Interfacial Interactions of a Myoglobin/DOPC Hybrid System at the Air–Water Interface and Its Physicochemical Properties

Abstract

In the present study, the intermolecular interactions between a water-insoluble phospholipid (DOPC) and watersoluble protein (myoglobin) and the interaction among themselves were investigated at the air−water interface using the Langmuir and Langmuir−Blodgett techniques. The effects of changes in physicochemical factors, like pH and temperature, on these interactions were also examined. Surface pressure−molecular area (π−A) isotherms of the DOPC monolayer at the air−water interface, with and without myoglobin (Myo) revealed the evolution of various physical properties, such as elastic, thermodynamic, and hysteric properties, in response to changes in subphase pH and temperature. With the increment of subphase pH from 5 to 7 at a fixed temperature (20 °C), the DOPC isotherm expanded, and the in-plane elasticity (C S −1) decreased, but no significant presence of hysteresis was encountered in either of the pH values. On the other hand, a diminution of temperature (from 20 to 5 °C) leads to an expansion of monolayers yielding low elasticity and significant hysteresis. The incorporation of Myo molecules within the DOPC monolayer decreased the C S −1 value of the DOPC monolayer. Such a decrement in C S −1 was also encountered while increasing the pH and decreasing the temperature (T) of the subphase in the absence of Myo. Systematic expansion of DOPC isotherm and increased hysteric area with the increase in Myo proportion were observed and the atomic force microscopy (AFM) observations suggested a strong conjugation between Myo and DOPC in the mixed monolayer. The denaturation effect of Myo molecules was studied using AFM at different temperatures. Furthermore, the Myo molecules were found to be most surface active at pH = 7, which is very close to its isoelectric point. These observations come up with the interaction mechanism between biomolecules under dynamically varied conditions.

Counterion Association of Ionic Drugs with Sodium Tetradecyl Sulfate in the Aqueous Medium

“…Numerous drug–surfactant assemblies have been researched recently because of the vital significance of the pharmacological and therapeutic interactions between the drugs and the surfactant. − Combining a drug and a surfactant shows interaction and provides greater features than the drug or surfactant functioning independently. − Ionic medications have grown in importance recently as organic counterions or additions to enhance the interfacial and micellization properties of a charged surfactant and also to boost the concentration of pharmaceuticals that are only partially dissolved in the aqueous medium. , Whenever there are extra ingredients such as electrolytes, the critical micelle concentration (CMC) of the surfactants decreases. , Since they decrease their efficacy surface area per headgroup by limiting undesirable contact between each headgroup, additives, remarkably, make it simpler to induce an appearance change in surfactant micelles. The total amount of counterions that are physically associated with a micelle is compared to the amount of surfactant molecules (aggregate number) that reside in an ionic micelle to determine the counterion binding constant. − The most often used acceptable methods for estimating the counterion binding constant are the Corrin–Harkins (CH), modified CH approach, and the slope–ratio of conductance method …”