Trace fluorescent labeling for protein crystallization.

Fluorescence can be a powerful tool to aid in the crystallization of proteins. In the trace-labeling approach, the protein is covalently derivatized with a high-quantum-yield visible-wavelength fluorescent probe. The final probe concentration typically labels ≤0.20% of the protein molecules, which has been shown to not affect the crystal nucleation or diffraction quality. The labeled protein is then used in a plate-screening experiment in the usual manner. As the most densely packed state of the protein is the crystalline form, then crystals show as the brightest objects in the well under fluorescent illumination. A study has been carried out on the effects of trace fluorescent labeling on the screening results obtained compared with nonlabeled protein, and it was found that considering the stochastic nature of the crystal nucleation process the presence of the probe did not affect the outcomes obtained. Other effects are realised when using fluorescence. Crystals are clearly seen even when buried in precipitate. This approach also finds `hidden' leads, in the form of bright spots, with ∼30% of the leads found being optimized to crystals in a single-pass optimization trial. The use of visible fluorescence also enables the selection of colors that bypass interfering substances, and the screening materials do not have to be UV-transparent.

Consolidation of carbon nanofiber/copper composites by hot-pressing and spark plasma sintering: a comparative study.

Vapour grown carbon nanofibers have been incorporated into a copper matrix at 20 and 40 volume fractions. The manufacturing route involves the dispersion of the carbon nanofibers and their subsequent coating by electroless plating with copper. The consolidation of the composite powders was performed by two different techniques: hot-pressing and spark plasma sintering. A comparative study of the two processes is reported, in terms of microstructure, dispersion and porosity. The consolidation by hot-pressing (at 900 degrees C, 30 MPa) led to poreless composites (relative density > 96%) and to a homogeneous microstructure. On the other hand, spark plasma sintering (at 400 degrees C, 75 MPa) led to lower densification (relative density < 96%) and heterogeneous microstructure.