An intercomparison of sampling techniques for measurements of radiocaesium in upland pasture and soil

An intercomparison of sampling procedures used by five laboratories for the determination of radiocaesium in vegetation and peaty soil was carried out at two locations in Cumbria. The multiple sampling has given information on the homogeneity of the parameters studied at each location. The parameters comprise soil bulk densities, total deposition of¹³⁷Cs, deposition of¹³⁷Cs in three soil layers, biomass densities, concentrations of¹³⁷Cs in pasture, and activity ratios (¹³⁴Cs/¹³⁷Cs) in soil and vegetation. The determination of total deposition of¹³⁷Cs gave no indication of differences between the laboratories. The results from the soil profiles do indicate significant differences between laboratories. One laboratory using a coring technique observed difficulties during sampling due to compression of the soil. The coring technique should thus be avoided or applied with extreme care for the sampling of depth profiles in peaty soil. The results from the sampling of pasture show no indication of differences between the laboratories. For the parameters studied the observed variabilities across soil depths and locations range from 10% to 81% in terms of relative standard deviations. A comparison across all results at the two locations indicate a 50% higher field variability at one of the sites relative to the other.     

Synthesis and burst strength of water‐swollen immunoisolatory tubules

A series of amphiphilic hydrogel tubules have been prepared by copolymerizing/crosslinking hydrophilic poly(dimethylacrylamide) segments with hydrophobic di‐, tri‐, and octamethacrylate‐telechelic polyisobutylene crosslinkers, and their elastic modulus and burst strength in the water‐swollen state were investigated. Because the burst characteristics of hydrogels have not yet been quantitatively investigated, equipment was designed and built to generate fundamental insight into the burst properties of thin‐walled (200–250 μm) narrow lumen (2–3 mm i.d.) water‐swollen tubules. The theory developed to describe quantitatively the inflation behavior of thin‐walled rubber tubules was adapted to treat our experimental observations. Changes in the burst strength, elastic modulus, and expansion during the inflation of hydrogel tubules were interpreted in terms of the molecular weight of the hydrophilic segments between crosslinking sites (M_{c,hydrophilic}), which in turn was calculated according to the rubber elasticity theory. According to these investigations, the burst strength of our water‐swollen amphiphilic tubules is in the 0.2–0.5 MPa range, which is sufficient for implantation and immunoisolatory applications. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2075–2084, 2002     

Isolation of ammonium-N as 1-sulfonato-iso-indole for measurement of delta15N

The conversion of ammonium (NH(4) (+)) to 1-sulfonato-iso-indole has been examined as a method for natural abundance measurement of delta(15)N of NH(4) (+). The reaction is complete within 2 h and is based on the derivatisation of NH(4) (+) by o-phthaldialdehyde and sodium sulfite at a high pH, 11.2. The product is readily concentrated from dilute solutions by reverse-phase solid-phase extraction (SPE). The method is compound-specific despite partial derivatisation of potentially interfering amino acids, as their derivatives are not extracted by SPE. delta(15)N values of NH(4) (+) in KCL soil extracts can be measured within 48 h by automated continuous-flow IRMS with a precision of 0.23 per thousand (1 SD). Parallel measurements of NH(4) (+) standards of known delta(15)N are made to allow correction for the isotopic dilution by non-sample NH(4) (+). The practicality of this method is demonstrated by measuring the changes in NH(4) (+) concentration and delta(15)N following the addition of urea as a nitrogen source to inorganic N-depleted soil.     

Reaction of carbonyl fluoride with fluorine in the presence of various fluorides as catalysts

The fluorides KF, RbF and CsF have been known to serve as catalysts for the reaction CF₂O + F₂→ CF₃OF. The list of catalysts for this process has now been enlarged to include NaF, MgF₂, CaF₂, SrF₂, BaF₂ and LaF₃. Lithium fluoride and thorium fluoride also give CF₃OF but are less active. Perhaps the substances CsF·HF, KAgF₄ and NiF₂ should be included in this list. Silver fluoride, usually as a mixture of AgF₂ with AgF, has been known to catalyze the reaction of CF₂O with F₂ to give both CF₃OF and CF₃OOCF₃. The proportion of the latter in the mixture of products increases with decreasing temperature. At 25°, the reaction is slow and the yield of CF₃OOCF₃ is very high. It has now been shown that TIF₃ behaves like silver fluoride. It has also been shown that many other fluorides of metals give higher yields of CF₃OOCF₃ than of CF₃OF but require higher temperatures than AgF₂ (100-ca. 150°) to be effective. Various possible mechanisms for these catalytic processes are discussed.     

(Z)-3-p-tolylsulfinylacrylonitrile as a chiral dienophile: diels-alder reactions with furan and acyclic dienes

The behavior of (Z)-3-p-tolylsulfinylacrylonitrile (1) as a chiral dienophile has been evaluated from its reactions with furan and acyclic dienes. Electrostatic interactions of the cyano group with the sulfinyl one restrict the conformational mobility around the C-S bond, thus controlling the pi-facial selectivity, which is almost complete in all cases, the approach of the diene from the less-hindered face of the dienophile (that bearing the lone electron pair) in the predominant rotamer being the favored one. The regioselectivity is also completely controlled by the cyano group. Additionally, the reactivity of compound 1 as well as its endo-selectivity are both higher than those observed for the corresponding (Z)-3-sulfinylacrylates, thus proving the potential of sulfinylnitriles as chiral dienophiles.     

Stereoselective enolizations mediated by magnesium and calcium bisamides: contrasting aggregation behavior in solution and in the solid state

The reactions of magnesium and calcium bis(hexamethyldisilazide) with propiophenone have been studied with a view to determine the utility of these bases in the stereoselective enolization of ketones and to uncover the nature of the metal enolate intermediates produced. Both base systems are highly Z-selective when the reactions are conducted in the presence of polar solvents. However, in situ monitoring of the magnesium system in arene solution revealed a preference for E-enolate formation, which was confirmed by silyl enol ether trapping studies. Solution NMR studies of the magnesium system in toluene-d8 show the presence of a monomer-dimer equilibrium for the intermediate amidomagnesium enolates. This assignment is supported by the characterization of a disolvated amidomagnesium enolate dimer by crystallographic analysis. Comparative studies of the calcium system show distinctly different behavior. This is exemplified by the characterization of a novel solvent-separated ion pair complex and a monomeric amidocalcium enolate in the solid state. Solution NMR studies of the calcium system in pyridine-d5 reveal the co-existence of the heteroleptic amidocalcium enolate, the bisamide, the bisenolate and the ion pair complex.     

CLEARANCE TIMES OF PORPHYRIN DERIVATIVES FROM MICE AS MEASURED BY in vivo FLUORESCENCE SPECTROSCOPY

The clearance times of 17 different porphyrin derivatives from SKH:HR-1 mice have been measured using the technique of in vivo fluorescence spectroscopy. This technique monitors the in vivo porphyrin fluorescence observed from the external skin surface. Most hydrophilic porphyrin derivatives show relatively short clearance times, in the order of 2.5-6 h. The dicarboxylic acid porphyrins, proto-, hydroxyethylvinyldeutero- and hematoporphyrin IX have clearance times of 7.8, 12.2 and 14.7 h respectively. The mixture hematoporphyrin derivative has an intermediate clearance time of 12.6 h. N-methylated porphyrins show clearance times in the vicinity of 15-22 h. Monoaspartyl chlorin e6 shows the longest clearance time of all porphyrin derivatives measured (30.3 h).     

Vinylation and polymerization with trivinylaluminum. I. Vinylation of organic halides as a model for termination in cationic polymerization leading to vinyl end groups

An improved synthesis of trivinylaluminum (V₃Al) is described. The proton magnetic resonance (PMR) spectrum of V₃Al was recorded and analyzed. A new vinylation method involving the use of V₃Al as the vinylating agent has been developed, and the vinylation of organic halides by V₃Al was studied at ?30, ?50 and ?70°C. Primary alkyl chlorides, such as methyl and methylene chloride, do not react with V₃Al and were used as solvents. Secondary chlorides such as 2-chloropropane also do not react. t-Butyl chloride gives rise to t-butylethylene (70–98%), depending on reaction conditions, and the allylic chlorides, 3-chloro-1-butene, and 3-chloro-3-methyl-1-butene, yield the expected vinylated products and their isomers (～90%). Allyl and benzyl chloride do not react under the conditions tried. The reaction between V₃Al and the ditertiary dichloride 2,6-dichloro-2,6-dimethylheptane yields several isomeric C₁₃H₂₄ and C₁₁H₂₀ hydrocarbons; however, surprisingly, C₉H₁₆ does not form. The C₁₃ hydrocarbons arise by divinylation at the termini of the dichloride, while the C₁₁ hydrocarbons are formed by vinylation at one and proton elimination at the other terminus of the dichloride. The presence of unsaturated C₁₃H₂₄ and C₁₁H₂₀ isomers is most likely due to proton induced isomerization. These results are explained by a proximity effect involving vinylation at one end of the dichloride by V₃Al followed by rapid reaction of the second chlorine (mostly) by V₂AlCl generated in situ during the first vinylation in the proximity of the chloride. At the other chlorine terminus V₂AlCl causes either a second vinylation (leading to C₁₃ hydrocarbons) or a proton elimination (leading to C₁₁ hydrocarbons). The absence of C₉H₁₆ among the reaction products indicates that V₃Al exclusively effects vinylation. The RCl + V₃Al ← RV + V₂AlCl reaction may be regarded as a model for initiation followed by immediate termination in cationic olefin polymerization, a process leading to vinyl-ended polymers.     

Determination of phosphorus in polymers by INAA

An INAA technique employing beta spectrometry was developed for the determination of phosphorus in polymers. The (n,γ) reaction on phosphorus produces³²P, half-life 14.3 days, a pure beta emitter with end-point energy 1.71 MeV. Polymer samples in the form of powders, films and pellets are irradiated and then counted with a plastic scintillator. The beta spectrum is corrected for interferences (especially Sb, Zn and Br which are quantified by gamma spectrometry) and for energy loss in the thick sample. Samples must also be analyzed for S and Cl which cause nuclear interferences. With an irradiation time of 4 hours at a neutron flux of 5·10¹¹ n·cm^{−2 s −1}, decay time 10 days and counting time 10 minutes, the sensitivity is 520 counts/μg phosphorus and the detection limit is typically 2μg/g.