Radiation-induced radicals in alpha-D-glucose: Comparing DFT cluster calculations with magnetic resonance experiments

Using density functional theory (DFT) calculations, an enhanced theoretical examination was made of the radiation-induced radicals in alpha-d-glucose. For the carbon-centred radicals in this sugar, the effect of the model space on the radical geometry as well as on the calculated radical hyperfine coupling tensors was examined. The findings were compared with previously published tensors, as determined by electron paramagnetic resonance (EPR) experiments and single molecule DFT calculations. A cluster approach was adopted, in which intermolecular interactions (predominantly hydrogen bonds) between the radical species and its environment were explicitly incorporated. This substantially improved the correspondence with experimental findings in comparison with single molecule calculations of an earlier examination. In a direct comparison between both computational methods for the glucose radicals, it was shown that the extent of the model space plays an important part in the determination of the radical geometry. Furthermore, the model space also has an impact on the calculated hyperfine coupling tensors. Full cluster EPR calculations, in which the paramagnetic properties are calculated for the entire model space of the cluster, give an excellent agreement with the experimental EPR measurements.     

N-Rich Porous Polymer with Isolated Tb3+-Ions Displays Unique Temperature Dependent Behavior through the Absence of Thermal Quenching

The challenge of measuring fast moving or small scale samples is based on the absence of contact between sample and sensor. Grafting lanthanides onto hybrid materials arises as one of the most promising accurate techniques to obtain noninvasive thermometers. In this work, a novel bipyridine based porous organic polymer (bpyDAT POP) was investigated as temperature sensor after grafting with Eu(acac)₃ and Tb(acac)₃ complexes. The bpyDAT POP successfully showed temperature-dependent behavior in the 10–310 K range, proving the potential of amorphous, porous organic frameworks. We observed unique temperature dependent behavior. More intriguingly, instead of the standard observed change in emission as a result of a change in temperature for both Eu³⁺ and Tb³⁺, the emission spectrum of Tb³⁺ remained constant. This work provides framework- and energy-based explanations for the observed phenomenon. The conjugation in the bpyDAT POP framework is interrupted, creating energetically isolated Tb³⁺ environments. Energy transfer from Tb³⁺ to Eu³⁺ is therefore absent, nor energy back transfer from Tb³⁺ to bpyDAT POP ligand (i.e. no thermal quenching) is detected.     

Squeezing flow of semi liquid foods between parallel Teflon coated plates

Samples of commercial tomato paste, low fat mayonnaise and mustard about 6–8 mm thick were squeezed to 0.8 mm at various speeds between 5 mm min⁻¹ and 25 mm min⁻¹ between Teflon-coated parallel plates 127 mm in diameter using an Instron UTM Model 5542. All the log force vs log height relationships had a clearly identified linear region. This indicated that a dominant squeezing flow regime was achieved at about 3 mm height, and that the machine has the proper stiffness to perform the tests. The stress level at a pre-selected height in this region is a measure of consistency, sensitive enough to distinguish between products of different brands. The residual stress after relaxation for about 2 min was on order of 10–50% of the initial stress, an indication that all three foods have a considerable structural integrity. In all three products there was a considerable discrepancy between the observed rate effects and predictions based on a pseudoplastic (power law) model. It could be described by the empirical relation (F_v1 − F_R)/(F_v2 − F_R)=(V₁/V₂)^m where F_v1 and F_v2 are the forces at the given displacement reached at speeds v₁ and v₂ respectively, F_R is the residual force after relaxation (found to be practically rate independent), and m is a constant of the order of 0.15–0.33, independent of the compression velocities ratio but characteristic of the food and brand. The calculated elongational viscosity was not a unique function of biaxial strain rate. To a certain extent, this was probably due to imperfect lubrication. But it was also a manifestation of these products considerable structural integrity which cannot be accounted for by models developed for ideal liquids. Received: 1 November 1999 Accepted: 2 May 2000     

Melt grafting of polymethyl methacrylate onto poly(ethylene‐co‐1‐octene) by reactive extrusion: Model compound approach

The grafting of poly(methylmethacrylate) onto poly(ethylene‐co‐1‐octene) by in situ radical polymerization of methyl methacrylate is a process where the side reactions are difficult to characterize. To increase the understanding of both the nature and the extent of such reactions, products resulting from the same chemical system, where polymer is replaced by squalane and/or pentadecane, are analyzed. The influence of the temperature, the nature of peroxides (used as radicals generators) and the monomer concentration are investigated toward the chain length of the grafts. The resulting grafted PMMA and PMMA homopolymer are qualitatively analyzed by MALDI‐TOF spectroscopy and size exclusion chromatography. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5215–5226, 2007     

Synthesis of unprotected and borane-protected cyclic phosphines using Ru- and Mo- based olefin metathesis catalysts

Ru- and Mo-based catalysts can be used in ring closing metathesis (RCM) reactions to synthesise cyclic phosphines protected as their borane complexes. The compatibility of the Schrock Mo-catalyst and the N-heterocyclic carbene Ru-catalysts with this class of substrates is particularly noteworthy as asymmetric RCM (ARCM) is now emerging as a new tool for the preparation of homochiral phosphines. One of the key results is that the Mo-catalyst allows the ring closure of the unprotected diallylphenylphosphine with 95% conversion.     

Facilitation of addition-elimination reactions in pyrimidines and purines using trifluoroacetic acid in trifluoroethanol

SNAr displacement reactions of 6-cyclohexylmethoxy-2-fluoropurine, 6-amino-2-butylsulfonyl-4-cyclohexylmethoxypyrimidine and 2-amino-6-chloropurine with substituted anilines (e.g. the weakly nucleophilic 4-aminobenzenesulfonamide) are dramaticallyaccelerated in the presence of trifluoroacetic acid and occur especially efficiently in 2,2,2-trifluoroethanol solvent.