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摘要
The thermo-responsive behavior of a unique biocompatible polymer, poly(N-substituted alpha/beta-asparagine) derivative (PAD), has been studied with several NMR methods. The H-1 and C-13 solution NMR measurements of the PAD in DMSO-d(6) were 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) C-13 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 degrees C, all of the peaks from the PAD were observed in the C-13 CP/MAS and C-13 solution NMR spectra, indicating the presence of polymer chain nodes. Increasing the temperature to 40 degrees C resulted in a partial disentanglement of the nodes due to thermal agitation and further heating resulted in little to no additional structural changes. Deuterium T-1-T-2 and T-2-T-2 two-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 degrees C the dynamical characteristics of water were manifested into one peak in the deuterium T-1-T-2 map. Increasing the temperature to 40 degrees 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 degrees 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 degrees C resulted in two non-exchanging water reservoirs probed by deuterium T-2-T-2 measurements.
- 出版日期2014-1-14
