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.
The majority of gels exhibit nanoscale spatial variations in crosslink density. We present the first 3D super-resolution microscopy images of dye tagged cross-link distributions in microgels and hydrogels. The morphology of nanoscale features never imaged previously in microgels, are revealed.
Thermoplastic copolyesters occupy an important segment in the materials market, finding use in a wide range of engineering plastic applications. This fact owes itself to the versatility underlying the synthetic preparation. However, the industry relies nearly exclusively on virgin feedstocks that are derived from fossil-based resources. With a keen interest in improving the deleterious environmental impact of this material class, we combine postconsumer recycled PET (rPET) with a bioderived dimer fatty acid (DFA) building block for the synthesis of segmented thermoplastic copolyesters (TPCs) via solvent-free melt polycondensation. The influence of (i) catalyst type, (ii) hard block (i.e., PET) precursor, and (iii) soft block (i.e., DFA) content on the microstructure and mechanical properties of TPCs was assessed. Samples that exhibit equivalent mechanical strength and segment distribution are accessible using either pristine bis-hydroxy ethylene terephthalate (BHET) or rPET as starting materials. Screening of reaction conditions and composition space within this context was performed with small-scale (2 g) reactions. Further optimization of reaction conditions in terms of catalyst concentration and ethylene glycol deconstruction agent content allowed for the upscaled synthesis (100 g) of engineering-grade TPCs in a custom-built reactor. We believe that our results contribute to a new paradigm in the efforts for more responsible manufacturing practices for TPCs and provide an additional outlet for the efficient handling of end-of-life, recyclable plastics.
Two well‐defined heptablock quaterpolymers of the ABCDCBA type [Α: polystyrene (PS), B: poly(butadiene) with ∼90% 1,4‐microstructure (PB1,4), C: poly(isoprene) with ∼55% 3,4‐microstructure (PI3,4) and D: poly(dimethylsiloxane) (PDMS)] were synthesized by combining anionic polymerization high vacuum techniques and hydrosilylation/chlorosilane chemistry. All intermediates and final products were characterized by size exclusion chromatography, membrane osmometry, and proton nuclear magnetic resonance spectroscopy. Fourier transform infrared spectroscopy was used to further verify the chemical modification reaction of the difunctional PDMS. The self‐assembly in bulk of these novel heptablock quarterpolymers, studied by transmission electron microscopy and small angle X‐ray scattering, revealed 3‐phase 4‐layer alternating lamellae morphology of PS, PB1,4, and mixed PI3,4/PDMS domains. Differential scanning calorimetry was used to further confirm the miscibility of PI3,4 and PDMS blocks. It is the first time that PDMS is the central segment in such multiblock polymers (≥3 chemically different blocks). © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 1443–1449
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