Catechol Concentration Research Articles

Sequential Electrochemical and Chemical Multi-Polymerization of Catechol for Abatement of Environmental Pollutants

Catechol is a substance that is commonly found in wastewaters from a variety of sectors including paper, paint, petroleum, dyes, antioxidants, pesticides, iron and steel, solvents, nylon, detergent, textile, plastic, rubber, cosmetics, and medicine. In this study, sequential electrochemical and chemical multi-polymerization of catechol was investigated for environmental pollution abatement. The effect of operating parameters like catechol concentration (2–10 g/L), ammonium persulphate (APS) concentration (2–10 g/L) and reaction temperature (20–60 °C) were evaluated using response surface methodology. Catechol concentration was determined using HPLC in a gradient mobile phase. The electrochemical behavior of the polymer was investigated by cyclic voltammetry (CV). The structural and morphological properties of polycatechol were characterized by Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy with energy dispersive X-ray (SEM–EDX) analysis. It was observed from the SEM images a polymeric structure developed from a crystalline and heterogeneous structure when the APS concentration increased. Similarly, it was seen in SEM images that the polymers transitioned from a bulk and heterogeneous structure to a homogeneous structure as the temperature increased, and back to a heterogeneous structure as the catechol concentration increased. It was also found that catechol removal increased and reaction selectivity decreased by increasing the reaction temperature. The optimum operating conditions were found as 4 g/L catechol concentration, 9.5 g/L APS concentration, 30 °C reaction temperature with 100 cycles at 50 mV/s of electrochemical polymerization and 72 h of chemical polymerization. The results of this study show the potential of challenging new routes not only facile polymerization of organic monomers but also to decrease the undesirable pollutant concentration in the wastewater.

Cerebrospinal fluid concentration gradients of catechols in synucleinopathies.

The synucleinopathies Parkinson disease (PD), multiple system atrophy (MSA), and the Lewy body form of pure autonomic failure (PAF) entail intra-cytoplasmic deposition of the protein alpha-synuclein and pathogenic catecholaminergic neurodegeneration. Cerebrospinal fluid (CSF) levels of catecholamines and their metabolites are thought to provide a "neurochemical window" on central catecholaminergic innervation and can identify specific intra-neuronal dysfunctions in synucleinopathies. We asked whether there are CSF concentration gradients for catechols such as 3,4-dihydroxyphenylacetic acid (DOPAC), the main neuronal metabolite of dopamine, and if so whether the gradients influence neurochemical differences among synucleinopathies. In a retrospective cohort study, we reviewed data about concentrations of catechols in the first, sixth, and twelfth 1-mL aliquots from 33 PD, 28 MSA, and 15 PAF patients and 41 controls. There were concentration gradients for DOPAC, dopamine, norepinephrine, and 3,4-dihydroxyphenylglycol (the main neuronal metabolite of norepinephrine) and gradients in the opposite direction for 5-S-cysteinyldopa and 5-S-cysteinyldopamine. In all 3 aliquots, CSF DOPAC was low in PD and MSA compared with controls (p < 0.0001 each) and normal in PAF. Synucleinopathies differ in CSF catechols regardless of concentration gradients. Concentration gradients for 5-S-cysteinyl derivatives in opposite directions from the parent catechols may provide biomarkers of spontaneous oxidation in the CSF space.

Preparation of surface molecular imprinting fluorescent sensor based on magnetic porous silica for sensitive and selective determination of catechol.

A magnetic fluorescent molecularly imprinted sensor was successfully prepared and implemented to determine catechol (CT). Fe3O4 nanoparticles were synthesized by the solvothermal technique and mesoporous Fe3O4@SiO2@mSiO2 imprinted carriers were prepared by coating nonporous and mesoporous SiO2 shells on the surface of the Fe3O4 subsequently. The magnetic surface molecularly imprinted fluorescent sensor was created after the magnetic mesoporous carriers were modified with γ-methacryloxyl propyl trimethoxy silane to introduce double bonds on thesurface of the carries and the polymerization was carried out in the presence of CT and fluorescent monomers. The magnetic mesoporous carriers were modified with γ-methacryloxyl propyl trimethoxy silane and double bonds were introduced on the surface of the carriers. After CT binding with the molecularly imprinted polymers (MIPs), the fluorescent intensity of the molecularly imprinted polymers (Ex = 400nm, Em = 523nm) increased significantly. The fluorescent intensity ratio (F/F0) of the sensor demonstrated a favorable linear correlation with the concentration of CT between 5 and 50μM with a detection limit of 0.025μM. Furthermore, the sensor was successfully applied to determine CT in actual samples with recoveries of 96.4-105% and relative standard deviations were lower than 3.5%. The results indicated that the research of our present work provided an efficient approach for swiftly and accurately determining organic pollutant in water.

Can the concentration of environmentally persistent free radicals describe its toxicity to Caenorhabditis elegans? Evidence provided by neurotoxicity and oxidative stress

Environmentally persistent free radicals (EPFRs) are emerging pollutants stabilized on or inside particles. Although the toxicity of EPFR-containing particles has been confirmed, the conclusions are always ambiguous because of the presence of various compositions. A clear dose–response relationship was always challenged by the fact that the concentrations of these coexisted components simultaneously changed with EPFR concentrations. Without these solid dose–response pieces of evidence, we could not confidently conclude the toxicity of EPFRs and the description of potential EPFR risks. In this study, we established a particle system with a fixed catechol concentration but different reaction times to obtain particles with different EPFR concentrations. Caenorhabditis elegans (C. elegans) in response to different EPFR concentrations was systematically investigated at multiple biological levels, including behavior observations and biochemical and transcriptome analyses. Our results showed that exposure to EPFRs disrupted the development and locomotion of C. elegans. EPFRs cause concentration-dependent neurotoxicity and oxidative damage to C. elegans, which could be attributed to reactive oxygen species (ROS) promoted by EPFRs. Furthermore, the expression of key genes related to neurons was downregulated, whereas antioxidative genes were upregulated. Overall, our results confirmed the toxicity from EPFRs and EPFR concentration as a rational parameter to describe the extent of toxicity.

A Facile One-Pot Synthetic Approach Towards CB@PCN-222(Fe) Composites for Simultaneous Electrochemical Detection of Dihydroxybenzene Isomers

A novel porphyrin-metal organic frameworks (MOFs) based hybrid composite was created by combining conductive carbon black (CB) and PCN-222(Fe) (PCN = porous coordination network) via a one-pot strategy. The proposed material unquestionably takes advantage of the high specific area from MOFs and the strong conductivity of CB, which contributes to the contact with analytes and detection sensitivity. A series of analyses showed that the proposed modified electrode could be an alternative candidate for electrochemical detection of dihydroxybenzene isomers. A good linear correlation occurred between the differential pulse voltammetry current and the concentration of hydroquinone (HQ), catechol (CC) and resorcinol (RC) under the optimized conditions. With low detection limits (0.122, 0.094 and 0.243 μM) at the ranges (0.5–280, 0.5–280 and 0.5–320 μM) of these isomers mentioned above, the sensor exhibited good cost-effectiveness, repeatability and stability. Our methodology drives us to directly analyze the dihydroxybenzene isomers in actual samples with dependable recovery, further broadening the electrochemical detection field for environmental pollutants based on porphyrin MOFs.

Investigating the gas-phase reaction mechanism of catechol with ozone: Product analysis and insights

Volatile aromatic compounds (VOCs) are ubiquitous in the environment, they can be emitted from biogenic and anthropogenic sources. They can contribute to the formation of many products leading to the formation of secondary organic aerosols (SOA). The products of the gas phase reaction of 1,2-benzenediol (catechol) with ozone were studied in a simulation chamber at atmospheric pressure and 294 ± 2 K in presence of different levels of relative humidity (0–60%). The gas phase products were monitored continuously by a PTR-ToF-MS for 2 h, whereas filters samples were collected directly from the reaction chamber and analyzed by thermo-desorption gas chromatography; TD-GC-MS. This study shows the different potential chemical pathways that catechol could follow to form a variety of products under dry, low and high humidity conditions. The molecular mass 98 was found to be distinctive and appears in the gas phase when humidity in the reaction chamber is between 20 and 60%. Other new masses (m/z) such as 176, 154, 116, 68, 72, 80, 96, 108, and 124 were also detected under different experimental conditions. Furthermore, the catechol concentration has been monitored continuously by a PTR-ToF-MS from low to high humidity conditions (RH = 7.5−78.8%). The purpose of the latter is to suggest that the formation of catechol-H2O clusters occurs in the gas phase of the reaction chamber causing a decrease in catechol reactivity towards ozone and other gases and subsequently a decrease in the rate constant.

Synthesis of small-sized gold nanorod using catechol as a reducing agent

Facile preparation of small gold nanorod with controllable and large surface plasmon resonance band is of great value for applications in especially the biomedical and sensing fields. In this work, we propose that without addition of additive to complicate the experimental system catechol of a very weak reducibility can be used as reducing agent for seed-mediated synthesis of gold nanorod. Under a temperature of 40 °C and a catechol concentration of 17.5 mM, monodisperse gold nanorod with a high shape yield, a largest plasmon wavelength of 918 nm, and especially a small diameter of 9.8 nm can be acquired simultaneously. A good tune over the plasmon wavelength is also shown by varying the amount of silver ion. Besides, the effects of experimental parameters including silver ion, cetyltrimethylammonium bromide, gold seed and catechol have also been carefully studied, and the morphological and structural evolutions of the particle have been discussed based on reported growth mechanism.

The Composite Material of (PEDOT-Polystyrene Sulfonate)/Chitosan-AuNPS-Glutaraldehyde/as the Base to a Sensor with Laccase for the Determination of Polyphenols.

The described research aimed to develop the properties of the conductive composite /poly(3,4-ethylenedioxy-thiophene-poly(4-lithium styrenesulfonic acid)/chitosan-AuNPs-glutaraldehyde/ (/PEDOT-PSSLi/chit-AuNPs-GA/) and to develop an electrochemical enzyme sensor based on this composite material and glassy carbon electrodes (GCEs). The composite was created via electrochemical production of an /EDOT-PSSLi/ layer on a glassy carbon electrode (GCE). This layer was covered with a glutaraldehyde cross-linked chitosan and doped with AuNPs. The influence of AuNPs on the increase in the electrical conductivity of the chitosan layers and on facilitating the oxidation of polyphenols in these layers was demonstrated. The enzymatic sensor was obtained via immobilization of the laccase on the surface of the composite, with glutaraldehyde as the linker. The investigation of the surface morphology of the GCE/PEDOT-PSSLi/chit-AuNPs-GA/Laccase sensor was carried out using SEM and AFM microscopy. Using EDS and Raman spectroscopy, AuNPs were detected in the chitosan layer and in the laccase on the surface of the sensor. Polyphenols were determined using differential pulse voltammetry. The biosensor exhibited catalytic activity toward the oxidation of polyphenols. It has been shown that laccase is regenerated through direct electron transfer between the sensor and the enzyme. The results of the DPV tests showed that the developed sensor can be used for the determination of polyphenols. The peak current was linearly proportional to the concentrations of catechol in the range of 2-90 μM, with a limit of detection (LOD) of 1.7 μM; to those of caffeic acid in the range of 2-90 μM, LOD = 1.9 μM; and to those of gallic acid in the range 2-18 μM, LOD = 1.7 μM. Finally, the research conducted in order to determine gallic acid in a natural sample, for which white wine was used, was described.

Analysis of catechol as an environmental pollutant based on electropolymerised methyl orange modified carbon paste sensor

ABSTRACT The present research work outlines a low-cost and green electrochemical approach for the assay of ecological toxin catechol (CT) based on electro-polymerised methyl orange (MO)-activated carbon paste electrode (CPE) as a responsive, simple and low-priced electrocatalyst. The CT electrochemical response was premeditated on the surface of poly methyl orange-activated carbon paste electrode (Poly(MO)ACPE) using different voltammetric methods such as cyclic voltammetry (CV) and differential pulse voltammetry (DPV) which recommends that the Poly(MO)ACPE shows good electrocatalytic nature for the electrochemical redox reaction of CT with high peak current response as associated to the bare carbon paste electrode (BCPE). The CT molecules expose electrochemical quasi-reversible reactions (oxidation and reduction nature) at Poly(MO)ACPE, which was done by a diffusion-controlled reaction kinetics. The practicability of this sensor was verified using the DPV method; here the CT peak current was improved with the varied concentration of CT in the range from 1.0 µM to 36.0 µM, and the corresponding limit of detection (LOD) and limit of quantification (LOQ) were 0.880 × 10−8 M and 2.935 × 10−8 M, respectively. The prepared sensor was efficiently tested with different interferents using the DPV method. Here, the sensor shows a lesser interference effect for the CT redox reaction nature. Finally, this sensor was applied for the analysis of CT in water and green tea samples, and the outcomes noticed a good CT recoveries.

Selective sensing of catechol based on a fluorescent nanozyme with catechol oxidase activity

Nanozymes, an unusual category of nanomaterials possessing enzymatic properties, and have generated considerable interest regarding their application feasibilities on several important fronts. In the present work, an innovative sensing device for catechol was established ground on a fluorescent nanozyme (Cu-BDC-NH2) that exhibited catechol oxidase activity. The fluorescent nanozyme combines both functions of catechol recognition and response signal output, and can realize the sensing of catechol without the addition of other chromogenic agents. In the existence of Cu-BDC-NH2, catechol can be oxidized efficiently to produce quinones or polymers with strong electron absorption capacity, which immediately results in efficient fluorescence quenching of Cu-BDC-NH2. However, other common phenolic compounds, such as phenol, the other two diphenols (hydroquinone and resorcinol), phloroglucinol, and chlorophenol, do not result in efficient fluorescence quenching of Cu-BDC-NH2. The method shows a nice linear relationship between catechol concentration prep the fluorescence intensity of Cu-BDC-NH2 in the scope of 0–10 μM, with a detection limit of 0.997 μM. The detection of catechol in actual water samples has also achieved the satisfactory consequences, which provides a new strategy for the convenient and selective detection of catechol.

Disposable Pencil Lead as an Electrochemical Transducer for Monitoring Catechol in River and Tap Water

A cheap and disposable pencil graphite electrode (PGE) was developed by the incorporation of amine groups (Am-PGE-1). A further improvement in the performance was observed when the aminated electrode (Am-PGE-1) was activated by applying a negative potential scan (Am-PGE-2). The electrochemical transport properties were evaluated through cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The Nyquist plot showed a reduced charge transfer resistance value of 24.3 Ω for Am-PGE-2, while it was 95.1 Ω for bare PGE. Thus, Am-PGE-2 was used as a sensing platform for the detection of catechol. It was found that the electrochemical response of catechol oxidation at Am-PGE-2 was twice than the current obtained for bare PGE. Additionally, the effect of pH of the supporting electrolyte and reaction kinetic were studied. The heterogeneous electron transfer rate constant was calculated to be 0.01 s−1. Moreover, CV study revealed that the redox reaction of catechol was a quasi-reversible and diffusion-controlled process. The square wave voltammetry (SWV) technique was applied for the quantitative determination of catechol. The peak current showed a linear dependency on the concentration of catechol from 3 to 150 µM. Furthermore, the analyte could be detected as low as 3.86 µM. Likewise, the sensor demonstrates a good selectivity towards the target analyte than the other possible interfering molecules or ions. Aiming to examine practical applicability, real samples, such as river and household tap water, were tested by using the proposed transducer, and the satisfactory recoveries demonstrate the effectiveness of Am-PGE-2 in real life applications.

Al plate supported MXene films modified with Ag nanoparticles: Highly sensitive and disposable SERS substrate for trace catechol in seawater

In this study, MXene films with an ordered layered structure were fabricated on Al plates via electrodeposition. Next, the Ag nanoparticles were modified on the MXene films through in situ reduction. Meanwhile, their surface enhanced Raman scattering effect for trace catechol was directly explored in catechol aqueous solution. It was found that these MXene films possess very strong surface enhanced Raman scattering effect for trace catechol in water. The detection limit is up to 5 × 10−8 mol L−1. In addition, these films possess high selectivity, excellent signal repeatability (relative standard deviation < 5.86%, spot-to-spot), high reproducibility (relative standard deviation < 5.86%, batch-to-batch) and good stability. More interestingly, the aforementioned films possess excellent salt tolerance and are highly sensitive to trace catechol in seawater. The detection limit is up to 1 × 10−7 mol L−1 in seawater. Moreover, there exists a good linear relationship between Raman signal intensity and catechol concentration within a broad concentration range of catechol (1 × 10−5 mol L−1 –1 × 10−7 mol L−1). These results imply that these MXene films possess great potential in timely monitoring of catechol in seawater. And its large-scale preparation and application might be simple and easy.

Effects of the modification of bacterial cellulose as a template for the in situ enzyme-catalyzed polymerization of catechol

In this study, we investigated the effects of the modification of bacterial cellulose used as a template on the in situ polymerization of catechol by laccase. The bacterial cellulose was modified by sulfonation and the entrapment of carboxymethyl cellulose. The catechol polymerization was optimized at a pH of 5.5, catechol concentration of 50 mM, and synthesis time of 24 h. After the in situ polymerization, conductive and colored bacterial cellulose composites were obtained. The bacterial cellulose composites containing oligomers/polymers were analyzed using Fourier-transform infrared spectroscopy, scanning electron microscopy, and color strength measurements, and the conductivity of the bacterial cellulose composites was evaluated using a four-probe method. The results revealed that the modification of bacterial cellulose as a template for catechol oxidation resulted in the production of fibers with enhanced coloration and conductive properties owing to the presence of the enzymatically-obtained polymers. The results suggest the promising potential of both sulfonated bacterial cellulose and carboxymethyl cellulose-bacterial cellulose as templates for the formation of other functional polymers and composite materials.

Electrochemical detection and quantification of catechol based on a simple and sensitive poly(riboflavin) modified carbon nanotube paste electrode

In the present research work, selective and sensitive catechol (CT) detection and quantification were shown in the presence of resorcinol (RS) in 0.2 M phosphate buffer (PB) solution by preparing a low-cost, simple, and green carbon nanotube paste electrode (CNTPE) surface activated with electropolymerized riboflavin (PRF). The morphological, conductivity, and electrochemical features of the modified electrode (PRFMCNTPE) and bare carbon nanotube paste electrode (BCNTPE) materials were analyzed using electrochemical impedance spectroscopy (EIS), field emission scanning electron microscopy (FE-SEM), cyclic voltammetry (CV), and differential pulse voltammetry (DPV). The PRF-activated electrode displays outstanding sensitivity, stability, selectivity, reproducibility, and repeatability for the redox feature of CT with improved electrochemical current and declined electrochemical potential compared to BCNTPE. The peak currents of CT are correlated to the different CT concentrations (CV method: 6.0–60.0 μM & DPV method: 0.5–7.0 μM), and the obtained detection limit (DL) and quantification limit (QL) are found to be 0.025 μM and 0.085 μM (CV method) and 0.0039 μM and 0.0132 μM (DPV method), respectively. The prepared PRFMCNTPE material was advantageous for the examination of CT in environmentally important tap water sample as a real-time application.

Using innovative copper-loaded activated alumina (Cu/AA) as the catalyst for catalytic wet peroxidation (CWPO) of catechol.

In this study, copper-loaded activated alumina (Cu/AA) was synthesized and used for the CWPO of catechol (a representative refractory organic pollutant).Various characterization techniques were deployed to characterize the catalysts, e.g., activated alumina (AA), as well as pristine and spent 1% Cu/AA. The innovative 1% Cu/AA catalyst exhibited good thermal stability up to 1173K with a marginal weight loss of 13%. The Cu species were well dispersed on the activated alumina framework with no significant cluster formation. Typically, the average copper particle size of 5nm was dispersed on the AA framework. Catechol removal was observed to be 92% with 87% mineralization at optimizedconditions (initial catechol concentration = 200mg/L, catalyst dose of 1% Cu/AA = 2g/L; temperature = 323K; pH = 6; and H2O2/catechol stoichiometric ratio = 0.5). The mineralization of catechol was analyzed using mass spectroscopy, with the associated mechanism has been elucidated. Results of this study indicated that synthesized catalyst has phenomenal advantages in terms of simple separation and high removal efficiency of catechol, suggesting the feasibility of employing Cu/AA as the effective catalyst for the CWPO of catechol.

Poly DY 11/Zn/CuO modified electrochemical sensor for the detection of catechol and hydroquinone: A voltammetric study

In the present work, Zn doped CuO nanoparticles (Zn/CuO Npcs) was synthesized by co-precipitation method for the fabrication of electrode towards the detection of Catechol (CA) and Hydroquinone (HY). The particle size and surface morphology of Zn/CuO Npcs was characterized by X-ray diffraction technique (XRD) and Scanning electron microscopy (SEM). Further cyclic voltammetric technique was used for the electropolymerization of Direct Yellow 11 (DY 11) on the surface of Zn doped CuO modified carbon paste electrode (MCPE) and applied for the determination of CA and HY at optimum pH 7.4. After the modification, the PolyDY11/Zn/CuO electrode exhibits very stable and sensitive current responses towards the CA and HY. The various parameters like scan rate, pH and concentration of both CA and HY were studied. Simultaneous determination of CA and HY in presence of Resorcinol (RE) was investigated by using cyclic voltammetry, Selectivity study of CA and HY was studied using the differential pulse voltametric technique. The fabricated electrode exhibits adsorption controlled and limit of detection (LOD) calculated for CA and HY in range (10–90 μM) was found to be CA(6 μM) and HY(7 μM) respectively, The real sample analysis in tap water showed better recovery between 90 and 96% for CA and 90–94% for HY respectively.

Sustainable recovery of phenolic antioxidants from real olive vegetation water with natural hydrophobic eutectic solvents and terpenoids

Olive oil production leads to the generation of olive mill wastewater (OMWW). Due to the presence of phenolic compounds, they are difficult to process, but they represent a source of high-added value chemicals since they have antioxidant and therapeutic properties. This work has studied the extraction of phenolic compounds from a type of OMWW, olive vegetation water, which presents these compounds in a more diluted dosage than in other studied to date, to revalue this waste stream. A real olive vegetation water from a Spanish olive oil producer was used, and liquid-liquid extraction was applied. Terpenoids and terpene-based hydrophobic eutectic solvents were systematically used to extract phenolic compounds following the concentrations of tyrosol, catechol, caffeic acid, and total phenolic content. By molecular simulation with the COSMO-RS method, 4 terpenoids, and 2 eutectic solvents were selected and compared with 2 conventional solvents. The Solvent/Feed ratio in the extraction of phenolic compounds was studied, showing that the solvents with the highest extraction results were geraniol, eucalyptol, and eutectic solvent menthol + camphor, which outperformed conventional solvents methyl isobutyl ketone and diisopropyl ether. Menthol + camphor gave total phenol extraction yields of 88.73% at a Solvent/Feed ratio in volume of 0.50, surpassing all solvents tested. A solvent reuse and regeneration process was applied by back-extraction of the 4 solvents: FTIR results showed the stability of the solvents while maintaining yields in the solvent reuse process. The phenolic compounds could be concentrated in the alkaline phase to factors up to 49.3 to the initial concentration in olive vegetation water. The alkaline phases were neutralized to obtain a precipitate with a caffeic acid content of up to 26 % wt%, and a tyrosol-rich supernatant with a concentration of up to 6.54 g/L. This work proposes a process using natural solvents to extract phenolic compounds from olive vegetation water.

Quantitative Determination of Catechol via Cyclic Voltammetry, Convolution-Deconvolution Voltammetry, and Differential Pulse Voltammetry at a Mesoporous Nanostructured Platinum Electrode

The electrochemical quantification of catechol (CC) was performed via cyclic voltammetry (CV), convolution-deconvolution voltammetry, and differential pulse voltammetry (DPV) at nanostructured mesoporous platinum film electrochemically deposited from a hexagonal liquid crystalline template of C16EO8 surfactant in 1.0 M HClO4.The cyclic voltammograms of catechol produced one oxidative peak in the forward sweep of potential coupled with a reductive peak on the reverse sweep potential. The effect of catechol concentration was examined using the various electrochemical methods mentioned before. The modified platinum electrode exhibits good sensitivity for the determination of catechol compound in 1.0 M HClO4. The best performance was found for i-t curve method developed from cyclic voltammetry of CC. It manifests a linear peak current response over the concentration range of 3 to 50 μM, with a detection limit of 2.11 μM and a quantification limit of 7.04 μM confirming the accuracy and sensitivity of this fast and simple method.

Facile preparation of silver nanoparticle decorated RGO nanostructures with enhanced simultaneous detection property for hydroquinone and catechol

Well-dispersed reduced graphene oxide (RGO) nanostructures with uniform decoration of silver nanoparticles (AgNPs) on them have been prepared through a hydrothermal process followed by the freeze-drying method. The obtained graphene-layer-like structure with uniform distribution of AgNPs have then been applied on the glassy carbon electrodes (GCE) to detect different concentration of hydroquinone (HQ) and catechol (CC) in their mixed solutions. Because of such well-dispersed structure and uniform distribution of AgNPs, the AgNPs/RGO/GCE illustrated enhanced simultaneous detection performance for HQ and CC. In the HQ and CC mixed solution with pH of 6.0, the AgNPs/RGO/GCE electrode exhibits a wide linear range of HQ (0.18–130 μM) and CC (0.07–120 μM), and accurate limit of detection (2.37 × 10−2 μM for HQ and 5.8 × 10−2 μM for CC). Thus, it is believed that the AgNPs/RGO nanostructures shows a great potential of applying as possible probes for simultaneous detection of HQ and CC in real environment.

Neuromelanins in brain aging and Parkinson's disease: synthesis, structure, neuroinflammatory, and neurodegenerative role.

Neuromelanins are compounds accumulating in neurons of human and animal brain during aging, with neurons of substantia nigra and locus coeruleus having the highest levels of neuromelanins. These compounds have melanic, lipid, peptide, and inorganic components and are contained inside special autolysosomes. Neuromelanins can participate in neuroprotective or toxic processes occurring in Parkinson's disease according to cellular environment. Their synthesis depends on the concentration of cytosolic catechols and is a protective process since it prevents the toxic accumulation of catechols-derived reactive compounds. Neuromelanins can be neuroprotective also by binding reactive/toxic metals to produce stable and non-toxic complexes. Extraneuronal neuromelanin released by dying dopamine neurons in Parkinson's disease activates microglia which generate reactive oxygen species, reactive nitrogen species, and proinflammatory molecules, thus producing still neuroinflammation and neuronal death. Synthetic neuromelanins have been prepared with melanic, protein structure, and metal content closely mimicking the natural brain pigment, and these models are also able to activate microglia. Neuromelanins have different structure, synthesis, cellular/subcellular distribution, and role than melanins of hair, skin, and other tissues. The main common aspect between brain neuromelanin and peripheral melanin is the presence of eumelanin and/or pheomelanin moieties in their structure.