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.
@johncarlosbaez I'm curious about this idea of an electron's wavefunction vibrating along the chain at visible light frequency. If I look up the length of C-C and C=C bonds, in simple hydrocarbons they're roughly 150pm each. So if I look at tumeric, this adds up to ~2nm for the length of the molecule, which is quite far from the ~500nm wavelength of yellow light. Do you happen to know what I'm misunderstanding here?
@xavier - what matters is not the length of the chain of carbons but the difference in energy levels between two states of an electron that's delocalized and spread over the whole chain. We can convert this energy difference E into a frequency ν by
ν = ℏ/E
where ℏ is Planck's constant, and the molecule will easily emit and absorb light of that frequency.
@johncarlosbaez Thanks for the explanation! This rings a bell, reminds me of some stuff I learnt in physics/chemistry at uni, though clearly I forgot most of it. The video's interesting, though most of it goes over my head 😅
@johncarlosbaez It's VERY hard to wash OFF but "lore" says that it's quite sensitive to alcohol and UV light. They say the way to "wash it off" is soak it in alcohol and expose to sunlight. Makes GREAT curries anyway :)
@johncarlosbaez So neat! Uses in India go way back. Refrigeration was not a thing, meat/poultry marinated in yogurt & turmeric b/c antimicrobial properties…. more here: https://www.ncbi.nlm.nih.gov/books/NBK92752/#_ch13_sec2_. Oxi-clean or oxygen bleach is your best friend to get stains out, or rubbing the stain with dishsoap like Dawn if you can’t wash it immediately.
@johncarlosbaez Much of the middle income and higher Indian diaspora build “haldi kitchens” (haldi=turmeric) in their garages, or outdoors because of the staining properties. I refuse to do this. Stains can be avoided with care and frequent handwashing. And by taking care of any stains from cooking splashes immediately. OFC choice of countertop material, etc all impt. Don’t get me started on poor ventilation and cooking….
I had a similar effect from white lilly pollen when this accidentally brushed against my white shirt when I was handling an arrangement of these flowers and the pollen coloured an area of the shirt strongly orange. Thankfully it came out completely in the wash as it was the first time I'd worn the shirt.
@ersatzmaus - it's an evil substance in my opinion. I don't think the flavor is worth it! But my wife disagrees, and she does most of the cooking. In general her use of spices is very nice. But turmeric is a nuisance.
@johncarlosbaez@ersatzmaus
Having been brought up on Indian food, the oh-so-familiar turmeric was taken for granted until neuroscientists started wondering why there was so little Alzheimers amongst India’s elderly.
@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:
@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
@samloonie@CompadredeOgum@b3nb3n@mc - red is longer frequency, lower wavelength but a chemical looks red if it absorbs a lot of green light. I think I'd need to see a bunch of extremely similar carbon chain molecules that form conjugated systems, before I could feel sure about the patterns.
@johncarlosbaez@b3nb3n@mc I vividly remember the moment in grad school twenty-odd years ago when it suddenly hit me that conjugated carbon-carbon double bonds are a hallmark of dyes "#chromophores" (as well as fluorescent molecules "#fluorophores"). Because they happen to have #electrons of just the right energies to absorb visible #photons! (Or ultraviolet photons, and then emit visible photons.)
One of my many post-undergrad "WHY oh WHY DIDN'T THEY MENTION THIS IN #OrganicChemistry?!" moments.
> "Anthocyanins have been used in organic solar cells because of their ability to convert light energy into electrical energy." https://en.wikipedia.org/wiki/Anthocyanin
> "The anthocyanins have other tasks in the plants: They should
absorb the sun's short-wave UV light in the shell and transfer the radiant energy to the plant as heat. This prevents damage to the proteins in the cell and the DNA in the cell nuclei." https://de.wikipedia.org/wiki/Anthocyane
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.
@johncarlosbaez When you say "Suppose you were trying to invent a bright orange powder that could easily dye clothes and be hard to wash off" it sounds like you're preparing a protest relevant to current events in the UK.
@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)
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:
@johncarlosbaez Aha, that explains why when I was washing a turmeric-covered spoon the other day, I saw a brief glimpse of red! I think the water sitting in our faucet can end up a bit basic at times, based on past observations. (Or possibly something else is going on with the chlorine in the water?)
@johncarlosbaez Huh! This booze I picked up recently has a VERY strong and persistent yellow color. It lists saffron as the top billing flavor/ingredient, but I always wondered how much of the color was really from the turmeric.
Did not think to try shining UV light on it before drinking it all!
@johncarlosbaez
In Tamil (the oldest language that is still widely spoken), turmeric is called 'manjal' ( மஞ்சள் ) and the color yellow is also called 'manjal'!
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