Akihiro Tsutsumi

Copper ion binding to N-phenylphthalamic acid studied by 13C nuclear magnetic resonance and electron paramagnetic resonance: model interaction of polyamic acid with copper

The interaction of copper with N-phenylphthalamic acid (PPA) cured at various temperatures was investigated by 13C NMR and EPR spectroscopies, as the model system of polyamic acid on copper. EPR spectra prove that copper is dissolved into the PPA–N-methylpyrrolidone solution, producing paramagnetic Cu2+ ions. The 13C NMR resonances of the phthalic group of PPA are selectively broadened due to the paramagnetic interaction between the 13C nuclei and Cu2+ ions, showing binding of Cu2+ to the carboxylate group. Cu2+ ion has no effect on the amide and phenyl groups. Cu2+ ion exchanges rapidly between the carboxylate groups at an exchange rate > 103 s–1 at 23 °C. PPA is imidized to N-phenylphthalimide (PPI) at 150 °C, accompanied by the dissociation of Cu2+. Paramagnetic effects from the Cu2+ ions is not exerted on PPI. The results obtained are compared with the interfacial interaction between polyamic acid and copper.

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

To study the segmental motion of poly (L-histidine) (PLH) in aqueous solution, the 13C spin-lattice relaxation time (T1) was measured at six resonance frequencies (ωC/2π) ranging from 15 to 100 MHz at temperatures from 10 to 80°C. For backbone Cα, plots of log (T1/ωC) against log (ωC) 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–Laupretre–Monnerie (DLM) model. One of the parameters relating to the segmental motion was τ0/τ1=15, where τ0 and τ1 are the correlation times for the isolated single and correlated pair conformational transitions, respectively. It was found that the spectral density function J(ωC) has the exponent to the correlation time τ1 as ωCJ(ωC)~(ωCτ1)0.71 in the region of ωCτ11.

1H–13C Nuclear Cross-Relaxation and Molecular Motion in Single Crystalline Film of Vinylidene Fluoride and Trifluoroethylene Copolymer with 75 mol% Vinylidene Fluoride

1H–13C nuclear cross relaxation and molecular motion in a highly double-oriented film of vinylidene fluoride (VDF) and trifluoroethylene (TrFE ) copolymer with 75 mol% VDF were studied using the cross-polarization/magic angle spinning nuclear magnetic resonance technique. A transient oscillation was observed in the 13C peak intensity vs. contact time plots for the CH2, CHF and CF2 groups. Based on the cross relaxation theory of the spin diffusion process, it was clarified that the oscillation behavior was caused by the TrFE-rich domain and that the crystal consisted of VDF-rich and TrFE-rich domains. The spin-lattice relaxation time T1ρH in the rotating frame in both domains showed the two T1ρH minimum processes of β and αb in the ferroelectric phase, which are respectively due to the flip-flop motion of the TrFE segment and the oscillational motion of the VDF segment, and the T1ρH minimum process of α1D is due to the one-dimensional diffusion motion of the conformational defects along the chain, accompanied by the trans and gauche transformations of the VDF conformers in the paraelectric phase on cooling. The anomaly of the T1ρH minimum at the Curie temperature depended on the conformational stability of both segments. The deflected trans TrFE segment did not experience any conformational change in the transition region, in contrast to the trans-gauche conformational change in the VDF segment.