抗坏血酸及L-半胱氨酸的流动注射动力学同时测定法

pH2～9时,抗坏血酸与L-半胱氨酸均可与Fe3+-邻菲咯啉混合液反应,生成Fe2+-邻菲咯咻有色配合物,但两者反应速度相差极大。根据这个原理,采用流动注射分析停流技术,建立了抗坏血酸与L-半胱氨酸的动力学吸光光度同时测定法。两者测定的线性范围分别为0～24mg·L-1和0～280mg·L-1,相应的检出限为1mg·L-1和16mg·L-1,抗坏血酸与L-半胱氨酸浓度分别为12.0mg·L-1和160.0mg·L-1时,测定的相对标准偏差分别为0.9％和0.6％,采样频率为30样·h-1。该法灵敏、快速、准确,选择性较高,且流路及设备简单,实用性强,用于实际样品测定,抗坏血酸及L-半胱氨酸的加标回收率分别可达95.2％和92.8％。     

催化比色法测定痕量钒的研究及应用

在抗坏血酸存在下,钒对溴酸钾氧化亮绿SF褪色具有催化作用,建立了一个简单、灵敏的测定轨的方法——催化比色法.线性范围为0.4～60ng·ml~(-1),检出限为1.03×10~(-11)g·ml~(-1).方法用于水和人发中钒的测定,结果满意.     

钒(Ⅴ)催化氧化二甲基黄的反应及其应用

在硫酸介质中 ,以抗坏血酸为活化剂 ,钒 (Ⅴ )强烈催化溴酸钾氧化二甲基黄的反应 ,由此建立了测定超痕量钒的又一新的催化光度法。方法的测定范围为 0 .8～ 10 0 pg·ml- 1,检出限为8.3× 10 - 13g·ml- 1,催化反应的表观活化能E′ =10 0 .2kJ·mol- 1,表观速率常数K =1.4× 10 - 3s- 1。方法用于井水、粮食中痕量钒的测定 ,结果满意。     

铜-鲁米诺化学发光法测定抗坏血酸

本文采用鲁米诺-铜-抗坏血酸体系,建立了一种化学发光测定抗坏血酸的方法,方法具有操作简单,灵敏度高,重复性好等优点,用该方法测定抗坏血酸的线性范围为2.0×10~(-6)～6.0×10~(-5)mol/L,对4.0×10~(-6)mol/L抗坏血酸连续11次测定的相对标准偏差(RSD)为1.1％,用建立的方法对市售饮料、复合维生素及维生素片剂中的抗坏血酸进行了测定,结果满意.     

荷移反应及其在分析化学中的应用 Ⅲ.氟哌酸测定方法研究

本文研究了氟哌酸与四氯对苯醌的荷移反应,确定了反应条件:在硼砂缓冲溶液中形成1:1的络合物,其λ_(max)=375.2nm,表观摩尔吸光系数ε=1.68×10~4·L·mol~(-1)·cm~(-1),应用拟定的方法测定药物制剂含量与文献方法一致,回收率在99％以上,相对标准偏差为1.14％。     

金属材料分析方法的选择和施行第三讲钢铁中钼的测定(续)

2 .5　对抗坏血酸还原 硫氰酸盐直接光度法的讨论(1)　抗坏血酸与钼 (Ⅵ )的还原反应据报道抗坏血酸在微酸性条件下的标准氧化还原电位值Ｅ°为 + 0 .32 6Ｖ(ｖｓ.ＳＣＥ)。其还原能力低于氯化亚锡 ,只能将钼 (Ⅵ )还原至五价状态。因此 ,使钼 (Ⅴ )与硫氰酸盐所形成的络合物在稳定性和灵敏度方面均有所改善。抗坏血酸与钼 (Ⅵ )的还原反应可用下式表示 :(2 )　显色反应的酸度条件在单纯钼 (Ⅵ )、硫氰酸盐与抗坏血酸反应体系的情况下 ,当溶液的硫酸浓度 [ｃ(1/ 2Ｈ2 ＳＯ4 ) ]大于2 .5ｍｏｌ·Ｌ- 1到 7.0ｍｏｌ·Ｌ- 1,显色反应可立即完…     

高效液相色谱电化学发光法检测抗坏血酸

基于在恒电流条件下电解产生不稳定化学发光试剂Mn(Ⅲ)能直接氧化抗坏血酸产生化学发光,将高效液相色谱法与电化学发光法相结合,建立了高效液相色谱电化学发光法测定抗坏血酸的检测方法。在优化的试验条件下,对啤酒、人体血清、尿液中抗坏血酸含量进行了分析,方法的检出限为3.0×10-5g.L-1,相对标准偏差为2.2%(n=11,5.0×10-2g.L-1VC),线性范围1×10-4~1×10-1g.L-1。     

锰C-抗坏血酸甲醛-化学发光体系的研究

实验观察到锰 氧化抗坏血酸可以产生弱的化学发光 ,甲醛对这一化学发光反应有较强的增敏作用 ,据此建立了测定抗坏血酸的流动注射化学发光分析法。方法的检出限为 2× 1 0 -8mol/L抗坏血酸 ;线性响应范围为 6 .0× 1 0 -8～ 2 .0× 1 0 -5mol/L。对 1 .0× 1 0 -6mol/L的抗坏血酸进行 1 1次测定 ,相对标准偏差为 2 3%。该方法已成功应用于维生素C针剂和片剂中抗坏血酸含量的测定 ,结果与药典方法测得值一致     

火焰原子吸收光谱法测定天然水中微量铁的形态

研究了用抗坏血酸为还原剂,使二价铁离子与邻菲啰啉(phen)形成螯合物,用硝基苯萃取,火焰原子吸收光谱法测定有机相中的铁。方法检出限为1.7ng·ml~(-1),回收率为98.0％～109.6％,线性范围为0～10.0μg·ml~(-1)(原水相),线性相关系数为0.9994。测定结果与ICP-AES法结果对照相对误差小于9.46％。     

贵金属高灵敏显色反应的研究(Ⅰ) 金(Ⅲ)-碘化钾-丁基罗丹明B-明胶体系

贵金属已知的显色反应中,除萃取浮选的以外,摩尔吸光系数(ε)达到或超过2×10~5I·mol~(-1)·cm~(-1)者为数甚少。就金来说,目前以乙基硫代米嗤酮的灵敏度最高(ε=1.95×10~5l·mol~(-1)·cm~(-1)),甲基硫代米嗤酮次之(ε=1.6×10~5l·mol~(-1)·cm~(-1))。碱性染料如罗丹明B与AuCl_4~-缔合萃取显色反应ε=9.7×10~4l·mol~(-1)·cm~(-1)。有关金(Ⅲ)-碘化钾-碱性染料体系显色反应仍未见报道。我们发现在明胶、TritonX-100和抗坏血酸存在下Au(Ⅲ)与KI、罗丹明B特别是丁基罗丹明B的显色反应具有很高的灵敏度,有色络合物的摩尔吸光系数分别为2.3×10~5l.mol~(-1)·cm~(-1)(罗丹明B)和1.2×10~6l·mol~(-1)·cm~(-1)(丁基罗丹明B),特别是后者,ε值之高实属罕见,故我们称之为超高灵敏显色反应。     

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.