Divergent and solvent dependent reactions of 4-ethoxycarbonyl-3-methyl-1-tert-butoxycarbonyl-1,2-diaza-1,3-diene with enamines

Starting from 1-tert-butyloxycarbonyl-3-methyl-4-ethoxycarbonyl-1,2-diaza-1,3-diene and β,β,β and α,β-substituted enamines a careful choice of solvents and temperatures allows the divergent synthesis of 5,6-dihydro-4H-pyridazines, 2-(1-N-boc-hydrazono-ethyl)-4-pyrrolidin-1-yl-but-3-enoic acid ethyl ester, and 1-amino-pyrroles. Moreover, some interesting conclusions about the mechanism(s) of the reaction have been drawn by careful analysis of products' structure and distribution. Thus, the reaction may proceed through a stereospecific [4+2] cycloaddition mechanism giving rise to 5,6-dihydro-4H-pyridazines or by simple addition or domino addition/cyclization pathways affording, respectively, 2-(1-N-boc-hydrazono-ethyl)-4-pyrrolidin-1-yl-but-3-enoic acid ethyl ester and 1-amino-pyrroles (formally the [3+2] cycloaddition product).     

Magnetic properties and induced current density in acetylene

Coupled Hartree–Fock perturbation theory, within the framework of an accurate calculation, has been employed to visualize the electronic current density vector field induced by an external uniform magnetic field in the acetylene molecule. The current regime in a plane containing the molecular axis is rather different from those usually accounted for, evidencing the presence of a toroidal vortex in the C? H bond. The maps are useful in rationalizing the experimentally observed proton and carbon NMR chemical shifts.     

The bent RC  N linkage: An AB initio study of NH2CN,NF2CN and PF2CN

The ab initio energies, nuclear and electron repulsions and charge distributions have been calculated using moderately large basis sets as a function of the RC  N angle (R  NH₂, NF₂ or PF₂). The optimum RC  N angles were calculated to be 178.9°, 176.6°, and 175° for NH₂CN, NF₂CN, and PF₂CN, respectively. A rationalization of the differing bends is presented in terms of nuclear-nuclear and electron-electron repulsions.     

Effect of beta-cyclodextrin on the hydrolysis of trifluoroacetate esters

The hydrolysis of p-F, p-Cl, and m-Cl phenyl trifluoracetates was studied in the presence of beta-cyclodextrin (beta-CD). The reactions are inhibited by beta-CD at pH 6 while they are catalyzed in alkaline solution. MM3 calculations reproduce some of the experimental results. The substrates form inclusion complexes with beta-CD which are of similar stability as those of the corresponding acetates; however, the association of the transition state is less favorable in these reactions than in those of the acetates, and consequently less stronger catalysis is observed.     

Hyperlayer hollow-fiber flow field-flow fractionation of cells

Interest in low-cost, analytical-scale, highly efficient and sensitive separation methods for cells, among which bacteria, is increasing. Particle separation in hollow-fiber flow field-flow fractionation (HF FlFFF) has been recently improved by the optimization of the HF FIFFF channel design. The intrinsic simplicity and low cost of this HF FlFFF channel allows for its disposable usage. which is particularly appealing for analytical bio-applications. Here, for the first time, we present a feasibility study on high-performance, hyperlayer HF FIFFF of micrometer-sized bacteria (Escherichia coli) and of different types of cells (human red blood cells, wine-making yeast from Saccharomyces cerevisiae). Fractionation performance is shown to be at least comparable to that obtained with conventional, flat-channel hyperlayer FIFFF of cells, at superior size-based selectivity and reduced analysis time.     

SOLVERSTAT: a new utility for multipurpose analysis. An application to the investigation of dioxygenated Co(II) complex formation in dimethylsulfoxide solution

A new utility for multipurpose analysis, SOLVERSTAT, taking advantage of the versatility of spreadsheets is here described. By means of this tool advanced statistical tests have introduced in Microsoft Excel Solver thus allowing regression diagnostic and discrimination between different models. The utility is here applied to the determination, by UV-Vis spectroscopy, of the stability constant for the uptake of molecular dioxygen by the 1:2 complex of Co(II) with N,N′-dimethylethylenediamine (dmen) in the aprotic solvent dimethylsulfoxide (dmso) at 298 K and in a medium adjusted to 0.1 mol dm⁻³ with Et₄NClO₄. The reliability of the model and parameters obtained are discussed and the results compared with those obtained by Dynafit, a different software package, and by independent voltammetric measurements. The validity of SOLVERSTAT has been also examined applying it to the discrimination between different models already discussed in the literature.     

Total synthesis of phytoprostane F1 and its 16 epimer

The first synthesis of the two enantiomers of phytoprostane F₁ methyl ester 1 and 2 is described using the syn-anti-syn alcoxy ester 3 as starting material.