Anesthetic activity and the electrostatic potential (revisited)

Molecular Bases for Anesthetic Agents: Halothane as a Halogen- and Hydrogen-Bond Donor

Although instrumental for optimizing their pharmacological activity, a molecular understanding of the preferential interactions given by volatile anesthetics is quite poor. This paper confirms the ability of halothane to work as a hydrogen-bond (HB) donor and gives the first experimental proof that halothane also works as a halogen-bond (HaB) donor in the solid state and in solution. A halothane/hexamethylphosphortriamide co-crystal is described and its single-crystal X-ray structure shows short HaBs between bromine, or chlorine, and the phosphoryl oxygen. New UV/Vis absorption bands appear upon addition of diazabicyclooctane and tetra(n-butyl)ammonium iodide to halothane solutions, indicating that nitrogen atoms and anions may mediate the HaB-driven binding processes involving halothane as well. The ability of halothane to work as a bidentate/tridentate tecton by acting as a HaB and HB donor gives an atomic rationale for the eudismic ratio shown by this agent.

Extension of the transferable aspherical pseudoatom data bank for the comparison of molecular electrostatic potentials in structure-activity studies

The transferable aspherical pseudoatom data bank, UBDB2018, is extended with over 130 new atom types present in small and biological molecules of great importance in biology and chemistry. UBDB2018 can be applied either as a source of aspherical atomic scattering factors in a standard X-ray experiment (d_min ≃ 0.8 Å) instead of the independent atom model (IAM), and can therefore enhance the final crystal structure geometry and refinement parameters; or as a tool to reconstruct the molecular charge-density distribution and derive the electrostatic properties of chemical systems for which 3D structural data are available. The extended data bank has been extensively tested, with the focus being on the accuracy of the molecular electrostatic potential computed for important drug-like molecules, namely the HIV-1 protease inhibitors. The UBDB allows the reconstruction of the reference B3LYP/6-31G** potentials, with a root-mean-squared error of 0.015 e bohr^-1 computed for entire potential grids which span values from ca 200 e bohr^-1 to ca -0.1 e bohr^-1 and encompass both the inside and outside regions of a molecule. UBDB2018 is shown to be applicable to enhancing the physical meaning of the molecular electrostatic potential descriptors used to construct predictive quantitative structure-activity relationship/quantitative structure-property relationship (QSAR/QSPR) models for drug discovery studies. In addition, it is suggested that electron structure factors computed from UBDB2018 may significantly improve the interpretation of electrostatic potential maps measured experimentally by means of electron diffraction or single-particle cryo-EM methods.