Schwartz Sarina C, Pinto-Pacheco Brismar, Pitteloud Jean-Philippe, Buccella Daniela
Department of Chemistry, New York University , New York, New York 10003.
Inorg Chem. 2014 Mar 17;53(6):3204-9. doi: 10.1021/ic5000606. Epub 2014 Mar 4.
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 Mg(2+) 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 Mg(2+) 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 Mg(2+) 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.
与目前用于生物镁研究的基于邻氨基苯酚-N,N,O-三乙酸（APTRA）的螯合剂相比，基于β-酮酸双齿配位基序的荧光指示剂显示出卓越的金属选择性。然而，这些低配位数的螯合剂可能会与镁离子（Mg(2+)）以及细胞环境中存在的常见配体形成三元络合物。在这项工作中，采用吸收光谱、荧光光谱和核磁共振光谱来研究基于4-氧代-4H-喹嗪-3-羧酸的开启型和比率型荧光指示剂与Mg(2+)和ATP（生物镁最丰富的螯合剂）之间的相互作用，从而揭示在与荧光成像相关的条件下三元络合物的形成。三元物种的形成引发的光学变化与仅归因于二元络合物形成的光学变化相当或更大。在pH 7和25°C条件下，荧光指示剂从三元和二元物种中的解离具有低毫摩尔范围内的表观平衡常数。这些结果表明，基于比率或强度的稳态荧光测量，这些双齿传感器无法区分游离Mg(2+)和MgATP，因此在解释富含核苷酸的生物样品中镁的荧光成像结果时面临挑战。
