Magnetic elastic electron scattering from 3Be and 13C

Elastic scattering through 180° from ⁹Be, ¹²C and ¹³C targets has been observed for electrons of 35 to 90 MeV. Magnetic scattering cross sections for ⁹Be and ¹³C have been obtained by subtracting charge scattering as deduced from the scattering from the spin-zero nucleus ¹²C. Theoretical shell model predictions for the magnetic cross sections are derived for (1s)⁴(1p)^A?4 configurations and various coupling schemes. Both harmonic oscillator and Woods-Saxon radial wave functions are used. A comparison of our results with magnetic cross sections calculated in DWBA yields magnetic rms radii $\text{〈r}{}^2\text{〉}{}_{\mathrm{<mtext>M</mtext>}}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 3.2 ± 0.3}\text{fm}$ and $\text{〈r}{}^2\text{〉}{}_{\mathrm{<mtext>M</mtext>}}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 3.3 ± 0.3}\text{fm}$ for ⁹Be and ¹³C. For ¹³C a combined flt to our low-q data and to earlier high-q data, yields $\text{〈r}{}^2\text{〉}{}_{\mathrm{<mtext>M</mtext>}}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 3.4 ± 0.1}\text{fm}$ and a strong preference for intermediate coupling (IC) wave functions. Magnetic dipole scattering from ⁹Be is also close to the IC prediction, as deduced from a fit to our data and earlier high-q data. The fitted value of the octupole moment $\text{Ω = 5±1 μ}{}_{\mathrm{<mtext>N</mtext><mtext>fm</mtext>}}{}^1$ can only be explained by a deformation of the average nuclear potential. The radial size $\text{〈r}{}^2\text{〉}{}_{\mathrm{<mtext>1</mtext><mtext>p</mtext>}}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 2.85 ± 0.05}\text{fm}$ for the 1p radial wave function is in agreement with both the ⁹Be and ¹³C data.     

Magnetic susceptibility and nuclear magnetic resonance of vanadium sulfides

Measurements of the magnetic susceptibility in the temperature range 4–1000°K are reported for the vanadium sulfides VS, V₃S₄-V₂S₃ and V₅S₈. At higher temperatures the susceptibility of all compounds approaches a constant, positive value, indicating a Pauli-paramagnetic contribution of itinerant electrons. At lower temperatures an increase of the susceptibility is observed. This effect is particularly pronounced in V₅S₈, and is taken as evidence for the presence of localized magnetic moments.Nuclear magnetic resonance spectra of V₅S₈ show two lines, one with a temperature-independent Knight shift, and one with a positive Knight shift which increases strongly at lower temperatures. The two lines are attributed to vanadium atoms with itinerant d electrons, and to vanadium atoms with localized d electrons, respectively. This interpretation is consistent with the magnetic susceptibility data. The difference in properties between two types of vanadium atoms in V₅S₈ can be understood by considering the crystal structure.     

On the eigenproblem for normal matrices

Summary The Householder-Givens method for the solution of the Hermitean eigenproblem is used for the solution of the skew-Hermitean and the normal eigenproblem.This research was performed at the (Mathematical Institute of the) State University in Utrecht.     

Force-field dependence of the conformational properties of α,ω-dimethoxypolyethylene glycol

A molecular dynamics (MD) study of α,ω-dimethoxypolyethylene glycol has been carried out under various conditions with respect to solvent composition, ionic strength, chain length, force field and temperature. A previous MD study on a 15-mer of polyethyleneglycol (PEG) suggested a helical equilibrium structure that was stabilised by hydrogen bonding and bridging water molecules. Experiments show that PEG is highly soluble in water, and indicate that clustering is not favoured. In the present study using different force fields, the GROMOS force fields 45A3 and 53A6, a variation on the latter 53A6_OE, and a force field by Smith et al. produced different results. For the GROMOS force fields 45A3 and 53A6 no helical structure was found, but formation of more or less compact random coils in aqueous solution due to hydrophobic interactions was observed. For the other two force fields used, α,ω-dimethoxypolyethylene glycol stayed flexible and more or less elongated in aqueous solution, more in agreement with experimental observations and the previous MD study.     

Parity- and time-reversal-violating moments of light nuclei

I present the calculation of parity- and time-reversal-violating moments of the nucleon and light nuclei, originating from the QCD $\bar \theta$ term and effective dimension-six operators. By applying chiral effective field theory these calculations are performed in a unified framework. I argue that measurements of a few light-nuclear electric dipole moments would shed light on the mechanism of parity and time-reversal violation.     

Base‐Free Iron Catalyzed Transfer Hydrogenation of Esters Using EtOH as Hydrogen Source

Herein, we report on the use of the iron pincer complex Iron‐MACHO‐BH, in the base‐free transfer hydrogenation of esters with EtOH as a hydrogen source. More than 20 substrates including aromatic and aliphatic esters and lactones were reduced affording the desired primary alcohols and diols with moderate to excellent isolated yields. It is also possible to reduce polyesters to the diols with this method, enabling a novel way of plastic recycling. Reduction of the renewable substrate methyl levulinate proceeds to form 1,4‐pentanediol directly. The yields are largely governed by the equilibrium between the alcohol and the ethyl ester.     

Nylon Intermediates from Bio‐Based Levulinic Acid

Use of ZrO₂/SiO₂ as a solid acid catalyst in the ring‐opening of biobased γ‐valerolactone with methanol in the gas phase leads to mixtures of methyl 2‐, 3‐, and 4‐pentenoate (MP) in over 95 % selectivity, containing a surprising 81 % of M4P. This process allows the application of a selective hydroformylation to this mixture to convert M4P into methyl 5‐formyl‐valerate (M5FV) with 90 % selectivity. The other isomers remain unreacted. Reductive amination of M5FV and ring‐closure to ?‐caprolactam in excellent yield had been reported before. The remaining mixture of 2‐ and 3‐MP was subjected to an isomerising methoxycarbonylation to dimethyl adipate in 91 % yield.     

Protecting‐Group‐Controlled Enzymatic Glycosylation of Oligo‐N‐Acetyllactosamine Derivatives

We describe a chemoenzymatic strategy that can give a library of differentially fucosylated and sialylated oligosaccharides starting from a single chemically synthesized tri‐N‐acetyllactosamine derivative. The common precursor could easily be converted into 6 different hexasaccharides in which the glucosamine moieties are either acetylated (GlcNAc) or modified as a free amine (GlcNH₂) or Boc (GlcNHBoc). Fucosylation of the resulting compounds by a recombinant fucosyl transferase resulted in only modification of the natural GlcNAc moieties, providing access to 6 selectively mono‐ and bis‐fucosylated oligosaccharides. Conversion of the GlcNH₂ or GlcNHBoc moieties into the natural GlcNAc, followed by sialylation by sialyl transferases gave 12 differently fucosylated and sialylated compounds. The oligosaccharides were printed as a microarray that was probed by several glycan‐binding proteins, demonstrating that complex patterns of fucosylation can modulate glycan recognition.     

Direct and Regioselective Di-α-fucosylation on the Secondary Rim of β-Cyclodextrin

A straightforward glycosylation method is described to regio- and stereoselectively introduce two α-l -fucose moieties directly to the secondary rim of β-cyclodextrin. Using NMR and MS fragmentation studies, the nonasaccharide structure was determined, which was also visualized using molecular dynamics simulations. The reported glycosylation method proved to be robust on gram-scale, and may be generally applied to directly glycosylate β-cyclodextrins to make well-defined multivalent glycoclusters.