Affinity separation by Langmuir–Blodgett deposition of bovine serum albumin using arachidic acid as specific ligand

Role of Sn(II) in Mediating the Formation and Organization of a Langmuir Monolayer

The influence of the Sn(II) ion on the formation and morphology of an arachidic acid (AA) monolayer was investigated using Langmuir film formation technology, pressure-area (Π-A) isotherm measurements, and Brewster angle microscopy (BAM). Our findings indicate that AA Langmuir monolayers exhibit organization that depends on subphase pH and Sn²⁺ concentration. There are multiple equilibria that are relevant to the complexation of AA monolayers, and the balance of Sn(OH)_n equilibria and Sn(AA)_n equilibria gives rise to unusual monolayer structural effects. With Sn²⁺ in the subphase, the AA monolayer exhibits an isotherm characterized by the absence of a collapse point and with a pH-dependent change in isotherm shape not consistent with the formation of an ordered solid phase. The amphiphile headgroup equilibrium mediates the absence of collapse seen experimentally and the ability of the monolayer to retain organization at a surface pressure of ca. 70 mN/m. BAM images show that the morphology of the monolayer depends on the Sn²⁺ concentration, consistent with several species of Sn(AA)_n, where n = 1, 2, or 3, contributing to the overall monolayer order.

Lipid-Protein Interactions in Langmuir Monolayers under Dynamically Varied Conditions

In the Langmuir monolayer technique, a single layer of molecules is formed on a water subphase. This approach was used to mimic the antitumoricidal lipid-protein complex of oleic acid and bovine α-lactalbumin called the BAMLET complex. Our previous studies have shown that at the interface, the BAMLET complex is stabilized by the hydrophobic forces supported by the hydrogen bonds. This study provides an insight into the influence of calcium ions and the experimental conditions (temperature and subphase pH) on the stability of the complex at the interface. The Langmuir technique was expanded using a dosing pump to exchange the subphase and deliver additional substances to the system. We investigated the interactions between oleic acid monolayer and α-lactalbumin in the presence of Ca²⁺ in the bulk and the effect of varied experimental conditions on the complex stability. The role of calcium ions in this system is important because (in addition to low pH and relatively high temperature) it affects the conformational changes within the protein molecule and facilitates the transition of α-lactalbumin into the molten globule state. A partially unfolded state is required to form the BAMLET complex. We found that the mixed monolayer spread at the interface is stable despite drastic changes in the process conditions and remains stable even after the subphase exchange. This study of molecular interactions explored by the Langmuir technique with peristaltic pump enabled to understand the role of Ca²⁺ in BAMLET complex formation.

Effects of Cu(II) on the Formation and Orientation of an Arachidic Acid Langmuir-Blodgett Film

The influence of the copper(II) ion on the formation, morphology, and organization of an arachidic acid monolayer was investigated using Langmuir-Blodgett (LB) monolayers, Π-A isotherms, and Brewster angle microscopy (BAM). Our findings indicate that a Cu²⁺-complexed LB film exhibits an order that depends on the subphase pH, analogous to other metal ions. Yazdanian , M. ; et al. Ionic Interactions of Fatty Acid Monolayers at the Air-Water Interface . Langmuir 1990 , 6 , 1093 - 1098 . Kurnaz , M. L. ; et al. Morphology of Microphase Separation in Arachidic Acid-Cadmium Arachidate Langmuir-Blodgett Multilayers . J. Phys. Chem. 1996 , 100 , 11113 - 11119 . The metal ion facilitates the formation of solid-phase films at surface pressures as low as 5 mN/m. The films exhibit a rigid, ordered phase, evidenced by the absence of a collapse point and an increase in surface pressure rather than the typical sharp decrease in surface pressure, indicative of film failure. Amphiphile ionic charge vs pH (i.e., the extent of arachidic acid protonation) plays a role in the observed absence of collapse and the ability of the films to maintain order and cohesion at high surface pressures (ca. 65 mN/m). Additionally, film thickness data suggest that the incorporation of Cu²⁺ ions induces a change in orientation of the aliphatic chains of the amphiphiles and that amphiphile solubility in the subphase may play a role in the observed film behavior at low surface areas and high pH.