Facial symmetry in protein self-assembly

Amyloids are self-assembled protein architectures implicated in dozens of misfolding diseases. These assemblies appear to emerge through a "selection" of specific conformational "strains" which nucleate and propagate within cells to cause disease. The short Abeta(16-22) peptide, which includes the central core of the Alzheimer's disease Abeta peptide, generates an amyloid fiber which is morphologically indistinguishable from the full-length peptide fiber, but it can also form other morphologies under distinct conditions. Here we combine spectroscopic and microscopy analyses that reveal the subtle atomic-level differences that dictate assembly of two conformationally pure Abeta(16-22) assemblies, amyloid fibers and nanotubes, and define the minimal repeating unit for each assembly.     

A fiber-optic absorption cell for remote determination of copper in industrial electroplating baths

A device for remote optical sensing is developed and evaluated for monitoring the concentration of copper(II) ions in an industrial plating bath. The sensor consists of an absorption cell which resides in the plating bath, and utilizes fiber optics to direct light into and out of the cell. The sensor is capable of being located in harsh environments for extended periods of time (on the order of weeks to years) and thus is ideal for long-term monitoring applications. The light source and detection electronics can be maintained in a controlled environment and can be multiplexed to several sensors of similar design, if desired. The sensor constructed operates by measuring the copper(II) absorbance with a near-infrared light-emitting diode (820 nm) as the light source. The device is capable of measuring copper(II) ion concentrations from 50 mM to 500 mM with relative standard deviations less than 1%. The construction and operation of the sensor are described and the effects of various interferences found in plating baths are evaluated, including those from temperature variations and variations in the concentrations of concomitant species in the plating bath. Also, drift compensation and noise sources are considered, with an evaluation of the long-term stability of the sensor and the feasibility of its use in an industrial environment.     

Plasma opening switch research for DECADE

Plasma opening switch (POS) research for the DECADE radiation effects test facility is reviewed. This research was first performed on a half-scale generator, DECADE Prototype Module 1, and indicated the importance of the POS electrode geometry to obtain the required impedance at appropriate conduction times. It also was demonstrated that the conduction time jitter was suitable for a multimodule system. Preliminary experiments at full energy were then conducted on DECADE Module 1 that indicated significant current loss when using a bremsstrahlung load, limiting the output radiation to about half of the DECADE requirement. These results initiated an effort to thoroughly diagnose the power-flow region downstream of the switch, an effort that ultimately provided improved understanding of POS operation and improved coupling to bremsstrahlung loads. At the conclusion of this effort, it had been demonstrated that it is possible for the POS-driven system to meet the DECADE requirements     

Macroscale assembly of peptide nanotubes

Simple oligopeptides that self-assemble into homogeneous nanotubes can be directed to further assemble into macroscale parallel arrays through protein "salting out" strategies.