A new macrocyclic tetraamine, 2,4-dinitrophenylcyclen (= 1-(2,4-dinitrophenyl)-1,4,7,10-tetraazacyclododecane): synthesis, cation reporter properties, and recognition of 1-methylthymine by its zinc(II) complex

A new functional macrocyclic ligand, 2,4-dinitrophenylcyclen (= 1-(2,4-dinitrophenyl)-1,4,7,10-tetraazacyclododecane has been synthesized and isolated as its trihydrochloric acid salt (L.3HCl). The protonation constants (log K-n) for three secondary nitrogens oft were determined by potentiometric pH titration to be 10.10, 7.33 and <2 with I = 0.10 (NaNO3) at 25 degrees C. The 2,4-dinitrophenylaniline chromophore was proven to be a good reporter signaling proton-and metal-binding events in the macrocyclic cavity, The UV absorption band (lambda(max) 370 nm, epsilon 8200) Of the 2,4-dinitrophenylaniline moiety at pH greater than or equal to 9 becomes quenched as pH is lowered (to pH 3.1, where the major species is L.2H(+)), due to the strong protonation effect extended to the aniline moiety within the macrocyclic cavity. This is in sharp contrast to the pH-independent UV absorption (lambda(max) 390 nm, epsilon 14 000) of a reference compound, N,N-diethyl-2,4-dinitroaniline. The UV absorption band of L is shifted to lower wavelengths with Zn2+ (lambda(max) 320 nm), Cd2+ (lambda(max) 316 nm) and Pb2+ (lambda(max) 317 nm), while it almost disappears with Cu2+ and Ni2+. The 1:1 Zn2+ and Cu2+ complexes with L were isolated and characterized. The Zn2+ complex recognizes 1-methylthymine anion (MT-) in aqueous solution at physiological pH to yield a stable ternary complex ZnL-MT-. The X-ray crystal structure of ZnL-MT- showed that Zn2+ is four-coordinate with three secondary nitrogens of L and the deprotonated imide anion that is cofacial to the 2,4-dinitrophenyl ring. (C) 1998 Elsevier Science S.A.