Enzymatic Conversion of Flavonoids using Bacterial Chalcone Isomerase and Enoate Reductase

Flavonoids are a large group of plant secondary metabolites with a variety of biological properties and are therefore of interest to many scientists, as they can lead to industrially interesting intermediates. The anaerobic gut bacterium Eubacterium ramulus can catabolize flavonoids, but until now, the pathway has not been experimentally confirmed. In the present work, a chalcone isomerase (CHI) and an enoate reductase (ERED) could be identified through whole genome sequencing and gene motif search. These two enzymes were successfully cloned and expressed in Escherichia coli in their active form, even under aerobic conditions. The catabolic pathway of E. ramulus was confirmed by biotransformations of flavanones into dihydrochalcones. The engineered E. coli strain that expresses both enzymes was used for the conversion of several flavanones, underlining the applicability of this biocatalytic cascade reaction.     

An Estimate for the Problem of Illumination of the Boundary of a Convex Body in E3

Let A be a convex body in Euclidean space E3. We denote by H(A) the smallest number of homothetic 'reduced copies of A by which it is possible to cover the whole of A. The conjecture of Hadwiger is H(A) 8. We prove that H(A) 16.     

Coarse nonlinear dynamics and metastability of filling-emptying transitions: water in carbon nanotubes

Using a coarse-grained molecular dynamics (CMD) approach we study the apparent nonlinear dynamics of water molecules filling or emptying carbon nanotubes as a function of system parameters. Different levels of the pore hydrophobicity give rise to tubes that are empty, water-filled, or fluctuate between these two long-lived metastable states. The corresponding coarse-grained free-energy surfaces and their hysteretic parameter dependence are explored by linking MD to continuum fixed point and bifurcation algorithms. The results are validated through equilibrium MD simulations.     

N1...N3 hydrogen bonds of A:U base pairs of RNA are stronger than those of A:T base pairs of DNA

Trans-hydrogen-bond deuterium isotope effects of Watson-Crick A:U and A:T base pairs of 10 homologous RNA and DNA duplexes are compared. The isotope effect at 13C2 of adenosine residues due to deuterium/protium substitution at the imino H3 site, 2hDelta13C2, is larger in RNA than in DNA. The virtually consistent larger isotope effects in RNA suggest that the N1...N3 hydrogen bonds of A:U base pairs of RNA are stronger than those of the A:T base pairs of DNA.     

On the role of organic adlayers in the anomalous water sorptivity of Lépine limestone

Sorptivity data are reported for the capillary absorption of water, ethanol, propan-2-ol, and n-heptane by the calcitic limestone Lépine (Lavoux à grain). The data confirm that the water sorptivity is anomalously low, an indication of partial wetting by water. Results are expressed in terms of a wetting index. The water sorptivity increases after heat treatment and chemical oxidation by hydrogen peroxide bleaching, while the sorptivity with organic liquids is unchanged. These treatments, therefore, increase the water wetting index. The results provide strong evidence that the presence of a natural organic adlayer is responsible for the anomalously low water sorptivity of this particular limestone. This natural water repellency effect may be exploited in developing chemical treatments to modify the water transport properties of stone.     

Expeditious copper-catalyzed conjugate 1,4-addition of bromo[2-(1,3-dioxolan-2-yl)ethyl]magnesium to alpha,beta-cycloalkenones and subsequent transformations

Expeditious CuI-catalyzed conjugate 1,4-addition of bromo[2-(1,3-dioxolan-2-yl)ethyl]magnesium to the five-, six-, seven-, and eight-membered alpha,beta-cycloalkenones is described. The reaction times are decreased dramatically compared to CuBr-(CH(3))(2)S catalysis. The resulting ketoacetals were subsequently cyclized to bicyclic beta-hydroxy ketones and alpha,beta-enones, followed by further transformations.