ABSTRACT
Biogenic purine crystals can function in vision as light scatters, mirrors, and multilayer reflectors and produce structural colors or depolarization for camouflage. Xanthine crystals form irregular multifocal mirrors in the median ocellus of Archaeognatha. It is important to broaden the study of crystallization strategies to obtain organic crystals with purine rings in the laboratory. In this work, a facile one-step synthesis route to fabricate bio-inspired xanthine crystals is reported for the first time. The obtained rhomboidal xanthine nanoplates have similar morphology and size to biogenic xanthine crystals. Their length and thickness are about 2-4 µm and 50 nm, respectively. Lattice parameters, crystal structure, formation mechanism and optical properties of synthetic single-crystalline xanthine nanoplates were investigated in detail in this work. The obtained xanthine nanoplate crystals are proposed to be anhydrous xanthine with monoclinic symmetry, and the xanthine nanoplates mainly expose the (100) plane. It is proposed that the anhydrous xanthine nanoplates are formed via an amorphous xanthine intermediate precursor. The synthetic anhydrous xanthine nanoplates exhibit excellent optical properties, including high diffuse reflectivity, strong depolarization and pearlescent luster. This work provides a new design to synthesize bio-inspired organic molecular crystals with excellent optical properties.
ABSTRACT
Biomimetic synthesis of guanine crystals has been focused on in the last years. However, multi-functional guanine crystals occluded with fluorescent molecules have not been realized in the laboratory. Here, the controllable synthesis of guanine crystal microplatelets with fluorescence and pearlescence was achieved for the first time by incorporating Nile red (NR) or fluorescein isothiocyanate (FITC) molecules into guanine crystals. The synthesized fluorescent guanine crystals are pure ß-phase anhydrous guanine single crystals. Aqueous suspensions with NR- and FITC-doped guanine crystals exhibit distinct pearlescence. The fluorescence intensities of NR and FITC were greatly enhanced after being doped into guanine crystals due to the inhibition of aggregation-caused quenching. Moreover, films composed of fluorescent guanine microplatelets exhibit high diffuse reflection intensity (70 %). This work provides a strategy to synthesize multifunctional materials composed of organic crystals occluded with dyes.
ABSTRACT
Agar/sodium alginate (AG/SA) nanocomposite films were prepared using solution casting method in presence of various concentrations of nano-SiO2 (2.5, 5, 7.5, and 10â¯wt%). The effect of nano-SiO2 concentration on the nanocomposite film was investigated. The result of Fourier transform infrared (FTIR) illustrated the formation of hydrogen bonding between nano-SiO2 and polysaccharide. As nano-SiO2 concentration rose from 0 to 10â¯wt%, the tensile strength and elongation at break all increased up to maximum, respectively. The tensile strength and elongation at break of film containing 10â¯wt% nano-SiO2 increased by 65.29% and 60.38% respectively when compared to those of film prepared without nano-SiO2. The reason for enhancing in tensile strength might be related to the formation of molecular interaction. The film containing 2.5â¯wt% nano-SiO2 had maximum water contact angle and minimum water vapor permeability among those of all films prepared in this work. However, the film containing 10â¯wt% nano-SiO2 had minimum swelling degree and water solubility, further demonstrating the formation of strong interaction. The addition of nano-SiO2 improved the properties of film against UV light and thermal stability. Overall, the addition of nano-SiO2 enhanced the mechanical properties, water resistance and thermal stability of polysaccharide film.
