Download Cluster Fragmentation and Catalysis

Peslherbe’s Laboratory
Theoretical/Computational Chemistry
Cluster Fragmentation and Catalysis
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.
Reaction occuring between Vanadium-oxides (VxOy)n+clusters and an
alkylfluorides.
Surface catalyzed dissociation of Buckminsterfullerene.
- Research Interests
Materials: Structural and Optical Properties
In recent years, there has been a mounting
interest in the use of lanthanide ions for
biochemical applications. Many organolanthanide 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 timefluorescence spectroscopy, markers in
protein assays, and as tools for determining
coordination 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.
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 Photophysics
We study photophysical processes occurring in molecules and molecular
clusters as well as photochemical reactions upon photoexcitation:
Solvation
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.
Charge transfer to solvent in I- . CH3CN cluster: upon photoexcitation, the
electron moves from the p orbital of iodide to s* orbitals of acetonitrile
The temperature dependence of activation barriers (green = 300 K, red =
1400 K) resolved the discrepancies between photochemical studies and
high-temperature thermal studies.
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.
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.
Organic Intermediates
Biological Chemistry
Theoretical/Computational studies of reaction pathways provide
invaluable information concerning transition states, reaction intermediates
and activation barriers for various organic reactions:
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.
L
l
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.
Relative MP2/6-31+G*
ZPE corrected electronic energies
A possible mechanism for the copper(I) catalyzed dissociation of nitric oxide
from s-nitrosocysteine.
TS
LUMO
10.0 kcal/mol
ELECTRON DENSITY
-16.7 kcal/mol
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 pp orbital,
and nucleophilic attack by the carbene lone pair at silicon. So far, our studies
seem to point towards the latter mechanism.
+
l
FRONTIER ORBITALS
HOMO
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.