The temperature-dependent effects on the ultraviolet photoluminescence enhancement, blueshift, thermal quenching of the two-dimensional Zn nanosheets, 2D-hierarchical ZnO nanostructures, and 2D-hierarchical ZnO/Zn nanostructures are presented.
A method for purifying and preparing rebaudioside A (RA) from steviol glycosides at preparative scale was developed with resin based on hydrophilic interaction liquid chromatography (HILIC). In pure water and acetone-water system, the adsorption capacity and selectivity of five anion resins for RA, rebaudioside C (RC) and stevioside (ST) were examined and discussed. Strongly basic IRA458 with the quaternary amine group was chosen as the resin used for separating and preparing RA. The hydroxide form of IRA458 (IRA458-OH) showed the best results in terms of the adsorption behaviors for RA, RC and ST. The retentions of RA, RC and ST on IRA458-OH resin at high concentration of acetone solution followed HILIC mode, in which retention is probably based on surface adsorption of the resin. Under optimized chromatographic conditions, the pooled purity and yield of RA were up to 98.18 and 98.62%, the relative standard deviations (n = 3) for these two parameters were 1.2 and 5.7%, respectively. The present method has the characteristics of simple, low cost, high purity and high yield. The study will be a promising tool for RA industrialized production and also provides a possible mode for purifying and preparing polar components from their analogs.
Self-assembled L,L-diphenylalanine (FF) nanostructures offer an attractive platform for photonics and nonlinear optics. The nonlinear optical (NLO) coefficients of FF nanotubes depend on the diameter of the tube [S. Khanra et al. Phys. Chem. Chem. Phys. 19(4), 3084–3093 (2017)]. To further enhance the NLO properties of FF, we search for structural modifications. Here, we report on the synthesis of fluorinated FF dipeptides by replacing one ortho-hydrogen atom in each of the phenyl groups of FF by a fluorine atom. Density-functional theoretical calculations yield insights into minimum energy conformers of fluorinated FF (Fl-FF). Fl-FF self-assembles akin to FF into micron-length tubes. The effects of fluorination are evaluated on the piezoelectric response and nonlinear optical properties. The piezoelectric d15 coefficient of Fl-FF is found to be more than 10 times higher than that of FF nanotubes, and the intensity of second harmonic generation (SHG) polarimetry from individual Fl-FF nanotubes is more than 20 times that of individual FF nanotubes. Furthermore, we obtain SHG images to compare the intensities of FF and Fl-FF tubes. This work demonstrates the potential of fluorine substitution in other self-assembled biomimetic peptides for enhancing nonlinear optical response and piezoelectricity.
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