Nonlinear Optical Properties of Fullerene C₉₆ (<i>D</i>_3<i>d</i>) and Related Heterofullerenes

The high stability, tailorability, and the π conjugation of fullerene-based nanomaterials render those nanomaterials potential nonlinear optical (NLO) materials. The sum-over-states model with linear scaling was employed to model the static and dynamic third order NLO properties of fullerene C₉₆ (<i>D</i>_3<i>d</i>) and C₉₆ based boron–nitrogen-doped and metal-doped fullerenes. Doping induces more electronic excitations in the heterofullerenes in the visible and infrared regions. The two-photon absorption cross-section of heterofullerene C₇₂B₁₂N₁₂(C₃) reaches 1.65 × 10⁵ × 10^–50 cm⁴·s/photon at 892.0 nm. The heterofullerenes have strong NLO responses to external fields from the ultraviolet–visible to infrared regions. The correlation between structure and NLO properties is disclosed for those cages

The Unexpected and Exceptionally Facile Chemical Modification of the Phenolic Hydroxyl Group of Tyrosine by Polyhalogenated Quinones under Physiological Conditions

The phenolic hydroxyl group of tyrosine residue plays a crucial role in the structure and function of many proteins. However, little study has been reported about its modification by chemical agents under physiological conditions. In this study, we found, unexpectedly, that the phenolic hydroxyl group of tyrosine can be rapidly and efficiently modified by tetrafluoro-1,4-benzoquinone and other polyhalogenated quinones, which are the major genotoxic and carcinogenic quinoid metabolites of polyhalogenated aromatic compounds. The modification was found to be mainly due to the formation of a variety of fluoroquinone–<i>O</i>-tyrosine conjugates and their hydroxylated derivatives via nucleophilic substitution pathway. Analogous modifications were observed for tyrosine-containing peptides. Further studies showed that the blockade of the reactive phenolic hydroxyl group of tyrosine in the substrate peptide, even by very low concentration of tetrafluoro-1,4-benzoquinone, can prevent the kinase catalyzed tyrosine phosphorylation. This is the first report showing the exceptionally facile chemical modification of the phenolic hydroxyl group of tyrosine by polyhalogenated quinones under normal physiological conditions, which may have potential biological and toxicological implications

Coupling of Ag Nanoparticle with Inverse Opal Photonic Crystals as a Novel Strategy for Upconversion Emission Enhancement of NaYF₄: Yb³⁺, Er³⁺ Nanoparticles

Rare-earth-ion-doped upconversion (UC) nanoparticles have generated considerable interest because of their potential application in solar cells, biological labeling, therapeutics, and imaging. However, the applications of UC nanoparticles were still limited because of their low emission efficiency. Photonic crystals and noble metal nanoparticles are applied extensively to enhance the UC emission of rare earth ions. In the present work, a novel substrate consisting of inverse opal photonic crystals and Ag nanoparticles was prepared by the template-assisted method, which was used to enhance the UC emission of NaYF₄: Yb³⁺, Er³⁺ nanoparticles. The red or green UC emissions of NaYF₄: Yb³⁺, Er³⁺ nanoparticles were selectively enhanced on the inverse opal substrates because of the Bragg reflection of the photonic band gap. Additionally, the UC emission enhancement of NaYF₄: Yb³⁺, Er³⁺ nanoparticles induced by the coupling of metal nanoparticle plasmons and photonic crystal effects was realized on the Ag nanoparticles included in the inverse opal substrate. The present results demonstrated that coupling of Ag nanoparticle with inverse opal photonic crystals provides a useful strategy to enhance UC emission of rare-earth-ion-doped nanoparticles

Mechanism of Intrinsic Chemiluminescence Production from the Degradation of Persistent Chlorinated Phenols by the Fenton System: A Structure–Activity Relationship Study and the Critical Role of Quinoid and Semiquinone Radical Intermediates

We found recently that intrinsic chemiluminescence (CL) could be produced by all 19 chlorophenolic persistent organic pollutants during environmentally friendly advanced oxidation processes. However, the underlying mechanism for the structure–activity relationship (SAR, i.e., the chemical structures and the CL generation) remains unclear. In this study, we found that, for all 19 chlorophenol congeners tested, the CL increased with an increasing number of chlorine atoms in general; and for chlorophenol isomers (such as the 6 trichlorophenols), the CL decreased in the order of meta- > ortho-/para-Cl-substituents with respect to the −OH group of chlorophenols. Further studies showed that not only chlorinated quinoid intermediates but also, more interestingly, chlorinated semiquinone radicals were produced during the degradation of trichlorophenols by the Fenton reagent; and the type and yield of which were determined by the directing effects, hydrogen bonding, and steric hindrance effect of the OH- and/or Cl-substitution groups. More importantly, a good correlation was observed between the formation of these quinoid intermediates and CL generation, which could fully explain the above SAR findings. This represents the first report on the structure–activity relationship study and the critical role of quinoid and semiquinone radical intermediates, which may have broad chemical and environmental implications for future studies on remediation of other halogenated persistent organic pollutants by advanced oxidation processes

Upconversion Emission Enhancement of NaYF₄:Yb,Er Nanoparticles by Coupling Silver Nanoparticle Plasmons and Photonic Crystal Effects

Metal nanoparticle plasmons or the photonic crystal effect are being widely used to modify luminescence properties of materials. However, coupling of surface plasmons with photonic crystals are seldom reported for enhancing luminescence of materials. In this paper, a new method for upconversion emission enhancement of rare-earth doped nanoparticles is reported, attributed to the coupling of surface plasmons with photonic band gap effects. Opal/Ag hybrid substrates were prepared by depositing Ag nanoparticles on the top layer of opals by magnetron sputtering. The selective enhancement of red or green upconversion emission of NaYF₄:Yb³⁺,Er³⁺ nanoparticles on the opal/Ag hybrid substrates is attributed to the coupling effect of surface plasmons and Bragg reflection of the photonic band gap. In addition, the upconversion emission enhancement of NaYF₄:Yb³⁺,Er³⁺ nanoparticles on the opal/Ag hybrid substrate is attributed to the excitation enhancement was obtained when the excitation light wavelengths overlap with the photonic band gaps of opal/Ag hybrid substrates. We believe that these enhancement effects based on the coupling of metal nanoparticles with the photonic band gap could be extended to other light-emitting materials, which may result in a new generation of lighting devices

Comparative study of dual 3‐phase permanent magnet machines with coil span of two slot‐pitches

In this study, the electromagnetic performances of dual 3-phase permanent magnet (PM) machines with coil span of two slot-pitches are comparatively investigated. It mainly focuses on two PM machines with different slot/pole number combinations (Ns/2p), that is, the 24-slot/10-pole and 24-slot/14-pole machines (2p = Ns/2 ± 2). First, winding configurations are illustrated for these two dual 3-phase machines with 30° angle displacement. Then, the winding factor, back electromotive force, average torque, torque ripple, iron and PM losses, short-circuit (SC) current, and PM irreversible demagnetisation are analysed and compared for both machines on the conditions of healthy operation and one set of three-phase fault, that is, SC or open circuit (OC), respectively. The comparative results show that on healthy condition the 14-pole PM machine has a slightly larger torque output. Besides, on 3-phase OC condition, the 14-pole machine also performs better over-rating torque capability. In terms of iron and PM losses, the 10-pole machine has smaller iron losses but larger PM losses than the 14-pole machine. Moreover, on 3-phase SC condition, the 14-pole machine has a significantly lower risk of PM irreversible demagnetisation than the 10-pole machine, although both machines have very similar SC currents. Finally, the 24-slot/10- and 14-pole dual 3-phase PM machines are both prototyped and some tests are carried out for validation. </p

Unusual Double Beckmann Fragmentation Reaction under Physiological Conditions

Pyridinium aldoximes, which are best-known as therapeutic antidotes for organophosphorus chemical warfare nerve-agents and pesticides, have been found to markedly detoxify polyhalogenated quinones, which are a class of carcinogenic intermediates and recently identified disinfection byproducts in drinking water. However, the exact chemical mechanism underlying this detoxication remains unclear. Here we demonstrate that pralidoxime can remarkably facilitate the dechlorination/hydroxylation of the highly toxic tetrachloro-1,4-benzoquinone in two-consecutive steps to generate the much less toxic 2,5-dichloro-3,6-dihydroxy-1,4-benzoquonine, with rate enhancements of up to 180 000-times. On the contrary, no accelerating effect was noticed with <i>O</i>-methylated pralidoxime. The major reaction product from pralidoxime was identified as its corresponding nitrile (2-cyano-1-methylpyridinium chloride). Along with oxygen-18 isotope-labeling studies, a reaction mechanism was proposed in which nucleophilic substitution coupled with an unprecedented double Beckmann fragmentation reaction was responsible for the dramatic enhancement in the detoxification process. This represents the first report of an unusually mild and facile Beckmann-type fragmentation that can occur under normal physiological conditions in two-consecutive steps. The study may have broad biomedical and environmental significance for future investigations of aldoxime therapeutic agents and carcinogenic polyhalogenated quinones