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).