Teruaki Fujito

Polyethylene structure in the solid state as studied by variable-temperature 13C CP/MAS n.m.r. spectroscopy

Abstract High-resolution 13 C n.m.r. spectra of melt-quenched polyethylene sample were measured within the temperature range of - 120 to 90°C by means of variable temperature/magic angle spinning technique. Based on these results, the temperature change of polyethylene structure in the solid state was discussed.

Spin-lattice relaxation of carbon-13 in the rotating frame

Abstract Measurements of T 1 ϱ on 13 C are performed by Fourier transform NMR with proton decoupling, and origins of systematic errors in the T 1 ϱ experiment are discussed in detail. Measurements on cis-decalin and chlorinated compounds are carried out to confirm the accuracy of T 1 ϱ values of 13 C under proton decoupling. The estimated value of chemical shift difference between the two chemical-exchange sites of cis -decalin by the T 1 ϱ experiment shows good agreement with the value from direct measurement at low temperature (−30°C). The activation energy of fast molecular motion for T 1 processes is estimated, as well as that of slow motion for T 1 ϱ , and the exchange rate of the two sites is calculated. For several chlorinated compounds, the scalar coupling constants J ccl and T 1 of the chlorine are estimated.

15N chemical shift tensors and conformation of solid polypeptides containing 15N-labeled glycine residue by 15N NMR

Abstract The correlation between the isotropic 15 N chemical shift ( δ iso ) and 15 N chemical shift tensor components ( δ 11 , δ 22 and δ 33 ) and the main-chain conformation such as the polyglycine I (PGI: β-sheet), II (PGII: 3 1 -helix), α-helix and β-sheet forms of solid polypeptides [Gly∗,X] n consisting of 15 N-labeled glycine (Gly∗) and other amino acids (X: natural abundance of 15 N) has been studied by solid-state 15 N NMR method. A series of polypeptides [Gly∗,X] n (X = glycine, l -alanine, l -leucine, l -valine, l -isoleucine, β-benzyl l -aspartate, γ-benzyl l -glutamate, ϵ-carbobenzoxy l -lysine, and sarcosine) were synthesized by the α-amino acid N -carboxy anhydride (NCA) method. Conformations of these polypeptides in the solid state were characterized on the basis of conformation-dependent 13 C chemical shifts in the 13 C cross-polarization-magic angle spinning (CP-MAS) NMR spectra and by the characteristic bands in the IR and far-IR spectra. The δ iso , δ 11 , δ 22 and δ 33 of the polypetides were determined from the 15 N CP-MAS and 15 N CP-static (powder pattern) spectra. It was found that the δ iso , δ 11 , δ 22 and δ 33 in the PGI form (δ 83.5, 185, 40.7 and 25 ppm, resp.) are upfield from those in the PGII form (88.5, 194, 42.1 and 29 ppm, resp.), which were reproduced by the calculated 15 N shielding constants using the finite perturbation theory (FPT)-INDO method. It was also found that the δ 22 of the Gly∗ of [Gly∗,X] n is closely related to the main-chain conformation and the neighboring amino acid sequence, although the δ iso is almost independent of the glycine content and conformation. Consequently, the δ 22 value of Gly∗ containing copolypeptides is useful for the structural (main-chain conformation and neighboring amino acid sequence) analysis in the solid state by 15 N NMR, if the 15 N-labeled copolypeptide or natural protein can be provided. In addition, it is shown that the δ iso of the glycine residue is useful for the conformational study of some fibrous proteins such as silk fibroins and collagen fibrils in the solid state.

Towards a beyond 1 GHz solid-state nuclear magnetic resonance: external lock operation in an external current mode for a 500 MHz nuclear magnetic resonance.

Achieving a higher magnetic field is important for solid-state nuclear magnetic resonance (NMR). But a conventional low temperature superconducting (LTS) magnet cannot exceed 1 GHz (23.5 T) due to the critical magnetic field. Thus, we started a project to replace the Nb(3)Sn innermost coil of an existing 920 MHz NMR (21.6 T) with a Bi-2223 high temperature superconducting (HTS) innermost coil. Unfortunately, the HTS magnet cannot be operated in persistent current mode; an external dc power supply is required to operate the NMR magnet, causing magnetic field fluctuations. These fluctuations can be stabilized by a field-frequency lock system based on an external NMR detection coil. We demonstrate here such a field-frequency lock system in a 500 MHz LTS NMR magnet operated in an external current mode. The system uses a (7)Li sample in a microcoil as external NMR detection system. The required field compensation is calculated from the frequency of the FID as measured with a frequency counter. The system detects the FID signal, determining the FID frequency, and calculates the required compensation coil current to stabilize the sample magnetic field. The magnetic field was stabilized at 0.05 ppm∕3 h for magnetic field fluctuations of around 10 ppm. This method is especially effective for a magnet with large magnetic field fluctuations. The magnetic field of the compensation coil is relatively inhomogeneous in these cases and the inhomogeneity of the compensation coil can be taken into account.

High-Field Nuclear Magnetic Resonance with a Newly Designed Hybrid Magnet System

Nuclear magnetic resonance (NMR) measurements using a newly designed hybrid magnet system installed at the National Institute for Materials Science were performed up to 28 T. A modified resistive insert magnet improved the field homogeneity of the hybrid magnet from 186 ppm/±5 mm to 16 ppm/±5 mm along the z-axis. Reconstruction of the power source for the resistive magnet suppressed the field instability from 30 to 3 ppmrms. These improvements enable us to obtain an NMR spectrum with narrower linewidth.

First observation of high-resolution solid-state 73Ge NMR spectra of organogermanium compounds

High-resolution solid-state MAS 73Ge NMR spectra of organogermanium compounds have been observed for the first time; the chemical shifts and half-widths of tetraphenylgermane and tetrabenzylgermane were recorded with and without high-power decoupling.