Biocompatible zinc(II) 8-(dihydroimidazolyl)quinoline complex and its catalytic application for synthesis of poly(L,L-lactide)

Abstract

A 1:1 reaction of 8-(dihydroimidazolyl)quinoline (abbreviated as L) with MCl2·2H2O (M = CoII, NiII, CuII, ZnII) conducted in EtOAc (for ZnII and CuII) or MeOH (NiII and CoII) at 50 °C for 10 min provided the respective air- and shelf-stable [MCl2L] complexes (94–96%). The catalytic activity of these well-defined species was evaluated in L-lactide ring-opening polymerization (ROP) that was conducted in the presence of 2-hydroxyethylmethacrylate (HEMA) as a nucleophilic initiator. The biocompatible zinc(II) complex was found to be more catalytically active in ROP compared to the other three complexes as well as SnOct2, a common reference catalyst. The zinc(II)-catalyzed ROP also gives the macromolecular product with the lowest polydispersity index (1.2). The applicability of the HEMA-terminated PLA, prepared in the presence of the [ZnCl2L] complex, was demonstrated when PLA was converted into amphiphilic copolymer PLA-PEG via the thiol-ene click reaction. The PLA-PEG copolymer was shown to form nanospheres (calculated mean diameter 95 ± 10 nm) characterized by low particle size distribution. This – along with anticipated lower toxicity of [ZnCl2L] traces in the polymer – makes these nanospheres potentially applicable as vehicles for intravenous drug delivery.