Cyclovoltammetric study of the homogenous keto-enol equilibrium of dihydroxyfumaric acid in acid and neutral media

1986 ◽  
Vol 51 (7) ◽  
pp. 1407-1410 ◽  
Author(s):  
Dimitra Sazou ◽  
Pantelis Karabinas ◽  
Dimitrios Jannakoudakis
Keyword(s):  
Cyclic Voltammetry ◽  
Thermodynamic Parameters ◽  
Enol Form ◽  
Keto Form ◽  
Buffer Solutions ◽  
Thermodynamic Constant ◽  
Neutral Media

The keto-enol equilibrium of dihydroxyfumaric acid (DHF) was investigated in acid and neutral buffer solutions by cyclic voltammetry. The keto-form decreases with increasing pH, so that in neutral region (pH = 6 - 8) the equilibrium is totally shifted to the enol-form of the acid. The thermodynamic constant, Kk, of the equilibrium: enol-DHF ⇄ keto-DHF, was estimated at different pH and temperatures. The thermodynamic parameters ΔG, ΔH, and ΔS of the above equilibrium were also determined in 0.5 M-H2SO4 solution.

Crystal structure, spectroscopic studies and theoretical studies of thiobarbituric acid derivatives: understanding the hydrogen-bonding patterns

2018 ◽  
Vol 74 (12) ◽  
pp. 1703-1714 ◽  
Author(s):  
Anamika Sharma ◽  
Sizwe J. Zamisa ◽  
Sikabwe Noki ◽  
Zainab Almarhoon ◽  
Ayman El-Faham ◽  
...  
Keyword(s):  
Hydrogen Bonding ◽  
Materials Science ◽  
Thiobarbituric Acid ◽  
Intramolecular Hydrogen Bonding ◽  
Spectroscopic Studies ◽  
Enol Form ◽  
Keto Form ◽  
X Ray Crystallography ◽  
Schiff Base Formation ◽  
Intramolecular Hydrogen

In addition to their wide-ranging applications in the pharmaceutical industry, thiobarbituric acid (TBA) derivatives are also known to possess applications in engineering and materials science. 20 TBA derivatives, with diversity at the N and C-5 positions through acylation, Schiff base formation, Knoevenagel condensation, thioamide and enamine formation, were studied. The absolute configurations for six derivatives, namely 5-acetyl-1,3-diethyl-2-thioxodihydropyrimidine-4,6(1H,5H)-dione, C10H14N2O3S, A01, 1,3-diethyl-5-propionyl-2-thioxodihydropyrimidine-4,6(1H,5H)-dione, C11H16N2O3S, A02, tert-butyl [1-(1,3-diethyl-4,6-dioxo-2-thioxohexahydropyrimidin-5-yl)-3-methyl-1-oxobutan-2-yl]carbamate, C18H29N3O5S, A06, 1,3-diethyl-4,6-dioxo-2-thioxo-N-(p-tolyl)hexahydropyrimidine-5-carbothioamide, C16H19N3O2S2, A13, 5-(1-aminoethylidene)-1,3-diethyl-2-thioxodihydropyrimidine-4,6(1H,5H)-dione, C10H15N3O2S, A17, and 5-(1-aminopropylidene)-1,3-diethyl-2-thioxodihydropyrimidine-4,6(1H,5H)-dione, C11H17N3O2S, A18, were confirmed by single-crystal X-ray crystallography, which indicates the formation of intramolecular hydrogen bonding in all six cases and intermolecular hydrogen bonding for A17. In A13, the presence of two intramolecular hydrogen bonds was observed. The stabilization of the enol form over the keto form was confirmed by computation. In order to convert the keto form to the enol form, an energy barrier of 55.05 kcal mol−1 needs to be overcome, as confirmed by transition-state calculations.

scholarly journals QSAR modeling of anxiolytic activity taking into account the presence of keto- and enol-tautomers by balance of correlations with ideal slopes

2011 ◽  
Vol 9 (5) ◽  
pp. 846-854 ◽  
Author(s):  
Alla. Toropova ◽  
Andrey Toropov ◽  
Emilio Benfenati ◽  
Giuseppina Gini ◽  
Danuta Leszczynska ◽  
...  
Keyword(s):  
External Validation ◽  
Test System ◽  
Enol Form ◽  
Anxiolytic Activity ◽  
Statistical Characteristics ◽  
Qsar Modeling ◽  
Keto Form ◽  
System 2 ◽  
Balance Of Correlations ◽  
Validation Set

AbstractOptimal descriptors calculated with simplified molecular input line entry system (SMILES) have been examined as a tool for prediction of anxiolytic activity. Descriptors calculated with SMILES (a) of keto-isomers; (b) of enol-isomers; and (c) of both keto-isomers together with enol-isomers have been studied. Three approaches have been compared: 1. classic’ training-test’ system 2. balance of correlations and 3. balance of correlations with ideal slopes. The best statistical characteristics for the external validation set took place for optimal descriptors calculated with SMILES of both keto-form and enol-form (i.e., molecular structure was represented in the format: ’sMILES of keto-form. SMILES of enol-form’) by means of balance of correlations with ideal slopes. The predictive potential of this model was checked with three random splits.

ISOTOPE RATE EFFECTS IN THE ENOLIZATION OF OXALACETIC ACID

1962 ◽  
Vol 40 (7) ◽  
pp. 1280-1284 ◽  
Author(s):  
George W. Kosicki
Keyword(s):  
Direct Evidence ◽  
Aqueous System ◽  
Enol Form ◽  
Rate Effect ◽  
Keto Form ◽  
Oxalacetic Acid ◽  
Rate Determining Step ◽  
Rate Effects ◽  
Acid Catalyzed ◽  
Catalyzed Reactions

Acid-catalyzed enolization of oxalacetic acid in H2O and D2O gives rise to a constant isotope rate effect [Formula: see text] of 2.4 over the pH (pD) range of 5.5 to 7.5. Base-catalyzed enolization of oxalacetic acid in H2O and D2O gives rise to a constant isotope rate effect [Formula: see text] of 4.5 over the pH (pD) range of 7.0 to 8.0. The percentage of enol form of oxalacetic acid was calculated to be 15.3% at pH 8.0, using the absorption of the enol form in ether at 255 mμ and the absorption of the keto form at pH 0.5 in an aqueous system. The spectrophotometric measurement of the isotope rate effect involved in the enolization of oxalacetic acid gives direct evidence for the rate-determining step in both the acid- and the base-catalyzed reactions without subsequent reactions.

ELECTROCHEMICAL EVALUATION OF THE POLYMER MODIFIED MICRO-ELECTRODE FOR METAL IONS

2006 ◽  
Vol 20 (25n27) ◽  
pp. 4057-4062
Author(s):  
JUNKO MOTONAKA ◽  
TOMOKI YABUTANI ◽  
KEIJI MINAGAWA ◽  
YUJI MISHIMA
Keyword(s):  
Room Temperature ◽  
Enol Form ◽  
Porous Carbon Material ◽  
Optimal Conditions ◽  
Buffer Solution ◽  
Keto Form ◽  
Dimethyl Sulfoxide Solution ◽  
Scan Rate ◽  
Ethylhexyl Phthalate ◽  
Electrochemical Evaluation

A porous micro-electrode with immobilized poly(methacryroyl alanine) (PMA) was developed for measuring copper(II) ion ( Cu 2+) and cadmium(II) ion ( Cd 2+). A porous carbon material was packed into the tip of the platinum micro-electrode with a cavity at the top. The porous micro-electrode was dipped in the coating dimethyl sulfoxide solution with PMA and di-2-ethylhexyl phthalate and dried overnight at room temperature. The immobilized PMA on the porous micro-electrode had predominantly a keto form in the buffer solution. In the enol form a metal complex can be formed under the simultaneous liberation of a proton. Calibration curves for measurements of Cu 2+ and Cd 2+, the effects of preconcentration condition, scan rate, pH, and temperature, and lifetime of the PMA modified micro-electrode were examined. Under optimal conditions, the responses of sensor were linear in the concentration range 0.0001~1 mmol 1-1 for Cu 2+ and 0.01~1 mmol 1-1 for Cd 2+. Analytical values determined with the modified electrode were constant for at least 3 month.

Cyclic voltammetry of ferrocene-containing β-diketones as a tool to obtain group electronegativities. The structure of 3-ferrocenoyl-1,1,1-trifluoro-2-hydroxyprop-2-ene

1999 ◽  
Vol 77 (3) ◽  
pp. 378-386 ◽  
Author(s):  
WC (Ina) du Plessis ◽  
Johannes JC Erasmus ◽  
Gert J Lamprecht ◽  
Jeanet Conradie ◽  
T Stanley Cameron ◽  
...  
Keyword(s):  
Cyclic Voltammetry ◽  
Structure Determination ◽  
Methyl Esters ◽  
Enol Form ◽  
X Ray ◽  
Reduction Potentials ◽  
Group Electronegativity ◽  
Ferrocenyl Group ◽  
Group A

Formal reduction potentials (E°' values vs. Ag/Ag+ given in parentheses) in acetonitrile of 1-ferrocenyl-4,4,4-trifluorobutane-1,3-dione (ferrocenoyltrifluoroacetone, Hfctfa, 0.394 V), 1-ferrocenyl-4,4,4-trichlorobutane-1,3-dione (ferrocenoyltrichloroacetone, Hfctca, 0.370 V), 1-ferrocenylbutane-1,3-dione (ferrocenoylacetone, Hfca, 0.313 V), 1-ferrocenyl-3-phenylpropane-1,3-dione (benzoylferrocenoylmethane, Hbfcm, 0.306 V), and 1,3-diferrocenylpropane-1,3-dione (diferrocenoylmethane, Hdfcm, 0.265 and 0.374 V for the two electrochemically nonequivalent ferrocenyl groups) were determined. A linear relationship between observed group electronegativity, χ, and E°' as well as observed infrared carbonyl stretching frequencies of methyl esters of the type RCOOMe resulted in average χ-values, on the Gordy scale, of 1.87 for the ferrocenyl group and 2.82 for the ferrocenium group. A single crystal X-ray structure determination of Hfctfa (monoclinic, P21/n, Z = 4, R = 0.029) showed that this β-diketone crystallizes in the enol form. Asymmetric enolization in a direction furthest from the aromatic ferrocenyl group was observed.Key words: ferrocene, β-diketone, group electronegativity, cyclic voltammetry.

The N-acylhydrazine grouping as a ligand. I. Coordination compounds of Keto- and Enol-N-acylhydrazines with cobalt(II), nickel(II), and copper(II)

1972 ◽  
Vol 25 (2) ◽  
pp. 289 ◽  
Author(s):  
JF Alcock ◽  
RJ Baker ◽  
AA Diamantis
Keyword(s):  
Complex Formation ◽  
Transition Metal ◽  
Metal Ions ◽  
Coordination Compounds ◽  
Chelating Agents ◽  
Transition Metal Ions ◽  
Enol Form ◽  
Oxidation States ◽  
Keto Form ◽  
Formation Of Complexes

Ligands containing the N-acylhydrazine grouping, RCONHKH2, act as bidentate chelating agents with transition metal ions. Cationic complexes of coba1t(11), nickel(11), and copper(11) containing the ligands coordinated in the keto form were isolated, but the ligands also reacted in the enol form producing neutral complexes with cobalt(111) and copper(11). Complex formation in the enol form was facilitated by condensation of the ligands with acetone to produce the N'-iso-propylidene derivatives, from which keto complexes were also isolated. Under certain conditions N-acylhydrazines can act as reducing agents, leading to the formation of complexes containing copper in both oxidation states (I) and (11). Using N-benzoylhydrazine, this reaction can be utilized as a benzoylating medium for amines.

Ultrarot-Untersuchungen an der Amidgruppe

1953 ◽  
Vol 8 (11) ◽  
pp. 644-654 ◽  
Author(s):  
A. gierer
Keyword(s):  
Enol Form ◽  
Keto Form

Vielfach zeigen Eiweißstoffe und assoziierte Amide in gleicher Weise Spektren, die eine Koexistenz zweier verschiedener Arten von Wasserstoffbrücken der Amidgruppe vermuten lassen. Es wird gezeigt, daß die eine der beiden Formen längere Ketten von Assoziaten voraussetzt. Die Spektren lassen sich sowohl durch die Annahme zweier verschiedener räumlicher Anordnungen von H-Brücken in der Keto-Form (gestreckt und geknickt) als auch einer Koexistenz von Keto- und Enol-Form im assoziierten Zustand deuten.

scholarly journals New Precursors to 3-Sulfanylhexan-1-ol? Investigating the Keto–Enol Tautomerism of 3-S-Glutathionylhexanal

Molecules ◽  
2021 ◽  
Vol 26 (14) ◽  
pp. 4261
Author(s):  
Jennifer R. Muhl ◽  
Lisa I. Pilkington ◽  
Rebecca C. Deed
Keyword(s):  
Aqueous Solutions ◽  
Functional Group ◽  
Enol Form ◽  
Keto Form ◽  
White Wines ◽  
Sauvignon Blanc ◽  
Thiol Compound ◽  
Volatile Precursors ◽  
First Time

The volatile thiol compound 3-sulfanylhexan-1-ol (3SH) is a key impact odorant of white wines such as Sauvignon Blanc. 3SH is produced during fermentation by metabolism of non-volatile precursors such as 3-S-gluthathionylhexanal (glut-3SH-al). The biogenesis of 3SH is not fully understood, and the role of glut-3SH-al in this pathway is yet to be elucidated. The aldehyde functional group of glut-3SH-al is known to make this compound more reactive than other precursors to 3SH, and we are reporting for the first time that glut-3SH-al can exist in both keto and enol forms in aqueous solutions. At wine typical pH (~3.5), glut-3SH-al exists predominantly as the enol form. The dominance of the enol form over the keto form has implications in terms of potential consumption/conversion of glut-3SH-al by previously unidentified pathways. Therefore, this work will aid in the further elucidation of the role of glut-3SH-al towards 3SH formation in wine, with significant implications for the study and analysis of analogous compounds.

Studies on Phenylpyruvic Acid

1976 ◽  
Vol 31 (1-2) ◽  
pp. 5-11 ◽  
Author(s):  
Tautomerism ◽  
O Sciacovelli ◽  
A Dell 'atti ◽  
A De Giglio ◽  
L Cassidei ◽  
...  
Keyword(s):  
Sodium Salt ◽  
Enol Form ◽  
Propanoic Acid ◽  
Keto Acid ◽  
Coupling Constant ◽  
Buffer Solution ◽  
Vicinal Coupling Constant ◽  
Phenylpyruvic Acid ◽  
Keto Form ◽  
Enol Tautomer

The tautomerism of phenylpyruvic acid (PPA) and its sodium salt was investigated. The 1H and 13C spectra of PPA in aprotic solvents and in methanol show almost complete prevalence of the enol form, whereas the keto form prevails only in water. The Z configuration was assigned to the sole enol tautomer present on the basis of the value of the vicinal coupling constant | 3J1H,13COOH |=3.7 Hz. A small amount of the hydrated form of PPA (1-phenyl-2,2-dihydroxyl- propanoic acid) was found in the aqueous solution of its sodium salt and in buffer solution (pD =6) of PPA. By means of infrared spectroscopy one can conclude that crystalline PPA is in the enol whereas its sodium salt is in the keto form. The keto-acid was not obtained in the solid state. The colori­metric method for testing PPA traces in urine depends on the formation of a enol-Fe3+ complex (2:1) which appears stable in dimethylsulfoxide (DMSO).

scholarly journals Spectroscopic and Electrochemical Studies on the Interaction of Epirubicin with Fish Sperm DNA

2012 ◽  
Vol 9 (3) ◽  
pp. 1587-1598 ◽  
Author(s):  
R. Hajian ◽  
E. Ekhlasi ◽  
R. Daneshvar
Keyword(s):  
Cyclic Voltammetry ◽  
Thermodynamic Parameters ◽  
Strong Interactions ◽  
Binding Force ◽  
Double Stranded Dna ◽  
Fish Sperm ◽  
Sperm Dna ◽  
Apparent Binding Constant ◽  
Different Temperatures ◽  
Voltammetric Behavior

The interactions between epirubicin (EPR) and double stranded DNA (ds-DNA) have been studied by UV-Vis spectrophotometry, cyclic voltammetry, fluorescence spectroscopy and viscometery. The apparent binding constant of epirubicin with DNA was found to be 3.8 × 105mol-1L and was studied at different temperatures. It indicated that the former method could be successfully applied to the determination of epirubicin. Also, the voltammetric behavior of EPR was investigated at glassy carbon electrode using cyclic voltammetry. Thermodynamic parameters including ∆H0, ∆G0and ∆S0were determined as -5.7×104, -3.13×104J mol-1and -87.96 J mol-1K-1 respectively. One indication of the strong interaction between DNA and EP was increasing of viscosity. The diffusion coefficients of EP in the absence (D0)fand presence of ds-DNA (D0)bwas calculated as 5.04×10-6and 1.13×10-6 Cm2s-1respectively. According to the thermodynamic parameters, the main binding force could be judged. The experimental results revealed that EPR and ds-DNA had strong interactions. The mechanism of quenching belonged to static quenching and the main sort of binding force was intercalation.

Sign in / Sign up

Export Citation Format

Share Document