“…We onwards focus on the two D-HMQC NMR signals centered at the {δ P , δ C } shift-pairs of {3.0, 184.2} ppm and {2.4, 170.0} ppm, which are tentatively assigned to COO – moieties that are strongly surface bound predominantly/solely via electrostatic C O ··· Ca 2+ interactions and C O ··· H bonds, respectively. While noting that those two contact modes were predicted by modeling (Section ), the NMR-peak assignments were based on the distinctly different 13 C and 31 P chemical shifts involved in each correlation: the high shifts of the {δ P , δ C } = {3.0, 184.2} ppm signal are well-aligned with COO – moieties nearby groups (see Sections and 3.2), whereas the lower chemical shifts of the {2.4, 170.0} ppm correlation are commensurate with H-bond-mediated 13 C OO – ··· contacts, whose 13 C chemical shift incidentally matches that of the 13 C OOH group of polycrystalline Pser that manifests analogous inter molecular COOH··· motifs. ,, Notably, Figure reveals a lower NMR-signal intensity at 184 ppm from the Ser16 cement relative to its Ser8 counterpart, suggesting a concurrently reduced number of C O ··· Ca 2+ contacts for increasing batched Ser content, along with earlier and more qualitative findings by Mathew et al and our inferences in Section .…”