ABSTRACT
This seems to be an appropriate junction to refl ect on which of the covalent forces discussed so for are genuine primary driving forces, and which are secondary interactions, caused by the primary interactions. In past years one has tended to be confronted with a growing number of different forces, which are commonly believed to play a role in the interactions between biological and other polar entities, such as cells, biopolymers and other polar polymers or particles, when immersed or dissolved in water. This expanding catalogue of (non-covalent) interaction forces comprises (van Oss, J. Dispersion Sci. Tech./Biocoll. Biosurf., 1991):
1. London-van der Waals, or dispersion forces; 2. Debye-van der Waals, or induction forces; 3. Keesom-van der Waals, or orientation forces; 4. Electrostatic, or Coulombic forces; 5. Hydrogen-bonding forces; 6. Hydrophobic interactions; 7. Hydration forces; 8. Brownian movement forces; 9. Osmotic pressure; 10. Disjoining pressure; 11. Structural forces; 12. Steric interactions; 13. Depletion interactions; 14. Entropy-driven interactions; 15. Enthalpy-driven interactions; 16. Cross-binding interactions; 17. Specifi c interactions.
