Bundle formations mechanism

Tang JX, janmey PA. The polyelcctrolyte nature of F-actin and the mechanism of actin bundle formation. J Biol Chem 1996 271 8556-8563. 

Figure 44 Proposed formation mechanism of polythiophene/protein wire bundles (a) structural image of polythiophene with an all trans backbone configuration (left). Structure of BI monomer (PDB file lAPH) with a tyrosine side chain shown for comparison (right), (b) Proposed interaction between a partially unfolded BI monomer (gray) and two polythiophenes (green), (c) Transmission electron microscopy of the wires after incubation for 6h at 65 °C and proposed structure, (d) Left Two fiuorescence micrographs of the corresponding poly thiophenes shown on the right (scale bar 20 pm). (Reproduced with permission from Ref. 78. Wiley-VCH, 2005.)...

Tungsten oxide is not the only nanomaterial that forms unusual morphologies in benzyl alcohol. Another example is ZnO that grows into fan-like nanorod bundles [168]. The chemical formation mechanism, elaborated from the analysis of the organic compounds detected by GC coupled with mass spectrometry, involved a nucleophilic attack of the hydroxyl function of benzyl alcohol on one of the carbonyl groups of the acetylacetonate ligand of the precursor molecule (Scheme 2.4). Release of acetone (in its enol form) and benzyl acetate resulted in the formation of a zinc hydroxyl species, which then underwent condensation to a Zn—O—Zn bridge. 

Fig. 5. Protein folding. The unfolded polypeptide chain coUapses and assembles to form simple stmctural motifs such as -sheets and a-hehces by nucleation-condensation mechanisms involving the formation of hydrogen bonds and van der Waal s interactions. Small proteins (eg, chymotrypsin inhibitor 2) attain their final (tertiary) stmcture in this way. Larger proteins and multiple protein assembhes aggregate by recognition and docking of multiple domains (eg, -barrels, a-helix bundles), often displaying positive cooperativity. Many noncovalent interactions, including hydrogen bonding, van der Waal s and electrostatic interactions, and the hydrophobic effect are exploited to create the final, compact protein assembly. Further stmctural...

A vertical cylindrical, and mechanical agitated pressure vessel, equipped with baffles to prevent vortex formation is the most widely used fermenter configuration. The baffles are typically one-tenth of the fermenter diameter in widtli, and are welded to supports tliat extend from the sidewall. A small space between the sidewall and the baffle enables cleaning. Internal heat transfer tube bundles can also be used as baffles. The vessels must withstand a 45 psig internal pressure and full vacuum of -14.7 psig, and comply with the ASME code. 

Sawada et al. [110] and the authors of this Chapter [104,111] have proposed another theory, the bundle-like nucleation theory, for the mechanism of ECC formation. Both groups of workers suggested that crystallization under high pressure starts from partially extended-chain nucleation rather than from the folded-chain nucleation as proposed by Hikosaka [103,104]. This theory was established on the basis of the following facts ... 

The possible fatigue failure mechanisms of SWCNT in the composite were also reported (Ren et al., 2004). Possible failure modes mainly include three stages, that is, splitting of SWCNT bundles, kink formation, and subsequent failure in SWCNTs, and the fracture of SWCNT bundles. As shown in Fig. 9.12, for zigzag SWCNT, failure of defect-free tube and tubes with Stone-Wales defect of either A or B mode all resulted in brittle-like, flat fracture surface. A kinetic model for time-dependent fracture of CNTs is also reported (Satapathy et al., 2005). These simulation results are almost consistent with the observed fracture surfaces, which can be reproduced reasonably well, suggesting the possible mechanism should exist in CNT-polymer composites. 

Displacement of the crack front—from the start of crack formation until final destruction—takes place at a variable rate. For the crack to overcome impediments (such as macromolecules, chain bundles, super-molecular structure formations, inclusions, and micropores), it needs varying time lengths, and the fissure perimeter takes on a sinuous form. The limit between different formations on the entire perimeter of the crack front is evidently determined by the equilibrium set up between elastic mechanical forces and bond forces displacement of the crack front results from this equilibrium. 

The C4 cycle can be viewed as an ATP-dependent C02 pump that delivers C02 from the mesophyll cells to the bundle-sheath cells, thereby suppressing photorespiration (Hatch and Osmond, 1976). The development of the C4 syndrome has resulted in considerable modifications of inter- and intracellular transport processes. Perhaps the most striking development with regard to the formation of assimilates is that sucrose and starch formation are not only compartmented within cells, but in C4 plants also may be largely compartmented between mesophyll and bundle-sheath cells. This has been achieved together with a profound alteration of the Benson-Calvin cycle function, in that 3PGA reduction is shared between the bundle-sheath and mesophyll chloroplasts in all the C4 subtypes. Moreover, since C4 plants are polyphyletic in origin, several different metabolic and structural answers have arisen in response to the same problem of how to concentrate C02. C4 plants have three distinct mechanisms based on decarboxylation by NADP+-malic enzyme, by NAD+-malic enzyme, or by phosphoenolpy-ruvate (PEP) carboxykinase in the bundle-sheath (Hatch and Osmond, 1976). 

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