julio 7

The chemistry of an avocado

Anyone who’s ever purchased an avocado will testify that, after taking several days to reach the point of perfect ripeness, they remain at that point for an incredibly short amount of time before morphing into a brown, sludgy mess. As if to confound this problem, if you do catch them at the optimum ripeness, they turn brown incredibly quickly after being cut open if not eaten straight away. As always, there are chemical processes at work that are to blame for this occurrence.

The flesh of avocados is made up of mainly fatty acids, such as oleic acid and linoleic acid. They contain very little sugar or starch. Avocados don’t start to ripen until they are picked from the tree, and if you put them into the fridge whilst still unripe, it can prevent them from ripening at all. Putting into the fridge once they have reached the point of ripeness, however, can prolong the time at which they stay at this point for several days.

The rapid browning of avocado flesh is a consequence of its exposure to oxygen in the air, as well as the presence of phenolic compounds in the avocado itself. In the presence of oxygen, an enzyme avocados contain, called polyphenol oxidase, aids the conversion of phenolic compounds to another class of compounds, quinones. Quinones are capable of polymerising, taking the smaller molecules and joining them together to form a long chain, to produce polymers called polyphenols. This polymerisation manifests itself as a brown colouration to the flesh. The browning doesn’t happen in the intact avocado, not only because the flesh isn’t exposed to oxygen, but because the phenolic compounds are stored in the vacuole of the plant cells, whilst the enzymes are found in the surrounding cytoplasm. So, both damage to these cell structures and exposure to oxygen is required for browning to occur.

This browning isn’t unique to avocados – the browning of many other fruits, such as apples, is also a consequence of this reaction. For the fruit, it’s not a purely aesthetic process. Quinones are compounds that are toxic to bacteria, so their creation from phenolic compounds serves a practical purpose for the fruit by enabling it to last a little longer after exposure to oxygen before beginning to rot.  

Browning of avocados can be prevented in several ways. One of the most effective is to rub lemon juice on the exposed flesh of the fruit. The enzymes which enable the enzymatic browning reactions to occur are sensitive to acidic conditions, and work much slower in them. Another option is covering the avocado flesh tightly in cling-film. This prevents oxygen from reaching the flesh, and thus browning cannot take place. Chilling the avocado in the fridge can also slow down the enzymes to an extent, as their activity is lower at lower temperatures. The commonly touted method of leaving the seed pit in the avocado to prevent browning does work – but only on the part of the avocado that it’s shielding from oxygen. Exposed areas of the flesh will still turn brown in time.

One final fact about avocados that I feel compelled to include here doesn’t actually have anything to do with chemistry, but with the fruit’s name. The Aztecs named the trees it grew on ‘āhuacacuahuitl’. The Aztec word for avocado was also used euphemistically for ‘testicle’ – so one reading of the tree’s name is ‘testicle tree’. Arguably, not the absolutely linguistically correct reading, but it’s a great fact to unsettle your fellow diners with.

 

FUENTE https://www.compoundchem.com/2014/08/03/why-do-avocados-turn-brown-the-chemistry-of-avocados/

Categoría: Biología, biology, Ciencias, Infografías | DEJA UN COMENTARIO
noviembre 3

Los gases y las medidas

Los gases y las disoluciones (enlaces)

FÍSICA Y QUÍMICA – 3º ESO
Unidad 2: Los gases y las disoluciones
Unidades didácticas:
Enlaces:
Ejercicios resueltos o con solución:
Ejercicios de Educamix:
Categoría: Física, Preguntas, química, questions, recursos, science | DEJA UN COMENTARIO
abril 15

Euorpean Union protect the biodiversity

To know more about this topic you can explore the following references:

 

EU Biodiversity Strategy 2030: https://ec.europa.eu/environment/nature/biodiversity/strategy/index_en.htm

EU Environment & Legislation: https://ec.europa.eu/environment/nature/legislation/habitatsdirective/index_en.htm

EU Knowledge Center for Biodiversity:

https://knowledge4policy.ec.europa.eu/biodiversity_en

https://www.iucn.org/news/world-commission-protected-areas/202005/conserving-nature-a-time-crisis-protected-areas-and-covid-19

EU Soil Observatory: https://ec.europa.eu/jrc/en/eu-soil-observatory

EU Parliament: https://www.europarl.europa.eu/news/en/headlines/society/20200109STO69929/biodiversity-loss-what-is-causing-it-and-why-is-it-a-concern

European Environmental Agency: https://www.eea.europa.eu/themes/biodiversity

Global Soil Biodiversity Atlas: https://esdac.jrc.ec.europa.eu/content/global-soil-biodiversity-atlas

IPBES: https://ipbes.net/global-assessment

IUCN: European Red List of endangered species:

https://www.iucn.org/regions/europe/our-work/species/european-red-list-threatened-species

https://www.europarl.europa.eu/news/en/headlines/society/20200519STO79424/endangered-species-in-europe-facts-and-figures-infographic

IUCN News: https://www.iucn.org/news/world-commission-protected-areas/202005/conserving-nature-a-time-crisis-protected-areas-and-covid-19

LIFE Programme: https://ec.europa.eu/easme/en/life

NATURA 2000 Network: https://ec.europa.eu/environment/nature/natura2000/index_en.htm

Nature and Biodiversity: https://ec.europa.eu/environment/nature/index_en.htm

EU Forest Strategy for 2030 – 3 Billion Trees: https://forest.eea.europa.eu/3-billion-trees/introduction

 

 

Categoría: Biología, biology, Ciencias, organización, Plantas, Preguntas, recursos, science, seres vivos, Videos | DEJA UN COMENTARIO
abril 3

Paneles solares.

 

 

https://acs-h.assetsadobe.com/is/image//content/dam/cen/100/11/WEB/10011-feature4-graphic.jpg/?$responsive$&wid=700&qlt=90,0&resMode=sharp2

 

Bourzac, Katherine. “Polymer Solar Cell espera reclamar un nuevo récord“. C&EN, 23 de mayo de 2018.

Desjardins, Jeff. “Animación: Cómo funcionan los paneles solares“. Visual Capitalist, 31 de enero de 2017.

Jacoby, Mitch. “Estabilización de células solares de perovskita“. C&EN, 14 de octubre de 2018.

Instituto Fraunhofer de Sistemas de Energía Solar ISE. Informe fotovoltaico. (Friburgo: Instituto Fraunhofer para Sistemas de Energía Solar ISE, 24 de febrero de 2022).

Una colaboración entre C&EN y Andy Brunning, autor del popular blog de gráficos Compound Interest

Para ver más del trabajo de Brunning, vaya a compoundchem.com. Para ver todos los gráficos periódicos de C&EN, visite http://cenm.ag/periodicgraphics.

Fuente Gráficos periódicos: ¿Cómo funcionan los paneles solares? (acs.org)

Categoría: Física, Infografías, química, questions, recursos, science | DEJA UN COMENTARIO
marzo 29

Crocus chemistry: Saffron, colours, and poisonous imposters

Did you know that saffron is obtained from a type of crocus? This is a fact that had somehow escaped me, and which I only discovered when wondering why saffron contains a compound called ‘crocin’. Turns out that, yes, there is a connection!

While the idea for this infographic was prompted by the eruption of crocuses currently taking place in our garden, these are Crocus vernus, the spring crocus. The crocus from which saffron is obtained is commonly called the saffron crocus, or sometimes the autumn crocus (more on that alternative later). As the latter name suggests, the saffron crocus, Crocus sativus, flowers in the autumn.

Saffron is obtained from the crocus stigmas, three deep red tendrils protruding from the centre of each flower. It takes a colossal 150 crocus flowers to produce a single gram of dried saffron, which goes a long way towards explaining why it’s the most expensive spice on supermarket shelves. Saffron’s deep red colour is due to the presence of crocin, a compound derived from the carotenoid compound crocetin. Crocin and related compounds are found in other crocuses, too, contributing to the range of yellows and oranges.

The purples and lilacs of crocus petals are due to a different group of compounds: anthocyanins. Researchers have identified nine key anthocyanin compounds as contributing to crocus colour, mainly glucosides of delphinidin and petunidin. They also identified some malonated anthocyanins which appear to be completely unique to crocuses.

While the crocus from which saffron is derived is sometimes referred to as “autumn crocus”, this moniker has the potential for deadly confusion. “Autumn crocus” is also commonly used as a name for several species in the Colchicum genus. These plants can look very similar to the saffron crocus, and also flower during the autumn, but you definitely don’t want to harvest any parts of them – all parts of the plant contain the toxic alkaloid colchicine.

Justin Brower over at Nature’s Poisons has a great post on colchicine, where he goes into the mechanism behind its toxicity:

Colchicine has two modes of action in the body.  In the first, colchicine inhibits neutrophil activity.  These are a type of white blood cell that kicks into gear during an immune response, causing inflammation.  […] The second mode of action is by binding to tubulin, which in turn inhibits mitosis […] the process in the cell cycle in which the chromosomes are split into two identical daughter cells.  We need mitosis for growth and replacement.

Colchicine: Don’t Eat the Crocus – Nature’s Poisons

Eating colchicine can lead to all manner of unpleasant symptoms, and more seriously can result in multiple organ failure and death. In short, you really don’t want to get autumn crocuses confused.

Despite its toxicity, colchicine has also been used as a treatment for gout due to its anti-inflammatory properties – usually when patients can’t take more standard anti-inflammatory painkillers. It’s another classic case of the dose making the poison, albeit one where there’s not a huge degree of difference: the dose required for therapeutic effects is not hugely distant from the dose at which toxicity is seen.

The good news is that true crocuses don’t contain colchicine. While eating bits of them still isn’t recommended – they still contain other compounds which, though they may not kill you, are still more than capable of kicking off unpleasant symptoms – saffron itself is safe to eat. Considering how many crocus plants it takes to make it, you’re probably still best off buying it at the supermarket.

The graphic in this article is licensed under a  Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License. See the site’s content usage guidelines.

Información obtenida  de https://www.compoundchem.com/2022/03/15/crocus/

Categoría: biology, Ciencias, Infografías, Plantas, química, recursos, science | DEJA UN COMENTARIO
marzo 25

What common stimulants do we get from plants? – in C&EN

 

 

To download a pdf of this article, visit http://cenm.ag/stimulants.

References used to create this graphic:

Oliver-Bever, B. “Why Do Plants Produce Drugs? Which Is Their Function in the Plants?” Q. J. Crude Drug Res. (1970). DOI: 10.3109/13880207009066221.

Spinella, Marcello. The Psychopharmacology of Herbal Medicine: Plant Drugs That Alter Mind, Brain, and Behavior. Cambridge, MA: MIT Press, 2001.

Wiart, Christophe. “Plants Affecting the Central Nervous System.” In Ethnopharmacology of Medicinal Plants: Asia and the Pacific, 57–153. Totowa, NJ: Humana Press, 2006.

A collaboration between C&EN and Andy Brunning, author of the popular graphics blog Compound Interest

Categoría: Infografías, Preguntas, química, questions, recursos, science, seres vivos | DEJA UN COMENTARIO
marzo 21

How do plant milks compare to cow’s milk?

For plant milk manufacturers, business is booming. In 2021, 32% of British people surveyed drank plant-based milk as part of their diet, compared to 25% in 2020. How are these milks made, and how do they compare to cow’s milk when it comes to their environmental impact and nutritional value? This graphic takes a look.

The graphic in this article is licensed under a  Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License. See the site’s content usage guidelines.

Información sacada de https://www.compoundchem.com/2022/01/11/plant-milk/

Categoría: biology, Ciencias, Infografías, química, recursos, science, seres vivos | DEJA UN COMENTARIO
marzo 20

The year in chemistry 2021

 

 

 

https://i0.wp.com/www.compoundchem.com/wp-content/uploads/2022/01/Chemistry-News-2021-Year-in-Review-v2.png?ssl=1

In 2020, science news was dominated by COVID and vaccine development. In many ways, 2021 has been little different, but away from the virus we’re now overly familiar with there were plenty of other chemistry-related news stories. This graphic highlights a selection of them – see below for more details as well as links to related articles and studies.

  1. Development of antivirals for COVID-19
    2021’s undoubted success story was the rollout of vaccines which brought us back to some semblance of normality. But development and trials of antivirals against COVID-19 also continued apace. A significant story was that of Molnupiravir, an antiviral pill initially hailed as a potent weapon against the disease. While full trial data has shown a lower effectiveness for Molnupiravir which has tempered some of the initial enthusiasm, it may still be beneficial. Another drug, Paxlovid, has been recently approved in the USA and UK and showed 89% efficacy in patients at risk of serious illness. However, producing sufficient Paxlovid to meet demand is likely to pose a challenge.
  2. Highly fluorinated compound restrictions
    Concerns around the use of per- and polyfluoroalkyl substances (commonly referred to as PFAS) have been growing over the past few years, particularly in relation to their potential toxicity and persistence in the environment. Their strong carbon-fluorine bonds resist being broken down by most means. In July, the US state of Maine became the first government to ban the use of PFAS where alternatives are available, and the EU also took steps towards potential future restrictions.
  3. Asymmetric organocatalysis wins chemistry Nobel Prize
    The Nobel Prize in Chemistry was awarded to Benjamin List and David MacMillan for developing asymmetric organocatalysis, which uses organic compounds to catalyse the creation of mirror image molecules.
  4. Use of leaded fuel finally phased out worldwide
    Leaded petrol, invented in 1921, was finally phased out 100 years later. Though its sale has been banned in many countries for some time, in July, Algeria became the last country in the world to halt sale of leaded petrol. The lead from leaded petrol will still be with us for some time, however; a study in June this year found that airborne particles in London still have  

    much higher levels of lead than the usual background level, 22 years after leaded petrol was banned in the UK.
  5. Amine catalysis claim debunked
    Early in the year, the chemistry world was abuzz with the publication of a study claiming that a carbon-carbon bond-forming reaction could be catalysed by an amine compound, instead of the usual expensive palladium catalyst. By the end of the year, however, the claims had been conclusively debunked. The observed catalytic activity was not, in fact, due to the amine, but due to the accidental creation of a palladium complex during the preparation of the amine.
  6. AI predicts protein structures
    AlphaFold, an AI tool produced by DeepMind (itself part of the the same company as Google) this year produced predicted protein structures for the nearly 20,000 proteins made by the human body. Proteins are built up from amino acids, and while determining the sequence of amino acids is relatively straightforward, predicting how the resultant protein chain arranges itself in 3D space is much more challenging. The structures have been made available for free online, and could give insights into protein function, as well a offering potential new targets for drug design.
  7. First malaria vaccine approved
    In October, the World Health Organisation approved the first vaccine for malaria in children. As well as being the first vaccine for malaria, it’s the first vaccine to be approved for any parasitic disease. The vaccine’s effectiveness is modest – it requires four doses, and prevents 30% of severe malaria cases in children under 5 – but it’s still estimated it could prevent the deaths of 23,000 children every year.
  8. Researchers create metallic water
    By dripping a liquid sodium-potassium alloy into a vacuum chamber containing small amounts of water vapour, researchers were able to observe metallic water, formed as electrons from the alloy were drawn into the water. Previously, metallic water’s existence had been theorised to occur only at extremely high pressures.
  9. Making jet fuel from captured carbon dioxide
    In November, details of a rooftop refinery which can convert carbon dioxide and water vapour from the air into jet fuel were published. The reactor uses a solar-powered redox reactor to reduce the carbon dioxide and water vapour to carbon monoxide and hydrogen, from which hydrocarbon fuels can be made. Commercialisation is planned, though an area a little larger than Switzerland would be required to meet current global aviation fuel demands.
  10. Controversial Alzheimer’s drug approved
    You might have thought that the first new approval of a drug for Alzheimer’s disease in 20 years might be a cause for fanfare. However, the drug in question, Aduhelm, which reduces amyloid-β plaques in the brain, has been met with scepticism about its effectiveness and cost – and questions remain over whether it slows cognitive decline. Despite its approval in the USA back in June, uptake of the drug has so far been limited.
  11. Skin oil changes identify Parkinson’s
    Several years ago, Joy Milne was dubbed “the woman who can smell Parkinson’s” after detecting a change in her husband’s smell years before he was diagnosed with the condition, and subsequently detecting a similar smell from other Parkinson’s sufferers. This year, research published in March identified 10 skin lipids that differed significantly between those with Parkinson’s and those without. It could help with diagnosis and monitoring the progression of the disease in sufferers.
  12. Home weed killers phase out glyphosate
    Glyphosate herbicides won’t be sold for home use in the US from 2023. The move follows concern about glyphosate’s effects on health, though the company that sells it, Bayer, says it’s primarily to avoid litigation. Glyphosate’s agricultural use will continue.

The graphic in this article is licensed under a  Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License. See the site’s content usage guidelines.

Informacion de https://www.compoundchem.com/2021/12/30/tyic2021/

Categoría: experimentos., Infografías, química, questions, recursos, science | DEJA UN COMENTARIO
enero 14

Lo más leído en SINC en 2021: vacunas y covid se apropian del ranking

El coronavirus y sus vacunas vuelven a copar por segundo año consecutivo la lista de nuestros contenidos con más clics, aunque también hay espacio para el descubrimiento de nuevas especies, enigmas paleontológicos y, cómo no, misterios del universo.

Portadas de las noticias más leídas este año. / SINC

Se acaba 2021 y, como no podía ser de otra manera, las noticias relacionadas con el virus, la enfermedad, y las medidas de protección están muy presentes en la lista de los contenidos más leídos en la web de SINC durante este segundo año en pandemia.

Hemos visto cómo se han aprobado diversas vacunas y a lo largo de 12 intensos meses se ha inmunizado a la mayor parte de la población europea, en la campaña de vacunación masiva más grande de la historia.

Comprobada su efectividad, con las vacunas han aparecido dudas —y algunos efectos secundarios— y la información relacionada con ellos ha captado el interés de nuestros lectores.

A pesar de la avalancha informativa que ha generado la covid-19 durante este año, también ha quedado espacio para otras noticias de ciencia, como la descripción de un nuevo carnívoro extinto,  una entrevista al divulgador Marcus Chown, o un enigma paleontológico que relaciona a tres uros con una mujer de hace 9.000 años.

1. El tiempo que ha de pasar entre una vacuna y otra

La mayoría de vacunas aprobadas contra la covid-19 requieren de varias dosis. En junio se estableció el lapso de tiempo ideal entre dosis para cada vacuna y ha sido lo más leído de SINC durante este año.

2. La efectividad de la vacuna de Pfizer/BioNtech

La noticia de que la vacuna de la farmacéutica germano-estadounidense era igual de efectiva —un 95 %— en la vida real que en los ensayos provocó una lluvia de clics en nuestra web, hasta situarla entre lo más leído de 2021.

Poco a poco, empezábamos a ganarle terreno a la enfermedad.

3. El virus no desaparecerá de nuestras vidas

“Este virus ha venido para quedarse, vamos a seguir conviviendo con él”, aseguraba en abril la viróloga del CNB-CSIC, Sonia Zúñiga, en otro de los artículos más leídos de 2021.

La comunidad científica está de acuerdo: el SARS-CoV-2 se convertirá en un virus respiratorio endémico —como la gripe estacional— y cuantas más personas estemos vacunadas, menos estragos causará.

4. Datos mal presentados generan confusión

El epidemiólogo Salvador Peiró explica en esta magnífica tribuna la importancia de una adecuada presentación en los medios de los datos de hospitalización, ingresos en UCI, o fallecimientos en personas vacunadas (o no vacunadas).

Nuestros lectores la han colocado entre las más leídas de este año, a pesar de haber sido publicada a principios de diciembre.

5. ¿La vacuna provoca irregularidades en el ciclo menstrual?

En agosto, la Agencia Europea de Medicamentos (EMA) reportó casos de trastornos menstruales tras la vacunación, un hecho que no estaba contemplado en los prospectos de ninguna de las vacunas aprobadas contra la covid-19.

Entre lo más leído de SINC se encuentra esta tribuna donde la ginecóloga del ISCIII Olga Ocón, denunciaba que el problema pasó inadvertido durante los ensayos debido a una falta de perspectiva de género en la metodología científica.

Las vacunas y el virus han copado casi todos los puestos del ranking. / Pixabay

6. Gripe española y covid: diferencias y semejanzas

“El nacimiento y la evolución de la covid-19 se entiende mejor desde el conocimiento de la pandemia de gripe española, de la de Hong Kong, de la rusa y del resto de pandemias víricas del siglo XX”, subrayaba Anton Erkoreta, director del Museo Vasco de Historia de la Medicina en esta interesante entrevista de nuestro compañero Enrique Sacristán, una de las más leídas de 2021.

7. AstraZeneca previene la enfermedad grave

Al ir avanzando el proceso de vacunación, también saltaron a la palestra algunos resultados inesperados, como que la vacuna de Oxford/AstraZeneca mantenía su efectividad hasta 90 días después de la primera dosis.

También se confirmó que el fármaco prevenía por completo la enfermedad grave. Esta noticia de Jesús Méndez, publicada en febrero de este año, también se encuentra entre lo más visitado por los lectores de SINC.

8. ¿Afecta la vacunación a la fertilidad?

Otra de las preocupaciones de este 2021 se vio reflejada en la cantidad de visitas que ha recibido esta tribuna del ginecólogo y obstetra Daniel Mataró.

En julio de este año, Mataró recopilaba toda la información disponible sobre cómo afecta el virus, o la vacunación, a la fertilidad. La conclusión: vacunarse no afecta a la salud reproductiva.

9. Un nuevo carnívoro descrito en Batallones

Casi 30 años después de su descubrimiento, el complejo de yacimientos de Cerro de los Batallones, al sur de Madrid, sigue deparando gratas sorpresas.

En junio se reportaba el hallazgo de una nueva especie de carnívoro que vivió hace 9 millones de años en este lugar, Ammitocyon kainos, perteneciente a la extinta familia de los anficiónidos —popularmente conocidos como `perros-oso’— y sin equivalente actual.

10. Momentos `mágicos´ que cambiaron la historia de la ciencia

Esta entrevista de Enrique al escritor y divulgador británico Marcus Chown se encuentra entre lo más leído de 2021.

En ella se habla del poder de las matemáticas para predecir y describir fenómenos físicos de toda índole: desde la gravedad al bosón de Higgs; pasando por el neutrino, las ondas gravitacionales, o el descubrimiento del planeta Neptuno.

11. Trombos

Tras la llegada de las vacunas a la población general, se reportaron raros cuadros de trombosis posterior a la administración que incluso hicieron que Estados Unidos pausara el uso de la vacuna monodosis Janssen.

Este reportaje de nuestro colaborador Sergio Ferrer se encuentra entre lo más visitado por los lectores de SINC durante este año 2021.

En resumen: tanto la trombosis como la trombocitopenia son fenómenos muy raros, y los beneficios de la vacunación superan ampliamente a los costes.

12. Un enigma paleontológico

La secuenciación del genoma mitocondrial de tres uros —antepasados extintos de las vacas— de hace 9.000 años encontrados junto a los restos de una mujer en la cueva gallega de Chan do Lindeiro (Lugo) abría un enigma paleontológico: ¿Por qué los animales iban con ella, si aún no se había domesticado el ganado?

Esta noticia, que cierra nuestra selección particular, la contaba nuestra compañera Eva Rodríguez.

Fuente: SINC
Derechos: Creative Commons.
Categoría: organización, Preguntas, questions | DEJA UN COMENTARIO