Novel sulfur and selenium containing bis-α-amino acids from 4-hydroxyproline

The synthesis of new substituted prolines carrying at C-4 a second α-amino acid residue is reported. The amino acid, l-cysteine or l-selenocysteine, is linked to the proline ring through the sulfur or the selenium atom, respectively. The products were prepared with different stereochemistry at C-4, in few and clean high-yielding steps, with suitable protections for solid phase applications. The introduction of both sulfur and selenium atoms at C-4 of the proline ring seems to enhance significantly the cis geometry at the prolyl amide bond

El historiador-científico y/ o el historiador-escritor: límites y transgresiones de la tarea cognitivo-literaria de escribir la historia

La pregunta acerca del estatus epistémico de la narración histórica ha sido formulada de manera tal que el espectro de respuestas posibles se reduce al delimitado por una alternativa excluyente; o bien la narración histórica es valorada positivamente como un discurso "científico", o bien es menospreciada como una rama de la literatura. En este contexto, pensar en apelar a la teoría literaria como recurso relevante para elaborar una teoría de la historia genera desconfianza, dado que se asume que tal asociación no puede sino redundar en una mirada debilitadora de la tarea del historiador

Apteniols A-F, oxyneolignans from the leaves of Aptenia cordifolia.

Abstract—Investigation of the organic extract of Aptenia cordifolia leaves revealed six new oxyneolignans named apteniols A–F. The structures were determined by means of spectroscopic methods. The C6C3 units are linked by an oxygen atom at C4–C40 or C4–C20 and they are dihydrophenylpropanoid acid units. Their effects on germination and growth of Lactuca sativa L. have been studied in the range concentration 10K4–10K7 M

The effects of verbal information on children's fear beliefs about social situations

Two experiments explored the role of verbal information in changing children’s fearrelated beliefs about social situations. In Experiment 1, 118 6- to 8- and 12- to 13-year-olds heard positive, negative, or no information about individuals’ experiences of three social situations. Fear beliefs regarding each situation were assessed before and after this manipulation. Verbal information had no significant influence on children’s fear beliefs. In Experiment 2, the same paradigm was used with 80 12- to 13-year-olds, but the information took the form of multiple attitude statements about the situations expressed by groups of peers, older children, or adults. An affective priming task of implicit attitudes was used to complement the explicit questions about fear beliefs. Negative information influenced both explicit and implicit fear beliefs. The source of information and the child’s own social anxiety did not moderate these effects. Implications for our understanding of the socialisation of childhood fears are discussed

Photochemical behavior of the drug atorvastatin in water.

Atorvastatin undergoes a self-sensitized photooxygenation by sunlight in water. The main photoproducts, isolated by chromatographic techniques, have been identified by spectroscopic means. They present a lactam ring arising from an oxidation of pyrrole ring and an alkyl/aryl shift. A mechanism involving singlet oxygen addition and an epoxide intermediate is suggested

TOXICITY OF PREDNISOLONE, DEXAMETHASONE AND THEIR PHOTOCHEMICAL DERIVATIVES ON AQUATIC ORGANISMS

Light exposure of aqueous suspensions of prednisolone and dexamethasone causes their partial phototransformation. The photoproducts, isolated by chromatographic techniques, have been identified by spectroscopic means. Prednisolone, dexamethasone and their photoproducts have been tested to evaluate their acute and chronic toxic effects on some freshwater chain organisms. The rotifer Brachionus calyciflorus and the crustaceans Thamnocephalus platyurus and Daphnia magna were chosen to perform acute toxicity tests, while the alga Pseudokircheneriella subcapitata (formerly known as Selenastrum capricornutum) and the crustacean Ceriodaphnia dubia to perform chronic tests. The photochemical derivatives are more toxic than the parent compounds. Generally low acute toxicity was found. Chronic exposure to this class of pharmaceuticals caused inhibition of growth population on the freshwater crustacean C. dubia while the alga P. subcapitata seems to be less affected by the presence of these drugs

Low-molecular-weight components of olive oil mill wastewaters

A new lignan 1-hydroxy-2-(4-hydroxy-3-methoxyphenyl)-6-(3-acetyl-4-hydroxy-5-methoxyphenyl)-3,7-dioxabicyclo[ 3.3.0]octane, the secoiridoid 2H-pyran-4-acetic acid,3-hydroxymethyl-2,3-dihydro-5-(methoxycarbonyl)-2- methyl-, methyl ester, the phenylglycoside 4-[β -D-xylopyranosyl-(1→6)]-β -D-glucopyranosyl-1,4-dihydroxy-2- methoxybenzene and the lactone 3-[1-(hydroxymethyl)-1-propenyl] δ -glutarolactone were isolated and identified on the basis of spectroscopic data including two-dimensional NMR, as components of olive oil mill waste-waters. The known aromatic compounds catechol, 4-hydroxybenzoic acid, protocatechuic acid, vanillic acid, 4-hydroxy- 3,5-dimethoxybenzoic acid, 4-hydroxyphenylacetic acid, 3,4-dihydroxyphenylacetic acid, tyrosol, hydroxytyrosol, 2-(4-hydroxy-3-methoxy)phenylethanol, 2-(3,4-dihydroxy)phenyl-1,2-ethandiol, p-coumaric acid, caffeic acid, ferulic acid, sinapic acid, 1-O-[2-(3,4-dihydroxy)phenylethyl]-(3,4-dihydroxy)phenyl-1,2-ethandiol, 1-O-[2-(4- hydroxy)phenylethyl]-(3,4-dihydroxy)phenyl-1,2-ethandiol, D(+)-erythro-1-(4-hydroxy-3-methoxy)-phenyl-1,2,3- propantriol, p-hydroxyphenethyl-β-D-glucopyranoside, 2(3,4-dihydroxyphenyl)ethanol 3β-D-glucopyranoside, and 2(3,4-dihydroxyphenyl)ethanol 4β-D-glucopyranoside were also confirmed as constituents of the waste-waters

Introducción de la teoría de la relatividad especial en el nivel medio/polimodal de enseñanza: identificación de teoremas-en-acto y determinación de objetivos-obstáculo

En este artículo se presenta un análisis de ciertas nociones que los alumnos del nivel medio/polimodal de Argentina poseen respecto de conceptos fundamentales de física clásica que son necesarios para una adecuada conceptualización de algunos de los aspectos más relevantes de la Teoría Especial de la Relatividad (TER). Los resultados parecen indicar que los alumnos del grupo estudiado no han conseguido desarrollar esquemas apropiados para abordar situaciones en donde estos conceptos aparecen. A partir de los invariantes considerados no adecuados, se han determinado objetivos-obstáculos que deberían ser superados por los alumnos, en el contexto del aula y con la mediación de una propuesta didáctica específica, para un aprendizaje significativo de la TERIn this work, we present an analysis of the representations that students, in high school/polimodal level in Argentina have about relevant classic concepts, necessaries for the understanding of the Special Relativity Theory (TER). The results seem to show that the analyzed students group has not developed appropriate schemas for them. From these incorrect conceptions, we try to determine some objectives – obstacles that should be pass over by the students, in classroom context with an specific didactic proposal for a significative learning of the TE

Modelos mentales y aprendizaje de física en electricidad y magnetismo

A study conducted under the framework of Johnson-Laird's mental model theory is described. The objective of such a study was an attempt to categorize introductory college physics students according to the type of mental representations --propositions, images, and models-- they used when solving problems and conceptual questions in electricity and magnetism. The basic features of each category are presented and several examples are given. At the end implications for research and instruction are discussed