Synthesis, spectroscopic properties and photodynamic activity of Zn(II) phthalocyanine-polymer conjugates as antimicrobial agents

Abstract

Conjugates of Zn(II) phthalocyanine to chitosan (CS) and polyethylenimine (PEI) were synthetized through the following stages: first a phthalonitrile substituted by a (carbomethoxy)phenoxy group (Pn 1) was obtained by nucleophilic aromatic substitution reaction, then a AB3 Zn(II) phthalocyanines (ZnPc 2) was synthesized by the ring expansion reaction of boron(III) subphthalocyanine (SubPc) chloride with Pn 1. After hydrolysis of ZnPc 2, a Zn(II) phthalocyanine bearing a carboxylic acid group (ZnPc 3) was obtained, which was conjugated to CS (CH-ZnPc 4) and PEI (PEI-ZnPc 5) by amide bond. UV–visible absorption and fluorescence spectra presented the characteristic bands of the Zn(II) phthalocyanine in N,N-dimethylformamide (DMF), with appropriate fluorescence quantum yield. Also, the conjugation of Zn(II) phthalocyanine to polymers was confirmed by IR spectra. These conjugates were able to photosensitize singlet molecular oxygen in DMF and aqueous medium. Moreover, they induced the formation of superoxide anion radical in the presence of NADH. The results showed that type II pathway is involved in the photodecomposition of Trp sensitized by these conjugates, although there is also a contribution from the type I mechanism. Photoinactivation of microorganisms was investigated in Candida albicans, Staphylococcus aureus and Escherichia coli and, varying the concentration of CH-ZnPc 4 and PEI-ZnPc 5 and the irradiation times. Both conjugates were efficient in the eradication of S. aureus by PDI, while that PEI-ZnPc 5 was the most effective for photokilling C. albicans. These conjugates were little active to photoinactivation of E. coli. However, the addition of CS allowed to improve the photocytotoxicity towards this Gram-negative bacterium. These results indicate that PEI-ZnPc 5 is an efficient photosensitizer to inactivate S. aureus and C. albicans. In addition, it is capable of killing E. coli cells in the presence of CS.