Phthalocyanines and related complexes as electrocatalysts for the detection of nitric oxide

Metallophthalocyanine (MPc) and metalloporphyrin complexes as well as some metalloproteins including myoglobin, hemoglobin, cyanocobalamin and cytochrome c catalyse the detection of nitric oxide (NO). The catalytic process often involve changes in the oxidation state of the catalyst. These complexes catalyse both the reduction and oxidation of NO. MPc complexes containing electroactive central metals such as CoPc and FePc generally show better catalytic activity towards the detection of NO than complexes containing electroinacive central metals. However, the involvement of ring based redox processes was confirmed for the homogenous NO catalysis using CoPc.     

Metalloporphyrin and heteropoly acid catalyzed oxidation of CNOH bonds in an ionic liquid: biomimetic models of nitric oxide synthase

Water soluble iron(III) porphyrins and phosphotungstic acid in an ionic liquid are effective catalysts for the H₂O₂ mediated oxidation of the CNOH bond in N-hydroxyarginine and other oximes. The carbonyl compounds generated as the oxidation products can be easily isolated from the reaction media. These systems serve as biomimetic models of nitric oxide synthase (NOS) and the catalyst immobilized in an ionic liquid can be easily recycled and reused.     

Robotic sequential analysis of a library of metalloporphyrins as electrocatalysts for voltammetric nitric oxide sensors

A library of 83 metalloporphyrins with varying substitution pattern at the meso-position of the porphyrins and different central metal ions in the core region has been synthesized in small quantities using a parallel synthesis strategy. By means of a specially designed electrochemical robotic device integrating a 96-well microtitre plate and an easily movable assembly of working, counter and reference electrodes, the different porphyrins were automatically applied in sequence to an in-well electrochemical preparation and testing of NO sensors. Screening the entire compound collection suggested initial considerations concerning the influence of varied functionalities of the metalloporphyrins on their electrocatalytic properties for the oxidation of NO and helped to identify the quality of the investigated catalyst candidates. As compared to manually performed quality tests, the proposed strategy of automation has advantages in convenience, rapidity and especially reproducibility avoiding any inaccuracies introduced by manually performing all steps of the complex sensor formation and testing sequence.     

Synthesis and biological evaluation of 2,4-diaminopteridine derivatives as nitric oxide synthase inhibitor

A series of novel 2,4-diamino-pteridines(9a-1)were synthesized and evaluated as inhibitors of inducible nitric oxide synthase (iNOS)in vitro.It was found that 9a,9d,9e,9h,9i and 91 showed potent inhibitory activities similar to that of methotrexate(MTX),while the activities of 9b,9c,9f,9g,9j and 9k ale stronger than MTX.     

Nitric oxide producing artificial enzymes based on metalloporphyrins

Artificial enzymes are synthetic materials or molecules that exhibit enzyme-like activities. Herein, we report artificial enzymes based on metalloporphyrins (MPs) that can mimic nitric oxide synthase (NOS) to produce nitric oxide (NO) from l-arginine (Arg) using hydrogen peroxide (H₂O₂) as an oxidant, and we determine the microenvironmental influence on their activity and stability. An assortment of structurally diverse water-soluble MPs was synthesized, and their NO production was compared. Improved catalytic activity and stability of the lead MP were observed when it was conjugated to the hydrophilic homopolymer poly(2-carboxyethyl acrylate) (PCEA). Micelles assembled from the amphiphilic block copolymer poly(cholesteryl methacrylate)-block-PCEA functionalized with the lead MP, and MP-conjugated PCEA polymer chains immobilized on silica particles resulted in moieties with ～3× higher catalytic activity compared to the monomeric MP. Finally, the PCEA-coated silica particles could use the MPs as motor units to exhibit enhanced diffusion in the presence of the required fuel molecules Arg and H₂O₂. Taken together, the microenvironments of the artificial enzymes have a marked impact on their activity and stability, and these NO-producing MPs offer an interesting synthetic alternative to their natural counterparts.     

Modified electrode approaches for nitric oxide sensing

Three different methods for the determination of nitric oxide (NO) in solution are described. These are based, respectively, on the use of a horseradish peroxidase (HRP) biosensor or on electrodes modified with films of redox-active transition metal complexes. In the case of the biosensor the enzyme was electrochemically immobilized onto a glassy carbon (GC) electrode. The activity of HRP is inhibited in presence of NO. Thus, the decrease in activity is correlated to the concentration of NO present in solution. The biosensor responds linearly over the range of 2.7×10⁻⁶-1.1×10⁻⁵ M NO with a detection limit (5% inhibition) of 2.0×10⁻⁶ M. In the case of chemically modified electrodes, particular emphasis is placed on materials capable of catalyzing the oxidation of NO. In terms of electrocatalyst, the discussion will centre on electrodeposited films of 6,17-diferrocenyldibenzo[b,i]5,9,14,18-tetraaza[14]annulen]-nickel(II) and indium(III) hexacyanoferrate(III). The resulting sensors exhibited potent and persistent electroacatalytic activity towards the oxidation of NO with low detection limits (1 μM) and good linear relationship between the catalytic current and NO concentrations. In addition, interference due to the presence of nitrate and nitrite have been significantly reduced. According to these results, the described modified electrodes have been used as sensors for the determination of NO generated by decomposition of a typical NO-donor, such as S-nitroso-N-acetyl-d,l-penicillamine (SNAP). A critical comparison of the various methodologies employed is made.     

Study of the selective catalysis of metalloporphyrins for 2-methyl-butane oxidation with PhIO under mild conditions

Nine ironporphyrins and eight manganeseporphyrins were synthesized, and their selective catalysis for the oxidation of the secondary and tertiary carbon–hydrogen bonds of 2-methyl-butane with PhIO was studied. The proportion of the oxidation product of tertiary carbon–hydrogen bond to the one of secondary carbon–hydrogen bond was 3:1 when ironporphyrins were used as catalysts, and 2.3:1 when manganeseporphyrins were used as catalysts. The research showed that the substituting groups on the porphyrin rings influenced the catalytic selectivity of metalloporphyrins for the oxidation of the secondary and tertiary carbon–hydrogen bonds as well as the reaction yields. The electron-attracting groups on benzene rings of ironporphyrins increased the catalytic selectivity of ironporphyrins for the tertiary carbon–hydrogen bond oxidation and the reaction speeds, and the electron-releasing groups increased the catalytic selectivity for secondary carbon–hydrogen bond oxidation and reduced the reaction speeds. Both electron-attracting and -releasing groups on benzene rings of manganeseporphyrins enhanced the catalytic selectivity of manganeseporphyrins for the secondary carbon–hydrogen bond oxidation.     

An efficient and convenient route for the synthesis of thiophene-2-carboxamidines as potential inhibitors of nitric oxide synthase (NOS)

A mild and efficient synthesis of substituted thiophene-2-carboxamidines which are potent inhibitors of nitric oxide synthase (NOS) is reported herein. The key step involves reaction of a BOC-protected imidazolyl thiophene-2-carboxamidine reactive intermediate with various primary amines to form BOC-thiophene-2-carboxamidines which could be readily deprotected using TFA to furnish free carboxamidines. The method is very mild and tolerates diverse substituents including sensitive peptide and amino acid fragments. This new methodology represents a substantial improvement to the literature method owing to its simplicity and hassle-free purification procedures.     

Measurement of nitric oxide production by the lesioned rat retina with a sensitive nitric oxide electrode

Nitric oxide (NO) plays multiple roles in the nervous system. It is produced as a result of damage or injury of the retina as a part of the central nervous system. Detailed knowledge of the extent and the time course of NO production is of great importance for the understanding of pathological processes and their appropriate medical treatment.Sections of rat retina were stained with antibodies against the three isoforms of NO synthase (NOS) at several time points after a lesion of the optic nerve. No significant changes of NOS expression could be seen at any of the checked time points.For the electrochemical detection of NO production, we modified small platinum electrodes with a NO-sensitive nickel porphyrin by electrochemical polymerisation. Compared to other substances, electrochemically polymerised eugenol was found to be most suitable for protection against interferences. For the measurements, differential pulse amperometry was used. The response to nitric oxide was linear.NO production of adult rat retinas was measured post axotomy after different time points with electrochemical electrodes ex vivo. With non-treated retinas, an NO concentration of approximately 15 M was measured. NO concentration is elevated after an axotomy reaching its highest value of up to 30 M 5 days after the lesion. The NO concentration is decreased below the initial value after 9–14 days post axotomy.     

Electrophilic reaction of nitric oxide with Wittig reagents

Reaction of nitric oxide (NO) with p-substituted benzyl triphenylphosphonium chlorides or bromides (Wittig reagents) in CH₂Cl₂ under argon undergoes electrophilic attack of NO on the carbon center of phosphonium ylides, producing benzonitriles.     

溶胶-凝胶-钴-邻菲啰啉修饰电极对一氧化氮的电催化氧化及其测定

报道了溶胶 凝胶 钴 邻菲口罗啉膜修饰电极的制备方法及其在一氧化氮(NO)检测中的应用,采用循环伏安法(CV)研究修饰电极的电化学特性,差示脉冲伏安法(DPV)对NO进行检测。该修饰电极对NO的电化学氧化具有很好的催化作用,使其氧化电位负移了210mV,氧化峰电流与NO浓度在5.6×10-8～2.8×10-5mol/L范围内呈良好的线性关系,相关系数r=0.999,检测限为1.4×10-8mol/L,且生物体内常见的干扰物质如抗坏血酸、NO2-和儿茶酚胺类神经递质的代谢物等不干扰测定。     

A novel oxygen-dependent deoximation by nitric oxide

A variety of aldoximes and ketoximes were oxidized to corresponding aldehydes and ketones by nitric oxide in the presence of oxygen.A presumed mechanism was suggested.     

Regio- and stereoselective ring opening of aziridines with nitric oxide

Reaction of N-tosyl aziridines with nitric oxide affords the corresponding ring-opened products in regio-, stereoselectivities and excellent yields.     

Electrochemical detection of nitric oxide using polymer modified electrodes

Electrochemical sensors based on chemical surface modification are very attractive because they combine high sensitivity of amperometry with new dimensions of selectivity and stability provided by the surface modifier. This review shows a few strategies employed to facilitate the detection, determination and monitoring of nitric oxide using polymer modified electrodes. Conducting and nonconducting polymer films and composite films are considered. The most significant achievements reached in this field, during the last decade, are critically reviewed. The collected data are also presented in three tables.     

Electrochemical determination of nitric oxide and of its derivatives

Nitric oxide (NO) is one of the simplest odd electron species. Furthermore, it is relatively hydrophobic, which is consistent with its role as a diffusible intracellular messenger or as an immune effector. NO is generated in biological systems and plays important roles as a regulatory molecule. The main problem in NO analysis is its extreme reactivity; in aerated water solution it is transformed into nitrite and nitrate, inactive biological forms. Moreover, it may lose an electron forming the NO⁺ ion, involved in the synthesis of nitrosothiols (RSNOs). The main problems encountered in the analytical determination of free NO and of RSNOs in biological systems are the low stability and the very low concentration of these compounds. The determination of nitrates and nitrites may also be difficult when their concentration is in the nmolar range. We describe an electrochemical assay for the determination in the same sample of free NO and of its derivatives in nmolar range. Owing to its high sensitivity, the procedure could also be applied to environmental analyses     

Highly sensitive voltammetric biosensor for nitric oxide based on its high affinity with hemoglobin

Although heme protein-based, amperometric nitric oxide (NO) biosensors have been well documented in previous studies, most have been conducted in anaerobic conditions. Herein we report a novel hemoglobin-based NO biosensor that is not only very sensitive but also usable in air. The heme protein was entrapped in a sodium montmorillonite film, which was immobilized at a pyrolytic graphite electrode surface. Film-entrapped hemoglobin can directly exchange electrons with the electrode, and this process has proven to favor the catalytic reduction of oxygen. In addition, NO induced a cathodic potential shift of the catalytic reduction peak of oxygen. This potential shift was proportional to the logarithm of NO concentration ranging from 4.0 × 10⁻¹¹ to 5.0 × 10⁻⁶ mol/L. The detection limit has been estimated to be 20 pM, approximately four orders lower than previously reported amperometric detectors.     

Original paper application of cyclodextrins as modifiers in electrophoretic separation of metalloporphyrins

Several metallocomplexes of tetrakis-carboxyphenylporphyrin (TCPP) were separated on fused-silica capillary using CZE with UV-VIS detection. Metalloporphyrins of Co(II), Cu(II), Mn(II), Ni(II), and Zn(II) were formed directly in TCPP solution with addition of Cd(II) to increase the formation reaction rate. The composition of BGE, its concentration, and pH were optimized to ensure the stability of complexes and proper resolution. In particular, the problem of signals' shape was investigated and discussed. The presence of beta-CD in borate buffer significantly improved separation efficiency and signal shapes due to formation of inclusion complexes. Under the best separation conditions (50 mM borate running buffer at pH 9 with addition of 2 mM beta-CD, 30 kV applied voltage) a separation of metal complexes with TCPP was accomplished in 16 min.     

Ring opening of 2,3-epoxy phenyl ketones upon reaction with nitric oxide

Epoxide rings of 2,3-epoxy phenyl ketones were cleaved by nitric oxide, affording regioselectively the C-3 ring-opened products, erythro-α-hydroxyl nitrates (2), in a highly syn-selective manner (isolated yield of the erythro products up to 91%). Products were identified by NMR, MS, and X-ray crystallography. The reaction is assumed to be initiated by NO₂, unlike a nucleophilic attack.     

A theoretical determination of the dissociation energy of the nitric oxide dimer

Summary Multi-reference CI methods have been applied to determine the dissociation energy and structure of thecis-N₂O₂ molecule. The convergence of the theoretical result has been checked with respect to a systematic expansion of the one-electron basis set and the multi-reference CI wave function. The best calculated value, 13.8 kJ/mol, is in agreement with the experimental value, 12.2 kJ/mol. It has been obtained with an extended ANO-type basis set [6s5p3d2f], including the effect of the basis set superposition error (BSSE) in the geometry optimization, and additional effects, such as the electron correlation of core electrons and relativistic corrections, using the average coupled pair functional (ACPF) approach. The optimal geometry computed at this level was found to be:r(NN)=2.284 Å,r(NO)=1.149 Å, and s5p3d2f] basis set, the BSSE was found to be 2 kJ/mol.     

Continuous electrochemical monitoring of nitric oxide production in murine macrophage cell line RAW 264.7

In this study, we realized the continual and long-term electrochemical detection of NO production by stimulated macrophages using modified porphyrinic microsensor. The NO release from RAW 264.7 cells stimulated by lipopolysaccharide started 5 h after the lipopolysaccharide administration. After reaching its maximum at the sixth hour, the stable level of NO production was observed between the seventh and 12th hour of the experiment. This phase was followed by a gradual decline in NO production. A close correlation between the NO signal detected with microelectrode and nitrite accumulation, which had been determined in supernatants removed from stimulated cells, was observed. This finding was utilized for the calibration of the electrochemical experiment. The presence of iNOS enzyme, which constitutes a main requirement for NO production by stimulated macrophages, was confirmed by Western blot analysis of iNOS protein expression at key time points of the corresponding electrochemical experiment. The capability of our microsensor to instantaneously monitor the changes in the NO production by stimulated RAW 264.7 cells was demonstrated by the immediate decrease in the signal due to NO as a response to the addition of iNOS inhibitor into the cell culture medium. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.