A convergent synthesis of the immunosuppressant FTY720 employing aqueous Wittig chemistry

A short, convergent synthesis of the immunosuppressant FTY720 is described involving the use of 4-hydroxymethylbenzaldehyde as a pivotal intermediate. A double Wittig strategy was developed to connect this dual-functional aldehyde with an alkyl-tether and to a readily available TRIS-derivative leading to an efficient synthesis of the target molecule.     

Directing/protecting groups mediate highly regioselective glycosylation of monoprotected acceptors

A directing/protecting group designed for regioselective functionalization of partially-protected glucopyrannosides has been successfully used to prepare disaccharides in high yields. Most importantly, it has been demonstrated that highly regioselective and stereoselective glycosylation can be achieved when disarmed donors are employed. This study demonstrates the ability of directing/protecting group to induce regioselective glycosylation of carbohydrates and opens the field to the design of other DPGs for other monosaccharides.     

Directed organization of C70 kagome lattice by titanyl phthalocyanine monolayer template

Controlled deposition of titanyl phthalocyanine (TiOPc) on Ag(111) produces a honeycomb monolayer phase consisting of TiOPc molecules with two distinctive tilt angles. This periodic arrangement of polar molecules is used to direct C(70) growth into low-density 3D films with novel C(70) kagome lattice arrangements. Structural models for the C(70) kagome lattice are determined from layer-by-layer scanning tunneling microscopy images and related to the dipolar TiOPc template and C(70)'s anisotropic polarizability. Molecular templates with designed electrostatic features offer a practical method to control 3D film organization on the nanoscale by harnessing anisotropic molecular interactions at the growth interface.     

Development of naturally selected and molecularly engineered intrachain and competitive FRET-aptamers and aptamer beacons

Several different approaches have been taken to development of homogeneous fluorescent aptamer assays including end-labeled beacons and signaling aptamers which are intrinsically quenched by nucleotides. Two new strategies dubbed "intrachain" and "competitive" FRET-aptamer assays are summarized in this review. Intrachain and competitive FRET-aptamers can be engineered on the molecular level through a series exploratory experiments involving prior knowledge of aptamer secondary or tertiary structures and hypotheses about aptamer conformational changes. However, there is an intrinsic risk of altering aptamer affinity or specificity associated with chemical modifications of an aptamer. Natural selection methods for FRET-aptamers have also been devised to potentially obviate the chemical modification problem. The naturally selected aptamers are subjected to fluorophore (F)- and or quencher (Q)-conjugated nucleotide triphosphate (NTP) incorporation by polymerase chain reaction (PCR) with permissive polymerases such as Deep Vent exo-, but still demonstrate sensitive and specific assay performance despite modified bases, because they are ultimately selected after decoration with F and Q. This paper summarizes work in this area and presents some new examples of the engineered and naturally selected FRET-aptamers for detection of vitamin D.     

Isotherm Theoretical Study of the AlxGa1−xAsySb1−y Quaternary Alloy Using the Regular Solution Approximation for Its Possible Growth via Liquid-Phase Epitaxy at Low Temperatures

This work presents the theoretical calculation of isotherm diagrams for quaternary alloys of III–V semiconductor compounds with the form III_xIII_1−xV_yV_1−y. In particular, the isotherm diagrams for the Al_xGa_1−xAs_ySb_1−y quaternary alloy at low temperatures were calculated (500 °C, 450 °C, 400 °C, and 350 °C). The Al_xGa_1−xAs_ySb_1−y quaternary alloy was formed from four binary compounds such as GaAs, AlAs, AlSb, and GaSb, all with direct bandgaps. The regular solution approximation was used to find the quaternary isotherm diagrams, represented in four linearly independent equations, which were solved using Parametric Technology Corporation Mathcad 14.0 software for different arsenic and antimony atomic fractions. The results support the possible growth of layers via liquid-phase epitaxy in a range of temperatures from 500 °C to 350 °C, where the crystalline quality could be improved at low temperatures. These semiconductor layers could have applications for optoelectronic devices in photonic communications, thermophotovoltaic systems, and microwave devices with good crystalline quality.     

Characterization of a protease produced by a Trichoderma harzianum isolate which controls cocoa plant witches' broom disease

Background  

Several Trichoderma strains have been reported to be effective in controlling plant diseases, and the action of fungal hydrolytic enzymes has been considered as the main mechanism involved in the antagonistic process. However, although Trichoderma strains were found to impair development of Crinipellis perniciosa, the causal agent of cocoa plant witches' broom disease, no fungal strain is available for effective control of this disease. We have then undertaken a program of construction of hydrolytic enzyme-overproducing Trichoderma strains aiming improvement of the fungal antagonistic capacity. The protease of an indian Trichoderma isolate showing antagonistic activity against C. perniciosa was purified to homogeneity and characterized for its kinetic properties and action on the phytopathogen cell wall.     

Mathematical simulation of oil reservoir properties

The study and computational representation of porous media properties are very important for many industries where problems of fluid flow, percolation phenomena and liquid movement and stagnation are involved, for example, in building constructions, ore processing, chemical industries, mining, corrosion sciences, etc. Nevertheless, these kinds of processes present a noneasy behavior to be predicted and mathematical models must include statistical analysis, fractal and/or stochastic procedures to do it. This work shows the characterization of sandstone berea core samples which can be found as a porous media (PM) in natural oil reservoirs, rock formations, etc. and the development of a mathematical algorithm for simulating the anisotropic characteristics of a PM based on a stochastic distribution of some of their most important properties like porosity, permeability, pressure and saturation. Finally a stochastic process is used again to simulated the topography of an oil reservoir.     

Comparison of agarose and cross-linked protein gels as magnetic resonance imaging phantoms

Measurements of the magnetic field dependence of spin-lattice relaxation rates and the response of the water-proton signal intensity to off-resonance radio frequency fields show that the commonly used agarose phantom provides a less faithful representation for the magnetic response of tissue than does a cross-linked protein system. The origin of these differences lies in the structure and intramolecular dynamics of the macromolecular system used to make the gel. These distinctions will also cause differences in the magnetic response of the water spin system when paramagnetic relaxation agents or contrast agents are incorporated. Use of a thermally cross-linked bovine serum albumin phantom is suggested.