Antibacterial Micelles Self-assembled from Copolypeptides through a One-step Acidification Process

We propose a one-step acidification method for facile preparation of antibacterial micelles. The random copolypeptide TPE-P(Lys(28)-stat-BLG16) was obtained by selective deprotection of the trifluoroacetyl groups from a TPE-P[Lys(Tfa)(28)-stat-BLG(16)] precursor. This initial random copolypeptide was synthesized by ring-opening copolymerization of N-epsilon-trifluoroacetyl-L-lysine N-carboxyanhydride [Lys(Tfa) NCA] and gamma-benzyl-L-glutamate Ncarboxyanhydride (BLG NCA) using 4-(1,2,2-triphenylvinyl)aniline (TPE-NH2) as initiator. After polymerization and deprotection, polymer micelles were formed by acidification of the crude aqueous TPE-P(Lys28-stat-BLG16) reaction mixture. Thus, this method is called a "one-step acidification process". The obtained micelles should have good antibacterial properties, given that this random copolypeptide comprises a large number of aromatic and amino groups. The antibacterial properties of these micelles were evaluated using the broth microdilution method and the plate paint method, to determine the minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC). These tests showed that these polymer micelles have indeed antibacterial properties: the determined MICs for E. coli and S. aureus were 256 and 64 mu g/mL; the determined MBCs for these bacteria were 400 and 100 mu g/mL, respectively. Interestingly, these antibacterial micelles produce bright blue fluorescence light under UV exposure, owing to the aggregation-induced emission (AIE) effect of the TPE end groups. Herein, this property was used to optically explore the antibacterial mechanism of these polymer micelles. This approach indicated that these polymer micelles kill bacteria by piercing their membrane via a physically damaging process.