Thiol–ene coupling reaction of fatty acid monomers

The reactivities and reaction rates of the thiol–ene coupling reaction of 2‐ethyl‐(hydroxymethyl)‐1,3‐propanediol trimercapto acetate and 2‐ethyl‐(hydroxymethyl)‐1,3‐propanediol trimercapto propionate with two common unsaturated fatty acid methyl esters (methyl oleate and methyl linoleate) were evaluated. The reactions were monitored with real‐time IR and ¹H NMR, which both showed that the mercapto acetate was more reactive than the mercapto propionate. Both thiols were more prone to add to the monounsaturated methyl oleate than to methyl linoleate, which contained two unconjugated double bonds. According to bond energy calculations, the thiol hydrogen of mercapto acetate was somewhat more difficult to abstract than the hydrogen of mercapto propionate. Consequently, the formed S? C bond in the acetate case was stronger than in the propionate case, and so the equilibrium was more shifted toward the addition products. The real‐time IR measurements also showed that the cis unsaturation in methyl oleate isomerized much more quickly than that in methyl linoleate, and this also had an impact on the overall addition rate of the thiols because a trans unsaturation was more reactive than a cis unsaturation. The higher isomerization rates in the oleate systems, compared with those of the linoleate systems, was suggested to be due to a more restricted rotation along the C? C bond of the reacted unsaturation in linoleate. This study showed the importance of trans unsaturations in obtaining reasonable reaction rates in thiol–ene reactions with fatty acid derivatives. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 6346–6352, 2004     

Comparison of small-angle p and pp elastic scattering at 52.8 GeV center-of-mass energy at the CERN intersecting storage rings

Proton-antiproton and proton-proton elastic scattering have been measured in the four-momentum transfer range 0.001|t|0.06 GeV² for center-of-mass energy 52.8 GeV at the CERN Intersecting Storage Rings (ISR). Using the known pp total cross section, a simultaneous fit to the p and pp differential cross sections yields the p total cross section; in addition, we obtain the ratio of the real-to-imaginary part of the forward nuclear-scattering amplitude and the nuclear-slope parameter for both p and pp. Our results show conclusively that the p total cross section is rising at ISR energies and lend support to conventional theories in which the difference between the p and pp total cross section vanishes at very high energy.     

Conditions for sulfite stabilization and determination by ion chromatography

The efficiencies of three groups of potential sulfite-stabilizing compounds were found to be in the order: carbonyls > alcohols = saccharides. A mole ratio of 1:1 between formaldehyde and sulfite was sufficient for stabilizing a sulfite solution for at least 72 h. The lower stabilizing efficiencies of the alcohols and saccharides examined could be compensated by using large excesses of these compounds. For example, if a 100-fold excess of glycerol over sulfite was used, the recovery of sulfite was 96% after 72 h compared with only 40% without addition of stabilizer. During separations by ion chromatography, almost no oxidation of the sample occurs provided the sample solution is directly injected into a deaerated eluent. For formaldehyde, the peak heights were found to depend on the molar ratio of the stabilizer to sulfite as well as on the concentration of sulfite. This effect was not found for the other stabilizers tested.     

Microwave-enhanced and metal-catalyzed functionalizations of the 4-aryl-dihydropyrimidone template

Progress in organometallic catalysis and recent advancements in the development of carbonylative reaction protocols without direct use of carbon monoxide have been utilized for efficient functionalizations of 4-aryl-dihydropyrimidone structures. The use of modern microwave technology enabled both high reaction rates and convenient handling. Examples of palladium-catalyzed cross-couplings, Heck reactions, amino- and alkoxycarbonylations, and direct N-amidations of 4-(bromophenyl)-dihydropyrimidones were performed. Further, the first N3-arylations of the dihydropyrimidone ring system were successfully completed using the copper-catalyzed Goldberg reaction. Altogether, these protocols provide new tools for rapid generation of novel and diverse dihydropyrimidone derivatives.     

Microstructural prototyping of ceramics by kinetic engineering: applications of spark plasma sintering

The significance of kinetics on the development of microstructures in connection with sintering of ceramics is well recognized. In practice, however, it still remains a challenge to prepare designed microstructures via engineering the sintering kinetics because of an insufficient understanding of the different operative mechanisms that are in many cases overlapping. In this article the kinetic issues involved in sintering are described and discussed with respect to their potential for prototyping microstructures that yield desired properties. By exploiting and mastering the differences present in the kinetics of grain sliding, densification, chemical reactions, and grain growth, respectively, we have established processing principles for producing bulk ceramics with microstructures consisting of nano-sized grains, aligned grains, and/or non-equilibrium-phase constitutions, and for achieving radically improved superplasticity in brittle ceramics. Although the studies quoted in this article were mainly carried out by spark plasma sintering, more general implications of them are expected, including efficient particle sliding, deformation-induced dynamic ripening, superplastic deformation-induced dynamic ripening, and non-equilibrium integration.     

Search for anomalous scattering of keV neutrons from H2O-D2O mixtures

We measured the neutron scattering intensities from pure liquid H2O relative to that of pure D2O and also relative to H2O-D2O mixtures, at room temperature. This study is relevant to the problem of quantum entanglement. The neutrons were generated from an electron Linac and the final energy of the scattered neutrons was fixed at 24.3 keV using a 20 cm thick pure iron filter. The scattering intensity ratios were found to agree with expected values deduced from the tabulated total cross sections within an accuracy of 3%. Thus no anomaly was observed.     

Generalized anisotropic scaling theory and the transverse meissner transition

We consider a depinning transition in vortex systems with columnar disorder and tilted applied magnetic fields. From scaling arguments and Monte Carlo simulations, we find that this transverse Meissner transition is governed by a fixed point which is anisotropic in all three directions. This generalization of conventional anisotropic scaling means that the correlation length in different directions diverges with different rates, and we derive exact results for the anisotropy exponents. We make predictions which can be tested in experiments on superconductors with columnar disorder.