金属材料分析方法的选择和施行 第六讲 金属材料中稀土元素的测定（续）

稀土元素的4f电子层受配位场的影响,较易形成离子型螯合剂,这种与偶氮胂Ⅲ所形成的呈色螯合物的吸收光谱趋向红移。偶氮胂Ⅲ[Ar(Ⅲ)]试剂在游离状态时,它的分子结构是对称的。但由于胂酸基团的空间位阻效应,分子的左右两部分不在一个面上,它与稀土离子的螯合反应只有一个分析特征功能结构参与,即螯合反应只在分子的一侧发生,因而使分子的对称性破坏,这一现象的产生也使其色泽有所加深,而且在试剂与稀土离子的螯合物形成后产生了在可见光区内出现两个吸收峰,一个峰位于610 nm左右,是不与稀土离子反应的功能结构所引起的;另一个峰位于665 nm…     

金属材料分析方法的选择和施行——第六讲 金属材料中稀土元素的测定（续）

2.3.4在稀土共存时钍的螯合滴定稀土矿石常有少量钍、钇或钪共存,例如以包头矿源为原料的一些含稀土元素的金属材料常同时含有一定量的钍,例如在稀土-硅-镁-铁合金中常含有微量钍,在此类金属材料的分析中,钍的测定不容忽视。钍的测定可采用光度法,也可用螯合滴定法,有关光度法测定钍将在以后论述。本节中只讨论钍的螯合滴定的有关问题。钍属锕系元素,仅有正四价一种稳定的原子价状态,其配位数为8,与EDTA或CyDTA能形成稳定的螯合物,lgK值达23.2,用上述滴定剂可进行螯合滴定。钍与稀土共存时,可进行钍和稀土的连续滴定,但如用XO作指示剂,…     

金属材料分析方法的选择和施行——第六讲 金属材料中稀土元素的测定（续）

2．1．2 沉淀草酸稀土时草酸的加入量及溶液的酸度条件与稀土的氢氧化物和氟化物相比,草酸稀土沉淀的溶解度相对较大,因此,溶液体积不宜太大和稀土离子的量不宜太少是进行草酸稀土沉淀时的两项基本要求。为使草酸稀土的沉淀尽可能地完全,一般要求     

金属材料分析方法的选择和施行第六讲金属材料中稀土元素的测定(续)

表6-21稀土(Ⅲ)与CPAⅢ的α型螯合物的光吸收特性在强酸性溶液中因质子化而可能出现以下两种形式上:式中R为-AsO目前,在成熟的分析方法中常用的试剂有偶氮氯膦-pN,偶氮氯膦-mN,偶氮氯膦-mA等几种。具有不对称结构的变色酸双偶氮类显色剂的优良分析性能与其分子结构有关。此类试剂在分子结构上的不对称性,使分子两端电子云分布不均匀且易于极化;在试剂分子中引入了电负性较大的助色基团,导致产生强烈的诱导效应,例如在偶氮氯膦型试剂的分子中,-PO3H2为较强的成盐基团,在-PO3H2基团的间位上,也就是在偶氮基的对位上引入了电负性较强的氯…     

金属材料分析方法的选择和施行第六讲金属材料中稀土元素的测定(续)

稀土(Ⅲ)与CPAⅢ生成的α型螯合物的可萃取性也是一种很有实用意义的特征。在pH 1.1~1.5的酸度条件下反应生成的α型螯合物可用正丁醇萃取。螯合物在有机相中吸光度可稳定至少24 h。与在水溶液的显色反应比较,螯合物在有机相中呈出3项特点:①稳定性好;②在水溶液中各单一稀土(Ⅲ)离子的螯合物的吸收峰波长略有差异,而在正丁醇中吸收峰的波长无差异,均为668 nm;③在正丁醇介质中,各单一稀土(Ⅲ)螯合物的摩尔吸光系数的值比在水溶液中的值高3倍左右;其值从镧至镝随原子序数增大而增加,而从镝至镥却随原子序数增大而减小(表6-21)。由于CPAⅢ…     

读者园地

问二硫代二乙酸氨基甲酸铵(以下简写作IDTC)试剂作为铜的显色剂有什么优点和缺点?答 :IDTC也属硫给予体光度显色剂 ,其结构式为 :NNH4OOCH2 CNH4OOCH2 CCSSNH4该试剂与铜 (Ⅰ、Ⅱ )离子在 pH 3～ 11的范围内反应生成棕黄色水溶性螯合物 ,其吸收峰位于 4 4 0nm波长处。螯合物形成后在2 4h内吸光度稳定不变。当有EDTA存在时 ,其稳定性随溶液的酸度不同而不同。在pH 3时 ,只能稳定 2 0min ;在 pH 4 .5时 ,可稳定 4 5min ;而在 pH 5 .7～ 6 .5范围内 ,可稳定 3h。镍 (Ⅱ )、钴 (Ⅱ )、铁 (Ⅲ )、钼 (Ⅵ )、银 (Ⅰ )及铋 (Ⅲ )也…     

金属材料分析方法的选择和施行第六讲金属材料中稀土元素的测定(续)

以0.01 mol·L-1PMBP萃取溶液可在pH5.5左右的溶液中将稀土(Ⅲ)萃取入有机相,从而与较大量的其他金属离子,如镁、铝、铬等分离。然后用稀盐酸将有机相中的RE(Ⅲ)反萃取入水相并在水相作稀土的光度测定。第三种方式是用较小体积的有机溶液从较大体积的水相中将RE(Ⅲ)的有色络合物萃取入有机相,这样由于有色络合物存在的溶液体积的缩小使其得到富集,其吸光度也相应地增大,而且这种吸光度的增大不仅由于体积的缩小,也由于有色络合物在有机溶剂中的离解度减弱,因为有机溶剂的介电常数通常比水小。例如RE(Ⅲ)与CPAⅢ所生成的有色螯合物在正…     

从钙热还原氟化稀土渣中提取稀土热力学分析

在已有较优直接酸浸和碱处理(碱煮、焙烧)-酸浸工艺条件下,对钙热还原稀土渣(简称稀土渣)进行酸浸热力学理论分析,应用X射线多晶衍射仪(XRD)分析碱处理过程物相变化,应用扫描电镜型附带的能谱仪(SEM+EDS)对碱煮的样品进行线性扫描和元素分析。热力学理论计算和实验结果均表明:碱煮条件下,氟化稀土能转化为氢氧化稀土;碱性添加剂焙烧条件下,氟化稀土能转化为氧化稀土,但NaOH,Na_2CO_3焙烧-酸浸工艺稀土却不能完全浸出,原因是酸浸过程CaF_2对稀土浸出影响大。此外,碱煮-酸浸的稀土提取率低,原因是碱煮时新生成的氢氧化稀土"包裹"了氟化稀土,阻碍了氟化稀土进一步碱转。在与添加Na_2SiO_3焙烧方面,Na_2SiO_3焙烧处理能削减CaF_2对稀土浸出的影响,使稀土接近完全浸出,因为酸浸Na_2SiO_3焙烧产物将生成偏硅酸和SiF~(6-)络合物,[SiF_6]~(2-)络合物的生成结合了CaF_2中大量的F-,同时抑制了稀土离子对CaF_2的解离作用,促进了稀土的浸出。此时,溶液中CaF_2固体与Ca~(2+),[SiF_6]~(2-)和稀土离子共存达到新的平衡。     

金属材料分析方法的选择和施行 第四讲金属材料中钛的测定（续）

2.6.3　变色酸作为显色剂应用于钛的测定酚类试剂,特别是含有两个相互处于邻位的试剂,一般都能与亲氧的钛(Ⅳ)离子产生显色反应。变色酸又称铬变酸(chromotropicacid),按系统命名应称为1,8 二羟基萘 3,6 二磺酸,结构式为:此试剂系羟基萘类试剂,两个羟基在分子中的位置,严格地说,相互不在邻位,但在与钛(Ⅳ)的络合反应中具有与两个相邻的羟基相似的作用。试剂级的变色酸为无色结晶,其二纳盐的相对分子质量为364.3,易溶于水,呈弱酸性(pH值约为3)。其水溶液不稳定,易被空气氧化而变成黄色或棕黄色。因此,在配制溶液时需采取防氧化措施。在弱酸…     

金属材料分析方法的选择和施行 第六讲 金属材料中稀土元素的测定（续）

上节中已提到了CPAⅢ与RE(Ⅲ)离子所生成的螯合物具有比偶氮胂Ⅲ的螯合物更好的光度分析特性,可归纳为以下几点:(1)可在较高一些的微度条件下反应;(2)所生成的螯合物有较高的稳定性;(3)所生成的螯合物的吸收峰向长波方向移动,其色泽的深度和强度明显增加,且与CPAⅢ试剂色泽之间     

Generation and detection of levuglandins and isolevuglandins in vitro and in vivo

Levuglandins (LGs) and isolevuglandins (isoLGs), formed by rearrangement of endoperoxide intermediates generated through the cyclooxygenase and free radical induced oxidation of polyunsaturated fatty acids (PUFAs), are extraordinarily reactive, forming covalent adducts incorporating protein lysyl ε-amino groups. Because they accumulate, these adducts provide a dosimeter of oxidative injury. This review provides an updated and comprehensive overview of the generation of LG/isoLG in vitro and in vivo and the detection methods for the adducts of LG/isoLG and biological molecules in vivo.     

Enthalpies of solution of purine and adenine in water and in dimethylsulfoxide

Journal of Solution Chemistry - Enthalpies of solution of purine and adenine in water and in demethylsulfoxide were measured calorimetrically in the temperature range 25–40°C. ΔH s...     

Determination of diazepam and nordazepam in milk and plasma in the presence of oxazepam and temazepam

For studies on the excretion of drugs into milk a sensitive high-performance liquid chromatographic assay was developed to quantitate diazepam and nordazepam in the milk and plasma of humans and rabbits in the presence of their major metabolites, oxazepam and temazepam. Flurazepam was used as an internal standard. The assay involves extractions with diethyl ether and an additional acid clean-up step. Chromatographic separation was achieved by a LiChrospher 60 RP-select B (5 microns) column and KH2PO4- acetonitrile (69:31, v/v) adjusted to pH 2.80 as a mobile phase. The same extraction and chromatographic conditions were suited to both types of samples, milk and plasma. The limits of determination using ultraviolet detection at 241 nm was for diazepam 20 ng/ml and for nordazepam 15 ng/ml. The absolute recoveries of diazepam, nordazepam and flurazepam in human milk were 84, 86 and 92% and in human plasma 97, 89 and 94%, respectively. The within- and between-day accuracy and precision for diazepam and nordazepam in milk and plasma at all concentrations tested (20-1500 ng/ml) were better than 8%. The high fat content which occurs in rabbit milk presented no limitation for the extraction of lipophilic diazepam: the method was successfully used to monitor milk and plasma concentrations of diazepam and nordazepam in lactating New Zealand White rabbits during 26-h infusions of diazepam (1.4 mg/h).     

Coassembly of Nanorods and Nanospheres in Suspensions and in Stratified Films

The entropically driven coassembly of nanorods (cellulose nanocrystals, CNCs) and nanospheres (dye‐labeled spherical latex nanoparticles, NPs) was studied in aqueous suspensions and in solid films. In mixed CNC‐latex suspensions, phase separation into an isotropic latex‐NP‐rich and a chiral nematic CNC‐rich phase took place; the latter contained a significant amount of latex NPs. Drying the mixed suspension resulted in CNC‐latex films with planar disordered layers of latex NPs, which alternated with chiral nematic CNC‐rich regions. In addition, fluorescent latex NPs were embedded in the chiral nematic domains. The stratified morphology of the films, together with a random distribution of latex NPs in the anisotropic phase, led to the films having close‐to‐uniform fluorescence, birefringence, and circular dichroism properties.     

Comparison and correlation of in vitro, in vivo and in silico evaluations of alpha, beta and gamma cyclodextrin complexes of curcumin

In the present study investigated the effect of curcumin (CUR) alpha (α), beta (β) and gamma (γ) cyclodextrin (CD) complexes on its solubility and bioavailability. CUR the active principle of turmeric is a natural antioxidant agent with potent anti-inflammatory activity along with chemotherapeutic and chemopreventive properties. Poor solubility and poor oral bioavailability are the main reasons which preclude CUR use in therapy. Extent of complexation was β-CD complex (82 %) > γ-CD (71 %) > α-CD (65 %). Pulverization method resulted in significant enhancement of CUR (0.002 mg/ml) solubility with CUR α-CD complex (0.364 mg/ml) > CUR β-CD complex (0.186 mg/ml) > CUR γ-CD complex (0.068 mg/ml). Gibbs-free energy and in silico molecular docking studies favour formation of α-CD complex > β-CD complex > γ-CD complex. With reference to CUR, relative bioavailability of CUR α-CD, CUR β-CD and CUR γ-CD complexes were 460, 365 and 99 % respectively. CUR–CD complexes exhibited increased bioavailability with an increase in t_½, tmax, Cmax, AUC, Ka, and MRT; and a decrease in Ke, clearance and Vd values. AUC increase was CUR α-CD complex > CUR β-CD complex > CUR γ-CD complex. Significant difference (p < 0.05) was observed between CUR α-CD complex and CUR γ-CD complex by one-way ANOVA and Dunnett’s post hoc test for multiple comparison analysis. Correlation observed between in vitro, in vivo and in silico methods indicates potential of in silico and in vitro methods in CD selection.     

Homo- and hetero-complexes of exchangeable apolipoproteins in solution and in lipid-bound form

The self-association state of human plasma apolipoprotein E (apoE) in solution and in complexes with dimyristoylphosphatidylcholine (DMPC) varying in stoichiometry was studied in sub-micromolar concentration range by gel filtration, fluorescence anisotropy, fluorescence quenching and energy transfer measurements with apolipoprotein labeled with lysine-specific fluorescent dyes. Together, these results confirm the equilibrium scheme for various apoE structures in solution: oligomer (in aged preparations) <==> 'closed' tetramer <==> 'open' tetramer ('molten globule' state) <==> native or partially denatured monomer <==> fully denatured monomer. Within DMPC:apoE discoidal complex (125:1) the apolipoprotein association state seems to be intermediate between that in solution and in larger vesicular complex (1000:1); for both complexes, the degree of exposure of fluorescein chromophores into water phase decreased. Hetero-associates of apoA-I and apoC-III-1 in solution and in the complexes with DMPC appear to behave similarly to apoE. When extrapolated to native HDL particles, 'molten globule' state seems to be a structure responsible for the interaction of exchangeable apolipoproteins with phospholipid. For a first time, the location of various apolipoprotein molecules on disc periphery was confirmed. The lysine residue(s) seems to locate closely to reacting residue(s) within apolipoprotein molecules in associates, however, with different package constraints for discoidal versus vesicular complexes with phospholipid.     

Structure of dimethoxyamine in the crystalline and gaseous phases and in solution

Conclusions It has been established by the methods of x-ray diffraction analysis and electron diffraction analysis and measurements of the dipole moments and the birefringence that in the crystalline and gaseous phases, as well as in solution, N,N-dimethoxyamine has a gauche-gauche conformation, which is stipulated by a stabilizing nO-N-O* orbital interaction. The geometric parameters of the molecule have been determined.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2235–2242, October, 1986.     

Fluorimetric quantification of clodronate and alendronate in aqueous samples and in serum

The bisphosphonates clodronate and alendronate are drugs in the therapy of osteoporosis or Paget's disease. They are highly hydrophilic and therefore of low oral bioavailability. Determination methods for bisphosphonates are often laborious and expensive equipment is needed. The presented quantification method based on kinetic measurement of the fluorescence decrease of an Al³⁺-morin complex can be used to determine the bisphosphonate content in aqueous and plasma samples. The intra- and inter-assay accuracies were found to be within 98.8% and 102.3% of the target samples for clodronate and within 97.2% and 105.0% of the target samples for alendronate. The LOQ was defined as 15.6 ng/ml for clodronate and 62.5 ng/ml for alendronate. In serum samples, intra- and inter-assay accuracy was found to be within 99.0% and 101.6% of the target samples for clodronate and within 97.8% and 102.6% of the target samples for alendronate. In serum samples, the LOQ was defined as 1.55 mg/ml for clodronate and 0.39 mg/ml for alendronate. Though less sensitive in serum, the presented method could support research on the development of drug delivery systems in vitro and in vivo for the investigated and other structurally related bisphosphonates.