Colloids

24 Sep 2000

We should all remember Don Kerr's great advice about communicating. He said, at some of the seminars I attended, that we should all learn to choose our terms to evoke the experiences of the listener.

Every group of humans that could be called a field, specialty, culture, cult, discipline, etc., has its own specialized terminology and viewpoint, frame of reference, orientation, etc., for which years ago I coined the term "framinology" - frame of reference - terminology. When addressing one of these divisions one should attempt to learn and use its terminology, which also means learning, at some levels, the models, principles, subject area, etc., that constitute the frame of reference in question. Presenting an idea, formulation, thought, etc., in one's own special framinology to somebody in another involves finding parallel structures, analogies, similarities, etc., between the frameworks of the two viewpoints and exhibiting, showing, explaining, etc., enough of the parallel points known to be commonly understood that the listener can make the connection between terms not commonly understood by both.

Colloidal theory deals with what we now could describe as an area of physics (theory) and engineering (practice) that involves particulate matter of a certain size. That size is such that electric charges on the particles strongly affect their behavior. The ratio of charge to mass is a critical factor. Water is composed of electrically dipolar molecules that hold colloidal sized particles in suspension (for a long time). Remove the water, and the colloids stick together. Cement is a perfect example. The balloon that you rub on your hair and stick to the ceiling is a macroscopic analog. The charge to weight ratio is such that the force of attraction overcomes gravity. The charges on colloidal particles are stable over much longer periods of time and the particles are much smaller. Once a colloidal structure is "solidified" by the removal of water or other dipolar medium, the matrix tends to keep the distribution of charges stable.

When we speak of colloids we are generally not concerned with how the charges are distributed on the particle. The distribution of the charge is largely variable within individual particles due to the more or less homogenous matter that the particle is made up of. The charges are often free to move about the particle because the atoms and molecules of the substance "share" the charges. The particles will stick together most any old way subject to some very simple rules. A positively charged particle will induce a bipolar charge in a neutral particle and "stick" to the negative end. This allows the positive end of the normally neutral particle to stick to another using the same method of "inducing" a dipolar charge distribution in another otherwise neutral particle or to stick to a negatively charged particle. As this chain gets weaker the longer it gets, the more charged particles you have the stronger the solid substance will be. For an example, take a strong magnet and pick up a nail with it. Now you can use the other end of the nail as a weaker magnet to pick up another, and so forth. The smaller the nails, the longer the chain you can make. Remember those fad toys using a magnet and lots of little metal diamond shapes? The principle structure is the same as in colloids, but it's done with magnetic force rather than electric force. Add another magnet to the chain and you increase the length even more - even indefinitely. Magnets are always dipoles, but colloidal particles may have a positive or a negative charge (monopoles), both (dipoles), or be neutral. Neutral particles can be induced to become temporary dipoles, although weaker, when in the presence of another charged particle. Water is composed of a vast array of small moving dipoles, so it can keep moving around particles with a weight small enough - whether these particles are charged or not.

"The" main differences between colloidal behavior and protoplasmic behavior are:

Colloidal particles are made of a more-or-less homogenous substances, while living matter is composed of many different kinds of molecules from sub-colloidal size to colloidal size.

Colloidal particles generally have particles with a small positive or negative charge that is often free to roam around the particle, while the charges on biological molecules are generally not free to move around. A large biological molecule, made up of thousands of atoms, has regions where there are negative charges and regions where there are positive charges, and, for most of these, the charges are not free to move around.

A biological molecule is "folded" around itself into a complex physical shape; some of the charges in the molecule attract each other and hold the molecule into its folded shape. Other charges are left exposed to the outside of the molecule, but as long as the molecule remains folded it's shape remains the same and the distribution of charges on its surface remains unchanged. Each molecule has its own electric "fingerprint". Two molecules will stick together only if the contact regions are mirror images of each other with a positive point on one matching a negative point on the other. Because of folding, this is not a "flat" mirror. The physical shape of the two molecules must match also. The common analogy used is that of lock and key. This is probably most well known to the public in the form of discussions of antibodies in the immune system. Not just antibodies work this way. Most structural elements of living tissue work this way. A chemical reaction can alter the charge and change the shape of the molecule. A good example is the heme molecule in hemoglobin - the molecule that carries oxygen in the blood. An easily reversible chemical reaction allows the molecule to open and close like a clam shell. I holds one oxygen molecule in one case and releases it in the other case.

In colloidal chemistry or physics - the particles are more or less homogenous in substance, and the charge distribution on the particles matters little. Chemical reactions are largely homogenous throughout the structure and occur in concert.

In biochemical substances the particles are of a great many different kinds, and the shapes of the particles, the distribution of charges on the particles, and the effect of chemical reactions on both of the factors are all very important.

Moreover, the chemical reactions involved in living tissue are highly individual and coordinated both in space and time.

Without colloidal sized reaction, life would be impossible. While colloidal sized reactions are necessary to life, life is so much more. Colloidal properties are particularly exploited by life for construction of shells, skeletons, and other more or less permanent structural units. Once deposited, the material in many of these non-living parts of the structure remain intact due, in part, to the laws that govern colloids.

Prior to the understanding of the double-helix and the manner in which biological molecules fold to form three dimensional structures, the high level abstraction that colloidal behavior was fundamental to life was not a bad historical insight. But, we know today that it's only a foundation. All the life part of the structure is in the details we have subsequently found out. Colloidal behavior is now understood as not fundamental, but merely necessary, like the foundation of a building. It's necessary, but it isn't the whole; it's only a tiny faction.