Dendritic encapsulation of amino acid–metal complexes. Synthesis and studies of dendron-functionalized L-tyrosine–metal (ZnII, CoII) complexes

摘要

This paper describes the synthesis, characterization and studies of dendrimers possessing an amino acid–metalncomplex as the core. Using Fréchet-type polyaryl ether dendrons, -tyrosine–metal (ZnII and CoII) complex coredndendrimers of 0–4 generations were synthesized. The metal complexation of the tyrosine unit at the focal pointnof these dendrons took place smoothly, in excellent yields, even though the sizes of the dendrons increase as thengenerations advance. Spectrophotometric titrations with CoII metal ion confirmed the formation of a 2 : 1 dendriticnligand to metal complex and the existence of a pseudotetrahedral geometry at the metal centre is also inferred. Cyclicnvoltammetric studies of dendrimer–CoII complexes showed that while the electron transfer of CoII to CoI was facilenfor generations 0–2, such a process was difficult with generations 3 and 4, indicating a rigid encapsulation of thenmetal ion centre by proximal dendron groups. Further reduction of CoI to Co0 and the corresponding oxidationnprocesses appear to be limited by adsorption at the surfaces of the electrodes.