Rational Development of Remote C−H Functionalization of Biphenyl: Experimental and Computational Studies

A simple and efficient nitrile-directed meta-C−H olefination, acetoxylation, and iodination of biaryl compounds is reported. Compared to the previous approach of installing a complex U-shaped template to achieve a molecular U-turn and assemble the large-sized cyclophane transition state for the remote C−H activation, a synthetically useful phenyl nitrile functional group could also direct remote meta-C−H activation. This reaction provides a useful method for the modification of biaryl compounds because the nitrile group can be readily converted to amines, acids, amides, or other heterocycles. Notably, the remote meta-selectivity of biphenylnitriles could not be expected from previous results with a macrocyclophane nitrile template. DFT computational studies show that a ligand-containing Pd–Ag heterodimeric transition state (TS) favors the desired remote meta-selectivity. Control experiments demonstrate the directing effect of the nitrile group and exclude the possibility of non-directed meta-C−H activation. Substituted 2-pyridone ligands were found to be key in assisting the cleavage of the meta-C−H bond in the concerted metalation–deprotonation (CMD) process.     

The di-π-methane rearrangement : The effect of 1,4-diene structure and conformation on the reaction efficiency and stereochemistry

The photochemistry of the stereoisomeric 1,3-dimethyl-3(2-phenylethenyl)cyclohexenes has been explored Direct irradiation of the cis- and trans-β-styrylcyclohexenes leads to di-π-methane rearrangement, producing the endo- and exo-3,7-dimethyl-8-phenybicyclo[5.1.0]oct-2-enes, and cis -trans isomerization, interconverting the 1,4-diene containing substrates. Triplet sensitized photolysis of both substituted cyclohexenes leads exclusively to cis-trans isomerization. Results from low conversion direct irradiations of the cis- and trans-β-styrylcyclohexenes indicate that the singlet rearrangements are stereospecific, and lead to formation of the 8-exo and 8-endo-phenylbicyclic octenes, respectively. The relationship between di-π-methane structure and triplet reaction efficiency, and the effect of conformation on the rearrangement stereochemistry are discussed.     

Solid-phase synthesis of the cyclic lipononadepsipeptide [N-Mst(Ser1), d-Ser4, L-Thr6, L-Asp8, L-Thr9]syringotoxin

An optimized solid-phase strategy for the preparation of the cyclic lipononadepsipeptide [N-Mst(L-Ser1), D-Ser4, L-Thr6, L-Asp8, L-Thr9]syringotoxin is reported. The strategy is based on the use of a mild orthogonal protection scheme and the incorporation of the nonproteinogenic amino acid (Z)-Dhb into the peptide chain as the dipeptide Fmoc-Thr(tBu)-(Z)-Dhb-OH. The didehydrodipeptide was synthesized by a water-soluble carbodiimide-induced beta-elimination of a protected dipeptide containing a residue of Thr with its free hydroxy side chain unprotected.     

Effect of total percent polyacrylamide in capillary gel electrophoresis for DNA sequencing of short fragments. A phenomenological model.

Polyacrylamide capillary gels were prepared with constant (5% C) cross-linker concentration and with total acrylamide concentration ranging from 2.5 to 6% T. At each acrylamide concentration, peak spacing was constant for DNA sequencing fragments ranging from 25 to 250 nucleotides in length. Peak spacing increased linearly with the total acrylamide concentration. The intercept of the retention time vs. fragment length plot was independent of % T. Ferguson plots were constructed for short DNA fragments; the polyacrylamide pore size falls in the 2.5 to 3.5 nm range for the gels studied. Theoretical plate count is independent of total acrylamide concentration; longitudinal diffusion, and not thermal gradients, limit the plate count. A phenomenological model is presented that predicts retention time, plate count, and resolution for sequencing fragments ranging in size from 25 to 250 bases and gels that range from 2.5 to 6% total acrylamide.     

Comparison of different derivatization approaches for mercury speciation in biological tissues by gas chromatography/inductively coupled plasma mass spectrometry

A novel interface design for coupling gas chromatography and inductively coupled plasma mass spectrometry (GC/ICP-MS) was used to perform mercury speciation in biological tissues. Three derivatization approaches were optimized and compared for this purpose: anhydrous butylation using a Grignard reagent, aqueous ethylation by means of NaEt(4)B and aqueous propylation with NaPr(4)B. The last reagent was synthesized in the laboratory as it is not commercially available. Detection limits obtained by GC/ICP-MS ranged between 100 and 200 fg (as absolute mass) for methylmercury and between 500 and 600 fg for inorganic mercury using a 1 microl injection. Quantification of methyl- and inorganic mercury was carried out by resorting to aqueous calibration, using ethylmercury as internal standard for both propylation and butylation derivatization techniques. For ethylation procedures, a methylpropylmercury solution was used as internal standard. The absence of transmethylation during sample preparation was checked using a 97% enriched (202)Hg inorganic standard. The accuracy of the three derivatization approaches was evaluated by the analysis of the certified reference material DOLT-2 (dogfish liver) from the National Research Council of Canada and certified for methylmercury, with satisfactory results.     

Metallophthalocyanines with rod-shaped substituents

4-(4′-Dioctylaminocarbonylbiphenyloxy) phthalonitrile was synthesized from 4-(4′-carboxybiphenyloxy)phthalonitrile and dioctylamine in the presence of Et₃N. Metallophthalocyanines (Zn, Co and Cu) substituted with four dioctylaminocarbonyl biphenyloxy groups on the peripheral positions were prepared from 4-(4′-dioctylaminocarbonylbiphenyloxy)phthalonitrile and the corresponding divalent metal salts (Zn(CH₃COO)₂, CoCl₂ and CuCl₂). The new phthalocyanines are soluble in common organic solvents. These compounds were characterised by ¹H-NMR, ¹³C-NMR, FT-IR, UV-Vis and mass spectroscopies.     

Trace element determination in vitamin E using ICP-MS

Vitamin E supplements are either isolated from plants sources or prepared synthetically. Isolation from plants includes eight different tocopherol structures. Vitamin E synthesis includes seven different stereoisomers, which involves the use of several catalysts that may lead to trace element contamination in the vitamin. The use of ICP-MS is an ideal technique for detecting these trace elements. However, the oily nature of the samples requires the development of a sample preparation methodology. This study was done upon the request of synthetic vitamin E manufacturers to test the trace metal purity of their samples. In this work, the comparison of an acid microwave digestion and emulsion preparation is discussed. Cromium, nickel, tin and lead were found in the synthetic vitamin E analyzed and 200, 60, 9 and 45 ppb were the concentrations found respectively for these elements.Digesting the samples gives slightly lower detection limits compared to the emulsion preparation.     

Electron and nuclear dynamics of molecular clusters in ultraintense laser fields. I. Extreme multielectron ionization

In this paper we present a theoretical and computational study of extreme multielectron ionization (involving the stripping of all the electrons from light, first-row atoms, and the production of heavily charged ions, e.g., Xe(+q) (q< or =36) from heavy atoms) in elemental and molecular clusters of Xe(n),(D(2))(n), and (CD(4))(n) (n=55-1061) in ultraintense (intensity I=10(15)-10(19) W cm(-2)) laser fields. Single atom or molecule multielectron ionization can be adequately described by the semiclassical barrier suppression ionization (BSI) mechanism. Extreme cluster multielectron ionization is distinct from that of a single atomic or molecular species in terms of the mechanisms, the ionization level and the time scales for electron dynamics and for nuclear motion. The novel compound mechanism of cluster multielectron ionization, which applies when the cluster size (radius R(0)) considerably exceeds the barrier distance for the BSI of a single constituent, involves a sequential-parallel, inner-outer ionization. The cluster inner ionization driven by the BSI for the constituents is induced by a composite field consisting of the laser field and inner fields. The energetics and dynamics of the system consisting of high energy (< or =3 keV) electrons and of less, similar 100 keV ions in the laser field was treated by molecular dynamics simulations, which incorporate electron-electron, electron-ion, ion-ion, and charge-laser interactions. High-energy electron dynamics also incorporates relativistic effects and includes magnetic field effects. We treat inner ionization considering inner field ignition, screening and fluctuation contributions as well as small [(< or =13%)] impact ionization contributions. Subsequent to inner ionization a charged nanoplasma is contained within the cluster, whose response to the composite (laser+inner) field results in outer ionization, which can be approximately described by an entire cluster barrier suppression ionization mechanism.     

Cyclic coordinate descent in hydrothermal nonsmooth problems

In this paper we present an algorithm, inspired by the cyclic coordinate descent method, which allows the solution of hydrothermal optimization problems involving pumped-storage plants. The proof of the convergence of the succession generated by the algorithm was based on the use of an appropriate adaptation of Zangwill’s global theorem of convergence. Finally, the algorithm proposed is implemented using the Mathematica Package and is applied to an example to illustrate the results obtained.