How amino acids are classified by R-groups?

Their polarity, or ten- dency to interact with water at biological pH from nonpolar and hydrophobic (water-insoluble) to highly polar and hydrophilic (water-soluble). Within each class there are grada- tions of polarity, size, and shape of the R groups. -, Aliphatic R Groups The R groups in this class of amino acids are nonpolar and hydrophobic. -Aromatic R Groups Phenylalanine, tyrosine, and tryp- tophan, with their aromatic side chains, are relatively nonpolar (hydrophobic). -Polar, Uncharged R Groups The R groups of these amino acids are more soluble in water, or more hydrophilic, than those of the nonpolar amino acids, because they contain functional groups that form hydrogen bonds -Positively Charged (Basic) R Groups The most hydrophilic R groups are those that are either positively or nega- tively charged. - Negatively Charged (Acidic) R Groups The two amino acids having R groups with a net negative charge at pH 7.0 are aspartate and glutamate, each of which has a second carboxyl group.