Polypeptide liquid crystals

The recent studies on the structure and properties of polypeptide liquid crystals, which are formed in solution as well as in the solid state, are reviewed in this article. Especially the cholesteric pitch and the cholesteric sense (right-handed or left-handed), which are characteristic factors of cholesteric liquid crystals, are discussed in detail in relation to the effects of temperature, concentration, and solvent. Further cholesteric liquid crystalline structure retained in cast fdms and thermotropic mesomorphic state in some copolypeptides are also discussed. 

Polypeptide Liquid Crystals with unity the formula reduces to kP... 

The temperature dependence of the cholesteric pitch in the polypeptide liquid crystals has been investigated in various solvents. The pitch P is related to the twisting angle (p between neighboring molecules separated by a distance d along the axis of torsion as follows. 

The analysis of the experimental results by the theory of Kimura et al. give interesting clues for understanding the polypeptide liquid crystal. In Fig. 22 the parameters fi, which are related to the attractive dispersion force proposed by Maier and Saupe and can be obtained from the slopes in the 1/S vs. 1/T plots or the values of Tj, are plotted against the dielectric constants of solvents. B is... 

In Fig. 23 the relationship between B/kg and XA/D are shown for the polypeptide liquid crystals in various solvents. Following Eq. (25), the compensation temperature is determined by the ratio (fi/kg)/(lA/D) at a constant polymer concentration. The solid and broken lines shown in Fig. 23 correspond to the theoretical values calculated for Tjj = 25 °C and 80 °C, respectively. The solvents located above and below the solid line support the right-handed and left-handed cholesteric liquid crystals, at 25 °C, respectively. The situation is the same for the broken line at 80 °C. The solvents located between the two straight lines invert the cholesteric sense from right-handed to left-handed in the range of measurements. 

We have discussed in detail the cholesteric pitch and the cholesteric sense in polypeptide liquid crystals, centering around our own work, which had not been investigated much since Robinson had presented excellent works about a quarter of a century ago. We have show that compensation of the cholesteric sense caused by temperature and solvent can be consistently explained by the theory of Kimura et al., in which the intermolecular force is assumed as the sum of a repulsion of a hardcore with shape of a twisted rod and of dispersion forces of Maier-Saupe-Goossens type. 

Space did not permit us to discuss the electromagnetic orientation of polypeptide liquid crystals. However excellent reviews are now available. 

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