Physico-chemical study of steroids from different matureness corn silk material

This study shows an ultrasonic assisted extraction procedure of steroids from corn silk (CS). The total steroids contents were positively correlated with the ultrasonic assisted extraction time. The extracted steroids contents varied according to the different maturity stages of CS. There were three tested CS maturity stages: silking stage (CS-S), milky stage (CS-M) and mature stage (CS-MS). The β - sitosterol standardization method with 530 nm wavelength colorimetric measurements were applied to determine the content of extracted steroids. Measured steroids concentrations range were from 38.3 × 10-3 mg.mL-1 to 368.9 × 10-3 mg.mL-1 in different extraction time and CS maturity stages. The highest concentration of steroids, 368.9 × 10-3 mg.mL-1 was found in CS-MS sample with the 75 minutes ultrasonic extraction time. The fluorescence mapping techniques were used to confirm the existence of steroids. The thermal analysis illustrated a typical multistep decomposition process for the CS-S, CS-M and CS-MS samples. Two endothermic peaks were found: The first one was 54.3 °C for CS-S and CS-MS, 60.2 °C for CS-M, the second one, 397 °C (CS-MS), 415.1 °C (CS-M) and 419.7 °C (CS-S) attributed to the total thermal decomposition. The observed exotheric process found at 524 °C corresponded to CS-MS sample decomposition. The optimal ultrasonic-assisted extraction time for all samples under study CS-S, CS-M and CS-MS was about 75 minutes and the optimal steroids extraction contents obtained were 92.8 × 10-3 mg.mL-1 (CS-S), 124.2 × 10-3 mg.mL-1 (CS-M) and 368.9 × 10-3 mg.mL-1 (CS-MS) respectively. © 2019 Potravinarstvo Slovak Journal of Food Sciences

Physico-chemical study of flavonoids from different matureness corn silk material

There was tested a simple extraction procedure of flavonoids separation from the original corn silk (CS) material. It was found, that the total flavonoids content differs with the extraction time and extraction temperature. There were found different flavonoids contents in extracts prepared from different maturity stages of the original corn silk material (silking stage (CS-S), milky stage (CS-M)). Extracted flavonoids content was quantified by the lutin standardization method by means of colorimetry at 510 nm wavelength. Obsreved flavonoids concentration was ranging from 2×10-3 mg.mL-1 to 7 ×10-3 mg.mL-1 dependent on the extraction time period and extraction temperature. The highest flavonoids concentration of 7.5×10-3 mg.mL-1 was found for CS-M after 20 minutes extraction time and 80 °C extraction temperature. There was confirmed the presence of flavonoids by fluorescence mapping experiments. There was found a typical multistep decomposition process for both CS-S and CS-M materials by TG analysis. There was found a melting temperature of flavonoids of 54.3 °C for corn silk silking stage material exhibiting 58.9 J.g-1 heat of fusion and 60.2 °C for corn silk milky stage material with 112.9 J.g-1 heat of fusion. The optimal conditions of corn silk flavonoids extraction were 40 °C, 50 minutes for CS-S, the optimal flavonoids extraction content was (6.8 ±2.1)×10-3 mg.mL-1, 80°C, 20 minutes for CS-M and the optimal extraction content was (7.2 ±0.3)×10-3 mg.mL-1. © 2018 Potravinarstvo Slovak Journal of Food Sciences

Impact of D₂O/H₂O solvent exchange on the emission of HgTe and CdTe quantum dots: Polaron and energy transfer effects

We have studied light emission kinetics and analyzed carrier recombination channels in HgTe quantum dots that were initially grown in H2O. When the solvent is replaced by D2O, the nonradiative recombination rate changes highlight the role of the vibrational degrees of freedom in the medium surrounding the dots, including both solvent and ligands. The contributing energy loss mechanisms have been evaluated by developing quantitative models for the nonradiative recombination via (i) polaron states formed by strong coupling of ligand vibration modes to a surface trap state (nonresonant channel) and (ii) resonant energy transfer to vibration modes in the solvent. We conclude that channel (i) is more important than (ii) for HgTe dots in either solution. When some of these modes are removed from the relevant spectral range by the H2O to D2O replacement, the polaron effect becomes weaker and the nonradiative lifetime increases. Comparisons with CdTe quantum dots (QDs) served as a reference where the resonant energy loss (ii) a priori was not a factor, also confirmed by our experiments. The solvent exchange (H2O to D2O), however, is found to slightly increase the overall quantum yield of CdTe samples, probably by increasing the fraction of bright dots in the ensemble. The fundamental study reported here can serve as the foundation for the design and optimization principles of narrow bandgap quantum dots aimed at applications in long wavelength colloidal materials forinfrared light emitting diodes and photodetectors.We acknowledge financial support by the grant from the Research Grants Council of the Hong Kong S.A.R., China (project CityU 11302114). MIV acknowledges financial support from the FCT (Portugal)

Magnetic polaron states in photoluminescent carbon dots enable hydrogen peroxide photoproduction

Photoactivation of aspartic acid-based carbon dots (Asp-CDs) induces the generation of spin-separated species, including electron/hole (e−/h+) polarons and spin-coupled triplet states, as uniquely confirmed by the light-induced electron paramagnetic resonance spectroscopy. The relative population of the e−/h+ pairs and triplet species depends on the solvent polarity, featuring a substantial stabilization of the triplet state in a non-polar environment (benzene). The electronic properties of the photoexcited Asp-CDs emerge from their spatial organization being interpreted as multi-layer assemblies containing a hydrophobic carbonaceous core and a hydrophilic oxygen and nitrogen functionalized surface. The system properties are dissected theoreti cally by density functional theory in combination with molecular dynamics simulations on quasi-spherical assemblies of size-variant flakelike model sys tems, revealing the importance of size dependence and interlayer effects. The formation of the spin-separated states in Asp-CDs enables the photoproduc tion of hydrogen peroxide (H2O2) from water and water/2-propanol mixture via a water oxidation reaction.Web of Science1932art. no. 220658

Ultrafast exciton dynamics in CdxHg(1-x)Te alloy quantum dots

Ultrafast transient absorption spectroscopy is used to investigate sub-nanosecond exciton dynamics in CdxHg(1−x)Te alloy colloidal quantum dots. A bleach was observed at the band gap due to state-filling, the mono-exponential decay of which had a characteristic lifetime of 91 ± 1 ps and was attributed to biexciton recombination; no evidence of surface-related trapping was observed. The rise time of the bleach, which is determined by the rate at which hot electrons cool to the band-edge, ranged between 1 and 5 ps depending on the pump photon energy. Measuring the magnitude of the bleach decay for different pump fluences and wavelengths allowed the quantum yield of multiple exciton generation to be determined, and was 115 ± 1% for pump photons with energy equivalent to 2.6 times the band gap

Robust dual cationic ligand for stable and efficient warm-white light emission in lead-free double perovskite nanocrystals

Bismuth-doped alloyed Cs2Ag1-xNaxInCl6 double perovskite nanocrystals (DP NCs) emerged as a new class of lead-free alternative for single-emitter-based solution-processed white-light-emitting devices (WLEDs). However, their thin-film processing and device fabrication have been limited due to low photoluminescence (PL) quantum yield (QY) and degradation during purification from the as-synthesized crude solution. Moreover, easy reduction of a silver ions by oleylamine also raised concern regarding stability issues of silver based DP NCs. Here, we report a facile synthesis and purification method for shape-pure and monodispersed bismuth-doped alloyed Cs2Ag1-xNaxInCl6 DP NCs with high PL QY and long-term stability. At optimized bismuth-doping, alloyed Cs2Ag1-xNaxInCl6 DP NCs showed warm white-light-emission with a PL QY of 40% due to suppressed non-radiative recombination. The synthesis of highly emissive and stable DP NCs was achieved by utilizing a combination of strongly coordinating silver-trioctylphosphine (Ag-TOP) complex along with additional TOP ligand. The Ag-TOP complex served as a highly reactive silver precursor and prevented the reduction of silver ions into metallic silver. While TOP facilitated the nucleophilic reaction with benzoyl chloride during nucleation and growth stage and forms benzoyl trioctylphosphonium chloride intermediate that served as both halide source and surface capping ligand which enabled the formation of high-quality DP NCs. The high tolerance of DP NCs against common antisolvents such as methyl acetate and isopropanol was attributed to the tight binding of dual cationic ligand benzoyl trioctylphosphonium and oleylammonium cations together with oleate anion to the surface of DP NCs.Web of Science26art. no. 10128

Aqueous manganese-doped core/shell CdTe/ZnS quantum dots with strong fluorescence and high relaxivity

Core/shell CdTe/ZnS colloidal quantum dots with varying dopant levels (4.7-9.7%) of paramagnetic manganese ions spatially distributed within the thin ZnS shell are synthesized by the aqueous approach. They exhibit both strong fluorescence originating from the CdTe core (up to 45% room temperature emission quantum yield) and high ionic relaxivity in the range of 10.7-5.4 mM s, which render them promising dual fluorescent/paramagnetic probes