P-(2-Diethylaminoet hylthiocarbamoy1) merc apt op i o-pionic acid and $-(3- diethylaniinopropylthiocarI~:~-iiioy1) niercaptopropionic acid were obtained a\ a ilihydrate and a monohydrate, respectively. It IY~. espected that both these propionic acids should h: i\(zwitterjonic structures. Surprisingly,~-(t'-dietliyla~ iiiiio~ tliyltl-iiocarl~ aii~ o~ l) inercaptopropioiiic acid (11-hydratt. showed uiiionized carboxyl cai hoiiyl ab-orptini I at. i 8 ...