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

3 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

Keywords

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

ASJC Scopus subject areas

  • Spectroscopy
  • Analytical Chemistry
  • Inorganic Chemistry
  • Organic Chemistry

Fingerprint Dive into the research topics of 'Some aspects of the aqueous solution chemistry of the Na<sup>+</sup>/Ca<sup>2+</sup>/OH<sup>-</sup>/Cit<sup>3-</sup> system: The structure of a new calcium citrate complex forming under hyperalkaline conditions'. Together they form a unique fingerprint.

  • Cite this