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161.
Rohde RD Agnew HD Yeo WS Bailey RC Heath JR 《Journal of the American Chemical Society》2006,128(29):9518-9525
A general method for the non-oxidative functionalization of single-crystal silicon(111) surfaces is described. The silicon surface is fully acetylenylated using two-step chlorination/alkylation chemistry. A benzoquinone-masked primary amine is attached to this surface via Cu(I)-catalyzed Huisgen 1,3-dipolar cycloaddition ("click" chemistry). The benzoquinone is electrochemically reduced, resulting in quantitative cleavage of the molecule and exposing the amine terminus. Molecules presenting a carboxylic acid have been immobilized to the exposed amine sites. X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), cyclic voltammetry (CV), and contact angle goniometry were utilized to characterize and quantitate each step in the functionalization process. This work represents a strategy for providing a general platform that can incorporate organic and biological molecules on Si(111) with minimal oxidation of the silicon surface. 相似文献
162.
The geometries of 35 conformers of Me(SiMe2)nMe (n = 4, 1; n = 5, 2; n = 6, 3; n = 7, 4) were optimized at the MP2/VTDZ level, and CCSD(T) single-point calculations were done at three MP2/VTDZ conformer geometries of 1. The relative ground-state energies of the conformers of 1-4 in the gas phase were obtained from the MP2/VTDZ electronic energy, zero-point vibrational energy, and thermal corrections at 0, 77, and 298 K. Relative energies in an alkane solvent at 77 and 298 K were obtained by the addition of solvation energies, obtained from the SM5.42R model. The calculated energies of 26 of the conformers (n = 4-6) have been least-squares fitted to a set of 15 additive increments associated with each Si-Si bond conformation and each pair of adjacent bond conformations, with mean deviations of 0.06-0.20 kcal/mol. An even better fit for the energies of 24 conformers (mean deviations, 0.01-0.09 kcal/mol) has been obtained with a larger set of 19 increments, which also contained contributions from selected combinations of conformations of three adjacent bonds. The utility of the additive increments for the prediction of relative conformer energies in the gas phase and in solution has been tested on the remaining nine conformers (n = 6, 7). With the improved increment set, the average deviation from the SM5.42R//MP2 results for solvated conformers at 298 K was 0.18 kcal/mol, and the maximum error was 0.98 kcal/mol. 相似文献
163.
Bashore CG Vetelino MG Wirtz MC Brooks PR Frost HN McDermott RE Whritenour DC Ragan JA Rutherford JL Makowski TW Brenek SJ Coe JW 《Organic letters》2006,8(26):5947-5950
[Structure: see text] The development of a concise enantioselective synthesis of nicotinic alkaloid 1 is presented. The route features the synthesis and use of a "stable" aliphatic triflate 21 in an alkylation step to generate Heck precursor 24 and an enantioselective cyclization to establish a compound with the key [3.2.1]-bicyclic core, 29. 相似文献
164.
For a signed graph G and function , a signed f‐factor of G is a spanning subgraph F such that sdegF(υ) = f(υ) for every vertex υ of G, where sdeg(υ) is the number of positive edges incident with v less the number of negative edges incident with υ, with loops counting twice in either case. For a given vertex‐function f, we provide necessary and sufficient conditions for a signed graph G to have a signed f‐factor. As a consequence of this result, an Erd?s‐Gallai‐type result is given for a sequence of integers to be the degree sequence of a signed r‐graph, the graph with at most r positive and r negative edges between a given pair of distinct vertices. We discuss how the theory can be altered when mixed edges (i.e., edges with one positive and one negative end) are allowed, and how it applies to bidirected graphs. © 2006 Wiley Periodicals, Inc. J Graph Theory 52: 27–36, 2006 相似文献
165.
Instrumental methods and challenges in quantifying polybrominated diphenyl ethers in environmental extracts: a review 总被引:1,自引:0,他引:1
Stapleton HM 《Analytical and bioanalytical chemistry》2006,386(4):807-817
Increased interest in the fate, transport and toxicity of polybrominated diphenyl ethers (PBDEs) over the past few years has
led to a variety of studies reporting different methods of analysis for these persistent organic pollutants. Because PBDEs
encompass a range of vapor pressures, molecular weights and degrees of bromine substitution, various analytical methods can
lead to discrimination of some PBDE congeners. Recent improvements in injection techniques and mass spectrometer ionization
methods have led to a variety of options to determine PBDEs in environmental samples. The purpose of this paper is therefore
to review the available literature describing the advantages and disadvantages in choosing an injection technique, gas chromatography
column and detector. Additional discussion is given to the challenges in measuring PBDEs, including potential chromatographic
interferences and the lack of commercial standards for higher brominated congeners, which provides difficulties in examining
degradation and debromination of BDE congeners, particularly for BDE 209. 相似文献
166.
Stapleton HM Harner T Shoeib M Keller JM Schantz MM Leigh SD Wise SA 《Analytical and bioanalytical chemistry》2006,384(3):791-800
Polybrominated diphenyl ethers (PBDEs) have been measured for the first time in three different indoor dust Standard Reference
Materials (SRMs) prepared by the National Institute of Standards and Technology (NIST). Two of these, SRM 2583 (Trace Elements
in Indoor Dust) and SRM 2584 (Trace Elements in Indoor Dust), have been certified previously for lead and other inorganic
constituents. A third, SRM 2585 (Organics in Indoor Dust), is a new indoor dust reference material prepared by NIST which
will be certified for various organic compounds (polycyclic aromatic hydrocarbons, pesticides and polychlorinated biphenyls)
in 2005 including certified concentrations for 16 individual PBDE congeners and reference values for an additional three PBDE
congeners. Dust SRMs were analyzed for 30 PBDE congeners using high-resolution gas chromatography combined with low-resolution
mass spectrometry operated in both negative chemical ionization (GC/ECNI–MS) and electron impact ionization (GC/EI–MS) modes.
Sensitivity was an order of magnitude higher using GC/ECNI–MS relative to GC/EI–MS. These SRMs have been characterized and
compared to the three PBDE commercial products (pentaBDE, octaBDE and decaBDE). PentaBDE and DecaBDE were present in all three
SRMs and were the dominant commercial products, making up approximately 33% and 58%, respectively. Recent studies suggest
that house dust may be a leading source of human exposure to PBDEs. These SRMs are the first reference materials with certified
concentrations for PBDEs, which will aid in validating future measurements of PBDEs in house dust and other similar matrices.
Electronic Supplementary Material Supplementary material is available for this article at http://dx.doi.org/ 10.1007/s00216-005-0227-y 相似文献
167.
Daniel Edelen Sarah B. Bush Heather Simpson Kristin L. Cook Aline Abassian 《School science and mathematics》2020,120(3):144-152
The mathematics education community has routinely called for mathematics tasks to be connected to the real world. However, accomplishing this in ways that are relevant to students’ lived experiences can be challenging. Meanwhile, mathematical modeling has gained traction as a way for students to learn mathematics through real-world connections. In an open problem to the mathematics education community, this paper explores connections between the mathematical modeling and the nature of what is considered relevant to students. The role of empathy is discussed as a proposed component for consideration within mathematical modeling so that students can further relate to real-world contexts as examined through the lens of Ecological Systems Theory. This is contextualized through a classroom-tested example entitled “Tiny Homes as a Solution to Homelessness” followed by implications and conclusions as they relate to mathematics education. 相似文献
168.
DeWitt KM Valadez L Abbott HL Kolasinski KW Harrison I 《The journal of physical chemistry. B》2006,110(13):6705-6713
The dissociative sticking coefficient for CH4 on Pt(111) has been measured as a function of both gas temperature (Tg) and surface temperature (Ts) using effusive molecular beam and angle-integrated ambient gas dosing methods. The experimental results are used to optimize the three parameters of a microcanonical unimolecular rate theory (MURT) model of the reactive system. The MURT calculations allow us to extract transition state properties from the data as well as to compare our data directly to other molecular beam and thermal equilibrium sticking measurements. We find a threshold energy for dissociation of E0 = 52.5 +/- 3.5 kJ mol(-1). Furthermore, the MURT with an optimized parameter set provides for a predictive understanding of the kinetics of this C-H bond activation reaction, that is, it allows us to predict the dissociative sticking coefficient of CH4 on Pt(111) for any combination of Ts and Tg even if the two are not equal to one another, indeed, the distribution of molecular energy need not even be thermal. Comparison of our results to those from recent thermal equilibrium catalysis studies on CH4 reforming over Pt nanoclusters ( approximately 2 nm diam) dispersed on oxide substrates indicates that the reactivity of Pt(111) exceeds that of the Pt nanocatalysts by several orders of magnitude. 相似文献
169.
Thompson M Wilkins SJ Compton RG Viles HA 《Journal of colloid and interface science》2003,260(1):204-210
The extent of passivation of calcite toward dissolution by aqueous acids arising from polymeric coatings based on polyacrylic acid or polyacrylonitrile is evaluated using a channel flow cell technique with microdisc electrode detection. In situ passivation with polyacrylic acid leads to a reduction in the reactivity of calcite toward acid attack with a reduction in the rate constant by up to an order of magnitude compared with untreated calcite. Ex situ passivation with polyacrylic acid for 24 h results in good coverage of the calcite by the polymer but it is shown to erode from the surface when exposed to an aqueous acid solution. In contrast, polyacrylonitrile is demonstrated to form a regular coating after exposure for just 1 h and offers robust potent protection from aqueous acid attack. 相似文献
170.
Burford N Phillips AD Spinney HA Robertson KN Cameron TS McDonald R 《Inorganic chemistry》2003,42(16):4949-4954
The isolation and characterization of the first intermolecular chalcogeno-urea complexes of iminophosphines are described. Trifluoromethylsulfonyloxy(2,4,6-tri-tert-butylphenylimino)phosphine, MesNPOTf, reacts quantitatively with chalcogenoimidazolines (ChIm, Ch = O, S, Se) and 1,3-dimethyldiphenylurea (OU) to give Lewis acid-base complexes, [MesNP.ChIm]OTf and [MesNP.OU]OTf. Single crystal X-ray diffraction studies indicate that the closest contact of the chalcogeno-urea donor occurs at phosphorus in all cases, representing compounds that contain examples of O-P, S-P, and Se-P coordinate bonds. In all complexes, coordination of the ligand causes significant displacement of the OTf anion, and the resulting cations [MesNP.L](+) are best described as complexes of a neutral ligand on a phosphadiazonium Lewis acceptor. As such, the complex ions [MesNP.L](+) are novel examples of cationic systems containing dicoordinate phosphorus centers. The complexes highlight the potential for electron-rich centers to behave as Lewis acids despite the presence of a lone pair of electrons at the acceptor site. 相似文献