Cholesteryl propionate

Surprisingly, some Diels-Alder cycloaddition reactions show no variation in endojexo product ratio with changes in solvent phase. Ordered liquid-crystalline solvents are not able to differentiate between endo- and exo-activated complexes in the Diels-Alder reaction of 2,5-dimethyl-3,4-diphenylcyclopentadienone with dienophiles of varying size (cyclopentene, cycloheptene, indene, and acenaphthylene), when it is carried out in isotropic (benzene), cholesteric (cholesteryl propionate), and smectic liquid-crystalline solvents at 105 °C [734]. 

Johnson and Miller (67) showed that cholesteryl propionate gave a curve with three transitions crystal - smectic at 99°C smectic - cholesteric at U0°C and cholesteric - isotropic at 110°C. However, on changing the heating rate to 30°C/min, they no longer detected the 110°C peak, but detected a new, small endothermic peak at about 64°C. 

It is well known that a nematic liquid crystal readily adopts a helical configuration if a small amount of a cholesteric is added to it. For low concentrations of the cholesteric, the inverse pitch is a linear function of the concentration, but at higher concentrations the linear law is not obeyed. 44 The curve attains a maximum at a certain concentration, beyond which it decreases. It turns out, for example, that the twist per unit length of pure cholesteryl propionate is actually less than that of its... 

Figure 25. Inverse of selective reflection maxima (o=p) as a function of composition for a number of binary chiral nematic mixtures. Here the components are O cholesteryl formate/cholesteryl chloride (at 50 °C), A cholesteryl propionate/cholesteryl chloride (at60°C), cholesteryl heptanoate/cholesteryl chloride (at 60 °C), A cholesteryl laurate/cholesteryl chloride (at 60°C) [105],...

Fig. 7.14. Dependence of at T = 0.99r j on the mole fraction of the cholesterol-containing component for the copolymers of series 5 (1), 6 (2), 7 (3), 8 (4), 9 (5), 10 (6), 12 (7) (Table 7.5) and for the mixtures cfiolesterylpropionate-p-butylhydroxyben lidene-p -butylaniline (8) and cholesteryl propionate-p-butoxybenzylidene-p -aminobenzonitrile (9).

These data show that the strong side interactions between mesogenic groups, the cause of the aj earance of smectogenic properties, impede helical twisting in these systems. The dependences of on shown in Fig. 7.14 for mixtures of cholesteryl propionate with a cyano-containing nematic liquid crystal, p-butoxybenzylidene-p -aminobenzonitrile [6], indicate that the values of the helix induction force for Ais system and the copolymers in series 10 and 12 coincide. 

Fig. 13. Chemical structures of cholesteryl iopanoate and glyceryl l,2,3-tris[3-(3-amino-2,4,6-triiodophenyl)]propionate [71]...

Fig. 11.6.1. HPLC separation of cholesterol and cholesteryl ester standards. Chromatographic conditions column, Supelcosil LC-18 (250x4.6 mm I.D.) mobile phase, acetonitrile-methanol-chloroform (1 1 1, v/v/v) flow rate, 1.0 ml/min temperature, ambient detection, differential refractometer. Peaks 1, cholesterol, 2, acetate 3, propionate 4, butyrate 5, nonanoate 6, decanoate 7, arachidonate 8, laurate 9, linoleate 10, oleate 11, elaidate 12, palmitate 13, stearate. The average mass of lipid chromatographed was 20-40 ng. Reproduced from Perkins et al. (1981), with...

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