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101.
The synthesis and magnetic properties of five new homo- and heterometallic nickel(II) complexes containing artificial amino acids are reported: [Ni(4)(aib)(3)(aibH)(3)(NO(3))](NO(3))(4)·3.05MeOH (1·3.05MeOH), [Ni(6)La(aib)(12)](NO(3))(3)·5.5H(2)O (2·5.5H(2)O), [Ni(6)Pr(aib)(12)](NO(3))(3)·5.5H(2)O (3·5.5H(2)O), [Ni(5)(OH)(2)(l-aba)(4)(OAc)(4)]·0.4EtOH·0.3H(2)O 6(4·0.4EtOH·0.3H(2)O), and [Ni(6)La(l-aba)(12)][La(2)(NO(3))(9)] (5; aibH = 2-aminoisobutyric acid; l-abaH = l-2-aminobutyric acid). Complexes 1 and 4 describe trigonal-pyramidal and square-based pyramidal metallic clusters, respectively, while complexes 2, 3, and 5 can be considered to be metallocryptand-encapsulated lanthanides. Complexes 4 and 5 are chiral and crystallize in the space groups I222 and P2(1)3, respectively. Direct-current magnetic susceptibility studies in the 2-300 K range for all complexes reveal the presence of dominant antiferromagnetic exchange interactions, leading to small or diamagnetic ground states. 相似文献
102.
Nucleophilic aromatic substitution of the nitro group of para- and meta-nitro-(pentafluorosulfanyl)benzene with alkoxides and thiolates generates a range of substituted 4- and 3-(pentafluorosulfanyl)benzenes in a single-step reaction. 相似文献
103.
铁矿选矿产品中低微量钍的X射线荧光光谱分析 总被引:2,自引:0,他引:2
本文介绍用粉末内标压片X射线荧光光谱法测定铁矿选矿工艺流程产品中的低微量钍,方法简便、快速、准确、经济,较之化学分析法,有它独到之处,满足了选矿研究对于分析的快速、准确的要求。本法以钼为内标元素,硼酸为低吸收粘结剂,与粉末试样混合均匀后,用15吨压片机压制成直径25mm的圆片状的样品,即可进机测量。 相似文献
104.
Afrati T Zaleski CM Dendrinou-Samara C Mezei G Kampf JW Pecoraro VL Kessissoglou DP 《Dalton transactions (Cambridge, England : 2003)》2007,(25):2658-2668
The use of di-2-pyridyl ketone oxime (Hpko)/X- "blends" (X- = OH-, Cl-, ClO4-) in copper chemistry has yielded neutral binuclear and cationic trinuclear, pentanuclear or hexanuclear complexes. Various synthetic procedures have led to the synthesis of compounds [Cu5(pko)7].[ClO4]3.2CH3OH.2H2O (1), [Cu3(pko)3(OH)(Cl)]2[Ph4B]2.4DMF.2H2O (2), [Cu2(pko)4] (3), {[Cu6(pko)6ClO4(CH3CN)6][Cu6(pko)6(ClO4)3(CH3CN)4]}.8ClO4.14CH3CN.H2O (4). The structures of the complexes have been determined by single-crystal X-ray crystallography. 相似文献
105.
Supercritical fluid chromatography (SFC) has become popular in the field of enantioselective separations. Many works have been reported during the last years. This review covers the period from 2000 till August 2013. The article is divided into three main chapters. The first one comprises a basic introduction to SFC. The authors provide a brief explanation of general principles and possibilities of this method. The advantages and drawbacks are also listed. Next part deals with chiral separation systems available in SFC, namely with the commonly used chiral stationary phases. Properties and interaction possibilities of the chiral separation systems are described. Recent theoretical papers are emphasized in this chapter. The last part of the paper gives an overview of applications of enantioselective SFC in analytical chemistry, in both analytical and preparative scales. Separation systems and conditions are summed up in tables so that they provide a helpful tool for analysts who search for a particular method of analysis. 相似文献
106.
Albta Kokaislov Tereza Heleicov Milan On
k Pavel Matjka 《Journal of Raman spectroscopy : JRS》2014,45(9):750-757
Folic acid is an essential nutrient involved in biosynthetic processes and cell growth. From an analytical point of view, folic acid can be used as an active part of sensors for substances with affinity to folic acid molecules. In biological environment, sensors can be exposed to temperatures that differ from room temperature. Thus, it is important to describe the influence of temperature on adsorbed molecules, especially on orientation of molecules towards the metal surface and on stability of adsorbed layer. Surface‐enhanced Raman scattering spectroscopy is a useful tool for investigation of architecture of molecular layers adsorbed on metal surfaces because the spectral features change with varying orientation of molecules towards the surface, as well as with changes in interactions among adsorbed molecules. In this study, folic acid was adsorbed on electrochemically prepared Au and Ag substrates, and both these substrates were exposed to temperature changes according to the temperature program consisting of stabilization, the substrate temperature at 10°C, at 50°C and back at 10°C. Decomposition of adsorbed folic acid at 50°C can be excluded on both metals, though the metal (Ag or Au) influences the arrangement of adsorbed molecules and its temperature‐induced changes. In the case of Ag substrate, significant and irreversible increase of certain Stokes band intensities is observed, whereas in the case of Au substrate, the band intensity increase is negligible. Experimental spectra were analyzed using principal component analysis and supplemented with calculated data for folic acid molecule adsorbed on small metal cluster using density functional theory. Moreover, it was proved that changes of surface plasmon resonance and collision frequency of Ag substrate are negligible in the studied temperature interval. Slight re‐orientation of adsorbed folic acid molecules was identified as the main source of band intensity variation in the spectra of folic acid adsorbed on Ag. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
107.
Tereza Ctvrtnickova Mari-Paz Mateo Armando Yaez Gines Nicolas 《Spectrochimica Acta Part B: Atomic Spectroscopy》2009,64(10):1093
The high sensitivity of laser-induced breakdown spectroscopy (LIBS) for the detection of most of the fly ash components enables the analysis of these residues produced during the combustion of coal. Fly ash consists of oxides (SiO2, Al2O3, Fe2O3, CaO…) and unburnt carbon which is the major determinant of combustion efficiency in coal fired boilers. For example, an excessive amount of residual carbon dispersed in the fly ash means a significant loss of energy (Styszko et al., 2004 [1]). Standard methods employed for the analysis of fly ash make not possible a control of boiler in real time. LIBS technique can significantly reduce the time of analysis, in some cases even an online detection can be performed. For this reason, some studies have been addressed in order to demonstrate the capability of the laser-induced breakdown spectroscopy technique for the detection of carbon content in high pressure conditions typical of thermal power plants (Noda et al., 2002 [2]) and for the monitoring of unburnt carbon for the boiler control in real time (Kurihara et al., 2003[3]).In particular, the content of unburnt carbon is a valuable indicator for the control of fly ash quality and for the boiler combustion. Depending on this unburnt carbon content, fly ash can be disposed as an industrial waste or as a raw material for the production of concrete in the construction sector. In this study, analyses were performed on specimens of various forms of preparation. Pressed pellets were prepared with two different binders. Presented results concern the nature and amount of the binder used to pelletize the powder, and the laser-induced breakdown spectroscopy parameters and procedure required to draw calibration curves of elements from the fly ash. Analysis “on tape” was performed in order to establish the experimental conditions for the future “online analysis”. 相似文献
108.
N lida Simona Marin-Huachaca Maria Tereza Lamy-Freund Jorge Mancini-Filho Henry Delinc e Anna Lú cia C. H. Villavicencio 《Radiation Physics and Chemistry》2002,63(3-6):419-422
Since about 1990, the amount of commercially irradiated food products available worldwide has increased. Commercial irradiation of foods has been allowed in Brazil since 1973 and now more than 20 different food products are approved. Among these products are a number of fresh fruits which may be irradiated for insect disinfestation, to delay ripening and to extend shelf-life. Today, there is a growing interest to apply radiation for the treatment of fruits instead of using fumigation or e.g. vapour-heat treatments, and an increased international trade in irradiated fruits is expected. To ensure free consumer choice, methods to identify irradiated foods are highly desirable. In this work, three detection methods for irradiated fruits have been employed: DNA Comet Assay, the half-embryo test and ESR. Both electron-beam (e-beam) and gamma rays were applied in order to compare the response with these two different kinds of radiation. Fresh fruits such as oranges, lemons, apples, watermelons and tomatoes were irradiated with doses in the range 0, 0.50, 0.75, 1.0, 2.0 and 4.0 kGy. For analysis, the seeds of the fruits were utilized. Both DNA Comet Assay and the half-embryo test enabled an easy identification of the radiation treatment. However, under our conditions, ESR measurements were not satisfactory. 相似文献
109.
A catalyst based on the readily available Cu2S/TMEDA system using a stable copper(I) source was developed for the Chan-Lam cross-coupling reaction. The capability of the catalyst was demonstrated with 1H-benzo[d]imidazol-2(3H)-one, 1H-benzo[d]imidazole, and 1H-imidazole together with electron-deficient, electron-rich, and sterically demanding boronic acids at room temperature in the presence of atmospheric oxygen to give the cross-coupling products in moderate to excellent yields. In addition, the coupling reaction of 1H-benzo[d]imidazole with several pinacol or neopentylglycol boronates indicated further potential of the catalyst. The reaction conditions tolerate the hydroxyl and bromo functional groups. The catalytic system also enables to synthesize the mono-N-substituted anilines from primary aliphatic amines. However, the two model compounds for the secondary and aromatic amines, piperidine and aniline, do not react. Two sterically demanding products with the restricted CN bond rotation, synthesized by the N-arylation of 1H-benzo[d]imidazol-2(3H)-one with o-tolylboronic acid, enabled to confirm the atropisomers prepared by the Chan-Lam cross-coupling reaction. Furthermore, an example of one-pot Chan-Lam and Suzuki-Miyaura reaction has been reported. 相似文献
110.
Spiwok V Lipovová P Skálová T Vondrácková E Dohnálek J Hasek J Králová B 《Journal of computer-aided molecular design》2005,19(12):887-901
Summary Aromatic amino acid residues are often present in carbohydrate-binding sites of proteins. These binding sites are characterized
by a placement of a carbohydrate moiety in a stacking orientation to an aromatic ring. This arrangement is an example of CH/π
interactions. Ab initio interaction energies for 20 carbohydrate–aromatic complexes taken from 6 selected ultra-high resolution X-ray structures
of glycosidases and carbohydrate-binding proteins were calculated. All interaction energies of a pyranose moiety with a side
chain of an aromatic residue were calculated as attractive with interaction energy ranging from −2.8 to −12.3 kcal/mol as
calculated at the MP2/6-311+G(d) level. Strong attractive interactions were observed for a wide range of orientations of carbohydrate
and aromatic ring as present in selected X-ray structures. The most attractive interaction was associated with apparent combination
of CH/π interactions and classical H-bonds. The failure of Hartree–Fock method (interaction energies from +1.0 to −6.9 kcal/mol)
can be explained by a dispersion nature of a majority of the studied complexes. We also present a comparison of interaction
energies calculated at the MP2 level with those calculated using molecular mechanics force fields (OPLS, GROMOS, CSFF/CHARMM,
CHEAT/CHARMM, Glycam/AMBER, MM2 and MM3). For a majority of force fields there was a strong correlation with MP2 values. RMSD
between MP2 and force field values were 1.0 for CSFF/CHARMM, 1.2 for Glycam/AMBER, 1.2 for GROMOS, 1.3 for MM3, 1.4 for MM2,
1.5 for OPLS and to 2.3 for CHEAT/CHARMM (in kcal/mol). These results show that molecular mechanics approximates interaction
energies very well and support an application of molecular mechanics methods in the area of glycochemistry and glycobiology. 相似文献