Riccardo Spezia's seminars

Tuesday, 28 June, 2022

Sergio Brutti is pleased to invite you to the seminars

Riccardo Spezia - Laboratoire de Chimie Théorique, Sorbonne Université, Parigi (Francia)

visiting professor at the Chemistry Department (call 2021)

Theoretical and computational modeling of chemical reactions: from gas to solution phase

G room - S. Cannizzaro building (CU014) floor 0 - Friday, June 24th at 02.00 pm (Google Meet link ubd-gypy-npk)

Abstract

In this seminar, I will show how it is possible to model and understand ground-state chemical reactivity by molecular simulations in different physical conditions. A common and unified approach is the use of molecular dynamics in conjunction with electronic structure calculations within the Born-Oppenheimer approximation.

First, we were able to describe and predicts mechanisms relevant to unimolecular fragmentation with applications in mass spectrometry: the use of an ensemble of reactive trajectories was at the basis to obtain qualitative information (nature of reaction products and corresponding mechanisms) but also quantitative kinetic data (rate constants and activation energies). This was done by coupling molecular simulations with kinetic theories and graph-theory base methods for data analysis.

We will then discuss how nowadays chemical reactions in solution can be understood using molecular simulations including explicit solvation: as an example we studied how pressure effects in Diels-Alder reactions can be modeled via QM/MM simulations. The explicit solute-solvent interaction can provide a microscopic understanding of the endo:exo diastereoselectivity under high-pressure conditions.

References: A.Martin-Somer, V.Macaluso, G.L.Barnes, L.Yang, S.Pratihar, K.Song, W.L.Hase and R.Spezia. Role of Chemical Dynamics Simulations in Mass Spectrometry Studies of Collision-Induced Dissociation and Collisions of Biological Ions with Organic Surfaces. J. Am. Soc. Mass Spectrom. 31, 2-24 (2020). D.Scuderi, A.F.Perez-Mellor, J.Lemaire, S.Indrajith, J.-X.Bardaud, A.Largo, Y.Jeanvoine and R.Spezia. Infra-Red Assisted Synthesis of Prebiotic Glycine. ChemPhysChem 21, 503-509 (2020). A.F. Perez-Mellor and R. Spezia. Determination of Kinetic Properties in Unimolecular Dissociation of Complex Systems from Graph-Theory Based Analysis of an Ensemble of Reactive Trajectories. J. Chem. Phys. 155, 124103 (2021). D.Loco, R.Spezia, F.Cartier, I.Chataigner and J.-P.Piquemal. Solvation Effects Drive the Selectivity in Diels-Alder Reaction Under Hyperbaric Conditions. Chem. Comm. 56, 6632-6635 (2020).

Diastereoselectivity in Diels-Alder Reactions: a Theoretical Chemistry Approach

C room - S. Cannizzaro building (CU014) floor 1st - Thursday, July 14th at 11.30 am (Google Meet link nsb-tbuc-tku)

Abstract

Diels-Alder reaction is a well-know process discovered by Diels and Alder almost 100 years ago which is pivotal in organic synthesis. It is at the basis of many fundamental processes, like de- aromatization, as well as in the synthesis of specific drugs. One important point is that the cycloaddition can give rise to endo and/or exo forms, which is related to possible different stereochemistry. The possibility of controlling the endo/exo ratio is thus pivotal in organic synthesis.

Such selectivity can be controlled in different ways, here we will discuss two interesting possibilities: (i) using specific solvents; (ii) performing the reaction at high-pressure.

We begun a theoretical study to clarify this aspect using a combination of accurate but fast density functional theory calculations and molecular dynamics simulations. Both classical, polarizable and QM/MM approaches were used at this end.

In particular, we will show how QM/MM simulations can explain on a simple Diels-Alder reaction how the intermolecular interactions can be crucial in selecting the reaction pathways. This coupled with a correct description of transition state energies (and more importantly the endo/exo energy difference) will be an important starting point to study a wider classes of Diels-Alder and, more in general, cycloaddition reactions.

References: D.Loco, R.Spezia, F.Cartier, I.Chataigner and J.-P.Piquemal. Solvation Effects Drive the Selectivity in Diels-Alder Reaction Under Hyperbaric Conditions. Chem. Comm. 56, 6632-6635 (2020). D.Loco, I.Chataigner, J.-P.Piquemal and R.Spezia. Efficient and accurate description of Diels-Alder reactions using density functional theory. ChemPhysChem, in press, DOI: 10.1002/cphc.202200349