Divalent Barium Research Articles

Ba(MoO2F)2(XO3)2 (X = Se and Te): First Cases of Noncentrosymmetric Fluorinated Molybdenum Oxide Selenite/Tellurite Through Unary Substitution for Enlarging Band Gaps and Second Harmonic Generation.

Nonlinear optical (NLO) materials have critically important applications in advanced laser technologies. However, achieving a good balance between the mutual competing NLO properties and band gap within one molecular structure remains a great challenge. In this study, two alkaline earth metal fluorinated molybdenum oxide selenite/tellurite, Ba(MoO2F)2(XO3)2 [X = Se (BMFS) and Te (BMFT)], were synthesized through a facile unary substitution: BMFS was obtained by partial substitution of oxygen atoms with highly electronegative fluorine in the parent compound BaMo2O5(SeO3)2 (BMS), while BMFT was achieved by further replacing lone-pair Se4+ cations in BMFS with heavier Te4+ cations in the same main group. By partially replacing oxygen with fluorine, BMFS shows a broadened band gap and enhanced second harmonic generation (SHG) response compared to BMS owing to the high electronegativity of fluorine anions and the favorable orientation and alignment of NLO-active [MoO5F]5- and [SeO3]2- groups, which is relatively rare for unary anion substitution. BMFS and BMFT are isostructural and both belong to the polar space group Aba2, featuring a three-dimensional (3D) double-layered framework composed of 2D [MoO4F(XO3)]∞ anionic layers interconnected by divalent barium cations. Both BMFS and BMFT exhibit good optical performance, including large SHG responses (3× and 4× KH2PO4), wide band gaps (3.30 and 3.27 eV) and optical transparency window, and high laser damage thresholds (60× and 53× AgGaS2), demonstrating their potential applications as promising second-order NLO crystals. DFT calculations have elucidated the crucial role of the [MoO5F]5- groups in the enlarged band gaps and enhanced SHG responses in BMFS and BMFT. This work proposes a feasible unary substitution strategy for synthesizing the first polar fluorinated molybdenum oxide selenite/tellurite with synchronously enlarged band gaps and SHG efficiency.

X-ray-induced colouring kinetics of (Ba2+, Eu2+)-doubly doped KCl single crystals: influence of the different aggregation–precipitation states of the doping ions

ABSTRACTThe effects of different aggregation–precipitation states of the doping Ba2+-ion on the X-ray-induced generation of F-centres in KCl:Ba2+(675 ppm):Eu2+(27 ppm) single crystals was investigated by optical absorption spectrophotometry. Such states were induced to occur in a controlled manner by subjecting the crystals to suitable thermal treatments. During these treatments, the aggregation–precipitation kinetics of the doping Ba2+-ions was monitored, by optical fluorescence spectrophotometry, utilising the doping Eu2+-ion as an optical probe. As dissolved into the host matrix as forming part of impurity–vacancy (I–V) dipole complexes and small aggregates, divalent barium increases the initial F-colouring rate and F-centre solubility limit by impressive factors of 2 ± 1 and 3 ± 1, respectively, in relation to those of a non-doped crystal. As a constituent of incipient metastable BaCl2-type second-phase precipitates, divalent barium reduces the initial F-colouring rate and F-centre concentration at which the second colouring stage begins by factors of 0.6 ± 0.1 and 0.8 ± 0.1, respectively, in relation to those of the crystal containing barium I–V dipole complexes and small aggregates. As forming part of stable BaCl2 second-phase precipitates and large metastable BaCl2-type second-phase precipitates, divalent barium modifies such a rate and concentration by factors of 1.4 ± 0.1 and 0.7 ± 0.1, respectively, in relation to those of the crystal containing incipient metastable BaCl2-type second-phase precipitates. Also, the doping with divalent barium disrupts the equilibrium between the generation and extinction of F-centres that exists characteristically during the F-curve second colouring stage in a non-doped KCl crystal so that such a rate increases as the aggregation–precipitation phenomena occur within the host matrix. This rate is 0.08 ± (0.08, 0.07), 0.10 ± 0.06 and 0.22 ± (0.05, 0.08) cm–1/h for crystals containing the divalent barium in the form of I–V dipole complexes and small aggregates, incipient precipitates of the metastable BaCl2-type second phase, and large precipitates of both the metastable BaCl2-type second phase and the stable BaCl2 second phase, respectively. The structural mechanisms that are behind the observed effects are discussed.

Luminescent Metal-Nucleobase Network Thin Films by Atomic/Molecular Layer Deposition

Controlled molecular deposition of natural organic molecules such as nucleobases (NBs) into well-defined thin films represents progress toward exciting new nanomaterials. The strongly emerging atomic/molecular layer deposition (ALD/MLD) technique provides us with an elegant way to realize the depositions through gas phase with atomic/molecular level accuracy. In the resultant thin films the organic molecules are bound together not only with hydrogen bonds but also via metal cation linkers and are likely to exhibit novel properties. Here we demonstrate the ALD/MLD of such thin films with monovalent sodium, divalent barium, or trivalent lanthanum as the metal linker and uracil or adenine as the NB component. Our metal-NB thin films are homogeneous, smooth, and in the case of sodium and barium also crystalline showing intense photoluminescence. We discuss the impact of the size and charge of the metal cation on the growth and properties of the films.

Study of Barium Cation Effects on Mechanical Characteristics of the Kahrizak Clay

Some recent research has indicated that certain alkaline contaminations may adversely affect mechanical properties of clayey soils. To examine the potential impact of alkaline divalent barium on the swelling characteristics of KAHRIZAK clay, the major solid-waste landfill at south of Tehran, a systematic set of experiments was conducted. Observations indicated that the swelling in the studied soil that belonged to the CH-MH group with a PI of 28.44, was reduced by about 17, 37, 48 and 54 percent, and swelling pressure by about 41, 55, 65 and 67 percent, respectively, after addition of barium chloride solutions to concentrations of 0.25, 0.5, 0.75 and 1.25 molal. It was also found that addition of barium chloride solutions to concentrations of higher than 1 molal had a little effect on reduction of swelling and swelling pressure.

Structural effects on incorporated water in carbonated apatites

Confirmation of structural H2O in apatites using 2H solid state NMR spectroscopy has been followed by the determination of the number of molecules of H2O per unit cell (MPUC) using thermal gravimetric analysis (TGA) in 10 series of carbonated apatites [CMApX; M10(PO4)6X2 = MApX] containing the divalent cations (M) calcium, strontium, barium, and lead, and monovalent anions (X) OH−, F−, and Cl−. For many of the series, the average MPUC ranges from ca. 1.5–2.5 and is independent of the concentration (wt%) of carbonate. For other series, the average MPUC is as low as ca. 0.8 or as high as ca. 4.0. We have found for six of the series, i.e., those in which carbonate predominantly (>90%) substitutes for phosphate that the average MPUC correlates with cation and anion atomic radii, with unit-cell axial lengths, and, especially, with our calculations of the void space available in the c -axis channels. We speculate that the volume of the channels in apatites affects the ability of H2O to occupy channel sites. In most low-temperature apatites of the type M10(PO4)6X2 that have been studied, carbonate prefers to substitute for phosphate (B-type substitution) rather than for monovalent anions in channel sites (A-type substitution), although computer simulations indicate that carbonate is more thermodynamically stable in the channel sites rather than the phosphate sites. In apatites with nearly total B-type carbonate substitution, there is no relationship between the number of molecules of H2O in the channels and the weight percent carbonate in the apatite. This lack of correlation would be expected when there is no competition within the channel between H2O and carbonate occupancy. In apatites with greater channel volumes, however, we infer that increased ease of carbonate incorporation in the channels also increases competition between H2O and carbonate. The originally incorporated amount of H2O is diminished to accommodate the thermodynamically favored carbonate ion substitution in the channels. We further speculate that these scenarios are most easily rationalized by incorporation of H2O early in the formation of nascent crystallites of apatites formed in aqueous solution, with carbonate entering the newly formed channels later and, in some cases, with difficulty.

Magnetic and Photocatalytic Behaviors of Ba‐Doped BiFeO3 Nanofibers

BiFeO3 nanofibers doped with divalent barium have been fabricated using electrospinning technique. Phase transition from space group R3c to C222 can be observed by the Ba doping. Our results indicate that these BiFeO3 nanofibers show obvious room temperature ferromagnetic behaviors, which can be enhanced remarkably with the increment of Ba doping. Microstructure and composition analysis indicates that barium effectively affected the magnetism after doping content was more than 5% and optical properties.

Low-Energy Ion Scattering spectroscopy of silicate glass surfaces

Low-Energy Ion Scattering (LEIS) spectroscopy is a technique with a unique sensitivity to the elemental composition of the surface top atomic layers of a solid. LEIS measurements of simple binary silicate glasses (with Na2O, Cs2O or BaO) have shown differences in composition between the as-cast glass surface and the vacuum-fracture surface. The as-cast surface is usually depleted of modifier ions compared to the nominal (batch) bulk glass composition, while the fracture surface is typically enriched with the monovalent modifier species, but not the divalent barium. While the melt surface depletion can probably be attributed to evaporation from the hot melt surface, the origin of the strong accumulation on the fracture surfaces is less clear. It is certainly possible that the fracture may have been preferentially guided by regions already alkali-enriched within the bulk of the glass. But considering the extreme surface sensitivity of this method, a surface-monolayer localized enrichment with alkali due to the stress gradient created by the fracture or the electric field created by dangling bonds on the vacuum-fractured surface is also possible. The Si/O ratio shows usually little deviation from the nominal glass batch value, falling within the estimated errors.

Analysis of trace degradation products (decarboxylated diastereoisomers) of S-adenosylmethionine by electrophoresis in capillaries with cationic coatings (N-methylpolyvinylpyridinium or divalent barium)

Commercial preparations of S-adenosylmethionine (SAM) when analyzed in uncoated capillaries show a minute impurity believed to be decarboxylated (dc) SAM. By using two types of cationic coatings, thus reducing the electro-endo-osmotic flow (EOF), it was possible to separate this impurity into two diastereoisomers of dcSAM. The coatings evaluated for this purpose were: (i) N-methylpolyvinylpyridinium, used under reversed EOF at acidic conditions (pH 4.0) and (ii) deposition of divalent barium at alkaline pH values (pH 9.4), providing reduced EOF. Under these conditions, it was possible to separate this impurity into two diastereoisomers, which by chemical synthesis were indeed proven to be dcSAM. It was further demonstrated that, in the alkylation of 5'-methylthioadenosine by 3-bromopropylamine in bromidric acid to dcSAM, another minute impurity was present, proven, via mass spectrometry, to consist of S-(5'-adenosyl)-3-thiopropylamine (decarboxylated and demethylated (dc-SAH)). The LOD for the two dcSAM diastereoisomers was assessed as 17.5 μg/mL and their LOQ as 25.5 μg/mL. By the barium-based protocol it was possible to quantify the dcSAM, present in a commercial sample of SAM, as a 0.1% impurity.

ChemInform Abstract: Divalent Europium-Activated Barium Magnesium Silicate Phosphors: Improvement and Characterization.

Divalent europium‐activated barium magnesium silicate phosphor has been significantly improved by either refiring or rewashing. The greatest improvement was obtained when the phosphor was refired with flux and rewashed with . This reprocessing resulted in a fluorescent lamp of higher maintenance and a lamp output of 100h, twice that of the original phosphor. Surface characterization of treated phosphors using ESCA indicated a dramatic change in the surface chemistry as a result of reprocessing. A strong correlation between phosphor surface composition and lamp performance was observed.

Cr(dmbipy)(ox)2]−: a new bis-oxalato building block for metal assembling. Crystal structures and magnetic properties of XPh4[Cr(dmbipy)(ox)2]·5H2O (X = P and As), {Ba(H2O)2[Cr(dmbipy)(ox)2]2}n·17/2nH2O and {Ag(H2O)[Cr(dmbipy)(ox)2]}n·3nH2O

The synthesis, X-ray structure and variable-temperature magnetic study of new compounds of formula PPh4[Cr(dmbipy)(ox)2]·5H2O (1), AsPh4[Cr(dmbipy)(ox)2]·5H2O (2), {Ba(H2O)2[Cr(dmbipy)(ox)2]2}n·17/2nH2O (3) and {Ag(H2O)[Cr(dmbipy)(ox)2]}n·3nH2O (4) (PPh4+ = tetraphenylphosphonium cation; AsPh4+ = tetraphenylarsonium cation; dmbipy = 4,4′-dimethyl-2,2′-bipyridine; ox2− = oxalate dianion) are reported herein. The isomorphous compounds 1 and 2 are made up of discrete [Cr(dmbipy)(ox)2]− anions, XPh4+ cations [X = P (1) and As (2)] and uncoordinated water molecules. The chromium environment in 1 and 2 is distorted octahedral with Cr–O and Cr–N bond distances varying in the ranges 1.950(2)–1.9782(12) and 2.047(3)–2.0567(14) Å, respectively. The angles subtended at the chromium atom by the two bidentate oxalate ligands cover the range 82.58(10)–83.11(5)°, and they are somewhat greater than those concerning the chelating dmbipy [79.04(10) (1) and 79.24(5)° (2)]. The [Cr(dmbipy)(ox)2]− unit of 1 and 2 also occurs in 3 and 4 but it adopts different coordination modes. It acts as a chelating ligand through its two oxalate groups towards the divalent barium cations in 3 affording neutral chains with diamond-shaped units sharing the barium atoms, while the two other corners are occupied by two crystallographically independent chromium atoms. The barium atom in 3 is coordinated by eight oxygen atoms from four oxalate groups and two aqua ligands. The structure of 4 consists of neutral bimetallic layers where the [Cr(dmbipy)(ox)2]− unit acts as a ligand towards the univalent silver(I) cation through its two oxalate groups, one of them being bidentate and the other bidentate/monodentate (outer). Each silver atom is six-coordinated with a water molecule and five oxygen atoms from three oxalate groups building a highly distorted octahedral environment. Magnetic susceptibility measurements for 1–4 in the temperature range 1.9–300 K show the occurrence of weak ferro- (1 and 2) and antiferromagnetic (3 and 4) interactions which are mediated by π–π stacking between dmbipy ligands through the spin polarization mechanism. A comparative study of the potentiality of the [Cr(AA)(ox)2]− unit (AA = bidentate nitrogen donor) as a building block for designing heterometallic species is carried out in the light of the available structural information.

Effects of Alkaline Earth Metal Ion Complexation on Amino Acid Zwitterion Stability: Results from Infrared Action Spectroscopy

The structures of isolated alkaline earth metal cationized amino acids are investigated using infrared multiple photon dissociation (IRMPD) spectroscopy and theory. These results indicate that arginine, glutamine, proline, serine, and valine all adopt zwitterionic structures when complexed with divalent barium. The IRMPD spectra for these ions exhibit bands assigned to carboxylate stretching modes, spectral signatures for zwitterionic amino acids, and lack bands attributable to the carbonyl stretch of a carboxylic acid functional group. Structural and spectral assignments are strengthened through comparisons with absorbance spectra calculated for low-energy structures and the IRMPD spectra of analogous ions containing monovalent alkali metals. Many bands are significantly red-shifted from the corresponding bands for amino acids complexed with monovalent metal ions, owing to increased charge transfer to divalent metal ions. The IRMPD spectra of arginine complexed with divalent strontium and barium are very similar and indicate that arginine adopts a zwitterionic form in both ions. Calculations indicate that nonzwitterionic forms of arginine are lowest in free energy in complexes with smaller alkaline earth metal cations and that zwitterionic forms are preferentially stabilized with increasing metal ion size. B3LYP and MP2 calculations indicate that zwitterionic forms of arginine are lowest in free energy for M = Ca, Sr, and Ba.

Ionic crosslinking of ionomer polymer electrolyte membranes using barium cations

Acidic polymer electrolyte membranes (PEM) based on sulfonated poly(ether ketone ketone) (SPEKK) with relatively moderate to high levels of sulfonation (ion-exchange capacity (IEC) > 1.7 meq/g) have excellent proton conductivities (∼0.1 S/cm), but they absorb excessive amounts of water at elevated temperatures (ca. 60–90 °C). To reduce the water sorption of the membranes and improve their mechanical properties and dimensional stability, the protons in acidic SPEKK membranes were partially exchanged with divalent barium cations to create ionic crosslinks between the sulfonate groups attached to the aromatic rings of the PEKK. The degree of crosslinking was varied by changing the degree of neutralization of the ionomer. The proton conductivity, water uptake, and methanol permeability at various levels of sulfonation and degree of crosslinking were measured. The conductivity was reduced by crosslinking, but the thermal stability, swelling, and barrier properties were improved. Crosslinking reduced the water swelling at room temperature by nearly a factor of two and prevented membrane dissolution at temperatures up to 80 °C. In a water/methanol mixture (72/28, v/v), swelling was reduced by a factor of four. The balance of transport and mechanical properties could be varied to produce a viable PEM for a direct methanol fuel cell by adjusting the crosslink density.

Interaction of Metal Ions with Caffeine and Theophylline: Stability and Structural Features

The interactions of caffeine and theophylline with divalent cadmium, mercury, strontium and barium ions were studied in aqueous solution and physiological pH. Fourier transform infrared spectroscopy (FTIR) and absorption spectra were used to determine the cation binding mode and association constants. Spectroscopic results showed that Cd2+, Hg2+, Sr2+ and Ba2++ bind strongly to caffeine and theophylline. Direct and indirect (through metal hydration shell) interactions were observed for caffeine and theophylline with Cd2+, Hg2+, Sr2+ and Ba2+ through O6 and N9 (caffeine) and O6, N9 and N7 atoms (theophylline). The overall binding constants are: k(Cd-caffeine) = 1.24 × 105 M−1, k(Hg-caffeine) = 1.74 × 105 M−1, k(Sr- caffeine) = 3.3 × 104 M−1, k(Ba-caffeine) = 1.8 × 104 M−1, k(Cd-theophylline) = 5.75 × 105 M−1, k(Hg-theophylline) = 2.14 × 105 M−1, k(Sr-theophylline) = 4.6 × 104 M−1, k(Ba-theophylline) = 3 × 104 M−1 These k values are evidence for weak and strong cation interactions in these metal complexes.

Cation-Induced Collapse of Low-Molecular-Weight Polyacrylic Acid in the Dispersion of Barium Titanate

Observations on the steric layers formed by the adsorption of low-molecular-weight polyacrylic acid (PAA) were taken using the colloidal probe method in an atomic force microscope. The effects of divalent barium ions and of monovalent potassium ions at varying concentrations were observed on the repulsive interaction profiles. High ionic concentrations screened double-layer forces to small distances, whereby the acting forces were reduced to steric interactions. De Gennes scaling theory was used to model the effect of electrolyte on an aqueous barium titanate system, which was stabilized with PAA. The brush model was found to represent the force curves better than the mushroom model. The collapse of PAA layers with increasing salt approximated a grafted polymer brush in monovalent electrolyte, but the addition of barium ions caused markedly less steric collapse. It is suggested that the formation of a Ba 2+–PAA complex in the adsorbed layer increases its compressibility parameter.

Combined configuration-superposition and many-particle perturbation calculations for atoms with two valence electrons

A new high-precision method is used to calculate the characteristics of atoms with two valence electrons. An effective Hamiltonian for the valence electrons is formulated by many-particle perturbation theory with respect to the residual interaction of the valence electrons with the core. The configuration-superposition method is then used to find the energy levels of the atom. The application of the combined method to divalent calcium, strontium, barium, and ytterbium atoms shows that the ionization potential is obtained within 0.5% error limits. The precision attained for the first few lowest levels of the energy spectra is significantly higher than is obtained by configuration-superposition calculations alone.

ESR studies of Mn 2+Ba 2+ Centres in Ca 1 − xBa xF 2:Mn

An orthorhombic Mn 2+ centre was observed with x-band ESR at room temperature in Ca 1 − x Ba x F 2:Mn crystals. A least-squares fit of the angular dependence of the ESR fields to an orthorhombic spin Hamiltonian gave values of g = 2.001, B 2 0 = −20.59, B 2 2 = −63.10, B 4 0 = −0.016, B 4 4 = −0.016, B 4 4 = 0.028 and A = −102.7 (Gauss). The observed ESR centre is a typical cubic Mn 2+ centre perturbed by a divalent barium ion replaced at the nearest neighbour divalent cation site to the Mn 2+ ion along the [100] direction. The theoretical spin Hamitonian parameters of B 2 0 and B 2 2 were estimated to be B 2 0 = −12.58 and B 2 2 = −45.34 (Gauss) with a polarizable point ion (PPI) model. By using lattice sites of eight displaced fluorine ions around the Mn 2+ ion and R 0 = 2.3085 A ̊ calculated with the PPI model, the superposition (SP) parameters were determined to be t = 5.1 and B ̄ 2 (R 0) = −77.32 (Gauss).

Electronic and Chemical Properties of Barium and Indium Clusters

AbstractThe ground state electronic and chemical properties of divalent barium and trivalent indium are investigated in a self‐consistent manner using the spin‐polarized local density approximation in the framework of the density functional theory. A jellium model is adopted in the spirit of Gunnarsson and Lundqvist's exchange and correlation energies and the calculated properties primarily associated with the s‐p orbitals in barium and p orbitals in indium provide deepend insight towards the understanding of the mechanisms to the magic numbers in both clusters.

Ba2-xKxPb1-yBiyO4- delta : Layered oxides with insulating or conducting properties and possible superconducting properties.

Superconductivity below 14 K has been found by magnetic-susceptibility measurements in a family of layered oxides ${\mathrm{Ba}}_{2\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{K}}_{\mathit{x}}$${\mathrm{Pb}}_{1\mathrm{\ensuremath{-}}\mathit{y}}$${\mathrm{Bi}}_{\mathit{y}}$${\mathrm{O}}_{4\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$. The structure is isomorphous of tetragonal ${\mathrm{La}}_{2}$${\mathrm{CuO}}_{4}$ but these materials do not contain any magnetic ions. Compounds of this family show a transition from insulator (for example, ${\mathrm{Ba}}_{2}$${\mathrm{PbO}}_{4}$, x=0,y=0) to conductor by injection of charge carriers induced by substitution of monovalent potassium onto the divalent barium site. The carrier concentrations are estimated from the screening of phonons by the plasmon deduced from the analysis of infrared-reflection spectra. In the tetragonal structure, ${\mathit{T}}_{\mathit{c}}$ is found twice higher than in the perovskite with the same bismuth concentration. This is achieved in spite of the fact that the carrier concentration remains low, and that the percentage of bismuth y does not exceed 15% in this series of experiments. A thermal treatment at 450 \ifmmode^\circ\else\textdegree\fi{}C under oxygen improves conducting properties in the normal phase but, at least for low bismuth rate, is detrimental to superconductivity. These materials are expected to help clarify the role played by phonons and possible highly anharmonic fluctuations in the mechanism of superconductivity of oxides since here no magnetic interaction can play any part to mediate Cooper pairing as it is often invoked in copper compounds.

ESR studies of Mn 2+ centres in Sr 1− xBa xF 2:Mn crystals

A new orthorhombic Ma 2+ centre was observed by ESR in Sr 1− x Ba x F 2:Mn crystals at room temperature. Least square fitting of the angular dependence of the ESR lines to the spin-Hamiltonian revealed that the spin-Hamiltonian parameters are g = 2.001, B 2 0 = −18.29, B 2 2 = −45.02, B 4 0 = 0.016, B 4 2 = −0.042, B 4 4 = −0.058 and A = −100.4 (Gauss). A probable model for the new ESR centre is a cubic Mn 2+ perturbed by a divalent barium ion placed at the nearest neighbour strontium site along the [110] direction. The spin-Hamiltonian parameters B 2 0 and B 2 2 are compared with theoretically estimated values using the polarizable point charge (PPI) and the superposition (SP) models.

Divalent cation dependence of the inhibition by phenothiazines of mediator release from mast cells

1. The divalent cations calcium, strontium and barium--and in that order of decreasing effectiveness--were capable of supporting the stimulated release of histamine from rat peritoneal mast cells (RPMC). 2. The responsiveness of mast cells to stimulation in the presence of divalent cations was, in general, markedly enhanced when the cells were first depleted of their intracellular calcium stores. 3. The putative calmodulin antagonists, chlorpromazine, promethazine, thioridazine (phenothiazines) and W-7 (a naphthalene sulphonamide) all inhibited histamine release in the presence of divalent cations in both untreated cells and in RPMC depleted of their intracellular calcium. 4. Histamine release induced by antigen, compound 48/80 and ionophore A23187 was inhibited by this class of compounds most effectively in the presence of extracellular barium, less so in the presence of strontium and least so in calcium-containing media. 5. In the experimental situation where the extracellular calcium concentration was reduced (less than 1 mM), the phenothiazines inhibited the stimulated release of histamine more effectively. 6. In toto, these results suggest that strontium and barium, as well as calcium, can support histamine release from RPMC by directly interacting with an intracellular divalent cation-binding site that may be calmodulin. As a consequence, one mechanism by which the phenothiazines and W-7 may modulate the secretory response could reflect an antagonism of a divalent cation interaction at that same site, although other additional potential sites of inhibitory action are indicated, dependent on the stimulus employed for secretion.