Theoretical studies of the cross-linking mechanisms between cytosine and tyrosine

DNA-protein cross-linking is one of the many DNA lesions mediated by hydroxyl radicals, the most damaging among the reactive oxygen species in biological systems. Density functional theory methods are employed to investigate the complex reaction mechanisms of the formation of cytosine-tyrosine cross-links as observed in gamma-irradiated aqueous solutions of cytosine and tyrosine, as well as in gamma-irradiated nucleohistone. The majority of the radical addition mechanisms considered are found to have significant barriers and therefore to be thermodynamically unfavorable for the formation of the initial cross-linked product. Our calculated reaction potential energy surfaces suggest that a feasible complete mechanism consists of radical combination forming the initial cross-linked product, a hydrogen shuffle within the initial cross-linked product, and an acid-catalyzed dehydration reaction. Water and hydrogen-bonding interactions are suggested to play a key role in catalyzing the hydrogen-transfer step of the reaction.     

Methyl 3‐O‐β‐l‐fucopyranosyl α‐d‐glucopyranoside trihydrate

The water content of the title compound, C₁₃H₂₄O₁₀·3H₂O, creates an extensive hydrogen‐bonding pattern, with all the hydroxyl groups of the disaccharide acting as hydrogen‐bond donors and acceptors. The water molecules are arranged in columns along the crystallographic b axis and form, together with one of the hydroxyl groups, infinite hydrogen‐bonded chains. The conformation of the disaccharide is described by glycosidic torsion angles of −38 and 18°.     

Simultaneous spectrophotometric determination of nitrite and nitrate by flow injection analysis

The flow injection principle is used in the photometric determination of nitrite and nitrate with sulfanilamide and N-(1-naphthyl)ethylenediamine as reagents. An on-line copper-coated cadmium reductor reduces nitrate to nitrite. The detection limit is 0.05 μM for nitrite and 0.1 mM for nitrate at a total sample volume of 200 μM. Up to 30 samples can be analyzed per hour with a relative precision of ca. 1%.     

Rapid prototyping of polymer microsystems via excimer laser ablation of polymeric moulds

This study presents a novel method for rapid prototyping of polymer microsystems. The method is based on excimer laser ablation of a thermally and mechanically stable polymer, such as PEEK (poly-ether-ether-ketone). A negative of the desired microsystem is laser machined in PEEK, which can then be used directly for hot embossing or injection moulding of a series of prototypes. This approach is very rapid and considerably cheaper than more traditional approaches to toolmaking, while still performing well in terms of reproduction of tool dimensions. The reduction in time and cost for a master tool using this method opens up new possibilities for testing small series in the R&D phase of a microsystem. Finally, two particular applications of the technique are presented.     

Asymmetric equilibria in dynamic two-sided matching markets with independent preferences

A fundamental fact in two-sided matching is that if a market allows several stable outcomes, then one is optimal for all men in the sense that no man would prefer another stable outcome. We study a related phenomenon of asymmetric equilibria in a dynamic market where agents enter and search for a mate for at most n rounds before exiting again. Assuming independent preferences, we find that this game has multiple equilibria, some of which are highly asymmetric between sexes. We also investigate how the set of equilibria depends on a sex difference in the outside option of not being mated at all.     

Fast method of XANES data collection suitable for oxidation state mapping

XANES has been recently used for the determination of oxidation states of actinides in environmental samples. To obtain reliable results, however, a sufficiently long counting time at every probing energy and a large number of experimental points per XANES spectrum are required, due to the complex mathematical model used to fit the measured spectrum. This makes micro-mapping difficult, since the time required for data collection becomes unacceptably long. A simplified model for data collection and evaluation is presented. Its effectiveness has been tested by measuring the distribution of Pu oxidation states in a “hot” particle coming from a nuclear weapon test site.     

2,2′,6,6′-Tetrachloro-4,4′-propane-2,2-diyldiphenol, 2,2′,6-tribromo-4,4′-propane-2,2-diyldiphenol and 2,2′,6,6′-tetrabromo-4,4′-propane-2,2-diyldiphenol

Three flame retardants with very similar molecular structures showing three different packing patterns have been studied. The crystal structure of 2,2′,6,6′-tetrachloro-4,4′-propane-2,2-diyldiphenol, C₁₅H₁₂Cl₄O₂, can be described as a packing of sheets. The packing shows a very short intermolecular Cl⋯Cl contact distance of 3.094 (2) Å between pairs of mol­ecules inside each sheet. The crystal structure of 2,2′,6-tribromo-4,4′-propane-2,2-diyldiphenol, C₁₅H₁₃Br₃O₂, can be described as a packing of doubly stranded helical square tubes. These square helices are interconnected through Br⋯Br contacts between different helices. Finally, a previously known structure, 2,2′,6,6′-tetrabromo-4,4′-propane-2,2-diyldiphenol [Simonov, Cheban, Rotaru & Bels'skii (1986). Kristallografiya, 31 , 397–399], C₁₅H₁₂Br₄O₂, which is the most commonly used flame retardant and which has twofold rotational symmetry, has been refined in the correct absolute configuration. The structure shows large differences from the chloro analogue with regard to packing, van der Waals distances and hydrogen-bond distances.