Six-dimensional quasiclassical and quantum dynamics of H2 dissociation on the c(2 × 2)-Ti/Al(100) surface

Based on a slab model of H(2) dissociation on a c(2 × 2) structure with Ti atoms in the first and third layers of Al(100), a six-dimensional (6D) potential energy surface (PES) has been built. In this PES, a molecular adsorption well with a depth of 0.45 eV is present in front of a barrier of height 0.13 eV. Using this PES, H(2) dissociation probabilities are calculated by the classical trajectory (CT), the quasiclassical trajectory (QCT), and the time-dependent wave-packet (TDWP) method. The QCT study shows that trajectories can be trapped by the molecular adsorption well. Higher incident energy can lead to direct H(2) dissociation. Vibrational pre-excitation is the most efficient way to promote direct dissociation without trapping. We find that both rotational and vibrational excitation have efficacies close to 1.0 in the entire range of incident energies investigated, which supports the randomization in the initial conditions making the reaction rate solely dependent on the total (internal and translational) energy. The H(2) dissociation probabilities from quantum dynamics are in reasonable agreement with the QCT results in the energy range 50-200 meV, except for some fluctuations. However, the TDWP results considerably exceed the QCT results in the energy range 200-850 meV. The CT reaction probabilities are too low compared with the quantum dynamical results.     

Synthesis and application of isocyanates radiolabeled with carbon-11

Carbon-11 labeled isocyanates are efficiently prepared by dehydration of [(11) C]carbamate salts, which in turn are easily formed from cyclotron-produced [(11) C]CO(2) and amines in the presence of a CO(2) fixation agent. The [(11) C]isocyanates are useful radiosynthons for the synthesis of a variety of [carbonyl-(11) C]-labeled asymmetrical ureas and carbamate esters. The method is well suited to incorporate any isotope of carbon, and is especially useful for positron emission tomography (PET) radiotracers for in vivo imaging. This is demonstrated by using the method to make [carbonyl-(11) C]-6-hydroxy-[1,1'-biphenyl]-3-yl cyclohexylcarbamate which is a novel radiotracer for PET imaging of fatty acid amide hydrolase.     

Addition of N-heterocyclic carbenes to a ruthenium(VI) nitrido polyoxometalate: a new route to cyclic guanidines

The scope of N-atom transfer from the electrophilic ruthenium(VI) nitrido containing polyoxometalate [PW(11)O(39)Ru(VI)N](4-) has been extended to the N-heterocyclic carbene {CH(2)(Mes)N}(2)C and the coupling product {CH(2)(Mes)N}(2)CNH(2)(+) characterized by (1)H NMR and high-resolution mass spectrometry. Because guanidines display many fields of applications ranging from biology to supramolecular chemistry, this could afford an original route to the synthesis of cyclic guanidines. This also enlarges the potential of nitrido complexes in the synthesis of heterocycles, mainly illustrated in the literature through the formation of aziridines through N-atom transfer to alkenes. In the course of the reaction, the ruthenium(III)-containing polyoxometallic intermediate [PW(11)O(39)Ru(III){NC{N(Mes)CH(2)}(2)}](5-) has been thoroughly characterized by continuous-wave and pulsed electron paramagnetic resonance, which nicely confirms the presence of the organic moiety on the polyoxometallic framework, Ru K-edge X-ray absorption near-edge structure, and electrochemistry.     

Teflon Magnetic Stirring Capsules (TMSC) as a Practical and Reusable Delivery System for Sensitive Reagents and Catalysts

The development of a user-friendly reusable laboratory equipment for the delivery of sensitive reagents and catalysts is described. The tightness of these Teflon Magnetic Stirring Capsules (TMSC) is ensured by the magnetic force and release of the reagent inside the solution is triggered by adjusting the stirring rate so that the centrifuge force exceeds the magnetic force. They can be loaded with several chemicals at the same time and do operate across a broad range of temperatures. The inertness of Teflon facilitates reaction purification.     

Synthese de pyrrolo[1,2-a]quinoleines

A-Acetoxypyrrolo[1,2a]quinolines 26-30 were synthesized by cyclization of 2-(1-pyrroly)phenylacetic acids 21-25 with acetic anhydride. The structures of the new compounds were determined by ¹H-nmr spectroscopy.     

C-O and C-C bond formation in the cyclisation of gem-(dialkoxymethyl)-1,6-dienes catalysed by tin(IV) triflimidate at room temperature

We described herein a Sn(NTf₂)₄-catalysed cyclisation of gem-(dialkoxymethyl)-1,6-dienes and derivatives where cyclohexane or tetrahydrofuran rings are formed following either a 6-enexo-endo-trig process or a 5-exo-trig process, respectively, depending on substitution patterns. The latter process features an unusual dealkylative ether cyclisation, triggered by the strong Lewis acid character of the tin(IV) triflimidate catalyst.     

Hydrogen activation on Mo-based sulfide catalysts,a periodic DFT study

Hydrogen adsorption on Mo[bond]S, Co[bond]Mo[bond]S, and Ni[bond]Mo[bond]S (10 1 macro 0) surfaces has been modeled by means of periodic DFT calculations taking into account the gaseous surrounding of these catalysts in working conditions. On the stable Mo[bond]S surface, only six-fold coordinated Mo cations are present, whereas substitution by Co or Ni leads to the creation of stable coordinatively unsaturated sites. On the stable MoS(2) surface, hydrogen dissociation is always endothermic and presents a high activation barrier. On Co[bond]Mo[bond]S surfaces, the ability to dissociate H(2) depends on the nature of the metal atom and the sulfur coordination environment. As an adsorption center, Co strongly favors molecular hydrogen activation as compared to the Mo atoms. Co also increases the ability of its sulfur atom ligands to bind hydrogen. Investigation of surface acidity using ammonia as a probe molecule confirms the crucial role of sulfur basicity on hydrogen activation on these surfaces. As a result, Co[bond]Mo[bond]S surfaces present Co[bond]S sites for which the dissociation of hydrogen is exothermic and weakly activated. On Ni[bond]Mo[bond]S surfaces, Ni[bond]S pairs are not stable and do not provide for an efficient way for hydrogen activation. These theoretical results are in good agreement with recent experimental studies of H(2)[bond]D(2) exchange reactions.     

Molecular design based on 3D-pharmacophore. Application to 5-HT subtypes receptors

A first definition of a pharmacophore for the serotonin reuptake inhibitors was carried out by considering a three-dimensional model which correlates the chemical structures of series of reuptake inhibitors with their biological affinities. A molecular design was described by analyzing two different 3D serotonin pharmacophores. This successful approach enabled us to consider the design of new serotonin ligands by the same method.     

Liquid chromatographic/mass spectrometric detection of the 3-(3-hydroxyalkanoyloxy) alkanoic acid precursors of rhamnolipids in Pseudomonas aeruginosa cultures

A series of pseudomolecular and fragment ions attributed to 3-(3-hydroxyalkanoyloxy)alkanoic acids (HAAs) were detected by liquid chromatography/mass spectrometry among the rhamnolipids observed in a Pseudomonas aeruginosa strain 57RP supernatant. The fragmentation mechanism leading to the formation of the fragment ions was determined by a deuterium exchange experiment and by using a standard HAA mixture obtained from the mild acidic hydrolysis of rhamnolipids of known composition. The structure and the response factor of these free HAAs were determined. The HAAs relative composition differs between free HAAs and those present in rhamnolipids, the former being enriched in lower molecular mass congeners and depleted in the heavier ones. Within an isomeric pair, the isomer with the shortest 3-hydroxyalkaloyl residue at the hydroxyl end was more abundant than the one with the heavier 3-hydroxyalkaloyl acid at this position, and the ratios of their relative abundances were similar for free HAAs and those in rhamnolipids. Experiments with deuterium-labeled rhamnolipids demonstrated that free HAAs are part of a pool used for rhamnolipid biosynthesis and are not rhamnolipid degradation products.