Analytical application of atomic emission and atomic absorption spectrometry for the determination of imidazoline derivatives based on formation of ion-associates with sodium cobaltinitrite and potassium ferricyanide

Ion-association complexes of Naphazoline HCl (I), Tolazoline HCl (II) and Xylometazoline HCl (III) with [Co(NO₂)₆]^3– and [Fe(CN)₆]^3– were precipitated and the excess of the unreacted iron or cobalt comples was determined. A new method using atomic emission and atomic absorption spectrometry for the determination of the above drags in pure solutions and in pharmaceutical preparations is given. The drugs have been determined in the ranges 0.98–14.76, 0.78–11.80 and 1.12–16.80 g/ml solutions of I, II and III. respectively, using [Co(NO₂)₆]^3–], with mean relative standard deviations of 0.4–1.5% and 1.92%–19.68, 1.52–5.68 and 2.24–22.4 g/ml solutions of I, II and III, respectively using [Fe(CN)₆]^3– with mean relative standard deviations of 0.6–1.6%. The recovery values of 98.12–101.26% indicate high precision and accuracy.     

Spectro- and electrochemical studies of some ruthenium and osmium complexes of 2-(2'-pyridyl)benzimidazole; complexes with intra-molecular charge transfer

Reaction of Ru3(CO)12, with 2-(2'-pyridyl)benzimidazole (HPBI) resulted in the formation of Ru(CO)3(HPBI) (I) complex. In presence of pyridine or dipyridine, the two derivatives [Ru(CO)3(HPBI)].Py (II) and [Ru(CO)3(HPBI)].dpy (III) were isolated. The corresponding reactions of Os3(CO)12 yielded only one single product; Os(CO)2(HPBI)2 (IV). Spectroscopic studies of these complexes revealed intramolecular metal to ligand CT interactions. Reactions of RuCl3 with HPBI gave three distinct products; [Ru(HPBI)2Cl2]Cl (V), [Ru(HPBI)(dipy)Cl2]C1 (VI) and [Ru(PBI)2(py)2]Cl (VII). The UV-vis studies indicated the presence of intramolecular ligand to metal CT interactions. Electrochemical investigation of the complexes showed some irreversible, reversible and quasi-reversible redox reactions due to tautomeric interconversions through electron transfer.     

Initial observation of magnetization hysteresis and quantum tunneling in mixed manganese-lanthanide single-molecule magnets

The preparation of a new family of mixed transition metal/lanthanide clusters is reported. The reaction of [Mn3O(O2CPh)6(py)2(H2O)] with Ln(NO3)3 (Ln = Nd, Gd, Dy, Ho, and Eu) in a 1:2 molar ratio in MeOH/MeCN (1:20 v/v) leads to dark crystals in 55-60% isolated yield of complexes all containing the [Mn11Ln4]45+ core. The Dy compound has been found to give out-of-phase AC susceptibility signals, suggesting it might be a single-molecule magnet (SMM). This was confirmed by the observation of magnetization hysteresis loops. An Arrhenius plot constructed from magnetization decay data gave a barrier to relaxation of 9.3 K and showed the temperature-independent relaxation at very low temperatures indicative of quantum tunneling of magnetization. This is the initial demonstration of hysteresis and quantum behavior in a mixed 3d/4f SMM.     

Simultaneous determination of U and Th by delayed fission neutron technique based on neutron generator

A method for simultaneous determination of uranium and thorium based on the deviation of their fission cross-section curves has been developed. Using a D-T neutron generator two different neutron spectra were produced with and without moderator around the target. The detection limits were found to be 0.044 mg and 0.25 mg in the presence of a moderator, while for fast neutrons 0.017 mg and 0.037 mg for uranium and thorium, respectively.This work was supported in part by the Ministry of Higher Education and the Hungarian Academy of Sciences.     

Infrared matrix isolation evidence for the formation of (η5-cyclopentadienyl)tricarbonyl-molybdenum and -tungsten radicals in carbon monoxide matrices at 12 K

Infrared spectroscopic evidence including ¹³CO labelling and energy-factored force-field fitting is presented for the first time to show that the radicals (η⁵-C₅H₅)-M(CO)₃^? (M = MO, W) and HCO are produced on photolysis of (η⁵-C₅H₅)M(CO)₃H complexes in CO matrices at 12 K.     

The synthesis and reactivity of a molybdenum (IV) stretched-dihydrogen complex

Reaction of [Mo(NPh)(PMe3)3(o-(Me3SiN)2C6H4)] (1) with molecular hydrogen (ca. 1 atm) at -10 degrees C in toluene-d8 results in the formation of dihydrogen complex [Mo(NPh)(PMe3)2(H2)(o-(Me3SiN)2C6H4)] (2) by 1H and 31P NMR spectroscopy. In solution at -50 degrees C 1 and 2 are present in a 1:3 ratio, respectively. The nature of dihydrogen ligand bonding in 2 was probed by T1 analysis and analysis of the JH-D coupling constant in the deuterium hydride isotopomer of 2 giving H-H distances of 1.18 A and 1.17 A, respectively. When allowed to warm to 30 degrees C, 2 reacts affording [Mo(NPh)(PMe3)3(o-(Me3SiN)(NH)C6H4)] (3) over a 1 h period. The X-ray structures of 1 and 3 are reported.     

Kinetic salt effects in the acid hydrolysis of potassium ethyl malonate in water and in 50% dioxane—Water mixture

The rates of the acid hydrolysis of potassium ethyl malonate in presence of KCl, NaCl, Li₂SO₄ and MgSO₄ in water and in 50% by weight of dioxane—water mixture were measured. The concentration of the added salts covered the range 0–1M. A negative salt effect on the rate of the half-ester hydrolysis was observed. The applicability ofBrønsted's equation was tested and deviations found were explained as due among other reasons, to the operation of an iondipole type of interaction. The correlation between the hydration numbers as well as the radii of the cations of the added electrolytes and the reaction rate were discussed. The activation energy was found to increase with an increase of the concentration of electrolyte due to the relative changes in solvation of the transition state as a result of hydration of the electrolytes added. The thermodynamic properties of the activated complex were calculated and discussed as functions of the salt concentration. A remarkable linear compensation between H and S was found.

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Der kinetische Salz-Effekt bei der sauren Hydrolyse von Kaliumethylmalonat in Wasser und in 50% Dioxan—Wasser

Zusammenfassung Es wurde die Kinetik der Hydrolyse von Kaliumethylmalonat in Gegenwart von KCl, NaCl, Li₂SO₄ und MgSO₄ (jeweils 0–1M) in Wasser und in 50% (w/w) Dioxan—Wasser untersucht. Es wurde ein negativer Salz-Effekt bezüglich der Hydrolysegeschwindigkeit des Halbesters beobachtet. Es werden sowohl Korrelationen zwischen Hydratationszahlen bzw. Ionenradien und der Reaktionsgeschwindigkeit, als auch zwischen Aktivierungsenergie und Elektrolytkonzentration diskutiert. Die thermodynamischen Parameter werden als Funktion der Salzkonzentration untersucht.

     

Anodic alumina supported dual-layer microporous silica membranes

We present a new processing scheme for the deposition of microporous, sol–gel derived silica membranes on inexpensive, commercially available anodic alumina (Anodisk™) supports. In a first step, a surfactant-templated mesoporous silica sublayer (pore size 2–6 nm) is deposited on the Anodisk support by dip-coating, in order to provide a smooth transition from the pore size of the support (20 or 100 nm) to that of the membrane (3–4 Å). Subsequently, the microporous gas separation membrane layer is deposited by spin-coating, resulting in a defect-free dual-layer micro-/mesoporous silica membrane exhibiting high permeance and high selectivity for size selective gas separations. For example, in the case of CO₂:N₂ separation, the CO₂ permeance reached 3.0 MPU (1 MPU = 10⁻⁷ mol m⁻² s⁻¹ Pa⁻¹) coupled with a CO₂:N₂ separation factor in excess of 80 at 25 °C. This processing scheme can be utilized for laboratory-scale development of other types of microporous or dense inorganic membranes, taking advantage of the availability, low cost and low permeation resistance of anodic alumina (or other metal oxide) meso- and macroporous supports.     

Ion-selective electrode for the determination of trazodone in tablets

A coated wire trazodone-selective electrode based on incorporation of trazodone-tetraphenylborate ion pair in a poly(vinylchloride) coating membrane was constructed. The influences of membrane composition, temperature, pH of the test solution, and foreign ions on the electrode performance were investigated. The electrode showed a Nernstian response over a trazodone concentration range from 1.41 x 10(-5) to 0.89 x 10(-2) M, at 25 degrees C, and was found to be very selective, precise, and usable within the pH range 2.4-9.0. The standard electrode potentials, E degree, were determined at 20, 25, 30, 35, 40 and 45 degrees C and used to calculate the isothermal temperature coefficient (dE degree/dT) of the electrode. Temperatures higher than 45 degrees C seriously affected the electrode performance. The electrode was successfully used for potentiometric determination of trazodone hydrochloride both in pure solutions and in pharmaceutical preparations.     

Stabilization of tandem dG-dA base pairs in DNA-hairpins: replacement of the canonical bases by 7-deaza-7-propynylpurines

The stabilizing effect of 7-propynylated 7-deazapurine nucleosides on DNA-hairpins and DNA-duplexes containing d(GA) mismatches was investigated. The corresponding oligonucleotides were synthesized using solid-phase synthesis. For this purpose, the phosphoramidite of 7-deaza-7-propynyl-2'-deoxyadenosine (3c) was prepared. The incorporation of 3c instead of dA into the tandem d(GA) base pair of a DNA-hairpin alters the secondary structure, but has a positive effect on the duplex stability. A complete replacement of the canonical nucleosides of the tandem d(GA) base pair by 3c and 7-deaza-7-propynyl-2'-deoxyguanosine results in a significant base pair stabilization.