a novel Schiff-base fluorescent sensor (HL) for Al 3+ has been synthesized.The addition of Al 3+ make the significant increase of its fluorescent intensity at 420 nm in ethanol, however, other metal ions have almost no influence on the fluorescence. The reason for this phenomenon might be attributed to the formation of a 1:1 stoichiometric L-Al complex which inhibits photo-induced electron transfer (PET) process. More importantly, the proposed binding mode of L-Al (III) is further identified by theoretical calculations.3 1-phenyl-3-methyl-5-hydroxypyrazole-4-acetone-(benzoyl) hydrazone (HL) for Al 3+ , which was prepared by condensing 1-phenyl-3-methyl-4-acetyl-pyrazolone-5 and benzohydrazide (Scheme 1). Upon addition of Al 3+ , HL shows a large fluorescence enhancement which is because that the formation of a 1:1 L-Al complex inhibits photo-induced electron transfer (PET) process. Other metal ions including Na + , K + , Ag + , Ca 2+ , In 3+ , Cd 2+ , Co 2+ , Ga 3+ , Ni 2+ , Fe 3+ , Mn 2+ , Mg 2+ , Pb 2+ , Cu 2+ , Cr 3+ , Ba 2+ , Zn 2+ and Al 3+ have almost no influence on the fluorescence. Moreover, the structure of L-Al is identified by theoretical calculations and the lowest detection limit for Al 3+ is determined as 2×10 -7 M.
Experimental
Reagents and apparatusUnless otherwise stated, the reagents were purchased from Aladdin Industrial Corporation and they were used without further purification. The solutions of metal ions were prepared by dissolving the desired amount of the corresponding metal nitrate in ethanol. 1 H NMR spectra was recorded on a Bruker Avance Drx 400 MHz spectrometer in DMSO-d 6 . Electrospray ionization-mass spectroscopy (ESI-MS) was determined on a Bruker Esquire 6000 spectrometer. UV-Vis absorption spectrum was measured on a Perkin Elmer Lambda 35 UV-Vis spectrophotometer. Fluorescence spectra were generated on a Hitachi RF-5301 spectrophotometer equipped with quartz cuvettes of 1 cm path length. Melting points were determined on a Beijing XT4-100x microscopic melting point apparatus.
Synthesis2.2.1 Synthesis of 1-phenyl-3-methyl-4-acetyl-pyrazolone-5 (PMAP) [31] 7 enhancement at 420 nm in the presence of Al 3+ , the addition of Na 2 EDTA, which is a good chelator, to a solution of L-Al resulted in diminution of the fluorescence intensity at 420 nm which indicated the regeneration of the free receptor HL.In addition, from the fluorescence titration data, the binding constant (log K a ) for L-Al in ethanol was 7.54 according to a reported method (Fig.S3). More importantly, the lowest detection limit for Al 3+ was determined as 2×10 -7 M (Fig.S4) which is sufficiently low to enable the detection of micromolar concentrations of Al 3+ in many chemical and biological systems
The complexation of HL with Al 3+In order to validate the binding mode of HL and Al 3+ , we carried out Job's plot IR spectra. As shown in Fig. 6, the total concentration of HL and Al 3+ was 10 µM. X Al = ([Al 3+ ]/ (Al 3+ ] + [HL]. The maximum point appeared at a mole fraction of 0.5, which indicated that it was a 1:1 ...
