A study of monolayers at low surface pressures

Abstract

A sensitive surface balance has been developed for the measurement of low surface pressures. It has been found that the surface pressure against area relationships of the gaseous films are affected by molecular cohesion at the air/aqueous interface so that molecular weights cannot be estimated reliably from the equation l7A = 17Ao + nRT.On the other hand, it is suggested that low surface pressure studies make it easy to distinguish between proteins and their dissociation products.

Proton-dependent dissociation equilibrium of hemoglobin. 2. Surface pressure measurements in monolayers of horse hemoglobin(III)

“…According to this equation, it is possible to calculate the molecular weight by measuring the surface pressure as a function of the surface concentration cs (cs = If A). Such investigations on protein monolayers result in molecular weights which agree fairly well with the molecular weight in solution found by other methods (Guastalla, 1939;Bull, 1945aBull, ,b, 1951 Imahori, 1952a,b; Fredericq, 1952;Allan and Alexander, 1954;Harrap, 1955;Benhamou, 1956;Muramatsu and Sobotka, 1962). For the parameter Ao, which has been termed "coarea" in analogy to the corresponding term in the van der Waals equation, a numerical value of roughly 107 cm2/g has been determined for different proteins.…”

Interfacial Behavior of Wheat Puroindolines: Study of Adsorption at the Air–Water Interface from Surface Tension Measurement Using Wilhelmy Plate Method

“…Bull (48) has studied the spread monolayers of proteins over a subphase containing an inorganic salt. The salt-induced ease of spreading and unfolding is generally explained either by the salting out phenomena (49) or by the diminution of intramolecular cohesion, caused by reduced electrostatic interaction involving ionizable groups (50). As the thickness of the interfacial double layer is expected to be thinner and the surface potential is expected to be lower at higher ionic strength, so an adsorbing protein molecule would experience a reduced repulsive force over longer distance from the interface.…”

New method of studying the low surface pressures of monolayer at air/water interface

“…The major causes limiting the sensitivity are the following: The contact angle of the lamella with water, the collection of dust, the evaporation of the subphase, and the effects of drainage that affect the obtention of a fast null detection as well as its stability. 7 On the other hand, based on the technique of Langmuir, various experimental set up such as the one of Guastalla 8 have offered a sensitivity in the 10-3 mN m-I range. Some other groups designed a system with a sensitivity ranging between 10-2 to 10-3 mN m-I , namely Puddington,9 Alexander, 10 Anderson and Evett, II Tvaroha, 12 Allan and Alexander, 7 Trurnit and Lauer, 13 Mann, Jr., and Hansen,14.1; Gaines,lf; Vroman et al, 17 and recently Gersfeld et al IH In this work, we report a new method to detect low surface pressures of a monolayer at air/water interface.…”