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Dissertation angenommen durch: Universität Duisburg-Essen, Campus
Duisburg, Fakultät für Naturwissenschaften, Institut für Physik,
2004-04-20
BetreuerIn: Prof. Dr. Peter Entel , Universität Duisburg-Essen, Campus Duisburg, Fakultät für Naturwissenschaften, Institut für Physik
GutachterIn: Prof. Dr. Peter Entel , Universität Duisburg-Essen, Campus Duisburg, Fakultät für Naturwissenschaften, Institut für Physik GutachterIn: PD Dr. Artur Baumgärtner , Universität Duisburg-Essen, Campus Duisburg, Fakultät für Naturwissenschaften, Institut für Physik
Schlüsselwörter in Englisch: binaphtyl, cyclodextrin
complexes, ice, liquid water, water clusters, phenol, density
functional theory, aspirin, pinacyanol dye
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Abstrakt in Englisch
In this work, a series of ab-initio calculations based on density
functional theory is presented. We investigated the properties of water
and the inclusion complexes of cyclodextrins with various guest
compounds such as phenol, aspirin, pinacyanol chloride dye and
binaphtyl molecules in the environment of water as solvent. Our
investigation of water includes the cluster units of water, the bulk
properties of the liquid water and the crystalline ice structure. Some
equilibrium structures of water clusters were prepared and their
binding energies were calculated with the self-consistency density
functional tight binding (SCC-DFTB) method. The global minimum water
clusters of TIP4P classical modelled potential were also calculated
using the DFTB method and Vienna Ab-initio Simulation Package (VASP).
All results show a non-linear behaviour of the binding energy per water
molecule against water cluster size with some anomalies found for the
lower clusters between 4 and 8 molecules. We also calculated the
melting temperatures of these water clusters having solid-like
behaviour by heating. Though, the melting region of the heated
structures is not well defined as a result of the pronounced
fluctuations of the bonding network of the system giving rise to
fluctuations in the observed properties, but nevertheless the range
where the breakdown occurs was defined as the melting temperature of
the clusters. The bulk properties of the liquid, such as radial
distribution functions, calculated with the VASP method show good
agreement with neutron diffraction scattering data with respect to
positions and height of the peaks. The DFTB method gives good positions
of the peaks but with too broad peaks due the approximations on which
the method relies, which makes it less accurate. Due to the complexity
of the hydrogen bonding network, it is difficult to obtain the real ice
structure by mere cooling liquid water under normal condition without
imposing external constraints such as extreme external pressure or
electric field. A special rule of proton ordering was followed in order
to prepare the real ice structure for our calculations. We succeeded in
preparing a hexagonal tetrahedrally coordinated type of ice. The
statical properties of this ice were calculated as well as the phonon
spectra. The results were compared with neutron diffraction data and
other available ab-initio} calculations. The molecular dynamics
simulations of inclusion complexes of beta-cyclodextrin with each of
these guest molecules, phenol and aspirin show the encapsulation which
are in good agreement with dichroism measurements. The inclusion
complex of a dimer calculation of pinacyanol dye with some droplet of
water inside gamma-cyclodextrin shows structural properties which can
be ascribed to the experimental observation of UV/CD spectra of the
chromophores, in which there is a split of the excited states of the
monomer units. The calculations on chiral molecules of
binaphtyl-beta-cyclodextrin complex shows a longitudinal axis as
preferred axis of entry of the binaphtyl during the inclusion process
rather than an axial propagation in agreement with circular dichroism
measurements. The investigated chiral separation ability of
beta-cyclodextrin on the enantiomeric pair of this compound R and S,
which differ in symmetry only by reflection, shows that the
S-enantiomer has lower energy than the R-enantiomer as revealed by our
ab-initio calculations.
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