Determination of mercury in human serum and packed blood cells by neutron activation analysis

A method is described for the determination of mercury in human blood serum and packed blood cells employing neutron activation analysis. Great attention was devoted to the collection and manipulation of the samples. The accuracy and precision of the method were tested by analyzing biological reference materials and by comparing the concentrations measured in a number of serum samples to those obtained by another, independent technique (cold vapor atomic absorption spectrometry) in the same samples. The article reports the levels measured in blood serum and packed blood cells samples from 15 adult volunteers, as well as the figures determined in a “second-generation” biological reference material (freeze-dried human serum), prepared and conditioned at the University of Ghent.     

Partitioning of (+-)-5,6-dihydro-6-phenyl-2-n-alkyl-imidazo- [2,1-b]thiazoles into large unilamellar liposomes: a steady-state fluorescence quenching study.

The interaction of the tetramisole derivative (+-)-5,6-dihydro-6-phenyl-imidazo[2,1-b]thiazole and a number of its 2-n-alkyl homologues (-ethyl through -n-pentyl and -n-heptyl) with large unilamellar phosphatidylcholine/phosphatidylethanolamine/dipalmitoylphosphatidic acid (2:1:0.06, w/w) vesicles was studied by means of steady-state fluorescence quenching using 8-(2-anthryl)octanoic acid as membrane probe. Linear Stern-Volmer plots were obtained for each derivative, indicating dynamic quenching. The slopes of the plots decreased with increasing liposomal concentration. For four short-chain homologues (-H, -ethyl, -n-propyl and -n-butyl), the respective membrane partition coefficients Kp and bimolecular quenching rate constants kq were determined from the plots of the reciprocal of the apparent quenching rate constant (kappq)-1 against the lipid volume fraction alpha L of the liposomes. The partition coefficients increased with increasing chain-length of the tetramisoles. A linear relationship was found between the free energy of partitioning and the number of methylene units of the homologues (-delta G degrees per methylene group = 1.6 +/- 0.1 kJ mol-1). For the n-pentyl and n-heptyl derivatives, the fluorescence quenching technique did not allow one to determine their membrane partition coefficients. Analysis of the fluorescence intensity measurements with Scatchard plots gave further evidence for the partitioning nature of the tetramisole derivatives' association with the liposomal membranes.     

Century‐long apparent decrease in intrinsic water‐use efficiency with no evidence of progressive nutrient limitation in African tropical forests

Forests exhibit leaf‐ and ecosystem‐level responses to environmental changes. Specifically, rising carbon dioxide (CO₂) levels over the past century are expected to have increased the intrinsic water‐use efficiency (iWUE) of tropical trees while the ecosystem is gradually pushed into progressive nutrient limitation. Due to the long‐term character of these changes, however, observational datasets to validate both paradigms are limited in space and time. In this study, we used a unique herbarium record to go back nearly a century and show that despite the rise in CO₂ concentrations, iWUE has decreased in central African tropical trees in the Congo Basin. Although we find evidence that points to leaf‐level adaptation to increasing CO₂—that is, increasing photosynthesis‐related nutrients and decreasing maximum stomatal conductance, a decrease in leaf δ¹³C clearly indicates a decreasing iWUE over time. Additionally, the stoichiometric carbon to nitrogen and nitrogen to phosphorus ratios in the leaves show no sign of progressive nutrient limitation as they have remained constant since 1938, which suggests that nutrients have not increasingly limited productivity in this biome. Altogether, the data suggest that other environmental factors, such as increasing temperature, might have negatively affected net photosynthesis and consequently downregulated the iWUE. Results from this study reveal that the second largest tropical forest on Earth has responded differently to recent environmental changes than expected, highlighting the need for further on‐ground monitoring in the Congo Basin.     

Radioassay of UDP-glucuronyltransferase-catalysed formation of bilirubin monoglucuronides and bilirubin diglucuronide in liver microsomes.

A radioassay for specific determination of the rates of UDP-glucuronic acid-dependent conversion of bilirubin into the two isomeric (C-8, C-12) bilirubin monoglucuronides and bilirubin diglucuronide is described and illustrated by its application to rat liver microsomes. The method is based on measurement of the relative amounts of radiolabel in unesterified bilirubin and its mono- and di-esterified reaction products after incubation with [14C]bilirubin as substrate. This analysis is performed by the alkaline-methanolysis procedure, combined with one of two t.l.c. systems developed in order to enhance the sensitivity, accuracy and precision of the radioassay. Results for rates of total bilirubin glucuronide formation obtained with the new assay and the standard enzyme assay based on the ethyl anthranilate diazo-method were identical. However, the sensitivity of the latter technique is approx. 10-fold lower than that of the radioassay.     

Characterization of Cultures Enriched from Acidic Polycyclic Aromatic Hydrocarbon-Contaminated Soil for Growth on Pyrene at Low pH

Two polycyclic aromatic hydrocarbon (PAH)-contaminated soils of pH 2 were successfully used as inoculum to enrich cultures growing on phenanthrene and pyrene at different pHs, including pH 3. Selected pyrene-utilizing cultures obtained at pH 3, pH 5, and pH 7 were further characterized. All showed rapid [¹⁴C]pyrene mineralization at pH 3 and pH 5 and grew on pyrene at pH values ranging from 2 to 6. Eubacterial and mycobacterial 16S rRNA gene denaturing gradient gel electrophoresis fingerprinting and sequencing indicated that the cultures were dominated by a single bacterium closely related to Mycobacterium montefiorense, belonging to the slow-growing Mycobacterium sp. In contrast, a culture enriched on pyrene at pH 7 from a slightly alkaline soil sampled at the same site was dominated by Pseudomonas putida and a fast-growing Mycobacterium sp. The M. montefiorense-related species dominating the pyrene-utilizing cultures enriched from the acidic soils was also the dominant Mycobacterium species in the acidic soils. Our data indicate that a slow-growing Mycobacterium species is involved in PAH degradation in that culture and show that bacteria able to degrade high-molecular-weight PAHs at low pH are present in acidic PAH-contaminated soil.     

Liposomes as carriers of poorly water-soluble substrates: linear modelling of membrane systems with catalytic or binding sites of different facedness. Significance of experimental membrane partition coefficients and of kinetic and equilibrium parameters.

1. A multiphasic modelling approach to systems containing membrane-bound receptors or catalytic sites and a liposomal preparation as a substrate carrier is described. Kinetic expressions are derived for a single-substrate enzymic reaction operating at constant liposome concentration or at a fixed substrate/liposome concentration ratio. 2. The assumption that accumulation of exchangeable components into the phospholipid bilayers can be described by linear bulk-phase partition leads to simple relationships between the initial reaction rate and (a) two kinetic coefficients (V and K'm), (b) the partition coefficients of the solutes for the lipid compartments of the membrane (Pms) and liposomal preparations (P1s) and (c) the total concentrations of substrate, membrane lipid and liposomal lipid. K'm is called the effective Michaelis constant. 3. For correct estimation of the coefficients V, K', Pms and P1s extrapolation to zero lipid concentration is required. 4. The distinction is introduced between hydrophilic and hydrophobic aqueous-faced sites, lipid-faced sites and mixed sites, i.e. sites overlapping an aqueous and a lipid region. For hydrophilic aqueous-faced sites K'm is equal to the true Km and for the other types of site to Km/Ps. For lipid-faced and for mixed sites Ps corresponds to the membrane partition coefficient Pms. For binding of homologous compounds to a hydrophobic aqueous-faced binding pocket Ps is the incremental site partition coefficient Pbss, which takes into account the energetic contribution to the binding process due to the hydrophobic tail of the ligands. 5. K'm accounts for any effects due to the facedness and nature of the enzymic sites. The dependence of the systems on the size of the lipidic partition compartment(s) is expressed exclusively by a distribution function F.6. When enzyme assays are performed with a series of chemically different substrates containing the same catalytically sensitive group, independence of K'm from partition indicates a hydrophilic aqueous-faced binding site. For the low-molecular-mass members of the homologous series a linear increase in -log (K'm) with the logarithm of the partition coefficient will be observed with any of the other site types considered 7. Equilibrium relationships for binding of a ligand to a membrane-bound receptor are also derived. 8. The significance of experimental membrane partition coefficients is discussed.     

The 'physical prophet' and the powers of the imagination. Part II: a case-study on dowsing and the naturalisation of the moral, 1685-1710

In the first paper of this pair, I argued the importance of theories of the imagination in debates on divination [Vermeir, K. (2004). The 'physical prophet' and the powers of the imagination. Part I: A case-study on prophecy, vapours and the imagination (1685-1710). Studies in History and Philosophy of Science C, 35, 561-591]. In the present article, I will rely on these results in order to unearth the role of the imagination in a discussion on dowsing. References to the imagination were often implicit because of its negative associations, but I show in detail how the imagination was used to negotiate between the material and the spiritual, and between the natural, the supernatural and the moral. Natural philosophers, theologians and moralists all struggled for authority over divinatory phenomena. The debate evolved around the questions whether moral states could be naturalised and whether subtle material vapours could have moral qualities.