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1,4,8,11-tetrakis{(2,2'-bipyridyl-5'-ylmethyl)-bis(2,2'-bipyridyl)ruthenium(II)}-1,4,8,11-tetraazacyclotetradecane (L(1)), a macrocyclic pH and transition metal ion fluorescence sensor. Equilibrium, and stopped-flow kinetic, fluorimetric studies of the reactions of L(1) with nickel(II) and copper(II) ions in aqueous solution at neutral pH



A new pendent-arm derivative of 1,4,8,11-tetraazacyclotetradecane (cyclam), 1,4,8,1 I-tetrakis(2,2'-bipyridyl-5'-ylmethyl)-1,4,8,11-tetraazacyclotetradecane (1) (L) has been synthesised and characterised. L reacts with four mole equiv, of cis-[Ru(bipy)(2)Cl-2] (bipy = 2,2'-bipyridine) to give the highly fluorescent macrocyclic ligand 2 (L(1)) (L(1) = [{(biPY)(2)Ru}(4)L](8+)), which has been isolated as the monoprotonated derivative, [{(bipy)(2)RU}(4)(LH)][ClO4](9). Molecular mechanics and dynamics calculations indicate that the cyclam group of 2 adopts the R,S,S,R (trans-IV) rather than the more common R,R,S,S (trans-III) set of N-configurations. This modified cyclam has four covalently attached [Ru(bipy)(3)](2+) units, and is highly fluorescent at pH 7 (lambda(ex) = 450 nm, lambda(em) = 600 nm). The fluorescence of 2 is much reduced upon protonation, or as metal ions enter the macrocyclic cavity. The compound is a pH and transition metal ion sensor, with a first photo excited state pK(a) of 5.92 +/- 0.11 (from fluorescence measurements) and a ground state pK(a) of 7.84 +/- 0.04 (from absorbance measurements). The results of kinetic and thermodynamic studies are reported for the fluorescence quenching which occurs when aqueous copper(II)or nickel(II) ions coordinate at the cyclam cavity of L(1)

Topics: QD
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