We realized a pure phase of anhydrous guanine (AG) β form for the first time via a transformation from hydrated amorphous guanine phase (HAmG). The specified transformation was probably due to the similar short-range order between AG β and HAmG.

b-Phase anhydrous guanine (b-AG) crystalsa re one of the most widespreado rganic crystals to construct optical structures in organisms. Currently,n os ynthetic method is available that allows for producing guanine crystals with similarc ontrol in size, morphology,a nd crystallographya si nb iological ones. Herein, af acile one-step synthesis route to fabricateb io-inspired guaninem icroplatelets with (100) exposing planesi na lmost pure b-phase is reported. Thes ynthesis is based on ap recipitation process of ag uanine sodium hydroxide solution in formamide with poly(1-vinylpyrrolidone-co-vinyl acetate) as a morphologicala dditive. Due to their uniform size (ca. 20 mm) and thickness (ca. 110nm), the crystals represent the first synthetic guanine microplatelets that exhibit strong structuralc olorationa nd pearlescent lusters. Moreover,t his synthesis route was utilized as am odel system to investigate the effects of guanine analogues, including uric acid, hypoxanthine, xanthine,a denine,a nd guanosine, during the crystallization process. Our results indicate that the introduction of guanine analogues not only can reduce the required synthesis temperature but also provide av ersatile control in crystal morphologya nd polymorph selection between the a-phase AG (a-AG)a nd bAG. Turbiditye xperiments showt hat the bAG microplatelets are formed with af ast precipitation rate in comparison to a-AG, suggesting that the formation of bAG crystals follows ak inetically driven process.