Annia Galano

Departamento de Química. Universidad Autónoma Metropolitana-Iztapalapa.
San Rafael Atlixco 186, Col. Vicentina. Iztapalapa. C. P. 09340. México D. F. México.

Video Recording

Video is available only for registered users.

Abstract

Oxidative stress is frequently caused by an excess of free radicals and has been associated with a wide variety of health disorders. Therefore, finding strategies for scavenging free radicals, or preventing their formation, has become an active area of research. Different reaction mechanisms involved in the chemical protection exerted by antioxidants will be discussed, as well as their relative importance depending on several aspects. A computational strategy designed to be a reliable tool in the study of radical-molecule reactions in solution is presented. It is referred to as Quantum Mechanics-based Test for Overall Free Radical Scavenging Activity (QM-ORSA). This methodology is intended to provide a universal and quantitative way of evaluating the free radical scavenging activity of chemical compounds. i.e. its primary antioxidant activity. This proposal includes a separated quantification of the activity in polar (aqueous) and non-polar (lipid) media. It also includes two different scales for quantification: absolute (based on overall apparent rate coefficients) and relative (using Trolox as the reference antioxidant). Using QM-ORSA also allows identifying the main mechanisms of reaction involved in the free radical scavenging activity of antioxidants, and establishing the influence of pH on such an activity. Validation of the QM-ORSA protocol by comparison with experimental results, is also presented, which demonstrate that its uncertainties are no larger than those arising from experiments.

Sharon Hammes-Schiffer

Stanford Institute for Materials and Energy Sciences,
SLAC National Accelerator Laboratory, Menlo Park, CA-94025, USA

Video Recording

Abstract

Proton-coupled electron transfer (PCET) reactions play a vital role in a wide range of chemical and biological processes. This talk will focus on the theory of PCET and applications to catalysis and energy conversion. The quantum mechanical effects of the active electrons and transferring proton, as well as the motions of the proton donor-acceptor mode and solvent or protein environment, are included in a general theoretical formulation. This formulation enables the calculation of rate constants and kinetic isotope effects for comparison to experiment. Recent extensions enable the study of heterogeneous as well as homogeneous interfacial PCET processes. Applications to PCET in molecular electrocatalysts for water splitting, CH bond activation, photoreduced zinc-oxide nanocrystals, and proton discharge on a gold electrode will be discussed. In addition, theoretical approaches for simulating the ultrafast dynamics of photoinduced PCET, along with applications to solvated molecular systems and photoreceptor proteins, will be discussed. Overall, these studies have identified the thermodynamically and kinetically favorable mechanisms, as well as the roles of proton relays, excited vibronic states, hydrogen tunneling, reorganization, and conformational motions. The resulting insights are guiding the design of more effective catalysts and energy conversion devices.

Shirin Faraji

Faculty of Science and Engineering
Theoretical Chemistry — Zernike Institute for Advanced Materials
The Netherlands