scholarly journals Delocalization of the Unpaired Electron in the Quercetin Radical: Comparison of Experimental ESR Data with DFT Calculations

2020 ◽  
Vol 21 (6) ◽  
pp. 2033 ◽  
Author(s):  
Zhengwen Li ◽  
Mohamed Moalin ◽  
Ming Zhang ◽  
Lily Vervoort ◽  
Alex Mommers ◽  
...  

In the antioxidant activity of quercetin (Q), stabilization of the energy in the quercetin radical (Q•) by delocalization of the unpaired electron (UE) in Q• is pivotal. The aim of this study is to further examine the delocalization of the UE in Q•, and to elucidate the importance of the functional groups of Q for the stabilization of the UE by combining experimentally obtained spin resonance spectroscopy (ESR) measurements with theoretical density functional theory (DFT) calculations. The ESR spectrum and DFT calculation of Q• and structurally related radicals both suggest that the UE of Q• is mostly delocalized in the B ring and partly on the AC ring. The negatively charged oxygen groups in the B ring (3′ and 4′) of Q• have an electron-donating effect that attract and stabilize the UE in the B ring. Radicals structurally related to Q• indicate that the negatively charged oxygen at 4′ has more of an effect on concentrating the UE in ring B than the negatively charged oxygen at 3′. The DFT calculation showed that an OH group at the 3-position of the AC ring is essential for concentrating the radical on the C2–C3 double bond. All these effects help to explain how the high energy of the UE is captured and a stable Q• is generated, which is pivotal in the antioxidant activity of Q.

2021 ◽  
Author(s):  
Jing Zhang ◽  
Shihan Liu ◽  
Tao Zhang ◽  
Tao Liu ◽  
Yu Lan

Density functional theory (DFT) calculation has been used to reveal the mechanism of Pd-catalyzed disilylation reaction of aryl halide. The DFT calculations indicate that the reaction starts with oxidative addition...


2012 ◽  
Vol 57 (6) ◽  
pp. 654-662 ◽  
Author(s):  
Fumihiko Yoshino ◽  
Ayaka Yoshida ◽  
Satoko Wada-Takahashi ◽  
Shuta Sugiyama ◽  
Fumiaki Tokutomi ◽  
...  

2020 ◽  
Author(s):  
Takahiro Toma ◽  
Ryo Maezono ◽  
Kenta Hongo

LiNiO<sub>2</sub> has high energy density but easily reacts with moisture in the atmosphere and deteriorates. We performed qualitative and quantitative evaluations of the degraded phase of LiNiO<sub>2</sub> and the influence of the structural change on the electrochemical properties of the phase. Li<sub>1-x</sub>H<sub>x</sub>NiO<sub>2</sub> phase with cation exchange between Li<sup>+</sup> and H<sup>+</sup> was confirmed by thermogravimetric analysis and Karl Fischer titration measurement. As the H concentration in LiNiO<sub>2</sub> increased, the rate capability deteriorated, especially in the low-temperature range and under low state of charge. Experimental and density functional theory (DFT) calculation results suggested that this outcome was due to increased activation energy of Li<sup>+</sup> diffusion owing to cation exchange. Rietveld analysis of X-ray diffraction and DFT calculation confirmed that the c lattice parameter and Li-O layer reduced because of the Li<sup>+</sup>/H<sup>+</sup> cation exchange. These results indicate that LiNiO<sub>2</sub> modified in the atmosphere has a narrowed Li-O layer, which is the Li diffusion path, and the rate characteristics are degraded.


2020 ◽  
Author(s):  
Takahiro Toma ◽  
Ryo Maezono ◽  
Kenta Hongo

LiNiO<sub>2</sub> has high energy density but easily reacts with moisture in the atmosphere and deteriorates. We performed qualitative and quantitative evaluations of the degraded phase of LiNiO<sub>2</sub> and the influence of the structural change on the electrochemical properties of the phase. Li<sub>1-x</sub>H<sub>x</sub>NiO<sub>2</sub> phase with cation exchange between Li<sup>+</sup> and H<sup>+</sup> was confirmed by thermogravimetric analysis and Karl Fischer titration measurement. As the H concentration in LiNiO<sub>2</sub> increased, the rate capability deteriorated, especially in the low-temperature range and under low state of charge. Experimental and density functional theory (DFT) calculation results suggested that this outcome was due to increased activation energy of Li<sup>+</sup> diffusion owing to cation exchange. Rietveld analysis of X-ray diffraction and DFT calculation confirmed that the c lattice parameter and Li-O layer reduced because of the Li<sup>+</sup>/H<sup>+</sup> cation exchange. These results indicate that LiNiO<sub>2</sub> modified in the atmosphere has a narrowed Li-O layer, which is the Li diffusion path, and the rate characteristics are degraded.


2007 ◽  
pp. 165-172 ◽  
Author(s):  
Aleksandra Velicanski ◽  
Dragoljub Cvetkovic ◽  
Sinisa Markov ◽  
Vesna Tumbas ◽  
Sladjana Savatovic

Kombucha is a beverage traditionally produced by metabolic activity of yeasts and acetic acid bacteria. The antimicrobial activity of lemon balm kombucha as well as of particular control samples was determined by agar-well diffusion method. Antioxidant activity on stable 1,1-diphenyl-2-picrylhydrazyl radicals of lemon balm kombucha and lemon balm tea was determined by electron spin resonance spectroscopy. Acetic acid, Kombucha samples and heat-denaturated kombucha showed significant antimicrobial activity against bacteria. However, there was no activity against yeasts and moulds. Kombucha showed higher antioxidant activity than tea sample for all applied sample volumes.


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