Cross-sections of 14 MeV neutron reactions on phosphorus and calcium

Cross-section values for 14.7 MeV neutrons are measured for the following reactions: $$\begin{gathered} ^{31} P(n,\alpha )^{28} Al,(132 \pm 10)mb;^{42} Ca(n,p)^{42} K,(173 \pm 19)mb; \hfill \\ ^{43} Ca(n,p)^{43} K,(111 \pm 9)mb;^{44} Ca(n,p)^{44} K,(42 \pm 2)mb; \hfill \\ ^{44} Ca(n,\alpha )^{41} Ar,(27 \pm 2)mb;^{48} Ca(n,2n)^{47} Ca,(616 \pm 54)mb. \hfill \\ \end{gathered}$$ An analysis of available cross-section data for these reactions is performed and preferred mean values for each reaction are given.     

Approach to hydrodynamic equilibrium and its time dependence in the system EHEC/SDS/Water

The properties of the system EHEC/SDS/water in solution show considerable time dependence during several hours after preparation. The paper discusses various reasons for this time dependence. Similar time dependence in polymer solutions has been observed elsewhere. It is found that although the system properties vary, a true equilibrium is finally attained for all compositions. The most pronounced time dependence is shown in a region close to and above the CMC of a pure surfactant solution and for polymer concentrations at least equal to the critical overlap concentration. It is proposed that part of the explanation resides in the fact that in the solution preparation there appears intermediate states corresponding to high local polymer concentrations. Some quantitative aspects of the time dependence are also discussed.     

Aggregation numbers of SDS micelles formed on EHEC. A steady state fluorescence quenching study

The present investigation proves that in the interaction between an uncharged polymer and a negatively charged amphiphilic ion (surfactant) clusters are actually formed and it provides data for the cluster concentration and the cluster size and their variation with composition. The polymer bound cluster size increases after a certain critical surfactant concentration and passes through a maximum. This maximum cluster size decreases with decreasing polymer concentration and attains a limiting value at infinite dilution. For the highest polymer concentration the cluster size is close to the size of normal surfactant micelles. The cluster concentration was determined by a fluorescence quenching technique and the amount surfactant adsorbed to the polymer by dialysis equilibrium measurements. Combining these independent sets of data permits the cluster aggregation number to be unambiguously determined. Solubilization experiments indicate the possibility to regulate the amount solubilized by varying the polymer concentration. The molecular properties of the system are sensitively monitored by the variation in two vibronic peaks in the pyrene fluorescence emission spectrum which defines a hydrophobic index. Very good agreement is found between all three experimental methods. Finally, the model suggested is analyzed in terms of coil size and cluster-cluster distance. Depending upon the degree of adsorption saturation and the density of polymer segments in solution the interaction may switch from being intramolecular to becoming intermolecular.     

Photon energy dependence of fragmentation of small argon clusters

Photofragmentation of small argon clusters with size below ten atoms is reported. In this size range significant modifications from the electronic properties and geometry take place. When tuning the photon energy through the argon 2p edge, the fragmentation pattern is changed. Specifically, cation dimer production is enhanced at the 2p(32)-->4s resonance, while above the 2p edge almost complete atomization is observed. In both cases, the widths of the peaks in the mass spectra indicate that a large amount of kinetic energy is imparted to the fragment due to the formation of multiply charged clusters. A model based on "Coulomb explosion"-charge separation, simply resulting in a complete atomization of the cluster with no dependence on the photon energy-is insufficient to explain the observed photofragmentation of small clusters.     

14 MeV neutron cross-sections on Mg,Cl and Sr

Cross-section values for 14.7 MeV neutrons have been measured for the following reactions: $$\begin{gathered} ^{24} Mg(n,p)^{24} Na - (187 \pm 7)mb;^{25} Mg(n,p)^{25} Na - (74 \pm 9)mb; \hfill \\ ^{26} Mg(n,\alpha )^{23} Ne - (55 \pm 6)mb;^{35} Cl(n,p)^{37} S - (22 \pm 3)mb; \hfill \\ ^{35} Cl(n,2n)^{34m} Cl - (9.3 \pm 1.5)mb;^{86} Sr(n,p)^{86m} Rb - (14 \pm 2)mb; \hfill \\ ^{88} Sr(n,p)^{88} Rb - (19 \pm 3)mb;^{86} Sr(n,2n)^{85m} Sr - (244 \pm 32)mb; \hfill \\ ^{88} Sr(n,2n)^{87m} Sr - (289 \pm 33)mb. \hfill \\ \end{gathered}$$ An analysis of available cross-section data for these reactions has been performed and preferred mean values for each reaction are given.     

Studies on dodecyl betainate in combination with its degradation products or with phosphatidyl choline-phase behavior and hemolytic activity

Surface active betaine esters contain a hydrolysable bond and give naturally occurring products (fatty alcohol and the amino acid betaine) on degradation. They are therefore interesting candidates for use as cationic surfactants in pharmaceutical applications. In this work the phase behavior of two systems of relevance for the utilization of dodecyl betainate as a pharmaceutical excipient is studied, namely dodecyl betainate/dodecanol/betaine hydrochloride/D2O and dodecyl betainate/phosphatidyl choline (PC)/ethanol/D2O. The techniques used for phase characterisation were 2H NMR measured on the solvent, small angle X-ray spectroscopy and optical microscopy. Dilute dodecyl betainate/PC dispersions were characterized using laser diffraction. It is shown that introduction of relatively small amounts of the hydrolysis products of dodecyl betainate, i.e., dodecanol and betaine (used in the form of betaine hydrochloride), has a strong effect on the phase behavior of the binary dodecyl betainate/D2O system. The degradation products change the average curvature of the surfactant film so that, instead of a hexagonal phase at concentrations above the micellar phase, a probably defective, lamellar phase seems to form. The dodecyl betainate/PC/ethanol/D2O system shows a large region of a highly swelling lamellar phase. Dispersions of dodecyl betainate/PC/ethanol in water can be prepared with low energy input; i.e., the preconcentrate can be regarded as a self-dispersing solution. Introduction of dodecyl betainate and its degradation products does not impair the ability of PC to form vesicles. Experiments for evaluating the toxicity of surface active betaine esters to erythrocytes were also performed. There are indications that the hemolytic activity of dodecyl betainate is lower than that of the stable surfactant tetradecyltrimethylammonium chloride, which has similar critical micelle concentration. A combination of dodecyl betainate and PC gives very low hemolytic activity.     

Hydrolyzable nonionic surfactants: stability and physicochemical properties of surfactants containing carbonate, ester, and amide bonds

A linear and a branched nonionic cleavable surfactants containing a carbonate bond have been prepared from tetra(ethylene glycol) and an alkylchloroformate. The stability of these carbonate surfactants was determined by investigating their hydrolysis and biodegradability characteristics. The hydrolysis was catalyzed by alkali or enzymes (esterase from porcine liver and lipases from Mucor miehei and Candida antarctica B) and was monitored using 1H NMR. It was found that the stability toward alkali was higher for a carbonate surfactant than for a corresponding surfactant with an ester as weak bond. Biodegradation tests resulted in more than 60% degradation after 28 days for both carbonate surfactants. Physicochemical properties, such as critical micelle concentration (CMC), cloud point, area per molecule, and surface tension at the CMC, were determined and compared to those obtained from similar surfactants containing ester, amide, or ether bonds. It was found that the carbonate linkage is hydrophobic and that the oxycarbonyl part of the carbonate group is equivalent, in a formal sense, to an extra methylene group in the alkyl chain of the surfactant.     

Kinetics of the Formation of Nano-Sized Platinum Particles in Water-in-Oil Microemulsions

The association between low-charge-density polyelectrolytes adsorbed onto negatively charged surfaces (mica and silica) and an anionic surfactant, sodium dodecyl sulfate (SDS), has been investigated using surface force measurements, ellipsometry, and XPS. All three techniques show that the polyelectrolyte desorbs when the SDS concentration is high enough. The XPS study indicates that desorption starts at a SDS concentration of ca. 0.1 unit of cmc (8x10(-4) M) and that the desorption proceeds progressively as the SDS concentration is increased. Surface force measurements show that for the polyelectrolyte studied here, having 1% of the segments charged, the desorption proceeds without any swelling of the adsorbed layer. This behavior differs from that observed when polyelectrolytes of greater charge density are used. Copyright 2001 Academic Press.     

Automated magnetic preparation of DNA templates for solid phase sequencing.

An integrated protocol for solid-phase DNA sequencing using a robotic work station is described involving magnetic separation of DNA and analysis of the sequencing product by electrophoresis with automated detection of the fluorescently labeled fragments. The method, which is based on magnetic beads in combination with streptavidin-biotin technology, can be used for sequencing both genomic and plasmid DNA. The DNA template is obtained by the polymerase chain reaction (PCR). Protocols to prepare five and ten immobilized samples is described, giving 10 and 20 single-stranded templates, respectively. The magnetic purification steps are performed in a microtiter plate and this allows for an integrated scheme involving a subsequent procedure for automated primer annealing and sequencing reactions. Here, the procedure is examplified by direct genomic sequencing of DNA in blood sample from a human immunodeficiency virus (HIV)-infected patient and a cloned human antibody DNA fragment using fluorescently labeled sequencing primers.