Electronic absorption spectra of pyridine and nicotine in aqueous solution with a combined molecular dynamics and polarizable QM/MM approach

Abstract

The electronic absorption spectra of pyridine and nicotine in aqueous solution have been computed using a multistep approach. The computational protocol consists in studying the solute solvation with accurate molecular dynamics simulations, characterizing the hydrogen bond interactions, and calculating electronic transitions for a series of configurations extracted from the molecular dynamics trajectories with a polarizable QM/MM scheme based on the fluctuating charge model. Molecular dynamics simulations and electronic transition calculations have been performed on both pyridine and nicotine. Furthermore, the contributions of solute vibrational effect on electronic absorption spectra have been taken into account in the so called vertical gradient approximation.

New atomistic model of pyrrole with improved liquid state properties and structure

“…It is worth to highlight that the charge adjustment procedure turned out to be of critical importance to reproduce the structural and the bulk properties in agreement with experimental finding. We have shown in past contributions that the use of CM5 method with a proper adjustment of the atomic charges allows to obtain the same accuracy at the molecular and bulk level using standard functional forms for force fields in the case of simple amides and pyridine even in different environmental conditions. The approach to determine the atomic charges is general, but the adjustment procedure can be slight modified to improve the directional character of the interactions, opportunely introducing lone pairs (virtual sites) or reproducing high order multipoles, as in the present study.…”

“…We have shown in past contributions that the use of CM5 method with a proper adjustment of the atomic charges allows to obtain the same accuracy at the molecular and bulk level using standard functional forms for force fields in the case of simple amides and pyridine even in different environmental conditions. The approach to determine the atomic charges is general, but the adjustment procedure can be slight modified to improve the directional character of the interactions, opportunely introducing lone pairs (virtual sites) or reproducing high order multipoles, as in the present study. It is also important to observe that simpler adjustment procedures, for example, based on the application of a scaling factor may indeed improve overall results when carrying out parameterization of a large number of compounds but fail when a higher degree of accuracy is sought.…”

“…Since the parameters to describe pyrrole as a solvent were not included in the adopted version of Gaussian package, tetrahydrofurane has been used as reference solvent due to the very similar dielectric constant. Using the same protocol adopted in the parameterization of the electrostatic part of formamide molecules, its N ‐methyl derivatives and pyridine (nicotine), a CM5 population analysis has been carried out to obtain the initial atomic charges, as reported in Table . To improve the description of the molecular multipoles, the atomic charges have been adjusted through a fitting procedure, using as reference the dipole and traceless quadrupole moments obtained at the end of the optimization procedure, as reported in Table .…”

Structural and Photophysical Properties of Various Polypyridyl Ligands: A Combined Experimental and Computational Study

“…Solvent effects have been taken into account in the static and TDDFT calculations using a polarizable continuum model (PCM). [87] For the pyridine molecule, expressed by ligand (1), different functionals and basis sets have already been tested in literature, [23,64] revealing that B3LYP/6-31 + G* yields good results. In all our calculations, we used the larger 6-31 + + G** basis set.…”

Synthesis, Crystal Structures, and Thermolysis Studies of Heteronuclear Transition Metal Aluminum Alcoholates

“…[33,42,46] In the UV/Vis spectrum of Cu + containing compound 5 just π-π* transitions of pyridine molecules are observed as well as a charge-transfer band at 335 nm. [56] In thermolysis studies under argon atmosphere a reduction of M 2+ to M Ϯ0 takes place depending on the type of M 2+ cation. Fe/Fe 2+ represents a limiting redox pair for the reduction process, whereat in presence of 2,2Ј-bipyridine reduction occurs more easily.…”