~(13)C、~(15)N双标记氨基脲的同位素丰度测定

采用微量高温灼烧法制备样品气,运用同位素质谱测定稳定性同位素13 C、15 N双标记氨基脲(13C、15 N3-SEM)产品的13C、15 N同位素丰度。通过实验对影响测定结果准确度的相关因素进行了考察,确定了最佳质谱转化条件为:称取1mg 13C、15 N3-SEM.HCl样品,10mg微粒状氧化铜,放入玻璃样品管,于真空状态下熔封样品管。将样品管放入马弗炉,530℃反应4h。实验表明:测定结果具有良好的精密度、重复性及再现性,满足了稳定性同位素13 C、15 N双标记氨基脲产品的同位素丰度测定的要求。     

稳定同位素标记莨菪亭-2-~(13)C的合成

以2,4,5-三甲氧基苯甲醛和乙酰氯-2-13C为原料,经3步反应合成目标化合物。以原料乙酰氯-2-13C计算,目标化合物总收率为26%,产品经LC-MS、1HNMR、13CNMR、IR检测,化学纯度99%,13C同位素丰度为98.5 atom%。     

苯甲酸-~(13)C合成研究

以溴苯为原料,和镁反应制得格式试剂后与~(13)CO_2反应,酸化后生成苯甲酸-~(13)C。以消耗的~(13)CO_2计算,苯甲酸-~(13)C收率为77.5%。产品结构经质谱和核磁共振波谱等表征确定,纯度99.2%,同位素丰度98.4 atom%~(13)C。     

硝基甲烷-~(15)N的合成

以丰度为98.7 atom%的Na15NO2为同位素原料,与硫酸二甲酯反应合成了硝基甲烷-15N,方法简便,同位素转化率为75%,纯度为98.8%,丰度为98.56 atom%。     

对乙酰氨基酚-2-13C的合成及表征

以乙酸-2-~(13)C与N,N'-羰基二咪唑为原料,反应得到中间体N-乙酰基咪唑-2-~(13)C,该中间体进一步与对氨基苯酚反应得到对乙酰氨基酚-2-~(13)C。考察了反应温度和反应时间对对乙酰氨基酚-2-~(13)C收率的影响。结果表明:合成产物的最佳反应温度和时间分别为40℃和12h。产物经GC-MS、FTIR、1HNMR和~(13)CNMR进行结构表征。对乙酰氨基酚-2-~(13)C的气相色谱纯度99%,同位素丰度为98.7%,总产率为87%,合成的产物可作为同位素内标物在定量分析测试中使用。     

稳定同位素标记3,5-二硝基水杨酰肼-~(15)N_2的合成

提出简便的方法合成3,5-二硝基水杨酰肼-15N2,即以水杨酸为前体,与硝酸钾-15N硝化得到3,5-二硝基水杨酸-15N2,再经过酯化、肼解反应得到目标产物。以消耗K15NO3计算,3,5-二硝基水杨酰肼-15N2的总收率为55.5%。产品结构经质谱和核磁共振波谱等表征确定,15N的同位素丰度为99.2 atom%15N,色谱纯度为97.3%,可作为食品安全领域检测用同位素内标试剂。     

双标记尿嘧啶核苷-(~(13)C,~(15)N_2)的合成研究

设计了以无水苯为溶剂,双标记尿素-(~(13)C,~(15)N_2)和丙炔酸为原料进行环化反应,粗品经脱色和重结晶后得到双标记尿嘧啶-(~(13)C,~(15)N_2)。在Ar气氛下,双标记尿嘧啶-(~(13)C,~(15)N_2)和1-乙酰氧基-2,3,5-三苯甲酰氧基-β-D-呋喃核糖反应,经处理后得到的中间体1-(2,3,5-三苯甲酰氧基-β-D-呋喃核糖基)尿嘧啶-(~(13)C,~(15)N_2)用氨水水解,即可得到双标记尿嘧啶核苷-(~(13)C,~(15)N_2)。该方法操作简单,中间体只需简单纯化,各步反应收率高,并且~(13)C、~(15)N同位素丰度不被稀释。产物经高效液相色谱法(HPLC)、MS、~1H NMR和~(13)C NMR表征,结果表明,双标记尿嘧啶核苷-(~(13)C,~(15)N_2)质量分数98%,~(15)N同位素丰度98%,~(13)C同位素丰度98%。     

简便的13C标记甘氨胆酸的合成方法

该文"一锅煮"合成13C标记甘氨胆酸。即以氯甲酸异丁酯为活化试剂,甘氨酸-1-13C和胆酸直接缩合制备甘氨胆酸-甘氨酰基-1-13C,合成产品使用HPLC、LC-MS和1HNMR等进行分析。优化的合成条件为:n(氯甲酸异丁酯)∶n(胆酸)∶n(甘氨酸)∶n(三乙胺)=1∶1∶1∶1,反应温度10℃,反应时间1 h,13C标记甘氨胆酸收率82.4%(以甘氨酸-1-13C计),13C丰度达99.1%atom13C,光学纯度99.2%,w(甘氨胆酸-甘氨酰基-1-13C)=97.7%。     

13C1-对乙酰氨基酚（-CO13CH3）的合成及结构表征

2-13C1-乙酸与N,N''-羰基二咪唑反应得到了中间体13C1-N-乙酰基咪唑（—CO13CH3），该中间体进一步与对氨基苯酚反应得到13C1-对乙酰氨基酚（—CO13CH3）。考察了反应温度和反应时间两个因素对13C1-对乙酰氨基酚收率的影响。结果表明，合成产物的最佳反应温度和时间分别为40 ℃和12 h。产物经GC-MS、FTIR、1HNMR和13CNMR进行结构表征及含量测定。化学纯度>99%，同位素丰度>98.7%，总产率为87%，标记合成的产物可作为同位素内标物在定量分析测试中使用。     

1-(3-氨基苯基)-3-(4-氨基苯基)-2-丙烯-1-酮的合成

以对乙酰氨基苯甲醛、间乙酰氨基苯乙酮为原料经两步反应合成具有光敏性能的1 (3 氨基苯基) 3 (4 氨基苯基) 2 丙烯 1 酮。通过优化实验得到最佳的合成工艺条件为:对乙酰氨基苯甲醛、间乙酰氨基苯乙酮在温度为0℃下,以乙醇为溶剂、氢氧化钠为催化剂,进行羟醛缩合反应3h。分离提纯后,加入盐酸溶液在100℃下水解3h,产物经重结晶提纯。总收率达到61 9%,较1998年的文献[6]提高39 3%。并对产物的结构进行了表征。     

High productivity analysis of15N and13C in soil/plant research

On-line sample preparation and analysis enables faster testing of hypotheses in biological research, particularly in field experiments where many samples must be processed to integrate spatial variability. Soil scientists were first to recognise the need for a fast, easy-to-use¹⁵N analyser to replace the isotope ratio mass spectrometer (IRMS) and Kjeldahl-Rittenberg sample preparation. Development has since led to a variety of continuous-flow methods. Today's instruments accept solid, liquid or gaseous samples in their naturally occurring form (leaves, soil, algae, soil gas) and process 100–125 samples per day. Automated sample preparation and analysis takes 3–10 minutes per sample.By 1984, three groups had interfaced an automated nitrogen analyser to an IRMS. Continuous-flow combustion converted N in plant tissue or soil to a pulse of N₂ gas, which was taken to the mass spectrometer by a helium carrier. Throughput increased from 20 to 100 analyses per day and only 5µg N was required compared with 50µg N for Kjeldahl-Rittenberg preparation and IRMS analysis. 1984 was also the year in which a gas chromatograph (GC) was first used on-line with an IRMS for isotopic analysis of individual compounds separated from a mixture (GC-IRMS).In 1987, a software-controlled Automated Nitrogen Carbon Analyser-Mass Spectrometer (ANCA-MS) was developed for solid and liquid samples. Both¹⁵N and¹³C were measured to (SD, n = 5) 0.0002 atom%, enough for tracer studies. Less hardware made it portable, enabling use at remote sites. Software control enabled submicrogram quantities of N to be measured by moving the O₂ pulse, with its N₂ blank, out of phase with the sample. Software also allows an accelerated mode for¹⁵N, doubling throughput for a small loss in precision.Several workers have developed micro-diffusion methods for ANCA-MS determination of NH ₄ ⁺ and NO ₃ ^- in KCl extracts. In 1990, a dual isotope mode was added for sequential analysis of¹³C and¹⁵N from the same sample. In 1992 a new, 120° deflection, mass analyzer was designed to improve accuracy and precision at the high pressures used in CF-IRMS. Its precision of < 0.1¹³C for > 100µg C and < 0.3¹⁵N for > 50µg N extends ANCA-MS to natural abundance applications.Gaseous samples were first analyzed by CF-IRMS by manually injecting into the carrier flow of an ANCA-MS instrument. The initial interest was for¹³C breath tests - radiation-free non-invasive tests of metabolic function. Demand for these led to the development in 1989 of an automated GC-IRMS method to separate and measure¹³C in CO₂ from human breath. The instrument was further developed for isotopes in other gases:¹³CO₂,¹⁵N₂,¹⁵N₂O, and¹³CH₄ above soil;¹⁸O from water equilibrated with CO₂ and¹⁵NO from NO ₃ ^- in KCl plant extracts. The dual isotope mode allows¹⁵N to be measured in both N₂ (mass 28) and N₂O (mass 44) separated from the same sample. Recently GC-IRMS has been used to determine¹⁵N in N₂O produced from NO ₂ ^- or NO ₃ ^- in KCl soil extracts.We predict that these simpler, automated instruments and the growth of analytical services will encourage more widespread use of stable isotope techniques by agricultural researchers.     

Fabrication and characterization of (Pb(Mg1/3Nb2/3)O3, Pb(Yb1/2Nb1/2)O3, PbTiO3) ternary system ceramics

New ternary compositions in the Pb(Mg_1/3Nb_2/3)O₃-Pb(Yb_1/2Nb_1/2)O₃–PbTiO₃ (PMN-PYbN-PT) system were prepared using 0.5Pb(Yb_1/2Nb_1/2)O₃-0.5PbTiO₃ (PYbNT) and (1-x)Pb(Mg_1/3Nb_2/3)O₃–xPbTiO₃ (x = 0.26; PMNT26 or x = 0.325; PMNT32.5) powders synthesized via the columbite method. Dense (≥ 96% of theoretical density) ceramics with PMN/PYbN mole ratios of 25/75 (R-25), 50/50 (R-50) and 75/25 (R-75T and R-75R) were fabricated by reactive sintering at 1000 °C for 4 h. Therefore, incorporation of PYbNT to PMNT successfully decreased sintering temperature of PMNT from 1200 °C-1250 °C to 1000 °C. Samples with higher density and perovskite ratio together with lower weight loss possessed higher dielectric and piezoelectric values in each composition. The R-75 samples had remanent polarization (P_r) values of 34-36 μC/cm² and piezoelectric charge coefficient (d₃₃) of 560 pC/N. The sharp phase transition PMNT as a function of temperature became broader or more diffuse with increasing PYbNT content. However, PYbNT addition to PMNT increased Curie temperature (T_c) from 183 °C (for PMNT32.5) to 220-242 °C (for R-75T and R-75R) to 336 °C (for R-25). Therefore, these ternary compositions can be tailored for various high temperature applications due to the relatively higher T_c with enhanced piezoelectric and dielectric properties as compared to PMNT.     

Conversion of N2O to N2 on TiO2(1 1 0)

In this study, we examine the interaction of N₂O with TiO₂(1 1 0) in an effort to better understand the conversion of NO_x species to N₂ over TiO₂-based catalysts. The TiO₂(1 1 0) surface was chosen as a model system because this material is commonly used as a support and because oxygen vacancies on this surface are perhaps the best available models for the role of electronic defects in catalysis. Annealing TiO₂(1 1 0) in vacuum at high temperature (above about 800 K) generates oxygen vacancy sites that are associated with reduced surface cations (Ti³⁺ sites) and that are easily quantified using temperature programmed desorption (TPD) of water. Using TPD, X-ray photoelectron spectroscopy (XPS) and electron energy loss spectroscopy (EELS), we found that the majority of N₂O molecules adsorbed at 90 K on TiO₂(1 1 0) are weakly held and desorb from the surface at 130 K. However, a small fraction of the N₂O molecules exposed to TiO₂(1 1 0) at 90 K decompose to N₂ via one of two channels, both of which are vacancy-mediated. One channel occurs at 90 K, and results in N₂ ejection from the surface and vacancy oxidation. We propose that this channel involves N₂O molecules bound at vacancies with the O-end of the molecule in the vacancy. The second channel results from an adsorbed state of N₂O that decomposes at 170 K to liberate N₂ in the gas phase and deposit oxygen adatoms at non-defect Ti⁴⁺ sites. The presence of these O adatoms is clearly evident in subsequent water TPD measurements. We propose that this channel involves N₂O molecules that are bound at vacancies with the N-end of the molecule in the vacancy, which permits the O-end of the molecule to interact with an adjacent Ti⁴⁺ site. The partitioning between these two channels is roughly 1:1 for adsorption at 90 K, but neither is observed to occur for moderate N₂O exposures at temperatures above 200 K. EELS data indicate that vacancies readily transfer charge to N₂O at 90 K, and this charge transfer facilitates N₂O decomposition. Based on these results, it appears that the decomposition of N₂O to N₂ requires trapping of the molecule at vacancies and that the lifetime of the N₂O–vacancy interaction may be key to the conversion of N₂O to N₂.     

CuO as a sintering additive for (Bi1/2Na1/2)TiO3-BaTiO3-(K0.5Na0.5)NbO3 lead-free piezoceramics

CuO as a sintering additive was utilized to explore a low-temperature sintering of 0.92(Bi_1/2Na_1/2)TiO₃-0.06BaTiO₃-0.02(K_0.5Na_0.5)NbO₃ lead-free piezoceramic which has shown a promise for actuator applications due to its large strain. The sintering temperature guaranteeing the relative density of greater than 98% is drastically decreased with CuO addition, and saturates at a temperature as low as ∼930 °C when the addition level exceeds ca. 1 mol.%. Two distinguished features induced by the addition of CuO were noted. Firstly, the initially existing two-phase mixture gradually evolves into a rhombohedral single phase with an extremely small non-cubic distortion. Secondly, a liquid phase induced by the addition of CuO causes an abnormal grain growth, which can be attributed to the grain boundary reentrant edge mechanism. Based on these two observations, it is concluded that the added CuO not only forms a liquid phase but also diffuses into the lattice. In the meantime, temperature dependent permittivity measurements both on unpoled and poled samples suggest that the phase stability of the system is greatly influenced by the addition of CuO. Polarization and strain hysteresis measurements relate the changes in the phase stability closely to the stabilization of ferroelectric order, as exemplified by a significant increase in both the remanent strain and polarization values. Electron paramagnetic resonance (EPR) spectroscopic analysis revealed that the stabilization of ferroelectric order originates from a significant amount of Cu²⁺ diffusing into the lattice on B-site. There, it acts as an acceptor and forms a defect dipole in association with a charge balancing oxygen vacancy.     

Electrical properties of (Bi2O3)0.75(RE2O3)0.25 ceramics (RE=Dy, Y, Ho, Er and Yb)

Five kinds of rare earth stabilized bismuth oxide ceramics, (Bi₂O₃)_0.75(RE₂O₃)_0.25 (RE=Dy, Y, Ho, Er and Yb), were synthesized by sintering a mixture of Bi₂O₃ and RE₂O₃ at 900–1100 °C and their electrical properties were investigated. The bulk density and the lattice constant linearly increased with an increase in the atomic weight of RE and the ionic radius of RE³⁺, respectively. The electrical conductivity at 300 °C slightly increased with the increasing ionic radius of RE³⁺, while at 500 and 700 °C, it was constant regardless of the ionic radius of RE³⁺. The migration activation energy and the association activation energy showed a maximum value and a minimum value at RE=Er, respectively.     

Fabrication and piezoelectric properties of BaTiO3/BaTiO3-Bi(Mg1/2Ti1/2)O3-BiFeO3 composites

We fabricated xBaTiO₃ (BT)/(1-x)[BaTiO₃-Bi(Mg_1/2Ti_1/2)O₃-BiFeO₃] (BT-BMT-BF)?+?0.1?wt%MnCO₃ composites by spark plasma sintering and investigated the effect of BT content x, BT powder size, and BT-BMT-BF composition on piezoelectric properties. For xBT/(1-x)(0.3BT-0.1BMT-0.6BF) +?0.1?wt%MnCO₃ (x?=?0–0.75) composites with a 0.5-µm BT powder, the dielectric constant was increased with x, and the relative density was decreased at x?=?0.67 and 0.75, creating optimum BT content of x?=?0.50 with a piezoelectric constant d₃₃ of 107?pC/N. When a larger 1.5-µm BT powder was utilized for the composite with x?=?0.50, the d₃₃ value increased to 150?pC/N due to the grain size effect of the BT grains. To compensate for a compositional change from the optimum 0.3BT-0.1BMT-0.6BF due to partial diffusion between the BT and 0.3BT-0.1BMT-0.6BF grains, a 0.5BT/0.5(0.275BT-0.1BMT-0.625BF)?+?0.1?wt%MnCO₃ composite with the 1.5-µm BT powder was fabricated. We obtained an increased d₃₃ value of 166?pC/N. These results provided a useful composite design to enhance the piezoelectric properties.     

Temperature dependence of electrical and electromechanical properties of Pb(Mg1/3Nb2/3)O3–Pb(Ni1/3Nb2/3)O3–Pb(Zr,Ti)O3 thin films

The electrical and electromechanical properties of Pb(Mg_1/3Nb_2/3)O₃–Pb(Ni_1/3Nb_2/3)O₃–Pb(Zr,Ti)O₃ (PMN–PNN–PZT, PMN/PNN/PZT = 20/10/70) on Pt/Ti/SiO₂/Si substrates by chemical solution deposition was investigated. The PMN–PNN–PZT films annealed at 650 °C exhibited slim polarization hysteresis curves and a high dielectric constant of 2100 at room temperature. A broad dielectric maximum at approximately 140–170 °C was observed. The field-induced displacement was measured by scanning probe microscopy, the bipolar displacement was not hysteretic, and the effective piezoelectric coefficient (d₃₃) was 66 × 10⁻¹² m/V. The effective d₃₃ decreased with temperature, but the value at 100 °C remained 45 × 10⁻¹² m/V.     

Structural anomaly and electrical relaxation in (Na2/3Pb1/3)(Mn1/2Nb1/2)O3 ceramics

The X-ray diffraction patterns of (Na_2/3Pb_1/3)(Mn_1/2Nb_1/2)O₃ ceramics were measured within 15–850 K temperature range. The anomaly in the thermal expansion temperature dependence occurred in 250–365 K range. The generalised Cole–Cole model was proposed to describe the measured effective electric permittivity influenced by high electric conduction and the coexistence of two contributions ?*(T,f) = ?*_lattice + ?*_carriers was considered. The analysis of the electric permittivity and conduction exhibited two relaxation processes. The electric conduction relaxation characteristic time values indicated the small polaron mechanism with τ₀ ≈ 10⁻¹³ s occurring in 240–345 K range and the ionic mechanism with τ₀ ≈ 10⁻¹¹ s involved in the other relaxation occurring in the 320–510 K range. The ionic relaxation process was ascribed to a subsystem of defects, which was weakly interrelated to the anomaly in thermal expansion of the (Na_2/3Pb_1/3)(Mn_1/2Nb_1/2)O₃ ceramics. The Gate model was proposed to describe the ionic relaxation mechanism.     

Mesomorphic behavior of polydiethylphosphazenes as described by13C,14N, and2H NMR

The existence of mesomorphism in polydiethylphosphazene was recently established by MAS NMR and X-ray diffraction characterization. In the present work the mechanism of motion of the ethyl side groups in the high-temperature polymorph tabove 45 C) is identified and compared to the arrangement of side groups in the low-temperature polymorph. For this purpose a few NMR active nuclei (¹³C,¹⁴N, and²H) were exploited to define the side-chain motions occurring at transition. Experiments performed at varying temperatures close to the onset of solid transition suggest the presence of jumps between two conformations in the pretransition state. Rotor-synchronized triple-resonance NMR of the high-temperature phase determined the average distances between the carbons and the nitrogens in the polymorphs. The theoretical prediction of the dipolar interaction between the nuclei supports the hypothesis that ethyl groups can undergo a complete rotation about the P CH₂ bond by jumping across a conformational barrier. The mechanism of motion of the ethyl groups must be cooperative and the collapse of the rigid shell around the main chain is described at the transition.Presented at the 1st Italian Workshop on Cyclo- and Poly (phosphazene) Materials. February 15 16, 1996, at the CNR Research Area in Padova, Italy.     

Effects of addition of Pb(Y1/2Nb1/2)O3 (PYN) on microstructure and piezoelectric properties of Pb(Zr0.53Ti0.47)O3

Pure and Pb(Y_1/2Nb_1/2)O₃ (PYN)-doped Pb(Zr_0.53Ti_0.47)O₃ have been characterized. The samples were prepared by conventional mixed-oxide ceramic technology. PYN dopant was added to PZT at content levels ranging from 1 to 2.5 mol%. The microstructures of the samples were examined using SEM and TEM. The average grain size was observed to decrease as the dopant content increased. Herringbone-like and wedge-shaped domain patterns were observed in all the samples. The piezoelectric properties of PZT were greatly improved by the addition of PYN. The highest piezoelectric constant d₃₁ was nearly twice that of pure PZT.