The bakkenolides from the root of Petasites formosanus and their cytotoxicity.

Thirty-two new bakkenolides, bakkenolides-Db (1)--Dh(7), -Fa(8), -Fb(9), -I(10)--M(14), -Na(15), -Nb(16), -O(17)--T(22), -Ua (23), -Ub(24), -V(25)--X(27), -Ya(28), -Yb(29), -Za(30), -Zb(31) and -III(32), from the roots of Petasites formosanus together with thirty known compounds were isolated. The structures were characterized by spectral analysis. The locations, C-1 and/or C-9 of bakkenolide skeleton, of the substituents, such as acetoxy, isobutyroyloxy and isovaleroyloxy groups, can be determined by the chemical shifts of their signals and the H-1 and/H-9 in the 1H-NMR spectra. The cytotoxicity was also discussed.     

Two-photon optical-beam-induced current imaging of indium gallium nitride blue light-emitting diodes

Epilayers of packaged indium gallium nitride light-emitting diodes (LED's) are characterized by optical-beam-induced current (OBIC) and photoluminescence laser-scanning microscopy through two-photon excitation. Light scattering and absorption in the packaging material and the p-doped top layer of the LED's are greatly reduced as a result of employing a longer excitation wavelength, with energy that is less than the bandgap of the top p layer. Compared with single-photon OBIC, two-photon OBIC imaging not only exhibits superior image quality but also reveals more clearly the characteristics of the epilayers that are being focused on.     

Synthesis and biological testing of aminoxyls designed for long-term retention by living cells

Owing to recent advances in electron paramagnetic resonance (EPR) imaging methodologies, it is now potentially possible to track and image, in real time in vivo, cells that had been tagged with aminoxyl spin probes. We had previously reported that living cells can accumulate 3-carboxy-2,2,5,5-tetramethyl-1-pyrrolidinyloxyl [1] to high (millimolar) intracellular concentrations through passive incubation with the corresponding acetoxymethyl (AM) ester [2]. In the present study, we show that under physiological conditions aminoxyl [1] is rapidly extruded by cells through an organic anion transport mechanism, resulting in an intracellular exponential lifetime (t(1/e) or tau) of just 9.84 min at 37 degree C. Through successive rational structural modifications, we arrived at (2,2,5,5-tetramethylpyrrolidin-1-oxyl-3-ylmethyl)amine-N,N-diacetic acid [10], which can still be accumulated by cells to high intracellular concentrations, but which, with an intracellular exponential lifetime of tau]= 114 min, is well retained by cells for long periods of time, where one expects 14% retention even after 5 h. These results suggest that it should be feasible to use EPR imaging to perform in vivo tracking of populations of cells that have accumulated high intracellular levels of aminoxyls.     

Biocompatibility of poly(carbonate urethane)s with various degrees of nanophase separation

Nanophase separation has been suggested to influence the biological performance of polyurethane. In a previous work, six different 4,4'-diphenylmethane diisocyanate (MDI)-based poly(carbonate urethane)s (PCUs) that exhibited various degrees of nanophase separation were synthesized and characterized. In the present work, these PCUs were used as a model system to study the effect of nanometric structures on the biocompatibility of polyurethane. Human blood platelet activation, monocyte activation, protein adsorption, and bacterial adhesion on PCU were investigated in vitro. It was found that human blood platelets as well as monocytes were less activated on the PCU surfaces with a greater degree of nanophase separation in general. This phenomenon was closely associated with the lower ratio of human fibrinogen/albumin competitively adsorbed on these surfaces. Bacterial adhesion was also inhibited in some nanophase-separated PCUs. [diagram in text].     

Ordering of hydrogen bonds in high-pressure low-temperature H2O

The near K-edge structure of oxygen in liquid water and ices III, II, and IX at 0.25 GPa and several low temperatures down to 4 K has been studied using inelastic x-ray scattering at 9884.7 eV with a total energy resolution of 305 and 175 meV. A marked decrease of the preedge intensity from the liquid phase and ice III to ices II and IX is attributed to ordering of the hydrogen bonds in the proton-ordered lattice of the latter phases. Density functional theory calculations including the influence of the Madelung potential of the ice IX crystal correctly account for the remaining preedge feature. Furthermore, we obtain spectroscopic evidence suggesting a possible new phase of ice at temperatures between 4 and 50 K.     

Synthesis and electrogenerated chemiluminescence of donor-substituted phenylquinolinylethynes and phenylisoquinolinylethynes: effect of positional isomerism

In furtherance of our research on the design, synthesis and study of electrogenerated chemiluminescence (ECL) of new donor substituted phenylquinolinylethynes, we report here more new series with the aim of studying the effect of positional isomerism on their overall photophysical properties with a special focus on ECL. For this study we have chosen 2-, 3-, and 4-(p-substituted phenyl)ethynylquinolines, and 1- and 4-(p-substituted phenyl)ethynylisoquinolines. These ethynes were synthesized in good yields by modified Sonogashira coupling of the corresponding terminal alkyne with the respective haloquinolines. The photophysical properties and ECL were studied in acetonitrile solvent and the various results are discussed.     

Enhanced biocompatibility in biostable poly(carbonate)urethane

In this work, we synthesized two MDI-based polyurethanes, including a poly(ether)urethane (PEU) and a poly(carbonate)urethane (PCU), by using different soft segments, poly(tetramethylene oxide) and poly(hexyl, ethyl)carbonate diol (M approximately 2,000). We demonstrated that, in addition to the enhanced biostability of PCU over PEU, the biological performances of PCU in vitro were also improved in general. These included, better cellular attachment and proliferation, less platelet activation, as well as reduced monocyte activation. The unusual wide-ranging enhancement in biocompatibility for PCU was believed to be related to the larger micro-phase separation in PCU (approximately 25 nm) that caused distinct protein adsorption on the surface. The total number of adherent monocytes (nonactivated and activated) on the bare sample surfaces, albumin pre-adsorbed sample surfaces, and fibrinogen pre-adsorbed sample surfaces.     

Multi-photon fluorescence microscopy--the response of plant cells to high intensity illumination

Multi-photon fluorescence microscopy has been cited for its advantage in increased depth penetration due to low linear absorption and scattering coefficient of biological specimen in the near infrared (NIR) range. Because of the need of high peak power for efficiently exciting two-photon fluorescence, the relationship between cell damage and peak power has become an interesting and much debated topic in the applications of multi-photon fluorescence microscopy. It is conceivable that at high illumination intensity, non-linear photochemical processes have impacts on cell physiology and viability in ways much different from low illumination in the linear domain. In this article, we discuss some of the issues in two-photon fluorescence microscopy, including the degree of transparency of the specimen, a comparison of single- and two-photon excited fluorescence spectra, and the cell damage under high intensity illumination, using plant cells as a model.     

Dynamic structure factor of diamond and LiF measured using inelastic X-Ray scattering

The dynamic structure factors S(q-->,omega) of diamond and LiF have been measured using inelastic x-ray scattering. The experimental data are compared to results of ab initio calculations, which take into account the interaction of the excited electron with the remaining hole. In diamond, the vicinity of the indirect band gap and its momentum dependence are studied. In LiF, a larger energy range, which covers the fundamental exciton, the plasmon, and several interband transitions, is investigated. Calculations and measurements agree quite well and emphasize the need to properly include the interaction of the excited electron in the conduction band with the hole in the valence band.     

Large near resonance third order nonlinearity in GaN

We have studied third order nonlinearities, including two-photon absorption coefficient and nonlinear refractive index n ₂, of GaN in below bandgap ultraviolet (UV) wavelength regime by using UV femtosecond pulses. Two-photon absorption was investigated by demonstrating femtosecond UV pulsewidth autocorrelation in a GaN thin film while femtosecond Z-scan measurements revealed information for both n ₂ and . The distribution of n ₂ versus wavelength was found to be consistent with a model described by the quadratic Stark effect, which is the dominant factor contributed to the nonlinear refractive index near the bandgap. Large on the order of 10 cm/GW and large negative n ₂ with a magnitude on the order of several 10^–12 cm²/W were obtained. The at near mid-gap infrared (IR) wavelength was also found to be on the order of several cm/GW by using two-photon-type autocorrelations in a GaN thin film. Taking advantage of the large two-photon absorption at mid-gap wavelengths, we have demonstrated excellent image quality on two-photon confocal microscopy, including two-photon-scanning-photoluminescence imaging and two-photon optical-beam-induced current microscopy, on a GaN Hall measurement sample and an InGaN green light emitting diode.