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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. Tying the alkoxides together: an iron complex of a new chelating bulky bis(alkoxide) demonstrates selectivity for coupling of non-bulky aryl nitrenes

   https://doi.org/10.1039/C9CC05319K  

   Kurup, Sudheer S. ; Wannipurage, Duleeka ; Lord, Richard L. ; Groysman, Stanislav ( September 2019 , Chemical Communications)

   New chelating bis(alkoxide) ligand H 2 [OO] Ph and its iron( ii ) complex Fe[OO] Ph (THF) 2 are described. The coordination of the ligand to the metal center is reminiscent of the coordination of two monodentate alkoxides in previously reported Fe(OR) 2 (THF) 2 species. Fe[OO] Ph (THF) 2 catalyzes selective and efficient dimerization of non-bulky aryl nitrenes to yield the corresponding azoarenes. 

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3. Heteroleptic nickel complexes of a bulky bis(carbene)borate ligand

   https://doi.org/10.1016/j.poly.2018.09.026  

   Martinez, Jorge L. ; Lee, Wei-Tsung ; Pink, Maren ; Chen, Chun-Hsing ; Smith, Jeremy M. ( December 2018 , Polyhedron)
4. Crystal structure of bulky-ligand-protected Au24(S-C4H9)16

   K. H. Wijesinghe, A. G. ( September 2022 , Acta crystallographica Section C Structural chemistry)

   Atomically precise thiol­ate-protected gold nanomolecules have attracted inter­est due to their distinct electronic and chemical properties. The structure of these nanomolecules is important for understanding their peculiar properties. Here, we report the X-ray crystal structure of a 24-atom gold nanomolecule protected by 16 tert-butylthiolate ligands. The com­position of Au24(S-C4H9)16 {poly[hexa­deca­kis­(μ-tert-butyl­thiol­ato)tetra­cosa­gold]} was confirmed by X-ray crystallography and electrospray ionization mass spectrometry (ESI–MS). The nanomolecule was synthesized in a one-phase synthesis and crystallized from a hexa­ne–ethanol layered solution. The X-ray structure confirms the 16-atom core protected by two monomeric and two trimeric staples with four bridging ligands. The Au24(S-C4H9)16 cluster follows the shell-closing magic number of 8. 

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5. Near quantitative synthesis of urea macrocycles enabled by bulky N-substituent

   https://doi.org/10.1038/s41467-021-21678-3  

   Yang, Yingfeng ; Ying, Hanze ; Li, Zhixia ; Wang, Jiang ; Chen, Yingying ; Luo, Binbin ; Gray, Danielle L. ; Ferguson, Andrew ; Chen, Qian ; Z, Y. ; et al ( March 2021 , Nature Communications)

   Macrocycles are unique molecular structures extensively used in the design of catalysts, therapeutics and supramolecular assemblies. Among all reactions reported to date, systems that can produce macrocycles in high yield under high reaction concentrations are rare. Here we report the use of dynamic hindered urea bond (HUB) for the construction of urea macrocycles with very high efficiency. Mixing of equal molar diisocyanate and hindered diamine leads to formation of macrocycles with discrete structures in nearly quantitative yields under high concentration of reactants. The bulkyN-tert-butyl plays key roles to facilitate the formation of macrocycles, providing not only the kinetic control due to the formation of the cyclization-promotingcisC = O/tert-butyl conformation, but also possibly the thermodynamic stabilization of macrocycles with weak association interactions. The bulkyN-tert-butyl can be readily removed by acid to eliminate the dynamicity of HUB and stabilize the macrocycle structures.

    

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