Polarizable Continuum Model (PCM) Calculations of Solvent Effects on Optical Rotations of Chiral Molecules

Abstract

A new theory of solvent effects on the optical rotations of chiral molecules is presented. The frequencydependent electric dipole-magnetic dipole polarizability, β Rβ (ν), is calculated using density functional theory (DFT). Solvent effects are included using the polarizable continuum model (PCM). DFT/PCM calculations of sodium D line specific rotations, [R] D , have been carried out for seven conformationally rigid chiral organic molecules (fenchone, camphor, R-pinene, β-pinene, camphorquinone, verbenone, and methyloxirane) for a diverse set of seven solvents (cyclohexane, carbon tetrachloride, benzene, chloroform, acetone, methanol, and acetonitrile). The predicted variation in [R] D for the solvents cyclohexane, acetone, methanol, and acetonitrile are in excellent agreement with experiment for all seven molecules. For the solvents carbon tetrachloride, benzene, and chloroform, agreement is much poorer. Since only electrostatic solute-solvent interactions are included in the PCM, our results lead to the conclusion that, for the seven molecules studied, in cyclohexane, acetone, methanol, and acetonitrile electrostatic effects are dominant while in carbon tetrachloride, benzene, and chloroform other nonelectrostatic effects are more important. The observed variations in [R] D with solvent are inconsistent, both qualitatively and quantitatively, with the variations predicted by the equation [R] D (solvent) ) {[R] D (gas)}(n D 2 + 2)/3.

Computational Redox Potential Predictions: Applications to Inorganic and Organic Aqueous Complexes, and Complexes Adsorbed to Mineral Surfaces

“…Solvation can be modeled by static or dynamic simulations of explicit water molecules around the ion or complex, by replacing the water by a homogenous dielectric fluid, or by a combination of the above, e.g., by calculating the first or first two hydration spheres with explicit water and the surroundings by a dielectric fluid. Several solvation models for the dielectric fluid approach are available in the literature and incorporated in some quantum-mechanical programs, such as PCM (polarizable continuum model) [62], CPCM (conductor-like polarizable continuum model) [63][64][65], IEF-PCM (integral equation formalism-polarizable continuum model) [66,67], SMD (solvation model density) [68], COSMO (conductor like screening model) [63], COSMO-RS (conductor like screening model for real solvents) [69,70], and PB (Poisson-Boltzmann) finite element model [71][72][73]. Among these solvation methods, CPCM solvation has been one of the most widely used solvation method to study solvation effects.…”

The initial and final states of electron and energy transfer processes: Diabatization as motivated by system-solvent interactions

“…There is a vast literature of research focused on computing these diabatic states when the surrounding solvent is modeled as a polarizable continuous medium [20][21][22][23][24] ͑PCM͒ designed to account for nuclear polarizability of the solvent. 24,25 For a comprehensive review, see Ref.…”

“…͑14͒ and ͑15͒ have been explored with great success over the past 30 years by Tomasi and co-workers. [20][21][22][23][52][53][54] The caveats in using PCM-like models for electron or energy transfer are ͑i͒ the dependence of the resulting diabatic states on cavity geometry and ͑ii͒ the difficulty computing a complete set of diabatic states for the system when the system nuclear geometry ͑R sys ͒ is biased toward one state and the effective solvent nuclear geometry needs to be very different for each of the diabatic states sought. In the future, when possible, it will be worthwhile to compare the diabatic states and diabatic coupling matrix elements ͑H AB ͒ produced with PCM with those produced by the algorithms presented below.…”

The Contribution of Molecular Modeling to the Knowledge of Pesticides

“…Thermodynamic properties (enthalpies and Gibbs free energies) were determined from vibrational frequencies computed at the fully optimized structures of stationary points along a reaction coordinate. To account for the influence of aqueous solvation, the polarizable continuum model (PCM) was applied (Mennucci et al, 2002). All calculations were performed using the Gaussian 03/Rev.…”