(Benzimidazolylmethyl)cyclen:: A potential sensitive fluorescent PET chemosensor for Zinc

A new fluorescent probe for Zn2+, methylbenzimidazole-pendant cyclen [LH: 1-(benzimidazol-2-ylmethyl)-1,4,7,10-tetraazacyclododecane] was designed and synthesized. The protonation constants of (benzimidazolylmethyl)cyclen and the stability constants of the corresponding zinc complex were determined by potentiometric titrations. The single-crystal X-ray diffraction analysis showed that LH and Zn2+ form a 1: 1 complex [ZnLH](2+). The results of potentiometric, H-1 NMR and UV titrations indicated that above pH 8, [ZnLH]2+ mainly deprotonates into [ZnL](+). On addition of successive amounts of Zn2+ at PH 10.4 (2 X 10(-2) molL(-1) CAPS, 25 degrees C), the fluorescence emission of cyclen(methylbenzimidazole) increases linearly by a factor of 3. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007).