2.1 Material
All the chemicals and solvents used in this work were purchased from local vendors and were reagent and analytical grade. Metal perchlorate salts were from Sigma-Aldrich and obtained from local sources. Thin layer chromatography (TLC) was performed on precoated silica gel plates (SiO2, PF254, Merck). FT-IR spectra of compounds were recorded on Perkin Elmer spectrum 100 FT-IR spectrometers (ATR). For 1H-NMR spectra, a 400 MHz Varian NMR spectrometer was used using CDCl3 and DMSO as solvents. UV /Vis spectra were taken with a Shimadzu UV-1700 spectrophotometer. Fluorescence spectra were recorded with a Perkin Elmer LS 55 spectrometer. All the metal ion solutions (perchlorate salts) were prepared in deionized water.
2.2 Synthesis
Fig.1 and 2 show the synthesis of the fluorophore (C) and calix[4]arene based fluorescence derivative (4). The parent compounds depicted in Fig.1, were synthesized according to reported methods 32. Compound 1-3 were also prepared according to the literature method [32-34]. The procedure for synthesis of compound 4 is given below: [35]
2.2.1 Preparation of 3-oxo-3,4-dihydro-[1,4]benzothiazin-2-ylidene) acetic acid (B)
0.3 g of compound A was refluxed in 10 M NaOH in ethanol for 40 hours. The reaction was monitored by 1H-NMR. The solvent was then evaporated and precipitated with acidic water, filtered and washed with distilled water and oven dried. Compound B was obtained in 80% yield. FT-IR: 1HNMR (DMSO) δ (ppm): 6.88 (s, 1H, -CH- ), 7.03-7.23 ( m, 2H, ArH ), 7.21 ( t, 1H, J= 7.14, ArH), 7.40 (d, 1H, J= 7.68, ArH), 11.5 ( s,1H, Ar-NH-),11.6 (s, 1H, O=C-OH). Anal. Calc.: C10H7NO3S. C, 54. 29; H, 3.19; N, 6.33; S, 14.49%. Found: C, 54.33; H, 3.28; N, 6.41; S, 14.51%.
2.2.2 Preparation of 3-oxo-3,4-dihydro-[1,4]benzothiazin-2-ylidene) acetic chloride (C)
0.3 g (1.35 mmol) of the compound B was dissolved in 35 ml of benzene. 4 ml of thionyl chloride was added to it and refluxed for 3.5 hours. The solvent was then completely distilled under a vacuum and used in the next step without further purification.
2.2.3 Reaction of compound C with p-tert-butylcalix[4]arene dihydrazide derivative (3)
Compound C contained in a 250 ml flask was dissolved in 10 ml benzene. 0.534g (0.675mmol) compound 3 was added by dissolving in 10 ml benzene. It was stirred at room temperature. Then 360 mL (1.35 mmol) of pyridine was added. It was stirred at room temperature for 16 hours. The reaction was followed by TLC. The product was washed with water to obtain compound 4. Yield; 0.454g (85%).1H-NMR(DMSO) δ (ppm):1.10 (s, 18H, but), 1.16 (s, 18H, but), 3.22-3.37 (m, 4H Ar-CH2-Ar),4.08-4.29 (m, 4H, Ar-CH2-Ar), 4.56 (s, 4H, -CH2-), 7.04-7.39 (m, 18H, ArHOxo), 8.33 (s, 2H, -NH-). 13C-NMR(DMSO) δ (ppm): 166.8, 149.9, 148.3, 142.3, 133.5, 127.5, 126.4, 126.1, 123.76, 117.4, 116.4, 34.5, 34.1, 31.8, 31.4. Anal. Calc.: C68H74N6O10S2. C, 68.09; H, 6.22; N, 7.01; S, 5.35%. Found: C, 68.13; H, 6.13; N, 7.09; S, 5.37%.
2.2.4 Procedure for UV-visible and fluorescencestudy
Interaction of metal with ligand was examined by UV-visible and fluorescence spectroscopy. For this, the stock solution of ligand 4 (1.0×10−3 M) was prepared in 10 mL of dimethylsulfoxide (DMSO) followed by dilution to 1.0×10−4 M into 100 mL for absorption study and 1.0×10−7 M for fluorescence study. Metal ion (perchlorate salts) solution (1.0×10−3 M) was prepared in a mixed solution of ethanol and water in a 1:1 ratio. Dilution was made according to absorption and fluorescence response. Briefly, 2 mL of ligand (1.0×10−4 M) was treated with metal ion solution (1.0×10−3 M) using micropipette of 100 µL and absorption was recorded [36] . The emission response of ligand 4 was estimated by titration experiments in DMSO. In 10 mL test tubes, 2 mL of ligand (1.0×10−7 M) and 2 mL of metal salt (1.0×10−4 M) were mixed together and emission intensities were measured at excitation wavelength 351 nm.
2.2.5 Stoichiometry, binding constant, and limit of detection.
Stoichiometry of ligand and metal was determined by Job’s method. For this, an equimolar solution (1.25×10-5 M) of ligand and metal ion was prepared in the varying rations of 1:9 to 9:1 [35]. Stern-Volmer method was applied to analyze the nature of the quenching or enhancement process in the complexation [37,38].
See formulas 1 and 2 in the supplementary files.