Identification of archaeal proteins that affect the exosome function in vitro

Background  

The archaeal exosome is formed by a hexameric RNase PH ring and three RNA binding subunits and has been shown to bind and degrade RNA in vitro. Despite extensive studies on the eukaryotic exosome and on the proteins interacting with this complex, little information is yet available on the identification and function of archaeal exosome regulatory factors.     

Thermal degradation in a trimodal poly(dimethylsiloxane) network studied by (1)H multiple quantum NMR

Thermal degradation of a filled, cross-linked siloxane material synthesized from poly(dimethylsiloxane) chains of three different average molecular weights and with two different cross-linking species has been studied by (1)H multiple quantum (MQ) NMR methods. Multiple domains of polymer chains were detected by MQ NMR exhibiting residual dipolar coupling () values of 200 and 600 Hz, corresponding to chains with high average molecular weight between cross-links and chains with low average molecular weight between cross-links or near the multifunctional cross-linking sites. Characterization of the values and changes in distributions present in the material were studied as a function of time at 250 degrees C and indicate significant time-dependent degradation. For the domains with low , a broadening in the distribution was observed with aging time. For the domain with high , increases in both the mean and the width in were observed with increasing aging time. Isothermal thermal gravimetric analysis reveals a 3% decrease in weight over 20 h of aging at 250 degrees C. Degraded samples also were analyzed by traditional solid-state (1)H NMR techniques, and off-gassing products were identified by solid-phase microextraction followed by gas chromatography-mass spectrometry. The results, which will be discussed here, suggest that thermal degradation proceeds by complex competition between oxidative chain scissioning and postcuring cross-linking that both contribute to embrittlement.     

High precision delta(17)O isotope measurements of oxygen from silicates and other oxides: method and applications

The use of infrared laser-assisted fluorination to release oxygen from milligram quantities of silicates or other oxide mineral grains is a well-established technique. However, relatively few studies have reported the optimisation of this procedure for oxygen-17 isotope measurements. We describe here details of an analytical system using infrared (10 μm) laser-assisted fluorination, in conjunction with a dual inlet mass spectrometer of high resolving power ( approximately 250) to provide (17)O and (18)O oxygen isotope measurements from 0.5-2 mg of silicates or other oxide mineral grains. Respective precisions (1) of typically 0.08 and 0.04 per thousand are obtained for the complete analytical procedure. Departures from the mass-dependent oxygen isotope fractionation line are quantified by Delta(17)O; our precision (1) of such measurements on individual samples is shown to be +/-0.024 per thousand. In turn, this permits the offset between parallel, mass-dependent fractionation lines to be characterised to substantially greater precision than has been possible hitherto. Application of this system to investigate the (17)O versus (18)O relationship for numerous terrestrial whole-rock and mineral samples, of diverse geological origins and age, indicates that the complete data set may be described by a single, mass-dependent fractionation line of slope 0.5244+/- 0.00038 (standard error). Copyright 1999 John Wiley & Sons, Ltd.     

A NEW FINITE ELEMENT APPROXIMATION OF A STATE-CONSTRAINED OPTIMAL CONTROL PROBLEM

In this paper, we study numerical methods for an optimal control problem with pointwise state constraints. The traditional approaches often need to deal with the deltasingularity in the dual equation, which causes many difficulties in its theoretical analysis and numerical approximation. In our new approach we reformulate the state-constrained optimal control as a constrained minimization problems only involving the state, whose optimality condition is characterized by a fourth order elliptic variational inequality. Then direct numerical algorithms （nonconforming finite element approximation） are proposed for the inequality, and error estimates of the finite element approximation are derived. Numerical experiments illustrate the effectiveness of the new approach.     

Sediments of Ypacarai Lake

Bottom and sestonic sediments of Ypacarai Lake were invesetigated with XRF and Mössbauer techniques. The 120 km² lake, depth averages 1.8 m. In addition to the lakes use for recreation, its basin has economic significance. Sediments play an important role in the distribution of trace elements in the aquatic system and as a sink for metals. Bottom and seston samples were taken from 4 different sampling stations which were selected according the morphology and population sites on the shore. The concentration of toxic metals was found to be low and no adverse ecological impact should be expected. The main metallic ion component is iron (1.68%). Mössbauer studies showed this element appears as Fe³⁺. Iron²⁺ was not detected. We suggest that Fe³⁺ acts as the limiting element which controls the eutrophication process.This is in agreement with low values of phytoplancton counting found in water samples.     

Accelerated degradation of syntactic polysulfide in the presence of Viton A

Headspace SPME GC/MS was used to monitor the volatile degradation products generated by syntactic polysulfide alone and in the presence of Viton A at elevated temperature. This approach allowed the identification of products from two distinct degradation mechanisms. In one degradation mechanism, which is associated with lead oxide-cured polysulfide, a single cyclic disulfide compound dominated the outgassing signature. The second mechanism was evident only when the polysulfide was in the presence of Viton A at 70 °C. In as little as 24 h, the Viton-exposed polysulfide generated multiple outgassing species indicative of an acid-catalyzed degradation process. Within one week of exposure to Viton A, the syntactic polysulfide softened significantly and lost over 6% of its initial mass, and after four weeks, the polysulfide was no longer a solid material.     

Application of density functional theory to the investigation of polymer degradation: Example of cross-linked ethylene–vinyl acetate–vinyl alcohol (EVA-OH) terpolymer de-acetylation

We report on the application of Density Functional Theory (DFT) methodologies to investigate the degradation of polymer materials and provide new insights into the effects of degradation on molecular geometry. The temperature- and radiation-assisted degradation of a cross-linked ethylene–vinyl acetate–vinyl alcohol (EVA-OH) elastomer was studied both experimentally and theoretically, in order to correlate observable parameters with theoretically calculated electronic properties. Experiments showed ‘yellowing’ of the material, outgassing of acetic acid, and attenuated IR deformation modes upon exposure to increased levels of gamma radiation or increased temperatures, consistent with the de-acetylation model in which acetic acid is abstracted from the vinyl acetate group via a molecular rearrangement involving the displacement of a hydrogen atom from the ethylene backbone toward the acetyl group, and the propagation of the mechanism to adjacent vinyl acetate groups, forming polyenes in the polymer backbone. DFT modeling predicted the molecular structures of the cross-linked EVA-OH polymer for various degrees of de-acetylation, with corresponding IR and UV–visible absorption spectra. Theoretical attenuated IR deformation modes matched experimental observations, and the theoretical absorption spectrum of polyenes with 5 double bonds matched the optical absorption data, shedding light onto the final chemical structure of the polymer fragment. In addition, DFT unveiled precise and local effects of de-acetylation on the geometry of both the remaining polymer chain and cross-linker, which could only be detected as methylene deformation mode reflectance changes by IR spectroscopy.