ENTHALPIES OF SUBLIMATION AND VAPOR-PRESSURES OF 14 AMINO-ACIDS AND PEPTIDES

Simultaneous torsion- and weighing-effusion techniques are used to measure the saturation vapour pressures as a function of temperature for 14 amino acids and peptides. The enthalpies of sublimation are derived from the temperature dependence of the vapour pressures. Overall mean values for both techniques are: α-glycine, ΔHs(418.93 K) = (136.5 ± 2) kJ mol-1; L-alanine, ΔHs(413.98 K) = (132.8 ± 1) kJ mol-1; DL-α-amino butanoic acid, ΔHs(408.84 K) = (132.0 ± 2) kJ mol-1; 2-amino-2-methyl-butanoic acid, ΔHs(412.77 K) = (134.2 ± 1) kJ mol-1; N-acetylglycine, ΔHs(389.30 K) = (127.1 ±1 ) kJ mol-1; L-proline, ΔHs(406.26 K) = (127.4 ± 1) kJ mol-1; DL-pyroglutamic acid (DL-5-oxo-proline), ΔHs(405.42 K) = (133.2 ± 1) kJ mol-1; 4-hydroxy-L-proline, ΔHs(470.90 K) = (162.6 ± 2) kJ mol-1; 2-amino benzoic acid II (anthranilic acid II), ΔHs(338.49 K) = (100.0 ± 1) kJ mol-1; 3-amino benzoic acid, ΔH(374.75 K) = (122.0 ± 1) kJ mol-1; 4-amino benzoic acid, ΔHs(372.88 K) = (112.3 ± 1) kJ mol-1. The temperatures given are mid-range values at which the saturation vapour pressure of each substance is 0.4 Pa. In the case of glycylglycine, L-azetidine-2-carboxylic acid, and DL-serine, decomposition was observed. © 1979.