Controlled crystallization of anhydrous guanine β nano-platelets via an amorphous precursor

Abstract

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.

Synthesis of Bio‐Inspired Guanine Microplatelets: Morphological and Crystallographic Control

“…Considering that the a and b phase guanine crystalsa re very similar to each other and both form p-p stacking interactions between the neighborl ayers of the guanine molecules, it is reasonable that these polymer additives can absorba nd stabilize the (100) planes of both phases. [36] To the best of our knowledge,t his work represents the first study on the effects of guanine analogues with very similar molecular structure of guanineo nt he crystallization process of guanine,w here we found both morphology and crystallography can be tailoredw ith different types of guanine analogues. This study was inspired by the fact that ap articular guanine analogue, hypoxanthine,h as been previous identified as the second mosti mportant constituent in biological guanine crystals.…”

“…An umber of previouss tudies aimed to achieve similarc ontrol of the polymorph and morphology of guanine crystalssyntheticallyi nt he last years. [34][35][36][37][38] Utilizing chitosans ubstrates in the presence of poly(l-glutamic acid), Oaki et al synthesized a thin layer of aggregates of platy AG crystals,w hile it is unclear whether the synthesized AG is a or b phased ue to the low quality of X-ray diffraction patterns. [35] Gur et al demonstrated the polymorph controlb etween GM and AG by controlling the pH in the aqueous environment.…”

“…[36] This is achievedt hrough ap hase transformation of ah ydrated amorphous guaninep hase in an organic solvent, such as dimethyl sulfoxide, with the presence of polyvinylpyrrolidone( PVP). [36] By using am ixed solvent of formamide andw ater with poly(1vinylpyrrolidone-co-vinyl acetate) (P(VP-co-VA)) as additive, twinned microplatelets with morphologies such as cross and square shapes can be obtained. [37] However,t he synthesis of b-AG microplatelets with (100) exposed plane with similar morphological and crystallographic controla si nb iological ones is still yet to be demonstrated.…”

“…Similar SGmPs were obtained by replacing P(VP-co-VA) with another polymera dditive poly(1vinylpyrrolidone) (PVP) for aw ider ange of concentrations as well (0.01-10 mg mL À1 )( Figure S5). Due to the hydrophobic nature of the vinylpyrrolidone (VP)g roup, we hypothesize that P(VP-co-VA) and PVP may preferentially absorb onto the more hydrophobic (100) plane insteado fo ther planeso fA G, [36][37] which contributest ot he formation of the guaninem icroplatelets with (100) exposing planes.…”

“…This is achieved by introducing surfactants such as P(VP-co-VA) or PVP and guanine analogues such as uric acid (UA), hypoxanthine (I), xanthine (X), adenine (A), and guanosine (GR) in the precipitation solution containing am ixture of guanine and NaOH in solvents such as formamide.W e previously demonstrated the synthesis of guaninen anocrystals through at wo-step method involving the first preparation of amorphousg uaninea nd subsequent transformation to crystal-line phases, [36] whereas the approachr eported here directly produces controlled guanine crystals. Following our previous work, [36] we propose that, due to their hydrophobic part, P(VPco-VA) and PVP tend to adsorb onto the more hydrophobic (100) plane [13] compared to other planes and do not contributing to the hydrogen-bonding between guanine molecules within (100) planes, resulting in the microplatelet morphology with the exposing (100) plane.O ur analysis indicates that the concentrationr ange of P(VP-co-VA) and PVP is wide for obtaining SGmPs (> three orders of magnitudes). Considering that the a and b phase guanine crystalsa re very similar to each other and both form p-p stacking interactions between the neighborl ayers of the guanine molecules, it is reasonable that these polymer additives can absorba nd stabilize the (100) planes of both phases.…”