title: Pronounced Dielectric and Hydration/Dehydration Behaviors of Monopolar Poly(N-alkylglycine)s in Aqueous Solution.
abstract: Poly(N-methylglycine) (NMGn) and poly(N-ethylglycine) (NEGn) obtained by polymerization reactions initiated by benzylamine have no carboxy termini, such as those in normal polyamides, but have only amino termini, which exist primarily as cations in aqueous media at a pH value of ca. 9.5, observed in aqueous solutions without any buffer reagents. Therefore, polypeptoids, such as NMGn and NEGn, possessing a degree of polymerization (DP) higher than a certain value behave as cationic monopolar polymeric chain molecules in aqueous solution. It has not been clarified so far whether such a monopolar chain molecule exhibits dielectric relaxation (DR) behavior resulting from its molecular motions in aqueous media as dipolar chain molecules. DR measurements revealed that NMG19 and NEG17, possessing DPs of 19 and 17, respectively, dissolved in pure water clearly demonstrated pronounced DR behavior caused by fluctuating molecular motions of cationic termini at relaxation times of ca. 4 and 9 ns at 10 °C (283 K). The hydration numbers of NMG19 and NEG17 per monomeric residue (nm) in aqueous solution were also evaluated via DR data as functions of temperature, and the nm value of ca. 4.5 at 10 °C showed a remarkable reduction to ca. 2.0 around 40 °C (313 K) and 30 °C (303 K), depending on differences in the substituted group: methyl and ethyl groups. This temperature-dependent hydration/dehydration behavior found in NMG19 and NEG17 slightly influenced the sizes and molecular dynamics of the monopolar chain molecules in aqueous solution.
authors: Kengo
authors: K
authors: Arai
authors: Naoya
authors: N
authors: Sagawa
authors: Toshiyuki
authors: T
authors: Shikata
authors: Department of Chemistry and Macromolecular Studies Group, Louisiana State University , Baton Rouge, Louisiana 70873, United States.
authors: Garrett L
authors: GL
authors: Sternhagen
authors: Department of Chemistry and Macromolecular Studies Group, Louisiana State University , Baton Rouge, Louisiana 70873, United States.
authors: Xin
authors: X
authors: Li
authors: The Molecular Foundry, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
authors: Li
authors: L
authors: Guo
authors: Biology and Soft Matter Division, Neutron Sciences Directorate, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States.
authors: Changwoo
authors: C
authors: Do
authors: Department of Chemistry and Macromolecular Studies Group, Louisiana State University , Baton Rouge, Louisiana 70873, United States.
authors: Donghui
authors: D
authors: Zhang