A highly selective and sensitive fluorescent Zn(2+) sensor, 2,6-bis(2-hydroxy-benzoic acid hydrazide)-4-methylphenol (1), was designed and synthesized. In aqueous THF (4 : 6 v/v) ligand 1 induces a 2 : 1 complex formation with respect to Zn(2+) at physiological pH. This probe features visible light excitation(390 nm) and emission (490 nm) profiles, excellent selectivity responses for Zn(2+)over other competing biological metal ions with K(d) < 1 pM(2), LOD < 1 ng L(-1) and about 680 fold enhancement in fluorescent intensity upon Zn(2+) binding. It also exhibits cell permeability and intracellular Zn(2+) sensing in A375 human melanoma cancer cell.

A diformyl-p-cresol (DFC)-8-aminoquinoline based dual signaling probe was found to exhibit colorimetric and fluorogenic properties on selective binding towards Mg(2+) and Zn(2+). Turn-on fluorescent enhancements (FE) as high as 40 fold and 53 fold in 9 : 1 MeCN/water (v/v) at pH 7.2 in HEPES buffer for Mg(2+) and Zn(2+), respectively, were observed. The binding constants determined from the fluorescence titration data are: K = (1.52 ± 0.21) × 10(5) M(-1) and (9.34 ± 4.0) × 10(3) M(-2) at n = 1 and 0.5, for Mg(2+) and Zn(2+), respectively. The L : M binding ratios were also determined by Job's method, which support the above findings. This is further substantiated by HRMS analysis. Due to solubility in mixed organo-aqueous solvents as well as cell permeability it could be used for the in vitro/in vivo cell imaging of Mg(2+) and Zn(2+) ions with no or negligible cytotoxicity. This probe could be made selective towards Mg(2+) over Zn(2+) in the presence of TPEN, both under intra- and extracellular conditions and is superior to other Mg(2+) probes which suffer from selectivity of Mg(2+) over Ca(2+) or Zn(2+). Furthermore the dissociation constant (Kd = 6.60 μM) of the Mg(2+)-() complex is far lower than the so far reported Mg(2+) probes which fall in the mM range.

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A new rhodamine-based dual signaling probe (L 3 ) has been found to display quick responses through visible colorimetric changes as well as fluorogenic properties on selective 1:1 binding to Hg 2+ , as delineated by absorption and fluorescence titrations as well as by JobЈs method and ESI-MS + studies. The fluorescent probe L 3 displays a 252-fold fluorescence enhancement on binding to Hg 2+ . A Benesi-Hilderband fit of the absorption titration data gives K d = (32.01 Ϯ 0.74) μM and a 1:1 binding stoichiometry. Owing to

A novel H3SAL-NH probe exhibits ESIPT from the phenolic OH group to the azomethine N atom in the excited state. This is blocked in the presence of Zn2+ and Al3+ giving turn on fluorescence which is useful for imaging in live HepG2 cells.