Here's why:

* Hydrophobicity: Hydrophobic amino acids have side chains that are not attracted to water. They prefer to be in the interior of proteins, away from the watery environment.

* Non-polar side chains: Their side chains don't have any groups that readily gain or lose protons (H+ ions) to become charged.

* pH and ionization: The pH of a solution affects the ionization state of amino acids. At pH 6, the carboxyl group (COOH) of amino acids is generally deprotonated (COO-), and the amino group (NH2) is generally protonated (NH3+). However, these charges are on the backbone of the amino acid, not on the side chains of hydrophobic amino acids.

Examples of hydrophobic amino acids:

* Alanine (Ala, A)

* Valine (Val, V)

* Leucine (Leu, L)

* Isoleucine (Ile, I)

* Proline (Pro, P)

* Phenylalanine (Phe, F)

* Tryptophan (Trp, W)

* Methionine (Met, M)

Note: While these amino acids are typically uncharged at pH 6, there might be some slight variations in charge depending on the specific protein environment. However, their primary characteristic is their lack of a significant charge.