Hydrophobic and hydrophilic
Water is a polar molecule. Electrons in the covalent OH bonds are shared unequally with the oxygen being more negative than the hydrogen. The OH bonds are referred to as polar covalent.Place your pointer over the diagram to see an electron density map showing regions of partial negative charge (δ–) at O and partial postive charge (δ–) at H.
Because both hydrogens are on the same side of the oxygen in the water molecule this molecule is also referred to as a polar molecule with the H side being more positive, and the O side being more negative.
The terms hydrophobic and hydrophilic are used to describe the interactions of the amino acid side chains with water.
Electrically charged side chains are hydrophilic.
Negatively charged side chains are attracted to the positive (H) side of the water molecule.
Positively charged side chains are attracted to the negative (O) side of the water molecule.
Positively charged side chains are attracted to the negative (O) side of the water molecule.
Polar side chains are hydrophilic.
This is again due to the attraction of oppositely charged regions to one another.
Nonpolar side chains are hydrophobic.
These do not have any positive or negative regions to interact with the positive and negative regions on water (just like the mostly hydrocarbon substance oil is insoluble in water).