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Two simple and low cost 2,4-di-tert-butyl-6-[(1-hydroxycyclohexylmethylimino)methyl]phenol (L1) and 2-[{(1-hydroxycyclohexyl)methylimino}methyl]phenol (L2) Schiff base sensors exhibiting selectivity for Zn(2+) in water:methanol (95:5, v/v, 10 mM HEPES) are described. L1 and L2 display an "off-on" fluorescence effect forming the L1·Zn and L2·Zn complexes, respectively. In the case of L1·Zn, the emission response is quenched by the addition of Cu(2+) forming the respective L1·Cu complex; in spite of that, the fluorescence signal can be completely restored only by the addition of tartrate anions (C4H4O6(2-)) forming again L1·Znvia the "off-on" displacement approach. However, in the case of L2·Zn no Cu(2+) interference is observed, which is a typical problem for Zn(2+) sensors. Here we describe that a very subtle structural change in the ligand during transition from the enol-imine tautomer in L1 to the keto-enamine tautomer in L2 is enough to modulate the Zn(2+)/Cu(2+) selectivity. Also, the Zn(2+)vs. Cd(2+) discrimination for L1 and L2 is proved. Moreover, we found that the interaction between both L·Zn complexes and tartrate anions completely restored the free ligands by the ligand substitution mechanism even in a more efficient association than phosphate anions. Further, a second colorimetric response channel upon addition of Fe(2+) was observed for L1 and L2. Then, TD-DFT theoretical calculations were conducted in order to study the efficiency of the sensors to give different responses in the presence of such metal ions. Finally, the L2 sensor successfully detects Zn(2+) in Jurkat cells cultured with and without Zn(2+) enriched medium.

The coordination properties and acid–base behavior of 2-[{(1 S ,2 R )-1-hydroxy-1-phenylpropan-2-ylimino}methyl]-4-bromophenol Schiff base probe ( L1 ) were characterized by UV–Vis and fluorescence titrations in water. The dissociation constants for the ligand account for a keto–enamine tautomer at pH 7. Detailed complexation studies were carried out, observing the formation of stable 1:1 complex for Zn 2+ , where a “turn-on” fluorescence effect is obtained. More importantly, no Cu 2+ interference is observed, which is a typical problem for Zn 2+ probes, this is awarded to the keto–enamine tautomeric form of the probe L1 according to UV–Vis and X-ray structure data. Also, the Zn 2+ vs . Cd 2+ ion discrimination for L1 is proved. Finally, TD-DFT theoretical calculations were conducted in order to stablish the detection mechanism of the probe. [ABSTRACT FROM AUTHOR]

Two simple and low cost 2,4-di-tert-butyl-6-[(1-hydroxycyclohexylmethylimino)methyl]phenol (L1) and 2-[{(1-hydroxycyclohexyl)methylimino}methyl]phenol (L2) Schiff base sensors exhibiting selectivity for Zn2+ in water : methanol (95 : 5, v/v, 10 mM HEPES) are described. L1 and L2 display an “off–on” fluorescence effect forming the L1·Zn and L2·Zn complexes, respectively. In the case of L1·Zn, the emission response is quenched by the addition of Cu2+ forming the respective L1·Cu complex; in spite of that, the fluorescence signal can be completely restored only by the addition of tartrate anions (C4H4O62−) forming again L1·Znvia the “off–on” displacement approach. However, in the case of L2·Zn no Cu2+ interference is observed, which is a typical problem for Zn2+ sensors. Here we describe that a very subtle structural change in the ligand during transition from the enol-imine tautomer in L1 to the keto-enamine tautomer in L2 is enough to modulate the Zn2+/Cu2+ selectivity. Also, the Zn2+vs. Cd2+ discrimination for L1 and L2 is proved. Moreover, we found that the interaction between both L·Zn complexes and tartrate anions completely restored the free ligands by the ligand substitution mechanism even in a more efficient association than phosphate anions. Further, a second colorimetric response channel upon addition of Fe2+ was observed for L1 and L2. Then, TD-DFT theoretical calculations were conducted in order to study the efficiency of the sensors to give different responses in the presence of such metal ions. Finally, the L2 sensor successfully detects Zn2+ in Jurkat cells cultured with and without Zn2+ enriched medium. [ABSTRACT FROM AUTHOR]

A simple (R)-(−)-2-phenylglycinol functionalized Schiff base exhibited a dual response to Zn 2+ , Cu 2+ and Fe 2+ ions in water:methanol, (90:10 v/v). The compound displays an “off–on” fluorescent effect with Zn 2+ ions. The emission response decreased with Cu 2+ forming a Cu 2+ /Zn 2+ specie. The fluorescence signal is restored upon addition of sulfide anion (S 2 − ) using the Cu 2+ displacement approach , forming again the Zinc complex. Additionally, the sensor exhibits a second channel (colorimetric) response with Fe 2+ even in the presence of competing Fe 3+ ions. The pH profiles allowed to determine the p K a values and the pH-dependent change in the sensor recognition process. In addition, TD-DFT quantum chemical calculations were implemented to analyze the sensing mechanism by means of Natural Transition Orbital (NTO) analysis. Flow cytometry experiments demonstrated that the sensor successfully detects either exogenous or endogenous (natural) Zn 2+ ions in Jurkat cells with high sensitivity. [ABSTRACT FROM AUTHOR]

Seven Schiff base derivatives of 4-dimethylamino-trans-cinnamaldehyde were synthesized in good yield. The structures of all new derivatives were established by IR, 1H, 13C NMR and HRMS experiments and three of them were corroborated by X-ray diffraction studies. Analysis of the supramolecular structures evidenced the presence of strong intermolecular hydrogen bonds (O–H…N) which promote the formation of molecular chains. The linear properties of this series of chromophores were investigated by UV-Vis and fluorescence spectroscopy in solution and in the solid state. The results revealed interesting photochromic properties for compound 2a promoted by a hydrogen bonding interaction in the solid state, which was established by absorption and emission spectra. Further evidence of the specific interactions that take place in compound 2a was obtained by studying the solvent effects observing a solvato- and acidochromic behavior. [ABSTRACT FROM AUTHOR]

Abstract: A simple (R)-(−)-2-phenylglycinol functionalized Schiff base L1 and its characterization as a fluorescent–colorimetric sensor for Hg2+ ion are described. The UV–vis and fluorescence analysis in methanol and aqueous solution show complex formation between L1 and Hg2+ ion with a micromolar association constant. Competition experiments performed for the acetate salts of Hg2+, Zn2+, Co2+, Pb2+, Cd2+, Mn2+, Cu2+, Ni2+, and Ba2+ revealed that compound L1 exhibits high selectivity toward Hg2+ displaying a color change easily detectable by naked-eye and a turn-off fluorescent effect due to a chelation-enhanced quenching (CHEQ) mechanism. Moreover, addition of EDTA to L1–Hg2+ recovers the fluorescence and color offering receptor L1 as a reversible sensor for real-time applications. [Copyright &y& Elsevier]