Potentiometric determination of aminal stability constants

Potentiometric titration was used to determine the logarithms of the stepwise equilibrium constants for the species formed between morpholine and formaldehyde in aqueous solution, ionic strength 0.5 and 2.5M (KCl) at 25 degrees C. The instrumental and computational techniques developed for metal-ligand stability constant determination were applied. Formaldehyde is equivalent to the metal-ion and is represented by M while neutral morpholine is equivalent to the ligand and is represented by L. The stability constants of the following equilibria were determined by non-linear regression (figures in parentheses are at ionic strength 2.5 M KCl): M + L left arrow over right arrow ML (hemi-aminal) logK(1) = 2.90 +/- 0.02 (2.980 +/- 0.004); ML + L left arrow over right arrow ML(2) (bis-aminal); log K(2) = 1.3 +/- 0.2 (1.41 +/- 0.07); MLH left arrow over right arrow ML + H(+) (protonated hemi-aminal) pK(a) = 5.87 +/- 0.01 (6.411 +/- 0.005); ML(2)H left arrow over right arrow ML(2) + H(+) (protonated bis-aminal) pK(a) = (7.6 +/- 0.2). the pK(a) of the protonated bis-aminal could only be determined at the higher ionic strength. The results are in good agreement with reported values determined using the classic formol titration. The automated titration system acquired the full time course of the pH change upon each titrant addition allowing a kinetic analysis to be performed as well as an equilibrium analysis. The forward and reverse rate constants for M + L left arrow over right arrow ML were 0.77M(-1) sec(-1) and 8.1 x 10(-4) sec(-1). respectively.     

Molecular dynamics study on the interaction of a mithramycin dimer with a decanucleotide duplex

The complex of a minor groove binding drug mithramycin (MTR) and the self-complementary d(TAGCTAGCTA) 10-mer duplex was investigated by molecular dynamics (MD) simulations using the AMBER 7.0 suite of programs. There is one disaccharide and trisaccharide segment projecting from opposite ends of an aglycone chromophore of MTR. A MTR dimer complex (MTR)2Mg2+ is formed in the presence of a coordinated ion Mg2+. A NMR solution structure of two (MTR)2Mg2+ complexes bound with one DNA duplex, namely, the 2:1 duplex complex, was taken as the starting structure for the MD simulation. The partial charge on each atom was calculated using the multiple-RESP fitting procedure, and all of the missing parameters in the Parm99 force field used were adapted comparably from the literature. The length of the MD simulation was 5 ns, and the binding free energy for the formation of a 1:1 or 2:1 duplex complex was determined from the last 4 ns of the simulation. The binding free energies were decomposed to components of the contributions from different energy types, and the changes in the helical parameters of the bound DNA duplex plus the glycosidic linkages between sugar residues of the bound MTR dimer were determined. It was found that binding of the first (MTR)2Mg2+ complex with the DNA duplex to form a 1:1 duplex complex does not cause stiffening of the duplex especially in the unoccupied site of the duplex. However, the overall flexibility of the DNA duplex is reduced substantially once the second (MTR)2Mg2+ complex is bound with the unoccupied site to form the 2:1 duplex complex. The van der Waals interactions were found to be dominant in the central part of the DNA duplex where sugar residues from each bound (MTR)2Mg2+ complex were inwardly pointing and the corresponding minor groove was widened.     

Kinetics of Dissociation of Iron(III) Complexes of Tiron in Aqueous Acid

The kinetics of dissociation of the mono, bis, and tris complexes of Tiron (1,2-dihydroxy-3,5-benzenedisulfonate) have been studied in acidic aqueous solutions in 1.0 M HClO(4)/NaClO(4), as a function of [H(+)] and temperature. In general, the kinetics can be explained by two reactions, (H(2)O)Fe(L)(n)(-1) + H(2)L right arrow over left arrow (H(2)O)Fe(L(n)H) + H(+) (k(n), k(-n)) and (HO)Fe(L)(n)(-1) + H(2)L right arrow over left arrow (H(2)O)Fe(L(n)H) (k(n)', k(-n)'), a rapid equilibrium, (H(2)O)Fe(L(n)H) right arrow over left arrow (H(2)O)Fe(L)(n) + H(+) (K(cn)), and the formation constant (H(2)O)Fe(L)(n)(-1) + H(2)L right arrow over left arrow (H(2)O)Fe(L)(n) + 2H(+). For n = 1, the reaction was observed at 670 nm, and at [H(+)] of 0.05-0.5 M at temperatures of 2.0, 14.0, 25.0, and 36.7 degrees C. For n = 2, the analogous conditions are 562 nm, at [H(+)] of 1.5 x 10(-3) to 1.4 x 10(-2) M at temperatures of 2.0, 9.0, and 14.0 degrees C. For n = 3, the conditions are 482 nm, at pH 4.5-5.7 in 0.02 M acetate buffer at temperatures of 1.8, 8.0, and 14.5 degrees C. The rate or equilibrium constants (25 degrees C) with DeltaH or DeltaH degrees (kcal mol(-1)) and DeltaS or DeltaS degrees (cal mol(-1) K(-1)) in brackets are as follows: for n = 1, k(1) = 2.3 M(-1) s(-1) (8.9, -27.1), k(-1) = 1.18 M(-1) s(-1) (4.04, -44.8), K(c1) = 0.96 M (-9.99, -33.6), K(f1) = 2.01 M (-5.14, -15.85); for n = 2, k(-2)/K(c2) = 1.9 x 10(7) (19.9, 41.5) and k(-2)'/K(c2) = 1.85 x 10(3) (1.4, -38.8) and a lower limit of K(c2) > 0.015 M; for n = 3, k(3) = 7.7 x 10(3) (15.8, 12.3), k(-3) = 1.7 x 10(7) (16.2, 28.9), K(c3) = 7.4 x 10(-5) M (4.1, -5.1), and K(f3) = 3.35 x 10(-8) (3.7, -21.7). From the variations in rate constants and activation parameters, it is suggested that the Fe(L)(2) and Fe(L)(3) complexes undergo substitution by dissociative activation, promoted by the catecholate ligands.     

Kinetic mechanism of acetyl-CoA synthase: steady-state synthesis at variable Co/Co2 pressures.

Steady-state initial rates of acetyl-CoA synthesis (upsilon/[E(tot)]) catalyzed by acetyl-CoA synthase from Clostridium thermoaceticum (ACS) were determined at various partial pressures of CO and CO2. When [CO] was varied from 0 to 100 microM in a balance of Ar, rates increased sharply from 0.3 to 100 min(-1). At [CO] > 100 microM, rates declined sharply and eventually stabilized at 10 min(-1) at 980 microM CO. Equivalent experiments carried out in CO2 revealed similar inhibitory behavior and residual activity under saturating [CO]. Plots of upsilon/[E(tot)] vs [CO2] at different fixed inhibitory [CO] revealed that Vmax/[E(tot)] (kcat) decreased with increasing [CO]. Plots of upsilon/[E(tot)] vs [CO2] at different fixed noninhibitory [CO] showed that Vmax/[E(tot)] was insensitive to changes in [CO]. Of eleven candidate mechanisms, the simplest one that fit the data best had the following key features: (a) either CO or CO2 (at a designated reductant level and pH) activate the enzyme (E' + CO right arrow over left arrow E, E' + CO2/2e-/2H+ right arrow over left arrow E); (b) CO and CO2 are both substrates that compete for the same enzyme form (E + CO right arrow over left arrow ECO, E + CO2/2e-/2H+ right arrow over left arrow ECO, and ECO --> E + P); (c) between 3 and 5 molecules of CO bind cooperatively to an enzyme form different from that to which CO2 and substrate CO bind (nCO + ECO right arrow over left arrow (CO)nECO), and this inhibits catalysis; and (d) the residual activity arises from either the (CO)nECO state or a heterogeneous form of the enzyme. Implications of these results, focusing on the roles of CO and CO2 in catalysis, are discussed.     

Intercalation of ethidium into triple-strand poly(rA).2poly(rU): a thermodynamic and kinetic study

The kinetics and equilibria of the interaction of ethidium bromide (EB) with the triple-stranded RNA, poly(rA).2poly(rU), have been investigated by stopped-flow, absorption, fluorescence, and circular dichroism methods; to properly assess the effect of the third strand on the polymer molar properties, molar volumes, adiabatic compressibilities, and heats of melting have also been measured for both poly(rA).2poly(rU) and poly(rA).poly(rU). The melting experiments reveal that ethidium tends to destabilize the triplex, whereas it stabilizes the duplex; however, the triplex/ethidium system in 0.1 M NaCl is stable below 37 degrees C. The static titrations reveal that one ethidium ion binds every three base triplets of the polymer; on the basis of the excluded-site model, this feature suggests intercalation, as in the duplex, but the binding affinity for the triplex is weaker compared to that for the duplex. The kinetic experiments displayed a two-phase behavior, which was rationalized assuming the sequence D + S right arrow over left arrow DS(I), DS(I) + S right arrow over left arrow DS(II) + S (D = drug, S = site), the second step involving direct transfer of the drug between strands. Comparison with the duplex/EB system reveals that the additional strand of poly(U), present in the triplex, hinders the formation of the intermediate complex DS(I), while stabilizing the structure of the final DS(II) complex by hampering the partial slipping out of the dye from the triplex cavity.     

Glucose and fructose hydrates in aqueous solution by IR spectroscopy

In the mid-infrared attenuated total reflectance (MIR-ATR) spectra of aqueous d-glucose and d-fructose solutions, two hydrates were found by factor analysis (FA) for each sugar, d-glucose penta- and dihydrates and d-fructose penta- and monohydrates. We obtained the spectra and abundances for these hydrates as a function of carbohydrate concentrations. The biggest difference in these spectra lies in the CO stretch region. From the distribution of the species, the equilibrium between d-glucose pentahydrate and dihydrate is 3(H2O)2+2(C6H12O(6).2H2O) right arrow over left arrow 2(C6H12O(6).5H2O), with the equilibrium constant KG=(3.2+/-0.6)x10(-5) L3 mol-3. For d-fructose, the equilibrium is between pentahydrate and monohydrate, 2(H2O)2+C6H12O6.H2O right arrow over left arrow C6H12O(6).5H2O, with the equilibrium constant KF=(7.1+/-1.2)x10(-3) L2 mol-2. The four hydrates are present only in aqueous solutions and cannot be obtained in the solid state.     

Role of the third strand in the binding of proflavine and pt-proflavine to poly(rA).2poly(rU): a thermodynamic and kinetic study

The interactions of triple strands of poly(rA).2poly(rU) with proflavine (PR) and the proflavine cis-platinum derivative [{PtCl (tmen)} 2{NC 13H 7(NCH 2CH 2) 2}] (+) (PRPt) are examined at pH 7.0, T = 25 degrees C, and 0.2 M ionic strength by spectrophotometry, spectrofluorometry, circular dichroism, viscosimetry, stopped-flow, and T-jump relaxation techniques. The melting experiments demonstrate that both drugs tend to destabilize the triplex structure, although the PRPt effect is more relevant. By contrast, both drugs tend to slightly stabilize the duplex structure. The viscosity and circular dichroism measurements show that, at a low dye-to-polymer ratio ( C D/ C P), the binding is intercalative, whereas at high C D/ C P values, the external binding dominates. The binding kinetics and equilibria have been investigated over the C D/ C P region, where intercalation is operative. Both drugs bind to the RNA triplex according to the excluded site model. With PR, two kinetic effects have been observed, whereas with PRPt, only one has been observed. The results are interpreted according to the reaction schemes D + S right arrow over left arrow DS I, with PRPt, and D + S right arrow over left arrow DS I right arrow over left arrow DS II, with PR. The electrostatic contribution to the formation activation energy for DS I is similar (40%) for both systems. The results suggest that DS I is a partially intercalated species. Absence of the second step with PRPt is put down to groove interaction of the Pt-containing moiety, which prevents the PR residue from further penetration through the base pairs to form the fully intercalated complex, DS II. Comparison with the binding of the same drugs to the duplex reveals that the occupation of the major groove in poly(rA).2poly(rU) by the third strand plays a critical role in the kinetic behavior.     

Modeling the adsorption of Cd(II) onto kaolinite and Muloorina illite in the presence of citric acid

The adsorption of cadmium onto kaolinite and Muloorina illite in the presence of citric acid has been measured as a function of pH and cadmium concentration at 25 degrees C. When citric acid is present in the systems cadmium adsorption is slightly enhanced below pH 5, but significantly suppressed between pH 5 and 8, for both substrates. At higher citric acid concentrations very little cadmium adsorbs onto kaolinite from pH 5 to 8. Above pH 8 adsorption of Cd(II) onto illite is enhanced in the presence of citric acid, especially at lower concentrations, but this does not occur for kaolinite. Adsorption and potentiometric titration data were fitted by simple extended constant-capacitance surface complexation models for the two substrates. Enhancement of adsorption at lower pH values was ascribed to the ternary reaction [X(-)--K(+)](0)+Cd(2+)+L(3-)+2H(+) right arrow over left arrow (0)+K(+) involving outer-sphere complexation with permanently charged X(-) sites on the "silica" faces of both clay minerals. The models suggested that suppression of adsorption in the intermediate pH range was due to the formation of a strong CdL(-) solution complex which adsorbed neither on the permanently charged sites nor on the surface hydroxyl groups at the edges of the clay crystals. At higher pH values the dominant solution complex, CdLOH(2-), apparently adsorbed as an outer-sphere complex at surface hydroxyl groups on illite, SOH+2Cd(2+)+L(3-) right arrow over left arrow [SOCd(+)--CdOHL(2-)](-)+2H(+), but not on kaolinite. This difference in behavior results from the presence of =FeOH groups on the illite surface which can form surface complexes with CdLOH(2-), while the =AlOH groups on the kaolinite surface cannot.     

Encapsulation of Mithramycin in Liposomes in Response to a Transmembrane Gradient of Calcium Ions

The recent discovery that mithramycin(MTR) in aqueous solution forms a high affinity[Ca(MTR)4]2- complex led us to the idea thatCa2+-loaded liposomes might be able to accumulateMTR in their aqueous internal compartment. Wetherefore investigated the uptake of MTR into largeunilamellar vesicles (LUV) containing NaCl orCaCl2. Our data show that MTR was efficientlyaccumulated within LUV made fromdipalmitoylphosphatidylcholine and cholesterol, onlywhen the liposomes contained Ca2+ and wereresuspended in a Ca2+-free medium. A drugencapsulation efficiency as high as 60% was achieved,at a drug to lipid molar ratio of 1/18. The circulardichroism and fluorescence excitation spectra ofliposome-encapsulated MTR (LMTR) displayed strongsimilarities with those of the [Ca(MTR)4]2-complex. LMTR was found to be stable, when submittedto conditions that destabilized the[Ca(MTR)4]2- complex. Upon dilution andincubation for 24 h at 37 °C, MTR-containingliposomes did not release a significant amount of MTR.These properties were attributed to the formation ofa high affinity complex between MTR and Ca2+inthe aqueous compartment of liposomes.     

Reaction dynamics of excited ketoprofen with triethylamine

The reaction dynamics of ketoprofen (KP) with and without triethylamine (TEA) in methanol both in the ground and the excited states was studied by laser flash photolysis and the pump-probe emission spectroscopy. After the excitation, triplet KP abstracted a hydrogen atom from methanol to form KP ketyl radical (KPH). In the presence of TEA, the acid-base equilibrium state was found to be KP + TEA right arrow over left arrow KP- + TEAH+ in the ground state. The equilibrium constant was determined to be 32 +/- 7. Excited KP- rapidly underwent decarboxylation to form a carbanion resonant with the 3-ethylbenzophenone ketyl biradical anion (3-EBP-), followed by a proton-transfer reaction with TEAH+ to produce the 3-ethylbenzophenone ketyl biradical (3-EBPH). Furthermore, 3-EBPH was found to make a complex with TEA, whose equilibrium constant was obtained to be 18 +/- 2 M(-1). The complex formation ability of 3-EBPH was discussed compared with benzophenone ketyl radical (BPH).     

Use of SDS micelles to stabilize a ternary intermediate in the reaction of ferrioxamine B and 1,10-phenanthroline

Spectrophotometric measurements of the reaction of ferrioxamine B (FeHDFB(+)) with 1,10-phenanthroline (phen) reveal the presence of a ternary intermediate complex in both aqueous solution and an aqueous solution of 0.16 M sodium dodecyl sulfate (SDS). The stoichiometry of the intermediate is Fe(H(2)DFB)(phen)(2+) on the basis of a Schwarzenbach analysis of spectrophotometric data obtained at variable pH and phen concentrations. The ternary complex formation constant for the reaction FeHDFB(+) + H(+) + phen right arrow over left arrow Fe(H(2)DFB)(phen)(2+) is log K = 6.96 in aqueous solution and log K = 8.64 in aqueous 0.16 M SDS. The enhanced stability of Fe(H(2)DFB)(phen)(2+) in micellar solution was analyzed in terms of the pseudophase ion-exchange (PPIE) model of micellar reactions. The association constants for the binding of each reactant to the micellar pseudophase were measured by ultrafiltration. According to PPIE model calculations, the enhanced stability of Fe(H(2)DFB)(phen)(2+) in micellar SDS arises from a proximity effect created by the high local concentrations of reactants in the micellar pseudophase. The calculations also indicate that an inhibitory medium or compartmentalization effect is operative since the observed micellar enhancement is much smaller than predicted by the PPIE model. The micellar stabilization of the Fe(H(2)DFB)(phen)(2+) intermediate and the overall conversion of FeHDFB(+) to Fe(phen)(3)(2+) are discussed as a possible model system for siderophore iron release in microbial organisms.     

Spectroelectrochemical studies on mixed-valence states in a cyanide-bridged molecular square, [Ru(II)(2)Fe(II)(2)(mu-CN)(4)(bpy)(8)](PF6)(4).CHCl(3).H(2)O

A cyanide-bridged molecular square of [Ru(II) (2)Fe(II) (2)(mu-CN)(4)(bpy)(8)](PF(6))(4).CHCl(3).H(2)O, abbreviated as [Ru(II) (2)Fe(II) (2)](PF(6))(4), has been synthesised and electrochemically generated mixed-valence states have been studied by spectroelectrochemical methods. The complex cation of [Ru(II) (2)Fe(II) (2)](4+) is nearly a square and is composed of alternate Ru(II) and Fe(II) ions bridged by four cyanide ions. The cyclic voltammogram (CV) of [Ru(II) (2)Fe(II) (2)](PF(6))(4) in acetonitrile showed four quasireversible waves at 0.69, 0.94, 1.42 and 1.70 V (vs. SSCE), which correspond to the four one-electron redox processes of [Ru(II) (2)Fe(II) (2)](4+) right arrow over left arrow [Ru(II) (2)Fe(II)Fe(III)] (5+) right arrow over left arrow [Ru(II) (2)Fe(III) (2)](6+) right arrow over left arrow [Ru(II)Ru(III)Fe(III) (2)](7+) right arrow over left arrow [Ru(III) (2)Fe(III) (2)](8+). Electrochemically generated [Ru(II) (2)Fe(II)Fe(III)](5+) and [Ru(II) (2)Fe(III) (2)](6+) showed new absorption bands at 2350 nm (epsilon =5500 M(-1) cm(-1)) and 1560 nm (epsilon =10 500 M(-1) cm(-1)), respectively, which were assigned to the intramolecular IT (intervalence transfer) bands from Fe(II) to Fe(III) and from Ru(II) to Fe(III) ions, respectively. The electronic interaction matrix elements (H(AB)) and the degrees of electronic delocalisation (alpha(2)) were estimated to be 1090 cm(-1) and 0.065 for the [Ru(II) (2)Fe(II)Fe(III) (2)](5+) state and 1990 cm(-1) and 0.065 for the [Ru(II) (2)Fe(III) (2)](6+) states.     

Amperometric biosensor for the determination of creatine

An amperometric biosensor for the determination of creatine was developed. The carbon rod electrode surface was coated with sarcosine oxidase (SOX) and creatine amidinohydrolase by cross-linking under glutaraldehyde vapour. The SOX from Arthrobacter sp. 1–1 N was purified and previously used for creation of a creatine biosensor. The natural SOX electron acceptor, oxygen, was replaced by an redox mediating system, which allowed amperometric detection of an analytical signal at +400-mV potential. The response time of the biosensor was less than 1 min. The biosensor showed a linear dependence of the signal vs. creatine concentration at physiological creatine concentration levels. The optimal pH in 0.1 M tris(hydroxymethyl)aminomethane (Tris)–HCl buffer was found to be at pH 8.0. The half-life of the biosensor was 8 days in 0.1 M Tris–HCl buffer (pH 8.0) at 20 °C. Principal scheme of consecutively followed catalytic reactions used to design a biosensor for the determination of creatine     

Proton transfers from carbon acids activated by pi-acceptors. Changes in intrinsic barriers and transition state imbalances induced by a cyano group. An ab initio study

We report an ab initio study of the identity carbon-to-carbon proton-transfer NCCH(2)Y + NCCH=Y(-) right arrow over left arrow NCCH=Y(-) + NCCH(2)Y in the gas phase, where Y = H, CH=CH(2), CH=O, CH=S, CN, NO, and NO(2). The main focus is on a comparison with the previously reported systems CH(3)Y + CH(2)=Y(-) right arrow over left arrow CH(2)=Y(-) + CH(3)Y, i.e., on the effect of the cyano group on acidities, proton-transfer barriers, and transition state structures. The conclusions of this study are as follows: (1) The transition state for the NCCH(2)Y/NCCH=Y(-) systems is more imbalanced than that for the CH(3)Y/CH(2)=Y(-) systems. (2) The cyano group leads to an increase in the acidities but to a decrease in the proton transfer barriers. This barrier reduction results from the fact that the stabilizing effect of the cyano group on the transition state is greater than that on the anion. (3) Within a reaction series, the barriers are largely dominated by the pi-acceptor strength of Y, i.e., the strongest pi-acceptors lead to the highest barriers. This is similar to proton transfers in solution but quite different from the CH(3)Y/CH(2)=Y(-) systems in the gas phase; in these latter systems pi-acceptor effects play a minor role while the barrier lowering field effect of Y is dominant.     

"Abnormal" salt and solvent effects on anion/cation electron-transfer reactions: an interpretation based on Marcus-Hush treatment

Salt and solvent effects on the kinetics of the reactions [Fe(CN)6]3- + [Ru(NH3)5pz](2+) right arrow over left arrow [Fe(CN)6]4- + [Ru(NH3)5pz]3+ (pz = pyrazine) have been studied through T-jump measurements. The forward and reverse reactions show different behaviors: "abnormal" salt and solvent effects in the first case and normal effects in the second one. These facts imply an asymmetric behavior of anion/cation reactions depending on the charge of the oxidant. The results can be rationalized by using the Marcus-Hush treatment for electron-transfer reactions.     

Synthesis and self-aggregation of cyclic alkynes containing helicene

[structure: see text]. All stereoisomers of a cyclic alkyne containing three helicene units, 1,12-dimethylbenzo[c]phenanthrene, are synthesized using a building block. Isomeric [3 + 3]cycloalkynes aggregate in organic solvents. Vapor pressure osmometry reveals dimer formation of (M,M,M)-[3 + 3]cycloalkynes in chloroform and benzene at concentrations above 2 mM. No higher aggregation is observed. The chirality of helicenes plays an important role in self-aggregation, and diastereomeric (M,P,M)-[3 + 3]cycloalkyne forms a dimer only above 15 mM. Aggregation of racemic (M,M,M)-[3 + 3]cycloalkyne or (M,P,M)-[3 + 3]cycloalkyne is much weaker than that of a single enantiomer.     

Structure of Complex Natural Anthocyanins

We proposed four types of stabilization mechanisms of anthocyanin in aqueous solutions; (1) self-association, (2) copigmentation, (3) intramolecular sandwich-type stacking, and (4) metal chelation associated with self-association and copigmentation. The driving force of these stackings would be mainly hydrophobic interactions between the aromatic nuclei which are surrounded by hydrophilic sugar moieties.     

Surface properties of hydrous manganite (gamma-MnOOH). A potentiometric, electroacoustic, and X-ray photoelectron spectroscopy study

The acid-base characteristics of the manganite (gamma-MnOOH) surface have been studied at pH above 6, where dissolution is negligible. Synthetic microcrystalline particles of manganite were used in the experiments. From potentiometric titrations, electrophoretic mobility measurements, and X-ray photoelectron spectroscopy (XPS), a one pK(a) model was constructed that describes the observed behavior. The data show no ionic strength effect at pH < 8.2, which is the pH at the isoelectric point (pH(iep)), but ionic strength effects were visible above this pH. To explain these observations, Na(+) ions were suggested to form a surface complex. The following equilibria were established: =MnOH(2)(+1/2) right harpoon over left harpoon =MnOH(-)(1/2) + H(+), log beta(0) (intr.) = -8.20; =MnOH(2)(+1/2) + Na(+) right harpoon over left harpoon =MnOHNa(+1/2) + H(+), log beta(0) (intr.) = -9.64. The excess of Na(+) at the surface was supported by XPS measurements of manganite suspensions containing 10 mM NaCl. The dielectric constant of synthetic manganite powder was also determined in this study.     

Capillary electrophoresis–electrochemiluminescence detection method for the analysis of ibandronate in drug formulations and human urine

A simple, rapid and sensitive CE method coupled with electrochemiluminescence (ECL) detection for direct analysis of ibandronate (IBAN) has been developed. Using a buffer solution of 20 mM sodium phosphate (pH 9.0) and a voltage of 13.5 kV, separation of IBAN in a 30‐cm length capillary was achieved in 3 min. ECL detection was performed with an indium tin oxide working electrode bias at 1.6 V (versus a Pt wire reference) in a 200‐mM sodium phosphate buffer (pH 8.0) containing 3.5 mM Ru(bpy)₃²⁺ (where bpy=2,2′‐bipyridyl). Derivatization of IBAN prior to CE‐ECL analysis was not needed. Linear correlation (r=0.9992, n=7) between ECL intensity and analyte concentration was obtained in the range of 0.25–50 μM IBAN. The LOD of IBAN in water was 0.08 μM. The developed method was applied to the analysis of IBAN in a drug formulation and human urine sample. SPE using magnetic Fe₃O₄@Al₂O₃ nanoparticles as the extraction phase was employed to pretreat the urine sample before CE‐ECL analysis. The linear range was 0.2–12.0 μM IBAN in human urine (r=0.9974, n=6). The LOD of IBAN in urine was 0.06 μM. Total analysis time including sample preparation was <1 h.     

Aluminum Oxide Coated Cellulose Fibers Modified with n-Propylpyridinium Chloride Silsesquioxane Polymer: Preparation, Characterization, and Adsorption of Some Metal Halides from Ethanol Solution

Aluminum oxide coated cellulose fibers were modified, by an impregnation procedure, with n-propylpyridinium chloride silsesquioxane polymer. Good adherence of the polymer to the surface of modified cellulose fibers was obtained due to the Al-O-Si bond formation. The metal X-ray mapping showed that aluminum oxide and the silsequioxane polymer (Al and Si mapping) are highly dispersed on the fiber's surface. The ion exchange capacity of the material, determined on basis of exchangeable chloride ions, was 1.1 mmol g-1. The adsorption isotherms of FeCl3, CuCl2, and ZnCl2 from ethanol solutions were determined for each metal. The adsorption capacities were (in mmol g-1): FeCl3 = 0.82, CuCl2 approximately ZnCl2 = 0.37. The metal ions are adsorbed as anionic complex species by the following equilibrium reaction: + MCln right arrow over left arrow Copyright 1999 Academic Press.