Synthesis, Characterization, and Bactericidal Activity of a 4-Ammoniumbuthylstyrene-Based Random Copolymer.

Silvana Alfei,Debora Caviglia,Anna Maria Schito,Gabriella Piatti

doi:10.3390/polym13071140

Abstract

The growing resistance of bacteria to current chemotherapy is a global concern that urgently requires new and effective antimicrobial agents, aimed at curing untreatable infection, reducing unacceptable healthcare costs and human mortality. Cationic polymers, that mimic antimicrobial cationic peptides, represent promising broad-spectrum agents, being less susceptible to develop resistance than low molecular weight antibiotics. We, thus, designed, and herein report, the synthesis and physicochemical characterization of a water-soluble cationic copolymer (P5), obtained by copolymerizing the laboratory-made monomer 4-ammoniumbuthylstyrene hydrochloride with di-methyl-acrylamide as uncharged diluent. The antibacterial activity of P5 was assessed against several multi-drug-resistant clinical isolates of both Gram-positive and Gram-negative species. Except for strains characterized by modifications of the membrane charge, most of the tested isolates were sensible to the new molecule. P5 showed remarkable antibacterial activity against several isolates of genera Enterococcus, Staphylococcus, Pseudomonas, Klebsiella, and against Escherichia coli, Acinetobacter baumannii and Stenotrophomonas maltophilia, displaying a minimum MIC value of 3.15 µM. In time-killing and turbidimetric studies, P5 displayed a rapid non-lytic bactericidal activity. Due to its water-solubility and wide bactericidal spectrum, P5 could represent a promising novel agent capable of overcoming severe infections sustained by bacteria resistant the presently available antibiotics.

Highlights

Cationic macromolecules including cationic dendrimers (CDs) [1], cationic polymers (CPs) and positively charged amphiphilic copolymers (CACs) [2] increasingly attract the attention of scientists and of various sectors of industry, such as food and food packaging, due to their capability to limit or inhibit bacterial growth, both in solution and on surfaces
Monomer M5 (5), whose structure was designed on the base of structure/activity relationship as reported in Section 3.6.1, was synthesized according to Scheme 1, starting from commercially available 4-chlorovinylbenzene to obtain a lab-prepared Grignard reagent (1), subsequently exploited to prepare the brome buthyl styrene derivative (2), applying a modified version of a procedure proposed by Bertini et al (2004) [12]
To limit the production of the product derived from the side reaction of double alkylation, the reaction was carried out in a strong excess of dibromide, which was removed largely by high vacuum distillation to prevent spontaneous polymerizations

Summary

Introduction

Cationic macromolecules including cationic dendrimers (CDs) [1], cationic polymers (CPs) and positively charged amphiphilic copolymers (CACs) [2] increasingly attract the attention of scientists and of various sectors of industry, such as food and food packaging, due to their capability to limit or inhibit bacterial growth, both in solution and on surfaces. Monomers containing permanently cationic tetra alkyl ammonium groups have been widely employed to prepare homo-polymers and copolymers, capable of interacting with negative constituents of bacterial surface of Gram-positive and Gram-negative pathogens, and to reach the cytoplasmic membranes by diffusion through the outer membrane (Gram-negative) and the cell walls (Gram-negative and Gram-positive) [1,2,3,4,5,6]. Due to these electrostatic interactions and diffusion processes, membranes depolarize and progressive permeabilization occur, leading to membrane disruption, loss of cytoplasmic content and bacterial death [1,2,3,4,5,6]. The preparation of random copolymers with uncharged acrylates, methacrylates, acrylamides and methacrylamides, with the aim of reducing the cationic charges, allowed to tune the balance between hydrophobic and cationic properties, as well as to control the length of the polymers [7]

Methods

Results

Conclusion