Certain mixtures of natural molecules, like choline chloride and urea, form a liquid at room temperature even though each solid melts above 50°C. This happens because they form a deep eutectic system, where hydrogen bonding between the molecules drastically reduces the melting point. This lets chemists use a non-toxic, biodegradable liquid (NADES) to dissolve everything from lignin to DNA, replacing harmful organic solvents in green chemistry.