Metathesis as a versatile tool in oleochemistry

Olefin metathesis, awarded with the Nobel Prize in Chemistry 2005 for Chauvin, Grubbs and Schrock, has emerged as a powerful tool for organic as well as polymer chemistry. In oleochemistry, this reaction is well known and has been applied for many decades. Examples include the functionalization of the double bonds of different oleochemicals or the (direct) polymerization of plant oils via metathesis. More recent developments, particularly the development of better and more robust catalysts, allow for highly efficient cross‐metathesis reactions opening new possibilities for the direct introduction of chemical functionalities. Within this contribution, the development of metathesis in oleochemistry will be discussed, covering self‐metathesis as well as more recent developments in the field of cross‐metathesis that lead to desired platform chemicals.     

An investigation of carbon nanotube jet grinding

Since their observation in 1976 and 1991, carbon nanotubes (CNTs) have generated much interest due to their properties and potential applications. CNTs are tubular carbon molecules with remarkable mechanical, electrical, chemical and thermal properties, which make them useful in various applications. Industries producing CNTs via the fluidized bed chemical vapor deposition technique face challenges related to the size of CNT bundles. The two main challenges are agglomeration and agglomerate size distribution control. A solution to these challenges involves the use of jet mills to grind the CNT agglomerates. The goal of this study was to determine whether the nanotubes could be ground with air jets using a commercial jet mill and apply a two-parameter model to describe the grinding process. The present study has indicated that air-jet grinding of CNTs is feasible with a typical commercial jet mill. This paper presents the effect of operational parameters on the arithmetic mean diameter of the ground product. Sonic velocity through the grinding nozzles was required to obtain reasonable grinding rates and relatively narrow particle size distributions. This occurs at high air to solids feedrate ratios. Additionally, a simple attrition model can describe the grinding process in the spiral jet mill.     

Pigmentation phenotypes of variant extension locus alleles result from point mutations that alter MSH receptor function

Coat colors in the chestnut horse, the yellow Labrador retriever, the red fox, and one type of yellow mouse are due to recessive alleles at the extension locus. Similarly, dominant alleles at this locus are often responsible for dark coat colors in mammals, such as the melanic form of the leopard, Panthera pardus. We show here that the murine extension locus encodes the melanocyte-stimulating hormone (MSH) receptor. In mice, the recessive yellow allele (e) results from a frameshift that produces a prematurely terminated, nonfunctioning receptor. The sombre (Eso and Eso-3J) and tobacco darkening (Etob) alleles, which both have dominant melanizing effects, results from point mutations that produce hyperactive MSH receptors. The Eso-3J receptor is constitutively activated, while the Etob receptor remains hormone responsive and produces a greater activation of its effector, adenylyl cyclase, than does the wild-type allele.     

Electrophilic chlorination of methane over superacidic sulfated zirconia

Catalytic chlorination of methane was studied over SO ₄ ^2– /ZrO₂, Pt/SO ₄ ^2– /ZrO₂, and Fe/Mn/SO ₄ ^2– /ZrO₂ solid superacid catalysts. The reactions were carried out in a continuous flow reactor under atmospheric pressure, at temperatures below 240°C, with a gaseous hourly space velocity of 1000 ml/g h and a methane to chlorine ratio of 4 to 1. At 200°C with 30% chlorine converted the selectivity in methyl chloride exceeds 90%. At more elevated temperatures, the selectivity decreases but stays above 80% in methyl chloride at 225°C using the sulfated zirconia catalysts. The selectivity can be enhanced by adding platinum to sulfated zirconia catalysts. An iron and manganese-doped catalyst exhibited excellent selectivities at somewhat lower conversions. Methyl chloride is obtained at 235°C in selectivities greater than 85%. No chloroform or carbon tetrachloride is formed. The electrophilic insertion involves electron-deficient metal-coordinated chlorine into the methane C-H bond.Catalysis by solid superacids, 29. For part 28 see ref. [14].     

Acquired carnitine abnormalities in critically ill children

In order to characterize the role of carnitine during metabolic stress, we prospectively determined carnitine profiles in plasma and urine on admission, days 2, 5, 10 and 15, among 28 critically ill children free of any known conditions associated with secondary carnitine deficiency. More than 25% of plasma and 50% of urinary carnitine measurements were abnormal; 96% (27/28) of patients displayed on at least one occasion an abnormal [< -2 SD or > +2 SD] carnitine value in plasma. Three children had extremely low [< 10 micromol/l] free carnitine (FC) levels in plasma. Plasma esterified and FC levels on admission were not related to the risk of mortality [PRISM score], to muscle lysis [CK values], and to the caloric intake. Levels of FC and esterified carnitine in plasma were unrelated to those measured in urine. Conclusion: Abnormal plasma and urine carnitine measurements are frequently found in critically ill children; the biological significance of these perturbations remains unclear. Caution must be exercised before concluding that an abnormal carnitine value is indicative of an underlying hereditary metabolic disorder in this population.     

Representations by Contact and Intersection of Segments

A necessary and sufficient condition is given for a connected bipartite graph to be the incidence graph of a contact family of segments and points. We deduce that any four-connected three-colorable plane graph is the contact graph of a family of segments and that any four-colored planar graph without an induced C₄ using four colors is the intersection graph of a family of straight line segments.     

DESCRIPTION AND ANALYSIS OF TIMBER DRYING KINETICS

In this paper an experimental and semi-analytical technique is described that provides a method of estimating a macroscopic drying kinetics curve and internal moisture content profiles is described. Moisture gradients and the time evolution of these gradients are analysed as a function of the air drying parameters (dry-bulb, wet-bulb temperature and the velocity) and the product parameters (thickness and density). The material used as an illustration is a maritime-pine-wood.