Damian Moran

Molecular structures and energetics of the neutral aluminum–trimethylaluminum complex: an Al–Al bonded global minimum?

Abstract From their recent laboratory kinetics studies, Parker and Nelson have proposed a monobridged molecular structure for the aluminum atom–trimethylaluminum system. Here molecular structures and energetics for the neutral aluminum atom–trimethylaluminum complex (AlTMA) are reported from theory. A second distinct minimum was located and characterized, corresponding to an unanticipated H 3 C–Al–Al(CH 3 ) 2 geometry. In addition, the transition state between the two minima was located. The relative energies of these stationary points are also reported, predicting that the monobridged AlTMA structure recently reported is higher in energy than the methylaluminum DMA discovered in this study by about 2 kcal mol −1 .

Impact of Hydrogen Bonding on the Susceptibility of Peptides to Oxidation

The tendency of peptides to be oxidized is intimately connected with their function and even their ability to exist in an oxidative environment. Here we report high-level theoretical studies that show that hydrogen bonding can alter the susceptibility of peptides to oxidation, with complexation to a hydrogen-bond acceptor facilitating oxidation, and vice versa, impacting the feasibility of a diverse range of biological processes. It can even provide an energetically viable mechanistic alternative to direct hydrogen-atom abstraction. We find that hydrogen bonding to representative reactive groups leads to a broad (≈400 kJ mol-1 ) spectrum of ionization energies in the case of model amide, thiol and phenol systems. While some of the oxidative processes at the extreme ends of the spectrum are energetically prohibitive, subtle environmental and solvent effects could potentially mitigate the situation, leading to a balance between hydrogen bonding and oxidative susceptibility.