Thermodynamic Study on the Protonation and Complexation of GLDA with Ca²⁺and Mg²⁺at Different Ionic Strengths and Ionic Media at 298.15 K

Abstract

The protonation constants (log K i H ) of L-glutamic acid N,Ndiacetic acid tetrasodium salt (GLDA) were determined at T = 298.15 K and various ionic strengths in NaCl (aq) , 0.18 ≤ I ≤ 3.20 mol•kg −1 , (CH 3 ) 4 NCl (aq) 0.17 ≤ I ≤ 4.00 mol•kg −1 , and (C 2 H 5 ) 4 NI (aq) 0.13 ≤ I ≤ 1.10 mol•kg −1 by using the potentiometric method. The calculation of ionic strength dependence parameters was performed by Debye−Huckel type equation, Specific ion Interaction Theory (SIT). and Pitzer equations (only for NaCl (aq) ). These equations make it feasible to calculate and predict the protonation constants of GLDA in the desired range of ionic strength theoretically. The values of pure water protonation constants are log K 1 H 10.558 ± 0.028, log K 2 H 5.348 ± 0.011, log K 3 H 3.088 ± 0.015 and log K 4 H 1.918 ± 0.009, the first protonation refers to the nitrogen group and the other three to carboxylate groups. The different values of log K i H obtained in NaCl (aq) , (CH 3 ) 4 NCl (aq) , and (C 2 H 5 ) 4 NI (aq) were interpreted in terms of formation of weak complexes between GLDA and the cations of the supporting electrolytes. Binding constants referring to the weak species formed by GLDA with sodium and tetramethylammonium cations were calculated. For example, the stability of the NaL and (CH 3 ) 4 NL species, at infinite dilution, are log K = 2.5 ± 0.2 and 1.6 ± 0.3, respectively. The complexing ability of GLDA versus calcium and magnesium was also determined in NaCl (aq) at various ionic strength values. The pure water formation constants are for calcium log K CaL 0 = 8.181 ± 0.024 and for magnesium log K MgL 0 = 7.263 ± 0.028.

Many-body effect determines the selectivity for Ca 2+ and Mg 2+ in proteins

“…The hard-ligand scale of Mg 2+ is barely larger than that of Ca 2+ (i.e., the two metal ions have similar binding affinities for hard ligands) (44). In Hofmeister series, Mg 2+ and Ca 2+ are close to each other while their order varies depending on the solute (41,(45)(46)(47). The similarity between Mg 2+ and Ca 2+ binding affinities may be explained by the dielectric screening of the solvent (48).…”

Enhancement of aragonite mineralization with a chelating agent for CO2 storage and utilization at low to moderate temperatures

“…1 . GLDA was chosen because of its biodegradability, environmental friendliness, and its good ability to chelate Ca (Ca-GLDA stability constant (log K ) = 5.9 at an ionic strength of 0.1 M and 25 °C 30 ) and lower the surface energy of the solvent-crystal interface for aragonite production 31 . In particular, GLDA was supposed to enhance Ca extraction from calcium silicate, promote the production of aragonite particles with controlled morphologies during the subsequent Ca carbonation, and subsequently be recovered.…”

Binding of divalent cations to acetate: molecular simulations guided by Raman spectroscopy

“…Prior metal carboxylate binding constant compilations 12 and individual studies include experimental potentiometric, [13][14][15][16][17] NMR, 18 vibrational spectroscopic, [19][20][21] and surface sum frequency 22,23 measurements, as well as theoretical classical 24 and quantum, 25 calculations. In the case of acetate, the range of previously reported binding constants consistently point to weak pairing with divalent cations.…”