Carel J. van Oss

LONG-RANGE AND SHORT-RANGE MECHANISMS OF HYDROPHOBIC ATTRACTION AND HYDROPHILIC REPULSION IN SPECIFIC AND ASPECIFIC INTERACTIONS

Among the three different non‐covalent forces acting in aqueous media, i.e. Lifshitz–van der Waals (LW), Lewis acid–base (AB) and electrical double layer (EL) forces, the AB forces or electron–acceptor/electron–donor interactions are quantitatively by far the predominant ones. A subset of the AB forces acting in water causes the hydrophobic effect, which is the attraction caused by the hydrogen‐bonding (AB) free energy of cohesion between the water molecules which surround all apolar as well as polar molecules and particles when they are immersed in water. As the polar energy of cohesion among water molecules is an innate property of water, the hydrophobic attraction (due to the hydrophobic effect) is unavoidably always present in aqueous media and has a value of ΔGhydrophobic = −102 mJ/m2, at 20 °C, being equal to the AB free energy of cohesion between the water molecules at that temperature. The strong underlying hydrophobic attraction due to this effect can, however, be surmounted by very hydrophilic molecules and particles that attract water molecules more strongly than the free energy of attraction of these molecules or particles for one another, plus the hydrogen‐bonding free energy of cohesion between the water molecules, thus resulting in a net non‐electrical double layer repulsion. Each of the three non‐covalent forces, LW, AB or EL, any of which can be independently attractive or repulsive, decays, dependent on the circumstances, as a function of distance according to different rules. These rules, following an extended DLVO (XDLVO) approach, are given, as well as the measurement methods for the LW, AB and EL surface thermodynamic properties, determined at ‘contact’. The implications of the resulting hydrophobic attractive and hydrophilic repulsive free energies, as a function of distance, are discussed with respect to specific and aspecific interactions in biological systems. The discussion furnishes a description of the manner by which shorter‐range specific attractions can surmount the usually much stronger long‐range aspecific repulsion, and ends with examples of in vitro and in vivo effects of hydrophilization of biopolymers, particles or surfaces by linkage with polyethylene oxide (PEO; also called polyethylene glycol, PEG). Copyright

The Modern Theory of Contact Angles and the Hydrogen Bond Components of Surface Energies

We owe a great debt to W. A. Zisman and his colleagues at the Naval Research Laboratory for their extensive, pioneering work that opened up the field of contact angles and made possible the development of the modern theory of wetting and adhesion. Their data on the wetting of solids by apolar liquids and by hydrogen bonding liquids pointed the way to the recent introduction of a theory of hydrogen bond interactions across interfaces. We will devote this chapter to a review of this new theory.

Receptor Biochemistry ahd Methodology

VOl.1: Membranes, Detergents and Receptor Solvbilization vol.2: Receptor Purification Procedures Vol.3: Molecular and Chemical Characteristics of Membrane Receptors Alan R. Liss, New York, 1984, hardbound; Vol.1: 238 pages,

Colloid And Surface Properties Of Clays And Related Minerals

46.00; Vol.2: 306 pages,

Hydrophobicity and hydrophilicity of biosurfaces

52.00; Vol.3: 184 pages,

Energetics of cell-cell and cell-biopolymer interactions

34.00

The Adjuvant Effect of Silicone-Gel on Antibody Formation in Rats

Applications of clays and clay minerals clay minerals other mineral colloids theory of colloids measurement of surface thermodynamic properties electrokinetic methods interactions between colloids surface thermodynamic properties of minerals biological interactions with mineral particles.

Cell microelectrophoresis simplified by the reduction and uniformization of the electroosmotic backflow

Hydrophobic interaction and hydrophilic repulsion occur in aqueous media and are caused by Lewis acid-base interactions of molecules, membranes or vesicles, with and among the surrounding water molecules. Recent scientific literature has been concerned with hydrophobicity/hydrophilicity of amino acids and proteins; protein adsorption and desorption (including influence of the secondary configuration of proteins, kinetics of protein adsorption and desorption, desorption and attenuation of adsorption of proteins, role of hydrophobic sites of proteins); hydrophilic repulsion and stabilization; aqueous partitioning (including coacervation and complex-coacervation); and phospholipids, membranes and vesicles (including inclusion of peptides into phospholipid layers, inclusion of polyethylene oxide into phospholipid layers, dissociation and lysis of phospholipid bilayers, removal of sterols from phospholipid monolayers, influence of plurivalent cations on charged and neutral phospholipid layers).

The valency of IgM and IgG rabbit anti-dextran antibody as a function of the size of the dextran molecule

The energy vs distance balance of cell suspensions (in the presence and in the absence of extracellular biopolymer solutions) is studied, not only in the light of the classical Derjaguin-Landau-Verwey-Over-beek (DLVO) theory (which considered just the electrostatic (EL) and Lifshitz-van der Waals (LW) interactions), but also by taking electron-acceptor/electron-donor, or Lewis acid-base (AB) and osmotic (OS) interactions into account. Since cell surfaces, as well as many biopolymers tend to have strong monopolar electron-donor properties, they are able to engage in a strong mutual AB repulsion when immersed in a polar liquid such as water. The effects of that repulsion have been observed earlier in the guise of hydration pressure. The AB repulsion is, at close range, typically one or two orders of magnitude stronger than the EL repulsion, but its rate of decay is much steeper. In most cases, AB interactions are quantitatively the dominant factor in cell stability (when repulsive) and in “hydrophobic interactions” (when attractive). OS interactions exerted by extracellularly dissolved biopolymers are weak, but their rate of decay is very gradual, so OS repulsions engendered by biopolymer solutions may be of importance in certain long-range interactions. OS interactions exerted by biopolymers attached to cells or particles (e.g., by glycocalix glycoproteins), are very short-ranged and usually are negligibly small in comparison with the other interaction forces, in aqueous media.

Measurements of the kinetic constants of protein adsorption onto silica particles

The extent of immunological adjuvancy of silicone-gel, from mammary implants, up to now, has not been determined definitively. This study compares the immune potentiation effects of silicone-gel with that of Freunds adjuvant, using bovine serum albumin (BSA) as the test antigen in rats. Sixty, 250 gr., male Sprague Dawley rats were divided into six groups: I- phosphate buffered saline (PBS) only, II- silicone oil (Dow Corning Medical Grade 360 liquid silicone), III- 50% silicone-gel (McGhan Medical Corp.- mammary implant) in silicone oil, IV- complete Freunds adjuvant (CFA), V- incomplete Freunds adjuvant (IFA), and VI- 50% silicone oil in IFA. Each adjuvant was mixed or emulsified with an equal volume of 50 micrograms of BSA in 150 microliters of PBS. Each immunization was given intramuscularly in a single injection. Cardiac puncture test bleeds were taken at 12, 22, 40 and 56 days post immunization and the serum anti-BSA-antibody was measured by ELISA. The results indicate that silicone-gel is a potent immunological adjuvant, compared to both CFA and IFA. Silicone oil alone is not as potent as adjuvant and seems to inhibit the immune response when mixed with IFA. There thus appears to be a distinct possibility that silicone-gel may also be able to mediate an auto-immune reaction.