title: Synthesis and characterization of amino derivatives of persistent trityl radicals as dual function pH and oxygen paramagnetic probes.
abstract: Triarylmethyl radicals, TAMs, are useful soluble paramagnetic probes for EPR spectroscopic and imaging applications because of their extraordinary stability in living tissues, narrow line width, high analytical resolution at micromolar concentrations and enhanced sensitivity to molecular oxygen. Recently we proposed the concept of dual function pH and oxygen TAM probes based on the incorporation of ionizable groups into the TAM structure (J. Am. Chem. Soc. 2007, 129 (23), 7240-7241). In this paper we report the synthesis of TAM derivatives containing amino groups. The synthesized TAMs combine stability with oxygen and pH sensitivity, in the range of pH from 6.8 to 9.0. To decrease the number of spectral components and improve probe solubility at physiological pH, asymmetric TAM derivatives containing both carboxyl and amino functions were synthesized. The presence of nitrogen and hydrogen atoms in direct proximity to protonatable amino groups resulted in strong pH-induced changes to the corresponding hyperfine splittings, Delta hfs approximately (300-1000) mG, comparable to the values of hfs themselves. Large pH-dependent line shifts of individual spectral components, with narrow linewidths of (160-280) mG, allow for easy discrimination between the pH effect and the observed oxygen-dependent line broadening of about (6 +/- 0.5) mG per % oxygen. The synthesized TAM derivatives represent the first dual function pH and oxygen paramagnetic probes with reasonably valuable properties for biomedical research.
authors.affiliation: Dorothy M. Davis Heart & Lung Research Institute, The Ohio State University, Columbus, Ohio 43210, USA.
authors.forename: Ilirian
authors.initials: I
authors.lastname: Dhimitruka
authors.forename: Andrey A
authors.initials: AA
authors.lastname: Bobko
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Hadad
authors.forename: Jay L
authors.initials: JL
authors.lastname: Zweier
authors.forename: Valery V
authors.initials: VV
authors.lastname: Khramtsov
mesh_terms: D004578:Electron Spin Resonance Spectroscopy; D006863:Hydrogen-Ion Concentration; D015335:Molecular Probes / Q000138:chemical synthesis / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry*; D013113:Spin Labels / Q000138:chemical synthesis*; D014320:Triphenylmethyl Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D014867:Water / Q000737:chemistry
chemical_list: D015335:Molecular Probes; D013113:Spin Labels; D014320:Triphenylmethyl Compounds; D014867:Water; D010100:Oxygen