A thermochemical study of acid-base interactions in aqueous solutions of citric acid

Kochergina, L. A.; Васильев, В. П.; Krutov, D. V.; Krutova, O. N.

doi:10.1134/s0036024407020070

Cited by 6 publications

(5 citation statements)

References 15 publications

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“…the values reported by De Robertis et al 50 (with I = 0.1 M and I = 0.5 M), Crea et al 8 (with I = 0.5 M), and Beńeźeth et al 7 (I = 0.1 m and I = 0.5 m). They also agree with other experimental studies, 9,53,54 and calculations using the Pitzer theory. 8,50,55 In contrast, they differ with the values obtained at infinite dilution.…”

Section: Nmr Titration Of Citric Acidsupporting

confidence: 91%

“…Especially remarkable is the agreement with the values reported by De Robertis et al (with I = 0.1 M and I = 0.5 M), Crea et al (with I = 0.5 M), and Bénézeth et al ( I = 0.1 m and I = 0.5 m ). They also agree with other experimental studies, ,, and calculations using the Pitzer theory. ,, In contrast, they differ with the values obtained at infinite dilution . This discrepancy is expected because the NMR experiments were done at a sodium citrate concentration 0.1 M, so that the minimum value of the ionic strength in the titration experiment was I = 0.3 M.…”

Section: Nmr Titration Of Citric Acidsupporting

confidence: 82%

“…Each protonation step is described by an equilibrium reaction characterized by a macroscopic equilibrium constant. Citric acid has three ionizable carboxylic groups, and the corresponding macroscopic dissociation constants have been mostly measured by using potentiometry, in a wide range of ionic strengths and temperatures, in the presence of different ground electrolytes. − However, in the macroscopic approach, no information is provided about the population of the microstates, for which the protonation state of every individual site is specified. − In the case of citric acid, there is still controversy about the microstate populations compatible with the macroscopic dissociation constants. − …”

Section: Introductionmentioning

confidence: 99%

“…Expressing the macroscopic probabilities in terms of θ i (a H ) by inverting equation (9), and using the fact that P 0 (a H ) = 1 − n=1,..., N P n (a H ), the chemical shift can be expressed in terms of 9 the site-speci c degrees of protonation as the linear combination…”

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confidence: 99%

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Ionization and Conformational Equilibria of Citric Acid: Delocalized Proton Binding in Solution

et al. 2017

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The microspeciation of citric acid is studied by analyzing NMR titration data. When the site binding (SB) model, which assumes fully localized proton binding to the carboxylic groups, is used to obtain microscopic energy parameters (dissociation constants, pair and triplet interaction energies between charged carboxylate groups), contradictory results are obtained. The resulting macroscopic constants are in very good agreement with the values reported in the literature using potentiometry. However, the found pair interaction energy between the terminal carboxylates and the triplet interaction energy are physically meaningless. To solve this apparent contradiction, we consider the possibility of delocalized proton binding, so that the proton can be exchanged at high velocity in the NMR time scale through short, strong, low-barrier (SSLB) hydrogen bonds. With this aim, ab initio MP2 calculations using the SMD polarizable continuum model for the solvent were performed and the fully roto-microspeciation elucidated. First, fully localized proton binding was assumed, and the resulting microstate probabilities are in reasonable agreement with those reported in previous works that use selective blocking of the carboxylic groups. They are, however, in clear disagreement with the microstate probabilities derived from the NMR titration data, which predict, within a very narrow confidence interval, a unique microspecies for the symmetric di-ionized form. Moreover, counterintuitively, the interaction between terminal charged groups is much larger than that between central and terminal groups. As a consequence, we have explored the possibility of delocalized proton binding by calculating the energy of intermediate proton positions between two carbolxylic groups. The results reveal that the exchange of the proton through the hydrogen bonds is in some cases produced without energetic barrier. This effect is specially relevant in the di-ionized form, with all the most stable conformations forming a SSLB, which together would constitute the only microstate detected by NMR. An alternative reaction scheme for the ionization process, based on proton delocalization, is proposed.

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Section: Nmr Titration Of Citric Acidsupporting

confidence: 91%

Section: Nmr Titration Of Citric Acidsupporting

confidence: 82%

Section: Introductionmentioning

confidence: 99%

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confidence: 99%

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Ionization and Conformational Equilibria of Citric Acid: Delocalized Proton Binding in Solution

et al. 2017

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“…The only known investigation dealing with heat effects in the ternary systems of citric acid with nitric acid and potassium nitrate is that of Kochergina et al [161].…”

Section: (291)mentioning

confidence: 99%