Speciation Study on O-Phosphorylethanolamine and O-Phosphorylcholine: Acid–Base Behavior and Mg2+ Interaction

• Published in: Frontiers in chemistry 2022-03, Vol.10, p.864648
• Main Authors: Aiello, Donatella, Cordaro, Massimiliano, Napoli, Anna, Foti, Claudia, Giuffrè, Ottavia
• Format: Article
• Language: English
• Subjects: 1H-NMR spectroscopy; Chemistry; ligands of biological interest; Mg2; potentiometry; sequestration; speciation
• ISSN: 2296-2646; 2296-2646
• DOI: 10.3389/fchem.2022.864648

In the present study, the acid–base behavior of compounds constituting the headgroups of biomembranes, O-phosphorylethanolamine ( PEA ), and O-phosphorylcholine ( PPC ) was investigated by potentiometric titrations in NaCl aqueous solutions at different temperatures (15 ≤ t /°C ≤ 37) and ionic strength (0.15 ≤ I /mol L −1 ≤ 1) values. The complexation properties and the speciation of these ligands with Mg 2+ were defined under different temperatures (15 ≤ t /°C ≤ 37) and I = 0.15 mol L −1 . The results evidenced the formation of three species for PEA , namely, MLH 2 , MLH, and ML and two species for PPC , namely, MLH and ML. 1 H-NMR titrations were performed on solutions containing ligand and metal–ligand solutions at t = 25°C and I = 0.15 mol L −1 . The estimated values of ligand protonation and complex formation constants and the speciation model are in accordance with the potentiometric data. The enthalpy changes were also determined at t = 25°C and I = 0.15 mol L −1 by the dependence of formation constants on the temperature, confirming the electrostatic nature of the interactions. Matrix-assisted laser desorption mass spectrometry (MALDI-MS) was applied for the characterization of Mg 2+ -L systems (L = PEA or PCC ). MS/MS spectra of free ligands and of Mg 2+ -L species were obtained. The observed fragmentation patterns of both Mg 2+ -L systems allowed elucidating the interaction mechanism that occurs via the phosphate group generating a four-membered cycle.