On the extendability of steiner t-designs

Necessary and sufficient conditions for the extendability of residual designs of Steiner systems S(t,t + 1,v) are studied. In particular, it is shown that a residual design with respect to a single point is uniquely extendable, and the extendability of a residual design with respect to a pair of points is equivalent to a bipartition of the block graph of a related design. © 1993 John Wiley & Sons, Inc.     

Ruthenium(II)-catalyzed homo-Diels-Alder reactions of disubstituted alkynes and norbornadiene

The homo-Diels-Alder (HDA) reaction of norbornadiene (NBD) and internal functionalized alkynes leading to 8,9-disubstituted deltacyclenes using readily available electron-rich phosphine-ruthenium(II) catalysts is described.     

Palladium-catalyzed addition of alkynes to cyclopropenes: an entry to stereodefined alkynylcyclopropanes

The Herrmann-Beller (H-B) phosphapalladacycle catalyzed the addition of terminal alkynes to unsymmetrical gem-disubstituted cyclopropenes to give alkynylcyclopropanes as single diastereomers in good to excellent yields. The stereofacial discrimination at the approach of the bulky alkynylpalladium species is believed responsible for the diastereoselectivity control of the addition reaction.     

Highly selective cobalt-mediated [6 + 2] cycloaddition of cycloheptatriene and allenes

[6 + 2] Cycloadditions between cycloheptatrienes with allenes have been investigated. Cobalt salts were found to promote this transformation efficiently. Moreover, this reaction was found to be highly selective since only one regioisomer was obtained with an excellent E/Z-selectivity.     

Determination of the First Excited Singlet State Dipole Moments of Coumarins by the Solvatochromic Method

The electronic absorption and fluorescence spectra of 4-hydroxycoumarin, 7-hydroxycoumarin, 7-methoxycoumarin, 7-hydroxy-4-methylcoumarin, 7-amino-4-methylcoumarin, and 7-diethylamino-4-methylcoumarin were measured at room temperature (298K) in several solvents and their first excited singlet-state dipole moments were determined by the solvatochromic shift method. The excited singlet-state dipole moments of the coumarins were compared with the ground-state values.

     

The uniaxial brickwork model,exact results,and CVM approximation

A complete phase diagram of the uniaxial brickwork lattice is determined first by using exact results, and then by using the cluster variation method. Both results are in very good agreement, which demonstrates the reliability of the CVM for two-dimensional systems. A well-defined maximum in the exact specific heat and a divergence of the CVM susceptibility provide strong indication for the occurrence of a floating phase.     

Palladium-Catalyzed Enantioselective Organic Transformations

Many palladium-catalyzed organic reactions with tailored ligands, besides the princess of asymmetric catalysis, allylic alkylation, are suitable for enantioselective organic synthesis. This is clearly illustrated by the large number of promising examples such as the Heck reaction, and Wacker-type oxidations, cycloadditions, cycloisomerizations, carbonylations, and copolymerization of alkenes with carbon monoxide.     

Validated LC–MS/MS method for the simultaneous determination of enalapril maleate,nitrendipine, hydrochlorothiazide,and their major metabolites in human plasma

Hypertension is a major risk factor for atherosclerosis and ischemic heart disease. Most hypertensive patients need a combination of antihypertensive agents to achieve therapeutic goals. A rapid, sensitive, and selective liquid chromatography-tandem mass spectrometric method was developed and validated for simultaneous determination of enalapril maleate (ENA) and its major metabolite enalaprilat (ENAT), nitrendipine (NIT) and its major metabolite dehydronitrendipine (DNIT), and hydrochlorothiazide (HCT) in human plasma using felodipine as an internal standard (IS). The drugs were extracted from plasma using one-step protein precipitation. Chromatographic separation was performed on a Symmetry C₁₈ column, with water and acetonitrile (10:90, v/v) as mobile phase. The detection was carried out using multiple reaction monitoring mode and coupled with electrospray ionization source. Multiple reaction monitoring transitions were m/z 377.1 → 234.1 for ENA, m/z 349.2 → 206.1 for ENAT, m/z 361.2 → 315.1 for NIT, m/z 359 → 331 for DNIT, m/z 295.9 → 205.1 for HCT, and m/z 384.1 → 338 for felodipine (IS). The method was linear over concentration ranges of 1–200, 20–500, 5–200, 2–100, and 5–200 ng/mL for ENA, ENAT, NIT, DNIT, and HCT, respectively, with r² ≥ 0.99. Method validation was performed according to U.S. Food and Drug Administration guidelines. The validated method showed good sensitivity and selectivity and could be applied for therapeutic drug monitoring and bioequivalence studies.     

Integrating Al with NiO nano honeycomb to realize an energetic material on silicon substrate

Nano energetic materials offer improved performance in energy release, ignition, and mechanical properties compared to their bulk or micro counterparts. In this study, the authors propose an approach to synthesize an Al/NiO based nano energetic material which is fully compatible with a microsystem. A two-dimensional NiO nano honeycomb is first realized by thermal oxidation of a Ni thin film deposited onto a silicon substrate by thermal evaporation. Then the NiO nano honeycomb is integrated with an Al that is deposited by thermal evaporation to realize an Al/NiO based nano energetic material. This approach has several advantages over previous investigations, such as lower ignition temperature, enhanced interfacial contact area, reduced impurities and Al oxidation, tailored dimensions, and easier integration into a microsystem to realize functional devices. The synthesized Al/NiO based nano energetic material is characterized by scanning electron microscopy, X-ray diffraction, differential thermal analysis, and differential scanning calorimetry.