The conformation of chloramphenicol in the ordered and disordered phases
Fecha
2019-03-15Autor
Sánchez Rexach, Eva Gloria
Butron Janices, Amaia
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Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 211 : 383-392 (2019)
Resumen
The conformational behavior of chloramphenicol (CHL) in the solid, liquid and
vapor phases is revisited here by means of FTIR spectroscopy and QM methods. In the
crystalline phase, both the IR analysis and QM computations discard the conformer
proposed by Acharya et al. (Acta Cryst., 1979, B35:1360-1363) and support the one
proposed by Chatterjee et al. (J. Cryst. Mol. Struct., 1979, 9:295-304), characterised by
an intramolecular O-H•••O hydrogen bond in which the primary hydroxyl group acts as
hydrogen bond donor. The conformational behavior of CHL in the liquid and gas phases
has been analyzed using QM calculations. The Self-Consistent Reaction Field (SCRF)
method with the Onsager solvation model has been used for the initial optimizations in
solution, and the lowest energy conformers have been refined using the Solvation Model
based on Density (SMD). In solution environment the intramolecular O-H•••O hydrogen
bond in CHL is reversed so that the secondary hydroxyl group acts as hydrogen bond
donor. In addition, the dichloroacetamide group folds back further over the phenyl ring
to form an intramolecular C-Cl•••π halogen bond. Two different halogen bonds are
actually observed (each one with a different chlorine atom) resulting in two different
stable conformers, that can be detected by FTIR spectroscopy due to the conformational
sensitivity of the C=O group to the conformation of the dichloroacetyl group. Finally, the
stability of the conformers with the polarity of the medium is also discussed.