We synthesized a combinatorial library of dendrons that display a cluster of cationic charges juxtaposed with a hydrophobic alkyl chain, using the so-called “molecular umbrella” design approach. Systematically tuning the generation number and alkyl chain length enabled a detailed study of the structure–activity relationships in terms of both hydrophobic content and number of cationic charges. These discrete, unimolecular compounds display rapid and broad-spectrum bactericidal activity comparable to the activity of antibacterial peptides. Micellization was examined by pyrene emission and dynamic light scattering, which revealed that monomeric, individually solvated dendrons are present in aqueous media. The antibacterial mechanism of action is putatively driven by the membrane-disrupting nature of these cationic surfactants, which we confirmed by enzymatic assays on E. coli cells. The hemolytic activity of these dendritic macromolecules is sensitively dependent on the dendron generation and the alkyl chain length. Via structural optimization of these two key design features, we identified a leading candidate with potent broad-spectrum antibacterial activity (4–8 μg/mL) combined with outstanding hemocompatibility (up to 5000 μg/mL). This selected compound is >1000-fold more active against bacteria as compared to red blood cells, which represents one of the highest selectivity index values ever reported for a membrane-disrupting antibacterial agent. Thus, the leading candidate from this initial library screen holds great potential for future applications as a nontoxic, degradable disinfectant.

Summary Combinations of ionic liquids (ILs) with antimicrobial compounds have been shown to produce synergistic activities in model liposomes. In this study, imidazolium chloride-based ILs with alkyl tail length variations are combined with commercially available, small-molecule antimicrobials to examine the potential for combinatorial and synergistic antimicrobial effects on P. aeruginosa, E. coli, S. aureus, and S. cerevisiae. The effects of these treatments in a human cell culture model indicate the cytotoxic limits of ILs paired with antimicrobials. The analysis of these ILs demonstrates that the length of the alkyl chain on the IL molecule is proportional to both antimicrobial activity and cytotoxicity. Moreover, the ILs which exhibit synergy with small-molecule antibiotics appear to be acting in a membrane permeabilizing manner. Collectively, results from these experiments demonstrate an increase in antimicrobial efficacy with specific IL + antimicrobial combinations on microbial cultures while maintaining low cytotoxicity in a mammalian cell culture model.

Despite considerable advances in recent years, challenges in delivery and storage of biological drugs persist and may delay or prohibit their clinical application. Though nanoparticle-based approaches for small molecule drug encapsulation are mature, encapsulation of proteins remains problematic due to destabilization of the protein. Reverse micelles composed of decylmonoacyl glycerol (10MAG) and lauryldimethylamino-N-oxide (LDAO) in low-viscosity alkanes have been shown to preserve the structure and stability of a wide range of biological macromolecules. Here, we present a first step on developing this system as a future platform for storage and delivery of biological drugs by replacing the non-biocompatible alkane solvent with solvents currently used in small molecule delivery systems. Using a novel screening approach, we performed a comprehensive evaluation of the 10MAG/LDAO system using two preparation methods across seven biocompatible solvents with analysis of toxicity and encapsulation efficiency for each solvent. By using an inexpensive hydrophilic small molecule to test a wide range of conditions, we identify optimal solvent properties for further development. We validate the predictions from this screen with preliminary protein encapsulation tests. The insight provided lays the foundation for further development of this system toward long-term room-temperature storage of biologics or toward water-in-oil-in-water biologic delivery systems.