Nucleation of Hematite: A Nonclassical Mechanism

Hematite (α-Fe₂O₃) is thermodynamically stable under ambient conditions, of vast geological importance, and widely used in applications, for example, as corrosion protection and as a pigment. It forms at elevated temperatures, whereas room-temperature reactions typically yield metastable akaganéite or ferrihydrite. The mechanistic key changes underlying this observation were explored in the present study. The entropic contribution to the prenucleation hydrolysis reaction categorically implies the presence of prenucleation clusters (PNCs) as fundamental precursors. The formation of hematite is then due to a change in the reaction mechanism above approximately 50 °C, whereby the reaction limitation towards oxolation in phase-separated clusters is overcome. A model that rationalizes the occurrence of hematite, akaganéite, and ferrihydrite based on the chemistry of olation PNCs is proposed. Supersaturation and the temperature dependence of olation and oxolation rates from monomeric precursors are irrelevant in this nonclassical mechanism.     

High‐Energy Long‐Lived Mixed Frenkel–Charge‐Transfer Excitons: From Double Stranded (AT)n to Natural DNA

The electronic excited states populated upon absorption of UV photons by DNA are extensively studied in relation to the UV‐induced damage to the genetic code. Here, we report a new unexpected relaxation pathway in adenine–thymine double‐stranded structures (AT)_n. Fluorescence measurements on (AT)_n hairpins (six and ten base pairs) and duplexes (20 and 2000 base pairs) reveal the existence of an emission band peaking at approximately 320 nm and decaying on the nanosecond time scale. Time‐dependent (TD)‐DFT calculations, performed for two base pairs and exploring various relaxation pathways, allow the assignment of this emission band to excited states resulting from mixing between Frenkel excitons and adenine‐to‐thymine charge‐transfer states. Emission from such high‐energy long‐lived mixed (HELM) states is in agreement with their fluorescence anisotropy (0.03), which is lower than that expected for π–π* states (≥0.1). An increase in the size of the system quenches π–π* fluorescence while enhancing HELM fluorescence. The latter process varies linearly with the hypochromism of the absorption spectra, both depending on the coupling between π–π* and charge‐transfer states. Subsequently, we identify the common features between the HELM states of (AT)_n structures with those reported previously for alternating (GC)_n: high emission energy, low fluorescence anisotropy, nanosecond lifetimes, and sensitivity to conformational disorder. These features are also detected for calf thymus DNA in which HELM states could evolve toward reactive π–π* states, giving rise to delayed fluorescence.     

Carbon fibers prepared from tailored reversible‐addition‐fragmentation transfer copolymerization‐derived poly(acrylonitrile)‐co‐poly(methylmethacrylate)

Reversible‐addition fragmentation‐transfer (RAFT) polymerization of acrylonitrile (AN) was performed with 2‐(2‐cyano‐2‐propyl‐dodecyl)trithiocarbonate as RAFT agent and azobis(isobutyronitrile) as initiator. Linear polyacrylonitrile (M_n = 133,000 g/mol, PDI = 1.34) was prepared within 7 h in 86% isolated yield. High‐yield copolymerization with methyl methacrylate (MMA) was performed and copolymerization parameters were determined according to Kelen and Tüdös at 90 °C in ethylene carbonate yielding r_AN = 0.2 and r_MMA = 0.42. The molecular weights, polydispersity indices (PDIs), and MMA content of the copolymer were adjusted in a way that precursor fibers could be prepared via wet spinning. These precursor fibers had round cross‐sections and a dense morphology, showing tenacities of 40–50 cN/tex and elastic moduli of 900–1000 cN/tex at a fineness of 1 dtex and an elongation of 13–17%. Precursor fibers were oxidatively stabilized and then carbonized at different temperatures. A maximum tensile strength of 2.5 GPa was reached at 1350 °C. Thermal analysis, infrared and Raman spectroscopy, wide‐angle X‐ray scattering, scanning electron microscopy, and tensile testing were used to characterize the resulting carbon fibers. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1322–1333     

Environmentally friendly synthesis of noble metal nanoparticles assisted by biodegradable dextran‐graft‐lactone copolymers

A simple “green synthesis” of noble metal nanoparticles by direct reaction between Dextran‐graft‐lactone copolymers and metal salts without the need to separately add reducing and stabilizing agents was carried out. The effects of the composition, molecular weights of copolymers and solvents on the characteristics of the nanoparticles were considered. The amphiphilic character of the copolymers seems to be an important factor in the results of the synthesis. According to the results, general correlations between experimental parameters of synthesis and characteristics of the obtained nanoparticles were established. Techniques such as, transmission electron microscopy, scanning electron microscopy, UV–visible spectroscopy, Zeta Potential, dynamic light scattering and Fourier transform Infrared Spectroscopy, were used for the characterization of the products. The results indicate the possibility of control of the characteristics of the nanostructured material. Copyright © 2014 John Wiley & Sons, Ltd.     

An Organoruthenium Anticancer Agent Shows Unexpected Target Selectivity For Plectin

Organometallic metal(arene) anticancer agents require ligand exchange for their anticancer activity and this is generally believed to confer low selectivity for potential cellular targets. However, using an integrated proteomics-based target-response profiling approach as a potent hypothesis-generating procedure, we found an unexpected target selectivity of a ruthenium(arene) pyridinecarbothioamide (plecstatin) for plectin, a scaffold protein and cytolinker, which was validated in a plectin knock-out model in vitro. Plectin targeting shows potential as a strategy to inhibit tumor invasiveness as shown in cultured tumor spheroids while oral administration of plecstatin-1 to mice reduces tumor growth more efficiently in the invasive B16 melanoma than in the CT26 colon tumor model.     

Beijing Lectures on the Grade Restriction Rule

The authors describe the relationships between categories of B-branes in different phases of the non-Abelian gauged linear sigma model.The relationship is described explicitly for the model proposed by Hori and Tong with non-Abelian gauge group that connects two non-birational Calabi-Yau varieties studied by Rφdland.A grade restriction rule for this model is derived using the hemisphere partition function and it is used to map B-type D-branes between the two Calabi-Yau varieties.     

Total Synthesis and Bioactivity Mapping of Geodiamolide H

The first total synthesis of the actin-stabilizing marine natural product geodiamolide H was achieved. Solid-phase based peptide assembly paired with scalable stereoselective syntheses of polyketide building blocks and an optimized esterification set the stage for investigating the key ring-closing metathesis. Geodiamolide H and synthetic analogues were characterized for their toxicity and for antiproliferative effects in cellulo, by characterising actin polymerization induction in vitro, and by docking on the F-actin target and property computation in silico, for a better understanding of structure-activity relationships (SAR). A non-natural analogue of geodiamolide H was discovered to be most potent in the series, suggesting significant potential for tool compound design.     

Actual Isothermal Effects of Water‐Filtered Infrared A‐Irradiation

In this study, the athermal effects of water‐filtered infrared A (wIRA)‐irradiation (780–1400 nm) on human dermal fibroblasts were investigated. For this purpose, cells were exposed to wIRA‐irradiation (178 mW cm^?2 for 1 h), while a sophisticated experimental setup prevented warming of the samples exceeding 0.1°C. The investigated parameters were the formation of reactive oxygen species (ROS), mitochondrial membrane potential and superoxide release, protein oxidation, proliferation rate, as well as intracellular Ca²⁺‐release in single cells, most of them quantified via fluorescence microscopy and fluorimetric techniques. The existence of actual athermal wIRA‐effects is still intensively discussed, since their detection requires a careful experimental setup and both efficient and powerful temperature regulation of the exposed samples. Here, we can definitively show that some of the supposed athermal wIRA‐effects may be rather artifacts, since wIRA did not reveal any impact on the above mentioned parameters—as long as the temperature of the exposed cells was carefully maintained. Though, we were able to identify an athermal DNA‐protective wIRA‐effect, since the induced DNA damage (quantified via 8‐Oxo‐G‐formation) was significantly decreased after a subsequent UVB‐exposure. These results suggest that many of the supposed athermal wIRA‐effects can be induced by pure warming of the samples, independent from any wIRA‐irradiation.