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Humans have blood based on iron, thus our blood is red.

Some aquatic life has copper based blood, thus their blood is blue. If we were gold based, what colour would our blood be, and why?

What would the pros & cons be, if any?

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    $\begingroup$ Downvoted because "does not show any research effort". $\endgroup$
    – Matthew
    Aug 24, 2020 at 2:02
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    $\begingroup$ Our blood isn't red because it's 'based on iron', out blood is red because hemoglobin bound to oxygen is red. The blood in a human's veins still contains iron. $\endgroup$
    – Halfthawed
    Aug 24, 2020 at 2:27
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    $\begingroup$ @Halfthawed: The blood in our veins is still red. Dark red, as opposed to the bright red of oxygenated blood. $\endgroup$
    – AlexP
    Aug 24, 2020 at 4:18
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    $\begingroup$ @Matthew kind of crude. I would accept that he could do a cursory search why iron or copper is in the blood, but this seems more like a personal attack that he should've known himself, which I thoroughly disagree with. $\endgroup$
    – Trioxidane
    Aug 24, 2020 at 10:06
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    $\begingroup$ @Matthew - seriously man, calm down. Trioxidane's comment makes perfect sense, and James' initial question isn't really THAT bad. $\endgroup$ Aug 24, 2020 at 17:44

5 Answers 5

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Frame challenge: Gold isn't reactive enough to react with oxygen (or most any common gas really) so that blood can carry be a transport for it. The reason our blood is iron-based is because iron is really good with reacting with oxygen (i.e. rust). The blood of other animals is blue and is copper-based for similar reasons. That's a big con to gold-based blood. ..it won't do what blood is supposed to do.

Since it is so non-reactive, I assume the blood, having no complex biological molecule to incorporate it, would just be gold coloured. Another con is that gold is rare, so it will be difficult to produce the blood. If you get a cut, you'll want to drink your own blood to keep that precious gold in your system. Or drink someone else's.

Apparently, there is about 4g of iron in a human body (not all of it is in blood though). So suppose it was best case where you could actually directly eat ore to minimize how much material you would have to consume to obtain the metal. If you were to replace 4g of iron with the same mass in gold you would need to eat at least half a ton of high grade gold ore to get that. Low grade ore would be 4 tons. But since gold is a lot denser than iron, it's probably more likely you would need similar number of atoms, not weight (don't really have a better number to go by since no gold blood exists), so you would have to eat about double the amount of ore I just mentioned. And if you can't eat actual gold ore ...well...you need to eat a LOT of plants of dirt or plants, or something else.

EDIT: It has been pointed out that gold particles mixed in glass produces tones of red.

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    $\begingroup$ It's possible this is outside the scope of the question, but gold nanoparticles are much more reactive than solid gold. Wikipedia says (1) gold colloids are bioreactive and (2) catalyze oxygenation reactions (!). So it's not obvious to me that gold-based biochemistry is in fact impossible. $\endgroup$ Aug 25, 2020 at 7:11
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    $\begingroup$ @JacobManaker I did bring up gold as a catalyst in the discussion, but I also brought up that if it were a catalyst, I think the best place would be in the lungs where the reaction actually takes place rather than strewn all about in the blood. $\endgroup$
    – DKNguyen
    Aug 26, 2020 at 4:11
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    $\begingroup$ @Narusan Well yeah, the specific reaction is different, but they both still rely on iron's reactivity with oxygen. I never meant to imply rust is literally used in hemogoblin. It was more an example for reactivity. $\endgroup$
    – DKNguyen
    Aug 26, 2020 at 13:24
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    $\begingroup$ @peacetype - The Counterweight Continent? $\endgroup$
    – Vilx-
    Aug 26, 2020 at 19:07
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    $\begingroup$ The reduction potential of gold when it is part of a coordination complex will be different from that of the uncomplexed form in aqueous solution, so you can't rule out the possibility of a gold-based transportation mechanism for oxygen so easily. $\endgroup$
    – Brian
    Aug 26, 2020 at 20:16
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Gold III Oxide is describe as being "brown or brownish-black powder at room temperature" though the pictures I can find look red or orange. If you had a gold based hemaglobin (auru-globin), you might expect it to be black or orange or red. That would follow the pattern of

  • orange-red iron rust => dark red blood
  • green-blue copper oxide => bright blue blood

But really, since it's a fictional chemical, it could have any color. Chemical compounds including a metal don't always have to follow a pattern.

DKNguyen pretty much has you covered on the pros and cons. The non-reactivity is a super strong point against the believably of gold serving this purpose.

P.S.

If you're open to suggestions, lead has a bright yellow oxide. Yellow blood would be cool, plus it would be interesting in the basic life on a planet were low-level toxic to humans on a fundamental level (all known compounds of lead being more or less dangerous to most earth life)

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    $\begingroup$ Interesting. I had read that gold doesn't react with oxygen at any temperature so I Guess that must be wrong. $\endgroup$
    – DKNguyen
    Aug 24, 2020 at 2:26
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    $\begingroup$ @DKNguyen I think that is true for metallic gold, but metallic gold does react with halides under the right conditions (see, e.g., gold (III) chloride, prepared either from chlorine gas at very high temperatures or from dissolution in aqua regia). Presumably you can get to the oxide from there. But it is worth noting that getting gold be anything other than a simple metal requires some really hostile chemistry. $\endgroup$
    – BBeast
    Aug 24, 2020 at 2:42
  • $\begingroup$ @BBeast but only a little more hostile as what's already in our stomach's, right? Maybe there's room for a small organ between the heart and lungs for these alternatively evolved humans, basically just contains aqua regia (we already produce HCL for stomach anyway), not sure where the nitric acid comes from to mix, but maybe not that implausible? $\endgroup$
    – TCooper
    Aug 25, 2020 at 0:11
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    $\begingroup$ @TCooper I've worked with aqua regia. It is heaps scarier than mere HCl. It's probably not impossible to handle biologically, but I'd file it next to "fire breathing dragons" for difficult biochemistry. $\endgroup$
    – BBeast
    Aug 25, 2020 at 2:36
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Most compounds of gold (Au) bound to a porphyrin recorded in the CCDC database are red, followed by orange and brown, as shown in the table:

SHORT IDENTIFIER    COLOR       FORMULA                                                             CHEMICAL NAME                                                                                                               REFERENCE URL                                   JOURNAL                                         AUTHORS
GAFTAI              Red         C8 N4 Pt1 S4 2-,2(C44 H28 Au1 N4 1+)                                bis(Dithiomaleonitrilo-S,S')-platinum(ii) bis(tetraphenylporphyrinato-gold(iii))                                            Not informed                                    Mem.Fac.Sci.Kyushu U.,Ser.C                     Zhung Jin Zhong; Y.Nishida; H.Okawa; S.Kida
GUTVAT              Red         C68 H44 Au1 N4 1+,Cl1 1-,C3 H7 N1 O1                                (5,10,15,20-tetrakis(Biphenyl-4-yl)porphyrinato)-gold(iii) chloride dimethylformamide solvate                               http://dx.doi.org/10.1002/chem.200902741        Chem.-Eur.J.                                    R.W.-Y.Sun; C.K.-L.Li; Dik-Lung Ma; J.J.Yan; Chun-Nam Lok; Chung-Hang Leung; Nianyong Zhu; Chi-Ming Che
GUTVEX              Red         C44 H24 Au1 F4 N4 1+,Au1 Cl2 1-                                     (5,10,15,20-tetrakis(4-Fluorophenyl)porphyrinato)-gold(iii) dichloro-gold(i)                                                http://dx.doi.org/10.1002/chem.200902741        Chem.-Eur.J.                                    R.W.-Y.Sun; C.K.-L.Li; Dik-Lung Ma; J.J.Yan; Chun-Nam Lok; Chung-Hang Leung; Nianyong Zhu; Chi-Ming Che
KOLWOA              Red         C38 H9 Au1 F15 N4 1+,Cl1 1-,C1 H2 Cl2                               (5,10,15-tris(pentafluorophenyl)porphyrinato)-gold(iii) chloride dichloromethane solvate                                    http://dx.doi.org/10.1002/asia.201900422        Chem.Asian J.                                   H.Tanaka; Y.Haketa; N.Yasuda; H.Maeda
KOLWUG              Red         C44 H8 Au1 F20 N4 1+,4(C1 H1 Cl3),Cl1 1-                            [5,10,15,20-tetrakis(pentafluorophenyl)porphyrinato]-gold(iii) chloride chloroform solvate                                  http://dx.doi.org/10.1002/asia.201900422        Chem.Asian J.                                   H.Tanaka; Y.Haketa; N.Yasuda; H.Maeda
KOLXAN              Red         C44 H8 Au1 F20 N4 1+,0.61(C2 H4 Cl2),B1 F4 1-                       [5,10,15,20-tetrakis(pentafluorophenyl)porphyrinato]-gold(iii) tetrafluoroborate 1,2-dichloroethane solvate                 http://dx.doi.org/10.1002/asia.201900422        Chem.Asian J.                                   H.Tanaka; Y.Haketa; N.Yasuda; H.Maeda
KOLXER              Red         C32 H10 Au1 F10 N4 1+,0.5(C2 H4 Cl2),F6 P1 1-                       [5,15-bis(pentafluorophenyl)porphyrinato]-gold(iii) hexafluorophosphate 1,2-dichloroethane solvate                          http://dx.doi.org/10.1002/asia.201900422        Chem.Asian J.                                   H.Tanaka; Y.Haketa; N.Yasuda; H.Maeda
KOLXIV              Red         C38 H9 Au1 F15 N4 1+,F6 P1 1-,1.46(C1 H2 Cl2)                       [5,10,15-tris(pentafluorophenyl)porphyrinato]-gold(iii) hexafluorophosphate dichloromethane solvate                         http://dx.doi.org/10.1002/asia.201900422        Chem.Asian J.                                   H.Tanaka; Y.Haketa; N.Yasuda; H.Maeda
KOLXUH              Red         C44 H8 Au1 F20 N4 1+,C10 N5 1-                                      [5,10,15,20-tetrakis(pentafluorophenyl)porphyrinato]-gold(iii) pentacyanocyclopentadienide                                  http://dx.doi.org/10.1002/asia.201900422        Chem.Asian J.                                   H.Tanaka; Y.Haketa; N.Yasuda; H.Maeda
ROBTOU              Red         C44 H28 Au1 N4 1+,C1 H1 Cl3,Cl1 1-                                  (5,10,15,20-tetraphenylporphyrinato)-gold chloride chloroform solvate                                                       http://dx.doi.org/10.1016/j.isci.2019.03.027    iScience                                        Y.Haketa; Yuya Bando; Y.Sasano; H.Tanaka; N.Yasuda; I.Hisaki; H.Maeda
ROBTUA              Red         C44 H28 Au1 N4 1+,4(C1 H1 Cl3),Cl1 1-                               (5,10,15,20-tetraphenylporphyrinato)-gold chloride chloroform solvate                                                       http://dx.doi.org/10.1016/j.isci.2019.03.027    iScience                                        Y.Haketa; Yuya Bando; Y.Sasano; H.Tanaka; N.Yasuda; I.Hisaki; H.Maeda
ROBVAI              Red         C44 H28 Au1 N4 1+,B1 F4 1-,C1 H2 Cl2                                (5,10,15,20-tetraphenylporphyrinato)-gold tetrafluoroborate dichloromethane solvate                                         http://dx.doi.org/10.1016/j.isci.2019.03.027    iScience                                        Y.Haketa; Yuya Bando; Y.Sasano; H.Tanaka; N.Yasuda; I.Hisaki; H.Maeda
ROBVEM              Red         C44 H28 Au1 N4 1+,C2 H4 Cl2,F6 P1 1-                                (5,10,15,20-tetraphenylporphyrinato)-gold hexafluorophosphate 1,2-dichloroethane solvate                                    http://dx.doi.org/10.1016/j.isci.2019.03.027    iScience                                        Y.Haketa; Yuya Bando; Y.Sasano; H.Tanaka; N.Yasuda; I.Hisaki; H.Maeda
ROBVIQ              Red         C44 H28 Au1 N4 1+,C10 N5 1-,0.416(C2 H4 Cl2),C2 H3 N1,0.5(H2 O1)    (5,10,15,20-tetraphenylporphyrinato)-gold pentacyanocyclopentadienide acetonitrile 1,2-dichloroethane solvate hemihydrate   http://dx.doi.org/10.1016/j.isci.2019.03.027    iScience                                        Y.Haketa; Yuya Bando; Y.Sasano; H.Tanaka; N.Yasuda; I.Hisaki; H.Maeda
FUJFEV              Orange      C44 H28 Au1 N4 1+,Au1 Cl4 1-                                        (5,10,15,20-Tetraphenylporphinato-N,N',N'',N''')-gold(iii) tetrachloro-gold(iii)                                            http://dx.doi.org/10.1107/S0108270187089789     Acta Crystallogr.,Sect.C:Cryst.Struct.Commun.   A.M.Schacter; E.B.Fleischer; R.C.Haltiwanger
KOLXOB              Orange      C32 H10 Au1 F10 N4 1+,C10 N5 1-,C4 H8 O1                            [5,15-bis(pentafluorophenyl)porphyrinato]-gold(iii) pentacyanocyclopentadienide tetrahydrofuran solvate                     http://dx.doi.org/10.1002/asia.201900422        Chem.Asian J.                                   H.Tanaka; Y.Haketa; N.Yasuda; H.Maeda
HAZMOM              Green       C112 H112 Au1 Cl1 N8,2(C1 H1 Cl3),C3 H8 O1                          (2,3,9,10,16,17,23,24-octakis(4-t-butylphenyl)phthalocyaninato)-chloro-gold(iii) chloroform isopropanol unknown solvate     http://dx.doi.org/10.1002/chem.201201701        Chem.-Eur.J.                                    E.W.Y.Wong; A.Miura; M.D.Wright; Qi He; C.J.Walsby; S.Shimizu; N.Kobayashi; D.B.Leznoff
XIVDUE              Dark Blue   C56 H52 Au1 N4 O12,2(C2 H3 N1)                                      [5,10,15,20-tetrakis(3,4,5-trimethoxyphenyl)porphyrinato]-gold(ii) acetonitrile solvate                                     Not informed                                    CSD Communication(Private Communication)        Guiyu Liu
ROBVOW              Brown       C44 H28 Au1 N4 1+,C38 H8 F15 N4 Ni1 O1 1-,0.682(C8 H18)             (5,10,15,20-tetraphenylporphyrinato)-gold (5-oxido-10,15,20-tris(pentafluorophenyl)porphyrinato)-nickel octane solvate      http://dx.doi.org/10.1016/j.isci.2019.03.027    iScience                                        Y.Haketa; Yuya Bando; Y.Sasano; H.Tanaka; N.Yasuda; I.Hisaki; H.Maeda
TEHZOY              Brown       C44 H28 Au1 N4                                                      (5,10,15,20-tetraphenylporphyrinato)-gold(ii)                                                                               http://dx.doi.org/10.1038/nchem.2836            Nature Chemistry                                S.Prei; C.Forster; Sven Otto; M.Bauer; P.Muller; D.Hinderberger; H.H.Haeri; L.Carrella; K.Heinze
ILIWIJ              Black       C44 H28 Au1 N4 1+,Cl1 O4 1-                                         (5,10,15,20-Tetraphenylporphyrinato)-gold(iii) perchlorate                                                                  http://dx.doi.org/10.1039/b303294a              Chem.Commun.                                    Chi-Ming Che; R.Wai-Yin Sun; Wing-Yiu Yu; Chi-Bun Ko; Nianyong Zhu; Hongzhe Sun

I have no idea if the Au center bound to a porphyrin can still bind oxygen, like iron bound to heme does in hemoglobin, probably not. But one of the compounds, the green one (HAZMOM) has a chloride bound to Au. So I wildly speculate a similar structure could be useful to some organism with a exotic biochemistry, that somehow breathes chlorine instead of oxygen.

As other people noticed, Earth crust is very poor in Au, as most of it sank together with iron and other siderophiles to the planet core as it formed. Lifeforms would have a hard time gathering the element, unless a planet somehow avoided to end with most of it trapped in the core. Cyanide is very poisonous to most earth life, but reacts with gold, so I imagine a environment rich in this compound could help mobilize the metal and make it available to any organisms with a biochemistry able to survive and thrive in its presence. I believe here on Earth the less abundant element to have important biological functions is iodine. Related:Abundances of the elements and Abundance of elements in Earth's crust.

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    $\begingroup$ Now I'm curious why a lab of Japanese scientists has spent the last year and a bit inventing over a dozen gold-based organic chemistry compounds. Is it pure "let's try this and see what happens", or is there a use for it? Is this exploratory drug research or something? $\endgroup$
    – nick012000
    Aug 26, 2020 at 2:46
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    $\begingroup$ @nick012000 the abstract of dx.doi.org/10.1002/chem.200902741 seems to explain it (chemotherapy drugs, in short) $\endgroup$
    – llama
    Aug 26, 2020 at 19:34
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    $\begingroup$ @nick012000 hmm ok another one talks about liquid crystals, so more likely they're just good at making gold complexes and figure out what they can do with them afterwards $\endgroup$
    – llama
    Aug 26, 2020 at 19:35
  • $\begingroup$ Cyanobacteria as a transport? $\endgroup$
    – Peter Wone
    Aug 27, 2020 at 4:25
  • $\begingroup$ @PeterWone It's not cyano like in bacteria. It's cyano like in the poisonous chemical compound. Picture a hypothetical planet with HCN oceans, full of HCN salts. Perhaps over billions of years they could leach gold compounds from the crust, just like here on Earth table salt leach from rocks into the oceans. This could be a possible enrichment mechanism to make gold bioavailable in useful concentrations, to any lifeforms able to develop in such environment. $\endgroup$
    – ksousa
    Aug 28, 2020 at 17:46
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The pros are ... [deafening silence]. The cons are it won't work on account of gold being chemically inert, as detailed by others. Evolution tries everything and keeps whatever works. Iron and copper work well enough and remain in use. Iron works better than copper. If anything else worked well it would almost certainly be in use.

If you want gold in blood for some narrative purpose you need to think of some other function it might fulfil. As to the colour, it will contribute a red-gold hue probably dominated by the colour of the iron or copper salts.

If you just want interesting blood colour, chromium salts are brilliant orange and cobalt salts are deep blue. Chromium is quite reactive. But you'll need rather different body chemistry for that. Both chromium and cobalt salts are hazardous to humans.

Platinoids are also largely inert but exhibit catalysis. Quite small quantities in the blood might give you accelerated metabolism with sparkly blood (not really, big enough to be seen would block capillaries but let's not ruin a good story).

To be honest if you want (say) brilliant orange blood there are less toxic ways to get it. Many proteins have strong colours — it's all in the bonding as mentioned by others. When you get sick sometimes you produce brilliant orange snot. Offhand I can think of only two things that colour, potassium dichromate and certain large proteins. I'm pretty sure my sinuses aren't full of potassium dichromate. This may help you.


MSalters takes exception to my observation that evolution tries everything. His objection is unclear but I suspect it is basically that evolution only tries variations on the current theme. Changes must be incremental and compatible with the rest of the organism, so fundamental changes like blood chemistry are out of the question.

This is true, but at any given moment the majority species of biomass are small, simple and not dependent on blood as we know it.


A counterargument to the proposition that anything viable would already be in use is that when something works well it becomes a stable part of the organism and systems are built on top of it, committing the organism to a particular strategy — like the blind spot in a human eye.

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    $\begingroup$ Evolution tries everything? Only if the easy things don't work. The reason is that evolution arrives at the easy solutions earlier (less complex chemistry needed, less enzymes required). A gold-based solution would have to replace iron-based solutions by offering higher survival. $\endgroup$
    – MSalters
    Aug 25, 2020 at 13:05
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    $\begingroup$ @MSalters, Evolution is a random process. So it doesn't try "everything" so much as it tries "anything". As long as a trait does not hurt reproductive viability, it is likely to be passed on. The "easier" solutions are more likely with evolution simply because they are more likely to help (or at least not hurt) the organism's ability to reproduce (and spread the trait). If there are 1000 ways to use iron, but 1 to use gold, then evolution will probably use iron, but we can't rule out gold unless it's impossible. $\endgroup$
    – Kyle A
    Aug 26, 2020 at 18:51
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It's hard to say. Gold does form coordination compounds somewhat similar to hemoglobin, but the color is in the details of the binding. Indeed, spectroscopy is part of how chemists work out the the structures of such compounds. That hemoglobin and rust are similar in color is coincidence.

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