Pd-catalyzed carbonylative cross-coupling reactions by triorganoindiums: highly efficient transfer of organic groups attached to indium under atmospheric pressure

[reaction: see text] A highly atom-efficient synthetic method of unsymmetrical ketones was developed by using trialkyl- and triarylindiums, which could be employed as effective cross-coupling partners in Pd-catalyzed carbonylative cross-coupling reactions with a variety of organic electrophiles. The present method produced unsymmetrical ketones and 1,4-diacylbenzenes in good yields with highly efficient transfer of almost all the organic groups attached to the indium under atmospheric pressure of CO gas in THF at 66 degrees C.     

A short synthetic route to (+)-austamide, (+)-deoxyisoaustamide,and (+)-hydratoaustamide from a common precursor by a novel palladium-mediated indole --> dihydroindoloazocine cyclization

The first synthesis of (+)-austamide (1), (+)-deoxyisoaustamide (2), and (+)-hydratoaustamide (10) by a very direct route is described (Scheme 1). Starting from tryptophan methyl ester (3) intermediate 5 is generated in two steps in >98% overall yield. The key step in the synthesis is a novel cyclization of 5 involving organopalladium intermediates which gives the dihydroazocine 6. From this key intermediate the target structures are accessible in just a few steps as shown in Scheme 1. The remarkable conversion of 5 --> 6 can be rationalized by the mechanistic pathway shown in Scheme 2 that involves a multistep sequence which includes palladation, cyclization, and rearrangement.     

Molecular dynamics study of the effect of atomic roughness on the slip length at the fluid-solid boundary during shear flow

A systematic study into the effect of solid roughness on the slip boundary condition during shear flow is presented. Atomic roughness is modeled by varying the size and spacing between solid atoms at constant packing fraction while the interaction parameters and the thermodynamic state of the fluid are kept constant. It is shown that the fluid structure as manifest in the amplitude of the density oscillations increases with increasing smoothness of the surfaces. The fluid-solid slip length is shown to exhibit nonmonotonic behavior as the solid structure is varied from smooth to rough. Slip occurs for both smooth and rough surfaces, and stick occurs only for surfaces commensurate with the fluid.     

Development of a novel multi-element detection system for trace metal determination based on chemiluminescence after separation by ion chromatography

A highly sensitive, non-selective trace metal detector based on chemiluminescence has been developed. The metals, separated by simple ion-exchange chromatography, bring about the displacement of cobalt from a Co-EDTA post-column reagent. The liberated cobalt is then detected by the luminol-peroxide chemiluminescence reaction using a modified spectrofluorimeter as the detector. The metals determined are Mg, Ca, Sr, Ba, Fe(II), Fe(III), Co, Ni, Cu, Zn, the lanthanides, Th, Al, Ga, In, Pb and Bi. The detection limits (three times the baseline noise) range between 2 and 100 μg l^?1, depending on the analyte, for a 200-μl injection. To demonstrate the quantitative performance of the detector, the zinc and aluminium contents of a fresh water certified reference material was determined and gave good agreement with the certificate values.     

Photorepair of Ultraviolet Radiation (UVR)-lnduced Pyrimidine Dimers in Lens Epithelial DNA of Monodelphis domestica

Abstract— The repair of UV radiation-induced pyrimidine dimers has been measured in lens epithelial DNA of the marsupial Monodelphis domestica using a pyrimidine dimerspecific endonuclease from Micrococcus luteus. Approximately 40% of the initially induced dimers were repaired during 90 min exposures to photoreactivating light. This capacity of the lens epithelium to photorepair pyrimidine dimers may provide a means with which to determine whether pyrimidine dimers in lens epithelial DNA are involved in UV radiation-induced pathologic changes of the lens.     

Fluoride-selective binding in a new deep cavity calix[4]pyrrole: experiment and theory

A new "super-extended cavity" tetraacetylcalix[4]pyrrole derivative was synthesized and characterized, and X-ray crystal structures of complexes bound to fluoride and acetonitrile were obtained. The binding behavior of this receptor was investigated by NMR titration, and the complex was found to exclusively bind fluoride ions in DMSO-d(6). This unusual binding behavior was investigated by Monte Carlo free energy perturbation simulations and Poisson calculations, and the ion specificity was seen to result from the favorable electrostatic interactions that the fluoride gains by sitting lower in the phenolic cavity of the receptor. The effect of water present in the DMSO on the calculated free energies of binding was also investigated. Owing to the use of a saturated ion solution, the effect of contaminating water is small in this case; however, it has the potential to be very significant at lower ion concentrations. Finally, the adaptive umbrella WHAM protocol was investigated and optimized for use in binding free energy calculations, and its efficiency was compared to that of the free energy perturbation calculations; adaptive umbrella WHAM was found to be approximately two times more efficient. In addition, structural evidence demonstrates that the protocol explores a wider conformational range than free energy perturbation and should therefore be the method of choice. This paper represents the first complete application of this methodology to "alchemical" changes.     

Metal-organic anion receptors: arranging urea hydrogen-bond donors to encapsulate sulfate ions

A new class of synthetic receptors for anions can be prepared by arranging urea hydrogen-bond donor groups on a simple metal-organic scaffold. The complex cation [PtL4]2+ (L = 8-(n-butylurea)iso-quinoline) can adopt four conformations reminiscent of calix[4]arene-based receptors; "cone", "partial cone", "1,2-alternate", or "1,3-alternate". 1H NMR solution data and solid-state X-ray structures show that a "1,2-alternate" conformation is used to bind spherical halide ions while a "cone" conformation is involved in strong binding with the tetrahedral oxy-anions such as the sulfate ion; even in a strongly competitive solvent such as DMSO.     

Role of phenoxy radicals in PCDD/F formation

In this work, the role of phenoxy radicals in polychlorinated dibenzo‐p‐dioxins and polychlorinated dibenzofurans (PCDD/F) formation was investigated by studying the slow oxidation of 2‐chlorophenol (2‐CP) and 2‐chloroanisole (2‐CA) at a gas‐phase concentration of 4 ppm (～2.1 × 10⁴ μg/m³) over a temperature range of 400–800°C. Residence times were maintained at 2.0 ± 0.10 s. PCDD/F reaction products were dibenzofuran, dibenzo‐p‐dioxin, 4‐chlorodibenzofuran, 1‐chlorodibenzo‐p‐dioxin, 4,6‐dichlorodibenzofuran, and 1,6‐dichlorodibenzo‐p‐dioxin (1,6‐DCDD). Major products observed in these experiments were 2,6‐dichlorophenol, 3‐phenyl‐2‐propenal, 1‐indanone, 1,3‐isobenzofurandione, and 3‐phenyl‐2‐propenoyl chloride. The 2‐CP and 2‐CA experiments, along with the variable concentration 2‐CA experiments, showed that the concentration of radicals present in the oxidation system has a significant effect on the PCDD/F product distribution and ultimately the PCDD/PCDF ratio. Also, the observation of dichlorinated phenoxy phenol and dichlorinated dihydroxybiphenyl, the proposed intermediate species in the radical–radical mechanism, suggests that radical–radical mechanism dominates gas‐phase PCDD/F formation. This information will be helpful in constructing a detailed kinetic mechanism of PCDD/F formation/destruction in combustor postcombustion zone. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 531–541, 2002     

Conformation and bonding in unsymmetrically 3,6-disubstituted dihydro-1,2,4,5-tetrazine

The molecular structure of the title compound, I, has been determined by single-crystal X-ray diffraction. The crystals are triclinic, space group PI. The analysis revealed that the dihydro-s-tetrazine molecule is in a slightly twisted boat conformation with the nitrogen atoms carrying the two hydrogens, N(2) and N(4), pointing upward. All substituents on the dihydro-s-tetrazine ring exist in pseudo-equatorial configurations. Adjacent hydrogen and bulky groups (CF₃ and p-Cl-C₆H₄) have cis-relationships. The p-chlorophenyl group is twisted with respect to the dihydro-s-tetrazine ring. The unit cell for I contains six molecules. Each dihydro-s-tetrazine ring participates in four intermolecular hydrogen bonds (N···H bond distance 2.23 to 2.41 A), two hydrogen bonds to each adjacent tetrazine ring in the same unit cell.     

Maniplating the phenolic acid content and digestibility of italian ryegrass (Lolium multiflorum)b y vacuolar-targeted epession of a fungal ferulic acid esterase

In grass cell walls, ferulic acid esters linked to arabinosyl residues in arabinoxylans play a key role in crosslinking hemicellulose. Although such crosslinks have a number of important roles in the cell wall, they also hinder the rate and extent of cell wall degradation by ruminant microbes and by fungal glycohydrolyase enzymes. Ferulic acid esterase (FAE) can release both monomeric and dimeric ferulic acids from arabinoxylans making the cell wall more susceptible to further enzymatic attack. Transgenic plants of Lolium multiflorum expressing a ferulic acid esterase gene from Aspergillus niger, targeted to the vacuole under a constitutive rice actin promoter, have been produced following microprojectile bombardment of embryogenic cell cultures. The level of FAE activity was found to vary with leaf age and was highest in young leaves. FAE expression resulted in the release of monomeric and dimeric ferulic acids from cell walls on cell death and this was enhanced severalfold by the addition of exogenous β-1,4-endoxylanase. We also show that a number of plants expressing FAE had reduced levels of cell wall esterified monomeric and dimeric ferulates and increased in vitro dry-matter digestibility compared with nontransformed plants.