D. R. Absolom

Surface thermodynamics of leukocyte and platelet adhesion to polymer surfaces

Adhesion of leukocytes and platelets to solid substrates of different surface tensions and hence different wettability is studied from a thermodynamic point of view. A simple thermodynamic model predicts that cellular adhesion should increase with increasing surface tension of the solid substrate if the surface tension of the medium in which the cells are suspended is lower than the surface tension of the cells. If the surface tension of the suspending medium is higher than that of the cells, the opposite behavior is predicted. These predictions are borne out completely by neutrophil adhesion tests, where the surface tension of the aequeous suspending medium is varied by addition of dimethyl sulfoxide (DMSO). Platelet adhesion experiments also confirm these predictions, the only difference being that surface tensions of the suspending medium above that of the platelets cannot be realized, owing to exudation of surface active solutes from the platelets. Utilization of the thermodynamic prediction that cellular adhesion should become independent of the surface tension of the substrate when the surface tensions of the cells and that of the suspending medium are equal leads to a value of the surface tension of neutrophils of 69.0 erg/cm2,† in excellent agreement with the value obtained from contact angles measured on layers of cells.

Repulsive van der Waals Forces. II. Mechanism of Hydrophobic Chromatography

Abstract When two materials with different interfacial free energies are immersed in a liquid with an interfacial free energy intermediate between those of the two materials, the net van der Waals forces between these two materials are repulsive. Thus by lowering the interfacial free energy of the liquid medium, solutes or particles previously adsorbed onto low energy surfaces can be readily eluted from such surfaces. This is demonstrated by the coupling to and subsequent elution from Octyl Sepharose and Phenyl Sepharose of serum and other proteins. The elution of all proteins commenced when the surface tension of the eluting liquid was decreased to a point just below that of the protein in question. The eluted serum proteins successively emerged from the column in the exact decreasing order of their own interfacial free energies. In hydrophobic chromatography, coupling is favored when the van der Waals forces between solutes (or particles) and ligand are attractive (and maximum, frequently through the ad...

Repulsive van der Waals Forces. I. Complete Dissociation of Antigen-Antibody Complexes by Means of Negative van der Waals Forces

When two types of particles and/or macromolecules with different inter- facial free energies are immersed (or dissolved) in a liquid medium with an interfacial free energy intermediate between those of the particles or macro- molecules, the net van der Waals forces between these particles or molecules are repulsive. Thus by lowering the interfacial free energy (proportional to the surface tension) of their liquid medium, antigen-antibody (Ag-Ab) complexes of the van der Waals type can be readily dissociated, as could be demonstrated with the antigen 3-azopyridine (P3) coupled to rabbit serum albumin (P3A) and rabbit anti-P3 antiserum. As surface tension lowering agents, ethylene glycol (EG) and dimethyl sulfoxide (DMSO) were principally used. Prevention of the formation of P3A-anti-P3 complexes could be effected with the addition of less EG or DMSO than was needed for the dissociation of the precipitate, once formed. The reasons for this effect are discussed. P3A-anti-P3 complexes dissociated with EG, re-...

The “hydrophobic effect”: Essentially a van der Waals interaction

SummaryIt has been shown thermodynamically, and illustrated by means of a typical example, that the preferential attraction between hydrophobic determinants immersed in water, commonly alluded to as the “hydrophobic effect”, can be entirely ascribed to van der Waals interactions. Quantitatively, in water, the attraction between two hydrophobic determinants is stronger than the attraction between a hydrophobic and a hydrophilic determinant, although the latter attraction is not so small as to be negligible. The interaction between hydrophilic determinants in water is attractive but small and may be easily overwhelmed by the electrostatic repulsion which occurs between such entities.There is no repulsion by the solvent. On the contrary, the attraction between water and a hydrophobic material as well as between water and a hydrophilic material is strong. This interaction does play a role in determining the overall strength of the interaction between hydrophobic and hydrophilic determinants but cannot render the attraction between such determinants negligible. The attraction between hydrophobic and hydrophilic determinants in an aqueous medium can be made exeedingly small and may indeed (after lowering the surface tension of the liquid) be changed into a repulsion. The latter phenomenon is used in the elution step of the protein separation method called “hydrophobic chromatography”.ZusammenfassungEs wird auf thermodynamischer Grundlage gezeigt und an Hand eines typischen Beispiels erläutert, daß die Anziehung zwischen hydrophoben Partikel in Wasser vollständig durch van der Waals-Wechselwirkungen erklärt werden kann. Die Anziehung zwischen solchen Teilchen oder Molekülen ist stärker als die Anziehung zwischen hydrophoben und hydrophilen Partikeln in Wasser, die jedoch nicht vernachlässigbar klein ist. Die Wechselwirkung zwischen hydrophilen Partikeln ist so klein, daß sie leicht von elektrostatischen Wechselwirkungen überdeckt werden kann.Eine Abstoßung durch das Lösungsmittel findet nicht statt. Im Gegenteil, die Anziehung zwischen Wasser und einem hydrophoben Material ebenso wie diejenige zwischen Wasser und einem hydrophilen Material ist beträchtlich. Diese Wechselwirkung spielt zwar eine Rolle in der gesamten Wechselwirkung zwischen hydrophoben und hydrophilen Partikeln, kann aber die Anziehung zwischen hydrophob und hydrophil in Wasser nicht zum Verschwinden bringen. Die Wechselwirkung zwischen hydrophob und hydrophil kann jedoch durch Erniedrigung der Oberflächenspannung des Wassers abstoßend gemacht werden. Dieser Umstand wird im Elutionsschritt des als “hydrophobe Chromatographie” bekannten Verfahrens zur Trennung von Proteinen benutzt.

Surface thermodynamics of normal and pathological human granulocytes

Surface tensions of normal and pathological granulocytes were determined by (1) adhesion to solid substrates of different surface tensions while suspended in liquid media of different surface tensions, and by (2) measurement of cell-liquid-vapor contact angles obtained with sessile drops of saline water on cell monolayers. The results obtained by the two different methods were in close conformation with one another. With the cell adhesion emthod some residual leukocyte adhesion still persists even under conditions where there no longer is a van der Waals attraction between cells and solid substrate. At low ionic strength and by the abolishment of all multivalent cations through the admixture of EDTA, that residual cell adhesion virtually disappears (with normal as well as with pathological granulocytes), indicating that the earlier residual cell adhesion did indeed arise from electrostatic interactions mediated by multivalent cations (probably Ca2+). Comparison of the capacities for engulfment and the surface thermodynamics data of normal and pathological granulocytes obtained in this study leads to the novel observation that the phagocytic episode from half to complete engulfment of bacterial particles by granulocytes appears to be the crucial step from the thermodynamic point of view.

Enhanced erythrocyte suspension layer stability achieved by surface tension lowering additives

ABSTRACT An electrostatic repulsion - van der Waals attraction mechanism was used to explain the stability of erythrocyte suspensions layered on a D2O cushion. By lowering the surface tension of D2O to values around 65 ergs/cm2 by admixture of varying concentrations of dimethyl sulfoxide (DMSO), the van der Waals attraction between cells was reduced to zero. The zeta potentials, as measured by microelectrophoresis, were reduced also by DMSO but at a slower rate than for the surface tensions as shown by total interaction energy calculations. In the presence of low van der Waals attraction and at large negative surface potentials, high cell concentrations were supported on a D2O cushion without the suspension layer becoming unstable. Reduction in the electrostatic repulsion while maintaining low van der Waals attraction significantly reduced the suspension layer stability. Clearly defined secondary minima varying in depths from 3.9kT to 7.8BkT at separation distances varying from 55A to 65A were obtained fr...

Affinity Diffusion II. Comparison Between Thermodynamic Data Obtained by Affinity Diffusion and Precipitation in Tubes

Association constants (Ka) of the precipitating system bovine serum albumin (BSA) goat anti-BSA were obtained at different temperatures via affinity diffusion (taking l/Kd - Ka) as well as via precipitation in tubes at optimal ratios. With affinity diffusion values of Ka of 0.6 to 1.1 x 10(5) l/M were found, whilst with precipitation in tubes Ka was from 3.3 to 11.2 X 10(7) l/M, using the same BSA and anti-BSA preparations. Via affinity diffusion binding energies delta F of approximately -6 to -7 kcal/M were found, with values of delta H close to zero, and a delta S of +23 entropy units. With precipitation in tubes these values were delta F -10.2 to -10.7 kcal/M, delta H -4.6 to -7.6 kcal/M and delta S +10 to +20 entropy units. The differences found with the two different methods must be ascribed to the fact that with affinity diffusion of precipitating antigen-antibody systems one just measures the interaction between the precipitating components with the highest dissociation constants, whilst with precipitation in tubes one measures the total energy of association of the system. With affinity diffusion and with precipitation in tubes, the same degree of positive entropy is observed. The system measured with affinity diffusion is approximately isothermic, whilst the total system, measured by precipitation in tubes, is strongly exothermic. Affinity diffusion still takes place at pH 9.5, at which pH no precipitation in the liquid phase takes place at optimal ratio; one may conclude from this that affinity diffusion mainly involves van der Waals interactions, as electrostatic bonding between BSA and anti-BSA is virtually abolished at that pH. This agrees well with the observation that the affinity diffusion reaction is isothermic.

Affinity Diffusion. I. Method for Measuring Dissociation Constants of Precipitating Antibodies

Dissociation constant (Kd) of antigen-antibody reactions can be obtained from the rates (measured by the progression of the precipitate vs. time) with which antigens diffuse into antibody-containing gels, as a function of antibody-concentration. A bovine serum albumin vs. rabbit anti-bovine serum albumin system was studied with whole antiserum and with its purified IgG fraction. A value was found for Kd of approximately 1.0 x 10-5 moles per liter. It is note- worthy that in monodimensional single diffusion gel precipitation systems of this type, the rate of progression of the precipitate front is significantly faster than the molecular diffusion coefficient of the antigen.

EFFECTS OF DMSO ON THE PROPERTIES OF RED BLOOD CELLS IT. ELECTROKINETICS AND SEDIMENTATION

Abstract ABSTRACT The Influence of dimethyl sulfoxide (DMSO) concentrations from 0 to 22% (v/v) was studied on the electrophoretlc nihilities, the droplet formation times, the cell sedimentation rates and the cell sedimentation volumes of fresh and aldehyde-fixed human erythrocytes and on fixed turkey erythrocytes. DMSO influenced the ζ-potentials of the different cells in various ways. These observations remain phenomenoncgical for the time being; it Is not as yet possible to predict quantitatively how the ζ-potentials of given cell types will be affected by the admixture of DMSO. Low concentrations of DMSO (up to 7.5%) cause red cells to swell, resulting in an Increase in sedimentation velocity due to their increased Stokes radius. At higher DMSO concentrations no further swelling occurs so that, due to a decrease in density difference between the cells and the liquid medium, the sedimputation velocities then decrease, Cell sedimentation volumes and droplet formation times reached maxima at 13% DMSO (fo...