IR low-temperature matrix, X-ray and ab initiostudy on l-isoserine conformationsElectronic supplementary information (ESI) available: schemes, energetics, geometries, coordinates, spectra. CCDC 770483. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c0cp00016g

The IR low-temperature Ar and Kr matrix spectra of l-isoserine were registered for the first time and interpreted by means of the anharmonic DFT frequencies calculated at the B3LYP/aug-cc-pVTZ and B3LYP/aug-cc-pVDZ levels. 54 l-isoserine conformers were predicted to be stable at the B3LYP/aug-cc-pVDZ level. Population of the 8 most stable conformers was based on the QCISD/aug-cc-pVDZ energies, corrected for thermal anharmonic factors obtained at the B3LYP/aug-cc-pVDZ level. We found several conformers to be present in the measured matrices and conformer 1to be dominating. Presence of the conformer 2is well confirmed by the ν(CO) band at 1790 cm−1and two bands at 1380 and 1350 cm−1. Presence of the conformer 4is quite well confirmed by the ν(C–O) bands at 1120 and 1095 cm−1. Slightly weaker arguments are found for the observation of conformers 6and 3. Calculations on 54 neutral and 5 zwitterionic conformers in water at the IEF-PCM/B3LYP/aug-cc-pVDZ level suggest that one neutral and one zwitterionic conformer co-exist in the aqueous environment. The crystal structure of l-isoserine was solved by X-ray diffraction analysis. The compound crystallizes without solvent in the chiral P21212 space group. The asymmetric unit contains a single molecule. The molecule is in its zwitterionic form with the CH2–NH3side chain in the gaucheconformation with respect to the hydroxyl group and in the anticonformation with respect to the carboxylate group. The structure of l-isoserine is dominated by a set of intermolecular hydrogen bonds. The strongest one appears between the OH and COOH groups of two neighbouring molecules: the OH contact is of 1.66(2) , which is amongst the shortest H-bonds of this kind observed in amino acid crystal structures. [ABSTRACT FROM AUTHOR]