Amino acids with charged (basic or acidic) side chains are very polar and they are nearly always found in the outside of protein molecules.
Carboxyl groups in water loose an H+ ion to become negatively charged.
They are therefore acid.
Amino acids with acidic side chains:
Amines in water combine with an H+ ion to become positively charged
They are therefore basic.
Amino acids with basic side chains:
Arg: The NH3+ group of Arg is very basic
because its positive charge is stabilized by resonance.
His: The nitrogens of the cycle have a relatively weak affinity for an H+ and are only partly positive at neutral pH.
Amino acids with uncharged polar side chains are relatively hydrophilic and are usually on the outside of proteins.
Amino acids with non polar side chains tend to cluster their side chains
together on the inside of proteins.
They are: G, P, A, V, L, I, F, M, W, C.
Paired cysteins allow disulphide bonds.