~(13)C NMR Relaxation Study of Segmental Motion of Poly(L-histidine) in Aqueous Solution

摘要

To study the segmental motion of poly (L-histidine) (PLH) in aqueous solution, the ~(13)C spin-lattice relaxation time (T_1) was measured at six resonance frequencies (ω_C/2π) ranging from 15 to 100 MHz at temperatures from 10 to 80℃. For backbone C_α, plots of log(T_1/ω_C) against log(ω_C) gave the well-superposed master curve, showing that the time-temperature reduction rule is realized. The shift factor obeyed the Arrhenius-type temperature dependence with the activation energy of 25.0 kJ mol~(-1). Using this activation energy for the temperature dependence of the correlation time, the master curve was well reproduced by the Dejean-Laupretre-Monnerie (DLM) model. One of the parameters relating to the segmental motion was τ_0/τ_1 = 15, where τ_0 and τ_1 are the correlation times for the isolated single and correlated pair conformational transitions, respectively. It was found that the spectral density function J(ω_C) has the exponent to the correlation time τ_1 as ω_CJ(豞C) ～ (ω_Cτ_1)~(0.71) in the region of ω_Cτ_1 1.