Determination of the acid dissociation constants for WR-1065 by proton NMR spectroscopy.
The acid dissociation constants for N-(2-mercaptoethyl)-1,3-diaminopropane (WR-1065) were determined in D2O by 360- and 500-MHz NMR spectroscopy. Results obtained at 0.21 M initial ionic strength and 26 degrees C were corrected to 25 degrees C yielding pKD1 = 8.28 +/- 0.04, pKD2 = 9.88 +/- 0.07, and pKD3 = 11.58 +/- 0.03. Correction of these values for the effect of the deuterium isotope upon the ionization reaction yielded dissociation constants in water of pKH1 = 7.69 +/- 0.09, pKH2 = 9.35 +/- 0.09, and pKH3 = 11.10 +/- 0.08. Analysis of the changes in chemical shift with pD indicated that the first ionization occurs largely through ionization of the thiol group (approximately 67%) and to a lesser extent the secondary ammonium group (approximately 30%), whereas the third ionization involves mainly the secondary ammonium group (approximately 65%) and to a lesser extent the primary ammonium group (approximately 30%). Estimates of the microscopic pK values for WR-1065 were also obtained from the results.
Newton
G L
GL
Department of Chemistry, University of California, San Diego, La Jolla 92093.
Dwyer
T J
TJ
Kim
T
T
Ward
J F
JF
Fahey
R C
RC
D006863:Hydrogen-Ion Concentration; D009682:Magnetic Resonance Spectroscopy; D008624:Mercaptoethylamines / Q000737:chemistry*; D011837:Radiation-Protective Agents / Q000737:chemistry*
D008624:Mercaptoethylamines; D011837:Radiation-Protective Agents; C020174:N-(2-mercaptoethyl)-1,3-diaminopropane