A quantitative 3D motility analysis of Trypanosoma brucei by use of digital in-line holographic microscopy.

We present a quantitative 3D analysis of the motility of the blood parasite Trypanosoma brucei. Digital in-line holographic microscopy has been used to track single cells with high temporal and spatial accuracy to obtain quantitative data on their behavior. Comparing bloodstream form and insect form trypanosomes as well as mutant and wildtype cells under varying external conditions we were able to derive a general two-state-run-and-tumble-model for trypanosome motility. Differences in the motility of distinct strains indicate that adaption of the trypanosomes to their natural environments involves a change in their mode of swimming.

Flow conditions in the vicinity of microstructured interfaces studied by holography and implications for the assembly of artificial actin networks.

Microstructured fluidic devices have successfully been used for the assembly of free standing actin networks as mechanical model systems on the top of micropillars. The assembly occurs spontaneously at the pillar heads when preformed filaments are injected into the channel. In order to reveal the driving mechanism of this localization, we studied the properties of the flow profile by holographic tracking. Despite the strong optical disturbances originating from the pillar field, 2 µm particles were traced with digital in-line holographic microscopy (DIHM). Trajectories in the pillar free region and local alterations of the flow profile induced by the channel structure in the pillar decorated region can be distinguished. Velocity histograms at different z-positions reveal that the laminar flow profile across the channel shows a difference between the minimum in the z-component of the velocity field and the maximum of the overall velocity. This minimum drag in vertical direction is present at the top of the pillars and explains why biopolymer networks readily assemble in this region instead of forming a homogeneous three-dimensional network in between the pillars. On the basis of the observations we propose a new mechanism for actin network formation on top of the microstructures.

Coordination chemistry of a new rigid, hexadentate bispidine-based bis(amine)tetrakis(pyridine) ligand.

The hexadentate bispidine-based ligand 2,4-bis(2-pyridyl)-3,7-bis(2-methylenepyridine)-3,7-diazabicyclo[3.3.1]nonane-9-on-1,5-bis(carbonic acid methyl ester), L(6m), with four pyridine and two tertiary amine donors, based on a very rigid diazaadamantane-derived backbone, is coordinated to a range of metal ions. On the basis of experimental and computed structural data, the ligand is predicted to form very stable complexes. Force field calculations indicate that short metal-donor distances lead to a buildup of strain in the ligand; that is, the coordination of large metal ions is preferred. This is confirmed by experimentally determined stability constants, which indicate that, in general, stabilities comparable to those with macrocyclic ligands are obtained with the relative order Cu(2+) > Zn(2+) >> Ni(2+) < Co(2+), which is not the typical Irving-Williams behavior. The preference for large M-N distances also emerges from relatively high redox potentials (the higher oxidation states, that is, the smaller metal ions, are destabilized) and from relatively weak ligand fields (dd-transition, high-spin electronic ground states). The potentiometric titrations confirm the efficient encapsulation of the metal ions since only 1:1 complexes are observed, and, over a large pH range, ML is generally the only species present in solution.