人工神经网络吸光光度法同时测定钛锆

在钛,锆-二溴羟基苯基荧光酮-CTMAB显色体系中,应用三层ANN—BP网络解析钛和锆的吸收光谱,不经分离吸光光度法同时测定钛和锆。钛和锆的表观摩尔吸光系数分别为ε_(547)=9.66×10~4,ε_(533)=1.80×10~5。同时测定合金钢中钛和锆,结果满意。使用改进的BP算法,避免了神经网络学习过程中可能产生的麻痹现象。提出了目标向量的简单变换方法及便于网络参数选择的收敛评价函数。     

人工神经网络吸光光度法同时测定钛和铌

确立了钛 4,5-二溴邻硝基苯基荧光酮 - CTMAB显色体系 ,在此基础上确立了钛和铌同时测定的显色体系 ,应用三层 ANN- BP网络解析钛和铌吸收光谱 ,吸光光度法同时测定铌和钛。方法选择性好 ,表观摩尔吸光系数 εTi557=1 .2 4× 1 0 5L· mol-1· cm-1,εNb54 0 =1 .63× 1 0 5L· mol-1·cm-1。对合金钢中铌和钛进行了同时测定 ,钛和铌的平均相对误差分别为 1 .30 %和 1 .0 8%。使用改进的 BP算法 ,避免了可能产生的麻痹现象。提出了便于网络参数选择的收敛评价函数。     

熔融制样-X射线荧光光谱法测定锆钛矿中主次成分

锆钛矿是一种稀缺资源,也是一种战略性矿产,准确分析锆、钛及其共伴生有用有害元素含量对综合评价锆钛矿资源具有重要意义。本文采用稀释比1:20的四硼酸锂-偏硼酸锂混合熔剂,先700℃预氧化7min,再1050℃熔融19min制样,建立了熔融制样-X射线荧光光谱法测定锆钛矿中SiO2、Al2O3、Fe2O3、CaO、MgO、MnO、TiO2、K2O、Na2O、P2O5、ZrO211种主次成分的分析方法。该方法解决了锆钛矿石前处理过程中锆钛易水解,分析周期长的问题。采用标准样品加入光谱纯的方式配制锆钛矿的标准系列样品解决锆钛矿石标准样品不足的问题。本方法各组分的检出限在0.004~0.13%之间,各组分测定结果的相对标准偏差(RSD,n=12)在0.060~2.6%之间。采用本方法对实际样品进行测定,测定值与传统方法测定值一致,并具有操作简便,分析周期短的优点。     

人工神经网络X射线荧光光谱法测定钢中酸溶铝

建立了一种人工神经网络-X射线荧光光谱法测定钢中酸溶铝的方法，用X射线荧光光谱法测定低合金钢中总铝值，应用所建立的ANN-BP网络模型，输入总铝含量直接预测出酸溶铝含量。同时使用改进的BP算法，避免了神经网络学习中可能产生的麻痹现象。该方法用于钢中酸溶铝的测定，结果满意。     

偏最小二乘法-BP神经网络光度法同时测定复方氨基酸中色氨酸、酪氨酸和苯丙氨酸

用偏最小二乘法与BP神经网络联用辅助吸光光度法,不经分离同时测定复方氨基酸注射液中色氨酸、酪氨酸和苯丙氨酸。使用改进的BP算法,避免了神经网络学习过程中可能产生的麻痹现象;提出了目标向量的简单交换方法;采用均匀试验设计法,对网络参数进行了优化,避免了过拟合现象。     

锆存在时铀中杂质元素的化学分离-ICP-AES法

采用磷酸三丁酯（TBP）－氢化煤油萃取油、过氧化氢掩蔽钛、磷酸氢二铵沉淀锆的方法，用ICP－AES法同时测定了锆存在在时铀中的铁、锰、铜、硅、铝、镍和钛7种杂质元素的含量。当测定范围在100μg/g-1000μg/g时，相对标准偏差＜9．0％，回收率为96％－109％。     

锆和铪的火焰原子吸收光谱分析特性

火焰原子吸收测定锆和铪需要用高温一氧化二氮-乙炔富燃火焰。Amos和Willis,Bond等人及Sastri等人研究过锆和铪的火焰原子吸收测定,发现氟化物、三价铁、含氮化合物有增感效应,并利用这种效应拟定了间接测定氟离子和氨的方法。Panday较系统地考察过各种共存元素对锆、铪、钛的原子吸收测定的干扰。本文在上述工作的基础上,探讨大量铪或者锆存在下,火焰原子吸收测定少量锆或铪的可能性。     

氯代磺酚 S 光度法测定矿石中锆(铪)

我们在试验氯代磺酚S光度法测定铌的条件时,锆(铪)有正干扰。因此,我们探讨了用该试剂测定锆(铪)的适宜条件、干扰离子及消除方法。进而拟定了测定矿石中锆(铪)的光度法。本法的优点是选择性较好、灵敏度较高,可在常温下显色。能允许较大量钍、铀、稀土和钛的存在。当同时存在铌时,     

在硝酸介质中用铜铁试剂分离铌、钛、锆后测定磷

以往,在测定含多量铌、钛、锆高温合金钢及其铁合金中的磷时,考虑到它们易水解析出的沉淀与磷共沉,使磷的结果偏低,需要用铜铁试剂分离铌、钛、锆以消除其对测定磷时的干扰。通常在此情况下,试样的溶解,干扰元素的分离和磷的萃取,大都在硫酸介质中进行。但硫酸介质存在下述缺陷:1.磷的萃取受温度影响严重,再现性差;2.磷钼酸形成较缓慢;在放置过程中磷钼酸易与铌、钛、锆形成三元络合物,影响磷的测定;3.目前广泛采用高氯酸氧化磷,有人怕残存的高氯酸破坏铜铁试剂,常采取硫酸驱除高氯     

X-射线荧光光谱法测定锆矿石中锆硅铁钛铝钙

采用熔片法制样,建立了X-射线荧光测定锆矿石中锆、硅、铁、钛、铝、钙的分析方法。使用国家一级标准物质与二氧化锆混合配制的混合标准物质,解决了锆矿石标准物质不足的问题。试样:硼酸锂混合熔剂为1:20,在熔样机中熔成玻璃片,采用经验系数法和散射线内标法校正元素间的谱线重叠效应和基体效应,对标准物质和混配的标准样品进行了分析,标准物质测定结果与推荐值一致,相对标准偏差（RSD%）均小于3.6%。方法能满足高含量锆矿石中主、次量元素的测定。     

A carbanion induced synthesis of highly congested pyrazole and imidazole containing heterocycles

An efficient approach to the synthesis of highly congested di, penta and hexacyclic pyrazoles as well as imidazole fragment containing novel heterocyclic molecule has been developed through a carbanion induced transformation of suitably functionalized 2H-pyran-2-ones, benzo[h]chromene and thiochromeno[4,3-b]pyrans. Due to the presence of fluorescence, we report their prime application metal sensor as off/on switching in ferric ions.     

α-Amino acid derived enaminones and their application in the synthesis of N-protected methyl 5-substituted-4-hydroxypyrrole-3-carboxylates and other heterocycles

A new and simple synthesis of novel N-protected methyl 5-substituted-4-hydroxypyrrole-3-carboxylates, which exist in equilibrium with their 4-oxo tautomers, has been developed in two steps starting from N-protected α-amino acids. The key intermediates are enaminones, which can also be isolated, characterized, and used for the construction of other functionalized heterocycles, before they spontaneously decompose to pyrrole products. 4-Hydroxypyrroles are prone to partial aerial oxidation but can be efficiently alkylated or reduced to stable polysubstituted pyrrolidine derivatives.     

Specific intramolecular aromatic CH insertion of diazosulfonamides

The chemoselectivity in the intramolecular CH insertion of various diazosulfonamides has been experimentally studied. The results reveal that the aliphatic 1,4-, 1,5-, or 1,6-C(sp³)?H insertions of diazosulfonamides are not accessible, while the aromatic 1,5-C(sp²)?H insertion can be realized specifically by adjusting the diazo-adjacent group. In addition, the general chemoselectivities in the intramolecular CH insertions of diazosulfonyl compounds are summarized. Generally, diazosulfones undergo both aromatic 1,5-C(sp²)?H and aliphatic 1,5- and 1,6-C(sp³)?H insertions, while diazosulfonates undergo aliphatic 1,5- and 1,6-C(sp³)?H insertions. However, diazosulfonamides only undergo aromatic 1,5-C(sp²)?H insertion.     

N-Heterocyclic carbene-palladacyclic complexes: synthesis,characterization and their applications in the C-N coupling and α-arylation of ketones using aryl chlorides

N-Heterocyclic carbene-palladacyclic complexes 3 were successfully achieved in a one-pot procedure under mild conditions. The structure of 3a was unambiguously confirmed by X-ray single crystal diffraction and it was an active catalyst in the Buchwald-Hartwig amination and α-arylation of ketones even at very low catalyst loadings (0.01?mol%).     

Selective synthesis of 4,5-dihydroimidazo- and imidazo[1,5-a]quinoxalines via modified Pictet–Spengler reaction

An efficient tandem approach for the selective synthesis of 4,5-dihydroimidazo[1,5-a]quinoxalines 6a–g and imidazo[1,5-a]quinoxalines 7a–h by the reaction of 2-imidazolyl anilines 4a–c with aryl aldehydes 5a–k under mild reaction conditions is described. Introduction of electron releasing alkyl groups in substrates 4a–b was found to be instrumental for the success of the reaction.     

Understanding the Diels-Alder reactivity of 1,2-azaborine analogues

The Diels-Alder reactivity of 1,2-heteroborines (H₄C₄B(H)X, X?=?NH, PH, AsH; O, S, Se) has been computationally explored by means of Density Functional Theory (DFT) calculations. The influence of the HB?=?X fragment on the reactivity of the system has been quantitatively analyzed in detail by means of the so-called Activation Strain Model (ASM) of reactivity. It is found that the interaction between these species and the dienophile is significantly stronger than that computed for their all-carbon isoelectronic counterpart, benzene. In addition, the strain energy plays a key role in the observed reactivity trends. The role of the aromaticity strength of these heteroarenes on the reactivity is also assessed.     

Synthesis of N-substituted carbazolones from α-iodo enaminones via Pd(0)-catalyzed intramolecular coupling under microwave irradiation

A variety of N-aryl and N-alkyl carbazolones were conveniently achieved in good to high yields via Pd₂(dba)₃-mediated intramolecular coupling of N-substituted α-iodo enaminones under microwave irradiation. The Pd(0)-catalyzed cyclization was found to proceed favorably with the more electron-deficient phenyl ring during the reactions involving unsymmetrical N,N-diaryl α-iodo enaminones. This unique property enables the construction of carbazolone skeleton containing nitro substituted benzenoid ring.     

Iodine-mediated oxidative Pictet-Spengler reaction using terminal alkyne as the 2-oxoaldehyde surrogate for the synthesis of 1-aroyl-β-carbolines and fused-nitrogen heterocycles

An efficient iodine-mediated oxidative Pictet-Spengler reaction in dimethyl sulphoxide (DMSO) using terminal alkynes as the 2-oxoaldehyde surrogate for the synthesis of aryl (9H-pyrido[3,4-b]indol-1-yl)methanones is described. The scope of the protocol includes the total synthesis of Fascaplysin, Eudistomins Y₁ and Y₂. The methodology is extended for preparing pyrrolo[1,2-a]-quinoxaline and indolo[1,5-a]quinoxaline derivatives. The utility of 1-aroyl-β-carbolines was demonstrated by performing palladium-catalyzed β-carboline directed ortho-C(sp2)-H functionalization of the phenyl ring with thiomethyl (SMe) group using DMSO as source and for accessing 4-aryl-canthin-6-ones.     

Facile synthesis of bicyclic 1-arylpyrazol-5-ones

In this Letter, we described a facile method for constructing fused bicyclic 1-arylpyrazol-5-one ring system. We employed various methylene-containing carboxylic acids as the substrates and proved that the pyrazolone ring closure requires activated methylene group in intermediate II. Accordingly, a series of structurally diversified, fused bicyclic 1-arylpyrazol-5-ones was prepared in moderate to high yields using the requisite substrates.     

Synthesis of substituted 2,4,5,6-tetrahydrocyclopenta[c]pyrazoles and 2,4,5,6-tetrahydropyrrolo[3,4-c]pyrazoles by intramolecular nitrilimine cycloaddition

Both substituted 2,4,5,6-tetrahydrocyclopenta[c]pyrazoles and 2,4,5,6-tetrahydropyrrolo[3,4-c]pyrazoles have been synthesized by the 3+2 intramolecular dipolar cycloaddition of nitrilimines to alkynes. This cyclization has been extended to more versatile 3-bromo derivatives by the use of alkynylbromides as dipolarophiles.