Forces between proteoheparan sulfate layers adsorbed at hydrophobic surfaces

• The forces between proteoheparan sulphate layers adsorbed at hydrophobic surfaces were investigated by direct surface force measurements. In 0.2 mg/ml proteoheparan sulphate and 0.1 mM NaCl, the forces were monotonically repulsive, with one distant regime having a decay length of about 180 Å, and one steeply repulsive proximal part at distances smaller than about 100 Å. Only small effects were observed on dilution with 0.1 mM NaCl, indicating ”irreversible” adsorption. The decay length of the distant force component was 280 Å after dilution, whereas the proximal repulsive component remained unchanged. Furthermore, after dilution, a weak adhesion (F/R = 200 mN/m) was observed. At addition of CaCl2, the decay length of the distant repulsion decreased from 280 Å in 0.1 mM NaCl to 86 Å and 77 Å in 1.25 and 2.5 mM CaCl2, respectively. The deacay-lenghts in CaCl2 solutions are significantly larger than the expected Debye-lengths, demonstrating the predominance of steric forces. Furthermore, on addition of CaCl2 the magnitude of the adhesion increased from 200 mN/m to 1000 mN/m, and the proximal repulsion was observed at slightly smaller distances. It was found that both steric and electrostatic forces contribute to the interactions between proteoheparan sulphate layers

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