Detailed Structural Analysis of a Self-Assembled Vesicular Amphiphilic NCN-Pincer Palladium Complex by Using Wide-Angle X-Ray Scattering and Molecular Dynamics Calculations.

Wide-angle X-ray scattering experiments and all-atomistic molecular dynamics calculations were performed to elucidate the detailed structure of bilayer vesicles constructed by self-assembly of an amphiphilic palladium NCN-pincer complex. We found an excellent agreement between the experimental and calculated X-ray spectra, and between the membrane thickness determined from a TEM image and that calculated from an electron-density profile, which indicated that the calculated structure was highly reliable. The analysis of the simulated bilayer structure showed that in general the membrane was softer than other phospholipid bilayer membranes. In this bilayer assemblage, the degree of alignment of complex molecules in the bilayer membrane was quite low. An analysis of the electron-density profile shows that the bilayer assemblage contains a space through which organic molecules can exit. Furthermore, the catalytically active center is near this space and is easily accessible by organic molecules, which permits the bilayer membrane to act as a nanoreactor. The free energy of permeation of water through the bilayer membrane of the amphiphilic complex was 12 kJ mol-1 , which is much lower than that for phospholipid bilayer membranes in general. Organic molecules are expected to pass though the bilayer membrane. The self-assembled vesicles were shown to be catalytically active in a Miyaura-Michael reaction in water.