Explicit Aqueous Solvation Treatment of Epinephrine from Car–Parrinello Molecular Dynamics: Effect of Hydrogen Bonding on the Electronic Absorption Spectrum

Abstract

The electronic absorption spectrum of the neurotransmitter epinephrine (EPN) in water solution is studied, combining ab initio Car-Parrinello molecular dynamics (CPMD) with a quantum mechanical approach within the framework of the time-dependent density functional theory (TDDFT) scheme. By selecting 52 uncorrelated snapshots, the excitation modes were calculated at the LC-ωPBE/6-31+G(d) level of theory, using an optimal range-separation parameter ω, determined by means of the gap-tuning scheme in the presence of the solvent molecules. By comparing with static approaches (vacuum and implicit solvation), we show here that explicit solvation treatment dramatically enhances the photophysical properties of the EPN, especially because of the more realistic dynamic description of the molecular geometry. The agreement between the simulated and experimental spectra is demonstrated when TDDFT calculations are performed with the optimally tuned version of the DFT hybrid, not only improving the relative intensities of the absorption bands but also the λ position. These results highlight that accounting for the nuclear motions, that is, thermal effects (of both chromophore and solvent molecules), is imperative to predict experimental absorption spectra. In this paper, we have addressed the critical importance of explicit solvation effects on the photophysics of the EPN, raking in performance when the simulation is performed based on first-principles molecular dynamics such as CPMD.

Water-Mediated Electronic Structure of Oligopeptides Probed by Their UV Circular Dichroism, Absorption Spectra, and Time-Dependent DFT Calculations

“…We specifically chose the ωB97X-D/cc-pVTZ functional for our studies since it contains an asymptotically correct (range-separated) portion of nonlocal exchange in conjunction with dispersion corrections, which are essential for accurately predicting charge-transfer excitations and hydrogen-bonding interactions. It is also important to note that prior work by Neto et al has shown that the optimal range-separated parameter, ω, required to accurately predict excited states in the explicit solvent is 0.25, which is already close to the default value of ω = 0.2 used in the ωB97X-D/cc-pVTZ functional. We showed in our previous work that (1) changing the range separation value, (2) using different exchange-correlation functionals, (3) utilizing a larger basis set (such as aug-cc-pVTZ), and (4) altering the positions of explicit water molecules did not change the spectra significantly within the relevant wavelength range (see Supporting Information).…”

A new interpretation of the structure and solvent dependence of the far UV circular dichroism spectrum of short oligopeptides

“…17 We specifically chose the ωB97X-D functional for our studies since it contains an asymptoticallycorrect (range-separated) portion of nonlocal exchange in conjunction with dispersion corrections, which are essential for accurately predicting charge-transfer excitations and hydrogenbonding interactions, 18 respectively. It is also important to note that prior work by Neto et al 19 has shown that the optimal range-separated parameter, ω, required to accurately predict excited-states in explicit solvent is 0.25, which is already close to the default value of ω = 0.2 used in the ωB97X-D functional. To test the effects of (1) changing the range-separation value,…”

A New Interpretation of the Structure and Solvent Dependence of the Far UV Circular Dichroism Spectrum of Short Oligopeptides

“…17 We specifically chose the ωB97X-D functional for our studies since it contains an asymptoticallycorrect (range-separated) portion of nonlocal exchange in conjunction with dispersion corrections, which are essential for accurately predicting charge-transfer excitations and hydrogenbonding interactions, 18 respectively. It is also important to note that prior work by Neto et al 19 has shown that the optimal range-separated parameter, ω, required to accurately predict excited-states in explicit solvent is 0.25, which is already close to the default value of ω = 0.2 used in the ωB97X-D functional. To test the effects of (1) changing the range-separation value, (2) using different exchange-correlation functionals, (3) utilizing a larger basis set (such as aug-cc-pVTZ), and (4) altering the positions of explicit water molecules, we spot-checked our calculations by comparing the computed ECD spectra obtained separately with each of these effects.…”