ALBERT

Notes: Divalent organochromium compounds, Cr(Lig)2, often become active catalysts for the polymerization of ethylene when deposited onto an oxide carrier such as silica or aluminophosphate. Hydroxyl groups are thought to react, releasing one ligand and binding the chromium to the surface. The behavior of the catalyst is then governed by the remaining ligand and the type of carrier. In this study two types of ligands were investigated: cyclopentadienyl and its open ring analog dimethylpentadienyl. This small difference in the type of ligand produces a fundamental difference in the polymerization mechanism. For comparison the mixed ligand chromocene, with one open and one closed ligand, was also synthesized and tested for polymerization.

Notes: This study examines the interaction of human low density lipoprotein (LDL) with a select group of biomedical polymers. The adsorption characteristics of LDL on cured filler-free poly(dimethyl Siloxane) (C-PDMS), Biomer, Cardiomat 610, Kraton 1650, poly(hydroxyethyl methacrylate) (PHEMA) and glass are presented. Adsorption of LDL to charged hydrophilic glass control surfaces occurred rapidly, reaching plateau concentrations within one minute (0.19 ± 0.01 ug/cm2). Adsorption of LDL to polymer surfaces appeared to be dependent upon both the polymer hydrophobicity (or apolar nature), and flexibility (or dynamic nature) at the interface. Increased surface concentrations were observed for Biomer (0.32 ± 0.01 ug/cm2) as well as other polymers which exhibited both hydrophobic and elastomeric próperties. Temperature changes between 25°C and 37°C were found to significantly influence the surface concentration of LDL on Biomer (0.16 ± 0.01 ug/cm2 at 25°C versus 0.32 ± 0.01 ug/cm2 at 37°C). A lipid core phase transition at 36°C was believed to be responsible for the temperature influence. Preliminary competitive adsorption studies of LDL with albumin (HSA) and serum on silicone surfaces suggests that LDL adsorption occurred rapidly and preferentially (0.25 ± 0.01 ug/cm2 for LDL alone; 0.33 ± 0.01 ug/cm2 for LDL + HSA; 0.15 ± 0.01 ug/cm2 LDL + serum). Preliminary studies on the role of LDL in calcification were not conclusive. It can be concluded that LDL adsorption is dependent upon polymer hydrophobicity, flexibility and temperature. Competitive adsorption experiments suggests that LDL may have substantial influence on protein adsorption.

Notes: Multi-element (52Cr, 56Fe and 66Zn) implanted GaAs samples have been prepared specially for SIMS calibration. Absolute chemical measurements gave retained ion doses which agreed to within 12% of the nominal implanted dose (2.0 × 1014 atoms cm-2). Comparative SIMS depth profiles with five instruments gave Cr mode depth data which showed a variability of 5%. After data normalization to a common mode depth (168 nm) the shape of all profiles showed good agreement. SIMS anàlysis of similar samples containing lower dose implants (1.0 × 1013 atoms cm-2) showed that ∼50% of the Cr was contained in the near surface region (0-0.03 μm). This surface peak was not observed in profiles of samples which had been singly implanted with Cr. It is proposed that the Cr surface peak results from radiation enhanced out-diffusion initiated by the subsequent Fe implant. Whilst the high dose multi-implant samples showed a similar Cr surface accumulation, its magnitude in relation to the ion implanted dose, was smaller. These samples therefore form reliable calibration specimens for the simultaneous determination of the secondary ion responses of Cr, Fe and Zn in GaAs.

Notes: The pyrolysis and gaseous combustion of poly(ethylene terephthalate) (PET) incorporating poly(4-bromostyrene), poly(vinyl bromide), and poly(vinylidene bromide) has been studied using thermogravimetry, flammability limit evaluation, and hydrogen bromide (HBr) evolution techniques. The data obtained have been compared with limiting oxygen index (LOI) flammability data to elucidate flame retardation mechanisms. All the organo bromides studied (applied either via topical treatment or radiation grafting) released HBr on pyrolysis which is capable of inhibiting the gas phase combustion reactions. Condensed phase interactions were also detected which were capable of altering the gaseous pyrolysates. Thermal stability considerations suggest that, although the aliphatic bromides are excellent sources of HBr, they are not ideal flame retardants for PET.

Notes: Melting points of copolymers of ethylene and 1-alkenes ranging from 1-butene to 1-octadecene have been determined. The copolymers were prepared by means of a homogeneous Et3Al2Cl3/VOCl3 initiating system so that in individual samples, comonomer contents do not vary with molecular weight. Evidence is presented for a random distribution of comonomer units in the copolymers. Melting points determined by differential scanning calorimetry are essentially independent of branch length at low comonomer contents. At higher comonomer contents (5-9 mol% 1-alkene), melting points decrease in the order 1-butene 〉 1-octene 〉 1-octadecene copolymers. The weight fraction of ethylene sequences drops to less than 60% in copolymers with 1-octadecene of high comonomer content and this results in a reduction in the crystallite thicknesses attained by these copolymers.

Notes: The thermal degradation behavior of polyacrylamide and poly(acrylamide-co-acrylate) was studied by differential scanning calorimetry, thermogravimetric analysis, gas chromatography/mass spectrometry, and carbon-13 solid state nuclear magnetic resonance. The degradation products over the temperature range of 115-450°C were characterized. Mechanisms are proposed for the degradation processes involved.

Notes: The rapid defluorination of fluoropolymer surfaces by their exposure to a hydrogen plasma excited by an inductively coupled RF field has been studied using ESCA. The results are interpreted in terms of a reaction/depth profile; the reaction is not uniform with depth leading to the formation of an approximately 20 Å thick boundary layer of defluorinated material.

Notes: Es wird über Untersuchungen mit ESCA, AES, ISS, TOF-SIMS und LAMMA zur Zusammensetzung und Dicke der Schutzschichten berichtet, die sich bei Inhibierung von Cu, Ni und Co mit Interface-Inhibitoren (Grenzflächeninhibitoren) (Benzotriazol, Tolytriazol, Mercaptobenzothiazol und 2-(5-Aminopentyl)-benzimidazol) bzw. auf unlegierten Stählen mit Interphase-Inhibitoren (Membraninhibitoren), wie z.B. Phosphonotricarbonsäure in Wässern bilden.Die von Interface-Inhibitoren gebildeten Schichten sind nur wenige Monolagen dick. Aussagen zur Molekülstruktur der Schichten wurden vor allem mit LAMMA und TOF-SIMS gewonnen. Im Falle von Cu und Ni werden quasipolymere Moleküle vom Typ Metall-(I)-Benzotriazol gebildet, während bei Co auch Komplexe mit höherer Wertigkeit auftreten. Die gleichen Molekülstrukturen werden auch auf oxidierten Metalloberflächen beobachtet. Die Inhibitorschichten lassen sich durch Lösemittel nicht von der Metalloberfläche entfernen und sind auch bei längerer Lagerung an Luft stabil.Bei Interphase-Inhibitoren bilden sich wesentlich dickere Schichten. Der Mechanismus der Schutzschichtbildung in Abhängigkeit verschiedener Parameter wird diskutiert.

Notes: The basic structural organization of striated muscle tissue consists of two types of filaments - thick and thin - which are interdigitated and slide past one another when muscle contracts. In the thick filaments the long matchsticklike myosin molecules are organized into a biopolar structure in which the tails form the core of the filament and the heads project out at both ends. The ATPase activity and acitin-binding properties are located in the projecting heads. It is the interaction of these heads with the thin filaments and the concomitant hydrolysis of ATP that provides the driving force for the sliding of thin over thick filaments. The core of the thin-filament structure is made up of a long double-stranded helical assembly of globular (G) acting monomers known as “F-actin.” Located in each of the two grooves of the F-actin structure is a filament of rodlike tropomyosin molecules aggregated head to tail and spanning the length of the thin filament. Each tropomyosin molecule spans seven G-actin monomers on each of the two strands of F-actin and interacts with one troponin complex. The latter consists of three proteins: troponin-C (TN-C), which binds calcium; troponin-I (TN-I), the inhibitory protein; and troponin-T (TN-T), which binds the troponin complex to tropomyosin. When a nerve impulse stimulates a muscle to contract there is an increase in the Ca2+ concentration in the fluid bathing the thick and thin filaments. Binding of this Ca2+ to the TN-C component triggers a series of conformational transitions in the troponin complex and a change in the position of tropomyosin from a blocking position in the grooves of F-actin. Myosin heads are then able to interact with F-actin and sliding of thick over thin filaments ensues. The research in our laboratory has been directed toward a fuller understanding of the detailed molecular mechanisms by which this intricate and sophisticated system operates in both skeletal and cardiac muscle. To this end we have explored the calcium-induced conformational change in TN-C and its propagation through the entire troponin-tropomyosin complex, using a combination of hydrodynamic (ultracentrifuge, viscosity, magnetic densitometry) and spectroscopic (CD, UV absorption difference, solvent perturbation difference, nmr, and fluorescence) approaches. Our studies to date have included the following: the development of highly purified troponin subunits, using high-performance liquid chromatography methodologies; the rigorous physicochemical characterization of the troponin subunits and their interaction properties; precise details of several of the functional groups (carboxyls, aromatics) involved in the Ca2+-induced conformational change in TN-C; the role of sulfhydryl groups in generating functionally active and conformationally sensitive troponin complexes; the molecular morphology of the troponin complex on the thin filament; the role of the two Ca2+-specific regulatory sites in TN-C in terms of their responsiveness to rapid Ca2+ transients; and the demonstration of a common regulatory mechanism for both skeletal and cardiac muscle, using bioassay and spectroscopic studies on ternary complexes made from hybrid subunits of both muscle types. The highlights of these studies are described, including the recently elucidated x-ray structure of TN-C and how the binding of calcium to such a structure may act as a conformational switch.

Notes: Wide-angle x-ray scattering (WAXS) has been used to characterize the ordered phases of spin-oriented nylon 6 fibers wound at speeds ranging from 5000 to 8000 m/min. Quantitative analysis of the radial diffractometer scans by a computerized curve-fitting procedure reveals that the unit-cell geometry of both the α and γ crystalline morphologies are highly dependent on winding speed and on annealing conditions. At 800° m/min, there is a particularly large reduction in the intermolecular distance along the van der Waals forces of the α unit cell, which is accompanied by substantial crystal growth in the hydrogen-bond direction. Similar increases in the width and perfection of the α crystals result from water annealing and steam treatment. The perfection of the γ crystals increases with winding speed and after annealing in water, but steam treatment increases the intermolecular distance along the hydrogen bonds while reducing it along the van der Waals forces. Using bulk density measurements and the experimentally determined crystalline density pc for each sample, the volume-fraction crystallinity (VFC) is shown to pass through a maximum at ca. 6500 m/min. This maximum arises from a decrease in α crystallinity with increasing winding speed together with an increase in γ crystallinity, which levels off above ca. 7000 m/min. It is demonstrated that the determination of VFC assuming constants pc would lead to large errors. The orientation of the α crystals is found to be much less than that of the γ crystals, but it increases quite rapidly with winding speed. Water and steam treatments cause increases in α orientation and decreases in γ orientation.