Search results for "Tautomer"
showing 10 items of 141 documents
Switching and redox isomerism in first-row transition metal complexes containing redox active Schiff base ligands.
2014
International audience; The reversible redox isomerisms in first row transition metal complexes of the type ML2 were studied. The six ML2 complexes (M = Mn(III) (), Fe(II) (), Co(III) (), Ni(II) (), Cu(II) () and Zn(II) ()) were synthesized with a redox active Schiff base ligand [2-(3,5-di-tert-butyl-2-hydroxyphenylamino)-4-chlorophenol] (H3L) presenting different oxidation states from -2 to 0 (L(2-), L(-) and L(0)). EPR spectra and magnetic susceptibility measurements indicate the presence of complexes of the type [Mn(III)(L(2-))(L(-))] () with S = 1/2, [Fe(II)(L(-))2] () with S = 2, [Co(III)(L(2-))(L(-))] () with S = 1/2, [Ni(II)(L(-))2] () with S = 1, [Cu(II)(L(-))2] () with S = 1/2 and …
Gold/Isophorone Interaction Driven by Keto/Enol Tautomerization
2016
The binding behavior of isophorone (C9H14O) to Au adatoms and clusters deposited on MgO/Ag(001) thin films is investigated by scanning tunneling microscopy (STM) and density functional theory (DFT). The STM data reveal the formation of various metal/organic complexes, ranging from Au1/isophorone pairs to larger Au aggregates with molecules bound to their perimeter. DFT calculations find the energetically preferred keto-isophorone to be unreactive toward gold, while the enol-tautomer readily binds to Au monomers and clusters. The interaction is governed by electrostatic forces between the hydroxyl group of the enol and negative excess charges residing on the ad-gold. The activation barrier b…
Theoretical study of the NH tautomerism in free base porphyrin
1997
Abstract The NH tautomerism of free base porphyrin is investigated at the semiempirical spin-unrestricted AM1 (UAM1) and ab initio RHF/3-21G levels. The UAM1 method provides delocalized geometries for all stationary structures without imposing any symmetry constraint. RHF/3-21G geometry optimizations have to be performed under symmetry restrictions to ensure that realistic delocalized structures are obtained. Both the semiempirical and the ab initio calculations predict that the interconversion between trans tautomers proceeds in an asynchronous two-step process via intermediate cis tautomers. The cis tautomers are characterized as minima in the potential energy surface and are 8–10 kcal m…
Effect of π-Electron Delocalization on Tautomeric Equilibria – Benzoannulated 2-Phenacylpyridines
2006
Most benzoannulated 2-methylpyridines react with phenyllithium and substituted alkyl benzoates to give the corresponding 2-phenacylpyridines. 3-Methylisoquinoline is transformed into 2-benzoyl-3-methyl-1-phenyl-1,2-dihydroisoquinoline under these conditions, but replacement of phenyllithium with lithium isopropylcyclohexylamide is effective for production of 3-phenacylisoquinolines. Except in the cases of some substituted 6-phenacylphenanthridines, tautomeric mixtures of benzoannulated 2-phenacylpyridines in chloroform solution always contain the ketimine forms.(Z)-2-(2-Hydroxy-2-phenylvinyl)pyridine (enolimine) forms also contribute if the pyridine ring is not benzoannulated or if such ann…
Antifungal activity and tautomeric cyclization equilibria of formylphenylboronic acids
2019
2-Formylphenylboronic acid and four isomeric fluoro-2-formylphenylboronic acids have been found active against a series of fungal strains: Aspergillus, Fusarium, Penicillium and Candida. The level of antifungal activity was evaluated by agar diffusion tests as well as the determination of minimum inhibitory concentrations (MICs) by serial dilution method. Among the tested compounds, 4-fluoro-2-formylphenylboronic acid - an analogue of the known antifungal drug Tavaborole (AN2690) - proved to be the most potent antifungal agent. The tautomeric equilibrium leading to the formation of 3-hydroxybenzoxaboroles as well as the position of the fluorine substituent were revealed to play a crucial ro…
Theoretical electronic spectra of 2-aminopurine in vapor and in water
2006
The accurate quantum chemical CASSCF and CASPT2 methods combined with a Monte Carlo procedure to mimic solvation effects have been used in the calculation of the spectroscopic properties of two tautomers of 2-aminopurine (2AP). Absorption and emission spectra have been simulated both in vacuum and in aqueous environment. State and transition energies and properties have been obtained with high accuracy, leading to the assignment of the most important spectroscopic features. The lowest-lying 1 (,*) ( 1 La) state has been determined as responsible for the first band in the absorption spectrum and also for the strong fluorescence observed for the system in water. The combined approach used in …
Proton Transfer versus Hydrogen Bonding: The Reduction of Ubiquinone Q2Incorporated in a Self-Assembled Monolayer in Unbuffered Aqueous Solution
2014
The electrochemical reduction of ubiquinone Q2 (UQ2) in unbuffered aqueous media was investigated over a pH range of 2 to 11, and the results were compared to those obtained in our previous work in buffered solutions. The short isoprene chains of UQ2 were incorporated in a self-assembled monolayer. Analysis of the mechanism and a study in D2O solutions allowed us to demonstrate the important role of hydrogen bonding in the stabilization of the reduced species, also in water. If the concentration of H+ is low relative to that of the quinone, the electrochemical reaction does not proceed through proton-coupled electron transfer, as it does in buffered medium or at low pH values (pH<4.4). We p…
A combined experimental and theoretical study of the thermal cycloaddition of aryl azides with activated alkenes.
2011
International audience; Reactions were performed from aryl azides on the one hand, and activated alkenes coming from β-dicarbonyl compounds or malonodinitrile on the other hand, either with recourse to conventional heating or to microwave activation, to afford 1-aryl-1H-1,2,3-triazoles. The mechanism and the regioselectivity of the reactions involving β-dicarbonyl compounds have been theoretically studied using DFT methods at the B3LYP/6-31G* level: they are domino processes comprising a tautomeric equilibrium of the β-dicarbonyl compounds with their enol forms, a 1,3-dipolar cycloaddition of the enol forms with the aryl azides (high activation energy), and a dehydration process (lower acti…
Isotopic Effect on the Kinetics of the Belousov-Zhabotinsky Reaction
2007
In this work we present results about the deuterium isotope effect on the global kinetics of a Belousov-Zhabotinsky reaction in batch conditions. A nonlinear dependence of the Induction Period upon the percentage of deuterated reactants was found. The isotopic effect on the bromination reaction of malonic acid was evaluated.
Theoretical absorption and emission spectra of 1H- and 2H-benzotriazole
2003
Excitation energies, dipole moments, and transition properties for the lowest-lying 1(π, π*) and 1(n, π*) electronic states of two benzotriazole tautomers have been studied at the complete active space (CAS) SCF and multiconfigurational second-order perturbation (CASPT2) levels. With these results, the UV absorption spectra of 1H- and 2H-benzotriazole were first described individually, and then they were considered simultaneously in order to better understand the experimental, observed spectrum of benzotriazole. Aspects of the fluorescence of the compound have been also analyzed. The spectrum of benzotriazole is finally related to those of other azo-compounds.