ABSTRACT
Two new tetradentate C2-symmetric pseudopeptidic ligands derived from Val and Phe containing two amino and two amido groups and a central o-substituted aromatic spacer have been prepared. Their complexes with Cu(2+), Zn(2+), and Ni(2+) have been studied by potentiometry, UV-vis spectrophotometry, FT-IR, and ESI-MS. The presence of the aromatic spacer provides Cu(2+) complexes with stability constants several orders of magnitude higher than those observed for related ligands containing aliphatic central spacers. Besides, the formation of [MH-2L] complex species is favored. Crystal structures for the corresponding Cu(2+) and Ni(2+) have been obtained, revealing the metal atom in an essentially square-planar geometry, although, in several instances, the oxygen atom of an amide carbonyl of a second complex species can act as a fifth coordination site. In the case of Zn(2+), the only crystal structure obtained displays a square-pyramidal arrangement of the metal center. Finally, preliminary experiments show the catalytic activity of some of these complexes, in particular, Zn(2+) complexes, for epoxide ring-opening with using aniline as the nucleophile in a ligand accelerated process.
ABSTRACT
The fluorescent diaminoterephthalate scaffold was equipped by amidation with three types of reactive functions: thiols for metal-surface binding, alkynes for click reactions, and maleimides for ligation with proteins. Starting from a succinyl succinate derivative with two orthogonally cleavable ester functions, three monoamides (38-57% yield over three steps) and two bisamides (19 and 25% yield over five steps) were prepared. Although alkyne and thiol derivatized compounds showed reasonable luminescence behavior (Φ≈1-4%), the fluorescence was quenched by the maleimide moiety. It was turned on (10- to 20-fold increase of fluorescence quantum yield) by conjugate addition of thiols.
