Tag Archives: Ideal gas law in 2 dimensions

The uses and abuses of molarity — III

2 dimensional gases were made years and years ago but no one talks about them any more. I found them fascinating as a neophyte chemistry student. Just take a typical fatty acid with a long hydrophobic tail (say stearic acid with 18 carbons) and place a small amount on water. The COOH groups hydrogen bond with the water, while the hydrocarbon tails lie on the surface of the water. Confine them to a small area, and the hydrophobic tails stick straight up away from the air water interface. Now constrict the area they are found in. The force on the wall forming the constriction is proportional to the number of molecules in the area and the area and the temperature — e.g. PA = nRT — the ideal gas law in two dimensions. So confined stearic acid on the surface of water is a two dimensional gas.

It would be nice if we could get a similar 2 dimensional arrangement of G Protein Coupled Receptors (GPCRs) — see the previous post — but we can’t (so far). 

Of course there is a darker side. The films are known as Langmuir Blodgett films.

Irving Langmuir won the Nobel prize in Chemistry for this (and other work). Blodgett who was instrumental in figuring out how to make the films got nothing. 

Why?  Probably because she was a woman — https://en.wikipedia.org/wiki/Katharine_Burr_Blodgett..  She was a Bryn Mawr graduate and the first woman to receive a PhD in physics from Cambridge. 

Moving along to another Bryn Mawr graduate; Candace Pert really discovered the opiate receptor at Johns Hopkins. She was screwed out of proper recognition by her PhD advisor, Solomon Snyder.  While he now has a department named after him at  Hopkins,  he will never receive the Nobel prize. 

The story of Rosalind Franklin and DNA is too well known to repeat.  So I’ll close with Lise Meitner who discovered nuclear fission and got nothing except a book from an old girl friend — https://www.amazon.com/Lise-Meitner-Ruth-Lewin-Sime/dp/0520208609.  The authoress notes in the preference that she was the female chemist that the department didn’t want.  Definitely a woman with an edge, which is why I was attracted to her. 

Now, as promised, here is the Nobelist who clearly doesn’t understand Molarity.

The chemist can be excused for not knowing what a nanodomain is. They are beloved by neuroscientists, and defined as the part of the neuron directly under an ion channel in the neuronal membrane. Ion flows in and out of ion channels are crucial to the workings of the nervous system. Tetrodotoxin, which blocks one of them, is 100 times more poisonous than cyanide. 25 milliGrams (roughly 1/3 of a baby aspirin) will kill you.

Nanodomains are quite small, and Proc. Natl. Acad. Sci. vol. 110 pp. 15794 – 15799 ’13 defines them as hemispheres having a radius of 10 nanoMeters from channel (a nanoMeter is 10^-9 meter — I want to get everyone on board for what follows, I’m not trying to insult your intelligence). The paper talks about measuring concentrations of calcium ions in such a nanodomain. Previous work by a Nobelist (Neher) came up with 100 microMolar elevations of calcium in nanodomains when one of the channels was opened. Yes, evolution has produced ion channels permeable to calcium and not much else, sodium and not much else, potassium and not much else. For details read the papers of Roderick MacKinnon (another Nobelist). The mechanisms behind this selectivity are incredibly elegant — and I can tell you that no one figured out just what they were until we had the actual structures of channels in hand. As chemists you’re sure to get a kick out of them.

The neuroscientist (including Neher the Nobelist) cannot be excused for not understanding the concept of concentration and its limits.

How many ions are in a cc. of a 1 molar solution of calcium — 6 * 10^20 (Avogadro’s #/1000).A cc. (cubic centimeter) is 1/1000th of a liter) How many ions  in a 10^-4 molar solution (100 microMolar) — 6 * 10^16. How many calcium ions in a nanoDomain at this concentration? Just (6 * 10^16)/(5 * 10^17) e.g. just over .1 ion/nanodomain. As Bishop Berkeley would say this is the ghost a departed ion.

Does any chemist out there think that speaking of a 100 microMolar concentration in a volume this small is meaningful? I’d love to be shown how my calculation is wrong, if anyone would care to post a comment.