Figure 3.

Relative binding of two chlorines to two phosphates for lysine and histidine bound with various cations. a, ΔΔG for the reaction of HisX⁺ with either two Cl⁻ or two H₂PO₄⁻ relative to lysine. Positive ΔΔG indicates preference for lysine to bind phosphates over HisX⁺. b, Interphosphate distance, i.e. distance between two negatively charged oxygens bound to cation, as indicated by green arrows in (c), as a function of the dielectric. Notice that distance between the two negatively charged oxygens increases down the Hofmeister series at all dielectrics. c, Optimized structures of histidine bound to 2(H₂PO₄⁾²⁻ with Na⁺, K⁺, and Cs⁺ in the gas phase. The cation is bound to histidine’s π-system forming a multidentate ligand.