title: New Amino-Acid-Based β-Phosphorylated Nitroxides for Probing Acidic pH in Biological Systems by EPR Spectroscopy.
abstract: There is increasing interest in measuring pH in biological samples by using nitroxides with pH-dependent electron paramagnetic resonance (EPR) spectra. Aiming to improve the spectral sensitivity (ΔaX) of these probes (i.e., the difference between the EPR hyperfine splitting (hfs) in their protonated and unprotonated forms), we characterized a series of novel linear α-carboxy, α'-diethoxyphosphoryl nitroxides constructed on an amino acid core and featuring an (α or α')-C-H bond. In buffer, the three main hfs (aN, aH, and aP) of their EPR spectra vary reversibly with pH and, from aPor aHtitration curves, a two- to fourfold increase in sensitivity was achieved compared to reference imidazoline or imidazolidine nitroxides. The crystallized carboxylate 10 b (pKa≈3.6), which demonstrated low cytotoxicity and good resistance to bioreduction, was applied to probe stomach acidity in rats. The results pave the way to a novel generation of highly sensitive EPR pH markers.
authors.affiliation: Aix Marseille Univ, CNRS, ICR, UMR 7273, Avenue Escadrile Normandie Niemen, 13397, Marseille, France.
authors.forename: Sophie
authors.initials: S
authors.lastname: Thétiot-Laurent
authors.affiliation: Aix Marseille Univ, CNRS, ICR, UMR 7273, Avenue Escadrile Normandie Niemen, 13397, Marseille, France.
authors.forename: Gaëlle
authors.initials: G
authors.lastname: Gosset
authors.affiliation: Aix Marseille Univ, CNRS, ICR, UMR 7273, Avenue Escadrile Normandie Niemen, 13397, Marseille, France.
authors.forename: Jean-Louis
authors.initials: JL
authors.lastname: Clément
authors.affiliation: Aix Marseille Univ, CNRS, ICR, UMR 7273, Avenue Escadrile Normandie Niemen, 13397, Marseille, France.
authors.forename: Mathieu
authors.initials: M
authors.lastname: Cassien
authors.affiliation: Aix Marseille Univ, CNRS, ICR, UMR 7273, Avenue Escadrile Normandie Niemen, 13397, Marseille, France.
authors.forename: Anne
authors.initials: A
authors.lastname: Mercier
authors.affiliation: Aix Marseille Univ, CNRS, ICR, UMR 7273, Avenue Escadrile Normandie Niemen, 13397, Marseille, France.
authors.forename: Didier
authors.initials: D
authors.lastname: Siri
authors.affiliation: Aix Marseille Univ, CNRS, ICR, UMR 7273, Avenue Escadrile Normandie Niemen, 13397, Marseille, France.
authors.forename: Anouk
authors.initials: A
authors.lastname: Gaudel-Siri
authors.affiliation: Research Centre for Natural Sciences of the Hungarian Academy of Sciences, Institute of Materials and Environmental Chemistry, Budapest University of Technology and Economics, 1117, Budapest, Hungary.
authors.forename: Antal
authors.initials: A
authors.lastname: Rockenbauer
authors.affiliation: Aix Marseille Univ, CNRS, ICR, UMR 7273, Avenue Escadrile Normandie Niemen, 13397, Marseille, France.
authors.forename: Marcel
authors.initials: M
authors.lastname: Culcasi
authors.affiliation: Aix Marseille Univ, CNRS, ICR, UMR 7273, Avenue Escadrile Normandie Niemen, 13397, Marseille, France.
authors.forename: Sylvia
authors.initials: S
authors.lastname: Pietri
mesh_terms: D000072283:A549 Cells; D000596:Amino Acids / Q000737:chemistry*; D000818:Animals; D002470:Cell Survival / Q000187:drug effects; D018360:Crystallography, X-Ray; D004578:Electron Spin Resonance Spectroscopy; D005744:Gastric Acid / Q000737:chemistry; D005753:Gastric Mucosa / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D056004:Molecular Dynamics Simulation; D009589:Nitrogen Oxides / Q000737:chemistry* / Q000633:toxicity; D063065:Organophosphonates / Q000138:chemical synthesis / Q000737:chemistry*; D010766:Phosphorylation; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D000596:Amino Acids; D009589:Nitrogen Oxides; D063065:Organophosphonates
keywords: EPR spectroscopy; molecular dynamics; nitroxide; sensors; stomach acidity