13C-NMR study of cellulose derivatives in the solid state

The application of NMR for natural organic compounds has been carried out from the early history of NMR. But they reported on the liquid state NMR and the samples were limited to the materials which dissolved in proper solvents. It has been possible to measure the samples in the solid state in 1970s and is widely used as a familiar analytical method in 1980s. Whereas some of the data is inadequate, concerning cellulose derivatives, in particular, only nitrate and acetate were reported by Patterson¹ and Doyle,² respectively. In this paper, the ¹³C CP/MAS solid state NMR spectra of several cellulose derivatives are shown and the relationship between the structure and spectrum is discussed.     

Comparative study of dielectric,mechanical, and nuclear magnetic relaxations in linear polyethylene. II. Relaxation spectroscopy of the α, β, and γ loss bands with special emphasis on fine structure

Dielectric, mechanical, and NMR retardation (correlation) spectra for relaxations in linear polyethylene were calculated in normalized form and intercompared. For each of the two local-mode relaxations in the γ region, called γ₁ and γ₂, these spectra are found to be in excellent agreement. For the α region, the spectra for two mechanical processes, called α₁ and α₂, two NMR processes, called α′ and α, and one dielectric process α were calculated. Excellent agreement is found between the spectra for the dielectric α and NMR α′ processes and also spectra for the mechanical α₂ and NMR α processes, due to molecular motion in the interior of crystals. However, the spectrum for the mechanical α₁ process is different from that for the dielectric α and NMR α′ processes, though the activation energy for the first process is almost the same as for the other two. This behavior is interpreted on the assumption that the dielectric α and NMR α′ processes are caused by molecular motion in lamellar surface layers while the mechanical α₁ process is due to grain-boundary slip with viscous resistance of the surface layers in the boundaries. The shapes of the spectra, including the spectrum for the β process, are not affected by diluent.     

Microdroplet evolution induced by a laser pulse

Interaction between high-power ultrashort laser pulse and giant clusters (microdroplets) consisting of 10⁹ to 10¹⁰ atoms is considered. The microdroplet size is comparable to the laser wavelength. A model of the evolution of a microdroplet plasma induced by a high-power laser pulse is developed, and the processes taking place after interaction with the pulse are analyzed. It is shown theoretically that the plasma is superheated: its temperature is approximately equal to the ionization potential of an ion having a typical charge. The microdroplet plasma parameters are independent of the pulse shape and duration. The theoretical conclusions are supported by experimental studies of x-ray spectra conducted at JAERI, where a 100-terawatt Ti-sapphire laser system was used to irradiate krypton and xenon microdroplets by laser pulses with pulse widths of 30 to 500 fs and intensities of 6×10¹⁶ to 2×10¹⁹W/cm².     

Excited-state dynamics of Yb in LiCaAlF6 single crystal

Single crystals of Yb²⁺-doped LiCaAlF₆ were grown by the Czochralski technique under CF₄ atmosphere. Photoluminescence, thermally stimulated luminescence and decay kinetics of Yb²⁺ centre in the LiCaAlF₆ host were measured in the 4–300 K temperature interval. Phenomenological two excited-state-level model is introduced to obtain quantitative characteristics of the excited state dynamics of Yb²⁺. The role of Yb²⁺ centre in trapping processes is discussed. Moreover, defect centres related to LiCaAlF₆ host were found.     

Sn-Pb合金颗粒异质成核及其冷却凝固行为预测

采用均匀颗粒成型法 (UniformDropletSpray ,UDS)在氮气氛下 (氧含量为 1.3 6μmol/L)制备了 15 0和 185μmSn 5 %Pb合金颗粒 .采用光学显微镜观测颗粒的外观形貌 ,结果表明 ,UDS方法制备的微粒是粒度均匀的球状颗粒 ;利用非绝热容量法确定了颗粒的形核点及过冷度 ;计算了以时间和温度为函数的颗粒表面被氧化的比例 ,提出了以颗粒表面氧化为催化媒质的异质成核理论模型 ,合理反映了颗粒的异质成核过程 .在此基础上计算了微粒表面异质形核条件下的连续冷却转变 (ContinuousCoolingTransformation ,CCT)曲线 ,同时以线性冷却条件为例预测了颗粒的冷却凝固行为 .     

Magnetic moments of proton drip-line nuclei13O and9C

The magnetic moments of the proton drip-line nuclei¹³O(I = 3/2^–,T _1/2 = 8.6 ms) and 9C(I = 3/2^–,T _1/2 = 126 ms) have been determined for the first time through the combined techniques of polarized radioactive nuclear beams and-NMR detection. The observed magnetic moments are ¦(¹³O)¦ = 1.3891 ±0.0003 _N and ¦(⁹C)¦ = 1.3914 ±0.0005 _N. Spin expectation values are deduced to be 0.76 and 1.44 for¹³O and⁹C, respectively. While the of¹³O is consistent with the systematics from isospinT= 1/2 mirror pairs, the of⁹C is unusually large, even far larger than the single particle value, = 1.     

Synthesis, spectroscopic, and electrochemical studies of 1,2-naphthalene-ring-fused tetraazachlorins, -bacteriochlorins, and -isobacteriochlorins: the separation and characterization of structural isomers

1,2-Naphthalene-ring-expanded tetraazachlorins (TACs), tetraazabacteriochlorins (TABCs), and tetraazaisobacteriochlorins (TAiBCs) have been synthesized. Procedures for the synthesis of the starting materials, that is, derivatives of 1,2-naphthalenedicarboxylic acid, have been reinvestigated and improved. Nine possible derivatives, including four, two, and three structural isomers of TACs, TABCs, and TAiBCs, respectively, were separated by using thin-layer chromatography (TLC) or high-performance liquid chromatography (HPLC), and the structure of each isomer was determined by (1)H NMR spectroscopy combined with the NOE technique. The formation ratio of each isomer was rationalized in terms of the intramolecular steric repulsion effect, which was predicted by geometry optimizations at the DFT level. The derived compounds were characterized by using IR, electronic, and magnetic circular dichroism (MCD) spectroscopy, and by electrochemical methods. Frequency calculations at the DFT level correctly reproduced the experimental IR spectra and, in particular, distinguished between the three isomers of the TAiBCs. In the electronic absorption and MCD spectra of the TAC and TABC species, the Q-band splits into two intense components similarly to the 2,3-naphthalene-fused derivatives described in our preceding paper, although no significant spectral differences were observed from species to species. On the other hand, the spectra of the TAiBCs showed moderate differences depending on the structure of the isomer. The spectroscopic properties as well as the electrochemical behavior of these chlorins resemble those of the corresponding benzene-fused derivatives rather than the 2,3-naphthalene-fused derivatives. Molecular-orbital and configuration-interaction calculations within the framework of the ZINDO/S method were helpful in the discussions of the above observations.     

Synthesis of 3,4,5-trisubstituted indoles via iterative directed lithiation of 1-(triisopropylsilyl)gramines

Directed lithiation of 1-(triisopropylsilyl)gramines 1 with tert-butyllithium followed by reaction with trimethylsilylmethyl azide produced 4-amino-1-(triisopropylsilyl)gramines 7. The N-tert-butoxycarbonyl derivatives 8 were lithiated selectively at C-5 with tert-butyllithium and the lithiated species were reacted with a variety of electrophiles to give 5-functionalized compounds, 9 and 10. A facile method to produce 3,4,5-trisubstituted indoles from readily available gramine derivatives is thereby established.