Synthesis and antimalarial effects of N,N-dialkyl-6-(substituted phenyl)-1,2,4,5-tetrazin-3-amines

The synthesis of a series of N,N-dialkyl-6-(substituted phenyl)-1,2,4,5-tetrazin-3-amines (IV) by two routes is described. The first route (Scheme I) involved the oxidative cyclization of formazans (II) to 3-bromo-6-(substituted phenyl)-1,2,4,5-tetrazines (III), followed by treatment with amines. The second (Scheme II) utilized the treatment of 3-(methylthio)-6-(substituted phenyl)-1,2,4,5-tetrazines (VII) with amines to provide the desired products. The intermediate 3-(methylthio)-6-(substituted phenyl)-1,2,4,5-tetrazines (VII) were obtained by thiobenzoylation of hydrazinecarbohydrazonothioic acid methyl ester with [[(substituted phenyl)thioxomethyl]thio]-acetic acids (V) to afford the 1,2-dihydro-3-(methylthio)-6-(substituted phenyl)-1,2,4,5-tetrazines (VI). Oxidation with bromine in acetic acid provided the desired intermediates. The target 6-(substituted phenyl)-1,2,4,5-tetrazin-3-amines (IV) displayed modest antimalarial activity.     

Er∶Yb∶YCOB晶体制备及其激光二极管抽运激光特性

研究了Er∶Yb∶YCa4O(BO3)3(简称Er∶Yb∶YCOB)的多晶制备和单晶生长,用提拉法生长出光学质量优良的Er∶Yb∶YCOB单晶,测量了其吸收光谱和荧光光谱,分析了其能级和泵浦原理,并进行了以激光二极管为抽运源的激光试验,实现了Er∶Yb∶YCOB晶体的在1.55μm附近110mW的激光输出,且斜效率达18.9;.     

A novel stereospecific synthesis of (±)-leukotriene A4(LTA4), methyl ester

The reaction of the phosphate $\text{1}$ with the expoxyaldehyde $\text{2}$ is reported as the key step in a novel stereospecific synthesis of (±)-LTA₄, methyl ester $\text{3}$.     

Wavelet-based Preconditioners for Dense Matrices with Non-Smooth Local Features

We present algorithms for the detection of local non-smooth features within a dense matrix and show how, by isolating such features, we are able to use wavelet compression to design preconditioners for the corresponding dense linear system. We illustrate our approach with examples from the solution of elastohydrodynamic lubrication problems and boundary integral equations.This revised version was published online in October 2005 with corrections to the Cover Date.     

Connecting Science and Mathematics: Using Inquiry Investigations to Learn About Data Collection,Analysis, and Display

The purpose of this study was to explore the effect of providing preservice teachers the opportunity to collect real data in a science methods inquiry investigation and using the data, design data displays in their mathematics methods course. The research questions focused on how preservice teachers' understandings of data displays, research design, and the specific content addressed improved when they used these displays to attempt to communicate the data they had collected themselves in their inquiry investigations. The 46 preservice teachers were given questionnaires at the beginning and end of the courses, twelve were interviewed both pre and post, all written work pertaining to data displays and the inquiry investigations was collected, methods class sessions were audio and videotaped, and the final data display and science investigation projects were photocopied. The findings show that by creating and scrutinizing their data displays, the preservice teachers were able to recognize the limitations of their inquiry investigation design. Through working with data in the context of inquiry projects of their own design, the preservice teachers realized meaningful connections and commonalities that exist in mathematics and science while strengthening their knowledge and skills in both disciplines.     

Incorporating Mathematics into the Science Program of Students Labeled “At‐Risk”

Twenty three at‐risk high school female students who had failed mathematics and science in a traditional school setting were the subjects of this study that integrated mathematics and science lessons over a period of four weeks. Using a combination of direct instruction, calculations, graphing, hands‐on projects, and discussion, the topic of mechanical advantage was studied, to find out how well students understood the topic. The study found that these students who initially knew very little about mechanical advantage, and who did not see any need to use mathematics in the study of science, indicated an increased understanding of mechanical advantage, and also seemed to realize that integrating mathematics and science enhanced learning.     

A delicate balance of energetics. Subtleties associated with alpha-ketol-based bridge migration to afford 9-keto-10beta-p-methoxybenzyloxytaxanes

The feasibility of the title reaction has been pursued for the purpose of advancing a concise total synthesis of Taxol. Of the two closely related series examined, the first featured an exo-methylene group at C4. The second consisted of an alpha-epoxide at that site. Strikingly, the olefinic construct proved inert to attempted alpha-ketol rearrangement. In contrast, the oxiranyl derivative isomerized smoothly. The reaction sequence associated with arrival at taxane 18 is short (15 steps from a D-camphor derivative) and notably efficient. The thermodynamic issues that are raised by this investigation have been clarified by an assessment of molecular mechanics-derived (MM3) steric energy calculations.     

Implementation of a genetically tuned neural platform in optimizing fluorescence from receptor-ligand binding interactions on microchips

This paper describes the use of a genetically tuned neural network platform to optimize the fluorescence realized upon binding 5-carboxyfluorescein-D-Ala-D-Ala-D-Ala (5-FAM-(D-Ala)(3) ) (1) to the antibiotic teicoplanin from Actinoplanes teichomyceticus electrostatically attached to a microfluidic channel originally modified with 3-aminopropyltriethoxysilane. Here, three parameters: (i) the length of time teicoplanin was in the microchannel; (ii) the length of time 1 was in the microchannel, thereby, in equilibrium with teicoplanin, and; (iii) the amount of time buffer was flushed through the microchannel to wash out any unbound 1 remaining in the channel, are examined at a constant concentration of 1, with neural network methodology applied to optimize fluorescence. Optimal neural structure provided a best fit model, both for the training set (r(2) = 0.985) and testing set (r(2) = 0.967) data. Simulated results were experimentally validated demonstrating efficiency of the neural network approach and proved superior to the use of multiple linear regression and neural networks using standard back propagation.     

Cationic Si−H−Si Bridges in Polysilanes: Their Detection and Targeted Formation in Stable Ion Studies

The ionization of 1,1‐dihydridocyclopentasilane 7 has been found to yield the cyclic polysilanylsilyl cation 8 instead of the expected hydrogen‐substituted silylium ion 6 . The silyl cation 8 is stabilized by the formation of an intramolecular Si?H?Si bridge, which also provides the thermodynamic driving force for its formation. In general, the preference for the formation of Si?H?Si bridges can be used to scavenge and identify transient intermediates in the Lewis acid induced rearrangement of polysilanes. The validity of this concept has been demonstrated for one central step in this chemistry, the ring‐contraction reaction of cyclohexasilanes to form silylcyclopentasilanes.