Ferrocene-containing tri- and tetranuclear cyclic copper(<Emphasis Type="SmallCaps">i</Emphasis>) and silver(<Emphasis Type="SmallCaps">i</Emphasis>) pyrazolates

New tri- and tetranuclear macrocyclic silver(i) and copper(i) 3-ferrocenyl-5-(trifluoromethyl)pyrazolates were prepared: [{(3-((η⁵-C₅H₄)Fe(η⁵-C₅H₅))-5-(CF₃)-Pz}M]₃ (M = Cu (1), Ag (2)) and [{(3-(( η⁵-C₅H₄)Fe(η⁵-C₅H₅))-5-(CF₃)-Pz}Cu]₄ (3). The structures of compounds were established by X-ray diffraction analysis. In the crystalline state, a planar trinuclear silver-containing macrocycliс pyrazolate and a saddle-shaped tetranuclear copper-containing macrocycle are formed. The introduction of a bulky substituent, ferrocene, into the pyrazole ligand results in complete shielding of the acidic metal sites, which precludes the coordination of base molecules.     

Spectrophotometric determination of <Emphasis Type="Italic">L</Emphasis>-ascorbic acid in pharmaceuticals

A simple and sensitive spectrophotometric method for the determination of L-ascorbic acid with leuco crystal violet is proposed. The determination is based on the oxidation of analyte by potassium iodate. The colourless oxidation products were formed in the quantity equivalent to iodide ions. The iodide ions react with the excess of iodate ions in acidic medium, to form free iodine which oxidized leuco crystal violet (LCV) to the liberated crystal violet (CV ⁺) dye, showing maximum absorption at 588 nm. The absorbance was measured at pH of 4.1–4.2 in 1 cm cuvettes. Beer’s law was obeyed in the concentration range 0.5–4.0 μg/mL. The molar absorptivity of the coloured compound is 4.14 × 10⁴ L/mol cm for L-ascorbic acid. The analytical parameters were optimized and the method was successfully applied to the determination of L-ascorbic acid in pharmaceuticals. The results were compared with those obtained by methods proposed in Polish Standard.     

Octacyanomolybdate-doped-poly(4-vinylpyridine) ionomer film electrode for the electrocatalytic oxidation of <Emphasis Type="SmallCaps">l</Emphasis>-ascorbic acid

Poly(4-vinylpyridine) (PVP)-based anion exchange polymers are not studied as much as cation exchange polymers Nafion and Eastman Kodak AQ for electroanalytical applications. Similarly, octacyanomolybdate [Mo(CN)₈ ⁴⁻] has not been studied much as a redox mediator. This communication presents results from examinations of the behaviour of Mo(CN)₈ ⁴⁻-doped PVP ionomer film electrode to highlight the opportunities for realization of the application of this composite electrode for l-ascorbic acid (AH₂) estimation via electrocatalytic mediation in acidic medium. The modified electrodes were characterized by cyclic voltammetry and rotating disc electrode voltammetry. PVP coatings possess strong anion-binding capacity for Mo(CN)₈ ⁴⁻ mediator with an extraction coefficient of 990, and electrostatically cross-linked PVP films offer insignificant resistance to permeation of AH₂, facilitating a cross-exchange reaction between the substrate and the mediator in the entire film volume. They show effective electrocatalytic oxidation of AH₂, with the oxidation potential of AH₂ decreased by ∼200 mV in overpotential compared to that at bare electrode. Mo(CN)₈ ⁴⁻/PVP composite electrode does not respond to the more common interferents of l-ascorbic acid estimation even at high positive potentials. These and several other attractive potentialities of the modified electrode are demonstrated by direct determination of AH₂ in a commercial vitamin C tablet without any special treatment, with the value closely agreeing (±0.75%) with the reference method.     

A <Emphasis Type="SmallCaps">l</Emphasis>-tryptophan sensor based on tellurium nanorods modified glassy carbon electrode

An electrochemical l-tryptophan sensor based on tellurium nanorods modified glassy carbon electrode was proposed. The tellurium nanorods were synthesized by a chemical reduction method. The morphology and structures of the nanorods were characterized by scanning electron microscope (SEM) and transmission electron microscope (TEM). Owing to the special structure of the tellurium nanorods, the sensor exhibits excellent electrocatalytic ability towards the oxidation of l-tryptophan and shows linearity in the range from 0.02 to 11.48 μM with a sensitivity of 256 μA mM^?1 cm^?2 with a correlation coefficient of 0.9945. The detection limit was 0.01 μM with signal-to-noise ratio of 3, and the response time was found to be 2 s. Moreover, the sensor also exhibited long-term stability, good reproducibility and anti-interference, thus holding promise for sensing of l-tryptophan in practice.     

New tin(<Emphasis Type="SmallCaps">iv</Emphasis>) <Emphasis Type="Italic">o</Emphasis>-iminosemiquinone complexes

New tin(iv) mono- and bis-o-iminosemiquinone complexes were obtained by the exchange reaction of radical anion lithium salt of 4,6-di-tert-butyl-N-(2,6-diisopropylphenyl)-o-imino-benzoquinone with tin(iv) organochlorides. The compounds synthesized were characterized by EPR spectroscopy and X-ray diffraction analysis. Substituents on the tin atom were found to affect stability of paramagnetic metal derivatives formed.     

Bioconversion of <Emphasis Type="SmallCaps">d</Emphasis>-glucose into <Emphasis Type="SmallCaps">d</Emphasis>-glucosone by Glucose 2-oxidase from <Emphasis Type="Italic">Coriolus versicolor</Emphasis> at Moderate Pressures

Glucose 2-oxidase (pyranose oxidase, pyranose:oxygen-2-oxidoreductase, EC 1.1.3.10) from Coriolus versicolor catalyses the oxidation of d-glucose at carbon 2 in the presence of molecular O₂ producing d-glucosone (2-keto-glucose and d-arabino-2-hexosulose) and H₂O₂. It was used to convert d-glucose into d-glucosone at moderate pressures (i.e. up to 150 bar) with compressed air in a modified commercial batch reactor. Several parameters affecting biocatalysis at moderate pressures were investigated as follows: pressure, [enzyme], [glucose], pH, temperature, nature of fluid and the presence of catalase. Glucose 2-oxidase was purified by immobilized metal affinity chromatography on epoxy-activated Sepharose 6B-IDA-Cu(II) column at pH 6.0. The rate of bioconversion of d-glucose increased with the pressure since an increase in the pressure with compressed air resulted in higher rates of conversion. On the other hand, the presence of catalase increased the rate of reaction which strongly suggests that H₂O₂ acted as inhibitor for this reaction. The rate of bioconversion of d-glucose by glucose 2-oxidase in the presence of either nitrogen or supercritical CO₂ at 110 bar was very low compared with the use of compressed air at the same pressure. The optimum temperature (55°C) and pH (5.0) of d-glucose bioconversion as well as kinetic parameters for this enzyme were determined under moderate pressure. The activation energy (E _a) was 32.08 kJ mol⁻¹ and kinetic parameters (V _max, K _m, K _cat and K _cat/K _m) for this bioconversion were 8.8 U mg⁻¹ protein, 2.95 mM, 30.81 s⁻¹ and 10,444.06 s⁻¹ M⁻¹, respectively. The biomass of C. versicolor as well as the cell-free extract containing glucose 2-oxidase activity were also useful for bioconversion of d-glucose at moderate pressures. The enzyme was apparently stable at moderate pressures since such pressures did not affect significantly the enzyme activity.     

Development of transition state analogue inhibitors for <Emphasis Type="Italic">N</Emphasis>-acetylglycosyltransferases bearing <Emphasis Type="SmallCaps">d</Emphasis>psico- or <Emphasis Type="SmallCaps">d</Emphasis>tagatofuranose scaffolds

New potential transition state analogue inhibitors for N-acetylglucosyltransferases (GnTs) were synthesised. These compounds based on psico- and tagatofuranose (structure) scaffold contained a 2-thiophenyl-1-O-diethylphosphate moiety mimicking the proposed model of the transition state of the enzymatic reaction catalysed by N-acetylglucosyltransferases. The synthesised compounds as well as their precursors were fully characterised by NMR, optical rotation and mass techniques. Anomeric configuration of tagatofuranose derivatives was confirmed by X-ray crystallography. Two types of potential human glycosyltransferase (GnTs) inhibitors representing donor UDP-GlcNAc, assigned for biological assays on human GnTs, were prepared.     

Optical enzyme sensor for determining <Emphasis Type="SmallCaps">l</Emphasis>-lysine content using <Emphasis Type="SmallCaps">l</Emphasis>-lysine oxidase from the rockfish <Emphasis Type="BoldItalic">Sebastes schlegeli</Emphasis>

l-Lysine (l-Lys) in living bodies is critical for metabolism; therefore, determination of its levels in food is important. Most enzymatic methods for l-Lys analysis are performed using l-lysine oxidase (LyOx), but commercially manufactured LyOx is generally not highly selective for l-Lys among amino acids. We previously isolated LyOx as an antibacterial protein secreted from the skin of the rockfish Sebastes schlegeli. In the present study, we developed an optical enzyme sensor system for rapid and continuous determination of l-Lys using this LyOx. The system comprised an immobilized LyOx membrane, an optical oxygen probe, a flow system, and a personal computer. The amount of l-Lys was detected as a decrease in the oxygen concentration due to the LyOx reaction. The specificity of the sensor was examined against various amino acids. The sensor response was specific for l-Lys. Good reproducibility was obtained in 58 assays. The response of the sensor using commercially prepared LyOx was unstable compared with the response using LyOx isolated in our laboratory. Our sensor system could be used for 5 weeks without our having to change the enzyme membrane. The calibration curve for a standard l-Lys solution was linear from 0.1 to 3.0 mmol L⁻¹. One assay could be completed within 2 min. The sensor was applied to determine the l-Lys content in food samples such as bonito cooking water and scallop hepatopancreas. The values obtained using the sensor and conventional high-performance liquid chromatography methods were well correlated.     

Extracellular Production and Characterization of Two <Emphasis Type="Italic">Streptomyces</Emphasis><Emphasis Type="SmallCaps">l</Emphasis>-Asparaginases

l-Asparaginase (ASNase) has proved its use in medical and food industries. Sequence-based screening showed the thermophilic Streptomyces strain Streptomyces thermoluteus subsp. fuscus NBRC 14270 (14270 ASNase) to positive against predicted ASNase primary sequences. The 14270 ASNase gene and four l-asparaginase genes from Streptomyces coelicolor, Streptomyces avermitilis, and Streptomyces griseus (SGR ASNase) were expressed in Streptomyces lividans using a hyperexpression vector: pTONA5a. Among those genes, only 14270 ASNase and SGR ASNase were successful for overexpression and detected in culture supernatants without an artificial signal peptide. Comparison of the two Streptomyces enzymes described above demonstrated that 14270 ASNase was superior to SGR ASNase in terms of optimum temperature, thermal stability, and pH stability.     

Thermal properties of amphiphilic biodegradable triblock copolymer of <Emphasis Type="SmallCaps">l</Emphasis>,<Emphasis Type="SmallCaps">l</Emphasis>-lactide and ethylene glycol

Samples of poly(l,l-lactide)-block-poly(ethylene glycol)-block-poly(l,l-lactide) (PLLA-PEG-PLLA) were synthesized from l,l-lactide polymerization using stannous 2-ethylhexanoate, Sn(Oct)₂ as initiator and di-hydroxy-terminated poly(ethylene glycol) (PEG) (M _n  = 4000 g mol⁻¹) as co-initiator. The chemical linkage between the PEG segment and the PLA segments was characterized by Fourier transform infrared spectroscopy (FTIR). Thermogravimetry analysis (TG) revealed the copolymers composition and was capable to show the deleterious effect of an excess of Sn(Oct)₂ in the polymer thermal stability, while Differential Scanning Calorimetry (DSC) allowed the observation of the miscibility between the PLLA and PEG segments in the different copolymers.     

Glutaraldehyde-modified electrode for nonlabeling voltammetric detection of <Emphasis Type="Italic">p16</Emphasis><Superscript><Emphasis Type="Italic">INK4A</Emphasis></Superscript> gene

A nonlabeling electrochemical detection method for analyzing the polymerase-chain-reaction-amplified sequence-specific p16 ^INK4A gene, in which the basis for the covalent immobilization of deoxyribonucleic acid (DNA) probe is described, has been developed. The self-assembly process was based on the covalent coupling of glutaraldehyde (GA) as an arm molecule onto an amino-functional surface. The p16 ^INK4A gene was used as the model target for the methylation detection of early cancer diagnosis. An amino-modified DNA probe was successfully assembled on the GA-coupling surface through the formation of Schiff base under potential control. The hybridization of amino-modified DNA probes with the target was investigated by means of electrochemical measurements, including cyclic voltammetry and square wave voltammetry. Furthermore, the functions of GA coupling for sequence-specific detection were compared with those obtained based on mercaptopropionic acid. Hybridization experiments indicated that the covalent coupling of GA was suitable for the immobilization of DNA probe and was sensitive to the electrochemical detection of single-base mismatches of label-free DNA targets in hybridization. Moreover, reported probe-modified surfaces exhibited excellent stability, and the hybridization reactions were found to be completely reversible and highly specific for recognition in subsequent hybridization processes. The strategy provided the potential for taking full advantage of existing modified electrode technologies and was verified in microarray technology, which could be applied as a useful and powerful tool in electrochemical biosensor and microarray technology.     

Hyperbranched polyester poly(3-diethylamino)propionates and their copper(<Emphasis Type="SmallCaps">ii</Emphasis>) complexes

Novel polydentate ligands were obtained from second and third generation hyperbranched polyesters containing terminal (3-diethylamino)propionate groups. Polynuclear Cu^II complexes with these ligands were synthesized. The degree of diethylamination of the polyesters increases when moving from the second to the third generation (from 56 to 81%). In polynuclear complexes, the ratios of Cu to hyperbranched ligand are 6 : 1 and 13 : 1 for second and third generation polyester polyamines, respectively. It was demonstrated using IR and ESR spectroscopy that each coordination polyhedron in the complexes is an isolated paramagnetic center of the formula CuN₂O₂Solv₂ (Solv = H₂O, DMSO).     

Inclusion of nickel(<Emphasis Type="SmallCaps">II</Emphasis>) and copper(<Emphasis Type="SmallCaps">II</Emphasis>) complexes with aliphatic polyamines in cucurbit[8]uril

The inclusion compound of macrocyclic cavitand cucurbit[8]uril (CB[8]) with the nickel(II) complex containing the tetraazamacrocyclic ligand cyclam, {[Ni(cyclam)]@CB[8]}Cl₂··16H₂O (1), and the inclusion compounds of CB[8] with the copper(II) bis-ethylene-diamine complex, {trans-[Cu(en)₂(H₂O)₂]@CB[8]}Cl₂·{CB[8]}·42H₂O (2a) and {trans-[Cu(en)₂(H₂O)₂]@CB[8]}Cl₂·17H₂O (2b), were synthesized and characterized by X-ray diffraction analysis, IR and ESR spectroscopy, and electrospray mass spectrometry. Guest—host inclusion compounds can be directly synthesized starting from a metal complex and cucurbit[8]uril, as was exemplified by the preparation of compounds 2a and 2b.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2414–2419, November, 2004.     

The electrochemical polymerization of <Emphasis Type="Italic">o</Emphasis>-phenylenediamine on <Emphasis Type="SmallCaps">l</Emphasis>-tyrosine functionalized glassy carbon electrode and its application

The polymerization of o-phenylenediamine (OPD) on l-tyrosine (Tyr) functionalized glassy carbon electrode (GCE) and its electro-catalytic oxidation towards ascorbic acid (AA) had been studied in this report. l-Tyrosine was first covalently grafted on GCE surface via electrochemical oxidation, which was followed by the electrochemical polymerization of OPD on the l-tyrosine functionalized GCE. Then, the poly(o-phenylenediamine)/l-tyrosine composite film modified GCE (POPD-Tyr/GCE) was obtained. X-ray photo-electron spectroscopy (XPS), field emission scanning electron microscope (SEM), and electrochemical techniques have been used to characterize the grafting of l-tyrosine and the polymerization and morphology of OPD film on GCE surface. Due to the doping of the carboxylic functionalities in l-tyrosine molecules, the POPD film showed good redox activity in neutral medium, and thus, the POPD-Tyr/GCE exhibited excellent electrocatalytic response to AA in 0.1 mol l⁻¹ phosphate buffer solution (PBS, pH 6.8). The anode peak potential of AA shifted from 0.58 V at GCE to 0.35 V at POPD-Tyr/GCE with a greatly enhanced current response. A linear calibration graph was obtained over the AA concentration range of 2.5 × 10⁻⁴–1.5 × 10^–3 mol l⁻¹ with a correlation coefficient of 0.9998. The detection limit (3δ) for AA was 9.2 × 10⁻⁵ mol l⁻¹. The modified electrode showed good stability and reproducibility and had been used for the determination of AA content in vitamin C tablet with satisfactory results.     

Determination of tyrosine using <Emphasis Type="Italic">p</Emphasis>-sulfonated calix[<Emphasis Type="Italic">n</Emphasis>]arene modified electrode

Cyclic voltammetry was used to detect p-sulfonated calix[n]arenas (SCnA) how to immobilize on gold surface. P-sulfonated calix[n]arenes not only increased the specific surface area of the modified electrode, but also improved the enrichment ability of tyrosine. This led to a significant increase in peak current, and improved the sensitivity of tyrosine determination on the p-sulfonated calix[n]arenes-modified electrode. The modified electrode showed good catalytic ability of l-tyrosine oxidation reaction. The peak current of l-tyrosine increased and the oxidation peak potential shifted negatively with cavity size of the SCnA-modified electrode, which indicated that the catalytic ability of the modified electrode to l-tyrosine oxidation reaction was also enhanced. For the tyrosine guest molecule, the order of electrochemical activity and magnitude of catalytic ability of the oxidation reaction of the three modified gold electrodes was as follows: SC4A?>?SC6A?>?SC8A. The electrode had high selectivity and stability for the determination of tyrosine, with a wide linear range, low detection limit and high sensitivity at different concentrations under different pH values. This resulted in an accurate, fast, sensitive electrochemical method for the determination of tyrosine. The sensor was used for the determination of tyrosine in human urine with satisfactory results.     

Low-temperature thermodynamic properties of <Emphasis Type="SmallCaps">dl</Emphasis>-cysteine

Heat capacity C _p(T) of the crystalline dl-cysteine was measured on heating the system from 6 to 309 K by adiabatic calorimetry; thermodynamic functions were calculated based on these data smoothed in the temperature range 6–273.15 K. The values of heat capacity, entropy, and enthalpy at 273.15 K were equal to 142.4, 153.3, and 213.80 J K⁻¹ mol⁻¹, respectively. At about 300 K, a heat capacity peak was observed, which was interpreted as an evidence of a first-order phase transition. The enthalpy and the entropy of the transition are equal, respectively, to 2300 ± 50 and 7.6 ± 0.1 J K⁻¹ mol⁻¹.     

<Emphasis Type="SmallCaps">d</Emphasis>-Amino Acids in Animal Peptides

Summary. Secreted peptides from diverse sources have been found to contain a d-amino acid. From the sequence of cloned mRNAs coding for the precursors of such peptides it could be deduced that in all cases tested so far the d-amino acid in the final product is derived from the corresponding l-amino acid present in the primary product of translation. Enzymes catalyzing such an l- to d-isomerization in peptide linkage have been isolated from the venom of a spider and the skin secretions of frogs. Even though these are completely different proteins, the reaction mechanism is the same, namely a de-protonation/re-protonation of the α-carbon of an amino acid with concomitant inversion of the chirality. Sequences potentially coding for homologues of the frog enzyme are present in the genome of different vertebrate species.     

Coordination polymers based on zinc(<Emphasis Type="SmallCaps">ii</Emphasis>) and manganese(<Emphasis Type="SmallCaps">ii</Emphasis>) with 1,4-cyclohexanedicarboxylic acid

Three new metal-organic coordination polymers were obtained namely, [Mn₃(chdc)₃-(NMP)₂(DMF)₂] (1, chdc^2– is trans-1,4-cyclohexanedicarboxylate, NMP is N-methylpyrrolidone, DMF is N,N-dimethylformamide), [Zn₃(chdc)₃(NMP)₂]?2NMP (2), and [Zn₃(chdc)₃(ur)-(DMF)_0.5]?DMF (3, ur is the urotropine). The crystal structures of polymers 1, 2, and 3 were determined by single-crystal X-ray crystallography. All three compounds were found to contain a trinuclear secondary building unit {M₃(OOC)₆}. Coordination polymers 1 and 2 have a layered structure, while polymer 3 has a three-dimensional coordination framework with isolated pores formed due to the presence of urotropine bridging molecules. Compounds 1 and 3 were characterized by IR spectroscopy, thermogravimetric and elemental analysis data, powder X-ray diffraction. Compound 3 was also characterized by UV-Vis diffuse reflectance spectrum.     

Poly(<Emphasis Type="SmallCaps">dl</Emphasis>-aspartic acid) and copper(II) acetate monohydrate interactions

A polychelate with poly(dl-aspartic acid) was prepared in order to study the influence of the polymer ligands on the copper(II) acetate monohydrate. This compound was characterized by elemental analysis, magnetic susceptibility measurements, spectroscopy and thermal analysis. It is suggested that in the unit Cu₂(acetate)₄ the breakage of two acetate groups occurs by the effect of polymer ligand group coordination. It coordinates through a carboxylate group, keeping the water molecules coordinated to Cu^II. A magnetic moment of the polychelate is observed which presents a value of 1.74 M.B, which corresponds to uncorrelated Cu²⁺ (S = 1/2) spins, separated by large Cu–Cu distances. According to the suggested structure, PM3 semi-empirical calculations of the polychelate of Cu^II were done.     

<Emphasis Type="Italic">Z</Emphasis>-and <Emphasis Type="Italic">E</Emphasis>-conformers of <Emphasis Type="Italic">N</Emphasis>-chloroacetylcytisine

N-Chloroacetylcytisine was synthesized by acylation of (–)-cytisine. Stable Z- and E-conformers with respect to rotational isomerism around the N-12–CO bond were found in PMR spectra at room temperature. The point at which PMR resonances of the Z- and E-conformers coalesced upon heating was measured. The transition barrier between the conformers was estimated.