The formation of Ca(II) enolato complexes with α- and β-ketoglutarate in strongly alkaline solutions

Csilla Dudás, Bence Kutus, G. Peintler, I. Pálinkó, P. Sipos

Research output: Contribution to journalArticle

Abstract

In the present study, the proton dissociation and calcium complex formation reactions of α- and β-ketoglutarate (2- and 3-oxopentane-dioate, α-Ket2− and β-Ket2−, respectively) in neutral and alkaline aqueous solutions were explored. From potentiometric measurements, the equilibrium constants of the [Ca(α-Ket)]0 and [Ca(β-Ket)]0 complexes formed in neutral medium were determined to be logK1,1 α = 1.15 ± 0.02 and logK1,1 β = 0.78 ± 0.02, respectively. In alkaline medium, it was found for both ligands that the methylene group underwent deprotonation yielding the carbanion-enolate anion. The deprotonation constants, pKa α and pKa β, were found to be 15.16 ± 0.01 and 14.41 ± 0.01, respectively. The calcium complexing behaviour of the two ligands was also studied in strongly alkaline medium. Under these conditions, the Ca2+ ion was capable of promoting the deprotonation of the ligands and forming various enolato-type complexes. The formation of both mono- and binuclear species were deduced, their formulae are suggested to be [Ca(α-Ket)H−1], [Ca2(α-Ket)H−3], [Ca(β-Ket)H−1], [Ca2(β-Ket)H−1]+ with the formation constants of log β11−1 α = −11.91 ± 0.02, log β21−3 α = −36.10 ± 0.06, log β11−1 β = −11.58 ± 0.01, log β21−1 β = −10.80 ± 0.03, respectively. Beside the formation of the rare Ca2+-enolato complexes, the deprotonation of the hydrating water molecules around the Ca2+ ion was also invoked in some cases.

Original languageEnglish
Pages (from-to)89-97
Number of pages9
JournalPolyhedron
Volume156
DOIs
Publication statusPublished - Dec 1 2018

Fingerprint

Deprotonation
Ligands
ligands
calcium
Calcium
Ions
Equilibrium constants
methylene
Anions
Protons
ions
Negative ions
dissociation
anions
aqueous solutions
Molecules
protons
Water
water
molecules

Keywords

  • Calcium
  • Enolato complexes
  • Hyperalkaline solution
  • Oxocarboxylates
  • Stability constants

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry
  • Materials Chemistry

Cite this

The formation of Ca(II) enolato complexes with α- and β-ketoglutarate in strongly alkaline solutions. / Dudás, Csilla; Kutus, Bence; Peintler, G.; Pálinkó, I.; Sipos, P.

In: Polyhedron, Vol. 156, 01.12.2018, p. 89-97.

Research output: Contribution to journalArticle

@article{c0ae2e442ca040b7987aca671201f755,
title = "The formation of Ca(II) enolato complexes with α- and β-ketoglutarate in strongly alkaline solutions",
abstract = "In the present study, the proton dissociation and calcium complex formation reactions of α- and β-ketoglutarate (2- and 3-oxopentane-dioate, α-Ket2− and β-Ket2−, respectively) in neutral and alkaline aqueous solutions were explored. From potentiometric measurements, the equilibrium constants of the [Ca(α-Ket)]0 and [Ca(β-Ket)]0 complexes formed in neutral medium were determined to be logK1,1 α = 1.15 ± 0.02 and logK1,1 β = 0.78 ± 0.02, respectively. In alkaline medium, it was found for both ligands that the methylene group underwent deprotonation yielding the carbanion-enolate anion. The deprotonation constants, pKa α and pKa β, were found to be 15.16 ± 0.01 and 14.41 ± 0.01, respectively. The calcium complexing behaviour of the two ligands was also studied in strongly alkaline medium. Under these conditions, the Ca2+ ion was capable of promoting the deprotonation of the ligands and forming various enolato-type complexes. The formation of both mono- and binuclear species were deduced, their formulae are suggested to be [Ca(α-Ket)H−1]−, [Ca2(α-Ket)H−3]−, [Ca(β-Ket)H−1]−, [Ca2(β-Ket)H−1]+ with the formation constants of log β11−1 α = −11.91 ± 0.02, log β21−3 α = −36.10 ± 0.06, log β11−1 β = −11.58 ± 0.01, log β21−1 β = −10.80 ± 0.03, respectively. Beside the formation of the rare Ca2+-enolato complexes, the deprotonation of the hydrating water molecules around the Ca2+ ion was also invoked in some cases.",
keywords = "Calcium, Enolato complexes, Hyperalkaline solution, Oxocarboxylates, Stability constants",
author = "Csilla Dud{\'a}s and Bence Kutus and G. Peintler and I. P{\'a}link{\'o} and P. Sipos",
year = "2018",
month = "12",
day = "1",
doi = "10.1016/j.poly.2018.09.005",
language = "English",
volume = "156",
pages = "89--97",
journal = "Polyhedron",
issn = "0277-5387",
publisher = "Elsevier Limited",

}

TY - JOUR

T1 - The formation of Ca(II) enolato complexes with α- and β-ketoglutarate in strongly alkaline solutions

AU - Dudás, Csilla

AU - Kutus, Bence

AU - Peintler, G.

AU - Pálinkó, I.

AU - Sipos, P.

PY - 2018/12/1

Y1 - 2018/12/1

N2 - In the present study, the proton dissociation and calcium complex formation reactions of α- and β-ketoglutarate (2- and 3-oxopentane-dioate, α-Ket2− and β-Ket2−, respectively) in neutral and alkaline aqueous solutions were explored. From potentiometric measurements, the equilibrium constants of the [Ca(α-Ket)]0 and [Ca(β-Ket)]0 complexes formed in neutral medium were determined to be logK1,1 α = 1.15 ± 0.02 and logK1,1 β = 0.78 ± 0.02, respectively. In alkaline medium, it was found for both ligands that the methylene group underwent deprotonation yielding the carbanion-enolate anion. The deprotonation constants, pKa α and pKa β, were found to be 15.16 ± 0.01 and 14.41 ± 0.01, respectively. The calcium complexing behaviour of the two ligands was also studied in strongly alkaline medium. Under these conditions, the Ca2+ ion was capable of promoting the deprotonation of the ligands and forming various enolato-type complexes. The formation of both mono- and binuclear species were deduced, their formulae are suggested to be [Ca(α-Ket)H−1]−, [Ca2(α-Ket)H−3]−, [Ca(β-Ket)H−1]−, [Ca2(β-Ket)H−1]+ with the formation constants of log β11−1 α = −11.91 ± 0.02, log β21−3 α = −36.10 ± 0.06, log β11−1 β = −11.58 ± 0.01, log β21−1 β = −10.80 ± 0.03, respectively. Beside the formation of the rare Ca2+-enolato complexes, the deprotonation of the hydrating water molecules around the Ca2+ ion was also invoked in some cases.

AB - In the present study, the proton dissociation and calcium complex formation reactions of α- and β-ketoglutarate (2- and 3-oxopentane-dioate, α-Ket2− and β-Ket2−, respectively) in neutral and alkaline aqueous solutions were explored. From potentiometric measurements, the equilibrium constants of the [Ca(α-Ket)]0 and [Ca(β-Ket)]0 complexes formed in neutral medium were determined to be logK1,1 α = 1.15 ± 0.02 and logK1,1 β = 0.78 ± 0.02, respectively. In alkaline medium, it was found for both ligands that the methylene group underwent deprotonation yielding the carbanion-enolate anion. The deprotonation constants, pKa α and pKa β, were found to be 15.16 ± 0.01 and 14.41 ± 0.01, respectively. The calcium complexing behaviour of the two ligands was also studied in strongly alkaline medium. Under these conditions, the Ca2+ ion was capable of promoting the deprotonation of the ligands and forming various enolato-type complexes. The formation of both mono- and binuclear species were deduced, their formulae are suggested to be [Ca(α-Ket)H−1]−, [Ca2(α-Ket)H−3]−, [Ca(β-Ket)H−1]−, [Ca2(β-Ket)H−1]+ with the formation constants of log β11−1 α = −11.91 ± 0.02, log β21−3 α = −36.10 ± 0.06, log β11−1 β = −11.58 ± 0.01, log β21−1 β = −10.80 ± 0.03, respectively. Beside the formation of the rare Ca2+-enolato complexes, the deprotonation of the hydrating water molecules around the Ca2+ ion was also invoked in some cases.

KW - Calcium

KW - Enolato complexes

KW - Hyperalkaline solution

KW - Oxocarboxylates

KW - Stability constants

UR - http://www.scopus.com/inward/record.url?scp=85054006919&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=85054006919&partnerID=8YFLogxK

U2 - 10.1016/j.poly.2018.09.005

DO - 10.1016/j.poly.2018.09.005

M3 - Article

AN - SCOPUS:85054006919

VL - 156

SP - 89

EP - 97

JO - Polyhedron

JF - Polyhedron

SN - 0277-5387

ER -