Photolyases can repair pyrimidine dimers on the DNA that are formed during UV irradiation. PhrB from Agrobacterium fabrum represents a new group of prokaryotic (6–4) photolyases which contain an iron-sulfur cluster and a DMRL chromophore. We performed site-directed mutagenesis in order to assess the role of particular amino acid residues in photorepair and photoreduction, during which the FAD chromophore converts from the oxidized to the enzymatically active, reduced form. Our study showed that Trp342 and Trp390 serve as electron transmitters. In the H366A mutant repair activity was lost, which points to a significant role of His366 in the protonation of the lesion, as discussed for the homolog in eukaryotic (6–4) photolyases. Mutants on cysteines that coordinate the Fe-S cluster of PhrB were either insoluble or not expressed. The same result was found for proteins with a truncated C-terminus, in which one of the Fe-S binding cysteines was mutated and for expression in minimal medium with limited Fe concentrations. We therefore assume that the Fe-S cluster is required for protein stability. We further mutated conserved tyrosines that are located between the DNA lesion and the Fe-S cluster. Mutagenesis results showed that Tyr424 was essential for lesion binding and repair, and Tyr430 was required for efficient repair. The results point to an important function of highly conserved tyrosines in prokaryotic (6–4) photolyases.

Rheological investigations as well as theoretical studies on ferrofluids have shown strong field and shear dependent changes in viscosity, which are correlated with the formation of chain-like clusters of magnetic nanoparticles. Moreover, the formation of these clusters leads to the appearance of viscoelastic effects or other non-Newtonian features in ferrofluids in the presence of a magnetic field. Previous investigations were carried out with differently composed ferrofluids, all of them containing particles of nearly spherical shape, but differing in the size of the nanoparticles, the volume concentration and the magnetic material. In the work presented here a ferrofluid with non-spherical cobalt nanoparticles is used, to get more information about the influence of the shape of the nanoparticles on their interparticle interaction and the resulting rheological behaviour of the suspension. For the experiments an especially designed stress controlled rheometer has been used. Experiments on yield stress as well as measurements of the magnetoviscous effect have been performed for this ferrofluid with nanodisc particles for different magnetic field strengths. The results from the yield stress experiments have been compared with those achieved for a cobalt-based ferrofluid containing spherical nanoparticles.

3D inkjet printing is moving from a technology of rapid prototyping to rapid manufacturing. The introduction of ultraviolet curable composites filled with functional ceramics could expand the possibilities of this technology. In this work, a simple and scalable process was investigated as a template for the production of inkjet printable functional ceramics. Pyrogenic alumina particles with an average size of 13 nm, 35 nm and 100 nm were used as fillers in an acrylate mixture. The physical coating of the ceramics with 2-[2-(2-methoxyethoxy)ethoxy] acetic acid results in a low-viscosity dispersion with a ceramic content of up to 2 vol%, Newtonian behavior and surface tension within the limits allowed for inkjet printing. The material has sufficient stability for printing tensile specimens. Tensile tests have shown that modulus of elasticity, tensile strength and toughness can be kept constant despite the light scatter caused by the particles. The final production steps could be reduced to grinding and drying of the powders, their resuspension in the organic matrix and inkjet printing. The process can be used in an industrial-scale production of materials for abrasion-resistant components with adapted tribology.