Novel 2,6-diformyl-4-methyl phenol based chemosensor for ZnII ion by ratiometric displacement of CdII ion and its application for cell imaging on human melanoma cancer cells

Experimental Nuclear Astrophysics Division, Saha Institute of Nuclear Physics, 1/AF Bidhan Nagar,

Kolkata-700 064, India

Catalysis Division, National Chemical Laboratory, Pashan Rd, NCL Colony, Pashan, Pune-411 008,

Maharashtra, India

Crystal Technology Laboratory, Technical Physics and Prototype Engineering Division,

Bhabha Atomic Research Centre, Mumbai-400 085, India

Radio Chemistry Division, Bhabha Atomic Research Centre, Mumbai-400 085, India

Chemistry Division, Bhabha Atomic Research Centre, Mumbai-400 085, India

Department of Condensed Matter Physics and Material Science, Tata Institute of Fundamental Research,

Dr. Homi Bhabha Road, Navy Nagar, Colaba, Mumbai-400 005, India

E-mail : das.sangbrita@gmail.com

Manuscript received online 13 August 2014, revised 30 March 2015, accepted 21 April 2015

A new chelating ligand [4-methyl-2,6-bis-(pyridin-2-yl-hydrazonomethyl)-phenol] (1) was prepared by the condensation of 2-hydrazinylpyridine with 2,6-diformyl-p-cresol. Compound 1 exhibits weak fluorescence due to intramolecular photoinduced electron transfer (PET). The sensor (1) demonstrates Zn²⁺-specific emission enhancement due to “PET off” process through a 1 : 1 binding mode with the metal ion. The fluorescence quantum yield of the chemosensor 1 is only 0.020, and it increases more than 14-fold (0.280) in the presence of one equivalent of the zinc ion. Interestingly, the introduction of other metal ions causes the fluorescence intensity to remain either unchanged or weakened except for Cd²⁺. Ratiometric displacement of Cd²⁺ ion from the complex by Zn²⁺ ion supports the formation of more stable sensor-Zn²⁺ complex over the sensor-Cd²⁺ complex. The experimental findings have been correlated with theoretical results using B3LYP functional and 6-31G(d,p), LANL2DZ basis set for Cd²⁺ (2) and Zn²⁺ (3) complex, respectively, by Density Functional Theory (DFT) method. Moreover, the ability of probe 1 to sense Zn ²⁺ within human melanoma cancer cells has been explored, and the Zn²⁺-probing process in living cells was reversible. [Mn₂ (PHMP)₂ ](ClO₄ )₂ (4) and [Ni₂ (PHMP)(H₂O)₅ ](NO₃ )₃ (5) have been also synthesized and characterized crystallographically and spectroscopically to understand the ligating behavior of the ligand PHMP.