Chain structure assembly followed

Despite their enormous structural diversity, polyketide metabolites are related by their common derivation from highly functionalised carbon chains whose assemblies are controlled by multifunctional enzyme complexes, the polyketide synthases (PKSs) which, like the closely related fatty acid synthases, catalyse repetitious sequences of decarboxylative condensation reactions between simple acyl thioesters and malonate, as shown in Fig. 3 [7]. Each condensation is followed by a cycle of modifying reactions ketoreduction, dehydration and enoyl reduction. In contrast to fatty acid biosynthesis where the full cycle of essentially reductive modifications normally follow each condensation reduction, the PKSs can use this sequence in a highly selective and controlled manner to assemble polyketide intermediates with an enormous number of permutations of functionality along the chain. As shown in Fig. 3, the reduction sequence can be largely or entirely omitted to produce the classical polyketide intermediate which bears a carbonyl on every alternate carbon and which normally cyclises to aromatic polyketide metabolites. On the other hand, the reductive sequence can be used fully or partially after each condensation to produce highly functionalised intermediates such as the Reduced polyketide in Fig. 3. Basic questions to be answered are (i) what is the actual polyketide intermediate... 

Polymer chain structures include the chemical structures (known as primary structures) and conformation structures (known as secondary structures and further assembly stmctures). We first introduce the characterizatiOTi of chemical structures of polymer chains, followed in the next chapters by the Gaussian treatment of their ideal-chain conformations and by the scaling analysis of their non-ideal-chain conformations, respectively. The conformations of self-assembled block copolymers as well as the conformations of crystalline polymers will be introduced in Chaps. 9 and 10, respectively. 

The HT-HT PATs undergo a solid-state macromolecular self-assembly and give self-oriented structures, as determined by X-ray diffraction studies. PDDT induces the formation of planar main chain structures and has the greatest effective conjugation length, followed by HT-HT POT, HT-HT PHT and HT-HT PBuT [99]. 

The growing polyketide chain passes from the ACP to the KS of the following downstream module, where further elongation and modification is carried out. The polyketide chain is therefore translocated from module to module until the final polyketide structure is assembled. Following the final elongation cycle, a thioester-ase (TE) domain catalyses hydrolysis or lactonisation, which releases the polyketide chain from the PKS (Fig. 1.5) [16]. 

A similar route has been followed most recently by Weiss et al. who have fabricated a multi-island SE device from self-assembled ID gold nanocrystal chains [28]. They assembled thiol-stabilized 50 nm Au particles in a chainlike structure and used subsequently electron-beam lithography for electrode fabrication. Here it has to be... 

As a result of the branched chain architecture, TASP molecules exhibit some unique conformational properties)5 12-14 47 75 76 148 For example, the folding to a compact state proceeds via two distinct steps the onset of secondary structure in the attached peptide blocks followed by their template-directed self-assembly to a three-dimensional packing topology. Due to its characteristic branched chain connectivity, the conformational space accessible in the unfolded state is considerably reduced compared to a linear chain of similar size (excluded volume effect), resulting in a smaller chain entropy. Thus, folded TASP molecules are expected to show higher thermodynamic stability compared to unbranched polypeptides of comparable size. 

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