Pyridiniums as potential synthetic substitutes for nitrogen mustards

Dialkylamino-alkyl primary amines 1b and 2b are converted by pyrylium salts into the corresponding pyridinium derivatives. The pyridinium salts act as aminoalkylating agents for representative O-, S-, N-, and C-nucleophiles and are potentially safe substitutes for nitrogen mustards in the reactions.     

Oscillatory shear flow of polymeric systems

On the basis of the Leonov viscoelastic constitutive equation, oscillatory shear flow of elastic fluids in the linear and nonlinear regimes has been considered. The Fourier components and associated phase angles of the shear and normal components of the elastic strain tensor have been found as functions of frequency and deformation amplitude in the range usually employed in experiment, and are presented in a form convenient for further rheological applications. In the linear case, the results correspond to many known theories. In the nonlinear case, the theoretical results have been compared with experiments, on different polymeric systems, with very good agreement being obtained for the shear stress in polymeric solutions but only qualitative agreement for the shear stress and first normal-stress difference in polymer melts.     

Oscillatory shear measurements on polystyrene melts in the terminal region

Oscillatory shear measurements have been made on a range of anionic polystyrene melts of molecular weights 1000--500,000. For M < 5000 the polymer chain is too short to act as a Gaussian coil and hence the compliance of the melt is very low. For 10,000 < M < 100,000 the compliance of the melt follows the Rouse model of the elasticity of isolated polymer molecules. It is necessary to use the Ferry, Landel and Williams extension of the Rouse theory for M > 40,000 to allow for the effect of entanglements on the complex modulus. For M > 200,000 the entangelment network dominates the compliance and the Rouse theory is no longer applicable.     

QSAR as a random event: criteria of predictive potential for a chance model

The CORAL software (http://www.insilico.eu/coral) was suggested as a tool to build up quantitative structure–property/activity relationships (QSPRs/QSARs). This software is based on conception “a QSPR/QSAR model should be interpreted as a random event.” This is reflection of fact: different distributions into the training set (substances involved in modeling process) and the validation set (substances, which are not known at the moment of the modeling process) give models with significant dispersion in the statistical quality of the QSPR/QSAR. Results of experiments with the software and possible ways of further improvement of this software are discussed. The most attractive new ways to estimate predictive potential of the CORAL model seem to be the following ones: (i) index of ideality of correlation and (ii) correlation contradiction index. These can be also proposed as criteria of predictive potential for arbitrary QSPR/QSAR.

     

Oscillatory shear and high-pressure dielectric study of 5-methyl-3-heptanol

The monohydroxy alcohol 5-methyl-3-heptanol is studied using rheology at ambient pressure and using dielectric spectroscopy at elevated pressures up to 1.03 GPa. Both experimental techniques reveal that the relaxational behavior of this liquid is intermediate between those that show a large Debye process, such as 2-ethyl-1-hexanol, or a small Debye-like feature, such as 4-methyl-3-heptanol, with which comparisons are made. Various phenomenological approaches assigning a time scale for the rheological signature of supramolecular dynamics in monohydroxy alcohols are discussed.     

Poly(ether imide) membranes modified with poly(ethylene imine) as potential carriers for epidermal substitutes

Poly(ether imide) (PEI) membranes were modified with a linear low-molecular weight (PETIM_0.6) and a branched high-molecular weight poly(ethylene imine) (PETIM_60). The membrane surfaces became more hydrophilic and the zeta potentials were shifted from negative to positive zeta values after immobilisation of both PETIM. These measurements also indicated the presence of a swollen surface layer in the case of PETIM_60, while a regular structuring of the surface was observed with scanning force microscopy for PETIM_0.6. A human keratinocyte cell line HaCaT was cultured on the different membranes. It was found that HaCaT cell growth was stimulated by PETIM_0.6. Cells reached earlier confluence on this substratum, while their growth was inhibited on a PEI membrane modified with PETIM_60, which makes PEI membranes modified with PETIM_0.6 a promising material for in vitro culture of epidermal transplants.     

On the viscoelastic fracture criteria for polymers: experiments and analysis

Creep deformation and fracture tests on two polymeric materials were performed at various temperatures and strain rates. The data obtained were analyzed and used to test four viscoelastic fracture criteria, based on different theoretical approaches. No definitive conclusion could be reached as to the identification of an appropriate invariant fracture parameter.     

Perfluoro compounds as blood substitutes.

Inconceivable as it is, it has been proved that animals can survive after having had their blood massively or even totally replaced by emulsions of perfluorinated compounds in salines. “Bloodles” rats charged with an emulsion of perfluorotri-n-butylamine survived a five hour period in an atmosphere containing 50% oxygen and 50% carbon monoxide, i.e. in conditions where the transport of oxygen by the red cells is entirely blocked. This review discusses: (1) the experiments which have demonstrated the capability of blood substitutes based on perfluorinated compounds to sustain life; (2) the characteristics and preparation of the relevant perfluoro compounds and the production and handling of their emulsions; (3) their “physiology”, i.e. toxicity, life-span in the blood-stream, effect on the organs and their functions, and excretion properties. Obstacles remaining to be overcome in order to provide a safe blood substitute for medical practice include the availability of numerous series of well-defined pure and inert perfluorinated chemicals, the production of stable emulsions, the optimization of fluid balance, and the attainment of reasonable excretion rates. The accent is placed upon the role of the chemist in the progress of this research.     

Polyurethane microporous membranes as pericardial substitutes

Pericardial substitutes were prepared from stable and degradable segmented polyurethanes and/or polyurethane/polyhydroxybutyrate composites.Polyurethane membranes implanted as pericardial substitute in the rabbit, did not activate adhesion and epicardial reaction over 3 months.Polyurethane/polyhydroxybutyrate membranes induced minimal adhesion or epicardial reaction, yet stimulated the growth of epithelium on the polymeric substrate and reduced the incidence of infection.     

Oscillatory shear response of moisture barrier coatings containing clay of different shape factor

Oscillatory shear rheology of barrier coatings based on dispersed styrene-butadiene latex and clay of various shape factors or aspect ratio has been explored. Barrier performance of these coatings when applied to paperboard has been assessed in terms of water vapour transmission rates and the results related to shape factor, dewatering and critical strain. It has been shown that a system based on clay with high shape factor gives a lower critical strain, dewatering and water vapour transmission rate compared with clays of lower shape factor. The dissipated energy, as calculated from an amplitude sweep, indicated no attractive interaction between clay and latex implying a critical strain that appears to be solely dependent on the shape factor at a constant volume fraction. Particle size distribution was shown to have no effect on the critical strain while coatings of high elasticity exhibited high yield strains as expected. The loss modulus demonstrated strain hardening before the elastic to viscous transition. The loss modulus peak was identified by a maximum strain which was significantly lower for a coating based on clay with a high shape factor. The characteristic elastic time was found to vary between 0.6 and 1.3s. The zero shear viscosity of barrier dispersion coatings were estimated from the characteristic elastic time and the characteristic modulus to be of the order of 25-100 Pa s.     

Blood substitutes and other potential biomedical applications of fluorinated colloids

An oxygen carrying, heat-sterilized phospholipid-based emulsion of a fast excreted lipophilic fluorocarbon, perfluorooctyl bromide (perflubron), stabilized against molecular diffusion, has been developed to serve as a temporary blood substitute. It is expected to reduce exposure to donor blood and thereby help mitigate the pressure on our blood supply. A phase III clinical trial in Europe has demonstrated that use of the emulsion resulted in avoidance and reduction of donor blood transfusion in surgery patients. Further potential applications for fluorocarbon emulsions include use as a bridge to transfusion, treatment of myocardial ischemia and stroke, potentiation of radio and chemotherapy and preservation of organs destined for transplantation. Echogenic, injectable gaseous microbubbles, osmotically stabilized by perfluorohexane, provide an effective contrast agent for ultrasound imaging. Clinical trials have established improved imaging of the walls of the heart and, hence, assessment of cardiac function. The ability of improving detection of myocardial perfusion, blood flow abnormalities and solid tumors is also being investigated. Various families of fluorinated amphiphiles with modular molecular structures and polar heads derived from natural products have been synthesized. Due to their highly hydrophobic perfluoroalkylated tail chains, these amphiphiles readily self-assemble into stable fluorinated vesicles, tubules and other organized molecular systems with distinctive properties. Fluorosurfactants also allowed preparation of direct, reverse, apolar and multiple emulsions and gels. These fluorinated colloids have potential for the delivery of drugs and other bioactive materials, and provide unique tools in biomedical research.     

Oscillatory heat production in cell free extract from yeast: Batch and infusion experiments

Microcalorimetric experiments on the periodic heat production in metabolizing cell free cytoplasmic extract from baker's yeast are described. The sugar substrates for glycolysis are supplied by two different techniques: (a) one-time addition of trehalose; (b) continuous infusion of glucose. For the first time the combination of calorimetry and substrate infusion technique is reported for oscillating biochemical reactions.

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Zusammenfassung Mikrokalorimetrische Experimente über oszillierende Wärmeerzeugung in stoffwechselndem zellfreiem Hefeextrakt werden beschrieben. Die Zuckersubstrate für die Glykolyse werden nach zwei verschiedenen Methoden zugeführt: (1) einmalige Addition von Trehalose, (b) Kontinuierliche Infusion von Glukose. Erstmalig wird die Kombination von Kalorimetrie und Substratinfusion bei oszillierenden biochemischen Reaktionen beschrieben.

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Surface potential and shear plane thickness for a treated concrete particulate

Concrete was treated for the removal of chlorides before the zeta potential (mV), zeta, was measured amphoterically to prepare the adsorbent for onward adsorption of silver on it. The Gouy-Chapman theory, which describes the relationship between the potential at any distance (X) from the surface, Psi(x), and the potential at the surface, Psi(0), was applied to determine the shear plane thickness X(S), and to calculate the surface potential Psi(0). The X(S), for a treated concrete particulate was calculated to be 7.0 A. The Psi(0) calculated was equivalent to the measured zeta potential (zeta), Psi(x) at high electrolyte concentrations, where in general the surface potential greatly deviates from the Nernstian response.     

Functional evaluation of hemoglobin-and lipidheme-vesicles as red cell substitutes

The two kinds of red cell substitutes, hemoglobin-vesicles (HbV) and lipidheme-vesicles (LihV, totally synthetic oxygen carrier), were evaluated in terms of physicochemical properties such as binding and dissociating reactions of ligands (CO, O₂ and NO), rheological and structural properties. Carbonylation of Hb during the purification of Hb and the preparation of HbV is effective to prevent Hb denaturation. The rates of oxygenation of both HbV and LihV are faster than that of red blood cells (RBC). Their oxygen affinities (P₅₀, HbV, 32 mmHg; LihV, 43 mmHg, cf. RBC, 28 mmHg) can be controlled to transport a sufficient amount of oxygen comparable with that of RBC. The smaller sizes of vesicles are advantageous for prompt ligand reaction and low viscosity. Both HbV and RBC show about 100 times less vasoconstrictive effects than stripped Hb. HbV shows only one sixth of the slow binding rate of NO (=endothelial derived relaxation factor) in comparison with stripped Hb. Inhibition of vasoconstriction by those vesicles is discussed from the kinetic data.     

Correlation between transient shear experiments and structure evolution of aqueous foams

This experimental work deals with rheological properties of aqueous foams and slip phenomena. Rheological measurements are performed on a stable foam with a parallel plate rheometer. When a constant shear rate is applied to foam, two regimes can be identified in the recorded stress vs time curve: a transient regime where the structure evolves and where the recorded stress varies, followed by a steady state regime where the stress is stabilized. Measurements, modeling, and elimination of the slip velocity are performed. Experiments with grooved surfaces allow elimination of slip at the wall. From measurements at two gaps with smooth surfaces, we use two slip correction methods and check their validity by a direct comparison with actual measurements (with grooved surfaces). A foam rheological equation can be determined from the measurements. Finally, using an optical device coupled with image analysis software, foam texture is investigated on the basis of its evolution with shear rate and time. Evolution of the bubbles size and arrangement into the gap with time of shearing are shown. The transient regime is identified as a regime where the intimate structure of the foam evolves. Slip velocity is also evidenced and measured with the visualization device.     

Borides and vitreous compounds sintered as high-energy fuels

Boron was chosen as fuel in view of its excellent thermodynamic values for combustion, as compared to traditional fuels. The problem of the boron in combustion is the formation of a surface layer of oxide, which delays the ignition process, reducing the performance of the rocket engine. This paper presents a high-energy fuel for rocket engines. It is composed of sintered boron (borides and carbides and vitreous compounds) with a reducing chemical agent. Borides and boron carbide were prepared since the combustion heat of the latter is similar to that of the amorphous boron (in: K.K. Kuo (Ed.), Boron-Based Solid Propellant and Solid Fuel, Vol. 427, CRC Press, Boca Raton, FL, 1993). Several chemical reducing elements were used, such as aluminum, magnesium, and coke. As the raw material for boron, different compounds were used: amorphous boron, boric acid and boron oxide.     

First principles potential for the acetylene dimer and refinement by fitting to experiments

We report the definition and refinement of a new first principles potential for the acetylene dimer. The ab initio calculations were performed with the DFT-SAPT combination of symmetry-adapted intermolecular perturbation method and density functional theory, and fitted to a model site-site functional form. Comparison of the calculated microwave spectrum with experimental data revealed that the barriers to isomerization were too low. This potential was refined by fitting the model parameters in order to reproduce the observed transitions, an excellent agreement within ~1 MHz being achieved.     

Nanostructured perovskite oxides as promising substitutes of noble metals catalysts for catalytic combustion of methane

In this review, we summarize the recent development of nanostructured perovskite oxide catalysts for methane combustion, and shed some light on the rational design of high efficient nanostructured perovskite catalysts via lattice oxygen activation, lattice oxygen mobility and materials morphology engineering.     

Preparation and characterization of superporous agarose-reticulated vitreous carbon electrodes as platforms for electrochemical bioassays

Three-dimensional flow-through electrodes were fabricated using superporous agarose (SPA) and reticulated vitreous carbon (RVC) composite materials that were suitable as a platform for sandwich assays. These SPA-RVC composite electrodes were fabricated by fitting a SPA-RVC composite cylinder inside a graphite tube and subsequently fixing the graphite tube onto a polypropylene micropipette tip. The electrode design allows for ease in reagent/washing steps involved in sandwich assay protocols and could easily be made portable. The electrode materials were characterized with respect to pore-size distribution, total free volume, ligament and bulk densities of the RVC, and physical structural characteristics. Coulometric detection of redox molecules such as K(3)Fe(CN)(6) and 4-aminophenol was possible using SPA-RVC electrodes by the trapping of these redox molecules inside the SPA-RVC electrodes. Avidin affinity molecules were covalently immobilized onto the SPA matrix inside the RVC electrodes by periodate-activation followed by reductive amination. The amount of avidin immobilized inside the SPA-RVC electrodes was (5+/-0.06)x10(-11) mol, which was determined by saturating the avidin sites with biotinylated fluorescein (b-fluo) and subsequently determining the amount of immobilized b-fluo via a standard addition method using fluorescence spectroscopy. Non-specific binding of labeled enzymes such as biotinylated alkaline phosphatase (b-ALP) onto the SPA-RVC electrodes without avidin capture sites was determined to be less than 1% compared to the specific binding of b-ALP on avidinylated SPA-RVC electrodes.