Year: 2026
Type: preprint
Abstract: Fe(II) complexes of TACN (1,4,7-triazacyclononane) containing two 6methyl-2-picolyl pendant groups are studied as redox-responsive agents for monitoring peroxide produced in inflammation. One Fe(II) complex has a pentadentate ligand with a sixth coordination site for binding water (FeII(MPB)) as confirmed by the crystal structure of [FeII(MPB)(CF3SO3)](CF3SO3) as well as by 17O NMR studies and the other has a hexadentate ligand to form a complex with no available coordination sites (FeII(MPH)). FeII(MPB) is inert towards oxidation under ambient levels of O2 in aqueous solution at pH 7.4 over 24 hours whereas FeII(MPH) is resistant to oxidation over 4 hours. FeII(MPB) oxidizes rapidly (> 3 min) upon addition of one equivalent of peroxide or with a half-life for oxidation of 8.9 minutes in the presence of 0.1 U/mL glucose oxidase (GOX). With one equivalent of peroxide in bu ered solutions, the major product is FeIII(MPB), most likely as a bu er or hydroxide complex, but with a 10-fold excess of peroxide, a Fe(III) phenolate complex is produced as supported by electronic absorbance spectroscopy and analysis of products by high resolution mass spectrometry. The r1 relaxivity for the FeIII(MPB) is increased by 14-fold over the FeII complex at 1.4 T, 34 °C and pH 7.4. Oxidation of FeII(MPH) by GOX proceeds with a half-life of 4.1 minutes and produces a 7-fold increase in relaxivity. Changes in relaxivity are reversed by addition of ascorbate. This data highlights the di erences between a probe containing a coordination site for binding peroxide and one that lacks a binding site. FeII(MPB) is one of the first reported examples of a Fe(II) macrocyclic MRI probe that is unreactive to O2 but reacts rapidly with micromolar concentrations of peroxide to increase signal for increased selectivity in monitoring inflammation.
Source: ChemRxiv
Language: English
Subfield: Materials Chemistry
Field: Materials Science
Domain: Physical Sciences
Open Access status: green
Awards: MRI: Acquisition of a 500 MHz Nuclear Magnetic Resonance (NMR) Spectrometer for Research and Training, G2224259305, G3448216593, MRI: Acquisition of a High Brilliance Dual-Source X-ray Diffractometer for Advanced Materials Research, Education, and Training in Western New York, G4087454866, G4224810292, MRI-R2: Acquisition of an Inductively Coupled Plasma Mass Spectrometer (ICP/MS), Acquisition of a 7T MR scanner for Translational Imaging Research at Roswell Park, Responsive Iron MRI probes with Enhanced Relaxivity, G7233916203, Roswell Park Cancer Center Support Grant
OpenAlex ID: W7143445085