Unveiling Antimony-Oxo Organic Complexes in Microorganisms Using Nontargeted High-Resolution Mass Spectrometry

Interactions of antimony (Sb) with various ligands present in environmental and biological media significantly impact its toxic effects and environmental processes. The complexation of Sb with organic ligands has been reported to be a detoxification mechanism utilized by higher plants. However, the speciation of Sb complexes and their roles in microorganisms remain largely unexplored. In this study, we investigated the speciation of Sb in two model cyanobacteria, Nostoc sp. PCC 7120 and Synechocystis sp. PCC 6803, exposed to antimonite using high-resolution mass spectrometry techniques including Fourier transform ion cyclotron resonance mass spectrometry, HPLC-ESI-Orbitrap-MS, and HPLC-ESI-QTOF-MS. Combining the newly developed software FindSbPeak v1.0, we identified a variety of Sb-oxo organic complexes including Sb-glycerol complexes (C6H14O8Sb– and C9H18O9Sb– with stoichiometries of 1:2 and 1:3) and Sb-glucosylglycerol complexes (C9H18O11Sb– and C18H34O18Sb– with stoichiometries of 1:1 and 1:2), which have not been reported previously. Density functional theory calculations revealed that the complexation of Sb with multihydroxyl molecules via bidentate configuration is thermodynamically favorable. Our results unraveled the overlooked Sb-oxo organic complexes in biological systems and raised new questions regarding their toxic effects.