Biology

Onsager appreciated that biology would be a large part of the future of chemical and physical science. He attended a number of biological conferences at which he soaked up information, often with eyes closed, but, as has been noted many times, that was a rather counterintuitive indicator of his neural activity. Another indication of the level of his interest was that biological issues accounted for about 10% of his Nobel address [75] and for four papers [72, 73, 79, 83]. Even though these papers were short and preliminary, his well known reluctance for writing papers indicates that he placed a high priority on biological issues. On a personal note, I asked his advice in 1968 where to go for a sabbatical to explore biological issues and he strongly urged me to come back to Yale because he had an interesting idea.

That idea is mentioned at the end of [72] and [75] and is the principal content of [73] and [79]. The general issue was how ions get through membranes. His specific idea utilized general principles of protein folding, which were not that well established at that time, to argue that there should be chains of hydrogen bonds, involving the amino acid side chains. These chains would then provide a relatively low impedance pathway for ion conduction. As is clear from [72] Onsager knew better than to try to be completely general — indeed, he subtly warned that general irreversible thermodynamics would not likely resolve biological issues — and so he focussed on the sodium channel in nerve axons. However, in 1970 it became clear to us from TTX poisoning experiments¹ that the current carried per channel was far in excess of the current of sodium ions that his putative channels could carry, and he did not pursue this idea further…