Single-wall fullerene nanotubes were converted from nearly endless, highly tangled ropes into short, open-ended pipes that behave as individual macromolecules. Raw nanotube material was purified in large batches, and the ropes were cut into 100- to 300-nanometer lengths. The resulting pieces formed a stable colloidal suspension in water with the help of surfactants. These suspensions permit a variety of manipulations, such as sorting by length, derivatization, and tethering to gold surfaces.

Ion mobility measurements have been used to examine the geometries of naked BPTI (bovine pancreatic trypsin inhibitor) and cytochrome c ions in the gas phase, as a function of charge. For BPTI, the measured cross sections are close to those estimated for the native solution-phase conformation. Furthermore, gas-phase BPTI retains its compact structure when collisionally heated. These results are consistent with the known stability of BPTI, where the three-dimensional structure is partly locked into place by three covalent disulfide bridges. For cytochrome c, geometries with cross sections close to those estimated for the native solution phase structure were observed for the low charge states. For intermediate charge states, the compact geometries are metastable, and when collisionally heated they gradually unfold, through a series of well-defined intermediates. Only extended conformations are observed for the higher charge states, and they become more extended as the charge increases. The gas-phase conformation of a protein ion results from a balance between attractive intramolecular interactions, intramolecular charge “solvation”, and Coulomb repulsion. For the low charge states, compact folded conformations have the lowest energy because they maximize intramolecular interactions. For intermediate charge states, elongated conformations, which minimize Coulomb repulsion while maximizing intramolecular interactions and intramolecular charge “solvation”, become favored. For the high charge states, the elongated conformations unravel to an extended string as Coulomb repulsion dominates.

Gas-phase ion mobility measurements have been used to characterize the conformations of the +4 to +22 charge states of apomyoglobin. For the +8 to +10 charge states, generated by electrospraying pH ≈3 solutions, two relatively compact conformations were resolved which may reflect the state of the protein in solution. These relatively compact conformations unfold into more extended conformations when collisionally heated. Only extended conformations are observed for the high (>+10) charge states, and they become more extended as the charge increases. Proton stripping of the higher (>+7) charge states to produce the +4 to +7 charge states results in spontaneous collapse into partially folded conformations. Further folding is observed upon collisional heating of the collapsed structures, indicating the presence of an activation barrier for protein folding in the gas phase. The barrier probably results from Coulomb repulsion and the reorganization of secondary structure. For the lower (<+7) charge states, the most stable conformations appear to be slightly more compact than the native protein in solution. The collision cross sections per residue for the extended conformations of apomyoglobin and cytochrome c are similar. The cross sections for the compact folded conformations of these proteins also scale with the number of residues. This suggests that different proteins share common structural motifs in the gas phase, as they do in solution.

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The fabrication of boron nitride nanotubules and BN-based composite nanostructures within the pores of anodic aluminum oxide is described. Boron nitride nanotubules are produced by pyrolyzing 2,4,6-trichloroborazine over alumina templates at 750 °C. The nanotubules are polycrystalline, with crystallites exhibiting an orientational ordering such that the BN (001) planes are tilted 25°with respect to the tube axis. Nanotubules at least 20 µm long are observed, longer than what is expected for a growth mechanism that assumes a uniform substrate coating. This suggests that tubes grow in the axial direction faster than in the radial direction. As an example of a CVD-fabricated composite nanostructure, we synthesized coaxial C/BN/C nanotubules by the sequential pyrolysis of acetylene and trichloroborazine over alumina templates. BN-insulated copper nanowires were also fabricated by electrochemical deposition of copper into BN-coated templates.

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Injected ion drift tube techniques have been used to examine the structures and to study the isomerization of Lac,+ (n = 2-90) clusters. Three families of metal-containing carbon rings ("ring Ia", "ring Ib", and "ring II"), metal-containing graphite sheets, and metallofullerenes have been resolved. Several plausible geometries with similar mobilities can be suggested for all of the ring isomers. The most likely geometries are a La inserted into a carbon ring (ring Ia), a La inside a carbon ring (ring Ib), and various Lac, and C, rings fused together (ring 11). The relative abundances of the graphite sheet and the metallofullerene isomers are substantially larger than for the pure carbon clusters. Both endohedral and non-endohedral Lac,+ metallofullerenes have been resolved. La&+ and all Lac,+ fullerenes with n = 38-90 are found to be endohedral, while LaC29+-LaC35+ fullerenes are non-endohedral. Annealing studies show that Lac,+ ring I1 isomers with an even number of carbon atoms convert into ring Ia isomers, while the odd-numbered ring I1 isomers convert into ring Ib isomers. For larger clusters, fullerenes and graphite sheets are formed when the rings are annealed. The efficiency of this annealing process in the Lac,+ system is much larger than in the C,+ system, although the activation energies appear to be approximately the same. Studies of the dissociation of Lac,+ show that loss of LaC4' is generally the dominant dissociation process for the Lac,+ rings with an even number of carbon atoms, while loss of C3 is also important for the odd-numbered ones.