Effects of magnesium ion on kinetic stability and spin distribution of phenoxyl radical derived from a vitamin E analogue: mechanistic insight into antioxidative hydrogen-transfer reaction of vitamin EElectronic supplementary information available: calculated spin density distributions and dependence of kHT on [Mg2+] for hydrogen transfer. See http://www.rsc.org/suppdata/p2/b2/b205380b/

Nakanishi, Ikuo; Fukuhara, Kiyoshi; Shimada, Tomokazu; Ohkubo, Kei; Iizuka, Yuko; Inami, Keiko; Mochizuki, Masahito; Urano, Shiro; Itoh, Shinobu; Miyata, Naoki; Fukuzumi, Shunichi

doi:10.1039/b205380b

Cited by 40 publications

(45 citation statements)

References 35 publications

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“…It is widely used as an EPR standard and serves as a radical scavenger/antioxidant, and, as such, it has numerous biological applications. 3,4 Since its discovery by G. Coppinger, 1 galvinoxyl and many of its derivatives have been studied extensively and electronic absorption, 5 photoelectron, 6 temperature dependent EPR spectra, 5,7,8 magnetic properties, 5,9,10 X-ray structure, 11,12 and photolysis experiments 13,14 have been published. Galvinoxyl has a C 2 rotational symmetry axis in crystals.…”

Section: Introductionmentioning

confidence: 99%

Photophysics of the galvinoxyl free radical revisited

Grilj

Zonca

Daku

et al. 2012

Phys. Chem. Chem. Phys.

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The photophysical properties of the free neutral radical galvinoxyl were studied by a combination of femtosecond time-resolved spectroscopy and quantum chemical calculations. The electronic absorption spectrum is dominated by an intense band at 430 nm that is ascribed to the D 9,10 ' D 0 transitions. Upon photoexcitation at 400 nm, the population of the D 9,10 states decays within less than 200 fs to the electronic ground state. This ultrafast internal conversion does not involve intramolecular modes with large amplitude motion as the measured dynamics does not show any significant dependence on the environment, but is most probably facilitated by a high density of electronic states of different character. Depending on the solvent, a weak transient band due to the galvinoxylate anion is also observed. This closed-shell species, which is fluorescent although its deactivation is also dominated by non-radiative decay, is generated upon biphotonic ionization of the solvent and electron capture. The ultrashort excited-state lifetime of the galvinoxyl radical precludes photoinduced disproportionation previously claimed to be at the origin of the formation of both anion and cation.

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Section: Introductionmentioning

confidence: 99%

Photophysics of the galvinoxyl free radical revisited

Grilj

Zonca

Daku

et al. 2012

Phys. Chem. Chem. Phys.

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“…Such a contrast effect (constant and acceleration in the rate) of added acetic acid can be attributed to the fact that in contrast to GO . (${E{{{\rm o}\hfill \atop {\rm red}\hfill}}}$ vs. saturated calomel electrode (SCE)=0.05 V),18 DPPH . has a relatively high reduction potential (${E{{{\rm o}\hfill \atop {\rm red}\hfill}}}$ vs. SCE=0.18 V),18 is thereby prone to undergo electron‐transfer reaction.…”

Section: Resultsmentioning

confidence: 99%

“…(${E{{{\rm o}\hfill \atop {\rm red}\hfill}}}$ vs. saturated calomel electrode (SCE)=0.05 V),18 DPPH . has a relatively high reduction potential (${E{{{\rm o}\hfill \atop {\rm red}\hfill}}}$ vs. SCE=0.18 V),18 is thereby prone to undergo electron‐transfer reaction. Nevertheless, for resveratrol, no acceleration was observed even in the case of DPPH .…”

Section: Resultsmentioning

confidence: 99%

“…However, in the case of DPPHC, an interesting acid-promoted reaction kinetics was observed for 4'-MeO-4-MS, 4-MS, and 4'-CF 3 -4-MS. Such a contrast effect (constant and acceleration in the rate) of added acetic acid can be attributed to the fact that in contrast to GOC (E o red vs. saturated calomel electrode (SCE) = 0.05 V), [18] DPPHC has a relatively high reduction potential (E o red vs. SCE = 0.18 V), [18] is thereby prone to undergo electrontransfer reaction. It is also noticeable that the ratios increase with increasing the electron-rich environment in the molecules, that is, the electron richer the molecule, the larger is the increased ratio of the k value, as demonstrated by the three 4-mercaptostilbenes.…”

Section: Acidity Constants Of the 4-mercaptostilbenesmentioning

confidence: 99%

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Extraordinary Radical Scavengers: 4‐Mercaptostilbenes

Cao

Yang

Dai

et al. 2012

Chemistry A European J

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In the past decade, there was a great deal of interest and excitement in developing more active antioxidants and cancer chemoprevention agents than resveratrol, a naturally occurring stilbene. In this work, eight resveratrol-directed 4-mercaptostilbenes were constructed based on the inspiration that thiophenol should be a stronger radical scavenger than phenol, and their reaction rates with galvinoxyl (GO(.)) and 2,2-diphenyl-1-picrylhydrazyl (DPPH(.)) radicals in methanol and ethyl acetate were measured by using stopped-flow UV/Vis spectroscopy at 25 °C. Kinetic analysis demonstrates that 4-mercaptostilbenes are extraordinary radical scavengers, and the substitution of the 4-SH group for the 4-OH group in the stilbene scaffold is an important strategy to improve the radical-scavenging activity of resveratrol. Surprisingly, in methanol, some of the 4-mercaptostilbenes are 10(4)-times more active than resveratrol, dozens of times to hundreds of times more effective than known antioxidants (α-tocopherol, ascorbic acid, quercetin, and trolox). The detailed radical-scavenging mechanisms were discussed based on acidified-kinetic analysis. Addition of acetic acid remarkably reduced the GO(.) and DPPH(.) radical-scavenging rates of the 4-mercaptostilbenes in methanol, a solvent that supports ionization, suggesting that the reactions proceed mainly through a sequential proton loss electron transfer mechanism. In contrast, an interesting acid-promoted kinetics was observed for the reactions of the 4-mercaptostilbenes with DPPH(.) in ethyl acetate, a solvent that weakly supports ionization. The increased ratio in rates is closely correlated with the electron-rich environment in the molecules, suggesting that the acceleration could benefit from the contribution of the electron transfer from the 4-mercaptostilbenes and DPPH(.). However, the addition of acetic acid had no influence on the GO(.)-scavenging rates of the 4-mercaptostilbenes in ethyl acetate, due to the occurrence of the direct hydrogen atom transfer. Our results show that the radical-scavenging activity and mechanisms of 4-mercaptostilbenes depends significantly on the molecular structure and acidity, the nature of the attacking radical, and the ionizing capacity of the solvent.

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“…In this case, solvents signicantly affect the radical-scavenging mechanism. 19 In fact, the radical-scavenging reaction of a vitamin E analogue proceeds via the one-step hydrogen-atom transfer in aprotic media, such as acetonitrile, 20 while the electron-transfer process is involved in protic solvents, such as methanol. 21 In this study, we focused on quercetin (2-(3,4-dihydroxyphenyl)-3,5,7-trihydroxy-4H-chromen-4-one), as a potential therapeutic agent to prevent illnesses caused by reactive oxygen radicals.…”

Section: Introductionmentioning

confidence: 99%