Magnetic moments in173YB

Properties of the [512] 5/2?, [633] 7/2+ and [514] 7/2? bands have been studied by experiments on the magnetic moments of the [512] 5/2? 7/2? (79 keV; g=0.058(19)), [512] 5/2? 9/2? (179 keV; g=+0.06(8)) and [633] 7/2 7/2 (351 keV; g=?0.13(13)) states.     

Solid-phase thiolsulfinates for the reversible immobilization of thiols

A new method for the reversible immobilization of thiol-containing substances on agarose beads is presented. It is based on the use of thiolsulfinate (disulfide monoxide) as a solid-phase reactive group. The thiolsulfinate groups are introduced by controlled oxidation of thiol agarose. The method comprises two steps: First, mild oxidation of the agarose thiol groups to disulfide structures with potassium ferricyanide. Second, the oxidation of the so-formed agarose disulfide groups to thiolsulfinate groups by use of a stoichiometric amount of the oxidizing agent magnesium monoperoxyphtalate. The solid-phase thiolsulfinate groups react very easily with thiols, which, as a result of the reaction, will be bound to the agarose beads by disulfide bonds. The adsorbent derivative is very suitable for the reversible immobilization of low as well as high-mol-wt thiols as demonstrated with reduced glutathione, penicillamine, mercaptoethanesulfonic acid, thiolated bovine serum albumin,β-galactosidase, and ±₁-antitrypsine. Since treatment of the agarose derivatives with an excess of low-mol-wt thiols (e.g., dithiothreitol) leads to release of the bound molecules and regeneration of the original thiol groups, the reactive thiolsulfinate groups can easily be regenerated by the mentioned two-step procedure. The cycle of oxidation, binding, reduction, and reoxidation can be performed several times while retaining thiol binding capacity.     

Surface characterization of unbleached kraft pulps by means of ESCA

The effect of digestion conditions (amount of effective alkali, digestion time) on the surface compositions of unbleached softwood (Pinus sylvestris) kraft pulp has been investigated by electron spectroscopy for chemical analysis (ESCA). The quantities monitored were the angular dependence of the total O/C ratio, the relative amounts of carbons in different states of oxidation and the adsorption of Al and Ca ions to the carboxyl groups in the surface. Examination of the angular dependence of ESCA intensities shows that the concentration of alkyl carbon is high in a very thin surface layer and that it decreases linearly with decreasing kappa number. The concentration of alkyl carbon is decreased by extraction of the fibres with dichloromethane, but the amount remaining in the surface after extraction still decreases linearly with decreasing kappa number (i.e. it decreases with increasing digestion time). It is suggested that the observed enrichment of alkyl carbon in the outermost surface layers most probably is due to reprecipitation of lignin. In pulp that has not been extracted, there is also strong enrichment of extractives in the surface. This amount increases with increasing effective alkali but is relatively independent of digestion time. ESCA analysis of the Al and Ca bound to the carboxyl groups shows that the amount depends on digestion time; the results are consistent with the notion that the reprecipitated lignin contains carboxyl groups.     

Flow analysis based on a pulsed flow of solution: theory, instrumentation and applications

The increased demands placed on solution propulsion by programmed flow systems, such as sequential injection analysis, lab-on-value technology, bead injection and multi-commutation, has highlighted the inability of many conventional pumps to generate a smooth, consistent flow. A number of researchers have examined ways to overcome the inadvertent, uncontrolled pulsation caused by the mechanical aciton of peristaltic pumps. In contrast, we have developed instruments that exploit the characteristics of a reproducible pulsed flow of solution. In this paper, we discuss our instrumental approaches and some applications that have benefited from the use of a reproducible pulsed flow rather than the traditional linear flow approach. To place our approach in the context of the continuously developing field of flow analysis, an overview of other programmed flow systems is also presented.     

Gamma-, photo-, and thermally-initiated oxidation of isotactic polypropylene

The detailed oxidation products have been identified and compared from the γ-, photo-, and thermally-initiated oxidation of unstabilized polypropylene films. Products were identified and quantified by a combination of iodometric analysis and infrared spectroscopy. Spectral resolution was enhanced by derivatization reactions which allow the quantification of primary, secondary, and tertiary hydroperoxide and alcohol groups as well as more reliable analysis of carbonyl species. In contrast to polyethylene oxidation which yields predominantly ketone with lesser amounts of secondary hydroperoxide and carboxylic acid, polypropylene oxidizes to give predominantly tertiary hydroperoxide and lesser quantities of secondary hydroperoxide and ketone. In addition carboxylic acid groups are a minor product except at high degrees of thermal and photoinitiated oxidation. © 1993 John Wiley & Sons, Inc.     

Possibility of heat sterilization of liposomes

Several kinds of liposomes were sterilized at 121 degrees C for 20 min. They tended to aggregate after heat sterilization (HS) in saline, while no aggregation was observed in an isotonized sugar or polyol solution. The dispersions containing egg phosphatidylcholine (EggPC) with a high peroxide value (POV) turned slightly yellowish after HS. This color change was prevented by using EggPC with a low POV, hydrogenated EggPC (H-EggPC) or dipalmitoylphosphatidylcholine (DPPC). Nitrogen gas bubbling at neutral pH also prevented the color change, but vitamin E did not. The particle size of the EggPC liposomes extruded through a 0.4 micron membrane filter did not change significantly after HS, whereas the H-EggPC or DPPC liposomes extruded through a 0.8 micron membrane filter tended to be reduced in size. On this change the type of medium had a considerable influence. The anionic 6-carboxyfluorescein leaked from the negatively charged liposomes (EggPC/cholesterol (Chol)/egg phosphatidylglycerol) during HS, while no leakage was observed from the positively charged liposomes (EggPC/Chol/stearylamine) not only during HS but also during a long period of storage. It was suggested that sterilization of liposomes by heating was practicable as well as that by filtration, if the liposomes were prepared as follows: the charged liposomes made of lipids with low POV's were dispersed in a sugar or polyol solution adjusted to nearly pH 6.5, where the amount of dissolved oxygen was minimized. An ionic water-soluble drug had to be encapsulated in the oppositely charged liposomes.     

Total Synthesis of Sialylgalactosylgloboside: Stage-Specific Embryonic Antigen 4

A versatile total synthesis of sialylgalactosylgloboside (SGG, 1), carrying the stage-specific embryonic antigen 4 (SSEA-4) is reported, illustrating a more general strategy for the synthesis of complex globo-series glycosphingolipids. Starting from readily available building blocks 7, 8, and 10, two different approaches to the synthesis of the key tetrasaccharide 6 have been developed in a highly convergent manner. Further glycosylations with galactosyl trichloroacetimidate (5) and sialyl phosphite (2) donors successively afforded the penta- and hexasaccharides 3 and 11. The latter was finally converted into the target molecule (SGG, 1) with the help of a azidosphingosine glycosylation procedure, favored in this case by the stereocontrolling properties of the 2a-O-pivaloyl protecting group. Valuable intermediates 6 and 3, having the oligosaccharidic skeletons of Gb(4) and Gb(5) (SSEA-3), respectively, were obtained in the course of the synthesis.     

Effect of gramicidin on phospholipid-modified monolayers and on ion transfer at a liquid-liquid interface.

The interaction of hybrid lipid/gramicidin A (gA) monolayers with dextran sulfate (DS) and the effect of this interaction on ion transfer at a liquid-liquid interface is reported. The interfacial and physicochemical properties are studied with Langmuir-Blodgett (LB) and electrochemical techniques. The results obtained from compression isotherms demonstrate that the interactions between the different species in the hybrid monolayer vary according to the chemical nature of the lipid (hydrocarbon region and charge of the head group). Interfacial capacitance measured with AC voltammetry indicates that the DS chains form a rather flat and compact layer when adsorbed to either zwitterionic or negatively charged phospholipid monolayers, and that calcium, even at low concentrations, interacts with the monolayers. These results are successfully described by a model based on the solution of the Poisson-Boltzmann equation in the interfacial region. Ion transfer and interactions with the lipid/gA/DS-modified monolayers were also studied with electrochemical techniques. Admittance data show that although the studied ions are not using gA channels for the transfer through the lipid membranes, the incorporation of gA in the lipid domain and the adsorption of DS at the interface have a significant effect on ion transfer across the monolayers. This effect can be explained as a consequence of the modified surface charge and of the compactness of the lipid domain due to its interaction with gA and to calcium and DS adsorption at the interface. The ion-transfer rate, therefore, depends on the composition of the monolayer and the chemical nature of the ion.