Synthesis of single crystalline tellurium nanotubes with triangular and hexagonal cross sections

Single crystalline tellurium (Te) nanotubes with triangular cross sections were successfully synthesized for the first time by a simple approach of vaporizing tellurium metal and condensing the vapor in an inert atmosphere onto a suitable substrate. Tellurium gas was evaporated by heating at 350 degrees C and was condensed on the Si (100) substrate at 150-200 degrees C, in the downstream of argon (Ar) gas at a flow rate of 25 sccm for 10 min. This led to the production of nanotubes of triangular cross section along with some hexagonal ones. The formation of the nanotubes was highly dependent upon the structure of the substrate surface, Ar gas flow rate, and the deposition temperature. When the substrate is Si (111) or sapphire (0001) or when the argon flow rate is increased to 500 sccm, nanowires and nanorods were exclusively formed. Irrespective of the morphologies, all the observed Te nanostructures grew in a regular [0001] direction. The facile approach to nanotubes with a triangular cross section may facilitate some new applications as well as stimulate theoretical studies pertaining to the stability of this high-energy configuration.     

Side-Chain Interactions in d/l Peptide Nanotubes: Studies by Crystallography,NMR Spectroscopy and Molecular Dynamics

Our understanding of the factors affecting the stability of cyclic d/l peptide (CP) nanotubes remains underdeveloped. In this work, we investigate the impact of side chain alignment, hydrophobicity and charge on CP nanotube stability through X-ray crystallography, NMR spectroscopy and molecular dynamics (MD) simulations. We characterise the distinct CP-CP alignments that can form and identify stable and unstable dimers by MD simulation. We measure H-bond half-lives of synthesised CPs by ¹H−D exchange experiments and find good correlation with predicted CP-CP stabilities. We find that hydrophobic amino acids improve CP dimer stability but experimentally reduce solubility. Charged amino acids either increase or decrease CP dimer stability depending on the relative orientation and composition of charged groups. X-ray crystal structures are solved for two CPs, revealing non-tubular folded conformations. Ultimately, this work will assist the educated design of stable tubular structures for potential applications in biomedicine.