Oxidation Of 2-mercaptoethanol Research Articles

Enhanced electrocatalytic activity of cobalt phthalocyanines when “clicked” to graphene oxide nanosheets

Alkyne-terminated Co phthalocyanine (CoPc) derivatives are linked to reduced graphene oxide nanosheets (GONS) via click chemistry and the conjugates are used for the electrocatalytic oxidation of 2-mercaptoethanol. CoPc derivatives where the alkyne group is separated from the Pc ring by an aliphatic and benzene ring (complex 3) showed the best catalytic activity (in terms of oxidation potential) in comparison to when only aliphatic chains were employed without the benzene ring (complex 2) and when there were no substituents (complex 1). The anodic oxidation of 2-mercaptoethanol on 3-GONS (linked) occurred at the least positive oxidation potential (-0.22 V vs. Ag|AgCl). 3-GONS (linked) was found to have the highest sensitivity with the lowest limit of detection of 0.08 [Formula: see text]M. When the CoPc derivative and GONS were not linked but placed sequentially on the electrode, the electrocatalytic activity (in terms of LOD) was poorer than when linked. The electrodes modified with CoPc clicked to GONS are highly promising electrochemical sensors in terms of stability, sensitivity, good catalytic activity and ease of fabrication.

Catalytic Oxidation of 2-Mercaptoethanol by Cobalt(II)phthalocyanines Bearing Chalcone with Furan and Thiophene

Cobalt (II) phthalocyanines carrying on the four of the peripheral positions furan and thiophene as chalcones were sythesized. THF is used to investigate the catalytic oxidation of 2-mercaptoethanol. The synthesized phthalocyanines show catalytic activity on the oxidation of 2-mercaptoethanol. Cobalt (II) phthalocyanine derived by chalcone with furan has given catalytic specifications such as turnover number TON as 16.6, initial reaction rate as 0.293 μmol/sec and the oxygen consumption as 10.06 μmol/min. The other cobalt (II) phthalocyanine derived by chalcone with thiophene has given catalytic specifications such as turnover number TON as 15.9, initial reaction rate as 0.213 μmol/sec and the oxygen consumption as 9.88 μmol/min. So chalcone derived phthalocyanines can be used as catalyst is oxidation of mercaptan by air.

Impact of Fluorinated Cobalt(II) Phthalocyanine Catalysts on Aerobic Thiol Oxidation Kinetics

Kinetic studies were conducted for the aerobic oxidation of 2-mercaptoethanol (2-ME) and 4-fluorobenzenethiol (4-FBT) catalyzed by cobalt(II) phthalocyanines: H16PcCo, F16PcCo, and F64PcCo, each exhibiting a metal center subject to increasing Lewis acidity and steric hindrance. The experiments were performed in a reaction-limited, isothermal, bench-scale, batch reactor, with thiol concentrations measured using GC/FID. Conversions of 2-ME to 2-hydroxyethyl disulfide and 4-FBT to 4-fluorophenyl disulfide in excess of 90% were achieved. Kinetic analyses suggest that the substrate binding and electron transfer are directly related to the Lewis acidity and steric bulkiness of catalyst molecules. Substrate binding was found to be the slow step for thiol oxidations catalyzed by H16PcCo. The rate-determining step for thiol oxidations, catalyzed by F16PcCo and F64PcCo, is the expulsion of the thiyl radical (RS•) from the catalyst molecule.

Fluorescein isothiocyanate-capped gold nanoparticles for fluorescent detection of reactive oxygen species based on thiol oxidation and their application for sensing glucose in serum

This study reports a simple and sensitive method for fluorescent detection of reactive oxygen species (ROS) based on the oxidation of 2-mercaptoethanol (2-ME) and 2-ME-induced increase in fluorescence of fluorescein isothiocyanate-capped gold nanoparticles (FITC-AuNPs). FITC molecules can be readily attached to the surface of citrate-capped AuNPs through their isothiocyanate group. FITC-AuNPs fluoresce weakly mainly due to the efficient fluorescence resonance energy transfer from FITC to AuNPs. It is found that the presence of 2-ME enables FITC to be removed from the surface of the AuNPs through the formation of Au–S bonds, thereby restoring the fluorescence of FITC. In contrast, when 2-ME is oxidized with ROS under alkaline condition, the generated 2-ME disulfide is unable to remove FITC from the NP surface. As a result, the weak fluorescence of FITC-AuNPs increased gradually after adding increasing concentrations of ROS. The sensitivity of this method toward ROS was significantly improved after removal of the AuNPs by centrifugation. Because the glucose oxidase-catalyzed oxidation of glucose yielded gluconic acid and H2O2, this method was also utilized to detect glucose. Under optimum conditions, the minimum detectable concentrations for H2O2, superoxide anion, hydroxyl radical, and glucose were found to be 1, 0.6, 0.6 and 1 μM, respectively. This method has been successfully applied to the determination of glucose in serum.

Thermosensitive copolymer with cobalt phthalocyanine and catalytic behavior based on adjustable LCST

Abstract Thermosensitive polymers with metallophthalocyanine were prepared by immobilizing cobalt tetra(2,4-dichloro-1,3,5-triazine)aminophthalocyanine (Co-TDTAPc) on poly(N-isopropylacrylamide) (PNIPA) and copolymers of N-isopropylacrylamide (NIPA) with acrylamide (AM) (P(NIPA-co-AM)) to obtain Co-TDTAPc–PNIPA and Co-TDTAPc–P(NIPA-co-AM). Examination of the thermosensitive behavior of these polymers showed that the proportion of AM in Co-TDTAPc–P(NIPA-co-AM) had a significant effect on the low critical solution temperature (LCST) in aqueous solution. The LCST of Co-TDTAPc–P(NIPA-co-AM) was adjustable from 34.5 °C to 90.0 °C by changing the AM molar fraction from 0% to 40%. The copolymers showed a high level of catalytic activity on the oxidation of 2-mercaptoethanol in the homogeneous phase when the reaction temperature was below the LCST, and the copolymers could be precipitated and recovered by heterogeneous separation when the temperature was above the LCST. Compared to Co-TDTAPc–PNIPA, the catalytic system with Co-TDTAPc–P(NIPA-co-AM) is able to maintain homogeneity at a higher temperature due to the higher LCST of the copolymers. In addition, strong salting-out salts, such as NaCl and Na2SO4, can decrease the LCST of the copolymers dramatically and obviate the need for more heat to drive the catalytic reaction system to achieve heterogeneous separation. Co-TDTAPc–P(NIPA-co-AM) was stable and remained efficient during repetitive test cycles with no obvious decrease of catalytic activity.

Synthesis and characterization of electrocatalytic conjugates of tetraamino cobalt (II) phthalocyanine and single wall carbon nanotubes

Abstract In this paper we report on the synthesis and characterization of electrocatalytic conjugates of tetraamino cobalt (II) phthalocyanine and single walled carbon nanotubes (CoTAPc–SWCNT-linked) for use as electrode surface modifiers. FTIR, UV–vis and Raman spectroscopies were used to ascertain the chemical linkage between CoTAPc and SWCNT while cyclic voltammetry and rotating disk electrode voltammetry were used to assess the electrocatalytic efficiency of the linked product towards the oxidation of 2-mercaptoethanol. The CoTAPc–SWCNT-linked-GCE demonstrated very good catalytic efficiency relative to CoTAPc–SWCNT-mixed-GCE, CoTAPc-GCE and f-SWCNTs-GCE (functionalised SWCNT). CoTAPc–SWCNT-linked-GCE gave a sensitivity of 0.2 μA/μM and a limit of detection (LOD) of 1.2 × 10 −7 M for 2-mercaptoethanol (2-ME) at pH 4.

Differently substituted phthalocyanines: Comparison of calculated energy levels, singlet oxygen quantum yields, photo-oxidative stabilities, photocatalytic and catalytic activities

Zinc(II) and cobalt(II) phthalocyanines bearing different electron-donating or -withdrawing substituents were prepared. The following properties of these phthalocyanines were investigated: singlet oxygen quantum yields, photo-oxidative stabilities, photocatalytic activities (photooxidation of ( S)-(−)-citronellol) and catalytic activities (oxidation of 2-mercaptoethanol). Furthermore, the positions of HOMO/LUMO energy levels of the ground state (S 0), first excited singlet state (S 1) and first excited triplet state (T 1) were calculated. Relationships between HOMO energy levels of S 0 and photodecompositions, photocatalytic activities and photo-decompositions, and catalytic activities and HOMO energy levels of S 0 were found. Singlet oxygen quantum yields of the different metallophthalocyanines are around 0.55 and independent from the calculated triplet energies.

Catalytic activity and stability of anionic and cationic water soluble cobalt(II) tetraarylporphyrin complexes in the oxidation of 2-mercaptoethanol by molecular oxygen

The catalytic activity and stability of anionic cobalt(II) porphyrin complexes: 5,10,15,20-tetrakis(2,6-dichloro-3-sulfonatophenyl)porphyrinatocobalt(II), 5,10,15,20-tetrakis(2,4,6-trimethyl-3,5disulfonatophenyl)porphyrinatocobalt(II) and the cationic cobalt(II) porphyrin: 5,10,15,20-tetrakis[4-(diethylmethylammonio)phenyl]porphyrinatocobalt(II) tertraiodide have been investigated in the oxidation of 2-mercaptoethanol by dioxygen. All complexes were efficient catalysts for the auto-oxidation of 2-mercaptoethanol. The cationic cobalt(II) porphyrin has been found to be the most reactive catalyst. The rate of auto-oxidation of 2-mercaptoethanol catalysed by 5,10,15,20-tetrakis(2,4,6-trimethyl-3,5disulfonatophenyl)porphyrinatocobalt(II) has been found to increase with increasing the pH from 7 to 9 then decreased at higher pH. The rate constants of auto-oxidation reaction showed linear dependence on catalyst concentration and saturation kinetics in both 2-mercaptoethanol concentrations and dioxygen pressure. Anionic cobalt(II) porphyrin complexes showed higher stability than the cationic catalyst in repeat oxidation reactions. Immobilizing the anionic catalysts on ion exchange resin and supporting the cationic catalyst on clay mineral montmorillonite improved their stabilities towards oxidation.

Novel aqueous soluble cobalt phthalocyanine: synthesis and catalytic activity on oxidation of 2-mercaptoethanol

A new aqueous soluble phthalocyanine, cobalt tetra( N-carbonylacrylic)aminephthalocyanine, was synthesized by modification of cobalt tetraaminophthalocyanine with maleic anhydride. The product was characterized by elemental analysis, FT-IR, and TGA. It is soluble in dilute sodium hydroxide solution. Its catalytic efficiency in the oxidation of 2-mercaptoethanol (MEA) was also evaluated in DMF and aqueous solution. Compared with cobalt tetraaminophthalocyanine and cobalt tetracarboxylphthalocyanine, cobalt tetra( N-carbonylacrylic)aminephthalocyanine had greater catalytic activity and solubility in aqueous solution. The UV–VIS spectra showed that the aggregation of the phthalocyanine molecular was restrained due to the bulky peripheral substitutions on the cobalt phthalocyanine rings, which leads to the increase of catalytic activity in the oxidation of MEA.

Environment effects on the oxidation of thiols: cobalt phthalocyanine as a test case

The reactivity of Co(II) phthalocyanine toward the oxidation of 2-mercaptoethanol was investigated using first principle theoretical methods. Calculations have been carried out using a hybrid Hartree–Fock/density functional approach (PBE0). Solvent effects have been included through a polarizable continuum model (C-PCM), while surface effects have been mimicked by a supramolecular (phthalocyanine + carbon cluster) approach. The influences of chemical environment and of the medium on reactivity were analyzed using two different reactivity descriptors, the donor–acceptor intermolecular hardness and the electrophilicity index. Our results show that solvent and surface have a cooperative effect, both increasing the reactivity of the adsorbed complex.

Overoxidized Polypyrrole/Cobalt Tetrasulfonated Phthalocyanine Modified Ultramicro‐Carbon‐Fiber Electrodes for the Electrooxidation of 2‐Mercaptoethanol

We report on the catalytic electrooxidation of 2-mercaptoethanol on ultramicro-carbon-fiber electrode (UMCF) modified with overoxidized polypyrrole-doped cobalt-tetrasulfonated phthalocyanine (CoTSPc) film. The easily prepared electrodes are stable and do not passivate after repetitive use. The sensitivity of the modified UMCF electrode towards the amperometric detection of 2-mercaptoethanol was tested with differential pulse voltammetry (DPV) and differential normal pulse amperometry (DNPA). A calculated detection limit as low as 8610 ˇ5 M was obtained by DPV. Our results show that UMCF electrodes are promising for the detection of low concentrations of thiols as mass transport limitations are minimized. The detection of thiol-derivated substances is an important field of research as they can be present as contaminants in fuels (1) and biological fluids (2) and they may be useful as markers of food deterioration (3, 4). During the last decade, several authors (5-17) have reported the catalytic electrooxidation of various thiols on electrodes modified with metallophthalocyanines. In general, electrodes of this type can be used as sensors (15-25) and various configurations have been developed such as carbon paste (15-17) and screen-printed carbon electrodes (19-25) containing cobalt phthalocyanines and derivatives. The advantage of the reported cobalt phthalocyanine-based electrodes is that the thiols (namely 2-mercaptoethanol, L-cysteine, reduced gluthathione etc.) can be monitored at considerable lower potentials compared with the nonmodified electrodes. Superior selectivity and sensitivity were also achieved. We and others have reported that much advantage can be obtained from the activity of cobalt phthalocyanines if they are electropolymerized forming conductive films that coat an electrode surface (14, 18), or if they are dispersed within a conductive polymeric matrix (12, 13). In addition, such an approach should allow the conception of various shapes and geometrical designs of electrode surfaces and a better control of their modification. In this work, we combine for the first time the use of electrochemically formed polypyrrole-doped cobalt tetra- sulfonated phthalocyanine (CoTSPc) with ultramicro-carbon-fiber electrode configuration (UMCF) to achieve the electrocatalytic oxidation of 2-mercaptoethanol (2-ME) in alkaline aqueous solu- tion and provide a miniaturized electrochemical sensor that is easily fabricated from low cost materials, providing an ultramicroprobe that may be developed for applications in biological systems. We have selected 2-ME as the examined analyte target since its elec- potential scan between ˇ0.2 and 0.7 V, at room temperature, starting at the lower potential limit. The incorporation of CoTSPc within the polypyrrole matrix (PPy) is based on the ion exchange properties of the oxidized polymer (26): the multianionic tetra- sulfonated cobalt phthalocyanine molecules are introduced into polypyrrole film as counterions (or ''doping'' ions) during the electrochemical growth of the polymer matrix. Note that in this operation, only CoTSPc was used as supporting electrolyte. The obtained film is denoted as PPy=CoTSPc. In order to avoid having a large electrical charge in the potentiodynamic response of the polypyrrole-based electrodes which creates a large background current that hinder the characterization of the electrocatalytic effects of the complex, the polymer was overoxidized by succes- sive potential scans betweenˇ0.2 and 0.4 V in 0.1 M NaOH (in the absence of pyrrole monomers) until the total suppression of its electroactivity. The obtained modified UMCF electrode is then denoted as OPPy=CoTSPc. In general, these electrodes are much more stable than those obtained by simple adsorption of phtha- locyanine monolayers on carbon or graphite surfaces since the

Electrocatalytic Response of Poly(2-Chloroaniline)/Cobalt Phthalocyanine Modified Electrodes

The electrochemical response of poly(2-chloroaniline) (PANiCl) synthesized by chemical oxidation at low temperature is described. The polymer obtained is soluble in methyl-pyrrolidone and it is possible to cast films which are good substrates for supporting metal complex catalysts such as cobalt phthalocyanine (CoPc) and are very stable to potentials upto 0.8 V vs. SCE. Films of PANiCl containing 1% of CoPc exhibit catalytic activity for the electrochemical oxidation of 2-mercaptoethanol, glutathione and hydra-zine in acid medium. Evaluation of the electrocatalytical response of PANiCl/CoPc films suggests that the diffusion rate of electroactive species into the film is improved when the polymer reaches the oxidized state.

Structure and mercaptan oxidation activity of cobalt(II) phthalocyanines covalently bonded to silica of low surface area

Cobalt(II) 2,9,16,23-tetracarboxyphthalocyanine and cobalt(II) 2,9,16,23-tetraamino-phthalocyanine were covalently bonded to two different species of modified silica with low surface area. The immobilized phthalocyanines exhibit high catalytic activity in the oxidation of 2-mercaptoethanol, being comparable to that of the dissolved low molecular weight tetracarboxy- or tetrasulfo-phthalocyanine cobalt complexes. The diffuse reflectance spectra of the complexes bonded to nonporous silica exhibit a vibrational fine structure which clearly appears in the Soret band region, indicating a coupling between the electronic 1A 1g → 1E u transition and a vibrational transition of the aromatic ring system around 1600 cm −1.

Functional metallomacrocycles and their polymers. 25. Kinetics and mechanism of the biomimetic oxidation of thiol by oxygen catalyzed by homogeneous polycarboxyphthalocyaninato metals

The oxidation of 2-mercaptoethanol (RSH) catalyzed by (polycarboxyphthalocyaninato) metal acid (M-papc, M=Fe(III), Co(II), Ni(II), Cu(II), pa=−(COOH) 2 , −(COOH) 4 , −(COOH) 8 ) in the presence of molecular oxygen has been studied in aqueous homogeneous solution at pH 7.0 and at 25 o C. The catalytic effects of M-papc have been determined the oxygen consumption in the reaction mixture with a Warburg respirometer. The central metal ions and the number of carboxylate ions on M-papc affected the catalytic activities for the aerobic oxidation of RSH. (Octacarboxyphthalocyaninato) iron (III) and -cobalt (II) are remarkably effective catalysts. (Dicarboxyphthalocyaninato) metals and Ni(II) ― as well as Cu(II) ― phthalocyanine derivatives are less effective catalysts. The kinetics of the aerobic oxidation catalyzed by (octacarboxyphthalocyaninato) iron (III) and -cobalt (II) have been characterized in terms of a bisubstrate Michaelis-Menten rate law (k 5 =600-800 min −1 , at pH 7.0, 25 o C

The promoting role of polycations in the cobalt(ii) phthalocyanine tetrasodium sulfonate catalysed oxidation of thiols

The oxidation of 2-mercaptoethanol with polymer-bound cobalt(II) phthalocyanine catalysts has been investigated. Poly(vinyl amine) (PVAm), poly(ethylenimine) (PEI), poly (L-ly sine) (PLL) and 2,4-, 2,6- and 2,10-ionene hydroxide have been studied as polymeric ligands. All these ligands appear to enhance the reaction rate considerably in comparison with their monomeric analogues and all exhibit a similar behaviour towards the effect of salt and pH. The reaction rate appears to increase virtually linearly with the linear charge density on the ionenes, which is consistent with recent findings for copolymers of vinyl amine and vinyl alcohol. Three main parameters seem to provide the enhanced polycationic catalytic effect: a high linear charge density on the polymer, a large amount of base groups in the polymer domain and a low ionic strength for the reaction solution. Furthermore, a comparison of the linear charge density, catalytic activity and activation parameters for the ionene catalysts with those obtained earlier for the vinyl amine-vinyl alcohol copolymers shows that the presence of hydrophilic side-groups has a promoting effect on the oxidation of the hydrophilic thiol. From catalyst re-use experiments, it appears that the polyamine catalysts (PVAm, PEI and PLL) have a poor stability, but that the ionene hydroxides can be re-used many times, probably as a result of the chemical inertness of the quaternary ammonium groups in the ionenes.

Oxidation of 2-mercaptoethanol in the presence of tris buffer

2-Mercaptoethanol is oxidized by molecular oxygen, especially at high pH. This reaction is markedly increased by primary amines such as asparagine, glutamine and their corresponding amino acids and by the buffer tris(hydroxymethyl)aminomethane. Thus, the use of 2-mercaptoethanol in Tris buffer may present several complications: an uptake of oxygen which could be confused with metabolic activity; destruction of the protective mercaptoethanol; and by inference, quite possibly an enhanced oxidation of the protein sulphydryls in need of protection.

Autoxidation of thiols with cobalt (II) phthalocyanine-tetra-sodium sulfonate, attached to poly(vinylamine)

The oxidation of 2-mercaptoethanol with molecular oxygen in water with cobalt(II)phthalocyanine-tetra-sodium sulfonate attached to poly(vinylamine) has been investigated.

Role and mechanism of peripheral fatty acid mobilization in 2-mercaptoethanol-induced fatty liver.

2-Mercaptoethanol-induced fatty liver involves an increased free fatty acid mobilization which is primarily due to an inhibition of free fatty acid reesterification in adipose tissue. Furthermore, increased free fatty acid mobilization as well as fatty liver induction are not induced by 2-mercaptoethanol per se but result most probably from 2-mercaptoacetate through oxidation of 2-mercaptoethanol.