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

概要

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To study the segmental motion of poly (l-histidine) (PLH) in aqueous solution, the 13C spin-lattice relaxation time ($T_{1}$) was measured at six resonance frequencies ($\omega_{\text{C}}/2\pi$) ranging from 15 to 100 MHz at temperatures from 10 to 80°C. For backbone Cα, plots of $\log(T_{1}/\omega_{\text{C}})$ against $\log(\omega_{\text{C}})$ 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 kJmol-1. Using this activation energy for the temperature dependence of the correlation time, the master curve was well reproduced by the Dejean–Lauprêtre–Monnerie (DLM) model. One of the parameters relating to the segmental motion was $\tau_{0}/\tau_{1}=15$, where $\tau_{0}$ and $\tau_{1}$ are the correlation times for the isolated single and correlated pair conformational transitions, respectively. It was found that the spectral density function $J(\omega_{\text{C}})$ has the exponent to the correlation time $\tau_{1}$ as $\omega_{\text{C}}J(\omega_{\text{C}})\sim(\omega_{\text{C}}\tau_{1})^{0.71}$ in the region of $\omega_{\text{C}}\tau_{1}\ll 1$.
2004-05-15