Assembly of a series of malarial glycosylphosphatidylinositol anchor oligosaccharides

We report an efficient and convergent synthesis of a series of oligosaccharides comprised of the malaria GPI glycan (2a), a promising anti-malaria vaccine candidate currently in preclinical trials and several related oligosaccharide sequences (3-8) that are possible biosynthetic precursors of the malarial GPI. A flexible synthetic strategy is disclosed that relies on a late-stage coupling between oligomannosides of varying length and pseudo-disaccharide glycosyl acceptor 11 to readily access various malarial GPI structures. Phosphorylation was accomplished by mild and efficient H-phosphonate chemistry before the final deprotection was carried out by using sodium in ammonia. The direct connection of a thiol group via a phosphate diester linkage to the inositol moiety provides a handle for easy conjugation of the GPI glycan to carrier proteins, immobilization on carbohydrate microarrays and photo-affinity labels identification. These synthetic oligosaccharides will serve as molecular probes.     

The Development of Mathematical Discussions: An Investigation in a Fifth-Grade Classroom

Promoting discussion and argumentation of mathematical ideas among students are aspects of the vision for communication in recent school mathematics reform efforts. Having rich mathematical discussions, however, can present a variety of classroom challenges. Many factors influence classroom discussions and need to be addressed in ways that will assist teachers in creating more inquiry-based mathematics classrooms. The study presented here examined the development of mathematical discussions in a fifth-grade classroom over the course of a school year. Various aspects of the participants' interactions, teacher's pedagogy, and the classroom microculture were investigated. One major result is the evolution of student participation from nonactive listening to active listening and use of others' ideas to develop new conjectures. These changes were paralleled by changes in the teacher's role in the classroom and the nature of her questions, in particular.     

Application of a Novel CO2 DC Thermal Plasma Torch Submerged in Aqueous Solution for Treatment of Dissolved Carboxylic Acid

Plasma Chemistry and Plasma Processing - A novel direct current (DC) plasma torch, operating with a gas mixture consisting of carbon dioxide and hydrocarbon (methane), has been adapted and used for...     

Thermogravimetric analysis of single-walled carbon nanotubes synthesized by induction thermal plasma

A standard procedure for thermogravimetric analysis (TG) of carbonaceous materials including single-walled carbon nanotubes was developed based on a statistical design to precisely study the effect of three main TG parameters: temperature ramp (TR, °C), initial mass (IM) of the sample (mg), and the rate of flowing gas (sccm) on the TG results. In addition, the effect of sampling including sample morphology and moisture content on TG were studied. The results of statistical design clearly showed that TG was affected by these three parameters and particularly by IM and TR. Interestingly, it was observed that the TG results are affected insufficiently by the sample morphology and low moisture content. This study also confirmed the potential of TG combined with high-resolution scanning electron microscopy to be a simple and straightforward method for purity evaluation of SWCNT-containing samples with a complex TG behavior such as those of induction thermal plasma grown. A complementary study on nano-metric catalysts indicated that these types of materials enable to gain or loss mass in an oxidative ambient during TG. A mass loss of 6% and a mass gain of 23% were observed for pure nano-metric yttrium oxide and nickel, respectively. A simple calculation showed a total mass gain of 1?wt% particularly by the catalysts in the SWCNT sample during TG.     

Diastereoselective synthesis of 2,3,5-trisubstituted tetrahydrofurans via cyclofunctionalization reactions. Evidence of stereoelectronic effects.

The work described herein considers the impact of stereoelectronic effects and allylic 1,3-strain in controlling the cyclofunctionalization reaction when a hydroxyl group is at the allylic position. The stereoelectronic arguments are supported by independent iodocyclization reactions performed using two secondary alcohols. The transition-state pathways involved in these reactions are established through a comparison of relative reaction rates. A bi-directional approach is used to demonstrate the potential of the iodocyclization reaction to differentiate a terminus in molecules with a pseudo C(2) axis of symmetry, showing that two-directional synthesis can be used to differentiate between alternative transition-state pathways.     

Spectrofluorimetric determination of formaldehyde in maple syrup

A quick and simple method was developed for determination of formaldehyde in maple syrup. In this method, formaldehyde reacts with Fluoral P to form a complex which is chemically extracted by isobutanol and determined by spectrofluorimetry. Performance, as gauged by the limits of detection (0.16 mg/kg) and quantitation (0.21 mg/kg), recovery (>79%), and variability (1.9-16.1%, depending on fortification level and class of syrup) were superior to the current official AOAC standard method.     

In situ purity enhancement/surface modification of single-walled carbon nanotubes synthesized by induction thermal plasma

A simple, cost-effective and energy-efficient approach was developed for in situ purity enhancement and surface modification of single-walled carbon nanotubes (SWCNTs) produced using an induction thermal plasma process. In this process, SWCNT-containing materials are thermally treated with oxygen flow inside a filtration chamber, while they are assembled into the sheets during the synthesis process. Owing to selective thermal oxidation, the amount of amorphous carbon was significantly reduced in the final product resulting in higher purity SWCNT-containing materials. Parametric study indicated that the amorphous carbon content was noticeably diminished in the product at an oxygen volume concentration of 10% in the synthesis system. Raman analysis indicated a decrease in the population of the SWCNTs with diameters smaller than 1.3 nm after in situ exposure to 10 vol.% of oxygen. In addition to the successful reduction of amorphous carbon content, the oxygen-functionalized SWCNTs were also observed in the final product using this process.     

Cryolitic vein XPS imaging from an industrial grade carbon

Aluminium carbide formation and subsequent dissolution is a generally accepted mechanism to explain the cathode wear in the Hall-Héroult industry. Carbide formation is thought to occur inside the cathode pores. Being dependent upon cathodic current density, it is believed to be an electrochemical process. It is also associated with the presence of cryolitic bath species involved in the dissolution of the carbide layer and thus enabling further carbide formation.     

Steric and Electronic Factors Influence Regio‐isomeric Thiazole Formations Between Substituted Benzothioamides and Ethyl Bromopyruvate

We observed unexpected thiazole 1B formation when 2,6‐dichlorobenzothioamide 1 and ethyl bromopyruvate were reacted under basic conditions at elevated temperatures in ethanol. Thiazole 1B , regio‐isomeric to that expected under conventional Hantzsch conditions, was extensively characterized and later confirmed by single crystal X‐ray structure. We carried out this transformation with several substituted benzothioamides and found that the formation of the unexpected thiazole regio‐isomer was highly dependent on the steric as well as the electronic characteristics of the ortho‐substituents on the phenyl ring. A mechanism to account for this novel transformation was proposed.