title: Base crystallization and base stacking in water.
abstract: 2H2O solutions of 6-methylpurine and N6,N9-dimethyladenine have been examined by neutron diffraction. Comparison of the scattering from various molar solutions of 6-methylpurine with the scattering from its crystalline precipitates indicated base stacking in solution with a separation of approximately 0.34 nm. In particular at 1.75 M the effective stacking number in 6-methylpurine, as seen by neutron diffraction, was found to be approximately nine. Attempts to observe similar scattering from N6, N9-dimethyladenine were hampered because solutions with a molarity greater than or approximately 0.02 tended to form filamentary crystallites as a function of time. An analysis of the autocatalytic reaction involved in the formation of these dendrites is given. The rate constant is found to be 2.12 +/- 0.05 M-1 h-1. By comparing the diffraction from wet and dry crystallites it is concluded that hydrophilic interactions mediate the aggregation of both bases in water.
mesh_terms: D003460:Crystallization; D008968:Molecular Conformation; D009502:Neutrons; D011687:Purines; D012996:Solutions; D014867:Water; D014961:X-Ray Diffraction
chemical_list: D011687:Purines; D012996:Solutions; D014867:Water