Novel Spin Labeled Azacrown Ethers

The ability of crown ethers [1—4] and cryptands [5—7] to selectively complex ions and neutral molecules has been the subject of extensive studies over the past two decades. One of the most impor­ tant problems under investigation was the transport of ionic species through membranes in biological sys­ tems [8 ]. Of several transport mechanisms proposed and demonstrated in natural and artificial systems, the coupled transport mediated by mobile carriers (ionophores) appears to be one of the simplest [8 ]. In such a system a flux of one ion, typically proton, moving down its concentration gradient effects the transport of the desired alkali ion up its concentra­ tion gradient. This cation-proton-coupled counter­ transport has been demonstrated in natural and arti­ ficial systems using sodium specific antibiotic monensin [9] and calcium specific lascalocid (X-537 A) and calcimycin ( A 23187) [10—13]. Recently, it was suggested by Keana and cowork­ ers [14] that the nitroxyl spin labeled crown ethers and cryptands may find an application in monitoring the concentration of alkali and alkaline earth metal ions in aqueous solutions by the ESR spectroscopy. The high sensitivity of the ESR method, coupled with its use in nontransparent systems would present certain advantages over the existing methods [14], Several nitroxyl spin labeled crown ethers and two spin labeled cryptands have been reported in recent years [8 , 14—18]. Some of the reported structures are represented by derivatives of the benzoor dibenzo18-crown-6 [15, 16] with nitroxyl moieties attached either by an ester or amide linkage and the nitroxyl group located in a relatively distant position from the cavity of the molecule. Keana and coworkers [14] described the syntheses of two spin labeled crown