Voltammetry of Os(VI)‐Modified Polysaccharides at Carbon Electrodes

We show that polysaccharides (PSs, such as dextran and mannan) can be chemically modified by Os(VI) complexes, yielding electroactive adducts. Os(VI) complexes with different ligands (e.g., temed and 2,2′‐bipyridine) produced at pyrolytic graphite electrodes redox couples at different potentials suitable for “multicolor” labeling of PSs and for studies of ligand exchange kinetics. PS‐Os(VI)L adducts can be determined not only in their purified forms but also in the reaction mixtures.     

Electrocatalytic detection of polysaccharides at picomolar concentrations

Electroinactive polysaccharides (PS) modified by osmium(VI) complexes with nitrogenous ligands produce redox couples at carbon and mercury electrodes. We show that PS adducts with Os(VI) 2,2'-bipyridine produce at ~-1.2 V (against Ag/AgCl/3 M KCl electrode) an additional peak at mercury and solid amalgam electrodes. This peak is due to the catalytic hydrogen evolution, allowing detection of PS (such as dextran and mannan) at picomolar concentrations.     

Modification of Poly‐ and Oligosaccharides with Os(VI)pyridine. Voltammetry of the Os(VI) Adducts Obtained by Ligand Exchange

Polysaccharides and oligosaccharides were modified with Os(VI)pyridine complex followed by ligand exchange with different ligands such as 2,2′‐bipyridine or N,N,N′,N′‐tetramethylethylenediamine. The time of the modification was much shorter (taking about 15 min) then direct modification with the given Os(VI) complex. The resulting saccharide adducts were analyzed by voltammetric methods at carbon and mercury electrodes. The results showed that the proposed technique gives promise for a new approach to analysis of glycoproteins.     

Voltammetry of Osmium End‐Labeled Oligodeoxynucleotides at Carbon,Mercury, and Gold Electrodes

Voltammetric behavior of oligodeoxynucleotide (ODN) 5′‐T₄₀ (GAA)₇–3′ end‐labeled with osmium tetroxide,2,2‐bipyridine [Os(VIII)bipy] was compared with Os(VIII)bipy‐base‐ and with Os(VI)bipy‐sugar‐modified thymine ribosides. Cyclic voltammograms of Os(VIII)bipy‐modified ODN at mercury and carbon electrodes were similar but not identical to those of Os(VIII)bipy‐modified thymine riboside. Treatment of the ODN with Os(VI)bipy did not result in the ODN modification, in agreement with the known specificity of the reagent to the sugar cis‐diols. We show that in addition to mercury and carbon electrodes, the gold electrode can be used to detect Os(VIII)bipy‐labeled ODN. Comparison of voltammetric behavior of end‐labeled ODN using three types of electrodes most frequently used in DNA analysis may help to optimize electrochemical DNA sensors.     

Facile end-labeling of RNA with electroactive Os(VI) complexes

Ribose at the 3′-end of oligonucleotides (oligos) selectively modified by Os(VI)2,2′-bipyridine (bipy) produced two CV redox couples at pyrolytic graphite electrode. Using square wave voltammetry (SWV) 22-mer oligos can be detected down to 250 nM. At mercury electrodes the Os(VI)bipy-oligo adducts produced an electrocatalytic peak at ~?1.2 V allowing their determination down to picomolar concentrations. High specificity of Os(VI)bipy for ribose in nucleic acids and high sensitivity of the determination at mercury and solid amalgam electrodes give promise for new efficient methods of microRNA determination.     

Voltammetric Behavior of Osmium‐Labeled DNA at Mercury Meniscus‐Modified Solid Amalgam Electrodes. Detecting DNA Hybridization

The complex of osmium tetroxide with 2,2′‐bipyridine has been utilized as a probe of DNA structure and an electroactive marker of DNA in DNA hybridization sensors. It produces several voltammetric signals, the most negative of them has been observed only at mercury electrodes. This signal is of catalytic nature affording a high sensitivity of DNA determination. The catalytic current due to evolution of hydrogen in voltammetry of DNA modified by complex of osmium tetroxide with 2,2′‐bipyridine (DNA‐Os,bipy) was studied. Solid amalgam electrodes (modified with mercury menisci) of silver (m‐AgSAE), copper (m‐CuSAE), gold, and of combined bismuth and silver, were used as possible substitutes for mercury electrodes. Besides the hanging mercury drop electrode (HMDE), the catalytic current was observed only on m‐AgSAE and m‐CuSAE. Electrodes of gold and bismuth amalgams did not give the catalytic current. The detection limit of DNA‐Os,bipy on HMDE was 0.1 ng mL^?1 (RSD=2.3 %, N=11), and on m‐AgSAE 0.2 ng mL^?1 (RSD=3.1%, N=11). The m‐AgSAE was successfully applied as a detection electrode in double‐surface DNA hybridization experiments offering highly specific discrimination between complementary (target) and nonspecific DNAs, as well as determination of the length of a repetitive DNA sequence. The m‐AgSAE has proved a convenient alternative to the HMDE or carbon electrodes used for similar purposes in previous work.     

End-labeling of peptide nucleic acid with osmium complex. Voltammetry at carbon and mercury electrodes

Peptide nucleic acid (PNA), the DNA mimic with electrically neutral pseudopeptide backbone, is intensively used in biotechnologies and particularly in single-base mismatch detection in DNA hybridization sensors. We propose a simple method of covalent end-labeling of PNA with osmium tetroxide, 2,2′-bipyridine (Os,bipy). Os,bipy-modified PNA (PNA–Os,bipy) produces voltammetric stripping peaks at carbon and mercury electrodes. Peak potential (E_p) of one of the anodic peaks of PNA–Os,bipy at the pyrolytic graphite electrode (PGE) differs from E_p of the reagent, allowing PNA–Os,bipy analysis directly in the reaction mixture. At the hanging mercury drop electrode (HMDE) the PNA–Os,bipy yields a catalytic peak Cat_p, in addition to the redox couples. Using Cat_p it is possible to detect purified PNA–Os,bipy down to 1 pM concentration at accumulation time 60 s. To our knowledge this is the highest sensitivity of the electrochemical detection of PNA.     

Voltammetry of osmium-modified DNA at a mercury film electrode: application in detecting DNA hybridization

Mercury film electrodes (MFE) have recently been used in nucleic acid electrochemical analysis as alternatives to the classical mercury drop ones. DNA modified with osmium tetroxide, 2,2'-bipyridine (Os,bipy) can be detected with a high sensitivity at mercury electrodes via measurements of a catalytic osmium signal. In this paper we show that mercury film on a glassy carbon electrode can be used in voltammetric analysis of Os,bipy-modified DNA. Application of the MFE as a detection electrode in double-surface electrochemical DNA hybridization assay involving osmium labeling of target DNA is demonstrated.     

Surface modification of multiwalled carbon nanotubes via nitroxide‐mediated radical polymerization

The nitroxide‐mediated radical polymerization of styrene was carried out on the surfaces of multiwalled carbon nanotubes (MWNTs) initiated by an MWNT‐supported initiator multiwalled carbon nanotube–2″,2″,6″,6″‐tetramethylpiperidinyloxy (MWNT–Tempo). The content of polystyrene grafted from the surface was controlled by changes in the polymerization conditions, such as the reaction times or the ratios of monomers to initiators. The obtained polystyrene‐grafted multiwalled carbon nanotubes (MWNT–PSs) were further used to initiate the polymerization of 4‐vinylpyridine to get polystyrene‐b‐poly(4‐vinylpyridine)‐grafted multiwalled carbon nanotubes (MWNT–PS‐b‐P4VPs). In contrast to unmodified MWNTs, MWNT–PSs had relatively good dispersibility in various organic solvents, such as tetrahydrofuran, CHCL₃, and o‐dichlorobenzene. The structures and properties of MWNT–PSs and MWNT–PS‐b‐P4VPs were characterized and studied with several methods, including thermogravimetric analysis, Fourier transform infrared, ultraviolet–visible, and transmission electron microscopy. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4656–4667, 2006     

Biosensor for Hepatitis B Virus DNA PCR Product and Electrochemical Study of the Interaction of Di(2,2′‐bipyridine)osmium(III) with DNA

The strategy for electrochemical detection of HBV DNA PCR product (181 bps) was designed by covalently immobilizing single‐stranded HBV DNA on preoxidized glassy carbon electrode surface. The immobilization of single stranded DNA was verified by AC impedance spectra. The following hybridization reaction on surface was evidenced by electrochemical methods using [Os(bpy)₂Cl₂]⁺ as an electroactive indicator. The interactions of [Os(bpy)₂Cl₂]⁺ with calf thymus single and double stranded DNA immobilized on preoxidized glassy carbon electrodes were studied. [Os(bpy)₂Cl₂]⁺ could bind preferentially to the duplex DNA by intercalating to base pairs. The intrinsic binding constant of [Os(bpy)₂Cl₂]⁺ with calf thymus DNA was calculated to be 1.21×10⁴ M^?1. Using [Os(bpy)₂Cl₂]⁺ as an electrochemical hybridization indicator, the HBV DNA sensor has been used to detect qualitatively target HBV DNA in solution with high sensitivity and selectivity.     

New reagent for indirect spectrophotometric red-ox determination of osmium (Ⅵ)

A highly sensitive indirect spectrophotometric red-ox method for the determination of osmium is reported. The method is based on the oxidation of iodide by osmium (VI) and the spectrophotometric detection of the liberated iodine in the form of complex anion and ion associate with 2-(4-diethylaminostyryl)-1,3,3-trimethyl-6-nitro-3H-indolium chloride reagent. The appropriate reaction conditions have been established. The molar absorptivity is (1.6-5.6)×104 L mol-1cm-1. Beer's law holds for the concentration range of 0.5-11.4μgmL-1 of Os(Ⅵ).     

Electrochemical Studies on New Chelating Compounds of the Mono‐ and Bis(imidazolyl)pyridine Type

Recently designed and synthetized mono‐imidazolinone (I and III) and bisimidazolinone (II and IV) chelating ligands were electrochemically characterized at mercury and carbon paste electrodes. Based on polarographic, voltammetric and coulometric investigations in buffered aqueous media, the general reduction pathway has been suggested. Reduction of the mono‐imidazolinone derivatives proceeds in acidic and neutral media in two two‐electron steps. In the first step, the 2,3‐C?N double bond of the imidazolone ring is reduced yielding a mixture of two diastereoisomers (V and VI). In the second step, the 2,3‐C? N single bond (in protonated form) is further reductively split and as the only final product the compound VII was formed. Both intermediates (V and VI) as well as the final product (VII) were prepared using controlled potential electrolysis on the first and second wave, respectively, isolated and identified by means of NMR. The reduction of bis‐derivatives proceeds most probably in an analogical way: in the first step, both imidazoles are reduced simultaneously at the same potential, whereas the following reduction (ring‐opening) proceeds stepwise. In the case of compound III, the covalent hydration of the parent compound takes place in acidic media, partially preventing its reduction. Finally, voltammetric behaviour of mono‐ and bisimidazolinones at carbon paste electrode is also discussed and, in prospect, possible electroanalytical applications outlined.     

New approaches in the development of DNA sensors: hybridization and electrochemical detection of DNA and RNA at two different surfaces

Up to now, the development of the electrochemical DNA hybridization sensors relied on solid electrodes, on which both the hybridization and detection steps have been performed. Here we propose a new method in which the DNA hybridization is performed at commercially available magnetic beads and electrochemical detection on detection electrodes (DE). Due to minimum nonspecific DNA adsorption at the magnetic beads, very high specificity of the DNA hybridization is achieved. Optimum DE can be chosen only with respect to the given electrode process. It is shown that high sensitivity and specificity in the detection of relatively long target DNAs can be obtained (a) by using cathodic stripping voltammetry at mercury or solid mercury amalgam DEs for the determination of purine bases, released from DNA by acid treatment, and (b) by enzyme-linked immunoassay of target DNA modified by osmium tetroxide,2,2'-bipyridine (Os,bipy) at carbon DEs. Direct determination of Os,bipy at mercury and carbon electrodes is also possible.     

Study of the Complexation,Adsorption and Electrode Reaction Mechanisms of Chromium(VI) and (III) with DTPA Under Adsorptive Stripping Voltammetric Conditions

The complexation of Cr(III) and Cr(VI) with diethylenetriaminepentaacetic acid (DTPA), the redox behavior of these complexes and their adsorption on the mercury electrode surface were investigated by a combination of electrochemical techniques and UV/vis spectroscopy. A homogenous two‐step reaction was observed when mixing Cr(III), present as hexaquo complex, with DTPA. The first reaction product, the electroactive 1 : 1 complex, turns into an electroinactive form in the second step. The results indicate that the second reaction product is presumably a 1 : 2 Cr(III)/DTPA complex. The electroreduction of the DTPA‐Cr(III) complex to Cr(II) was found to be diffusion rather than adsorption controlled.The Cr(III) ion, generated in‐situ from Cr(VI) at the mercury electrode at about ?50 mV (vs. Ag|AgCl) (3 mol L^?1 KCl), was found to form instantly an electroactive and adsorbable complex with DTPA. By means of electrocapillary measurements its surface activity was shown to be 30 times higher than that of the complex built by homogenous reaction of DTPA with the hydrated Cr(III). Both components, DTPA and the in‐situ built complex Cr(III) ion were found to adsorb on the mercury electrode.The effect of nitrate, used as catalytic oxidant in the voltammetric determination method, on the complexation reaction and on the adsorption processes was found to be negligible.The proposed complex structures and an overall reaction scheme are shown.     

乙腈溶液中锇氮化合物电化学诱导桥氮偶联过程的原位FTIR反射光谱研究(英)

采用原位 红外反射 光谱（ｉｎ＿ｓｉｔｕ Ｆ Ｔ Ｉ Ｒ Ｓ） 结合紫 外可见 光谱（ Ｕ Ｖ／ Ｖｉｓ） 和 电化学循 环伏安技术（ Ｃ Ｖ） ,研究了［ Ｏｓ Ｖ Ｉ（ Ｎ）（ Ｎ Ｈ３） ４］（ Ｃ Ｆ３ Ｓ Ｏ３） ３ 的 电化 学诱 导桥 氮偶 联过 程． 首次 在 Ｐｔ 电 极上检测到桥 氮 混 合 价 锇 物 种［ Ｏｓ＿ Ｎ ≡ Ｎ＿ Ｏｓ］ 及 其 随 电 位 的 变 化 过 程 ． 在 约 ２ ｍ ｍ ｏｌ／ Ｌ 〔 Ｏｓ Ｖ Ｉ（ Ｎ）（ Ｎ Ｈ３） ４〕（ Ｃ Ｆ３ Ｓ Ｏ３） ３ ＋ ０ ．１ ｍ ｏｌ／ Ｌ Ｔ Ｂ Ａ Ｈ 的乙腈溶 液中,选 取０ ．４ ～－ １ ．０ Ｖ 电位 区间 １００ ｍ Ｖ／ｓ 扫描速度 ,对 Ｐｔ 或 Ｇ Ｃ 电 极进行电 化学循环 伏安处 理,处 理 后的 电极 表 面均 可积 累 一层 深绿 色 的沉积物,表 明电化 学诱导 Ｎ＿ Ｎ 偶联效 应已在 电极上 发生, 并形 成了 混合 价 桥氮 络合 物． 同时 ,在 上述过程中 所生成 的混合价 锇氮物种 ,有可能 较强地 吸附在电 极表 面,且 形成 一定 厚度 的表 面层, 从而减缓了 体系中 Ｏｓ Ｖ Ｉ≡ Ｎ 物种在电 极上的 继续还 原．同 时可 以看 到,随 着 Ｃ Ｖ 的 不 断进 行,溶 液 颜色将逐渐 地由黄变 绿．经过 长时间（ 约     

Speciation Analysis of Osmium(VIII) and Osmium(IV) by UV‐VIS Spectrophotometry Using Quercetin as the Reagent

Abstract

The UV‐VIS spectrophotometric methods for the determination of Os(VIII) (as OsO₄) and Os(IV) (as OsCl₆ ^2? complex) in their mixtures were developed. Quercetin (Q), a flavonoid compound, was used as a chromogenic reagent. Both direct and derivative spectrophotometry can be employed for the determination of Os(VIII). The calculation of the first‐derivative spectrum of the examined mixture and the use of the signal at 285.1 nm allows reaching a better detection limit (0.01 µg mL^?1 Os) as compared with direct spectrophotometry (0.1 µg mL^?1 Os). Relative standard deviations of the results are in the range of 0.87%–4.65% and 0.45%–1.15% for direct and derivative mode, respectively. Selective redox reaction of OsO₄ with Q under the conditions used (0.05 M HCl, 1×10^?4 M Q, 15 min heating at 70°C) makes the basis of its determination in mixtures with the OsCl₆ ^2? complex. Quercetin does not react with the OsCl₆ ^2? complex. The signals of the OsCl₆ ^2? complex can be isolated from the examined mixtures by the calculation of the third‐order derivative spectra and the use of the values at 340.0 nm. The effectiveness of the reduction of OsO₄ in chloride solutions has been studied by the developed method.     

A Study on Stripping Voltammetric Determination of Osmium(IV) at a Carbon Paste Electrode Modified In Situ with Cationic Surfactants

This article deals with the development of a method for the determination of osmium at a carbon paste electrode (CPE) modified with cationic surfactants of the quaternary ammonium salt type; namely, cetyltrimethylammonium bromide (CTAB) and 1‐(ethoxycarbonyl)‐pentadecyltrimethyl‐ammonium bromide (Septonex); both being added in situ and serving for preconcentration of osmium via its hexachloroosmate(IV) anion. The proper electrochemical detection was performed by cathodic scanning in the differential pulse voltammetric mode. Optimization studies concerning important experimental parameters also included a specially performed potentiometric titration, helping to define the actual stoichiometry for the ion‐pairing process, the main principle and driving force of the accumulation step. In a chloride/acetate buffer based supporting medium and with Septonex as the modifier of choice, the reduction signal for osmium was found to be proportional to the Os(IV) concentration in a range from 5×10^?9 to 5×10^?7 mol L^?1 with a limit of detection close to 5×10^?9 mol L^?1 (with preconcentration for 60 s). The method capable to determine Os(IV) in the presence of both Pt(IV) and Ir(III) was tested on model solutions as well as with real sample of industrial waste water (spiked with the analyte); both yielding the recovery rates within 88–99%.     

偶氮氯膦-mA-锇-高碘酸钾催化光度法测定微量锇

在碱性介质中,锇（Ⅳ）对KIO4氧化偶氮氯膦－mA的褪色反应有明显的催化作用,据此建立了催化光度法测定微量锇（Ⅳ）的新方法,并用正交实验设计对反应条件进行了优化。方法的检测限为2．0μg/L。锇（Ⅳ）含量在7．0－25．0μg/L范围内服从比尔定律。此方法已用于贵金属精矿和二次合金中微量锇的测定,相对误差均为0．9％,回收率在95．38％－106．0％之间。     

Butylacrylate‐nucleobase Conjugates as Targets for Two‐step Redox Labeling of DNA with an Osmium Tetroxide Complex

Modification of nucleic acids with osmium tetroxide reagents (Os,L, such as OsO₄,2,2′‐bipyridine, Os,bpy) has been applied in redox DNA labeling, in probing DNA structure as well as in studies of DNA interactions with other molecules. In natural DNA, primarily thymine residues form adducts with the Os,bpy in a structure selective manner. In this paper we introduce a new two‐step technique of DNA modification with the electroactive Os,bpy, consisting in enzymatic construction of DNA bearing butyl acrylate (BA) moieties attached to uracil at C5 or to 7‐deaza adenine at C7, followed by chemical modification of a reactive C=C double bond in the acrylate residue. We demonstrate a facile modification of the BA conjugates in both single‐ and double‐stranded (ds) DNA under conditions when modification within the nucleobase rings in ds DNA is hindered. Various DNA−Os,bpy adducts can easily be analyzed electrochemically and distinguished by different redox potentials. The two‐step procedure appears to be applicable in osmium redox labelling of ds DNA.     

Neue wasserlösliche Osmiumkomplexe des 5,10,15,20‐Tetrakis(4‐sulfonatophenyl)‐porphyrin‐Anions

Metal Complexes with Tetrapyrrole Ligands. LXXVI. New Water‐soluble Osmium Complexes of 5,10,15,20‐Tetrakis(4‐sulfonatophenyl)porphyrin‐Anion The new symmetrical osmium(II) porphyrinates [Os(tpps₄)L₂]^4– ( 1 b – g ) are formed from [OsO₂(tpps₄)]^4– ( 1 a ) by reduction in presence of the ligands L. 1 e – g react with 1‐methylimidazole to yield the unsymmetrical complexes [Os(tpps₄)LL′]^4– ( 1 h – j ). Except for 1 g – h the osmium(II) porphyrinates are not inert in presence of air and are oxidized to the osmium(III) porphyrinates [Os(tpps₄)L₂]^3– ( 2 b – f ) and [Os(tpps₄)LL′]^3– ( 2 i – j ). These anions are deposited as sodium salts.