Controlling Radical Formation in the Photoactive Yellow Protein Chromophore

To understand how photoactive proteins function, it is necessary to understand the photoresponse of the chromophore. Photoactive yellow protein (PYP) is a prototypical signaling protein. Blue light triggers trans–cis isomerization of the chromophore covalently bound within PYP as the first step in a photocycle that results in the host bacterium moving away from potentially harmful light. At higher energies, photoabsorption has the potential to create radicals and free electrons; however, this process is largely unexplored. Here, we use photoelectron spectroscopy and quantum chemistry calculations to show that the molecular structure and conformation of the isolated PYP chromophore can be exploited to control the competition between trans–cis isomerization and radical formation. We also find evidence to suggest that one of the roles of the protein is to impede radical formation in PYP by preventing torsional motion in the electronic ground state of the chromophore.     

In vitro characterization of an electroactive carbon-nanotube-based nanofiber scaffold for tissue engineering

In an effort to reduce organ replacement and enhance tissue repair, there has been a tremendous effort to create biomechanically optimized scaffolds for tissue engineering applications. In contrast, the development and characterization of electroactive scaffolds has attracted little attention. Consequently, the creation and characterization of a carbon nanotube based poly(lactic acid) nanofiber scaffold is described herein. After 28 d in physiological solution at 37 °C, a change in the mass, chemical properties and polymer morphology is seen, while the mechanical properties and physical integrity are unaltered. No adverse cytotoxic affects are seen when mesenchymal stem cells are cultured in the presence of the scaffold. Taken together, these data auger well for electroactive tissue engineering.

     

Controllable selective exfoliation of high-quality graphene nanosheets and nanodots by ionic liquid assisted grinding

Bulk quantities of graphene nanosheets and nanodots have been selectively fabricated by mechanical grinding exfoliation of natural graphite in a small quantity of ionic liquids. The resulting graphene sheets and dots are solvent free with low levels of naturally absorbed oxygen, inherited from the starting graphite. The sheets are only two to five layers thick. The graphene nanodots have diameters in the range of 9-29 nm and heights in the range of 1-16 nm, which can be controlled by changing the processing time.     

An extension of a result of Grannan and Swindle on the poisoning of catalytic surfaces

Grannan and Swindle considered a model in which molecules of several types of reactant land on a catalytic surface. When two different reactants find themselves adjacent, they diffuse from the surface and leave the sites vacant. They showed that if the rate of bonding onto the surface of one reactant is sufficiently close to one, then the surface becomes poisoned by that type. In this paper we show that a sufficient condition for poisoning is that one reactant should bond at rate greater than that of the other reactants combined.     

Nucleon spectra in heavy ion collision prior to equilibrium

Energy spectra and angular distribution of nucleons emitted in intermediate energy heavy ion collisions prior to equilibrium are calculated. The spectra have two components: (a) promptly emitted particles (PEPS) or Fermi jets; (b) emission from a localized excited region at the interface of the two colliding ions. The results obtained with this model have been compared with experiment and the agreement is good.