Synthesis and metal ion complexation of spin labeled 18-crown-6 ethers containing an acridone or an acridine fluorophore unit

Comparison in practical applications of crown ether sensor molecules containing an acridone or an acridine unit – a study on protonation and complex formation

Crown ethers containing an acridone or an acridine unit are successfully applied opto- and electrochemical cation sensors. The heteroaromatic unit of these macrocycles can be in different forms during the applications, which have a strong influence on the sensing behavior. Moreover, in the case of acridono-macrocycles a prototropic equilibrium takes place upon complexation, which is effected by the physicochemical characteristics. A Pb2+-selective acridono-18-crown-6 ether and its 9-phenylacridino-analogue were used as model compounds for comparing the different forms of the heterocyclic units of these sensor molecules. Since in most practical sensor applications of the fluorescent hosts a non-neutral aqueous medium is present, studies on complexation and signaling were carried out from the aspect of the relationship among protonation, coordinating ability, complex stability and tautomeric equilibrium. A strong interdependence among these factors was found and limitations of using unsubstituted acridino- and acridono-sensor molecules in comparison with their 9-substituted-acridino-analogues were discussed. This study will hopefully serve as a useful standpoint for future development of ionophore-based sensors containing an acridone or an acridine unit.

A novel profluorescent paramagnetic diaza-crown ether: synthesis, characterization and alkaline metal-ion complexation

Starting from Kryptofix 22 two different branches were covalently attached through the nitrogen atoms, one containing a fluorescent moiety and the other the stable free radical TEMPO. The novel derivative exhibits fluorescence and paramagnetic properties, while the diaza-crown part ensures the affinity for alkaline metal-ions.

Starting from Kryptofix 22 two different branches were covalently attached through the nitrogen atoms, one containing a fluorescent moiety and the other the stable free radical TEMPO.

Synthesis and pKa determination of new enantiopure dimethyl-substituted acridino-crown ethers containing a carboxyl group: Useful candidates for enantiomeric recognition studies

New enantiopure dimethyl-substituted acridino-18-crown-6 and acridino-21-crown-7 ethers containing a carboxyl group at position 9 of the acridine ring [(S,S)-8, (S,S)-9, (R,R)-10] were synthesized. The pK_a values of the new crown ethers [(S,S)-8, (S,S)-9, (R,R)-10] and of an earlier reported macrocycle [(R,R)-2] were determined by UV-pH titrations. Crown ether (S,S)-8 was attached to silica gel by covalent bonds and the enantiomeric separation ability of the newly prepared chiral stationary phase [(S,S)-CSP-12] was studied by high-performance liquid chromatography (HPLC). Homochiral preference was observed and the best separation was achieved for the enantiomers of 1-NEA. Ligands (S,S)-9 and (R,R)-10 are precursors of enantioselective sensor and selector molecules for the enantiomers of protonated primary amines, amino acids, and their derivatives.

Highly selective and sensitive fluorescence detection of Zn(2+) and Cd(2+) ions by using an acridine sensor

Fluorescence spectroscopy investigations of the new acridine derivative bis(N,N-dimethylaminemethylene)acridine (3) show remarkable selectivity and sensitivity towards Zn(2+) and Cd(2+) ions in methanol and for the latter even in water. Through the chelation of the metal ions the present PET effect is quenched, significantly enhancing the emission intensity of the fluorophore. In solution, the bonding situation is studied by fluorescence and NMR spectroscopy, as well as ESI-TOF mass-spectrometry measurements. The solid state environment is investigated by X-ray diffraction and computational calculations. Here, we can show the complexation of the zinc and cadmium ions by the methylene bridged amine receptors as well as by the nitrogen atom of the acridine system.

Surface enhanced Raman scattering of new acridine based fluorophore adsorbed on silver electrode

4,5-Bis(N,N-di(2-hydroxyethyl)iminomethyl)acridine (BHIA) is a new acridine based fluoroionophore and a highly-selective sensor for cadmium ion. The direct interaction of the aromatic nitrogen atom with a surface is impossible since there are bulky substituents in the 4,5-positions of the acridine fragment. Nevertheless BHIA molecule shows a reliable SERS spectrum while adsorbed on a silver electrode. The analysis of SERS spectra pH dependence reveals that BHIA species adsorbed on a surface can exist in both non-protonated and protonated forms. The adsorption of BHIA from alkaline solution is accompanied by carbonaceous species formation at the surface. The intensity of such "carbon bands" turned out to be related with the supporting electrolyte (KCl) concentration. Upon lowering the electrode potential the SERS spectra of BHIA do not undergo changes but the intensity of bands decreases. This indicates that the adsorption mechanism on the silver surface is realized via aromatic system of acridine fragment. In case of such an adsorption mechanism the chelate fragment of the BHIA molecule is capable of interaction with the solution components. Addition of Cd(2+) ions to a system containing BHIA adsorbed on a silver electrode in equilibrium with the solution leads to the formation of BHIA/Cd(2+) complex which desorption causes the loss of SERS signal.

1-Nitronyl nitroxide pyrene as a new off–on fluorescent chemosensor for Cu2+

A highly selective and sensitive colorimetric chemosensor based on nitronyl nitroxide was developed for detection of Cu²⁺.

Synthesis and potential use of 1,8-naphthalimide type (1)O2 sensor molecules

New double (fluorescent and spin) sensor molecules containing 4-amino substituted 1,8-naphthalimide as a fluorophore and a sterically hindered amine (pre-nitroxide) or pyrroline nitroxide as a quencher and radical capturing moiety were synthesized. All sensors were substituted with a diethylaminoethyl side-chain to increase the water solubility. Steady state fluorescence properties of these compounds and their responses to ROS in vitro are reported with perspectives of plant physiology use in vivo.