L)RUTHENIUM(II))-1,4,8,11-TETRAAZACYCLOTETRADECANE (L(1)), A MACROCYCLIC PH AND TRANSITION-METAL ION FLUORESCENCE SENSOR - EQUILIBRIUM, ANDSTOPPED-FLOW KINETIC, FLUOROMETRIC 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 (cyc lam), 1,4,8,1 dyl-5'-ylmethyl)-1,4,8,11-tetraazacyclotetradecane (1) ( L) has been synthesised and characterised. L reacts with four mole equ iv, of cis-[Ru(bipy)(2)Cl-2] (bipy = 2,2'-bipyridine) to give the high ly fluorescent macrocyclic ligand 2 (L(1)) (L(1) = [{(biPY)(2)Ru}(4)L] (8+)), which has been isolated as the monoprotonated derivative, [{(bi py)(2)RU}(4)(LH)][ClO4](9). Molecular mechanics and dynamics calculati ons 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-configuration s. 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 q uenching which occurs when aqueous copper(II)or nickel(II) ions coordi nate at the cyclam cavity of L(1).