To investigate the effects of pH on the structure and the properties of DNA anisotropic gels and their growth process, we have observed the morphology of DNA anisotropic gel films prepared from DNA solutions with various initial pH, and measured the pH dependences of the shrinking ratio, the birefringence, and the relaxation modulus of the gel as well as the time courses of the gel front and pH-change front lines. The gel films prepared from DNA solutions with high pH have inhomogeneous macroscopic structure, large shrinking ratio, and high optical anisotropy whereas those prepared from DNA solutions with low pH have homogeneous macroscopic structure, small shrinking ratio, and low optical anisotropy. The difference observed at different pH is attributed to the difference in the interaction between DNA molecules and aluminum cations. The time courses of the gel front and pH-change front lines were analyzed with theories based on assumptions for each condition. Both two-stage dynamics observed under high initial pH and one-stage dynamics under low initial pH were explained consistently with the theories.
A new series of chiral dopants, (R)-6,6 0 -halogenated (1b-1e, X ¼ F, Cl, Br and I) and -methylated (1f) binaphthyl compounds, were designed and synthesized to create chiral liquid crystals by doping them into an achiral nematic liquid crystal (NLC). The influence of halogen (X ¼ F, Cl, Br and I) and methyl substituent factors, such as steric, polar, and polarizability properties, on the helical twisting power (HTP) and their temperature dependences on the chiral dopants were investigated in two host NLCs with different characteristics, fluorinated JC-1041XX and N-(4-methoxybenzylidene)-4-butylaniline (MBBA). The chiral dopants possessing less steric and larger polarizability factors increased the HTP values. The structural similarity and electrostatic arene-arene interactions between the chiral dopants and the NLC molecules also exerted important influences on these values. The temperature dependence of the HTP (HTP t.d. ) values also correlated well with the steric and polarizability substituents factors in the two host NLCs. Their correlation coefficients (R 2 ) depended on the molecular structural similarity between the chiral dopant and the NLC. Fig. 1 The chemical structures of synthesized chiral dopants.Fig. 2 (a) The optimized structure; (b) the numbering of 1a. Scheme 1 Synthetic route for the synthesis of 1a-f. 972 | RSC Adv., 2018, 8, 971-979 This journal is
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