Spectrophotometric Determination of Trace Amount of Total Fe II /Fe III and Live Cell Imaging of a Carboxylato Zn(II) Coordination Polymer.

The coordination polymer, (Zn(II)-CP, 1 ), {[Zn(2,6-NDC)(4-Cltpy)](H 2 O) 4 } ( 1 ) (2,6-H 2 NDC = 2,6-naphthalene dicarboxylic acid and 4-Cltpy = 4'-chloro-[2,2';6',2″]terpyridine) is structurally characterized by single crystal X-ray diffraction measurement and other physicochemical studies (PXRD, FTIR, thermal analysis, microanalytical data). 4-Cltpy acts as end-capping ligand, and NDC 2- is a carboxylato bridging motif to constitute ZnN 3 O 2 distorted trigonal bipyramid core that propagates to construct 1D chain. The coordination polymer, 1 , detects total iron (Fe 3+ and Fe 2+ ) in aqueous solution by visual color change, colorless to pink. Absorption spectrophotometric technique in aqueous medium measures the limit of detection (LOD) 0.11 μM (Fe 2+ ) and 0.15 μM (Fe 3+ ), and binding constants (K d ) are 6.7 × 10 4 M -1 (Fe 3+ ) and 3.33 × 10 4 M -1 (Fe 2+ ). Biocompatibility of 1 is examined in live cells, and intracellular Fe 2+ and Fe 3+ are detected in MDA-MB 231 cells. Zn(II) substitution is assumed upon addition of Fe III /Fe II solution to the suspension of the coordination polymer, 1 , in water-acetonitrile (41:1) (LZn II + Fe III/II → LFe III + Zn II , where L is defined as coordinated ligands), which is accompanied by changing from colorless to pink at room temperature. The color of the mixture may be assumed to the charge transfer transition from carboxylate-O to Cltpy via Fe(II/III) bridging center (carboxylate-O-Fe-CltPy). The product isolated from the reaction is finally characterized as Fe(III)@1 -CP. It is presumed that product Fe(II)@1 -CP may undergo fast aerial oxidation to transform Fe(III)@1 -CP. The Fe III exchanged framework ( Fe(III)@1 -CP) has been characterized by PXRD, IR, TGA and energy dispersive X-ray analysis (EDX)-SEM. The MTT assay calculates the cell viability (%), and the tolerance limit is 100 μM to total Fe 2+ and Fe 3+ .