EPR study of phenolic radical stabilization by grafting on SiO2

Stathi, Panagiota; Louloudi, Maria; Deligiannakis, Yiannis

doi:10.1016/j.cplett.2009.02.080

Cited by 27 publications

(47 citation statements)

References 23 publications

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“…The high reactivity of 2 · in comparison with 1 · is not immediately obvious from the DFT calculations. The radicals [2a] · , [2b] · , and [2c] · should be quite persistent compared with typical phenoxyl and ferrocenium radicals such as 4 · , 5 · , FcH ·+ , [H‐2] ·+ , and [3c] · (see Figures S18 and S13 in the Supporting Information and refs 16,26,47–52…”

Section: Resultsmentioning

confidence: 99%

How Hydrogen Bonds Affect Reactivity and Intervalence Charge Transfer in Ferrocenium‐Phenolate Radicals

2016

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The ferrocenyl-phenol 2,4-di-tert-butyl-6-(ferrocenylcarbamoyl)phenol (H-1) forms intramolecular hydrogen bonds which are absent in its constitutional isomer 2,6-di-tert-butyl-4-(ferrocenylcarbamoyl)phenol (H-2). Their corresponding bases 1and 2show intra-and intermolecular NH···O hydrogen bonds, respectively. The phenolate 1is reversibly oxidized to 1 · , whereas 2only undergoes a quasi-reversible oxidation to 2 · , which suggests a higher reactivity. The radical pools of 1 · and 2 · formed by the oxidation/deprotonation of H-1 and H-2 have been probed by (rapid-freeze) electron paramagnetic resonance (EPR) spectroscopy and by spin-trapping techniques to elucidate the types of radicals present. Ferrocenium phenolate [1a] · featuring an NH···O intramolecular hydrogen bond is the most stable radical and undergoes thermal and photoinduced valence isomerization to the phenoxyl radical valence [a] Scheme 1. Hydrogen bonding in salicyl amides H-1, H-4, and H-4 Me , their corresponding phenolates 1 -, 4 -, and [4 Me ] -, and their corresponding phenoxyl radicals 1 · , 4 · , and [4 Me ] · . [16,25] the IHB. Large potential differences are observed between hydrogen-bonded and non-hydrogen-bonded phenolate/phenoxyl couples such as 4 -/4 · (E 1/2 = -160 mV vs. FcH/FcH + in CH 3 CN/[nBu 4 N][BF 4 ]) [25] and [4 Me ] -/[4 Me ] · (E 1/2 = -425 mV vs. FcH/FcH + in CH 3 CN/[nBu 4 N][BF 4 ]; [25] Scheme 1, b, c). [25] Similarly, the hydrogen-bonded ferrocenyl-NH moiety in H-A (E 1/2 = -115 mV vs. FcH/FcH + in CH 3 CN/[nBu 4 N][PF 6 ]) [27,28] is oxidized at a lower potential than N-acetylaminoferrocene H-3 (E 1/2 = -50 mV vs. FcH/FcH + in CH 2 Cl 2 /[nBu 4 N][B(C 6 F 5 ) 4 ]; [26,27,29,30] Scheme 2, a).Another intriguing example of this kind of PCET with the crucial NH···O IHB is found for the amide-linked ferrocenyl-quin-Eur. Scheme 2. a,b) IHBs in the ferrocene/ferrocenium amide redox couples H-A/ [H-A] ·+ and H-B/[H-B] ·and c) ET and PT from the ferrocenyl-phenol ferrocifen (H-C).1276 corresponding ferrocenyl-phenols H-1 and H-2 in the presence of base and oxidant was probed by the spin-trapping technique. The possible presence of different radical types is relevant for the reactivity of cytostatic drugs based on the ferrocenyl-phenol motif, such as ferrocifen (H-C).

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Section: Resultsmentioning

confidence: 99%

How Hydrogen Bonds Affect Reactivity and Intervalence Charge Transfer in Ferrocenium‐Phenolate Radicals

2016

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“…Herein, we used EPR spectroscopy to estimate the radical-forming phenolic units in each hybrid material. To obtain the maximum stable radicals, the hybrid NPs were incubated in aqueous solution at pH 12, as described in [20]. All EPR data in Fig.…”

Section: Epr Spectroscopymentioning

confidence: 99%

“…According to Deligiannakis et al [7,20], the preparation protocol for the SiO 2 -HALP NPs consisted of two main steps. First, aminopropyl-SiO 2 (APTES-SiO 2 ) was prepared by reacting 5 g of dry SiO 2 with 5 ml of aminopropyl-triethoxy-silane in 50 ml of toluene.…”

Section: Preparation Of Sio 2 -Halp Npsmentioning

confidence: 99%

“…Maximum radical concentration was achieved via oxidation of HALP by O 2 in aqueous solution at alkaline pH [20,28,29]. (ii) To monitor the radical reactions, for example, between DPPH and SiO 2 -HALP NPs.…”

Section: Epr Spectroscopymentioning

confidence: 99%

“…Recently, we have shown that grafting of simple polyphenols e.g. gallic acid [20] or natural HAs [21] on SiO 2 improves their radical-stabilization [20] and interfacial chemistry [21] properties. In this context, it has been demonstrated recently that grafting of gallic acid on SiO 2 nanoparticles [7] results in a hybrid material that is very efficiently as Hydrogen Atom Transfer agent [7].…”

Section: Introductionmentioning

confidence: 99%

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Interfacial Hydrogen Atom Transfer by nanohybrids based on Humic Acid Like Polycondensates

Bletsa

Stathi

Dimos

et al. 2015

Journal of Colloid and Interface Science

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Α {Silk@Gallic‐Acid} hybrid material with controllable antioxidant hydrogen‐atom‐transfer activity

Theofanous,

Deligiannakis,

Louloudi

2024

Applied Research

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Silk fiber, often acclaimed as the pinnacle of textile materials, finds contemporary applications in the textile industry, health, and cosmetics. Gallic acid (GA) is a well‐established natural antioxidant. In the present study, a novel hybrid material SFd@GA was conceptualized and produced via surface grafting of GA onto degummed silk‐fibers (SFd). Successful covalent‐grafting of gallic acid onto the silk fabric surface was confirmed through Fourier‐transform infrared, Raman, thermogravimetric analysis (TG‐DTA), and scanning electron microscopy (SEM). electron paramagnetic resonance spectroscopy demonstrates that gallic moieties grafted on SFd@GA retain their radical/redox activity. The antioxidant capacity of the hybrid material SFd@GA was validated by quantitative analysis of antioxidant hydrogen‐atom‐transfer (HAT) to DPPH radicals. Our data reveal a 550% increase in antioxidant‐HAT activity of SFd@GA versus natural intact silk fiber, and a 1400% increase in antioxidant‐HAT activity compared to the degummed silk fiber. The paramount discovery of the present work lies in the capacity for repeated utilization of the hybrid material SFd@GA, without any discernible compromise in its antioxidant‐HAT activity. Specifically, we show that SFd@GA can be employed for at least 15 consecutive cycles, retaining >98% of its HAT efficiency, for up to many days of storage under ambient conditions. We discuss this expositional performance via the controllable Hat‐activity process that we propose.

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EPR study of phenolic radical stabilization by grafting on SiO2

Cited by 27 publications

References 23 publications

How Hydrogen Bonds Affect Reactivity and Intervalence Charge Transfer in Ferrocenium‐Phenolate Radicals

How Hydrogen Bonds Affect Reactivity and Intervalence Charge Transfer in Ferrocenium‐Phenolate Radicals

Interfacial Hydrogen Atom Transfer by nanohybrids based on Humic Acid Like Polycondensates

Α {Silk@Gallic‐Acid} hybrid material with controllable antioxidant hydrogen‐atom‐transfer activity

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