4P9V:
reference: Protein-ligand interactions: Probing the energetics of a putative cation-pi interaction., Myslinski JM, Clements JH, Martin SF, Bioorg Med Chem Lett. 2014 Jul 15;24(14):3164-7. doi: 10.1016/j.bmcl.2014.04.114., Epub 2014 May 9. PMID: 24856058

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