Prediction of pKa s of Late Transition-Metal Hydrides via a QM/QM Approach

Potential energy surfaces and dynamic properties via ab initio composite and density functional approaches

Vibrational spectroscopy enables critical insight into the structural and dynamic properties of molecules. Presently, the majority of theoretical approaches to spectroscopy employ wavefunction-based ab initio or density functional methods that rely on the harmonic approximation. This approximation breaks down for large molecules with strongly anharmonic bonds or for molecules with large internuclear separations. An alternative to these methods involves generating molecular anharmonic potential energy surfaces (potentials) and using them to extrapolate the vibrational frequencies. This study examines the efficacy of density functional theory (DFT) and the correlation consistent Composite Approach (ccCA) in generating anharmonic frequencies from potentials of small main group molecules. Vibrational self-consistent field Theory (VSCF) and post-VSCF methods were used to calculate the fundamental frequencies of these molecules from their potentials. Functional choice, basis set selection, and mode-coupling are also examined as factors in influencing accuracy. The absolute deviations for the calculated frequencies using potentials at the ccCA level of theory were lower than the potentials at the DFT level. With DFT resulting in bending modes that are better described than those of ccCA, a multilevel DFT:ccCA approach where DFT potentials are used for single vibrational mode potentials and ccCA is used for vibrational mode-mode couplings can be utilized for larger polyatomic systems. The frequencies obtained with this multilevel approach using VCIPSI-PT2 were closer to experimental frequencies than the scaled harmonic frequencies, indicating the success of utilizing post-VSCF methods to generate more accurate representations of computed infrared spectra.

Simultaneous identification and enantioseparation of ofloxacin and duloxetine without the single standard and computational calculation of their inclusion complexes

Given the markedly different pharmacological activities between enantiomeric isomers, it is crucial to encourage the stereoselective determination of chiral drugs in the biological and pharmaceutical fields, and the combination of drugs makes this analysis more complicated and challenging. Herein, a capillary electrophoresis (CE) method for the enantioseparation of ofloxacin and duloxetine was established, enabling the simultaneous identification of four isomers in nonracemic mixtures with enantiomeric excess (ee%) values exceeding 5%. This was achieved through the integration of theoretical simulation and electron circular dichroism (ECD), all without reliance on individual standards. Molecular modeling explained and verified the migration time differences of these isomers in electrophoretic separation. Moreover, the correlation coefficients (R2 ) between the enantiomeric peak area differentials and ee% were both above 0.99. Recovery rates were quantified using bovine serum as the matrix, with results ranging from 93.32% to 101.03% (RSD = 0.030) and 92.69% to 100.52% (RSD = 0.028) for these two chiral drugs at an ee value of 23.1%, respectively.

Enantioseparation and mechanism study on baclofen by capillary electrophoresis and molecular modeling

Enantioselective analysis of chiral drugs plays a significant role in chemistry, biology and pharmacology. Baclofen, an antispasmodic chiral drug, has been widely studied due to the obvious differences in toxicity and medical activity between enantiomers. Herein, a simple and efficient method for separation of baclofen enantiomers by capillary electrophoresis was established without complicated sample derivatization and expensive instruments. Then, the molecular modeling and density functional theory were used to simulate and investigate the chiral resolution mechanism of electrophoresis, the calculated intermolecular forces were directly presented by visualization softwares. Moreover, the theoretical and experimental electronic circular dichroism (ECD) spectra of ionized baclofen were compared, and the configuration of dominant enantiomer in the nonracemic mixture can be determined by ECD signal intensity, which was proportional to the electrophoresis peak area difference of the corresponding enantiomer excess experiments. In this way, the peak order identification and configuration quantification of baclofen enantiomers in electrophoretic separation were successfully achieved without relying on a single standard.