Peslherbe’s LaboratoryTheoretical/Computational Chemistry - Research Interests

Cluster Fragmentation and Catalysis

Reaction occuring between Vanadium-oxides (VxOy)n+clusters and an

alkylfluorides.

Clusters are aggregates of atoms or molecules of arbitrary size, and as such, they are usually thought of as bridging the gap between the gas and condensed phases; they can be used as tools for selective microsolvation, or they can be a distinct class of materials with unique properties. Clusters, upon impact with a rigid surface at supersonic velocities, can also catalyze reactions that would normally not occur under normal conditions.

Materials: Structural and Optical PropertiesIn recent years, there has been a mounting interest in the use of lanthanide ions for biochemical applications. Many organo-lanthanide complexes have found their way into mainstream science with varied uses. For example, many lanthanide-chelate complexes have been used as contrast agents for MRI, as probes in time-fluorescence spectroscopy, markers in protein assays, and as tools for determiningcoordination of metal-binding sites in proteins. Our main goal is to study the structural and spectroscopic characteristics of these systems employing Monte Carlo techniques.As a preliminary to this study, we wish to study the coordination properties of Ln3+-solvent clusters. Our initial system is Eu3+-H2O. This system is ideal to look at since the energy levels of Eu3+ are rather simple to interpret. In addition it is known that europium and other lanthanides prefer oxygen over nitrogen and carbon as a coordinating ligand. Eventually, this project will be extended towards studying the effects of alternative solvents on europium and the other lanthanides.

Surface catalyzed dissociation of Buckminsterfullerene.

Silicon and oxygen based materials are one of the focus of our current research. We perform computer simulations of silica and silicates (figures 1 and 2). They are environmentally safe and abundant materials which can be used for numerous technological applications: thermal insulation, solar energy collection devices, particle detectors, catalysis, glasses, and optical fiber communications. Also, another aspect studied is the oxidation of silicon surfaces reactions, which are of great technological importance in the field of microelectronic materials. In particular, the adsorption reaction of oxygen clusters on silicon surfaces (figure 3) exhibit interesting features, which are currently theoretically under investigation in our laboratory.

Photochemistry and PhotophysicsWe study photophysical processes occurring in molecules and molecular clusters as well as photochemical reactions upon photoexcitation:

Charge transfer to solvent in I- . CH3CN cluster: upon photoexcitation, the electron moves from the p orbital of iodide to * orbitals of acetonitrile

Solvation

The temperature dependence of activation barriers (green = 300 K, red = 1400 K) resolved the discrepancies between photochemical studies and high-temperature thermal studies.

Because a large fraction of chemical reactions occur in solution, it is of fundamental interest to study solvent effects on the thermodynamic and dynamic properties of species. Hence, theoretical investigations of clusters are extremely useful to study basic processes such as the role of microsolvation in chemical reactions. For example, the study of simple ion-cluster properties can show the role played by the microscopic interactions between species. As well, when exploring properties of ion pairs in clusters, it is possible to investigate solvent effects on chemical reactions. Specifically, a prototypical reaction studied in our group is solvent induced charge transfer in an ion pair, a crucial and ubiquitous type of reaction.

Some NaI(H2O)32 and NaI(CH3CN)36 clusters at 300K obtained from Monte Carlo simulations with model potentials. Comparison of cluster properties highlight the differences between the characteristics of the solvent involved. These properties have implications for the NaI(solvent)n cluster photodissociation dynamics.

The large iodine anion becomes hydrophobic in relatively small water clusters because it disrupts the hydrogen bonding network. Therefore, for I-(H2O)64, the most stable structure occurs when the anion lays at the surface of the water cluster. However, the center structure, as shown in the second figure, becomes more and more stable as the cluster size is increased.

Organic Intermediates Biological Chemistry

A combination of quantum chemistry and FMO theory is used to investigate the regioselectivity of the nitrilimine cycloaddition with alkenes. A detailed investigation of the reaction pathways allows the determination of the favored products thereby reconciling previous experimental results.

Computational analysis of biochemical molecules can be used to predict reaction mechanisms. However, because the ab initio level of theory required to generate reliable results is much too demanding, models are built on a small scale which represent a larger system. Our study focuses on the interactions of chemical denaturants such as guanadine hydrochloride with lysine. We also study amino acid interactions with metal ions. These studies can help to better understand the process of protein denaturation and to explain enzymatic activities.

A possible mechanism for the copper(I) catalyzed dissociation of nitric oxide from s-nitrosocysteine.

Theoretical/Computational studies of reaction pathways provide invaluable information concerning transition states, reaction intermediates and activation barriers for various organic reactions:

L

l

l

+NO

FT-IR spectroscopy is used to determine how chemical denaturants such as guanidine hydrochloride (GdnHCl) interact with homopolypeptide made of lysine residues. Analysis of FT-IR spectrum suggests that the denaturant may be interacting with the polypeptide at the side chain level. We also make use of theoretical studies to prove the possibility of this interaction. Ab Initio level of theory in Gaussian is used for calculations and structure determination.

HOMO LUMO

Relative MP2/6-31+G*ZPE corrected electronic energies

TS

10.0 kcal/mol

-16.7 kcal/mol

FRONTIER ORBITALS

ELECTRON DENSITY

We are currently investigating the mechanism of intramolecular 1,2-silyl migration in methoxysiloxycarbene. Possible mechanisms include the silyl group migrating with anion-like character to the “empty” carbene p orbital, and nucleophilic attack by the carbene lone pair at silicon. So far, our studies seem to point towards the latter mechanism.