Oxidation Of L-cysteine Research Articles

Improving the Electrocatalytic Activity of Iron Phthalocyanines and Porphyrines Towards the Oxidation of l-Cysteine Due to the Incorporation of Multiwall Carbon Nanotubes and Modulation of the Fe(II)/(I) Formal Potential

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Synthesis of l-cystine nanotubes by alkalinization of l-cysteine in the presence of gallium nitride

The alkaline oxidation of l-cysteine (l-Cys) was conducted in aqueous media forming the insoluble l-cystine dimer as confirmed by X-ray diffraction. In another experiment, a gallium nitride film was added to the l-Cys solution and the l-cystine crystals presented a preferential growth. The transmission electron microscopy images showed the formation of single- and multi-wall l-cystine nanotubes. The infrared and high resolution electron microscopy data suggested that the growth of the tubes resulted from the successive staking of l-cystine dimers onto the (001) family of planes, which was a consequence of the ionic assembly between l-cystine over a layer of l-Cys molecules previously grafted to the gallium nitride particles.

Optimizing the reactivity of surface confined cobalt N4-macrocyclics for the electrocatalytic oxidation of l-cysteine by tuning the Co(II)/(I) formal potential of the catalyst

The redox potential of macrocyclic complexes is a very predictive reactivity index for the electrocatalytic activity of these molecules and it can be easily measured under the same conditions of the kinetic experiments. It reflects directly the catalytic activity of a given complex. We have investigated the effect of the Co(II)/(I) formal potential of CoN4 macrocyclics complexes on the catalytic activity of a series of Co porphyrins and Co phthalocyanines for the electrooxidation of l-cysteine. The complexes were adsorbed on ordinary pyrolytic graphite. A correlation of log i (at constant potential) versus the Co(II)/(I) formal potential of the catalysts gives a volcano curve. Our results clearly show that the Co(II)/(I) formal potential of N4-macrocyclic complexes needs to be adjusted to values around −0.96V vs. SCE to obtain the highest catalytic activity for the oxidation of l-cysteine at pH 13.

SENSITIVE L-CYSTEINE AMPEROMETRIC SENSOR BASED ON A GLASSY CARBON ELECTRODE MODIFIED BY MnO2 NANOPARTICLES

A sensitive amperometric sensor for the determination of L-cysteine was fabricated by electrodeposition of modified MnO2 nanoparticles on a glassy carbon electrode. The morphology of the nanoparticles was characterized by scanning electron microscopy. Cyclic voltammetry was applied to investigate the mechanism of film formation and the electrochemical properties of the MnO2 nanoparticle-modified electrode. The results of electrochemical experiments showed that the modified electrode had a favorable catalytic ability for the electrochemical oxidation of L-cysteine. Under optimized conditions, the MnO2 nanoparticle-modified electrode exhibited a linear dependence on the concentration of L-cysteine from 1.0 × 10−6 to 6.4 × 10−4 M, and a detection limit of 8.0 × 10−7 M (signal/noise = 3). The modified electrode was highly resistant towards typical inorganic salts and some biomolecules. In addition, the sensor was applied for the determination of L-cysteine in human serum with high accuracy, demonstrating its potential for practical applications.

A very low potential electrochemical detection of l-cysteine based on a glassy carbon electrode modified with multi-walled carbon nanotubes/gold nanorods

A nanohybrid platform built with multi-walled carbon nanotubes and gold nanorods, prepared via a cationic surfactant-containing seed-mediated sequential growth process, in aqueous solution, on a glassy carbon substrate has been successfully developed to be used in the electrocatalytic oxidation of l-cysteine (Cys). The nanohybrid was characterized by transmission electron microscopy, Raman spectroscopy and electrochemical measurements. Cyclic voltammetry results had shown that the modified electrode allows the oxidation of Cys at a very low anodic potential (0.00V vs. Ag/AgCl). The kinetic constant kcat for the catalytic oxidation of Cys was evaluated by chronoamperometry and provided a value of 5.6×104Lmol−1s−1. The sensor presents a linear response range from 5.0 up to 200.0µmolL−1, detection limit of 8.25nmolL−1 and a sensitivity of 120nALµmol−1.

Novel cysteic acid/reduced graphene oxide composite film modified electrode for the selective detection of trace silver ions in natural waters

Novel cysteic acid/reduced graphene oxide composite film on a glassy carbon electrode has been prepared through the electrochemical oxidation of L-cysteine for silver sensing. Differential pulse anodic stripping voltammetry (DPASV) was employed for the detection of trace Ag(I) in aqueous solutions with the composite film modified electrode, which is referred to as an efficient method for the detection of trace heavy metals. We found the linear relationship between the peak current of the stripping voltammetry of Ag(I) and the concentration of Ag(I) in the range of 1.0 × 10−8 ∼ 2.0 × 10−4 M with a correlation coefficient R2 = 0.996, and the detection limit can be down to 1.0 × 10−9 M (S/N = 3). The as-developed cysteic acid/reduced graphene oxide composite film modified electrode demonstrated ultrahigh sensitivity, reproducibility and recovery for the selective detection of trace Ag(I) without any interference from other metal ions.

Kinetic studies on oxidation of l-cysteine and 2-mercaptoethanol by a trinuclear Mn(IV) species in aqueous acidic media

In aqueous media, the trinuclear MnIV complex, [MnIV3(μ-O)4(phen)4(H2O)2]4+ (phen=1,10-phenanthroline) (1) behaves like a monobasic acid, equilibrates with its deprotonated conjugate base (2) (1⇌2+H+, pKa=4.00 (± 0.15) at 25.0°C, I=1.0M, maintained with NaNO3). An aqueous solution of 1 in the pH range 2.2–4.0 smoothly oxidizes 2-mercaptoethanol (mercap) and l-cysteine (cys) to their respective disulfides; itself being reduced to [Mn(phen)3]2+ in presence of excess 1,10-phenanthroline which also masks Cu2+, if any, present in the reaction media as impurity as well as acting as a buffer that controls pH range during the reaction. The observed rate constants in H2O media were found to be considerably lowered in media enriched with D2O and a proton-coupled single electron transfer rate step is proposed. Interestingly, we found that deprotonated oxidant (2) reacts faster than the protonated species (1) in oxidizing both the thiols.

A novel electrochemical sensor based on metal-organic framework for electro-catalytic oxidation of L-cysteine

A novel electrochemical sensor based on Au-SH-SiO2 nanoparticles supported on metal-organic framework (Au-SH-SiO2@Cu-MOF) has been developed for electrocatalytic oxidation and determination of L-cysteine. The Au-SH-SiO2@Cu-MOF was characterized by scanning electron microscopy, transmission electron microscopy, x-ray diffraction and cyclic voltammetry. The electrochemical behavior of L-cysteine at the Au-SH-SiO2@Cu-MOF was investigated by cyclic voltammetry. The Au-SH-SiO2@Cu-MOF showed a very efficient electrocatalytic activity for the oxidation of L-cysteine in 0.1M phosphate buffer solution (pH 5.0). The oxidation overpotentials of L-cysteine decreased significantly and their oxidation peak currents increased dramatically at Au-SH-SiO2@Cu-MOF. The potential utility of the sensor was demonstrated by applying it to the analytical determination of L-cysteine concentration. The results showed that the electrocatalytic current increased linearly with the L-cysteine concentration in the range of 0.02–300μM and the detection limit was 0.008μM. Finally, the sensor was applied to determine L-cysteine in water and biological samples.

Simultaneous determination of ofloxacin and gatifloxacin on cysteic acid modified electrode in the presence of sodium dodecyl benzene sulfonate

A novel cysteic acid modified carbon paste electrode (cysteic acid/CPE) based on electrochemical oxidation of l-cysteine was developed to simultaneously determine ofloxacin and gatifloxacin in the presence of sodium dodecyl benzene sulfonate (SDBS). Fourier transform infrared spectra (FTIR) indicated that l-cysteine was oxidated to cysteic acid. Electrochemical impedance spectroscopy (EIS) and cyclic voltammograms (CV) indicated that cysteic acid was successfully modified on electrode. The large peak separation (116mV) between ofloxacin and gatifloxacin was obtained on cysteic acid/CPE while only one oxidation peak was found on bare electrode. And the peak currents increased 5 times compared to bare electrode. Moreover, the current could be further enhanced in the presence of an anionic surfactant, sodium dodecyl benzene sulfonate. The differential pulse voltammograms (DPV) exhibited that the oxidation peak currents were linearly proportional to their concentrations in the range of 0.06–10μM for ofloxacin and 0.02–200μM for gatifloxacin, and the detection limits of ofloxacin and gatifloxacin were 0.02μM and 0.01μM (S/N=3), respectively. This proposed method was successfully applied to determine ofloxacin and gatifloxacin in pharmaceutical formulations and human serum samples.

Kinetics and mechanism of oxidation of L-cysteine by pyridinium bromochromate in perchloric acid medium

Kinetics and mechanism of oxidation of L-cysteine by pyridinium bromochromate in perchloric acid medium

Addition of an external electron donor to in vitro assays of cysteine dioxygenase precludes the need for exogenous iron

Cysteine dioxygenase (CDO) utilizes a 3-His facial triad for coordination of its metal center. Recombinant CDO present in cellular lysate exists primarily in the ferrous form and exhibits significant catalytic activity. Removal of CDO from the reducing cellular environment during purification results in the loss of bound iron and oxidation of greater than 99% of the remaining metal centers. The as-isolated recombinant enzyme has comparable activity as the background level of l-cysteine oxidation confirming that CDO is inactive under the aerobic conditions required for catalysis. Including exogenous ferrous iron in assays resulted in non-enzymatic product formation; however, addition of an external reductant in assays of the purified protein resulted in the recovery of CDO activity. EPR spectroscopy of CDO in the presence of a reductant confirms that the recovered activity is consistent with reduction of iron to the ferrous form. The as-isolated enzyme in the presence of l-cysteine was nearly unreactive with the dioxygen analog, but had increased affinity when pre-incubated with an external reductant. These studies shed light on the discrepancies among reported kinetic parameters for CDO and also juxtapose the stability of the 3-His and 2-His/1-carboxylate ferrous enzymes in the presence of dioxygen.

DNA/nickel oxide nanoparticles/osmium(III)-complex modified electrode toward selective oxidation of l-cysteine and simultaneous detection of l-cysteine and homocysteine

The modification of glassy carbon (GC) electrode with electrodeposited nickel oxide nanoparticles (NiOxNPs) and deoxyribonucleic acid (DNA) is utilized as a new efficient platform for entrapment of osmium (III) complex. Surface morphology and electrochemical properties of the prepared nanocomposite modified electrode (GC/DNA/NiOxNPs/Os(III)-complex) were investigated by FESEM, cyclic voltammetry and electrochemical impedance spectroscopy techniques. Cyclic voltammetric results indicated the excellent electrocatalytic activity of the resulting electrode toward oxidation of l-cysteine (CySH) at reduced overpotential (0.1V vs. Ag/AgCl). Using chronoamperometry to CySH detection, the sensitivity and detection limit of the biosensor are obtained as 44μAmM−1 and 0.07μM with a concentration range up to 1000μM. The electrocatalytic activity of the modified electrode not only for oxidation of low molecular-mass biothiols derivatives such as, glutathione, l-cystine, l-methionine and electroactive biological species ( dopamine, uric acid, glucose) is negligible but also for very similar biothiol compound (homocysteine) no recognizable response is observed at the applied potential window. Furthermore, the simultaneous voltammetric determination of l-cysteine and homocysteine compounds without any separation or pretreatment process was reported for the first time in this work. Finally, the applicability of sensor for the analysis of CySH concentration in complex serum samples was successfully demonstrated. Highly selectivity, excellent electrocatalytic activity and stability, remarkable antifouling property toward thiols and their oxidation products, as well as the ability for simultaneous detection of l-cysteine and homocysteine are remarkably advantageous of the proposed DNA based biosensor.

Perovskite nanoparticles LaNi0.5Ti0.5O3 modified carbon paste electrode as a sensor for electrooxidation and detection of amino acids

A sensitive electrochemical sensor for amino acids was built based on perovskite LaNi0.5Ti0.5O3 (LNT) modified carbon paste electrode. The modified electrode was characterized by electrochemical impedance spectroscopy and cyclic voltammetry. The electrocatalysis of LNT to the oxidation of l-cysteine (l-cys) was studied by cyclic voltammetry in NaOH solution, and the experimental conditions were investigated in detail, such as NaOH concentration and the applied potential. Under the optimal conditions, the reported sensor was applied to the detection of l-cys, l-tryptophane (l-trp), l-alanine (l-ala) and l-phenylalanine (l-phe). In addition, the reported amino acids sensor exhibited good reproducibility, long-term stability, and fast current response.

Cathodic Synthesis of Birnessite-Type Layered Manganese Oxides for Electrocapacitive Catalysis

Cathodic reduction of aqueous MnO4− ions in the presence of various alkaline metals except for Na+ ions led to the deposition of birnessite-type layered MnO2. The highest crystallinity was obtained when electrolyzed in a 2 mM KMnO4 and 50 mM KCl at a constant potential of 0 V vs Ag/AgCl. The cathodic formation of MnO2 was prevented by the presence of divalent cations, and Na+ ions gave rise to an amorphous or low crystalline product. The birnessite film thus formed exhibited an excellent pseudocapacitive behavior in the as-deposited state, with a specific capacitance as high as 322 F g−1 at a scan rate of 2 mV s−1, which is much larger than that (75 F g−1) of the birnessite film grown anodically. The resulting pseudocapacitive electrode functioned as an efficient catalyst toward the oxidation of L-cysteine, where the anodic overpotential was reduced by 0.15 to 0.3 V.

Single Turnover of Substrate-Bound Ferric Cysteine Dioxygenase with Superoxide Anion: Enzymatic Reactivation, Product Formation, and a Transient Intermediate

Cysteine dioxygenase (CDO) is a non-heme mononuclear iron enzyme that catalyzes the O(2)-dependent oxidation of L-cysteine (Cys) to produce cysteine sulfinic acid (CSA). In this study we demonstrate that the catalytic cycle of CDO can be "primed" by one electron through chemical oxidation to produce CDO with ferric iron in the active site (Fe(III)-CDO, termed 2). While catalytically inactive, the substrate-bound form of Fe(III)-CDO (2a) is more amenable to interrogation by UV-vis and EPR spectroscopy than the 'as-isolated' Fe(II)-CDO enzyme (1). Chemical-rescue experiments were performed in which superoxide (O(2)(•-)) anions were introduced to 2a to explore the possibility that a Fe(III)-superoxide species represents the first intermediate within the catalytic pathway of CDO. In principle, O(2)(•-) can serve as a suitable acceptor for the remaining 3-electrons necessary for CSA formation and regeneration of the active Fe(II)-CDO enzyme (1). Indeed, addition of O(2)(•-) to 2a resulted in the rapid formation of a transient species (termed 3a) observable at 565 nm by UV-vis spectroscopy. The subsequent decay of 3a is kinetically matched to CSA formation. Moreover, a signal attributed to 3a was also identified using parallel mode X-band EPR spectroscopy (g ~ 11). Spectroscopic simulations, observed temperature dependence, and the microwave power saturation behavior of 3a are consistent with a ground state S = 3 from a ferromagnetically coupled (J ~ -8 cm(-1)) high-spin ferric iron (S(A) = 5/2) with a bound radical (S(B) = 1/2), presumably O(2)(•-). Following treatment with O(2)(•-), the specific activity of recovered CDO increased to ~60% relative to untreated enzyme.

Kinetics and mechanism of oxidation of L-cysteine and DL-methionine by morpholinium chlorochromate in aqueous acidic medium

Kinetics and mechanism of oxidation of L-cysteine and DL-methionine by morpholinium chlorochromate in aqueous acidic medium

Electrochemical biosensor based on graphene oxide–Au nanoclusters composites for l-cysteine analysis

In this paper, a linker-free connected graphene oxide/Au nanocluster (GO–Au NCs) composite was prepared under sonication through electrostatic interactions, and characterized by transmission electron microscope (TEM), atomic force microscope (AFM), ultraviolet–visible (UV–vis) and FT-IR spectrum. The morphological and structural characterizations evidence that the Au NCs can be efficiently decorated on the GO. The electrochemical investigations indicated that GO–Au NCs composite has an important role in the electrocatalytic activity towards the oxidation of l-cysteine (CySH). The GO–Au NCs composite modified electrode shows a large determination range from 0.05 to 20.0μmol/L, a remarkably low detection limit is 0.02μmol/L and low oxidation potential (+0.387). It was found that metal ions, carbohydrates, nucleotide acids and amino acids had no distinct effect on the determination of l-cysteine. In addition, the sensor has some important advantages such as simple preparation, fast response, good stability and high reproducibility. The direct determination of free reduced and total CySH in human urine samples has been successfully carried out without the assistance of any separation techniques.

Preparation and Electrochemical Behaviour of Silver Pentacyanonitrosylferrate Film Modified Glassy Carbon Electrode and Its Electrocatalytic Oxidation to L‐cysteine

AbstractA glassy carbon (GC) electrode modified with silver pentacyanonitrosylferrate (AgPCNF) film as a redox mediator was fabricated. Cyclic voltammetry was used to study the redox property of AgPCNF modified electrode. The modified electrode showed a well‐defined redox couple due to [AgIFeIII/II(CN)5NO]1‐/2‐system. The effects of scan rates, supporting electrolytes and solution pHs were studied on the electrochemical behavior of the modified electrode. The feasibility of using the AgPCNF modified electrode to measure L‐cysteine was investigated. It showed an excellent electrocatalytic activity towards the oxidation of L‐cysteine and the anodic currents were proportional to the L‐cysteine concentration in the range of 0.1 μM to 20 μM, the linear regression equation is Ipa(μA) = ‐68.58 ‐ 5.78CL‐cysteine (μM), with a correlation coefficient 0.998 for N = 23. The detection limit was down to 3.5 × 10‐8 M (three times the ratio of signal to noise).

A voltammetric sensor for the simultaneous determination of L-cysteine and tryptophan using a p-aminophenol-multiwall carbon nanotube paste electrode.

Two amino acids, L-cysteine and tryptophan, could be simultaneously determined in an aqueous solution (pH 6.0) using a carbon nanotube paste electrode (CNPE) modified with p-aminophenol as a mediator. The results indicate that the electrode is efficient in terms of its electrocatalytic activity for the oxidation of L-cysteine, leading to an overpotential reduced by more than 550 mV. Using differential pulse voltammetry, we could measure L-cysteine and tryptophan in one mixture independently from each other by a potential difference of about 600 mV. Electrochemical techniques are used to determine the diffusion coefficients, kinetic parameters such as electron transfer coefficient, and the rates of electro-oxidation of L-cysteine at the surface of the p-aminophenol-modified CNPE. The peak current is found to depend linearly on L-cysteine and tryptophan concentrations within the ranges of 0.5 - 100 µmol L(-1) L-cysteine and 10.0 - 300 µmol L(-1) tryptophan. The detection limits for L-cysteine and tryptophan are found to be 0.3 and 5.7 µmol L(-1), respectively. The proposed method is also used for the determination of L-cysteine and tryptophan in urine, river water, blood plasma, and serum samples using standard addition methods.

Oxidation and detection of L-cysteine using a modified Au/Nafion/glass carbon electrode

In this work, the electrochemical oxidation of L-cysteine (CySH) was investigated on a composite film modified electrode with Au nanoparticles dispersed in the fluorocarbon polymer (Nafion). The excellent electrocatalytic effect on CySH oxidation was attributed to the role of Au nanoparticles. The voltammetric studies revealed two anodic peaks for the oxidation of CySH in the pH range of 2.0–8.0. The electrode was used to detect cysteine at pH 2.0 and pH 7.0. At pH 2.0, a determination range of 3.0–50.0 μmol/L was obtained with the detection sensitivity of 22.7 μA/(mmol L−1), while at pH 7.0, a determination range of 2.0–80.0 μmol/L was obtained with the detection sensitivity of 4.08 μA/(mmol L−1). The detection limits were estimated to be as low as 1.0 μmol/L at both pH 7.0 and pH 2.0. Additionally, at pH 7.0, the interferences of ascorbic acid and uric acid were reduced for the detection of cysteine. These made the Au/Nafion/GC electrode a promising candidate for efficient electrochemical sensors for the detection of CySH.