Characterization of 4,5‐Dihydro‐1H‐Pyrazole Derivatives by 13C NMR Spectroscopy

The ¹³ C NMR resonances of 19 1‐acyl‐3‐(2‐nitro‐5‐substitutedphenyl)‐4,5‐dihydro‐1H‐pyrazoles, and 19 1‐acyl‐3‐(2‐amino‐5‐substituted)‐4,5‐dihydro‐1H‐pyrazoles, were completely assigned using the concerted application of one‐ and two‐dimensional NMR experiments (DEPT, gs‐HSQC and gs‐HMBC). Copyright © 2012 John Wiley & Sons, Ltd.     

The geometry of circumscribing polygons of minimal perimeter

LetC be a closed strictly convex curve in the Euclidean plane, and letC(n) denote the class ofn-sided polygons which circumscribeC. Geometric conditions are given for polygonsP C(n) which have minimum perimeter in the classC(n).     

Modular solid-phase synthetic approach to optimize structural and electronic properties of oligoboronic acid receptors and sensors for the aqueous recognition of oligosaccharides

This article describes the design and optimization of the first entirely modular, parallel solid-phase synthetic approach for the generation of well-defined polyamine oligoboronic acid receptors and fluorescence sensors for complex oligosaccharides. The synthetic approach allows an effective building of the receptor polyamine backbone, followed by the controlled diversification of the amine benzylic side chains. This approach enabled the testing, in a modular fashion, of the effect of different arylboronic acid units substituted with unencumbering para electron-withdrawing or electron-donating groups. The feasibility of this approach toward automated synthesis was also investigated with the assembly of a sublibrary of receptors by means of the Irori MiniKan technology. Several sublibraries of anthracene-capped sensors containing two or three arylboronic acids were synthesized, and their binding to a series of model disaccharides was examined in neutral aqueous media. The calculation of association constants by fluorescence titrations confirmed that subtle changes in the structures of the interamine spacers in the polyamine backbone can have a significant effect on the stability of the resulting complexes. Most importantly, this study led to the determination of the preferred electronic characteristics for the arylboronate units, and suggests that a new generation of receptors containing very electron-poor arylboronic acids could lead to a significant improvement of binding affinities.     

A new computational microscope for molecules: High resolution MEDLA images of taxol and HIV-1 protease,using additive electron density fragmentation principles and fuzzy set methods

Based on the molecular electron density lego assembler (MEDLA) method, a computational microscope was developed that generates accurate images of bodies of large molecules at a resolution far exceeding current experimental techniques. The MEDLA microscope can be tuned to display the high electron density regions of formal chemical bonds; or to show the low density regions of hydrogen bonds and secondary interactions, or to display local shape requirements important in molecular recognition. The power of the method is illustrated by examples of detailed images of taxol, an important anti-cancer agent, and HIV-1 protease, a protein of 1564 atoms. A mathematical framework of the approach, based on fuzzy sets, and the fundamentals of several additional applications of the additive, fuzzy fragmentation principle are presented.     

Synthesis of fluorinated biphenyls via aryne reaction

Synthesis of fluorinated biphenyls via attack of a benzyne by an anion of 3-fluoroanisole.     

A mechanistic investigation of the decacarbonyldimanganese-catalyzed carbonylation of amines

The Mn₂(CO)₁₀-catalyzed reactions of n-butylamine and cyclohexylamine with CO to give the corresponding ureas have been examined under a variety of conditions of temperature, CO pressure, reaction time, solvent and potential co-catalysts. With the diamines, ethylenediamine and 1,4-diaminobutane, there was no catalyzed reaction with CO. On the other hand, 1,3-diaminopropane gave 1,4,5,6-tetrahydropyrimidine, and 1,6-diaminohexane yielded a polyurea. In an effort to elucidate the mechanism of these reactions, several stoichiometric reactions were carried out. The reaction of Mn₂(CO)₁₀ with primary aliphatic amines proceeds to give a carbamoyl complex as follows: Mn₂(CO)₁₀ + 3 RNH₂ ? cis-Mn(CO)₄(NH₂R)(CONHR) + RNH₃⁺ + Mn(CO)₅^? Under CO pressure the isolated carbamoyl complex reacted to give the urea as follows: cis-Mn(CO)₄(NH₂R)(CONHR) + CO → (RNH)₂CO + HMn(CO)₅ The mechanism of this latter reaction is proposed to involve the intermediate formation of the organic isocyanate RNCO. These reactions are discussed as part of an overall mechanism for the Mn₂(CO)₁₀-catalyzed formation of ureas. The mechanism successfully accounts for factors which affect the yields of the reaction. Other metal carbonyl complexes, Re₂(CO)₁₀, (η-CH₃C₅H₄)Mn(CO)₃ and [η-C₅H₅Cr(CO)₃]₂, did not catalyze the reactions.     

Synthesis and X-ray crystal structure of three polyazamacrocycles having sulfonate pendant groups: Piperazinyl-monomethanesulfonic acid,sodium hydrogen 1,4,7-triazacyclononane-N,N′-di(methanesulfonate) and 1,4,7,10-tetraazacyclododecane-N,N′-di(methanesulfonic acid)

C₅H₁₀N₂O₃S,1, monoclinicC2/c,a=17.545(5),b=6.822(8),c=13.928(2),=108.36(7),Z=8, MoK, =0.7107 Å,=3.56cm^–1,R=0.061,R _w =0.099. C₈H₁₆N₃O₆S₂Na·2H₂O,2, orthorhombicPna2₁,a=17.964(8),b=10.157(1),c=8.263(4),Z=4, MoK, =0.7107 Å,=4.07 cm^–1,R=0.040,R _w =0.043. C₁₀H₂₀N₄O₆S₂·2H₂O,3, monoclinicP2₁/n,a=9.142(9),b=13.576(7),c=14.028(8),=94.096(8),Z=4, MoK, =0.7107 Å,=3.37 cm^–1,R=0.063,R _w =0.074. Compounds1, 2, and3 were prepared from the pH-dependent sulfomethylation of the di- and polyazamacrocycles.     

Physical separation of straw stem components to reduce silica

In this paper, we describe ongoing efforts to solve challenges to using straw for bioenergy and bioproducts. Among these, silica in straw forms a low-melting eutectic with potassium, causing slag deposits, and chlorides cause corrosion beneath the deposits. Straw consists principally of stems, leaves, sheaths, nodes, awns, and chaff. Leaves and sheaths are higher in silica, while chaff, leaves, and nodes are the primary sources of fines. Our approach to reducing silica is to selectively harvest the straw stems using an in-field physical separation, leaving the remaining components in the field to build soil organic matter and contribute soil nutrients.