D.R. Absolom

Determination of the surface tension of proteins I. Surface tension of native serum proteins in aqueous media

The desorption patterns of serum proteins in hydrophobic chromatography suggest that serum proteins that remain immersed in an aqueous medium and do not become in a protein-air interface are very hydrophilic. Contact angle measurements on fairly thick layers of hydrated serum proteins, formed on ultrafiltration membranes, yield surface tensions that correlate well with the degree of hydrophilicity derived from desorption data obtained by hydrophobic chromatography. For further confirmation the absorptivity of four human serum proteins was measured with respect to surfaces of different polymers of various surface tensions, for solution in aqueous solvents of different surface tensions. The surface tension of the solvent from which a dissolved protein adsorbs to precisely the same extent onto all solid substrates (regardless of their surface tensions) is equal to the surface tension of that protein. The surface tensions found by the contact angle (first value given) and by the protein adsorption methods (second value given) were. in erg/cm2; alpha 2-macroglobulin, 71.0, 71.0; serum albumin, 70.5, 70.2; immunoglobulin M, 69.5, 69.4; immunoglobulin G, 67.4, 67.7.

Erythrocyte adhesion to polymer surfaces

Abstract Thermodynamic model considerations suggest that the adhesion of biological cells to polymeric surfaces depends on the relative magnitude of the surface tension γSV of the substrates, the surface tension γCV of the cells, and the surface tension γLV of the suspending liquid medium. Glutaraldehyde-fixed erythrocytes are identified as suitable model particles for such studies. Experimental results of the extent of erythrocyte adhesion from suspension of mixtures of buffer and varying amounts of dimethyl sulfoxide (DMSO) confirm qualitatively and in certain aspects quantitatively the thermodynamic predictions. Specifically, the prediction that the extent of cell adhesion should become independent of substrate surface tension when γLV = γCV is confirmed by experiment. On the other hand for this case the free energy of adhesion predicting zero cell adhesion is not experimentally confirmed completely. However, performing these experiments with distilled water rather than buffer reduces erythrocyte adhesion to a negligible level. It emerges that van der Waals interactions are, by a large margin, the most important forces involved in cell adhesion to polymer surfaces. Nevertheless, not only divalent cations (through bridging effects), but also monovalent cations play a certain, though limited, role.

Measurement of surface tensions of blood cells and proteins.

Department o f Mechanical Engineering Institute of Biomedical Engineering f Institute of Medical Sciences University of Toronto Toronto, Canada, M5S IA4 lJ Research Institute Hospital for Sick Children Toronto, Canada, M5G 1x8 Department o f Microbiology Department of Chemical Engineering State University of New York at Buffalo Buffalo, New York 14214 Separation Processes Branch NASAIGeorge C. Marshall Space Flight Center Huntsville, Alabama 35812

Applications of net repulsive van der Waals forces between different particles, macromolecules, or biological cells in liquids

Abstract When the sum of the interactions of two different materials with a liquid medium is larger than the sum of the interactions between the two materials and those between the molecules of the liquid medium themselves, the net van der Waals interaction between the two materials, immersed in that liquid medium, will be repulsive. It can be demonstrated that this situation prevals when the surface tension of the liquid medium has a value intermediate between the values of the interfacial tensions of the two materials. Net repulsive van der Waals interactions are shown to be responsible for the rejection of particles by solidifying melts, and for the incompatibility of polymers in solution. Repulsive van der Waals forces can be employed in the dissociation of antigen—antibody complexes, in the elution steps of hydrophobic chromatography, affinity chromatography and reversed-phase chromatography, and generally in the detachment of liquid and solid materials from solid substrates (e.g., washing, dry-cleaning, petroleum extraction from oil shales or tar sands). Finally, the implications of extremely small van der Waals attractions are discussed in connection with the stability of particle suspensions, and the strategy for devising optimal destabilization procedures.

Determination of surface tensions of proteins II. Surface tension of serum albumin, altered at the protein-air interface

Serum albumin, which itself has a surface tension of congruent to 70.3 erg/cm2, when dissolved in water lowers the surface tension of water from 72.5 to congruent to 50 erg/cm2, as measured by a variety of means, including the pendant drop, the Wilhelmy plate and the platinum ring methods. Equally low and even lower surface tensions are found with the contact angle method, on a thin layer of albumin that had been adsorbed onto a low energy surface and subsequently exposed to air. Surface tensions of drops of albumin solutions varying in concentration from 0.01 to 5.5% (w/v) yielded, with a contact angle method, values that only varied between 67 and 61 erg/cm2. With the pendant drop, the Wilhelmy plate and the platinum ring methods, one essentially measures the surface tension at the air-liquid interface, at which proteins tend to adsorb, and where reversible or irreversible reorientation can be expected. The same holds for a thin layer of protein adsorbed onto a low energy surface, exposed to air. Thus, when through the very act of surface tension measurement, or after adsorbing protein onto a substrate, protein is exposed at the air-liquid interface, it apparently loses the pronounced hydrophilicity characteristic of its native hydrated state and manifests through reorientation a much more hydrophobic tertiary configuration.

Effects of zero van der Waals and zero electrostatic forces on droplet sedimentation

Abstract The stability of concentrated suspensions of glutaraldehyde-fixed human erythrocytes layered on a D2O cushion was studied by taking as a criterion the maximum cell concentration that could be sustained without giving rise to droplet sedimentation. Greatest stability of the cell suspensions prevailed under conditions of zero van der Waals attraction and high negative cellular surface potential. The van der Waals attraction between the cells could be reduced to zero by lowering the surface tension of the medium by the admixture of 12% (v/v) dimethyl sulfoxide (DMSO), corresponding to a surface tension of the liquid of ≈65 ergs/cm2. This conforms closely to the surface tension of ≈64.5 ergs/cm2 found for the fixed erythrocytes by means of a freezing front technique. The electrostatic repulsion between the cells could be reduced to zero by the admixture of 5 × 10−8M lanthanum nitrate. In the region of zero electric charge, maximum stability, although occurring at significantly lower cell concentrations, also was achieved at zero van der Waals attraction. Mechanisms other than electrostatic repulsion and van der Waals attraction, such as density differences, mass diffusion, etc., clearly also play a role in droplet sedimentation.

Phagocytosis of bacteria by platelets: Surface thermodynamics

Abstract Engulfment of four species of bacteria by pig platelets was investigated under well defined in vitro conditions from a surface thermodynamics aspect. A simple thermodynamic model predicts that bacterial ingestion should increase with increasing bacterial surface tension if the surface tension of the liquid medium in which the platelets and bacteria are suspended is lower than the surface tension of the platelets themselves. The opposite behavior is predicted if the surface tension of the liquid medium is higher than that of the platelets. These predictions have been confirmed by phagocytosis experiments, where the platelets and bacteria opsonized and nonopsonized) have been suspended in aqueous media of different surface tensions achieved through the addition of varying amounts of dimethyl sulfoxide. Use of the thermodynamic prediction that bacterial engulfment should become independent of the surface tension of the ingested bacteria when the surface tensions of the platelets and that of the suspending medium are equal gives rise to an experimental value of the surface tension of platelets of 67.6 ergs/cm 2 , in excellent agreement with the value obtained via an equation—of-state approach from contact angles measured on layers of platelets. In addition the maximum value of the free energy of engulfment for any particular bacterium—platelet system occurs when the surface tension of the liquid equals that of the bacteria. The level of engulfment should be a minimum under such conditions thus permitting the surface tension determination of the bacteria. Experimental determinations of the minima for the four bacterial species employed gives rise to bacterial surface tensions which conform very closely to the values obtained from contact angle measurements on layers of bacteria. Thus platelet phagocytosis of bacteria provides an independent alternative method for determining the surface tension of both platelets and bacteria. The experimental data further suggest that platelet interaction with bacteria is nonspecific in the sense that the phagocytosis does not appear to be modulated by immunoglobulin F c receptors.

SURFACE TENSION EFFECTS IN THE SEDIMENTATION OF COAL PARTICLES IN VARIOUS LIQUID MIXTURES

The sedimentation volume, V sed, of coal particles in mixtures of pairs of non-polar and more polar organic liquid combinations as well as in aqueous solutions was determined at 20°C. The liquid combinations were chosen such that the surface tension, γSV, of the coal particles fell between the surface tensions, γLV, of the two liquids. A constant mass of a given coal sample was suspended in constant volumes of liquid mixtures of different concentrations. It was found that the sedimentation volume changed with varying composition of the liquid mixtures, as did the surface tension. A maximum or a minimum occurred in V sed when the surface tension of the suspending liquid was equal to that of the coal particles, i.e. when γLV = γSV. Maxima occurred in more polar and minima in the non-polar or less polar liquid mixtures. The position of the extrema, and hence the surface tension, γsv, of the particles, was found to change with particle size, in agreement with findings from other independent techniques. It was...

Determination of the surface tension of biological cells using the freezing front technique

The freezing front technique for solid surface tension measurements was used to obtain the surface tensions of glutaraldehyde-fixed human erythrocytes, and fresh human lymphocytes and grnulocytes in aqueous media. The results agree well with the values obtained by other methods and indicate that the freezing front technique is sufficiently sensitive to detect small differences (of the order of 0.1 ergs/cm2) in surface tension. This property, along with a number of applications for which it is uniquely suited makes the freezing front technique an important new approach to the measurement of the surface tensions of biological cells and of small particles in general.

Zeta Potentials, van der Waals Forces and Hemagglutination

Abstract. It has recently become possible to determine the van der Waals (Hamaker) coefficient of erythrocytes, whilst their ζ‐potential has been known for some time. With these two data the net potential energy of interaction versus distance diagrams could be elaborated for unsensitized human erythrocytes suspensed in saline water, as well as for erythrocytes monogamously sensitized with anti‐D (Rh0) antibodies of the IgG class. Unsensitized erythrocytes can approach each other, to within ≅ 79 Å of their sialoglycoprotein surfaces, leaving a distance between their actual cell membranes of ≅ 180 Å, which is considerably more than the maximum distance between the two valencies of an IgG molecule (≅ 120 Å). This explains why unaided anti‐D (Rh0) antibodies of the IgG class cannot cross‐link two D (Rh0)‐positive erythrocytes, although cross‐linking can easily be achieved with IgM class antibodies. D (Rh0)‐positive erythrocytes, monogamously sensitized with antibodies of the IgG class, can approach each other to within ≅ 60 Å (between the Fc ends of the protruding antibodies), which makes cross‐linking by means of anti‐IgG antibodies of the IgG class feasible.