One-dimensional assembly of β-form anhydrous guanine microrods.

Biogenic guanine crystals exhibit excellent optical properties owing to their extremely high refractive index. However, there is no report related to the highly-ordered guanine assemblies in the synthetic systems. Herein, β-phase anhydrous guanine (β-AG) microrods were formed in mixed solvents of formamide and water in the presence of small organic molecules such as uric acid, pyrrole (Py), N-methyl-2-pyrrolidone (NMP), N-vinyl-2-pyrrolidone (NVP). The one-dimensional (1D) assembly of β-AG microrods form spontaneously in water, which is the first reported highly ordered 1D assembly of organic micro- or nanocrystals in the solution. The obtained β-AG microrods obtained in Py system can form reversible 1D assembly in water after being treated in organic solvents such as ethanol, acetone and isopropanol, which have high solubility in water. However, no reversible 1D assembly but only dispersed or aggregated guanine microrods formed in water after similar treatment in the other three organic solvents such as n-hexane, dichloroethane and petroleum ether with low solubility in water. Similar reversible assembly features can also be observed in other three systems, standard system, and NVP and NMP systems. The reversible 1D assemblies of guanine microrods in water and organic solvents with high solubility in water indicate that there is a strong interaction between the (100) planes of β-AG microrods in water. The oriented 1D assembly of guanine microrods with long axes perpendicular to the horizontal magnetic field can form in water under magnetic field.