Conformational properties of cylindrical rod brushes consisting of a flexible polystyrene main chain and poly(n-hexyl isocyanate) (PHIC) rod side chains have thoroughly been studied by static light and small-angle X-ray scattering (SAXS) in tetrahydrofuran (THF) at 25 °C. These rod brushes were prepared by radical homopolymerization of 4-vinylbenzyloxy-ended PHIC macromonomers (1) (VB-HIC-N s , where N s is the weight-averaged degree of polymerization of HIC and in a range from 21 to 80) in n-hexane at 60 °C. The mean-square cross-sectional radius of gyration (〈R c 2 〉 0 ) of the brush at an infinite dilution is determined by SAXS measurement and rationalized as a function of N s . The experimental value of 〈R c 2 〉 0 gradually increases with N s but above N s higher than 20 increases to follow the scaling law of 〈R c 2 〉 0 ∝ N s 0.87 . The experimental N s dependence of 〈R c 2 〉 0 is compared to that from the wormlike comb model whose main and side chains have different stiffness parameters. The molecular weight dependence of z-averaged mean-square radius of gyration (〈R g 2 〉 z ) of the brush is determined and analyzed in terms of the wormlike cylinder model taking into account the end effects. The parameters characteristic of the rod brush in THF solution, such as the main chain stiffness parameter (λ M -1 ), the molecular weight per unit contour length (M L ), and the excluded-volume strength (B), are determined and rationalized as a function of the contour length of the side rod. The polystyrene main chain stiffness of the rod brush remarkably increases by the densely located rod side chains to follow the scaling law of λ M -1 ∝ N s 1 . The backbone stiffness of the rod brush is higher than that of the flexible brush consisting of flexible polystyrene side chains with the corresponding contour length. A single rod brush of poly(VB-HIC-47) deposited on a mica surface is observed by the scanning force microscopy to reasonably demonstrate the cylindrical rod brushes.

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Small-angle X-ray scattering (SAXS), which determines the radius of gyration, R(g), and the pair distance distribution function, was used to investigate the conformational changes of calmodulin (CaM) on binding to an antagonist, trifluoperazine (TFP), with or without Ca(2+) in solution. We previously applied this SAXS method to CaM complexed with N-(6-aminohexyl)-5-chloro-1-naphthalenesulphonamide (W-7) [Osawa, Kuwamoto, Izumi, Yap, Ikura, Shibanuma, Yokokura, Hidaka and Matsushima (1999) FEBS Lett. 442, 173-177] and found that the binding of two W-7 TFP molecules to one Ca(2+)-saturated CaM molecule induces structural changes from a 'dumb-bell' shape to a compact globular shape. We report here that the most compact globular shape whose size is consistent with that of the 1:2 Ca(2+)-saturated CaM-W-7 complex is formed by the binding of four TFP molecules to one Ca(2+)-saturated CaM molecule. Even in the absence of Ca(2+), the conformational changes of CaM occur on TFP binding, giving a slightly smaller R(g) than Ca(2+)-free CaM alone.

ABSTRACT:SEC-MALS, small-angle X-ray scattering (SAXS), and viscosity measurements were made on tetrahydrofuran (THF) and n-hexane of a series of 4-vinylbenzyl and methacrylate ended poly(n-hexyl isocyanate) (PHIC) macromonomers (VB-HIC-n and MA-HIC-n, where n is a degree of polymerization of HIC and in a range from 21 to 192), together with higher molecular weight PHIC chains than the macromonomers. The molecular weight dependence of z-average mean-square radius of gyration hRg 2 i z and intrinsic viscosity [] of the macromonomers and PHIC chains in THF at 25 C were quantitatively described by the wormlike chain model with the stiffness parameter ð À1 Þ ¼ 63 nm, the molecular weight per unit contour length ðM L Þ ¼ 725 nm À1 , and the hydrodynamic diameter ðd B Þ ¼ 1:6 nm. The SAXS scattering profile of VB-HIC-57 in n-hexane at 25 C was also perfectly described in terms of the straight cylinder model. The results imply that the macromonomers may be regarded as a rigid rod molecule in THF and n-hexane. Cylindrical brushes consisting of polystyrene as a main chain and PHIC chains as a side chain were prepared by homopolymerizations of VB-HIC-46 and their dimensional properties were investigated in THF at 25 C by SAXS and SEC-MALS measurements. The molecular weight dependence of hRg 2 i z of the brushes was quantitatively explained by the wormlike cylinder model with the parameters of À1 ¼ 48 nm, M L ¼ 2:40 Â 10 4 nm À1 , the cross-sectional radius of gyration of the cylinder hRc 2 i o 1=2 ¼ 4:66 nm, and the end effect ( ¼ 16:7 nm) arising from side chains near the mainchain ends. It was concluded, therefore, that the main chain stiffness of the brush remarkably increases by the presence of densely located rodlike side chains. Direct observation of single brush of the poly(VB-HIC-46) deposited on a mica was made by scanning force microscopy (SFM) to reveal the cylindrical brushes consisting of rodlike side chains with ca. 15 nm in a thickness.

The isotropic-liquid crystal (cholesteric) phase boundary concentrations for aqueous solutions of xanthan, an ionic double-helical polysaccharide, were determined as functions of the molecular weight of xanthan and the added sodium chloride concentration. The phase boundary concentrations increased sharply with decreasing molecular weight at low molecular weights, as in the case of neutral stiff polymer solutions, and depended strongly on the added salt concentration. The latter dependence demonstrates the importance of the electrostatic interaction between polymers in the isotropic-liquid crystal phase equilibrium. These experimental results were compared with two theories: the Onsager theory extended by Odijk to semiflexible polyelectrolyte solutions and a perturbation theory proposed by us (Sato, T.; Teramoto, A. Physica A 1991, 176,72). The latter theory succeeded in almost quantitative prediction of the experimental phase boundary concentrations for xanthan. The same comparison was performed on two other rigid polyion systems: tobacco mosaic virus and DNA.