h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

I watched the film 'Blade' the other day (it's nowhere near as violent and gory as people say) and it caught my ear when they mentioned how EDTA makes vampire blood explode. I knew about EDTA from mychemistry lectures, and it was even mentioned today. As a hexadentate ligand which bonds extremely well to metal centres (it's used in mining and extraction), is there any chance that this stuff might actually act in this kind of way? I asked my co-ordination chemistry lecturer, and he seemed intrigued at the possibility...

I think the idea is that it removes all the iron from haemoglobin?

Dunno but I like the film

I like the film, but I think the EDTA is a typical example of film science bulls**t. It just keep a ligand to keep metals in solution isnt it, no way it could make blood explode.

As far as I can see, there are two possibilities for explosion. One is a sudden, vast increase in volume, which would be disastrous in the restricted environment of blood vessels. Dynamite, nitroglycerine, gunpowder and other such primitive explosives work by this method, turning a certain amount of solid into a much larger amount of gas very quickly. This would be borne out by the appearance of the vampires as they were undergoing the process, with their skin becoming bulbous and expanding until they 'pop'.
The other possibility is a process that is merely extremely exothermic, producing lots and lots of energy. EDTA does produce among the most stable complexes of any known ligand, so all that would be required is for the iron centre in vampire haemoglobin to be particularly loosely bonded and vulnerable to reaction.

EDTA is also an anti-coagulant. Don't know if that makes any difference, but it has implications for blood-clotting.



Ste

Do you think that the script writers sit around thinking 'Well technically it isn't true, but hell who in the audience is going to know that? And besides it sounds good!'

EDTA-metal complexes are pretty darn insoluble a lot of the time so it would likely precipitate - this would block all your capilliaries - causing a high backpressure of blood which will then explode out of your arteries.

Honest guv'

And that is bad, right?

I thought that EDTA was a chelating agent used to keep metals IN solution...

I thought it was just a handy thingy that chemists used to sound clever and confuse people reading inrgedients on toiletries

Its one of those as well...


*wanders what us chemists would do without those complicated names that confuse people.*

dunno, geologists are the same

Is there any science which doesn't bury you in jargon?

PQ (admiring a gneiss schist )

"I thought that EDTA was a chelating agent used to keep metals IN solution"
Chealating agents go around mopping up all free metal ions..

Some complexes are soluble, some are not. In the amounts they used it in Blade, the EDTA itself would likely be insoluble. EDTA-calcium is a particularly insoluble complex I believe and there would certainly be a lot of that around

Well, put it this way: it's about as likely as someone who works on-line, lives on-line then is sent (on-line) a virus, then taking that virus and putting one copy only on a floppy disk, which lo and behold becomes the only existing copy of that virus (just so that the baddies have got something to chase).

Film-makers don't live in a universe tied by the same laws of physics and chemistry.

The only way I'd see EDTA working in that way is if vampire blood was somehow super-saturated with haemoglobin-bound oxygen such that when the EDTA chelates to the iron core (which I ain't convinced it would be able to get at through the protein around it, but what the heck), a huge amount of oxygen would be given off, causing the rather spectacular effect that you see. But my chemistry was a long, long time ago

Phil

I work in a Lab and do a HNC chemistry part time. I hate chemistry. The moneys good, what more can I say?

Philbo - chelating agents don't go around like hungry little fish searching for ions to chelate - nor do they burrow through proteins - it's a diffusion thing. Once a metal has bound to a strong chelator like EDTA it just comes off again very, very slowly - same with Haemogolobin.

Orcus - yes I know... that's why I'm not convinced that the EDTA would be able to get through the Hb protein; but it seemed slightly less inconceivable than the EDTA forming insoluble complexes which cause a vampire's capillaries to block and explode - the vampire heart and blood pressure would need to be way, way off the scale to give that kind of effect (and a blockage causing an explosion doesn't seem to be a survival feature to me, not to mention anything which causes a raised blood pressure possibly having the same effect )

...but if we're seriously going to argue about impossible science in films, what about the lack of any take-off angle for the bus in "Speed", which still managed to jump a 50' break in the road at only 60-70mph?

Phil

Yeah, that was definitely intriguing.

My favourite one was in Relic. Here they had a mutant monster that was part human-part South American Spider. They got a bit of tissue from this mutant monster and DNA tested it. Feeding the part-human bit of the DNA from this creature they fed it into a computer which whirred and clicked for a while and not only identified the exact human it came from but even provided a photograph

I bet every forensic lab in the country's got one of them

*mutters & curses @ Dante's peak*

At least volcano didn't pretend to be realistic...