Puzzling Aqueous Solubility of Guanine Obscured by the Formation of Nanoparticles.

Dissolution of guanine in neutral solutions was obscured by peculiar behavior of guanine, indicating an apparent dependence of solubility on the amount of solid guanine used. Here, we demonstrate that the problem is caused by the formation of tiny guanine nanoparticles that tend to grow forming stable particles of ca. 800 nm size. This effect can be minimalized by using small quantities of guanine powder for dissolution. We also show that assuming a constant, independent of pH, concentration of neutral form of guanine, at 25 °C equal 25.4 µM, and applying known p Ka values related to its dissociation or protonation, it is possible to calculate the concentrations of all conjugate acids and bases of guanine at the given pH value, and by summing them up, the guanine solubility.

Bis(3-methyl-phenolato-κO)(nitros-yl-κN)[tris-(3,5-dimethyl-pyrazol-1-yl-κN)hydridoborato]molybdenum(II).

The title complex, [Mo(C(15)H(22)BN(6))(C(7)H(7)O)(2)(NO)], contains an {MoNO}(4) core stabilized by κ(3)--hydrotris-(3,5-dimethyl-pyrazol-1-yl)borate, [Tp(Me2)](-), and two anionic m-cresolate ligands, leading to a distorted octa-hedral geometry for the Mo atom. The short Mo-O bond lengths [1.935 (2) and 1.971 (2) Å], as well as large Mo-O-Csp(2) angles [134.2 (2) and 143.54 (19)°], indicate dπ(Mo)-pπ(O) inter-actions, which are clearly weaker when compared with {Mo(NO)(Tp(Me2))} alkoxides. The nitrosyl system is virtually linear [179.3 (3)°] with Mo-N and N-O bond lengths of 1.760 (2) and 1.205 (3) Å, respectively. Intra- and inter-molecular C-H((Ph or CH(3)))⋯π((Ph)) inter-actions between adjacent phenyl rings are found in the crystal structure (d(H⋯Ph) in the range 2.743-2.886 Å). One of the Ph rings shows disorder, i.e. swinging in the ring plane.