Nouvelles tendances dans la Didactique de la Chimie et rôle du Comité pour l'Enseignement de la Chimie de l'IUPAC

We call attention to the enormous spreading undergone by the didactic of chemistry in the last few years and comment on some of the trends that are significant in this field from the point of view of the author. We also comment on some of the projects developed by the committee for teaching chemistry in the IUPAC

La reacción química : descripciones e interpretaciones de los alumnos de liceo

We have carried out a piece of research about the assimilation of the chemical reaction by secondary students, based on the study of their spontaneous descriptions of the process, their ability to explain it in corpuscular terms and of correctly applying the law of matter preservation. The experimental sample were 19 students between 13 and 14 years of age who had been introduced to the subject the previous year. We have introduced a variant in the technique of interviews

A sensory 3-D map of the odor description space derived from a comparison of numeric odor profile databases

Many authors have proposed different schemes of odor classification, which are useful to aid the complex task of describing smells. However, reaching a consensus on a particular classification seems difficult because our psychophysical space of odor description is a continuum and is not clustered into well-defined categories. An alternative approach is to describe the perceptual space of odors as a low-dimensional coordinate system. This idea was first proposed by Crocker and Henderson in 1927, who suggested using numeric profiles based on 4 dimensions: fragrant, acid, burnt, and caprylic. In the present work, the odor profiles of 144 aroma chemicals were compared by means of statistical regression with comparable numeric odor profiles obtained from 2 databases, enabling a plausible interpretation of the 4 dimensions. Based on the results and taking into account comparable 2D sensory maps of odor descriptors from the literature, a 3D sensory map (odor cube) has been drawn up to improve understanding of the similarities and dissimilarities of the odor descriptors most frequently used in fragrance chemistry.Zarzo Castelló, M. (2015). A sensory 3-D map of the odor description space derived from a comparison of numeric odor profile databases. Chemical Senses. 40(5):305-313. doi:10.1093/chemse/bjv012S30531340

On the role of chirality in structure-odor relationships

The influence of chirality on odors was studied on 16 enantiomeric pairs according to the dispersion/hydrogen bonding theory of receptor-odorant interaction. Comparisons of molecular structures were made by superimposition of optimized conformations, using the Alchemy II package. The quality of fit was assessed using the RMS parameter included in Alchemy II and a new index for hydrogen bonding: the angle between H-bonds in the two molecules. In the case of camphoraceous odorants where an interaction model was already known superimposition according to the model led to correct predictions of the high similarity of odors observed in enantiomeric pairs. For several urinous odorants comparisons were made using d-androstenone as a reference compound for the urinous odor. Correct predictions were obtained for l-androstenone, both enantiomers of androsta-4, 16-dienone, and (+)-2-methyl-4-(5,5,6-exo-trimethy1-2-exonorbornyl)-cyclobexane. The (−) enantiomer of the latter compound was correctly predicted only if it was assumed that its weak intensity is due to a partial interaction with the hydrophobic zone of the receptor. For ambergris odorants which have a complex odor (−)-Ambrox was selected as the reference compound. The odors of (+)-Ambrox and enantiomers of four other compounds (ambergris or woody) were correctly predicted by superimposition. For nootkatone and three derivatives which have a grapefruit note for one enantiomer and a woody note for the other no models or reference compounds were available. The superimpositions were made between grapefruit enantiomers, on the one hand, and woody enantiomers on the other hand. Woody and grapefruit characters were correctly predicted in all cases. The limits of this approach based on molecular modelling are discusse

Relations structure-odeur soufrée pour une série de composés organiques

Les relations structure-odeur soufrée sont établies en choisisant les fragments de molécules comme descripteurs selon les principes de la méthode GESDEM (Genération et Sélection de Descripteurs et Elaboration de Motifs). La série étudiée comporte 48 molécules soufrées et 34 non-soufrées. 96 % des molécules ont été classées en tant que telles par un modèle obtenu en utilisant un réseau neuronal (RN) de configuration 8-5-1

Molecular complexity determines the number of olfactory notes and the pleasantness of smells

One major unresolved problem in olfaction research is to relate the percept to the molecular structure of stimuli. The present study examined this issue and showed for the first time a quantitative structure-odor relationship in which the more structurally complex a monomolecular odorant, the more numerous the olfactory notes it evokes. Low-complexity odorants were also rated as more aversive, reflecting the fact that low molecular complexity may serve as a warning cue for the olfactory system. Taken together, these findings suggest that molecular complexity provides a framework to explain the subjective experience of smells

Narcolepsy patients have antibodies that stain distinct cell populations in rat brain and influence sleep patterns.

Narcolepsy is a chronic sleep disorder, likely with an autoimmune component. During 2009 and 2010, a link between A(H1N1)pdm09 Pandemrix vaccination and onset of narcolepsy was suggested in Scandinavia. In this study, we searched for autoantibodies related to narcolepsy using a neuroanatomical array: rat brain sections were processed for immunohistochemistry/double labeling using patient sera/cerebrospinal fluid as primary antibodies. Sera from 89 narcoleptic patients, 52 patients with other sleep-related disorders (OSRDs), and 137 healthy controls were examined. Three distinct patterns of immunoreactivity were of particular interest: pattern A, hypothalamic melanin-concentrating hormone and proopiomelanocortin but not hypocretin/orexin neurons; pattern B, GABAergic cortical interneurons; and pattern C, mainly globus pallidus neurons. Altogether, 24 of 89 (27%) narcoleptics exhibited pattern A or B or C. None of the patterns were exclusive for narcolepsy but were also detected in the OSRD group at significantly lower numbers. Also, some healthy controls exhibited these patterns. The antigen of pattern A autoantibodies was identified as the common C-terminal epitope of neuropeptide glutamic acid-isoleucine/alpha-melanocyte-stimulating hormone (NEI/alphaMSH) peptides. Passive transfer experiments on rat showed significant effects of pattern A human IgGs on rapid eye movement and slow-wave sleep time parameters in the inactive phase and EEG theta-power in the active phase. We suggest that NEI/alphaMSH autoantibodies may interfere with the fine regulation of sleep, contributing to the complex pathogenesis of narcolepsy and OSRDs. Also, patterns B and C are potentially interesting, because recent data suggest a relevance of those brain regions/neuron populations in the regulation of sleep/arousal

Conditional corticotropin-releasing hormone overexpression in the mouse forebrain enhances rapid eye movement sleep

Impaired sleep and enhanced stress hormone secretion are the hallmarks of stress-related disorders, including major depression. The central neuropeptide, corticotropin-releasing hormone (CRH), is a key hormone that regulates humoral and behavioral adaptation to stress. Its prolonged hypersecretion is believed to play a key role in the development and course of depressive symptoms, and is associated with sleep impairment. To investigate the specific effects of central CRH overexpression on sleep, we used conditional mouse mutants that overexpress CRH in the entire central nervous system (CRH-COE-Nes) or only in the forebrain, including limbic structures (CRH-COE-Cam). Compared with wild-type or control mice during baseline, both homozygous CRH-COE-Nes and -Cam mice showed constantly increased rapid eye movement (REM) sleep, whereas slightly suppressed non-REM sleep was detected only in CRH-COE-Nes mice during the light period. In response to 6-h sleep deprivation, elevated levels of REM sleep also became evident in heterozygous CRH-COE-Nes and -Cam mice during recovery, which was reversed by treatment with a CRH receptor type 1 (CRHR1) antagonist in heterozygous and homozygous CRH-COE-Nes mice. The peripheral stress hormone levels were not elevated at baseline, and even after sleep deprivation they were indistinguishable across genotypes. As the stress axis was not altered, sleep changes, in particular enhanced REM sleep, occurring in these models are most likely induced by the forebrain CRH through the activation of CRHR1. CRH hypersecretion in the forebrain seems to drive REM sleep, supporting the notion that enhanced REM sleep may serve as biomarker for clinical conditions associated with enhanced CRH secretion

Enseñanza de las ciencias : revista de investigación y experiencias didácticas

Resumen basado en el de la publicaciónResumen en inglésSe ha llevado a cabo una investigación sobre la la reacción química de estudiantes de secundaria, basada en el estudio de sus descripciones espontáneas del proceso, su capacidad para explicarlo en términos corpusculares y de aplicar correctamente la ley de preservación de la materia. La muestra experimental fue de 19 estudiantes entre 13 y 14 años de edad a los que se les había presentado el tema el año anterior. Se ha introducido una variante en la técnica de entrevistas.ES