Oligomer asymmetry

Association constant. See Formation constant Astacin 627 Asthma 26, 385 Asymmetric unit of crystal 134 Asymmetry of molecules 41-43 handedness 41-43 in oligomers 344 Ataxia telangiectasia 566, 574 Atomic force microscope 131 diagram of 131... 

Polymers are substances of high molecular weight made up of repeating monomer units. Substances with short chains containing relatively few monomers are called oligomers. Polymers owe their unique properties to their size, their three-dimensional shape and sometimes to their asymmetry. The chemical reactivity of polymers depends on the chemistry of their monomer units, but their properties depend to a large extent on the way the monomers are put together it is this fact that leads to the versatility of synthetic polymers. 

In a similar manner, the coalescence temperature for the methyl groups of the tetramer was determined as 4°C. AG was calculated as 12.7 kcal/mol which was 3.7 kcal/mol smaller than that for the pentamer. The hexamer showed a total of seven signals with narrow linewidth due to two methyl groups and six methine protons even at 70°C, indicating that the rate of helix sense reversal is much slower than the rate for the pentamer. This suggests the possibility that the symmetrical oligomers over the pentamer level may be optically resolved at room temperature based entirely on conformational asymmetry. This was confirmed by the chiral HPLC technique using (+)poly(triphenylmethyl methacrylate) as a stationary phase.282... 

Asymmetric induction (See also Enantioselective) chiral ketones, 62, 106-107 chiral sulfoxides, 8-9 steroid synthesis, 27, 278-281 Asymmetric syntheses. See Enantioselective. .. Asymmetry of vesicle membranes, 351 dATP. See 2 -Deoxynucleoside 5 -triphosphates Atropisomers binap chelands, 102-103 Kemp s acid arylimides, 347 porphyrin oligomers, 348—349 5,10,15,20-tetraarylporphyrins, 253 Axial/equatorial stereoselectivity ... 

Rg. 9. The stability of an oligomer depends on concentration. (A) The variation of Tmax with concentration is shown for a dimer with 7 ° = 100 C, AH = lOOkcal/mohandACp = lOOOcal/deg/mol. The concentration dependence is logarithmic (B) and does not plateau at high concentrations. The T° is defined as the T at 1.0 Af protein, 100°, which differs slightly from the T az that would be observed at 1.0 A/ protein because of the asymmetry of the endotherm. 

The superimposition of contact forces reduces the asymmetry of particles. For large association constants, elongated columnar assemblies L/D > 1) will be formed with individual disks separated by short separation distances and no longer freely rotating. The A d phase is disfavored with an evolution toward cubatic phases L/D = 1) [168] and rodlike L/D > 1) behavior. For weak equilibrium constants only short oligomers are expected, and the A d phase will be simply shifted to larger critical concentrations due to the modest increase of particle thickness. 

Mesoscopic supramolecular assemblies are also obtainable in organic media from amphiphilic linear networks of complementary hydrogen-bonds. An equimolar mixture of bw-barbituric acid derivative 18 and 1 gave helical superstructures with a minimum width of 50 A (Figure 12(c), note that the components are achiral, but compound 18 displays molecular asymmetry) [86]. The observed thickness corresponds to the three-layered membrane structure schematically depicted in Figure 12(d). Soluble, tapelike supramolecular oligomers can be also prepared, by the covalent preorganization of melamine units [87]. 

Helical polymers with optical activity arising entirely from macromolecular asymmetry are a relatively new development and represent an exciting area for future study. From our oligomer studies. 

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