University of Bremen                                  Hybrid Materials Interfaces Group Fachbreich Produktionstechnik
 

Conrad Naber Endowed Chair
Hybrid Materials Interfaces
Grenzflächen in der Bio-Nano-Werkstofftechnik

 

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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 biomedical sytems.

Chymotrypsin on SiO2
 
CT CD Temperature ramp

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 and catalysts.


 
TiO2 nanoparticles AFM TiO2 nanoparticles DPD

 

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.

Adenosine sensing scheme

 

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.

Ferritin H unit FeOx nucleation FeOx on SiO2 nanoparticles

 

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.


 
HSSH structural model HSSH free energy landscape

 

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.


 
Li8O8 oxidised DMSO
 
Pore filling reverse funnel