CU(II), ZN(II), AND PB(II) STABILITY-CONSTANTS OF CYCLAM AMPHIPHILES

1-Hexadecyl-1,4,8,11-tetraazacyclotetradecane (hexadecyl cyclam) and 1 -(3,7,11,15-tetramethyl) hexadecyl-1,4,8,11-tetraazacyclotetradecane ( tetramethylhexadecyl cyclam) have been synthesized and their deprotona tion and ligand-metal formation constants, K, determined for Cu(II), Z n(II) and Pb(II). The coupling of a long hydrocarbon chain to a ring n itrogen decreased the general ability of the cyclam ring to complex wi th metal ions. The greatest effect appeared to be for Cu(II) decreasin g from a pK of 27 for cyclam to about 17. The titrations were fitted b y HYPERQUAD and the concentrations of the intermediate complexes obtai ned as a function of pH. Metal-ligand complexes LMH(2)(4+), LMH(2+) an d LM(2+) can co-exist through a wide pH range. We have also calculated a composite metal-binding constant, K', to reflect more accurately th e overall ability of these ligands to bind a metal at any particular p H. K', which is 14.6 for (hexadecyl cyclam)-Cu(II), is constructed fro m the concentrations of all the metal-chelated species at pH = 7. Gene rally, K' is much lower than K.