Common chelator serves as detector for health-relevant metals

Calcium, magnesium, and zinc are divalent metal ions essential for good health. Other divalent metals, such as cadmium, lead, and arsenic, are toxic. Turning to common metal-chelating agents, researchers have found that they can use nuclear magnetic resonance spectroscopy and magnetic resonance imaging to quantitatively sense and distinguish among all these metals in blood serum (Anal. Chem. 2016, DOI: 10.1021/acs.analchem.6b03546). Gil G. Westmeyer of the Technical University of Munich and colleagues labeled the metal-coordinating carboxyl groups of ethylenediaminetetraacetic acid (EDTA) or ethylene glycol bis(2-aminoethyl ether)-N,N,N′,N′-tetraacetic acid (EGTA) with ¹³C. When either of the compounds binds the metals, ¹³C NMR spectra show well-separated chemical shifts that allow the researchers to distinguish between the metals. For example, they were able to quantitate millimolar concentrations of Ca²⁺ in human serum in the presence of competing concentrations of Mg²⁺. The researchers were further able to increase the sensitivity to micromolar concentrations for NMR and MRI by using dynamic nuclear polarization, which involves transferring spin polarization from electrons of a radical to the ¹³C nuclei to enhance their NMR signals.