Synthesis of porous microplatelets of alpha form anhydrous guanine in DMSO/water mixed solvents

Guanine crystals have been utilized as optical systems such as tunable structural colors, diffusive light scatters, broad-band and narrow-band reflectors, imaging mirrors, and polarization sensitive reflectors in many organisms. It is still a big challenge to realize the controlled synthesis of guanine crystals with particular polymorphs and morphologies in the laboratory. In this work, microplatelets of alpha form anhydrous guanine (alpha-AG) exposing the (100) face were obtained under mild conditions in DMSO/water mixed solvents with polyvinylpyrrolidone K30 (PVP) as an additive. The obtained alpha-AG microplatelets are 2.7 +/- 0.9 mu m in length, 0.48 +/- 0.16 mu m in width and about 90 nm in thickness. PVP is supposed to be adsorbed on the (100) face of alpha-AG, resulting in the formation of a plate-like morphology. The alpha-AG microplatelets have a porous feature, which was supposed to be formed during the dissolution of co-precipitated Na2SO4 nanoparticles together with the guanine crystals. The delicate control on the polymorph and morphology of the guanine crystals may shed light on the controlled crystallization of organic crystals with unique optical properties.