title: Mass-spectrometric investigations on hydration of nucleic acid components in vacuum. II. N-methylated adenines.
abstract: Association reactions between water and N-methylated adenines (M), occurring under field-ionization conditions in a mass spectrometer at the tungsten point emitter surface, were studied at a number of temperatures. The origin of the peaks observed in the mass spectra at m/e ratios corresponding to MH+ was assigned to M X H2O monohydrates , of those corresponding to (MH X H2O)+ and (MH2)2+ to double hydrates M(H2O)3. Measurements of the relative peak intensities allowed calculation of apparent equilibrium constants, Kass, for successive hydration steps, and hence the respective van't Hoff enthalpies of hydration. Both the equilibrium and the energy parameters obtained support the available quantum-mechanical single-layer hydration schemes of adenine and of its N-methylated derivatives.
mesh_terms: D000225:Adenine / Q000031:analogs & derivatives* / Q000032:analysis; D013058:Mass Spectrometry / Q000295:instrumentation / Q000379:methods; D009696:Nucleic Acids; D013816:Thermodynamics
chemical_list: D009696:Nucleic Acids; D000225:Adenine