Some aspects of the aqueous solution chemistry of the Na+/Ca2+/OH-/Cit3- system: The structure of a new calcium citrate complex forming under hyperalkaline conditions

Attila Gácsi, Bence Kutus, Ákos Buckó, Zita Csendes, G. Peintler, I. Pálinkó, P. Sipos

Research output: Contribution to journalArticle

2 Citations (Scopus)

Abstract

In the present study, we show that in hyperalkaline (pH > 13) aqueous solutions, Ca2+ forms a new, so far unknown complex species with the citrate ion, the structure of which is different from the well-known CaCit- (aq) species present in solutions of close to neutral pH. The solubility of Ca3Cit2(s) was found to increase significantly under hyperalkaline conditions. The decrease in the electric conductivity and the variations observed in the freezing point depression of such solutions also indicate complexation. From 1H NMR measurements, in this complex, the citrate ion is suggested to be in quadruply deprotonated form. From the variation of the 2JHH geminal proton coupling constant, two neighboring carboxylate groups are coordinated to the calcium ion in a monodentate mode (besides the alcoholate). The optimal structure of the complex with the composition of CaCitH2- -1(aq) has also been calculated using DFT calculations, applying the Polarizable Continuum Model. Sodium ion-pairing was found to compete efficiently with this calcium complexation process, and in solutions with high Na-ion content, the equilibria are shifted towards the formation of NaCit2- (aq) and Na2Cit- (aq) ion pairs.

Original languageEnglish
Pages (from-to)110-116
Number of pages7
JournalJournal of Molecular Structure
Volume1118
DOIs
Publication statusPublished - Aug 15 2016

Fingerprint

Calcium Citrate
Ions
Complexation
Citric Acid
Calcium
Discrete Fourier transforms
Freezing
hydroxide ion
Protons
Solubility
Sodium
Nuclear magnetic resonance
Chemical analysis

Keywords

  • H NMR
  • Calcium
  • Citrate
  • Complexation
  • DFT calculations
  • Hyperalkaline solutions

ASJC Scopus subject areas

  • Spectroscopy
  • Analytical Chemistry
  • Inorganic Chemistry
  • Organic Chemistry

Cite this

@article{2e1b5ce332164b4b892934266b6f1d0c,
title = "Some aspects of the aqueous solution chemistry of the Na+/Ca2+/OH-/Cit3- system: The structure of a new calcium citrate complex forming under hyperalkaline conditions",
abstract = "In the present study, we show that in hyperalkaline (pH > 13) aqueous solutions, Ca2+ forms a new, so far unknown complex species with the citrate ion, the structure of which is different from the well-known CaCit- (aq) species present in solutions of close to neutral pH. The solubility of Ca3Cit2(s) was found to increase significantly under hyperalkaline conditions. The decrease in the electric conductivity and the variations observed in the freezing point depression of such solutions also indicate complexation. From 1H NMR measurements, in this complex, the citrate ion is suggested to be in quadruply deprotonated form. From the variation of the 2JHH geminal proton coupling constant, two neighboring carboxylate groups are coordinated to the calcium ion in a monodentate mode (besides the alcoholate). The optimal structure of the complex with the composition of CaCitH2- -1(aq) has also been calculated using DFT calculations, applying the Polarizable Continuum Model. Sodium ion-pairing was found to compete efficiently with this calcium complexation process, and in solutions with high Na-ion content, the equilibria are shifted towards the formation of NaCit2- (aq) and Na2Cit- (aq) ion pairs.",
keywords = "H NMR, Calcium, Citrate, Complexation, DFT calculations, Hyperalkaline solutions",
author = "Attila G{\'a}csi and Bence Kutus and {\'A}kos Buck{\'o} and Zita Csendes and G. Peintler and I. P{\'a}link{\'o} and P. Sipos",
year = "2016",
month = "8",
day = "15",
doi = "10.1016/j.molstruc.2016.03.100",
language = "English",
volume = "1118",
pages = "110--116",
journal = "Journal of Molecular Structure",
issn = "0022-2860",
publisher = "Elsevier",

}

TY - JOUR

T1 - Some aspects of the aqueous solution chemistry of the Na+/Ca2+/OH-/Cit3- system

T2 - The structure of a new calcium citrate complex forming under hyperalkaline conditions

AU - Gácsi, Attila

AU - Kutus, Bence

AU - Buckó, Ákos

AU - Csendes, Zita

AU - Peintler, G.

AU - Pálinkó, I.

AU - Sipos, P.

PY - 2016/8/15

Y1 - 2016/8/15

N2 - In the present study, we show that in hyperalkaline (pH > 13) aqueous solutions, Ca2+ forms a new, so far unknown complex species with the citrate ion, the structure of which is different from the well-known CaCit- (aq) species present in solutions of close to neutral pH. The solubility of Ca3Cit2(s) was found to increase significantly under hyperalkaline conditions. The decrease in the electric conductivity and the variations observed in the freezing point depression of such solutions also indicate complexation. From 1H NMR measurements, in this complex, the citrate ion is suggested to be in quadruply deprotonated form. From the variation of the 2JHH geminal proton coupling constant, two neighboring carboxylate groups are coordinated to the calcium ion in a monodentate mode (besides the alcoholate). The optimal structure of the complex with the composition of CaCitH2- -1(aq) has also been calculated using DFT calculations, applying the Polarizable Continuum Model. Sodium ion-pairing was found to compete efficiently with this calcium complexation process, and in solutions with high Na-ion content, the equilibria are shifted towards the formation of NaCit2- (aq) and Na2Cit- (aq) ion pairs.

AB - In the present study, we show that in hyperalkaline (pH > 13) aqueous solutions, Ca2+ forms a new, so far unknown complex species with the citrate ion, the structure of which is different from the well-known CaCit- (aq) species present in solutions of close to neutral pH. The solubility of Ca3Cit2(s) was found to increase significantly under hyperalkaline conditions. The decrease in the electric conductivity and the variations observed in the freezing point depression of such solutions also indicate complexation. From 1H NMR measurements, in this complex, the citrate ion is suggested to be in quadruply deprotonated form. From the variation of the 2JHH geminal proton coupling constant, two neighboring carboxylate groups are coordinated to the calcium ion in a monodentate mode (besides the alcoholate). The optimal structure of the complex with the composition of CaCitH2- -1(aq) has also been calculated using DFT calculations, applying the Polarizable Continuum Model. Sodium ion-pairing was found to compete efficiently with this calcium complexation process, and in solutions with high Na-ion content, the equilibria are shifted towards the formation of NaCit2- (aq) and Na2Cit- (aq) ion pairs.

KW - H NMR

KW - Calcium

KW - Citrate

KW - Complexation

KW - DFT calculations

KW - Hyperalkaline solutions

UR - http://www.scopus.com/inward/record.url?scp=84963550662&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=84963550662&partnerID=8YFLogxK

U2 - 10.1016/j.molstruc.2016.03.100

DO - 10.1016/j.molstruc.2016.03.100

M3 - Article

AN - SCOPUS:84963550662

VL - 1118

SP - 110

EP - 116

JO - Journal of Molecular Structure

JF - Journal of Molecular Structure

SN - 0022-2860

ER -