ABSTRACT
This study demonstrates dynamically tunable multicolor emissions from a single component, zero-dimensional (0-D) cesium europium chloride (Cs3EuCl6) and cesium terbium chloride (Cs3TbCl6) nanocrystals (NCs). Highly uniform colloidal Cs3EuCl6 and Cs3TbCl6 NCs are synthesized via the heating-up method. Excitation-wavelength-dependent multicolor emissions from Cs3EuCl6 and Cs3TbCl6 NCs are observed. Under excitation of 330-400 nm, both NCs exhibit blue photoluminescence (PL). Under wavelengths shorter than 330 nm, characteristic red and green emissions are observed from Cs3EuCl6 and Cs3TbCl6, respectively, owing to the atomic emissions from the f-orbitals in trivalent europium (Eu3+) and terbium (Tb3+) ions. Cs3EuCl6 and Cs3TbCl6 NCs exhibit broadband excitation spectra and enhanced absorption properties. Particularly, Cs3EuCl6 NCs exhibit a very narrow full-width at half-maximum in both blue and red PL and no overlap between the two spectra. The photophysical properties of these NCs are further investigated to understand the multicolor PL origins by time-resolved and temperature-dependent PL measurements. Finally, the potential applications of Cs3EuCl6 and Cs3TbCl6 NCs as anti-counterfeiting inks for high-level security are demonstrated. Given their broadband excitation with enhanced absorption properties and dynamically tunable colors with a wide color gamut, Cs3EuCl6 and Cs3TbCl6 NCs have great potential as novel multicolor NC emitters for many emerging applications.
ABSTRACT
In this study, we demonstrate the colloidal synthesis of nearly monodisperse, sub-100-nm phase change material (PCM) nanobeads with an organic n-paraffin core and poly(methylmethacrylate) (PMMA) shell. PCM nanobeads are synthesized via emulsion polymerization using ammonium persulfate as an initiator and sodium dodecylbenzenesulfonate as a surfactant. The highly uniform n-paraffin/PMMA PCM nanobeads are sub-100 nm in size and exhibit superior colloidal stability. Furthermore, the n-paraffin/PMMA PCM nanobeads exhibit reversible phase transition behaviors during the n-paraffin melting and solidification processes. During the solidification process, multiple peaks with relatively reduced phase change temperatures are observed, which are related to the phase transition of n-paraffin in the confined structure of the PMMA nanobeads. The phase change temperatures are further tailored by changing the carbon length of n-paraffin while maintaining the size uniformity of the PCM nanobeads. Sub-100-nm-sized and nearly monodisperse PCM nanobeads can be potentially utilized in thermal energy storage and drug delivery because of their high colloidal stability and solution processability.
ABSTRACT
Acetolactate synthase (ALS) catalyzes the first common step in the biosynthesis of valine, leucine, and isoleucine. The ALS is the target of several classes of herbicides, including the sulfonylureas, the imidazolinones, and the triazolopyrimidines. The roles of three well-conserved lysine residues (K219, K255, K299) in tobacco ALS were determined using site-directed mutagenesis. The mutation of K219Q inactivated the enzyme and abolished the binding affinity for cofactor FAD. However, the secondary structure of the enzyme was not changed significantly by the mutation. Both mutants, K255F and K255Q, showed strong resistance to three classes of herbicides Londax (a sulfonylurea), Cadre (an imidazolinone), and TP (a triazolopyrimidine). In addition, there was no difference in the secondary structures of wALS and K255F. On the other hand, the mutation of K299Q did not show any significant effect on the kinetic properties or any sensitivity to the herbicides. These results suggest that Lys219 is located at the active site and is likely involved in the binding of FAD, and that Lys255 is located at a binding site common for the three herbicides in tobacco ALS.