The conformation of chloramphenicol in the ordered and disordered phases
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2019-03-15
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Abstract
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), characterized 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[dbnd]O group to the conformation of the dichloroacetyl group. Finally, the stability of the conformers with the polarity of the medium is also discussed.
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Publisher Copyright: © 2018 Elsevier B.V.
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Chloramphenicol (CHL) , Conformation , Halogen bonding , Hydrogen bonding , Interactions , Chloramphenicol (CHL) , Conformation , Halogen bonding , Hydrogen bonding , Interactions , Analytical Chemistry , Atomic and Molecular Physics, and Optics , Instrumentation , Spectroscopy , Funding Info , The authors are thankful for funds from the Spanish Ministry of In-novation and Competitiveness MINECO (MAT2016-78527-P), theBasque Government, Department of Education (IT-927-16) and the EUiPROMEDAI COST Action TD1305. , The authors are thankful for funds from the Spanish Ministry of In-novation and Competitiveness MINECO (MAT2016-78527-P), theBasque Government, Department of Education (IT-927-16) and the EUiPROMEDAI COST Action TD1305.
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Meaurio , E , Sanchez-Rexach , E , Butron , A & Sarasua , J-R 2019 , ' The conformation of chloramphenicol in the ordered and disordered phases ' , Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy , vol. 211 , pp. 383-392 . https://doi.org/10.1016/j.saa.2018.12.021