Advanced organic materials. esters of the free stable radical 3-carboxy-proxyl having fluorescent or complexing properties

In order to design new advanced organic structures, possessing prestablished hybrid properties, the stable free radical the esters 3a-c (where: a 3-(2-phenoxathiinacetylcarbonyloxy)-2,2,5,5-tetramethyl-1-pyrrolidinyloxy; b 3-(3-phenoxathiinacetylcarbonyloxy)-2,2,5,5-tetramethyl-1-pyrrolidinyloxy; c 3-(3-hydroxy-6-methylcarbonyloxy-4H-pyran-4-one)-2,2,5,5-tetramethyl-1-pyrrolidinyloxy) were synthesized, starting from the persistent and stable nitroxide free radical 3-carboxy-2,2,5,5-tetramethyl-1-pyrrolidinyloxy, 1, (3-CARBOXY-PROXYL) and the bromoderivatives 2a-c (where: a 2-(α-bromoacetyl)-phenoxathiin; b 3-(a-bromoacetyl) phenoxathiin; c 6-bromomethyl-3-hydroxy-4H-pyran-4-one) in the presence of 18C6 and potassium hydroxide. The new compounds, bearing the phenoxathiin fluorescent fragment (3a,b) or the 3-hydroxy-4pyrone chelating structure (3c) linked to the proxyl-paramagnetic unit may be suitable labels in physico-chemical or biomedical processes. The spectral characteristics (IR, UV-VIS, fluorescence and EPR), the lipophilicities (determined by the RPTLC method) and the purities (from TLC densitometric analysis) of the synthesized compounds 3a-c are presented. The nitroxide free radical esters 3a-c were reduced, using ascorbic acid, cysteine, or glutathione, to the corresponding diamagnetic hydroxylamines 4a-c (where: a 3-(2-phenoxathiinacetylcarbonyloxy)-2,2,5,5-tetramethyl-1-hydroxypyrrolidine; b 3-(3-phenoxathiinacetylcarbonyloxy)-2,2,5,5-tetramethyl-1-hydroxypyrrolidine; c 3-(3-hydroxy-6-methylcarbonyloxy-4H-pyran-4-one)-2,2,5,5-tetramethyl-1-hydroxypyrrolidine). This process is reversible, the compounds 4a-c undergoing rapid reoxidation to the initial nitroxides 3a-c by air exposure. The hydroxylamines 4a-c were found to exhibit a greater fluorescence than the nitroxide radicalic species 3a-c.