Tetraacylgermanes as highly efficient photoinitiators for visible light cured dimethacrylate resins and dental composites

Tetrabenzoylgermane 1 and various substituted tetrabenzoylgermanes 2 – 7 were investigated as visible light (VL) photoinitiators (PIs) for dental dimethacrylate resins and dimethacrylate‐based composites. The tetrabenzoylgermanes 1 – 7 show a very strong VL absorption between 400 and 450 nm. Substituents on the benzoyl chromophore strongly influence their properties such as melting point, solubility, absorption behavior, or PI reactivity. A good photobleaching behavior and a very high reactivity as VL PI was found in photo‐differential scanning calorimeter experiments for selected tetrabenzoylgermanes. Composite pastes containing only ～0.1 wt % of Ge‐PI exhibited a sufficient photocuring due to the high PI‐reactivity of the tetraacylgermanes. Among the investigated germane PIs, tetrakis(2‐methylbenzoyl)germane 2 shows the best performance as VL PI for restorative composites and enables the composites to be photocured using an LED with an emission maximum of 500 nm. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46115.     

Low temperature ferroelectric behavior in morphotropic Pb (Zr1−xTix)O3

We provide an insight into the switching of near‐morphotropic composition of PZT, using molecular dynamics simulations and electrical measurements. The simulations and experiments exhibit qualitatively similar hysteretic behavior of the polarization for different temperatures showing widening of the P‐E loops and the decrease in the coercive field toward high temperatures. Remarkably, we have shown that polarization switching at low temperatures occurs via polarization rotation, that is a fundamentally different mechanism from high‐temperature switching, which is nucleation driven.     

Porosity effect on microstructure,mechanical, and fluid dynamic properties of Ti2AlC by direct foaming and gel‐casting

In this study, Ti₂AlC foams were fabricated by direct foaming and gel‐casting using agarose as gelling agent. Slurry viscosity, determined by the agarose content (at a fixed solids loading), as well as surfactant concentration and foaming time were the key parameters employed for controlling the foaming yield, and hence the foam porosity after sintering process. Fabricated foams having total porosity in the 62.5‐84.4 vol% range were systematically characterized to determine their pore size and morphology. The effect of the foam porosity on the room‐temperature compression strength and elastic modulus was also determined. Depending on the amount of porosity, the compression strength and Young's modulus were found to be in the range of 9‐91 MPa and 7‐52 GPa, respectively. Permeability to air flow at temperatures up to 700°C was investigated. Darcian (k₁) and non‐Darcian (k₂) permeability coefficients displayed values in the range 0.30‐93.44 × 10^?11 m² and 0.39‐345.54 × 10^?7 m, respectively. The amount of porosity is therefore a very useful microstructural parameter for tuning the mechanical and fluid dynamic properties of Ti₂AlC foams.     

Boundary Limit Theory for Functional Local to Unity Regression

This article studies functional local unit root models (FLURs) in which the autoregressive coefficient may vary with time in the vicinity of unity. We extend conventional local to unity (LUR) models by allowing the localizing coefficient to be a function which characterizes departures from unity that may occur within the sample in both stationary and explosive directions. Such models enhance the flexibility of the LUR framework by including break point, trending, and multidirectional departures from unit autoregressive coefficients. We study the behavior of this model as the localizing function diverges, thereby determining the impact on the time series and on inference from the time series as the limits of the domain of definition of the autoregressive coefficient are approached. This boundary limit theory enables us to characterize the asymptotic form of power functions for associated unit root tests against functional alternatives. Both sequential and simultaneous limits (as the sample size and localizing coefficient diverge) are developed. We find that asymptotics for the process, the autoregressive estimate, and its t‐statistic have boundary limit behavior that differs from standard limit theory in both explosive and stationary cases. Some novel features of the boundary limit theory are the presence of a segmented limit process for the time series in the stationary direction and a degenerate process in the explosive direction. These features have material implications for autoregressive estimation and inference which are examined in the article.     

毛细管电泳分析中的样品预富集新技术

本文综述了pH调制样品堆积、浊点萃取、固相萃取三种用于毛细管电泳分析 中的样品预富集新技术的原理、特点。     

Novel concept of polymers preparation with high photoluminescent quantum yield

A series carbazolyl-containing polymers were synthesized by anionic polymerization of various oxiranes and methyl methacrylate. The polymerization was carried out using as initiator carbazylpotassium activated 18-crown-6 in THF. The polymers were prepared and found using size exclusion chromatography to have a degree of polymerization (DP_n) about 20 relatively and low dispersity in the range of 1.07–1.66. Their optical properties were investigated by means of UV–vis and photoluminescence spectroscopies. The obtained polymers emitted light with maximum emission about 370 nm and high quantum yield ranging up to 79 %. Thus, it was confirmed that the utilization of fluorophore initiator for polymerization of non photoresponsive monomers is quite efficient for the preparation of photoluminescent polymers.     

Monomolecular and Bimolecular Recombination of Electron–Hole Pairs at the Interface of a Bilayer Organic Solar Cell

While it has been argued that field‐dependent geminate pair recombination (GR) is important, this process is often disregarded when analyzing the recombination kinetics in bulk heterojunction organic solar cells (OSCs). To differentiate between the contributions of GR and nongeminate recombination (NGR) the authors study bilayer OSCs using either a PCDTBT‐type polymer layer with a thickness from 14 to 66 nm or a 60 nm thick p‐DTS(FBTTh₂)₂ layer as donor material and C₆₀ as acceptor. The authors measure JV‐characteristics as a function of intensity and charge‐extraction‐by‐linearly‐increasing‐voltage‐type hole mobilities. The experiments have been complemented by Monte Carlo simulations. The authors find that fill factor (FF) decreases with increasing donor layer thickness (L_p) even at the lowest light intensities where geminate recombination dominates. The authors interpret this in terms of thickness dependent back diffusion of holes toward their siblings at the donor–acceptor interface that are already beyond the Langevin capture sphere rather than to charge accumulation at the donor–acceptor interface. This effect is absent in the p‐DTS(FBTTh₂)₂ diode in which the hole mobility is by two orders of magnitude higher. At higher light intensities, NGR occurs as evidenced by the evolution of s‐shape of the JV‐curves and the concomitant additional decrease of the FF with increasing layer thickness.     

Activation of the glmS Ribozyme Confers Bacterial Growth Inhibition

The ever‐growing number of pathogenic bacteria resistant to treatment with antibiotics call for the development of novel compounds with as‐yet unexplored modes of action. Here, we demonstrate the in vivo antibacterial activity of carba‐α‐d ‐glucosamine (CGlcN). In this mode of action study, we provide evidence that CGlcN‐mediated growth inhibition is due to glmS ribozyme activation, and we demonstrate that CGlcN hijacks an endogenous activation pathway, hence utilizing a prodrug mechanism. This is the first report describing antibacterial activity mediated by activating the self‐cleaving properties of a ribozyme. Our results open the path towards a compound class with an entirely novel and distinct molecular mechanism.