A highly selective chemodosimeter for fast detection and intracellular imaging of Hg 2 + ions based on a dithiocarbamate-isothiocyanate conversion in aqueous ethanol

A new naphthalene diimide-dithiocarbamate based fluorescence probe was synthesized and its fluorogenic behavior towards various metal ions was studied. Upon addition of various metal ions, the probe afforded an irreversible change only with Hg(2+) ions in aqueous-ethanol media (4 : 1 v/v) with a fourfold enhancement of the fluorescence (Φ = 0.03 → 0.11) along with a distinct 43 nm blue shift of the emission maxima. The mechanism of the chemodosimetric behavior of the probe has been attributed to a Hg(2+) induced transformation of a weakly fluorescent dithiocarbamate to a highly fluorescent isothiocyanate which has been characterized by a number of spectroscopic techniques and a crystal structure. Intracellular detection of Hg(2+) ions was achieved using the probe.

Electronic Supplementary Material (ESI) for Organic & Biomolecular Chemistry This journal is © The Royal Society of Chemistry 2013 S 4

Detection limit
The detection limit for the Hg 2+ ions were calculated based on the fluorescence titration experiments.To determine the S/N ratio, the fluorescence intensity of the blank (1 (10 µM) in absence of Hg 2+ ) was recorded 10 times in mixed solvent media (H 2 O/EtOH, 4:1, v/v, with 1% DMSO as a cosolvent, 1 mM HEPES buffered at pH 7.0) and the standard deviation of the blank measurements was determined.Under the same conditions, the fluorescence spectra of dosimeter 1 (10 µM) was recorded in presence of Hg 2+ (0 to 50 µM) .A linear curve (0 -15 µM, R 2 = 0.98, figure S3) was obtained when fluorescence intensity was plotted against the concentration of Hg 2+ .The detection limit thus calculated was found to be 2.1 × 10 -7 (M).

Determination of quantum yield
Relative quantum yield was calculated from the equation stated below: Where ϕ s is the quantum yield of the standard, A is the absorbance at the excitation wavelength (subscript S for standard*and U for unknown), F is the area under the emission spectra and η is the refractive index of the solvent. 1 *Quinine sulphate was used as reference.
ion................................. S10The structures of the compounds were determined by 1D and 2D nuclear magnetic resonance spectroscopy and other spectroscopic and spectrometric techniques. 1 H and 13 C NMR spectra were recorded with 400 MHz Jeol and 500 MHz Bruker instruments.Chemical shifts are reported in δ values relative to an internal reference of tetramethylsilane (TMS) or the solvent peaks.IR data were obtained with a Perkin-Elmer-spectrum-100 spectrophotometer.Mass spectrometry data were obtained from Waters Acuity Ultra Performance LC.Emission spectra were recorded in Horiba Jobin Yvon (Fluoromax-3).UV absorption spectra were recorded in Varian Cary 300 Bio spectrophotometer.Fluorescence imaging experiments were carried out using an Olympus IX 51 inverted microscope with UV excitation.pH data were recorded with a Sartorius Basic Meter PB-11 calibrated at pH 4, 7, and 10.Solvents used were purified and dried by standard methods.Reactions were monitored by thin layer chromatography using Merck plates (TLC Silica Gel 60 F 254 ).Developed TLC plates were visualized with UV light (254 and 366 nm).Silica gel (100−200 mesh, Merck) was used for column chromatography.Yields indicate the chromatographically and spectroscopically pure compounds.The solvents used for the spectroscopy experiments were of the spectroscopic grades and were free from any fluorescent impurity.Milli-Q ultrapure water was used for the experiments.Crystal Data were collected on a Bruker SMART APEXII CCD area-detector diffractometer using graphite monochromated Mo Kα radiation (λ= 0.71073 Å).For both thecrystals, X-ray data reduction was carried out using the Bruker SAINT program.The structures were solved by direct methods using the SHELXS-97 program and refinement using SHELXL-97 program.Selected crystal data and data collection parameters are given inTable 1. X-ray data reduction, structure solution and refinement were done using the SHELXL-97 program package.2+ Figure S1.Absorption spectra of 1(10 µM) upon addition of various metal ions (20 µM) in mixed solvent media (H 2 O/EtOH, 4:1, v/v, with 1% DMSO as a cosolvent, 1 mM HEPES buffered at pH 7.0) at 25 o C.
Electronic Supplementary Material (ESI) for Organic & Biomolecular Chemistry This journal is © The Royal Society of Chemistry 2013