Ru Inclusions Research Articles

One Stone, Three-Birds Approach: Ultra-active Ru/N, S-MoO2/CNTs Electrocatalyst for Overall Water Splitting in Wide Electrode Applications (NF, GC, and CC).

The construction of exceptionally multifunctional electrocatalysts is essential for various applications, but it poses significant challenges. A novel electrocatalyst, denoted as Ru/N, S-MoO2/CNTs, was successfully synthesized using a combination of mechano-grinding and hydrothermal/calcination techniques. The Ru/N, S-MoO2/CNTs demonstrates ultrasmall overpotentials of 12 and 163 mV in NF, 51 and 167 mV in GCE, and 54 and 173 mV in CC for HER and OER, respectively, at a current density of 10 mA/cm2 in alkaline medium. To accomplish electrocatalytic OWS, a current density of 10 mA/cm2 can be obtained by using a cell voltage of 1.446 V. Theoretical studies demonstrated that the inclusion of Ru, N, and S triggers a change in the composition of MoO2; produces oxygen vacancies; and forms Ru, N, and S-oxygen-Mo catalytic centers. The combination of Ru, N, and S nanoclusters; Ru, N, and S-oxygen-Mo catalytic centers; and OVs-enriched MoO2 would position it among the top electrocatalysts.

Preparation and electrochemistry study of a new Ti-based PbO2 electrode with Ta-Ti-Sn(Ru)Ox interlayer in Cu electrowinning

Copper (Cu) is a crucial non-ferrous material, and in this research, a new composite layered anode, Ti/Ta-Ti-Sn(Ru)Ox/PbO2, was developed for the hydrometallurgical process. The anode was created using thermal decomposition and subsequent electrodeposition, with Ti serving as the matrix and Ta-Ti-Sn(Ru)Ox as the interlayer. The study identified that the optimal molar ratio of Ta:Ti was 4:1, the ideal number of coating layers was 3, and the preparation temperature was 550 °C. The addition of Sn element improved the bonding force of the coating, preventing it from detaching even if it fails, while the inclusion of Ru enhanced the electrode’s service life. Moreover, the deposited PbO2 layer demonstrated a rich porous structure. In a long-cycle copper electrodeposition application, anodes with optimal preparation parameters showed higher current efficiencies and reduced energy consumptions compared to the Ti/Sn-SbOx/PbO2 baseline electrode, energy consumption reduced by 220.8 kWh per ton of copper product. This research presents a valuable strategy for designing and constructing high-performance electrodes for nonferrous electrolysis and other similar applications.

Dual active sites for ammonia synthesis at ambient pressure

Numerous theoretical calculations indicate the synergistic role of bimetals to efficiently activate nitrogen molecules and facilitate ammonia formation through dissociative routes. Here, we experimentally demonstrated the use of dual active sites comprised of Fe with Ru, Co, and Ni. The findings reveal that Ru/Fe and Co/Fe catalysts are stable and effective to form ammonia at ambient pressure and in the temperature range (400–550 °C) with an activation energy of 45.73 kJ∙mol−1 and 46.38 kJ∙mol−1, respectively. In addition to extensive characterizations, an in-depth kinetic study unveils that the inclusion of Ru or Co to the Fe can shift the rate-determining steps to NHx formation. The co-catalysts are negatively charged because of electron-donating Fe sites, which helps to favor N2 dissociation on the bimetallic catalysts.

Exploring the use of a Ruthenium complex incorporated into a methacrylate-based dental material for antimicrobial photodynamic therapy.

To evaluate the effects of a blue light photosensitizer (PS), Ruthenium II complex (Ru), on the chemical, physical, mechanical, and antimicrobial properties of experimental dental resin blends. The experimental resin (BisEMA, TEEGDMA, HPMA, ethanol, and photoinitiator) was loaded with Ru at 0.00%, 0.07%, 0.14%, 0.28%, 0.56%, 1.12%, 1.2%, 1.5%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10% w/w. Samples were evaluated for the degree of conversion (DC) after 30 and 60 s curing-time (n = 6). Selected formulations (0.00%, 0.28%, 0.56%, 1.12%) were further tested for shear bond strength (SBS) (n = 15); flexural strength (FS) (n = 12); and antimicrobial properties (CFUs), in dark and light conditions. These latter tests were performed on specimens stored for 24-h or 2-month in 37°C water. Water sorption (WS) and solubility (SL) tests were also performed (n = 12). Data were analyzed either by a one- or two-factor general linear model (α = 0.05). Overall, Ru concentration above 1.2% resulted in reduced DC. In SBS results, only the 1.12%Ru resin blend samples had statistically lower values compared to the 0.00%Ru resin blend at 24-h storage (p = 0.004). In addition, no differences in SBS were detected among the experimental groups after 2-month storage in water. Meanwhile, FS increased for all experimental groups under similar aging conditions (p < 0.001). Antimicrobial properties were improved upon inclusion of Ru and application of light (p < 0.001 for both) at 24-h and 2-month storage. Lastly, no detectable changes in WS or SL were observed for the Ru-added resins compared to the 0.00%Ru resin blend. However, the 0.28% Ru blend presented significantly higher WS compared to the 0.56% Ru blend (p = 0.007). Stable SBS, improved FS, and sustained antimicrobial properties after aging gives significant credence to our approach of adding the Ruthenium II complex into dental adhesive resin blends intended for an aPDT approach.

Platinum-group minerals from the Malaya Kamenushka River placer, Middle Urals, Russia

AbstractThis work presents a detailed study of platinum-group mineral (PGM) assemblages from the Malaya Kamenushka River placer, whose formation is associated with the weathering of the Kamenushensky Uralian–Alaskan type massif, Middle Urals, Russian Federation. The deposit is characterised by the dominance of isoferroplatinum, together with significant numbers of inclusions of Os–Ir–Ru alloys and platinum-group element (PGE) sulfides. A study of the Os–Ir–Ru alloys permitted recognition of two types of iridium with different morphology and composition. The similarity of the PGM assemblages from the Malaya Kamenushka River placer and the lode mineralisation of the Kamenushensky massif is demonstrated. A comparison of PGM assemblages from the Malaya Kamenushka River placer with other placers and massifs of the Ural platinum belt demonstrates significant differences in the number of Os–Ir–Ru inclusions. Such differences for minerals of refractory elements cannot be explained by the vertical zoning of the lode mineralisation. Most probably this is associated with the enrichment of the primary substrate with Os, Ir and Ru and/or the degree of melting, depending on the chosen model of formation of the Uralian–Alaskan type massifs.

Crystal growth of the Ca2RuO4–Ru metal system by the floating-zone technique

Abstract In the last few decades there has been growing interest in studying Mott insulators due to their ability to host novel quantum phenomena when the system is perturbed by various stimuli. Recently the antiferromagnetic Mott insulator Ca2RuO4 has received considerable attention due to superconductivity and metal-insulator transition induced by pressure and electric field respectively. Here we report the details of the synthesis of a novel systems made by Ca2RuO4 and Ru metal inclusions. Samples with lamellae, rods and globules of Ru embedded in Ca2RuO4 single crystals were successfully synthesized by floating zone technique with an excess of Ru in the starting material. The morphology and structural studies revealed a randomly orientated distribution of the shining Ru inclusions with an average size of few microns. Magnetic and electrical properties showed a behavior similar to the one observed in single crystals with the only Ca2RuO4 phase. We also measured the current-voltage characteristics of the whole Ca2RuO4–Ru system and of a single Ru rod by electric micro-contacts estimating the room temperature resistivity of the Ru embedded inclusions. This study shows that physical properties of Ca2RuO4–Ru metal system are related to the properties of the constituent phases, similarly to the case of Sr2RuO4–Ru metal.

Flexible IGZO Schottky diodes on paper

With the development of novel device applications, e.g. in the field of robust and recyclable paper electronics, came an increased demand for the understanding and control of IGZO Schottky contact properties. In this work, a fabrication and characterization of flexible Ru–Si–O/IGZO Schottky barriers on paper is presented. It is found that an oxygen-rich atomic composition and microstructure of Ru–Si–O containing randomly oriented Ru inclusions with diameter of 3–5 nm embedded in an amorphous SiO2 matrix are effective in preventing interfacial reactions in the contact region, allowing to avoid pre-treatment of the semiconductor surface and fabricate reliable diodes at room temperature characterized by Schottky barrier height and ideality factor equal 0.79 eV and 2.13, respectively.

Multicomponent order parameter superconductivity of Sr2RuO4 revealed by topological junctions

Single crystals of the Sr$_2$RuO$_4$-Ru eutectic system are known to exhibit enhanced superconductivity at 3~K, in addition to the bulk superconductivity of Sr$_2$RuO$_4$ at 1.5~K. The 1.5-K phase is believed to be a spin-triplet, chiral $p$-wave state with the multi-component order parameter, giving rise to chiral domain structure. In contrast, the 3-K phase is attributable to enhanced superconductivity of Sr$_2$RuO$_4$ in the strained interface region between Ru inclusion of a few to tens of micrometers in size and the surrounding Sr$_2$RuO$_4$. We investigate the dynamic behavior of a topological junction, where a superconductor is surrounded by another superconductor. Specifically, we fabricated Nb/Ru/Sr$_2$RuO$_4$ topological superconducting junctions, in which the difference in phase winding between the $s$-wave superconductivity in Ru micro-islands induced from Nb and the superconductivity of Sr$_2$RuO$_4$ mainly governs the junction behavior. Comparative results of the asymmetry, hysteresis and noise in junctions with different sizes, shapes, and configurations of Ru inclusions are explained by the chiral domain-wall motion in these topological junctions. Furthermore, a striking difference between the 1.5-K and 3-K phases is clearly revealed: the large noise in the 1.5-K phase sharply disappears in the 3-K phase. These results confirm the multi-component order-parameter superconductivity of the bulk Sr$_2$RuO$_4$, consistent with the chiral $p$-wave state, and the proposed non-chiral single-component superconductivity of the 3-K phase.

Probing chiral superconductivity in Sr2RuO4 underneath the surface by point contact measurements

Sr2RuO4 (SRO) is the prime candidate for a chiral p-wave superconductor with critical temperature K. Chiral domains with opposite chiralities have been proposed, but are yet to be confirmed. We measure the field dependence of the point contact (PC) resistance between a tungsten tip and an SRO–Ru eutectic crystal, where micrometer-sized Ru inclusions are embedded in SRO with an atomically sharp interface. Ruthenium is an s-wave superconductor with K; flux pinned near the Ru inclusions can suppress its superconductivity, as reflected in the PC resistance and spectra. This flux pinning effect originates from SRO underneath the surface and is very strong once flux is introduced. To fully remove flux pinning, one needs to thermally cycle the sample above Tc(SRO) or apply alternating fields with decreasing amplitude. With alternating fields, the observed hysteresis in magnetoresistance can be explained by domain dynamics, providing support for the existence of chiral domains. The origin of the strong pinning could be the chiral domains themselves.

Development of CaMn1−xRuxO3−y(x = 0 and 0.15) oxygen reduction catalysts for use in low temperature electrochemical devices containing alkaline electrolytes: ex situ testing using the rotating ring-disk electrode voltammetry method

Various inorganic solid state catalysts are of interest for use as cathode catalysts in low temperature alkaline fuel cells including alkaline polymer electrolyte fuel cells. This ex situ study compares the oxygen reduction reaction in aqueous KOH (1 mol dm−3) electrolyte on solid state and sol–gel synthesised CaMn1−xRuxO3 (x = 0 and 0.15) catalysts along with fuel-cell-grade Pt-based benchmark catalysts. The inclusion of Ru (e.g. in the CaMn0.85Ru0.15O3 examples) led to enhanced electronic conductivities compared to the Ru free exemplars. Rotating ring disk electrode hydrodynamic voltammetry was successfully used to determine the electron transfer numbers and hydrogen peroxide production yield for each catalyst. The electron transfer numbers of a number of the catalysts promisingly approach n = 4 (the same as for the platinum benchmarks). However, the on-set potentials of the CaMn1−xRuxO3 (x = 0 and 0.15) catalysts were less than that of the Pt-based benchmarks and they also degraded in the alkaline conditions used (with a further decrease in onset potentials on degradation): the results from the study lead to the hypothesis that the degradation is related to the electrochemically generated peroxide.

Topological competition of superconductivity in Pb/Ru/Sr2RuO4junctions

We devise a new proximity junction configuration where an s-wave superconductivity and the superconductivity of Sr2RuO4 interfere with each other. We reproducibly observe in such a Pb/Ru/Sr2RuO4 junction with a single Pb electrode that the critical current Ic drops sharply just below the bulk Tc of Sr2RuO4 and furthermore increases again below a certain temperature below Tc. In order to explain this extraordinary temperature dependence of Ic, we propose a competition effect involving topologically distinct superconducting phases around Ru inclusions. Thus, such a device may be called a "topological superconducting junction".

Layered γ-zirconium phosphate as novel semiconductor for dye sensitized solar cells: Improvement of photovoltaic efficiency by intercalation of a ruthenium complex-viologen dyad

The performance of photovoltaic cells using as semiconductor a film of layered γ-zirconium phosphate (γ-ZrP) containing Ru(bpy)3 and bipyridinium ions (viologens) as electron relays has been studied. The materials are easily prepared by intercalation of Ru complexes and the bipyridinium ions into preformed γ-ZrP nano sheets as colloidal solutions in the appropriate solvent and concentration. High loading of these two guests has been obtained as determined by elemental analysis. Inclusion of Ru(bpy)3 complex and bipyridinium in the intergallery spaces of γ-ZrP can be assessed by powder XRD monitoring of the d100 peak. A dyad was also synthesized where the Ru(bpy)3 and the 4,4′-bipyridinium were covalently connected by a four-methylene tether. The semiconducting behavior of layered γ-ZrP was supported by cyclic voltammetry (reversible reduction peak at −0.6 V), observation of photocurrent and Mott-Schottky measurements (flat band potential ∼−1.3 V vs.NHE) of thin films of this material supported on FTO electrode. Photovoltaic cells based on γ-ZrP containing Ru(bpy)3, exhibited similar VOC (∼0.5 V) and fill-factor values (0.3–0.4), differing in the current density and therefore in their efficiency. The maximum efficiency was obtained for the material containing high loading of the dyad (JSC = 0.383 mA/cm2, efficiency 0.1%). The photo response spectrum shows that the main limitation of these materials is still the inefficient photo sensitization of the semiconductor by the dye, probably due to the high negative flat band potential of γ-ZrP.

Phase Transition in the 3-Kelvin Phase of Eutectic Sr2RuO4–Ru

The inhomogeneous 3-Kelvin (3K) phase of the eutectic Sr2RuO4 with Ru inclusions nucleates superconductivity at the interface between Ru and Sr2RuO4. The structure of the interface state and its physical properties are examined here. Two superconducting phases are identified between the transitions to the bulk phase at 1.5K and to the 3K phase. The nucleation of the 3K phase results in a state conserving time reversal symmetry, which generates an intrinsically frustrated superconducting network in samples with many Ru inclusions. At a lower temperature (>1.5K), a discontinuous (first order) transition to an interface state breaking time reversal symmetry is found leading to an unfrustrated network phase. It is shown that this phase transition located at a temperature between 1.5 and 3K would yield the anomalous property that the critical current in such a network depends on the sign of the current, reproducing recent experimental observations.

Chiral superconducting phase transition in 3-K phase of Sr 2RuO 4

We have investigated the transports of micro-fabricated sample of 3-K phase superconductivity ( T c ∼ 3 K) in Sr 2RuO 4–Ru eutectic system in order to clarify the pairing symmetry. Up to now, pure Sr 2RuO 4 ( T c = 1.5 K: 1.5-K phase) is widely recognized to be a spin-triplet odd-parity superconductor. However, the enhancement mechanism of T c up to 3 K and the pairing symmetry of the 3-K phase have not been cleared yet. By using micro fabrication technique with focused ion beam, we have succeeded to extract individual superconducting channels for the 3-K phase in which only a few pieces of Ru inclusions are contained. Multiple kink structures observed in differential resistance–current ( dV/ dI − I) characteristics indicate serially connected superconducting filaments in the 3-K phase. We confirm that the 3-K phase is an odd-parity superconductor similar to pure Sr 2RuO 4 from the monotonous temperature dependence of the critical currents. In addition, we observed a quite unusual hysteresis in dV/ dI − I below 2 K, which suggests the internal degrees of freedom in the superconducting state: the most probably the chiral p-wave state.

Recent developments in the 3-Kelvin phase of Sr 2RuO 4

Enhanced superconductivity in the eutectic system Sr 2RuO 4–Ru is referred to as the 3-K phase of Sr 2RuO 4 because of its enhanced superconducting transition temperature T c of ∼3 K whilst the superconductivity in Sr 2RuO 4 ( T c of ∼1.5 K) is called the 1.5-K phase. We describe basic properties of the 3-K phase and focus on its field–temperature ( H– T) phase diagram. We suggest that the 3-K phase is attributable to surface superconductivity with a two-component order parameter (chiral state) occurring at the interface between Sr 2RuO 4 and Ru inclusions.

Separating innocence and non-innocence of ligands and metals in complexes [(L)Ru(acac)2](n) (n = -1, 0, +1; L = o-iminoquinone or o-iminothioquinone).

The diamagnetic title complexes were obtained from Ru(acac)(2)(CH(3)CN)(2) and 2-aminophenol or 2-aminothiophenol. X-ray structure analysis of (L(1))Ru(acac)(2) (L(1) = o-iminoquinone) revealed C-C intra-ring, C-O, and C-N distances which suggest a Ru(III)-iminosemiquinone oxidation state distribution with antiparallel spin-spin coupling. One-electron oxidation and reduction of both title compounds to paramagnetic monocations [(L)Ru(acac)(2)](+) or monoanions [(L)Ru(acac)(2)](-) occurs reversibly at widely separated potentials (deltaE > 1.3 V) and leads to low-energy shifted charge transfer bands. In comparison with clearly established Ru(II)-semiquinone or Ru(III)-catecholate systems the g tensor components 2.23 > g(1) > 2.09, 2.16 > g(2) > 2.07, and 1.97 > g(3) > 1.88 point to considerable metal contributions to the singly occupied MO, corresponding to Ru(III) complexes with either o-quinonoid (--> cations) or catecholate-type ligands (--> anions) and only minor inclusion of Ru(IV)- or Ru(II)-iminosemiquinone formulations, respectively. The preference for the Ru(III) oxidation state for all accessible species is partially attributed to the monoanionic 2,4-pentanedionate (acac) co-ligands which favor a higher metal oxidation state than, e.g., neutral 2,2'-bipyridine (bpy).

Interface superconductivity in the eutecticSr2RuO4−Ru:3-K phase ofSr2RuO4

Enhanced superconductivity in the eutectic system ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}\ensuremath{-}\mathrm{Ru}$ is referred to as the 3-K phase of the spin-triplet superconductor ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$ because of its enhanced superconducting transition temperature ${T}_{c}$ of $\ensuremath{\sim}3\mathrm{K}.$ We have investigated the field-temperature $(H\ensuremath{-}T)$ phase diagram of the 3-K phase for fields parallel and perpendicular to the ab plane of ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4},$ using out-of-plane resistivity measurements. We have found an upturn curvature in the ${H}_{\mathrm{c}2}(T)$ curve for $H\ensuremath{\Vert}c,$ and a rather gradual temperature dependence of ${H}_{c2}$ close to ${T}_{c}$ for both $H\ensuremath{\Vert}\mathrm{ab}$ and $H\ensuremath{\Vert}c.$ We have also investigated the dependence of ${H}_{c2}$ on the angle between the field and the ab plane at several temperatures. Fitting the Ginzburg-Landau effective-mass model apparently fails to reproduce the angle dependence, particularly near $H\ensuremath{\Vert}c$ and at low temperatures. We propose that all of these characteristic features can be explained, at least in a qualitative fashion, on the basis of a theory by Sigrist and Monien that assumes surface superconductivity with a two-component order parameter occurring at the interface between ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$ and Ru inclusions. This provides evidence of the chiral state postulated for the 1.5-K phase by several experiments.

Field–temperature phase diagram of the 3-K phase of Sr2RuO4

We have investigated the field–temperature phase diagram of the 3-K phase (Sr2RuO4–Ru eutectic) for two field directions (H∥ab and H∥c) using resistivity data. We have found an upturn curvature in the Hc2(T) curve for H∥c and a rather gradual temperature dependence of Hc2 close to Tc. We propose that these characteristic features can be explained, at least in a qualitative fashion, on the basis of a theory that assumes surface superconductivity with a two-component order parameter at the interface between Sr2RuO4 and Ru inclusions.

Glucocorticoid modulation of Ca2+ homeostasis in human B lymphoblasts.

1. We determined the effect of cortisol (200 nM for 48 h) on the intracellular Ca2+ concentration ([Ca2+]i) and parameters of Ca2+i signalling in 19 lymphoblastoid cell lines (LCLs). 2. Using the fluorescent dye fura-2, the basal [Ca2+]i in Ca2+-containing medium was 63.5 +/- 2.4 nM in vehicle (ethanol)-treated LCLs and 55.7 +/- 2. 6 nM (mean +/- s.e.m.) in cortisol-treated LCLs. 3. Ca2+i signalling following platelet-activating factor (PAF, 100 nM) addition was enhanced by cortisol treatment, with LCLs having small PAF responses showing the largest percentage increase after cortisol treatment. Mean peak [Ca2+]i responses to PAF were enhanced 67.0% and 55.7% in Ca2+-free and Ca2+-containing medium, respectively. 4. The endoplasmic reticulum Ca2+-ATPase inhibitor thapsigargin (100 nM) caused a transient increase in [Ca2+]i in Ca2+-free medium in which the peak change was increased in cortisol-treated cells (98.5 +/- 5.8 vs. 79.8 +/- 4.5 nM). Peak changes in the freely exchangeable Ca2+ in response to 5 microM ionomycin were also enhanced in cortisol-treated cells (923.7 +/- 113.9 vs. 652.2 +/- 64.5 nM) and correlated to the PAF-evoked [Ca2+]i response. 5. Cortisol-treated LCLs exposed to thapsigargin to empty intracellular Ca2+ stores (10 min treatment in Ca2+-free medium) and exposed to CaCl2 or MnCl2 had a greater rate of Ca2+ entry (18.6 +/- 1.8 vs. 13.8 +/- 1.5 nM s-1) and higher rate constant for Mn2+ entry (0.0345 +/- 0.0029 vs. 0. 0217 +/- 0.0020) than vehicle-treated cells. Peak [Ca2+]i in cells exposed to CaCl2 was also enhanced (869.4 +/- 114.7 vs. 562.6 +/- 61.7 nM). Parameters of divalent cation influx were highly correlated to the peak [Ca2+]i elicited by thapsigargin or ionomycin. 6. Inclusion of RU 486 (a glucocorticoid antagonist) with cortisol prevented the decrease in basal [Ca2+]i and stimulatory actions of cortisol on all Ca2+i parameters. RU 486 alone had no apparent effects on basal [Ca2+]i or Ca2+i signalling. 7. Based on data obtained over a wide range of responses (in the presence and/or absence of cortisol or RU 486), the results show that cortisol stimulation of glucocorticoid receptors decreases basal [Ca2+]i and enhances PAF-evoked [Ca2+]i signalling, most probably through its effects on intracellular Ca2+ stores. In turn, the extent of Ca2+ entry via store-operated plasma membrane Ca2+ channels is closely linked to the size of the Ca2+ stores.

Binding Characteristics of Mineralocorticoid and Glucocorticoid Receptors in Dog Brain and Pituitary

A series of studies was started to gain insight into the functioning of the canine hypothalamo-pituitary-adrenocortical axis during normo- and hypercortisolemic states. In this first study, we have focused on the binding characteristics of the mineralocorticoid receptor (MR) and the glucocorticoid receptor (GR) in the brain and pituitary of the adrenalectomized dog. In hippocampal cytosol at 0 C, corticosterone had the highest association rate, followed by cortisol and aldosterone. Cortisol had the most rapid rate of dissociation from MR at 0 C (t1/2 = 45.5 h), followed by aldosterone (70.4 h) and corticosterone (102 h). The selective glucocorticoid RU 28362 associated rapidly with hippocampal GR, attaining maximum binding within 4 h, and dissociated with a t1/2 of 34.8 h. Saturation binding of [3H]cortisol in adrenalectomized dog hippocampal cytosol produced a curvilinear Scatchard plot. After inclusion of RU 28362, [3H]cortisol bound solely to MR [dissociation constant (Kd) = 0.34 nM, Bmax = 72.8 fmol/mg]. GR capacity was determined with [3H]RU 28362 (Kd = 0.39 nM, Bmax = 120 fmol/mg). Competition binding analyses of various steroids for MR and GR revealed markedly different patterns of steroid binding specificity for these receptors. The rank order for displacement of [3H]aldosterone binding of MR was: corticosterone greater than aldosterone = cortisol greater than dexamethasone greater than ZK 91587 greater than RU 26752 greater than spironolactone much greater than RU 38486, and for displacement of [3H]RU 28362 binding of GR: RU 28362 much greater than corticosterone = cortisol greater than dexamethasone greater than aldosterone greater than ZK 91587 greater than RU 26752 = RU 38486 much greater than spironolactone. MR was located in all brain regions examined, with highest levels in the septo-hippocampal complex, whereas GR was rather evenly distributed. Substantial amounts of MR and GR were present in the anterior part of the pituitary as well as in the neurointermediate lobe. Our findings show that the ligand binding specificity of canine MR and GR is remarkably different from that of rodent MR and GR, but is similar to that of recombinant-derived human receptors. Spironolactone and RU 38486 are selective antagonists for MR and GR, respectively. In contrast to other species, the dog has relatively large quantities of MR widely distributed in the brain and pituitary, which makes this species an interesting animal model to study the role of corticosteroid receptor diversity in control of homeostasis.