Transformation of a hydroxyl into an acyl group on α-pyrone ring: a novel route to 3,4-diacylcoumarins

The transformation of a hydroxyl into an acyl group, a transformation which has been extensively investigated on the benzene nucleus of several substrates, is now applied successfully for the first time to a heterocyclic ring and specifically to the pyrone ring of coumarin to yield novel 3,4-diacylcoumarins in good yields. The reaction involves formation of a new C–C bond.     

Calculus in European classrooms: curriculum and teaching in different educational and cultural contexts

In this paper we provide a first overview of the landscape with respect to calculus teaching in European classrooms, an area where research is very limited. In particular through a small expert-based survey and a literature review, we trace the development of calculus teaching at schools in a number of European countries and identify commonalities and differences. In the current curriculum developments, we notice a reduction in the content of calculus and a more informal approach. The use of digital tools has started to be integrated in calculus teaching in most countries. However in some nations, teaching of calculus in the classroom is rather traditional, focusing on procedural aspects of knowledge. Moreover, in cases where more informal and conceptual teaching approaches are used in the classroom, often contradictions seem to exist with other contextual matters such as examination requirements. Finally, we discuss the future of calculus teaching in Europe.     

The nature of surface barriers on nanoporous solids explored by microimaging of transient guest distributions

Nanoporous solids are attractive materials for energetically efficient and environmentally friendly catalytic and adsorption separation processes. Although the performance of such materials is largely dependent on their molecular transport properties, our fundamental understanding of these phenomena is far from complete. This is particularly true for the mechanisms that control the penetration rate through the outer surface of these materials (commonly referred to as surface barriers). Recent detailed sorption rate measurements with Zn(tbip) crystals have greatly enhanced our basic understanding of such processes. Surface resistance in this material has been shown to arise from the complete blockage of most of the pore entrances on the outer surface, while the transport resistance of the remaining open pores is negligibly small. More generally, the revealed correlation between intracrystalline diffusion and surface permeation provides a new view of the nature of transport resistances in nanoporous materials acting in addition to the diffusion resistance of the regular pore network, leading to a rational explanation of the discrepancy which is often observed between microscopic and macroscopic diffusion measurements.     

The Role of Visual Representations in Advanced Mathematical Problem Solving: An Examination of Expert-Novice Similarities and Differences

Expert mathematicians are contrasted with undergraduate students through a two-part analysis of the potential and actual use of visual representations in problem solving. In the first part, a classification task is used to indicate the extent to which visual representations are perceived as having potential utility for advanced mathematical problem solving. The analysis reveals that both experts and novices perceive visual representation use as a viable strategy. However, the two groups judge visual representations likely to be useful with different sets of problems. Novices generally indicate that visual representations would likely be useful mostly for geometry problems, whereas the experts indicate potential application to a wider variety of problems. In the second part, written solutions to problems and verbal protocols of problem-solving episodes are analyzed to determine the frequency, nature, and function of the visual representations actually used during problem solving. Experts construct visual representations more frequently than do novices and use them as dynamic objects to explore the problem space qualitatively, to develop a better understanding of the problem situation, and to guide their solution planning and enactment of problem-solving activity. In contrast, novices typically make little use of visual representations.     

Organic residue analysis of Neolithic pottery from North Greece

Organic residues associated with Neolithic pottery from two Late Neolithic sites, Paliambela and Makriyalos (Northern Greece), were analyzed by gas chromatography-mass spectrometry. The study aimed at identifying the origin of the tar used for waterproofing and gluing broken pots. Reference tars were prepared in laboratory conditions by pyrolysis of the bark from three tree species, namely from Betula pendula (silver birch), Ostrya carpinifolia (hop hornbeam) and Carpinus orientalis (Eastern hornbeam). The results suggest that mostly birch bark tar was used as glue for fixing broken pieces of the pots as well as for waterproofing close-shaped vessels. None of the archaeological tars derived from the two hornbeams. The analysis shows certain variability in the composition of birch bark tar, which is related to the production technique and to the re-use of tar. Of particular interest is the presence of characteristic diterpenoid biomarkers in several samples, which indicates that pine pitch was used for gluing and pine resin for waterproofing vessels for liquids. Correspondence: Sophia Mitkidou, Department of Science, School of Technological Applications, Technological Institute of Kavala, Greece     

Opposite stereochemical courses for enzyme-mediated alkene reductions of an enantiomeric substrate pair

Rat NADP-dependent leukotriene B4 12-hydroxydehydrogenase (Ltb4dh) catalyzes olefin reductions for some activated alkenes at the expense of NADPH in the absence of a flavin cofactor. Unlike flavoprotein alkene reductases, where net trans-addition of hydrogen has been consistently observed, Ltb4dh reduced both enantiomers of perillaldehyde to the same cis-product. To uncover the reason for this unexpected result, the stereochemical courses of perillaldehyde reductions by Ltb4dh were determined by deuterium labeling followed by (2)H NMR analysis. These data showed unequivocally that Ltb4dh mediated net trans-addition of hydrogen to (R)-perillaldehyde but followed the opposite stereochemical course (net syn-addition) for (S)-perillaldehyde. To the best of our knowledge, such divergent stereochemical pathways for a single enzyme have not previously been reported.     

Conformational studies of immunodominant myelin basic protein 1�C11 analogues using NMR and molecular modeling

Τwo dimensional nuclear magnetic resonance studies complimented by molecular dynamics simulations were conducted to investigate the conformation of the immunodominant epitope of acetylated myelin basic protein residues 1-11 (Ac-MBP(1-11)) and its altered peptide ligands, mutated at position 4 to an alanine (Ac-MBP(1-11)[4A]) or a tyrosine residue (Ac-MBP(1-11)[4Y]). Conformational analysis of the three analogues indicated that they adopt an extended conformation in DMSO solution as no long distance NOE connectivities were observed and seem to have a similar conformation when bound to the active site of the major histocompatibility complex (MHC II). The interaction of each peptide with MHC class II I-A(u) was further investigated in order to explore the molecular mechanism of experimental autoimmune encephalomyelitis induction/inhibition in mice. The present findings indicate that the Gln(3) residue, which serves as a T-cell receptor (TCR) contact site in the TCR/peptide/I-A(u) complex, has a different orientation in the mutated analogues especially in the Ac-MBP(1-11)[4A] peptide. In particular the side chain of Gln(3) is not solvent exposed as for the native Ac-MBP(1-11) and it is not available for interaction with the TCR.     

Analysis of leukocyte membrane protein interactions using protein microarrays

Background  

Protein microarrays represent an emerging class of proteomic tools to investigate multiple protein-protein interactions in parallel. A sufficient proportion of immobilized proteins must maintain an active conformation and an orientation that allows for the sensitive and specific detection of antibody and ligand binding. In order to establish protein array technology for the characterization of the weak interactions between leukocyte membrane proteins, we selected the human leukocyte membrane protein CD200 (OX2) and its cell surface receptor (hCD200R) as a model system. As antibody-antigen reactions are generally of higher affinity than receptor-ligand binding, we first analyzed the reactivity of monoclonal antibodies (mAb) to normal and mutant forms of immobilized CD200R.