Heavy water

[mmitchell]

Re: http://www.straightdope.com/mailbag/mheavywater.html

I did deuterium MRI and spectroscopy as part of my dissertation work, and along the way (around 1990), I deuterated a rat by giving him D2O for drinking water. We didn’t weigh the rat or anything, but I estimate we enriched him to about 10 atom% D. As suggested in the column, there were no adverse effects on the rat. We got an image, but it wasn’t all that good, since the NMR signal from deuterium is much less than the signal from ordinary hydrogen nuclei (protons)

Matthew Mitchell, PhD (University of Pennsylvania, 1991)
(also tried drinking a bottle of D2O [with a beer chaser of course] in the magnet, to see if we could detect the uptake)

[Q.E.D]

*Originally posted by mmitchell *
We got an image, but it wasn’t all that good, since the NMR signal from deuterium is much less than the signal from ordinary hydrogen nuclei (protons)

That’s very interesting. What is the specific reason for that. Also, could you tell if D[sub]2[/sub]O was preferentially uptaken in any specific areas of the body? Or was the distribution more or less random?

[mmitchell]

The inherent NMR sensitivity of 2H is much (about 100-fold) smaller than that of 1H, for equal numbers of nuclei at equal field strength. Though you may have learned it in chemistry class, NMR is a nuclear function, so it will differ between different isotopes of an element, while those isotopes will behave the same chemically (aside from the tertiary effects you explained quite well)

We could not detect any preferential uptake, but the rat was deuterated over a period of weeks, so there was a lot of time for equilibration. The aforementioned human experiment (besides being an excuse to drink beer for scientific purposes) was intended to see how the uptake went, but we did not get enough signal to image.

BTW, in case anyone was wondering, the natural abundance of deuterium is about 1 per 6,000 hydrogen atoms, so a 12 ounce beer would have roughly 1.9 x 10^21 deuterium atoms. Light beer (ptui) is the same.

[aerodave]

One thing not made clear in the staff report was the number of deuterium atoms necessary to make heavy water. Is a sample in which every molecule consists of one protium, one deuterium, and one oxygen atom considered heavy water? Does heavy water normally have molecule like that, or are they all have to be deuterium-oxygen-deuterium?

If heavy water requeires two deterium atoms in all the molecules, what would you call water that was all protium-oxygen-deuterium? And what about tritium-based water? What’s that called?

[C_K_Dexter_Haven]

And by the way, welcome to the Straight Dope Message Boards, mmitchell, glad to have you with us!

[mmitchell]

The number of deuterium atoms in each molecule is just an equilibrium function of the total 2H/1H ratio in the water. The atom on the one side of the oxygen doesn’t care what isotope the atom on the other side is, and they all come and go randomly.

IIRC, the typical D2O one would use in an experiment like this is 99.8 atom% 2H, meaning that for every 1000 hydrogen atoms, 998 would be deuterium (2H) and 2 would be protium (1H). Since the odds are a quarter-million to one against both of those 1H atoms being in the same molecule, you would then expect there to be 2 DHO molecules (deuterium-oxygen-protium) and 498 D2O molecules (deuterium-oxygen-deuterium) in that sample.

Now if we assume the rat was 10% deuterated, some simple arithmetic tells us that 1% of the water in the cells making up the rat would be D2O, 18% would be DHO, and 81% would be H2O.

Just to check our work: in 100 water molecules, there would be 1 D2O (2 2H atoms), 18 DHO (18 2H and 18 1H), and 81 H2O (162 1H). They total 20 2H and 180 1H, or 20 out of 200 2H = 10%.

Now, what happens if you mix 50 atoms of H2O and 50 of D2O?
Because of the equilibrium, they would soon exchange with each other, and you would get a mixture of H2O, D2O, and DHO.

For the same reason, you can’t have pure DHO. It would soon equilibrate into the mixture of H2O, D2O, and DHO. And you could call that “heavy water,” though it wouldn’t be as heavy as pure D2O.

One of the suppliers of D2O is Sigma-Aldrich, so if you’re interested in finding out about what the prices and purities of different grades of D2O are, go to http://www.sigmaaldrich.com/ and search for “deuterium oxide” or CAS number 7789-20-0

HTH…

–MDM

[jsleek]

If I had two glasses of water, one heavy and one light, could I tell which is which by physical appearance? Of course I could weigh it or some such test, but would it look or feel different?

[commasense]

Rather than start a new thread, I’ll just tack this on here.

Q.E.D.: Did you know that around 1936, Robert Benchley (one of my favorite humorists) wrote a short artilce called “Skol!” that begins

Professor Klaus Hansen , of Norway, has announced that he recently drank a 98 per cent solution of “heavy water” (H O) [sic] without experiencing any ill effects. That’s what he thinks. That’s what the man said who first drank an Alexander cocktail (one-half gin, one-quarter creme de Cacao, one-quarter sweet cream).

The professor admitted that he had “to fight against hysteria” when he saw a mouse that drank heavy water at the same time show signs of illness immediately after the experiment. The mouse was no fool, obviously. He didn’t even have to fight against hysteria.

It’s a pretty amusing piece that reveals that at the time, heavy water cost 10,000 kroner (about $2,540) per liter. Benchley comments

Now, in the first place, that runs into money. You don’t order drinks “for further experiments” at $2,000 a throw unless there are certain pleasing features connected with it. It says that “Professor Hansen was so pleased,” which is probably the scientific way of saying that “Professor Hansen was still cockeyed.”

The piece is in “My Ten Years in a Quandary.”

[Q.E.D]

*Originally posted by commasense *
****Q.E.D.: Did you know that around 1936, Robert Benchley (one of my favorite humorists) wrote a short artilce called “Skol!”…

No, my research for this Staff Report didn’t turn up this particular article. Thanks! I’ll have to see if I can find the whole thing.

[commasense]

I’ll scan it and e-mail it to you tomorrow.

[Q.E.D]

Tomorrow is over now. Just so you know.

[commasense]

In case you didn’t notice, I posted at 2:10 am on Thursday. So today is tomorrow!

Actually, I just forgot that I’d be out all day Thursday. So it was the first thing I did this morning, and it’s in the e-mail to you right now.

[Q.E.D]

Got it. Thanks!

[antechinus]

Deuterium (2H) has a spin number I of 1, whereas 1H and 13C have spin numbers of 1/2.

A spin number I of 1/2 means that there are two orientations of the nucleus and a uniform charge distribution which leads to strong coupling with neighbouring nuclei. Having a I of 1 or more leads to an asymmetrical charge distribution in the nuclei leading to poor coupling in nearby nuclei. It is the coupling that allows you to work out molecular structure.

But NMR is good for working out the amount of deuterium in a sample (quantitative NMR, as used by our friend mmitchell). Deuterium content in water varies between samples taken from biological material to geological bodies of water, such as oceans. This is due to different rates of evaporation and transpiration of heavy water wrto light water. Thus the origin of a water sample can be determined (to an extent).

[Bryan_Ekers]

*Originally posted by mmitchell *
**I deuterated a rat **

I hope you bought him dinner first.

[Akatsukami]

*Originally posted by mmitchell *
**BTW, in case anyone was wondering, the natural abundance of deuterium is about 1 per 6,000 hydrogen atoms, so a 12 ounce beer would have roughly 1.9 x 10^21 deuterium atoms. Light beer (ptui) is the same. **

Which, of course, raises the question: what would a light beer brewed with heavy water be called?