Enantioselective Redox‐Divergent Chiral Phosphoric Acid Catalyzed Quinone Diels–Alder Reactions

An efficient enantioselective construction of tetrahydronaphthalene‐1,4‐diones as well as dihydronaphthalene‐1,4‐diols by a chiral phosphoric acid catalyzed quinone Diels–Alder reaction with dienecarbamates is reported. The nature of the protecting group on the diene is key to the success of achieving high enantioselectivity. The divergent “redox” selectivity is controlled by using an adequate amount of quinones. Reversible redox switching without erosion of enantioselectivity was possible from individual redox isomers.     

Interaction of Functionalized Naphthalenophanes with Abasic Sites in DNA: DNA Cleavage,DNA Cleavage Inhibition,and Formation of Ligand–DNA Adducts

Ligands interacting with abasic (AP) sites in DNA may generate roadblocks in base-excision DNA repair (BER) due to indirect inhibition of DNA repair enzymes (e.g., APE1) and/or formation of toxic byproducts, resulting from ligand-induced strand cleavage or covalent cross-links. Herein, a series of 12 putative AP-site ligands, sharing the common naphthalenophane scaffold, but endowed with a variety of substituents, have been prepared and systematically studied. The results demonstrate that most naphthalenophanes bind to AP sites in DNA and inhibit the APE1-induced hydrolysis of the latter in vitro. Remarkably, their APE1 inhibitory activity, as characterized by IC₅₀ and K_I values, can be directly related to their affinity and selectivity to AP sites, as assessed by means of fluorescence melting experiments. On the other hand, the molecular design of naphthalenophanes has a crucial influence on their intrinsic AP-site cleavage activity (i.e., ligand-catalyzed β- and β,δ-elimination reactions at the AP site), as illustrated by the compounds either having an exceptionally high AP-site cleavage activity (e.g., 2,7-BisNP-S , 125-fold more efficacious than spermine) or being totally devoid of this activity (four compounds). Finally, the unprecedented formation of a stable covalent DNA adduct upon reaction of one ligand ( 2,7-BisNP-NH ) with its own product of the AP-site cleavage is revealed.     

On the effect of glass composition in the dissolution of glasses by water

The dissolution rate in aqueous solution has been measured for three families of glasses of technological interest (borosilicates, aluminosilicates and lead-silicates). Borosilicates have been altered at a slightly basic pH (8–9), whereas the aluminosilicates and the lead-silicate glasses have been corroded in acidic solutions. In these conditions, silica is always less soluble than all other glass components. In each glass family, the effect of the silica content on the glass dissolution rate has been studied. The three series display a similar behavior as a function of the glass composition, namely a sharp increase of the dissolution rate with the content in soluble oxides. These experimental results have been explained in the framework of a Monte-Carlo simulation of glass dissolution. The simulations show that the fast extraction of the soluble species as compared to that of silica generates a porous surface layer, which becomes thicker and thicker when the percentage of soluble oxide increases in the glass. This increases the interface area between the glass and the solution, and consequently the dissolution rate in the same proportion. The numerical simulations reproduce quite well the experimental variations of the dissolution rates with glass composition.     

Kinetics of the reaction of OH radicals with CH3OH and CD3OD studied by laser photolysis coupled to high repetition rate laser induced fluorescence

A new experimental set-up coupling laser photolysis to a 10 kHz dye laser as the excitation source for OH fluorescence has been validated by measuring the rate constant of the reaction CH₃OH + OH. The rate constant of the deuterated homologue CD₃OD + OH has been measured under the same conditions.     

Radiative lifetime and oscillator strength determinations in Xe VI

Transition probabilities have been calculated for n = 0 and n = 1 transitions connecting the 5s2nl [ np (n=5-8); nf (n=4-5); nh (n=6-8); nk (n=8)] , 5s5pnl (nl=5d,6s), 5p3 and 5s2nl [ (ns (n=6-8); nd (n=5-8); ng (n=5-6); ni (n=7-8)] and 5s5p2 configurations of Xe VI. Core-polarization effects have been included in the framework of a Hartree-Fock approach. The accuracy of the present set of results has been assessed through comparisons with radiative lifetime measurements. Good agreement has been observed between theory and experiment.     

Glottal behavior in the high soprano range and the transition to the whistle register

The high soprano range was investigated by acoustic and electroglottographic measurements of 12 sopranos and high-speed endoscopy of one of these. A single laryngeal transition was observed on glissandi above the primo passaggio. It supports the existence of two distinct laryngeal mechanisms in the high soprano range: M2 and M3, underlying head and whistle registers. The laryngeal transition occurred gradually over several tones within the interval D#5-D6. It occurred over a wider range and was completed at a higher pitch for trained than untrained sopranos. The upper limit of the laryngeal transition during glissandi was accompanied by pitch jumps or instabilities, but, for most singers, it did not coincide with the upper limit of R1:f(0) tuning (i.e., tuning the first resonance to the fundamental frequency). However, pitch jumps could also be associated with changes in resonance tuning. Four singers demonstrated an overlap range over which they could sing with a full head or fluty resonant quality. Glottal behaviors underlying these two qualities were similar to the M2 and M3 mechanisms respectively. Pitch jumps and discontinuous glottal and spectral changes characteristic of a M2-M3 laryngeal transition were observed on decrescendi produced within this overlap range.     

Quaternary ammoniums and a cationic sodium complex as supramolecular catalysts in ring-opening of epoxides by amines

Supramolecular ionic organocatalysts and a metal-based catalyst were investigated in the ring-opening of epoxides by amines, without any artifice to enhance conversion (i.e., solvophobic effect, extended reaction time, heating, excess of amine, high catalyst loading). Different β-amino-alcohols were obtained in satisfying conversion (50–80%) in 24 h, under mild conditions.