A Chemical Recognition Element for Lithium Ions Based on Optical Electronic Absorption

Xerogel samples with entrapped series of four optical absorption chemosensors were prepared by sol-gel process. These materials are proposed as chemical recognition elements of an optical chemical sensor. The roles of the chemosensors play proton-dissociable chromogenic azocrown ethers bearing phenol and two azo groups as parts of macrocycles. Occurrence of the alkali ion—receptor interaction is signalled by the chemosensors changing their electronic absorption spectra. By this way chemosensor 4O-CH₃ is able to distinguish Li⁺ ions from other alkali metal ions present in aqueous solution, if the chemosensor is entrapped in Glymo-silica (1:1) xerogel matrix. The proposed recognition element for Li⁺ has been exposed to the cycles chemisorption—desorption many times. Besides DRIFT spectra of the used xerogel matrices were analyzed.     

Monothiourea-3-nitrophthalic acid as a new reagent for spectrophotometric analyses : II. Determination of ruthenium(III) ions

The results of the examination of the reaction between a new reagent, MT3NF acid, and palladium(II) ions, as well as the composition of the formed complexes have been discussed. The new extraction-spectrophotometric method for the determination of palladium(II) ions by using MT3NF acid was presented. Beer's law is obeyed over the range 0.1 to 3 μg of Pd/cm³. Molar absorptivity is 2.9 × 10⁴ liter mol⁻¹ cm⁻¹ at the absorption maximum of 306 nm. The influence of different ions has been described.     

Gradual transformation of Ca(OH)<Subscript>2</Subscript> into CaCO<Subscript>3</Subscript> on cement hydration

The low temperature of decomposition of some calcium carbonates and the bending of the TG curves of hydrated cement between 500 and 800°C suggested the presence of some complex compound(s), which needed complementary investigation (XRD, TG). Stepwise transformation of portlandite (and/or lime) into calcium carbonate, with intermediate steps of calcium carbonate hydroxide hydrates (CCH-1 to CCH-5), was indicated by the previous study of two OPC. This was checked here on four cements ground for t _g=15, 20, 25 and 30 min and hydrated either in water vapour, successively at RH=1.0, 0.95 and 0.5 for 2 weeks each (WR1, WR2 and WR3, respectively) or as mortars in liquid water (1m), followed by WR as above. The d[001] spacing of portlandite was confirmed to vary: here between the lowest and the highest standard values. The diffractograms of n=32 different samples were analyzed for presence of standard CCH peaks, generally slightly displaced. These were: CCH-1 [Ca₃(CO₃)₂(OH)₂]: N=11 peaks, of three different d[hkl] spacings, CCH-2 [Ca₆(CO_2.65)₂(OH₆₅₇)₇(H₂O)₂]: N=10 for two d[hkl], CCH-3 [Ca₃(CO₃)₂(OH)₂·1.5H₂O]: N=14 for five d[hkl], CCH-4, ikaite [CaCO₃(H₂O)₆]: N=13 for six d[hkl], CCH-5[CaCO₃(H₂O)]: N=15 for five d[hkl]. Thus the most probable is the presence of the last three. The stepwise transformation of Ca(OH)₂ into CaCO₃ was confirmed:     

A kinetic study on the iron(III)-promoted aquation of [Cr(C2O4)2(picolinato)]2− and [Cr(C2O4)2(2-pyridineacetato)]2− complexes

Two [Cr(C₂O₄)₂(AB)]^2– type complexes, obtained from the reaction of cis-[Cr(C₂O₄)₂(H₂O)₂]^– with the AB ligand, [AB = picolinic (pyac) or 2-pyridine-ethanoic acid (pyeac) anions], were converted into [Cr(C₂O₄)(pyac)(H₂O)₂]⁰ and [Cr(C₂O₄)(pyeac)(H₂O)₂]⁰ compounds, respectively via Fe^III-induced substitution of the oxalato ligand. The aquation products were separated chromatographically and their spectral characteristics and acid dissociation constants determined. The kinetics of the oxalato ligand substitution were studied with a 10–40 fold excess of Fe^III over [Cr^III] at [H⁺] = 0.2 M and at constant ionic strength 1.0 M (Na⁺, H⁺, Fe³⁺, ClO^– ₄). The reaction rate law is of the form: r = k _obs[Cr^III], where k _obs = kQ[Fe^III]/(1 + Q[Fe^III]). The first-order rate constants (k), preequilibria quotients (Q) and activation parameters derived from the k values have been determined. The reaction mechanism is discussed in terms of a Lewis acid catalyzed (induced) ligand substitution.     

Chromium speciation study in polluted waters using catalytic adsorptive stripping voltammetry and tangential flow filtration

The catalytic adsorptive stripping voltammetry (CAdSV) has been applied to physico-chemical chromium speciation study in the upper Dunajec catchment, severely polluted by the tannery wastewater. The method is based on the adsorptive preconcentration of the Cr(III)-diethylenetriammine-N,N,N′,N″,N″-pentaacetic acid (DTPA) complex and the utilization of the catalytic reaction in the presence of nitrate. Under optimized conditions the CAdSV enables the oxidation state speciation study of Cr content by direct determination of Cr(VI) in the presence of the predominant Cr(III) concentration with the detection limit for chromium(VI) of 0.08 nM and the linearity range from 0.1 to 80 nM obtained for 20 s of accumulation, as well as the determination of total Cr after UV oxidation of Cr(III) to Cr(VI). Due to the difference in the chemical properties of different chromium species the CAdSV method makes possible a speciation study of Cr(III) and Cr(VI) oxidation state. The RSD of the determination of Cr(VI) and Cr(III) varies from 0.5 to 5%. It has been proved that in natural water in which strong complexants of Cr(III) such a humid acids are presented, Cr(VI) can be determined accurately in the presence of high excess of Cr(III). Fractionation of selected water samples with tangential flow filtration (TFF, cut-off 10 and/or 1 kDa) provides insight into physical Cr speciation, i.e. partitioning of the Cr(VI) and Cr(III) between the colloidal and the dissolved fractions. It has been shown that the content of the Cr species in the Dunajec river depends on the season, and is significantly higher in autumn and winter during the most intensive tanneries production processes. The concentration of total Cr exceeds occasionally the legally admissible level. A large fraction of total Cr(III) concentration is associated with the colloidal material, while Cr(VI) occurs solely in the truly dissolved form.     

Homogeneous fluorescence assay for cyclic AMP

The objective of these studies was to develop a new homogeneous fluorescence assay for determining the concentrations of cAMP in biological samples. The assay is based on a novel general concept of using ligand-dependent sequence-specific DNA binding proteins as sensors for their respective ligands. CAP protein, a bacterial DNA binding protein whose DNA binding activity depends on cAMP, was used to develop the assay. In the presence of cAMP, DNA binding activity of CAP is greatly increased. Signaling of cAMP presence was achieved by detecting cAMP-dependent formation of CAP-DNA complex using a recently developed fluorescence assay for DNA binding proteins (Heyduk, T., and Heyduk, E. Nature Biotechnology 20,171-176, 2002). Both 96-well and 384-well black microplate formats of the assay were developed and used to detect cAMP in low nanomolar concentrations. The assay involves mixing of the sample with the assay solution containing all necessary components for cAMP determination followed by fluorescence intensity readout; no washing or reagent addition steps are necessary. Excellent reproducibility of fluorescence signal change as a function of cAMP concentration was observed. Experiments with HEK 293 cells stimulated with forskolin were performed to demonstrate that the assay could be used for cAMP determination in cellular extracts. In summary, the obtained data fully validated the new homogenous assay for measuring cAMP based on cAMP-dependent DNA binding activity of CAP protein. It is expected that the development of assays for many other ligands of DNA binding proteins will be possible using the same overall assay design developed for cAMP.     

Synthesis,crystal and molecular structure of the novel complex [dinitrato{N,N-bis(1–methylbenzimidazol-2–ylmethyl)methylamine}]cobalt(II)

Co(NO3)2·6H2O reacts with N,N-bis(1–methylbenzimidazol-2–ylmethyl)methylamine (Me2L) in MeOH/ Et2O solution at ca. 5°C, yielding a novel, penta-coordinate complex, formulated as [Co(NO3)2(Me2L)], which was characterized by means of structural, spectroscopic and magnetic measurements. The Co atom is coordinated in distorted trigonal bipyramidal geometry by three N and two O atoms. The ligand Me2L is coordinated in a facial mode and two coordinated O atoms from the nitrato ligands are in cis-positions.     

Novel soluble aromatic poly(amideimide)s containing 9,9-diphenylfluorene moieties: characterization and optical properties

A series of aromatic poly(amideimide)s containing 9,9-diphenylfluorene moieties and the amide units in the main chain have been synthesized by solution polycondensation reaction of newly prepared diamidedianhydride with several aromatic diamines: 1,3-phenylenediamine, 3,3′-dimethoxy-biphenyl-4,4′-diamine, 4,4′-oxydianiline, 4,4′-(1,3-phenylenedioxy)dianiline, 4,4′-(9-fluorenylidene)dianiline and 1,5-diaminonaphthalene. Molecular structures of the polymers obtained have been characterized using ¹³C NMR, ¹H NMR and FTIR spectroscopies. The polymers prepared are readily soluble in aprotic polar solvents, and form optically transparent films by solution casting. The resultant poly(amideimide)s have been analyzed by differential scanning calorimetry (DSC), thermogravimetry (TG) and wide-angle X-ray diffraction measurements. They exhibited high levels of thermal stability, with decomposition temperatures in the range 452–494 °C, and high glass transition temperatures (181–278 °C). The optical behavior of these polymers has been investigated in NMP solution as well as in the films. The photoluminescence (PL) spectra of the free-standing films prepared from the poly(amideimide)s exhibited maximum emission bands around 506–525 nm in the green region.     

Regio- and stereoselective reactions between cyclic Baylis-Hillman type adducts and N-nucleophiles and P-nucleophile

New important organic compounds multifunctionalized cyclic 6-membered and 7-membered allylic amines, azide and phosphonates have been obtained via regio- and diastereoselective reactions of cyclic Baylis-Hillman type adducts 1 with N-nucleophiles and P-nucleophile. We have found that the reactions proceed by S_N2 or S_N2′ processes exclusively, or by both processes simultaneously. The S_N2′ process occurs with anti stereochemistry.     

Oxathiaphospholane approach to N- and O-phosphorothioylation of amino acids

A method of highly efficient synthesis of N- and O-phosphorothioylated amino acids was developed. N- and O-(2-Thiono-1,3,2-oxathiaphospholanyl)amino acid methyl esters (3) were prepared in high yields in reaction of amino acid methyl esters with 2-chloro-1,3,2-oxathiaphospholane in pyridine in the presence of elemental sulfur. Compounds 3 were converted in high yield into the corresponding methyl or benzyl phosphorothioamides 6 and 7 by DBU-assisted treatment with methanol or benzyl alcohol. When 3-hydroxypropionitrile was used instead of methanol or benzyl alcohol, the corresponding 2-cyanoethylphosphorothioamidates 4 were obtained in high yield, from which the 2-cyanoethyl group was removed with concentrated ammonium hydroxide. The oxathiaphospholane methodology was also applied for the phosphorylation of amino acids. Thus, 2-oxo-1,3,2-oxathiaphospholane derivatives 10 were prepared by oxidation of compounds 3 with SeO(2.) Compounds 10 were transformed into the corresponding phosphate diesters or amidoesters upon treatment with 3-hydroxypropionitrile in the presence of DBU. The DBU-assisted oxathiaphospholane ring-opening process in 3 and 10 did not cause any measurable C-racemization of phosphorothioylated/phosphorylated amino acids.