Tubule arrays

Key Words—Single-wall, multi-wall, vibrational inodes, chiral nanotubes, electronic bands, tubule arrays. 

Fig. 6. Self-consistent band structure (48 valence and 5 conduction bands) for the hexagonal II arrangement of nanotubes, calculated along different high-symmetry directions in the Brillouin zone. The Fermi level is positioned at the degeneracy point appearing between K-H, indicating metallic behavior for this tubule array[17. ...

Within the scope of thermoelectric nanostructures, Sima et al. [161] prepared nanorod (fibril) and microtube (tubule) arrays of PbSei. , Tej by potentiostatic electrodeposition from nitric acid solutions of Pb(N03)2, H2Se03, and Te02, using a 30 fim thick polycarbonate track-etch membrane, with pores 100-2,000 nm in diameter, as template (Cu supported). After electrodeposition the polymer membrane was dissolved in CH2CI2. Solid rods were obtained in membranes with small pores, and hollow tubes in those with large pores. The formation of microtubes rather than nanorods in the larger pores was attributed to the higher deposition current. 

Abstract—The fundamental relations governing the geometry of carbon nanotubes are reviewed, and explicit examples are pre.sented. A framework is given for the symmetry properties of carbon nanotubes for both symmorphic and non-symmorphic tubules which have screw-axis symmetry. The implications of symmetry on the vibrational and electronic structure of ID carbon nanotube systems are considered. The corresponding properties of double-wall nanotubes and arrays of nanotubes are also discussed. 

Fig. 5. Schematic representation of arrays of carbon nanotubes with a common tubule axial direction in the (a) tetragonal, (b) hexagonal I, and (c) hexagonal II arrangements. The reference nanotube is generated using a planar ring of twelve carbon atoms arranged in six pairs with the symmetry [16,17,30].

No superconductivity has yet been found in carbon nanotubes or nanotube arrays. Despite the prediction that ID electronic systems cannot support supercon-ductivity[33,34], it is not clear that such theories are applicable to carbon nanotubes, which are tubular with a hollow core and have several unit cells around the circumference. Doping of nanotube bundles by the insertion of alkali metal dopants between the tubules could lead to superconductivity. The doping of individual tubules may provide another possible approach to superconductivity for carbon nanotube systems. 

A very different model of tubules with tilt variations was developed by Selinger et al.132,186 Instead of thermal fluctuations, these authors consider the possibility of systematic modulations in the molecular tilt direction. The concept of systematic modulations in tubules is motivated by modulated structures in chiral liquid crystals. Bulk chiral liquid crystals form cholesteric phases, with a helical twist in the molecular director, and thin films of chiral smectic-C liquid crystals form striped phases, with periodic arrays of defect lines.176 To determine whether tubules can form analogous structures, these authors generalize the free-energy of Eq. (5) to consider the expression... 

A perusal of Table I makes clear the general conclusion that alkyl modification at the C-20 position of the VBL molecule is function sensitive for all and each of the three basic reactions of the drug with microtubules in vitro. If we begin the discussion with deoxydesethyl VBL (5) as the prototype compound for this series of congeners, we find that the 10-fold increase in the IC50 for microtubule assembly observed in our earlier work was accompanied by an eilteration in the structure of the assembled microtubules. As exemplified in Fig. 4a, there are opened areas along the length of the tubule, and in some cases the linear array of protofilaments... 

Metal microtubules were prepared in a similar marmer, with lower internal diameters of 0.8 nm, and the authors could demonstrate that ion transport through such tubules can be switched from positive to negative ions with external potentials applied to the membrane. 2 Gold nanowires (of as little as 10 nm diameter) deposited in nanoporous filtration disks can also act as nanoelectrodes with sensitive cyclic voltammetric detection limits. Finally, the template membrane approach has also been extended to arrays of cadmium chalcogenide phases. Thus, 200 nm-diameter CdSe or graded CdSe/CdTe cylinders were electrodeposited in the pores of Anopore membranes. A Ni-CdSe array was found to be rectifying.i ... 

A Structure similar to this gyroid PCS membrane was reported in the retinal pigment epithelial cells of Latimeria chalumane [93]. This membrane structure which is continuous with the SER, and described as "regular arrays of tubules" [93], is in fact yet another gyroid membrane. This structural assignment is based on the recognition of a section normal the [111] plane of the G-PCS ([93], fig. 4). 

In terms of drug disposition, OATl is the most important member of this transport family. Expressed mainly in the kidney tubule cell, OATl is a dicarboxylate exchange protein that is responsible for basolateral uptake of organic anions such as para-aminohippurate (PAH). OATl mediates the excretion of a diverse array of substrates, including environmental toxins. Substrates for this transporter include antibiotics, antiviral nucleoside analogs, and nonsteroidal anti-inflammatory medications. In fact, more than 100 medications and toxic compounds have been found to interact with OATl. 

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