Mitochondria-Targeting Iron(III) Catecholates for Photoactivated Anticancer Activity under Red Light

Iron(III) catecholates Fe(R-bpa)(R-dopa)Cl] (1, 2) with a triphenylphosphonium (TPP) moiety, where R-bpa is 2-(TPP-N,N-bis((pyridin-2-yl)methyl)ethanamine) chloride (TPPbpa) and R-dopa is 4-{2-(anthracen-9-yl)methylamino]ethyl}benzene-1,2-diol (andopa, 1) or 4-{2-(pyren-1-yl)-methylamino]ethyl}benzene-1,2-diol (pydopa, 2), were synthesized and their photocytotoxicity studied. Complexes 3 and 4 with phenyl-N,N-bis(pyridin-2-yl)methyl]methanamine (phbpa) were used as controls. The catecholate complexes showed an absorption band near 720 nm. The 5e(-) paramagnetic complexes showed a Fe-III/Fe-II irreversible response near -0.45 V and a quasi-reversible catechol/semiquinone couple near 0.5 V versus saturated calomel electrode (SCE) in DMF/0.1 M tetrabutylammonium perchlorate. They showed photocytotoxicity in red/visible light in HeLa, HaCaT, MCF-7, and A549 cells. Complexes 1 and 2 displayed mitochondrial localization, reactive oxygen species (ROS) generation under red light, and apoptotic cell death. Control complexes 3 and 4 exhibited uniform distribution throughout the cell. The complexes showed DNA photocleavage under red light (785 nm), forming hydroxyl radicals as the ROS.

Low Threshold Quantum Dot Lasers

Semiconductor quantum dots have replaced conventional inorganic phosphors in numerous applications. Despite their overall successes as emitters, their impact as laser materials has been severely limited. Eliciting stimulated emission from quantum dots requires excitation by intense short pulses of light typically generated using other lasers. In this Letter, we develop a new class of quantum dots that exhibit gain under conditions of extremely low levels of continuous wave illumination. We observe thresholds as low as 74 mW/cm(2) in lasers made from these materials. Due to their strong optical absorption as well as low lasing threshold, these materials could possibly convert light from diffuse, polychromatic sources into a laser beam.

Novel synergistic photocatalytic degradation of antibiotics and bacteria using V-N doped TiO2 under visible light: the state of nitrogen in V-doped TiO2

We report the synthesis of vanadium and nitrogen co-doped TiO2 for photocatalysis mainly emphasizing the state of nitrogen doping into TiO2 in the presence of vanadium ions. Considering the increase in antibiotic resistance developed by microbes due to the excess of pharmaceutical waste in the ecosystem, the photocatalytic activity was measured by degrading an antibiotic, chloramphenicol. A novel experiment was conducted by degrading the antibiotic and bacteria in each other's vicinity to focus on their synergistic photo-degradation by V-N co-doped TiO2. The catalysts were characterized using XRD, DRS, PL, TEM, BET and XPS analysis. Both interstitial and substitutional nitrogen doping were achieved with V-TiO2, showing high efficiency under visible light for antibiotic and bacterial degradation. In addition, the effect of doping concentration of nitrogen and vanadium in TiO2 and catalyst loading was studied thoroughly. Reusability experiments show that the prepared V-N co-doped TiO2 was stable for many cycles.

Enhanced photocatalytic activity of ultra-high aspect ratio ZnO nanowires due to Cu induced defects

We report the synthesis of ZnO nanowires in ambient air at 650 degrees C by a single-step vapor transport method using two different sources Zn (ZnO nanowires-I) and Zn:Cu (ZnO nanowires-II). The Zn:Cu mixed source co-vaporize Zn with a small amount of Cu at temperatures where elemental Cu source does not vaporize. This method provides us a facile route for Cu doping into ZnO. The aspect ratio of the grown ZnO nanowires-II was found to be higher by more than five times compared ZnO nanowires-I. Photocatalytic activity was measured by using a solar simulator and its ultraviolet-filtered light. The ZnO nanowires-II shows higher catalytic activity due to increased aspect ratio and higher content of surface defects because of incorporation of Cu impurities.

A Nanomechanical Device Based on Light-Driven Proton Pumps

In this paper, a hybrid device based on a microcantilever interfaced with bacteriorhodopsin (bR) is constructed. The microcantilever, on which the highly oriented bR film is self-assembled, undergoes controllable and reversible bending when the light-driven proton pump protein, bR, on the microcantilever surface is activated by visible light. Several control experiments are carried out to preclude the influence of heat and photothermal effects. It is shown that the nanomechanical motion is induced by the resulting gradient of protons, which are transported from the KCl solution on the cytoplasmic side of the bR film towards the extracellular side of the bR film. Along with a simple physical interpretation, the microfabricated cantilever interfaced with the organized molecular film of bR can simulate the natural machinery in converting solar energy to mechanical energy.

Correct biological timing in Arabidopsis requires multiple light-signaling pathways.

Circadian oscillators provide rhythmic temporal cues for a range of biological processes in plants and animals, enabling anticipation of the day/night cycle and enhancing fitness-associated traits. We have used engineering models to understand the control principles of a plant's response to seasonal variation. We show that the seasonal changes in the timing of circadian outputs require light regulation via feed-forward loops, combining rapid light-signaling pathways with entrained circadian oscillators. Linear time-invariant models of circadian rhythms were computed for 3,503 circadian-regulated genes and for the concentration of cytosolic-free calcium to quantify the magnitude and timing of regulation by circadian oscillators and light-signaling pathways. Bioinformatic and experimental analysis show that rapid light-induced regulation of circadian outputs is associated with seasonal rephasing of the output rhythm. We identify that external coincidence is required for rephasing of multiple output rhythms, and is therefore important in general phase control in addition to specific photoperiod-dependent processes such as flowering and hypocotyl elongation. Our findings uncover a fundamental design principle of circadian regulation, and identify the importance of rapid light-signaling pathways in temporal control.

Bayesian separation and recovery of convolutively mixed autoregressive sources

In this paper we address the problem of the separation and recovery of convolutively mixed autoregressive processes in a Bayesian framework. Solving this problem requires the ability to solve integration and/or optimization problems of complicated posterior distributions. We thus propose efficient stochastic algorithms based on Markov chain Monte Carlo (MCMC) methods. We present three algorithms. The first one is a classical Gibbs sampler that generates samples from the posterior distribution. The two other algorithms are stochastic optimization algorithms that allow to optimize either the marginal distribution of the sources, or the marginal distribution of the parameters of the sources and mixing filters, conditional upon the observation. Simulations are presented.

Efficiency measurement of GaN-based quantum well and light-emitting diode structures grown on silicon substrates

The optical efficiency of GaN-based multiple quantum well (MQW) and light emitting diode (LED) structures grown on Si(111) substrates by metal-organic vapor phase epitaxy was measured and compared with equivalent structures on sapphire. The crystalline quality of the LED structures was comprehensively characterized using x-ray diffraction, atomic force microscopy, and plan-view transmission electron microscopy. A room temperature photoluminescence (PL) internal quantum efficiency (IQE) as high as 58% has been achieved in an InGaN/GaN MQW on Si, emitting at 460 nm. This is the highest reported PL-IQE of a c-plane GaN-based MQW on Si, and the radiative efficiency of this sample compares well with similar structures grown on sapphire. Processed LED devices on Si also show good electroluminescence (EL) performance, including a forward bias voltage of ∼3.5 V at 20 mA and a light output power of 1 mW at 45 mA from a 500 ×500 μm2 planar device without the use of any additional techniques to enhance the output coupling. The extraction efficiency of the LED devices was calculated, and the EL-IQE was then estimated to have a maximum value of 33% at a current density of 4 A cm-2, dropping to 30% at a current density of 40 A cm-2 for a planar LED device on Si emitting at 455 nm. The EL-IQE was clearly observed to increase as the structural quality of the material increased for devices on both sapphire and Si substrates. © 2011 American Institute of Physics.