The Properties of Water and their Role in Colloidal and Biological Systems

Carel Jan van Oss

• Publisher: Academic Press
• Year: 2008
• ISBN:
  9780080921570
• Topic: Technology & Engineering
• Subtopic: Chemical & Biochemical Engineering
• Index: Technology & Engineering

This book treats the different current as well as unusual and hitherto often unstudied physico-chemical and surface-thermodynamic properties of water that govern all polar interactions occurring in it. These properties include the hyper-hydrophobicity of the water-air interface, the cluster formation of water molecules in the liquid state and the concomitant variability of the ratio of the electron-accepticity to electron-donicity of liquid water as a function of temperature, T. The increase of that ratio with T is the cause of the increase in hydration repulsion ("hydration pressure") between polar surfaces upon heating, when they are immersed in water.The book also treats the surface properties of apolar and polar molecules, polymers, particles and cells, as well as their mutual interaction energies, when immersed in water, under the influence of the three prevailing non-covalent forces, i.e., Lewis acid-base (AB), Lifshitz-van der Waals (LW) and electrical double layer (EL) interactions. The polar AB interactions, be they attractive or repulsive, typically represent up to 90% of the total interaction energies occurring in water. Thus the addition of AB energies to the LW + EL energies of the classical DLVO theory of energy vs. distance analysis makes this powerful tool (the Extended DLVO theory) applicable to the quantitative study of the stability of particle suspensions in water. The influence of AB forces on the interfacial tension between water and other condensed-phase materials is stressed and serves, inter alia, to explain, measure and calculate the driving force of the hydrophobic attraction between such materials (the "hydrophobic effect"), when immersed in water. These phenomena, which are typical for liquid water, influence all polar interactions that take place in it. All of these are treated from the viewpoint of the properties of liquid water itself, including the properties of advancing freezing fronts and the surface properties of ice at 0o C.

• Explains and allows the quantitative measurement of hydrophobic attraction and hydrophilic repulsion in water
• Measures the degree of cluster formation of water molecules
• Discusses the influence of temperature on the cluster size of water molecules
• Treats the multitudinous effects of the hyper-hydrophobicity of the water-air interface

Chapter One

General and Historical Introduction

Carel Jan van Oss

Publisher Summary

This chapter presents some examples of polar forces interacting in the mammalian blood circulation, early examples of the treatment of non-covalent interactions in water, rules for repulsive apolar (van der Waals) forces between different polymers dissolved in an apolar liquid, the fallacy of designating only one single component to represent the polar properties of the surface tension of a polar condensed-phase material, and discusses macroscopic-scale interactions, Chaudhury's thesis and Lifshitz–van der Waals forces. The elucidation of the mechanisms of hydrophobic attraction as well as of hydrophilic repulsion of materials or molecules immersed in water has occurred only relatively recently. The mechanisms of these two phenomena are best understood by using the equation defining the free energy of interaction between two similar materials, immersed in water. Both hydrophobic attraction in water (the “hydrophobic effect”) and hydrophilic repulsion in water (“hydration pressure”) are caused by Lewis acid–base forces.

PREAMBLE

Water is the most polar¹ liquid known to Man. At room temperature (20 °C) its total free energy of cohesion, $\mathrm{\Delta }{\mathrm{G}}^{\mathrm{cohesion}}=-145.6\text{mJ}/{\text{m}}^2$

, consisting of $\mathrm{\Delta }{\mathrm{G}}^{\mathrm{van}\mathrm{der}\mathrm{Waals}}=-43.6\text{mJ}/{\text{m}}^2$

and $\mathrm{\Delta }{\mathrm{G}}^{\mathrm{Polar}}=-102\text{mJ}/{\text{m}}^2$

. Thus the van der Waals part of the free energy of cohesion of liquid water represents only 30% and the polar part represents 70% of the total. This was already known since Fowkes (1963, 1964, 1965). In addition, with respect to the interaction energies between non-polar molecules (e.g., alkanes), when these are immersed in water, the combining rules for apolar interactions in such cases generally causes $\mathrm{\Delta }{\mathrm{G}}^{\mathrm{van}\mathrm{der}\mathrm{Waals}}$

to be rather small, leaving mainly the polar free energy of attraction of $-102\text{mJ}/{\text{m}}^2$

, which thus represents close to 100% of the total free energy of interaction in water among non-polar molecules or particles.

As was only realized much later, these $-102\text{mJ}/{\text{m}}^2$

, representing the polar (in this case the hydrogen-bonding) free energy of cohesion of water, also happen to be the sole driving force for the hydrophobic effect. Notwithstanding these new data and probably mainly due to a continuing indecisiveness as to which forces were apolar and which were polar (see Sub-section 2.3, below) no significant advances were made in this matter for about another 20 years after Fowkes (1963, 1964, 1965). Finally, based on important clarifications proposed by Chaudhury (1984) and starting in early 1985, Chaudhury and I began (mainly via long-distance telephone) to develop the combining rules which allow the quantitative expression of polar free energies in SI units (van Oss, Chaudhury and Good, 1987, 1988). The ensuing results allowed the polar free energies of interaction to be combined with the van der Waals interaction energies (and the electrical double layer interaction energies where applicable), into a complete system comprising all non-covalent interactions taking place in and with liquid water (see also van Oss, 1994, 2006).

Now, more than another two decades past 1987, this book aims to treat the combined non-covalent non-polar, polar and electrical double layer interactions taking place in and with water, from the viewpoint of all the germane physical and physico-chemical properties of liquid water.

1 SOME EXAMPLES OF POLAR FORCES INTERACTING IN THE MAMMALIAN BLOOD CIRCULATION

Essentially all repulsive as well as attractive non-covalent interactions at a colloidal scale occurring in biological systems take place in water. Some examples of such interactions in water, looking for instance at the mammalian peripheral blood circulation, include:

1. Repulsion:
The mutual, non-specific repulsion between protein molecules, which keeps them dissolved in blood serum and permits them to avoid precipitation.
The mutual, non-specific repulsion between leukocytes, platelets, etc., which keeps them in stable suspension in the blood and lymph circulation and thus prevents the formation of thrombi.
(Thus the principal constituents of blood can safely circulate in their aqueous environment.)

2. Attraction:
The specific attraction between pseudopodia of phagocytic leukocytes and bacteria that have found their way into the bloodstream allows the phagocytic cells to internalize such bacteria and destroy them.
The specific attraction between the epitope of a (foreign) antigen and the paratope of a complementary antibody molecule (immunoglobulin) triggers a series of events leading to the foreign antigen's destruction, see also Chapter 4, Section 6.
Whilst electrical double layer forces sometimes play a role in both the specific attractions and the non-specific repulsions alluded to above, polar, Lewis acid–base (AB) forces tend to accompany such electrical double layer forces and are often stronger than these, especially in high ionic strength media, such as the human blood circulation, in which electrostatic interactions are significantly attenuated. However, polar AB forces also act quite well in the absence of any electrical double layer force...