An ab initio theoretical study is presented on the interaction of trimethylsulfonium ion [S(CH3)3+] with H3PO4, H2PO4−, HPO42− and PO43− (HnPO4n-3, n = 0-3 phosphate species). Computational results with MP2/aug-cc-pVDZ reveal a proton- and charge-dependent complexation between the sulfonium ion and phosphate species. They predict through-space S●●●O chalcogen bond (ChB) interactions, in addition to the expected H-bonding interactions in the [S(CH3)3-HnPO4]n-2 complexes. We find there is an increase in the S●●●O (ChB) interaction upon sequential deprotonation of the phosphate ions in the series, in the order SMe3PO4H3+ &lt; SMe3PO4H2 &lt; SMe3PO4H− &lt; SMe3PO42−. For example, the interaction of SMe3+ with PO43− leads to a complex, SMe3PO42−, bearing a S●●●O interaction and distorted trigonal bipyramid (TBP) structure. By comparison, the interaction of SMe3+ with H3PO4 led to an SMe3H3PO4+ complex bearing a ~10-fold weaker S●●●O interaction, but accompanied by hydrogen bonds. Basis set superposition error (BSSE), atom in molecules (AIM), and natural bond orbital (NBO) calculations were also used to evaluate the complexation. The computed results are proposed to have implications for the peptide sulfonium ion binding with phosphate species.

Theoretical study of S●●●O and hydrogen bond interactions between trimethylsulfonium ion and phosphate ions or acids

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