JEE Main · 2023 · 15 Apr 2023 · Shift 1 · Biomolecules

Arginine is an $\alpha$-amino acid that also bears a strongly basic guanidinium side chain. Like other amino acids it exists in the solid as a dipolar zwitterion, so it is a crystalline solid and, because of the strong electrostatic forces in its lattice, melts at a fairly high temperature. Its carboxyl, $\alpha$-amino and guanidinium groups each ionise, so it is associated with more than one $\mathrm{p}{K}_a$ value. Being a highly polar, charged species it dissolves readily in water but is almost insoluble in a non-polar solvent such as benzene. The claim that arginine has high solubility in benzene is therefore not true.