A total synthesis of tarchonanthuslactone exploiting N-pyrrole carbinols as efficient stereocontrolling elements

[reaction: see text] A short stereoselective total synthesis of the polyketide natural product, tarchonanthuslactone, has been achieved. The key sequence involves the first reported catalytic enantioselective reduction of an N-acyl pyrrole and subsequent use of this stereocenter in a diastereoselective reductive cascade. This proceeded with unprecedentedly high stereocontrol and offered an elegant method of generating the desired syn stereochemistry present in the final target in one step.     

The determination of aluminium in seawater and freshwater by cathodic stripping voltammetry

Dissolved aluminium in seawater and freshwater is determined by cathodic stripping voltammetry (c.s.v.) preceded by adsorptive collection of complex ions with 1,2-dihydroxyanthraquinone-3-sulphonic acid (DASA) on the hanging mercury drop electrode. Complexation of aluminium by DASA is rapid and no waiting period or heating of the sample is required. Optimal conditions are a DASA concentration of 10^?5 M, a solution pH of 7.1–7.3 and an adsorption potential of ?0.9 V; the c.s.v. scan is done in the differential-pulse mode. The limit of detection is 1 nM aluminium for an adsorption time of 45 s. The total time needed, including 50min deaeration and a standard addition, is 10–15 min per sample. No serious interferences were found; u.v. irradiation is recommended for samples containing high levels of organic materials.     

Computing the Fukui function from ab initio quantum chemistry: approaches based on the extended Koopmans’ theorem

The extended Koopmans’ theorem is related to Fukui function, which measures the change in electron density that accompanies electron attachment and removal. Two approaches are used, one based on the extended Koopmans’ theorem differential equation and the other based directly on the expression of the ionized wave function from the extended Koopmans’ theorem. It is observed that the Fukui function for electron removal can be modeled as the square of the first Dyson orbital, plus corrections. The possibility of useful generalizations to the extended Koopmans’ theorem is considered; some of these extensions give approximations, or even exact expressions, for the Fukui function for electron attachment.     

Repeat Space Theory Applied to Carbon Nanotubes and Related Molecular Networks. I

The present article is the first part of a series devoted to extending the Repeat Space Theory (RST) to apply to carbon nanotubes and related molecular networks. Four key problems are formulated whose affirmative solutions imply the formation of the initial investigative bridge between the research field of nanotubes and that of the additivity and other network problems studied and solved by using the RST. All of these four problems are solved affirmatively by using tools from the RST. The Piecewise Monotone Lemmas (PMLs) are cornerstones of the proof of the Fukui conjecture concerning the additivity problems of hydrocarbons. The solution of the fourth problem gives a generalized analytical formula of the pi-electron energy band curves of nanotube (a, b), with two new complex parameters c and d. These two parameters bring forth a broad class of analytic curves to which the PMLs and associated theoretical devices apply. Based on the above affirmative solutions of the problems, a central theorem in the RST, called the asymptotic linearity theorem (ALT) has been applied to nanotubes and monocyclic polyenes. Analytical formulae derived in this application of the ALT illuminate in a new global context (i) the conductivity of nanotubes and (ii) the aromaticity of monocyclic polyenes; moreover an analytical formula obtained by using the ALT provides a fresh insight into Hückel’s (4n+2) rule. The present article forms a foundation of the forthcoming articles in this series. The present series of articles is closely associated with the series of articles entitled ‘Proof of the Fukui conjecture via resolution of singularities and related methods’ published in the JOMC.     

Star-shaped azo-based dipolar chromophores: design, synthesis, matrix compatibility, and electro-optic activity

Three new azo-benzene-based push-pull chromophores with dendritic architecture were synthesized as active materials for electro-optic applications. These chromophores were synthesized in six or seven synthetic steps with an overall yield of around 80% per step and high purity. UV-vis spectroscopy showed significant influence of the transient dipole moment on the observed r(33) values. The chromophores were stable to photochemical oxidation in ambient light and air. The electrical poling conditions were optimized for each chromophore as the T(g) of the composite material varied significantly. The highest EO coefficient achieved was 22-25 pm/V at 1550 nm wavelength. STEM analysis of the blends enabled the correlation of the activity of these large chromophores with the blend morphology. An amorphous polycarbonate host effectively disperses the chromophores in 2-20 nm aggregates in the active materials. However, macrophase separation into 200-500 nm aggregates was observed in a methacrylate host matrix.     

A simple and very sensitive spectrophotometric method for the direct determination of copper ions

A sensitive spectrophotometric method for the direct determination of copper in aqueous samples without a preconcentration step has been developed. It is based on the formation of a yellow complex with the chromogenic reagent di-2-pyridyl ketone benzoylhydrazone (dPKBH) in an alkaline medium. The complex stoichiometry was 1:2 (Cu:dPKBH) and presents maximum absorbance at 370 nm. The influence of chemical variables affecting the behaviour of the system such as pH, concentration of dPKBH, buffer solution and ethanol, order of addition of the reagents and stability of the complex, were evaluated. The molar absorptivity (epsilon) was 3.92x10(4) L mol(-1) cm(-1), and Beer's law was obeyed up to 3 mg L(-1) of copper. The relative standard deviation was 0.46% (n=11) for a sample containing 1 mg L(-1) Cu(II). The limit of detection was 2.5 micro g L(-1) and was therefore more sensitive than the direct methods reported previously. Finally, the method was successfully validated by analysing several real samples with different matrices, such as tap water, natural water or copper alloys, with an average relative error of 2.46%.     

Writing with DNA and protein using a nanopipet for controlled delivery

We present a new, general method for the controlled deposition of biological molecules on surfaces, based on a nanopipet operating in ionic solution. The potential applied to the pipet tip controls the flux of biological molecules from the pipet, allowing fine control of the delivery rate. We used the ion current to control the distance of the pipet from the surface of a glass slide and deposited the fluorescently labeled DNA or protein G at a defined location onto the surface. Features of 830 nm size were obtained by depositing the biotinylated DNA onto a streptavidin surface; 1.3 mum size spots were obtained by depositing protein G onto a positively charged glass surface.     

Thermal and mechanical-induced phase transformations during YAG and alumina–YAG syntheses

The preparation of pure Y₃Al₅O₁₂ (YAG) and 50 vol% Al₂O₃–YAG composite powders by a wet chemical route is presented. The role of the synthesis temperature during reverse-strike precipitation has been investigated, showing its relevant effect on the purity and homogeneity of YAG powder. The composite material was prepared by comparing two different synthesis routes. A composite powder was synthesized via reverse-strike temperature-controlled co-precipitation. In the latter case, a pure-alumina precursor was firstly reverse-strike precipitated and then doped with an yttrium salt solution. For both syntheses, the role of thermal and mechanical pre-treatments on the phase development was demonstrated.     

Additional peaks in the cluster size distribution of amphiphile + water systems: a clue for shape/phase transition or statistical uncertainty

In some works on the lattice Monte Carlo simulation of amphiphilic systems additional peaks in the cluster size distribution has been interpreted as a clue for the phase or shape transition of micellar aggregates. On the other hand, some other works showed that the additional peaks are a result of finite size of the lattice box. In this paper using calculating energy-auto-correlation function and statistical error in correlated data, it is shown that how these apparently contradictory results are the same. To do this, we have simulated a pure system containing amphiphile and water molecules. A simple model of potential containing the main feature for these systems (the hydrophobicity of surfactant molecules) that cause the aggregates to be formed is considered to avoid any synthetic results due to additional non-real parameters. To relax the initial configuration faster, configurational bias Monte Carlo move is used in addition to reptation move. Periodic boundary condition and self-avoiding walks are used as former published works in this field. It is shown that the additional peaks is a result of the statistical errors for averaged cluster size distribution and can not be interpreted as a clue for shape or phase transition.