Intramolecular cholesteric phase

Shivaprakesh et al.(16) found that Intensities and fine structure of carbonyl IR absorptions of several cholesteryl esters decrease in the cholesteric phase relative to the solid phase. Presumably, the greater motion in the cholesteric phase destroys the inter- and Intramolecular couplings responsible for fine structure. Earlier, Bulkin and Krlshnan (17) reached a similar conclusion based upon Raman studies of cholesteryl esters. They determined that alkyl chains of the esters are... 

For instance, mechanistically important inductions of optical activity have been observed in products from unlmolecular transformations of achiral solutes when conducted in cholesteric phases. These transformations involve selection by solvent matrices between subtle intramolecular shape changes of the solutes. Thus, Nakazakl et al.(20) found that irradiation of phenyl - 2-(2-benzo-[c]phenanthryl)ethylene and I2 in the cholesteric phase of 3/2 (w/w) cholesteryl nonanoate/... 

These considerations are exemplified by the efficiency of intramolecular fluorescence quenching of N,N-dimethyl-4-[3-(l-pyrenyl)propyl]aniline (PID.) as studied in the isotropic and cholesteric phases of M(38). The mechanism for (non-eraissive) exciplex formation could be accommodated in both phases to Scheme 2. 

Subsequently, the kinetics of intramolecular pyrenyl excimer formation were examined in CH for a series of PnP which includes polymet - lene chains much longer than that of P3P (i.e., n-3, 5, 6, /, " 10, 11, 12, 13, 22). The dynamic behavior of these compo in normal isotropic solvents of low viscosity is known to be Vm j complex(45). However, in both the isotropic and cholesteric phases of CH, all of the temporal emission data for the PnP could be accommodated by Scheme 2. The pyrenyl decay waveforms were monoexponential and the excimer waveforms could be expressed as the difference between two exponentials (representing the growth and decay of excimer emission). Temperature dependent ki+k2 values for P3P were obtained as before from Z the ki+k2 for the other PnP were taken from experiments with 1-dodecyIpyrene (DP). 

LCs were the earliest studied structures, in which polypeptide homopolymer rods pack in an ordered manner to form smectic, nematic, and cholesteric phases. The smectic LCs are mainly formed by polypeptide homopolymers with identical polymer length. The cholesteric phase can be prepared by synthetic polypeptides with polydisperse chain length. The nematic phase can be regarded as a special example of the cholesteric phase with an infinite cholesteric pitch. The cholesteric pitch and chirahty in the polypeptide LCs are dependent on many factors, such as temperature, polymer concentration, solvent nature, and polypeptide cOTiformation. Deep understanding of such phenomena is necessary for preparation of ordered polypeptide assembles with delicate stmctures. The addition of denaturing solvent to polypeptide solution can lead to an anisotropic-isotropic reentrant transition at low temperatures where the intramolecular helix-coil transformation occurs. However, the helical structure is more stable in LC phase than in dilute solution due to the conformational ordering effect. 

PROPERTIES OF SPECIAL INTEREST Exists in a highly ordered, well-defined, a-helical conformation held intact by intramolecular hydrogen bonds. The a-helical structure renders the polymer as a relatively stiff rigid rod and is retained when the polymer is dissolved in many solvents. In these helicogenic solvents, PBLG exists as a single isotropic phase at low concentration. At higher concentrations a liquid-crystalline cholesteric phase is present. 

Sixou et al. (101) showed the circular dichroism of cholesteric CTA solutions in TFA depends on the CTA molecular weight. The intensity of the circular dichroic peak increases with molecular weight. Meeten and Navard (97) studied gel formation and liquid crystallinity in TFA-H2O solutions of CTA. When water was added to a liquid crystalline solution of CTA in TFA a gel phase formed presumably by the formation of crosslinks due to hydrogen bonding. They interpreted their results that liquid crystalline ordering involves both inter- and intramolecular forces. 

FLUORESCENCE QUENCHING OF PYRENE AS A MONITOR OF INTERMOLECULAR DIFFUSION AND INTRAMOLECULAR CHAIN BENDING IN CHOLESTERIC LIQUID CRYSTALLINE PHASES(1)... 

The rates of Intramolecular processes in anisotropic media (such as cholesteric liquid-crystalline phases) are a function of the same solvent and solute properties mentioned above and, additionally, the exigencies imposed by solvent order on the frequency and orientations of head-to-tall coll is ions(36). The importance of the latter considerations is demonstrated by the... 

Fluorescence Quenching of Pyrene as a Monitor of Inter-molecular Diffusion and Intramolecular Chain Bending in Cholesteric Liquid Crystalline Phases(l)... 

It is well known that molecules of PBG in a numbo of solvents (called coiling solvents) exist in the form of a-helixes stabilized by intramolecular hydrogen bonds. Separation of the solution into isotropic and anisotropic phases is observed in these solvents (such as dioxane, chloroform, methylene chloride, etc.) for a certain critical concentration of the polypeptide (c ) in accordance with the theoretical concepts of Flory [3] (see also Chapter 1). The anisotropic phase in a solution of PBG is separated as liquid spherulites which become larger and form a continuous anisotropic phase of the cholesteric type in cooling or concentration of the solution. 

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