Formation of ternary complexes with MgATP: Effects on the detection of Mg2+ in biological samples by bidentate fluorescent sensors

Sarina C. Schwartz, Brismar Pinto-Pacheco, Jean Philippe Pitteloud, Daniela Buccella

Research output: Contribution to journalArticlepeer-review


Fluorescent indicators based on β-keto-acid bidentate coordination motifs display superior metal selectivity profiles compared to current o-aminophenol-N,N,O-triacetic acid (APTRA) based chelators for the study of biological magnesium. These low denticity chelators, however, may allow for the formation of ternary complexes with Mg2+ and common ligands present in the cellular milieu. In this work, absorption, fluorescence, and NMR spectroscopy were employed to study the interaction of turn-on and ratiometric fluorescent indicators based on 4-oxo-4H-quinolizine-3-carboxylic acid with Mg2+ and ATP, the most abundant chelator of biological magnesium, thus revealing the formation of ternary complexes under conditions relevant to fluorescence imaging. The formation of ternary species elicits comparable or greater optical changes than those attributed to the formation of binary complexes alone. Dissociation of the fluorescent indicators from both ternary and binary species have apparent equilibrium constants in the low millimolar range at pH 7 and 25 C. These results suggest that these bidentate sensors are incapable of distinguishing between free Mg2+ and MgATP based on ratio or intensity-based steady-state fluorescence measurements, thus posing challenges in the interpretation of results from fluorescence imaging of magnesium in nucleotide-rich biological samples.

Original languageEnglish (US)
Pages (from-to)3204-3209
Number of pages6
JournalInorganic Chemistry
Issue number6
StatePublished - Mar 17 2014

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry


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