β-Selective One-Pot Fluorophosphorylation of d,d-Heptosylglycals Mediated by Selectfluor

This study describes the development of a novel procedure of glycal fluorophosphorylation applied to the synthesis of a fluorinated analogue of an important bacterial metabolite. This procedure was applied to several heptose-derived glycals, and the stereochemical outcome of the reaction was analyzed. Under optimized conditions, the reaction is β-gluco selective, but a significant amount of the α-gluco diastereomer is also generated.     

Microwave-Induced Chemotoxicity of Polydopamine-Coated Magnetic Nanocubes

Polydopamine-coated FeCo nanocubes (PDFCs) were successfully synthesized and tested under microwave irradiation of 2.45 GHz frequency and 0.86 W/cm² power. These particles were found to be non-toxic in the absence of irradiation, but gained significant toxicity upon irradiation. Interestingly, no increase in relative heating rate was observed when the PDFCs were irradiated in solution, eliminating nanoparticle (NP)-induced thermal ablation as the source of toxicity. Based on these studies, we propose that microwave-induced redox processes generate the observed toxicity.     

Energy Transfer to a Stable Donor Suppresses Degradation in Organic Solar Cells

Despite many advances toward improving the stability of organic photovoltaic devices, environmental degradation under ambient conditions remains a challenging obstacle for future application. Particularly conventional systems employing fullerene derivatives are prone to oxidize under illumination, limiting their applicability. Here, the environmental stability of the small molecule donor DRCN5T together with the fullerene acceptor PC₇₀BM is reported. It is found that this system exhibits exceptional device stability, mainly due to almost constant short‐circuit current. By employing ultrafast femtosecond transient absorption spectroscopy, this remarkable stability is attributed to two separate mechanisms: 1) DRCN5T exhibits high intrinsic resistance toward external factors, showing no signs of deterioration. 2) The highly sensitive PC₇₀BM is stabilized against degradation by the presence of DRCN5T through ultrafast, long‐range energy transfer to the donor, rapidly quenching the fullerene excited states which are otherwise precursors for chemical oxidation. It is proposed that this photoprotective mechanism be utilized to improve the device stability of other systems, including nonfullerene acceptors and ternary blends.     

Effect of window layer composition in Cd1−xZnxS/CdTe solar cells

To improve CdS/CdTe cell/module efficiencies, CdS window layer thinning is commonly applied despite the risk of increased pin‐hole defects and shunting. An alternative approach is to widen the band gap of the window layer (2.42 eV for CdS) via alloying, for example, by forming compositions of Cd_1−xZn_xS. In this study, the performance of Cd_1−xZn_xS/CdTe thin‐film solar cells has been studied as a function of x (from x = 0 to 0.9), widening the window layer band gap up to and over 3.4 eV. Optimum Cd_1−xZn_xS compositions were clearly identified to be around x = 0.7, and limitations to the achievable photocurrent and conversion efficiencies have been addressed. Copyright © 2012 John Wiley & Sons, Ltd.     

Large increases in1H metaboliteT 2's after cerebral hypoxia-ischemia correlate with ATP depletion

In vivo proton (¹H) magnetic resonance spectroscopy (MRS) can measure cerebral metabolite concentrations and nuclear relaxation times. Function of the sodium (Na⁺)/potassium (K⁺) pump in cell membranes depends on adequate adenosine triphosphate (ATP) levels: intracellular Na⁺ is normally extruded in exchange for extracellular K⁺. Low ATP will cause pump dysfunction and loss of K⁺ accompanied by influx of Na⁺and water. Raised intracellular water may increase molecular mobility and this might be detectable as increased apparent transverse relaxation times (T ₂'s).¹H-MRS of the brains of newborn piglets during acute hypoxia-ischemia revealed enigmatic increases in the peak area of creatine + phosphocreatine (Cr) relative to those of choline-containing compounds (Cho) andN-acetylaspartate (NAA). Interleaved¹H and phosphorus (³¹P) MRS showed that theT ₂'s of both Cr and lactate (Lac) increased during acute hypoxia-ischemia and these changes correlated with reductions in nucleotide triphosphate (NTP; largely ATP). Within 50 h of metabolic recovery from the primary insult, as delayed energy failure developed, theT ₂'s of Cho, Cr, NAA, and Lac increased greatly. TheseT ₂ changes also correlated with NTP depletion. These observations demonstrate important relationships betweenT ₂'s and function of the ATP-dependent Na⁺/K⁺ pump.     

DC pulsed plasma deposition of nanocomposite coatings for improved tribology of gray cast iron stamping dies

Automotive stamping dies are very large in size with sizes ranging up to 2 m × 2 m × 1 m. The primary material used in the manufacturing of these dies is gray cast iron that is relatively cheap with good castability, machinability and reparability. Due to its lack of adequate hardness, die wear is a major problem at highly loaded die features such as corners, bead-radii, punch-radii etc. The greater is this wear, the greater is the die-related down times and production losses. This problem of die wear has become even more significant in recent times due to the introduction of Advanced High Strength Steels (AHSS) and Ultra High Strength Steels (UHSS) in automotive stamping. Stamping of these materials is accompanied by higher contact pressures on the die surface, higher abrasion and higher surface temperature from frictional heat.This paper presents a novel DC pulsed plasma based approach to the deposition of triplex coating on cast iron substrates that can withstand high normal pressures, shears, sliding and abrasion experienced during stamping. This triplex coating consists of silicon enhanced nanocomposite a-C:H film supported by plasma nitrocarburized duplex case. This nanostructured-composite film is shown to have high toughness and extremely low coefficients of friction. A unique feature of this plasma processing is the industrial size of chambers used in the coating development. This paper also includes results of film characterization and its performance evaluation in simulated wear tests that generate stresses similar to actual stamping dies. By carefully designing the plasma processing treatment, a good hardness gradient and elastic modulus gradient is achieved that provide an improvement in life of about 5 times that of the currently used hard chrome plating.