Tuesday, 1 November 2011

Crystal violet lactone

This is not a post written by me. This post is been written by a proper chemist called Sarah Murray who lives in  Manchester, like me. You can find her in twitter as @SarahScientist I hope you like it.

Cristal Violet. Courtesy of Chemblink
One of the great joys of being a scientist, is that there is always the opportunity to learn something new ( and meet and work with amazingly talented  and lovely people). It is now the end of October and this means that in the UK, the half term holiday is over and so sadly is the Manchester Science Festival which takes place during these holidays. At this festival I reprise my role as STEM Ambassador, i.e. in essence I'm a science communicator and I love it! I could write about what a STEM Ambassador is, and what it means to be one. That could be an entirely separate post altogether.  Alas as I write, it is over for another year, always a time of feeling a little sad but so very pleased to have been part of it. As 2011 is officially the International Year of Chemistry, I fully expected this years festival to have many chemistry themed events and I wasn't disappointed.

On my second day (the fourth actual day of the festival) I had the good fortunate to assist a great chemist from the University of Bristol with his demonstrations. Declan was his name and he was very enthusiastic. He managed to hold the children's interest even after demo's were over whilst explaining the science. This I confess I always find to be the tricky part. Amongst his entertaining demo's was one which truly amazed me too. So finally, I am now going to talk about what I learned from Declan about a beautiful molecule called crystal violet lactone. I guess I have chosen this because it combines my favourite science, chemistry, with my favourite colour purple.

Cristal Violet.Courtesy of 3D Wolfram Alpha
There is an acid base indicator called crystal violet which I personally somehow have never in my career managed to use. Biologists also use it as a generic stain for looking at cell organelles. As you may correctly suspect, crystal violet lactone is a derivative of this indicator and its real chemical name is: 6-(dimethylamino)-3,3-bis(p-(dimethylamino)phenyl)-6-(dimethylamino)phthalide.

It is what is known as a leuco dye and it was the first dye to be used in carbonless copy papers, and is still widely used in this application. Declan had a molecular model structure of this lactone which was wonderful to see, especially when used to explain what was going on. He took some crystal violet lactone and blew some purple bubbles with it. I've never seen purple bubbles before! They look like this:
Courtesy of Geekologie
He deliberately got some on his hands and the table and followed this up with the question "what problem may a substance like this cause do you think?" Of course he was given the correct answer from some of the kids. It is messy and will stain things. Then amazingly he rubbed his skin and the splashes on the table and we all watched fascinated as it disappeared! He explained, using his molymod that it hadn't really disappeared and was still there and is a very toxic substance. There is just a slight change in the structure of the molecule which occurs when a bit of friction or pressure is applied. This happens quite easily as the molecule wants it to happen readily. The 3 rings within the structure are no longer exactly aligned, the one with the lactone group is twisted slightly. Declan referred to this as a 'mousetrap' within the structure. Now the molecule is absorbing light in the UV region rather than in the visible region of the electromagnetic spectrum as it was before, meaning it is no longer visible to the human eye.

 I find this truly stunning and is why I love chemistry. So far, this is not a reversible process and researcher's haven't found any applications for it though it is thought it may be useful for security purposes. Detecting fingerprints on stolen /counterfeit money perhaps.

I hope you have found this as interesting as I did. You have now learned as much as I have about crystal violet lactone. This just goes to show that attending science festivals in any capacity is good for you. Thank you very much Declan.

This post takes part of the VIII edition of the Carnival of Chemistry hosted in the blog Science Box. I know it's already November but it was written in October and because of different reasons it hasn't been able to be publish before.

1 comment:

  1. CVL is an example of a halochromic compound. It is sensitive to acid-base equilibria. If the blue form is exposed to a basic compound, the lactone ring can be closed and the white form returned. The white form can be turned blue in the presence of an acid.

    This colouring behaviour can be made reversible by mixing CVL with other chemicals. If CVL is mixed, for example, bis-phenol A and lauryl alcohol (dodecyl alcohol) a mixture which is blue in the solid state is formed. If the mixture is heated past the melting point of the alcohol, the blue colour is lost. This phenomenon is called thermochromism.

    Pilot ink company has released a line of pens and highlighters, the Frixion line, which employ this technology. The heat produced by rubbing the eraser against the page (i.e. friction) causes the decolourization reaction to occur.



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