Complementary surfaces, attractive force

FIGURE 16.1 Hydro-gen bonding between diethyl ether and water. The dashed line represents the attractive force between the negatively polarized oxygen of diethyl ether and one of the positively polarized hydrogens of water. The electrostatic potential surfaces illustrate the complementary interaction between the electron-rich (red) region of diethyl ether and the electron-poor (blue) region of water. 

The measured strength of this attractive hydration force, especially its sensitivity to the identity and activity of the condensing agent, makes it a likely candidate for explaining the strong fit of complementary surfaces. The old lock-and-key idea is revitalized by the quantitative idea of the nature of the attractive force that radically differs from the much weaker van der Waals forces usually invoked to explain the formation of molecular arrays. 

Since heterocoagulation is a stochastic process, great care needs to be taken not to end up with large fractal clusters or flocks of the two colloidal components. Driving forces to promote adhesion of inorganic nanoparticles onto the surface of polymer latex particles, or vice versa, can be based on a variety of forces, such as electrostatic attraction, hydrophobic interactions, and secondary molecular interactions such as (multiple) hydrogen bond interactions and specific molecular recognition (e.g. complementary proteins like avidin-biotin). 

From the standpoint of molecular structure and the quantum mechanical theory of chemical reaction, the only reasonable picture of the catalytic activity of enzymes is that which involves an active region of the surface of the enzyme which is closely complementary in structure not to the substrate molecule itselfi in its normal configuration, but rather to the substrate molecule in a strained configuration, corresponding to the activated complex for the reaction catalyzed by the enzyme the substrate molecule is attracted to the enzyme, and caused by the forces of attraction to assume the strained state which favors the chemical reaction—that is, the activation energy of the reaction is decreased by the enzyme to such an extent as to cause the reaction to proceed at an appreciably greater rate than it would in the absence of the enzyme. This is, I believe, the picture of enzyme activity which is usually accepted. 

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