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Université de Fribourg

Indirect solvent assisted tautomerism in 4-substituted phthalimide 2-hydroxy-Schiff bases

Yordanov, Dancho ; Deneva, Vera ; Georgiev, Anton ; Crochet, Aurélien ; Fromm, Katharina M. ; Antonova, Liudmil

In: Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2020, vol. 237, p. 118416

The paper presents the synthesis and characterization of two 4-substituted phthalimide 2-hydroxy-Schiff bases containing salicylic (4) and 2-hydroxy-1-naphthyl (5) moieties. The structural differences of 2-hydroxyaryl substituents, resulting in different enol/keto tautomeric behaviour, depending on the solvent environment were studied by absorption UV–Vis spectroscopy. Compound 5 is...

Université de Fribourg

Tautomerism and self-association in the solution of new pinene-bipyridine and pinene-phenanthroline derivatives

Solea, Atena B. ; Cornu, Ivan ; Deneva, Vera ; Crochet, Aurélien ; Fromm, Katharina M. ; Antonov, Liudmil ; Allemann, Christophe ; Mamula, Olimpia

In: Molecules, 2020, vol. 25, no. 2, p. 298

Two novel pinene-type ligands have been synthesized and their tautomeric and self- associating behavior studied in solution and in the solid state. The first ligand, an acetylated derivative of 5,6-pinene-bipyridine, displays keto-enol tautomerism in solution. This tautomeric equilibrium was studied by NMR and UV-Vis spectroscopy in various solvents, and the results were compared with the ones...

Université de Fribourg

Tautomerism as primary signaling mechanism in metal sensing: the case of amide group

Deneva, Vera ; Dobrikov, Georgi ; Crochet, Aurélien ; Nedeltcheva, Daniela ; Fromm, Katharina M. ; Antonov, Liudmil

In: Beilstein Journal of Organic Chemistry, 2019, vol. 15, no. 1, p. 1898–1906

The concept for sensing systems using the tautomerism as elementary signaling process has been further developed by synthesizing a ligand containing 4- (phenyldiazenyl)naphthalene-1-ol as a tautomeric block and an amide group as metal capturing antenna. Although it has been expected that the intramolecular hydrogen bonding (between the tautomeric hydroxy group and the nitrogen atom from the...

Université de Fribourg

Isomerization and aggregation of 2-(2-(2-hydroxy-4-nitrophenyl)hydrazono)-1-phenylbutane-1,3-dione: Recent evidences from theory and experiment

Hristova, Silvia ; Kamounah, Fadhil S. ; Crochet, Aurélien ; Hansen, Poul Erik ; Fromm, Katharina M. ; Nedeltcheva, Daniela ; Antonov, Liudmil

In: Journal of Molecular Liquids, 2019, vol. 283, p. 242–248

The title compound potentially can exist as four isomers in solution. Recently Lycka has proposed a protocol for distinguishing two of them based on 15N NMR. This approach has been confirmed theoretically, in the current study, and further developed into a logical scheme that allows the existence of each of the isomers to be proven in solution. The experimental data, obtained by NMR and...

Université de Fribourg

Tautomerism in azo dyes: Border cases of azo and hydrazo tautomers as possible NMR reference compounds

Deneva, Vera ; Lyčka, Antonin ; Hristova, S. ; Crochet, Aurélien ; Fromm, Katharina M. ; Antonov, Liudmil

In: Dyes and Pigments, 2019, vol. 165, p. 157–163

In order to meet the need for NMR reference compounds in the study of tautomeric azo dyes, two series of azo dyes, derived from 3-methyl-1-phenyl-4- (phenyldiazenyl)-1H-pyrazol-5-amine and 5-methyl-2-phenyl-4-(2- phenylhydrazono)-2,4-dihydro-3H-pyrazol-3-one, have been studied by using molecular spectroscopy (UV–Vis and NMR) and quantum-chemical calculations (M06- 2X/TZVP) in solution. The...

Université de Fribourg

Betti bases from 4-(3-pyridazo)-1-naphthol: synthesis, coordination behaviour and unusual substitution reactions

Kurteva, Vanya B. ; Lubenov, Lubomir A. ; Shivachev, Boris L. ; Nikolova, Rositsa P. ; Fromm, Katharina M.

In: ChemistrySelect, 2018, vol. 3, no. 43, p. 12017–12021

A series of Betti bases from 4‐(3‐pyridyl)azo‐1‐naphthol dye, possessing flexible methylene or more constrained aryl‐methyne spaced NH‐containing side‐chains, were obtained and characterized. It was shown by NMR spectroscopy that the ligands exist in keto form. The products’ structure was confirmed by single crystal XRD of a selected sample. A study on the coordination ability...

Université de Fribourg

A concept for stimulated proton transfer in 1-(phenyldiazenyl)naphthalen-2-ols

Hristova, S. ; Deneva, Vera V. ; Pittelkow, M. ; Crochet, Aurélien ; Kamounah, Fadhil S. ; Fromm, Katharina M. ; Hansen, P. E. ; Antonov, Liudmil

In: Dyes and Pigments, 2018, vol. 156, p. 91-99

A series of aryl azo derivatives of naphthols (1–3) were studied by means of UV–Vis and NMR spectroscopy in different solvents as well as by quantum chemical calculations and X-ray analysis. Previous studies have shown that Sudan I (1) exists as a tautomeric mixture. The effect of the solvents is minimized by the existing intramolecular hydrogen bond. Therefore, the influence on the...