Search

Sorghum-agricultural waste in nature (SAWN) and chemically activated with phosphoric acid (SAWAC) was used as a solid phase extraction material for determination of cadmium, copper, manganese and lead ions in aqueous solutions by flame atomic absorption spectrometry (FAAS). The effect of pH, sample flow rate and volume, eluent type, volume and flow rate, and the effects of potentially interfering ions on the recovery of the analytes were investigated. Adsorption capacity of SAWN and SAWAC was determined by batch method under the optimized conditions. Adsorption capacity of SAWAC was found to be 9.53, 11.77, 11.64, and 15.01 mg/L for Cd, Cu, and Mn and Pb ions, respectively. The limit of detection (LOD) for the analytes was found in the range of 0.16-1.21 µg/L with a theoretical preconcentration factor of 50. The method was validated by analyzing certified material (GBW 07605--Tea) and the results were in a good agreement with the certified value. In addition, the proposed method was applied to the determination of analytes in tea and river water samples. Keywords: sorghum-agricultural waste, solid phase extraction, heavy metals, flame atomic absorption spectrometry DOI: 10.1134/S1061934814050098, The heavy metals originate from industrial activities (metal plating, mining, smelting, battery, paint, and pigment manufacture, tanneries, petroleum refining, pesticides, pigment manufacture, printing and photographic industries, etc.) and agricultural activities [...]

Abnormalities in repolarization and its rate dependence are known to related to increased proarrhythmic risk. A number of repolarization-related electrophysiological properties are commonly used as preclinical biomarkers of arrhythmic risk. However, the variability and complexity of repolarization mechanisms make the use of cellular biomarkers to predict arrhythmic risk preclinically challenging. Our goal is to investigate the role of ionic current properties and their variability in modulating cellular biomarkers of arrhythmic risk to improve risk stratification and identification in humans. A systematic investigation into the sensitivity of the main preclinical biomarkers of arrhythmic risk to changes in ionic current conductances and kinetics was performed using computer simulations. Four stimulation protocols were applied to the ten Tusscher and Panfilov human ventricular model to quantify the impact of [+ or -] 15 and [+ or -] 30% variations in key model parameters on action potential (AP) properties, [Ca.sup.2+] and [Na.sup.+] dynamics, and their rate dependence. Simulations show that, in humans, AP duration is moderately sensitive to changes in all repolarization current conductances and in L-type [Ca.sup.2+] current ([I.sub.CaL]) and slow component of the delayed rectifier current ([I.sub.Ks]) inactivation kinetics. AP triangulation, however, is strongly dependent only on inward rectifier [K.sup.+] current ([I.sub.KI]) and delayed rectifier current ([I.sub.Kr]) conductances. Furthermore, AP rate dependence (i.e., AP duration rate adaptation and restitution properties) and intracellular [Ca.sup.2+] and [Na.sup.+] levels are highly sensitive to both [I.sub.CaL] and [Na.sup.+]/[K.sup.+] pump current ([I.sub.NaK]) properties. This study provides quantitative insights into the sensitivity of preclinical biomarkers of arrhythmic risk to variations in ionic current properties in humans. The results show the importance of sensitivity analysis as a powerful method for the in-depth validation of mathematical models in cardiac electrophysiology. biological variability: arrhytbmia: computer simulation doi:10.1152/ajpheart.00263.2009

The regulation of metal ion transport within neurons is critical for normal brain function. Of particular importance is the regulation of redox metals such as iron (Fe), where excess levels can contribute to oxidative stress and protein aggregation, leading to neuronal death. The divalent metal transporter 1 (DMT1) plays a central role in the regulation of Fe as well as other metals; hence, failure of DMT1 regulation is linked to human brain pathology. However, it remains unclear how DMT1 is regulated in the brain. Here, we show that DMT1 is regulated by Ndfip1 (Nedd4 family-interacting protein 1), an adaptor protein that recruits E3 ligases to ubiquitinate target proteins. Using human neurons we show the Ndfip1 is upregulated and binds to DMT1 in response to Fe and cobalt (Co) exposure. This interaction results in the ubiquitination and degradation of DMT1, resulting in reduced metal entry. Induction of Ndfip1 expression protects neurons from metal toxicity, and removal of Ndfip1 by shRNAi results in hypersensitivity to metals. We identify Nedd4-2 as an E3 ligase recruited by Ndfip1 for the ubiquitination of DMT1 within human neurons. Comparison of brains from [Ndfip1.sup.-/-] with [Ndfip1.sup.+/+] mice exposed to Fe reveals that [Ndfip1.sup.-/-] brains accumulate Fe within neurons. Together, this evidence suggests a critical role for Ndfip1 in regulating metal transport in human neurons. cobalt | iron | Nedd4-2 | ubiquitin

Problem statement: Microstructure of the grain will influence the properties of a polycrystalline manganites when different dopant is introduced. In this work, an effort had been made to investigate the influence of Ca, Ba and Sr substitution in La site. Approach: Polycrystalline manganites compound of [La.sub.0.67][A.sub.0.33]Mn[O.sub.3] where A = Ba, Sr and Ca had been prepared via conventional solid-state reaction method. The structure, microstructure, magnetic and electrical properties had been investigated using XRD, SEM, VSM and four-point probe techniques. Results: XRD spectrums showed that LBMO and LCMO were in single-phase orthorhombic structure whereas LSMO was rhombohedral structure. Scanning electron micrographs showed that LSMO had smaller average grain size as compared to LBMO. However, for LCMO, there was no clear grain boundary that can be observed and all the grains were well connected. The difference in the microstructure image might be due to the variance A-site cation that differs in grain growth. The Curie temperature, [T.sub.c] of LBMO and LSMO was 343.0 and 363.5 K, respectively. But the [T.sub.c] for LCMO was lower then 300 K. The [T.sub.p] for LCMO was 215 K while it was near or above 300K for LBMO and LSMO. All samples showed extrinsic Magnetoresistance (MR) effect. Higher MR was observed well below [T.sub.c] or [T.sub.p] where MR value increased monotonically with the decrease of temperature. This was associated with the different grain and grain boundary formation when different cation was substituted. LCMO displayed the highest low-field MR value (-15.82% at 0.2 T, 90 K) and high-field MR (-25.60% at 1 T, 300 K). Conclusion: Hence, electrical and magnetic transition temperature ([T.sub.p] and [T.sub.c]) were affected by the average A-site cation radius. Key words: Ceramic, low field magnetoresistance, magnetoresistance, INTRODUCTION In recent year there has been a lot of research study in Colossal Magnetoresistance (CMR) effects in rare-earth manganite perovskite with general formula [La.sub.[1-x]][A.sub.x]Mn[O.sub.3] (A = Ba, Sr, Pb [...]

The metal ions in the complexes of [Fe.sup.II], [Co.sup.II], [Ni.sup.II], [Cu.sup.II] and [Zn.sup.II] containing the photoactive dipyridoquinoxaline (dpq) ligand have played a vital role in the photoinduced DNA cleavage activity under ultraviolet (UV) and visible light. The studies have shown a photoredox pathway in preference to a type-2 process forming singlet oxygen for the visible-light-induced DNA cleavage activity of the 3d-metal complexes.

The reactions of group 2 metal cations with salicylic acid in the presence of pyridine bases are examined and the structural variations are observed based on the ability of the added pyridinic ligand to chelate the metal ions. Chelating 1,10-phenanthroline is incorporated in the coordination sphere, whereas 4,4'-bipyridine has acted as a lattice filler without the coordination to the metal.

A novel zero-dimensional (0D) octacyanotungstate(V)-manganese(II) bimetallic assembly is prepared in methanol solution containing oxalic acid. The magnetostructural correlation has disclosed that cyanide and oxalate bridges have mediated weak intracluster antiferromagnetic coupling between Mn and W ions and between Mn ions, respectively.

The synthesis of a series of monovalent metal ions with a new trispyrazolyl ligand bearing hemilabile ether appendages is reported.

The investigation results of the base tautomerization processes of uracil/5-bromouracil in a microcosmic environment with both [H.sub.2]O and [Na.sup.} (W-M environment) revealed uracil to be more stable in the W-M environment than in the microscopic environment with only water.

Malic enzymes (MEs) catalyze the oxidative decarboxylation of malate in the presence of a divalent metal ion. In eukaryotes, well-conserved cytoplasmic, mitochondrial, and plastidic MEs have been characterized. On the other hand, distinct groups can be detected among prokaryotic MEs, which are more diverse in structure and less well characterized than their eukaryotic counterparts. In Escherichia coli, two genes with a high degree of homology to ME can be detected: sfcA and maeB. MaeB possesses a multimodular structure: the N-terminal extension shows homology to ME, while the C-terminal extension shows homology to phosphotransacetylases (PTAs). In the present work, a detailed characterization of the products of E. coli sfcA and maeB was performed. The results indicate that the two MEs exhibit relevant kinetic, regulatory, and structural differences. SfcA is a NAD(P) ME, while MaeB is a NADP-specific ME highly regulated by key metabolites. Characterization of truncated versions of MaeB indicated that the PTA domain is not essential for the ME reaction. Nevertheless, truncated MaeB without the PTA domain loses most of its metabolic ME modulation and its native oligomeric state. Thus, the association of the two structural domains in MaeB seems to facilitate metabolic control of the enzyme. Although the PTA domain in MaeB is highly similar to the domains of proteins with PTA activity, MaeB and its PTA domain do not exhibit PTA activity. Determination of the distinct properties of recombinant products of sfcA and maeB performed in the present work will help to clarify the roles of MEs in prokaryotic metabolism.

Three fluorescence signaling DNA enzymes (deoxyribozymes or DNAzymes) were successfully immobilized within a series of sol--gel-derived matrixes and used for sensing of various metal ions. The DNAzymes are designed such that binding of appropriate metal ions induces the formation of a catalytic site that cleaves a ribonucleotide linkage within a DNA substrate. A fluorophore (fluorescein) and a quencher (DABCYL, [4-(4-dimethylaminophenylazo)benzoic acid]) were placed on the two deoxythymidines flanking the ribonucleotide to allow the generation of fluorescence upon the catalytic cleavage at the RNA linkage. In general, all DNAzymes retained at least partial catalytic function when entrapped in either hydrophilic or hydrophobic silica-based materials, but displayed slower response times and lower overall signal changes relative to solution. Interestingly, it was determined that maximum sensitivity toward metal ions was obtained when DNAzymes were entrapped into composite materials containing ~40% of methyltrimethoxysilane (MTMS) and ~60% tetramethoxysilane (TMOS). Highly polar materials derived from sodium silicate, diglycerylsilane, or TMOS had relatively low signal enhancements, while materials with very high levels of MTMS showed significant leaching and low signal enhancements. Entrapment into the hybrid silica material also reduced signal interferences that were related to metal-induced quenching; such interferences were a significant problem for solution-based assays and for polar materials. Extension of the solid-phase DNAzyme assay toward a multiplexed assay format for metal detection is demonstrated, and shows that sol--gel technology can provide new opportunities for the development of DNAzyme-based biosensors.

The role of [Ca.sup.2} in oxygen evolution is examined by monitoring the [S.sub.1] to [S.sub.2] state transition in photosystem II (PSII) membranes and PSII core complexes upon inhibition of oxygen evolution by [Dy.sup.3}, [Cu.sup.2} and [Cd.sup.2} ions. The results show that [Ca.sup.2} has played a vital structural role in the early S-state transitions and that the functional role of [Ca.sup.2} to activate water in the O-O bond-forming reaction that occurs in the final step of the S state cycle can only be fulfilled by [Ca.sup.2} and [Sr.sup.2}.

Many of the essential metalloproteins are located in the cell, whose cytoplasmic fluid contines several small inorganic anions, such as [Cl.sup.-], [NO2.sup.-], [NO3.sup.-], [H2PO4.sup.-] and [SO4.sup.3-], that play an indispensable role in determining the cell's volume, regulating the cell's pH, signal transduction, muscle contraction and cell growth and metabolism. The physiochemical basis for the competition between these abundant, intracellular anions and protein or nucleic acid residues in binding to cytoplasmic metal cations such as [Na.sup.}, [K.sup.1], [Mg.sup.2} and [Ca.sup.2} is delineated using density functional theory in conjunction with the continuum dielectric method.

The various physicochemical factors that influence the flux of carrier-transported metal ions through permeation liquid membranes (PLM) are studied systematically. Understanding PLM behavior is important (i) to optimize the application of PLM as metal speciation sensors in environmental media and (ii) because PLM may serve as bioanalogical devices that help to elucidate the environmental physicochemical processes occurring at the surface of biological membranes. Diffusion of free and complexed metal ions in solution, as well as diffusion of the metal carder complex in the membrane, is considered. The respective roles of diffusion layer thickness, ligand concentration, complex stability, carder concentration, and membrane thickness are studied experimentally in detail and compared with theory, using various labile complexes, namely, Pb(II)--diglycolate, Cu(II)--diglycolate, and Cu(II)--N-(2-carboxyphenyl)glycine. Conditions where either membrane diffusion or solution diffusion is rate limiting are clearly discriminated. It is shown in particular, that, by tuning the carder concentration or membrane thickness, either the free metal ion concentration or the total labile metal species are measured. PLM can thus be used to determine whether models based on the free ion activity in solution (such as BLM or FIAM models) are applicable to metal uptake by microorganisms in a real natural medium.

A sensor technique is described that captures analyte species on a preconcentrating minicolumn containing a selective solid-phase sorbent. In this approach, the sample is pumped through the column until the sorbent phase is fully equilibrated with the sample concentration, and the exit concentration equals the inlet concentration. Oncolumn detection of the captured analytes using radiometric and spectroscopic methods is demonstrated. In trace level detection applications, this sensor provides a steady-state signal that is proportional to sample analyte concentration and is reversible. The method is demonstrated for the detection of Tc-99 using anion-exchange beads mixed with scintillating beads and light detection, Sr-90 using SuperLig 620 beads mixed with scintillating beads and light detection; and hexavalent chromium detection using anion-exchange beads with spectroscopic detection. Theory has been developed to describe the signal at equilibration and to describe analyte uptake as a function of volume and concentration, using parameters and concepts from frontal chromatography. It is shown that experimental sensor behavior closely matches theoretical predictions and that effective sensors can be prepared using low plate number columns. This sensor modality has many desirable characteristics for in situ sensors for trace level contaminant long-term monitoring where the use of consumable reagents for sensor regeneration would be undesirable. Initial experiments in groundwater matrixes demonstrated the detection of Tc-99 at drinking water level standards (activity of 0.033 Bq/ mL) and detection of hexavalent chromium to levels below drinking water standards of 50 ppb.

A GAAA tetraloop domain and receptor domain are connected by a single-strander A7 linker to investigate the metal ion dependence, kinetics and thermodynamics for the isolated tertiary interaction in RNA of the GAAA-tetraloop motif. Studies of docking induced using a variety of metal ions show that the single-stranded region functions primarily as a flexible tether and inhibition of docking by oligonucleotides complementary to the linker is investigated.

The demonstration of gain-saturated high repetition rate table-top soft X-ray lasers producing microwatt average powers at wavelengths ranging from 13.9 to 33nm is discussed. Results are obtained by heating precreated plasma with a picosecond optical laser pulse impinging at grazing incidence onto precreated plasma.

The diphtheria toxin repressor (DtxR) is a metal ion-activated transcriptional regulator that has been linked to the virulence of Corynebacterium diphtheriae. Structure determination has shown that there are two metal ion binding sites per repressor monomer, and site-directed mutagenesis has demonstrated that binding site 2 (primary) is essential for recognition of the target DNA repressor, leaving the role of binding site 1 (ancillary) unclear. Calorimetric techniques have demonstrated that although binding site 1 (ancillary) has high affinity for metal ion with a binding constant of 2 x [10.sup.-7], binding site 2 (primary) is a low-affinity binding site with a binding constant of 6.3 x [10.sup.-4]. These two binding sites act in an independent fashion, and their contribution can be easily dissected by traditional mutational analysis. Our results clearly demonstrate that binding site 1 (ancillary) is the first one to be occupied during metal ion activation, playing a critical role in stabilization of the repressor. In addition, structural data obtained for the mutants Ni-DtxR(H79A,C102D), reported here, and the previously reported DtxR(H79A) have allowed us to propose a mechanism of metal activation for DtxR. iron | homeostasis | transcription regulation

The di-Mn(II) and di-Co(II) derivatives of variants of the DF1 metalloprotein exhibit an increased number and polarity of exogenous ligands with an increase in the size of the active site cavity. The geometric parameters defining the DF structures, which show significant helix tilting and sliding motions, are compared to natural diron proteins and it is seen that DF proteins have a restricted active site cavity, which imply substrate rocognition and chemical stability.

How does iron enter enterocytes? Ablating SLC11A2, the gene for the divalent metal ion transporter DMT1, supports evidence from the Belgrade rat and mk mouse models establishing DMT1 as the primary mechanism serving apical uptake of nonheme iron. DMT1 harnesses the energy from the proton electrochemical potential gradient to drive active transport of [Fe.sup.2+] (and perhaps [Mn.sup.2+] and other metal ions) into enterocytes. Fe(III) must first be reduced by ascorbic acid and surface ferrireductases. Among these is duodenal cytochrome B (DcytB), but lack of an obvious phenotype in DcytB (Cybrd1) knockout mice suggests ferrireductase redundancy. Our understanding of heine absorption has lagged, but the time is ripe for gains. anemia: duodenal cytochrome B; divalent metal ion transporter; ferroportin; hemochromatosis; iron absorption; Nramp2; SLC11A2

In the study reported here, we study the nature of the metal ion complexes of EDTA as solute systems for analysis of lipoproteins by density gradient ultracentrifugation (DGU) by varying both the complexing metal ion and the counterion. Specifically, the sodium and cesium salts of complexes of Bi/EDTA, Pb/EDTA, Cd/EDTA, Fe/ EDTA, and Cu/EDTA were chosen for this study. We show that useful gradients can be formed within a few hours beginning with a homogeneous solution. Data are presented that provide insight into the nature of how these gradients are formed from these complexes and how the selection of a specific complex can be used to enhance particular regions of the lipoprotein density profile for clinical studies. We also examine the use of equilibrium sedimentation theory to correlate the measured density profiles generated by these complexes with their molecular weight.

The unique ligation properties of metal ions are widely exploited by proteins, with approximately one-third of all proteins estimated to be metalloproteins. Although antibodies use various mechanisms for recognition, to our knowledge, none has ever been characterized that uses an interfacial metal. We previously described a family of CD4-reactive antibodies, the archetype being Q425. CD4:Q425 engagement does not interfere with CD4:HIV-1 gp120 envelope glycoprotein binding, but it blocks subsequent steps required for viral entry. Here, we use surface-plasmon resonance to show that Q425 requires calcium for recognition of CD4. Specifically, Q425 binding of calcium resulted in a 55,000-fold enhancement in affinity for CD4. X-ray crystallographic analyses of Q425 in the presence of [Ca.sup.2+], [Ba.sup.2+], or EDTA revealed an exposed metal-binding site, partially coordinated by five atoms contributed from four antibody complementarity-determining regions. The results suggest that Q425 recognition of CD4 involves direct ligation of antigen by the Q425-held calcium, with calcium binding each ligating atom of CD4 with [approximately equal to] 1.5 kcal/mol of binding energy. This energetic contribution, which is greater than that from a typical protein atom, demonstrates how interfacial metal ligation can play a unique role in antigen recognition. antibody Q425 | CD4 | crystal structure | HIV

Experimental data are presented showing that, for a light heavy ion such as Carbon, large collection-efficiency losses appear in Silicon Surface Barrier detectors for large enough ion fluences. This effect, apparently related to the onset of radiation damage of the detector, shows an S-shape behavior with the fluence above threshold. Index Terms--Ion fluence, pulse height defect, Rutherford backscattering, silicon detector.

The parameters of metallic plasma in the interelectrode gap of vacuum-arc discharge have been studied over a wide range of gas pressures. Emission spectroscopy methods and electric probe techniques were used for diagnostics. In the 1-10 Pa pressure range, the action of the mechanism of activation (excitation and ionization) of metal (Ti) ions and atoms was observed. This mechanism was realized through interaction of erosion products released from the cathode spot with the excited gas particles. The energy transfer from gas particles to the titanium particles existing in the form of drops, and also as neutral vapors and ions, leads to drop evaporation and additional excitation/ionization of metal vapors and ions. In the 1-10 Pa pressure range, this leads to a significant increase in titanium ion concentrations. The possibility of the mechanism of plasma chemical synthesis of metal-gas compounds at pressures higher than 1 Pa not on the substrate but in the plasma volume with formation of fine dust is discussed. Index Terms--Excited particles, intensity lines, interelectrode plasma, metal ions, vacuum arc.

Electron paramagnetic resonance (EPR) spectroscopy is used to examine changes in internal structure and dynamics of the hammerhead ribozyme upon metal ion induced folding, changes in pH, and the presence and absence of ribozyme inhibitors. Results reveal that different U7 dynamics are observed in the presence of catalytically efficient divalent metal ion concentrations than in the presence of high concentrations of monovalent metal ions.

We report the 3.4 angstrom crystal structure of a catalytically active group I intron splicing intermediate containing the complete intron, both exons, the scissile phosphate, and all of the functional groups implicated in catalytic metal ion coordination, including the 2'-OH of the terminal guanosine. This structure suggests that, like protein phosphoryltransferases, an RNA phosphoryltransferase can use a two-metal-ion mechanism. Two [Mg.sup.2+] ions are positioned 3.9 angstroms apart and are directly coordinated by all six of the biochemically predicted ligands. The evolutionary convergence of RNA and protein active sites on the same inorganic architecture highlights the intrinsic chemical capacity of the two-metal-ion catalytic mechanism for phosphoryl transfer., Divalent metal ions are used in the active sites of a variety of protein phosphoryltransfer enzymes, including those required for replication, transcription, and cell signaling (1-3). Structural and biochemical studies [...]

Two bis(calix[4]diquinone) compounds and one double (calix[4]diquinone) are synthesized from their corresponding double calix[4]arenas. It is demonstrated that double calix[4]arenas can be synthesized in reasonable yields under high pressure.

A report on electrochemistry of 16 different water-soluble porphyrins of the type [(TMpyP)M(super II)](super 4+)(X-)4 or [(TMpyP)M(super III)Cl](super 4+)(Cl(super -))4 in nonaqueous media is presented where TMpyP is the dianion of the meso-tetrakis(N-methylpyridiniumyl)porphyrin and X= Cl(super -) or BPh4(super -). The effect of the metal ion and porphyrin counterion (X-) on the electrochemical properties of the TMpyP complexes is examined.

A new optical metal ion sensor based on diffusion followed by an immobilizing reaction has been developed. The current sensor is based on a model that unifies two fundamental processes which a metal analyte undergoes when it is exposed to a porous, ligand-grafted monolith: (a) diffusion of metal ions to the binding sites and (b) metal--ligand ([ML.sub.n]) complexation. A slow diffusion of the metal ions is followed by their fast immobilizing reaction with the ligands in the monolith to give a complex. Inside the region where the ligands have been saturated, the diffusion of the metal ions reaches a steady state with a constant external metal ion concentration (Co). If the complex [ML.sub.n] could be observed spectroscopically, the absorbance of the product [A.sub.p] follows: Ap = [Kt.sup.1/2], K = 2 [square root of 2][member of] [([L.sub.0][C.sub.0]D).sup.1/2]. D = diffusion constant of the metal ions inside the porous solid; [L.sub.0] = concentration of the ligands grafted in the monolith; and t = time. This equation is straightforward to use, and the K vs [C.sub.0.sup.1/2] plot provides the correlations with the concentrations ([C.sub.0]) of the metal ions. This is a rare optical sensor for quantitative metal ion analysis. The use of the model in a mesoporous sol--gel monolith containing grafted amine ligands for quantitative [Cu.sup.2+] sensing is demonstrated. This model may also be used in other chemical sensors that depend on diffusion of analytes followed by immobilizing reactions in porous sensors containing grafted/encapsulated functional groups/molecules.

Abstract: An extraction and sensitive differential pulse anodic stripping voltammetric (DPASV) method at a hanging mercury drop electrode (HMDE) is described for the determination of Zn, Cu, Pb ([micro]g [g.sup.1]) [...]

The detailed stoichiometry of the reaction between the aldopentoses, ribose, arabinose, lyxose, and xylose, and the cis rhodium(III) complex of the macrocyclic tetraamine ligand rac-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane in weakly acidic aqueous solution is studied by (super 13)C NMR, using deuterium- and carbon-13-labeled substrates.

The study investigated some novel properties of organized molecular films of 10,12-tricosadiynoic acid (TDA), which were modulated by transition metal ions. It concluded that metal ions such as Cu(super 2+), Zn(super 2+), Ni(super 2+), Cd(super 2+), and Ag(super +) in the subphase can greatly affect the monolayer formation of TDA and the properties of the subsequently deposited Langmuir-Blodgett (LB) films, particularly in the case of Ag(super +), Zn(super 2+), and Cu(super 2+) ions.

Abstract -- Methods for rhenium extraction from plant materials were studied using model systems and the [.sup.186.Re] isotope. Conditions are described for the quantitative extraction of rhenium with acid and [...]

A theoretical study of the static and dynamic polarizabilities of two series of polyatomic molecules and their molecular ions is described. The trends in polarizability are investigated as a function of molecular size and pi electron conjugation.

Unlike metal-ion-catalyzed hydrolysis processes, metal-ion-catalyzed methanolysis processes have received scant attention in the literature particularly from the standpoint of mechanistic studies. [La.sup.3+], introduced into methanol solution as its triflate or perchlorate salt, is particularly effective in promoting methanolysis reactions of unactivated and activated esters, phosphate triesters, and activated amides such as acetyl imidazoles and lactams. Studies of the kinetics of methanolysis of these substrates as a function of solution pH and [[La.sup.3+]] indicate that the solution comprises lanthanum dimers with one to five associated methoxides ([[La.sub.2.sup.3+] ([sup.-]OC[H.sub.3]).sub.1-5]), the most catalytically active form being [La.sub.2.sup.3+]([[sup.-]OC[H.sub.3]).sub.2], which is produced at near neutral pH in methanol (8.4). Mechanisms for all the acyl and phosphoryl transfer reactions are proposed where the metal ion serves a dual role of acting as a Lewis acid to activate the C=O or P=O system to nucleophilic attack by a metal-coordinated methoxide nucleophile. In cases where direct comparisons can be made, the [La.sub.2.sup.3+] catalyst system is more active for the methanolysis of nonactivated substrates than for activated substrates. Another general characteristic of this system is that the catalytic rate constant for the metal complex exceeds the second-order rate constant for free methoxide, in some cases by as much as 4600-fold. Overall the catalytic effects exhibited by the [La.sub.2.sup.3+] system is spectacular for such substrates as paraoxon, where as little as 2 mmol [L.sup.-1] La[(OTf).sub.3] in the presence of equimolar NaOC[H.sub.3] accelerates the methanolysis by [10.sup.9]-fold relative to the background reaction at neutral pH and ambient temperature. Key words: kinetics of methanolysis, metal ion catalysis, lanthanides, methanolysis of carboxylate esters and phosphate esters.

The study focuses on metal ion-ligand complexes of biological relevance and measurements of the bond dissociation energies of such species. The importance of ion-dipole and ion-induced dipole interactions, chelation, conformation, tautomeric form, steric interactions, chelation, conformation, tautomeric form, steric interactions, and electronic effects such as hybridization and promotion is elucidated.

The incorporation of lipophilic ligands into the bilayer membrane of vesicles offers the possibility to induce, upon binding of suitable metal ions, a variety of processes, in particular vesicle aggregation and fusion and generation of vesicle arrays, under the control of specific metal-ligand recognition events. Synthetic bipyridine lipoligands Bn bearing a bipyridine unit as head group were prepared and incorporated into large unilamellar vesicles. The addition of [Ni.sup.2+] or [Co.sup.2+] metal ions led to the formation of complexes MBn and M[Bn.sub.2] followed by spontaneous fusion to generate giant multilamellar vesicles. The metal ion complexation was followed by UV spectroscopy and the progressive fusion could be visualized by optical dark-field and fluorescence microscopies. Vesicle fusion occurred without leakage of the aqueous compartments and resulted in the formation of multilamellar giant vesicles because of the stacking of the lipoligands Bn. The fusion process required a long enough oligoethylene glycol spacer and a minimal concentration of lipoligand within the vesicle membrane. Metal-losupramolecular systems such as the present one offer an attractive way to induce selective intervesicular processes, such as vesicle fusion, under the control of molecular recognition between specific metal ions and lipoligands incorporated in the bilayer membrane. They provide an approach to the design of artificial 'tissue-mimetics' through the generation of polyvesicular arrays of defined architecture and to the control of their functional properties. vesicle fusion | molecular recognition

The low-valent and coordinatively unsaturated cobalt(I) triscarbene complex[(TIMEN(super xyl))]CO]CI is synthesized and characterized. The results suggest that nucleophilic character of the Eta(super 2)-bound dioxygen ligand is confirmed by density functional theory (DFT) studies and allows for oxygen-transfer reactions with electron-deficient organic substrates, such as benzoyl chloride.

A study is conducted to synthesize N-(2-(5-cyanopyridyl) cyclen 10(L5) and N-(2-pyridyl) cyclen 11(16) in order to control TICT in aqueous solution utilizing the potent binding properties of cyclen. Chelation-controlled TICT with a considerable shift of emission wavelength may provide new methodologies for designing novel fluorescence sensors for metal ions and biologically relevant anions in aqueous solution.

The structural and thermodynamic characterization of the assembly process leading to [Ln29L2)(sub 3)(super 6+) provides an initial set of absolute affinities for the terminal N6O3 site, Together with acceptable intermetallic interactions. A single intermetallic interaction between two adjacent metal ions in the complexes successfully models the experimental macroscopic constants and allows the rational molecular programming of the extended trimetallic homologues.

A copper compound structure with peptide Gly-Trp belongs to the P212121 space group with Z=4. These magnitudes are studied on the basis of structural information about intervening long chemical paths.

Four crystal structures of EcoRV endonuclease mutants K92A and K38A gives new insight into the mechanism of DNA bending and the structural basis for metal-dependent phosphodiester bond cleavage. The studies suggest a novel mechanism in which a single initially bound metal ion in a third distinct site undergoes a shift in position together with movement of the scissile phosphate deeper into the active site cleft, which reconfigures the local environment to permit binding of second metal ion.

To improve the detection sensitivity of metal ions in capillary zone electrophoresis (CZE), a novel method that combines complex formation and on-line sample preconcentration by sweeping was developed. Sweeping is defined as the picking and accumulating of analytes by a carrier in the background solution, with which they have considerable affinity. In this sweeping method, using ethylenediaminetetraacetic acid as carrier, dynamic complexation to form a UV-absorbing chelate and on-line preconcentration occur simultaneously during a run. The technique was validated in terms of the limit of detection, reproducibility, and sensitivity enhancement. Detection responses of some divalent metal ions, in terms of peak heights, were improved from 60- to 180-fold, relative to conventional CZE which employed precapillary complexation. The limits of detection were in the range of (1.823.4) x [10.sup.-8] M. This method was applied to the analysis of trace metal ions in factory wastewater. Furthermore, sweeping in conjunction with sample stacking accompanying electrokinetic injection, cation-selective exhaustive injection (CSEI-sweeping), was also examined. Up to 140 000-fold improvement in detector responses for some divalent and trivalent metal ions was realized by CSEI-sweeping. The limits of detection were in the range (2.4-25.2) x [10.sup.-11] M.

Concentration of the salts and the charge of metal ion on swelling behavior, composition and structure of the gels poly (PAMPS) salts in aqueous medium are studied. The existence of the reentrant conformational transition in the anionic PAMPS gel is due to the increase of concentration of trivalent metal cations in the solutions.

J-aggregate phase transition at air-water interface was done using infrared reflection absorption spectroscopy. The phase transition from LT phase to HT phase is accompanied by the exchange of metal ions.

The ion sensing properties of a conjugated polymer composed of a rigidly planar unit 1,10-phenanthroline (phen) (P2), having stronger co-ordination ability with metal ions compared with 2,2'-bipyridine as molecular recognition sites is examined. A significant improvement in the sensing activity of a phen-based polymer is observed compared with that of a by-based polymer.

A binding site for metal ions has been created on the surface of horse heart myoglobin (Mb) near the heme 6-propionate group by replacing K45 and K63 with glutamyl residues. One-dimensional [sup.1]H NMR spectroscopy indicates that [Mn.sup.2+] binds in the vicinity of the heme 6-propionate as anticipated, and potentiometric titrations establish that the affinity of the new site for [Mn.sup.2+] is 1.28(4) x [10.sup.4] [M.sup.-1] (pH 6.96, ionic strength I = 17.2 [micro]M, 25[degrees]C). In addition, these substitutions lower the reduction potential of the protein and increase the p[K.sub.a] for the water molecule coordinated to the heme iron of metmyoglobin. The peroxidase [2,2'-azinobis(3-ethylbenzthiazoline-6-sulfonic acid), ABTS, as substrate] and the [Mn.sup.2+]-peroxidase activity of the variant are both increased [approximately equal to]-fold. In contrast to wild-type Mb, both the affinity for azide and the midpoint potential of the variant are significantly influenced by the addition of [Mn.sup.2+]. The structure of the variant has been determined by x-ray crystallography to define the coordination environment of bound [Mn.sup.2+] and [Cd.sup.2+]. Although slight differences are observed between the geometry of the binding of the two metal ions, both are hexacoordinate, and neither involves coordination by E63.