Using Time‐Resolved Electrochemical Patterning to Gain Fundamental Insight into Aryl‐Radical Surface Modification

Scanning electrochemical microscopy is used to carry out local free‐radical grafting at a gold surface through mild oxidation of an aryl hydrazine. The process can be deliberately controlled by creation of a local pH gradient at the tip. Comparison of the experimental results with simulations shows that the radial expansion of the pH profile in which successful grafting can be accomplished increases with increasing generation time of OH^? and with decreasing initial concentration of the grafting precursor. Furthermore, the radial expansion is faster than the nucleation of the grafting process.     

Chemical degradation of crosslinked ethylene-propylene-diene rubber in an acidic environment. Part II. Effect of peroxide crosslinking in the presence of a coagent

An investigation on the time-dependent chemical degradation of ethylene-propylene diene rubber containing 5-ethylidene-2-norbornene as diene cured by peroxide crosslinking in the presence of a coagent in an acidic environment (20% Cr/H₂SO₄) has been made. Two types of rubber, with comparable monomer composition, but having significant differences in molar mass and levels of long chain branching were tested. Dicumyl peroxide and triallylcyanurate under similar conditions were used for curing the rubbers. The molecular mechanisms of chemical degradation at the surface were studied using X-ray photoelectron spectroscopy and attenuated total reflectance Fourier transform infrared spectroscopy, which demonstrate that several oxygenated species evolve during exposure. The primary process of degradation is hydrolytic attack on the crosslink sites, which is manifested by a decrease in crosslink density. The surface degradation is found to be strong enough to alter the bulk mechanical properties as observed by the change in retention in tensile strength, elongation at break, modulus at 50% elongation and, the change in micro-hardness. Retention in modulus at 50% elongation is found to follow a negative linear correlation with decrease in crosslink density. With higher molar mass and level of long chain branching more crosslinking occurs and thus comparatively more hydrolytic attack ensues. Scanning electron microscopy shows that the surface topography is significantly altered upon exposure and supports the notion of the dependence of degradation on the crosslinking density of the samples. Importantly, the coagent used in this study is shown to enhance the chemical degradation through formation of weaker sites for hydrolysis. The results also show that upon prolonged exposure the resulting oxygenated species tend to combine with each other.     

Total synthesis of (+/-)-mitorubrinic acid

[reaction: see text] (+/-)-Mitorubrinic acid, a member of the azaphilone family of natural products, has been constructed in 12 steps. Key aspects of the synthesis include elaboration and oxidative dearomatization of an isocoumarin intermediate to provide the azaphilone nucleus with a disubstituted, unsaturated carboxylic acid side chain.     

Activation of the stress-activated JNK and p38 MAP kinases in human cells by Photofrin-mediated photodynamic therapy

We have examined the possible role of the stress-activated JNK and p38 protein kinases in cellular sensitivity following Photofrin-mediated photodynamic therapy (PDT). Previously we reported that immortalized Li-Fraumeni syndrome (LFS) cells are more resistant to Photofrin-mediated PDT compared to normal human fibroblasts (NHF) at equivalent cellular Photofrin levels. In the current work we report that Photofrin-mediated PDT increased the activity of JNK1 and p38 within 30 min in both cell types. However, the increased activity of JNK1 and p38 was transient in the sensitive NHF cells and returned back to near basal levels by 3 h after PDT. In contrast, the resistant LFS cells exhibited a more prolonged activation of JNK and p38, which lasted for at least 11 h and 7 h after PDT, respectively. Blocking of the p38 pathway in LFS cells by transient infection with a recombinant adenovirus expressing a dominant negative mutant of p38 or in HeLa cells by stable transfection with a dominant negative mutant of p38 had no effect on cell survival following PDT. These data suggest that although Photofrin-mediated PDT is able to induce JNK1 and p38 in human cells, the p38 pathway alone does not play a major role in the sensitivity of LFS cells to Photofrin-mediated PDT.     

What is a ‘gel’?

Some of the existing definitions of the term ‘gel’ are discussed and shortcomings are identified. A purely phenomenological definition is proposed: a gel is a soft, solid or solid-like material consisting of two or more components one of which is a liquid, present in substantial quantity. ‘Solid-like gels’ are further defined in terms of the dynamic mechanical properties.     

Phase behavior of diblock copolymers; pressure and temperature dependence studied by small-angle neutron scattering

The structure factor of a poly(ethylene-propylene)poly(dimethylsiloxane) diblock copolymer has been measured by SANS as a function of temperature and pressure. In contradiction to the random phase approximation the conformational compressibility exhibits a pronounced maximum at the order-disorder phase transition. The phase boundary shows an unusual shape: with increasing pressure it first decreases and then increases. Its origin is an increase in, respectively, the entropic and the enthalpic part of the Flory-Huggins interaction parameter. The Ginzburg parameter describing the limit of the mean-field approximation is not influenced by pressure.     

A novel method for monitoring chemical degradation of crosslinked rubber by stress relaxation under tension

This paper describes a novel test method for monitoring chemical degradation of a crosslinked rubber by stress relaxation under tension. An accelerated sulphur cured ethylene propylene diene rubber (EPDM) was subjected to stress relaxation under tension while exposing to 50% aqueous solution of nitric acid (HNO₃). An experimental set up was designed and built in-house for this purpose. The tensile test specimen was stretched to a constant elongation. The stress decay was monitored upon exposure to the harsh chemical. Stress decay was found much faster in the exposure media than in air. Decrosslinking was the main reason for quicker stress decay as observed by decrease in crosslink density. To compare, experiments were conducted by exposing similar specimens in the same exposure media under unstressed conditions. It was found that monitoring chemical degradation under given stressed condition yielded relatively quicker yet reliable and reproducible results.     

A truncated Kv1.1 protein in the brain of the <Emphasis Type="Italic">megencephaly</Emphasis>mouse: expression and interaction

Background  

The megencephaly mouse, mceph/mceph, is epileptic and displays a dramatically increased brain volume and neuronal count. The responsible mutation was recently revealed to be an eleven base pair deletion, leading to a frame shift, in the gene encoding the potassium channel Kv1.1. The predicted MCEPH protein is truncated at amino acid 230 out of 495. Truncated proteins are usually not expressed since nonsense mRNAs are most often degraded. However, high Kv1.1 mRNA levels in mceph/mceph brain indicated that it escaped this control mechanism. Therefore, we hypothesized that the truncated Kv1.1 would be expressed and dysregulate other Kv1 subunits in the mceph/mceph mice.     

How molecular internal‐geometric parameters affect PB‐PEO polymersome size in aqueous solution

Amphiphilic polybutadiene polyethylene oxide (PB‐PEO) is one of the best known chemistries to form stable vesicular morphologies, stated as polymersomes, in aqueous environment. Mimicking cell membranes, these structures self‐assemble in an “amphiphilic window” determined by 0.15 < f < 0.35 where f is the ratio between the hydrophilic block volume and the entire diblock volume. However the polymersome size distribution also depends on molecular weight (M_n) and in order to gain insight on how f and M_n together determine polymersome size, we prepared PB‐PEO diblock copolymers with different block lengths and analyzed vesicle morphology via Dynamic light scattering (DLS) and Freeze‐fracture transmission electron microscopy (FF‐TEM). We found three main regimes: high f / low M_n with polymersomes of mixed diameter, high f / high M_n with mainly large polymersomes and low f, with mainly small polymersomes. In the first region, the polymersomes are highly polydisperse. There is a tendency towards increased diameter with increasing f and M_n. Taken together our findings can help to identify how polymersome self‐assembly can be controlled to achieve size distribution specificity alleviating the need for subsequent tuning of size via extrusion. This can pave the way for cost‐effective upscaling of polymersome production for biomedical and biomimetic applications. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 699–708