Aminoacid N-substituted 1,4,7-triazacyclononane and 1,4,7,10-tetraazacyclododecane Zn2+, Cd2+ and Cu2+ complexes. A preparative, potentiometric titration and NMR spectroscopic study

The pK(a)s and Zn2+, Cd2+ and Cu2+ complexation constants (K) for 1,4,7-tris(2'S)-acetamido-2'-(methyl-3'-phenylpropionate)]-1,4,7-triazacyclononane, 1, 1,4,7-tris(2'S)-acetamido-2'-(1'-carboxy-3'-phenylpropane)]-1,4,7-triazacyclononane, H(3)2, 1,4,7-tris(2'S)-acetamido-2'-(methyl-3'-(1H-3-indolyl)propionate)]-1,4,7-triazacyclononane, 3, and 1,4,7,10-tetrakis(2'S)-acetamido-2'-(methyl-3'-phenylpropionate)]-1,4,7,10-tetraazacyclododecane, 4, 1,4,7,10-tetrakis(2'S)-acetamido-2'-(1'-carboxy-3'-phenylpropane)]-1,4,7,10-tetraazacyclododecane, H(4)5, in 20 : 80 v/v water-methanol solution are reported. The pK(a)s within the potentiometric detection range for H(3)1(3+) = 8.69 and 3.59, for H(6)2(3+) = 9.06, 6.13, 4.93 and 4.52, H(3)3(3+) = 8.79 and 3.67, H(4)4(4+) = 8.50, 5.62 and 3.77 and for H(8)5(4+) = 9.89, 7.06, 5.53, 5.46, 4.44 and 4.26 where each tertiary amine nitrogen is protonated. The complexes of 1: Zn(1)]2+(9.00), Cd(1)]2+ (6.49), Cd(H1)]3+ (4.54) and Cu(1)]2+ (10.01) are characterized by the log(K/dm3 mol(-1)) values shown in parentheses. Analogous complexes are formed by 3 and 4: Zn(3)]2+ (10.19), Cd(3)]2+ (8.54), Cu(3)]2+ (10.77), Zn(4)]2+ (11.41) Cd(4)]2+ (9.16), Cd(H4)]3+ (6.16) and Cu(4)]2+ (11.71). The tricarboxylic acid H(3)2 generates a greater variety of complexes as exemplified by: Zn(2)-] (10.68) Zn(H2)] (6.60) Zn(H(2)2)+] (5.15), Cd(2)](-) (4.99), Cd(H2)] (4.64), Cd(H2(2))]+ (3.99), Cd(H(3)2)]2+ (3.55), Cu(2)](-) (12.55) Cu(H2)] (7.66), Cu(H(2)2)]+ (5.54) and Cu(2)2](4-) (3.23). The complexes of H(4)5 were insufficiently soluble to study in this way. The 1H and 13C NMR spectra of the ligands are consistent with formation of a predominant Zn2+ and Cd2+ Delta or Lambda diastereomer. The preparations of the new pendant arm macrocycles H(3)2, 3, 4 and H(4)5 are reported.