Tetrahedral (T) closed-shell cluster of 29 silver atoms & 12 lipoate ligands, [Ag29(R-a-LA)12](3-): antibacterial and antifungal activity

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Lopez, Priscilla
Lara, Humberto H.
Mullins, Sean M.
Black, David M.
Ramsower, Heidi M.
Alvarez, Marcos M.
Williams, Tayler L.
Lopez-Lozano, Xochitl
Weissker, Hans-Christian
Garcia, A. Patricio
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American Chemical Society
Here we report on the identification and applications of an aqueous 29-atom silver cluster stabilized with 12 lipoate ligands, i.e. Ag29(R-α–LA)12 or (29,12), wherein R-α–LA = R-α-lipoic acid, a natural dithiolate. Its uniformity is checked by HPLC-ESI-MS and analytical ultracentrifugation, which confirms its small dimension (∼3 nm hydrodynamic diameter). For the first time, this cluster has been detected intact via electrospray ionization mass spectrometry, allowing one to confirm its composition, its [3-] charge-state, and the 8-electron shell configuration of its metallic silver core. Its electronic structure and bonding, including T-symmetry and profound chirality in the outer shell, have been analyzed by DFT quantum-chemical calculations, starting from the known structure of a nonaqueous homologue. The cluster is effective against Methicillin-Resistant Staphylococcus aureus bacteria (MRSA) at a minimum inhibitory concentration (MIC) of 0.6 mg-Ag/mL. A preformed Candida albicans fungal biofilm, impermeable to other antifungal agents, was also inhibited by aqueous solutions of this cluster, in a dose–response manner, with a half-maximal inhibitory concentration (IC50) of 0.94 mg-Ag/mL. Scanning electron micrographs showed the post-treatment ultrastructural changes on both MRSA and C. albicans that are characteristic of those displayed after treatment by larger silver nanoparticles.
Accepted author manuscript
Silver clusters , Lipoic acid , Antibiotic , Analytical ultracentrifuge , Electrospray ionization mass spectroscopy , Ag29
Lopez, P., Humberto, H., Mullins, S. M., Black, D. A., Ramsower, H. M., Alvarez, M. M., Williams, T. L., Lopez-Lozano, X., Weissker, H.-C., Garcia, A. P., Garzon, I. L., Demeler, B., Lopez-Ribot, J. L., Yacaman, M. J., & Whetten, R. L. (2018). Tetrahedral (T) closed-shell cluster of 29 silver atoms & 12 lipoate ligands, [Ag29(R-a-LA)12](3-): Antibacterial and antifungal activity. ACS Applied Nano Materials, 1(4), 1595-1602. https://doi.org/10.1021/acsanm.8b00069