Preparation of ethyl 5(s),6-epoxy-3(r)-(methoxymethoxy)hexanoate: a key chiral intermediate for mevinolin and compactin.

The synthesis of Ethyl 5(S),6-Epoxy-3(R)-(methoxymethoxy)hexanoate, a key chiral synthon for the β-hydroxy-δ-lactone portion of Mevinolin and Compactin, $\text{via}$ a regiospecific ring opening of a tetrahydrofuran derivative by dimethylboron bromide, is described.     

Synthesis and stereochemistry of some new 1,3,5-tris(1,3-dioxan-2-yl)-benzene derivatives

The synthesis and the stereochemistry of new 1,3,5-tris(1,3-dioxan-2-yl)-benzene derivatives are reported. The anancomeric structure and the axial orientation of the aryl group with respect to all 1,3-dioxane rings, and the cis-trans isomerism of some of the compounds are revealed. The data are supported by NMR investigations and by the molecular structure of one compound determined by single crystal X-ray diffractometry.     

On the convergence rate of the conjugate gradients in presence of rounding errors

Summary We investigate here rounding error effects on the convergence rate of the conjugate gradients. More precisely, we analyse on both theoretical and experimental basis how finite precision arithmetic affects known bounds on iteration numbers when the spectrum of the system matrix presents small or large isolated eigenvalues.The present work was supported by the Programme d'impulsion en Technologie l'Information, financed by Belgian State, under contract No. IT/IF/14Supported by the Fonds National de la Recherche Scientifique, Chargé de recherches     

The dielectric function of LnSF rare-earth fluorosulfides (Ln=La, Ce): experiment and theory

The absorption properties of LaSF and CeSF in the UV-Visible range have been investigated on the basis of first principles density functional theory (DFT) calculations and from electron energy-loss spectroscopy (EELS) measurements. The extinction coefficient k, as well as the refractive index n, determined experimentally from the loss function Im(−1/ε), were compared with the corresponding factors extracted from the calculated dielectric tensor ε₂. The k and n values for the two compounds were expected to be very close to each other, owing to the chemical similarity of La and Ce. However, it was found that the nature of the electronic transitions in LaSF and CeSF strongly influences the k and n values with the result that the refractive index n and the extinction coefficient k are substantially larger for LaSF than for CeSF.     

Coupled structural and magnetic properties of ferric fluoride nanostructures: Part II,a Monte Carlo–Heisenberg study

We present a numerical study of the magnetic structure of nanostructured iron fluoride, using the Monte Carlo Metropolis simulated annealing technique and a classical Heisenberg Hamiltonian with superexchange angle dependent interactions. The parameters are adjusted on experimental results, and the atomic structure and topology taken from a previous atomistic model of grain boundaries in the same system. We find perfect antiferromagnetic crystalline grains and a disordered magnetic configuration (speromagnetic) at the grain boundary, in agreement with experimental features. Both the lowest magnetic energy and the rate of magnetic frustration are found to be dependent on the relative disorientation of crystalline grains, i.e. on the cationic topology. We conclude on possible extensions of the model.     

Pressure‐assisted CEC versus CEC using methacrylate‐based monolithic columns: Influence of the polymerization‐mixture composition

Pressure‐assisted CEC (pCEC) can either be performed on a CE instrument by adding pressure at the column inlet, or by applying voltage on a capillary liquid chromatography system. This study investigates the pressure's added value in pCEC using an LC instrument as well as the influence of the polymerization‐mixture composition on monolithic columns in such experimental circumstances. Two factors of the polymerization mixture, which is used to prepare the monolithic capillary columns, were varied according to an experimental design approach: the pore‐forming solvent/total monomer ratio and the pore‐forming solvents composition. Initially, the effect of the resulting stationary phase on the elution behavior of mainly pharmaceutical compounds was studied. Four responses were used to evaluate the effects on the chromatography: retention time, retention factor, peak asymmetry and number of theoretical plates. After processing the results, the stationary phase composition with the best chromatographic behavior was determined and tested. The advantageous properties of this stationary phase compared with the design center‐point column were demonstrated. Secondly, the results of these pCEC experiments were compared with those generated in an identical experimental setup previously performed using CEC. Chromatographic conditions were chosen so that the center‐point column showed similar retention in CEC and pCEC. The expected advantage (faster analysis) and drawback (decreased efficiency) of pCEC in the analysis of pharmaceuticals was evaluated. Analysis time and efficiency were both found to depend greatly on the porosity of the column. The conclusion of this comparison is that pCEC did not have a significant added value to CEC. However, this was mainly due to the instrument's limitation of the pressure‐driven flow over the column. A clear benefit of the pCEC setup was apparatus‐related, i.e. the presence of a loop injection system on the pCEC instrument, which avoids the injection problems that were occasionally observed in CEC.     

Microfluidics in macro-biomolecules analysis: macro inside in a nano world

Use of microfluidic devices in the life sciences and medicine has created the possibility of performing investigations at the molecular level. Moreover, microfluidic devices are also part of the technological framework that has enabled a new type of scientific information to be revealed, i.e. that based on intensive screening of complete sets of gene and protein sequences. A deeper bioanalytical perspective may provide quantitative and qualitative tools, enabling study of various diseases and, eventually, may offer support for the development of accurate and reliable methods for clinical assessment. This would open the way to molecule-based diagnostics, i.e. establish accurate diagnosis and disease prognosis based on identification and/or quantification of biomacromolecules, for example proteins or nucleic acids. Finally, the development of disposable and portable devices for molecule-based diagnosis would provide the perfect translation of the science behind life-science research into practical applications dedicated to patients and health practitioners. This review provides an analytical perspective of the impact of microfluidics on the detection and characterization of bio-macromolecules involved in pathological processes. The main features of molecule-based diagnostics and the specific requirements for the diagnostic devices are discussed. Further, the techniques currently used for testing bio-macromolecules for potential diagnostic purposes are identified, emphasizing the newest developments. Subsequently, the challenges of this type of application and the status of commercially available devices are highlighted, and future trends are noted.     

MRS study of the effects of minocycline on markers of neuronal and microglial integrity in ALS

Objective

Magnetic resonance spectroscopy (MRS) allows to monitor brain metabolites noninvasively in amyotrophic lateral sclerosis (ALS). The objective of this study was to use MRS to monitor the effect of minocycline treatment (200 mg/day) over a short period (6 weeks) on the brain metabolites in the precentral gyrus and brainstem in newly diagnosed ALS patients.

Methods

Ten ALS patients (not on riluzole treatment) were recruited and submitted to single-voxel proton MRS longitudinal examinations (1) before minocycline treatment, (2) 3 weeks and (3) 6 weeks after initiation of treatment.

Results

Results did not show the expected decrease of N-acetylaspartate/creatine (NAA/Cr) in the precentral gyrus, and an increased NAA/Cr ratio in the brainstem suggested neuronal recovery. The myo-inositol (mI)/Cr ratio was unchanged in the precentral gyrus, but increased in the brainstem, indicating a glial reaction.

Conclusions

MRS results suggest that minocycline treatment could be beneficial in the early stages of ALS.     

Influence of the spatial position of a trifluoromethyl group on the 13C chemical shifts in the cyclohexane series

The influence of the introduction of a trifluoromethyl group on the 13C chemical shifts in cyclohexane was examined. The two main effects observed are located at the alpha and gamma positions relative to the carbon bearing the fluorine atoms. By comparison of the collected data it was possible to calculate the increments corresponding to the substitution of a hydrogen atom by a CF3 group at axial or equatorial positions on the cyclohexane ring.     

Future of high pressure liquid chromatography: do we need porosity or do we need pressure?

Making a theoretical study supported by experiments of the kinetic advantages of increased inlet pressures versus increased external porosity using impedance plots of analysis time versus required plate number, it is found that both approaches more or less have the same effect on the kinetic performance. The need to change a given system to one with an increased inlet pressure or with an increased external porosity can best be assessed from the optimal plate number (N(opt)) of the system. When the pursued application requires a plate number that is larger than N(opt), any increase in inlet pressure and external porosity is beneficial. When the required plate number is smaller than N(opt), any increase in inlet pressure and external porosity should preferentially be accompanied by an overall reduction of the feature sizes of the support. The degree to which this feature size reduction can be realized in practice will to a large extent determine which of the two approaches will be the dominant system of the future.