Mutational analysis of the Mu transposase. Contributions of two distinct regions of domain II to recombination

Mu transposase is a member of a protein family that includes many transposases and the retroviral integrases. These recombinases catalyze the DNA cleavage and joining reactions essential for transpositional recombination. Here we demonstrate that, consistent with structural predictions, aspartate 336 of Mu transposase is required for catalysis of both DNA cleavage and DNA joining. This residue, although located 55 rather than 35 residues NH2-terminal of the essential glutamate, is undoubtedly the analog of the second aspartate of the Asp-Asp-35-Glu motif found in other family members. The core domain of Mu transposase consists of two subdomains: the NH2-terminal subdomain (IIA) contains the conserved Asp-Asp-Glu motif residues, whereas the smaller COOH-terminal subdomain (IIB) contains a large positively charged region exposed on its surface. To probe the function of domain IIB, we constructed mutant proteins carrying deletion or substitution mutations within this region. The activity of the deletion proteins revealed that domains IIA and IIB can be provided by different subunits in the transposase tetramer. Substitution mutations at two pairs of exposed lysine residues within the positively charged surface of domain IIB render transposase defective in transposition at a reaction step after DNA cleavage but prior to DNA joining. The severity of this defect depends on the structure of the DNA flanking the cleavage site. Thus, these data suggest that domain IIB is involved in manipulating the DNA near the cleavage site and that this function is important during the transition between the DNA cleavage and the DNA joining steps of recombination.     

Single-ion-conducting nanocomposite polymer electrolytes based on PEG400 and anionic nanoparticles: Part 2. Electrical characterization

Molecular relaxation and polarization phenomena of twelve single-ion-conducting nanocomposite polymer electrolytes (nCPEs) are studied using Broadband Electrical Spectroscopy (BES). The electrolytes are obtained by combining PEG400 oligomers with increasing amounts of anionic nanofiller comprised of fluorinated-TiO₂ associated with Li⁺ cations (LiFT^®), resulting in [PEG400/(LiFT)_y] systems with 0 ≤ y ≤ 26.4. This new class of [PEG400/(LiFT)_y] electrolytes allows us to achieve a significant single-ion conductivity (1.1·10⁻⁵ S cm⁻¹ at 30 °C for n_Li/n_O = 0.113) without the addition of lithium salts. To the best of our knowledge, this is the highest conductivity value reported for this class of electrolytes. This study, in conjunction with the results reported in Part 1, leads us to hypothesize a conduction mechanism in terms of two types of long-range charge-transfer processes. The first charge-transfer occurs at the interface between the filler nanoparticles and filler-PEG domains, while the second occurs through the PEG400 matrix with the assistance of polymer segmental motion. The measured Li⁺ transference numbers confirm that the studied materials are single-ion conductors.     

Inorganic–organic membranes based on Nafion, [(ZrO2)·(HfO2)0.25] and [(SiO2)·(HfO2)0.28]. Part I: Synthesis,thermal stability and performance in a single PEMFC

This work reports the preparation, characterization and test in a single fuel cell of two families of hybrid inorganic-organic proton-conducting membranes, each based on Nafion and a different “core-shell” nanofiller. Nanofillers, based on either a ZrO₂ “core” covered with a HfO₂ “shell” (ZrHf) or a HfO₂ “core” solvated by a “shell” of SiO₂ nanoparticles (SiHf), are considered. The two families of membranes are labelled [Nafion/(ZrHf)_x] and [Nafion/(SiHf)_x], respectively. The morphology of the nanofillers is investigated with high-resolution transmission electron microscopy (HR-TEM), energy dispersive X-ray spectroscopy (EDX) and electron diffraction (ED) measurements. The mass fractions of nanofiller x used for both families are 0.05, 0.10 or 0.15. The proton exchange capacity (PEC) and the water uptake (WU) of the hybrid membranes are determined. The thermal stability is investigated by high-resolution thermogravimetric measurements (TGA). Each membrane is used in the fabrication of a membrane-electrode assembly (MEA) that is tested in single-cell configuration under operating conditions. The polarization curves are determined by varying the activity of the water vapour (a_H2O) and the back pressure of the reagent streams. A coherent model is proposed to correlate the water uptake and proton conduction of the hybrid membranes with the microscopic interactions between the Nafion host polymer and the particles of the different “core–shell” nanofillers.     

Efficient,high photostability,high brightness,co-polymer solid state dye lasers

Abstract

We report an investigation of the laser beam quality, efficiency and photostability of rhodamine 590 solid state dye lasers with hosts based upon 2-hydroxyethylmethacrylate and methylmethacrylate P(HEMA:MMA) co-polymers and modified methylmethacrylate (MPMMA) polymers with ethanol and dimethylsulphoxide additives. Highest efficiencies were obtained with MPMMA, with slope efficiencies of up to 44% (corresponding to 61% optical-optical conversion) measured for ethanolic MPMMA. P(HEMA:MMA) hosts gave superior photostability, with the highest normalized photostability of 240 GJ mol^?1 obtained for a P(HEMA:MMA) 1:1 rod. A simple resonator has been used to compensate the effects of thermal lensing and pump mode-mismatch, resulting in optimized beam quality for MPMMA lasers.     

Thermal and optical properties of polymer hosts for solid-state dye lasers.

We present measurements of thermal and optical properties of poly(methyl methacrylate) (PMMA), PMMA modified by the addition of ethanol (MPMMA), and copolymers of methyl methacrylate with 2-hydroxyethyl methacrylate [P(HEMA:MMA)]. Spectral transmission of the polymers is excellent (alpha = 0.5 cm(-1) at 400 nm, decreasing to 0.04 cm(-1) at 633 nm). Measured laser damage thresholds of MPMMA and P(HEMA:MMA) show at least a twofold increase over PMMA. Thermal lensing measured in these hosts doped with Rhodamine 6G is shown to be similar (f = -450 mm for pump power of 200 mW in a 2-mm-diameter spot, scaling with pump intensity). Compared with MPMMA, P(HEMA:MMA) offers an improved surface quality and a more uniform dye distribution.     

Prediction of Carbon BTEX Adsorption Capacity Using Field Monitoring Data

The need for predicting adsorption capacity for benzene, toluene, ethylbenzene, and xylenes (BTEX) onto granular-activated carbon (GAC) is a problem commonly associated with petroleum-spill remediation. In this study, monitoring data are compiled from operational records of ground-water pump and treat remediation sites where GAC adsorption is utilized as a primary treatment mechanism for BTEX. The monitoring data are reduced to adsorbed and equilibrium concentrations from which Freundlich isotherms and various linear and multivariate models are calibrated for prediction of BTEX capacity on GAC. The models are employed by themselves and with Ideal Adsorbed Solution Theory to predict capacity for total BTEX and benzene. Several models are selected based on prediction ability and are tested with independent data. Two simple models, a multivariate model and a Freundlich isotherm, are recommended. Complex empirical models and Ideal Adsorbed Solution Theory did not perform as well as the selected models and were rejected. From the Freundlich isotherm, new Freundlich constants are reported that describe adsorption of total BTEX on GAC from gasoline-contaminated ground water.     

Prospective study of lung volumes in young asthmatic children

In a 9-y prospective study, the occurrence and duration of lung volume abnormalities in 21 young asthmatic children (median age at recruitment 4 y, range 3-8 y) was determined. The median functional residual capacity (FRC) at recruitment was 135% of that predicted for height (range 79-187%) and 13 children were hyperinflated. The median FRC decreased significantly after 3 y of follow-up and by 9 y only one child remained hyperinflated. We conclude that persistent elevation of lung volume in young asthmatic children appears to be uncommon.     

Group Counseling for Speech Anxiety: An Approach and a Rationale

This paper describes a program of group counseling for speech anxiety (sometimes called “stage fright”) which is based upon theory and research in the general area of group counseling and therapy. The suggested approach is supported by a rationale based upon existing research on the problem of speech anxiety.     

Spectroscopic investigation of proton-conducting, cross-linked linear poly(ethylenimine) hydrochloride membranes

The degree of cross-linking for linear poly(ethylenimine) hydrochloride, cross-linked using malonaldehyde generated in situ, was determined from the ratio of the cross-link to backbone hydrogens obtained using ¹H NMR spectroscopy. The a.c. conductivity is highest at intermediate degrees of cross-linking (ca. 0.45), approximately 1 × 10⁻³ S/cm at room temperature and 75% relative humidity. IR and Raman spectroscopy were used to characterize the cross-linked network. The presence of the β-aminoethenyliminium cross-linker units can be identified through a series of bands between 1570 and 1640 cm⁻¹. Other changes in the spectra identified as a function of degree of cross-linking are discussed.     

Efficient 550-600-nm tunable laser based on noncritically phase-matched frequency doubling of room-temperature LiF:F2- in lithium triborate

We report on efficient conversion of a 1064-nm Nd:YAG laser to tunable visible light. The conversion scheme uses noncritically phase-matched second-harmonic generation of a pulsed Nd:YAG-pumped LiF:F2- laser in lithium triborate. Optimization yields 42% LiF:F2- laser efficiency and 56% frequency-doubling efficiency, providing >20% conversion from 1064 nm to broadly tunable visible output. A dramatic sensitivity of laser efficiency to pump pulse duration is recorded, with a fundamental efficiency improvement of over 30-fold measured for an increase in pump pulse duration from 5 to 34 ns.