N‐Vinylcarbazole as Versatile Photoinaddimer of Photopolymerization under Household UV LED Bulb (392 nm)

N‐vinylcarbazole (NVK) can act simultaneously as a photoin itiator, an addi tive, and a mono­mer (photoinaddimer) of photopolymerization upon exposure to the household ultraviolet (UV) light‐emitting diode (LED) bulb (emission wavelength centered at 392 nm). Even though the light absorption spectrum of NVK exhibits weak overlapping with the emission spectrum of the UV LED, the active species (i.e., radicals and cations) can be generated from the interaction between NVK and diphenyliodonium hexafluorophosphate (Iod) under irradiation of this LED device, which is investigated by steady state photolysis and electron spin resonance spin‐trapping methods. Interestingly, the generated radicals and cations from the NVK/Iod system demonstrate high efficiency to initiate the free radical photopolymerization of (meth)acrylates and the cationic photopolymerization of epoxide and divinyl ether under the UV LED irradiation, and the one‐step simultaneous catonic/radical photopolymerization of expoxide/acrylate blend can lead to the formation of tack free polyacrylate/polyether‐based interpenetrated polymer network film within 10 min even when the polymerization process is exposed to the atmosphere highlighting the high efficiency of the system to reduce the oxygen inhibition effect. More interestingly, NVK/Iod system can also initiate the photopolymerization of NVK under the UV LED irradiation to produce polyvinylcarbazole, and NVK acts as both a photoinitiator and a monomer in the system.

     

SERS microRaman spectral probing of adsorbate‐containing,liquid‐overlayed nanosponge Ag aggregates assembled from fractal aggregates

Adsorbate‐containing, nanosponge Ag aggregates overlayed by a thin (~1.5 mm) liquid layer are reported as a new type of sample for Surface‐enhanced Raman scattering (SERS) microRaman spectral measurements and adsorbate (analyte) detection. Macroscopic Ag aggregates (of about 1.5 × 1.0 × 0.025 mm size) with the nanosponge internal morphology (revealed by Scanning electron microscopy (SEM)) were prepared by 3D assembling of fused fractal aggregates (D = 1.84 ± 0.04) formed in Ag nanoparticle hydrosol/HCl/adsorbate systems with 2,2’‐bipyridine (bpy) and/or a cationic free‐base tetrakis(2‐methyl‐4‐pyridiniumyl) porphine (H₂TMPyP) as the testing adsorbates. For SERS microRaman measurements, the macroscopic aggregate was overlayed by a thin (~1.5 mm) layer of the residual liquid. Preparation procedure, nanoscale imaging, and SERS spectral probing including the determination of the detection limits of the adsorbates revealed the following advantages of the adsorbate‐containing, liquid‐overlayed 3D nanosponge aggregate as a sample for SERS microRaman spectral measurements: (1) localization of adsorbate (analyte) into hot spots and, simultaneously, prevention of the analyte decomposition during the spectral measurement (carried out without an immersion objective), (2) fast and simple sample preparation, and (3) minimization of sample volume and an efficient concentration of hot spots into the focus of the laser beam. The advantages of the nanosponge Ag aggregates are further demonstrated by the 40 fmol limit of detection of bpy as Ag(0)‐bpy surface complex, as well as by preservation of the native structure of the cationic free‐base porphyrin H₂TMPyP. Copyright © 2015 John Wiley & Sons, Ltd.     

The Reaction of β-Aminoenones with Cyanamide. A High Efficient Synthesis of 2-Aminopyrimidines

β-aminoenones react with cyanamide, molar ratio 1:2, to yield 2-aminopyrimidines in nearly quantitative yields.     

Size and branching effects on the fluorescence of benzylic dendrimers possessing one apigenin fluorophore at the core

Different generations of dendrimers incorporating one fluorescent core of apigenin and three Fréchet benzylic dendrons have been prepared. The chief geometric features of these dendrimers have been obtained by Molecular Dynamics simulations. These computational data suggest that the asphericities of dendrimers belonging to the third and fourth generations are considerably larger than those associated with lower radii of gyration. Fluorescence spectra of high generation dendrimers evolve along time and quantum yields show an appreciable lowering for the fourth generation dendrimer. All these data suggest aggregation phenomena and lower quantum yields for nonspheric dendrimers in solution.     

Simulation of short crack propagation under hydrogen influence using a hybrid boundary element technique for anisotropic elastic solids

A two-dimensional model for stage I short crack propagation on multiple slip planes under the influence of hydrogen is presented. It considers elastic-plastic material behaviour by allowing sliding on the active slip planes in the corresponding slip directions. A crack propagation law based on the crack tip sliding displacement is used to simulate crack growth. The activation of slip bands and the sliding on these active slip bands will be influenced by the local hydrogen concentration. The model is solved numerically using the boundary element method. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

A Two-Armed Probe for In-Cell DEER Measurements on Proteins**

The application of double electron-electron resonance (DEER) with site-directed spin labeling (SDSL) to measure distances in proteins and protein complexes in living cells puts rigorous restraints on the spin-label. The linkage and paramagnetic centers need to resist the reducing conditions of the cell. Rigid attachment of the probe to the protein improves precision of the measured distances. Here, three two-armed Gd^III complexes, Gd^III-CLaNP13a/b/c were synthesized. Rather than the disulfide linkage of most other CLaNP molecules, a thioether linkage was used to avoid reductive dissociation of the linker. The doubly Gd^III labeled N55C/V57C/K147C/T151C variants of T4Lysozyme were measured by 95 GHz DEER. The constructs were measured in vitro, in cell lysate and in Dictyostelium discoideum cells. Measured distances were 4.5 nm, consistent with results from paramagnetic NMR. A narrow distance distribution and typical modulation depth, also in cell, indicate complete and durable labeling and probe rigidity due to the dual attachment sites.     

The Glucosamine-derivative NAPA Suppresses MAPK Activation and Restores Collagen Deposition in Human Diploid Fibroblasts Challenged with Environmental Levels of UVB

The ultraviolet (UV) component of solar radiation is the driving force of life on earth, but it can cause photoaging and skin cancer. In this study, we investigated the effects of the glucosamine-derivative 2-(N-Acetyl)-L-phenylalanylamido-2-deoxy-β-D-glucose (NAPA) on human primary fibroblasts (FBs) stimulated in vitro with environmental levels of UVB radiation. FBs were irradiated with 0.04 J cm⁻² UVB dose, which resulted a mild dosage as shown by the cell viability and ROS production measurement. This environmental UVB dose induced activation of MAP kinase ERK 1/2, the stimulation of c-fos and at lower extent of c-jun, and in turn AP-1-dependent up-regulation of pro-inflammatory factors IL-6 and IL-8 and suppression of collagen type I expression. On the contrary, 0.04 J cm⁻² UVB dose was not able to stimulate metalloprotease production. NAPA treatment was able to suppress the up-regulation of IL-6 and IL-8 via the inhibition of MAP kinase ERK phosphorylation and the following AP-1 activation, and was able to attenuate the collagen type I down-regulation induced by the UVBs. Taken together, our results show that NAPA, considering its dual action on suppression of inflammation and stimulation of collagen type I production, represents an interesting candidate as a new photoprotective and photorepairing agents.     

Double Bonds? Studies on the Barrier to Rotation about the Cumulenic C=C Bonds of Tetraaryl[n]cumulenes (n=3, 5, 7, 9)

Bonding is a fundamental aspect of organic chemistry, yet the magnitude of C=C bonding in [n]cumulenes as a function of increasing chain length has yet to be experimentally verified for derivatives longer than n=5. The synthesis of a series of apolar and unsymmetrically substituted tetraaryl[n]cumulenes (n=3, 5, 7, 9) was developed and rotational barriers for Z/E isomerization were measured using dynamic VTNMR spectroscopy. Both experiment and theory confirm a dramatic reduction in the rotational barrier (through estimation of ΔG^≠_rot for the isomerization) across the series, from >24 to 19 to 15 to 11 kcal^?1 in [n]cumulenes with n=3, 5, 7, 9, respectively. The reduction in cumulenic bonding in longer cumulenes thus affords bond rotational barriers that are more characteristic of a sterically hindered single bond than that of a double bond.     

Determination of organotin compounds (OTC) at low levels in seawater by solid-phase extraction (SPE) and gas chromatography-pulsed flame photometric detection (GC-PFPD)

In this work, a simple, sensitive and affordable analytical method for the simultaneous determination of nine organotin compounds (butyltins, phenyltins and methyltins) in seawater using solid-phase extraction (SPE) and gas chromatography-pulsed flame photometric detection was developed and validated. The performance of three different SPE cartridges (Envi C₁₈, Oasis HLB and Oasis MCX) and three elution solvents of different polarity (hexane, methanol and acetonitrile) was evaluated. The extraction parameters, such as solvent volume, presence of complexing and ion-pairing reagents, sample volume and pH and breakthrough volume, were also investigated. Tributyltin, as the organotin compound of special interest, was efficiently extracted using any of the cartridges and solvents tested. However, the simultaneous extraction of all nine organotin compounds was the most efficient using reversed-phase Envi C₁₈ cartridge and 0.1% (w/v) tropolone in methanol as eluent. The optimised method resulted in good recovery, precision and linearity for all compounds, particularly for tri- and disubstituted species. Method detection limits ranged from 0.22 to 1.27 ng(Sn) L^?1 for butyltins, 0.37 to 4.91 ng(Sn) L^?1 for phenyltins and 0.45 to 1.16 ng(Sn) L^?1 for methyltins. The accuracy of butyltins determination was further verified by the comparison with purchased derivatised standards. The developed method was successfully applied to the environmental samples.