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In the search for a cure for metastatic bone cancer, 117mSn with its conversion electrons and low energy photons both of discrete energies shows little bone marrow toxicity, providing the opportunity to increase the administered dose. Selective accumulation in lesions would capitalise on this advantage. The 10-30 kDa fraction of the water-soluble polymer polyethyleneimine, functionalised with methyl phosphonate groups (PEI-MP) and labelled with 99mTc, has shown selective uptake into bone tumours. Furthermore using speciation calculations it was predicted that the Sn(II)-PEI-MP complex would remain intact in the blood plasma. Because of this positive indication animal experiments were carried out to test this prediction. This paper relates the labelling, biodistribution and pharmacokinetics of various fractions of 117mSn-(II) PEI-MP in the normal primate model, and points to promising therapeutic possibilities.

The valence stability of tin in its complexes with 1-hydroxyethylene-diphosphonate (HEDP) and with N,N′,N′-trimethylenephosphonate-polyethyleneimine (PEI-MP) was investigated. With particular interest in the possible interconversion between Sn2+ and Sn4+, the complexes were monitored with the aid of 31P NMR spectroscopy. The extent of complex formation with both ligands was evaluated for systems with tin in their respective oxidation states. The Sn2+-complexes underwent initial, but limited oxidation upon preparation, and beyond which were rather stable, irrespective of pH or time. Both Sn2+- and Sn4+-complexes were found to exist in solution without change. Oxidation of Sn2+ was achieved by addition of hydrogen-peroxide and was partially reversed by the addition of glutathione (GSH). The amount of H2O2 needed for complete oxidation of the Sn2+- into Sn4+-complexes was determined for both ligands, as well as the time taken for that oxidation.

The adsorption on hydroxyapatite of three conjugates of a bisphosphonate and a macrocycle having C1, C2, and C3 spacers and their terbium complexes was studied by the radiotracer method using 160Tb as the label. The radiotracer-containing complex of the conjugate with the C3 spacer was used as a probe for the determination of the adsorption parameters of other bisphosphonates that lack a DOTA unit. A physicochemical model describing the competitive adsorption was successfully applied in the fitting of the obtained data. The maximum adsorption capacity of bisphosphonates containing bulky substituents is determined mainly by their size. For bisphosphonates having no DOTA moiety, the maximum adsorption capacity is determined by the electrostatic repulsion between negatively charged bisphosphonate groups. Compounds with a hydroxy or amino group attached to the alpha-carbon atom show higher affinities. Macrocyclic compounds containing a short spacer between the different bisphosphonic acid groups and the macrocyclic unit exhibit high affinities, indicating a synergic effect of the bisphosphonic and the macrocyclic groups during adsorption. The competition method described uses a well-characterized complex and allows a simple evaluation of the adsorption behavior of bisphosphonates. The application of the macrocycle-bisphosphonate conjugates allows easy radiolabeling via complexation of a suitable metal isotope.

No-carrier-added 31Si was produced by 31P(n,p)31Si in the nuclear reactor of the Delft University of Technology. Several methods were investigated to remove the side product 32P, and the chemical form of 31Si was investigated. All methods except one gave good results. Anion exchange with Dowex resin gave the best results in activity concentration (3.8 × 106 Bq/ml, with only 3.2 × 103 Bq/ml 32P as by-product) and specific activity (As>17 TBq/g). The product is suitable for biological systems. Copyright © 2006 John Wiley & Sons, Ltd.

Blood plasma modeling has proved effective in the evaluation of clinical observations recorded for baboon and rat tests with 153Sm- ethylenediaminetetraphosphonic acid (EDTMP) as well as for 166Ho-EDTMP. In the search for a cure for metastatic bone cancer, 117mSn with its conversion electrons of discrete energies shows low bone marrow toxicity, providing the opportunity to increase the administered dose. Selective accumulation in lesions would capitalize on this advantage. The 10-30 kDa fraction of the water-soluble polymer polyethyleneimine, functionalized with methylene phosphonate groups (PEI-MP) and labeled with 99mTc, has shown selective uptake into bone tumours. This paper relates the speciation of Sn(II)-PEI-MP and other known 117mSn(II) containing bone-seeking radiopharmaceuticals in blood plasma. Apparent formation constants for the complexation of SnII with PEI-MP, DTPA, HEDP and other important blood plasma ligands were measured potentiometrically or estimated by linear free energy relationships (LFER). These data were added to the ECCLES database in order to construct a blood plasma model for SnII. From this model it is predicted that SnII will remain bound to the polymer (PEI-MP) in blood plasma and therefore, have only slight reticuloendothelial uptake. Preliminary primate studies indeed proved that the complex between SnII and PEI-MP remains intact in blood plasma, which is consistent with the observation for PEI-MP labeled with 99mTc. From these data, it was also possible to explain in retrospect the lower bone uptake, the slow blood clearance and the liver uptake of the agents 117mSn(II) DTPA and 117mSn(II) HEDP agents as reported in the literature.

The adsorption, exchange, and oxidation of formaldehyde have been studied on gold at various potentials, temperatures, concentrations, and pH values by voltammetry and the radiotracer thin-gap method and compartmental analysis. Two adsorption rates were identified in the overall adsorption process at the open circuit potential (OCP): a rapid physisorption and a slow chemisorption. Compartmental analysis of the adsorption kinetic data revealed that the physisorption and chemisorption steps proceed in a catenary (serial), reversible fashion. Approximately linear adsorption isotherms were obtained under most conditions, implying that the Gibbs free energy of the reaction depends only a little on the potential, temperature, and pH (the activation energy was previously seen to be strongly affected by these variables). The strong dependence of the quantity of species adsorbed on the formaldehyde concentration in the solution and the invariance of the adsorption isotherms with increasing potentials support the ...

The technique of Positron Emission Particle Tracking (PEPT) is applied to analyse non-intrusively solids flow in a laboratory scale Interconnected Fluidized Beds system. It is shown that, with a high performance tracking system, it is possible to extract from the data not only the Eulerian ensemble average velocity field, but also to reconstruct density profiles and to calculate mass flows in a solids circulation system. The most interesting flow characteristics inside the Interconnected Fluidized Bed system are highlighted. Although the data analysis is largely Eulerian, a first approach to a Lagrangian analysis has been performed through the computation of velocity autocorrelation functions. Characteristic frequencies of the solids movement could not be identified, but the velocity autocorrelations did provide insight in the dynamics of the solids movement. On a applique la technique de tracage de particules par emission de positrons (PEPT) afin d'analyser l'ecoulement de solides de maniere non intrusive dans un systeme a lits fluidises interrelies a l'echelle du laboratoire. On montre que, avec un systeme de tracage de haute performance, il est possible d'extraire a partir des donnees non seulement le champ de vitesse moyen de l'ensemble eulerien, mais egalement de reconstruire les profils de masse volumique et de calculer les ecoulements massiques dans un systeme de circulation de solides. Les caracteristiques d'ecoulement les plus interessantes dans le systeme a lits fluidises interrelies sont soulignees. Bien que l'analyse soit largement eulerienne, une premiere approche vers une analyse lagrangienne a ete realisee par le calcul des fonctions d'autocorrelation des vitesses. Les frequences caracteristiques du mouvement des solides n'ont pu etre determinees, mais les autocorrelations des vitesses nous eclairent sur la dynamique du mouvement des solides.

Mg2+ transport across the brush border of proximal intestinal epithelium of the teleost fish Oreochromis mossambicus was investigated, using 27Mg2+ to trace movement of Mg2+. Mg2+ uptake in brush border membrane vesicles was stimulated by a K+ diffusion potential (inside negative). Electrodiffusive Mg2+ transport obeyed simple Michaelis–Menten kinetics and was strongly temperature dependent, indicative of a carrier mechanism. The metal ion specificity of this electrodiffusive pathway (inhibition potency order: Co > Mn = Ni > La > Ca > Gd > Ba), predicts a specific role in Mg2+ transport. Competitive inhibition by Co(III) hexammine [Co(NH3] suggests that this transport system interacts with the solvated Mg ion. We propose that this novel transport system allows the uptake of Mg2+ across the apical brush border membrane, and is involved in transcellular Mg2+ transport. Consequently, the prevailing potential difference across the apical membrane represents a major driving force for intestinal Mg2+ absorption.

Double-focusing sector field inductively coupled plasma mass spectrometry (ICP-MS) was used for the determination of 26Mg/24Mg isotope ratios in order to quantify intestinal Mg2+ transport in the fish tilapia (Oreochromis mossambicus). As the sample medium contained substantial amounts of C, Na, P, S, Cl and K, the occurrence of molecular (e.g., C2+, C2H+, CN+ and NaH+) and doubly charged (48Ca2+) ions and tailing of the 23Na+ ion signal resulted in spectral overlap at low mass resolution. Application of a higher mass resolution (R = 3000), however, permitted accurate determination of Mg isotope ratios. The usefulness of cool plasma conditions was also evaluated, but this approach was insufficient to resolve all interferences completely. After careful optimisation of the measurement parameters, it was possible to measure the 26Mg/24Mg isotope ratio with a relative standard deviation (RSD) of 0.2–0.5% (n = 10 × 30 s) at R = 3000. From the isotope ratio results obtained, net intestinal Mg2+ fluxes were calculated, providing evidence for secretory Mg2+ transport. Conclusively, the measurement of stable isotope ratios with sector field ICP-MS presents a sophisticated tool for the study of Mg2+ transport processes in biological systems that may provide an effective alternative for the use of radiotracers.

Two simple diphosphonates, CH6P2 O6(MDP) and C2 H8 P2 O7 (HEDP),have been irradiated with neutrons to produce the corresponding 32P-labeled compounds. After irradiation for 0.5–5 hours in a thermalneutron flux of 4.2 . 1016 n . m —2 s—1 the irradiated compounds were dissolved and fractionated using a SephadexG10 column. The separated fractions were identified using planar paper chromatographyand autoradiography. The labeling yield was ca 35% for each of the compounds,and the specific activity attainable ranged up to 4.8 GBq . mol —1 . For practical applications, the labeled diphosphonates have to bepurified further.

The adsorption of tin(II) on hydroxyapatite (a model for the mineral phase of bone) was studied in vitro in the presence of either 1-hydroxy ethylidene-1,1-diphosphonate (HEDP) or methylenediphosphonate (MDP). Experimental results suggest the separate adsorption of tin and diphosphonate after dissociation of the tin diphosphonate complex. A detailed analysis of these results was performed using a set of equations (including acid dissociation, complex stability, and affinity constants of tin and diphosphonate) to describe the binding on hydroxyapatite of the various species in solution. By varying guessed values for the affinity constants for adsorption of tin diphosphonate and uncomplexed tin, the deviations between experimental and calculated adsorption results were minimized. Accurate fitting was obtained when attributing a value of 10-3 L mmol-1 to the affinity constant of the tin diphosphonate complex and a value of 3.5 × 1011 L mmol-1 to the affinity constant of uncomplexed tin(II). The latter appear...

The anodic oxidation of formaldehyde on gold in alkaline aqueous solutions was studied by electrochemical impedance spectroscopy. One equivalent circuit was found to mimic all impedance spectra measured for normal formaldehyde and deuterated formaldehyde in various alkaline solutions at various voltages. The resistors and capacitors constituting the circuit depend logarithmically on the voltage applied, and the circuit can be explained in terms of reaction steps proposed in the literature. A negative capacitance (inductive loop) was encountered at low frequencies, which is explained by a rate‐determining C‒H bond rupture step in the overall kinetics of the reaction, as it was more apparent for solutions containing instead of . Data were Kramers‐Kronig transformable and a ‐value of or less was attained in all fits. At least four time constants were revealed by the impedance spectra as a result of positive capacitive, negative capacitive, resistive, and diffusive effects. © 1999 The Electrochemical Society. All rights reserved.

[32P]-labelled sodium monofluorophosphate (Na2FPO3) was prepared according to a procedure, which is based on melting of a mixture of carrier-added [32P]-phosphoric acid and ammonium bifluoride, both solid. Monofluorophosphate was precipitated as the silver salt from the reaction mixture, then it was converted to the sodium salt by using a cation exchange column in Na+ form. The influence of the molar ratios of the reactants, and the reaction time on the final yield was studied. Powder X-ray diffraction showed a chemical purity of about 98% and absence of NaF in the final product. After a reaction time of 2 hours and a molar ratio of the reactants of 1 : 1, the yield for the reaction was 30% of the initial 32P activity, corresponding to a specific activity of 56 MBq 32P per mmol. An increase in yield is possible by increasing the reaction time, a higher specific activity may be obtained by a decrease of carrier phosphoric acid. The advantages of the procedure developed are the availability of [32P]-phosphoric acid, and the simple preparation of the compound. Copyright © 1999 John Wiley & Sons, Ltd.

It was found that long-lived, subnanometer-sized silver clusters can be prepared by anodic dispersion of a silver electrode in aqueous NaOH solutions (pH 10.5−12), free of stabilizing polymers. The method, described by Nouhuys in 1938, is based upon the application of a dc voltage (10−65 V) between two silver electrodes and yields a range of different clusters, colloids, and oxides. The large colloids and oxides can be removed by centrifugation leaving small colloids and clusters in the sols as revealed by the strong absorption of light at wavelengths between 210 and 400 nm. Absorption spectra of the sols remain fairly unchanged for weeks, implying the stabilization of the clusters by hydroxyl ions. Significant formation of the clusters is only observed between pH ∼10.5 and 12 and is explained by Joule heat generated in the Ag2O surface layer at the anode. At pH above 12, a passivating AgO layer forms, preventing the dispersion of clusters while no significant amounts of clusters form either at pH below 1...

The magnesium handling of freshwater teleost fish is discussed, with an emphasis on the role of branchial, intestinal and renal transport. In response to the eminent threat of constant diffusive losses of minerals such as magnesium, freshwater fish have developed efficient mechanisms for magnesium homeostasis. Magnesium losses are overcome by the uptake of magnesium from the food, making the intestine an important route for magnesium uptake. Some evidence suggests that intestinal magnesium uptake in fish is a regulated, cellular process. The ambient water is an additional magnesium source for fish, implicating the gills as a secondary route for magnesium uptake. Certainly, in some species, direct uptake from the water, probably via branchial routes, ameliorates the effects of a low-magnesium diet. The hard tissues, representing over 50 % of the total body magnesium pool, form a reservoir from which magnesium can be recruited to perform its functions in the cellular metabolism of soft tissues such as muscle. In fish, as in terrestrial vertebrates, the balance of a variety of elements becomes disturbed when the magnesium homeostasis of the soft tissues is disrupted. However, fish appear to be less sensitive than terrestrial vertebrates to these perturbations. Magnesium is reabsorbed in the kidneys to minimise losses. For renal cells, part of a cellular pathway has been elucidated that would allow absorptive magnesium transport (a magnesium conductive pathway in renal brush-border membranes). In some euryhaline teleosts, the kidneys appear to switch instantaneously to rapid magnesium secretion upon magnesium loading, a response common to marine fish that are threatened by diffusive magnesium entry. This enigmatic mechanism underlies the capacity of some euryhaline species to acclimate rapidly to sea water. Despite the progress made over the last decade, much of the cellular and molecular basis of magnesium transport in the gills, intestine and kidneys remains obscure. The application of fluorescent, radioactive and molecular probes, some of which have only recently become available, may yield rapid progress in the field of magnesium research.

The work presented illustrates the feasibility of using radiotracers with size exclusion chromatography (SEC) as a means of studying the kinetics of metal-ligand interactions in environmental systems. To simulate such systems a pre-equilibrated Eu(III)-humic acid model system was chosen in which 152mEu3+ as a radiotracer was used to study the isotopic exchange between Eu3+ and Eu(III)-humic acid complexation.

In this paper the technique of cross-correlating the void fractions derived from the transmission signals of two γ-sources is used for the non-intrusive study of bubble phenomena in gas-solid fluidized beds. Special attention is given to the optimization of this method with respect to the statistical uncertainty inherent to radioactive decay. Experiments in a 40 cm gas-solid fluidized bed illustrate that bubble velocity distributions can be obtained.

A radiotracer-based laboratory method for measuring the rates of metal volatilisation loss, i.e. emission from solid, metal(s) containing catalysts was developed and tested. The details of the method are illustrated on an alumina-supported CuO catalyst in which some CuO was labelled with 64 Cu. The method enables determination of emission rates of copper at pmol s −1 level and partial pressures of copper at nbar level.

The euryhaline Mozambique tilapia (Oreochromis mossambicus) shows a more marked ability to adapt to low magnesium levels in food and water than many other fish species. Nonetheless, the internal distribution of magnesium is altered under low-magnesium conditions. The amount of magnesium in scales, and to a lesser extent the vertebral bone, is reduced and hence serve as magnesium reservoirs. The magnesium concentration of muscle is only marginally reduced by low external magnesium, suggesting that magnesium is partitioned to ensure normal muscle functioning. The water magnesium is of vital importance, as exposure to low-magnesium water markedly deminished the ability of tilapia to adapt to low-magnesium feeding. However, magnesium intake from the water, eithervia the integument or drinking, does not increase in lowmagnesium fed fish, despite an increased opercular chloride cell density. The growth related magnesium accumulation of tilapia under low-magnesium conditions approximates the total intake of the element (from the food and from the water), indicating that magnesium losses are minimized and that the magnesium absorption from the gastrointestinal tract may be highly efficient and very important.

In tilapia (Oreochromis mossambicus) intestine, Mg2+ transport across the epithelium involves a transcellular, Na+- and Na+/K+-ATPase dependent pathway. In our search for the Mg2+ extrusion mechanism of the basolateral compartment of the enterocyte, we could exclude Na+/Mg2+ antiport or ATP-driven transport. Evidence is provided, however, that Mg2+ movement across the membrane is coupled to anion transport. In basolateral plasma membrane vesicles, an inwardly directed Cl- gradient stimulated Mg2+ uptake (as followed with the radionuclide 27Mg) twofold. As Cl--stimulated uptake was inhibited by the detergent saponin and by the ionophore A23187, Mg2+ may be accumulated intravesicularly above chemical equilibrium. Valinomycin did not affect uptake, suggesting that electroneutral symport activity occurred. The involvement of anion coupled transport was further indicated by the inhibition of Mg2+ uptake by the stilbene derivative, 4,4'-diisothiocyanato-stilbene-2,2'-disulfonic acid. Kinetic analyses of the Cl--stimulated Mg2+ uptake yielded a Km (Mg2+) of 6.08 +/- 1.29 mmol . l-1 and a Km (Cl-) of 26.5 +/- 6.5 mmol . l-1, compatible with transport activity at intracellular Mg2+- and Cl--levels. We propose that Mg2+ absorption in the tilapia intestine involves an electrically neutral anion symport mechanism.

A method is described for the utilization of 41 Ar as radiotracer for oxygen in a standard Rushton air-water contactor at steady state conditions without oxygen depletion. The compartmental analysis method is applied to appraise the mass transfer kinetics of the system. Results demonstrate the suitability of 41 Ar as a radiotracer for oxygen and that the system can be described as an open, three-compartmental model.

The euryhaline tilapia Oreochromis mossambicus kept in fresh water takes up calcium mainly from the water via the gills, like other freshwater fish. In the gills specialized mitochondria-rich cells, the chloride cells, are thought to mediate a transcellular Ca2+ transport. Second messenger operated calcium channels (SMOCs) in the apical membrane, regulated by the hormone stanniocalcin, allow minute-to-minute control over the entry of Ca2+. In the basolateral plasma membranes of these cells, an ATP-consuming Ca2 + transporting enzyme provides the major driving force for extrusion of Ca2+ into the blood; in addition, an Na+ /Ca2+ exchanger is present in these membranes. The kinetics of the exchanger in vitro indicate that this extrusion mechanism dominates when intracellular calcium levels reach micromolar levels. In the gills, the transport of calcium appears primarily ATPase mediated and therefore largely independent of the Na+ status of the transporting cell. In enterocytes, similar mechanisms for transcellular transport of Ca2+ exist. However, in the intestinal epithelium the extrusion of Ca2+ is primarily via the Na+/Ca2+ exchanger and to a very limited extent mediated via the Ca2+-ATPase. Indeed, calcium transport over the intestinal epithelium is dependent on the Na+ -status and the Na+/K+-ATPase activity of the epithelium. Prolactin and cortisol are endocrine factors determining the relative densities of calcium pumps in basolateral plasma membranes. At least 80% of the magnesium required for growth and homeostasis is absorbed from the food via the intestine. Magnesium is transported transcellularly and actively via enterocytes. The movement of Mg2+ over the apical membrane is passive, down an electrochemical gradient. The cytosolic Mg2+ concentration is kept well below its equilibrium concentration. The extrusion over the basolateral plasma membrane is mediated by an ATP-consuming enzyme. The gills contribute less than 20% to magnesium uptake, but up to 50% in tilapia fed a magnesium deficient diet. Evidence is accruing that prolactin is involved in the adaptation to low magnesium diets. © 1993 Wiley-Liss, Inc.

The severe pain associated with many disorders affecting bone account for a large proportion of cases of patient morbidity, due to the encumbrance of mobility and therefore, compromised quality of life. Skeletal metastasis is one such condition, which generally complicates the treatment of the primary cancers such as that of the breast, prostate and lung - causing intense pain and eventually even mortality. This paper presents examples of various approaches explored and proposed in the ongoing search to identify better radiopharmaceuticals for the treatment of bone disorders such as metastases. The primary objective of these developments is to alleviate the debilitating pain commonly associated with bone lesions. The efficacy of a radiotherapeutic agent intended for the treatment of diseased bone is particularly dependent on the radiation dose to the tumor cells and on the extent to which suppression of bone marrow or other critical organs can be avoided. Therefore, the design rationale requires careful consideration of the choice radionuclide and especially ensuring that the drug selectively targets the lesion or tumor site. The options pursued include the use of radioisotopes with an intrinsic affinity for bone, such as (89)Sr or (223)Ra, or the design of bone-seeking ligands, such as phosphonates, to selectively deliver the radionuclide to the target, e.g. [(153)Sm]Sm-EDTMP. A combination of the above may too be possible, where the bone seeking ligand facilitates the selective accumulation of a radionuclide, which by itself is also bone homing. In terms of therapeutic application radionuclides with various decay modes are proposed, including beta (-) emitters: (153)Sm, (89)Sr, (186)Re, (188)Re, (32)P, (177)Lu and (170)Tm; alpha (α) emitters: (223)Ra and (225)Ra; and Auger or conversion electron emitter: (117)mSn. From a purely diagnostic perspective, the radioisotopes used for imaging include the well known photon emitting (99)mTc, and positron emitters (18)F and (68)Ga. The current status in the development and application of internal radiotherapy for the palliative treatment of bone pain will be discussed, summarizing the progress made and challenges encountered in the process to realizing an effective drug candidate.

Common carp (Cyprinus carpio) initially weighing about 100 g were fed a low-magnesium diet for 17 weeks. The fish survived this treatment and had a healthy appearance. However, the fish became hypomagnesemic and their growth rate decreased. The bone sodium concentration increased and the magnesium concentration decreased. It thus appears that in carp, under dietary magnesium deficiency, magnesium is mobilized from internal stores and that magnesium in the bone mineral is replaced by sodium. Low-magnesium fed carp further showed a decreased branchial Na+/K+ -ATPase specific as well as total activity. Unexpectedly, the opercular chloride cell density increased. We tentatively conclude that more and new chloride cells with a lower Na+/K+-ATPase content develop during this treatment. We further conclude that adult carp require dietary magnesium for the maintenance of their magnesium balance as well as for the proper functioning of branchial ionoregulatory mechanisms. Low-magnesium fed carp do not acclimate but appear to tolerate a dietary magnesium deficiency. © 1992 Wiley-Liss, Inc.

The temperature-dependent adsorption on hydroxyapatite (HAP) of the Tb complexes of two macrocyclic DOTA-like ligands containing HAP-binding phosphonate groups was studied by a radiotracer method using 160Tb as the label. One ligand (DOTP) contains four separate phosphonate groups, while the second ligand (BPPED) contains a single bisphosphonate group coupled via a phosphinate spacer group. The equilibrium isotherms were fitted by models according to Langmuir, Freundlich, Langmuir-Freundlich, Toth, and Dubinin-Radushkevich, with the Langmuir-Freundlich and the Toth models resulting in the best fits. These models take into account the energetic surface heterogeneity of HAP for the binding of the complexes, which was confirmed by the dependence of the reversibility of the adsorption on the complex concentration. The affinity of the Tb-BPPED complex toward the HAP surface was substantially higher than that of the Tb-DOTP complex. Thermodynamic parameters obtained from the temperature-dependence of the adsorption and the Van't Hoff relation showed that the adsorption of both complex types is endothermic and entropy-driven, due to dehydration of the complex and the HAP surface during adsorption. The kinetics of the adsorption were very fast, and of the tested models (pseudo-first-order, pseudo-second-order, intraparticle diffusion, and Elovich) only the Elovich model described the experimental data suitably. The activation energy of the adsorption was calculated by application of an Arrhenius-type relation, showing chemisorption for both complex types. Adsorption rates were reduced when HAP with larger particle size was used.

The growth rate and magnesium concentration in scales, bone and muscle of freshwater tilapia, Oreochronus mossambicus (Peters), initially weighing between 70 and 300 g, were followed during low-magnesium feeding. The growth rate decreased in fish on low-magnesium diets, but no changes were observed in the magnesium concentration in the scales, bone or muscle. No changes were observed in calcium or sodium concentrations in these tissues. We conclude that adult tilapia fed a low-magnesium diet manage, in contrast to other fish species, to maintain their magnesium balance and must therefore obtain magnesium from the water.

Neutron activation analysis and 28Mg2+ as radiotracer were used to measure magnesium distribution in fish and magnesium flows between carp and water. A novel tracer kinetic approach was applied to determine magnesium flows “to fish from water” (F ƒw ) and “to water from plasma (fish)” (Fwp). This revealed that F ƒw wp and thus pointing to another magnesium source than water, namely food.

Lanthanide complexes of DOTA derivatives 2a (BPAMD) and 2b (BPAPD), having a monoamide pendant arm with a bis(phosphonate) moiety, were comparatively tested for application in MRI, radiotherapy, and bone pain palliation. (1)H, (31)P, and (17)O NMR spectroscopy show that they are nine-coordinated, with one water molecule in the first coordination sphere of the Ln(III) ion. The bis(phosphonate) moieties are not coordinated to the lanthanide and predominantly mono- and diprotonated at physiological pH. The parameters governing the longitudinal relaxivities of the Gd complexes are similar to those of other monoamides of DOTA reported in the literature. Upon adsorption on hydroxyapatite, the relaxivities at 20 MHz and 25 degrees C of Gd-2a and Gd-2b were 22.1 and 11 s(-1) mM(-1), respectively. An in vivo gamma-ray imaging study showed that the (177)Lu complexes of 2a and 2b have a high affinity for bones, particularly for growth plates and teeth with a prolonged retention.

Isotopic exchange based approaches have for many years been applied in soil and solute research. However, acquiring and elaboration of experimental data were not always straightforward and complete. A strict and correct use of combined isotopic exchange-compartmental analysis may widen the knowledge database and provide information not available as yet. The experiments were carried out with arsenic (arsenate) from IAEA-SOIL-5 in contact with water or phosphate solution in dynamic equilibrium. After contacting the soil suspension for 28 days, the amount of arsenate released is 2.8 and 6.3 % of arsenic (solutes) in the soil, respectively. Addition of a radioactive arsenate (73)As(V)-spike and following the distribution of this radiotracer from the aqueous to the solid phase in time shows that the accessible fraction, i.e. available for exchange, is in both cases 12%. This implies that the remainder of the arsenic is enclosed in the lattice of minerals and for that reason unavailable for exchange, at least on the time scale of the experiment (weeks). From deconvolution of compartmental analysis results the distribution of accessible arsenate in the soil could be attributed to sorption onto external surfaces (2.6 and 2.0% of total arsenic present for the water and phosphate system, respectively) and sorption onto internal surfaces after diffusion through soil particle pores (6.5 and 4.2% of total arsenic present for the water and phosphate system, respectively). The mean residence time in two out of three compartments was in the order of minutes for the external surfaces and in the order of days for the diffusion-controlled internal surfaces.

A new macrocyclic DOTA-like ligand (BPAMD) for bone imaging and therapy containing a monoamide bis(phosphonic acid) bone-seeking group was designed and synthesized. Its lanthanide(III) complexes were prepared and characterized by 1H and 31P NMR spectroscopy. The Gd(III)-BPAMD complex was investigated in detail by 1H and 17O relaxometric studies to inspect parameters relevant for its potential application as an MRI contrast agent. Sorption experiments were conducted with Gd(III) and Tb(III) complexes using hydroxyapatite (HA) as a model of bone surface. Very effective uptake of the Gd-BPAMD complex by the HA surface was observed in NMR experiments. Radiochemical studies with the (160Tb-BPAMD)-HA system proved the sorption to be remarkably fast and strong on one hand and fully reversible on the other hand. The strong (Gd-BPAMD)-HA interaction was also supported by 1H NMRD measurements in the presence of a hydroxyapatite slurry, which showed an increase of the rotational correlation time upon adsorption of the complex on the HA surface, resulting in a significant relaxivity enhancement. The amide-bis(phosphonate) moiety is the only factor responsible for the binding of the complex to HA.

In 1903 W. Crookes demonstrated in England his “spinthariscope” for the visual observation of individual scintillations caused by alpha particles impinging upon a ZnS screen. In contrast to the analogue methods of radiation measurements in that time the spinthariscope was a single-particle counter, being the precursor of scintillation counters since. In the same period F. Giesel, J. Elster and H. Geitel in Germany also found that scintillations from ZnS represent single particle events. This paper summarises the historical events relevant to the advent of scintillation counting.

In a quest for more effective radiopharmaceuticals for pain palliation of metastatic bone cancer, this paper relates results obtained with ( 117m Sn labelled) Sn(II) complexed to the bone seeking bisphosphonate, N , N -dimethylenephosphonate-1-hydroxy-3-aminopropylidenediphosphonate (APDDMP). APDDMP is synthesised from the known bone cancer pain palliation agent 1-hydroxy-3-aminopropylidenediphosphonate (APD, Pamindronate). This work is performed to utilise the idea that the low bone marrow radio toxicity of 117m Sn could afford a highly effective radiopharmaceutical in pain palliation but also in the curative treatment of bone metastasis. Complex-formation constants of APDDMP with the important blood plasma metal-ions, Ca 2+ , Mg 2+ , Zn 2+ as well as the added metal ion, Sn 2+ were measured by glass electrode potentiometry at 25 °C and I =150 mM. Blood plasma models were constructed using the computer code ECCLES and the results compared with those gathered from tests on a rodent model. The ( 117m Sn-labelled) Sn(II)–APDDMP complex was found to have only some liver and bone uptake although a high trabecular to normal bone ratio was recorded. From the blood plasma model this was shown to be primarily due to the high affinity of APDDMP for Ca(II) causing some of the Sn(II)–APDDMP complex to dissociate. High kidney uptake and excretion as well as high bladder uptake was recorded which was shown to be due to the dissociation of the Sn(II)–APDDMP complex in blood plasma. Animal model observations could be explained by the blood plasma modelling.

Much controversy exists concerning the way calcium phosphate is linked to milk phosphoproteins including caseins. Homoionic exchange of inorganic phosphate between micellar calcium phosphates (MCP) of casein micelles and solute phosphates in cows’ milk was investigated using H 32 PO 4 2− as radiotracer. Compartmental analysis and modelling revealed the presence of three MCP-related inorganic phosphate compartments each representing a separate phosphate entity. The relative phosphate quantities per compartment, i.e. the quantities of kinetically identical phosphate ions per MCP-ion cluster, and their mean residence times are 2:1:1 and 818, 0.24 and 23 h, respectively. Hence each MCP-ion cluster comprises four inorganic phosphate ions divided over three intra-MCP binding sites each characterised by a mean residence time for homomolecular phosphate exchange at solution/MCP interface.

Using high specific activity 64Cu2+ as radiotracer, the distribution kinetics among Cu species were established in natural organic-rich freshwaters under steady-state conditions, i.e., with minimal disturbance of existing equilibria. Study sites with contrasting suspended particulate matter (SPM) characteristics were investigated. Our analytical protocol allowed the differentiation between the following Cu species: SPM associated Cu, dissolved reactive (free and labile) Cu, and organically complexed Cu. The data obtained were successfully evaluated by compartmental analysis, which showed the importance of organically complexed Cu in freshwaters, and the dominant role of the interactions between organically complexed Cu and SPM in a SPM-rich water. The kinetic 54Cu measurements indicated that the attainment of equilibrium between dissolved reactive and organically complexed Cu took ca.

A new and simple method is described to plate silicon structures with metallic silver for ultralarge-scale integration in dimensions down to 100 nm at an aspect ratio of 4.25. The silver deposition is initiated by an exchange reaction of silicon with silver ions, and the subsequent layer growth of the activated wafers occurs by electroless plating from supersaturated aqueous silver salt solutions at pH ∼ 11. No extra reducing agents are needed since silver ions are reduced at the catalytic silver surface by hydroxyl ions. The spontaneous ion-metal transition only proceeds at pH ∼ 11 and is likely mediated by the formation of subnanometer-sized [Ag 4 (OH) 2 ] 2+ clusters. The silver plating proceeds more easily in smaller structures and yields void-free, crystallized deposits.

To elucidate the mechanisms involved in Mg2+ transport at the apical and basolateral poles of the renal tubular epithelium, apical and basolateral plasma membrane vesicle preparations were derived from kidney tissue of freshwater- and seawater-adapted Mozambique tilapia Oreochromis mossambicus. Brush-border preparations were enriched 15.8-fold in alkaline phosphatase activity and consisted almost exclusively of right-side-out membrane vesicles. Basolateral membrane preparations were enriched 7.5-fold in Na+/K+-ATPase activity and contained resealed vesicles and leaky membrane fragments. Mg2+ association with brush-border and basolateral plasma membranes, traced using radioactive 27Mg, occurred in an osmotically active space. In all instances, Mg2+ binding to the vesicular membrane was low compared with the vesicular uptake. Mg2+ equilibration across the vesicular membrane of brush-border preparations was rapid and sensitive to the presence of extravesicular Ca2+, suggesting that the apical membrane of the renal epithelium contains a transport pathway for divalent cations. Application of various ionic gradients did not affect vesicular Mg2+ transport in apical and basolateral membrane preparations, suggesting the presence of an ion-coupled transport mechanism. ATP or ATP-γ-S did not stimulate Mg2+ fluxes, indicating that Mg2+ transport does not proceed via an ATP-driven or activated transporter. In these aspects, vesicular Mg2+ transport was similar in seawater and freshwater preparations. These results suggest that the apical membrane of renal epithelial cells lacks an active secretory Mg2+ transport mechanism. We propose that the Mg2+ conductivity of the apical membrane reflects a route for downhill Mg2+ entry and is involved in renal Mg2+ reabsorption.

The mechanism that underlies transcellular Ca2+ reabsorption in the kidney of the euryhaline teleost Oreochromis mossambicus was studied. Preparations of membrane vesicles made from the kidneys of freshwater-and seawater-adapted fish were more than sevenfold enriched in the basolateral plasma membrane marker Na+/K+-ATPase. Significant recovery of NADH– cytochrome c reductase enzyme activity and of oxalate-stimulated Ca2+ pump activities in the membrane preparations indicated that the membrane fraction was of endoplasmic reticular origin. Indeed, thapsigargin specifically inhibited Ca2+ pump activity that could be attributed to oxalate-permeable endoplasmic reticular fragments. Kinetic analysis of thapsigargin-insensitive Ca2+ pump activity indicated the existence of a homogeneous, high-affinity, ATP-driven Ca2+ pump. No Na+-driven Ca2+ transport mechanism could be demonstrated. Plasma membrane Ca2+ pump activity was 56 % lower in preparations from seawater-adapted fish than in preparations from freshwater-adapted fish, suggesting a physiological role for this Ca2+ pump activity in renal Ca2+ handling by euryhaline species, with an involvement in the regulation of Ca2+ reabsorption.

In East-American mudminnows, obtained from lakes and bogs of different water pH levels, prolactin cell size and ultrastructure reflect higher secretory activity in neutral water than in water of pH 3.5–6.5. This contrasts with observations on other species in which prolactin cell activity is higher at low water pH. Laboratory experiments involving acute exposure of mudminnows from pH 5.5 for 48 hr to different pH levels showed that prolactin secretion increased in water below pH 3 and above pH 6.5, which could be correlated with losses of blood electrolytes. No osmoregulatory stress was noticeable in the pH range of 3.5 to 5.5. Acclimation of fish for 5 to 6 months to either pH 4.5 or 7.2 confirmed that prolactin cell activity, as estimated with ultrastructural morphometry, was significantly higher in water of neutral pH than of pH 4.5. The growth rate was significantly higher at the lower pH. Determination of whole body sodium fluxes, with 24 Na as a tracer, showed that both groups had a positive sodium balance. However, total body Na + influx as well as efflux values were slightly but significantly reduced at pH 7.0 when compared to pH 4.5. The reduction of Na + efflux at pH 7.0 is in line with increased secretion of prolactin since this hormone is known to limit the branchial permeability to water and ions, including Na + . The results show that the mudminnow is extremely acid tolerant, having an optimum water pH range of about 3.5 to 6.0, which is consistent with ecological observations. Prolactin secretion is at a minimum in this range. Exposure to neutral water represents osmoregulatory stress for the mudminnow, in contrast to all other teleost species examined so far.

A new and simple method is described to plate silicon structures with metallic silver for ultralarge-scale integration in dimensions down to 100 nm at an aspect ratio of 4.25. The silver deposition is initiated by an exchange reaction of silicon with silver ions, and the subsequent layer growth of the activated wafers occurs by electroless plating from supersaturated aqueous silver salt solutions at pH ∼ 11. No extra reducing agents are needed since silver ions are reduced at the catalytic silver surface by hydroxyl ions. The spontaneous ion-metal transition only proceeds at pH ∼ 11 and is likely mediated by the formation of subnanometer-sized [Ag 4 (OH) 2 ] 2+ clusters. The silver plating proceeds more easily in smaller structures and yields void-free, crystallized deposits.

Hydrothermal heating to 433 K is shown to reduce drastically the time needed for attaining 70–100% ammonium exchange of zeolite Na-Y without impairing the zeolite. Upon approaching complete ammonium exchange the affinity of zeolite Y for ammonium falls sharply. Complete exchange requires a total molar ammonium : sodium ratio of more than 200. Extensive ammonium exchange is accompanied by an expansion of the faujasite framework eventually leading to sodalite cages of sufficient size to accommodate two ammonium ions.

In tilapia exposed for 3 months to water of pH 4.5, prolactin cell activity, as estimated by ultrastructural morphometry and determination of prolactin synthesis in vitro, was significantly higher than in controls from neutral water. Sodium influx from the water was 50% lower than in the controls, indicating impaired branchial sodium uptake mechanisms. In contrast to predictions based on the results of short-term exposure to acid water--which is known to induce an increase of sodium efflux--the sodium efflux rate was reduced to 70% of the control value. It is concluded that tilapia are able to acclimate to acid water by successful control--probably via prolactin--of diffusional sodium losses across the integument, in particular the gill surface. This compensates for the impaired sodium uptake, and enables the fish to reestablish a positive sodium balance in acid water.

Radiotracer techniques were used to measure influx and efflux rates of Ca2+ in freshwater-adapted Oreochromis mossambicus. The influx rate of Ca2+ is related to body weight (W) as Fin = 50W0.805 nmol Ca2+/h. For a 20-g fish the calculated influx rate was 558 nmol Ca2+/h, and this was attributed largely to extraintestinal uptake since the drinking rate was estimated to be only 28 microliter water/h, which corresponds to an intake of 22.4 nmol Ca2+/h. The Ca2+ efflux rate was calculated using the initial rate of appearance of radiotracer in the ambient water and the specific activity of plasma Ca2+. Tracer efflux rates were constant over 6-8 h, which indicated that there was no substantial loss of tracer in either the urine or the feces because this would have resulted in random bursts of tracer loss. Efflux rates then primarily represent integumentary and presumably branchial efflux rates. The efflux rate of Ca2+ is related to body weight as Fout = 30W0.563 nmol Ca2+/h, which means an efflux rate of 162 nmol Ca2+/h for a 20-g fish. The net whole-body Ca2+ influx, calculated as Fnet = Fin - Fout, was 396 nmol/h for a 20-g fish, which proves that the ambient water is an important source of Ca2+.

Polycrystalline and predominately mixed-phase CdS particles are obtained by H 2 S precipitation from acidic cadmium solutions with various concentrations of SO 4 2− , ClO 4 − , NO 3 − , and/or Cl − . None of the precipitates is free of interstitial (void) space. The roughness of the particle surface increases with the number of crystallites in one particle. Chloride is shown to play an exceptional role in the precipitation: (i) Chloride promotes the formation of hexagonal CdS, while in the presence of the other anions the cubic phase predominates at low supersaturation or anion concentration. The fraction of hexagonal CdS increases with the concentration of anions present in the precipitation media. The higher the complex formation constant between the anion and Cd 2+ , the stronger this effect proves to be. (ii) Chloride promotes the formation of more particles and inhibits the aggregation of crystallites into one single particle. (iii) Chloride is present in considerable amounts, mainly at grain boundaries inside the particles, while sulfate and perchlorate are adsorbed mainly at the particle surface.

Ovine prolactin stimulated the net uptake rate of Ca2+ from the water by 96%, produced frank hypercalcemia, and increased total bone calcium content in fed rapidly growing freshwater male tilapia, Oreochromis mossambicus. It did not, however, alter the size of the readily exchangeable bone calcium pool. The increase in calcium accumulation resulted from an increase in whole-body Ca2+ influx and a decrease in Ca2+ efflux. It is concluded that prolactin exerts an important control over Ca2+ exchange between the fish and its environment and that through its hypercalcemic action prolactin indirectly facilitates bone mineralization.

Calcium fluxes and internal calcium pools were measured in fed, rapidly growing, male tilapia, Oreochromis mossambicus, acclimated to 0·8 mmol l−1 (FW) and 0-2 mmol l−1 (LFW) Ca2+. Plasma calcium levels were slightly and significantly higher in the LFW tilapia, but muscle calcium concentrations were independent of ambient Ca2+. At the time of the experiments, the LFW fish were growing and accumulated calcium, although the calcium content of their hard tissues was reduced. The LFW fish had higher Ca2+ influx and efflux rates than the FW fish. The increase in the influx of Ca2+ in LFW fish was, however, substantially greater than the increase in the efflux of Ca2+, giving these fish a more than four-fold increase in net Ca2+ influx from the water: for a 20-g tilapia net uptake rates of Ca2+ from the water were 390 and 1620 nmol Ca2+ h−1 for FW-and LFW-adapted fish, respectively. These values were calculated to represent at least 69 % of the total calcium accumulated by these growing fish. This indicates that even in low-calcium water, tilapia absorb a significant amount of their calcium requirement directly from the water. The pool of readily exchangeable calcium in the bone of FW fish was estimated to be about 7 % of the total hard tissue calcium. In the fish acclimated to LFW, this percentage increased to about 15 % as total hard tissue mineralization decreased. This may indicate that tilapia can increase the mobility of their h