Assemblies rings with chains

Assemblies of different rings, and of rings with chains... 

An important feature of this program is its ability to provide conformation search capability and to generate next best models. Because the program finds and evaluates more than one analogy for each subcomponent, the user can ask to see what the model would look like if a specified ring assembly, ring or chain is replaced with the closest substructure analogy. 

The F0 portion of bacterial ATP synthase, which is embedded in the membrane, consists of one 271-residue subunit a, an integral membrane protein probably with five transmembrane helices,231 232 two 156-residue b subunits, and - twelve 79-residue c subunits. The c subunit is a proteolipid, insoluble in water but soluble in some organic solvents. The structure of monomeric c in chloroform methanol H20 (4 4 1) solution has been determined by NMR spectroscopy. It is a hairpin consisting of two antiparallel a helices.233 Twelve of the c subunits are thought to assemble into a ring with both the N and C termini of the subunit chains in the periplasmic (or intermembrane) face of the membrane.234 235 The ratio of c to a subunits has been difficult to measure but has been estimated as 9-12. The fact that both genetically fused c2 dimers and c3 trimers form function F0 suggested that they assemble... 

The assembly of polypeptide chains into functional fibrinogen molecules has been studied in several expression systems. The order in which the polypeptide chains are joined together by disulfide bonds has been determined and specific structural features that are important for assembly, such as the coiled-coil, have been identified (Xu et al., 1996). Substitution of the cysteines with serine showed that the interchain disulfide ring at the proximal end of the coiled-coil, in addition to the disulfides between the two halves of the molecule, are necessary for assembly of the two half molecules (Zhang and Redman, 1996). The distal interchain disulfide ring is not necessary for assembly of the two half molecules but is necessary for secretion. Disruption of intrachain disulfide bonds and deletions of portions of the polypeptide chains have revealed which... 

The strategy of this synthesis is different from that for the examples described above. Heathcock assembles a peptide chain of the S-protected 2-methylcysteines and closes all four thiazoline rings simultaneously at the end. The synthesis of the peptide (Scheme 16) starts with the coupling of the 2-methylcysteine compounds ent-25 and 26. 

Fig. 23 Schematic illustration of the different types of motion (a) axial directional motion with chain assembly, (b) in-plane rotation, and (c) axial spinning and pattern formation, of metal microrods in a 3.7-MHz acoustic field. AuRu rods (gold-silvery colour in dark image) showed similar behaviour to of Au rods, except that they moved from the Ru ends (silvery end in the image) forward and aligned heat-to-tail into chains. Images (d) and (e) show chain structures and ring patterns formed by Au and AuRu rods. Reproduced with permission from [125]. Copyright 2012 American Chemical Society...

Finally, we mention the supramolecular structure of an inorganic (naked) thal-lium(I) derivative of the ferrocenyltris(pyrazolyl)borate ligand [179]. In this complex two pyrazole groups close a chelate ring with thallium(I) (Tl-N 2.638 and 2.676 A) and the third forms an intermolecular TI- -N bond (2.780 A) leading to self-assembly into infinite chains. 

An alternative way to construct an anion-controlled, self-assembled polymer is with 57, which has a shortened ethylene chain instead of the pentamethylene spacer used in 56. In this case, the molecules are assembled through trigonal Ag(I) nodes to form a hexanuclear ring with a diameter of about 31.5 A. As shown in Figure 32, three urea groups are directed toward the cavity and involved in coordinating two nitrates via a total of 12 H-bonds (N- O = 2.960 to 2.944 A) to form a Borromean weave. Each nitrate ion is surrounded by three urea groups from three different molecules with six H-bonds, whereas the other nitrate (interanion distance of 3.21 A) is linked with... 

Oligorotaxanes of the order Mn 9000 Daltons (nine repeat units) have been prepared by reacting a polyether chains, symmetrically substituted with hydroquinol rings with methylene bis(4-phenyl-isocyanate). The solubility of the system in typical solvents imposed limitations on characterisation. The intense orange colours did indicate that we had accomplished the objective of self-assembling pseudo-oligorotaxanes. 

The synthesis of polypeptides by ring-opening polymerization is an area that has been under study for more than five decades. Initially, this field suffered from limitations that necessitated excessive sample purification and fractionation to obtain well-defined polypeptides. Over the last 15 years, vast improvements in NCA polymerizations now allow the synthesis of a variety of block copolypeptides of controlled dimensions (molecular weight, sequence, composition, and molecular weight distribution). Many different block copolypeptides have now been prepared and used to form self-assembled structures with promising properties. The ability to easily adjust chain conformation and functionality in polypeptides, in combination with advanced synthetic methods that enable preparation of complex sequences, has opened up a new, promising field of materials with a wide range of tunable properties. 

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