The previously described FliTrx E. coli flagellin protein was genetically engineered to display rationally designed histidine, arginine-lysine, and aspartic acid-glutamic acid peptide loops on the solvent-accessible outer domain region. The resulting flagellin monomers were self-assembled to obtain the corresponding oligomeric flagella bionanotubes in which the peptide loops were 5 nm apart. These flagella nanotubes were equilibrated with solutions of various metal ions (Co(II), Cu(II), Cd(II), Ag(I), Au(I), and Pd(II)). Controlled reduction of these metal ions yielded ordered arrays of nanoparticles or nanotubes, and in some cases, extensive aggregation resulted in formation of metal nanotube bundles. Both metal nanoparticles and nanotubes were generated with Cu(II) and Au(I), depending on the initial concentration of Cu(II) ions, while Ag(I) consistently formed metal nanowires, even under relatively mild conditions of reduction. The covalent attachment of separately synthesized Au nanoparticles to the flagella scaffold was also demonstrated. Controlled reduction of Co(II), Cd(II), and Pd(II) complexed with histidine and aspartic acid-glutamic acid peptide loops yielded ordered arrays of the respective metal nanoparticles on individual flagella nanotubes with minimal aggregation. The peptide loop modified flagella nanotubes have been demonstrated to be useful scaffolds for the generation of ordered arrays of metal nanoparticles or uniform nanotubes.

Powder Mn 2+ EPR spectra of 5-nm ZnS:Mn quantum dots have been analyzed in detail to account for all the observed fine spectral features. The same spectral features are observed in samples with low doping of Mn 2+ (0.003-0.008%), showing 10 weak forbidden transitions between the six-line pattern of the M S ) -1 / 2 to M S ) 1 / 2 transition for the six M I values. Spectral simulations have been performed with the Simfonia program with parameters g xx ) 2.0064, g yy ) 2.0064, g zz ) 2.0066, D ) 37.4 × 10 -4 cm -1 , E ) 12.5 × 10 -4 cm -1 , A xx ) 63.9 × 10 -4 cm -1 , A yy ) 64.0 × 10 -4 cm -1 , and A zz ) 64.4 × 10 -4 cm -1 , suggesting a lower than T d site symmetry for the doped Mn 2+ in the cubic ZnS structure. At higher doping concentration (15.9%), a single broad line is observed with isotropic g and A.

An E. coli flagellin protein, termed FliTrx, was investigated for use as a novel form of self-assembling protein nanotube. This protein was genetically engineered to display constrained peptide loops with a series of different thiol, cationic, anionic, and imidazole functional groups. "Cys-loop" thiol variants consisting of 6 and 12 cysteine residues were isolated in the form of disulfide-linked nanotube bundles, a novel nanomaterial. Bundles were characterized by fluorescence microscopy, transmission electron microscopy, and optical trapping.

Three types of rationally designed peptide loops were genetically engineered for display on the surface of the FliTrx E. coil flagella scaffold, a type of bacterial bionanotube adapted for the multivalent display of peptide loops. The resulting three types of loop flagella fibers were used to demonstrate the feasibility of templating synthesis of inorganic nanotubes and nanoparticles and organic nanotubes. Purified flagella fibers displaying a cationic arginine-lysine loop peptide with three guanidine and three amine functional groups were used to form silica bionanotubes, using two types of silicate ion precursors. Purified flagella fibers displaying a tyrosine-serine-glycine loop peptide with six phenolic and three aliphatic hydroxyl groups were used to initiate formation of titania bionanotubes. Purified flagella fibers displaying an anionic aspartate-glutamate loop peptide with 18 carboxylate groups were used to initiate formation of polyaniline nanotubes and hydroxyapatite nanoparticles, a key component of bones. The resulting nanomaterials were mainly characterized by transmission electron microscopy and additionally by scanning electron microscopy, in the case of polyaniline nanotubes. The studies demonstrate the versatility of employing bioengineered flagella for the generation of a variety of nanoparticle arrays and nanotubes.