Nobel Centennial Symposia
"Frontiers of Molecular Science"

December 4-7, 2001
Friiberghs Manor, Örsundsbro and Stockholm University

Flaws in the Fabric of Physical Chemistry

by Barry Ninham
Australian National University, Canberra

The remarkable developments in the biological and biochemical sciences would not have been possible without access to experimental tools of the physical sciences. Yet the fact remains that the physical sciences, and the intuition derived from theories, have hardly contributed conceptually at all, and appear irrelevant to the biological sciences.

This problem is genuinely puzzling to physicists and physical chemists. The reasons for this state of affairs is explored. Several long standing conceptual locks have been far more important barriers to progress than factual locks.

Some of these conceptual locks are identified. They have to do with:

1. Theories of molecular interactions in solution. These are deficient due to failure to take account of "Hofmeister", specific ion effects.

2. Theories of self assembly and of microstructure have only recently admitted non euclidean geometries into the pantheon of allowed structures--for micelles, vesicles, microemulsions, cell membranes and organelles. Bicontinuous structures, random, cubic phases, cubosomes, and the new "mesh" phases of membranes turn out to be ubiquitous.

3. Theories have been bedeviled by long ranged "hydrophobic" interactions. (these turn out to be a red herring)

4. Nowhere in theories has the role of dissolved atmospheric gas been considered.

All of these matters are related.

A number of examples, from restriction enzyme activity as a function of salt concentration and kind, and pH and buffer; through to direct force measurements; and the apparently absurdly simple problem of bubble bubble interactions, are used to illustrate flaws in the theoretical fabric.

More detailed examination shows that the basic theories of interactions in colloid and surface science are not just flawed, but fundamentally in error. Especially is this so in the biological regime. This is so not just for the DLVO theory of colloid science, but also for theories of interfacial tension and Debye-Huckel theory and their extensions.

The error lies in separating electrostatic forces, treated in a non linear theory (the Gibbs adsorption isotherm), from dispersion forces, treated in a linear theory. The theories violate the gauge condition on the electromagnetic field and are thermodynamically inconsistent.

The matter is not just esoteric. When the deficiency is remedied, specific ion effects, and forces consequent on them can be predicted quantitatively and begin to fall into place.

Taken together progress from 1-4 represents a paradigm shift.

Once these conceptual locks are recognised, the disjunction between the biological and physical sciences is no longer so stark.