Matrix-assisted laser desorption/ionization Fourier transform mass spectrometric analysis of oxygenated triglycerides and phosphatidylcholines in egg tempera paint dosimeters used for environmental monitoring of museum display conditions

Oxidative changes in triacylglycerols and diacylphosphatidylcholines in egg tempera paint strips are used for chemical dosimetry of the quality of the museum environment. High-resolution matrix-assisted laser desorption/ionization Fourier transform mass spectrometry (MALDI-FTMS) was used as a rapid method for the determination of the exact elemental composition of the alteration products from diacylphosphatidylcholines and triacylglycerols. Light exposure of the egg tempera paints yields oxygenated diacylphosphatidylcholines and triacylglycerols. In the latter multiple incorporation of oxygen was observed as a recurring mass difference of 15.995, the exact atomic mass of oxygen. Owing to the high resolution of the FTMS data (routinely 20 000 at m/z 1000 in broadband mode), oxidation products with different elemental compositions but identical nominal mass could be distinguished. Products of oxidative cleavage of triacylglycerols were observed in samples exposed for longer times. The relative intensities of the peaks of singly and multiply oxygenated triacylglycerols were used to derive the degree of oxygenation of the egg lipids in the tempera paint dosimeters. The degree of oxygenation was found to be directly related to the light exposure time. Exposure to elevated temperature (60 degrees C) for a period of 21 days did not lead to oxygenation of the triacylglycerols and diacylphosphatidylcholines. Exposure to NO(x) and SO(2) in the dark greatly increased the degree of oxygenation. Addition of lead- or copper-containing pigments to the egg binding medium (and subsequent storage for 6 months in the dark) led to accelerated conversion of egg lipids to oxidised products.     

In-Situ Electrodeposition of Rhodium nanoparticles Anchored on Reduced Graphene Oxide nanosheets as an Efficient Oxygen Reduction Electrocatalyst

A simple, versatile, and cost-effective one-pot electrochemical deposition is used to fabricate rhodium (Rh) nanoparticles decorated surface of reduced graphene oxide (rGO) functionalized glassy carbon electrode (GCE) for oxygen reduction reaction (ORR) in alkaline media. The chemical and physical structure of the sample is probed via transmission electron microscopy, rotating disk electrode (RDE), X-ray photoelectron spectroscopy, linear sweep voltammetry, and Raman spectroscopy. The synergistic effects between the unique properties of Rh nanoparticles and rGO creates such innovative hybrid that exhibits a catalytic activity comparable to that of the commercial platinum electrocatalyst (Pt/C). As a result, the as-electrodeposited Rh@rGO hybrid exhibits outstanding ORR activity in alkaline media, as evidenced by a larger diffusion-limited current, greater positive onset potential, much better stability and methanol tolerance than Pt/C under the same conditions.     

Overall approaches and experiences of first-time participants in the Nuclear Forensics International Technical Working Group’s Fourth Collaborative Material Exercise (CMX-4)

Journal of Radioanalytical and Nuclear Chemistry - The Fourth Collaborative Material Exercise (CMX-4) of the Nuclear Forensics International Technical Working Group (ITWG) registered the largest...     

Designing Upconversion Nanocrystals Capable of 745 nm Sensitization and 803 nm Emission for Deep‐Tissue Imaging

A crystal design strategy is described that generates hexagonal‐phased NaYF₄:Nd/Yb@NaYF₄:Yb/Tm luminescent nanocrystals with the ability to emit light at 803 nm when illuminated at 745 nm. This is accomplished by taking advantage of the large absorption cross‐section of Nd³⁺ between 720 and 760 nm plus efficient spatial energy transfer and migration through Nd³⁺→Yb³⁺→Yb³⁺→Tm³⁺. Mechanistic investigations suggest that a cascaded two‐photon energy transfer upconversion process underlies the emission mechanism. This protocol enables deep‐tissue imaging to be achieved while mitigating the attenuation effect associated with the visible emission and the overheating constraint imposed by conventional 980 nm excitation.     

Observation of green emission from Ce-doped gadolinium oxide nanoparticles

Green emission at around 500 nm is observed in Gd₂O₃:Ce³⁺ nanoparticles and the intensity is highly dependent on the concentration of Ce³⁺ in the nanoparticles. The luminescence of this emission displays both picosecond (ps) and millisecond (ms) lifetimes. The ms lifetime is over four orders of magnitude longer than typical luminescence lifetimes (10-40 ns) of Ce³⁺ in traditional Ce³⁺ doped phosphors and therefore likely originates from defect states. The picosecond lifetime is shorter than the typical Ce³⁺ value and is also likely due to defect or surface states. When the samples are annealed at 700 °C, this emission disappears possibly due to changes in the defect moieties or concentration. In addition, a blue emission at around 430 nm is observed in freshly prepared Gd₂O₃ undoped nanoparticles, which is attributed to the stabilizer, polyethylene glycol biscarboxymethyl ether. On aging, the undoped particles show similar emission to the doped particles with similar luminescence lifetimes. When Eu³⁺ ions are co-doped in Gd₂O₃:Ce nanoparticles, both the green emission and the emission at 612 nm from Eu³⁺ are observed.     

A Local Realistic Theory for the Greenberger-Horne-Zeilinger Experiment

As a counterexample to conventional belief, a realistic theory, which is both local and reproduces all the probabilistic predictions of quantum theory, is constructed for the Greenberger-Horne-Zeilinger three-photon experiment.