Low-temperature infrared spectra and hydrogen bonding in polycrystalline dl-serine and deuterated derivatives

The FT-IR spectra of polycrystalline dl-serine [α-amino-β-hydroxypropionic acid; HO-CH₂-CH(NH₃)⁺-COO^-] and isotopically substituted [ND/OD_Alcohol (<10% and >90% D); CD₂ (>98% D)] dl-serine were recorded in the range 4000-500 cm^-1 in the temperature range 300-10 K, and fully assigned. The isotopic-doping/low-temperature methodology, which allows for decoupling of individual proton vibrational modes from the crystal bulk vibrations, was used to estimate the energies of the different H-bonds present in dl-serine crystal. To this end, the frequency shifts observed in both the NH/OH stretching and out-of-plane bending spectral regions (relatively to reference values for these vibrations in non-hydrogen-bonded dl-serine molecules) were used, together with previously developed empirical correlations. The results are compared with available structural data on this amino acid.