Conformation of poly(γ-glutamic acid) in aqueous solution.

Local conformation and overall conformation of poly(γ-DL-glutamic acid) (PγDLGA) and poly(γ-L-glutamic acid) (PγLGA) in aqueous solution was studied as a function of degree of ionization ε by (1) H-NMR, circular dichroism, and potentiometric titration. It was clarified that their local conformation is represented by random coil over an entire ε range and their overall conformation is represented by expanded random-coil in a range of ε > ε(*) , where ε(*) is about 0.3, 0.35, 0.45, and 0.5 for added-salt concentration of 0.02M, 0.05M, 0.1M, and 0.2M, respectively. In a range of ε < ε(*) , however, ε dependence of their overall conformation is significantly differentiated from each other. PγDLGA tends to aggregate intramolecularly and/or intermolecularly with decreasing ε, but PγLGA still behaves as expanded random-coil. It is speculated that spatial arrangement of adjacent carboxyl groups along the backbone chain essentially affects the overall conformation of PγGA in acidic media.

Studies on the conformation of a polyelectrolyte in solution: local conformation of cucumber green mottle mosaic virus RNA compared with tobacco mosaic virus RNA.

The thermal stability of the local structures of cucumber green mottle mosaic virus RNA, CGMMV-RNA, and tobacco mosaic virus RNA, TMV-RNA, was studied by circular dichroism (CD) and small-angle X-ray scattering (SAXS) and compared with each other in the temperature domain from 20 to 50 degrees C. The temperature dependence of the molar ellipticity and mean-square radius of the cross section of a chain shows that the structure of CGMMV-RNA is more vulnerable than that of TMV-RNA. Such a different thermal stability of their structures was also reflected in the temperature dependence of the length and number of the constituent rods when the structures of the two RNA chains were represented by a model which consisted of rods joined with freely hinged joints. From these results, a possibility was suggested that the structural stability of CGMMV-RNA and TMV-RNA might be correlated with the infectivity of the corresponding virus, CGMMV and TMV, respectively.

Change of the persistence lengths in the conformational transitions of pullulan- and amylose-tricarbanilates.

With raising temperature in the domain of 20 to 60 degrees C, the intrinsic viscosity [eta] for pullulan-tricarbanilate PTC and amylose-tricarbanilate ATC in solutions was found to decrease, indicating that they exhibited thermal-induced conformational transition from expanded form to compact form. The persistence length P(l) of the chains, evaluated with small-angle X-ray scattering, has also decreased as the temperature is raised and, moreover, it significantly depended on the solvents employed, where as P(l) of pullulan, having no carbanilate groups, has exhibited neither temperature- nor solvent-dependence. The temperature dependence of [eta] for PTC and ATC was well elucidated in terms of the temperature-dependent P(l) with the wormlike chain model. From these results, it is suggested that intramolecular hydrogen bonds would be formed between carbanilate groups neighboring along the backbone chain, but they are gradually and cooperatively collapsed as the temperature is raised, inducing the conformational transition.

Conformation of poly(sodium ethacrylate) in solution studied by small-angle X-ray scattering.

The pH-induced conformational transition of poly(sodium ethacrylate) PNaEA in aqueous solution, which occurs between a compact form at low charge-density and an extended coil at high charge-density, was studied by small-angle X-ray scattering and the structure at an each conformational state was analyzed and compared with the corresponding one of poly(sodium methacrylate) PNaMA. The conformational transition for PNaEA induced a remarkable change in the scattering data plotted in the form of the Kratky plot. By comparing the scattering data with theoretical scattering functions, it was clarified that the structures of the compact form and the extended coil are well mimicked by a swollen gel having a network structure and by a wormlike chain, respectively. Although such a structure of the extended coil of PNaEA is similar to the corresponding one of PNaMA, the structure of the compact form of PNaEA is different from the corresponding one of PNaMA, which is still represented by a wormlike chain in a Theta medium.