钙锶氯化物体系中钙和锶的重量法分析

针对氯化钙氯化锶混合体系,探索出能够准确分析该体系中钙和锶含量的分析方法。首先,用碳酸盐重量法分别对氯化钙和氯化锶单盐溶液进行分析,能够获得比较准确的测定结果且确定了碳酸盐沉淀适宜的烘干温度和烘干时间分别为200 ℃和20 h。在此基础上,结合碳酸盐重量法和经典的氯化银重量法对氯化钙和氯化锶的混合溶液进行准确地分析,分别获得碳酸盐沉淀的总质量和总氯的物质的量,再通过联立方程组求解得到钙锶氯化物共存体系中各组分的含量。最后,将实验方法用于分析钙和锶物质的量之比YB(YB=nCa∶nSr)为49、9.4、0.98、0.10和0.030的氯化物体系中氯化钙和氯化锶的组分含量时,测定结果比较准确,绝对误差小于0.5%。     

Recycling of synaptic vesicles at the frog neuromuscular junction in the presence of strontium

In these experiments, we followed the exocytosis and endocytosis of synaptic vesicles with the vital dye FM1-43 and asked whether calcium is important for membrane retrieval at the frog neuromuscular junction. We replaced calcium with equimolar amounts of strontium and monitored the staining of recycling vesicles by inducing exocytosis with electrical stimulation. Trains of 2,400 (2 or 20 Hz) or 4,200 (20 Hz) pulses failed to induce FM1-43 internalization in the presence of strontium, but they did in the presence of calcium. This effect of strontium was not due to a decrease in exocytosis, because FM1-43 release was similar in the presence of calcium or strontium. The impairment in endocytosis, observed as inhibition of FM1-43 internalization, could be overcome by longer periods of stimulation (6,000 pulses at 2 or 20 Hz) in the presence of strontium (1.8 mM) or by increasing the extracellular concentration of strontium to 10 mM (2,400 action potentials at 20 Hz). It is suggested that endocytosis is dependent on calcium influx and that strontium is much less effective in replacing calcium for endocytosis than it is for exocytosis.     

原子吸收分光光度法连续测定钨精矿中铜钙

基于国标原子吸收光度法测定铜钙元素,在锶镧元素共存下,尝试了钨精矿中铜钙元素的连续测定方法.结果显示,铜的质量分数0～10 mg/L,钙的质量分数为0～15 mg/mL符合比尔定律.加标回收率铜为99%～101%,钙为96%～103%.     

Identification of the calcium binding site and a novel ytterbium site in blood coagulation factor XIII by x-ray crystallography

The presence or absence of calcium determines the activation, activity, oligomerization, and stability of blood coagulation factor XIII. To explore these observed effects, we have determined the x-ray crystal structure of recombinant factor XIII A2 in the presence of calcium, strontium, and ytterbium. The main calcium binding site within each monomer involves the main chain oxygen atom of Ala-457, and also the side chains from residues Asn-436, Asp-438, Glu-485, and Glu-490. Calcium and strontium bind in the same location, while ytterbium binds several angstroms removed. A novel ytterbium binding site is also found at the dimer two-fold axis, near residues Asp-270 and Glu-272, and this site may be related to the reported inhibition by lanthanide metals (Achyuthan, K. E., Mary, A., and Greenberg, C. S. (1989) Biochem. J. 257, 331-338). The overall structure of ion-bound factor XIII is very similar to the previously determined crystal structures of factor XIII zymogen, likely due to the constraints of this monoclinic crystal form. We have merged the three independent sets of water molecules in the structures to determine which water molecules are conserved and possibly structurally significant.     

Modeling calculations of pesticide contamination of horticultural products

Addition of calcium ions increased 2- to 3-fold the growth of Saccharomyces carlsbergensis 2I in a minimal glucose-containing medium. The minimal concentration enhancing growth was 25 to 50 mug/ml CaCl2. Other divalent and trivalent cations tested, except for strontium ions, did not duplicate the calcium effect. Actively growing and dividing cells took up 45Ca2+, while resting yeast cells did not. The radiocalcium taken up was incorporated into newly synthesized structural material, presumably into the membrane protein.     

Occupational allergic contact dermatitis caused by epoxy diacrylate in ultraviolet-light-cured paint, and bisphenol A in dental composite resin

Calcium ion-dependent reactivation of O2 evolution activity has been investigated in Hydrilla verticillata thylakoid preparations. Washing the thylakoids in calcium-free buffer or calcium-free buffer containing 1.5 M NaCl or 1.5 M NaCl plus 20% methanol, reversibly inhibited O2 evolution activity. The activity was restored on addition of calcium as calcium chloride and partially by strontium chloride. Immobilization of thylakoids with glutaraldehyde (GA) arrested the loss in O2 evolution activity caused by calcium-free high salt washing. However, calcium sensitivity was discernible in GA immobilized thylakoids subjected to calcium-free high salt washing. Since glutaraldehyde checks the loss of extrinsic thylakoid polypeptides due to washing, it is assumed that the calcium ion has regulatory functions in the photosynthetic electron transport, besides its interaction with thylakoid proteins.     

人体微量元素与冠心病之间关系的研究

通过对人体血清中多种微量元素的分析,发现其中钙、镁、铜、硒和锶五种元素的含量与冠心病有密切关系。运用多因子回归分析法其识别有效率达83％。     

电感耦合等离子体原子发射光谱法同时测定磷矿中12种组分

样品采用偏硼酸锂熔剂,加入溴化锂脱模剂、硝酸锂氧化剂在1 050℃高频熔样机上熔融4min,硝酸酸化提取定容后,采用基体匹配法配制校准曲线消除基体效应的影响,选取高盐雾化器进样直接用电感耦合等离子体原子发射光谱法(ICP-AES)测定磷矿中五氧化二磷、氧化镁、氧化铁、氧化铝、二氧化硅、氧化钙、氧化钾、氧化钠、二氧化钛、氧化锰、氧化锶、总硫。试验进行了熔剂与样品的稀释比、脱模剂选择、氧化剂选择、熔样温度、熔样时间、溶液酸度和溶液稳定性等条件试验,确定了最佳试验条件。方法检出限为0.000 2~0.025 8μg/g。按照实验方法测定磷矿样品中五氧化二磷、氧化镁、氧化铁、氧化铝、二氧化硅、氧化钙、氧化钾、氧化钠、二氧化钛、氧化锰、氧化锶、总硫,结果的相对标准偏差(RSD,n=11)为0.48%~1.3%。按照实验方法测定GBW 07210、GBW 07211、GBW 07212共3个磷矿石标准样品中五氧化二磷、氧化镁、氧化铁、氧化铝、二氧化硅、氧化钙、氧化钾、氧化钠、二氧化钛、氧化锰、氧化锶、总硫,测定值与认定值(或者国家标准方法 GB/T 1880—1995的测定值)基本一致。     

The oral strontium load test in the assessment of intestinal calcium absorption

A close correlation between calcium and strontium intestinal absorption has been described. In this study, a test using Stable Strontium has been assessed in women without abnormal calcium or bone metabolism, with no history of drugs which might affect calcium or bone metabolism. Decreasing values of Strontium intestinal absorption, according to the length of the postmenopausal period, have been observed. Besides, the Stable Strontium Test has been given in postmenopausal women with osteoporotic femur fractures. In comparison with age matched healthy women, this latter group showed a significantly lower Strontium intestinal absorption. Analogous behaviour has been reported for Calcium intestinal absorption.     

Oxidation of alkaline earth sulfides to sulfates: Thermodynamic aspects

The emf of the galvanic cell, Pt, Ni + NiO/(CaO) ZrO₂/MS + MSO₄, Ir, Pt, where M is calcium, strontium, or barium, has been measured in the temperature range 850 to 1100 K. From these measurements the Gibbs’ energy changes for the oxidation of sulfides of alkaline earth metals to their respective sulfates have been calculated. The results are compared with available thermodynamic data in the literature. The agreement varies from ±2 kJ for the strontium system to ±20 kJ in the case of barium. Trends in the stabilities of alkaline earth sulfates are discussed in relation to the properties of the cationic species involved.     

原子吸收法测定电解质各组分的分析方法研究

准确测定电解质混合物中各组分的含量对于合理调配电解质混合物的组成、提高电解效率有着重要的意义。采用原子吸收法测定电解质中Ca、Mg、Na三种元素含量。测定Ca、Mg、Na三元素最佳波长分别为393．3nm、202．6nm、330．2nm,体系选用SrCl2作为稀释剂、CsCl作为电离抑制剂时检测结果重现性好,加标回收率在96．1％-104．4％之间,回收率较好。提出了测定镁电解过程中电解质混合物中钙、镁、钠含量的方法,实验表明应用该方法进行电解质混合物中钙、镁、钠含量的测定有着较高的准确度和精密度,且测定快速,操作简单。     

Determinants of weddellite formation: chondroitin sulfates and citrate determine weddellite formation in vitro

In synthetic urine (SU), addition of oxalate tends to form monohydrates of calcium oxalate. However, addition of oxalate to natural urine preferably forms calcium oxalate dihydrate (COD). Urine apparently contains a determinant for COD formation. To identify the determinant, the effects of pH, temperature, oxalate, calcium, urate, citrate, magnesium, sulfate and chondroitin sulfates (CS) on calcium oxalate crystal formation were studied. Lower temperatures, higher oxalate concentrations and higher pH favored COD formation in a SU. Mixed CS in the presence of citrate were the most decisive determinant of COD formation. Substitution of CS for agar and gelatin produced similar results, indicating that the colloidal effect of the macromolecules determines COD formation. Identification of the determinants led to a simple, reproducible method of COD formation in SU without natural urine. Addition of strontium to SU resulted in dodecahedral bipyramids. Interpenetration twinning of bipyramids occur within seconds of the crystal formation.     

Some factors determining the type of phase diagram in binary systems formed by refractory oxides

Summary From literature data on the investigation of binary oxide systems an approximate correlation has been established between the ionic radii and electronegativities on the one hand and the type of phase diagram on the other. The conditions in which systems are formed with a eutectic structure of the liquidus—solidus region, or with solid solutions or chemical compounds, were determined in advance. Hitherto uninvestigated binary systems formed by oxides of rare earth elements, yttrium and scandium with oxides of group II elements (beryllium, calcium, magnesium, strontium, and barium) were analyzed.     

Production of high-manganese steel in arc furnaces. Part 2

Metallographic data are presented for manganese steel before and after ladle treatment—specifically, treatment with calcium–strontium carbonate or argon injection in the ladle or both. Quantitative analysis of the nonmetallic inclusions is undertaken. The position of the inclusions relative to the grain boundaries is determined. Electron microscopy permits detailed study of the composition and form of the inclusions that appear during ladle treatment and without such treatment. The influence of various types of ladle treatment on the impact strength of manganese steel is discussed. Alloying of the manganese steel with vanadium is considered. Practical data regarding the influence of alloying with vanadium on the impact strength of the manganese steel are presented.     

Structure and activity of the hairpin ribozyme in its natural junction conformation: effect of metal ions

The natural form of the hairpin ribozyme consists of a four-way RNA junction of which the single-stranded loop-carrying helices are adjacent arms. The junction can be regarded as providing a framework for constructing the active ribozyme, and the rate of cleavage can be modulated by changing the conformation of the junction. We find that the junction-based form of the hairpin ribozyme is active in magnesium, calcium, or strontium ions, but not in manganese, cadmium, or sodium ions. Using fluorescence resonance energy transfer experiments, we have investigated the global structure of the ribozyme. The basic folding of the construct is based on pairwise helical stacking, so that the two loop-carrying arms are located on opposite stacked helical pairs. In the presence of magnesium, calcium, or strontium ions, the junction of the ribozyme undergoes a rotation into a distorted antiparallel geometry, creating close physical contact between the two loops. Manganese ions induce the same global folding, but no catalytic activity; this change in global conformation is therefore necessary but not sufficient for catalytic activity. Fitting the dependence of the conformation on ionic concentration to a two-state model suggests that cooperative binding of two ions is required to bring about the folding. However, further ion binding is required for cleavage activity. Cobalt hexammine ions also bring about global folding, while spermidine generates a more symmetrical form of the antiparallel structure. Cadmium ions generate a different folded form, interpreted in terms of close loop-loop association while the junction is unfolded. Sodium ions were unable to induce any folding of the ribozyme, which remained slightly parallel. These results are consistent with a folding process induced by the binding of two group IIA metal ions, distributed between the junction and the loop interface.     

Stable properties of spontaneous EPSCs and miniature retinal EPSCs during the development of ON/OFF sublamination in the ferret lateral geniculate nucleus

Retinal projections to the lateral geniculate nucleus (LGN) in ferrets progressively segregate into eye-specific laminae and subsequently into sublaminae that receive inputs from either ON-center or OFF-center afferents. To study the development of synaptic efficacy during a period of activity-dependent growth and reorganization in the CNS, we recorded spontaneous EPSCs (sEPSCs) from cells of the LGN during ON/OFF sublamination. We also examined retinal inputs specifically by stimulating the optic tract in the presence of strontium and recording evoked miniature EPSCs (emEPSCs). The rise times, areas, half-widths, and decay times of sEPSCs and emEPSCs and interevent intervals of sEPSCs recorded at the beginning of ON/OFF sublamination were not different from those recorded after its completion. Typically EPSC areas were small (10-20 fC) but varied greatly both within and between neurons. The frequency of sEPSCs was also quite variable, ranging from 0.2 to 5 Hz. sEPSCs were equivalent to miniature EPSCs recorded in the presence of tetrodotoxin, and both sEPSCs and emEPSCs were CNQX-sensitive. No difference was observed between sEPSCs recorded at room temperature and those recorded at 34 degreesC, and strontium could be substituted for calcium with no effect on sEPSC shape. These data argue for a remarkable stability in the components of at least AMPA-mediated synaptic transmission during a period of major synaptic rearrangement in the LGN.     

Seasonal variations in vitamin D status and calcium absorption do not influence bone turnover in young women

OBJECTIVE: To evaluate the effect of seasonal variations in UV B-exposure on calcium absorption and bone turnover in young women with the overall goal to assess the potential benefit of a vitamin D supplementation during wintertime. DESIGN: Cross-sectional study. SETTING: Area of Bonn, Germany (51 degrees N). SUBJECTS: Thirty-eight women (24.5+/-0.5 y) studied in winter and 38 females of the same age (24.7+/-0.4 y) studied in summer. RESULTS: As estimated by a 4 d food record, both groups had similar dietary calcium and phosphorus intakes (> 1200 mg/d, respectively) covering actual recommendations. Significant reductions in serum concentrations of 25-hydroxyvitamin D (25OHD) and calcitriol, fractional calcium absorption (Fc220, measured by means of a stable strontium test), 24h urinary calcium and 24h urinary phosphorus excretion were observed during wintertime. 25OHD but not calcitriol was correlated with Fc220 values and with 24h urinary phosphorus excretion. Moreover, Fc220 was related to 24 h urinary calcium excretion. Fasting 2 h-urinary deoxypyridinoline concentrations (biomarker of bone resorption) and serum levels of carboxyterminal propeptide of type I procollagen (biomarker of bone formation) showed no differences between summer and winter. CONCLUSIONS: Our data indicate a decrease in intestinal calcium and phosphorus absorption during wintertime, most likely because of a reduction in serum 25OHD levels. Since bone turnover was not affected by the seasonal differences in mineral metabolism, there is no objective for young women with high calcium intake to supplement vitamin D during wintertime.     

锗酸锶纳米线光催化降解罗丹明B的研究

以锗酸锶纳米线作为光催化材料,分析了光照时间、锗酸锶纳米线用量及罗丹明B浓度对锗酸锶纳米线光催化降解罗丹明B的影响。固体紫外漫散射光谱表明锗酸锶纳米线属于典型的半导体,禁带宽度为3.67eV。随着光照时间的增加,罗丹明B的降解率增加。罗丹明B的起始浓度为10mgL-1、锗酸锶纳米线用量为20mg及光照时间4h时,罗丹明B的降解率为72.39%。随着罗丹明B浓度的增加,其降解率降低至34.92%。     

Thermodynamic characteristics of strontium and barium in dilute liquid alloys with tin

The changes in the partial molar thermodynamic characteristics of strontium and barium in binary alloys with tin are determined by the emf method in the temperature range 973?C1073 K. The changes in the partial molar enthalpies are found to agree satisfactorily with the data of calorimetric measurements. The activity coefficients of strontium and barium point to a strong interparticle interaction between the alloy components, which increases in going from strontium to barium.     

接触阴极法制取金属锶

本文用接触阴极在 SrCl_2-KCl 熔盐中进行了金属锶的电解。在电解试验的基础上,确定了在 SrCl_2-KCl 盐系中,用接触阴极制取锶的最佳工艺条件和锶电解的技术经济指标。从阴极上取下被熔盐结壳覆盖的锶棒,经在密闭充氩的容器中重熔铸锭,其纯度接近99％Sr。