Antibacterial Activity of Geminized Amphiphilic Cationic Homopolymers

The current study is aimed at investigating the effect of cationic charge density and hydrophobicity on the antibacterial and hemolytic activities. Two kinds of cationic surfmers, containing single or double hydrophobic tails (octyl chains or benzyl groups), and the corresponding homopolymers were synthesized. The antimicrobial activity of these candidate antibacterials was studied by microbial growth inhibition assays against <i>Escherichia coli</i>, and hemolysis activity was carried out using human red blood cells. It was interestingly found that the homopolymers were much more effective in antibacterial property than their corresponding monomers. Furthermore, the geminized homopolymers had significantly higher antibacterial activity than that of their counterparts but with single amphiphilic side chains in each repeated unit. Geminized homopolymers, with high positive charge density and moderate hydrophobicity (such as benzyl groups), combine both advantages of efficient antibacterial property and prominently high selectivity. To further explain the antibacterial performance of the novel polymer series, the molecular interaction mechanism is proposed according to experimental data which shows that these specimens are likely to kill microbes by disrupting bacterial membranes, leading them unlikely to induce resistance

Adsorption and Orientation of 3,4-Dihydroxy‑l‑phenylalanine onto Tunable Monolayer Films

3,4-Dihydroxy-l-phenylalanine (l-DOPA) is considered to be responsible for the mussel adhesion to a variety of surfaces. A molecular level understanding of the interactions between DOPA molecules and surfaces with different wettability and chemistry, however, posts significant challenges to control marine antifouling. Here, different self-assembled monolayers (SAMs) on gold surfaces were fabricated: (i) OH-, (ii) COOH-, and (iii) CH₃-terminations. The effect of surface wettability and chemistry on the adsorption of DOPA upon the series of surfaces was investigated in situ, showing that the adsorbed mass was lower and the water content of DOPA layer was higher on hydrophilic surfaces (including OH- and COOH-terminated SAMs) than that on hydrophobic ones (including CH₃-terminated SAMs and gold surface). Direct evidence regarding the DOPA orientation and the interaction between DOPA and film surfaces were obtained: on the OH-terminated surface a flexible and loose structure formed via coordinate hydrogen bonds of the hydroxyl end groups of the surface interacting with carboxyl groups of DOPA, while for the CH₃-terminated surface, DOPA molecules mainly adopt a flat conformation due to the formation of hydrophobic “bonds” between the hydrophobic functional groups of alkyl chains on surface and aromatic rings of DOPA molecules. This study led a new insight into the adsorption mechanisms based on the adsorption processes and layer structures, and it proposed novel concepts for the design of antifouling and adhesive surfaces