Fast oxidation of secondary alcohols by the bromate-bromide system using cyclic microwave heating in acidic water

We report an improved, gentle, cyclic microwave activation technique for the oxidation of secondary alcohols using nonhazardous hypobromous acid (BrOH) as the reagent in acidic water. Several aliphatic and aromatic secondary alcohols were successfully oxidized to the corresponding ketones using this technique in high yields and with only minor amounts of side products.     

New results on elements 111 and 112

Experiments on the synthesis and identification of the nuclei ²⁷²111 and ²⁷⁷112 were performed in order to confirm previous results. Three additional decay chains were measured in the reaction ⁶⁴Ni + ²⁰⁹Bi →²⁷³111^*. The study revealed considerably improved data on the decay chain originating from ²⁷²111. One additional chain was measured in the reaction ⁷⁰Zn + ²⁰⁸Pb →²⁷⁸112^*. The decay properties of the chain starting at ²⁷⁷112 are in excellent agreement with the second chain of the first experiment down to ²⁶⁵Sg, where the new chain ends by a previously unknown spontaneous-fission branch. A re-analysis of all the data on elements 110, 111, and 112 measured at GSI since 1994 (a total of 34 decay chains was investigated) revealed that for 2 chains (the second chain of ²⁶⁹110 measured in 1994 and the first chain of ²⁷⁷112 measured in 1996) the results of the new analysis differed from the previous one. In all other cases the earlier data are exactly reproduced. Received: 21 December 2001 / Accepted: 15 January 2002     

A crystalline sponge based on dispersive forces suitable for X-ray structure determination of included molecular guests

A crystalline porous material showing one-dimensional (1-D) rectangular micropores (12 × 9 Ų) has been assembled from a semirigid macrocyclic tetraimine and EtOAc as the templating agent. The 1-D nature of the material is intrinsic to the conformationally rigid structure of a macrocyclic sub-unit bearing four cyclohexylidene residues. The multiple dispersive forces established among the aliphatic residues glutted the 1-D channels and provided thermal stability to the material at temperatures below 160 °C. Upon removal of the template, the structure of the empty solid exhibited permanent microporosity (S _BET = 342 m² g^–1). Being a true molecular sponge, the channel framework of this material allowed the inclusion of a variety of molecular sample guests without compromising its crystalline nature. Remarkably, this crystalline material enabled the structure determination by X-ray diffraction of the included molecules. Theoretical studies demonstrated the vital role played by the dispersive forces in the overall stabilization of the crystal packing.     

Feasibility of using atmospheric pressure matrix-assisted laser desorption/ionization with ion trap mass spectrometry in the analysis of acetylated xylooligosaccharides derived from hardwoods and Arabidopsis thaliana

The atmospheric pressure matrix-assisted laser desorption/ionization with ion trap mass spectrometry (AP-MALDI-ITMS) was investigated for its ability to analyse plant-derived oligosaccharides. The AP-MALDI-ITMS was able to detect xylooligosaccharides (XOS) with chain length of up to ten xylopyranosyl residues. Though the conventional MALDI–time-of-flight/mass spectrometry (TOF/MS) showed better sensitivity at higher mass range (>m/z 2,000), the AP-MALDI-ITMS seems to be more suitable for detection of acetylated XOS, and the measurement also corresponded better than the MALDI-TOF/MS analysis to the actual compositions of the pentose- and hexose-derived oligosaccharides in a complex sample. The structures of two isomeric aldotetrauronic acids and a mixture of acidic XOS were elucidated by AP-MALDI-ITMS using multi-stages mass fragmentation up to MS³. Thus, the AP-MALDI-ITMS demonstrated an advantage in determining both mass and structures of plant-derived oligosaccharides. In addition, the method of combining the direct endo-1,4-β-d-xylanase hydrolysis of plant material, and then followed by AP-MALDI-ITMS detection, was shown to recognize the substitution variations of glucuronoxylans in hardwood species and in Arabidopsis thaliana. To our knowledge, this is the first report to demonstrate the acetylation of glucuronoxylan in A. thaliana. The method, which requires only a small amount of plant material, such as 1 to 5 mg for the A. thaliana stem material, can be applied as a high throughput fingerprinting tool for the fast comparison of glucuronoxylan structures among plant species or transformants that result from in vivo cell wall modification.     

Management of periodic demands in distribution systems

The problem of the optimal scheduling of periodic demands for a given facility or commodity is presented and some properties of an integer programming model are discussed. Algorithms (both of implicit enumeration type and heuristic) are also given.     

On the behavior of α-brominated dimethyl o-benzenediacetate toward nitrogen nucleophiles . Part I. Reaction of dimethyl α,α'-dibromo o-benzenediacetate with hydrazines

Meso- ( 1a ) and racemic dimethyl α,α'-dibromo o-benzenediacetate ( 1b ) when condensed with hydrazine and methylhydrazine furnished respectively 1,3-dicarbomethoxyisoindole ( 5a ) and its N-methyl derivative ( 5b ). Reaction of phenylhydrazine with 1a led to the N-phenylisoindole ( 5c ) and to the N-anilino isoindoline ( 6 ) as the cis isomer; conversely, 1b was transformed into a mixture of the 2-phenyl-1,2,3,4-tetrahydrophthalazine ( 7 ), the trans isomer of ( 6 ), the N-anilinoisoindole ( 5d ) and dimethyl α-(N'-phenylhydrazino)-o-benzenediacetate ( 8 ). Compounds 1a and 1b were also condensed with acetylhydrazine to give a mixture of the N-acetylaminoisoindoline ( 12 ) and of the 2-acetyl-1,2,3,4-tetrahydrophthalazine ( 13 ).     

Decay studies of K isomers in 254No

A detailed $ \gamma$ spectroscopic decay study of two K isomers in ²⁵⁴No was performed. In addition to the previously reported $ \gamma$ lines two new transitions of E = 778 , 856keV could be attributed to the decay pattern of ^254m1No ( T _1/2 = 275±7 ms). The population of an excited band built up on this isomer ( $\ensuremath K^{\pi} =8^{-}$ by the decay of ^254m2No ( T _1/2 = 198±13 μs) could be proven by measuring delayed $ \gamma$ - $ \gamma$ coincidences between transitions stemming from the decay of both isomeric states. The energies of the band members could be established up to $\ensuremath I^{\pi} = 15^{-}$ . A spontaneous fission branch of (2.0±1.2)×10^-4 was measured for ^254m1No , an upper limit of $ \le$ 1.2×10^-4 was estimated for ^254m2No . These values demonstrate the high stability of multi-quasiparticle configurations against spontaneous fission. Evidence for an $ \alpha$ decay branch of ^254m1No in the order of 1×10^-4 was found.     

Small values of signed harmonic sums

For every $\tau \in \mathbb{R}$ and every integer N, let ${\mathfrak{m}}_N(\tau )$ be the minimum of the distance of τ from the sums ${\sum }_{n=1}^N{s}_n/n$, where $s_1,\dots ,s_n\in \{?1,+1\}$. We prove that ${\mathfrak{m}}_N(\tau )<\exp ?(?C{(\log ?N)}^2)$, for all sufficiently large positive integers N (depending on C and τ), where C is any positive constant less than $1/\log ?4$.     

Synthesis and characterization of graphene-based nanocomposites with potential use for biomedical applications

In this paper, GaN nanoparticles were synthesized from the complex Ga(H₂NCONH₂)₆Cl₃ in the flow of NH₃ at a mild temperature (350 °C). Further purification was performed by the ethanol-thermal method. The ethanol-thermal method also prompted the GaN nanoparticles to grow into an anisotropic morphology. XRD patterns reveal that GaN nanoparticles have crystallized in a hexagonal wurtzite structure. TEM observation shows that the average size of the as-prepared nanoparticles is about 5–10 nm. The photoluminescence spectrum exhibits a broad green emission band with a peak at 510 nm. It can be known from the first-principle theoretic simulation by the TDDFT method that this fluorescence emission band is attributed to the hydride defects of V _N-H on the surface of GaN nanoparticles.