NUCLEAR MAGNETIC-RESONANCE STUDIES OF ACID-BASE CHEMISTRY OF AMINO-ACIDS AND PEPTIDES .3. DETERMINATION OF MICROSCOPIC AND MACROSCOPIC ACID DISSOCIATION-CONSTANTS OF ALPHA,OMEGA-DIAMINOCARBOXYLIC ACIDS

The acid-base chemistry of 2,3-diaminopropionic acid (dap), 2,4-diaminobutyric acid (dab), ornithine (orn), and lysine (lys) was studied by 13C and proton NMR spectroscopy. Macroscopic acid Kd for titration of the 2 ammonium groups of each molecule were calculated from the 13C chemical shift titration curves for the alkyl C atoms by nonlinear least squares curve fitting methods. Microscopic acid Kd for the simultaneous titration of the 2 ammonium groups of protonated orn and lys were obtained from their proton chemical shift titration curves and from their proton chemical shift titration curves and from the 13C titration curves for orn and dap. The .alpha.-ammonium group of each of these .alpha.,.omega.-diaminocarboxylic acids is apparently more acidic than its .omega.-ammonium group, but the difference probably decreases as the number of C separating the ammonium groups decreases, so that the acidities of the 2 ammonium groups of dap are almost identical. Results of PMR studies of the acid-base chemistry of glycyl-L-lysine and L-lysylglycine are reported.