人工神经网络分光光度法同时测定钼和铬

在钼，铬－二溴邻硝基苯基荧光酮－ＣＴＭＡＢ显色体系中，应用三层ＡＮＮ－ＢＰ网络解析钼和铬的吸收光谱，不经分离分光光度法同时测定钼和铬。钼和铬的表观摩尔吸光系数分别为ε５４５＝ ６．４８×１０４Ｌ·ｍ ｏｌ－ １·ｃｍ － １，ε５４７＝ １．５４×１０４Ｌ·ｍ ｏｌ－ １·ｃｍ － １。对合成样品和合金钢中钼和铬进行了同时测定，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。     

直接进样-电感耦合等离子体质谱法测定特殊医用配方食品中铬、钼和硒

本文采用1%四甲基氢氧化铵溶液溶解样品,单氦碰撞池模式直接分析特殊医用配方食品中的铬、钼和硒。研究表明:铬、钼和硒在质量浓度2.0~50.0μg/L范围内呈良好的线性关系,铬、钼、硒的检出限分别为0.012、0.009和0.009mg/kg;加标回收率在94%~117%之间,相对标准偏差在1.47%~5.78%之间。本方法对NIST 1849a和FAPAS T07216QC标准物质中铬、钼和硒的测定值与参考值相符。该方法操作简单、快速,适合特殊医用配方食品中铬、钼和硒的同时测定。     

微波消解-电感耦合等离子体质谱法测定乳制品中铬、钼和硒

本文采用HNO3密闭微波消解样品,手动添加内标碲,电感耦合等离子体质谱(ICP-MS)法分析乳制品中的铬、钼和硒。研究表明:铬和钼在0.8~20.0μg/L质量浓度范围内,硒在0.4~10.0μg/L质量浓度范围内,呈良好的线性关系。方法检出限分别为:铬0.012mg/kg、钼0.009mg/kg和硒0.009mg/kg;加标回收率在86%~115%之间,相对标准偏差在1.46%~6.81%(n=8)之间。该方法操作简单,适合乳制品中铬、钼和硒的同时测定。     

湿式消化-ICP-AES法测定航空润滑油中镍钛镁铬钼锡

研究采用硝酸-高氯酸混合酸湿式消化法，建立ICP-AES法同时测定航空润滑油中痕量金属元素镍、钛、镁、铬、钼、锡。样品消化完全、快速，检出限分别为(μg．L^-1)：镍4．1、钛2．1、镁4．2、铬3．2、钼3．6、锡24．4，RSD小于5％，回收率为96．0％～104．0％。     

ICP–OES法测定锰钢中的铬、钼、磷

采用电感耦合等离子体发射光谱法测定锰钢中的铬、钼、磷。以盐酸–硝酸混合酸处理试样,通过选择元素的分析线来优化测试条件,利用基体匹配法消除基体干扰。结果表明,铬、钼、磷3种元素测定结果的相对标准偏差为0.86%~2.31%,加标回收率为96.7%~103.2%。该法能够满足日常分析对锰钢中铬、钼、磷含量测定的需要。     

过渡金属氨基酸席夫碱配合物的合成

合成了6个过渡金属氨基酸席夫碱配合物——L-酪氨酸缩水杨醛合铬(钼),L-赖氨酸缩水杨醛合铬(钼),DL-α-丙氨酸缩水杨醛合铬(钼),其结构经UV,IR和元素分析表征。UV测定结果表明,配合物均可与DNA发生插入作用。     

高铬合金铸铁中铬、铜、钼、镍、锰的快速联合测定

耐磨高铬合金铸铁以其良好的耐磨、耐蚀及耐热性能，得到了广泛应用。因该类样品不易溶解，单个元素分析难以满足快速分析的需要。本文在文献的基础上，采用王水溶解、硫一磷混酸高温下滴加硝酸氧化发烟以破坏碳化物。控制试验条件，对其中的铬、铜、镍、钼、锰采用联合测定，减少了重复操作，提高了分析速度。本方法应用于耐磨高铬合金铸铁中铬、铜、钼、镍、锰的联合测定，结果满意。     

直读光谱法测定合金工具钢中铬、锰和钼

建立了ARL-4460直读光谱仪对Cr12、Cr12MoV中铬、锰、钼元素的快速检测方法。使用基体铁作为内标元素,测定标准样品中铬、锰、钼元素的相对强度,减少了外界电压不稳对绝对强度稳定性的影响;由于标准样品中基体铁含量不同,为减少内标元素含量的变化对工作曲线相关系数和估计标准差的影响,使用相对含量校正工作曲线。在优化的实验条件下,试样中三种元素的相对标准偏差分别为0.68%、0.79%和1.7%(n=11)。测定结果与化学分析方法测定结果一致,可实现合金工具钢中铬、锰和钼的快速检测。     

微波消解–ICP–MS法测定格隆溴铵注射液中的铬、镍、钼

建立了电感耦合等离子体质谱法测定格隆溴铵注射液中铬、镍、钼3种残留金属元素的方法。分别在0,500,1 200 W功率下,样品采用硝酸和过氧化氢混合溶液微波消解,在选定的仪器工作条件下测定。铬、镍、钼的质量浓度在5～200 ng/mL范围内具有良好的线性关系,相关系数不小于0.995,方法检出限为0.22～0.49 ng/mL,定量限为1.08～2.46 ng/mL。测定结果的相对标准偏差为1.4%～3.0%(n=11),样品加标回收率为92.88%～111.94%。该方法操作简单、快速,结果准确、可靠,适用于格隆溴铵注射液中铬、镍、钼的测定。     

电感耦合等离子体原子发射光谱法测定不锈钢中8种合金元素

采用硝酸-盐酸-水(1+3+6)混合酸溶液溶解不锈钢样品,用电感耦合等离子体原子发射光谱法同时测定试样溶液中铬、镍、铜、锰、磷、硅、钼和钛等8种合金元素。选择钇元素作为内标元素,选择波长为357.869,231.604,327.396,257.610,178.284,251.611,202.030,337.280 nm8条谱线依次作为铬、镍、铜、锰、磷、硅、钼和钛的分析线。方法用于分析了12种标准物质,测定值同证书值一致,各元素的相对标准偏差(n=7)均小于5.5%。     

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.