Molecular surface hydrophilic regions

A similar argument can be made for electronic features such as electron density, polarization and polarizability. These are critically dependent on the ionization state of the molecule, but the conformahonal state is also highly influential. One highly approximate yet useful reflection of electron density is afforded by the polar surface area (PSA), a measure of the extent of polar (hydrophilic) regions on a molecular surface (see Chapter 5). 

Fig. 6. a Model of [Gd(teta)], and division of the surrounding space into hydrophilic (above) and hydrophobic (below) hemispheres, b Electrostatic potential [au] at the molecular surface of [Gd(teta)] in the hydrophilic (carboxylate, left) and hydrophobic (macrocycle, right) regions... 

Color-coded molecular surfaces can provide qualitative or quantitative displays of hydrophobic and hydrophilic regions, neutral and charged amino acid side chains, electrostatic potential, and conformational mobility of side chains (based on the temperature factors from X-ray crystallographic refinement or moelcular dynamics simulation). Color-coding by hydro-... 

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