A water soluble calcium–sodium based coordination polymer: selective release of calcium at specific binding sites on proteins

Abstract

A calcium–sodium based water soluble coordination complex [{Ca₄Na(EGTA)₂(H₂O)₁₃}_n·NO₃] (EGTA = ethylene bis(oxyethylenenitrilo)tetraaceticacid), henceforth named Ca/Na-1, has been synthesized hydrothermally and characterized using spectroscopic and single crystal X-ray diffraction techniques. Single crystal X-ray diffraction of the assembly affirms a two dimensional self assembled net-like supramolecular structure. The complex serves as a biological mimic of a calcium buffer and dispenses felicitous amounts of Ca²⁺ ions at the binding sites on proteins, as shown by SEM imaging and MALDI-TOF spectroscopy. The thermodynamics of binding has also been measured by isothermal titration calorimetry. Protein conformational changes have been characterized by NMR spectroscopy.