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1. Biocidal Potency of Polymers with Bulky Cations

   https://doi.org/10.1021/acsmacrolett.2c00726  

   Lou, Yang ; Gaitor, Jamie ; Treichel, Megan ; Noonan, Kevin J. ; Palermo, Edmund F. ( January 2023 , ACS Macro Letters)

   Melissa Grunlan (Ed.)

   The performance of antimicrobial polymers depends sensitively on the type of cationic species, charge density, and spatial arrangement of cations. Here we report antimicrobial polymers bearing unusually bulky tetraaminophosphonium groups as the source of highly delocalized cationic charge. The bulky cations drastically enhanced the biocidal activity of amphiphilic polymers, leading to remarkably potent activity in the submicromolar range. The cationic polynorbornenes with pendent tetraaminophosphonium groups killed over 98% E. coli at a concentration of 0.1 μg/mL and caused a 4-log reduction of E. coli within 2 h at a concentration of 2 μg/mL, showing very rapid and potent bactericidal activity. The polymers are also highly hemolytic at similar concentrations, indicating a biocidal activity profile. Polymers of a similar chemical structure but with more flexible backbones were made to examine the effects of the flexibility of polymer chains on their activity, which turned out to be marginal. We also explore variants with different spacer arm groups separating the cations from the backbone main chain. The antibacterial activity was comparably potent in all cases, but the polymers with shorter spacer arm groups showed more rapid bactericidal kinetics. Interestingly, pronounced counterion effects were observed. Tightly bound PF6– counteranions showed poor activity at high concentrations due to gross aggregate formation and precipitation from the assay media, whereas loosely bound Cl– counterions resulted in very potent activity that monotonically increased with increasing concentration. In this paper, we reveal that bulky phosphonium cations are associated with markedly enhanced biocidal activity, which provides an innovative strategy to develop more effective self-disinfecting materials. 

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2. Photophysics of Oligothiophenes End‐Capped with Platinum(II) Auxochromes

   https://doi.org/10.1002/cptc.202000123  

   Gundogan, Ali S. ; Jagadesan, Pradeepkumar ; Schanze, Kirk S. ( October 2020 , ChemPhotoChem)

   A series of four oligothiophenes end‐capped with −Pt(PBu₃)₂Cl moieties on both ends of the oligomers was synthesized, and their excited state properties were investigated. The observation of low fluorescence quantum yield (<2 %) for the oligomers indicates the strong effect of platinum on the intersystem crossing (ISC) efficiency. No phosphorescence was detected for any of the oligomers; however, strong triplet‐triplet absorption was observed by nanosecond transient spectroscopy for oligomers with more than one thiophene unit. The oligomers displayed short triplet lifetimes (∼1–2 μs) compared to the unmetallated oligomers, due to large spin‐orbit coupling induced by the platinum atom. The lower limits of the ISC yields were indirectly determined by measuring the singlet oxygen quantum yields. Femtosecond–picosecond transient absorption studies revealed that the ISC rate ranges from 10¹²–10¹⁰ s⁻¹, decreasing with increasing oligomer length. Electrochemical studies showed that the oligomers exhibit relatively low oxidation potentials (ca. 0.1 V vs. Fc/Fc⁺). Quenching of the oligomers’ triplet state absorption, simultaneously with the rise of their corresponding cationic radical absorption band in nanosecond transient spectra in the presence of methyl viologen, as an electron acceptor, established that the electron transfer occurs from their triplet state.

    

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3. Antibacterial isoamphipathic oligomers highlight the importance of multimeric lipid aggregation for antibacterial potency

   https://doi.org/10.1038/s42003-018-0230-4  

   Brown, Joseph S. ; Mohamed, Zeinab J. ; Artim, Christine M. ; Thornlow, Dana N. ; Hassler, Joseph F. ; Rigoglioso, Vincent P. ; Daniel, Susan ; Alabi, Christopher A. ( December 2018 , Communications Biology)

   Cationic charge and hydrophobicity have long been understood to drive the potency and selectivity of antimicrobial peptides (AMPs). However, these properties alone struggle to guide broad success in vivo, where AMPs must differentiate bacterial and mammalian cells, while avoiding complex barriers. New parameters describing the biophysical processes of membrane disruption could provide new opportunities for antimicrobial optimization. In this work, we utilize oligothioetheramides (oligoTEAs) to explore the membrane-targeting mechanism of oligomers, which have the same cationic charge and hydrophobicity, yet show a unique ~ 10-fold difference in antibacterial potency. Solution-phase characterization reveals little difference in structure and dynamics. However, fluorescence microscopy of oligomer-treatedStaphylococcus aureusmimetic membranes shows multimeric lipid aggregation that correlates with biological activity and helps establish a framework for the kinetic mechanism of action. Surface plasmon resonance supports the kinetic framework and supports lipid aggregation as a driver of antimicrobial function.

    

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4. Effect of Carbon Doping on CO 2 ‐Reduction Activity of Single Cobalt Sites in Graphitic Carbon Nitride

   https://doi.org/10.1002/cnma.202100164  

   Huang, Peipei ; Huang, Jiahao ; Li, Junying ; Zhang, Lei ; He, Jie ; Caputo, Christine A. ; Frenkel, Anatoly I. ; Li, Gonghu ( June 2021 , ChemNanoMat)

   Single‐atom catalysts have demonstrated interesting activity in a variety of applications. In this study, we prepared single Co²⁺sites on graphitic carbon nitride (C₃N₄), which was doped with carbon for enhanced activity in visible‐light CO₂reduction. The synthesized materials were characterized with a variety of techniques, including microscopy, X‐ray powder diffraction, UV‐vis spectroscopy, infrared spectroscopy, photoluminescence spectroscopy, and X‐ray absorption spectroscopy. Doping C₃N₄with carbon was found to have profound effect on the photocatalytic activity of the single Co²⁺sites. At relatively low levels, carbon doping enhanced the photoresponse of C₃N₄in the visible region and improved charge separation upon photoactivation, thereby enhancing the photocatalytic activity. High levels of carbon doping were found to be detrimental to the photocatalytic activity of the single Co²⁺sites by altering the structure of C₃N₄and generating defect sites responsible for charge recombination.

    

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5. Synthetic mimics of cyclic antimicrobial peptides via templated ring-opening metathesis (TROM)

   https://doi.org/10.1039/C9PY01271K  

   Zhou, Zhe ; Ergene, Cansu ; Palermo, Edmund F. ( January 2019 , Polymer Chemistry)

   We utilized a templated ring-opening metathesis (TROM) strategy to synthesize a series of precision macrocyclic olefins, each containing two, three or four repeating units of a cyclooctene with pendant carboxylic acid side chains. The structures were confirmed by a combination of NMR spectroscopy, MALDI, and MALDI ms/ms fragmentation studies. In accordance with previous work, we found that cyclooctene monomers covalently tethered to precision oligo(thiophene)s yield exclusively macrocyclic products when subjected to the Grubbs 3 rd generation catalyst in highly dilute solution (10 −4 M in DCM, 0 °C). Upon hydrolytic liberation of the daughter oligo(olefin) product, further derivatization with cationic groups confers antibacterial and hemolytic activities. We compare the biological activity of these precision macrocycles to that of a polydisperse sample prepared by direct ROM in the absence of a template. Surprisingly, the relatively ill-defined, disperse mixture of oligomeric species exerted biological activity comparable to that of the precision oligomeric macrocycles, suggesting a remarkable degree of tolerance for heterogeneity. These findings provide nuance to the structure–activity relationships understood thus far for AMPs and their mimics, especially in the context of relatively underexplored macrocyclic compounds. 

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