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.     

Solid state electrochemical of the erbium hexacyanoferrate-modified carbon ceramic electrode and its electrocatalytic oxidation of <Emphasis Type="SmallCaps">l</Emphasis>-cysteine

A kind of erbium hexacyanoferrate (ErHCF)-modified carbon ceramic electrodes (CCEs) fabricated by mechanically attaching ErHCF samples to the surface of CCEs derived from sol–gel technique was proposed. The resulting modified electrodes exhibit well-defined redox responses with the formal potential of +0.215 V [vs saturated calomel electrode (SCE)] at a scan rate of 20 mV s⁻¹ in 0.5 M KCl (pH 7) solution. The voltammetric characteristics of the ErHCF-modified CCEs were investigated by voltammetry. Attractively, the ErHCF-modified CCEs presented good electrocatalytic activity with a marked decrease in the overvoltage about 400 mV for l-cysteine oxidation. The calibration plot for l-cysteine determination was linear at 5.0 × 10⁻⁶–1.3 × 10⁻⁴ M with a linear regression equation of I(A) = 0.558 + 0.148c (μM) (R ² = 0.9989, n = 20), and the detection limit was 2 × 10⁻⁶ M (S/N = 3). At last, the ErHCF-modified CCEs were used for amperometric detection of l-cysteine in real samples.     

Electrocatalytic oxidation of pyridoxine (vitamin B<Subscript>6</Subscript>) on aluminum electrode modified by metallic palladium particles/iron (III) hexacyanoferrate (II) film

The electrocatalytic activity of a Prussian blue (PB) film on the aluminum electrode by taking advantage of the metallic palladium characteristic as an electron-transfer bridge (PB/Pd–Al) for electrooxidation of 2-methyl-3-hydroxy-4,5-bis (hydroxyl–methyl) pyridine (pyridoxine) is described. The catalytic activity of PB was explored in terms of Fe^III [Fe^III (CN)₆]/Fe^III [Fe^II (CN)₆]¹⁻ system. The best mediated oxidation of pyridoxine (PN) on the PB/Pd–Al-modified electrode was achieved in 0.5 M KNO₃ + 0.2 M potassium acetate of pH 6 at scan rate of 20 mV s⁻¹. The mechanism and kinetics of the catalytic oxidation reaction of PN were monitored by cyclic voltammetry and chronoamperometry. The results were explained using the theory of electrocatalytic reactions at chemically modified electrodes. The charge transfer-rate limiting reaction step is found to be a one-electron abstraction, whereas a two-electron charge transfer reaction is the overall oxidation reaction of PN by forming pyridoxal. The value of α, k, and D are 0.5, 1.2 × 10² M⁻¹ s⁻¹, and 1.4 × 10⁻⁵ cm² s⁻¹, respectively. Further examination of the modified electrodes shows that the modifying layers (PB) on the Pd–Al substrate have reproducible behavior and a high level of stability after posing it in the electrolyte or Pyridoxine solutions for a long time.     

<Emphasis Type="Italic">N</Emphasis>-Bromoacetyl-β-<Emphasis Type="SmallCaps">D</Emphasis>-glycopyranosylamines in the synthesis of glycoconjugates of nitrogen-containing physiologically active compounds

A series of nitrogen-containing physiologically active compounds underwent smooth N-monoalkylation with N-bromoacetyl-β-glycopyranosylamines derived from N-acetyl-D-glucosamine and lactose. This reaction was demonstrated to be promising for the introduction of carbohydrate residues into heterocyclic compounds, viz., pyridine, imidazole, pyrimidinetrione, carboline, and piperazine derivatives, and into an amino acid, 5-hydroxy-L-tryptophan, which is unstable in alkaline media. Dedicated to Academician N. K. Kochetkov on the occasion of his 90th birthday. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1256–1259, May, 2005.     

Automated Solid-Phase Extraction and Liquid Chromatography Tandem Mass Spectrometry Determination of N-methyl-2-pyrrolidone and its Metabolites in Urine and Plasma

A method for the simultaneous determination of N-methyl-2-pyrrolidone (NMP) and its metabolites 5-hydroxyl-N-pyrrolidone (5HNMP), N-methylsuccinimide (MSI) and 2-hydroxy-N-methylsuccinimide (2HMSI) in plasma and urine has been developed. Samples were purified by SPE using an ASPEC XL4. Analysis was performed using LC–MS equipped with an APCI interface. The analysis provided linear responses in the range of 0.125–12 μg mL⁻¹ for all of the analytes and up to 150 μg mL⁻¹ for 5HNMP and 2HMSI. The within day precision was in the range of 0.9–19.1% for plasma samples and 1.9–10.4% for urine samples whereas the between day precisions were 4.5–11.9% and 1.2–17.5%, respectively. The method was deemed to be suitable for monitoring the levels of NMP and its metabolites in the plasma and urine of occupationally exposed persons.     

Voltammetric sensor for nitrite determination based on its electrocatalytic reduction at the surface of p-duroquinone modified carbon paste electrode

A p-duroquinone (tetramethyl-p-benzoquinone) modified carbon paste electrode (DMCPE) was employed to study the electrocatalytic reduction of nitrite in aqueous solutions using cyclic voltammetry (CV), double potential-step chronoamperometry, and differential pulse voltammetry (DPV). It has found that under an optimum condition (pH 1.00), the reduction of nitrite at the surface of DMCPE occurs at a potential of about 660 mV less negative than that of an unmodified carbon paste electrode (CPE). The catalytic rate constant, k′_h, based on Andrieux and Saveant theoretical model was calculated as for scan rate 10 mV s^-1. Also, the apparent diffusion coefficient, D _app, was found as 2.5 × 10^–10 and 3.61 × 10^–5 cm² s^-1 for p-duroquinone in carbon paste matrix and nitrite in aqueous buffered solution, respectively. The values for αn_α were estimated to be −0.65 and −0.19 for the reduction of nitrite at the surface of DMCPE and CPE, respectively. The electrocatalytic reduction peak currents showed a linear dependence on the nitrite concentration, and a linear analytical curve was obtained in the ranges of 5.0 × 10^–5 M to 8.0 × 10^–3 M and 6.0 × 10^–6 M to 8.0 × 10^–4 M of nitrite concentration with CV and DPV methods, respectively. The detection limits (2σ) were determined as 2.5 × 10^–5 M and 4.3 × 10^–6 M by CV and DPV methods. This method was also applied as a simple, selective and precise method for determination of nitrite in real samples (the weak liquor from the wood and paper factory of Mazandaran province in Iran) by using a standard addition method.     

A sensitive semi-micro column HPLC method with peroxyoxalate chemiluminescence detection and column switching for determination of MDMA-related compounds in hair

A sensitive semi-micro column HPLC method with peroxyoxalate chemiluminescence (POCL) detection and column switching has been developed for simultaneous determination of 3,4-methylenedioxymethamphetamine (MDMA) and related compounds, for example 3,4-methylenedioxyamphetamine, methamphetamine, and amphetamine, in hair. After digestion of the hair with 1 mol L⁻¹ sodium hydroxide the compounds were extracted with n-heptane and derivatized with 4-(N,N-dimethylaminosulfonyl)-7-fluoro-2,1,3-benzoxadiazole. A mixture of hydrogen peroxide and bis(2,4,5-trichloro-6-carbopentoxyphenyl)oxalate in acetonitrile was used as post-column CL reagent. Calibration plots showed linearity was good (r = 0.999); detection limits were 0.02–0.16 ng mg⁻¹ hair at a signal-to-noise ratio of 3. The precision of the method, as RSD (n = 5), in intra-day and inter-day assays was better than 5.0 and 6.9%, respectively. The proposed method was sufficiently sensitive to detect low ng mg⁻¹ levels of MDMA and related compounds in hair, and could be used for quantification of the compounds in hair samples from patients treated in a chemical dependency unit.     

Electrochemical behaviors of metol on ionic-liquid-modified carbon paste electrode and its analytical application

The electrochemical behaviors of metol on an ionic liquid N-butylpyridinium hexafluorophosphate modified carbon paste electrode (IL-CPE) were studied in this paper. The results indicated that a pair of well-defined quasi-reversible redox peaks of metol appeared with the decrease of overpotential and the increase of redox peak current, which was the characteristics of electrocatalytic oxidation. The electrocatalytic mechanism was discussed and the electrochemical parameters were calculated with results of the charge-transfer coefficient (α) as 0.45, the electrode reaction rate constant (k _s) as 4.02 × 10⁻³ s⁻¹, and the diffusion coefficient (D) as 6.35 × 10⁻⁵ cm²/s. Under the optimal conditions, the anodic peak current was linear with the metol concentration in the range of 5.0 × 10⁻⁶ ∼ 1.0 × 10⁻³ mol/L (n = 11, γ = 0.994) and the detection limit was estimated as 2.33 × 10⁻⁶ mol/L (3σ). The proposed method was successfully applied to determination of metol content in synthetic samples and photographic solutions.     

Polymer supported 5,10,15,20-tetrakis(phenoxy acetic acid)porphyrin derivative for separation and preconcentration of d- and f-electron metals

5,10,15,20-tetrakis(phenoxy acetic acid) porphyrin (PAAP) was covalently linked to Merrifield chloromethylated resin. Characterization of PAAP and the modified polymeric matrix were performed by ¹H NMR, FTIR and elemental analysis. The sorbent was used for the separation and enrichment of the d-electron metals (Mn(II), Co(II), Ni(II), Cu(II) and Zn(II)) at pH 6–8 and of the f-electron metals U(VI) and Th(IV) at pH 4–5. The metals ions were preconcentrated with a concentration factor range of 115–215 and then determined by flame atomic absorption spectrometry or visible spectrophotometry using Arsenazo(III). The retained metals were eluted with 2.0 mol L⁻¹ HNO₃ in the case of the d-electron metals and 0.1/0.25 mol L⁻¹ HCl in the case of the f-electron metals. The procedure was validated by analyzing the NIST standard reference material 2709 (San Joaquin Soil). Correspondence: Melek Merdivan, Chemistry Department, Faculty of Arts and Sciences, Dokuz Eylul University, 35160 Buca, Izmir, Turkey     

Determination of 13C isotopic enrichment of valine and threonine by GC-C-IRMS after formation of the N(O,S)-ethoxycarbonyl ethyl ester derivatives of the amino acids

We describe a new method of assessing, in a single run, ¹³C isotopic enrichment of both Val and Thr by gas chromatography–combustion–isotope-ratio mass spectrometry (GC–C–IRMS). This method characterised by a rapid one-step derivatisation procedure performed at room temperature to form the N(O,S)-ethoxycarbonyl ethyl ester derivatives, and a polar column for GC. The suitability of this method for Val and Thr in in-vivo samples (mucosal hydrolysate) was demonstrated by studying protein metabolism with two tracers (¹³C-valine or ¹³C-threonine). The intra-day and inter-day repeatability were both assessed either with standards or with in-vivo samples at natural abundance and at low ¹³C isotopic enrichment. For inter-day repeatability CVs were between 0.8 and 1.5% at natural abundance and lower than 5.5% at 0.112 and 0.190 atom% enrichment for Val and Thr, respectively. Overall isotopic precision was studied for eleven standard amino acid derivatives (those of Val, Ala, Leu, Iso, Gly, Pro, Asp, Thr, Ser, Met, and Phe) and was assessed at 0.32‰. The ¹³C isotopic measurement was then extended to the other amino acids (Ala, Val, Leu, Iso, Gly, Pro, Thr, and Phe) at natural abundance for in-vivo samples. The isotopic precision was better than 0.002 atom% per amino acid (for n = 4 rats). This analytical method was finally applied to an animal study to measure Thr utilization in protein synthesis.     

Flow-injection solid surface lanthanide-sensitized luminescence sensor for determination of <Emphasis Type="Italic">p</Emphasis>-aminobenzoic acid

A single optosensing device based on lanthanide-sensitized luminescence was developed for determination of p-aminobenzoic acid (PABA). The method is based on the formation of a complex between PABA and Tb(III) immobilized on the solid phase (QAE A-25 resin) placed inside the flow cell. NaCl (1 M) was used as carrier solution and HCl (0.05 M) as eluent. The sample solutions of PABA (100 μL) containing Tb(III) and buffered at pH = 6.0 were injected into the carrier stream and the luminescence was measured at λ _ex = 290 nm and λ _em = 546 nm. The method shows a linear range from 0.2 to 6.0 μg mL⁻¹ with an RSD of 1.2% (n = 10) and a sampling frequency of 22 h⁻¹. A remarkable characteristic of the method is its high selectivity which allows it to be satisfactorily applied to the analysis of PABA in pharmaceutical samples without prior treatment. Figure Typical emission bands of Tb(III) in a solid-phase PABA–Tb(III) luminescence spectrum     

Study of the metabolism on tobacco-specific N-nitrosamines in the rabbit by solid-phase extraction and liquid chromatography–tandem mass spectrometry

Metabolism of four tobacco-specific N-nitrosamines (TSNAs), N′-nitrosonornicotine (NNN), N′-nitrosoanatabine (NAT), N′-nitrosoanabasine (NAB), and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) has been studied by solid-phase extraction (SPE) and liquid chromatography–tandem mass spectrometry (LC–MS–MS). 4-(Methylnitrosamino)-4-(3-pyridyl)-1-butanol (iso-NNAL) was used as internal standard. SPE and LC–MS–MS was found to be a rapid, simple, sensitive, and selective method for analysis of TSNAs in rabbit serum. The relative standard deviation (R.S.D., n = 6) for analysis of 5 ng mL⁻¹ and 0.5 ng mL⁻¹ standards and of serum sample spiked with 5 ng mL⁻¹ standards of five TSNAs was 2.1–11% and recovery of 5 ng mL⁻¹ standards from serum was 100.2–112.9%. A good linear relationship was obtained between peak area ratio and concentration in the range of 0.2–100 ng mL⁻¹ for NNAL and 0.5–100 ng mL⁻¹ for other four TSNAs, with correlation coefficients (R ²) >0.99 (both linear and log–log regression). Detection limits for standards in solvent were between 0.04 and 0.10 ng mL⁻¹. Doses of TSNAs administered to rabbits via the auricular vein were 4.67 μg kg⁻¹ and 11.67 μg kg⁻¹, in accordance with the different levels in cigarettes. Metabolic curves were obtained for the four TSNAs and for 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), a metabolite of NNK; on the basis of these curves we modeled metabolic kinetic equations for these TSNAs by nonlinear curve fitting.     

Functionalization of <Emphasis Type="Italic">N-tert</Emphasis>-butoxycarbonyl-7-and <Emphasis Type="Italic">N-tert</Emphasis>-butoxycarbonyl-8-bromo-10-azabicyclo[4.3.1]deca-3,7-dienes. A route to a ferruginine homolog

N-tert-Butoxycarbonyl-7-and N-tert-butoxycarbonyl-8-bromo-10-azabicyclo[4.3.1]deca-3,7-dienes are convenient substrates for further modification using replacement of the Br atom by a cyano group or a Li atom. Treatment of lithium derivatives with dimethylformamide and N-methoxy-N-methylacetamide gave the corresponding α,β-unsaturated aldehydes (67–84%) and ketones (∼70%). Ketone 4b is a direct precursor of a homolog of the alkaloid ferruginine. Dedicated to Academician G. A. Abakumov on the occasion of his 70th birthday. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1794–1796, September, 2007.     

Synthesis and cycloaddition of <Emphasis Type="Italic">N</Emphasis>-substituted pyrroles with polyfluorinated substituents

Reactions of N-pyrrolylpotassium with fluorinated electrophiles yielded N-substituted pyrroles containing polyfluoroalkyl, polyfluoroalkenyl, polyfluoroalkylsulfonyl, and polyfluoroaryl substituents. N-Polyfluoro-substituted pyrroles did not isomerize at ≥100 °C; they were found to be reactive in [4+2] cycloaddition reactions with perfluorobut-2-yne. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1890–1895, August, 2005.     

RuO<Subscript>4</Subscript>-mediated oxidation of<Emphasis Type="Italic">N</Emphasis>-benzylated tertiary amines. Are amine<Emphasis Type="Italic">N</Emphasis>-oxides and iminium cations reaction intermediates?

N-Benzylmorpholine,-piperidine, and-pyrrolidine (1A-C, resp.) are oxidised by RuO₄ (generated in situ) at both endocyclic and exocyclic (benzylic) N—α-methylene positions to afford lactams (and dioxo-derivatives) and benzaldehyde (and benzoyl derivatives), respectively. The N-oxides of 1A-C, formed by a minor side reaction, are not involved as intermediates. Control experiments showed the transient formation of endo- and exocyclic iminium cations trapped with NaCN as the corresponding nitriles. The proposed course of the RuO₄-mediated oxidation of 1A-C involves the consecutive steps 1⇒iminium cations+cyclic enamine⇒oxidation products. The endocyclic/exocyclic regioselectivity of the oxidation reaction lies between 0.8 (for 1A) and 2.1 (for 1B). The amine cation radical and the N-α-C· carbon-centered radical seem not to be involved.     

<Superscript>1</Superscript>H NMR spectra of water contained in solutions of poly(<Emphasis Type="Italic">N</Emphasis>-vinylpyrrolidone) and its modification products in CDCl<Subscript>3</Subscript>

¹H NMR spectra in CDCl₃ of poly(N-vinylpyrrolidone), epoxidized poly(N-vinyl-pyrrolidone), and products derived from the latter by modification with amino acids (glycine, β-alanine, γ-aminobutyric acid, and ε-aminocaproic acid) were examined. The ¹H NMR spectra of the modified polymers contain signals for water protons due to different centers of water sorption. These signals differ in chemical shift and integral intensity and indicate a changed spatial packing of the polymer as the result of its modification. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2377–2380, October, 2005.     

Purification and Characterization of Thermostable Chitinase from <Emphasis Type="Italic">Bacillus licheniformis</Emphasis> SK-1

Chitinase was purified from the culture medium of Bacillus licheniformis SK-1 by colloidal chitin affinity adsorption followed by diethylamino ethanol-cellulose column chromatography. The purified enzyme showed a single band on sodium dodecyl sulfate polyacrylamide gel electrophoresis. The molecular size and pI of chitinase 72 (Chi72) were 72 kDa and 4.62 (Chi72) kDa, respectively. The purified chitinase revealed two activity optima at pH 6 and 8 when colloidal chitin was used as substrate. The enzyme exhibited activity in broad temperature range, from 40 to 70°C, with optimum at 55°C. It was stable for 2 h at temperatures below 60°C and stable over a broad pH range of 4.0–9.0 for 24 h. The apparent K _m and V _max of Chi72 for colloidal chitin were 0.23 mg ml⁻¹ and 7.03 U/mg, respectively. The chitinase activity was high on colloidal chitin, regenerated chitin, partially N-acetylated chitin, and chitosan. N-bromosuccinamide completely inhibited the enzyme activity. This enzyme should be a good candidate for applications in the recycling of chitin waste.     

[1-B<Subscript>10</Subscript>H<Subscript>9</Subscript>N<Subscript>2</Subscript>]<Superscript>−</Superscript> and [1-CB<Subscript>9</Subscript>H<Subscript>10</Subscript>]<Superscript>−</Superscript> anions: an attempt of quantum chemical calculations

Comparative quantum chemical calculations of structural parameters, chemical shifts of ¹¹B NMR spectra, and atomic charges in 10-vertex boron hydride anions [1-CB₉H₁₀]⁻ and [1-B₁₀H₉N₂]⁻ were performed using the restricted Hartree-Fock method with the 6-31++G(D,P) basis set. Dedicated to Academician G. A. Abakumov on the occasion of his 70th birthday. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1853–1855, September, 2007.     

Theoretical Study of the Interactions between Isolated <Emphasis Type="Italic">DNA</Emphasis> Bases and Various Groups IA and IIA Metal Ions by <Emphasis Type="Italic">Ab Initio</Emphasis> Calculations

Summary. Interactions of the DNA bases adenine (A), guanine (G), cytosine (C), and thymine (T) with various metal ions (M) of groups IA and IIA of the periodic table of the elements were studied at the HF, MP2, and DFT levels of theory. The structures and thermodynamic stabilities of these species were studied at the gas phase. The calculations uphold that there exist two active sites in G and one in A, C, and T. The calculations also show that the O² atom in T is a more active site for metal ion bindings than that in C. The stability energies for G … M complexes are larger than those for A … M complexes and the stability energies for T … M complexes are larger than those for C … M complexes. As z/r ratio for the metal ion increases, the interaction energy for the complex increases systematically. Thermodynamic quantities such as ΔH, ΔG, ΔS, and ln K were determined for each complexation reaction, [Base+M ⁿ⁺ →(Base … M) ⁿ⁺]. A, G, and C complexation reactions except for C … Rb⁺ are exothermic. The situation is quite different for T complexation reactions and all except for T … Be²⁺ and T … Mg²⁺ are endothermic.     

A neutral polysaccharide from <Emphasis Type="Italic">Glycyrrhiza inflata</Emphasis>

A neutral polysaccharide Gi-A1 was isolated from the roots of Glycyrrhiza inflata Bat. It had a molecular mass of over 2000 kDa and showed [α]_D²⁰ + 81.4° (c 1.05, H₂O). Acid hydrolysis and methylation analysis indicated that Gi-A1 was mainly composed of α-D-glucose, α-L-arabinose, and α-D-galactose with a molar ratio of 8.0:1.8:1.0. It can significantly stimulate spleen cell proliferation in vitro (P < 0.01). Published in Khimiya Prirodnykh Soedinenii, No. 1, pp. 13–14, January–February, 2009.