INVESTIGATION OF HYDROPHOBIC INTERACTIONS IN COLLOIDAL AND BIOLOGICAL-SYSTEMS BY MOLECULAR-DYNAMICS SIMULATIONS AND NMR-SPECTROSCOPY

Interactions of hydrophobic molecular domains determine many of the fu nctional properties of food proteins and colloidal food aggregates, su ch as emulsification, gelation, and foaming ability. A molecular basis for macromolecular interactions and conformational stability is estab lished through investigation of simple model systems. Molecular modeli ng and dynamics simulations have been used to study the role of hydrop hobic 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 mo dels for Aerosol-OT (AOT)/water/oil microemulsions, micelles of AOT in water, and a stacked AOT/para-chlorophenol gel in either CCl4 or benz ene. One- and two-dimensional NMR spectroscopic methods have been used to characterize the pH and temperature dependent conformational chang es in the model poly-peptide poly(L-lysine). Changes in proton chemica l 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 mea surements, suggest that lysyl side chain mobility remains largely unre stricted upon formation of periodic secondary structure. Molecular dyn amics simulations of poly(L-lysine) conformers substantiate the import ance of hydrophobic side chain domains in stabilizing secondary struct ural features in aqueous solution.