Small-angle X-ray scattering study on conformation of poly(sodium L-glutamate) in NaCl and NaF aqueous solutions

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The effect of anions F− and Cl− on the conformation of poly(sodium l-glutamate) (PNaGA) in added-salt aqueous solution was studied using potentiometric titration, high-resolution proton nuclear magnetic resonance (NMR), circular dichroism (CD) and small-angle X-ray scattering (SAXS) techniques. In the titration curve for PNaGA in NaCl aqueous solution, four conformation regions, i.e. aggregation-, helical-, helix-to-coil transition- and random-coiled, were clearly observed but these regions were gradually obscured when the concentration of F− was increased. Both CD and NMR spectra have clarified that the local conformation of PNaGA in NaF aqueous solution is a random-coiled state, independent of the degree of neutralization (DN). SAXS studies show that the conformation of a larger dimension for PNaGA having DN = 0.25 in 0.2 NaF aqueous solution is roughly mimicked by a worm-like chain having persistence length of ca 5.9 Å, but the conformation at DN = 0.80 is far from an isolated worm-like chain.