Frank Model and Spontaneous Emergence of Chirality in Closed Systems

In a closed system an irreversible enantioselective autocatalysis coupled to a mutual inhibition reaction, corresponding to a fast and low exergonic formation of the heterochiral dimer which reverts to the monomers in the final reaction work‐up, yields absolute asymmetric synthesis even in the absence of chiral polarizations. This is due to the very high chiral amplifications of the initial small statistical deviations from the ideal racemic composition. Moreover, this system is sensitive to very small chiral polarizations (energy differences between transition states below the mJ mol^?1 range). This behaviour can also be observed in reversible exergonic reactions, because the racemization time scale is substantially longer than that of the transformation of the initial reagents. The effect of the presence of other reactions likely to occur (i.e. non‐catalytic transformations, non‐enantioselective catalysis and homodimer formation) is discussed. Even if these decrease the sensitivity of the network in several chemical scenarios, the emergence of kinetically controlled spontaneous symmetry breaking is not hindered. These features, together with the response of the system to a sequential reaction procedure, suggest that a similar type of network is at the heart of the Soai reaction.     

Adaptable choosability of planar graphs with sparse short cycles

Given a (possibly improper) edge colouring F of a graph G, a vertex colouring of G is adapted toF if no colour appears at the same time on an edge and on its two endpoints. A graph G is called (for some positive integer k) if for any list assignment L to the vertices of G, with |L(v)|≥k for all v, and any edge colouring F of G, G admits a colouring c adapted to F where c(v)∈L(v) for all v. This paper proves that a planar graph G is adaptably 3-choosable if any two triangles in G have distance at least 2 and no triangle is adjacent to a 4-cycle.     

A holding cost bound for the economic lot-sizing problem with time-invariant cost parameters

We show that in an optimal solution of the economic lot-sizing problem the total holding cost in an order interval is bounded from above by a quantity proportional to the setup cost and the logarithm of the number of periods in the interval. We present two applications of this result.     

Periodic motions in a simplified brake system with a periodic excitation

In this paper, periodic motions for a simplified brake system under a periodical excitation are investigated, and the motion switchability on the discontinuous boundary is discussed through the theory of discontinuous dynamical systems. The onset and vanishing of periodic motions are discussed through the bifurcation and grazing analyses. Based on the discontinuous boundary, the switching planes and the basic mappings are introduced, and the mapping structures for periodic motions are developed. From the mapping structures, the periodic motions are analytically predicted and the corresponding local stability and bifurcation analysis is completed. Periodic motions will be illustrated for verification of analytical predictions. In addition, the relative force distributions along the displacement are illustrated for illustrations of the analytical conditions of motion switchability on the discontinuous boundary.     

Protein expression dynamics during replicative senescence of endothelial cells studied by 2-D difference in-gel electrophoresis

Endothelial senescence contributes to endothelium dysfunctionality and is thereby linked to vascular aging. A dynamic proteomic study on human umbilical vein endothelial cells, isolated from three umbilical cords, was performed. The cells were cultured towards replicative senescence and whole cell lysates were subjected to 2-D difference gel electrophoresis (DIGE). Despite the biological variability of the three independent isolations, a set of proteins was found that showed senescence-dependent expression patterns in all isolations. We focused on those proteins that showed significant changes, with a paired analysis of variance (RM-ANOVA) p-value of < or =0.05. Thirty-five proteins were identified with LC-Fourier transform MS, and functional annotation revealed that endothelial replicative senescence is accompanied by increased cellular stress, protein biosynthesis and reduction in DNA repair and maintenance. Nuclear integrity becomes affected and cytoskeletal structure is also changed. Such important changes in the cell infrastructure might accelerate endothelium dysfunctionality. This study provides biological information that will initiate studies to further unravel endothelial senescence and gain more knowledge about the consequences of this process in the in vivo situation.     

NMR spectroscopic structure elucidation of the products of the reaction of 3-(3-aryl-3-oxopropenyl)- chromen-4-ones with 1,2-phenylenediamine

The reaction of 3-(3-aryl-3-oxopropenyl)chromen-4-ones with 1,2-phenylenediamine resulted in the unexpected formation of 10a-aryl-1,2,10,10a-tetrahydrobenzo-[4,5]-imidazo[1,2-a]pyridin-3-yl(2-hydroxyphenyl)-1-methanones. Their structure elucidation and complete 1H and 13C assignments have been performed by a combination of various one- and two-dimensional NMR experiments.     

Deamination of the amino acid fragment in imine metallacycles: unexpected synthesis of an NH-aldimine organometallic compound

We report that the action of Lewis bases, such as triphenylphosphine, pyridine, or trimethylamine, on imine metallacycles derived from amino acids leads to the formation of the first organometallic compound of an NH aldimine, a highly reactive organic species, and the corresponding alpha-ketoester, in a deamination reaction that mimics the metabolism of alpha-amino acids. The synthesis of different cyclopalladated compounds by a reaction between palladium acetate and the Schiff bases 2,4,6-Me(3)C(6)H(2)CH=NCH(R(1))COOR(2) (R(1) = CH(2)Ph, R(2) = Et and R(1) = Ph, R(2) = Me) is also reported.     

Highly enantioselective addition of in situ prepared arylzinc to aldehydes catalyzed by a series of atropisomeric binaphthyl-derived amino alcohols

The direct addition of in situ prepared arylzinc to aldehydes with chiral binaphthyl-derived amino alcohols as catalysts can afford optically active diarylmethanols in high yields and with excellent enantioselectivities (up to 99 % ee, ee = enantiomeric excess). By using a single catalyst, both enantiomers of many pharmaceutically interesting diarylmethanols can be obtained by the proper combination of various arylzinc reagents with different aldehydes; this catalytic system also works well for the phenylation of aliphatic aldehydes to give up to 96 % ee.