Email or username:

Password:

Forgot your password?
John Carlos Baez

Suppose you were trying to invent a bright orange powder that could easily dye clothes and be hard to wash off. Using your knowledge of quantum mechanics you'd design this symmetrical molecule where an electron's wavefunction can vibrate back and forth along a chain of carbons at the frequency of green light. Absorbing green light makes it look orange! And this molecule doesn't dissolve in water.

Yes: you'd invent turmeric!

Or more precisely 'curcurmin', the molecule that gives turmeric its special properties.

The black atoms are carbons, the white are hydrogens and the red are oxygens.

Read on and check out what pure curcurmin looks like.

(1/n)

19 comments
John Carlos Baez

Ain't it pretty? People extract curcumin from turmeric to use as a food coloring in curry powders, mustards, butters, cheeses, and prepared foods. It's also used in dietary supplements due to its unproven and dubious health benefits.

It doesn't dissolve well in water, but it does in alcohol. If you dissolve some curcurmin in vodka and shine a black light on it, you'll see it's fluorescent! That is: it absorbs the high-energy ultraviolet photons and emits lower-energy green photons... the same kind of light it usually likes to *absorb.* Due to the principle of reciprocity, if a substance is good at absorbing some frequency of light, it's also good at emitting that frequency.

Let's see that fluorescence! Check out my next post.

(2/n)

Ain't it pretty? People extract curcumin from turmeric to use as a food coloring in curry powders, mustards, butters, cheeses, and prepared foods. It's also used in dietary supplements due to its unproven and dubious health benefits.

It doesn't dissolve well in water, but it does in alcohol. If you dissolve some curcurmin in vodka and shine a black light on it, you'll see it's fluorescent! That is: it absorbs the high-energy ultraviolet photons and emits lower-energy green photons... the same kind...

John Carlos Baez

Here's curcumin dissolved in a hydrocarbon called xylene with ultraviolet light shining on it! It's fluorescent. You can also dissolve it in ethanol, e.g. vodka.

Curcurmin also makes a good pH detector: if you mix it with a base it turns red. This video by @compoundchem illustrates it:

youtube.com/watch?v=PsVtME5o69

(3/n, n = 3)

Matteo Capucci

@johncarlosbaez @compoundchem this explains many culinary experiences I had, amazing

John Carlos Baez

@mc - I've spent a lot of time trying to wash turmeric out of my clothes; I should have been using vodka.

Jos Dingjan

@johncarlosbaez In Dutch turmeric is called either “kurkuma” (after the Sanskrit name, I guess the source of both the name of the genus and of “curcumin”), “geelwortel” (= yellowroot), or kunyit/koenjit (from Indonesian)

John Carlos Baez

@happydisciple - nice! I was wondering where that word 'curcumin' came from, and I was confused by 'cucurbits'.

en.wikipedia.org/wiki/Cucurbit

Matteo Capucci

@johncarlosbaez lol does this work with any color you want? just stick enough Cs between the aromatic groups?

John Carlos Baez

@mc - basically yes! But the aromatic groups appear to be optional. The reason tomatoes are red is 'lycopene':

(1/3)

John Carlos Baez

@mc - and the reason carrots are orange is beta-carotene.

(2/3)

John Carlos Baez

@mc - I got into this when I saw a bunch of autumn leaves again in Washington DC, and realized it's all due to quantum delocalization of electrons! I wrote about it here:

(3/3)

johncarlosbaez.wordpress.com/2

418 I'm a Teapot

@johncarlosbaez @mc anthocyanin. How is it that I had never heard this word before last week and now it’s everywhere?

Benoît Valiron

@johncarlosbaez @mc is it somehow possible to guess the color from the length of the chain of carbons?

John Carlos Baez

@b3nb3n @mc - yes if you're smart enough, but I'm not. The frequency of vibration will be lower for longer carbon chains, just like for a violin string, but I bet the side-groups attached to the chains also affect the frequency - like the oxygens in curcurmin. So you should get the cleanest patterns for very simple chains like

C-C=C-C=C-C=C-C

(with appropriate hydrogens attached).

Compadre de Ogum :Ryyca:

@johncarlosbaez @b3nb3n @mc lycopene is red and is the longest chain you showed. Shouldn't it be the opposite? Longer = lower frequency?

canusfeminacanis

@johncarlosbaez

Nope. I'd make an azo dye of the most hideous orange that would permanently stain my lab coat.

Organic chemistry at work. 😉

Turmeric can be removed with a washing additive. Azo dye can't.

John Carlos Baez

@canusfeminacanis - okay, you're an actual chemist! So I should have added an extra requirement: you can cook with it.

canusfeminacanis

@johncarlosbaez

Nope, but I was one of three students who didn't leave an explosion on the lab ceiling. 😆
Sometimes successes are the better teachers.

Still have the lab coat with the orange dye, though.

That said, if you'd specified 'must be able to cook with it, I would have understood turmeric to be THE answer. 😉

Go Up