Morphological characterization of elastin-mimetic block copolymers utilizing cryo- and cryoetch-HRSEM.

Elastin-mimetic block copolymers were produced by genetic engineering. Genetically driven synthesis permitted control of the final physiochemical characteristics of the block copolymers. We designed BB and BAB block copolymers in which the A-block was hydrophilic and the B-block was hydrophobic. By designing the copolymers in this manner, it was proposed that they would self-assemble into micellar aggregates that, at high concentration, would form thermoreversible hydrogels. To analyze the three-dimensional fine surface morphology of the copolymers, to the resolution level of a few nanometers, we employed cryo-HRSEM. This method provided vast expanses of the specimen in its frozen hydrated state for survey. In our initial cryo-HRSEM studies, we observed the protein filaments and micelles surrounded by lakes of vitreous ice. Upon examination at low and intermediate magnifications, there was an extensive honeycomb-like filamentous network. To delineate the fine morphology of the hydrogel network at high magnification and to greater depths, we cryoetched away unbound water from the sample surface, in high vacuum, prior to chromium deposition. By using this technique, we were able to visualize for characterization purposes the fine fibril networks formed from the micellar aggregates over the surface of the hydrogel.     

Proteomic analysis of simulated occupational jet fuel exposure in the lung

We analyzed protein expression in the cytosolic fraction prepared from whole lung tissue in male Swiss-Webster mice exposed 1 h/day for seven days to aerosolized JP-8 jet fuel at concentrations of 1000 and 2500 mg/m3, simulating military occupational exposure. Lung cytosol samples were solubilized and separated via large scale, high resolution two-dimensional electrophoresis (2-DE) and gel patterns scanned, digitized and processed for statistical analysis. Significant quantitative and qualitative changes in tissue cytosol proteins resulted from jet fuel exposure. Several of the altered proteins were identified by peptide mass fingerprinting, confirmed by sequence tag analysis, and related to impaired protein synthetic machinery, toxic/metabolic stress and detoxification systems, ultrastructural damage, and functional responses to CO2 handling, acid-base homeostasis and fluid secretion. These results demonstrate a significant but comparatively moderate JP-8 effect on protein expression and corroborate previous morphological and biochemical evidence. Further molecular marker development and mechanistic inferences from these observations await proteomic analysis of whole tissue homogenates and other cell compartment, i.e., mitochondria, microsomes, and nuclei of lung and other targets.     

The electronic structure of small lithium clusters

Ab initio molecular orbital calculations using the STO-6G and STO6-21G basis sets have been performed for the cluster series Li _n ⁺ , Li _n , and Li _n ^– (wheren=2–7). Thirty-two optimized structures are discussed and reported, many of which (especially for the anionic structures) have not yet been considered. The calculations suggest that for all three species the optimum geometries are planar. Of the two levels of theories that were investigated, STO-6G//STO-6G and STO6-21G//STO-6G, the latter hybrid theory was found to be less reliable. In particular, for the anionic structures these calculations should provide a platform from which more sophisticated, i.e., configuration interaction, geometry optimization can be performed.     

Structural Consequences of S → Se Substitution in some Symmetrical [M(S2CNR2)3] Complexes

The consequences of replacement of the symmetrically chelate ligands in [M(E₂CNR₂)₃] (E = S, Se) complexes of potential 32 symmetry by analogous mixed S,Se unsymmetrical chelates are explored for both small (M = Co) and large (M = In) metal atoms, and R = primary (Et) and secondary (ⁱPr) alkyl substituents by way of low‐temperature single crystal X‐ray studies of [(Co(SSeCNEt₂)₃] ([Co(Se₂CNEt₂)₃] also determined as datum), and [In(SSeCNR₂)₃], R = Et, ⁱPr. The structure of [(ⁱPr₂N·CS·Se)₂] is also recorded.     

Thin-layer chromatography combined with diode laser desorption/atmospheric pressure chemical ionization mass spectrometry

The desorption of an analyte by a continuous wave diode laser from a porous surface of a thin-layer plate covered with a graphite suspension is presented. The thermally desorbed analyte molecules are ionized in the gas phase by a corona discharge at atmospheric pressure. Therefore, both essential processes--the desorption and the ionization of analyte molecules, which are often performed in one step--are separated. The target preparation is easy and fast since no additional extraction process is required. The mass spectrometric background signal was mostly limited to the low mass range showing no interference with typical compounds of interest. In this study, the calmative and antihypertensive drug reserpine was chosen as model analyte, which is often used for specification of mass spectrometers. No fragmentation was observed because of efficient collisional cooling under atmospheric pressure. The influence of diode laser power and the composition of the graphite suspension were investigated, and a primary optimization was performed.     

Activation energy of single-stranded DNA moving through cross-linked polyacrylamide gels at 300 V/cm effect of temperature on sequencing rate in high-electric-field capillary gel electrophoresis

In DNA sequencing, single-stranded DNA fragments are separated by gel electrophoresis. This separation is based on a sieving mechanism where DNA fragments are retarded as they pass through pores in the gel. In this paper, we present the mobility of DNA sequencing fragments as a function of temperature; mobility is determined in 4% T LongRanger gels at an electric field of 300 V/cm. The temperature dependence is compared with the predictions of the biased reptation model. The model predicts that the fragment length for the onset of biased reptation with stretching increases with the square of temperature; the data show that the onset of biased reptation with stretching decreases with temperature. Biased reptation fails to model accurately the temperature dependence of mobility. We analyzed the data and extracted the activation energy for passage of sequencing fragments through the gel. For fragments containing less than ca. 200 bases, the activation energy increases linearly with the number of bases at a rate of 25 J/mol per base; for longer fragments, the activation energy increases at a rate of 6.5 J/mol per base. This transition in the activation energy presumably reflects a change in conformation of the DNA fragments; small fragments exist in a random coil configuration and larger fragments migrate in an elongated configuration.     

Synthesis and structural characterization of tin(II) and zinc(II) derivatives of cyclic alpha-hydroxyketones, including the structures of Sn(maltol)(2), Sn(tropolone)(2), Zn(tropolone)(2), and Zn(hinokitiol)(2)

Zinc(II) and tin(II) derivatives of maltol (Hmalt), ethylmaltol (HEtmalt), tropolone (Htrop), hinokitiol (Hhino), and kojic acid (Hkoj) have been prepared and characterized, and the crystal structures of M(trop)(2) (M = Zn, Sn), Zn(hino)(2).EtOH, and Sn(malt)(2) have been determined. The Zn(trop)(2) is a polymeric structure in which tropolone has both a bridging and chelating role; zinc(hino)(2) crystallizes as an ethanol adduct of which the structure is a dimeric fragment of the Zn(trop)(2) polymer and in which each metal is "capped" by a molecule of alcohol. The tin complexes are notably air-stable despite adopting monomeric pseudo-trigonal-bipyramidal structures (SnO(4)E; E is a stereochemically active lone electron pair) in which the ligands only chelate a single metal center.     

Rectangles inscribed in symmetric continua

LetQ be any rectangle and letK ^d (d 2) be a continuum which is either symmetric across a hyperplane or symmetric through a pointz K. We show thatK contains the vertices of a rectangle similar toQ which exhibits the same symmetry as doesK.     

Detailed large-signal dynamic modelling of DFB laser structures and comparison with experiment

This paper describes the first general large-signal dynamic multiple-mode laser model that incorporates all the main mechanisms known to influence the dynamic behaviour of DFB laser structures with the exception of thermal effects: longitudinal mode spatial hole burning, carrier transport effects, nonlinear gain, and laser and submount parasitics. The time evolution of the output power and wavelength of all modes is predicted, and full spectra can be plotted as a function of time. The model has been extended to include an approximation to the effects of propagation down dispersive fibre, thereby allowing the simulation of filtered received eye diagrams. Detailed comparison of the model with the experimental performance of 2×/8 DFB lasers has shown good agreement, allowing the performance to be optimized, particularly with respect to longitudinal hole burning and carrier transport. The model is also applied to gain-switched operation of 2×/8 DFB structures, fast pulsing of three-section /4 DFB lasers, and the dynamic behaviour of complex coupling coefficient DFB laser structures.