Selection of peptides with semiconductor binding specificity for directed nanocrystal assembly.

In biological systems, organic molecules exert a remarkable level of control over the nucleation and mineral phase of inorganic materials such as calcium carbonate and silica, and over the assembly of crystallites and other nanoscale building blocks into complex structures required for biological function. This ability to direct the assembly of nanoscale components into controlled and sophisticated structures has motivated intense efforts to develop assembly methods that mimic or exploit the recognition capabilities and interactions found in biological systems. Of particular value would be methods that could be applied to materials with interesting electronic or optical properties, but natural evolution has not selected for interactions between biomolecules and such materials. However, peptides with limited selectivity for binding to metal surfaces and metal oxide surfaces have been successfully selected. Here we extend this approach and show that combinatorial phage-display libraries can be used to evolve peptides that bind to a range of semiconductor surfaces with high specificity, depending on the crystallographic orientation and composition of the structurally similar materials we have used. As electronic devices contain structurally related materials in close proximity, such peptides may find use for the controlled placement and assembly of a variety of practically important materials, thus broadening the scope for 'bottom-up' fabrication approaches.

Subcellular distributions and excited-state processes of hypericin in neurons.

The photodynamic drug, hypericin, is studied in fetal rat neurons using fluorescence microscopy. Hypericin has an extremely high affinity for the cell membrane and is found to a smaller extent in the nucleus. Fluorescent excitation of hypericin is shown to cause irreversible damage to the cell membranes of living neurons. Fixed cells were used to make ultrafast time-resolved measurements to avoid the deleterious effects of long-term exposure to intense light and room temperatures. To our knowledge, these are the first ultrafast time-resolved measurements of the fluorescence lifetime of hypericin in a subcellular environment. Nonexponential fluorescence decay is observed in hypericin in the neurons. This nonexponential decay is discussed in terms of other examples where nonexponential decay is induced in hypericin upon its binding to biomolecules. The nonradiative processes giving rise to the nonexponential hypericin decay are attributed to excited-state electron transfer, excited-state proton transfer or both.

The role of oxygen in the antiviral activity of hypericin and hypocrellin.

The light-induced antiviral activity of hypericin and hypocrellin in the presence and absence of oxygen was examined under experimental conditions where the effect of oxygen depletion could be quantified. There was a significant reduction of light-induced antiviral activity of hypericin and hypocrellin under hypoxic conditions. Interestingly, antiviral activity of hypocrellin was not observed at low oxygen levels at which hypericin retained measurable virucidal activity. This suggests that additional pathways, such as the generation of protons from excited states of hypericin, may enhance the biological activity of activated oxygen species.

Electrophoretic and cytogenetic studies of Chironomus utahensis.

Cellulose acetate electrophoresis of Chironomus utahensis hemolymph demonstrated a six-band pattern for hemoglobins. Three major and three minor bands made up the electropherogram. Slight variations from this general pattern were found in less than 10 percent of the population and may represent ontogenetic changes, genetic variation or slight changes in the electrophoretic conditions. No variations could be correlated with the age of the culture, sex, or site of collection. Cytogenetic observations of the salivary glands revealed three large and one small pair of independent polytene chromosomes. Comparisons of electrophoretic patterns of hemoglobins and chromosome banding patterns with other chironomid species will help to clarify their taxonomic and evolutionary relationships.

Multiplicity of hemoglobins in the genus Chironomus (Tendipes).

The number of hemoglobins found in individual mature larvae of several Chironomus species is six to nine. The consistency of this number and of the electrophoretic mobilities of these separable forms seems to indicate the synchronous production of polypeptide chains by several genetic loci.