Dye-induced photoluminescence quenching of quantum dots: role of excited state lifetime and confinement of charge carriers.

We investigate the role of quantum confinement and photoluminescence (PL) lifetime of photoexcited charge carriers in semiconductor core/shell quantum dots (QDs) via PL quenching due to surface modification. Surface modification is controlled by varying the number of dye molecules adsorbed onto the QD shell surface forming QD-dye nanoassemblies. We selected CuInS2/ZnS (CIS) and InP/ZnS (InP) core/shell QDs exhibiting relatively weak (664 meV) and strong (1194 meV) confinement potentials for the conduction band electron. Moreover, the difference in the emission mechanism gives rise to a long and short excited state lifetime of CIS (ca. 290 ns) and InP (ca. 37 ns) QDs. Dye molecules of different ionic characters (rhodamine 575: zwitterionic and rhodamine 560: cationic) are used as quenchers. A detailed analysis of Stern-Volmer data shows that (i) quenching is generally more pronounced in CIS-dye assemblies as compared to InP-dye assemblies, (ii) dynamic quenching is dominating in all QD-dye assemblies with only a minor contribution from static quenching and (iii) the cationic dye shows a stronger interaction with the QD shell surface than the zwitterionic dye. Observations (i) and (ii) can be explained by the differences in the amplitude of the electronic component of the exciton wavefunction near the dye binding sites in both QDs, which results in the breaking up of the electron-hole pair and favors charge trapping. Observation (iii) can be attributed to the variations in electrostatic interactions between the negatively charged QD shell surface and the cationic and zwitterionic dyes, with the former exhibiting a stronger interaction. Moreover, the long lifetime of CIS QDs facilitates us to easily probe different time scales of the trapping processes and thus differentiate the origins of static and dynamic quenching components that appear in the Stern-Volmer analysis.

Role of Bisphenol A in Autophagy Modulation: Understanding the Molecular Concepts and Therapeutic Options.

Bisphenol A (4,4'-isopropylidenediphenol) is an organic compound commonly used in plastic bottles, packaging containers, beverages, and resin industry. The adverse effects of bisphenol A in various systems of the body have been studied. Autophagy is a lysosomal degradation process that leads to the regeneration of new cells. The role of bisphenol A in autophagy modulation involved in the pathogenesis of diseases is still debatable. A few research studies have shown bisphenol Ainduced adverse effects to be associated with autophagy dysregulation, while a few have shown the activation of autophagy to be mediated by bisphenol A. Such contrasting views make the subject more interesting and debatable. In the present review, we discuss the different steps of autophagy, genes involved, and the effect of autophagy modulation by bisphenol A on different systems of the body. We also discuss the methods for monitoring autophagy and the roles of drugs, such as chloroquine, verteporfin, and rapamycin, in autophagy. A proper understanding of the role of bisphenol A in the modulation of autophagy may be important for future treatment and drug discovery.

Perinatal Exposure to Bisphenol A and Developmental Programming of the Cardiovascular Changes in the Offspring.

Bisphenol A (BPA) is an industrial ubiquitous compound, frequently used to produce synthetic polymers and epoxy resins. BPA is a well-recognized endocrine disruptor and xenoestrogen compound. Evidence from epidemiological and experimental studies suggests that perinatal BPA exposure (gestation and/or lactation) increases the risk of developing various diseases, including the cardiovascular system. Developmental programming refers to environmental insults during the critical window of development that affect the structure and physiology of body systems, causing permanent changes in later stages. BPA influences the developmental programming of non-communicable diseases in the offspring. In the present review, we discuss the developmental programming of cardiovascular diseases related to perinatal exposure to BPA, supported by epidemiological and experimental evidence from published literature. The majority of the reported studies found a positive association between perinatal BPA exposure and adverse cardiovascular repercussions in the fetal, neonatal, and adulthood stages. The possible underlying mechanisms include epigenetic modifications of genes involved in cardiac muscle development, autonomic tone, collagenous and non-collagenous extracellular matrix, cardiac remodeling and calcium homeostasis, and mitochondrial energy metabolism. Epigenetics can modify the outcome of any disease. Hence, in the present review, we also discuss the role of epigenetics in preventing cardiovascular diseases following perinatal exposure to BPA. We also highlight how future treatment and drug delivery related to cardiovascular involvement could be based on epigenetic markers.

Mn2Au: body-centered-tetragonal bimetallic antiferromagnets grown by molecular beam epitaxy.

Mn(2)Au, a layered bimetal, is successfully grown using molecular beam epitaxy (MBE). The experiments and theoretical calculations presented suggest that Mn(2)Au film is antiferromagnetic with a very low critical temperature. The antiferromagnetic nature is demonstrated by measuring the exchange-bias effect of Mn(2)Au/Fe bilayers. This study establishes a primary basis for further research of this new antiferromagnet in spin-electronic device applications.

Electrically driven phase transition in magnetite nanostructures.

Magnetite (Fe3O4), an archetypal transition-metal oxide, has been used for thousands of years, from lodestones in primitive compasses to a candidate material for magnetoelectronic devices. In 1939, Verwey found that bulk magnetite undergoes a transition at TV approximately 120 K from a high-temperature 'bad metal' conducting phase to a low-temperature insulating phase. He suggested that high-temperature conduction is through the fluctuating and correlated valences of the octahedral iron atoms, and that the transition is the onset of charge ordering on cooling. The Verwey transition mechanism and the question of charge ordering remain highly controversial. Here, we show that magnetite nanocrystals and single-crystal thin films exhibit an electrically driven phase transition below the Verwey temperature. The signature of this transition is the onset of sharp conductance switching in high electric fields, hysteretic in voltage. We demonstrate that this transition is not due to local heating, but instead is due to the breakdown of the correlated insulating state when driven out of equilibrium by electrical bias. We anticipate that further studies of this newly observed transition and its low-temperature conducting phase will shed light on how charge ordering and vibrational degrees of freedom determine the ground state of this important compound.