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排序方式: 共有952条查询结果,搜索用时 46 毫秒
51.
Michio Iwaoka Shuji Tomoda 《Phosphorus, sulfur, and silicon and the related elements》2013,188(3-4):755-766
Weak nonbonded interaction between a divalent selenium and an oxygen atom (i.e., Se···O interaction) frequently plays important roles in chemical and biological functions of selenium compounds. To establish that 77 Se NMR is an easy experimental probe to diagnose the strength of an Se···O interaction, 3 series of 2-substituted benzeneselenenyl derivatives, which have an intramolecular Se···O interaction in solution, were employed. By comparing the 77 Se NMR chemical shifts (δ Se ) with those observed for other series of selenium compounds, which have an intramolecular Se···Y (Y = N, O, F, Cl, or Br) interaction, approximate linear correlation was found between the δ Se values and the strengths of the nonbonded Se···Y interactions evaluated by natural bond orbital analysis at the B3LYP level. The correlation will be useful for estimating the strength of an Se···O interaction simply from the 77 Se NMR chemical shift. By extending the chemistry of nonbonded Se···O interactions to structural biology, analogous S···O interactions have been discovered in protein architecture. The directional features were, however, different from those of Se···O and S···O interactions of small organic compounds. 相似文献
52.
Recent development of aminophosphine chalcogenides and boranes as ligands in s-block metal chemistry
Chowan Ashok Kumar 《Phosphorus, sulfur, and silicon and the related elements》2017,192(10):1084-1101
The coordination chemistry of the aminophosphine chalcogenide ligands [Ph2P(O)NHR], [Ph2P(S)NHR], and [Ph2P(Se)NHR] (R = 2,6-Me2C6H3,tBu, CHPh2, CPh3) or corresponding borane derivative [Ph2P(BH3)NHR] toward group 1 and 2 metals is reviewed. The structural characterization of a huge number of mono- and bis-aminophosphine chalcogenide/borane complexes with group 1 and 2 metals—in most cases lithium, sodium, potassium, magnesium, calcium, strontium, and barium complexes—reveals a poly-metallacyclic motif in each case. The coordination takes place from adjacent chalcogen/borane and nitrogen as donor atom or group of the ligand confirming the direct bond between metal and chalcogen/borane to develop homoleptic and heteroleptic complexes. The heteroleptic group 2 metal complexes were used as pre-catalysts in hydrophosphination and hydroamination reactions. Similarly, aminophosphine chalcogenide alkaline earth metal complexes were used in the catalytic ring-opening polymerization (ROP) study of ?-caprolactone. 相似文献
53.
目的:测定白砂糖和红糖中硒含量为研制富硒糖提供科学依据。方法采用微波消解-原子荧光光谱法测定白砂糖和红糖中硒含量。结果在确定的最佳仪器条件下,原子荧光光谱法测定白砂糖和红糖中硒的检出限为0.063μg · L-1;白砂糖硒的RSD为2.28%,红糖的RSD为2.13%;白砂糖回收率为103.4%,红糖回收率为99.7%。结论该法具有方法简便、快捷、准确等优点,适用于白砂糖和红糖中硒含量测定。 相似文献
54.
Prof. Xiaoguang Bao Dr. David A. Hrovat Prof. Weston Thatcher Borden 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(18):5687-5693
Cyclobutane‐1,2,3,4‐tetraone, (CO)4, was computationally predicted and, subsequently, experimentally confirmed to have a triplet ground state, in which a b2g σ MO and an a2u π MO were each singly occupied. In contrast, the (U)CCSD(T) calculations reported herein found that cyclobutane‐1,2,3,4‐tetrathione, (CS)4, and cyclobutane‐1,2,3,4‐tetraselenone, (CSe)4, both had singlet ground states, in which the b2g σ MO was doubly occupied and the a2u π MO was empty. Our calculations showed that both the longer C?X distances and smaller coefficients on the carbon atoms in the b2g and a2u MOs of (CS)4 and (CSe)4 contributed to the difference between the ground states of these two molecules and the ground state of (CO)4. An experimental test of the prediction of a singlet ground state for (CS)4 is proposed. 相似文献
55.
Kristýna Urbánková Martin Moos Jiří Machát 《International journal of environmental analytical chemistry》2013,93(11):1077-1087
This paper deals with a simplified multi-element profiling of inorganic arsenic, antimony, selenium and tellurium in the form of 75As, 82Se, 121Sb and 125Te by ICP-MS for amounts less than 10?µg?L?1. Internal standards such as 72Ge and 209Bi were successfully used for the suppression of both influence of macro elements Na+, K+, Ca2+, Mg2+ or Al3+, and interference of limited concentrations of heavy metal ions. Modified silica sorbents Separon? SGX C18, C8, CN, NH2, RPS and Phenyl were tested for the preconcentration of As, Sb, Se and Te (0.25–5?µg?L?1) in the form of ion associates with cationic surfactants from 50–250?mL sample volume. 1-etoxycarbonyl-pentadecyltrimethylammonium bromide (Septonex®, 0.005?mol?L?1) was suitable for this purpose in the presence of 4-(2-pyridylazo) resorcinol, 2-pyrrolidinecarbodithioate and 8-hydroxyquinoline-5-sulphonic acid. The quantitative retention occurred at pH 7?±?0.2 and the mixture of acetone with ethanol in ratio 1?:?1 in the presence of 0.1?mol?L?1 HCl was used for the quantitative elution. Organic solvents and the excess of acid were removed by evaporation prior to the determination by ICP-MS. The determination of the above trace metalloids in various kinds of water with enrichment factor till 50 times on silica Separon? SGX C18 and the above reagents were compared with the standard addition method. 相似文献
56.
在氩气保护下,以邻位-碳硼烷、正丁基锂、硒粉和CpCo(CO)I2为起始原料,合成、分离得到配合物CpCo(Se2C2B10H10)(1)、(CpCo)2(Se2C2B10H10)(2)和(CpCo)4(μ3-Se)4Co2(μ3-Se2C2B10H10)4Co·CH2Cl2(3),并用元素分析、质谱、IR、1H NMR及X-射线单晶衍射对配合物(3)进行了表征。晶体属正交晶系,空间群P212121,其晶胞参数为:a=1.30720(13)nm,b=1.39137(11)nm,c=3.88533(15)nm,β=90°,Z=4,V=7.0666(9)nm3,μ=7.890mm-1,Dc=2.138g·cm-3,F(000)=4268,R1=0.0543,wR2=0.1363。配合物中4个(Se2C2B10H10)2-配体和4个单硒基团形成了1个Co7Se12核。 相似文献
57.
Dajiang Mei Wenlong Yin Kai Feng Lei Bai Zheshuai Lin Jiyong Yao Yicheng Wu 《ChemInform》2012,43(16):no-no
The new title compound is prepared from a mixture of AgGaSe2 (obtained from the elements at 900 °C, 2 d) and CsI in the molar ratio 1:2 (silica tube, Ar, 800 °C, 48 h). 相似文献
58.
微量元素硒和糖耐量异常 总被引:5,自引:2,他引:3
非胰岛素依赖型糖尿病(NIDDM)已成为现代社会的主要疾病之一,尤其各种并发平给机体带来的致命后果使倍受重视。而预防的关键是,在耐量异常阶段发现并治疗,效果更佳。已发现在糖耐量异常(ICT)时存在各种抗氧化缺陷,因此,硒(Se)的抗氧化作用对IGT可能有一定的疗效。 相似文献
59.