title: NMR Studies of Thermo-responsive Behavior of an Amphiphilic Poly(asparagine) Derivative in Water.
abstract: The thermo-responsive behavior of a unique biocompatible polymer, poly(N-substituted α/β-asparagine) derivative (PAD), has been studied with several NMR methods. The1H and13C solution NMR measurements of the PAD in DMSO-d6were used to investigate the isolated polymer and perform spectral assignments. By systematic addition of D2O we have tracked structural changes due to aggregation and observed contraction of hydrophilic side chains. Solution and cross polarization / magic angle spinning (CP/MAS)13C NMR approaches were implemented to investigate the aggregates of the PAD aqueous solution during the liquid to gel transition as the temperature was increased. At temperatures near 20 °C, all of the peaks from the PAD were observed in the13C CP/MAS and13C solution NMR spectra, indicating the presence of polymer chain nodes. Increasing the temperature to 40 °C resulted in a partial disentanglement of the nodes due to thermal agitation and further heating resulted in little to no additional structural changes. DeuteriumT1-T2andT2-T2two-dimensional relaxation spectroscopies using an inverse Laplace transform, were also implemented to monitor the water-PAD interaction during the phase transition. At temperatures near 20 °C the dynamical characteristics of water were manifested into one peak in the deuteriumT1-T2map. Increasing the temperature to 40 °C resulted in several distinguishable reservoirs of water with different dynamical characteristics. The observation of several reservoirs of water at the temperature of gel formation at 40 °C is consistent with a physical picture of a gel involving a network of interconnected polymer chains trapping a fluid. Further increase in temperature to 70 °C resulted in two non-exchanging water reservoirs probed by deuteriumT2-T2measurements.
authors.affiliation: Department of Biotechnology, Tokyo University of Agriculture and Technology, Koganei 184-8588, Japan.
authors.forename: Eiji
authors.initials: E
authors.lastname: Watanabe
authors.affiliation: Department of Physics, Brooklyn College of The City University of New York, Brooklyn, New York 11210, United States.
authors.forename: Gregory S
authors.initials: GS
authors.lastname: Boutis
authors.affiliation: Mitsui Chemical Analysis & Consulting Service, Inc., Sodegaura, 299-0265, Japan.
authors.forename: Hiroko
authors.initials: H
authors.lastname: Sato
authors.affiliation: Mitsui Chemical Analysis & Consulting Service, Inc., Sodegaura, 299-0265, Japan.
authors.forename: Sokei
authors.initials: S
authors.lastname: Sekine
authors.affiliation: Department of Biotechnology, Tokyo University of Agriculture and Technology, Koganei 184-8588, Japan.
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Asakura