The structure of DMPC. The molecule is divided into three portions of the hydrophobic tail, the glycerol backbone, and hydrophilic headgroup. In the present work, the division is done as denoted in the figure, though the diving scheme is always of some ambiguity.
The densities of the hydrophobic tail, the glycerol backbone, the hydrophilic headgroup, and water as functions of the separation along the -axis from the center of mass of the 128 DMPC molecules. The densities obtained over the positive and negative -domains are averaged, and the averaged density is shown against the positive -abscissa. The densities of the tail and glycerol refer to the sums of the (number) densities of the carbons and oxygens contained in the tail and glycerol portions of Fig. 1, respectively, and the density of the headgroup is the sum of the (number) densities of the carbons, oxygens, nitrogen, and phosphorus in the corresponding portion. The water density is expressed with respect to the center of mass of the water molecule. Six regions are introduced by dividing the domain of with an interval of and are numbered from the membrane inside to outside.
The solvation free energy in regions I–VI and in bulk water. Regions I–VI are numbered from the membrane inside to outside by identifying the solute position in terms of the center-of-mass separation along the -axis from the membrane center and dividing the domain of with an equal interval of . The bulk denotes the region far from the membrane, and in the bulk is equal to the solvation free energy of the solute inserted into neat water. The error bar is expressed at confidence level and is smaller than the size of the corresponding data symbol when it is not shown. The lines connecting the data are drawn for eye guide.
and for the DMPC and water contributions and for the total in regions I–VI and in bulk water for (a) CO, (b) , (c) benzene, and (d) ethylbenzene. In the bulk, the DMPC contribution is absent and the water contribution is equal to the total. The total values are the same as the corresponding ones shown in Fig. 3. The error bar is expressed at confidence level and is smaller than the size of the corresponding data symbol when it is not shown. The lines connecting the data are drawn for eye guide.
The energy distribution functions and of the benzene solute against the solute-solvent interaction energy . (a) and for benzene-DMPC, (b) for benzene-water, and (c) for benzene-water. In all of (a)–(c), the logarithmic graduation is adopted for both the left and right ordinates. In (a) and (c), the graduation for the abscissa is changed at . When , the abscissa is linearly graduated and the ordinate refers to the left. When , the graduation is logarithmic also for the abscissa and is plotted against the right ordinate. In (a) and (b), is simply zero for .
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