH, in various media has been examined by pulsed laser and steady state methods. In alkaline polar media the photophysics of the ionized form, Py-O(-), the pyrenolate ion, is reported. From the data the pK(a) is calculated to be 8.93 for the ground state and 4.5 for the excited state. However, the excited singlet state lifetime of Py-OH is too short to lead to significant dissociation into excited Py-O(-*) and H+, and no equilibrium between the species exists. Excitation of Py-OH leads to the excited singlet, the triplet, electrons (trapped), and a short-lived radical cation. The radical cation rapidly dissociates to give the pyrenyloxyl radical. Excitation of Py-O(-) gives the excited singlet state, the triplet state, solvated electrons and the pyrenyloxyl radical. No evidence of a radical cation of Py-O(-), i.e.,(+.)Py-O(-) is forthcoming, and only the neutral pyrenyloxyl radical is observed. Low temperature experiments in glasses are used to identify the various species produced.
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Affiliation(s)
- B H Milosavljevic
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, IN 46556, USA
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Brede O, Hermann R, Naumann W, Naumov S. Monitoring of the Heterogroup Twisting Dynamics in Phenol Type Molecules via Different Characteristic Free-Electron-Transfer Products. J Phys Chem A 2002. [DOI: 10.1021/jp013334z] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Ortwin Brede
- Interdisciplinary Group for Time-Resolved Spectroscopy, University of Leipzig, Permoserstrasse 15, D-04303 Leipzig, Germany, and Institute of Surface Modification, D-04303 Leipzig, Germany
| | - Ralf Hermann
- Interdisciplinary Group for Time-Resolved Spectroscopy, University of Leipzig, Permoserstrasse 15, D-04303 Leipzig, Germany, and Institute of Surface Modification, D-04303 Leipzig, Germany
| | - Wolfgang Naumann
- Interdisciplinary Group for Time-Resolved Spectroscopy, University of Leipzig, Permoserstrasse 15, D-04303 Leipzig, Germany, and Institute of Surface Modification, D-04303 Leipzig, Germany
| | - Sergej Naumov
- Interdisciplinary Group for Time-Resolved Spectroscopy, University of Leipzig, Permoserstrasse 15, D-04303 Leipzig, Germany, and Institute of Surface Modification, D-04303 Leipzig, Germany
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Brede O, Hermann R, Naumov S, Mahal H. Discrete ionization of two different short-living conformers of selenophenol by rapid free electron transfer to solvent parent radical cations. Chem Phys Lett 2001. [DOI: 10.1016/s0009-2614(01)01281-7] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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