title: The evaluation of new and isotopically labeled isoindoline nitroxides and an azaphenalene nitroxide for EPR oximetry.
abstract: Isoindoline nitroxides are potentially useful probes for viable biological systems, exhibiting low cytotoxicity, moderate rates of biological reduction and favorable Electron Paramagnetic Resonance (EPR) characteristics. We have evaluated the anionic (5-carboxy-1,1,3,3-tetramethylisoindolin-2-yloxyl; CTMIO), cationic (5-(N,N,N-trimethylammonio)-1,1,3,3-tetramethylisoindolin-2-yloxyl iodide, QATMIO) and neutral (1,1,3,3-tetramethylisoindolin-2-yloxyl; TMIO) nitroxides and their isotopically labeled analogs ((2)H(12)- and/or (2)H(12)-(15)N-labeled) as potential EPR oximetry probes. An active ester analogue of CTMIO, designed to localize intracellularly, and the azaphenalene nitroxide 1,1,3,3-tetramethyl-2,3-dihydro-2-azaphenalen-2-yloxyl (TMAO) were also studied. While the EPR spectra of the unlabeled nitroxides exhibit high sensitivity to O(2) concentration, deuteration resulted in a loss of superhyperfine features and a subsequent reduction in O(2) sensitivity. Labeling the nitroxides with (15)N increased the signal intensity and this may be useful in decreasing the detection limits for in vivo measurements. The active ester nitroxide showed approximately 6% intracellular localization and low cytotoxicity. The EPR spectra of TMAO nitroxide indicated an increased rigidity in the nitroxide ring, due to dibenzo-annulation.
authors.affiliation: EPR Centre for Viable Systems, Department of Radiology, Dartmouth Medical School, Hanover, NH 03755, USA. nadeem.khan@dartmouth.edu
authors.forename: Nadeem
authors.initials: N
authors.lastname: Khan
authors.forename: James P
authors.initials: JP
authors.lastname: Blinco
authors.forename: Steven E
authors.initials: SE
authors.lastname: Bottle
authors.forename: Kazuyuki
authors.initials: K
authors.lastname: Hosokawa
authors.forename: Harold M
authors.initials: HM
authors.lastname: Swartz
authors.forename: Aaron S
authors.initials: AS
authors.lastname: Micallef
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000737:chemistry / Q000494:pharmacology; D016466:CHO Cells; D002855:Chromatography, Thin Layer; D002999:Clone Cells; D006224:Cricetinae; D003412:Cricetulus; D003497:Cyclic N-Oxides / Q000737:chemistry*; D003903:Deuterium; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods*; D007202:Indicators and Reagents; D007211:Indoles; D054833:Isoindoles / Q000737:chemistry*; D007553:Isotope Labeling; D008744:Methylamines; D009589:Nitrogen Oxides / Q000737:chemistry; D009590:Nitrogen Radioisotopes; D010092:Oximetry / Q000379:methods*; D010100:Oxygen / Q000737:chemistry; D010101:Oxygen Consumption / Q000187:drug effects; D014343:Trypan Blue
chemical_list: C568286:1,1,3,3-tetramethyl-2,3-dihydro-2-azaphenalen-2-yloxyl; C502049:1,1,3,3-tetramethylisoindolin-2-yloxy; C568287:5-(N,N,N-trimethylammonio)-1,1,3,3-tetramethylisoindolin-2-yloxyl; C480578:5-carboxy-1,1,3,3-tetramethylisoindolin-2-yloxyl; D000970:Antineoplastic Agents; D003497:Cyclic N-Oxides; D007202:Indicators and Reagents; D007211:Indoles; D054833:Isoindoles; D008744:Methylamines; D009589:Nitrogen Oxides; D009590:Nitrogen Radioisotopes; D003903:Deuterium; C005855:trimethyloxamine; D014343:Trypan Blue; D010100:Oxygen