scholarly journals Deprotonation Mechanism of Methyl Gallate: UV Spectroscopic and Computational Studies

2018 ◽  
Vol 19 (10) ◽  
pp. 3111 ◽  
Author(s):  
Liangliang Zhang ◽  
Yuchen Liu ◽  
Yongmei Wang
Keyword(s):  
Quantum Chemical Calculations ◽  
Quantum Chemical ◽  
Acid Dissociation ◽  
Acid Dissociation Constant ◽  
Methyl Gallate ◽  
Deprotonated Form ◽  
Ph Influence ◽  
Combined Use ◽  
Deprotonation Reaction ◽  
Uv Visible

In the present paper, methyl gallate (MeG), a simple polyphenol and also the monomer of hydrolysable tannins, was selected to study the deprotonation process for the hydroxyls of the galloyl group by the combined use of spectroscopic measurements and quantum chemical calculations. The results of quantum chemical calculations show that the deprotonated form of methyl gallate undergoes the para-quinoid localization in the benzene ring, compared with free methyl gallate. The predicted spectra obtained from the free and deprotonated methyl gallate models are in agreement with the experimental UV-visible (UV-vis) absorption spectra. In the same way, the vibrational spectra of the para-quinoid MeG models validate the proposed mechanism of the deprotonation of MeG molecule. The pH influence on the deprotonation reaction and oxidization of phenolic groups has been also investigated. The pKa values of MeG were evaluated using the chemometric modeling method. The first acid dissociation constant (pKa1) for MeG was evaluated to be 4.20 ± 0.01, and the second one (pKa2) was 10.78 ± 0.06.

scholarly journals Assignment of hydrogen-bond structure in a ligand-nucleobase complex inside duplex DNA: Combined use of quantum chemical calculations and 15N NMR experiments

2005 ◽  
Vol 49 (1) ◽  
pp. 255-256 ◽  
Author(s):  
Keitaro Yoshimoto ◽  
Seiichi Nishizawa ◽  
Hiroyuki Koshino ◽  
Yusuke Sato ◽  
Norio Teramae ◽  
...  
Keyword(s):  
Hydrogen Bond ◽  
Quantum Chemical Calculations ◽  
Quantum Chemical ◽  
15N Nmr ◽  
Duplex Dna ◽  
Combined Use

scholarly journals Study of interaction of metal ions with methylthymol blue by chemometrics and quantum chemical calculations

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Zolaikha Rasouli ◽  
Mehdi Irani ◽  
Sonia Jafari ◽  
Raouf Ghavami
Keyword(s):  
Charge Transfer ◽  
Metal Ions ◽  
Quantum Chemical Calculations ◽  
Quantum Chemical ◽  
Multivariate Curve Resolution ◽  
Molar Ratio ◽  
Ligand Charge Transfer ◽  
Visible Spectra ◽  
Uv Visible ◽  
Methylthymol Blue

AbstractIn this study, we determine the acidity constants of methylthymol blue (MTB) and association constants of its complexes with the ZnII, CuII, and FeII metal ions (MIs), through theoretical and experimental means. The complexes were characterized using UV–Visible absorption spectroscopy combined with soft/hard chemometrics methods and quantum chemical calculations. Quantum chemical calculations revealed that electronic transitions in the UV–Visible spectra of MTB have mixed n → π* and π → π* characters. The results of molar ratio and multivariate curve resolution alternating least squares (MCR-ALS) revealed the formation of successive 1:2 and 1:1 complexes (MI:MTB) for the ZnII and CuII systems. However, the formation of successive 1:1 and 2:1 complexes are suggested for FeII by the molar ratio and MCR-ALS. The majority of transitions observed in the UV–Visible spectra of the Zn(MTB) and Cu(MTB) complexes have ligand-to-ligand charge transfer (LLCT) characters. However, the transitions in the UV–Visible spectrum of the Fe(MTB) complex have LLCT and metal-to-ligand charge transfer (MLCT) characters. For the Fe2(MTB) complex, the lowest energy transition of has an LLCT character. However, its higher energy transitions are a mixture of LLCT, MLCT, and metal-to-metal charge transfer (MMCT) characters. The correlation between experimental and computed wavelengths revealed that the 1:1 complexes of ZnII and CuII prefer square pyramidal geometries. However, the FeII complexes always show octahedral geometry.

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