Obtaining Cross-Sections of Paint Layers in Cultural Artifacts Using Femtosecond Pulsed Lasers.

Recently, ultrafast lasers exhibiting high peak powers and extremely short pulse durations have created a new paradigm in materials processing. The precision and minimal thermal damage provided by ultrafast lasers in the machining of metals and dielectrics also suggests a novel application in obtaining precise cross-sections of fragile, combustible paint layers in artwork and cultural heritage property. Cross-sections of paint and other decorative layers on artwork provide critical information into its history and authenticity. However, the current methodology which uses a scalpel to obtain a cross-section can cause further damage, including crumbling, delamination, and paint compression. Here, we demonstrate the ability to make controlled cross-sections of paint layers with a femtosecond pulsed laser, with minimal damage to the surrounding artwork. The femtosecond laser cutting overcomes challenges such as fragile paint disintegrating under scalpel pressure, or oxidation by the continuous-wave (CW) laser. Variations in laser power and translational speed of the laser while cutting exhibit different benefits for cross-section sampling. The use of femtosecond lasers in studying artwork also presents new possibilities in analyzing, sampling, and cleaning of artwork with minimal destructive effects.

Acoustic-optical phonon up-conversion and hot-phonon bottleneck in lead-halide perovskites.

The hot-phonon bottleneck effect in lead-halide perovskites (APbX3) prolongs the cooling period of hot charge carriers, an effect that could be used in the next-generation photovoltaics devices. Using ultrafast optical characterization and first-principle calculations, four kinds of lead-halide perovskites (A=FA+/MA+/Cs+, X=I-/Br-) are compared in this study to reveal the carrier-phonon dynamics within. Here we show a stronger phonon bottleneck effect in hybrid perovskites than in their inorganic counterparts. Compared with the caesium-based system, a 10 times slower carrier-phonon relaxation rate is observed in FAPbI3. The up-conversion of low-energy phonons is proposed to be responsible for the bottleneck effect. The presence of organic cations introduces overlapping phonon branches and facilitates the up-transition of low-energy modes. The blocking of phonon propagation associated with an ultralow thermal conductivity of the material also increases the overall up-conversion efficiency. This result also suggests a new and general method for achieving long-lived hot carriers in materials.

Comparative ecotoxicity of imidacloprid and dinotefuran to aquatic insects in rice mesocosms.

There are growing concerns about the impacts of neonicotinoid insecticides on ecosystems worldwide, and yet ecotoxicity of many of these chemicals at community or ecosystem levels have not been evaluated under realistic conditions. In this study, effects of two neonicotinoid insecticides, imidacloprid and dinotefuran, on aquatic insect assemblages were evaluated in experimental rice mesocosms. During the 5-month period of the rice-growing season, residual concentrations of imidacloprid were 5-10 times higher than those of dinotefuran in both soil and water. Imidacloprid treatment (10kg/ha) reduced significantly the populations of, Crocothemis servilia mariannae and Lyriothemis pachygastra nymphs, whereas those of Orthetrum albistylum speciosum increased slightly throughout the experimental period. However, Notonecta triguttata, which numbers were high from the start, later declined, indicating possible delayed chronic toxicity, while Guignotus japonicus disappeared. In contrast, dinotefuran (10kg/ha) did not decrease the populations of any species, but rather increased the abundance of some insects, particularly Chironominae spp. larvae and C. servilia mariannae nymphs, with the latter being 1.7x higher than those of controls. This was an indirect effect resulting from increased prey (e.g., chironomid larvae) and lack of competition with other dragonfly species. The susceptibilities of dragonfly nymphs to neonicotinoids, particularly imidacloprid, were consistent with those reported elsewhere. In general, imidacloprid had higher impacts on aquatic insects compared to dinotefuran.

Imaging the motion of electrons across semiconductor heterojunctions.

Technological progress since the late twentieth century has centred on semiconductor devices, such as transistors, diodes and solar cells. At the heart of these devices is the internal motion of electrons through semiconductor materials due to applied electric fields or by the excitation of photocarriers. Imaging the motion of these electrons would provide unprecedented insight into this important phenomenon, but requires high spatial and temporal resolution. Current studies of electron dynamics in semiconductors are generally limited by the spatial resolution of optical probes, or by the temporal resolution of electronic probes. Here, by combining femtosecond pump-probe techniques with spectroscopic photoemission electron microscopy, we imaged the motion of photoexcited electrons from high-energy to low-energy states in a type-II 2D InSe/GaAs heterostructure. At the instant of photoexcitation, energy-resolved photoelectron images revealed a highly non-equilibrium distribution of photocarriers in space and energy. Thereafter, in response to the out-of-equilibrium photocarriers, we observed the spatial redistribution of charges, thus forming internal electric fields, bending the semiconductor bands, and finally impeding further charge transfer. By assembling images taken at different time-delays, we produced a movie lasting a few trillionths of a second of the electron-transfer process in the photoexcited type-II heterostructure-a fundamental phenomenon in semiconductor devices such as solar cells. Quantitative analysis and theoretical modelling of spatial variations in the movie provide insight into future solar cells, 2D materials and other semiconductor devices.

Excited-state dynamics of the medicinal pigment curcumin in a hydrogel.

Curcumin is a yellow polyphenol with multiple medicinal effects. These effects, however, are limited due to its poor aqueous stability and solubility. A hydrogel of 3% octadecyl randomly substituted polyacrylate (PAAC18) has been shown to provide high aqueous stability for curcumin under physiological conditions, offering a route for photodynamic therapy. In this study, the excited-state photophysics of curcumin in the PAAC18 hydrogel is investigated using a combination of femtosecond transient absorption and fluorescence upconversion spectroscopy. The transient absorption results reveal a multiexponential decay in the excited-state kinetics with fast (1 ps & 15 ps) and slow (110 ps & ≈5 ns) components. The fast decay component exhibits a deuterium isotope effect with D2O in the hydrogel, indicating that the 15 ps decay component is attributable to excited-state intramolecular hydrogen atom transfer of curcumin in the PAAC18 hydrogel. In addition, solvent reorganisation of excited-state curcumin is investigated using multiwavelength femtosecond fluorescence upconversion spectroscopy. The results show that the dominant solvation response (τ = 0.08 ps) is a fast inertial motion owing to the presence of bulk-like water in the vicinity of the hydrophobic octadecyl substituents of the PAAC18 hydrogel. The results also show an additional response with longer time constants of 1 and 6 ps, which is attributable to translational diffusion of confined water molecules in the three-dimensional, cross-linking network of the octadecyl substituents of PAAC18. Overall, we show that excited-state intramolecular hydrogen atom transfer and solvent reorganisation are major photophysical events for curcumin in the PAAC18 hydrogel.

Unified Total Synthesis of Five Gelsedine-Type Alkaloids: (-)-Gelsenicine, (-)-Gelsedine, (-)-Gelsedilam, (-)-14-Hydroxygelsenicine, and (-)-14,15-Dihydroxygelsenicine.

The systematic arrangement of a two-carbon unit, hydrogen atom, and oxygen atom on the versatile enal moiety of a non-natural synthetic intermediate successfully led to the unified access to the gelsedine-type alkaloids. The development and use of this new synthetic hub and an array of site-selective transformations resulted in the asymmetric synthesis of (-)-gelsenicine, (-)-gelsedine, (-)-gelsedilam, (-)-14-hydroxygelsenicine, and (-)-14,15-dihydroxygelsenicine.

Nanoprecipitation and Spectroscopic Characterization of Curcumin-Encapsulated Polyester Nanoparticles.

Curcumin-encapsulated polyester nanoparticles (Cur-polyester NPs) of approximately 100 nm diameter with a negatively charged surface were prepared using a one-step nanoprecipitation method. The Cur-polyester NPs were prepared using polylactic acid, poly(D,L-lactic-co-glycolic acid) and poly(ϵ-caprolactone) without any emulsifier or surfactant. The encapsulation of curcumin in these polyester NPs greatly suppresses curcumin degradation in the aqueous environment due to its segregation from water. In addition, the fluorescence of curcumin in polyester NPs has a quantum yield of 4 to 5%, which is higher than that of curcumin in micellar systems and comparable to those in organic solvents, further supporting the idea that the polyester NPs are capable of excluding water from curcumin. Furthermore, the results from femtosecond fluorescence upconversion spectroscopy reveal that there is a decrease in the signal amplitude corresponding to solvent reorganization of excited state curcumin in the polyester NPs compared with curcumin in micellar systems. The Cur-polyester NPs also show a lack of deuterium isotope effect in the fluorescence lifetime. These results indicate that the interaction between curcumin and water in the polyester NPs is significantly weaker than that in micelles. Therefore, the aqueous stability of curcumin is greatly improved due to highly effective segregation from water. The overall outcome suggests that the polyester NPs prepared using the method reported herein are an attractive system for encapsulating and stabilizing curcumin in the aqueous environment.

Ultrafast Intrinsic Photoresponse and Direct Evidence of Sub-gap States in Liquid Phase Exfoliated MoS2Thin Films.

2-Dimensional structures with swift optical response have several technological advantages, for example they could be used as components of ultrafast light modulators, photo-detectors, and optical switches. Here we report on the fast photo switching behavior of thin films of liquid phase exfoliated MoS2, when excited with a continuous laser of λ = 658 nm (E = 1.88 eV), over a broad range of laser power. Transient photo-conductivity measurements, using an optical pump and THz probe (OPTP), reveal that photo carrier decay follows a bi-exponential time dependence, with decay times of the order of picoseconds, indicating that the photo carrier recombination occurs via trap states. The nature of variation of photocurrent with temperature confirms that the trap states are continuously distributed within the mobility gap in these thin film of MoS2, and play a vital role in influencing the overall photo response. Our findings provide a fundamental understanding of the photo-physics associated with optically active 2D materials and are crucial for developing advanced optoelectronic devices.

Femtosecond transient absorption spectroscopy of the medicinal agent curcumin in diamide linked γ-cyclodextrin dimers.

Curcumin is a biologically active polyphenol and a yellow pigment extracted from turmeric. Our previous study has shown effective encapsulation of curcumin using diamide linked γ-cyclodextrin dimers, namely 66γCD2su and 66γCD2ur, through cooperative 1:1 host-guest complexation. In this study, the excited-state dynamics of curcumin complexed with either 66γCD2su or 66γCD2ur in water are investigated using femtosecond transient absorption spectroscopy. Both 66γCD2su-curcumin and 66γCD2ur-curcumin complexes in water show only an excited-state absorption (ESA) band at 530 nm without any stimulated emission (SE) signals, indicating non-radiative decays as the major relaxation pathways. The ESA dynamics of 66γCD2su-curcumin are similar to those of 66γCD2ur-curcumin, consisting of a rapid growth component and three decay components. The growth component, which has a time constant of 0.25-0.41 ps, is assigned to solvent reorganization. The relatively fast decay components with time constants of 9.3-21.8 ps show significant deuterium isotope effect, consistent with the presence of excited-state intramolecular hydrogen atom transfer (ESIHT) of curcumin. The small-amplitude and slow decay components may be attributed to the dynamics of complexed curcumin and molecular motions due to flexibility of 66γCD2su and 66γCD2ur. In addition, transient absorption anisotropy measurements reveal slow rotational motions of 66γCD2su-curcumin and 66γCD2ur-curcumin complexes. The overall results show that complexation in 66γCD2su and 66γCD2ur has pronounced effects on the photophysics of curcumin.

The capture and stabilization of curcumin using hydrophobically modified polyacrylate aggregates and hydrogels.

Hydrophobically modified polyacrylates are shown to suppress the degradation of the medicinal pigment curcumin under physiological conditions. In aqueous solution, the 3% octadecyl randomly substituted polyacrylate, PAAC18, forms micelle-like aggregates at a concentration of <1 wt % and a hydrogel at >1 wt %. Under both conditions, PAAC18 shows a remarkable ability to suppress the degradation of curcumin at pH 7.4 and 37 °C such that its degradation half-life is increased by 1600-2000-fold. The suppression of degradation is attributed to hydrophobic interactions between curcumin and the octadecyl substituents of PAAC18 within the micelle-like aggregates and the hydrogel, as indicated by 2D NOESY (1)H NMR spectroscopy. UV-visible absorption titration results are consistent with the interaction of curcumin with five octadecyl substituents on average, which appears to substantially exclude water and greatly decrease the curcumin degradation rate. Dynamic light scattering and zeta potential measurements show the average hydrodynamic diameters of the PAAC18 aggregates to be 0.86-1.15 µm with a negative surface charge. In contrast to the octadecyl substitution, the 3% dodecyl randomly substituted polyacrylate, PAAC12, shows a negligible effect on slowing the degradation of curcumin, consistent with the dodecyl substituents being insufficiently long to capture curcumin in a adequately hydrophobic environment. These observations indicate the potential for PAAC18 to act as a model drug delivery system.

Diamide linked γ-cyclodextrin dimers as molecular-scale delivery systems for the medicinal pigment curcumin to prostate cancer cells.

Diamide linked γ-cyclodextrin (γ-CD) dimers are proposed as molecular-scale delivery agents for the anticancer agent curcumin. N,N'-Bis(6(A)-deoxy-γ-cyclodextrin-6(A)-yl)succinamide (66γCD2su) and N,N'-bis(6(A)-deoxy-γ-cyclodextrin-6(A)-yl)urea (66γCD2ur) markedly suppress the degradation of curcumin by forming a strong 1:1 cooperative binding complexes. The results presented in this study describe the potential efficacy of 66γCD2su and 66γCD2ur for intracellular curcumin delivery to cancer cells. Cellular viability assays demonstrated a dose-dependent antiproliferative effect of curcumin in human prostate cancer (PC-3) cells that was preserved by the curcumin-66γCD2su complex. In contrast, delivery of curcumin by 66γCD2ur significantly delayed the antiproliferative effect. We observed similar patterns of gene regulation in PC-3 cells for curcumin complexed with either 66γCD2su or 66γCD2ur in comparison to curcumin alone, although curcumin delivered by either 66γCD2su or 66γCD2ur induces a slightly higher up-regulation of heme oxygenase-1. Highlighting their nontoxic nature, neither 66γCD2su nor 66γCD2ur carriers alone had any measurable effect on cell proliferation or candidate gene expression in PC-3 cells. Finally, confocal fluorescence imaging and uptake studies were used to demonstrate the intracellular delivery of curcumin by 66γCD2su and 66γCD2ur. Overall, these results demonstrate effective intracellular delivery and action of curcumin when complexed with 66γCD2su and 66γCD2ur, providing further evidence of their potential applications to deliver curcumin effectively in cancer and other treatment settings.

Delivery of curcumin and medicinal effects of the copper(II)-curcumin complexes.

Curcumin, a yellow pigment extracted from the rhizome of Curcuma longa, commonly known as turmeric, is the most active agent of this herbal medicine. The therapeutic activities of curcumin are exemplified not only by its enhancement in wound healing but also in the treatment of inflammation, cystic fibrosis, Alzheimer's disease and cancer. There are two critical issues involving low aqueous stability and solubility that limit the bioavailability and application of curcumin as a therapeutic agent. To address these issues, delivery systems of curcumin including surfactant micelles, liposomes, polymer nanoparticles, casein micelles, plasma proteins and cyclodextrins have been developed and characterized. From a biochemical perspective, the medicinal activities of curcumin are proposed to be related to an elevated level of transition metals including copper, zinc and iron in many disease sites, especially those in cancer and Alzheimer's disease. Previous studies have demonstrated the importance of copper(II)-curcumin complexes in DNA damage owing to the strong interaction between curcumin and copper(II). Curcumin, as an anti-oxidant, possesses the abilities to scavenge radicals and maintain the levels of anti-oxidant enzymes in the presence of copper. On the other hand, copper(II)-curcumin complexes show pro-oxidant effects by generating reactive oxygen species at a high free copper level in a reducing environment. This condition results in DNA damage and inhibition of vital signaling pathways in cancer cells, leading to apoptosis. In short, curcumin has dual roles as an anti-oxidant and a prooxidant in the presence of copper and these fascinating phenomena contribute greatly to its multiple medicinal effects.

Total synthesis of gelsemoxonine.

The first total synthesis of gelsemoxonine (1) has been accomplished. Divinylcyclopropane-cycloheptadiene rearrangement of the highly functionalized substrate was successfully applied to assemble the spiro-quaternary carbon center connected to the bicyclic seven-membered core structure. A one-pot isomerization reaction of the α,ß-unsaturated aldehyde to the saturated ester via the TMSCN-DBU reagent combination allowed a facile diastereoselective introduction of the latent nitrogen functionality of the unique azetidine moiety.

Cooperative binding and stabilization of the medicinal pigment curcumin by diamide linked γ-cyclodextrin dimers: a spectroscopic characterization.

Diamide linked γ-cyclodextrin (γ-CD) dimers are used to capture curcumin and suppress its decomposition in water. In this study, succinamide and urea linked γ-CD dimers joined through the C6(A) carbon on each γ-CD are used. The γ-CD dimers, 66γCD(2)su and 66γCD(2)ur, show a remarkable ability to suppress the decomposition of curcumin and extend its half-life from less than 30 min to greater than 16 h. The 1:1 association of curcumin with 66γCD(2)su and 66γCD(2)ur has high stability constants of 8.7 × 10(6) M(-1) and 2.0 × 10(6) M(-1), respectively. In addition, 2D (1)H NOESY NMR results show specific hydrogen interactions in the association of curcumin with 66γCD(2)su and 66γCD(2)ur, consistent with the cooperative binding of curcumin by both γ-CD annuli of 66γCD(2)su and 66γCD(2)ur. The interactions between curcumin in the linked γ-CD dimers and surfactant micelles were studied using fluorescence spectroscopy. While linked γ-CD dimer-bound curcumin has a negligible fluorescence quantum yield, a significant increase in fluorescence intensity (Φ(fl) > 2%) in the presence of micelles suggests that curcumin is delivered to the micelle. The overall results indicate that the diamide linked γ-CD dimers are highly promising systems for curcumin delivery in vivo due to effective curcumin stabilization.

Phylogenetic analysis and Shiga toxin production profiling of Shiga toxin-producing/enterohemorrhagic Escherichia coli clinical isolates.

Shiga toxin-producing Escherichia coli (STEC) can cause severe illnesses in humans such as hemorrhagic colitis and hemolytic-uremic syndrome. In this study, we carried out genotypic analysis of the Shiga toxin (stx) gene in 120 clinical isolates of STEC and enterohemorrhagic E. coli (EHEC) from patients in a southern district of Japan. We identified 88 stx(1)(+) and 103 stx(2)(+) strains. We further identified 12 stx(1)(+) and stx(2)(+) isolates expressing little or no Shiga toxin 1 (Stx(1)) and/or 2 (Stx(2)) by reversed passive latex agglutination (RPLA) and Vero cell toxicity assays. Among them, 1 strain could not produce Stx(1), 8 could not produce Stx(2), and 3 strains could produce neither. Two of the latter three strains were of the non-O157 serotype. Most of the Stx RPLA-negative strains belonged to the stx(1)/stx(2) subtype (11/12, [91.7%]). Our quantitative reverse transcription PCR analysis indicated that the stx genes were not effectively transcribed in the RPLA-negative strains. This is the first report of the isolation of stx-positive strains showing Stx-negative phenotype from stx(1)-bearing strains and non-O157 strains.