Main research themes
Protein adsorption on solid surfaces
In this research area we make combined use of atomistic simulations techniques
(quantum mechanical and classical Molecular Dynamics) and experimental methods
(Atomic Force Microscopy and Spectroscopy, Circular Dichroism Spectroscopy) to
characterize protein/material interfaces at the atomic level.
To this aim we compare experimentally accessible observables such as the
free energies of adsorption, the adhesion forces as well as CD spectra of the
adsorbed molecules with the corresponding theoretical predictions.
This requires a further development of advanced MD techniques capable
of predicting the adsorption-induced conformational changes in medium-sized
protein sysmtes (a few hundreds of amino acids). An important application of
our research is the enzymatic functionalization of ceramic supports such as
nanoparticles, colloids or microporous materials in biotechnological and
Adhesion between oxide nanoparticles in films and aggregates
Combining AFM Force Spectroscopy with MD simulations we have elucidated the
dependence of the contact forces between oxide nanoparticles on the environmental
humidity, particle size and materials properties at the atomic scale.
On the basis of this knowledge we are currently developing Coarse-Grained Force Fields
in order to simulate the mechanical response of nanoparticle films on external
loads at the μm scale. Discrete Element Method Simulations and Force
Spectroscopy measurements are conducted hand in hand for different film
porosities, connectivities and distributions of particle sizes. Important
applications comprise the fluidization and dispersion of nanoparticle powders
as well as the handling of nanoparticle films for the fabrication of gas sensors
Detection of dissolved analytes in sub-nM concentration
We are developing a series of strategies based on AFM Force Spectroscopy to
detect the presence of polypeptides, nucleic acids, organic molecules (adenosine,
cocaine) or inorganic ions (Hg2+) in water solutions. In our approach,
AFM tips are functionalized with oligonucleotides with sequences engineered to
display very large affinities towards specific analytes. The measured adhesion
forces between the functionalized tips and generally passive substrates (graphite,
silica, gold) change when in the presence of absence of the molecules of interest.
With this method we are able to detect molecules in concentrations as low as
100 pM or even less. Challenges in this field are the reproducibility of the
results, the automatization of the process as well as the optimization of the
selectivity in complex samples such as physiological fluids or soils.
Biomimetic fabrication of magnetic nanostructues
Biomineralization principles are used in this research area to coat ceramic
supports (nanostructures, diatom skeletons, microporous materials) with thin
magnetic films made of iron oxyhydroxide phases. In order to understand and
optimize the deposition process we are performing atomistic simulations of the
growth of iron oxyhydroxides on ferritin protein subunits, mesoscopic simulations
of the ion diffusion and material growth in narrow pores as well as micromagnetic
simulations using realistic geometries. Biomineralization experiments are conducted
in parallel by our collaborators in the
Advanced Ceramics group.
From the point of view of the simulations, the major challenges are represented
by the coupling of quantum mechanical and classical MD techniques in appropriate
QM/MM approaches on one side and the coupling of atomistic with mesoscopic simulations
on the other side. Eventually, we aim to predict the behaviour of the system all
the way from the pm up to the μm scale.
Prediction of oligopeptide structures
The deceptively simple question "what is the structure of an oligopeptide?" is in fact
very difficult to answer if one realizes that the free energy landscape in the
conformational phase space of most oligopeptides is very flat. This means that
a very large number of structures are present at the same time in a single macroscopic
state, each with a probability dictated by Boltzmann statistics. This makes particularly
challenging to associate measurable macroscopic quantities, such as the CD spectra of
oligopeptides in solution or adsorbed on materials surfaces, with atomistic structural
information. Needed is a knowledge of the complete oligopeptide phase space along appropriate
collective variables, as accessible through advanced sampling MD techniques such as Metadynamics
and Parallel Tempering. Similary difficult is the experimental analysis of CD spectra in terms of secondary
structure elements, also because the most evident differences are visible in the far UV
spectral region (150-190 nm) which requires use of synchrotron light sources.
Multiscale modelling of Li/air battery cathodes
In cooperation with our partners of the
Electrical Energy Storage
unit of the Fraunhofer IFAM
in Oldenburg we are investigating fundamental processes at the cathodes of novel Li/air
batteries. We are performing quantum mechanical MD simulations of the charge process in which
Li2O2 phases decompose to Li+ and O2 after
electron depletion. Important is to understand the role played by the electrolyte, upon
which both the efficiency and the capacity of the battery strongly depend. We are also
studying the clogging of narrow pore structures during the inverse discharge process and
the associated deposition of Li2O2 with the help of numerical solutions
of appropriate reaction-diffusion equations. Of particular interest here is the use of
mathematical optimization algorithms to predict the best possible distributions of catalytically
active sites within the pores in order to minimize the remaining free pore volume after clogging.
A challenge in the project is to conceive and carry out experimental studies which take
into account and validate our theoretical predictions.