title: IR low-temperature matrix, X-ray and ab initio study on L-isoserine conformations.
abstract: 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 1 to be dominating. Presence of the conformer 2 is well confirmed by the nu(C=O) band at 1790 cm(-1) and two bands at 1380 and 1350 cm(-1). Presence of the conformer 4 is quite well confirmed by the nu(C-O) bands at 1120 and 1095 cm(-1). Slightly weaker arguments are found for the observation of conformers 6 and 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 P2(1)2(1)2 space group. The asymmetric unit contains a single molecule. The molecule is in its zwitterionic form with the CH(2)-NH(3) side chain in the gauche conformation with respect to the hydroxyl group and in the anti conformation 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 O...H contact is of 1.66(2) A, which is amongst the shortest H-bonds of this kind observed in amino acid crystal structures.
authors.affiliation: National Medicines Institute, 30/34 Chełmska Street, 00-725 Warsaw, Poland. janek@il.waw.pl
authors.forename: Jan Cz
authors.initials: JC
authors.lastname: Dobrowolski
authors.forename: Michał H
authors.initials: MH
authors.lastname: Jamróz
authors.forename: Robert
authors.initials: R
authors.lastname: Kołos
authors.forename: Joanna E
authors.initials: JE
authors.lastname: Rode
authors.forename: Michał K
authors.initials: MK
authors.lastname: Cyrański
authors.forename: Joanna
authors.initials: J
authors.lastname: Sadlej
mesh_terms: D018360:Crystallography, X-Ray; D005740:Gases / Q000737:chemistry; D008958:Models, Molecular; D008968:Molecular Conformation; D011789:Quantum Theory; D012694:Serine / Q000031:analogs & derivatives* / Q000737:chemistry; D013055:Spectrophotometry, Infrared; D013696:Temperature; D013816:Thermodynamics
chemical_list: D005740:Gases; D012694:Serine; C072421:isoserine