Now, THIS is a very cool Ph.D thesis: Francesco Ricci and the origins of chirality. [View all]

[NNadir]

Life is asymmetric, and why this is so is one of the greatest mysteries of the universe. By asymmetric we are referring to the property that your hands have, they are mirror images of one another, but cannot be superimposed upon one another.

We refer to this property as chirality.

Here is a picture of the two forms of the simple amino acid alanine, with, by convention, the black wedge being representative of coming out of the plane of the page, the dashed wedge representative of being representative of going back behind the plane of the page:



In the laboratory, one can easily make alanine by the hydrogenation, in the presence of ammonia of the symmetric molecule pyruvic acid, with, say for example, a nickel or platinum catalyst. When one does this however, one will get a 50:50 mixture (exactly) of the two molecules above. We refer to such a 50:50 mixture as "racemic."

In living systems, by contrast, which also synthesize alanine from pyruvic acid, one will only get one of these isomers, the S isomer, 100%, exactly.

In fact, one can only synthesize pure chiral molecules in the laboratory (and this has been a subject of vast amounts of research over the last century or so) if one conducts the reaction in the presence of molecules that are also chiral. This is, in fact, what happens in living systems; the vast majority of molecules in living things (other than water) are chiral. But where did it come from? What was the first chiral molecule to exist in the absence of its mirror image, which we call its "enantiomer?"

I have wondered about this a lot while daydreaming over several decades; I've generally assumed with a vague sense, that it somehow resulted from certain types of chiral radiation associated with nuclear decay in cataclysmic stellar events. (Yes, light can be, and often is, chiral.) Here and there, I've pulled some papers down, but none were very satisfactory.

Today, while going through files I collected but never actually read, I came across a recent Ph.D. thesis at Princeton University, written by a young scientist named Francesco Ricci. It's entitled "Theoretical and Computational Studies of Condensed-Phase Phenomena: The Origin of Biological Homochirality, and the Liquid-Liquid Phase Transition in Network-Forming Fluids."

The thesis can be accessed here: Ricci, Ph.D Thesis, Princeton

Very early in the text I came across a concept of which I'd never ever heard, "Viedma ripening" involving homochiral molecules.

Viedma ripening...

Never heard of it.

It doesn't get any better than this, being old and fairly broadly exposed and then run across something from some very charming young guy talking about something about which you know nothing.

I'm going to be pulling up this kid's papers and his references in the next several weeks. Beautiful, very, very, beautiful.

It's going to be a fun Christmas break!