{"id":5195,"date":"2025-02-12T10:38:43","date_gmt":"2025-02-12T09:38:43","guid":{"rendered":"https:\/\/spgoo.org\/?p=5195"},"modified":"2025-03-01T15:18:29","modified_gmt":"2025-03-01T14:18:29","slug":"simplification-de-la-recherche-des-pka-dune-molecule-donnee","status":"publish","type":"post","link":"https:\/\/spgoo.org\/?p=5195","title":{"rendered":"Simplification de la recherche des pKa d&#8217;une mol\u00e9cule donn\u00e9e."},"content":{"rendered":"\n<p>Par Pascal KREZEL, ICOA, le 12\/02\/2025<\/p>\n\n\n\n<p>Les mod\u00e8les actuels de pr\u00e9diction de pKa cherchent \u00e0 d\u00e9finir un pKa pour tous les sites d&#8217;une mol\u00e9cule. Or exp\u00e9rimentalement, une mol\u00e9cule poss\u00e8de moins de pKa que de fonctions acido-basiques.  L&#8217;exemple suivant illustre ce probl\u00e8me. Dans SAMPL6 pKa Challenge, on trouve par exemple la mol\u00e9cule suivante avec 2 pKa.<\/p>\n\n\n\n<figure class=\"wp-block-image size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"753\" height=\"318\" src=\"https:\/\/spgoo.org\/wp-content\/uploads\/2025\/02\/image-80.png\" alt=\"\" class=\"wp-image-5196\" srcset=\"https:\/\/spgoo.org\/wp-content\/uploads\/2025\/02\/image-80.png 753w, https:\/\/spgoo.org\/wp-content\/uploads\/2025\/02\/image-80-300x127.png 300w\" sizes=\"auto, (max-width: 753px) 100vw, 753px\" \/><\/figure>\n\n\n\n<p>Si on demande \u00e0 molGpKa, une pr\u00e9diction des pKa, sa r\u00e9ponse est la suivante:<\/p>\n\n\n\n<figure class=\"wp-block-image size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"572\" height=\"191\" src=\"https:\/\/spgoo.org\/wp-content\/uploads\/2025\/02\/image-81.png\" alt=\"\" class=\"wp-image-5197\" srcset=\"https:\/\/spgoo.org\/wp-content\/uploads\/2025\/02\/image-81.png 572w, https:\/\/spgoo.org\/wp-content\/uploads\/2025\/02\/image-81-300x100.png 300w\" sizes=\"auto, (max-width: 572px) 100vw, 572px\" \/><\/figure>\n\n\n\n<figure class=\"wp-block-image size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"572\" height=\"191\" src=\"https:\/\/spgoo.org\/wp-content\/uploads\/2025\/02\/image-82.png\" alt=\"\" class=\"wp-image-5198\" srcset=\"https:\/\/spgoo.org\/wp-content\/uploads\/2025\/02\/image-82.png 572w, https:\/\/spgoo.org\/wp-content\/uploads\/2025\/02\/image-82-300x100.png 300w\" sizes=\"auto, (max-width: 572px) 100vw, 572px\" \/><\/figure>\n\n\n\n<figure class=\"wp-block-image size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"572\" height=\"191\" src=\"https:\/\/spgoo.org\/wp-content\/uploads\/2025\/02\/image-83.png\" alt=\"\" class=\"wp-image-5199\" srcset=\"https:\/\/spgoo.org\/wp-content\/uploads\/2025\/02\/image-83.png 572w, https:\/\/spgoo.org\/wp-content\/uploads\/2025\/02\/image-83-300x100.png 300w\" sizes=\"auto, (max-width: 572px) 100vw, 572px\" \/><\/figure>\n\n\n\n<figure class=\"wp-block-image size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"572\" height=\"191\" src=\"https:\/\/spgoo.org\/wp-content\/uploads\/2025\/02\/image-84.png\" alt=\"\" class=\"wp-image-5200\" srcset=\"https:\/\/spgoo.org\/wp-content\/uploads\/2025\/02\/image-84.png 572w, https:\/\/spgoo.org\/wp-content\/uploads\/2025\/02\/image-84-300x100.png 300w\" sizes=\"auto, (max-width: 572px) 100vw, 572px\" \/><\/figure>\n\n\n\n<p>MolGpKa pr\u00e9dit donc 4 pKa.<\/p>\n\n\n\n<p>Pour essayer de r\u00e9soudre ce probl\u00e8me, nous proposons une nouvelle m\u00e9thode passant par la pr\u00e9diction d&#8217;une seule valeur, la charge moyenne \u00e0 un pH donn\u00e9.<\/p>\n\n\n\n<p>Soit le cas extr\u00eame d&#8217;une mol\u00e9cule poss\u00e9dant 4 pKa dont il faut pr\u00e9dire les valeurs. Supposons qu&#8217;elle ait 2 fonctions acides et 2 fonctions basiques soit les \u00e9quilibres suivants:<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter size-full is-resized\"><img loading=\"lazy\" decoding=\"async\" width=\"463\" height=\"239\" src=\"https:\/\/spgoo.org\/wp-content\/uploads\/2025\/02\/image-85.png\" alt=\"\" class=\"wp-image-5201\" style=\"width:459px;height:auto\" srcset=\"https:\/\/spgoo.org\/wp-content\/uploads\/2025\/02\/image-85.png 463w, https:\/\/spgoo.org\/wp-content\/uploads\/2025\/02\/image-85-300x155.png 300w\" sizes=\"auto, (max-width: 463px) 100vw, 463px\" \/><\/figure>\n<\/div>\n\n\n<p>A pH fix\u00e9, on a les \u00e9quations suivantes:<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"643\" height=\"329\" src=\"https:\/\/spgoo.org\/wp-content\/uploads\/2025\/02\/image-86.png\" alt=\"\" class=\"wp-image-5202\" srcset=\"https:\/\/spgoo.org\/wp-content\/uploads\/2025\/02\/image-86.png 643w, https:\/\/spgoo.org\/wp-content\/uploads\/2025\/02\/image-86-300x153.png 300w\" sizes=\"auto, (max-width: 643px) 100vw, 643px\" \/><\/figure>\n<\/div>\n\n\n<p>Ceci nous permet d&#8217;en d\u00e9duire la charge moyenne \u00e0 un pH donn\u00e9:<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"775\" height=\"174\" src=\"https:\/\/spgoo.org\/wp-content\/uploads\/2025\/02\/image-88.png\" alt=\"\" class=\"wp-image-5204\" srcset=\"https:\/\/spgoo.org\/wp-content\/uploads\/2025\/02\/image-88.png 775w, https:\/\/spgoo.org\/wp-content\/uploads\/2025\/02\/image-88-300x67.png 300w, https:\/\/spgoo.org\/wp-content\/uploads\/2025\/02\/image-88-768x172.png 768w\" sizes=\"auto, (max-width: 775px) 100vw, 775px\" \/><\/figure>\n<\/div>\n\n\n<p>On en d\u00e9duit une valeur de Ch d\u00e9pendant uniquement de h et de C, la concentration totale.<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"865\" height=\"231\" src=\"https:\/\/spgoo.org\/wp-content\/uploads\/2025\/02\/image-89.png\" alt=\"\" class=\"wp-image-5205\" srcset=\"https:\/\/spgoo.org\/wp-content\/uploads\/2025\/02\/image-89.png 865w, https:\/\/spgoo.org\/wp-content\/uploads\/2025\/02\/image-89-300x80.png 300w, https:\/\/spgoo.org\/wp-content\/uploads\/2025\/02\/image-89-768x205.png 768w\" sizes=\"auto, (max-width: 865px) 100vw, 865px\" \/><\/figure>\n<\/div>\n\n\n<p>Finalement en fixant C \u00e0 1M, avec 4 valeurs de Ch pour diff\u00e9rentes valeurs de pH, il est possible d&#8217;en d\u00e9duire la valeur des diff\u00e9rents Ka.<\/p>\n\n\n\n<p>Si le syst\u00e8me ne poss\u00e8de pas de solutions approximatives ou si les valeurs de Ka ne sont pas sont aberrantes, il faut en d\u00e9duire que l&#8217;hypoth\u00e8se des 2 fonctions acides et des 2 fonctions basiques \u00e9tait fausse et en prendre une autre.<\/p>\n\n\n\n<p>Ainsi, en faisant au moins 4 mod\u00e8les de pr\u00e9diction de Ch pour diff\u00e9rentes valeurs de pH, on doit \u00eatre en mesure d&#8217;en d\u00e9duire les diff\u00e9rents pKa d&#8217;une mol\u00e9cule ayant au plus 4 pKa.<\/p>\n\n\n\n<p><\/p>\n","protected":false},"excerpt":{"rendered":"<p>Par Pascal KREZEL, ICOA, le 12\/02\/2025 Les mod\u00e8les actuels de pr\u00e9diction de pKa cherchent \u00e0 d\u00e9finir un pKa pour tous les sites d&#8217;une mol\u00e9cule. Or exp\u00e9rimentalement, une mol\u00e9cule poss\u00e8de moins de pKa que de fonctions acido-basiques. L&#8217;exemple suivant illustre ce probl\u00e8me. Dans SAMPL6 pKa Challenge, on trouve par exemple la mol\u00e9cule suivante avec 2 pKa. [&hellip;]<\/p>\n","protected":false},"author":4,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-5195","post","type-post","status-publish","format-standard","hentry","category-non-classe"],"_links":{"self":[{"href":"https:\/\/spgoo.org\/index.php?rest_route=\/wp\/v2\/posts\/5195","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/spgoo.org\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/spgoo.org\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/spgoo.org\/index.php?rest_route=\/wp\/v2\/users\/4"}],"replies":[{"embeddable":true,"href":"https:\/\/spgoo.org\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=5195"}],"version-history":[{"count":2,"href":"https:\/\/spgoo.org\/index.php?rest_route=\/wp\/v2\/posts\/5195\/revisions"}],"predecessor-version":[{"id":5208,"href":"https:\/\/spgoo.org\/index.php?rest_route=\/wp\/v2\/posts\/5195\/revisions\/5208"}],"wp:attachment":[{"href":"https:\/\/spgoo.org\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=5195"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/spgoo.org\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=5195"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/spgoo.org\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=5195"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}