γ‐Irradiation of ultrahigh‐molecular‐weight polyethylene: Electron paramagnetic resonance and nuclear magnetic resonance spectroscopy and imaging studies of the mechanism of subsurface oxidation

The shelf aging of irradiated ultrahigh‐molecular‐weight polyethylene (UHMWPE) causes subsurface oxidation, which leads to failure in UHMWPE orthopedic components, yet the mechanisms causing subsurface oxidation remain unclear. The shelf aging of γ‐irradiated UHMWPE bars has been studied with electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR) imaging and with microtoming and Fourier transform infrared microscopy. The bars initially contained only allyl radicals, and upon air exposure, a surface layer of peroxyl radicals formed through the reaction of allyl radicals with oxygen. Importantly, a band of low radical intensity just beneath the peroxyl layer became apparent. NMR imaging showed a zone of altered proton relaxation in this zone. With increasing time, surface peroxyl radicals persisted in comparison with the interior allyl radicals, although oxygen did not appear to penetrate any more deeply into the bar. The area of maximal oxidation and mechanical disruption, measured after 3 years, was at the interface between the zone of exterior peroxyl radicals and the zone of low radical intensity. We present a mechanism involving the intermediacy of sterically strained reactive dialkyl peroxides at this interface to explain subsurface oxidation. We also demonstrate that EPR and NMR imaging provides information that could potentially be used to identify subsurface oxidized UHMWPE components before failure. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5929–5941, 2004     

A one-pot diastereoselective synthesis of cis-3-hexene-1,6-diols via an unusually reactive organozinc intermediate

A highly diastereoselective method for the synthesis of cis-3-hexene-1,6-diols has been developed. This new reaction proceeds with excellent control of diastereoselectivity over four stereocenters and the double bond geometry. The diols are made in a one-pot procedure involving hydroboration of a terminal alkyne and transmetalation to zinc to give a divinylzinc intermediate. This intermediate undergoes reductive elimination, forming a C=C bond. In the absence of a trapping reagent, diene is liberated (70% yield); however, in the presence of ketones or aldehydes, the proposed intermediate metallocyclopentene is trapped via a double insertion of the carbonyl substrate. Workup provides the diols in 47-86% yield.     

Evaluation of seasonal chemical composition,antibacterial, antioxidant and anticholinesterase activity of essential oil from Eugenia brasiliensis Lam.

This study describes the seasonal composition and the antibacterial, antioxidant and anticholinesterase activity of the essential oil from Eugenia brasiliensis leaves. Analysis by using GC allowed the identification of 40 compounds. It was observed that the monoterpenes varied more (42%) than the sesquiterpenes (14%), and that the monoterpene hydrocarbons suffered the greatest variation throughout the year (64%). Major compounds were spathulenol in the spring (16.02 ± 0.44%) and summer (18.17 ± 0.41%), τ-cadinol in the autumn (12.83 ± 0.03%) and α-pinene (15.94 ± 0.58%) in the winter. Essential oils were tested for their antibacterial activity, and the best result was obtained from the autumn oil, with MIC = 500 μg mL^? 1 against Staphylococcus saprophyticus and Pseudomonas aeruginosa. Antioxidant activity was evaluated using DPPH, lipid peroxidation and iron-reducing power assays, as well as the anticholinesterase activity. Both tests showed a weak performance of the essential oils.     

Approximated solutions in rational form for systems of differential equations

In this paper we present a technique to study the existence of rational solutions for systems of differential equations — for an ordinary differential equation, in particular. The method is relatively straightforward; it is based on a rationality characterisation that involves matrix Padé approximants. It is important to note that, when the solution is rational, we use formal power series “without taking into account” their circle of convergence; at the end of this paper we justify this. We expound the theory for systems of linear first-order ordinary differential equations in the general case. However, the main ideas are applied in numerical resolution of partial differential equations. This revised version was published online in June 2006 with corrections to the Cover Date.     

Reversible pH‐Responsive Coacervate Formation in Lipid Vesicles Activates Dormant Enzymatic Reactions

In situ, reversible coacervate formation within lipid vesicles represents a key step in the development of responsive synthetic cellular models. Herein, we exploit the pH responsiveness of a polycation above and below its pK_a, to drive liquid–liquid phase separation, to form single coacervate droplets within lipid vesicles. The process is completely reversible as coacervate droplets can be disassembled by increasing the pH above the pK_a. We further show that pH‐triggered coacervation in the presence of low concentrations of enzymes activates dormant enzyme reactions by increasing the local concentration within the coacervate droplets and changing the local environment around the enzyme. In conclusion, this work establishes a tunable, pH responsive, enzymatically active multi‐compartment synthetic cell. The system is readily transferred into microfluidics, making it a robust model for addressing general questions in biology, such as the role of phase separation and its effect on enzymatic reactions using a bottom‐up synthetic biology approach.     

Stereospecific 5JHortho,OMe couplings in methoxyindoles,methoxycoumarins, and methoxyflavones

Long‐range coupling constants ⁵J_Hortho,OMe were measured in series of methoxyindoles, methoxycoumarins, and methoxyflavones by the modified J doubling in the frequency domain method. The COSY and NOESY spectra revealed the coupling of the –OMe group with a specific proton at the ortho position and its preferred conformation. Homonuclear ¹H–¹H couplings were confirmed by irradiation of the –OMe signal. Density functional theory calculations of ⁵J_Hortho,OMe using the modified aug‐cc‐pVTZ basis set evidenced that the Fermi contact term shows good agreement with the experimental J values. Accurate chemical shift and coupling constant values followed after iterative quantum mechanical spectral analysis using the PERCH software. Copyright © 2014 John Wiley & Sons, Ltd.     

Stability of Lead(II) Arsenates

 Predictions of lead arsenate solubility and thermodynamic stability have been based on the value of the solubility constant for a precipitate with the general composition Pb₃(AsO₄)₂. The solubility of this precipitate is high and lead arsenate is considered to be unsuitable for lead and arsenic control in the environment. Standard Gibbs energy of formation for bayldonite, duftite, mimetite, philipsbornite, and schultenite can be found in the literature from solubility studies. From these data, stability diagrams were established for the environmentally relevant lead containing solid phases – anglesite, cerussite, schultenite, and mimetite. The diagrams lead to the conclusion that mimetite is a lead arsenate that can be used for remediation techniques.     

Switching time optimization for a PDE constrained optimal control problem of bang-bang type

We consider a well-known optimal control problem subject to the heat equation where the control variable appears linearly as a boundary control in a Robin type boundary condition. Here, we describe an alternative numerical method to solve the problem by a switching time optimization approach. The method has so far been successfully applied to ODE problems and offers several advantages according to second order sufficient conditions and sensitivity analysis. We discuss theoretical aspects and present numerical results to illustrate the effectiveness of the method. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)