Search Results (8)

We report the synthesis, spectroscopic, structural, and ultrafast photophysical investigation of a series of homoleptic and heteroleptic Zn(II) complexes based on the donor-acceptor β-diketonate ligand 4,4,4-trifluoro-1-phenylbutane-1,3-dione. Mass spectrometry, infrared, and NMR analyses confirm complexation and indicate possible fragmentation pathways involving the sequential loss of β-diketonate ligands. Single-crystal X-ray diffraction revealed that all complexes adopt monomeric octahedral geometries, with the ancillary nitrogen-based ligands introducing variable distortions. Thermal analyses confirmed that the complexes are non-volatile and have an onset >250 °C, with thermal decomposition primarily to ZnO and ZnF₂. Complexes with aromatic Lewis base led to higher residue percentages, likely due to the final graphitic carbon content. UV-Vis absorption and femtosecond transient absorption spectroscopy demonstrate that the chelated β-diketonate ring serves as the main optically active chromophore, a property unaffected by the nitrogen ligands. The free ligand undergoes rapid internal conversion, whereas coordination to Zn stabilizes the triplet state via LMCT, producing long-lived and chemically reactive species relevant to dissociation processes. This study demonstrates how tailored ligand environments can be exploited to tune excited-state properties, offering a rational framework for the design of functional precursors suitable for nonlinear photolysis and advanced nanomaterial synthesis. Full article

In this work, we investigate the relaxation processes of 2-thiouracil after UV photoexcitation to the S₂ state through the use of ultrafast, single-colour, pump-probe UV/UV spectroscopy. We place focus on investigating the appearance and subsequent decay signals of ionized fragments. We complement this with VUV-induced dissociative photoionisation studies collected at a synchrotron, allowing us to better understand and assign the ionisation channels involved in the appearance of the fragments. We find that all fragments appear when single photons with energy > 11 eV are used in the VUV experiments and hence appear through 3+ photon-order processes when 266 nm light is used. We also observe three major decays for the fragment ions: a sub-autocorrelation decay (i.e., sub-370 fs), a secondary ultrafast decay on the order of 300–400 fs, and a long decay on the order of 220 to 400 ps (all fragment dependent). These decays agree well with the previously established S₂ → S₁ → Triplet → Ground decay process. Results from the VUV study also suggest that some of the fragments may be created by dynamics occurring in the excited cationic state. Full article

Beetroot (Beta vulgaris L.) is an important root vegetable crop and a valuable food source of micronutrients and bioactive constituents. In this study, the bioaccessibility of minerals, organic acids, and betacyanins in beetroot powder during simulated gastrointestinal digestion was investigated, as well as the antioxidant activity of the final fractions of each phase of the process. Mineral elements were analyzed by inductively coupled plasma optical emission spectroscopy (ICP-OES), organic acids by ultra-fast liquid chromatography with photodiode array detection (UFLC-PDA), and betacyanins by liquid chromatography with diode-array detection and mass spectrometry (HPLC-DAD-ESI/MSⁿ). The oxidative hemolysis inhibition assay was used to assess the ex vivo antioxidant activity. The bioaccessibility of minerals at the end of gastrointestinal digestion ranged from 43 to 65%, depending on the mineral element. Among these, Mg was the most bioaccessible, while Ca and Fe had the lowest bioaccessibility. For organic acids, a major release during digestion was observed for quinic acid. It was also found that betanin (the major betalain in beetroot) was highly unstable during the digestion process, probably due to its hydrophilic nature, which agreed with the significant (p < 0.05) decrease in antioxidant/antihemolytic activity. These results suggest that beetroot antioxidant compounds are unstable under gastrointestinal conditions, and could be useful for future development of novel and more stable beetroot food formulations. Full article

Bimetallic Au/Ag core–shell cuboid nanoparticles (NPs) exhibit a complex plasmonic response dominated by a dipolar longitudinal mode and higher-order transverse modes in the near-UV, which may be exploited for a range of applications. In this paper, we take advantage of the strong signature of these modes in the NP ultrafast transient optical response, measured by pump-probe transient absorption (TA) spectroscopy, to explore the NP vibrational landscape. The fast Fourier transform analysis of the TA dynamics reveals specific vibration modes in the frequency range 15–150 GHz, further studied by numerical simulations based on the finite element method. While bare Au nanorods exhibit extensional and breathing modes, the bimetallic NPs undergo more complex motions, involving the displacement of facets, edges and corners. The amplitude and frequency of these modes are shown to depend on the Ag shell thickness, as the silver load modifies the NP aspect ratio and mass. Moreover, the contributions of the vibrational modes to the experimental TA spectra are shown to vary with the probe laser wavelength at which the signal is monitored. Using the combined simulations of the NP elastic and optical properties, we elucidate this influence by analyzing the effect of the mechanisms involved in the acousto-plasmonic coupling. Full article

Microparticles encapsulated with orange essential oil were prepared by improved emulsifying solvent volatilization technology, and modified with chitosan to improve their loading and adhesion properties on paper. Characterization was performed by Zetasizer Nano ZS instrument, transmission electron microscope (TEM), scanning electron microscopy (SEM), Fourier transform infrared spectrometer (FTIR) spectroscopy, thermogravimetric analyzer (TGA), gas-chromatography-mass spectrometry (GC-MS) and the ultrafast GC Electronic Nose Heracles II, etc. The results showed that for poly (lactic-co-glycolic acid) (PLGA) microparticles and chitosan–PLGA microparticles, respectively, the particle sizes were 233.2 and 277.6 nm, loading capacity was 19.17% and 24.36%, Zeta potential was −8.27 and 5.44 mV, adhesive capacity was 76.32 and 324.84 mg/g, and encapsulation efficiency was 93.23% and 94.06%. GC-MS demonstrated that the embedding process minimally effected the aroma quality of orange essential oil. The ultrafast GC Electronic Nose Heracles II showed that chitosan–PLGA microparticles could effectively slow the release of the orange essential oil. Therefore, this work provides a proposal for a better understanding of biodegradable functional packaging paper. Full article

Industrial pollution by heavy metal ions such as Hg²⁺ and Ag⁺ is a universal problem owing to the toxicity of heavy metals. In this study, a novel nano-adsorbent, i.e., poly-2-mercapto-1,3,4-thiadiazole (PTT), was synthesized and used to selectively adsorb mercury and silver ions from aqueous solutions. PTT nanoparticles were synthesized via chemical oxidative dehydrogenation polymerization under mild conditions. Oxidant species, medium, monomer concentration, oxidant/monomer molar ratio, and polymerization temperature were optimized to obtain optimum yields. The molecular structure and morphology of the nanoparticles were analyzed by ultraviolet-visible (UV-Vis), Fourier transform infrared (FT-IR), matrix-assisted laser desorption/ionization/time-of-flight (MALDI/TOF) mass and X-ray photoelectron (XPS) spectroscopies, wide-angle X-ray diffraction (WAXD), theoretical calculations and transmission electron microscopy (TEM), respectively. It was found that the polymerization of 2-mercapto-1,3,4-thiodiazole occurs through head-to-tail coupling between the S(2) and C(5) positions. The PTT nanoparticles having a peculiar synergic combination of four kinds of active groups, S–, –SH, N–N, and =N– with a small particle size of 30–200 nm exhibit ultrarapid initial adsorption rates of 1500 mg(Hg)·g⁻¹·h⁻¹ and 5364 mg(Ag)·g⁻¹·h⁻¹ and high adsorption capacities of up to 186.9 mg(Hg)·g⁻¹ and 193.1 mg(Ag)·g⁻¹, becoming ultrafast chelate nanosorbents with high adsorption capacities. Kinetic study indicates that the adsorption of Hg²⁺ and Ag⁺ follows the pseudo-second-order model, suggesting a chemical adsorption as the rate-limiting step during the adsorption process. The Hg²⁺ and Ag⁺-loaded PTT nanoparticles could be effectively regenerated with 0.1 mol·L⁻¹ EDTA or 1 mol·L⁻¹ HNO₃ without significantly losing their adsorption capacities even after five adsorption–desorption cycles. With these impressive properties, PTT nanoparticles are very promising materials in the fields of water-treatment and precious metals recovery. Full article

Poly(2,5-dimercapto-1,3,4-thiadiazole) (PBT) nanosheets were synthesized by chemical oxidative synthesis under mild conditions. The media, oxidant species, monomer concentrations, oxidant/monomer molar ratio, and temperature were optimized to achieve higher yields and better performance. The molecular structure, morphology, and properties of the nanosheets were analyzed by Fourier transform infrared (FT-IR), ultraviolet-visible (UV-Vis), and fluorescence spectroscopies, wide-angle X-ray diffraction (WAXD), matrix-assisted laser desorption/ionization/time-of-flight (MALDI-TOF) mass spectrometry, X-ray photoelectron spectroscopy (XPS), scanning electronic microscopy (SEM), transmission electron microscopy (TEM), and simultaneous thermogravimetry and differential scanning calorimetry (TG-DSC). It was found that the polymerization of 2,5-dimercapto-1,3,4-thiadiazole occurs via dehydrogenation coupling between two mercapto groups to form the –S–S– bond. PBTs show the highest polymerization yield of up to 98.47% and form uniform nanosheets with a thickness of 89~367 nm. poly(2,5-dimercapto-1,3,4-thiadiazole) polymers (PBTs) exhibit good chemical resistance, high thermostability, interesting blue-light emitting fluorescence, and wonderful heavy metal ion adsorption properties. Particularly, the PBT nanosheets having a unique synergic combination of three kinds of active –S–, –SH, and =N– groups with a moderate specific area of 15.85 m² g⁻¹ exhibit an ultra-rapid initial adsorption rate of 10,653 mg g⁻¹ h⁻¹ and an ultrahigh adsorption capacity of up to 680.01 mg g⁻¹ for mercury ion, becoming ultrafast chelate nanosorbents with a high adsorption capacity. With these impressive properties, PBT nanosheets are very promising materials in the fields of water treatment, sensors, and electrodes. Full article

X-ray free electron lasers (XFELs) providing ultrashort intense pulses of X-rays have proven to be excellent tools to investigate the dynamics of radiation-induced dissociation and charge redistribution in molecules and nanoparticles. Coincidence techniques, in particular multi-ion time-of-flight (TOF) coincident experiments, can provide detailed information on the photoabsorption, charge generation, and Coulomb explosion events. Here we review several such recent experiments performed at the SPring-8 Angstrom Compact free electron LAser (SACLA) facility in Japan, with iodomethane, diiodomethane, and 5-iodouracil as targets. We demonstrate how to utilize the momentum-resolving capabilities of the ion TOF spectrometers to resolve and filter the coincidence data and extract various information essential in understanding the time evolution of the processes induced by the XFEL pulses. Full article