Direct Imaging of Cl‐ and Cu‐Induced Short‐Circuit Efficiency Changes in CdTe Solar Cells

To achieve high‐efficiency polycrystalline CdTe‐based thin‐film solar cells, the CdTe absorbers must go through a post‐deposition CdCl₂ heat treatment followed by a Cu diffusion step. To better understand the roles of each treatment with regard to improving grains, grain boundaries, and interfaces, CdTe solar cells with and without Cu diffusion and CdCl₂ heat treatments are investigated using cross‐sectional electron beam induced current, electron backscatter diffraction, and scanning transmission electron microscope techniques. The evolution of the cross‐sectional carrier collection profile due to these treatments that cause an increase in short‐circuit current and higher open‐circuit voltage are identified. Additionally, an increased carrier collection in grain boundaries after either/both of these treatments is revealed. The increased current at the grain boundaries is shown to be due to the presence of a space charge region with an intrinsic carrier collection profile width of ≈350 nm. Scanning transmission electron microscope electron‐energy loss spectroscopy shows a decreased Te and increased Cl concentration in grain boundaries after treatment, which causes the inversion. Each treatment improves the overall carrier collection efficiency of the cell separately, and, therefore, the benefits realized by each treatment are shown to be independent of each other.     

Leaf-applied sodium chloride promotes cadmium accumulation in durum wheat grain

Cadmium (Cd) accumulation in durum wheat grain is a growing concern. Among the factors affecting Cd accumulation in plants, soil chloride (Cl) concentration plays a critical role. The effect of leaf NaCl application on grain Cd was studied in greenhouse-grown durum wheat (Triticum turgidum L. durum, cv. Balcali-2000) by immersing (10 s) intact flag leaves into Cd and/or NaCl-containing solutions for 14 times during heading and dough stages. Immersing flag leaves in solutions containing increasing amount of Cd resulted in substantial increases in grain Cd concentration. Adding NaCl alone or in combination with the Cd-containing immersion solution promoted accumulation of Cd in the grains, by up to 41%. In contrast, Zn concentrations of grains were not affected or even decreased by the NaCl treatments. This is likely due to the effect of Cl complexing Cd and reducing positive charge on the metal ion, an effect that is much smaller for Zn. Charge reduction or removal (CdCl₂⁰ species) would increase the diffusivity/lipophilicity of Cd and enhance its capability to penetrate the leaf epidermis and across membranes. Of even more significance to human health was the ability of Cl alone to penetrate leaf tissue and mobilize and enhance shoot Cd transfer to grains, yet reducing or not affecting Zn transfer.     

A Facile Synthesis of ε-Pyridoxinyl-L-Iysines

The intracellular cadmium (Cd) content was measured with early stationary phase cells of a highly Cd-tolerant moderately halophilic bacterium Pseudomonas sp. No. 40 cultivated in 1M and 3M NaCl medium containing 0 to 2500 μg of CdCl₂/ml. It was found that the Cd contents were greatly affected by the NaCl concentration of the medium. When the bacterium was cultivated in the 1, 2, 3, and 4M NaCl medium containing 1500 μg of CdCl₂/ml, the intracellular Cd content was 25.0, 4.1, 3.1, and 2.0 mg Cd per g of dry cells, respectively. The intracellular Cd content decreased with increases of NaCl concentration of the medium. The fact seems to reflect Cd-tolerance of the bacterium towards the growth in the medium of different NaCl concentration. It is worthwhile to note that the bacterium showed the highest Cd-tolerance (in 3M NaCl) and the lowest Cd content among the bacteria so far known. The bacterial cells grown in the 1M NaNO₃ and 1M Na₂SO₄ medium accumulated 1.8–1.3 times as much Cd²⁺ as those in the 1M NaCl medium in the presence of 50–200 μg of CdCl₂/ml. It would also explain the difference in the Cd toxicity in the medium of NaNO₃, Na₂SO₄, or NaCl.     

Effect of black cumin (Nigella sativa) on cadmium-induced oxidative stress in the blood of rats

The protective effect of black cumin (Nigella sativa=NS) on cadmium-induced oxidative stress was studied in rats. The rats were randomly divided into three experimental groups: A (conrol), B (Cd treated), and C (Cd+NS treated), each containing 10 animals. The Cd-treated and Cd+NS-treated groups were injected subcutaneously daily with CdCl₂ dissolved in isotonic NaCl in the amount of 2 mL/kg for 30 d, resulting in a dosage of 0.49 mg Cd/kg/d. The control group was injected with only isotonic NaCl (2 mL/kg/d) throughout the experiment (for 30 d). Three days prior to induction of CdCl₂, the Cd+NS-treated group received a daily intraperitoneal injection of 0.2 mL/kg NS until the end of the study. Cd treatment increased significantly the malondialdehyde levels in plasma and erythrocyte (p<0.01 and p<0.05, respectively) and also increased significantly the antioxidant levels (superoxide dismutase, glutathione peroxidase, and catalase) (p<0.05) compared to the control group. Cd+NS treatment decreased significantly the elevated malondialdehyde levels in plasma and erythrocyte (p<0.01 and p<0.05, respectively) and also reduced significantly the enhanced antioxidant levels (p<0.05). Cd treatment increased significantly the activity of iron levels (p<0.05) in the plasma compared to the control group. Cd+NS treatment decreased the activity of iron levels (p<0.05) in the plasma compared to the Cd-treated group. In the control group with no treatment, histology of erythrocytes was normal. In the Cd-treated group, there were remarkable membrane destruction and hemolytic changes in erythrocytes. In the Cd+NS treated group, these changes were less than in the Cd-treated group. Our results show that N. sativa exerts a protective effect against cadmium toxicity.     

Nucleosomal arrays self‐assemble into supramolecular globular structures lacking 30‐nm fibers

The existence of a 30‐nm fiber as a basic folding unit for DNA packaging has remained a topic of active discussion. Here, we characterize the supramolecular structures formed by reversible Mg²⁺‐dependent self‐association of linear 12‐mer nucleosomal arrays using microscopy and physicochemical approaches. These reconstituted chromatin structures, which we call “oligomers”, are globular throughout all stages of cooperative assembly and range in size from ~50 nm to a maximum diameter of ~1,000 nm. The nucleosomal arrays were packaged within the oligomers as interdigitated 10‐nm fibers, rather than folded 30‐nm structures. Linker DNA was freely accessible to micrococcal nuclease, although the oligomers remained partially intact after linker DNA digestion. The organization of chromosomal fibers in human nuclei in situ was stabilized by 1 mM MgCl₂, but became disrupted in the absence of MgCl₂, conditions that also dissociated the oligomers in vitro. These results indicate that a 10‐nm array of nucleosomes has the intrinsic ability to self‐assemble into large chromatin globules stabilized by nucleosome–nucleosome interactions, and suggest that the oligomers are a good in vitro model for investigating the structure and organization of interphase chromosomes.     

Cadmium uptake in Elodea canadensis leaves and its interference with extra‐ and intra‐cellular pH

This study investigated cadmium (Cd) uptake in Elodea canadensis shoots under different photosynthetic conditions, and its effects on internal (cytosolic) and external pH. The plants were grown under photosynthetic (light) or non‐photosynthetic (dark or in the presence of a photosynthetic inhibitor) conditions in the presence or absence of CdCl₂ (0.5 μm ) in a medium with a starting pH of 5.0. The pH‐sensitive dye BCECF‐AM was used to monitor cytosolic pH changes in the leaves. Cadmium uptake in protoplasts and leaves was detected with a Cd‐specific fluorescent dye, Leadmium Green AM, and with atomic absorption spectrophotometry. During cultivation for 3 days without Cd, shoots of E. canadensis increased the pH of the surrounding water, irrespective of the photosynthetic conditions. This medium alkalisation was higher in the presence of CdCl₂. Moreover, the presence of Cd also increased the cation exchange capacity of the shoots. The total Cd uptake by E. canadensis shoots was independent of photosynthetic conditions. Protoplasts from plants exposed to 0.5 μm CdCl₂ for 3 days did not exhibit significant change in cytosolic [Cd²⁺] or pH. However, exposure to CdCl₂ for 7 days resulted in increased cytosolic [Cd²⁺] as well as pH. The results suggest that E. canadensis subjected to a low CdCl₂ concentration initially sequesters Cd into the apoplasm, but under prolonged exposure, Cd is transported into the cytosol and subsequently alters cytosolic pH. In contrast, addition of 10–50 μm CdCl₂ directly to protoplasts resulted in immediate uptake of Cd into the cytosol.     

H2O2 and cytosolic Ca2+ signals triggered by the PM H+‐coupled transport system mediate K+/Na+ homeostasis in NaCl‐stressed Populus euphratica cells

Using confocal microscopy, X‐ray microanalysis and the scanning ion‐selective electrode technique, we investigated the signalling of H₂O₂, cytosolic Ca²⁺ ([Ca²⁺]_cyt) and the PM H⁺‐coupled transport system in K⁺/Na⁺ homeostasis control in NaCl‐stressed calluses of Populus euphratica. An obvious Na⁺/H⁺ antiport was seen in salinized cells; however, NaCl stress caused a net K⁺ efflux, because of the salt‐induced membrane depolarization. H₂O₂ levels, regulated upwards by salinity, contributed to ionic homeostasis, because H₂O₂ restrictions by DPI or DMTU caused enhanced K⁺ efflux and decreased Na⁺/H⁺ antiport activity. NaCl induced a net Ca²⁺ influx and a subsequent rise of [Ca²⁺]_cyt, which is involved in H₂O₂‐mediated K⁺/Na⁺ homeostasis in salinized P. euphratica cells. When callus cells were pretreated with inhibitors of the Na⁺/H⁺ antiport system, the NaCl‐induced elevation of H₂O₂ and [Ca²⁺]_cyt was correspondingly restricted, leading to a greater K⁺ efflux and a more pronounced reduction in Na⁺/H⁺ antiport activity. Results suggest that the PM H⁺‐coupled transport system mediates H⁺ translocation and triggers the stress signalling of H₂O₂ and Ca²⁺, which results in a K⁺/Na⁺ homeostasis via mediations of K⁺ channels and the Na⁺/H⁺ antiport system in the PM of NaCl‐stressed cells. Accordingly, a salt stress signalling pathway of P. euphratica cells is proposed.     

Acquired tolerance of tomato (Lycopersicon esculentum cv. Micro‐Tom) plants to cadmium‐induced stress

The effects of varying concentrations of cadmium (Cd) on the development of Lycopersicon esculentum cv. Micro‐Tom (MT) plants were investigated after 40 days (vegetative growth) and 95 days (fruit production), corresponding to 20 days and 75 days of exposure to CdCl₂, respectively. Inhibition of growth was clearly observed in the leaves after 20 days and was greater after 75 days of growth in 1 mM CdCl₂, whereas the fruits exhibited reduced growth following the exposure to a concentration as low as 0.1 mM CdCl₂. Cd was shown to accumulate in the roots after 75 days of growth but was mainly translocated to the upper parts of the plants accumulating to high concentrations in the fruits. Lipid peroxidation was more pronounced in the roots even at 0.05 mM CdCl₂ after 75 days, whereas in leaves, there was a major increase after 20 days of exposure to 1 mM CdCl₂, but the fruit only exhibited a slight significant increase in lipid peroxidation in plants subjected to 1 mM CdCl₂ when compared with the control. Oxidative stress was also investigated by the analysis of four key antioxidant enzymes, which exhibited changes in response to the increasing concentrations of Cd tested. Catalase (EC 1.11.1.6) activity was shown to increase after 75 days of Cd treatment, but the major increases were observed at 0.1 and 0.2 mM CdCl₂, whereas guaiacol peroxidase (EC 1.11.1.7) did not vary significantly from the control in leaves and roots apart from specific changes at 0.5 and 1 mM CdCl₂. The other two enzymes tested, glutathione reductase (EC 1.6.4.2) and superoxide dismutase (SOD, EC 1.15.1.1), did not exhibit any significant changes in activity, apart from a slight decrease in SOD activity at concentrations above 0.2 mM CdCl₂. However, the most striking results were obtained when an extra treatment was used in which a set of plants was subjected to a stepwise increase in CdCl₂ from 0.05 to 1 mM, leading to tolerance of the Cd applied even at the final highest concentration of 1 mM. This apparent adaptation to the toxic effect of Cd was confirmed by biomass values being similar to the control, indicating a tolerance to Cd acquired by the MT plants.     

X‐Ray Microscopy of Halide Perovskites: Techniques,Applications, and Prospects

X‐ray microscopy can provide unique chemical, electronic, and structural insights into perovskite materials and devices leveraging bright, tunable synchrotron X‐ray sources. Over the last decade, fundamental understanding of halide perovskites and their impressive performance in optoelectronic devices has been furthered by rigorous research regarding their structural and chemical properties. Herein, studies of perovskites are reviewed that have used X‐ray imaging, spectroscopy, and scattering microscopies that have proven valuable tools toward understanding the role of defects, impurities, and processing on perovskite material properties and device performance. Together these microscopic investigations have augmented the understanding of the internal workings of perovskites and have helped to steer the perovskite community toward promising directions. In many ways, X‐ray microscopy of perovskites is still in its infancy, which leaves many exciting paths unexplored including new ptychographic, multimodal, in situ, and operando experiments. To explore possibilities, pioneering X‐ray microscopy along these lines is briefly highlighted from other semiconductor systems including silicon, CdTe, GaAs, CuIn_xGa_1?xSe₂, and organic photovoltaics. An overview is provided on the progress made in utilizing X‐ray microscopy for perovskites and present opportunities and challenges for future work.     

Molecular spectroscopic studies on the interactions of rhein and emodin with thioglycolic acid‐capped core/shell CdTe/CdS quantum dots and their analytical applications

Water‐soluble thioglycolic acid (TGA)‐capped core/shell CdTe/CdS quantum dots (QDs) were synthesized. The interactions of rhein and emodin with TGA‐CdTe/CdS QDs were evaluated by fluorescence and ultraviolet‐visible absorption spectroscopy. Experimental results showed that the high fluorescence intensity of TGA‐CdTe/CdS QDs could be effectively quenched in the presence of rhein (or emodin) at 570 nm, which may have resulted from an electron transfer process from excited TGA‐CdTe/CdS QDs to rhein (or emodin). The quenching intensity was in proportion to the concentration of both rhein and emodin in a certain range. Under optimized conditions, the linear ranges of TGA‐CdTe/CdS QDs fluorescence intensity versus the concentration of rhein and emodin were 0.09650–60 µg/mL and 0.1175–70 µg/mL with a correlation coefficient of 0.9984 and 0.9965, respectively. The corresponding detection limits (3σ/S) of rhein and emodin were 28.9 and 35.2 ng/mL, respectively. This proposed method was applied to determine rhein and emodin in human urine samples successfully with remarkable advantages such as high sensitivity, short analysis time, low cost and easy operation. Based on this, a simple, rapid and highly sensitive method to determine rhein (or emodin) was proposed. Copyright © 2014 John Wiley & Sons, Ltd.     

Storage Capacity and Cycling Stability in Ge Anodes: Relationship of Anode Structure and Cycling Rate

Operando X‐ray diffraction (XRD) and X‐ray absorption spectroscopy (XAS) studies of Ge anodes are carried out to understand the effect of cycling rate on Ge phase transformation during charge/discharge process and to relate that effect to capacity. It is discovered that the formation of crystalline Li₁₅Ge₄ (c‐Li₁₅Ge₄) during lithiation is suppressed beyond a certain cycling rate. A very stable and reversible high capacity of ≈1800 mAh g^?1 can be attained up to 100 cycles at a slow C‐rate of C/21 when there is complete conversion of Ge anode into c‐Li₁₅Ge₄. When the C‐rate is increased to ≈C/10, the lithiation reaction is more heterogeneous and a relatively high capacity of ≈1000 mAh g^?1 is achieved with poorer electrochemical reversibility. An increase in C‐rate to C/5 and higher reduces the capacity (≈500 mAh g^?1) due to an impeded transformation from amorphous Li_xGe to c‐Li₁₅Ge₄, and yet improves the electrochemical reversibility. A proposed mechanism is presented to explain the C‐rate dependent phase transformations and the relationship of these to capacity fading. The operando XRD and XAS results provide new insights into the relationship between structural changes in Ge and battery capacity, which are important for guiding better design of high‐capacity anodes.     

A refined parameterization of the analytical Cd–Zn–Te bond-order potential

This paper reports an updated parameterization for a CdTe bond order potential. The original potential is a rigorously parameterized analytical bond order potential for ternary the Cd–Zn–Te systems. This potential effectively captures property trends of multiple Cd, Zn, Te, CdZn, CdTe, ZnTe, and Cd_1-xZn_xTe phases including clusters, lattices, defects, and surfaces. It also enables crystalline growth simulations of stoichiometric compounds/alloys from non-stoichiometric vapors. However, the potential over predicts the zinc-blende CdTe lattice constant compared to experimental data. Here, we report a refined analytical Cd–Zn–Te bond order potential parameterization that predicts a better CdTe lattice constant. Characteristics of the second potential are given based on comparisons with both literature potentials and the quantum mechanical calculations.     

Nanoscale Microstructure and Chemistry of Cu2ZnSnS4/CdS Interface in Kesterite Cu2ZnSnS4 Solar Cells

Sulfurization with various atmosphere and postheat treatments has been reported for earth abundant kesterite Cu₂ZnSnS₄ (CZTS) preparation as cost‐effective material for next‐generation solar cells. A full understanding of the nanoscale microstructure and chemistry of CZTS/CdS interface obtained from these different fabrication routes is currently lacking, yet is critical to developing optimal processing routes for high‐performance kesterite solar cells. Here, the first detailed investigation of the interfacial microstructure and chemistry of CdS/Cu₂ZnSnS₄ heterojunctions is presented. For CZTS obtained from sulfurization in a sulfur‐only atmosphere where highly defective surfaces are present, air annealing followed by etching in the initial stage of chemical bath deposition (CBD) process can effectively eliminate interfacial defects and allow the epitaxial growth of CBD‐CdS, improving the minority lifetime, open circuit voltage (V_OC), and fill factor (FF) of the devices, while blocking Cd diffusion and deteriorating short circuit current (J_sc). For CZTS from sulfurization in a combined sulfur and SnS atmosphere where CBD‐CdS can directly epitaxially grow on CZTS and Cd‐diffusion is clearly observed, associated devices show the longest lifetime and the highest efficiency of 8.76%. Epitaxial growth of CdS and Cd diffusion into CZTS are found to be two crucial features minimizing interfacial recombination and achieving high‐efficiency devices. This will not only enhance the understanding of the device structure and physics of kesterite based solar cells, but also provide an effective way for designing other chalcogenide heterojunction solar cells.     

Calcium-cadmium interaction on sugar absorption across the rabbit jejunum

The element Cd is considered to have no biological function and is highly toxic to humans and animals. Toxic effects of this metal upon cell membrane structure and function have been shown. On the other hand, Ca is an essential element in a wide variety of cellular activities. The present study was initiated to research whether the interaction between Ca and Cd could affect D-galactose absorption across the rabbit jejunum in vitro. In media with Ca²⁺, when CdCl₂ was present at 0.5 or 1 mM, Cd was found to significantly reduce the sugar absorption. In Ca²⁺-free media, where CaCl₂, was omitted and replaced isotonically with choline chloride, the sugar transport was not modified by Cd, but when CaCl₂ was replaced isotonically with MgCl₂, the inhibition is observed. Verapamil at 10⁻⁶ M (blocking mainly Ca²⁺ transport) did not modify the inhibitory effect of cadmium on D-galactose transport. When 10⁻⁶ M of A 23187 (Ca²⁺ specific ionophore) was added in media with/without Ca²⁺; CdCl₂ produced no change in D-galactose transport. These results suggest that Ca and Cd could have affinity for the same chemical groups of enterocyte membrane, which would be related with the intestinal absorption of D-galactose.     

Effect of Cl on Cd uptake by Swiss chard in nutrient solutions

Swiss chard (Beta vulgaris L., cv. Fordhook Giant) was grown in nutrient solution with Cl concentrations varying between 0.01 mM and 120 mM. Solution Na concentration and ionic strength were maintained in all treatments by compensating with NaNO₃. All solutions contained Cd (50 nM, spiked with ¹⁰⁹Cd). Three different Cd²⁺ buffering systems were used. In one experiment, Cd²⁺ activity was unbuffered; its activity decreased with increased Cl concentration as a result of the formation of CdCl_n ^2–n species. In the other experiments, Cd²⁺ activity was buffered by the chelator nitrilotriacetate (NTA, 50 M) and ethylene-bis-(oxyethylenenitrilo)-tetraacetate (EGTA, 50 M) at about 10^–9 M and 10^–11 M, respectively. Plant growth was generally unaffected by increasing Cl concentrations in the three experiments. In unbuffered solutions, Cd concentrations in plant tissue decreased significantly (p<0.01) (approximately 2.4-fold) as solution Cl concentration increased from 0.01 mM to 120 mM. However, this decrease was smaller in magnitude than the 4.7-fold decrease in Cd²⁺ activity as calculated by the GEOCHEM-PC program for the same range of Cl concentrations. In solutions where Cd²⁺ activity was buffered by NTA, Cd concentrations in plant tissue increased approximately 1.4-fold with increasing Cl concentration in solution, while the Cd²⁺ activity was calculated to decrease 1.3-fold. In solutions where Cd²⁺ activity was buffered by EGTA, Cd concentrations in the roots increased 1.3-fold with increasing Cl concentration in solution but there was no effect of Cl on shoot Cd concentrations. The data suggest that either CdCl_n ^2–nspecies can be taken up by plant roots or that Cl enhances uptake of Cd²⁺ through enhanced diffusion of the uncomplexed metal to uptake sites.Abbreviations DAS days after sowing - EGTA ethylene-bis-(oxyethylenenitrilo)-tetraacetate - HBED N,N-bis(2-hydroxybenzyl)-ethylenediamine-N,N-diacetate - NTA nitrilotriacetate     

Highly luminescent CdTe/CdS/ZnO core/shell/shell quantum dots fabricated using an aqueous strategy

To create core/shell/shell quantum dots (QDs) with high stability against a harmful chemical environment, CdTe/CdS QDs were coated with a ZnO shell in an aqueous solution. An interfaced CdS layer sandwiched between a CdTe core and ZnO shell provided relaxation of the strain at the core/shell interface since lattice parameters of CdS are intermediate between those of CdTe and ZnO. The photoluminescence (PL) peak wavelength of the core/shell/shell QDs was shifted from 569 to 615 nm by adjusting the size of CdTe cores and thickness of CdS and ZnO shells, along with the highest PL quantum yield of the core/shell/shell QDs reaching 80%, which implies promising applications in the field of biomedical labeling. Due to the decrease of surface defects, it was observed that PL lifetimes significantly increased at room temperature as follows: 29.6 34.2, and 47.5 ns for CdTe (537 nm), CdTe/CdS (555 nm) and CdTe/CdS/ZnO (581 nm) QDs, respectively. Copyright © 2012 John Wiley & Sons, Ltd.     

Influence of CdCl2 and CdSO4 supplementation on Cd distribution and ligand environment in leaves of the Cd hyperaccumulator Noccaea (Thlaspi) praecox

Background and aims

The aim was to investigate whether different Cd salts in the nutrient solution of the Cd/Zn hyperaccumulator Noccaea (Thlaspi) praecox alter leaf Cd distribution and Cd ligand environment, and plant fitness.

Methods

Plants were grown for 8 weeks with 100/300 μM CdCl₂ or CdSO₄. Leaf biomass, and total chlorophyll, anthocyanin, Cd, Cl, S and P concentrations were monitored. Cd localisation and ligand environment in leaves were analysed using quantitative synchrotron-based micro-X-ray fluorescence imaging, and Cd K-edge X-ray absorption fine structure and Cd L₃-edge micro-X-ray absorption near-edge structure measurements.

Results

Cd uptake and plant fitness were comparable for CdCl₂ and CdSO₄ treatments, and depended on applied Cd concentration. In all treatments, Cd preferentially accumulated with high concentrations of Cl in vacuoles of large vacuolarised epidermal cells, bound mainly to oxygen-based (O)-ligands. In the mesophyll of CdCl₂? treated plants, Cd was preferentially sequestered in vacuoles, while for CdSO₄, Cd accumulated preferentially in the apoplast. In the symplast, O-ligands increased with increasing Cd concentrations; in the apoplast, sulphur-based (S)-ligands prevailed.

Conclusions

Cd partitioning between leaf mesophyll apoplast and symplast and the Cd ligand environment in N. praecox depend on the Cd salt type and concentration added to the nutrient solution.     

Comparison of molecular interactions of Ag2Te and CdTe quantum dots with human serum albumin by spectroscopic approaches

Ag₂Te quantum dots (QDs) have attracted great attention in biological applications due to their superior photoluminescence qualities and good biocompatibility, but their potential biotoxicity at a molecular biology level has been rarely discussed. In order to better understand the basic behavior of Ag₂Te QDs in biological systems and compare their biotoxicity to cadmium‐containing QDs, a series of spectroscopic measurements was applied to reveal the molecular interactions of Ag₂Te QDs and CdTe QDs with human serum albumin (HSA). Ag₂Te QDs and CdTe QDs statically quenched the intrinsic fluorescence of HSA by electrostatic interactions, but Ag₂Te QDs exhibited weaker quenching ability and weaker binding ability compared with CdTe QDs. Electrostatic interactions were the main binding forces and Sudlow's site I was the primary binding site during these binding interactions. Furthermore, micro‐environmental and conformational variations of HSA were induced by their binding interactions with two QDs. Ag₂Te QDs caused less secondary structural and conformational change in HSA, illustrating the lower potential biotoxicity risk of Ag₂Te QDs. Our results systematically indicated the molecular binding mechanism of Ag₂Te QDs with HSA, which provided important information for possible toxicity risk of these cadmium‐free QDs to human health.     

Increase in the Figure of Merit by Cd‐Substitution in Sn1–xPbxTe and Effect of Pb/Sn Ratio on Thermoelectric Properties

The effects of Cd‐doping on the thermoelectric properties of Sn_1–xPb_xTe are investigated and compared to the properties of the corresponding Sn_1–xPb_xTe solid solutions. The addition of Cd results in a reduction in the carrier concentration and changes in the physical properties, as well as in the conduction type of Sn_1–xPb_xTe. A significant increase in the power factor accompanied by a reduction in the thermal conductivity result in a higher figure of merit (ZT) for (Sn_1–xPb_x)_0.97Cd_0.03Te than that of undoped Sn_1–xPb_xTe. The maximum ZT (～0.7) values are observed for p‐type material with x = 0.36 at 560 K. Much higher values (ZT ～ 1.2 at 560 K for x = 0.73) are obtained on n‐type samples.     

Heteromerous Bistricyclic Aromatic Enes: Dynamic Stereochemistry of Xanthylidene‐Anthrones

The heteromerous bistricyclic aromatic ene (BAE) 2,2'‐dimethyl‐10‐(9H‐xanthylidene)‐9(10H)‐anthrone (DMXA) was synthesized by a condensation of 10,10‐dichloro‐2‐methylxanthene with 2‐methylanthrone. X‐ray crystallography of (E)‐DMXA and xanthylidene‐anthrone (XA) indicated that the molecules adopt anti‐folded conformations with folding dihedral angles of 44°/44° and 39°/41°, respectively . The crystal structure of anti‐folded (E)‐DMXA does not indicate any xanthenylium–anthracenolate push–pull effect. E,Z‐diastereomerization of DMXA was studied by ¹H‐NMR coalescence‐temperature measurements at different magnetic field strengths and by kinetic equilibration experiments . Free energy of activation for this process was 81.5 (±1.3) kJ/mol. B3LYP/6‐311+G(d,p) calculations showed that anti‐folded conformers of XA, (E)‐DMXA, bianthrone (AA), and dixanthylene (XX) were global minima. The twisted conformers of XA, AA, and XX were local minima (ΔG₂₉₈ = 16, 18, and 24 kJ/mol) with a substantial dipolar xanthenylium–anthracenolate dipolar contribution for XA. Chirality 27:919–928, 2015. © 2015 Wiley Periodicals, Inc.