Aggregation of Cationic Amphiphilic Block and Random Copoly(vinyl ether)s with Antimicrobial Activity

Abstract

In this study, we investigated the aggregation behaviors of amphiphilic poly(vinyl ether)s with antimicrobial activity. We synthesized a di-block poly(vinyl ether), B38₂₆, composed of cationic primary amine and hydrophobic isobutyl (iBu) side chains, which previously showed antimicrobial activity against Escherichia coli. B38₂₆ showed similar uptake behaviors as those for a hydrophobic fluorescent dye, 1,6-diphenyl-1,3,5-hexatriene, to counterpart polymers including homopolymer H44 and random copolymer R40₂₅, indicating that the iBu block does not form strong hydrophobic domains. The cryo-TEM observations also indicated that the polymer aggregate of B38₂₆ appears to have low-density polymer chains without any defined microscopic structures. We speculate that B38₂₆ formed large aggregates by liquid-liquid separation due to the weak association of polymer chains. The fluorescence microscopy images showed that B38₂₆ bonds to E. coli cell surfaces, and these bacterial cells were stained by propidium iodide, indicating that the cell membranes were significantly damaged. The results suggest that block copolymers may provide a new platform to design and develop antimicrobial materials that can utilize assembled structures and properties.

Keywords: aggregation; amphiphilic block copolymer; antimicrobial activity; poly(vinyl ether).

Figure 1

Chemical structure of poly(IBVE-co-AEVE)s.

Figure 2

Fluorescence intensity of DPH (50 nM) versus polymer concentrations of (A) homopolymer, H44 and (B) poly(IBVE-co-AEVE)s with MP_IBVE ~25 mol % in HEPES buffer (pH 7). The data points represent the average from duplicate measurements.

Figure 3

The cryo-TEM image of B38₂₆ rapidly freeze-dried from 10 mg/mL solution in HEPES buffer.

Figure 4

(A) Absorption and (B) emission spectra of B38₂₆ containing F-B38₂₆ in HEPES (1% DMSO), and (C) the maximum absorbance and (D) maximum fluorescent intensity versus polymer concentration.

Figure 5

Confocal fluorescent microscopic images of (A) 50 µg/mL solution of B38₂₆ containing F-B38₂₆ (FITC: 5.3 mol %) in HEPES buffer, (B) E. coli (OD₆₀₀ ~ 0.05) incubated with 100 µg/mL solutions of B38₂₆ containing F-B38₂₆ and (C) PI (1.6 µM) in HEPES buffer (0.5% DMSO). The images are projected images of 42 image stacks acquired with a z-step of 0.1 µm (total height: 4.2 µm).