Antimicrobial polymer surfaces often fail because debris of killed bacteria accumulates on the coating, which is then covered and deactivated. To overcome this deficiency, two synthetic approaches are developed that combine polycationic antimicrobial polymers with polyzwitterionic protein‐repellent polymers. In the first approach, these polymers are site‐selectively immobilized on surfaces with a chemical contrast, which is obtained by colloidal lithography. In the second approach, a thin corona of polyzwitterions is grafted onto a carpet of polycationic antimicrobial polymers. Results recently obtained in our laboratory suggest that precisely controlling the surface architecture and geometry can lead to the desired dual functionality.

The article describes the interactions between poly (oxonorbornenes) (PONs)-coated gold nanoparticles (AuNPs) with phospholipid vesicles and shows that the strength of these interactions strongly depends on the molecular structure of PONs, specifically their amine/alkyl side chain ratio. PONs, which are a recently introduced class of cationic polyelectrolytes, can be systematically varied to control the amine/alkyl ratio and to explore how the chemical character of cationic polyelectrolytes affects their interactions and the interactions of their nanoparticle conjugates with model membranes. Our study shows that increasing the amine/alkyl ratio by copolymerization of diamine and 1:1 amine/butyl oxonorbornene monomers impacts the availability of PONs amine/ammonium functional groups to interact with phospholipid membranes, the PONs surface coverage on AuNPs, and the membrane disruption activity of free PONs and PONs-AuNPs. The study makes use of transmission electron microscopy, UV-vis spectroscopy, dynamic light scattering, thermogravimetric analysis, fluorescamine assay, ζ-potential measurements, and X-ray photoelectron spectroscopy measurements to characterize the PONs-AuNPs' size, size distribution, aggregation state, surface charge, and PONs surface coverage. The study also makes use of real-time fluorescence measurements of fluorescent liposomes before and during exposure to free PONs and PONs-AuNPs to determine the membrane disruption activity of free PONs and PONs-AuNPs. As commonly observed with cationic polyelectrolytes, both free PONs and PONs-AuNPs display significant membrane disruption activity. Under conditions where the amine/alkyl ratio in PONs maximizes PONs surface coverage, the membrane disruption activity of PONs-AuNPs is about 10-fold higher than the membrane disruption activity of the same free PONs. This is attributed to the increased local concentration of ammonium ions when PONs-AuNPs interact with the liposome membranes. In contrast, the hydrophobicity of amine-rich PONs, which are made for example from diamine oxonorbornene monomers, is significantly reduced. This leads to a significant reduction of PON surface coverage on AuNPs and in turn to a significant decrease in membrane disruption.

Abstract:The synthesis of different photo-reactive poly(alkenyl norbornenes) and poly(oxonorbornenes) containing benzophenone (BP) via ring-opening metatheses polymerization (ROMP) is described. These polymers are UV irradiated to form well-defined surface-attached polymer networks and hydrogels. The relative propensity of the polymers to cross-link is evaluated by studying their gel content and its dependency on BP content, irradiation wavelength (254 or 365 nm) and energy dose applied (up to 11 J·cm −2 ). Analysis of the UV spectra of the polymer networks demonstrates that the poly(oxonorbornenes) show the expected BP-induced crosslinking behavior at 365 nm, although high irradiation energy doses and BP content are needed. However, these polymers undergo chain scission at 254 nm. The poly(alkenyl norbornenes), on the other hand, do not cross-link at 365 nm, whereas moderate to good cross-linking is observed at 254 nm. UV spectra demonstrate that the cross-linking at 254 nm is due to BP cross-linking combined with a [2 + 2] cylcoaddition of the alkenyl double bonds. This indicates limitations of benzophenone as a universally applicable cross-linking for polymer networks and hydrogels.

Most antimicrobial peptides (AMPs) and their synthetic mimics (SMAMPs) are thought to act by permeabilizing cell membranes. For antimicrobial therapy, selectivity for pathogens over mammalian cells is a key requirement. Understanding membrane selectivity is thus essential for designing AMPs and SMAMPs to complement classical antibiotics in the future. This study focuses on membrane permeabilization induced by SMAMPs and their selectivity for membranes with different lipid compositions. We measure release and fluorescence lifetime of a self-quenching dye in lipid vesicles. Apart from the dose-response, we quantify the strength of individual leakage events, and, employing cumulative kinetics, categorize permeabilization behavior. We propose that differing selectivities in a series of SMAMPs arise from a combination of the effect of the antimicrobial agent and the susceptibility of the membrane (with a given lipid composition) for certain types of leakage behavior. The unselective and hemolytic SMAMP is found to act mainly by the asymmetry stress mechanism, mediated by hydrophobic insertion of SMAMPs into lipid layers. The more selective SMAMPs induced leakage events occurring stochastically over several hours. Lipid intrinsic properties might additionally amplify the efficiency of leakage events. Leakage behavior changes with both the design of the SMAMP and the lipid composition of the membrane. Understanding how leakage behavior contributes to the selectivity and activity of antimicrobial agents will aid the design and screening of antimicrobials. An understanding of the underlying processes facilitates the comparison of membrane permeabilization across in vitro and in vivo assays.

Abstract:From the aerial parts of Acmella ciliata (H.B.K.) Cassini (basionym Spilanthes ciliata Kunth; Asteraceae), three alkamides were isolated and identified by mass-and NMR spectroscopic methods as (2E,6E,8E)-N-isobutyl-2,6,8-decatrienamide (spilanthol, (1)), N-(2-phenethyl)-2E-en-6,8-nonadiynamide (2) and (2E,7Z)-6,9-endoperoxy-N-isobutyl-2,7-decadienamide (3). While 1 and 2 are known alkamides, compound 3 has not been described until now. It was found that the unusual cyclic peroxide 3 exists as a racemate of both enantiomers of each alkamide; the 6,9-cis-as well as the 6,9-trans-configured diastereomers, the former represents the major, the latter the minor constituent of the mixture. In vitro tests for activity against the human pathogenic parasites Trypanosoma brucei rhodesiense and Plasmodium falciparum revealed that 1 and 3 possess activity against the NF54 strain of the latter (IC 50 values of 4.5 and 5.1 µM, respectively) while 2 was almost inactive. Compound 3 was also tested against multiresistant P. falciparum K1 and was found to be even more active against this parasite strain (IC 50 = 2.1 µM) with considerable selectivity (IC 50 against L6 rat skeletal myoblasts = 168 µM).