Milan Ghosh

Exploring the Scope of Photo-Induced Electron Transfer–Chelation-Enhanced Fluorescence–Fluorescence Resonance Energy Transfer Processes for Recognition and Discrimination of Zn2+, Cd2+, Hg2+, and Al3+ in a Ratiometric Manner: Application to Sea Fish Analysis

A rhodamine-based smart probe (RHES) has been developed for trace-level detection and discrimination of multiple cations, viz. Al3+, Zn2+, Cd2+, and Hg2+ in a ratiometric manner involving photo-induced electron transfer–chelation-enhanced fluorescence–fluorescence resonance energy transfer processes. The method being very fast and highly selective allows their bare eye visualization at a physiological pH. The optimized geometry and spectral properties of RHES and its cation adducts have been analyzed by time-dependent density functional theory calculations. RHES detects as low as 1.5 × 10–9 M Al3+, 1.2 × 10–9 M Zn2+, 6.7 × 10–9 M Cd2+, and 1.7 × 10–10 M Hg2+, whereas the respective association constants are 1.33 × 105 M–1, 2.11 × 104 M–1, 1.35 × 105 M–1, and 4.09 × 105 M–1. The other common ions do not interfere. The probe is useful for intracellular imaging of Zn2+, Cd2+, and Hg2+ in squamous epithelial cells. RHES is useful for the determination of the ions in sea fish and real samples.

Pyridine-antipyrine appended indole derivative for selective recognition of Fe(3+): Concentration dependent coloration.

Combination of pyridine, antipyrine and indole in a single molecule (L2) allows selective recognition of Fe3+ colorimetrically in CH3CN. The structure of L2 is confirmed from single crystal X-ray diffraction analysis. The probe displays two different visible bands at 541nm and 715nm in the presence of Fe3+, associated with two different colors, viz. green and pink-violet allowing determination of unknown Fe3+ concentration. Interestingly, removal of 2-picolyl group from indole N-center of L2 generates L3 that behaves similarly at low Fe3+ concentration (>0 to 1.1mM) but differently at higher Fe3+ concentration (>1.1mM), indicating involvement of pyridyl-N donor towards Fe3+, and hence different coordination environment around Fe3+ at higher concentration.

A unique benzimidazole-naphthalene hybrid molecule for independent detection of Zn2+ and N3− ions: Experimental and theoretical investigations

Single crystal X-ray structurally characterized benzimidazole-naphthalene hybrid (NABI) functions as a unique dual analyte sensor that can detect Zn2+ cation and N3- anion independently. The NABI forms chelate with Zn2+ to inhibit internal charge transfer (ICT) and CHN isomerisation resulting chelation enhanced fluorescence (CHEF). On the other hand, the sensing of N3- is based on formation of supramolecular H-bonded rigid assembly. The association constant of NABI for Zn2+ and N3- ions are 19 × 104 M-1 and 11 × 102 M-1, respectively. Corresponding limit of detections (LOD) are 6.85 × 10-8 and 1.82 × 10-7 M, respectively. NABI efficiently detects intracellular Zn2+ and N3- ions with no cytotoxicity on J774A.1cells under fluorescence microscope. DFT studies unlock underlying spectroscopic properties of free NABI and Zn2+/N3- bound forms.