Interfacial energetics of blood plasma and serum adsorption to a hydrophobic self-assembled monolayer surface.

Interfacial energetics of blood plasma and serum adsorption to a hydrophobic, methyl-terminated self-assembled monolayer (SAM) surface (solid-liquid SL interface) are shown to be essentially the same as to the buffer-air interface (liquid-vapor LV interface). Specifically, spreading pressure (Pia) isotherms scaled on a w/v concentration basis constructed from advancing contact angles (thetaa) of serially diluted plasma/serum derived from four different mammalian species (bovine, equine, human, and ovine) on the SAM surface are not resolvable at the 99% confidence level and furthermore are found to be strikingly similar to isotherms of purified human-blood proteins. Maximum advancing spreading pressures Piamax for protein mixtures fall within a relatively narrow 17<Piamax<26 mN/m band, mirroring results obtained at the LV surface. These observations lead to the conclusion that neither depletion of coagulation proteins in the conversion of plasma to serum nor variation in the plasma proteome among species has a substantial affect on adsorption energetics to these test hydrophobic surfaces. Experimental results are rationalized on the basis that there is a generic mechanism controlling adsorption of globular-blood proteins to test hydrophobic surfaces. We conclude that this generic mechanism is the hydrophobic effect by which proteins are expelled from aqueous solution in order to increase hydrogen-bonding (self-association) among water molecules at the expense of less favorable water-protein interactions. Expelled protein readily displaces water within the hydrophobic-surface region and becomes adsorbed. The amount of water displaced per gram of adsorbed protein does not vary greatly among globular proteins because the partial specific volume v0 of globular proteins is quite conserved (0.70<or=v0<or=0.75 cm3/g protein). Any single blood protein or mixture of proteins consequently displaces nearly an equivalent amount of interfacial water and hence adsorption is observed to scale similarly with solution concentration expressed in w/v units.