Bio-based approaches to inorganic material synthesis

Nature is an exquisite designer of inorganic materials using biomolecules as templates. Diatoms create intricate silica wall structures with fine features using the protein family of silaffins as templates. Marine sponges create silica spicules also using proteins, termed silicateins. In recent years, our group and others have used biomolecules as templates for the deposition of inorganic materials. In contrast with the traditional materials science approach, which requires high heat, extreme pH and non-aqueous solutions, the bio-based approaches allow the reactions to proceed usually at near ambient conditions. Additionally, the biological templates allow for the control of the inorganic nanoparticle morphology. The use of peptides and biomolecules for templating and assembling inorganics will be discussed here.

Ceramic nanoparticle assemblies with tailored shapes and tailored chemistries via biosculpting and shape-preserving inorganic conversion

A novel biosynthetic paradigm is introduced for fabricating three-dimensional (3-D) ceramic nanoparticle assemblies with tailored shapes and tailored chemistries: biosculpting and shape-preserving inorganic conversion (BaSIC). Biosculpting refers to the use of biomolecules that direct the precipitation of ceramic nanoparticles to form a continuous 3-D structure with a tailored shape. We used a peptide derived from a diatom (a type of unicellular algae) to biosculpt silica nanoparticle based assemblies that, in turn, were converted into a new (nonsilica) composition via a shape-preserving gas/silica displacement reaction. Interwoven, microfilamentary silica structures were prepared by exposing a peptide, derived from the silaffin-1A protein of the diatom Cylindrotheca fusiformis, to a tetramethylorthosilicate solution under a linear shear flow condition. Subsequent exposure of the silica microfilaments to magnesium gas at 900 degrees C resulted in conversion into nanocrystalline magnesium oxide microfilaments with a retention of fine (submicrometer) features. Fluid(gas or liquid)/silica displacement reactions leading to a variety of other oxides have also been identified. This hybrid (biogenic/synthetic) approach opens the door to biosculpted ceramic microcomponents with multifarious tailored shapes and compositions for a wide range of environmental, aerospace, biomedical, chemical, telecommunications, automotive, manufacturing, and defense applications.

The thermostability of an alpha-helical coiled-coil protein and its potential use in sensor applications

Coiled-coil proteins are assemblies of two to four alpha-helices that pack together in a parallel or anti-parallel fashion. Coiled-coil structures can confer a variety of functional capabilities, which include enabling proteins, such as myosin, to function in the contractile apparatus of muscle and non-muscle cells. The TlpA protein encoded by the virulence plasmid of Salmonella is an alpha-helical protein that forms an elongated coiled-coil homodimer. A number of studies have clearly established the role of TlpA as a temperature-sensing gene regulator, however the potential use of a TlpA in a thermo-sensor application outside of the organism has not been exploited. In this paper, we demonstrate that TlpA has several characteristics that are common with alpha-helical coiled-coils and its thermal folding and unfolding is reversible and rapid. TlpA is extremely sensitive to changes in temperature. We have also compared the heat-stability of TlpA with other structurally similar proteins. Using a folding reporter, in which TlpA is expressed as a C-terminal fusion with green fluorescent protein (GFP), we were able to use fluorescence as an indicator of folding and unfolding of the fusion protein. Our results on the rapid conformational changes inherent in TlpA support the previous findings and we present here preliminary data on the use of a GFP-TlpA fusion protein as temperature sensor.

Ultrafast holographic nanopatterning of biocatalytically formed silica

Diatoms are of interest to the materials research community because of their ability to create highly complex and intricate silica structures under physiological conditions: what these single-cell organisms accomplish so elegantly in nature requires extreme laboratory conditions to duplicate-this is true for even the simplest of structures. Following the identification of polycationic peptides from the diatom Cylindrotheca fusiformis, simple silica nanospheres can now be synthesized in vitro from silanes at nearly neutral pH and at ambient temperatures and pressures. Here we describe a method for creating a hybrid organic/inorganic ordered nanostructure of silica spheres through the incorporation of a polycationic peptide (derived from the C. fusiformis silaffin-1 protein) into a polymer hologram created by two-photon-induced photopolymerization. When these peptide nanopatterned holographic structures are exposed to a silicic acid, an ordered array of silica nanospheres is deposited onto the clear polymer substrate. These structures exhibit a nearly fifty-fold increase in diffraction efficiency over a comparable polymer hologram without silica. This approach, combining the ease of processability of an organic polymer with the improved mechanical and optical properties of an inorganic material, could be of practical use for the fabrication of photonic devices.

Thermal modeling of snake infrared reception: evidence for limited detection range

For more than 40 years, information has circulated with regard to the sensitivity of infrared pit organs in both boid and crotaline snakes (pythons and pit vipers, respectively). The most often quoted sensitivity is 0.003 degrees C and this value is based on the work of Bullock and co-workers (1956). Missing from previous work was a quantitative model of radiation transfer that would report sensitivity not in terms of degrees Celsius, but rather sensing distance. Since prey detection is often cited as the function of the infrared pit organ, quantification of this sensing distance seemed to be an important value that was missing from the literature. In this paper, we model the radiation transfer process from a 37 degrees C object, i.e. warm-blooded prey, to an infrared pit organ. The model tries to answer a very basic question-at what distance does the thermal signature of a 37 degrees C object blend into the background for a non-imaging biological infrared sensor? The output of the model, the sensing distance, is of particular interest in comparing biological infrared sensors to current semiconductor-based infrared (IR) detectors-largely because of inappropriate comparisons between the temperature sensitivity of IR snake reception and imaging IR cameras. The purpose of the presented work to make more appropriate comparisons, i.e. sensing distance. This sensing distance output indicates an extremely short detection distance (<5 cm)-contradictory to what is observed experimentally. This dichotomy raises further questions regarding how the biological system amplifies this weak signal.

Use of small fluorescent molecules to monitor channel activity

The Mechanosensitive channel of Large conductance (MscL) allows bacteria to rapidly adapt to changing environmental conditions such as osmolarity. The MscL channel opens in response to increases in membrane tension, which allows for the efflux of cytoplasmic constituents. Here we describe the cloning and expression of Salmonella typhimurium MscL (St-MscL). The amino acid sequence encoding for this MscL exhibits a high degree of similarity to Escherichia coli MscL (Eco-MscL). Using a fluorescence efflux assay, we demonstrate that efflux through the MscL channel during hypoosmotic shock can be monitored using endogenously produced fluorophores. These fluorophores are synthesized by a cotransformed gene, cobA. In addition, we observe that thermal stimulation, i.e., heat shock, can induce efflux through MscL.

Surface ultrastructure of pit organ, spectacle, and non pit organ epidermis of infrared imaging boid snakes: A scanning probe and scanning electron microscopy study

Boid snakes possess unique infrared imaging pit organs. The ultrastructure of the surfaces of these organs scatter or reflect electromagnetic radiation of specific wavelengths. Pit organ epidermal surfaces of boid snakes are covered with arrays of pore-like structures called micropits. In order to determine the dimensions of this complicated surface structure, we have performed the first ultrastructural analysis on snake epidermis by high-resolution microscopy techniques. Using scanning probe microscopy and scanning electron microscopy, we found that the epidermis of pit organ, maxillary non pit organ, spectacle, and ventral scales contain arrays of micropits. These scale surfaces also contain major surface features of overlapping plate-like structures. Pit organ micropits averaged 319 nm in diameter and 46 nm in depth and were spaced an average of 808 nm from each other. These micropits were significantly deeper, of greater diameter, and spaced at greater distances apart than those of the other scales. Plate structures of the pit organs had a mean distance between plates of 3.5 microm and a mean plate step height of 151 nm. These differences serve to strengthen the argument that arrays of micropit and plate surface structures function as spectral filters or anti-reflective coatings with respect to incident electromagnetic radiation.

Investigation of light-induced conformation changes in spiropyran-modified succinylated poly(L-lysine)

To determine the maximum range of coupling between side-chain photochromism and polypeptide conformation change, we modified the carboxylate side chains of succinylated poly(L-lysine) with a spiropyran to form polypeptide I. The extent of modification was determined to be 35.5%. The spacer group length between the polypeptide alpha-carbon and the dye was 12 atoms, providing minimum polypeptide-dye interaction. Conformation changes were monitored by circular dichroism as a function of light adaptation and solvent composition (hexafluoroisopropanol [HFIP] vs trifluoroethanol [TFE]). Under all solvent compositions, the dark-adapted dye was in the merocyanine form. Light adaptation by visible light converted the dye to the spiropyran form. When dissolved in TFE, I adopted a helical conformation insensitive to light adaptation. With increasing percentage HFIP, a solvent-induced helix-to-coil transition was observed around 80% (vol/vol) HFIP. At 100% HFIP, both light- and dark-adapted forms of I were in the coil state. Near the midpoint of the solvent-induced helix-to-coil transition, light adaptation caused conformation changes. Applying helix-to-coil transition theory, we measured a statistically significant difference in coil segment-HFIP binding constant for light- vs dark-adapted solutions (6.38 +/- 0.03 M-1 vs 6.56 +/- 0.03 M-1), but not for the nucleation parameter sigma (1.2 +/- 0.4 10(-3) vs 1.3 +/- 0.3 x 10(-3). The small binding constant difference translated to a light-induced binding energy difference of 17 cal/mol/monomer. Near the midpoint of the helix-to-coil transition, collective interactions between monomer units made possible the translation of a small energy difference (less than RT) into large macromolecular conformation changes.(ABSTRACT TRUNCATED AT 250 WORDS)