Tubular polymers

Harada and coworkers proceeded further to obtain a tubular polymer from a PEG-a-CD polyrotaxane by using Scheme 2. The polyrotaxane was prepared... 

Harada, A., Li, J., and Kamachi, M. (1993). Synthesis of a tubular polymer from threaded cyclodextrins. Nature (London) 364 516-518. 

Figure 11 (see color section). Longitudinal H-bond relay comprised of CHQs and water, (a) Tubular polymer structure of a single nanotube obtained with X-ray analysis for the heavy atoms and with ab initio calculations for the H-orientations (top and side views), (b) One of the four pillar frames of short H-bonds represents a 1-D H-bond relay composed of a series of consecutive OH groups [hydroxyl groups (—OH) in CHQs and the OHs in water molecules]. Reproduced by permission of American Chemical Society Ref. [54]. 

However, in 1942 it was removed from U. S. pharmacopeia because of its severe gastrointestinal toxicity. Currently, it still remains as an effective therapy for treatment of venereal warts [25]. Furthermore, podophyllotoxin and its derivatives have been extensively studied in the last 60 years for their powerful antitumor effects. Podophyllotoxin itself is a powerful microtubule inhibitor. Microtubules are tubular polymers whose protomeric unit (a and 3-tubulin) forms an heterodimer and are the dynamic constituents of the cytoskeleton. The cytoplasm of eukaryotic cells contains a soluble pool of unpolymerised tubulin protomers as well as an organised array of microtubules. Microtubules can be rapidly assembled or disassembled in response to various stimuli with little or no change in the total amount of tubuline. Cytoplasmatic microtubules are... 

Here there is a more substantive range of possibilities for long tubular polymers. From a chemical or physical viewpoint one anticipates that end-structures may be neglected. Mathematically one sees that the ends of the tube can be viewed to be capped... 

MAJOR APPLICATIONS Starting materials for tubular polymers. Potential use for curing of PEG. 

Tubulin polymerizes into MTs by mechanisms that are qualitatively similar to those of artin polymerization but quantitatively different. Tubulin dimers loaded with GTP are presumed to be the subunits that add to the growing ends of MTs. Once a tubular polymer has formed, tubulin dimers are thought to add to each end, with the p-tubuUn part of the heterodimers oriented toward the plus end of the MT. The rates at which tubulin adds to the two ends of the polymer are different, and the rate constants for these additions have been somewhat more difficult to quantify than those for actin monomer addition. Recent studies surest that the on-rate at a given concentration of free tubulin dimers might not be a constant, but rather varies from MT to MT and even over time for the same growing MT. The variable rate appears to depend on the spatial pattern and extent to which GTP has hydrolyzed at the MT end. 

Fig. 11.1 Complexation energies of self-assembled CHQ iV-mers without top) and with (below) water molecules dimer, trlmer, tetramer, octahedral hexamer, and tubular octamer as a repeating unit of the tubular polymer of CHQs. The value below each structure is the calculated binding energy (kcal/mol) at the B3LYP/6-31G level of theory. In the absence of water, the hexamer structure is favoured, while in the presence of water, the polymer chtiin is favoured [18]...

Rigid and tubular polymers are more sharp and result in higher passive tumor accumulation due to better pore penetration. 

The self-assembly of natural and synthetic multifunctional unimers occurs, in fact, by a combination of classical molecular recognition and growth mechanisms. Self-assembled, reversible structures include linear, helical, columnar, and tubular polymers micelles monolayers and three-dimensional phases and networks. Self-assembled systems based on an interplay between covalent chains and supramolecular interactions are also important. Typical examples are side-chain SPs (Chapter 5), host-guest polymeric composites and dendrimers (Chapters 2 and 7), polymers with mechanical bonds (Chapter 8), and block copolymers (Chapters 9-11). 

Since then, the polymerization of various protein molecules was found to have similar features. There is a critical concentration for polymerization and the polymerization consists of nucleation and growth. Bacterial flagella are helically curved tubular polymers of flagellin molecules. Flagella are formed from purified flagellin molecules in solution, although spontaneous nucleation of flagella can hardly occur [10]. The polymerization of tubulin molecules to microtubules is... 

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