研究目的
To explore the complex relationships between the dispersive optical activity of a conformationally flexible chiral molecule, (R)-glycidyl methyl ether (R-GME), and the pervasive interactions sustained from a surrounding environment of liquid water, using combined experimental and theoretical approaches.
研究成果
The research concludes that traditional conformer-averaging with implicit solvation models is inadequate for quantitatively describing optical rotatory dispersion in aqueous solutions of flexible molecules like R-GME. The mixed QM/FQ approach revealed the dynamical nature of solvated chiroptical responses, emphasizing the importance of explicit solvation and conformational dynamics. Despite not achieving full quantitative accord, the study highlights the complexity of modeling such systems and warns against oversimplified approaches, suggesting that further work is needed to develop accurate computational protocols.
研究不足
The study faced limitations in achieving quantitative agreement between theory and experiment, attributed to inaccuracies in conformational sampling, solvation models (e.g., PCM's inability to capture atomistic details like hydrogen bonding), and the sensitivity of chiroptical properties to microsolvation environments. The use of classical MD and approximate QM methods may not fully capture quantum effects, and the absence of experimental data for low-lying electronic states due to solvent cut-off wavelengths hindered validation.
1：Experimental Design and Method Selection:
The study involved experimental polarimetric measurements of specific optical rotation (SOR) at discrete wavelengths using a commercial polarimeter, complemented by theoretical calculations using density functional theory (DFT) with polarizable continuum model (PCM) for implicit solvation and a mixed quantum-mechanical/molecular-mechanical (QM/MM) approach with fluctuating charges (FQ) for explicit solvation. Molecular dynamics (MD) simulations were used to sample conformational space.
2：Sample Selection and Data Sources:
(R)-glycidyl methyl ether (R-GME) was obtained commercially (Sigma-Aldrich, 97% purity) and dissolved in spectrophotometric grade water (Alfa-Aesar) at low concentrations (<10^-3 g/mL) to minimize solute-solute interactions. Data were extrapolated to infinite dilution.
3：List of Experimental Equipment and Materials:
Equipment included a Perkin-Elmer 341 polarimeter with quartz sample cell (10.000 cm length), Applied Photophysics Chirascan for electronic circular dichroism (ECD), and computational software (Gaussian16, Joyce program). Materials included R-GME, water, and virtual sites for MD simulations.
4：000 cm length), Applied Photophysics Chirascan for electronic circular dichroism (ECD), and computational software (Gaussian16, Joyce program). Materials included R-GME, water, and virtual sites for MD simulations.
Experimental Procedures and Operational Workflow:
4. Experimental Procedures and Operational Workflow: Experimental measurements involved preparing aqueous solutions, performing polarimetry at specific wavelengths (e.g., 589.3 nm), and conducting dilution experiments. Theoretical procedures included geometry optimizations, DFT calculations with PCM, MD simulations with TIP3P water model, and QM/FQ calculations for optical activity.
5：3 nm), and conducting dilution experiments. Theoretical procedures included geometry optimizations, DFT calculations with PCM, MD simulations with TIP3P water model, and QM/FQ calculations for optical activity.
Data Analysis Methods:
5. Data Analysis Methods: Data were analyzed using linear least-squares regressions for extrapolation to infinite dilution, nonlinear regressions to Drude-like expressions for ORD profiles, and statistical analysis of MD snapshots. Computational analyses used various DFT functionals (e.g., B3LYP, CAM-B3LYP) and basis sets (e.g., aug-cc-pVDZ).
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