Nanomolar Detection of Al(III) Ion by Hydrazones Carrying Benzothiazole and Substituted Phenol Groups

摘要

Two new hydrazones L1H (2-(2-(2,3-dihydroxy)benzylidenehydrazinyl) benzothiazole) and L2H (2-((2-(2-hydroxy)(4-N,N-diethylamino)) benzylidenehydrazinyl)benzothiazole) were synthesized using 2-hydrazinylbenzothiazole and 2,3- dihydroxybenzaldehyde or 4-(diethylamino)-2-hydroxybenzaldehyde. The probe L1H showed an absorption peak at 340 nm while L2H at 375 nm, in MeOH/HEPES buffer (pH=7.3; 8:2, v/v). Upon gradual addition of AlCl3 to L1H, intensity of the peak at 340 nm decreased and a new band appeared with a peak at 400 nm. Similarly upon adding AlCl3 to L2H, new peaks at 405 and 420 nm grew in intensity with concomitant decrease in absorbance peak at 375 nm, having quasi isosbestic point at 395 nm. Both these probes are weakly emissive in nature. Incremental addition of AlCl3 to the MeOH/HEPES buffer solution of L1H gave turn-on response having emission maximum at 480 nm and L2H at 450 nm with a shoulder at 468 nm. Turn-On responses of L1H and L2H towards Al3+ ion were result of inhibition of PET process which in turn allowed chelation induced enhanced fluorescence (CHEF) effect becoming operational. Job’s plot obtained from the titration experiments yielded 1:1 stoichiometry for Al~(3+) ion, hence the formulae [Al(L1)Cl2(H2O)] and [Al(L2)Cl2(H2O)] were assigned. Addition of Na2EDTA to [Al(L1)Cl2(H2O)] and [Al(L2)Cl2(H2O)] reproduced UV-visible spectrum that is characteristic of free L1H/L2H.