On generalized Erd?s spaces

During the last years both Erd?s space and complete Erd?s space were topologically characterized by Dijkstra and van Mill. Applications include results about Erd?s type spaces in ?p-spaces as well as results about Polishable ideals on ω. We present an unifying theorem in terms of sets with a reflexive relation that among other things contains these apparently dissimilar results as special cases.     

Steric factors override thermodynamic driving force in regioselectivity of proline hydroxylation by prolyl-4-hydroxylase enzymes

Prolyl-4-hydroxylase is an important nonheme iron-containing dioxygenase in humans involved in the regioselective hydroxylation of a proline residue in a peptide chain on the C(4) position. In biosystems this process is important to create collagen cross-linking and cellular responses to hypoxia. We have performed a series of density functional theory (DFT) studies into the origin of the regioselectivity of proline hydroxylation by P4H enzymes using a minimal active site model (where substrate is unhindered in the binding site) and a larger active site model that incorporates steric hindrance of the substrate by several secondary sphere aromatic residues. Our studies show that thermodynamically the most favorable hydrogen atom abstraction position of proline is from the C(5) position; hence, the small model gives a low reaction barrier and large exothermicity for this process. However, stereochemical repulsions of the substrate with aromatic residues of Tyr(140) and Trp(243) in the second coordination sphere prevent C(5) hydroxylation and make C(4) hydroxylation the dominant mechanism, despite a lesser driving force for the reaction. These studies explain the remarkable regioselectivity of proline hydroxylation by P4H enzymes and show that the regioselectivity is kinetically controlled but not thermodynamically. In addition, we calculated spectroscopic parameters and found good agreement with experimental data.     

Non-destructive bulk analysis of the Buggenum sword by neutron resonance capture analysis and neutron diffraction

Two neutron based techniques, neutron resonance capture analysis (NRCA) and time-of-flight neutron-diffraction (TOF-ND) have been used to determine the elemental composition and structure of a precious and very well preserved all-metal sword from the Bronze Age. This Buggenum sword was on loan from the National Museum of Antiquities (NMA) in Leiden (NL). NRCA and TOF-ND experiments have been carried out at a number of more or less identical positions of the sword. The tin-bronze ratio and the relative amounts of some minor elements (Sb, As, Ag, In) have been determined. The results of neutron diffraction measurements showed considerable tin-segregation, and clear indications of hardening on the edges of the blade. In addition, radiographs using Bremsstrahlung revealed the construction of the hilt–blade connection. The work was carried out at the EC Joint Research Centre IRMM in Geel (B) and at the ISIS facility of the Rutherford Appleton Laboratory (UK).     

Isolation and characterisation of products from the reactions between [Co2(nta)2(μ-OH)2]2− and different ligands. The crystal structure of [Co(nta)(N,N-Et2en)]

The crystal structure of [Co(nta)(N,N-Et₂en)] (nta = nitrilotriacetate and N,N-Et₂en = N,N-diethylethylenediamine) was determined from three-dimensional X-ray diffraction data. The substituted nitrogen of N,N-diethylethylenediamine is bonded trans to the nta nitrogen with the Co—N_{(N,N Et2en)}= 2.011(5) and Co—N_(nta) = 1.950(4) Å while the cis Co—N bond is 1.953(4) Å. The Co—O bond lengths are 1.905(2) and 1.884(4) Å respectively.