Hisashi Sugisawa

207Pb chemical shift thermometer at high temperature for magic angle spinning experiments.

The temperature dependence of 207Pb chemical shift in magic angle spinning (MAS) NMR spectrum of Pb(NO3)2 provides a sensitive method to calibrate sample temperatures in MAS NMR. The temperature dependence is uniform in the temperature range between 30 degrees C and 400 degrees C. The NMR sensitivity and the line width are also favorable.

Evidence for radiation induced crosslinking in polytetrafluoroethylene by means of high-resolution solid-state 19F high-speed MAS NMR

Radiation effects on molecular structure of polytetrafluoroethylene (PTFE) were studied by high-resolution solid-state 19F high speed magic angle spinning (HS MAS) NMR spectroscopy. Samples used for the NMR studies were prepared by electron beam irradiation of PTFE with a wide range of irradiation doses from 0.5–10 MGy in the molten state at 340°C under oxygen-free atmosphere. While the non-irradiated PTFE displayed only an intense peak of the internal CF2, several new signals corresponding to CF3, CF2 and CF groups were observed for the PTFE which was high temperature irradiated at 340°C in oxygen-free atmosphere (hti-PTFE). Intensities of these new signals increased with an increase of irradiation dose. The present solid-state 19F HS MAS NMR studies provide not only the first experimental evidence regarding the existence of crosslinking structure in hti-PTFE, directly detected as the CF signal, but also the crosslinking density which can be estimated from a proportion of the CF versus total fluorine signal intensities. The higher the irradiation dose, the higher the crosslinking density; hti-PTFE with 10 MGy contains one crosslinking site per approximately 24 CF2 groups, while the hti-PTFE with 5 MGy contains one crosslinking site per approximately 36 CF2 groups. Further, G value of crosslinking (G(x)) was estimated from the signal intensities of 19F HS MAS NMR spectra. The highest G(x)-value, 1.85, was observed for the 2MGy hti-PTFE sample, suggesting that crosslinking of PTFE is formed most efficaciously with 2 MGy irradiation in the molten state at 340°C under oxygen-free atmosphere.

Structural study of α-amino-acid crystals by 1H CRAMPS NMR spectroscopy

Abstract 1 H CRAMPS (combined rotation and multiple pulse spectroscopy) NMR was applied to structural analysis of polymorphic forms of α-amino acid crystals in order to test the power of 1 H CRAMPS NMR compared with the 13 C and 15 N NMR methods. We have studied two different stages of α-amino acid crystals: α-glycine and γ-glycine, and A-histidine and B-histidine. As a result, it was found that the α-methylene proton (H α ) signal of α-glycine splits into two peaks (4.4 and 3.4 ppm), but that of γ-glycine gives a singlet peak (3.3 ppm), which was reasonably explained by the 1 H electrostatic potential charge calculation for this glycine system. Furthermore, it was found that the 1 H chemical shift difference between the H 2 and H 5 peaks from the imidazole ring of A-histidine (0.4 ppm) could easily be distinguished from that of B-histidine (0.9 ppm). Thus, the 1 H chemical shifts of α-amino acids are very sensitive to a slight difference in magnetic surroundings of protons as well as to differences of the hydrogen bond network. Therefore, the 1 H CRAMPS NMR spectra are very useful for the structural analysis of α-amino acid crystals.

Highly efficient self-condensation of benzaldehyde to benzyl benzoate over KF-loaded alumina

The self-condensation of benzaldehyde to benzyl benzoate was carried out over KF-loaded alumina. The catalytic activity strongly depends on the loading amount of KF. The pretreatment of the catalyst at high temperature under vacuum is essential for the high catalytic activity. When KF (5 mmol/g-alumina) loaded alumina was evacuated at 673 K, the catalyst gave selectively benzyl benzoate, whose yield was 94.2% in 3 h at 323 K.

Chemisorption of hydrogen on Ag-Y studied by 1H MAS NMR

Abstract The chemisorbed state of hydrogen on partially reduced Ag+- exchanged Y zeolite was studied by means of 1H MAS NMR spectroscopy. When AgY was reduced with hydrogen, a peak appeared at −0.1 ppm besides peaks at 4.6 ppm and 4.0 ppm. The latter two peaks were attributed to bridging hydroxyl groups in sodalite cages and supepercages, respectively. The peak at −0.1 ppm was ascribed to atomic hydrogen species adsorbed on cationic silver clusters (Agn+). The chemisorption is reversible and this species exist only when hydrogen molecules are in the vapor phase. The following equation is proposed as a plausible mechanism for hydrogen chemisorption. ZO−Agn++ H2AgnH + ZOH

Nature of acidic protons in metallosilicate molecular sieves as studied by variable temperature 1H MAS NMR

The dynamic properties of protons in H-[Ga]-ZSM-5, H-[B]-ZSM-5 and H-[Al-B]-ZSM-5 were compared with that of protons in H-[Al]-ZSM-5 by temperature dependence of 1H MAS NMR in the range of 298 k and 473 K. The temperature dependence of the line width of 1H MAS NMR reveals that protons in H-[Ga]-ZSM-5 were more mobile than those in H-[Al]-ZSM-5 at temperature as low as 373 K. The protons in H-[B]-ZSM-5 were not mobile at 473 K and fixed in the zeolite frame work as the bridging hydroxyl groups, ≡B-OH-Si≡. The thermal motion of protons in ≡Al-OH-Si≡ was suppressed by introducing B3+ cations into the framework of H-[Al]-ZSM-5.