Simple organocatalysts in multi-step reactions: An efficient one-pot Morita-Baylis-Hillman-type α-hydroxymethylation of vinyl ketones followed by the convenient,temperature-controlled one-pot etherification using alcohols

1,4-Diazabicyclo[2.2.2]octane (DABCO) was utilized as versatile catalyst in a one-pot synthesis: First, for the preparation of alcoholic formaldehyde solutions from para-formaldehyde catalysed by using low loadings of inexpensive DABCO. Second, for the fast α-hydroxymethylation of alkylic and aromatic vinyl ketones in high yields. In a third step, the same catalyst can be used for an optional, temperature controlled in situ etherification of the Morita-Baylis-Hillman product with various alcohols on a multi-gram scale in moderate to good overall yields and high purities. Furthermore, an application of the ether in the enantioselective synthesis of a common building block for total synthesis is shown, thus providing a gram-scale access from inexpensive bulk chemicals.     

Tartrazine: physical,thermal and biophysical properties of the most widely employed synthetic yellow food-colouring azo dye

Journal of Thermal Analysis and Calorimetry - The food-colouring dye tartrazine is a significant additive and in the same time a biologically active material. Thermal behaviour of trisodium...     

A remark on the conjecture of Erdös, Faber and Lovász

The celebrated Erd?s, Faber and Lovász Conjecture may be stated as follows: Any linear hypergraph on ν points has chromatic index at most ν. We show that the conjecture is equivalent to the following assumption: For any graph , where ν(G) denotes the linear intersection number and χ(G) denotes the chromatic number of G. As we will see for any graph G = (V, E), where denotes the complement of G. Hence, at least G or fulfills the conjecture.      

Development of a quantitative, validated capillary electrophoresis-time of flight-mass spectrometry method with integrated high-confidence analyte identification for metabolomics

A CE-MS method was developed and validated for the quantitative analysis of negatively charged metabolites by making use of the high mass accuracy and the quantitation capabilities of a TOF mass analyzer in combination with automated feature extraction and database search. Metabolites of the central carbon metabolism were quantified with an LOD and lower LOQ (LLOQ) of 0.2-2 and 1-4 microM, respectively. The method was used to elucidate metabolic changes in the Escherichia coli deletion mutant PntAB-UdhA that lacks nicotinamide nucleotide transhydrogenase function, under both stationary and exponential growth conditions. The reproducibility of metabolite extraction and CE-TOF-MS analysis ranged from 3.7 to 22.7 and 7.9 to 22.6%, respectively, while the biological variance was 3.4-31.3%. We observed significant differences in metabolite abundance, particularly in the citrate cycle, between wild-type and mutant E. coli. Overall, more than 600 features were found by automated feature detection, which resulted in approximately 150 high-confidence metabolite identifications. Concomitant analyses with two different GC-MS methods allowed not only crossvalidation of the quantitative results obtained by the various methods, but also led to a more comprehensive coverage of the E. coli metabolome.     

Structural and electronic effects involving pyridine rings in 4-methylpyridine Cu4OX6L4 complexes. II. Correlations based on molecular structure of the Cu4OCl6(4-Mepy)4 complex

Correlations involving bond lengths and bond angles in the molecular structure of the Cu₄OCl₆(4-Mepy)₄ complex (4-Mepy = 4-methylpyridine) with four symmetrically independent molecules present in the unit cell showed that the donor-acceptor behavior involving the π-back donation into the pyridine rings of the 4-Mepy ligands is most effectively stimulated by a suitable orientation of the pyridine rings in the trigonal bipyramidal geometry. The pyridine ring planes are almost in parallel orientation with one of the three Cu-Cl bonds. The bond lengths of these Cu-Cl bonds are in a significant linear correlation with the Cu-N bond lengths and the bonds lengths of the pyridine rings. The pyridine rings orientation is affected by distortion of the trigonal bipyramidal geometry to tetragonal pyramidal coordination, by out-of plane pyridine rings deviation and in-plane pyridine rings tilting, by puckering of the pyridine rings and by the effects of the methyl groups. The pyridine rings in at least seven of the sixteen trigonal bipyramidal coordinations exhibit an orientation supporting the π-back bonding between the Cu(II) atoms and the pyridine rings.     

A Dinuclear Mercury(II)‐Mediated Base Pair in DNA

The first dinuclear metal‐mediated base pair containing divalent metal ions has been prepared. A combination of the neutral bis(monodentate) purine derivative 1,N⁶‐ethenoadenine (ϵA), which preferentially binds two metal ions with a parallel alignment of the N−M bonds, and the canonical nucleobase thymine (T), which readily deprotonates in the presence of Hg^II and thereby partially compensates the charge accumulation due to the two closely spaced divalent metal ions, yields the dinuclear T‐Hg^II₂‐ϵA base pair. This metal‐mediated base pair stabilizes the DNA oligonucleotide duplex as shown by an increase of 8 °C in its melting temperature. Formation of the base pair was demonstrated by temperature‐dependent UV spectroscopy as well as by titration experiments monitored by UV and CD spectroscopy.     

Minimal Translation Hypersurfaces in Euclidean Space

The graph of a function f defined in some open set of the Euclidean space of dimension (p + q) is said to be a translation graph if f may be expressed as the sum of two independent functions ? and ψ defined in open sets of the Euclidean spaces of dimension p and q, respectively. We obtain a useful expression for the mean curvature of the graph of f in terms of the Laplacian, the gradient of ? and ψ as well as of the mean curvatures of their graphs. We study translation graphs having zero mean curvature, that is, minimal translation graphs, by imposing natural conditions on ? and ψ, like harmonicity, minimality and eikonality (constant norm of the gradient), giving several examples as well as characterization results.