DFT-MD and vibrational anharmonicities of a phosphorylated amino acid. Success and failure

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Following our work on the phosphorylated deprotonated serine amino acid pSerH(-) [J. Chem. Theory Comput., 2009, 5, 2388], we investigate here the room temperature infrared spectroscopy of pSerH(+) (phosphorylated protonated serine) in the gas phase in relation with IR-MPD experiment. To that end, DFT-based Car-Parrinello molecular dynamics (DFTMD) are performed, giving a direct probe of vibrational anharmonicities. Agreement and disagreement with the experiment are explored in the light of DFT/functional, vibrational mode couplings and potential energy surface anharmonicities. Trends on the phosphate vibrational signatures in relation with its protonation state and environment are analysed, for the purpose of transferability into more complex phosphorylated peptide chains.