Trimeric complexes representation

Color plate 11. Schematic representations of the transmembrane a-helices of a PS-I monomer complex in top (A) and side view (B) and a trimer complex in top view (C). 

C) Schematic representation of a PS-I trimer complex. It includes all identified a-helices, core antenna Chl-a molecules and cofactors of the electron-transfer chain. Note the greater separation between the Chl-a molecules in the trimerization domain than inside the monomer domain. 

Figure 7. The s-Keggin (top, left) and the 5-Keggin isomers (top, right) of the Ain complex in polyhedral representation. The s- and 5-Keggin isomers differ by rotation of a single trimeric group of Al(0)e octahedra by 60°. These combine to form the AI30 structure (bottom), which consists of two 5- isomers linked by four AlOe octahedra.

A) The quaternary structure of aspartate transcarbamoylase as viewed from the top. The schematic drawing at the right is a simplified representation of the relationships between subunits. A single trimer [catalytic (c) chains, shown in orange and yellow] is visible in this view, the second trimer is hidden behind the one visible. (B) A side view of the complex. 

Recent independent syntheses of both the symmetrical (240a) and unsymmetrical (2400) trimers have shown that it was in fact the former which was produced in the above reactions. Its preparation involves the reaction of 2-iodo-iV-methylindole with activated copper-bronze or simply heating A-methyl-2-indolyl copper. Only a small amount of the unsymmetrical trimer (240b) was obtained from these reactions by a path which was concluded not to involve 2,2 -biindolyl species similar to 243. The mechanism of formation of the trimers (240) was proposed to proceed by the stepwise trimerization of the hetaryne-Cu complex (246). While these results are consistent with a copper-containing intermediate, it is not clear that 246 would be its best representation. An oligiomeric structure as proposed for JV-methyl-2-indolyl copper and the o-phenylenemercury compound 125 (Section II. 1.F) cannot be excluded. 

Figure 9.9 (Left) Structural representations of pillararene trimer H9.14, guest G9.1, and the proposed mechanism for the formation of vesicular assemblies under low concentration. (Right) Morphologies of the complex between pillararene trimer H9.14 and guest G9.1 at low concentration, (a) Negative-stained TEM image (scale bar 0.5 pm), and (b) gold sputtering SEM image (scale bar 10 pm) at a sample concentration of 1 mM.

Fragmentation after intramolecular transfer results in the formation of a long-chain radical and trimer species or a dimer radical and an unsaturated dead chain (Scheme 4.13). Consideration of all possible pathways and structures becomes complex, but the resulting model requires no additional parameters from the homopolymerization back-biting/scission case and provides a good representation of high temperature acrylate-methacrylate copolymerization [70]. 

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