鸡精调味料中谷氨酸钠含量测量不确定度的评定

分析鸡精调味料中谷氨酸钠含量测量不确定度的影响因素,建立数学模型,对各不确定度分量进行了分析和计算。当鸡精调味料中谷氨酸钠的含量为49．15％时,谷氨酸钠含量测定结果的扩展不确定度为0．34％(k=2)。     

离子色谱法和分光光度法测定调味品中硫化物的含量

<正>近年来我国的现代调味新品竞相推出,尤其是复合调味品的大量出现令人关注[1]。为了增加调味品的鲜味,味精被广泛应用到各种调味品中,其主要成分为谷氨酸钠。根据国家标准GB 2760-2011《食品安全国家标准食品添加剂使用标准》,味精是可在各类食品中按生产需要适量使用的食品添加剂,其中鸡精中谷氨酸钠的质量分数达35%以上[2];据统计,80%的酱油中含有谷氨酸钠。传统的味精生产中,为了改善味精的感官色泽,普遍使用硫     

碘元素概念发展史及其教育价值

通过对碘元素概念发展历程的考证可知,1813年,盖·吕萨克首次提出碘元素概念,但当时碘元素和碘单质概念界定不清。至道尔顿提出原子论,赋予碘元素新的含义,首次将碘原子和碘元素结合在一起。20世纪40年代,碘同位素的发现完善了碘元素概念,形成现代碘元素观念。在化学教育中,须让学生认识到碘元素概念的发展史不仅是元素概念的发展史,也是科学思想的演进史和科学方法的发展史。     

HPLC法测定鸡精中谷氨酸钠的含量

以邻苯二甲醛与谷氨酸钠中的氨基进行柱前在线衍生化反应,采用C18色谱柱分离、荧光检测器（激发340nm,发射450nm）进行测定,建立了柱前衍生反相高效液相色谱测定鸡精中谷氨酸钠含量的方法。该方法相对标准偏差为0．69％,加标回收率为99．1％～101％,在0．10~50．0mg／L范围内,谷氨酸钠的峰面积和浓度之间的相关系数为0．9999,保留时间和峰面积的相对标准偏差分别为1．22％和0．71％,鸡精中谷氨酸钠定量下限为0．2μg／g。     

分光光度法测定味精中谷氨酸钠

谷氨酸钠是味精的主要成分,其含量的高低直接影响味精的质量,因此研究味精中谷氨酸钠的测定方法具有一定的实用价值.目前测定谷氨酸钠的方法只有GB/T 5009.43-2003中的旋光法和酸度计法.酸度计法设备简单,操作方便,在基层实验室得到广泛应用,但终点pH值的确定存在争议.本工作采用分光光度法测定味精中谷氨酸钠的含量.方法快速简便、结果准确.     

差示扫描量热法对味精中L-谷氨酸钠的分析

采用差示扫描量热法(DSC)研究了一水谷氨酸钠的热分解过程,结果表明一水谷氨酸钠的热分解过程分为两个阶段,在155℃开始脱去结晶水,脱结晶水阶段动力学参数n=0.89,Ea1=152.8kJ·mol-1,A1=7.8×1018s-1,分子内脱水阶段动力学参数n=0.75,Ea2=274.4kJ·mol-1,A2=1.1×1030s-1,半寿命期为t1/2=1.3×109月。     

谷氨酸锌的合成最佳条件研究

报道了以谷氨酸钠与氧化锌反应合成谷氨酸锌,原料易得,条件温和,操作简便,产率为86％,有潜在应用价值。     

基于化工发展史的“硫酸工业”教学设计

从基础化工发展史角度进行硫酸工业的教学设计,将硫酸工业发展史的3个不同阶段的原理及方法进行对比、归纳,挖掘在其发展史中蕴含的科学与人文内涵,加深学生对硫酸工业的理解及其重要性认识,培养技术素养与创造精神,促成三维教学目标有效达成.     

钾元素概念的发展史及其意义

通过对钾元素概念的发展史考证分析可知,钾是电化学兴起后最先发现的活泼金属。19世纪初,随着科学思想和实验条件的发展,通过电解法首次制取到钾的单质,但并未确定为元素。19世纪中期,对钾元素性质的实验验证和原子论的发展,使得钾元素的概念被确认。20世纪20年代,钾元素同位素的发现,形成了现代的钾元素概念。钾元素概念的发展史不仅是元素概念的发展史,也是科学方法的发展史与科学思想的演变史。     

谷氨酸的硫化锌法原子吸收光谱间接测定

利用ZnS悬浮液与谷氨酸在碱性条件下生成可溶性谷氨酸锌络合物 ,研究了塞曼原子吸收间接测定谷氨酸的方法 ;谷氨酸测定的质量浓度线性范围为0～3g·L-1,特征质量浓度为27.3mg·L-1;该法可用于调味品中的谷氨酸或谷氨酸钠的测定 ,其相对标准偏差为0.4 %(n=7) ,方法的回收率在97 %～103%之间     

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%.     

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.     

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.     

A general and convenient synthesis of 4-(tosylmethyl)semicarbazones and their use in amidoalkylation of hydrogen,heteroatom, and carbon nucleophiles

A general synthesis of previously unknown semicarbazone-based α-amidoalkylating reagents, 4-(tosylmethyl)semicarbazones, has been developed. The synthesis involved three-component condensation of semicarbazones of aliphatic or aromatic aldehydes with the same or other aldehydes and p-toluenesulfinic acid. The scope and limitations of this reaction were investigated. The compounds obtained were demonstrated to be an efficient α-(4-semicarbazono)alkylating agents. They were reacted with H- (sodium borohydride), O- (sodium methylate), S- (sodium phenylthiolate), N- (pyrrolidine, sodium succinimide), P- (trialkyl phosphites), and C-nucleophiles (sodium diethyl malonate) to give the corresponding products of the tosyl group substitution, 4-substituted semicarbazones, including analogues of nitrofurazone. Among the prepared compounds tested in vitro for antibacterial and antifungal activity, three nitrofuryl-containing semicarbazones exhibited high biological activities with minimum inhibitory concentration (MIC) values of 8–32 μg/mL.     

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.     

Synthesis of novel chiral bidentate hydroxyalkyl-N-heterocyclic carbene ligands and their application in palladium-catalyzed Mizoroki–Heck couplings and asymmetric addition of diethylzinc to benzaldehyde

A small library of new chiral bidentate hydroxyalkyl-imidazolium salts 1 is conveniently synthesized on multi-gram scale from inexpensive and commercially available chiral pool amino acids. The corresponding carbenes, generated by deprotonation of imidazolium salts 1, in combination with palladium(II) chloride were tested in the Mizoroki–Heck coupling reaction. The most significant results in terms of yields and reactivities were achieved with low catalyst loading. The catalytic activities of these imidazolium salts were also investigated in the asymmetric addition of diethylzinc to benzaldehyde. The use of MgO nanoparticles as an additive in conjunction with these ligands played a crucial role in increasing the efficiency of these reactions.