A step further in Peer Instruction: Using the Stepladder technique to improve learning

International audiencePeer Instruction (PI) is an instructional strategy for engaging students during class through a structured questioning process that improves the learning of the concepts of fundamental sciences. Although all students are supposedly engaged in discussions with their peers during Peer Instruction, the learning gains generally remain at a medium level, suggesting a lack of participation of certain students who do not benefit from social interactions. The present study examined whether the Stepladder technique might optimize the Peer Instruction method and increase learning gains. With this technique, students enter a group sequentially, forcing every group member to participate in discussions. Eighty-four chemistry students were asked to answer easy and difficult multiple-choice questions before and after being randomly assigned to one of three instructional conditions during a chromatography lesson (Classic PI vs. Stepladder PI vs. Individual Instruction without any discussion with peers). As predicted, results showed that learning gains were greatest in the Stepladder PI group, and that this effect was mainly observed for difficult questions. Results also revealed higher perceived satisfaction when students had to discuss the questions with their peers than when they were not given this possibility. By extending the Stepladder technique to higher education, these findings offer a step forward in the Peer Instruction literature, showing how it can enhance learning gains

4-Nitro­phenyl α-l-rhamnopyran­oside hemihydrate

In the title compound, C12H15NO7·0.5H2O, there are two independent mol­ecules in the asymmetric unit, together with one water molecule. The pyran­oside rings each have close to a 1 C 4 chair conformation and the nitro groups are almost coplanar with the benzene rings. The water mol­ecule links the two independent mol­ecules through O—H⋯O hydrogen bonds. All the hydroxyl groups are involved in hydrogen-bond inter­actions, giving rise to a three-dimensional network

General One-Step Synthesis of Free Hexofuranosyl 1-Phosphates Using Unprotected 1-Thioimidoyl Hexofuranosides

A general one-step strategy is developed for the synthesis of hexofuranosyl 1-phosphates starting from new unprotected glycofuranosyl donors. It required first the preparation of new 1-thiohexofuranosides bearing a thioimidoyl heterocycle as a leaving group. The presence of sulfur and/or nitrogen atom(s) on the aglycon allowed remote activation of these thioglycofuranosides by anhydrous phosphoric acid and led to the target phosphates 9, 27, 29, and 30 in good to excellent selectivities and, more importantly, with very limited or no ring expansion. Moreover, this one-step phosphorylation reaction could be significantly improved by avoiding any tedious protecting group manipulations on negatively charged compounds and by focusing on a simple but general procedure of purification. This approach was applied to the diastereocontrolled synthesis of D-galacto- and D-glucofuranosyl 1-phosphates and also to the preparation of rare epimer and/or deoxy counterparts, that is, D-manno- and D-fucofuranosyl derivatives

Araf51 with improved transglycosylation activities: One engineered biocatalyst for one specific acceptor

International audienceA random mutagenesis of the arabinofuranosyl hydrolase Araf51 has been run in order to access to efficient biocatalysts for the synthesis of alkyl arabinofuranosides. The mutants were selected on their ability to catalyze the transglycosylation reaction of p-nitrophenyl α-L-arabinofuranoside (pNP-Araf) used as a donor and various aliphatic alcohols as acceptors. This screening strategy underlined 5 interesting clones, each one corresponding to one acceptor. They appeared to be much more efficient in the transglycosylation reaction compared to the wild type enzyme whereas no self-condensation or hydrolysis products could be detected. Moreover, the high specificity of the mutants towards the alcohols for which they have been selected validates the screening process. Sequence analysis of the mutated enzymes revealed that, despite their location far from the active site, the mutations affect significantly the kinetics properties as well as the substrate affinity of these mutants towards the alcoholacceptors in the transglycosylation reaction

Environmentally benign glycosylation of aryl pyranosides and aryl/alkyl furanosides demonstrating the versatility of thermostable CGTase from Thermoanaerobacterium sp.

International audienceAn extensive study on the specificity of transglycosylation and disproportionation of Thermoanaerobacterium sp. cyclodextrin glucosyltranferases against aryl glucopyranosides or furanosides was achieved. While a mixture of maltoside and isomaltoside was obtained respectively using p-nitrophenyl glucopyranoside as acceptor, only one regioisomer, namely the p-nitrophenyl α-D-Glcp-(1,3)-α-L-Araf was isolated using p-nitrophenyl arabinofuranoside as acceptor. Interestingly, similar outcomes were found when using p-nitrophenyl galactofuranoside. Furthermore, activation by microwave irradiation resulted in faster reaction times and higher yields and led to glucosidic oligosaccharides with up to 70% conversion. The influence of the anomeric and C-4 configurations of the glycosidic acceptors on the transglycosylation, previously stated for the CGTase family, was not observed and unconventional substrate specificity towards alkyl furanosides was highlighted

Graphical Abstract Biocatalyzed synthesis of difuranosides and their ability to trigger production of TNF-D D Biocatalyzed synthesis of difuranosides and their ability to trigger production of TNF-D D

International audienceTransglycosylation reactions biocatalyzed by the native arabinofuranosidase Araf51 and using D-galactosyl, D-fucosyl and 6-deoxy-6-fluoro-D-galactosyl derivatives as donors and acceptors provided di-to pentahexofuranosides. The immunostimulatory potency of these compounds, and more especially their ability to induce production of TNF-α, was evaluated on the murine macrophage cell line, Raw 264.7. The results obtained showed concentration-dependent and most importantly, structure-dependent responses. Interestingly, oligoarabinofuranosides belonging to the oligopentafuranoside family displayed concentration-, chain length and aglycon-dependent bioactivities irrespective of their fine chemical variations. Thus, neo-oligofuranosides in D-Galf series, as well as their D-Fucf and 6-fluorinated counterparts are indeed potential sources of immunostimulating agents

Exploring the synthetic potency of the first furanothioglycoligase through original remote activation.

International audienceThioglycosidic bonds are of utmost importance in biomolecules as their incorporation led to more stable glycomimetics with potential drug activities. Until now only chemical methods were available for their incorporation into glycofuranosyl conjugates. Herein, we wish to describe the use of the first furanothioglycoligase for the preparation of a great variety of thioaryl derivatives with moderate to excellent yields. Of great interest, a stable 1-thioimidoyl arabinofuranose, classically used in chemical glycosylation, was able to efficiently act as a donor through an original enzymatic remote activation mechanism. Study of the chemical structure as well as the nucleophilicity of the thiol allowed us to optimize this biocatalyzed process. As a consequence, this mutated enzyme constitutes an original, mild and eco-friendly method of thioligation

The versatile enzyme Araf51 allowed efficient synthesis of rare pathogen-related β-d-galactofuranosyl-pyranoside disaccharides.

International audienceThe preparation of galactofuranosyl-containing disaccharidic parts of natural glycoconjugates was performed according to a chemo-enzymatic synthesis. Our goals were firstly to develop an alternative approach to standard chemical strategies by limiting the number of reaction and purification steps, and secondly to evaluate the scope of the Araf51 biocatalyst to transfer a galactofuranosyl moiety to a set of pyranosidic acceptors differing from each other by the series, the anomeric configuration as well as the conformation. The study of binding mode of the resulting disaccharides was also performed by molecular modeling and showed significant differences between (1→2)- and (1→6)-linked disaccharides