An unknown -amino acid X has three ionizable groups with pK _ a values of 2.2 , 9.0 , and 10.5 . Which of the following correctly describes the physical nature of X at room temperature and its direction of migration during electrophoresis in a buffer solution at pH = 6.0 ?

Step-by-step solution

All -amino acids exist as zwitterions, which leads to strong electrostatic forces between molecules. Thus, they are high-melting crystalline solids and are insoluble in non-polar solvents like benzene. The given pK _ a values ( 2.2 , 9.0 , 10.5 ) indicate a basic amino acid, as it has one acidic carboxyl group and two basic groups. The isoelectric point ( pI ) for a basic amino acid is calculated as the average of the two highest pK _ a values: pI = 9.0 + 10.5 2 = 9.75 Since the given pH ( 6.0 ) is less than the pI