Canthaxanthin (Tanning pills or blinding pills?)
29th June 2006
Today’s molecule, canthaxanthin, is a member of the carotenoid family. This includes beta-carotene and lutein. These molecules are all strongly colored. This is a function of the degree of conjugation in the system.
A conjugated system has alternating double and single bonds, as you see in that long central chain. Small conjugated systems like benzene absorb in the UV, and larger conjugated systems, like our carotenes, absorb lower-energy light, yielding a visible color. For more information, see particle in a box (warning to the uninitiated: this ventures into quantum mechanics and gets a bit esoteric).
As you can see, the structures of canthaxanthin and beta-carotene are very close. All the carotenes are closely related, actually. If you’ve been reading regularly, you’ll probably make the connection that this is a terpene derivative and biosynthetically derived from a previous MoTD, isopentenyl pyrophosphate.
OK, structure considerations aside, how is it interesting? Well, you probably know that carrots contain quite a bit of beta-carotene. You might also know that this can make you turn orange, over time (just ask my mom about my carrot phase). It turns out that canthaxanthin is the right color to make you a little bit more tan than orange. I’m told it was quite a convincing fake tan. You got it by taking tablets with megadoses of canthaxathin. Hopefully this raises an eyebrow with you. It caused some colorblindness and other problems in individuals taking it. Fortunately, the effects of carotenoid overdose usually aren’t permanent, just like your author’s orange skin. I am now a healthy chemist’s pale white.
It is also used to color farm-raised salmon pink in some areas. Carotenoids in general are responsible for a myriad of orange-red colors in nature. Flamingos, crabs, and leaves (after the chlorophyll decomposes, you see the carotenoids and flavonoids in the fall) all use them.
Night!
June 29th, 2006 at 10:38 pm
So if im reading this right “eating all your carrots because they are good for your eyes” was all a bunch of bullshit and in fact could lead to color blindness from the high amount of beta-carotene (closely related to the canthaxanthin known to cause color blindness).
Insane.
June 29th, 2006 at 11:14 pm
Nope, beta-carotene is benign as far as I know. An active form of it in vivo, retinoic acid, can be quite toxic at high doses. The isomeric isotretinoin is also quite toxic and is given medically as Accutane, a drug of last resort for acne. It can cause birth defects. Aside from that and the obvious skin side effects, it can alter liver function and raise blood lipids.
June 30th, 2006 at 4:33 pm
Another retinoid, Tegison (etretinate) is even nastier–you can’t donate blood or have children if you’ve ever taken it.
June 30th, 2006 at 6:57 pm
For comparison:
I’m not sure of the cis-trans isomerism here.