Physicochemical Properties of a Bi-aromatic Heterocyclic-Azo/BSA Hybrid System at the Air–Water Interface

Abstract

The interaction of a heterocyclic azo compound with itself and with bovine serum albumin (BSA) is realized by probing the structural modifications in Langmuir (L) monolayers and Langmuir–Blodgett (LB) films. It was found from the pressure–area/molecule isotherms that the elastic, thermodynamic, and hysteretic properties of the pure azo L monolayer were strongly altered due to the variation of temperature and pH of subphase water. In addition to that, the modification of such properties of the azo L monolayer due to mixing with BSA was also studied. The incorporation of BSA within the azo molecular assembly reduced the elasticity of that assembly. Such reduction of in-plane elasticity of the pure azo monolayer can also be achieved by reducing the temperature and pH of subphase water without adding BSA. A reduction in area per molecule of the azo assembly at the air–water interface associated with the conformational change from horizontal to vertical orientation facilitating π–π interaction was observed with increase in temperature and pH of the subphase. Such parameters also affected the interactions between azo and BSA molecules within the azo/BSA binary system. The structures of pure azo and binary films can be determined after they are transferred to hydrophilic and hydrophobic Si surfaces using the LB technique. Their out-of-plane and in-plane structures, as extracted from two complementary surface sensitive techniques, X-ray reflectivity and atomic force microscopy, were found to be strongly dependent on mixing with BSA, subphase pH, temperature, and substrate nature.

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

“…Furthermore, to probe into the elastic nature of the mixed system at the air–water interface, in-plane elasticity or compressional modulus ( C S –1 ) ,,, was calculated and tabulated in Figure b as a function of surface pressure and area/mol (shown in the inset of Figure b) for the five different mixtures. Interestingly, the peak C S –1 value increases systematically with an increment of the content of DOPC in the mixed system.…”

“…In the C S –1 versus π plots (shown in Figure b), these regimes are labeled as 1, 2, 3, and 4, separated by horizontal dashed lines. The following equation can be used to compute the C S –1 from the π– A isotherms ,,, C normalS − 1 = prefix− A true( ∂ π ∂ A true) T where A is the area/molecule at a certain surface pressure π. The stiffness of the isotherm curves is represented by in-plane elasticity, which also displays differences in the physical state of monolayers and aids in understanding the molecular organization.…”

“…To understand how the individual components, i.e., DOPC and Myo, are interacting with each other at the interface in the mixed system, as well as to examine the miscibility of the mixed monolayer components, the excess area per molecule ( A exc ) was calculated. The A exc is defined in the following way , A normale normalx normalc = A 12 − A normali normald where A normali normald = A normalD normalO normalP normalC X normalD normalO normalP normalC + A normalM normaly normalo X normalM normaly normalo Here, A DOPC and A Myo are the experimentally determined mean molecular areas of individual pure monolayers, X Myo and X DOPC are the mole fractions of Myo and DOPC, respectively, and A 12 is the experimentally determined area per molecule from the isotherm of the composite mixture.…”

“…In the C S −1 versus π plots (shown in Figure 1b), these regimes are labeled as 1, 2, 3, and 4, separated by horizontal dashed lines. The following equation can be used to compute the C S −1 from the π−A isotherms 14,35,41,42…”

“…To understand how the individual components, i.e., DOPC and Myo, are interacting with each other at the interface in the mixed system, as well as to examine the miscibility of the mixed monolayer components, the excess area per molecule (A exc ) was calculated. The A exc is defined in the following way 35,42 = A A A…”