Journal
PHYSICAL CHEMISTRY CHEMICAL PHYSICS
Volume 20, Issue 10, Pages 6891-6904Publisher
ROYAL SOC CHEMISTRY
DOI: 10.1039/c7cp08579f
Keywords
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Funding
- Deutsche Forschungsgemeinschaft (DFG) through Emmy-Noether grant [MU 2820/2-1]
- Cluster of Excellence RESOLV - Deutsche Forschungsgemeinschaft [EXC 1069]
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To determine the preferred water molecule binding sites of the polybasic sulfa drugs sulfamethoxazole (SMX) and sulfisoxazole (SIX), we have studied their monomers and monohydrated complexes through laser-desorption conformer-specific UV and IR spectroscopy. Both the SMX and SIX monomer adopt a single conformer in the molecular beam. On the basis of their conformer-specific IR spectra in the NH stretch region, these conformers were assigned to the SMX and SIX global minimum structures, both exhibiting a staggered sulfonamide group and an intramolecular C-H center dot center dot center dot O=S hydrogen bond. The SMX-H2O and SIX-H2O complexes each adopt a single isomer in the molecular beam. Their isomeric structures were determined based on their isomer-specific IR spectra in the NH/OH stretch region. Quantum Theory of Atoms in Molecules analysis of the calculated electron densities revealed that in the SMX-H2O complex the water molecule donates an O-H center dot center dot center dot N hydrogen bond to the heterocycle nitrogen atom and accepts an N-H center dot center dot center dot O hydrogen bond from the sulfonamide NH group. In the SIX-H2O complex, however, the water molecule does not bind to the heterocycle but instead donates an O-H center dot center dot center dot O=S hydrogen bond to the sulfonamide group and accepts an N-H center dot center dot center dot O hydrogen bond from the sulfonamide NH group. Both water complexes are additionally stabilized by a C-ph-H center dot center dot center dot OH2 hydrogen bond. Interacting Quantum Atoms analysis suggests that all intermolecular hydrogen bonds are dominated by the short-range exchange-correlation contribution.
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