13C NMR Relaxation Study of Segmental Motion of Poly(Nε-hydroxyethyl L-glutamine) in Aqueous Solution

Abstract

To study the segmental motion of poly(N "-hydroxyethyl L-glutamine) (PHEG) in aqueous solution, the 13 C spin-lattice relaxation time (T 1) and the nuclear Overhauser enhancement (NOE) were measured at six resonance frequencies (! C =2) ranging from 15 to 150 MHz and at 100 MHz, respectively, at the temperatures from 20 to 90 C. For the backbone C, plots of logðT 1 =! C Þ against logð! C Þ gave the well superposed master curve, showing that the frequency-temperature reduction rule is realized. The shift factor obeyed the Arrhenius type temperature dependence with the activation energy of 29.6 kJ mol À1. Using this activation energy for the temperature dependence of the correlation time, the master curve and NOE were well reproduced by the Dejean-Lauprêtre-Monnerie (DLM) model. One of parameters relating to the segmental motion was 0 = 1 ¼ 5, where 0 and 1 are the correlation times for the isolated single and correlated pair conformational transitions, respectively. Comparison of this parameter with that for other vinyl polymers showed that PHEG having planar peptide groups in the backbone belongs to polymer group with smaller values of 0 = 1. 0 = 1 was discussed in the relation to the distribution width of the correlation time. The spectral density function Jð!Þ has the exponent to the correlation time a as !Jð!Þ $ ð! a Þ 0:61 in the region of ! a < 0:2 which is close to the value of 0.5 from the DLM model.