Synthesis of 1,2-amino alcohols by sigmatropic rearrangements of 3-(N-tosylamino)allylic alcohol derivatives

Sigmatropic rearrangements of 3-(N-tosylamino)allylic alcohol derivatives, a particular subclass of functionalized enamides, have been investigated. Whereas the presence of the nitrogen atom alters the stereochemical outcome of Ireland-Claisen rearrangements of glycolates derived from such substrates, [2,3]-Wittig rearrangements of α-allyloxy acetamides or propargylic ethers derivatives provide access to a wide variety of functionalized 1,2-amino alcohols usually with high levels of stereocontrol, as well as to heterocyclic compounds. The stereoselectivity issues of these rearrangements (1,2-diastereoselectivity, auxiliary-induced diastereoselection, chirality transfer, and double stereodifferentiation) were thoroughly investigated.     

General Anisotropy Identification of Paperboard with Virtual Fields Method

This work extends previous efforts in plate bending of Virtual Fields Method (VFM) parameter identification to include a general 2-D anisotropic material. Such an extension was needed for instances in which material principal directions are unknown or when specimen orientation is not aligned with material principal directions. A new fixture with a multi-axial force configuration is introduced to provide full-field strain data for identification of the six anisotropic stiffnesses. Two paper materials were tested and their Q _ij compared favorably with those determined by ultrasonic and tensile tests. Accuracy of VFM identification was also quantified by variance of stiffnesses. The load fixture and VFM provide an alternative stiffness identification tool for a wide variety of thin materials to more accurately determine Q ₁₂ and Q ₆₆.     

Synthesis, characterization, and calculated electronic structure of the crystalline metal-organic polymers [Hg(SC6H4S)(en)]n and [Pb(SC6H4S)(dien)]n

The reaction of Hg(OAc)(2) with 1,4-benzenedithiol in ethylenediamine at 80 °C yields [Hg(SC(6)H(4)S)(en)](n), while the reaction of Pb(OAc)(2) with 1,4-benzenedithiol in diethylenetriamine at 130 °C yields [Pb(SC(6)H(4)S)(dien)](n). Both products are crystalline materials, and structure determination by synchrotron X-ray powder diffraction revealed that both are essentially one-dimensional metal-organic polymers with -M-SC(6)H(4)S- repeat units. Diffuse reflectance UV-visible spectroscopy indicates band gaps of 2.89 eV for [Hg(SC(6)H(4)S)(en)](n) and 2.54 eV for [Pb(SC(6)H(4)S)(dien)](n), while density functional theory (DFT) band structure calculations yielded band gaps of 2.24 and 2.10 eV, respectively. The two compounds are both infinite polymers of metal atoms linked by 1,4-benzenedithiolate, the prototypical molecule for single-molecule conductivity studies, yet neither compound has significant electrical conductivity as a pressed pellet. In the case of [Pb(SC(6)H(4)S)(dien)](n) calculations indicate fairly flat bands and therefore low carrier mobilities, while the conduction band of [Hg(SC(6)H(4)S)(en)](n) does have moderate dispersion and a calculated electron effective mass of 0.29·m(e). Hybridization of the empty Hg 6s orbital with SC(6)H(4)S orbitals in the conduction band leads to the band dispersion, and suggests that similar hybrid materials with smaller band gaps will be good semiconductors.     

Glycogen as a Biodegradable Construction Nanomaterial for in vivo Use

It is demonstrated that glycogen as a biodegradable and inexpensive material coming from renewable resources can be used as a carrier for the construction of in vivo imaging nanoagents. The model system considered is composed of glycogen modified with gadolinium and fluorescent labels. Systematic studies of properties of these nanocarriers by a variety of physical methods and results of in vivo tests of biodegradability are reported. This represents, to the authors' best knowledge, the first such use of glycogen.

     

Accumulation and efflux of polychlorinated biphenyls in Escherichia coli

Polychlorinated biphenyls (PCBs) are environmental pollutants that have been associated with numerous adverse health effects in human and animals. Hydroxylated PCBs (HPCBs) are the product of the oxidative metabolism of PCBs. The presence of hydroxyl groups in HPCBs makes these compounds more hydrophilic than the parent PCBs. One of the best approaches to break down and remove these contaminants is bioremediation; an environmentally friendly process that uses microorganisms to degrade hazardous chemicals into non-toxic ones. In this study, we investigated the cellular accumulation and toxicity of selected PCBs and HPCBs in Gram-negative bacteria, using Escherichia coli as a model organism. We found that none of the five PCBs tested were toxic to E. coli, presumably due to their limited bioavailability. Nevertheless, different HPCBs tested showed different levels of toxicity. Furthermore, we demonstrated that the primary multidrug efflux system in E. coli, AcrAB-TolC, facilitated the efflux of HPCBs out of the cell. Since AcrAB-TolC is constitutively expressed in E. coli and is conserved in all sequenced Gram-negative bacterial genomes, our results suggest that the efflux activities of multidrug resistant pumps may affect the accumulation and degradation of PCBs in Gram-negative bacteria.     

Functional twin boundaries

Functional interfaces are at the core of research in the emerging field of ‘domain boundary engineering’ where polar, conducting, chiral, and other interfaces and twin boundaries have been discovered. Ferroelectricity was found in twin walls of paraelectric CaTiO₃. We show that the effect of functional interfaces can be optimized if the number of twin boundaries is increased in densely twinned materials. Such materials can be produced by shear in the ferroelastic phase rather than by rapid quench from the paraelastic phase.