Interaction of Np(v) with borate in alkaline, dilute-to-concentrated, NaCl and MgCl2 solutions.

The interaction of Np(v) with borate was investigated in 0.1-5.0 M NaCl and 0.25-4.5 M MgCl2 solutions with 7.2 ≤ pHm ≤ 10.0 (pHm = -log[H+]) and 0.004 M ≤ [B]tot ≤ 0.16 M. Experiments were performed under an Ar-atmosphere at T = (22 ± 2) °C using a combination of under- and oversaturation solubility experiments, NIR spectroscopy, and extensive solid phase characterization. A bathochromic shift (≈5 nm) in the Np(v) band at λ = 980 nm indicates the formation of weak Np(v)-borate complexes under mildly alkaline pHm-conditions. The identification of an isosbestic point supports the formation of a single Np(v)-borate species in dilute MgCl2 systems, whereas a more complex aqueous speciation (eventually involving the formation of several Np(v)-borate species) is observed in concentrated MgCl2 solutions. The solubility of freshly prepared NpO2OH(am) remained largely unaltered in NaCl and MgCl2 solutions with [B]tot = 0.04 M within the timeframe of this study (t ≤ 300 days). At [B]tot = 0.16 M, a kinetically hindered but very significant drop in the solubility of Np(v) (3-4 log10-units, compared to borate-free systems) was observed in NaCl and dilute MgCl2 solutions with pHm ≤ 9. The drop in the solubility was accompanied by a clear change in the colour of the solid phase (from green to white-greyish). XRD and TEM analyses showed that the amorphous NpO2OH(am) "starting material" transformed into crystalline solid phases with similar XRD patterns in NaCl and MgCl2 systems. XPS, SEM-EDS and EXAFS further indicated that borate and Na/Mg participate stoichiometrically in the formation of such solid phases. Additional undersaturation solubility experiments using the newly formed Na-Np(v)-borate(cr) and Mg-Np(v)-borate(cr) compounds further confirmed the low solubility ([Np(v)]aq ≈ 10-6-10-7 M) of such solid phases in mildly alkaline pHm-conditions. The formation of these solid phases represents a previously unreported retention mechanism for the highly mobile Np(v) under boundary conditions (pHm, [B]tot, ionic strength) of relevance to certain repository concepts for nuclear waste disposal.

The surface chemistry of sapphire-c: A literature review and a study on various factors influencing its IEP.

A wide range of isoelectric points (IEPs) has been reported in the literature for sapphire-c (α-alumina), also referred to as basal plane, (001) or (0001), single crystals. Interestingly, the available data suggest that the variation of IEPs is comparable to the range of IEPs encountered for particles, although single crystals should be much better defined in terms of surface structure. One explanation for the range of IEPs might be the obvious danger of contaminating the small surface areas of single crystal samples while exposing them to comparatively large solution reservoirs. Literature suggests that factors like origin of the sample, sample treatment or the method of investigation all have an influence on the surfaces and it is difficult to clearly separate the respective, individual effects. In the present study, we investigate cause-effect relationships to better understand the individual effects. The reference IEP of our samples is between 4 and 4.5. High temperature treatment tends to decrease the IEP of sapphire-c as does UV treatment. Increasing the initial miscut (i.e. the divergence from the expected orientation of the crystal) tends to increase the IEP as does plasma cleaning, which can be understood assuming that the surfaces have become less hydrophobic due to the presence of more and/or larger steps with increasing miscut or due to amorphisation of the surface caused by plasma cleaning. Pre-treatment at very high pH caused an increase in the IEP. Surface treatments that led to IEPs different from the stable value of reference samples typically resulted in surfaces that were strongly affected by subsequent exposure to water. The streaming potential data appear to relax to the reference sample behavior after a period of time of water exposure. Combination of the zeta-potential measurements with AFM investigations support the idea that atomically smooth surfaces exhibit lower IEPs, while rougher surfaces (roughness on the order of nanometers) result in higher IEPs compared to reference samples. Two supplementary investigations resulted in either surprising or ambiguous results. On very rough surfaces (roughness on the order of micrometers) the IEP lowered compared to the reference sample with nanometer-scale roughness and transient behavior of the rough surfaces was observed. Furthermore, differences in the IEP as obtained from streaming potential and static colloid adhesion measurements may suggest that hydrodynamics play a role in streaming potential experiments. We finally relate surface diffraction data from previous studies to possible interpretations of our electrokinetic data to corroborate the presence of a water film that can explain the low IEP. Calculations show that the surface diffraction data are in line with the presence of a water film, however, they do not allow to unambiguously resolve critical features of this film which might explain the observed surface chemical characteristics like the dangling OH-bond reported in sum frequency generation studies. A broad literature review on properties of related surfaces shows that the presence of such water films could in many cases affect the interfacial properties. Persistence or not of the water film can be crucial. The presence of the water film can in principle affect important processes like ice-nucleation, wetting behavior, electric charging, etc.

Recurrent amebic liver abscesses over a 16-year period: a case report.

BACKGROUND: Amebic liver abscess is a rare disease in high-income countries. Recurrence of amebic liver abscess is even rarer with only a few previous reports. Here we present a patient who developed three subsequent amebic liver abscesses over a sixteen-year period. CASE PRESENTATION: A Caucasian male developed recurrent amebic liver abscesses, when aged 23, 27 and 39 years. Only on the first occasion did this coincide with a recent visit to the tropics. The patient received adequate treatment during each episode. Possible explanations are persistent asymptomatic carrier state, cysts passage in his family, re-infection or chance. CONCLUSION: We describe the unusual case of a healthy male who developed recurrent amebic liver abscesses over a long period despite adequate treatment. Possible pathophysiological explanations are explored.

Fusobacterium necrophorum, an emerging pathogen of otogenic and paranasal infections?

Fusobacterium necrophorum is a rare causative agent of otitis and sinusitis. Most commonly known is the classic Lemièrre's syndrome of postanginal sepsis with suppurative thrombophlebitis of the jugular vein. We report five patients diagnosed recently with a complicated infection with F. necrophorum originating from otitis or sinusitis. Two patients recovered completely, one patient died due to complications of the infection, one patient retained a slight hemiparesis and one patient had permanent hearing loss. Diagnosis and management are discussed. A possible factor in the emergence of F. necrophorum is proposed.

Structure of selenium incorporated in pyrite and mackinawite as determined by XAFS analyses.

Selenium has a toxic potential leading to diseases by ingestion and a radiotoxic potential as (79)Se radionuclide if discharged from a high-level nuclear waste repository in deep geological formations into the biosphere. Selenium is often associated with sulfides, such as pyrite, the most important near-surface iron sulfide and constituent of host rocks and bentonite backfills considered for radioactive waste disposal. This study was aimed at investigating the incorporation of Se(2-) and Se(4+) into pyrite and mackinawite to determine the relevance of iron sulfides to Se retention and the type of structural bonding. The syntheses of pyrite and mackinawite occurred via direct precipitation in batches and also produced coatings on natural pyrite in mixed-flow reactor experiments (MFR) under anoxic conditions at Se concentrations in the solutions of up to 10(-3) mol/L. Mineralogical analyses by SEM and XRD reveal the formation of pyrite and mackinawite phases. The average Se(2-) uptake in pyrite in batch experiments amounts to 98.6%. In MFR syntheses, it reaches 99.5%, both suggesting a high potential for retention. XAFS results indicate a substitution of sulfur by selenide during instantaneous precipitation in highly supersaturated solutions only. In selenide-doted mackinawite S(2-) was substituted by Se(2-), resulting in a mackinawite-type compound. S(-) is substituted by Se(-) in selenide-doted pyrite, yielding a FeSSe compound as a slightly distorted pyrite structure. Under slighter supersaturated conditions, XAFS results indicate an incorporation of Se(2-) and Se(4+) predominantly as Se(0). This study shows that a substitution of S by Se in iron sulfides is probable only for highly supersaturated solutions under acidic and anoxic conditions. Under closer equilibrium conditions, Se(0) is expected to be the most stable species.

Outpatient treatment in patients with acute pulmonary embolism: the Hestia Study.

BACKGROUND: Traditionally, patients with pulmonary embolism (PE) are initially treated in the hospital with low molecular weight heparin (LMWH). The results of a few small non-randomized studies suggest that, in selected patients with proven PE, outpatient treatment is potentially feasible and safe. OBJECTIVE: To evaluate the efficacy and safety of outpatient treatment according to predefined criteria in patients with acute PE. PATIENTS AND METHODS: A prospective cohort study of patients with objectively proven acute PE was conducted in 12 hospitals in The Netherlands between 2008 and 2010. Patients with acute PE were triaged with the predefined criteria for eligibility for outpatient treatment, with LMWH (nadroparin) followed by vitamin K antagonists. All patients eligible for outpatient treatment were sent home either immediately or within 24 h after PE was objectively diagnosed. Outpatient treatment was evaluated with respect to recurrent venous thromboembolism (VTE), including PE or deep vein thrombosis (DVT), major hemorrhage and total mortality during 3 months of follow-up. RESULTS: Of 297 included patients, who all completed the follow-up, six (2.0%; 95% confidence interval [CI] 0.8-4.3) had recurrent VTE (five PE [1.7%] and one DVT [0.3%]). Three patients (1.0%, 95% CI 0.2-2.9) died during the 3 months of follow-up, none of fatal PE. Two patients had a major bleeding event, one of which was fatal intracranial bleeding (0.7%, 95% CI 0.08-2.4). CONCLUSION: Patients with PE selected for outpatient treatment with predefined criteria can be treated with anticoagulants on an outpatient basis. (Dutch Trial Register No 1319; http://www.trialregister.nl/trialreg/index.asp).

Characterization of acid-base properties of two gibbsite samples in the context of literature results.

Two different gibbsites, one commercial and one synthesized according to a frequently applied recipe, were studied in an interlaboratory attempt to gain insight into the origin of widely differing reports on gibbsite acid-base surface properties. In addition to a thorough characterization of the two solids, several methods relevant to the interfacial charging were applied to the two samples: potentiometric titrations to obtain the "apparent" proton related surface charge density, zeta-potential measurements characterizing the potential at the plane of shear, and Attenuated Total Reflection Infrared Spectroscopy (ATR-IR) to obtain information on the variation of counter-ion adsorption with pH (using nitrate as a probe). Values of the IEP at 9-10 and 11.2-11.3 were found for the commercial and synthesized sample, respectively. The experimental observations revealed huge differences in the charging behavior between the two samples. Such differences also appeared in the titration kinetics. A detailed literature review revealed similar disparity with no apparent systematic trend. While previously the waiting time between additions had been advocated to explain such differences among synthesized samples, our results do not support such a conclusion. Instead, we find that the amount of titrant added in each aliquot appears to have a significant influence on the titration curves. While we can relate a number of observations to others, a number of open questions and contradictions remain. We suggest various processes, which can explain the observed behavior.

An attempt to explain bimodal behaviour of the sapphire c-plane electrolyte interface.

A tentative picture for the charging of the sapphire basal plane in dilute electrolyte solutions allows reconciliation of the available experimental observations within a dual charging model. It includes the MUltiSIte Complexation (MUSIC) model and auto-protolysis of interfacial water. The semi-empirical MUSIC model predicts protonation and deprotonation constants of individual surface functional groups based on crystal structure and bond-valence principles: on the ideal sapphire c-plane only doubly co-ordinated hydroxyl groups exist which cause quasi zero surface potential (defined as the potential in the plane of the surface hydroxyl groups) from pH 5 to 7 and rather weak charging beyond (compared to typical oxide behaviour). MUSIC predictions concur strikingly with recently published sum frequency data for the pH dependence of the so-called "ice-like" water band (interfacial water) and contact angle titrations. Zeta potential as well as second harmonic generation data reveal a sharp IEP of around 4 and a negative surface charge at the pristine point of zero charge predicted by the MUSIC model. New zeta-potential data corroborate (i) the low IEP and its insensitivity to salt concentration and (ii) the second harmonic results. We thus establish two groups of conflicting results arising from different techniques. A conventional model of the mineral electrolyte interface such as the MUSIC model is at odds with the negative zeta potentials in the pH range 5 to 7. Therefore an additional charging mechanism is invoked to explain all the observations. Enhanced auto-protolysis of interfacial water is the most probable candidate for this additional mechanism, in agreement with net water orientation observed with sum frequency generation and second harmonic generation. Our phenomenological explanation is further corroborated by the similarity of the zeta potential vs. pH curves of the c-plane with those of hydrophobic surfaces. Additional support comes from infrared spectroscopic data on thin water films on sapphire c-plane samples. Most stunningly, theoretical calculations on basal planes of this kind suggest a 2D water bilayer that makes such surfaces hydrophobic towards further adsorption of water. The proposed dual charging mode approach comprises the MUSIC model for protonation/deprotonation of the surface aluminols affecting the surface potential and the currently advocated enhanced auto-protolysis picture for hydrophobic surfaces controlling the zeta-potential and can explain the available information in a qualitative way. The respective contributions from the two components of this dual charging mechanism may be different for different single crystal cuts of alumina. Thus interplay between protonation/deprotonation of surface functional groups and auto-protolysis of interfacial water will cause the observed zeta potentials and isoelectric points. Repercussions of one mechanism on the other will result in the most favourable interfacial water structure, which can be followed by non-linear optic techniques like sum frequency generation.

Highly specific responses to amine odorants of individual olfactory receptor neurons in situ.

The main olfactory system of larval Xenopus laevis is made up of at least two subsystems consisting of subsets of olfactory receptor neurons (ORNs) with different transduction mechanisms. One ORN subset lacks the canonical cAMP transduction pathway and responds to amino acid odorants. The second subset has the cAMP transduction pathway but as yet suitable odorants are unknown. Here we report the identification of amines as proper olfactory stimuli for larval X. laevis using functional Ca(2+) imaging and slice preparations of the olfactory system. The response profiles of individual ORNs to a number of amines were extremely complex and mostly highly specific. The great majority of amine-sensitive ORNs responded also to forskolin, an activator of the olfactory cAMP transduction pathway. Most amine-induced responses could be attenuated by the cyclic nucleotide-gated channel inhibitor LY83583. This confirms that most amine-responsive olfactory receptors (ORs) are coupled to the cAMP-dependent transduction pathway. Furthermore, we show that trace amine-associated receptors (TAARs), which have been shown to act as specific ORs for amines in mammals, are expressed in the olfactory organ of X. laevis. The TAARs expressed in Xenopus cannot, however, explain the complex responses of individual ORNs to amines because there are too few of them. This indicates that, in addition to TAARs, there must be other receptor families involved in the detection of amines.

Autologous osteoblasts enhance osseointegration of porous titanium implants.

The goal of this study was to assess the osseointegration of porous titanium implants by means of coating with autologous osteoblasts. Titanium implants (8 x 5 x 4 mm) having drill channels with diameters of 400, 500, and 600 microm were coated with autologous osteoblasts obtained from spongiosa chips. The implants were inserted into the distal femora of 17 adult Chinchilla Bastard rabbits (group I). Uncoated implants were inserted as controls in the contralateral femur (group II). The animals were sacrificed after 5, 11, and 42 days. Intravital fluorochrome labeling and microradiography were used for the assessment of bone ingrowth into the titanium channels. In both groups, no bone tissue was formed in the channels up to day 5. On day 11, group I exhibited significantly more (p<0.05) bone tissue (19.8+/-14.0% vs. 5.8+/-9.1%) with greater bone-implant contact (13.3+/-15.1% vs. 5.7+/-5.3%, p<0.05) at the channel mouths than group II. Bone tissue was formed mainly between day 15 and 30 in group I, in group II between day 25 and 40. Six weeks after implantation, bone tissue filled on an average 68.8+/-15.1% of the mouths of the drill channels in implants in group I, the filling for group II was 49.8+/-18.1% (p<0.05). The average bone-implant contact at the channel mouths after six weeks was 56.5+/-13.5% in group I, 40.2+/-21.9% in group II (p<0.05). 600-microm channels showed at this time point the best osseous integration (p<0.05). Coating with autologous osteoblasts accelerates and enhances the osseointegration of titanium implants and could be a successful biotechnology for future clinical applications.

Mediator function of the human Rad51B-Rad51C complex in Rad51/RPA-catalyzed DNA strand exchange.

Five Rad51-like proteins, referred to as Rad51 paralogs, have been described in vertebrates. We show that two of them, Rad51B and Rad51C, are associated in a stable complex. Rad51B-Rad51C complex has ssDNA binding and ssDNA-stimulated ATPase activities. We also examined the functional interaction of Rad51B-Rad51C with Rad51 and RPA. Even though RPA enhances Rad51-catalyzed DNA joint formation via removal of secondary structure in the ssDNA substrate, it can also compete with Rad51 for binding to the substrate, leading to suppressed reaction efficiency. The competition by RPA for substrate binding can be partially alleviated by Rad51B-Rad51C. This recombination mediator function of Rad51B-Rad51C is likely required for the assembly of the Rad51-ssDNA nucleoprotein filament in vivo.

Local photolysis using tapered quartz fibres.

We describe a versatile, low-cost photolysis system in which sub-millisecond flashes generated by a xenon flash lamp are conveyed through a silica fibre directly onto a cell. The fibre, which is tapered to a sub-micrometre diameter and sputtered with chromium and aluminium, illuminates an area of about 1 microm2. Site and timing of photolysis can be chosen independently from other experimental parameters. As an application example we show the spatially heterogeneous distribution of Ca2+-dependent Cl- channels in olfactory receptor neurons.

The role of heat shock proteins and their receptors in the activation of the immune system.

Heat shock proteins (HSPs) have been described as potent tumor vaccines in animal models and are currently studied in clinical trials. The underlying immune response relies on immunogenic peptides that the HSPs have acquired intracellularly by interfering with the classical antigen processing pathways. There have been numerous reports shedding light on how HSPs are able to gain this function and a number of important requirements for HSP-mediated specific immunity have been described: first, the ability of HSPs to bind immunogenic peptides. Second, the acquisition of HSPs by specialized antigen presenting cells with efficient antigen processing pathways capable of inducing cellular immune responses. Third, the existence of specific receptors on the surfaces of antigen presenting cells, allowing efficient and rapid uptake of HSP-peptide complexes from the extracellular fluid. And fourth, the ability of heat shock proteins to activate antigen presenting cells, enabling the latter to prime cytotoxic T cell responses against the peptides associated to HSPs.

Homologous recombinational repair of DNA ensures mammalian chromosome stability.

The process of homologous recombinational repair (HRR) is a major DNA repair pathway that acts on double-strand breaks and interstrand crosslinks, and probably to a lesser extent on other kinds of DNA damage. HRR provides a mechanism for the error-free removal of damage present in DNA that has replicated (S and G2 phases). Thus, HRR acts in a critical way, in coordination with the S and G2 checkpoint machinery, to eliminate chromosomal breaks before the cell division occurs. Many of the human HRR genes, including five Rad51 paralogs, have been identified, and knockout mutants for most of these genes are available in chicken DT40 cells. In the mouse, most of the knockout mutations cause embryonic lethality. The Brca1 and Brca2 breast cancer susceptibility genes appear to be intimately involved in HRR, but the mechanistic basis is unknown. Biochemical studies with purified proteins and cell extracts, combined with cytological studies of nuclear foci, have begun to establish an outline of the steps in mammalian HRR. This pathway is subject to complex regulatory controls from the checkpoint machinery and other processes, and there is increasing evidence that loss of HRR gene function can contribute to tumor development. This review article is meant to be an update of our previous review [Biochimie 81 (1999) 87].

Slice culture of the olfactory bulb of Xenopus laevis tadpoles.

We report on the development of a slice culture of amphibian brain tissue. In particular, we cultured slices from Xenopus laevis tadpoles that contain the olfactory mucosae, the olfactory nerves, the olfactory bulb and the telencephalon. During 6 days in roller tubes the slices flattened, starting from 250 microm and decreasing to approximately 40 microm, corresponding to about three cell layers. Dendritic processes could be followed over distances as long as 200 microm. Neurons in the cultured slice could be recorded using the patch clamp technique and simultaneously imaged using an inverted laser scanning microscope. We characterized the main neuron types of the olfactory bulb, i.e. mitral cells and granule cells, by correlating their typical morphological features in the acute slice with the electrophysiological properties in both the acute slice and slice culture. This correlation allowed unambiguous identification of mitral cells and granule cells in the slice culture.

Noradrenergic modulation of calcium currents and synaptic transmission in the olfactory bulb of Xenopus laevis tadpoles.

Norepinephrine (NE) has various modulatory roles in both the peripheral and the central nervous systems. Here we investigate the function of the locus coeruleus efferent fibres in the olfactory bulb of Xenopus laevis tadpoles. In order to distinguish unambiguously between mitral cells and granule cells of the main olfactory bulb and the accessory olfactory bulb, we used a slice preparation. The two neuron types were distinguished on the basis of their location in the slice, their typical branching pattern and by electrophysiological criteria. At NE concentrations lower than 5 microM there was only one effect of NE upon voltage-gated conductances; NE blocked a high-voltage-activated Ca(2+)-current in mitral cells of both the main and the accessory olfactory bulbs. No such effect was observed in granule cells. The effect of NE upon mitral cell Ca(2+)-currents was mimicked by the alpha(2)-receptor agonists clonidine and alpha-methyl-NE. As a second effect, NE or clonidine blocked spontaneous synaptic activity in granule cells of both the main and the accessory olfactory bulbs. NE or clonidine also blocked the spontaneous synaptic activity in mitral cells of either olfactory bulb. The amplitude of glutamate-induced currents in granule cells was modulated neither by clonidine nor by alpha-methyl-NE. Taken together, the main effect of the noradrenergic, presynaptic, alpha(2)-receptor-mediated block of Ca(2)+-currents in mitral cells appeared to be a wide-spread disinhibition of mitral cells in the accessory olfactory bulb as well as in the main olfactory bulb.

Chromosome instability and defective recombinational repair in knockout mutants of the five Rad51 paralogs.

The Rad51 protein, a eukaryotic homologue of Escherichia coli RecA, plays a central role in both mitotic and meiotic homologous DNA recombination (HR) in Saccharomyces cerevisiae and is essential for the proliferation of vertebrate cells. Five vertebrate genes, RAD51B, -C, and -D and XRCC2 and -3, are implicated in HR on the basis of their sequence similarity to Rad51 (Rad51 paralogs). We generated mutants deficient in each of these proteins in the chicken B-lymphocyte DT40 cell line and report here the comparison of four new mutants and their complemented derivatives with our previously reported rad51b mutant. The Rad51 paralog mutations all impair HR, as measured by targeted integration and sister chromatid exchange. Remarkably, the mutant cell lines all exhibit very similar phenotypes: spontaneous chromosomal aberrations, high sensitivity to killing by cross-linking agents (mitomycin C and cisplatin), mild sensitivity to gamma rays, and significantly attenuated Rad51 focus formation during recombinational repair after exposure to gamma rays. Moreover, all mutants show partial correction of resistance to DNA damage by overexpression of human Rad51. We conclude that the Rad51 paralogs participate in repair as a functional unit that facilitates the action of Rad51 in HR.

Fluorescence correlation spectroscopy in small cytosolic compartments depends critically on the diffusion model used.

Fluorescence correlation spectroscopy (FCS) is a powerful technique for measuring low concentrations of fluorescent molecules and their diffusion constants. In the standard case, fluorescence fluctuations are measured in an open detection volume defined by the confocal optics. However, if FCS measurements are carried out in cellular processes that confine the detection volume, the standard FCS model leads to erroneous results. In this paper, we derive a modified FCS model that takes into account the confinement of the detection volume. Using this model, we have carried out the first FCS measurements in dendrites of cultured neurons. We further derive, for the case of confined diffusion, the limits within which the standard two- and three-dimensional diffusion models give reliable results.

Structure of the olfactory bulb in tadpoles of Xenopus laevis.

The structure of the olfactory bulb in tadpoles of Xenopus laevis (stages 54-56) was studied using axon tracing (with biocytin or low-weight dextran) and immunocytochemical techniques. Filling the olfactory nerve with biocytin made the nerve layer and the glomeruli visible. Dye injections into the glomerular layer labeled the lateral olfactory tract. Vice versa, dye injections into the lateral olfactory tract made mitral cells and their glomerular branching patterns visible. Anti-GABA antiserum stained periglomerular and granule cells, while the olfactory nerve and mitral cells were labeled by antiglutamate antiserum. We describe the layering, the numbers of cells and glomeruli, and their localization in both the main and the accessory olfactory bulb.