Estudio teórico de procesos fundamentales en carbohidratos

Tesis doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Química. Fecha de lectura: 18-06-201

Unraveling the Causes of the Instability of Aun(SR)x Nanoclusters on Au(111)

Properties of small metal nanoclusters rely on the exact arrangement of a few atoms. Minor structural changes can rapidly destabilize them, leading to disintegration. Here, we evaluate the energetic factors accounting for the stabilization and integrity of thiolate-capped gold nanoclusters (AuNCs). We found that the core-cohesive and shell-binding energies regulate the disintegration process on a solid substrate by investigating the different energetic contributions, as shown here in a combined experimental and theoretical study. As the AuNC size increases, the core-cohesive energy and shell stability (imposed by S-Au and hydrocarbon chain interactions) counterbalance the AuNC− substrate interaction and slow down the AuNC disintegration. Thus, the decomposition can not only be understood in terms of desorption and transfer of the capping molecules to the support substrate but conversely, as a whole where ligand and core interactions play a role. Taken together, our experimental and theoretical results serve as guidelines for enhancing the stability of AuNCs on solid-state devices, a key point for reliable nanotechnological applications such as heterogeneous catalysis and sensing.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

An Exploration of the Ozone Dimer Potential Energy Surface

The (O3)2 dimer potential energy surface is thoroughly explored at the ab initio CCSD(T) computational level. Five minima are characterized with binding energies between 0.35 and 2.24 kcal/mol. The most stable may be characterized as slipped parallel, with the two O3 monomers situated in parallel planes. Partitioning of the interaction energy points to dispersion and exchange as the prime contributors to the stability, with varying contributions from electrostatic energy, which is repulsive in one case. Atoms in Molecules analysis of the wavefunction presents specific O⋯O bonding interactions, whose number is related to the overall stability of each dimer. All internal vibrational frequencies are shifted to the red by dimerization, particularly the antisymmetric stretching mode whose shift is as high as 111 cm−1. In addition to the five minima, 11 higher-order stationary points are identified

Substituent Effects in the Noncovalent Bonding of SO2 to Molecules containing a Carbonyl Group. The Dominating Role of the Chalcogen Bond

The SO2 molecule is paired with a number of carbonyl-containing molecules, and the properties of the resulting complexes are calculated by high-level ab initio theory. The global minimum of each pair is held together primarily by a S···O chalcogen bond wherein the lone pairs of the carbonyl O transfer charge to the π* antibonding SO orbital, supplemented by smaller contributions from weak CH···O H-bonds. The binding energies vary between 4.2 and 8.6 kcal/mol, competitive with even some of the stronger noncovalent forces such as H-bonds and halogen bonds. The geometrical arrangement places the carbonyl O atom above the plane of the SO2 molecule, consistent with the disposition of the molecular electrostatic potentials of the two monomers. This S···O bond differs from the more commonly observed chalcogen bond in both geometry and origin. Substituents exert their influence via inductive effects that change the availability of the carbonyl O lone pairs as well as the intensity of the negative electrostatic potential surrounding this atom