{"id":3335,"date":"2014-06-03T00:00:49","date_gmt":"2014-06-02T22:00:49","guid":{"rendered":"https:\/\/www-new.ias.u-psud.fr\/?p=3335"},"modified":"2026-09-23T17:42:28","modified_gmt":"2026-09-23T15:42:28","slug":"chiral-micmoc-a-lorigine-de-lasymetrie-des-molecules-du-vivant-sur-terre","status":"publish","type":"post","link":"https:\/\/www.ias.u-psud.fr\/index.php\/2014\/06\/03\/chiral-micmoc-a-lorigine-de-lasymetrie-des-molecules-du-vivant-sur-terre\/","title":{"rendered":"Chiral-MICMOC : \u00e0 l\u2019origine de l\u2019asym\u00e9trie des mol\u00e9cules du vivant sur Terre ?"},"content":{"rendered":"\t\t<div data-elementor-type=\"wp-post\" data-elementor-id=\"3335\" class=\"elementor elementor-3335\" data-elementor-post-type=\"post\">\n\t\t\t\t<div class=\"elementor-element elementor-element-f4f600f e-flex e-con-boxed e-con e-parent\" data-id=\"f4f600f\" data-element_type=\"container\" data-e-type=\"container\">\n\t\t\t\t\t<div class=\"e-con-inner\">\n\t\t\t\t<div class=\"elementor-element elementor-element-63f7b05 elementor-widget elementor-widget-theme-post-title elementor-page-title elementor-widget-heading\" data-id=\"63f7b05\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"theme-post-title.default\">\n\t\t\t\t\t<h1 class=\"elementor-heading-title elementor-size-default\">Chiral-MICMOC : \u00e0 l\u2019origine de l\u2019asym\u00e9trie des mol\u00e9cules du vivant sur Terre ?<\/h1>\t\t\t\t<\/div>\n\t\t<div class=\"elementor-element elementor-element-9b7c05e e-con e-atomic-element e-flexbox-base e-9b7c05e-607ee4c \" data-id=\"9b7c05e\" data-element_type=\"e-flexbox\" data-e-type=\"e-flexbox\" data-interaction-id=\"9b7c05e\">\n    \t\t<div class=\"elementor-element elementor-element-d72e17c elementor-widget elementor-widget-text-editor\" data-id=\"d72e17c\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t\t\t\t\t\t<p>Les organismes vivants utilisent des acides amin\u00e9s chiraux pr\u00e9sentant uniquement la forme \u00e9nantiom\u00e9rique L pour la fabrication des prot\u00e9ines, une propri\u00e9t\u00e9 connue sous le nom d\u2019homochiralit\u00e9. L\u2019origine de cette asym\u00e9trie est \u00e0 ce jour encore mal connue mais il est g\u00e9n\u00e9ralement admis un processus en deux \u00e9tapes : tout d\u2019abord l\u2019apparition de faibles exc\u00e8s \u00e9nantiom\u00e9riques (e.e.s) dans un mat\u00e9riau organique chiral, suivi par un m\u00e9canisme d\u2019amplification menant \u00e0 la s\u00e9lection compl\u00e8te d\u2019un seul des deux \u00e9nantiom\u00e8res.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\n<\/div>\n\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t<div class=\"elementor-element elementor-element-5612ae1 e-flex e-con-boxed e-con e-parent\" data-id=\"5612ae1\" data-element_type=\"container\" data-e-type=\"container\">\n\t\t\t\t\t<div class=\"e-con-inner\">\n\t\t<div class=\"elementor-element elementor-element-8d2c731 e-con e-atomic-element e-flexbox-base e-8d2c731-bc6f834 \" data-id=\"8d2c731\" data-element_type=\"e-flexbox\" data-e-type=\"e-flexbox\" data-interaction-id=\"8d2c731\">\n    \t\t<div class=\"elementor-element elementor-element-10d0162 elementor-widget elementor-widget-text-editor\" data-id=\"10d0162\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t\t\t\t\t\t<p>L\u2019une des hypoth\u00e8ses privil\u00e9gi\u00e9es pour expliquer l\u2019apparition des e.e.s initiaux provient de l\u2019interaction de lumi\u00e8re circulairement polaris\u00e9e (CPL) avec la mati\u00e8re, introduisant ainsi l\u2019asym\u00e9trie initiale. Faisant suite aux r\u00e9sultats obtenus en 2011 sur un acide amin\u00e9 (l\u2019alanine), l\u2019exp\u00e9rience interdisciplinaire Chiral MICMOC (Mati\u00e8re Interstellaire et Com\u00e9taire, Mol\u00e9cules Organiques Complexes) de l\u2019\u00e9quipe \u00ab Astrochimie et Origines \u00bb de l\u2019IAS a obtenu de nouveaux r\u00e9sultats sur cette probl\u00e9matique en \u00e9largissant la mesure \u00e0 cinq acides amin\u00e9s qui montrent un comportement identique au rayonnement UV circulairement polaris\u00e9, ce qui permet ainsi de pr\u00e9ciser un possible sc\u00e9nario astrophysique \u00e0 l\u2019origine de l\u2019asym\u00e9trie biomol\u00e9culaire sur la Terre primitive.<\/p><p>Depuis 2003, l\u2019\u00e9quipe \u00ab Astrochimie et Origines \u00bb a mis en \u0153uvre une exp\u00e9rience de simulation de photochimie sur des analogues de glaces interstellaires avec la particularit\u00e9 d\u2019utiliser, pour effectuer cette photochimie, un faisceau de lumi\u00e8re \u00ab asym\u00e9trique \u00bb, c\u2019est-\u00e0-dire polaris\u00e9e circulairement, fournie par un rayonnement synchrotron. Un premier r\u00e9sultat avait permis d\u2019obtenir une s\u00e9lectivit\u00e9 \u00e9nantiom\u00e9rique sur un acide amin\u00e9 prot\u00e9ique, l\u2019alanine, sur la ligne DESIRS du synchrotron SOLEIL (Figure 1). Gr\u00e2ce aux performances de cette ligne, fournies par Laurent Nahon et son \u00e9quipe ainsi qu\u2019aux m\u00e9thodes analytiques de chromatographie en phase gazeuse multidimensionnelle coupl\u00e9es \u00e0 la spectrom\u00e9trie de masse (GCxGC-TOFMS) install\u00e9es et calibr\u00e9es par Uwe Meierhenrich et son \u00e9quipe \u00e0 l\u2019Universit\u00e9 de Nice (ICN, Nice), de nouveaux r\u00e9sultats marquants ont \u00e9t\u00e9 obtenus.<\/p><p>En effet, des exc\u00e8s \u00e9nantiom\u00e9riques de m\u00eame signe (Figure 2) ont \u00e9t\u00e9 mesur\u00e9s sur cinq acides amin\u00e9s : \u03b1-alanine, valine (prot\u00e9iques) ; acide 2,3-diaminopropionic, acide 2-aminobutyric et norvaline (non-prot\u00e9iques). Ces exc\u00e8s sont toujours faibles (inf\u00e9rieurs \u00e0 2%) mais comparables \u00e0 ceux observ\u00e9s dans certaines m\u00e9t\u00e9orites primitives et permettent de renforcer le sc\u00e9nario astrophysique menant \u00e0 la source d\u2019asym\u00e9trie n\u00e9cessaire \u00e0 la chimie pr\u00e9biotique pour d\u00e9clencher l\u2019apparition de l\u2019homochiralit\u00e9, une caract\u00e9ristique fondamentale du vivant. Le fait que ces cinq acides amin\u00e9s se comportent de fa\u00e7on identique (exc\u00e8s de m\u00eame signe) est par ailleurs fondamental pour la validit\u00e9 de l\u2019hypoth\u00e8se physique \u00e0 la base du sc\u00e9nario : l\u2019irradiation par UV-CPL de glaces inter\/circumstellaires menant non seulement \u00e0 la formation d\u2019acides amin\u00e9s mais \u00e9galement \u00e0 un certain degr\u00e9 d\u2019enrichissement \u00e9nantiom\u00e9rique.<\/p><p>Concernant l\u2019alanine, des exp\u00e9riences plus pouss\u00e9es ont \u00e9t\u00e9 r\u00e9alis\u00e9es dans lesquelles l\u2019h\u00e9licit\u00e9 (polarisation gauche et droite) ainsi que la longueur d\u2019onde (6.6 eV et 10.2 eV) des photons utilis\u00e9s ont \u00e9t\u00e9 chang\u00e9es. Un lien direct a \u00e9t\u00e9 observ\u00e9 entre ces param\u00e8tres et le signe des exc\u00e8s mesur\u00e9s, sugg\u00e9rant un effet de dichro\u00efsme circulaire \u00e0 l\u2019origine du ph\u00e9nom\u00e8ne. De plus, des exc\u00e8s de m\u00eame signe ont \u00e9t\u00e9 obtenus en irradiant uniquement les glaces ou uniquement le r\u00e9sidu organique obtenu \u00e0 temp\u00e9rature ambiante. Ce r\u00e9sultat indique tout d\u2019abord la formation d\u2019esp\u00e8ces chirales dans la phase glac\u00e9e, pr\u00e9curseurs des acides amin\u00e9s contenus dans le r\u00e9sidu organique final, esp\u00e8ces qui pourraient \u00eatre pr\u00e9sentes dans les nuages mol\u00e9culaires et se retrouver par la suite dans les corps parents des m\u00e9t\u00e9orites.<\/p><p>L\u2019application astrophysique repose sur un sc\u00e9nario plausible: d\u2019une part les analogues de glaces utilis\u00e9s en laboratoire sont de composition chimique proches de celle des glaces interstellaires\/circumstellaires. D\u2019autre part, des sources d\u2019UV-CPL intenses et donnant jusqu\u2019\u00e0 22% de taux de polarisation circulaire ont \u00e9t\u00e9 mises en \u00e9vidence dans des r\u00e9gions de formation d\u2019\u00e9toiles massives dans la n\u00e9buleuse d\u2019Orion et NGC 6334. L\u2019extension spatiale d\u2019une seule h\u00e9licit\u00e9 (droite ou gauche) est largement sup\u00e9rieure (d\u2019un facteur sup\u00e9rieur \u00e0 100) aux dimensions d\u2019un \u00ab syst\u00e8me solaire \u00bb en formation, ce qui permet d\u2019assurer effectivement un exc\u00e8s \u00e9nantiom\u00e9rique de m\u00eame forme sur des mol\u00e9cules organiques chirales, L dans le cas des acides amin\u00e9s, sur l\u2019ensemble de notre Syst\u00e8me Solaire.<\/p><p>Ce r\u00e9sultat d\u2019une exp\u00e9rience d\u2019astrophysique de laboratoire pourrait donc valider l\u2019hypoth\u00e8se ancienne selon laquelle la s\u00e9lection \u00e9nantiom\u00e9rique des mol\u00e9cules du \u00ab vivant \u00bb, constat\u00e9e en premier par Pasteur en 1848, proc\u00e8de d\u2019une origine physique d\u00e9terministe, par ailleurs discut\u00e9e par Pierre Curie en 1897.<\/p><p>Finalement, une des implications indirectes de ce r\u00e9sultat sugg\u00e8re que la n\u00e9buleuse solaire est vraisemblablement n\u00e9e dans une r\u00e9gion d\u2019\u00e9toiles massives. Cette id\u00e9e est envisag\u00e9e depuis trente ans et confort\u00e9e par la d\u00e9tection de radioactivit\u00e9s \u00e9teintes dans les m\u00e9t\u00e9orites primitives, cons\u00e9quence de l\u2019explosion d\u2019\u00e9toiles massives en supernovae.<\/p><p>Cette exp\u00e9rience se poursuit en prenant maintenant pour cible d\u2019autres mol\u00e9cules pr\u00e9biotiques importantes dont l\u2019homochiralit\u00e9 (D) biologique est \u00e0 l\u2019oppos\u00e9 de celle des acides amin\u00e9s (L) : les sucres.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\n<\/div>\n\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t<div class=\"elementor-element elementor-element-72b19574 e-con-full e-flex e-con e-parent\" data-id=\"72b19574\" data-element_type=\"container\" data-e-type=\"container\" data-settings=\"{&quot;background_background&quot;:&quot;classic&quot;}\">\n\t\t<div class=\"elementor-element elementor-element-53a7b892 e-con-full e-flex e-con e-child\" data-id=\"53a7b892\" data-element_type=\"container\" data-e-type=\"container\">\n\t\t\t\t<div class=\"elementor-element elementor-element-13a0d604 elementor-invisible elementor-widget elementor-widget-heading\" data-id=\"13a0d604\" data-element_type=\"widget\" data-e-type=\"widget\" data-settings=\"{&quot;_animation&quot;:&quot;fadeIn&quot;}\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<h2 class=\"elementor-heading-title elementor-size-default\">Contacts<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-3108905 elementor-invisible elementor-widget elementor-widget-heading\" data-id=\"3108905\" data-element_type=\"widget\" data-e-type=\"widget\" data-settings=\"{&quot;_animation&quot;:&quot;fadeIn&quot;}\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<h2 class=\"elementor-heading-title elementor-size-default\">R\u00e9f\u00e9rents (scientifiques et techniques) <\/h2>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-1c63b2a5 elementor-widget elementor-widget-text-editor\" data-id=\"1c63b2a5\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t\t\t\t\t\t<p>Pour tout renseignement compl\u00e9mentaire : Louis Le Sergeant d\u2019Hendecourt, ldh @ ias.u-psud.fr<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t<div class=\"elementor-element elementor-element-fadb250 e-con-full e-flex e-con e-child\" data-id=\"fadb250\" data-element_type=\"container\" data-e-type=\"container\">\n\t\t\t\t<div class=\"elementor-element elementor-element-5640f83 elementor-invisible elementor-widget elementor-widget-heading\" data-id=\"5640f83\" data-element_type=\"widget\" data-e-type=\"widget\" data-settings=\"{&quot;_animation&quot;:&quot;fadeIn&quot;}\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<h2 class=\"elementor-heading-title elementor-size-default\">R\u00e9f\u00e9rences<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-f6323b3 elementor-widget elementor-widget-text-editor\" data-id=\"f6323b3\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t\t\t\t\t\t<p>Modica, P. et al, ApJ 788, 79 (2014)<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t","protected":false},"excerpt":{"rendered":"<p>Les organismes vivants utilisent des acides amin\u00e9s chiraux pr\u00e9sentant uniquement la forme \u00e9nantiom\u00e9rique L pour la fabrication des prot\u00e9ines,<\/p>\n","protected":false},"author":3,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"elementor_header_footer","format":"standard","meta":{"inline_featured_image":false,"site-sidebar-layout":"default","site-content-layout":"","ast-site-content-layout":"default","site-content-style":"default","site-sidebar-style":"default","ast-global-header-display":"","ast-banner-title-visibility":"","ast-main-header-display":"","ast-hfb-above-header-display":"","ast-hfb-below-header-display":"","ast-hfb-mobile-header-display":"","site-post-title":"","ast-breadcrumbs-content":"","ast-featured-img":"","footer-sml-layout":"","ast-disable-related-posts":"","theme-transparent-header-meta":"","adv-header-id-meta":"","stick-header-meta":"","header-above-stick-meta":"","header-main-stick-meta":"","header-below-stick-meta":"","astra-migrate-meta-layouts":"default","ast-page-background-enabled":"default","ast-page-background-meta":{"desktop":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center 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