New water-soluble and film-forming aminocellulose tosylates as enzyme support matrices with Cu<Superscript>2+</Superscript>-chelating properties

Within the framework of our studies on enzyme-compatible support matrix structures, we succeeded in making further derivatives of the new aminocellulose type P–CH₂–NH–(X)–NH₂ (P = cellulose); (X) = –(CH₂)₂– (EDA), –(CH₂)₂–NH–(CH₂)₂– (DETA), –(CH₂)₃–NH–(CH₂)₃– (DPTA), –(CH₂)₂–NH–(CH₂)₂–NH–(CH₂)₂– (TETA) accessible by nucleophilic substitution reaction with ethylenediamine (EDA) and selected oligoamines starting from 6(2)-O-tosylcellulose tosylate (DS_tosylate = 0.8). The ¹³C-NMR data show that the EDA and oligoamine residues are at C6 of the anhydroglucose unit (AGU) and that OH and tosylate are also (partially) present at C6. OH and partially tosylate are at C2/C3. All the synthesized aminocellulose tosylates were soluble in water and formed transparent films from their solutions. The aminocellulose tosylate solutions and the films prepared from them formed blue-coloured chelate complexes with Cu²⁺ ions, whose absorption maxima at wavelengths in the VIS region were located similarly to those of the Cu²⁺ chelate complexes with EDA and with the oligoamines. AFM investigations have shown that the aminocellulose films, depending on structural and environment-induced factors influencing e.g. SiO₂ polymer films, exhibit flat topographies (<1 nm), and on protonated NH₂ polymer films, such as aminopropyl-functionalized polysiloxane films, nanostructured topographies of derivative-dependent shape and nanostructure size as film supports in the form of nanotubes. The aminocellulose films could be covalently coupled with glucose oxidase enzyme by various known and novel bifunctional reactions via NH₂-reactive compounds. In this connection, it was confirmed again that the immobilized enzyme parameters, such as enzyme activity/area and K_M value, can be changed by the interplay of aminocellulose film, coupling structure and enzyme protein in the sense of an application-relevant optimization.     

Synthesis and structure of tris(4-ferrocenylphenyl)boroxine and its utility in cross-coupling reaction

The reaction of 4-bromophenylferrocene with butyllithium followed by treatment of the organolithium compound with tributyl borate afforded tris(4-ferrocenylphenyl)boroxine (2). X-ray diffraction study of the solvate 2·2C₆H₆ revealed an intermolecular stacking interaction between the boroxine ring and the Cp rings in the crystal structure. Cross-coupling of compound 2 with 4-bromo-4-nitro-1,1-biphenyl produced 4-ferrocenyl-4-nitro-1,1:4,1-terphenyl (3). X-ray diffraction study of terphenyl 3 showed that this compound crystallizes in the noncentrosymmetric space group P2₁. In the crystal, molecules 3 are packed in an antiparallel head-to-tail fashion, which is unfavorable for generation of strong nonlinear optical effects.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2657–2662, December, 2004.     

Reactions of superoxide anion radical with antioxidants and their use in voltammetry

Kinetic parameters were calculated for the electrochemical reduction of oxygen at a glassy-carbon electrode with the generation of superoxide radical anions in a 0.05 M solution of (C₂H₅)₄NI in dimethylformamide in the presence of fat-soluble antioxidants, retinol and -tocopherol. A procedure based on the protonation of the radical anion with antioxidant molecules is proposed for the voltammetric determination of antioxidants to determine milligram amounts of retinol and -tocopherol in model solutions (RSD = 1–2%). The calibration graphs for retinol and -tocopherol are linear in the concentration ranges 9.7 × 10^–5–2.3 × 10^–3 and 6.2 × 10^–4–3.1 × 10^–3 M, respectively. The detection limits for retinol and -tocopherol are 4.8 × 10^–5 and 4.1 × 10 ^–4 M, respectively. The procedure was applied to the determination of the active component (retinol and -tocopherol) in pharmaceuticals.Translated from Zhurnal Analiticheskoi Khimii, Vol. 60, No. 1, 2005, pp. 56–59.Original Russian Text Copyright © 2005 by Ziyatdinova, Gilmetdinova, Budnikov.     

Structural aspects of crown complexes with alkali and alkaline earth cations. Benzo-15-crown-5 as a discriminating macrocycle

X-ray structural results have been reviewed for the related M^z+ L _z ^– -B15C5 complexes where M^z+=Li⁺ to Cs⁺ and Mg²⁺ to Ba²⁺, L^–=2,4,6-trinitrophenolate (Picrate or Pic) and 3,5-dinitrobenzoate (Dnb), and B15C5=benzo-15-crown-5. These results combined with those for come MX_z-B15C5 (X=NCS^–, I^–, NO ₃ ^– , ClO ₄ ^– , BPh ₄ ^– ) complexes have revealed that B15C5 is a useful macrocycle with regard to the within-the-group and between-the-groups discriminations of M^z+ in the solid state.     

Electrochemical deposition: the concept of residence times in structure development

The concept of the residence time of an atom in a kink position was introduced to predict the structure of electrochemically deposited surface coatings. The residence time is obtained from the reciprocal value of the rate constant for separation from the kink position. Residence times and deposition rates determine the density of kink positions [ksp] on the growing metal film. For equilibrium conditions (Nernst potential), the density of kink positions [ksp]₀ depends on the exchange current density i₀ and on the residence time by the equation:

Hydrogen bonding motif in 2-hydroxy-1,4-naphthoquinone

Self-assemblies of 2-hydroxy-1,4-naphthoquinone (HNQ) have been investigated using the (HNQ)_n (n=1–4) series as modeled systems employing ab initio Hartree–Fock calculations. The energetics and charge distribution in these molecular systems are presented. As revealed from the electron density in the highest occupied molecular orbital of the lowest energy conformers of (HNQ)_n (n=1–4) the charge percolates to the end unit of the assembly. This has been supported by the molecular electrostatic potential topography.     

Studies on the non-isothermal kinetics of the thermal decomposition of [Cu(NBOCTB)][Cu(NO3)4]· H2O

The thermal decomposition process of the complex [Cu(NBOCTB)][Cu(NO₃)₄] H₂O has been studied by TG and DTG technique, and possible intermediates of the thermal decomposition have also been conjectured from the TG and DTG curves. The results suggest that the decomposition of the complex involves five steps: The non-isothermal kinetics of steps 1, 2 and 3 have been studied by means of the Achar and Coats-Redfern method based on TG and DTG curves. Step 1 is a Coring and Growth mechanism (n= 1), its kinetic equation may be expressed as: d/dt=Ae^–E/RT(1–). Steps 2 and 3 are both two order chemical reaction mechanisms, their kinetic equations can be expressed as: d/dt=Ae^–E/RT(1–)².This project was supported by the National Natural Science Youth Fundation of China.     

A novel spiroheterocyclization: synthesis of 1-ethoxycarbonylmethylidene-8-(2’-ethoxycarbonylmethylidene-5’,5’-dimethyl-3’-pyrrolidinylidene)-3,3,6-trimethyl-2-azaspiro[4,5]deca-6,9-diene

It was shown that isobutyraldehyde and cyanoacetic ester enter into reaction with meta-xylene initially at the fourth carbon atom with the formation of a spiropyrroline ring and then at the newly formed exomethylene bond with closure of the 1-ethoxycarbonylmethylidene-8-(2-ethoxycarbonylmethylidene-5,5-dimethyl-3-pyrrolidinylidene)-3,3,6-trimethyl-2-azaspiro[4,5]deca-6,9-diene system.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1487–1491, October, 2004.     

Comparative study of the electrosynthesis and characterization of films made from 1,1′-binaphthyl and 2-methoxynaphthalene

Oligomers of 2-methoxynaphthalene and 1,1-binaphthyl were electrochemically synthesized by cyclic voltammetry (CV) in 0.1 M tetrabutylammonium hexafluorophosphate–nitrobenzene (TBAPF₆–NB). The redox characterization of the films was studied in monomer-free 0.1 M TBAPF₆–NB and 0.1 M tetrabutylammonium hexafluorophosphate–acetonitrile (TBAPF₆–ACN) solutions. The electrochemical response from the anodic charging (p-doping) of an oligo(1,1-binaphthyl) film in both solvents consists of a continously increasing current without a well-defined oxidation peak. Upon discharging the film a distinct reduction peak can be seen. The p-doping response of an oligo(2-methoxynaphthalene) film in both solvents consists of a prepeak followed by a plateau until the new electrochemical process starts. On the reverse scan two poorly resolved reduction peaks which merge into a broad cathodic peak as the scan rate increases can be observed. The cathodic charging and discharging (n-doping) response of 2-methoxynaphthalene film in 0.1 M TBAPF₆–ACN consists of a broad and well-defined redox peak. The structures of the film were studied by Raman and Fourier transform infrared spectroscopy (FTIR). Both techniques provide complementary vibrational information on the coupling of the starting materials studied. The morphologies of the electrosynthesized films were studied by scanning electron microscopy (SEM). The influence of the two substituents, the methoxy and naphthyl groups, on the electrosynthesis properties of the naphthalene molecule was studied.     

Supramolecular Assembly Formation in Monolayers of tert-Butyl Substituted Copper Phthalocyanine and Tetrabenzotriazaporphin

The effect is studied of the layer formation conditions on the molecular arrangement of copper tetra- tert-butyl phthalocyanine (CuPctBu₄) and copper tetra- tert-butyl tetrabenzotriazaporphin (CuThptBu₄) at the air–water interface. The decrease in initial surface concentration of these compounds is shown to affect the molecular orientation, as indicated by the increase in the area per molecule. The data are interpreted in terms of formation of CuPctBu₄ and CuThptBu₄ monolayers with a face-on molecular arrangement when the initial surface concentration is sufficiently small (N less than 1.6 × 10^–7 mole/m² for CuPctBu₄ and N less than 4 × 10^–7 mole/m² for CuThptBu₄) and changes in the molecular orientation to edge-on when the N values are higher. It is emphasized that the edge-on orientation on the water surface is not only a molecular but a collective property of the azaporphyrine supramolecular assembly.     

Electrochemical behaviour of p-Si in methanol solutions of chlorides

The mechanism of anodic dissolutions of p-Si single crystals in CH₃OH–LiCl and CH₃OH–LiCl–HCl solutions was investigated by means of the following electrochemical methods: linear sweep voltammetry, the potentiostatic transient technique and XPS surface analysis. The dissolution of p-Si proceeds by a two-step mechanism with the creation of a Si(II) surface intermediate. At low anodic overvoltage the dissolution proceeds with the formation of porous silicon, probably through the reaction: 2Si(II)Si+Si(IV). Structural etching of the single crystals surface was observed at high anodic overvoltage (E>2 V). At this potential range, silicon dissolves with the formation of a Si(IV) soluble product. Electrolysis of the methanol solvent containing Si(IV) in the cell p-Si|CH₃OH–LiCl–Si(IV)|M, where M=Pt, Cu or 18/8 stainless steel, leads to the deposition of an amorphous organosilicon layer on the cathode. The analysis of the deposit performed by means of XPS, FTIR and SEM allows determination of the morphology and composition of the film. The layer consists of Si–OCH₃ compounds and can be created only in methanol solvent. The film is unstable in a humid atmosphere and undergoes transformation into a Si–OH layer.Contribution to the 3rd Baltic Conference on Electrochemistry, Gdansk-Sobieszewo, Poland, 23–26 April 2003Dedicated to the memory of Harry B. Mark, Jr. (28 February 1934–3 March 2003)     

Synthesis and properties of a new family of cyclodextrin analogues

The chemical synthesis of a series of cyclic oligosaccharides built up from (14)-linked alternatingD– andl-pyranosidic units is described for the first time. Key intermediates employed were disaccharides representing minimal repeating units. These disaccharides (monomers) have been prepared in specifically modified forms so that they bear both glycosyl donor (cyanoethylidene group) and glycosyl acceptor (trityloxy group) functions. Polycondensation-cyclisation of these disaccharide monomers, catalysed by TrC1O₄ under normal conditions of dilution, has led to series of homologous cyclic oligosaccharides with an even number of sugar residues (6, 8, 10, 12,etc.) in each case. Cyclic hexa- and octa-saccharides, based onl-rhamnose andD-mannose as the alternating monosaccharides units, have been deprotected to produce analogues of - and -cyclodextrins (CDs) and the X-ray crystal structure of the cyclic octasaccharide has been determined.     

Molecular dynamics and the structure of macrocycles —Solvent acetonitrile interactions

Microwave complex permittivities,* = -J, are reported in the 1–90 GHz frequency range for the macrocycles 18-crown-6 (18C6) and 15C5 added to acetonitrile in stoichiometric proportions, in the solvent CCl₄ at 25°C. Digitized infrared spectra of the CN stretch ₂ vibration of acetonitrile for the same systems are reported in the 2300–2200 cm^–1 spectral region. The macrocycle 12C4 added to CH₃CN has also been investigated in the infrared. Both the dielectric relaxation and infrared results are interpreted in terms of macrocycle-acetonitrile interactions, probably involving a methyl-hydrogen to ethereal-oxygen interaction. These interactions with CH₃CN diminish in strength according to the sequence: 18C6 > 15C5 > 12C4.This paper is dedicated to the memory of the late Dr C. J. Pedersen.     

Coordination compounds of copper(II), nickel(II), and cobalt(II) with β-thiosemicarbazones of isatin and <Emphasis Type="Italic">N</Emphasis>-methylisatin

Isatin thiosemicarbazone (HL) reacts in aquoeus-ethanolic medium with copper(II) chloride and bromide (pH 7–7.5, ethanolic KOH) to give coordination compounds CuLXnH₂O (X = Cl, Br; n = 3, 4). In the presence of amines (A = C₅H₅N, 3-CH₃C₅H₄N, and 4-CH₃C₅H₄N), complexes CuALX2H₂O and CuA₂LXH₂O (X = Cl, Br) are formed. With nickel(II) or cobalt(II) chlorides, thiosemicarbazone HL, and pyridine (1:1:3) as starting compounds, compounds MPy₂LClH₂O (M = Ni, Co) are isolated. Under similar conditions, N-methylisatin -thiosemicarbazone (HL) reacts with chlorides of the above-noted metals in the presence of pyridine to give complexes MPy₂LClH₂O (M = Cu, Ni, Co). All the complexes are monomeric and have a pseudooctahedral structure of the coordination unit. Thiosemicarbazones HL and HL in these complexes behave as tridentate monodeprotonated O,N,S-ligands. Thermolysis of these substances passes through the stages of dehydration (60–90°C), deaquation (135–140°C) or deamination (160–215°C), and complete thermal decomposition (560–670°C).Translated from Zhurnal Obshchei Khimii, Vol. 74, No. 9, 2004, pp. 1539–1543.Original Russian Text Copyright © 2004 by Samus, Tsapkov, Gulya.This revised version was published online in April 2005 with a corrected cover date.     

Using enzymes isolated from diverse sources to determine metal ion cofactors

Oxidoreductases and hydrolases isolated from different sources (horseradish and peanut peroxidases, alcohol dehydrogenases from bakers yeast and horse liver, and alkaline phosphatases from Escherichia coli, chicken and seal intestine) were used to determine their metal ion cofactors: Fe(III), Zn(II) and Mg(II), respectively. Studying the effects of the metal ion cofactors on the catalytic activity of the enzymes of different origin showed that the extent of their inhibition, activation, or reactivation of their apoenzymes depended on the structure and accessibility of the enzyme active site, which varies among the biocatalysts isolated from different sources. The developed procedures are based on the inhibiting (Zn(II)) or activating (Mg(II)) effects of the metal ions on the catalytic activity of the enzymes, or on reactivating effects (Fe(III) and Zn(II)) on the apoenzymes. The procedures are characterized by high sensitivity and selectivity; the detection limits of Fe(III) using horseradish peroxidase, Zn(II) using alcohol dehydrogenase from bakers yeast, alkaline phosphatase from seal intestine and its apoenzyme, and Mg(II) using alkaline phosphatase from chicken intestine equal 10 ng L^–1, 20 ng L^–1, 3 g L^–1, 8 g L^–1 and 0.2 g L^–1, respectively.Presented at the 8th Symposium Kinetics in Analytical Chemistry, Rome, Italy, 5–8 July 2004.     

Specific radiation and recoil energy effects in recoil implantation reaction of51Cr in metal acetylacetonates

In recoil implantation reaction of⁵¹Cr in Cr/acac/₃ a polymer component which was sensitive to radiation dose was found. However, a retention type component⁵¹Cr/acac/₃ was not so sensitive to radiation dose. A remarkable dependence of the yield of⁵¹Cr/acac/₃ on recoil energy was found in the range 10²–10⁶ eV in recoil implantation using a thin film technique. This suggests a special role of implantation reaction in solids.     

The thermal decomposition of (NH4)[VO(O2)2(NH3)]

The compound, (NH₄)[VO(O₂)₂(NH₃)], thermally decomposes to ammonium metavanadate, which then decomposes to vanadium pentoxide. Using a heating rate of 5 deg·min^–1, the first decomposition step occurs between 74° and 102°C. The transformation degree dependence of the activation energy (-E) is shown to follow a decreasing convex form, indicating that the first decomposition step is a complex reaction with a change in the limiting stage of the reaction. Infrared spectra indicated that the decomposition proceeds via the gradual reduction of the ratio of the (NH₄)₂O to V₂O₅ units from the original 11 ratio in ammonium metavanadate, which may be written as (NH₄)₂O·V₂O₅, to V₂O₅.The assistance of Professor A. M. Heyns (University of Pretoria) and Professor K. L. Range (University of Regensburg) is gratefully acknowledged as well as the financial assistance of the University of Pretoria and the FRD.     

Reactions of solute species at an electrode modified with titanocene functionalized polypyrrole film: ferrocene and titanocene dichloride

We have studied for the first time the ability of a conducting polymer film, p(Tc3Py), representing a polypyrrole matrix with covalently attached titanocene dichloride (TcCl₂) centers, to serve as an intermediator for the electron charge transport between the electrode and the reaction sites of solute reactants. The standard potential of the first of these electroactive species, ferrocene (Fc), is in the range where the polymer matrix is in its slightly oxidized state so that solute Fc species give a reversible response at the surface of this modified electrode. Another solute reactant, TcCl₂, was studied in solutions in which it demonstrates a (quasi)reversible behavior at bare electrode surfaces, THF+TBAPF₆ and AN+TEACl. The standard redox potential of this species belongs to the range of the electroactivity of immobilized TcCl₂ centers (where the matrix is in its non-conducting state) so that the electron charge has to be transported via stepwise redox reactions between neighboring centers inside the film. The combination, solute reactant+film, results in a greater CV current compared to the response of the film in background solution or of the solute species at the bare electrode surface. This current for THF solution even exceeds the sum of separate currents for the film and the reactant. This finding is attributed to a catalytic effect of solute species as redox intermediators for the transformation of immobilized electroactive centers leading to a greater degree of the film reduction. The presence of solute TcCl₂ species results in a much greater stability of immobilized centers (compared to the corresponding reactant-free solution), both in the course of CV with the passage of the range of their response and in experiments with the film holding at the potential within this range. This holding leads to an almost constant current related to the reaction of solute species at the film/solution interface. Our estimate shows that immobilized centers undergo above 10,000 reversible transformations (without an observed tendency to the degradation) to ensure the passage of this current. The conclusion has been drawn that immobilized TcCl₂ centers are able to serve as sufficiently stable redox intermediators for the electron charge transport across the film, a prerequisite for the catalytic applications of such films.Abbreviations AN acetonitrile - THF tetrahydrofuran - Cp cyclopentadienyl, C₅H₅ - Cp cyclopentadienyl radical, C₅H₄ - Fc ferrocene, Cp₂Fe - TcCl₂ titanocene=bis(cyclopentadienyl)titanium dichloride, Cp₂TiCl₂ or its radical CpCpTiCl₂ - PPy polypyrrole - Tc3Py titanocene-propyl-pyrrole, Cl₂TiCpCp(CH₂)₃NC₄H₄ - p(Tc3Py) polymer obtained from Tc3Py - TBAPF₆ tetrabuthylammonium hexafluorophosphate - TEACl tetraethylammonium chlorideDedicated to Zbigniew Galus on the occasion of his 70th birthday.     

On-line glucose monitoring by using microdialysis sampling and amperometric detection based on ‘wired’ glucose oxidase in carbon paste

In-vitro on-line glucose monitoring is described, based on microdialysis sampling and amperometric detection operated in a flow-injection system. Samples were injected into a two-electrode microcell containing an Ag/AgCl quasi-reference electrode and a glucose enzyme electrode as the working electrode, operated at + 0.15 Vvs. Ag/AgCl. The enzyme electrode is constructed by mixing the wired glucose oxidase into carbon paste. {Poly[1-vinylimidazole osmium(4,4-dimethylbipyridine)₂Cl)]}^+/2+ was used to wire the enzyme. The non-coated electrodes, cross-linked with poly(ethylene glycol) diglycidyl ether, responded linearly to glucose concentrations up to 60 mM, and were characterized by a sensitivity of 0.23 A mM^–1 cm^–2, when operated in flow injection mode and of 5.4 AmM ^–1 cm^–2 in steady-state conditions. This sensitivity of the resulting enzyme electrode was 50% lower than that of similarly prepared but non-cross-linked electrodes. However, the cross-linked electrodes showed superior operational and storage stabilities, which were further improved by coating the electrodes with a negatively charged Eastman AQ film. An in-house designed microdialysis probe, equipped with a polysulphone cylindrical dialysis membrane, yielded a relative recovery of 50–60% at a perfusion rate of 2.5 l/min^–1 in a well stirred glucose solution. The on-line set up effectively rejected common interferences such as ascorbic acid and 4-acetaminophen when present at their physiological concentrations.