Fig. 2

Characterization of guanine monohydrate crystals produced by 34mel. A ESI–MS spectrum of biogenic guanine compared to the simulated data for guanine. B ESI MS/MS spectrum of the [M + H]⁺ ion m/z 152.0574. Solvent: methanol: H₂O. In color, proposed structures for MS/MS obtained ions are shown. C Powder X-ray diffraction pattern of the biogenic guanine crystals and the simulated powder X-ray diffraction pattern obtained from the guanine monohydrate single-crystal X-ray data [12]. D FT-IR spectra of biogenic crystals and commercial guanine, signals associated with water molecules are highlighted in green and those of carbonyl and amine groups in orange