Investigation of Hydrophobic Interactions in Colloidal and Biological Systems by Molecular Dynamics Simulations and NMR Spectroscopy

Abstract

Interactions of hydrophobic molecular domains determine many of the functional properties of food proteins and colloidal food aggregates, such as emulsification, gelation, and foaming ability. A molecular basis for macromolecular interactions and conformational stability is established through investigation of simple model systems. Molecular modeling and dynamics simulations have been used to study the role of hydrophobic interaction forces in driving the formation of model amphiphile aggregate systems. An approximation to hydrophobic attraction between hydrocarbon tails was required to achieve stable, dynamic aggregate models for Aerosol-OT (AOT)/water/oil microemulsions, micelles of AOT in water, and a stacked AOT/para-chlorophenol gel in either CCl4 or benzene. One- and two-dimensional NMR spectroscopic methods have been used to characterize the pH and temperature dependent conformational changes in the model polypeptide poly(l-lysine). Changes in proton chemical shifts and line widths indicate that the backbone mobility of poly(l-lysine) is not greatly diminished by the coil−helix transition. ROESY and transverse-ROESY couplings, as well as T 1 and T 2 relaxation measurements, suggest that lysyl side chain mobility remains largely unrestricted upon formation of periodic secondary structure. Molecular dynamics simulations of poly(l-lysine) conformers substantiate the importance of hydrophobic side chain domains in stabilizing secondary structural features in aqueous solution.

The Structure and Thermodynamic Stability of Reverse Micelles in Dry AOT∕Alkane Mixtures

“…Comprehensive MD simulations have also been performed to study the stability of micelles with respect to aggregation [6] and the optimum solvation shells of AOT molecules [7]. Both of these studies reported good agreement with experimental observations.…”

“…β α (14) where the charges on the sulfonate and sodium ions are q = -1 and +1, respectively, and α Na-Na = 0.021025 kJmol -1 nm 12 , α AOT-AOT = 2.6341 kJmol -1 nm 12 , β Na-Na = 0.7206 x 10 -4 kJmol -1 nm 6 and β AOT-AOT = 0.002617 kJmol -1 nm 6 . The cross terms are obtained using…”

Using Microemulsions: Formulation Based on Knowledge of Their Mesostructure

“…315 To our best knowledge, Alaimo et al were the first to investigate the hydrophobic interaction forces that drive the formation of amphiphile aggregate systems by means of MD simulations with all-atom description. 318 Indeed, they simulated water/AOT/toluene microemulsion at 300 K during 250 ps considering both implicit and explicit diluent (toluene) and pointed out that the explicit description of the solvent molecules, that takes into account the hydrophobic force, is essential for an accurate description of the microemulsion phases. However, the systems simulated were very small compared to the length of the long-range weak forces measured experimentally (more than 10−60 nm).…”

Atomic Force Microscopy Study of Non-DLVO Interactions between Drops and Bubbles

“…Hydrophobic bodies are found to possess attractions stronger than the VDW force in close contact with each other in water. Such water-mediated attraction, defined as hydrophobic (HB) interaction, extensively exists between hydrophobic matters and is believed to play a vital role in self-assembly processes such as protein folding, membrane formation, molecular recognition, and even micellization. − A large body of literature exists on the characterization of hydrophobic interactions, though the origin of such unique force still remains incompletely understood. − Among the hydrophobic bodies extensively studied, bubbles are remarkable due to their strong hydrophobicity and are usually adopted as hydrophobic probes in AFM measurements. − The hydrophobic interaction between air bubbles and hydrophobic surfaces has been studied and well characterized by Zeng's research group, with a decay length in the range of 0.35–1.6 nm depending on the specific surface chemistry being reported. ,,− Hydrophobic attraction has also been found between oil drops and is reported to act in a shorter range compared to bubble systems. , It is therefore hypothesized that the heterocoalescence between bubbles and oil drops has a strong relationship with hydrophobic interaction …”