Chirality order

It is considered that, if ideal, optically active poly(alkyl(aryl)silane) homopolymer and copolymer systems could be obtained which had stiffer main-chain structures with longer persistence lengths, it should be possible to clarify the relationship between the gabs value and the chiral molar composition. The magnitude of the chirality of the polyisocyanates allowed precise correlations with the cooperativity models.18q In the theory of the cooperative helical order in polyisocyanates, the polymers are characterized by the chiral order parameter M, which is the fraction of the main chain twisting in one helical sense minus the fraction of the main chain twisting in the opposing sense. This order parameter is equal to the optical activity normalized by the value for an entirely one-handed helical polymer. The theory predicts... 

The mixing of nematogenic compounds with chiral solutes has been shown to lead to cholesteric phases without any chemical interactions.147 Milhaud and Michels describe the interactions of multilamellar vesicles formed from dilauryl-phosphotidylcholine (DLPC) with chiral polyene antibiotics amphotericin B (amB) and nystatin (Ny).148 Even at low concentrations of antibiotic (molar ratio of DLPC to antibiotic >130) twisted ribbons are seen to form just as the CD signals start to strengthen. The results support the concept that chiral solutes can induce chiral order in these lyotropic liquid crystalline systems and are consistent with the observations for thermotropic liquid crystal systems. Clearly the lipid membrane can be chirally influenced by the addition of appropriate solutes. 

Very recently, an exciting approach to control the chiral ordering in optically active polythiophenes by a doping process has been reported [130]. It was found that the addition of Fe(C104)3, NaS03CF3, or AgS03CF3 to chiral polythiophenes had a dramatic effect on the chiral arrangement of the polymer chains. No detailed description of the nature of the helical... 

ZB Zhang, M Fujiki, M Motonaga, and CE McKenna, Control of chiral ordering in aggregated poly 3-(S)-[2-methylbutyl]thiophene by a doping-dedoping process, J. Am. Chem. Soc., 125 7878-7881, 2003. 

For chiral classes we showed above, under the restriction to achiral ligands, that the chirality order has the lower limit n — 3 and the upper limit n which characterizes chiral skeletons. If chiral ligands are admitted we have the relation o o+ and therefore the same limits for o. 

It is possible for chiral mesogens to produce essentially achiral mesophases. For instance, in certain ranges of concentration and molecular weight, DNA will form an achiral line hexatic phase. A curious recent observation is of the formation of chiral mesophases from achiral mesogens. Specifically, bent-core molecules (sometimes called banana LCs) have been shown to form liquid crystal phases that are chiral. In any particular sample, various domains will have opposite handedness, but within any given domain, strong chiral ordering will be present. 

Simidjiev, L, Barzda, V., Mustardy, L., and Garab, G. 1997. Isolation of lamellar aggregates of the light-harvesting chlorophyll a/b protein complex of photosystem II with long-range chiral order and structural flexibility. Anal. Biochem. 250 169-75. 

A theoretical study of numerous chiral molecules including bridged biaryls 5 and 6 has been undertaken using a molecular Monte Carlo simulation approach coupled with calculations of molecular chirality based on a chirality order parameter. The method successfully predicts the helical twisting powers <2003JCP10280>. 

Ernsting, M.J., Labow, R.S., and Santerre, J.P. "Human monocyte adhesion onto RGD and PHSRN peptides delivered to the surface of a polycarbonate polyurethane using bioactive fluorinated surface modifiers". ] Biomed. Mater. Res. A 83A(3), 759-769 (2007). Ewbank, P.C., Nuding, G., Suenaga, H., McCullough, R.D., and Shinkai, S. "Amine functionalized polythiophenes Synthesis and formation of chiral, ordered structures on DNA substrates". Tetrahedron Lett 42(2), 155-157 (2001). 

An analogous enhancement in the optical rotatory power of the isotropic phase of a thermotropic liquid crystal has been observed near the isotropic-cholesteric phase transition. Patel and DuPre concluded that it is attributable to short-range chiral ordering of the long axes of the macromolecules. 

It is worth mentioning that the helix-coil model without long-range interactions found applications far beyond the area of DNA biophysics. Among other applications, the model has been extensively used to study of helix-coil transition in polypeptides and most recently it was used by Selinger and Selinger (1996) [64] to explain experimental data on chiral order in random copolymers consisting of two enantiomers. 

Figure 40. Order-disorder patterns in artificial me-sogens and native biomesogens promoting spatial chiral order-disorder distributions into spatiotempo-ral coherences (top to bottom) amphotropic DNA/ prealbumin complex [10], reminiscent in its order-disorder distributions of the simple achiral thermotropic n-alkoxybenzoic acid dimers [52 fj periodic and chaotic oscillations of multiple oscillatory states in glycolysis [78] - all this superimposed on the details of the very event - modeling in all its interfacial relationships early evolutionary origins of the nu-cleoproteinic system and its inherent structure-phase dualities [7 a, 16,17, 18].

With LC (Nikolova et al., 1997) or preoriented amorphous samples (Ivanov et al., 2000), one can photoinduce a chiral domain structure. Incident circularly polarized light becomes elliptically polarized because of the first oriented layer. This ellipse subsequently reorients deeper chromophores, which in turn modify the ellipticity of the light. This reorientation continues throughout the film depth. Overall, a chiral ordering of the chromophore domains is established (Nikolova et al., 2000). Remarkably, one can switch between a right- and left-handed... 

The maximum number of identical ligands which may occur for chiral molecules is the chirality order o (15). It is a characteristic for the chirality phenomenon of a given molecular class with n ligands. Then, N — n — o) is the... 

R. Macdonald, F. Kentischer, P. Warnick and G. Heppke, Antiferroelectric-ity and chiral order in new liquid crystals of nonchiral molecules studied by optical second harmonic generation, Phys. Rev. Lett. 81(20), 4408-4411,... 

Ewbank, P.C., G. Nuding, H. Suenaga, R.D. McCullough, and S. Shinkai. 2001. Amine functionalized polythiophenes Synthesis and formation of chiral, ordered structures on DNA substrates. Tetrahedron Lett 42 (2) 155—157. 

A better mechanical performance of the all-cellulosic composites reported here could also be achieved taking advantage of Uquid crystalline projjerties of aqueous suspensions of acid hydrolysed microdystaUine cellulose (MCC) [43,44]. A chiral ordering of MCC aqueous suspensions was observed for various cellulose origins... 

Deb, R. Nath, R. K. Paul, M. K. Rao, N. V. S. Tuluri, F. Shen, Y Shao, R. Chen, D. Zhu, C. Smalyukh, I. I. Clark, N. A. Four-ring achiral unsymmetrical bent core molecules forming strongly fluorescent smectic hquid crystals with spontaneous polar and chiral ordered B7 and B1 phases. J. Mater. Chem. 2010, 20, 7332-7336. 

Weissflog, W. Sokolowski, S. Dehne, H. Das, B. Grande, S. Schroder, M. W. Eremin, A. Diele, S. Pelzl, G. Kresse, H. Chiral ordering in the nematic and an optically isotropic mesophase of bent-core mesogens with a halogen substituent at the central core. Liq. Cryst. 2004, 31, 923-933. 

Figure 3 An example of a VT-CD experiment. A dithienopyr-role polymer 2 shows a temperature-controlled random coil-helix transition. The bisignate Cotton effect observed at lower temperatures indicates the helical chiral ordered conformation, while the CD becomes almost silent at higher temperatures, which suggests the absence of the chiral orientation of chromophores. Schematic representations of a random coil and a helix conformation of 2 are also shown. (Reprinted with permission from Ref. 8. Copyright 2008 American Chemical Society.)...

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