Determination of the pKa value of the hydroxyl group in the α-hydroxycarboxylates citrate, malate and lactate by 13C NMR: implications for metal coordination in biological systems

  title={Determination of the pKa value of the hydroxyl group in the $\alpha$-hydroxycarboxylates citrate, malate and lactate by 13C NMR: implications for metal coordination in biological systems},
  author={Andr{\'e} M. N. Silva and Xiaole Kong and Robert C. Hider},
Citric acid is an important metal chelator of biological relevance. Citric acid helps solubilizing metals, increasing their bioavailability for plants and microbes and it is also thought to be a constituent of both the extracellular and cytoplasmic low molecular iron pools occurring in plants and vertebrates. Metal coordination by citric acid involves coordination both by the carboxylate and hydroxyl groups, of particular interest is its α-hydroxycarboxylate function. This structural feature is… 
Aluminum speciation in biological environments. The deprotonation of free and aluminum bound citrate in aqueous solution.
Light is shed on how the deprotonation process of the citric acid takes place, and it is shown that Al(III) not only increases the acidity of the molecule, but also changes qualitatively the depROtonation pattern of thecitric acid.
Iron(III) citrate speciation in aqueous solution.
The aqueous speciation of ferric citrate has been investigated by mass spectrometry and EPR spectroscopy and the most relevant species are a monoiron dicitrate species and dinuclear and trinuclear oligomeric complexes, the relative concentration of which depends on the solution pH value and the iron : citric acid molar ratio.
The Role of the OH Group in Citric Acid in the Coordination with Fe3O4 Nanoparticles.
The role of the C-OH group in citric acid (CA) in the molecular coordination with Fe3O4 nanoparticles (NPs) has been elusive for a long time. In this study, attenuated total reflection-Fourier
Structure of 3-mercaptopropionic acid dioxygenase with a substrate analog reveals bidentate substrate binding at the iron center
Aluminum interaction with glutamate and α-ketoglutarate: a computational study.
The results confirm that Al(III) indeed displaces the tautomerization reaction and favors the enol form of α-KG by 28 kcal/mol, and propose that the ternary complexes formed by Al( III), citrate, and α-kG or glutamate can be the more likely species.
Mechanism and kinetics of ligand exchange between ferric citrate and desferrioxamine B.
A kinetic model containing the following three mechanisms for ligand exchange between ferric citrate and desferrioxamine B is proposed, suggesting that the first and second mechanisms were significant under experimental conditions where [Cit] ≫ [DFB] with the relative importance of these two pathways depending on citrate concentration.
Effects of carboxylic acids on the uptake of non-transferrin-bound iron by astrocytes
Equilibria and Dynamics of Sodium Citrate Aqueous Solutions: The Hydration of Citrate and Formation of the Na3Cit0 Ion Aggregate.
The affinity of citrate toward Na+ binding not only governs solution equilibria but also has a strong impact on water dynamics.
FecB, a periplasmic ferric-citrate transporter from E. coli, can bind different forms of ferric-citrate as well as a wide variety of metal-free and metal-loaded tricarboxylic acids.
The Escherichia coli Fec system, consisting of an outer membrane receptor (FecA), a periplasmic substrate binding protein (FecB) and an inner membrane permease-ATPase type transporter (FecC/D), plays


Synthesis, spectroscopic, and structural characterization of the first aqueous cobalt(II)-citrate complex: toward a potentially bioavailable form of cobalt in biologically relevant fluids
The spectroscopic and structural properties of the first aqueous, soluble, mononuclear complex has been synthesized and isolated from reaction mixtures containing Co(II) and citrate in a 1 :2 molar ratio at pH∼8.
New trends in the chemistry of iron(III) citrate complexes: correlations between X-ray structures and solution species probed by electrospray mass spectrometry and kinetics of iron uptake from citrate by iron chelators.
Kinetic studies of iron uptake from citrate species by iron chelators confirmed the results indicated by the ESI-MS studies, and allowed the relative molar fraction of mononuclear versus polynuclear complexes to be determined, which depends on the Fe:cit molar ratio.
Coordination Chemistry of the Carboxylate Type Siderophore Rhizoferrin: The Iron(III) Complex and Its Metal Analogs.
The Rh and Cr rhizoferrin complexes are unusual in that they appear to adopt a chirality about the metal center that is the opposite of the native iron analog.
Ionization behavior of aqueous short-chain carboxylic acids: a carbon-13 NMR study.
The results provide necessary background data for 13C NMR studies of higher fatty acids in lipid-lipid and lipid-protein systems and propose that the local (microscopic) ionization state of the carboxyl group can be determined directly by NMR without need for pH or pK determinations.
The mechanism of aconitase action. 3. Detection and properties of enzyme-metal-substrate and enzyme-metal-inhibitor bridge complexes with manganese(II) and iron(II).
The data are consistent with direct coordination of the substrate, citrate, by the metal ion on aconitase, and three mechanisms for the role of Fe(II) in the catalysis, consistent with the data, the forward and reverse ferrous wheel mechanisms, and the Bailar twist mechanism are discussed.
Composition and Stability of Iron and Copper Citrate Complexes in Aqueous Solution
The acidity constants of citric acid and the stability constants of the citrate complexes of copper(II), iron(II), and iron(III) have been measured at 25 °C in 0.1 M KNO3 background. The measurements
Citrate as a siderophore in Bradyrhizobium japonicum
A role for ferric citrate in the iron nutrition of this strain, which has been shown to be an efficient nitrogen-fixing strain on a variety of soybean cultivars, is indicated.
Manganese citrate chemistry: syntheses, spectroscopic studies, and structural characterizations of novel mononuclear, water-soluble manganese citrate complexes.
Corroborative evidence is obtained from the magnetic susceptibility measurements in the range 5-300 K and the EPR spectra attest to the presence of paramagnetic Mn2+ and Mn3+ species in the solid state.