iodine + methylene blue

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Brwagur
Posts: 81
Joined: Sat May 09, 2009 12:51 am UTC

iodine + methylene blue

Postby Brwagur » Sun Aug 09, 2009 3:18 am UTC

some time ago i was playing with potassium iodide and an aqueous solution of methylene blue. i dissolved elemental iodine in mineral oil by pouring mineral oil to a vial of KI, adding bleach (NaClO), and shaking until the mineral oil turned violet. when i poured the mineral oil/iodine solution into a container containing methylene blue the most curious thing happened: at the interface between the aqueous methylene blue and the oil a metallic, gold-colored membrane formed. shaking the vial produced golden globules. what gives? heating the mixture destroyed the gold color.
That there is an 80's cell. See, it's got plasma legwarmers.

opsomath
Posts: 89
Joined: Wed Nov 01, 2006 1:58 pm UTC

Re: iodine + methylene blue

Postby opsomath » Tue Aug 11, 2009 2:19 pm UTC

First I would like to say that this is my favorite question I've seen on here so far.

Based on my experience with aromatic, ionic species such as methylene blue,

(http://en.wikipedia.org/wiki/Methylene_blue)

gold colored complexes are due to the formation of some kind of donor-acceptor complex or other strong non-covalent aggregate between pi-systems. For instance, impure benzoquinone is frequently gold-colored due to traces of its reduced form hydroquinone, which forms a strong donor-acceptor complex which is gold. http://en.wikipedia.org/wiki/1,4-Benzoquinone

Many spiropyran compounds are gold in the solid state due to aggregation between the open, charged forms of the molecules. http://en.wikipedia.org/wiki/Photochrom ... rooxazines

So, I'm going to infer that something's reacting with your methylene blue to make the reduced form, which then complexes with the oxidized form. It could be molecular iodine, especially in the presence of light, although iodine is a pretty decent oxidizer itself. Or, perhaps some complex forms between iodine itself and Me blue. According to the wiki article, an alkaline solution of glucose (dextrose) will reduce Me blue; you could try that and see if you get your gold complex again; if not, it's probably some iodine-containing product.

Hmm, if I can find some Me blue, I might have to try this in the lab.

Brwagur
Posts: 81
Joined: Sat May 09, 2009 12:51 am UTC

Re: iodine + methylene blue

Postby Brwagur » Sun Aug 16, 2009 1:42 am UTC

interesting, i figured it had something to do with methylene blue's aromaticity... i would be curious to find out if adding iodine directly to MB would produce the same effect. also, when it was heated, although the gold color was gone, there was still some kind of membrane between the oil/iodine solution and the water/methylene blue solution.
That there is an 80's cell. See, it's got plasma legwarmers.


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