Volume expansion and loss of sample due to initial self-heating in capillary electroseparation (CES) systems

Summary The application of a high voltage, V, in capillary electroseparations following sample injection, can cause loss of analyte if the rate of thermal expansion of the liquid in the capillary (due to ohmic heating) is more rapid than the rate of electro-migration of the slowest moving analyte into the column. We show that the limiting condition for avoidance of this undesirable effect requires that the ramp-up rate for the applied voltage is below a critical value. This critical (maximum) value is given to a good approximation by a simple formula (Eq. (30)). Limiting values of dV/dt are in the region of 1000 V s^–1 when the power loss in the capillary is around 3 W m^–1 (e.g. with a field of 30,000 V m^–1 and a current of 100 A). A detailed mathematical analysis which takes full account of the thermal dependence of key variables, indicates that thermal explosion will occur at fields above a critical value (Eq. (21)). We recommend that commercial CES instrumentation incorporates manual or software led ramp-up voltage control.     

Synthesis,Spectral Properties,and Crystal Structure of {Methoxo[4-phenylbutane-2,4-dione(p-nitrobenzoyl) hydrazonato(2-)]oxovanadium(V)}

The hydrazino complex {methoxo[4-phenylbutane-2,4-dione(p-nitrobenzoyl)hydrazonato(2-)]oxovanadium(V)}, VO(p-NO₂bhbzac)OCH₃, (1), has been prepared by the direct reaction of bis(benzoylacetonato) oxovanadium(IV), VO(bza)₂, with p-NO₂-C₆H₄C(O)NHNH₂, p-NO₂bh, in CH₃OH. The resulting compound contains benzoylacetone-(p-NO₂)benzoyl hydrazone as tridentate Schiff base-type ligand and OCH₃ group as Lewis base, both ligated to vanadium. The crystals are orthorhombic, with Z = 8, space group Pbca, a = 11.699(5) Å, b = 14.035(5) Å, c = 22.564(5) Å, R1 = 0.0756 and wR2 = 0.1302. The crystal structure demonstrated the square-pyramidal geometry of the VO_oxo(ONO)O coordination sphere with the oxo ligand at the apical position. The electronic absorption spectra revealed a ligand-to-metal charge-transfer (LMCT) band in the near UV region at _max = 23,700 cm^–1 (B = 5640 dm³ mol^–1 cm^–1) in CH₃CN, _max = 23,420 cm^–1 (B = 5550 dm³ mol^–1 cm^–1) in DMSO, and _max near 26,950 (sh) cm^–1 (B = 10,550 dm³ mol^–1 cm^–1) in CH₂Cl₂. The FT-IR spectra of (1) show the characteristic strong (V = O) stretching vibration at 993 cm^–1 and support the view that the oxovanadium complex is pentacoordinated and monomeric.     

Alkali metal ion-selective electrodes based on relevant alkali metal ion doped manganese oxides

Potentiometric properties of manganese oxides doped with alkali metal ions (Na⁺, K⁺, Rb⁺ and Cs⁺), which were prepared by heating mixed solutions (starting solution) of each alkali metal and Mn²⁺ ions, were examined. Electrodes based on mixed phases of Nao₄₄MnO₂/Mn₂O₃ and hollandite KMn₈O₁₆/M₂O₃ found by X-ray powder diffraction (XRD) exhibited Na⁺- and K⁺-selective responses with a near-Nernstian slope, respectively, when the molar ratio of alkali metal ion to Mn²⁺ ion in the starting solution was 0.1. When no alkali metal ions were added in the manganese oxide films, no significant potentiometric response was observed to any alkali metal ions. The selectivity coefficients of these electrodes were = 6.7 × 10^–2, = 7.1 × 10^–3, < 9 × 10^–4 and < 9x 10^–4 for the Na_0.44MnO₂/Mn₂O₃, and <4 × 10^–4 <4x 10^–4, =60 × 10^–2 ×10^–4, < 4 × 10^–4, for the KMn₈O₁₆/Mn₂O₃, respectively. Electrodes based on manganese oxides made from mixed solutions of Rb⁺/Mn²⁺ and Cs⁺/Mn²⁺ also responded to the respective primary ions, that is, Rb⁺ and Cs⁺ ions, although XRD patterns for the manganese oxides thus made did not show any peaks except for Mn₂O₃ (bixbyite); it was concluded in these cases that some amorphous type manganese oxides were formed in the Rb⁺/Mn²⁺ and Cs⁺/Mn²⁺ systems and they responded to the respective ions. Conditioning of these electrodes in an aerated indifferent electrolyte solution, 0.1M tetramethylammonium nitrate (TMA-NO₃), for relatively long time, typically more than 2 hours, was found to be a prerequisite for near-Nernstian response to the respective alkali metal ions. During this electrode conditioning, vacant sites (template) suitable in size for selective uptake of primary ions seemed to be formed by releasing the doped alkali metal ions from the solid phase into the adjacent electrolyte solution accompanying oxidation of the manganese oxide film.     

Aqueous Solution Chemistry of Scandium(III) Studied by Raman Spectroscopy and ab initio Molecular Orbital Calculations

Aqueous solutions of Sc(ClO₄)₃,ScCl₃, and Sc₂(SO₄)₃ were studied by Ramanspectroscopy over a wide concentration range. In aqueous perchlorate solutionSc(III) occurs as an hexaaqua cation. The weak, polarized Raman band assignedto the ₁(a _1g) ScO₆ mode of the hexaaqua-Sc (III) ion has been studied as afunction of concentration and temperature. The ₁(a _1g) ScO₆ mode at 442 cm^–1of the hexaaqua—Sc(III) shifts only 3 cm^–1 to lower frequency and broadensabout 20 cm^–1 for a 60°C temperature increase. The Raman spectroscopic datasuggest that the hexaaqua-Sc (III) ion is stable in perchlorate solution within theconcentration and temperature range measured. Besides the polarized componentat 442 cm^–1, two weak depolarized modes at 295 and 410 cm^–1 were measuredin the Raman effect. These two modes of the ScO₆ unit were assigned to ₃(f _2g)and ₂(e ), respectively. The infrared active mode ₃(f _1u) was measured at 460cm^–1. The frequency data confirm the centrosymmetry of the Sc(III) aquacomplex, contrary to earlier Raman results. The powder spectrum of crystallineSc(ClO₄) ₃ · 6H₂O shows the above described Raman modes as well. Thesefindings are in contrast to Sc₂(SO₄)₃ solutions, where sulfate replaces water inthe first hydration sphere and forms thermodynamically strong sulfato complexes.In ScCl₃ solutions thermodynamically weak chloro complexes could be detected.Ab initio molecular orbital calculations were performed at the HF and MP2 levelsof theory using different basis sets up to 6–31 + G(d). Gas-phase structures,binding energies, and enthalpies are reported for the Sc³⁺(OH₂)₆ and Sc³⁺(OH₂)₇cluster. The Sc—O bond length for the Sc³⁺(OH₂)₆ cluster reproduces theexperimentally determined bond length of 2.18 Å (recent EXAFS data) almost exactly.The theoretical binding energy for the hexaaqua Sc(III) ion was calculated andaccounts for ca. 54–59% of the experimental hydration enthalpy of Sc(III). Thethermodynamic stability of the Sc³⁺(OH₂)₆(OH₂) cluster was compared to thatof the Sc³⁺(OH₂)₇ cluster, demonstrating that hexacoordination is inherently morestable than heptacoordination in the scandium (III) system. The calculated ₁ScO₆frequency of the Sc⁺(OH²)⁶ cluster is ca. 12% lower than the experimentalfrequency. Adding an explicit second hydration sphere to give Sc³⁺ (OH²)¹⁸,denoted Sc[6 + 12], is shown to correct for the discrepancy. The frequencycalculation and the thermodynamic parameters for the Sc[6 + 12] cluster aregiven and the importance of the second hydration sphere is stressed. Calculatedfrequencies of the ScO₆ subunit in the Sc[6 + 12] cluster agree very well withthe experimental values (for example, the calculated ₁ScO₆ frequency was foundto be 447 cm^–1, in excellent agreement with the above-reported experimentalvalue). The binding enthalpy for the Sc[6 + 12]cluster predicts the single ionhydration enthalpy to about 89%.     

Solution equilibria and stability of the complexes of pyridinecarboxylic acids: Complexation reaction of mercury(II) with 2-hydroxynicotinic acid

Summary The solution equilibria of 2-hydroxynicotinic acid (hyna) complexes with mercury(II) have been studied spectrophotometrically in 50% (v/v) ethanol at 20°C and an ionic strength of 0.1mol dm^–3 (NaClO₄). Three mercuric complexes are formed in solution in dependence on the acidity of the medium. The basic characteristics of the different complexes are determined and the analytical aspects of the complexation reaction are demonstrated. A critical investigation has also been presented of the solution equilibria and stability of the mixed complex of mercury(II) withhyna and thiosalicylic acid (tsa). The various complex transitions leading to the formation of the 1 : 1 : 1 Hg(tsa)(hyna) ternary complex in solution are investigated. The non-charged mono-ligand complex Hg(hyna) is used for UV-spectrophotometric determination of mercury atpH 4.5–5 (_max=325nm, =0.8·10⁴lmol^–1cm^–1). The system obeyed Beer's law up to 36.1 µg ml^–1 of Hg(II). The optimum concentration range (Ringbom) is between 6 and 28.5µg ml^–1. Interference caused by a number of ions was masked by the addition of fluoride ions.

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Lösungsgleichgewichte und Stabilitätskonstanten von Komplexen der Pyridincarbonsäuren: Die Komplexierungsreaktion von Quecksilber(II) mit 2-Hydroxynikotinsäure

Zusammenfassung Die Lösungsgleichgewichte von 2-Hydroxynikotinsäure (hyna) mit Hg(II) wurde spektrophotometrisch in 50% (v/v) Ethanol bei 20°C und einer Ionenstärke von 0.1 mol dm^–3 (NaClO₄) untersucht. In Abhängigkeit von der Acidität des Mediums werden drei Quecksilberkomplexe gebildet. Die grundlegenden Charakteristika der Komplexe wurden bestimmt und die analytischen Aspekte aufgezeigt. Die gemischten Komplexe von Hg(II) mithyna und Thiosalicylsäure (tsa), insbesondere die verschiedenen Komplexübergänge zum ternären 1 : 1 : 1 Hg(tsa)(hyna)-Komplex, wurden ebenfalls untersucht. Der ungeladene Monoligandenkomplex Hg(hyna) kann beipH 4.5–5 zur UV-spektroskopischen Quecksilberbestimmung eingesetzt werden (_max=325nm, =0.8·10⁴lmol^–1cm^–1). Das System gehorcht bis zu einer Hg(II)-Konzentration von 36.1µgml^–1 dem Beerschen Gesetz. Der optimale Konzentrationsbereich (Ringbom) liegt zwischen 6 und 28.5µgml^–1. Interferenzen mit einer Reihe anderer Ionen konnten durch Maskierung mit Fluoridionen umgangen werden.

     

Electronic structure and the unimolecular reactions of imine peroixde HNOO

Summary Electronic structure and possible unimolecular reaction paths of a linear four-atom molecule HNOO to be formed by the addition of NH(^3–) toward O₂(³ _g ^– ) are investigated by the SCF and MRD-CI calculations employing the 6–31G** basis functions. HNOO in its ground state (¹ A) is an ozone-like diradicaloid, whose N–O binding energy is only 27 kJ/mol. Geometries and excitation energies of various diradical (excited) states, both singlet and triplet, are examined. The isomerization paths of the ground-state HNOO(¹ A) are traced by a multi-configuration (MC) SCF procedure and the activation barrier heights evaluated by the CI treatment. It has proved that energetically the most favorable is the 1,3-hydrogen migration to give hydroperoxynitrene NOOH(¹ A) with the barrier height of 62 kJ/mol. The nitrene should be extremely unstable; it is liable to be decomposed to NO + OH with virtually no activation barrier.Presented at the 7th International Congress on Quantum Chemistry, Menton, July 1991     

Resonance Raman spectra of tris(acetylacetonato)iron(III) and ruthenium(III) complexes and their solvent effect

The resonance Raman spectra of tris(acetylacetonatoiron(III)) and ruthenium(III) complexes in various solvents and in water-acetonitrile (W-AN) mixtures were measured. The resonance Raman spectra of both complexes indicated peaks near 460 and around 1580 cm^–1. Thev(C-O) peak (around 1580 cm^–1) is shifted to low frequency with an increase in the dielectric constant _T of the solvents, whereas thev(M-O) (M=Fe and Ru, near 460 cm^–1) are constant, independent of _T. It implies that the C-O bond in the acac^– ligand is lengthened by the polarizability effect of the solvents, while both the Fe-O and Ru-O bonds, which are located in the inside of the complexes, are not influenced by the solvents indicating that the interaction does not depend on the properties of individual solvent molecules but on those of the aggregate.     

Complex formation followed by internal electron transfer: The reaction between cysteine and iron(III)

Summary A kinetic study of the anaerobic oxidation of cysteine (H₂ L) by iron(III) has been performed over thepH-range 2.5 to 12 by use of a stopped-flow high speed spectrophotometric method. Reaction is always preceded by complex formation. Three such reactive complex species have been characterized spectrophotometrically: FeL ⁺ (_max=614 nm, =2 820 M^–1cm^–1); Fe(OH)L (_max=503 nm; shoulder at 575 nm, =1 640 M^–1cm^–1); Fe(OH)L ₂ ^2– (_max=545 nm; shoulder at 445 nm, =3 175 M^–1 cm^–1). Formation constants have been evaluated from the kinetic data: Fe³⁺+L ^2– FeL ⁺: logK ₁ ^M =13.70±0.05; Fe(OH)²⁺+L ^2– Fe(OH)L: logK ₁ ^MOH =10.75±0.02; Fe(OH)L+L ^2– Fe(OH)L ₂ ^2– ; logK ₂ ^MOH =4.76±0.02. Furthermore the hydrolysis constant for iron(III) was also obtained: Fe(OH)²⁺+H⁺ Fe _aq ³⁺ : logK ^FeOH=2.82±0.02). Formation of the mono-cysteine complexes, FeL ⁺ and Fe(OH)L, is via initial reaction of Fe(OH)²⁺ with H₂ L (k=1.14·10⁴M^–1s^–1), the final product depending on thepH. FeL ⁺ (blue) formed at lowpH decomposes following protonation with a second-order rate constant of 1.08·10⁵M^–1s^–1. Fe(OH)L (purple) decomposes with an apparent third order rate constant ofk=3.52·10⁹M^–2s^–1 via 2 Fe(OH)L+H⁺ products, which implies that the actual (bimolecular) reaction involves initial dimer formation. Finally, Fe(OH)L ₂ ^2– (purple) is remarkably stable and requires the presence of Fe(OH)L for electron transfer. A rate constant of 8.36·10³M^–1s^–1 for the reaction between Fe(OH)L and Fe(OH)L ₂ ^2– is evaluated.Dedicated to Prof. Dr. mult. Viktor Gutmann on the occasion of his 70th birthday     

Pharmacokinetic detection of penicillin excreted in urine using a totally internally reflected resonance light scattering technique with cetyltrimethylammonium bromide

A quantitative analysis method for penicillins including ampicillin (AmP), benzyl penicillin (BP), oxacillin (OA) and amoxycillin (AmO) is proposed that makes use of the totally internally reflected resonance light scattering (TIR-RLS) signal from the penicillin at the H₂O/CCl₄ interface in the presence of cetyltrimethylammonium bromide (CTMAB), and enables the pharmacokinetics of penicillin taken orally and excreted through urine to be monitored. Penicillin is coadsorbed with CTMAB at the H₂O/CCl₄ interface in neutral solution, resulting in the formation of ion associates that display greatly enhanced TIR-RLS signals (maximum at 368–372 nm). This enhanced TIR-RLS intensity was found to be proportional to the penicillin concentration over the range 0.2×10^–6 to 2.2×10^–6 mol L^–1, with limits of determination (3) of 5.0×10^–8 to 7.0×10^–8 mol L^–1. Pharmacokinetics studies performed using the present method show that the excretion of orally-taken ampicillin through urine has a half-time of 1.05 h and an excremental quantum over 8 h of 49.3%, respectively.     

Activity coefficients of electrolytes from the emf of liquid membrane cells. III: LaCl3, K3Fe(CN)6, and LaFe(CN)6

The activity coefficients of LaCl₃, K₃Fe(CN)₆, and LaFe(CN)₆ were measured down to about 1×10^–4, 3×10^–5, and 2×10^–5 mol-kg^–1 respectively, by means of cells with ion-exchange liquid membranes. In the diluted region, the trend of lanthanum chloride agrees with the Debye-Huckel theory and corroborates earlier findings in the literature relevant to more concentrated solutions, with minor systematic corrections of the _± values. K₃Fe(CN)₆ attains (rather than tends to attain) the Debye-Huckel limiting slope at1×10^–3 mol-kg^–1, and lanthanum ferricyanide in the diluted region shows negative deviations from the limiting law, similar to the ones predicted for large-sized, highly-charged ions in the diluted region by Bjerrum's, IPBE, and Mayer's theories. The behavior of LaCl₃ in the concentrated solutions proves that lanthanum ion drags along with it into the membrane many molecules of water which were then found to be twelve. Pitzer's theory best-fit coefficients that meet the experimental curves to be reproduced satisfactorily are reported.     

Determination of traces of bismuth by quenching of solid-substrate room-temperature phosphorescence from morin-labeled silicon dioxide nano-particles

Silicon dioxide nano-particles, diameter 50 nm, containing morin (morin–SiO₂) have been synthesized by the sol–gel method. They emit strong and stable room-temperature phosphorescence (SS-RTP) on filter paper as substrate, and bismuth can quench the intensity of the SS-RTP. On this basis a new morin–SiO₂ solid-substrate room-temperature phosphorescence-quenching method has been established for determination of traces of bismuth. Reduction of phosphorescence intensity (I_p) is directly proportional to the concentration of bismuth in the working range 0.16–14.4 ag spot^–1 (sample volume 0.40 L spot^–1, corresponding to the concentration range 0.40–36.0 fg mL^–1). The regression equation of the working curve is I_p=14.86+5.279×[Bi³⁺] (ag spot^–1) (n=6, r=0.9982). The detection limit of this method is 0.026 ag spot^–1 (corresponding to a concentration of 6.5×10^–17 g mL^–1).This sensitive, reproducible and accurate method has been used for successful analysis of real samples.     

Zinc(II) Hydration in Aqueous Solution: A Raman Spectroscopic Investigation and An ab initio Molecular Orbital Study of Zinc(II) Water Clusters

Raman spectra of aqueous Zn(II)–perchlorate solutions were measured over broad concentration (0.50–3.54 mol-L^–1) and temperature (25–120°C) ranges. The weak polarized band at 390 cm^–1 and two depolarized modes at 270 and 214 cm^–1 have been assigned to ₁(a _1g), ₂(e _g), and ₅(f _2g) of the zinc–hexaaqua ion. The infrared-active mode at 365 cm^–1 has been assigned to ₃(f _1u). The vibrational analysis of the species [Zn(OH₂) ₂ ⁺ ] was done on the basis of O _h symmetry (OH₂ as point mass). The polarized mode ₁(a _1g)-ZnO₆ has been followed over the full temperature range and band parameters (band maximum, full width at half height, and intensity) have been examined. The position of the ₁(a _1g)-ZnO₆ mode shifts only about 4 cm^–1 to lower frequencies and broadens by about 32 cm^–1 for a 95°C temperature increase. The Raman spectroscopic data suggest that the hexaaqua–Zn(II) ion is thermodynamically stable in perchlorate solution over the temperature and concentration range measured. These findings are in contrast to ZnSO₄ solutions, recently measured by one of us, where sulfate replaces a water molecule of the first hydration sphere. Ab initio geometry optimizations and frequency calculations of [Zn(OH₂) ₂ ⁺ ] were carried out at the Hartree–Fock and second-order Møller–Plesset levels of theory, using various basis sets up to 6-31 + G*. The global minimum structure of the hexaaqua–Zn(II) species corresponds with symmetry T _h. The unscaled vibrational frequencies of the [Zn(OH₂) ₂ ⁺ ] are reported. The unscaled vibrational frequencies of the ZnO₆, unit are lower than the experimental frequencies (ca. 15%), but scaling the frequencies reproduces the measured frequencies. The theoretical binding enthalpy for [Zn(OH₂) ₂ ⁺ ] was calculated and accounts for ca. 66% of the experimental single-ion hydration enthalpy for Zn(II).Ab initio geometry optimizations and frequency calculations are also reported for a [Zn(OH₂) ₂ ¹⁸ ] (Zn[6 + 12]) cluster with 6 water molecules in the first sphere and 12 in the second sphere. The global minimum corresponds with T symmetry. Calculated frequencies of the zinc [6 + 12] cluster correspond well with the observed frequencies in solution. The ₁-ZnO₆ (unscaled) mode occurs at 388 cm^–1 almost in perfect correspondence to the experimental value. The theoretical binding enthalpy for [Zn(OH₂) ₂ ¹⁸ ] was calculated and is very close to the experimental single ion-hydration enthalpy for Zn(II). The water molecules of the first sphere form strong hydrogen bonds with water molecules in the second hydration shell because of the strong polarizing effect of the Zn(II) ion. The importance of the second hydration sphere is discussed.     

Migration of Ethylene Terephthalate Oligomers from Roasting Bags into Olive Oil

Summary A high-performance liquid-chromatographic method with UV detection (HPLC–UV) has been developed for quantification of ethylene terephthalate oligomers in olive oil, from which they were extracted with acetonitrile. Oligomers, from monomers (M₁) to pentamers (M₅), were jointly and/or individually identified by liquid chromatography with mass spectrometry (electron-impact mass spectrometry (EIMS) low- and high-resolution) and were quantified by HPLC–UV using an acetonitrile solution of the major oligomer (the trimer M₃) as standard. For M₃ recovery was 98.9%, the detection limit was 60 g L^–2, and method precision was 2.03% (RSD). Migration of oligomers M₁–M₅ into 50 mL olive oil sealed in each of two brands of 10 cm × 10 cm poly(ethylene terephthalate) roasting bag was evaluated under two sets of conditions that approached but remained below the limit at which the bag material became physically deformed – heating for 7 min at 850 W in a microwave oven, or for 60 min at 200 °C in a conventional oven. Total migration was approximately 2.7 mg dm^–2 under the former conditions and 3.5–4.1 mg dm^–2 under the latter.Presented at the International Symposium on Separation and Characteristics of Natural and Synthetic Macromolecules, Amsterdam, The Netherlands, February 5–7, 2003     

Spectrophotometric determination of 1-naphthylamine in urine with pentacyanonitrosylmanganate (II)

A new Spectrophotometric method is proposed for the determination of 1-naphthylamine (R), based on its reaction with Mn(CN)₅NO^2– to form Mn(CN)₅NH₂R^3– and measurement of the absorbance at 472 nm. In aqueous medium the molar absorptivity of the manganese complex is maximum ( = 8.0 × 10³1 · mole^–1 ·cm^–1) in the pH range 5.0–10.0, the colour develops more rapidly at pH 10.0. The absorptivity is increased by a factor of 3.5 if the complex is extracted as an ion-associate into chloroform. The extraction efficiency is 99.2% for a single-step extraction, and a concentration factor of 5 can also be achieved. Linearity of response extends over the range 0.04–1.4 gmg/ml 1-naphthylamine, the coefficient of variation being 1.4% at the 0.29 g/ml level (n = 6). The detection and determination limits are 0.005 and 0.018 g/ml, respectively. The method is selective enough to allow the determination of 1-naphthylamine in the presence of considerable amounts of other amines, such as aminophenols and phenylenediamines. Results obtained in the determination of 1-naphthylamine in human urine were very satisfactory.     

Kinetics of the anation reaction of pentaamineaquacobalt(III) by phosphorous acid/hydrogenphosphite

Summary The kinetics of the anation reaction of [Co(NH₃)₅H₂O]³⁺ by H₃PO₃/H₂PO ₃ ^– , to give [CoH₂PO₃(NH₃)₅]²⁺, have been studied at 60, 70 and 80°C, in the acidity range [H⁺](M)=1.5 · 10^–1 –2.0 · 10^–3. Only H₂PO₃ is found to be reactive. The rate data is consistent with an I_d mechanism. The mean value of outer sphere association of [Co(NH₃)H₂O]³⁺ with H₂PO ₃ ^– is 1.5 M^–1. Values of the interchange constants are: 10⁴4k_i(s^–1)= 0.29, 1.47, 5.13, at 60, 70 and 80 °C respectively (H= 1.4 · 10²KJmol^–1, S=8.3 · 10 JK^–1 mol^–1). The first acidity constant of H₃PO₃ at I=1.0 has also been determined: 10²K_a(M)=4.8, 5.2 and 5.5, at 25, 40 and 50 °C respectively.     

1,10-Phenanthrolinium hydrogensquarate monohydrate—A non-centrosymmetric structure from two non-chiral agents

Four different dimethyltin(IV) complexes of Schiff bases derived from 2-amino-3-hydroxypyridine and different substituted salicylaldehydes have been synthesized. The compounds, with the general formula [Me₂Sn(2-OArCHNC₅H₃NO)], where Ar = –C₆H₃(5-CH₃) [Me₂SnL¹], –C₆H₃(5-NO₂) [Me₂SnL²], –C₆H₂(3,5-Cl₂) [Me₂SnL³], and –C₆H₂(3,5-I₂) [Me₂SnL⁴], were characterized by IR, NMR (¹H and ¹³C), mass spectroscopy and elemental analysis. Me₂SnL³ was also characterized by X-ray diffraction analysis and shows a fivefold C₂NO₂ coordination with distorted square pyramidal geometry. H₃C–Sn–CH₃ angles in the complexes were calculated using Lockhart's equations with the ¹J(^117/119Sn–¹³C) and ²J(^117/119Sn–¹H) values (from the ¹H-NMR and ¹³C-NMR spectra). The in vitro antibacterial and antifungal activities of dimethyltin(IV) complexes were also investigated.     

Preparation of BaCe0.8Gd0.2O3−δ by the citrate method and its application in the synthesis of ammonia at atmospheric pressure

BaCe_0.8Gd_0.2O_3– is a kind of high-temperature proton conductor. A precursor of BaCe_0.8Gd_0.2O_3– solid electrolyte was synthesized by the citrate method and characterized by thermal analysis (thermogravimetric analysis–differential thermal analysis), X-ray diffraction and scanning electron microscopy. Using the sintered samples as a solid electrolyte and silver–palladium alloy as electrodes, we synthesized ammonia from nitrogen and hydrogen at atmospheric pressure in the solid-state proton-conducting-cell reactor. The rate of evolution of ammonia was up to 3.09×10^–9 mol s^–1 cm^–2.     

An evaluation of rate constants for radiation induced decomposition of alkali metal nitrates

Radiation induced decomposition of solid alkali metal nitrates at room temperature has been studied up to an absorbed dose of 300 kGy. [NO ₂ ^– ] increases with absorbed dose. From the kinetic scheme and , rate constants have been evaluated for the overall radiolytic decomposition of alkali metal nitrates. This kinetic scheme is applicable in the low dose range. At higher doses, however, the radiation induced reaction, NO ₂ ^– +1/2 O₂NO ₃ ^– may also contribute. The overall rate constants are 0.13×10^–6 (LiNO₃), 1.05×10^–6 (NaNO₃), 10.10×10^–6 (KNO₃), 9.50×10^–6 (RbNO₃) and 25.50×10^–6 (CsNO₃) kGy^–1.     

Electrosurface and Ion-Selective Properties of Track-Etched Nanofilters: The Effect of Polyvalent Metal Adsorption

The effect of polyvalent metal adsorption on the performance and ion selectivity of poly(ethylene terephthalate) track-etched membranes with pores of 10 nm in diameter was studied. Membrane samples were prepared from the track-etched membranes with pores of 20 nm in diameter by thermal shrinkage. It was shown that an effective pore diameter decreases and selectivity of track-etched membranes increases upon filtration of Al(NO₃)₃ and Cr(NO₃)₃ solutions. The results obtained are explained by ion adsorption leading to the formation of complexes between polyvalent metals and carboxyl groups on the pore surface that is confirmed by IR spectroscopy data. The study of electrosurface properties of modified membranes and the dependence of ion selectivity of track-etched membranes on the concentration of Al³⁺ ions in 10^–2 M KCl solution indicates the decrease of membrane negative surface charge resulted from Al³⁺ adsorption and membrane charge reversal at Al³⁺ concentration in a solution higher than 10^–6 M. The dependences of the ion selectivity on pH and Al³⁺ concentration C _Al in a solution are similar. At pH < 3 and C _Al > 10^–6 M, the _1–2 > _1–1 > _2–1 ion selectivity series characteristic of the initial negatively charged membranes for the 1–1, 1–2, and 2–1 electrolyte solutions is reversed into the _2–1 > _1–1 > _1–2 series characteristic of positively charged membranes.     

Aqueous Uranyl Complexes 1. Raman Spectroscopic Study of the Hydrolysis of Uranyl(VI) in Solutions of Trifluoromethanesulfonic Acid and/or Tetramethylammonium Hydroxide at 25°C and 0.1 MPa

Raman spectra have been used to identify and characterize aqueous hydroxouranyl(VI) complexes from 0.0038 to 0.647M at pH from 0.24 to 14.96 adjusted witheither HCF₃SO₃ and/or (CH₃)₄NOH under ambient conditions. In acidic media(0.24 pH 5.63), the existence of four species UO²⁺ ₂,(UO₂)₂(OH)³⁺,(UO₂)₂(OH)²⁺ ₂, and (UO₂)₃(OH)⁺ ₅ was confirmed. At high uranium concentrations(U 0.1M) and in strongly acidic solutions (pH 1.94), one additional weakband was observed at 883±1 cm^–1. This band was assumed torepresent thespecies UO²⁺ ₂ with a reduced hydration number.In neutral and basic solutions(5.63 pH 14.96), five complexes were postulated: (UO₂)₃(OH)^– ₇,(UO₂)₃(OH)^2– ₈,(UO₂)₃(OH)^4– ₁₀,(UO₂)₃(OH)^5– ₁₁, andUO₂(OH)^2– ₄, based on theassigned symmetrical stretching frequencies of the UO₂ group in each complex.(UO₂)₃(OH)^– ₇ is the dominant species over mostof the pH range (4.53–12.78).The stability ranges of the other trinuclear species are:(UO₂)₃(OH)^2– ₈ (10.97 pH 13.83), (UO₂)₃(OH)^4– ₁₀ (10.97 pH 13.85) and (UO₂)₃(OH)^5– ₁₁(12.53 pH 14.10), which were identified for the first time. Finally, the monomericuranate anion OU₂(OH)^2– ₄ dominates in highly basic solution (12.48 pH 14.96). The linear correlation between the symmetrical vibrational frequency v ₁of the linear O = U = O entity and the average number of hydroxide ligandscoordinated to each uranium atom in a given species has been reaffirmed andexpanded: The v ₁ correlation was also used to predict the vibration frequencies of theundetected monomers UO₂(OH)⁺, UO₂(OH)^o ₂,UO₂(OH)^– ₃ at 848±2, 826±2, and804±2 cm^±1, respectively. Characteristic band areas for eachuranyl hydrolyzedspecies were determined by Raman spectra decomposition and their hydrolysisquotients log Q, were calculated. Structures of the four triuranylspecies are proposed.