锡钨杂多酸-耐尔蓝光度法测定纳克量锡

本文报道一个光度法测定纳克量锡的新方法。在聚乙烯醇（ＰＶＡ）存在下锡（Ⅳ）与钨酸盐和耐尔蓝（ＮＢ）反应形成离子缔合物,离子缔合物的最大吸收位于５８０ｎｍ,表观摩尔吸光系数ε值２．９５×１０７Ｌ·ｍｏ１－１·ｃｍ－１,服从比耳定律范围０～２．０μｇ／Ｌ,检出限（３σ）０．０８３μｇ／Ｌ（ｎ＝１０）,对２．０μｇ／Ｌ锡测定的ＲＳＤ为１．４２％（ｎ＝１１）,离子缔合物至少稳定７２ｈ。考察了４０多种共存离子的影响,大多数常见元素不干扰。测定锡的适宜条件［Ｈ２ＳＯ４］＝１．２０ｍｏ１／Ｌ,［ＷＯ２－４］＝６．０５×１０－５ｍｏ１／Ｌ,［ＮＢ］＝５．５×１０－５ｍｏ１／Ｌ和ＰＶＡ０．０８％。本法已用于某些合金钢和锌合金中纳克量锡的测定,结果与推荐值吻合,回收率满意。     

锡钨杂多酸—耐尔蓝光度法测定纳克量易

本文报道一个光度法测定纳克量锡的新方法,在聚乙烯醇（ＰＶＡ）存在下锡与钨酸盐和耐尔蓝（ＮＢ）反应形成离子缔合物,离子缔合物的最大吸收位于５８０ｎｍ,表现摩尔吸光系数ε值２．９５×１０＾７Ｌ·ｍｏｌ＾－１·ｃｍ＾－１。服从比耳定律范围０－２．０μｇ／Ｌ,检出限（３σ）０．０８３μｇ／Ｌ,对２．０μｇ／Ｌ锡测定的ＲＳＤ为２１．４２％,离子缔合物至少稳定７２ｈ。考察了４０多种共存离子的影响,大多数常见元     

金钨杂多酸-丁基罗丹明B光度法测定痕量金

研究了金钨杂多酸（ＡｕＷ）－丁基罗丹明Ｂ（ＢＲＢ）－聚乙烯醇（ＰＶＡ）体系的显色反应．离子缔合物的最大吸收位于５６５ｎｍ，表现摩尔吸光系数ε值为２．９６×１０７ｄｍ３·ｍｏｌ－１·ｃｍ－１，金量在０～２．８μｇ／Ｌ范围内服从比耳定律，检出限为０．１２μｇ／Ｌ（ｎ＝１２），对２．４μｇＡｕ（Ⅲ）／Ｌ测定的相对标准偏差为１．９％（ｎ＝１１）．离子缔合物至少稳定２４０ｈ．研究了离子缔合物的红外光谱，考察了４０多种共存离子的影响，大多数常见离子不干扰，允许２００倍量Ｐｔ（ＩＶ）、４００倍量Ｐｄ（Ⅱ）存在．本法用于某些矿物和炭粉中金的测定，结果与ＡＡＳ法吻合     

用丁基罗丹明B和钨酸盐测定痕量锡的研究

聚乙烯醇（ＰＶＡ）存在下，锡与钨酸盐形成锡钨杂多络阴离子，继而与丁基罗丹明Ｂ（ＢＲＢ）形成离子缔合物。离子缔合物的最大吸收位于５６５ｎｍ，表观摩有光系数ε为３．５４×１０＾７Ｌ．ｍｏｌ＾－１．ｃｍ＾－１，服从比耳定律范围０－６０ｎｇ／２５ｍＬ，测定限（３σ）０．０７３ｎｇ／ｍＬ（ｎ＝１２），对４０ｎｇ／２５ｍＬ锡测定的相对标准１．４５％，离子缔合物至少稳定２４０ｈ。考察了４０多种共存离子的影响，大     

碘化物-结晶紫-聚乙烯醇体系分光光度法测定自来水中痕量二氧化氯

在稀磷酸介质中，二氧化氯（ＣｌＯ２）氧化Ｉ离子形成 Ｉ３配阴离子，Ｉ３进一步与结晶紫（ＣＶ）阳离子形成离子缔合物［ＣＶ］［Ｉ３」。在聚乙烯醇存在下，该离子缔合物最大吸收波长λｍａｘ位于５５２ ｎｍ处，摩尔吸光系数ε＝２５ × １０５Ｌ·ｍｏｌ－１·ｃｍ－１，对 ＣｌＯ２的检出限为 ０．６ μｇ／Ｌ，线性范围是 ０．６～２８０μｇ／Ｌ。加入适量 ＫＦ溶液可消除自来水中Ｆｅ（Ⅲ）的干扰。方法对μｇ／Ｌ级ＣｌＯ２ 的测定有较好的选择性，可成功地用于自来水样品分析。     

锡—β—巯基丙酸极谱络合吸附波的研究及在食品分析中的应用

在ｐＨ４．２的ＨＣｌ－ＮａＡｃ缓冲溶液中，Ｓｎ（Ⅳ）－β－巯基丙酸（ＭＰＡ）络合物产生一灵敏的极谱吸附波，峰电位在－０．６０Ｖ（ｖｓ．ＳＣＥ），峰高与Ｓｎ浓度在４．２×１０－９～３．４×１０－６ｍｏｌ／Ｌ范围内呈线性关系，检出限为２．０×１０－９ｍｏｌ／Ｌ。本文对极谱波的性质和电极反应机理进行了研究。本法用于罐头食品中痕量锡的测定，结果满意。     

阻抑褪色光度法测定痕量汞

提出一种测定痕量汞的新的光度法。该法基于Ｈｇ（Ⅱ）对Ｈ２Ｏ２与离子缔合物ＡｇＣｌ·ＰＶＡ·Ａｇ~＋·Ｆｉｎ~－褪色反应的抑制效应,该离子缔合物对应于聚乙烯醇存在下Ｆａｊａｎｓ（法扬斯）法的终点,线性回归方程△Ａ＝０．０２＋ ４．０×１０~（－３）Ｃ_（Ｈｇ（Ⅲ））（μｇ／Ｌ）,相关系数ｒ＝０．９９９２,Ｈｇ（Ⅱ）浓度在４．０～２０．０μｇ／Ｌ范围内服从比耳定律,检出限０．０４μｇ／Ｌ。该法用于废水样中Ｈｇ（Ⅱ）的测定,结果与双硫腙法结果相符。     

大量锆存在下铪镧钼杂多酸—耐尔蓝体系测定给

本文研究了耐尔蓝（ＮＢ）－给镧钼杂多酸（ＨｆＬａＭｏ－聚乙烯醇（ＰＶＡ）体系测定铪的超高灵敏光度法。在ＰＶＡ存在下，铪，镧和钼酸铵形成杂多酸，继而与耐尔蓝形成离子缔合物。其适宜条件为〔ＨＣｌｏ４〕＝１．２ｍｏｌ／Ｌ，〔Ｌａ×３＋〕＝２．９×１０＾－７ｍｏｌ／Ｌ，〔ＭｏＯ４×２－〕＝１．１×１０＾－３ｍｏｌ／Ｌ，〔ＮＢ〕＝２．７×１０＾－６ｍｏｌ／Ｌ，ＰＶＡ０．０８％。离子缔合物的最大吸收波长在５９     

3,5—二溴—PADAP分光光度法测定微量NO2—离子的研究

系统研究了３,５－二溴－ＰＡＤＡＰ在酸性介质中质子化后与ＮＯ２和ＳＣ怙元离子缔合物的最佳条件。提出了测定微量ＮＯ２的光度新方法,表观摩尔吸光系数ε６３０＝１．２×１０＾４Ｌ·ｍｏｌ＾－１·ｃｍ＾－１,缔合物组成比为ｎ（３,５－ｆｇ ｉｔｈｄ－ＰＡＤＡＰ）：ｎ（ＮＯ２）：ｎ（ＳＣＮ）＝１：１：！。ｓｇ ｉｆ ｙｉｅｔｇｇｆｕｉｉ ｗｓｇ ｋ ｔｍｇ ｊｇ ＮＯ２ｒ ｉｍｐｇ,ｇｎ ｘ ｍａｗ ｙｙｉ     

丁基罗丹明B-铜钨杂多酸光度法测定微量铜

在聚乙烯醇（ＰＶＡ）存在下，丁基罗丹明Ｂ（ＢＲＢ）与铜钨杂多酸形成离子缔合物。缔合物的形成条件为ｃＨ２ＳＯ４＝１．２ｍｏｌ／Ｌ，ｃＷＯ２－４＝６．１×１０－５ｍｏｌ／Ｌ，ｃＢＲＢ＝３．８×１０－５ｍｏｌ／Ｌ和ＰＶＡ０．０８％。缔合物的最大吸收波长位于５７０ｎｍ，摩尔吸光系数ε＝１．６６×１０６Ｌ·ｍｏｌ－１·ｃｍ－１，铜量在每２５ｍＬ０～０．５μｇ范围内服从比耳定律，检测限为每ｍＬ０．６５ｎｇ（ｎ＝１２），对每ｍＬ１８ｎｇＣｕ测定的ＲＳＤ为０．８５％（ｎ＝１０）。缔合物至少稳定１５０ｈ，其摩尔比为Ｃｕ∶Ｗ∶ＢＲＢ＝１∶１２∶５，红外图谱表明铜钨杂多酸具有Ｋｅｇｇｉｎ结构。考察了４０多种共存离子的影响，大多数常见元素不干扰。本法已用于天然水、自来水、降水、人发、中药和蔬菜中铜的测定，结果满意。     

A walk around the A3-coupling

In recent years, the transition-metal catalyzed three-component coupling of an aldehyde, an alkyne and an amine, commonly called A(3)-coupling, has been established as a convenient and general approach towards propargylamines. Furthermore, the A(3)-coupling has found a broad application as a key step in the construction of various nitrogen-containing heterocycles, biologically active compounds and natural products. Several interesting modifications of the A(3)-coupling as well as different tandem reactions involving A(3)-coupling have been developed. This tutorial review aims to highlight the current achievements in the field of A(3)-couplings and related transformations.     

A method for the preparation of corchoroside A

Chemistry of Natural Compounds -     

Apoptolidinone A: synthesis of the apoptolidin A aglycone

An efficient stereocontrolled synthesis of apoptolidinone A, the aglycone of apoptolidin A is described. The synthetic strategy relies on a cross coupling between C11/C12 of a northern half (C1-C11) and a southern part (C12-C28) followed by a ring-size selective macrolactonization. Key steps for the introduction of the southern half stereocenters are a stereoselective aldol reaction, a substrate controlled dihydroxylation and a chelation-controlled Grignard/aldehyde addition. The conjugated triene of the northern half was built up successively by E-selective Wittig reactions. L-Malic acid was chosen as the chiral pool source for the C8/C9 stereocenters. The final cleavage of the silyl ethers and the conversion of the C21 methyl ketal into the hemiketal was achieved by HF.pyridine.     

Asymmetric Synthesis of the Ring A Substructure of Genkwadane A

A practical approach to the asymmetric synthesis of the ring A substructure of genkwadane A, a daphnane diterpenoid, was developed. This synthesis features the Mukaiyama aldol reaction to introduce the quaternary stereogenic center at C4 and VO(acac)₂‐catalyzed Jackson‐Ellman‐Bolm sulfoxidation to deliver the corresponding sulfoxide. The Dieckmann‐type condensation was efficiently promoted by KHMDS and the ring A substructure was finally accomplished through Barton iodination condition.     

A Chiron Approach for the Total Synthesis of Crassalactone A

The total synthesis of crassalactone A ( 1 ) has been achieved in twelve steps starting from commercially available 1,5‐D ‐gluconolactone. Still? Gennari olefination, one‐pot deprotection, and lactonization are the key reactions involved in the synthesis.     

Toward the natural didemnaketal A: total synthesis of the isomer of didemnaketal A

The total synthesis of isomer of didemnaketal A was achieved in 26 steps. The position of esters is switched at C7 and C8 with respect to their proposed position in natural didemnaketal A, which shows potent anti-HIV activity but so far has not been synthesized in the laboratory. Structural analysis of synthetic isomer of didemnaketal A indicates that the esters at C7 and C8 are correctly assigned, suggesting that the problems for the structural reassignment of natural didemnaketal A lie elsewhere.     

Observation of the A1A" state of isocyanogen

The A1A" state of isocyanogen, CNCN, is observed using photofragment fluorescence excitation spectroscopy in a room temperature cell and in a molecular beam. The spectra are highly congested, but progressions that correspond to the Franck-Condon active C-N-C bending vibration in the excited state are evident. Linewidth measurements indicate that the excited state lifetime is <10 ps. These measurements are consistent with previous ab initio calculations, which predicted a bent excited state with a short lifetime due to predissociation. Although we do not believe that we have observed the origin band of the electronic transition, we place an upper limit of 42,523 cm(-1) on the energy of the excited state zero point level.