530 Physik
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- Biomimetic sensors (1)
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- Institut für Biochemie und Biologie (6) (remove)
Current evidence suggests that migratory animals extract map information from the geomagnetic field for true navigation. The sensory basis underlying this feat is elusive, but presumably involves magnetic particles.
A common experimental manipulation procedure consists of pre-treating animals with a magnetic pulse, with the aim of re-magnetising particles to alter the internal representation of the external field prior to a navigation task.
Although pulsing provoked deflected bearings in caged songbirds, analogous studies with free-flying songbirds yielded inconsistent results.
Here, we pulsed European robins (Erithacus rubecula) at an offshore stopover site during spring migration and monitored their free-flight behaviour with a regional-scale network of radio-receiving stations.
We found no pulse effect on departure probability, nocturnal departure timing departure direction or consistency of flight direction.
This suggests either no use of the geomagnetic map by our birds, or that magnetic pulses do not affect the sensory system underlying geomagnetic map detection.
Simple and robust
(2021)
A spectrum of 7562 publications on Molecularly Imprinted Polymers (MIPs) has been presented in literature within the last ten years (Scopus, September 7, 2020). Around 10 % of the papers published on MIPs describe the recognition of proteins. The straightforward synthesis of MIPs is a significant advantage as compared with the preparation of enzymes or antibodies. MIPs have been synthesized from only one up to six functional monomers while proteins are made up of 20 natural amino acids. Furthermore, they can be synthesized against structures of low immunogenicity and allow multi-analyte measurements via multi-target synthesis. Electrochemical methods allow simple polymer synthesis, removal of the template and readout. Among the different sensor configurations electrochemical MIP-sensors provide the broadest spectrum of protein analytes. The sensitivity of MIP-sensors is sufficiently high for biomarkers in the sub-nanomolar region, nevertheless the cross-reactivity of highly abundant proteins in human serum is still a challenge. MIPs for proteins offer innovative tools not only for clinical and environmental analysis, but also for bioimaging, therapy and protein engineering.
In addition to (bacterio)chlorophylls, (B)Chls, light-harvesting complexes (LHCs) bind carotenoids, and/or their oxygen derivatives, xanthophylls. Xanthophylls/carotenoids have pivotal functions in LHCs: in stabilization of the structure, as accessory light-harvesting pigments and, probably most importantly, in photoprotection. Xanthophylls are assumed to be involved in the not yet fully understood mechanism of energy-dependent (qE) non-photochemical quenching of Chl fluorescence (NPQ) in higher plants and algae. The so called "xanthophyll cycle" appears to be crucial in this regard. The molecular mechanism(s) of xanthophyll involvement in qE/NPQ have not been established, yet. Moreover, excitation energy transfer (EET) processes involving carotenoids are also difficult to study, due to the fact that transitions between the ground state (S-0, 1(1)A(g)(-)) and the lowest excited singlet state (S-1, 2(1)A(g)(-)) of carotenoids are optically one-photon forbidden ("dark"). Two-photon excitation spectroscopic techniques have been used for more than two decades to study one-photon forbidden states of carotenoids. In the current study, two-photon excitation profiles of LHCII samples containing different xanthophyll complements were measured in the presumed 1(1)A(g)(-) -> 2(1)A(g)(-) (S-0 -> S-1) transition spectral region of the xanthophylls, as well as for isolated chlorophylls a and b in solution. The results indicate that direct two-photon excitation of Chls in this spectral region is dominant over that by xanthophylls. Implications of the results for proposed mechanism(s) of qE/NPQ will be discussed.
Negatively charged flat gold nanotriangles, formed in a vesicular template phase and separated by an AOT-micelle-based depletion flocculation, were reloaded by adding a cationic polyelectrolyte, that is, a hyperbranched polyethylenimine (PEI). Heating the system to 100 degrees C in the presence of a gold chloride solution, the reduction process leads to the formation of gold nanoparticles inside the polymer shell surrounding the nanoplatelets. The gold nanoparticle formation is investigated by UV-vis spectroscopy, small-angle X-ray scattering, and dynamic light scattering measurements in combination with transmission electron microscopy. Spontaneously formed gold clusters in the hyperbranched PEI shell with an absorption maximum at 350 nm grow on the surface of the nanotriangles as hemispherical particles with diameters of similar to 6 nm. High-resolution micrographs show that the hemispherical gold particles are crystallized onto the {111} facets on the bottom and top of the platelet as well as on the edges without a grain boundary. Undulated gold nanoplatelet superstructures with special properties become available, which show a significantly modified performance in SERS-detected photocatalysis regarding both reactivity and enhancement factor.
In this Thesis, the properties of aqueous hemicellulose polysaccharides are investigated using computer simulations. The high swelling capacity of materials composed of these molecules allows the generation of directed motion in plant materials entirely controlled by water uptake.
To explore the molecular origin of this swelling capacity, a computational model with atomistic resolution for hemicellulose polysaccharides is build and validated in comparison with experiments. Using this model, simulations of small polysaccharides are employed to gain an understanding of the interactions of these molecules with water, the influence of water on their conformational freedom, and the swelling capacity quantified in terms of osmotic pressure. It is revealed that the branched hemicellulose polysaccharides show different hydration characteristics compared to linear polysaccharides.
To study swelling properties on length and time scales that exceed the limitations imposed by atomistic simulations, a procedure to obtain transferable coarse-grain models is developed. The transferability of the coarse-grain models over both different degrees of polymerization as well as different solute concentrations is demonstrated. Therefore, the procedure allows the construction of large coarse-grained systems based on small atomistic reference systems. Finally, the coarse-grain model is applied to demonstrate that linear and branched polysaccharides show a different swelling behavior when coupled to a water bath.