Quasi-classical trajectory study of the S + OH → SO + H reaction: from reaction probability to thermal rate constant

First quasi-classical trajectory calculations have been carried out for the S((3)P) + OH(X?(2)Π) → SO(X?(3)Σ(-)) + H((2)S) reaction on an ab initio global potential energy surface for the ground electronic state, X?(2)A', of HSO. Cross sections, computed for collision energies up to 1 eV, show no energy threshold and decrease with the increasing collision energy. Rate constants have been calculated in the 5-500 K temperature range. The thermal rate constant is in good agreement with approximate quantum results, while a disagreement is found at 298 K with the experimental data. Product energy distributions have also been reported at four collision energies from 0.001 to 0.5 eV. The shapes of the rovibrational and angular distributions suggest the formation of an intermediate complex that is more and more long-lived as the collision energy increases.     

Controlled pinewood fractionation with supercritical ethanol: A prerequisite toward pinewood conversion into chemicals and biofuels

The objective of this work was to investigate the ability of supercritical (SC) ethanol conditions to attack preferentially the lignin fraction against the carbohydrate fraction and their effects on the product distribution among gases, light products, bio-oils, and chars. In this study, the conversion of each pinewood component was determined by the analysis of solid residues to quantify cellulose, hemicellulose, lignin, and char contents. It is shown that, by tuning the temperature, hemicellulose and lignin are already transformed in subcritical ethanol conditions, lignin being more reactive than hemicellulose. In contrast, native wood cellulose is recalcitrant to liquefaction in SC ethanol near the critical point (T_c = 241 °C and P_c = 61 bar), but 20% of native wood cellulose is converted in SC ethanol at 280 °C. Besides, the severity of the conditions, in terms of temperature and treatment time, does not significantly influence the yields of gases, light products, and bio-oils but strongly enhances char formation. Interestingly, the increase in SC ethanol density does not change the conversion of biomass components but has a marked effect on bio-oil yield and prevents char formation. The optimum fractionation conditions to convert the lignin component, while keeping unattacked the cellulose fraction with a minimum formation of char, are dense SC ethanol, at 250 °C for 1 h, in batch conditions. However, although lignin is more reactive than hemicellulose under these conditions, these fractions are converted, in a parallel way, to around 50% and 60%, respectively.     

Incorporation of a minimal nucleotide into DNA

Abasic sites are amongst the most frequent DNA lesions and result from spontaneous hydrolysis of the glycosidic bond or from the removal of damaged nucleobases. These depurination events can also occur on free deoxyribonucleoside triphosphates present in cells and lead to the formation of an abasic site triphosphate of which very little is known. Herein, we report the synthesis and biochemical characterization of the minimal triphosphate dФTP. Unexpectedly, dФTP is tolerated by various DNA polymerases and the incorporation efficiency obeys the A-rule. Single incorporation of dФMP units were also observed opposite abasic sites and the addition of prosthetic molecules mimicking base-pairs do not seem to favor the process.     

An Exceptionally Close,Non‐Bonded Hydrogen–Hydrogen Contact with Strong Through‐Space Spin–Spin Coupling

Condensation of 1,8,13‐tris(mercaptomethyl)triptycene and tris(bromomethyl)methane yields an in,in‐cyclophane with two inwardly directed methine groups. Based on X‐ray analysis and DFT and MP2 calculations, the hydrogen–hydrogen non‐bonded contact distance is estimated to be 1.50–1.53 Å. Furthermore, the two in‐hydrogen atoms show obvious spin–spin coupling with J=2.0 Hz.     

Direct HPLC resolution of beta-aminoalcohol (tazifylline,ranolazine, sotalol) enantiomers

Summary A routine chiral analysis has been developed to control the optical purity of chiral drugs and to monitor their asymmetric synthesis. The recent advent of new chiral stationary phases for HPLC enabled us to achieve the direct resolution of chiral drugs without any derivatization. The factors affecting chiral resolution on a new alpha₁-acid glycoprotein column (EnantioPac, LKB) were assessed with three beta-aminoalcohols.     

The design, synthesis and photochemical study of a biomimetic cyclodextrin model of photoactive yellow protein (PYP)

The design, synthesis and study of the photophysical and photochemical properties of the first biomimetic cyclodextrin (CD) model of photoactive yellow protein (PYP) are described. This model bears a deprotonated trans-p-coumaric acid chromophore, covalently linked via a cysteine moiety to a permethylated 6-monoamino β-CD. NMR and UV/Visible spectroscopy studies showed the formation of strong self-inclusion complexes in water at basic pH. Steady-state photolysis demonstrated that, unlike the free chromophore in solution, excitation of the model molecule leads to the formation of a photoproduct identified as the cis isomer by NMR spectroscopy. These observations provide evidence that the restricted CD cavity offers a promising framework for the design of biomimetic models of the PYP hydrophobic pocket.