Ce(Ⅲ)在辣根体中的迁移

应用放射性同位素示踪法,即结合放射自显影和液体闪烁器检测及电镜放射自显影技术,首次定性、定量地研究Ce(Ⅲ)离子在辣根植物中的迁移.结果表明:(1)Ce(Ⅲ)离子能被辣根植物吸收并随时间发生迁移;(2)电镜放射自显影结果显示,Ce(Ⅲ)离子迁移是通过质外体至共质体进入细胞的.Ce(Ⅲ)离子在辣根植物体中的行为,为稀土离子植物环境效应机理及辣根植物安全防护提供借鉴.     

镧、铈和铽作用于细胞的靶点差异

稀土可通过食物链进入生命体并累积已成为不争的事实,但稀土离子的植物细胞化学行为尚不清楚.本文通过~(140)La(Ⅲ)、~(141)Ce(Ⅲ)、~(160)Tb(Ⅲ)在植物体内放射自显影技术和量子化学计算等研究发现,化学性质相似的稀土离子La(Ⅲ)、Ce(Ⅲ)、Tb(Ⅲ)在细胞质膜和质膜外作用靶点显著不同,即Ce(Ⅲ)主要与质膜物质发生键合,La(Ⅲ)还能与细胞质膜外的细胞外物质和胞外基质分子键合,Tb(Ⅲ)更可与细胞壁物质键合;La(Ⅲ)和Tb(Ⅲ)与胞吞作用进入细胞的物质发生键合而进入细胞,Ce(Ⅲ)尚未观察到此现象;La(Ⅲ)和Tb(Ⅲ)与细胞质膜和质膜外物质通过配位共价键及分子间氢键形成稳定的路易斯酸碱配合物,Ce(Ⅲ)则可能仅靠库仑力与细胞质膜物质发生作用.由此导致La(Ⅲ)、Ce(Ⅲ)、Tb(Ⅲ)3种离子对细胞的作用靶点具有明显选择性,其中Ce(Ⅲ)的选择性La(Ⅲ)Tb(Ⅲ).可见,3种稀土离子不同数量f电子的成键活性所致细胞质膜及膜外靶分子键长、键角等参数差异,将导致下游信号转导及细胞化学行为迥异,终致其毒理不同.本文结果可为科学探究稀土累积对生物危害的细胞学机理提供新的思考与借鉴,也为稀土食品安全及人类健康预防提供重要指导.     

铬(III)离子催化铈(IV)离子氧化四氢糠醇的反应动力学及机理

在酸性介质中用氧化还原滴定法研究了铈(IV)离子在铬(III)离子催化作用下,于25～40℃区间氧化四氢糠醇的反应动力学.结果表明反应对铈(IV)和四氢糠醇均为一级.准一级速率常数kobs随催化剂[Cr(III)]增加而增大,亦随[H+]增加而增大,而随[HSO-4]增加而减小.在氮气保护下,反应不能引发丙烯酰胺聚合,说明在反应中没有自由基产生.提出了催化剂、底物和氧化剂间生成双核加合物的反应机理.通过kobs与HSO-4的依赖关系,并结合Ce(IV)在溶液中的平衡,找到了本反应体系的动力学活性物种是Ce(SO4)2.还计算出一些速率常数及相应的活化参数.     

CaO或BaO与Sm2O3共掺杂CeO2体系电子结构和氧离子迁移的DFT+U研究

使用GGA+U方法研究了Ca O或Ba O与Sm2O3共掺杂Ce O2体系几何和电子结构及氧离子迁移。计算结果表明,Ba和Sm均靠近氧空位时Ba Sm Ce30O63体系最稳定;Sm靠近,Ca远离氧空位时Ca Sm Ce30O63体系最稳定。Ba Sm Ce30O63和Ca Sm Ce30O63体系中均不存在Ce4+变价。对Ca Sm Ce30O63体系氧离子迁移的研究发现,当氧离子迁移到空位时,迁移能大小顺序为Em(3→V)Em(1→V)Em(4→V)Em(2→V),这一规律源于氧离子与低价掺杂离子产生负电势之间的排斥作用;对Ba Sm Ce30O63体系氧离子迁移的研究发现,当空位迁移到周围氧离子时,迁移能大小顺序为Em(V→3)Em(V→5)Em(V→1),这一规律源于氧空位产生的正电势与低价掺杂离子产生的负电势之间的吸引作用。此外,Ca Sm Ce30O63体系最小迁移能小于Sm Ce31O63体系,证实了Ce O2-Sm2O3-Ca O体系离子电导率大于Ce O2-Sm2O3体系的实验结果。     

铬(III)离子催化铈(IV)离子氧化四氢糠醇的反应动力学及机理

在酸性介质中用氧化还原滴定法研究了铈(IV)离子在铬(III)离子催化作用下, 于25～40 ℃区间氧化四氢糠醇的反应动力学. 结果表明反应对铈(IV)和四氢糠醇均为一级. 准一级速率常数k_obs随催化剂[Cr(III)]增加而增大, 亦随[H^＋]增加而增大, 而随增加而减小. 在氮气保护下, 反应不能引发丙烯酰胺聚合, 说明在反应中没有自由基产生. 提出了催化剂、底物和氧化剂间生成双核加合物的反应机理. 通过k_obs与的依赖关系, 并结合Ce(IV)在溶液中的平衡, 找到了本反应体系的动力学活性物种是Ce(SO₄)₂. 还计算出一些速率常数及相应的活化参数.     

铱(III)离子催化铈(IV)离子氧化四氢糠醇的动力学及机理

在酸性介质中用氧化还原滴定法研究了铈(IV)离子在痕量铱(III)离子催化作用下,于298￣313K区间氧化四氢糠醇(THFA)的反应动力学.结果表明,反应对铈(IV)离子为一级,对铱(III)离子也为一级,对四氢糠醇的表观反应级数为正分数.准一级速率常数kobs随[H ]增加而增大,而随[HSO-4]增加而减小.在氮气保护下,反应能引发丙烯腈聚合,说明在反应中有自由基产生.通过kobs与[HSO4-]的依赖关系,找到本反应体系的动力学活性物种是Ce(SO4)2,并计算出平衡常数,速控步骤的速率常数及相应的活化参数.     

非化学计量组成Ba_(1.03)Ce_(0.5)Zr_(0.4)La_(0.1)O_(3-α)的化学稳定性和离子导电性

用高温固相反应法合成了非化学计量组成的Ba1.03Ce0.5Zr0.4La0.1O3-α质子导体.粉末X射线衍射(XRD)结果表明,该材料为单一钙钛矿型BaCeO3斜方晶结构,在高温下、CO2或水蒸气气氛中具有较高的稳定性.扫描电子显微镜(SEM)观察分析表明,材料经1550℃烧结20h非常致密.在500～900℃温度范围内,用交流阻抗谱技术测定了材料在湿润氢气和湿润空气气氛中的电导率;用气体浓差电池方法测定了材料在湿润氢气、湿润空气气氛中和氢-空气燃料电池条件下的离子迁移数,研究了材料的离子导电特性,并与化学计量组成的BaCe0.5Zr0.4La0.1O3-α材料进行了比较.结果表明,在500～900℃温度范围内、湿润氢气气氛中,Ba1.03Ce0.5Zr0.4La0.1O3-α材料的质子迁移数为1,是一个纯质子导体.在湿润空气气氛中,材料的氧离子迁移数为0.688～0.170,质子迁移数为0.218～0.017,是一个氧离子、质子和电子空穴的混合导体.在氢-空气燃料电池条件下,材料的离子(氧离子+质子)迁移数为0.990～0.796,是一个氧离子、质子和电子的混合导体.与化学计量组成的BaCe0.5Zr0.4La0.1O3-α材料相比较,在相同实验条件下非化学计量组成的Ba1.03Ce0.5Zr0.4La0.1O3-α材料具有较高的电导率和离子迁移数.     

Ba0.9La0.1Ce0.9Nd0.1O3-α陶瓷的离子导电性

用高温固相反应法制备了Ba0.9La0.1Ce0.9Nd0.1O3-α质子导电性陶瓷,粉末X-射线衍射(XRD)分析表明,该陶瓷为单一钙钛矿型斜方晶结构。在500~900℃温度范围内,分别用气体浓差电池方法和交流阻抗谱技术研究了材料在不同气体气氛中的离子导电性,并与Ba0.9Ca0.1Ce0.9Nd0.1O3-α材料的离子导电性进行了比较。结果表明,在500~900℃温度范围内、湿润氢气中,Ba0.9La0.1Ce0.9Nd0.1O3-α材料的质子迁移数为1,是一个纯的质子导体。在干燥空气中,该材料是一个氧离子和电子空穴的混合导体,氧离子迁移数为0.295~0.081,氧离子电导率高于Ba0.9Ca0.1Ce0.9Nd0.1O3-α。在湿润空气中,该材料是一个质子、氧离子和电子空穴的混合导体,质子迁移数为0.151~0.009,氧离子迁移数为0.300~0.107,质子电导率低于Ba0.9Ca0.1Ce0.9Nd0.1O3-α材料。在氢-空气燃料电池条件下,Ba0.9La0.1Ce0.9Nd0.1O3-α材料是一个质子、氧离子和电子的混合导体,离子迁移数为0.964~0.853,离子电导率与Ba0.9Ca0.1Ce0.9Nd0.1O3-α材料相近。     

Ba0.95Ce0.9Y03-α固体氧化物燃料电池性能

以Ba0.95Ce0.9Y0.1O3-α为固体电解质,Pt为电极,组成氢-空气燃料电池,测定了该电池600～1000℃下电流-电压特性、电极极化特性和电解质中各电荷载流子(质子、氧离子、电子空穴)迁移数及其电导率.实验表明,该电池放电性能良好,能稳定地输出电能,1000℃时的最大输出电流密度为680 mA@cm-2.正、负Pt电极极化特性很小,放电时的电压耗损主要由电解质电阻产生.在氢-空气燃料电池条件下,Ba0.95Ce0.9Y0.1O3-α显示混合离子(质子+氧离子)导电性.随着温度升高,质子迁移数减小而氧离子迁移数增大,当温度为780℃时,质子和氧离子迁移数相同(0.46),在低于780℃时,质子电导占优势,而在高于780℃时,氧离子电导占优势.     

国产CP-1型氚片

氚片是一种对氚的β射线非常敏感的特种胶片,它被广泛地应用在放射自显影技术中。所谓放射自显影术就是利用放射性样品中的示踪剂发射出的射线使感光材料感光,这种利用感光胶片记录、测量示踪剂在标本中的准确位置和强度的方法称为放射自显影术。在农业、林业以及医药科学研究领域中,放射自显影术已成为示踪研究的重要手段之一,而同位素氚则是最重要的示踪元素之一,由它所标记的化合物制备简便、价格低廉。     

Preparation and adsorption mechanism of rare earth-doped adsorbent for arsenic(V) removal from groundwater

Human poisoning and death from arsenic(As) have occurred as a result of drinking water contaminated with As in some regions and countries, such as Taiwan, Chile, Bangladesh, and In-dia[1]. Chronic arsenism poses a serious health problem in China also[2]. If China lowers its current drinking water standard of As from 0.05 to 0.01 mg/L[3], a level adopted by WHO[4] and some industrialized countries[5], the population affected will increase significantly. It is of great impor-tance to develo…     

Fluorimetric trace determination of cerium(III) with sodium triphosphate

Sodium triphosphate acts as a specific reagent for enhancing the fluorescence intensity of cerium(III). The purpose of this study was to investigate the spectrofluorimetric determination of trace amounts of Ce(III) in sodium triphosphate solution. The excitation and emission wavelengths are 303.5 nm and 353 nm respectively. Optimum sodium triphosphate concentration is found to be 0.074 g l(-1) at room temperature. The fluorescence varies linearly with the concentration of cerium(III) in the range 0.001-45 mug ml(-1). The detection limit is 9.4 x 10(-4)mug ml(-1). The relative standard deviations for 30 mug ml(-1) and 0.05 mug ml(-1) Ce(III) in 0.074 g l(-1) sodium triphosphate solution are 1.1% and 0.72% respectively. Quenching effects of other lanthanides and some inorganic anions are described. This method is a direct and rapid analytical method for the determination of Ce(III) in rare earth mixtures and cerium concentrates.     

Determination of rare earth elements in recent and fossil shells by radiochemical neutron activation analysis

Seven rare earth elements (La, Ce, Sm, Eu, Tb, Yb and Lu) in marine shell samples were determined by neutron activation analysis. In order to measure γ-ray using a Ge(Li) detector without serious interference from the intense Compton background from²⁴Na, a simple radiochemical separation was performed by a co-precipitation method with hydrated iron(III) oxide. The chemical yields for shell samples (91–99%) were determined by a re-activation technique for Gd and Yb. The interference from the²³⁵U(n, fission) reaction was corrected for determination of La and Ce. The data obtained in this study showed the behavior of rare earth elements in shells during the process of fossilization.     

Spectrofluorometric trace determination of cerium(III) in sodium hexametaphosphate solutions

The use of sodium hexametaphosphate in the spectrofluorometric determination of trace amounts of cerium(III) ions is described. Sodium hexametaphosphate acts as a specific reagent for enhancing the fluorescence intensity of cerium(III) in aqueous solutions. The apparent excitation and fluorescence wavelength used are 304 and 344 nm, respectively. Maximum fluorescence intensity is obtained by irradiating Ce(III) dissolved in 5.346 g/l sodium hexametaphosphate solution at room temperature. The fluorescence varies linearly with the concentration of cerium(III) in the range of 0.001-60 microg/ml. The coefficient of variation for 45 microg/ml Ce(III) in 5.346 g/l sodium hexametaphosphate solution is 1. The quenching effects of other lanthanides and some inorganic anions are given. This technique permits a direct and rapid determination of cerium(III) in rare earth mixtures and cerium concentrates.     

Adsorptive Voltammetric Studies on the Cerium(III)–Alizarin Complexon Complex at a Carbon Paste Electrode

A novel procedure was developed for the determination of trace cerium on the basis of anodic adsorption voltammetry of the Ce(III)–alizarin complexon (ALC) complex at a carbon paste electrode (CPE). The procedure is convenient to determine cerium individually in the presence of other rare earths because there is a 100 mV difference between the peak potentials of Ce(III)–ALC and other rare earth(III)–ALC complexes in a supporting electrolyte of 0.08 M HAc–NaAc and 0.012 M potassium biphthalate (pH 4.7) when performing linear-scanning from −0.2 to 0.8 V (vs. SCE) at 100 mV/s. The second-order derivative peak currents are directly proportional to the Ce(III) concentration over a range of 6.0 × 10⁻⁹–3.0 × 10⁻⁷ M. The detection limit is as low as 2.0 × 10⁻⁹ M (S/N = 3) for a 120 s preconcentration. An RSD of 3.5% was obtained for 15 determinations of Ce(III) at a concentration of 4.0 × 10⁻⁸ M on the same CPE surface. The method was applied successfully to the determination of cerium in samples of rare earth nodular graphite cast iron.     

Syntheses, Structures, and Spectroscopic Properties of Plutonium and Americium Phosphites and the Redetermination of the Ionic Radii of Pu(III) and Am(III)

A series of isotypic rare earth phosphites (RE = Ce(III), Pr(III), Nd(III), Pu(III), or Am(III)) with the general formulas RE(2)(HPO(3))(3)(H(2)O) along with a Pu(IV) phosphite, Pu[(HPO(3))(2)(H(2)O)(2)], have been prepared hydrothermally via reactions of RECl(3) with phosphorous acid. The structure of RE(2)(HPO(3))(3)(H(2)O) features a face-sharing interaction of eight- and nine-coordinate rare earth polyhedra. By use of the crystallographic data from the isotypic series along with data from previously reported isotypic series, the ionic radii for higher coordinate Pu(III) and Am(III) were calculated. The (VIII)Pu(III) radius was calculated as 1.112 ± 0.004 ?, and the (IX)Pu(III) radius was calculated to be 1.165 ± 0.002 ?. The (VIII)Am(III) radius was calculated as 1.108 ± 0.004 ?, and the (IX)Am(III) radius was calculated as 1.162 ± 0.002 ?.     

Infrared spectroscopic characteristics of octa-substituted bis(phthalocyaninato) rare earth complexes peripherally substituted with (4-methoxy)phenoxy derivatives

The infrared (IR) spectroscopic data for a series of 15 rare earth double-deckers M[Pc(MeOPhO)(8)](2) [M=Y, La, ..., Lu, except Pm; H(2)Pc=2, 3, 9, 10, 16, 17, 23, 24-octakis(4-methoxyphenoxy)phthalocyanine] with tervalent rare earths M(III)[Pc(MeOPhO)(8)](2) (M=Y, La, ..., Lu except Ce and Pm) and intermediate-valent cerium Ce[Pc(MeOPhO)(8)](2) have been collected with resolution of 2cm(-1). For M(III)[Pc(MeOPhO)(8)](2), typical IR marker band of the monoradical anion Pc(MeOPhO)(8)(-) shows characteristic absorption band whose frequency linearly varies in the range from 1,313 cm(-1) as a weak band for La[Pc(MeOPhO)(8)](2) to 1,324 cm(-1) as a medium band for Lu[Pc(MeOPhO)(8)](2) along with the decrease of rare earth ionic size. For Ce[Pc(MeOPhO)(8)](2), a weak band at 1,324 cm(-1) with contribution from pyrrole stretching was the marker IR band of phthalocyanine dianion Pc(2-). In conclusion, all the metal size-dependent IR absorptions should be contributed primarily from the vibrations of pyrrole, isoindole stretching, breathing or deformation or aza stretching of the Pc ring.     

稀土(III)-冠醚配位反应的热力学性质I:稀土(III)高氯酸盐与苯-15-冠-5-在乙腈溶液中配位反应的量热滴定研究

用量热滴定法于298.15K测定了除钪、钷以外的全部十五种稀土(III)高氯酸盐与苯并-15-冠-5在乙腈溶液中的配位作用。借助计算机算出了配合物的稳定常数和配位焓, 进而算出了配位自由能和配位熵。结果表明:十五种稀土(III)离子与苯并-15-冠-5都可以配位, 配位焓为正值;La^3^+配合物最稳定, Ce^3^+次之, 其余稀土(III)离子配合物稳定性变小, 但彼此差别不大, 在Tb处有突变;熵在配合物形成时起稳定化作用。     

Preconcentration of trace transition metal and rare earth elements from highly saline solutions

Quantitative recovery and preconcentration of trace amounts of Ce(III), Co(III), Eu(III), Fe(III), Gd(III), Mn(II), Y(III) and Zn(II) ions from nearly saturated brines on the chelating resin Chelex-100 are described. Carrier-free radioactive isotopes were used. Only manganese was significantly affected by the high ionic strength of the brines. Chromium (III) was retained quantitatively by the resin but not eluted quantitatively. The results indicate that transition metal and rare earth ions can be quantitatively preconcentrated from solutions of low and high ionic strength.     

Polarographic determination of Ce(III) and Tm(III) using rare earth-DBF-chlorophosphonazo complex

The electrochemical behaviour of the DBF—chlorophosphonazo (DBF—CPA)—rare earth (RE) complex has been investigated in this paper. A highly sensitive polarographic adsorption wave was found in the RE(III)—DBF—CPA system and a new method for determination of trace total RE(III) has been established. The limit of detection was 1.8 × 10⁻⁸M. The results of determination of the total RE(III) content in Chinese standard reference materials of cast-iron and alloy steel were in good agreement with the certified values. The polarographic adsorptive waves of Ce(III) and Tm(III)—DBF—CPA overlap seriously. In order to improve the selectivity of determination, a non-linear regression model was employed to fit the peak height of the polarographic wave and the concentrations of Ce(III) and Tm(III). The predictive accuracy of this model for simulant mixtures was satisfied.