Biochemical and biomedical application of monodisperse polymer particles

Macroporous particles with large pores are used for size exclusion chromatography of carbohydrates with very high molecular weights. Macroporous particles of different sizes are used for multiple immunofluorometric analysis by flow cytometry. Porous magnetic particles with protein A coupled to the surface of the pores combine a high capacity in binding of IgG with easy handling of the particles. Magnetic beads with boronic acid coupled to the surface are applied for selective isolation of subclasses of cells. The beads are detached from the cells by addition of sorbitol, leaving free, pure cell fractions in good yield. The use of magnetic particles in molecular biology is described.     

A semisynthetic glutathione peroxidase with high catalytic efficiency. Selenoglutathione transferase

Glutathione peroxidase (GPX) protects cells against oxidative damage by catalyzing the reduction of hydroperoxides by glutathione (GSH). GPX therefore has potential therapeutic value as an antioxidant, but its pharmacological development has been limited because GPX uses a selenocysteine as its catalytic group and it is difficult to generate selenium-containing proteins with traditional recombinant DNA technology. Here, we show that naturally occurring proteins can be modified to generate GPX activity. The rat theta-class glutathione transferase T2-2 (rGST T2-2) presents an ideal scaffold for the design of a novel GPX catalyst because it already binds GSH and contains a serine close to the substrate binding site, which can be chemically modified to bind selenium. The modified Se-rGST T2-2 efficiently catalyzes the reduction of hydrogen peroxide, and the GPX activity surpasses the activities of some natural GPXs.     

Beta decay of neutron-rich 118Rh and the lowest excited states in 118Pd

Beta decay of a refractory isotope ¹¹⁸Rh produced in symmetric fission and mass separated by the ion guide technique has been applied for the study of low-lying excited states of ¹¹⁸Pd. The yrast band in ¹¹⁸Pd has been observed up to a 6⁺ state and the lowest states of the asymmetric γ-band have been identified. The measured half-life of ¹¹⁸Rh is (300±60)ms. The systematics of the excited states in neutron-rich Pd-isotopes implies the saturation towards an O(6) symmetry at N = 70. Received: 19 June 2000 / Accepted: 1 August 2000     

Tetrazolic acid functionalized dihydroindol: rational design of a highly selective cyclopropanation organocatalyst

Herein we wish to report our development of an improved catalyst (S)-(-)-indoline-2-yl-1H-tetrazole (1) for the enantioselective organocatalyzed cyclopropanation of alpha,beta-unsaturated aldehydes with sulfur ylides. The new organocatalyst readily facilitates the enantioselective organocatalytic cyclopropanation, providing cyclized product in excellent diastereoselectivities ranging from 96% to 98% along with enantioselectivities exceeding 99% enantiomeric excess for all reacted alpha,beta-unsaturated aldehydes. The new catalyst provides the best results so far reported for intermolecular enantioselective organocatalyzed cyclopropanation.     

Maximal estimates for solutions to the nonelliptic Schrodinger equation

Maximal estimates are studied for solutions to an initial valueproblem for the nonelliptic Schrödinger equation. A resultof Rogers, Vargas and Vega is extended.     

Experimental investigation of post-dryout heat transfer in annulus with spacers

Experimental investigations of post-dryout heat transfer in 10 × 22.1 annulus test section with spacers were carried out in the high-pressure two-phase flow loop at the Royal Institute of Technology (KTH). The test section was manufactured of Inconel 600 to withstand high temperatures. Several thermocouples were installed on tube and rod surfaces to measure the local wall temperature. Measurements were performed for mass flow rate in range from 500 to 2000 kg m⁻² s⁻¹, with inlet subcooling equal to 10 and 40 K, heat flux in a range from 480 to 1380 kW m⁻² and for the system pressure of 7 MPa. Uniform axial power distributions were applied on rod and tube walls. Using different distributions of heat flux between walls, post-dryout was achieved either on the inner or on the outer wall. The experimental results indicate a very strong influence of spacers on post-dryout heat transfer. For low mass flow rates the wall superheat was significantly reduced downstream of spacers, even though the whole distance between spacers was still under post-dryout conditions when heat flux was high enough. At high mass flow rates and under investigated range of heat flux the dryout patches were effectively quenched downstream of spacers.     

Nanofibrillated cellulose/nanographite composite films

Though research into nanofibrillated cellulose (NFC) has recently increased, few studies have considered co-utilising NFC and nanographite (NG) in composite films, and, it has, however been a challenge to use high-yield pulp fibres (mechanical pulps) to produce this nanofibrillar material. It is worth noting that there is a significant difference between chemical pulp fibres and high-yield pulp fibres, as the former is composed mainly of cellulose and has a yield of approximately 50 % while the latter is consist of cellulose, hemicellulose and lignin, and has a yield of approximately 90 %. NFC was produced by combining TEMPO (2,2,6,6-tetramethypiperidine-1-oxyl)-mediated oxidation with the mechanical shearing of chemi-thermomechanical pulp (CTMP) and sulphite pulp (SP); the NG was produced by mechanically exfoliating graphite. The different NaClO dosages in the TEMPO system differently oxidised the fibres, altering their fibrillation efficiency. NFC–NG films were produced by casting in a Petri dish. We examine the effect of NG on the sheet-resistance and mechanical properties of NFC films. Addition of 10 wt% NG to 90 wt% NFC of sample CC2 (5 mmol NaClO CTMP-NFC homogenised for 60 min) improved the sheet resistance, i.e. from that of an insulating pure NFC film to 180 Ω/sq. Further addition of 20 (CC3) and 25 wt% (CC4) of NG to 80 and 75 wt% respectively, lowered the sheet resistance to 17 and 9 Ω/sq, respectively. For the mechanical properties, we found that adding 10 wt% NG to 90 wt% NFC of sample HH2 (5 mmol NaClO SP-NFC homogenised for 60 min) improved the tensile index by 28 %, tensile stiffness index by 20 %, and peak load by 28 %. The film’s surface morphology was visualised using scanning electron microscopy, revealing the fibrillated structure of NFC and NG. This methodology yields NFC–NG films that are mechanically stable, bendable, and flexible.