The importance of the monolayer structure in bidimensional miscibility in mixed films

Favourable Interfacial Characteristics of A2 Milk Protein Monolayer

Shielding of the specific body organ using the biocompatible material helps preventing direct exposure of that part to the foreign entities responsible for infections. Here we show the potential of the A2 milk protein recovered from the milk of cow from Indian origin for possible prevention of the direct exposure to other foreign molecules. We measured the surface pressure of the monolayers of different types of protein samples using Langmuir isotherm experiments. The surface pressure measurements for the monolayer of four types of protein macromolecules have been carried out using the Wilhelmy plate micro pressure sensor. We studied the self-organization of different protein macromolecules and their monolayer compression characteristics. The electrochemical behaviour is studied using electrochemical impedance spectroscopy. We found the highest surface pressure for the monolayer of A2 protein. Further, it is also found that A2 protein exhibited the highest surface activity amongst the other proteins. This property can be effectively used for making the envelope of the A2 protein surrounding the targeted entity.

The Effect of pH on Monoglyceride-Caseinate Mixed Monolayers at the Air-Water Interface

The surface pressure (pi) area (A) isotherms and Brewster angle microscopy (BAM) of monoglyceride-caseinate mixed films spread on buffered water at pH 5 and 7 and at 20 degrees C were determined as a function of the mass fraction (X) of monoglyceride (monopalmitin or monoolein) in the mixture. The structural characteristics, miscibility, and morphology of monoglyceride-caseinate mixed films are very dependent on surface pressure and monolayer composition. The monolayer structure was more expanded as the pH and the monoglyceride concentration in the mixture were increased. From the concentration and surface pressure dependence on excess area, free energy, and collapse pressure, it was deduced that, at a macroscopic level, monoglyceride (either monopalmitin or monoolein) and caseinate form a practically immiscible monolayer at the air-water interface. The BAM images and the evolution with the surface pressure of the relative reflectivity of BAM images give complementary information on the interactions and structural characteristics of monoglyceride-caseinate mixed monolayers, which at a microscopic level corroborated in part the conclusions derived from the pi-A isotherm at a macroscopic level. Over the overall range of existence of the mixed film the monolayer presents some heterogeneity due to the fact that domains of monoglyceride (especially of monopalmitin) and spots of collapsed caseinate residues are present during the monolayer compression-expansion cycle, giving relative intensity peaks with high relative film thickness. At higher pi, after the caseinate collapse, characteristic squeezing-out phenomenon was observed. At the monoglyceride monolayer collapse the mixed film is practically dominated by the presence of monoglyceride. The prevalence of monoglyceride in the interface increases with the amount of monoglyceride in the mixture and at higher pi. However, some degree of interactions exists between monoglyceride and caseinate in the mixed film and these interactions are more pronounced as the monolayer is compressed at the highest surface pressures. Copyright 2001 Academic Press.