Unprecedented gas-phase chiroselective logic gates

The gas-phase encounters between 2-aminobutane and proton-bound chiral resorcin[4]arene/nucleoside complexes behave in the gas phase as supramolecular "chiroselective logic gates" by releasing the nucleoside depending on the resorcin[4]arene and the 2-aminobutane configurations.     

Dual asymmetric-flow microdialysis for in vivo monitoring of brain neurochemicals

Microdialysis is an extensively used technique for both in vivo and in vitro experiments, applicable to animal and human studies. In neurosciences, the in vivo microdialysis is usually performed to follow changes in the extracellular levels of substances and to monitor neurotransmitters release in the brain of freely moving animals. Catecholamines, such as dopamine and their related compounds, are involved in the neurochemistry and in the physiology of mental diseases and neurological disorders. It is generally supposed that the brain's energy requirement is supplied by glucose oxidation. More recently, lactate was proposed to be the metabolic substrate used by neurons during synaptic activity. In our study, an innovative microdialysis approach for simultaneous monitoring of catecholamines, indolamines, glutamate and energy substrates in the striatum of freely moving rats, using an asymmetric perfusion flow rate on microdialysis probe, is described. As a result of this asymmetric perfusion, two samples are available from the same brain region, having the same analytes composition but different concentrations. The asymmetric flow perfusion could be a useful tool in neurosciences studies related to brain's energy requirement, such as toxin-induced models of Parkinson's disease.     

The "bridge" game: role of the fourth player in chiral recognition

A new team player: The "three-point interaction" model, which is usually employed to rationalize chiral recognition, does not account for the amazing enantioselectivity measured for the receptors of many proteic acceptors. Gas-phase experiments have indicated that at least a fourth "player" must be considered: the rigidity that a receptor opposes to distortions of its cavity resulting from noncovalent interactions with a chiral molecule (see picture).     

Optimal solutions for routing problems with profits

In this paper, we present a branch-and-price algorithm to solve two well-known vehicle routing problems with profits, the Capacitated Team Orienteering Problem and the Capacitated Profitable Tour Problem. A restricted master heuristic is applied at each node of the branch-and-bound tree in order to obtain primal bound values. In spite of its simplicity, the heuristic computes high quality solutions. Several unsolved benchmark instances have been solved to optimality.     

On the effectiveness of scenario generation techniques in single-period portfolio optimization

In single-period portfolio selection problems the expected value of both the risk measure and the portfolio return have to be estimated. Historical data realizations, used as equally probable scenarios, are frequently used to this aim. Several other parametric and non-parametric methods can be applied. When dealing with scenario generation techniques practitioners are mainly concerned on how reliable and effective such methods are when embedded into portfolio selection models. In this paper we survey different techniques to generate scenarios for the rates of return. We also compare the techniques by providing in-sample and out-of-sample analysis of the portfolios obtained by using these techniques to generate the rates of return. Evidence on the computational burden required by the different techniques is also provided. As reference model we use the Worst Conditional Expectation model with transaction costs. Extensive computational results based on different historical data sets from London Stock Exchange Market (FTSE) are presented and some interesting financial conclusions are drawn.     

Gaseous ion activation dynamics: the role of the bulk gas in the racemization of chiral oxonium ions.

The kinetics of the inversion of configuration of a family of chiral oxonium ions, that is, O-protonated 1-aryl-1-methoxyethanes [YMe+], were investigated in two different gaseous media (in CH3X with X=F and X=Cl) at 720 torr of pressure and in the temperature range: 25-140 degrees C. The activation parameters of the [YMe+] inversion reaction were found to obey two different isokinetic relationships (IKR), depending on the nature and the position of the substituents in the oxonium ions and on the nature of the bulk gas employed. The observation of two IKR for the same family of reactions was related to a switchover in the resonant vibrational energy exchange between the reactants' critical mode, active in the transition state (omega), and the discrete vibrational levels v of the bulk gas. In CH3F, this vibrational-vibrational coupling switchover concerns the out-of-plane C-F...H-O bending) the phi family) and the H3C-F stretching (the gamma family) modes in the proton-bound [CH3F.YMe+] complex. In CH3Cl, the coupling switchover concerns the out-of-plane C-Cl...H-O bending (the phi family) and the H3C-Cl methyl group rocking (the gamma family) modes in the proton-bound [CH3Cl.YMe+] complex. The [YMe+] activation dynamics also determine the inversion dynamics. The [YMe+]ret<==>[YMe+]inv isomerization for the phi family involves the same "thermodynamically most favorable" transition state in both the CH3F and the CH3Cl media, whereas the same process for the gamma family proceeds through different, dynamically favored transition states.     

First evidence for automerization of gaseous phenylium ion.

Tritium atom distribution in the anisole formed from the attack of a nucleogenic tritiated phenylium ion on gaseous methanol provides the first experimental evidence for a gas-phase automerization of phenylium ion.     

Suppression of plasma turbulence during optimized shear configurations in JET

Correlation of density turbulence suppression and reduced plasma transport is observed in the internal transport barrier (ITB) region of JET tokamak discharges with optimized magnetic shear. The suppression occurs in two stages. First, low frequency turbulence and ion transport are reduced across the plasma core by a toroidal velocity shear generated by intense auxiliary heating. Then with the ITB formation, high frequency turbulence and electron transport are reduced locally within the steep pressure gradient region of the ITB.     

Stereochemistry and Fate of Hydrogen Atoms in the Diol-Dehydratase-Catalyzed Dehydration of meso-Butane-2,3-diol

The transformation of meso-butane-2,3-diol into butan-2-ol by a strain of Lactobacillus brevis occurs through a diol-dehydratase-catalyzed conversion of the diol into butan-2-one, which is then reduced to the secondary alcohol by dehydrogenases. Experiments performed with deuterated meso-butane-2,3-diols showed that the dehydration reaction brings about an inversion of configuration at the (R)-configured C-atom of meso-butane-2,3-diol as a consequence of the substitution of the OH group by a H-atom; at the same time, the H-atom already bound to the (R) C-atom is retained in the resulting methylene group. The H-atom replacing the OH group was assessed to come from the medium since the H-atom at the (S)-configured C-atom was completely lost. By contrast, in the case of the conversion of (RS)-propane-1,2-diol into propan-1-ol under the same fermentation conditions, an extensive H-transfer (ca. 80%) from the primary-alcohol function to the adjacent C-atom was observed. This fact is taken as an indication of different modes in which the two substrates are processed by the enzyme (despite the same stereochemical outcome). A speculative hypothesis is presented to interpret such a dissimilarity.