硅烷化衍生-气相色谱-质谱联用法测定橙汁粉中维生素C

橙汁粉样品用N,N-二甲基甲酰胺提取,并离心分离,所得上清液中抗坏血酸与六甲基二硅氨烷和三甲基氯硅烷进行衍生反应,产物用正庚烷萃取。萃取液加入棕榈酸甲酯作为内标,供气相色谱-质谱分析。在气相色谱分离中用HP-5MS毛细管柱(30 m×250μm,0.25μm)为固定相,在质谱测定中采用全扫描模式。硅烷化抗坏血酸标准与内标峰面积的比值与硅烷化抗坏血酸的质量在1.0～5.0 mg范围内呈线性关系。方法用于橙汁粉样品中维生素C的测定,橙汁粉中维生素C的平均质量分数(n=6)为0.195 4%,回收率在92.3%～98.5%之间。     

2,6-二氯靛酚钠动力学分光光度法测定西红柿及草莓中的抗坏血酸

本文提出用2，6－二氯靛酚纳（以下简写DIS）作氧化剂动力学分光光度测定L－抗坏血酸的新方法。DIS与L－抗坏血酸混合．在固定时间间隔于611nm处测得吸光度A值的变化（△A／△t）与抗坏血酸含量成线性关系。线性范围为0～12mg／L。在样品处理时采用偏磷酸作为提取剂，以减缓抗坏血酸被氧化的速度结果表明，该方法有较高灵敏度，且操作简便，试剂易得，容易推广，是测定水果和蔬菜中L-抗坏血酸的好方法。     

金电极介质交换-阴极伏安法对抗坏血酸的测定

提出了一种测定抗坏血酸的新方法.采用金电极作为工作电极,在0.20 mol/L的NaOH溶液中,于0.8 V电解50 s后,改换介质,在含抗坏血酸的试液中反应约10 s,再放入0.20 mol/L的NaOH溶液中向阴极化方向扫描,可在-0.1 V产生灵敏的还原峰,加入抗坏血酸后峰高下降,且下降的幅度与抗坏血酸的质量浓度成正比.抗坏血酸质量浓度在8.0 ～264 mg/L范围内与还原峰电流ΔI呈良好的线性关系.检出限为3.6 mg/L.介质交换法提高了方法的选择性,样品测试中,常见的干扰物质如多巴胺、尿酸等不干扰测定.方法用于血液和饮料中抗坏血酸的测定,结果与国标法相吻合.     

离子色谱法测定药品中抗坏血酸

建立离子色谱法测定药品中抗坏血酸含量的方法。以SH-AC-3型阴离子交换柱为分离柱,以12.0 mmol/LNaHCO₃溶液为淋洗液,流量为1.0 mL/min,柱温为30 ℃,采用等度洗脱的方式将抗坏血酸与氟化物、氯化物、亚硝酸盐、溴化物、硝酸盐、磷酸盐和硫酸盐等常见阴离子完全分离,通过抑制电导检测器检测,色谱峰面积标准曲线法定量。抗坏血酸的色谱峰面积与其质量浓度在3.0～500.0 mg/L范围内线性关系良好,相关系数为0.999 3,方法检出限为2.7 mg/L。该方法用于维生素C针剂和片剂中抗坏血酸含量的测定,样品加标回收率为95.1%～101.6%,5次平行测定结果的相对标准偏差为1.55%～2.79%(n=5)。该方法操作简便,检测快速,可用于维生素C针剂和片剂中抗坏血酸含量的测定。     

聚乙撑二氧噻吩修饰电极的电化学行为及对抗坏血酸的电催化作用

研究了聚乙撑二氧噻吩修饰电极在水溶液中的电化学行为及对抗坏血酸的电催化作用,实验表明抗坏血酸在聚乙撑二氧噻吩修饰电极上的氧化峰电位为+0.23V,较其在铂电极上的氧化峰电位负移220mV.在1.0×10^-1～1.0×10^-1mol/L浓度范围内,峰电流和抗坏血酸的浓度有线性关系,可用于水果等样品中抗坏血酸的测定。     

抑制荧光动力学法测定痕量抗坏血酸

在Na2HPO4-NaH2PO4弱碱性介质中,痕量抗坏血酸对氮氧自由基使CdTe量子点荧光猝灭具有抑制作用,由此建立了动力学荧光法测定痕量抗坏血酸的新方法。考察了不同pH、CdTe量子点和氮氧自由基的用量、反应时间等条件对抑制反应的影响。在最佳实验条件下,方法线性范围为2×10-7～1.5×10-5mol/L,检出限为5×10-8mol/L。该方法用于饮料等实际样品中抗坏血酸的测定,回收率为98%～103%。     

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％。     

石墨炉原子吸收法测定生物材料中微量银

用浓硫酸将生物样品中与白蛋白结合的银离子游离出来,在硫酸-碘化钾-抗坏血酸介质中,用甲基异丁基酮萃取银和碘的络合物,用石墨炉原子吸收法测定微量银,方法简便,检出限低,线性范围为1～100ng·ml~(-1),回收率为88.8％～109.9％。     

纳米铁氰化镍修饰铝电极对抗坏血酸的电催化氧化

利用多孔阳极氧化铝作模板,用化学修饰方法在铝基体上制备了纳米铁氰化镍修饰电极。研究了修饰电极的电化学特征及其电催化氧化抗坏血酸的行为。结果表明,纳米铁氰化镍修饰铝电极的循环伏安图上呈现一对可逆氧化还原峰。检测抗坏血酸,纳米铁氰化镍修饰铝电极比铁氰化镍修饰铝电极有更高的灵敏度。用安培法测定抗坏血酸,线性范围为1×10-6～1.5×10-2mol/L,检出限为2.4×10-7mol/L。本方法应用于实际样品中抗坏血酸的检测,结果令人满意。     

超声提取-抗坏血酸还原-催化光度法测定土壤中的碘

建立超声提取-抗坏血酸还原-催化光度法测定土壤中碘含量的方法。将碳酸钠和氧化锌研磨后过孔径为0.25 mm筛，按质量比为3∶2混合均匀，制成艾斯卡试剂。将土壤样品与艾斯卡试剂半熔后用超声提取试样中的碘，分取上清液依次加入抗坏血酸和乙酸，使氧化态的碘和碘单质全部变为碘离子，最后加入4,4’-四甲基二氨基苯甲烷、氯胺T，用分光光度计测定。该方法碘元素的质量浓度在0.002 5～0.08 mg/L范围内与吸光度具有良好的线性关系，相关系数为0.999 5，检出限为0.25 mg/kg。采用所建方法对土壤样品进行6次平行测定，测定结果的相对标准偏差为3.50%～9.40%；对国家标准物质GBW 07409、GBW 07408a、GBW 07407a 3种标准物质进行测定，测定值均在标准值范围内，相对误差分别为3.41%、0.63%、1.05%。该方法适合于大批量土壤样品中碘的测定。     

二氧化碳和丙烯直接合成甲基丙烯酸的NiPMo/TiO2催化剂的研究

用溶胶-凝胶法以磷钼酸(MPA)的镍盐溶液水解钛酸四丁酯制备了NiPMo/TiO2催化剂.使用ICP、 XRD、 TG-DTA、 IR、 TPD-MS和微反应技术研究了催化剂的化学组成、热稳定性、化学吸附性质和催化反应性能.杂多钼酸盐与TiO2通过O2-在TiO2表面发生了键合.在623 K下,杂多阴离子仍保持原有的Keggin结构.CO2在Lewis酸位Ni(Ⅱ)和Lewis碱位Ni-O-Mo的桥氧协同作用下生成CO2卧式吸附态Ni(Ⅱ)←O-(CO)←(O--Ni).丙烯有多种吸附态在催化剂上吸附.在563 K、 1 MPa和空速1500 h-1的反应条件下,丙烯的摩尔转化率为3.2%,产物MAA选择性为95%.     

Toward new camptothecins. Part 6: Synthesis of crucial ketones and their use in Friedländer reaction

In the context of the preparation of camptothecin and luotonin A analogs, the synthesis of some key keto-precursors and their use in Friedländer condensation are described. This paper also focuses on the stability of these keto intermediates and emphasizes the major differences between indolizinones and pyrroloquinazolinones series. Noteworthy is also the report of some original structures isolated as by-products of some experiments.     

CoFe2O4自形成磁性液体场致结构化对磁化的影响

The Langevin paramagnetic theory can’t describe the relation between magnetization of ferrofluids and applied magnetic field. The structuralization of ferrofluids, which is considered the main influence factor of the magnetization, is regarded. The part of magnetization works is deposited when the structure is forming. This action influences the magnetization of ferrofluids directly or indirectly. On the base of the “compressing” model, the Langevin function that usually describes the magnetization of ferrofluid is modified, and a well-fitted curve is obtained. An equation of the relation between the equivalent volume fraction after being “compressed” and the intensity of magnetic field is discovered, which approximately describes the process of magnetization. The relation between the approximate initial susceptibility and the volume fraction can be obtained from modified formula.     

Highly regioselective Buchwald–Hartwig amination at C-2 of 2,4-dichloropyridine enabling a novel approach to 2,4-bisanilinopyridine (BAPyd) libraries

The highly regioselective Buchwald–Hartwig amination at C-2 of the cheap and readily accessible reagent, 2,4-dichloropyridine with a range of anilines and heterocyclic amines is described. This new methodology is robust and provides a facile access to 4-chloro-N-phenylpyridin-2-amines on 0.25 mol scale. These intermediates undergo a further Buchwald–Hartwig amination at higher temperature to enable rapid exploration of the chemical space at C-4 and to provide a library of 2,4-bisaminopyridines.     

KMnO4-mediated oxidative CN bond cleavage of tertiary amines: Synthesis of amides and sulfonamides

KMnO₄-mediated oxidative CN bond cleavage of tertiary amines producing secondary amine was introduced, which was trapped by electrophiles (acyl chloride and sulfonyl chloride) to form amides and sulfonamides. The reaction could take place at mild condition, tolerating a wide range of function groups and affording products in moderate to excellent yields.     

Chemistry of heterocyclic compounds at the A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences, over 50 years (Review)

The review contains a concise historical account and information on the most significant researches undertaken by the staff at the A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences on the Chemistry of Heterocyclic Compounds. Dedicated to Academician of the Russian Academy of Sciences B. A. Trofimov on his 70th jubilee. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1443–1502, October, 2008.     

Sulfur-directed metal-free and regiospecific methyl C(sp3)–H imidation of thioanisoles

Regiospecific and direct imidation of the methyl C(sp³)–H bond of thioanisoles is realized under mild and metal-free conditions with N-fluorobis(benzenesulfonyl)imide as an oxidant and nitrogen source. Proposed mechanism suggests that thionium ion intermediates and a Pummerer-type reaction are involved. The imidation has advantages such as high step-economy, excellent functionality tolerance, and regiospecificity, giving structurally diverse imidation products.     

Selective syntheses of 2H-1,3-oxazines and 1H-pyrrol-3(2H)-ones via temperature-dependent Rh(II)-carbenoid-mediated 2H-azirine-ring expansion

The Rh(II)-catalyzed reaction of 2-carbonyl-substituted 2H-azirines with ethyl 2-cyano-2-diazoacetate or 2-diazo-3,3,3-trifluoropropionate provides an easy access to 2H-1,3-oxazines and 1H-pyrrol-3(2H)-ones. These compounds can be selectively prepared from the same starting material using temperature as the only varied parameter. The 2-azabuta-1,3-diene intermediate, a common precursor for both heterocyclic products, isomerizes into 2H-1,3-oxazine under kinetic control, while 1H-pyrrol-3(2H)-one is the sole product of the reaction at elevated temperatures. According to DFT-calculations a one-atom oxazine ring contraction involving ring-opening to a 2-azabuta-1,3-diene intermediate, followed by a 1,5- and 1,2-prototropic shift leads to the consecutive formation of imidoylketene and azomethine ylide, which then further undergo cyclization to the pyrrole derivative.     

Synthesis of 1-benzyloxypyrazin-2(1H)-one derivatives

Different approaches for the synthesis of 1-benzyloxypyrazin-2(1H)-one derivatives from simple amino acids have been investigated. A library of 33 precursors for the preparation of N-hydroxy pyrazinones was obtained in moderate to good yields.