Solid state 1H, 7Li, and 13C NMR studies on new ionic plastic crystals of crown ether-Li-TFSA complexes.

This study provides the first evidence that a Li ion can form ionic plastic crystals using crown ether with a bis-(trifluoromethanesulphonyl) amide (TFSA) anion. 1H, 7Li, and 13C nuclear-magnetic-resonance (NMR) measurements of the 15-crown-5-Li-TFSA complex revealed that the constituents underwent isotropic reorientation in the plastic crystalline phase. The NMR data of the 12-crown-4-Li-TFSA salt showed that the complex is a rotator crystal (the complexes are denoted as [Li 15C5] and [Li 12C4] in this paper). The X-ray diffraction (XRD) reflection patterns of the [Li 15C5] crystal recorded in the highest-temperature solid phase (plastic phase) could be indexed to a cubic structure. Conversely, [Li 12C4] could be fitted to a trigonal structure. In this study, [M (3n)Cn] (M = Li, Na, K; n = 4-6) complexes were also prepared, and NMR, DSC, XRD, and electrical conductivity measurements were performed. Based on these results, we additionally revealed that the [Na 15C5] and [K (15C5)2] complexes are also new rotator crystals. Single-crystal XRD measurements also revealed that the [Na 15C5] compound has two stable sites in the crystal. Activation energies of molecular motions in the [M (3n)Cn] crystals were estimated using 1H NMR relaxation time (T1 and T2) measurements. The electrical conductivity measurements of [Li 12C4], [Li 15C5], and [Na 15C5] showed high ionic conductivities (∼10-2 S cm-1).

Development of the novel pre-emergence herbicide pyroxasulfone.

Pyroxasulfone, which was discovered and developed by K-I Chemical Research Institute Co., Ltd.; Kumiai Chemical Industry Co., Ltd.; and Ihara Chemical Industry Co., Ltd., is a novel pre-emergence herbicide for wheat, corn, and soybean. Pyroxasulfone inhibits the biosynthesis of very-long-chain fatty acids in plants and has shown excellent herbicidal activity against grass and broadleaf weeds at lower application rates compared with other commercial herbicides. This pesticide has been registered in Japan, Australia, the USA, Canada, Saudi Arabia, and South Africa, and we sell pyroxasulfone products through domestic partner companies in each of these countries. With its high efficacy and relatively low application rates, we believe that pyroxasulfone will contribute to efficient global food production in the future.

Soil and environmental factors affecting the efficacy of pyroxasulfone for weed control.

Pyroxasulfone inhibits very-long-chain fatty acid elongase in susceptible weeds and facilitates preemergence weed control. Pyroxasulfone showed 98% control of Echinochloa crus-galli (ECHCG) for up to 63 days at a use rate lower than that of chloroacetamide herbicides. ED90 of pyroxasulfone against ECHCG in soil with high organic matter (OM) content did not differ significantly from that in lower OM soils. The low water solubility and the low vapor pressure of pyroxasulfone resulted in limited horizontal diffusion on the soil surface and low risk of volatilization, respectively. The herbicidal efficacy of pyroxasulfone was affected by clod size and improved with smooth soil surface preparation.

¹H-MAS-NMR chemical shifts in hydrogen-bonded complexes of chlorophenols (pentachlorophenol, 2,4,6-trichlorophenol, 2,6-dichlorophenol, 3,5-dichlorophenol, and p-chlorophenol) and amine, and H/D isotope effects on ¹H-MAS-NMR spectra.

Chemical shifts (CS) of the ¹H nucleus in N···H···O type hydrogen bonds (H-bond) were observed in some complexes between chlorophenols [pentachlorophenol (PCP), 2,4,6-tricholorophenol (TCP), 2,6-dichlorophenol (26DCP), 3,5-dichlorophenol (35DCP), and p-chlorophenol (pCP)] and nitrogen-base (N-Base) by solid-state high-resolution ¹H-NMR with the magic-angle-spinning (MAS) method. Employing N-Bases with a wide range of pKa values (0.65-10.75), ¹H-MAS-NMR CS values of bridging H atoms in H-bonds were obtained as a function of the N-Base's pKa. The result showed that the CS values were increased with increasing pKa values in a range of DpKa < 0 [DpKa = pKa(N-Base)-pKa(chlorophenols)] and decreased when DpKa > 2: The maximum CS values was recorded in the PCP (pKa = 5.26)-4-methylpyridine (6.03), TCP (6.59)-imidazole (6.99), 26DCP (7.02)-2-amino-4-methylpyridine (7.38), 35DCP (8.04)-4-dimethylaminopyridine (9.61), and pCP (9.47)-4-dimethylaminopyridine (9.61) complexes. The largest CS value of 18.6 ppm was recorded in TCP-imidazole crystals. In addition, H/D isotope effects on ¹H-MAS-NMR spectra were observed in PCP-2-amino-3-methylpyridine. Based on the results of CS simulation using a B3LYP/6-311+G** function, it can be explained that a little changes of the N-H length in H-bond contribute to the H/D isotope shift of the ¹H-MAS-NMR peaks.

Both experimental and theoretical investigations of solid-state 17O NMR for L-valine and L-isoleucine.

We have presented an experimental investigation of the carboxyl oxygen NMR parameters for four distinct sites in l-valine and l-isoleucine. The carboxyl (17)O quadrupolar coupling constant, C(Q), and isotropic chemical shift, delta(iso), for these compounds are obtained by analyzing two-dimensional (17)O multiple-quantum magic-angle spinning (MQMAS) and/or 1D MAS spectra. The values of C(Q) and delta(iso) found to be in the range of 7.00-7.85 MHz, and 264-314 ppm, respectively. Extensive quantum chemical calculations at the density functional levels have been performed for a full cluster of l-valine molecules and a few theoretical models. The calculated results indicated that there was a correlation between the (17)O NMR parameters and C-O bond lengths, which was helpful for the spectral assignment. They also demonstrated that the torsion angle of l-valine plays an important role in determining the magnitudes of (17)O NMR parameters.

Solid-state 17O NMR study of the electric-field-gradient and chemical shielding tensors in polycrystalline gamma-glycine.

We report the first experimental determination of the carboxylate oxygen electric-field-gradient (EFG) and chemical shielding (CS) tensors in polycrystalline gamma-glycine. Analysis of magic-angle spinning (MAS) and stationary (17)O NMR spectra of [(17)O]-gamma-glycine obtained at 9.4, 14.1, 16.4, and 18.8 T yields the magnitudes of the (17)O EFG and CS tensors and the relative orientations between the two tensors. Extensive quantum chemical calculations at both the restricted Hartree-Fock and density functional levels have been performed to present the absolute tensor orientations in term of the molecular frame. We have demonstrated that (17)O NMR tensor information could be unambiguously derived by the multiple field analyses of stationary (17)O NMR spectra.