{"id":26199,"date":"2023-08-07T11:02:07","date_gmt":"2023-08-07T10:02:07","guid":{"rendered":"https:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/?p=26199"},"modified":"2023-08-22T16:29:58","modified_gmt":"2023-08-22T15:29:58","slug":"blue-blood","status":"publish","type":"post","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=26199","title":{"rendered":"Blue blood."},"content":{"rendered":"
\n

Respiratory pigments<\/a> are metalloproteins that transport O2<\/sub>, the best known being the bright red\/crimson coloured hemoglobin in human blood. The colour derives from Fe2+<\/sup> at the core of a tetraporphyrin ring<\/a>. But less well known is blue blood<\/strong>, and here the colour derives from an oxyhemocyanin unit based on Cu1+<\/sup> (the de-oxy form is colourless) rather than iron. See below for the carapace of a red rock crab.<\/p>\n

\"\" Here I take a look at this very unusual structure, the core of which is an imidazole ring coordinated via nitrogen to the metal Cu.
\n\"\"<\/a> A search of the crystal structure database for the following sub-structure \"\" reveals 12 hits, with a range of\u00a0O-O distances ranging from 1.37 to 1.54\u00c5. A histogram of the O-O lengths in the Cu(O-O)Cu sub structure shown below shows quite a distribution amongst the 12 known examples.<\/p>\n

\"\"<\/p>\n

Of these, one (UTETEU[1]<\/a><\/span>, DOI: [2]<\/a><\/span>) is perhaps the closest to the oxyhemocyanin core, albeit with the imidazole heterocycle replaced by the isomeric pyrazole ring (no Ag or Au examples are known). The overall 2+<\/sup> charge deriving from two Cu1+<\/sup> units is internally balanced with two 4-coordinate B1-<\/sup> end caps, and this system was chosen as the starting model for some computational studies.[3]<\/a><\/span><\/p>\n

Firstly, the crystal structure reveals an O-O distance of 1.531\u00c5; the O=O distance (from crystal structures where it is present) is ~1.24\u00c5 (DOI: 10.5517\/cct597h<\/a>) for neutral (triplet?) oxygen, ~1.50\u00c5 for the dianion O2<\/sub>2-<\/sup> and 1.32\u00c5 for the monoanion O2<\/sub>1-<\/sup>[4]<\/a><\/span>.<\/p>\n

Computational models were constructed at the \u03c9B97XD\/Def2-SVPP level, FAIR Data DOI: 10.14469\/hpc\/12584<\/a>.<\/p>\n

\"\"\"\"<\/p>\n

The computed O-O distance for a singlet state of the complex is shorter than that measured in the crystal structure (1.368 vs 1.531\u00c5). At the better Def2-TZVPP basis set level, the O-O bond length is 1.379\u00c5, still shorter. A model of singlet state oxyhemocyanin itself (Def2-TZVPP) as a di-cation (these charges are balanced by carboxylate anions from the surrounding protein) shows a very similar O-O bond length (1.361\u00c5).<\/p>\n

\"\"<\/p>\n

How about the oxyhemocyanin as a triplet state, the same state of isolated oxygen itself? Oxyhemocyanin now has a O-O distance of 1.477\u00c5 (Def2-TZVPP) and a Cu-O distance of 1.972 (1.934 from crystal structure of UTETEU). The UTETEU analogue has a calculated distance of\u00a01.483\u00c5 (crystal structure 1.531\u00c5), which strongly suggests that\u00a0this system exists as a triplet rather than as a singlet spin state (click on image below to view as a 3D model).<\/p>\n

\"\"<\/p>\n

The spin density in UTETEU\u00a0is shown above, which indicates that the two unpaired electrons are delocalised on Cu, nitrogen and O atoms, compared to only the oxygen in O2<\/sub> itself.<\/p>\n

So we may conclude from this brief investigation into the structures of this component of “blue blood” captures oxygen as a sandwich between two copper atoms (a mode very unlike the iron equivalent in hemoglobin), and moreover that the spin state in this capture retains the triplet motif of gaseous oxygen itself, whilst the spin density of the unpaired electrons is delocalised over both copper, nitrogen and oxygen.<\/p>\n

\n

This post has DOI: 10.14469\/hpc\/13111<\/p>\n

\n

References<\/h2>\n
  1. R. Dalhoff, R. Schmidt, L. Steeb, K. Rabatinova, M. Witte, S. Teeuwen, S. Benjama\u00e2, H. H\u00fcppe, A. Hoffmann, and S. Herres-Pawlis, \"The bridge towards a more stable and active side-on-peroxido (Cu<sub>2<\/sub><sup>II<\/sup>(\u00b5-\u03b7<sup>2<\/sup>:\u03b7<sup>2<\/sup>-O<sub>2<\/sub>)) complex as a tyrosinase model system\", Faraday Discussions<\/i>, vol. 244, pp. 134-153, 2023. https:\/\/doi.org\/10.1039\/d2fd00162d<\/a>\n\n<\/li>\n
  2. Zhang, Shiyu., Fallah, Hengameh., Gardner, Evan J.., Kundu, Subrata., Bertke, Jeffery A.., Cundari, Thomas R.., and Warren, Timothy H.., \"CCDC 1468787: Experimental Crystal Structure Determination\", 2016. https:\/\/doi.org\/10.5517\/ccdc.csd.cc1l9d7j<\/a>\n\n<\/li>\n
  3. N. Kitajima, K. Fujisawa, C. Fujimoto, Y. Morooka, S. Hashimoto, T. Kitagawa, K. Toriumi, K. Tatsumi, and A. Nakamura, \"A new model for dioxygen binding in hemocyanin. Synthesis, characterization, and molecular structure of the .mu.-.eta.2:.eta.2 peroxo dinuclear copper(II) complexes, [Cu(HB(3,5-R2pz)3)]2(O2) (R = isopropyl and Ph)\", Journal of the American Chemical Society<\/i>, vol. 114, pp. 1277-1291, 1992. https:\/\/doi.org\/10.1021\/ja00030a025<\/a>\n\n<\/li>\n
  4. H. Seyeda, and M. Jansen, \"A novel access to ionic superoxides and the first accurate determination of the bond distance in O2\u2212\", Journal of the Chemical Society, Dalton Transactions<\/i>, pp. 875-876, 1998. https:\/\/doi.org\/10.1039\/a800952j<\/a>\n\n<\/li>\n<\/ol>\n\n<\/div> ","protected":false},"excerpt":{"rendered":"

    Respiratory pigments are metalloproteins that transport O2, the best known being the bright red\/crimson coloured hemoglobin in human blood. The colour derives from Fe2+ at the core of a tetraporphyrin ring. But less well known is blue blood, and here the colour derives from an oxyhemocyanin unit based on Cu1+ (the de-oxy form is colourless) […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_feature_clip_id":0,"_jetpack_memberships_contains_paid_content":false,"activitypub_content_warning":"","activitypub_content_visibility":"","activitypub_max_image_attachments":5,"activitypub_interaction_policy_quote":"anyone","activitypub_status":"","footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2},"jetpack_post_was_ever_published":false},"categories":[1745],"tags":[2648],"ppma_author":[2661],"class_list":["post-26199","post","type-post","status-publish","format-standard","hentry","category-crystal_structure_mining","tag-interesting-chemistry"],"yoast_head":"\nBlue blood. - Henry Rzepa's Blog<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=26199\" \/>\n<meta property=\"og:locale\" content=\"en_GB\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Blue blood. - Henry Rzepa's Blog\" \/>\n<meta property=\"og:description\" content=\"Respiratory pigments are metalloproteins that transport O2, the best known being the bright red\/crimson coloured hemoglobin in human blood. 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Although colour in fact was the topic that sparked my interest in chemistry many years ago (the fantastic reds produced by diazocoupling reactions), I had never really tracked down the origin of\u2026","rel":"","context":"In "Interesting chemistry"","block_context":{"text":"Interesting chemistry","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=4"},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2018\/06\/delphindin-1024x856.jpg?resize=350%2C200&ssl=1","width":350,"height":200},"classes":[]},{"id":7068,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=7068","url_meta":{"origin":26199,"position":3},"title":"More joining up of pieces. Stereocontrol in the ring opening of cyclopropenes.","author":"Henry Rzepa","date":"July 12, 2012","format":false,"excerpt":"Years ago, I was travelling from Cambridge to London on a train. I found myself sitting next to a chemist, and (as chemists do), he scribbled the following on a piece of paper. When I got to work the next day Vera (my student) was unleashed on the problem, and\u2026","rel":"","context":"In "Interesting chemistry"","block_context":{"text":"Interesting chemistry","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=4"},"img":{"alt_text":"","src":"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2012\/07\/dichlorocarbene.svg","width":350,"height":200},"classes":[]},{"id":17543,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=17543","url_meta":{"origin":26199,"position":4},"title":"Stable “unstable” molecules: a crystallographic survey of cyclobutadienes and cyclo-octatetraenes.","author":"Henry Rzepa","date":"March 5, 2017","format":false,"excerpt":"Cyclobutadiene is one of those small iconic molecules, the transience and instability of which was explained theoretically long before it was actually detected in 1965. Given that instability, I was intrigued as to how many crystal structures might have been reported for this ring system, along with the rather more\u2026","rel":"","context":"In "crystal_structure_mining"","block_context":{"text":"crystal_structure_mining","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=1745"},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2017\/03\/134-1024x722.jpg?resize=350%2C200","width":350,"height":200},"classes":[]},{"id":16573,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=16573","url_meta":{"origin":26199,"position":5},"title":"How does an OH or NH group approach an aromatic ring to hydrogen bond with its \u03c0-face?","author":"Henry Rzepa","date":"June 22, 2016","format":false,"excerpt":"I previously used data mining of crystal structures to explore the directing influence of substituents on aromatic and heteroaromatic rings. Here\u00a0I explore, quite literally, a different angle to the hydrogen bonding interactions between a benzene ring and\u00a0OH or NH groups. I start by defining a benzene ring with a centroid.\u2026","rel":"","context":"In "Chemical IT"","block_context":{"text":"Chemical IT","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=2"},"img":{"alt_text":"aromatic-pi-query","src":"https:\/\/i0.wp.com\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2016\/06\/aromatic-pi-query-1-e1466580253270.jpg?resize=350%2C200","width":350,"height":200},"classes":[]}],"jetpack_likes_enabled":false,"authors":[{"term_id":2661,"user_id":1,"is_guest":0,"slug":"admin","display_name":"Henry Rzepa","avatar_url":"https:\/\/secure.gravatar.com\/avatar\/897b6740f7f599bca7942cdf7d7914af5988937ae0e3869ab09aebb87f26a731?s=96&d=blank&r=g","author_category":"1","first_name":"Henry","last_name":"Rzepa","user_url":"https:\/\/orcid.org\/0000-0002-8635-8390","job_title":"","description":"Henry Rzepa is Emeritus Professor of Computational Chemistry at Imperial College London."}],"_links":{"self":[{"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/posts\/26199","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=26199"}],"version-history":[{"count":44,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/posts\/26199\/revisions"}],"predecessor-version":[{"id":26271,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/posts\/26199\/revisions\/26271"}],"wp:attachment":[{"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=26199"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=26199"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=26199"},{"taxonomy":"author","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fppma_author&post=26199"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}