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911.
912.
James A. Shymansky Sandra Enger Jennifer L. Chidsey Larry D. Yore Margaret Jorgensen Laura Henriques Edward W. Wolfe 《School science and mathematics》1997,97(4):172-183
The Iowa Assessment Project was funded by the National Science Foundation to explore the feasibility of combining the expertise of science teachers, science educators, and test developers to build innovative performance assessments that complement traditional, norm-referenced, multiple-choice science tests. The science teachers, graduate students, and science educators designed and tested performance assessment tasks to enhance the picture of science understanding in students through multiple points of evidence. This paper describes the design of four science performance tasks for Grade 9 students and the relationship between their performance on these tasks and multiple-choice items in the Iowa Tests of Educational Development. Students and schools used to develop the tasks were not included in the verification sample. 相似文献
913.
Poole JS Hadad CM Platz MS Fredin ZP Pickard L Guerrero EL Kessler M Chowdhury G Kotandeniya D Gates KS 《Photochemistry and photobiology》2002,75(4):339-345
The absorption and fluorescence spectra of 3-aminobenzo-1,2,4-triazine di-N-oxide (tirapazamine) have been recorded and exhibit a dependence on solvent that correlates with the Dimroth ET30 parameter. Time-dependent density functional theory calculations reveal that the transition of tirapazamine in the visible region is pi-->pi* in nature. The fluorescence lifetime is 98+/-2 ps in water. The fluorescence quantum yield is approximately 0.002 in water. The fluorescence of tirapazamine is efficiently quenched by electron donors via an electron-transfer process. Linear Stern-Volmer fluorescence quenching plots are observed with sodium azide, potassium thiocyanate, guanosine monophosphate and tryptophan (Trp) methyl ester hydrochloride. Guanosine monophosphate, tyrosine (Tyr) methyl ester hydrochloride and Trp methyl ester hydrochloride appear to quench the fluorescence at a rate greater than diffusion control implying that these substrates complex with tirapazamine in its ground state. This complexation was detected by absorption spectroscopy. 相似文献
914.
Perissinotti LL Turjanski AG Estrin DA Doctorovich F 《Journal of the American Chemical Society》2005,127(2):486-487
We report an investigation of the reaction between (S)-nitroso-l-cysteine ethyl ester and l-cysteine ethyl ester as a model of physiologically relevant transnitrosation processes. Our theoretical and experimental evidence clearly supports the existence of a nitroxyl disulfide intermediate in solution. 相似文献
915.
William J. Kerr Mark McLaughlin Laura C. Paterson Colin M. Pearson 《Tetrahedron》2018,74(38):5062-5068
Herein we target the total synthesis of 2-epi-α-cedren-3-one, a natural compound isolated from the essential oil of Juniperus thurifera. Overall, our synthetic sequence presents an optimised and robust series of chemical transformations, with prominent features including a low temperature and highly (Z)-selective Wittig olefination reaction, which is vital for the establishment of the relative stereochemistry within the final natural product, and a microwave-assisted, catalytic, intramolecular Pauson-Khand cyclisation reaction, which is used to construct the intriguing tricyclic core of the target molecule. Our optimum cyclisation protocol utilises only 20?mol% of transition metal, and delivers the complex tricyclic structure in just 10?min. Further manipulations of the annulation product culminate in the first total synthesis of the described natural target. 相似文献
916.
Colloids for Catalysts: A Concept for the Preparation of Superior Catalysts of Industrial Relevance 下载免费PDF全文
Dr. Jonathan Quinson Sara Neumann Tanja Wannmacher Laura Kacenauskaite Masanori Inaba Jan Bucher Francesco Bizzotto Dr. Søren B. Simonsen Dr. Luise Theil Kuhn Dajana Bujak Dr. Alessandro Zana Prof. Dr. Matthias Arenz Dr. Sebastian Kunz 《Angewandte Chemie (International ed. in English)》2018,57(38):12338-12341
Compared to conventional preparation methods for supported heterogeneous catalysts, the use of colloidal nanoparticles (NPs) allows for a precise control over size, size distribution, and distribution/location of the NPs on the support. However, common colloidal syntheses have restrictions that limit their applicability for industrial catalyst preparation. We present a simple, surfactant‐free, and scalable preparation method for colloidal NPs to overcome these restrictions. We demonstrate how precious‐metal NPs are prepared in alkaline methanol, how the particle size can be tuned, and how supported catalysts are obtained. The potential of these colloids in the preparation of improved catalysts is demonstrated by two examples from heterogeneous catalysis and electrocatalysis. 相似文献
917.
Matthew V. Vollmer Dr. Jing Xie Ryan C. Cammarota Dr. Victor G. Young Jr. Dr. Eckhard Bill Prof. Laura Gagliardi Prof. Connie C. Lu 《Angewandte Chemie (International ed. in English)》2018,57(26):7815-7819
Formal nickelate(?I) complexes bearing Group 13 metalloligands (M=Al and Ga) were isolated. These 17 e? complexes were synthesized by one‐electron reduction of the corresponding Ni0→MIII precursors, and were investigated by single‐crystal X‐ray diffraction, EPR spectroscopy, and quantum chemical calculations. Collectively, the experimental and computational data support: 1) the strengthening of the Ni?M bond upon one‐electron reduction, and 2) the delocalization of the unpaired spin across the Ni and M atoms. An intriguing electronic configuration is revealed where three valence electrons occupy two σ‐type bonding interactions: Ni(3d )2→M and σ‐(Ni?M)1. The latter is an unusual Ni?M σ‐bonding molecular orbital that comprises primarily the Ni 4pz and M npz/ns atomic orbitals. 相似文献
918.
Ayodeji A. Agbowuro Rami Mazraani Laura C. McCaughey Wilhelmina M. Huston Allan B. Gamble Joel D.A. Tyndall 《Tetrahedron》2018,74(12):1184-1190
JO146, a mixture of two diastereomers of a peptidic phosphonate inhibitor for Chlamydial HtrA (CtHtrA), has reported activity against Chlamydia species in both human and koala. In this study we isolated the individual diastereomers JO146-D1 and JO146-D2 (in ≥90% purity) and assessed their individual inhibitory activity against the serine protease human neutrophil elastase (HNE) which is structurally and functionally related to CtHtrA, as well as in Chlamydia trachomatis cell culture. JO146-D2 [S,S,R-Boc-Val-Pro-ValP(OPh)2], the isomer with the physiologically relevant valine at P1, had an approximate 2.5 – fold increase in in vitro HNE inhibition potency over JO146-D1 [S,S,S-Boc-Val-Pro-ValP(OPh)2] and greater than 100 – fold increase in cellular anti-chlamydial activity compared to JO146-D1 which possesses the unnatural valine at P1. JO146 and the individual diastereomers had excellent selectivity for the serine protease HNE over the potential off-target serine proteases trypsin and chymotrypsin. Docking studies supported the biological data with a geometrically unfavoured interaction observed between the P1 valine residue of JO146-D1 and the enzyme S1 sub-pocket. 相似文献
919.
Trifluoromethyl aldimines derived from α-amino esters have proven to be very good starting materials to obtain the title compounds. A Ag2O-catalyzed Mannich-type/cyclization cascade reaction starting from suitable α-isocyano acetates leads to enantiopure valuable trans-carboxylic trifluoromethyl substituted 2-imidazolines by a highly stereoselective addition without the need to add organocatalysts. 相似文献
920.
A Staudinger reaction between methoxyketene and two different imines formed from citral afforded, after chemical transformation, the (E/Z)-4-alkenylepoxy-2-azetidinones 2, 3 and 4. These compounds, by reaction with Cp2TiCl, did not cyclize to afford the expected polycyclic β-lactams, but the corresponding allylic alcohols 12, 13 and 15 were obtained instead. Unexpectedly, the treatment of cyanoepoxide (E)-3 with Cp2TiCl also gave the hydroxyl aldehyde (E)-14 whose formation suggests to us that a possible radical reduction of the cyano group might have occurred, and we lastly succeeded in the capture of the N-titanoimidoyl radicals. The behaviour observed for the isoprenoid side chain in the Staudinger reaction, the reactions with Cp2TiCl, as well as the trapping of N-titanoimidoyl radicals generated from benzocyanoformyl-2-azetidinones with the Ti(III) reagent, are discussed. 相似文献