The de novo design of peptides and proteins has recently emerged as an approach for investigating protein structure and function. Designed, helical peptides provide model systems for dissecting and quantifying the multiple interactions that stabilize secondary structure formation. De novo design is also useful for exploring the features that specify the stoichiometry and stability of alpha-helical coiled coils and for defining the requirements for folding into structures that resemble native, functional proteins. The design process often occurs in a series of discrete steps. Such steps reflect the hierarchy of forces required for stabilizing tertiary structures, beginning with hydrophobic forces and adding more specific interactions as required to achieve a unique, functional protein.

Photoinitiation of relaxation of two peptides (labeled 1 and 2) and spectroscopic studies of the ensuing dynamics have led to new information about peptide conformational dynamics. Following photolysis of the aryl disulfide chromophore that constrains a peptide to be distorted from its equilibrium form, the S−S bond is broken in <200 fs, and the liberated thiyl radicals either undergo geminate recombination or diffuse apart to allow the peptides to change conformation. From anisotropy measurements, overall peptide rotation is on the time scale of 600 ps. At an even earlier time (ca. 100 ps), transient IR measurements show a bleaching of the amide I‘ region, arising from a vibrational Stark effect produced upon ring opening of peptide 2. We did not detect any significant shift in the amide I‘ region up to 2 ns, suggesting no significant helix formation in this time domain. Thiyl radicals arising from peptide 2 recombine with a power law rate over the time range from picoseconds to microseconds signaling an unusual type of scaled kinetics.

The high carrier mobility of films of semiconducting single-walled carbon nanotubes (SWNTs) is attractive for electronics applications, but the presence of metallic SWNTs leads to high off-currents in transistor applications. The method presented here, cycloaddition of fluorinated olefins, represents an effective approach toward converting the "as grown" commercial SWNT mats into high-mobility semiconducting tubes with high yield and without further need for carbon nanotube separation. Thin-film transistors, fabricated from percolating arrays of functionalized carbon nanotubes, exhibit mobilities >100 square centimeters per volt-second and on-off ratios of 100,000. This method should allow for the use of semiconducting carbon nanotubes in commercial electronic devices and provide a low-cost route to the fabrication of electronic inks.