2JKH:
reference: Cation-pi Interactions at the Active Site of Factor Xa: Dramatic Enhancement upon Stepwise N-Alkylation of Ammonium Ions., Salonen LM, Bucher C, Banner DW, Haap W, Mary JL, Benz J, Kuster O, Seiler P, Schweizer WB, Diederich F, Angew Chem Int Ed Engl. 2008 Dec 19;48(4):811-814. PMID: 19101972

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