The protonation reactions of catechin, epicatechin and related compounds

1984 ◽  
Vol 37 (4) ◽  
pp. 885 ◽  
Author(s):  
JA Kennedy ◽  
MHG Munro ◽  
HKJ Powell ◽  
LJ Porter ◽  
LY Foo
Keyword(s):  
Time Scale ◽  
Protocatechuic Acid ◽  
Equilibrium Constants ◽  
Basic Solution ◽  
Ionic Mechanism ◽  
Model Compounds ◽  
Specific Solvation ◽  
Experimental Time ◽  
Protonation Sequence ◽  
Related Compounds

The protonation reactions for catechin and epicatechin have been studied at 25�C, I 0.10M (KCl). Equilibrium constants Kn for the protonation steps of the anions L4- have been determined from potentiometric and/or spectrophotometric measurements. The logKn values for the epimers differed significantly only for logKl and logK4 (values for catechin 13.26 � 0.05, 11.26 � 0.06, 9.41 � 0.02, 8.64 � 0.01, and epicatechin 13.40 � 0.05, ll.23 � 0.06, 9.49 � 0.02, 8.72 � .01, n = 1-4 respectively). These differences are ascribed to specific solvation effects or ion associations between K+ and the ligand anions. Epimerization was studied by h.p.l.c., and was found to be minimal over the experimental time scale at pH c. 13.5. The ring on which each stepwise protonation occurs was elucidated by reference to log Kn values measured for the model compounds catechol, 4-methylbenzene-1,2-diol, protocatechuic acid and 3',4'-di-O-methylcatechin. The protonation sequence is B ring, A ring, B ring and A ring. In contrast to earlier results, it has been established that the epimerization of catechin or epicatechin at C2, and the formation of catechinic acid in basic solution, may proceed through a radical rather than ionic mechanism.

Heats of formation of RuO4, RuO42−, and related compounds

1969 ◽  
Vol 47 (4) ◽  
pp. 581-586 ◽  
Author(s):  
E. E. Mercer ◽  
D. T. Farrar
Keyword(s):  
Sodium Periodate ◽  
Heats Of Formation ◽  
Basic Solution ◽  
Heat Of Reaction ◽  
Kcal Mole ◽  
Heats Of Reaction ◽  
Related Compounds

The heat of reaction of ruthenium metal with bromine in basic solution, according to the equation[Formula: see text]has been measured calorimetrically. In addition, the heat of oxidation of barium ruthenate hydrate by sodium periodate to form RuO4(aq) has been determined. From these heats of reaction, and several other heats measured here, the heats of formation of several ruthenium species have been calculated. The more important of these are: Na2RuO4(aq), ΔHf = −224.1 ± 0.8; RuO42−(aq), ΔHf = −109.4 ± 1.0; RuO4(aq), ΔHf = −57.5 ± 1.1; RuO4(l), ΔHf = −57.0 ± 1.1 kcal/mole.

Infrared and photoelectron spectra, and keto—enol tautomerism of acetylacetones and acetoacetic esters

1975 ◽  
Vol 342 (1630) ◽  
pp. 327-339 ◽  
Keyword(s):  
Wide Temperature Range ◽  
Photoelectron Spectrum ◽  
Equilibrium Constants ◽  
Ionization Potentials ◽  
Photoelectron Spectra ◽  
Temperature Range ◽  
Related Compounds

The infrared and photoelectron spectra of some substituted acetylacetones have been measured, and interpreted in terms of enolic and ketonic structures. Ionization potentials from specific orbitals have been assigned. With different substituents, the proportion of the two forms varies considerably. From measurements of the photoelectron spectrum over a wide temperature range, the equilibrium constants for keto-enol forms have been determined and estimates made of the enthalpy of the tautomeric change. Conclusions about the tautomerism have been correlated with earlier measurements by other methods. For comparison, the spectra of acetoacetic esters and related compounds have been measured. The proportions of keto-enol forms have been estimated and ionization potentials assigned to particular orbitals.

A 1H NMR Study of the Syn-Anti Dynamic Equilibrium in Adenine Nucleosides and Nucleotides with the Aid of Some Synthetic Model Analogues with Fixed Conformations

1979 ◽  
Vol 34 (5-6) ◽  
pp. 359-373 ◽  
Author(s):  
Lech Dudycz ◽  
Ryszard Stolarski ◽  
Reynaldo Pless ◽  
David Shugar
Keyword(s):  
Dynamic Equilibrium ◽  
Glycosidic Bond ◽  
Bulky Substituent ◽  
Model Compounds ◽  
H Nmr ◽  
Nmr Study ◽  
Sugar Ring ◽  
Intramolecular Bonding ◽  
Solvent Systems ◽  
Related Compounds

Abstract The syn-anti equilibrium about the glycosidic bond in adenosine and some related analogues was studied by means of 1H NMR spectroscopy, with the aid of several model analogues fixed in given conformations either by intramolecular bonding, or by introduction of a bulky substituent. A model unambiguously and exclusively in the syn conformation is 8-(α-hydroxyisopropyl) adenosine; while one fixed in the a n ti conformation is 8,5′-anhydro-8-oxoadenosine. A new analogue, fixed in the high an ti conformation, is 8,2′-O-isopropylidenearabinofuranosyladenine. Several additional new model compounds were synthesized and their properties are described.With the aid of these models, the syn-anti dynamic equilibrium was examined for adenosine and some related compounds in different solvent systems, and the conformer populations evaluated quantitatively. The validity of the procedure applied, and the accuracy of the results, are critically examined, and compared with findings obtained by other procedures. Available literature data on the syn-anti equilibrium in other 8-substituted adenosines are re analyzed in the light of the present results. An analysis is also presented of the interdependence of the various conformational parameters, i. e. conformation about the glycosidic bond and those of the sugar ring and exocyclic carbinol group, in adenosine and 2′,3′-O-isopropylideneadenosine.

Die molare freie Zusatzenthalpie am kritischen Entmischungspunkt als Kriterium für Modelltheorien flüssiger Mischungen / Molar Excess Free Energy at the Critical Solution Point as a Criterion of Model Theories for Liquid Mixtures

1976 ◽  
Vol 31 (6) ◽  
pp. 602-610
Author(s):  
Friedrich Becker ◽  
Michael Kiefer ◽  
Peter Rhensius
Keyword(s):  
Excess Free Energy ◽  
Equilibrium Constants ◽  
Liquid Mixtures ◽  
Model Parameters ◽  
Specific Solvation ◽  
Binary Liquid ◽  
Nearest Neighbours ◽  
Critical Solution Point ◽  
Solution Point ◽  
Critical Mixing

Theoretical expressions of GΕ/RT for symmetric and unsymmetric binary liquid mixtures, as proposed by Guggenheim, Redlich and Kister, van Laar, Renon and Prausnitz, are compared with the equilibrium model theory which we have developed some years ago, with respect to their predictions of GcΕ/RTc, and its dependence on the number of nearest neighbours, on the critical mole fraction, and on other model parameters. Equilibrium models allow discussion of critical mixing by means of a relation between the two equilibrium constants used. This is done for two typical examples: Mutual unspecific solvation of both components, coupled with (1) unsymmetric selfassociation. and (2) unsymmetric specific solvation. A discussion of phase separation at negative values of GcΕ/RTc is given

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