Binding Pocket Response of EDTA Complexes with Alkaline Earth Dications to Stepwise Hydration─Structural Insight from Infrared Spectra

Abstract

We investigate the microhydration structures of complexes of alkaline earth dications and ethylenediaminetetraacetic acid (EDTA) for up to two water molecules, using cryogenic ion vibrational spectroscopy in concert with density functional theory (DFT). The interaction with water shows a clear dependence on the chemical identity of the bound ion. For Mg2+, microhydration mostly involves the carboxylate groups of EDTA and does not entail direct contact with the dication. In contrast, the larger ions (Ca2+, Sr2+, and Ba2+) interact electrostatically with the microhydration environment, and this interaction increases in importance with the size of the ion. This trend reflects the ion position in the EDTA binding pocket, which comes closer to the rim of the pocket with increasing ion size.

Temporary Consolidation of Marine Artifact Based on Polyvinyl Alcohol/Tannic Acid Reversible Hydrogel

“…The Na 2 EDTA solution exhibited antisymmetric stretching vibration peaks and symmetric stretching vibration peaks of the carboxyl group of COO-Na at 1637 cm −1 and 1489 cm −1 . Part of the EDTA present in the leaching solution formed complexes with the calcium ions in the hydrogel, resulting in the appearance of a symmetric stretching vibration peak at 1404 cm −1 [ 39 ]. The B-O bond in the EDTA compound exhibited a distinct peak at a wavenumber of 841 cm −1 .…”

Mutual Impact of Four Organic Calcium Salts on the Formation and Properties of Micro-Arc Oxidation Coatings on AZ31B Magnesium Alloys

“…On the contrary, in the MAO solution wherein the combination of GP-Ca and EDTA-Ca, CaGlu 2 , and CaLac 2 were used as the Ca sources, EDTA-Ca would dissociate to release EDTA 4− with two -N= and four -COO − groups, and, similarly, CaGlu 2 and CaLac 2 would separately release Glu − and Lac − , both containing -OH and -COO − groups. The anchoring effects of -COO − groups made EDTA 4− , Glu − , and Lac − , especially EDTA 4− , easily chelate with Ca 2+ to form highly stable six-membered complexes [EDTACa] 2− , CaGlu(OH) 2 − , and CaGlu(OH) 2 − [34,35,45,46], ultimately assisting in the migration of Ca 2+ to the anode surface and then participation in the MAO coating formation. As a result, there was a synergistic effect between GP-Ca and EDTA-Ca, CaGlu 2 , and CaLac 2 in increasing the Ca content of the coatings.…”