Cationic Dopamine Research Articles

A structural comparison of salt forms of dopamine with the structures of other phenylethylamines.

The structures of four salt forms of dopamine are reported. These are dopamine [2-(3,4-dihydroxyphenyl)ethan-1-aminium] benzoate, C8H12NO2+·C7H5O2-, I, dopamine 4-nitrobenzoate, C8H12NO2+·C7H4NO4-, II, dopamine ethanedisulfonate, 2C8H12NO2+·C2H4O6S22-, III, and dopamine 4-hydroxybenzenesulfonate monohydrate, C8H12NO2+·C6H5O4S-·H2O, IV. In all four structures, the dopamine cation adopts an extended conformation. Intermolecular interaction motifs that are common in the salt forms of tyramine can be found in related dopamine structures, but hydrogen bonding in the dopamine structures appear to be more variable and less predictable than for tyramine. Packing analysis discovered three dopamine-containing groups of structures that can be described as isostructural with regards to the cation positions. Two of these groups contain both dopamine and tyramine species, and one of these is also highly variable in other ways too, containing anhydrous and hydrated forms, different anion types and ionized and neutral phenylethylamine species. As such, the group illustrates that packing behaviour can be robust and similar even where intermolecular interactions such as hydrogen bonds are very different.

Intramolecular interactions (O-H∙∙∙O, C-H∙∙∙N, N-H∙∙∙π) in isomers of neutral, cation, and anion dopamine molecules: A DFT study on the influence of solvents (water and ethanol).

Dopamine (DA) is one of the most important neurotransmitters associated with numerous neural disorders. This investigation reports the intramolecular interactions present in the isomers of neutral (DA0), anionic (DA-), and cationic (DA+) dopamine isomers in gas, water, and ethanol mediums. Neutral and anion isomers have O-H∙∙∙O, C-H∙∙∙N intramolecular hydrogen bonds and N-H∙∙∙π interactions. All the interactions are electrostatic in nature. Isomers of cation dopamine show no intramolecular interactions in the solvent. Natural charges from natural bond orbital (NBO) analysis show that O-H∙∙∙O bonds and the N-H∙∙∙π interactions are the most and least polar, respectively. 1H NMR study reveals the inverse linear correlation between shielding constant and electron density in a solvent medium. HOMO-LUMO energy gap indicates higher stability for neutral and cationic forms of dopamine isomers in water and ethanol medium. We have optimized all the structural forms of dopamine molecule using the Becke three hybrid exchange and Lee-Yang-Parr correlation functional with Grimme's dispersion correction, B3LYP-D3(BJ), and aug-cc-pVTZ basis set using the Gaussian16 software. Vibrational frequency analysis with no imaginary frequencies confirms the nature of global minima. The solvent studies (water and ethanol) were carried out using the SCRF keyword and the polarisable continuum model (PCM) of Miertus and Tomasi. NBO analysis and NMR studies were also performed for all conformers. Topology analysis was explored using the software Multiwfn.

Different Electrochemical Behavior of Cationic Dopamine from Anionic Ascorbic Acid and DOPAC at CNT Yarn Microelectrodes

Carbon nanotube yarn microelectrodes (CNTYMEs) have micron-scale surface crevices that momentarily trap molecules. CNTYMEs improve selectivity among cationic catecholamines because secondary reactions are enhanced, but no anions have been studied. Here, we compared fast-scan cyclic voltammetry (FSCV) of dopamine and anionic interferents 3,4 dihydroxyphenylacetic acid (DOPAC) and L-ascorbic acid (AA) at CNTYMEs and carbon fiber microelectrodes (CFMEs). At CFMEs, dopamine current decreases with increasing FSCV repetition frequency at pH 7.4, whereas DOPAC and AA have increasing currents with increasing frequency, because of less repulsion at the negative holding potential. Both DOPAC and AA have side reactions after being oxidized, which are enhanced by trapping. At pH 4, the current increases for DOPAC and AA because they are not repelled. In addition, AA has a different oxidation pathway at pH 4, and an extra peak in the CV is enhanced by trapping effects at CNTYMEs. At pH 8.5, co-detection of dopamine in the presence of DOPAC and AA is enhanced at 100 Hz frequency because of differences in secondary peaks. Thus, the trapping effects at CNTYMEs affects anions differently than cations and secondary peaks can be used to identify dopamine in mixture of AA and DOPAC with FSCV.

Fabrication of an in-situ co-immobilized enzyme in mesoporous silica for synthesizing GSH with ATP regeneration

We report here adopting a glucose template for synthesizing mesoporous silica for enzyme in-situ immobilization. Bifunctional GSH synthetase (GSHF) and polyphosphate kinase (PPK) were selected as model system for synthesizing GSH with ATP regeneration. Results indicated that a pore size that was slightly smaller than that of enzyme was responsible for the high performance of immobilized enzyme inside mesoporous without protein leaking. Then, the cationic dopamine was used for PPK immobilization by self-polymerization. The co-immobilized enzyme activity was much higher than that of the free enzyme. The catalytic efficiency kcat/Km of co-immobilized enzyme was higher than that of the free enzyme (8.5 and 1.5 times higher for GSHF and PPK, respectively). After optimizing the reaction parameters, the co-immobilized enzymes exhibited excellent operational and storage stability, and could be re-used seven times and retained the original activity after 30 days. It is hoped that these findings will pave the way for applying enzyme co-immobilization to biocatalytic system.

Two-Dimensional Infrared Spectra of Cationic Dopamine under Different Electric Fields: Theoretical Studies from the Density Function Theory Anharmonic Potential

The geometry optimizations and vibrational frequencies of cationic dopamine (DAH+) under different intensity of electric fields (IEFs) are investigated using density function theory (DFT)/B3LYP/6-311G(d,p) and two-dimensional infrared spectra are pictured based on anharmonic approximation. In spite of some differences, the optimized structural parameters calculated by DFT/B3LYP/6-311G(d,p) can well reproduce the experimental ones. Anharmonic approximation greatly improves the agreement between experimental and calculated fundamental frequencies. This study mainly focuses on the potential energy distributions and rotational isomerization of DAH+ under different electric fields. The results showed that there were very strong absorption peaks at 3571 and 3683 cm–1 for O–H stretching vibrations. The symmetric and asymmetric peaks of C–H stretching vibrations with benzene ring and amidogen were calculated by anharmonic approximation and observed at 2921, 2904, 2997, and 3007 cm–1. In addition, strong absorption peaks were also observed at 3266, 3313, and 3316 cm–1 for N–H stretching vibrations. For C–H stretching vibrations with amidogen, when IEF is increasing from −30 × 10–4 to 20 × 10–4 a.u., the vibrations of symmetry and asymmetry are coupled. However, the two vibrations were no longer coupled while IEF goes on increasing to 30 × 10–4 a.u.; For C–H stretching vibrations with benzene ring, the vibrations of symmetry and asymmetry were uncoupled when IEFs are −20 × 10–4, −10 × 10–4, 0 × 10–4, and 30 × 10–4 a.u. In addition, DAH+ undergoes rotational isomerization only when IEF ranges from −20 × 10–4 to 10 × 10–4 a.u.

Beneficial impact of oxygen on the electrochemical performance of dopamine sensors based on N-doped reduced graphene oxides

Graphene-based electrochemical sensors are promising devices for direct and easy dopamine determination. In this work, N-doped reduced graphene oxides (N-rGOs) were prepared via hydrothermal treatment of graphene oxide (GO) and amitrole (3-amino-1,2,4-triazole) under different experimental conditions (varying reaction temperature and time), which resulted in each material having different oxygen content. Furthermore, the dopant nitrogen content was comparable in the three N-rGOs and it was primarily pyridinic in nature. The three synthesized N-rGOs were characterized by X-ray photoelectron spectroscopy, Fourier transformed infrared spectroscopy, scanning electron microscopy, and nitrogen sorption at 77K. Glassy carbon electrodes modified with N-rGOs were prepared and used as active electrode materials in electrochemical sensors of dopamine (DA). The optimal operational pH was determined to be 7.4, which is also the physiological value. During the electrochemical detection of DA, it was found that there is a direct relationship between the oxygen content in N-rGO and electrochemical performance of these sensors. Thus, the detection of DA in the presence of ascorbic and uric acids was more sensitive and selective when the least reduced N-rGO sample was used. The attraction between the electronegative oxygen in the graphene structure and cationic DA facilitates the adsorption process which could explain these results. However, the limit of detection (LOD) was also higher in this case due to decreased conductivity.

Raman Computational and Experimental Studies of Dopamine Detection.

A combined theoretical and experimental analysis of dopamine (DA) is presented in this work with the objective of achieving more accurate detection and monitoring of this neurotransmitter at very low concentrations, specific to physiological levels. Surface-enhanced Raman spectroscopy on silver nanoparticles was employed for recording DA concentrations as low as 10−11 molar. Quantum chemical density functional calculations were carried out using Gaussian-09 analytical suite software. Relatively good agreement between the simulated and experimentally determined results indicates the presence of different DA molecular forms, such as uncharged DA±, anionic DA−, and dopaminequinone. Disappearance of the strongest bands of dopamine around 750 cm−1 and 790 cm−1, which suggests its adsorption onto the metallic surface, is not only consistent with all of these DA configurations, but also provides additional information about the analyte’s redox process and voltammetric detection. On the other hand, occurrence of the abovementioned Raman lines could indicate the formation of multilayers of DA or its presence in a cationic DA+ form. Thus, through coordinated experiment and theory, valuable insights into changes observed in the vibrational signatures of this important neurotransmitter can be achieved for a better understanding of its detection at physiological levels, which is crucial if further optovoltammetric medical device development is envisioned.

Poly(zwitterionic liquids) functionalized polypyrrole/graphene oxide nanosheets for electrochemically detecting dopamine at low concentration

Poly(3-(1-vinylimidazolium-3-yl)propane-1-sulfonate) (PVIPS), a novel kind of poly(zwitterionic liquids) (PZILs) containing both imidazolium cation and sulfonate anion, was successfully modified on the surface of polypyrrole/graphene oxide nanosheets (PPy/GO) by covalent bonding. The obtained novel PZILs functionalized PPy/GO nanosheets (PVIPS/PPy/GO) modified glassy carbon electrode (GCE) presented the excellent electrochemical catalytic activity towards dopamine (DA) with high stability, sensitivity, selectivity and wide linear range (40–1220nM), especially having a lower detection limit (17.3nM). The excellent analytical performance is attributed to the strongly negative charges on the surface of modified GCE in aqueous solution, which is different from conventional poly(ionic liquids) modified GCE. DA cations could be quickly enriched on the electrode surface by electrostatic interaction in solution due to the existence of SO3− groups with negative charge at the end of pendant groups in zwitterionic PVIPS, resulting in a change of the electrons transmission mode in the oxidation of DA, that is, from a typical diffusion-controlled process at conventional poly(1-vinyl-3-ethylimidazole bromide) (PVEIB)/PPy/GO modified GCE to a typical surface-controlled process.

Using of anionic adsorption property of a surfactant modified clinoptilolite nano-particles in modification of carbon paste electrode as effective ingredient for determination of anionic ascorbic acid species in presence of cationic dopamine species

A novel carbon paste electrode containing modified clinoptilolite nano-particles with hexadecyltrimethylammonium surfactant (or surfactant modified zeolite (SMZ)) was constructed and used for selective voltammetric determination of ascorbic acid (AA) in the presence of dopamine (DA), because the SMZ present in the modified electrode adsorbs anionic AA species and repels cationic DA species. This caused to increase the over-voltage of electro-oxidation of DA by ∼600mV with respect to AA in square wave voltammetry (SqW). Hence, AA and DA can be effectively determined by the modified electrode in their aqueous mixture. Comprehensive CV, SqW and chronoamperometry (ChA) studies were done on AA using the proposed electrode. The widest linear responses with detection limits of 6.1×10−8moldm−3 and 5.9×10−12moldm−3 were respectively obtained for AA in SqW and ChA techniques. The diffusion coefficient of ascorbic acid was equal to 4.1×10−5cm2s−1. The proposed method was successfully applied for the determination of AA in different pharmaceutical and food samples which of their AA contents were obtained as: 497.4±1.2 mg per Chewable tablet, 246.9±1.4mg per Vitamin C tablet, 501.3±0.8mg per Vitamin C ampoule, 45.2±1.1mg per 100g of Sweet lemon, 50.6±0.7mg per 100g of Orange, 36.9±0.9 mg per 100g of Grapefruit, 31.2±1.3 mg per 50g of Sour lemon, 9.5±1.0 mg per 250mg of Lemonade.

Electrochemical detection of nanomolar dopamine in the presence of neurophysiological concentration of ascorbic acid and uric acid using charge-coated carbon nanotubes via facile and green preparation

Negatively charged multi-walled carbon nanotubes (MWCNTs) were prepared using simple sonication technique with non-toxic citric acid (CA) for the electrochemical detection of dopamine (DA). CA/MWCNTs were placed on glassy carbon (GC) electrodes by drop-casting method and then electrochemical determinations of DA were performed in the presence of highly concentrated ascorbic acid (AA). For the comparison of the charge effect on MWCNTs surface, positively charged polyethyleneimine (PEI)/MWCNT/GC electrode and pristine MWCNT/GC electrode were also prepared. Contrary to conventional GC electrode, all three types of MWCNT modified electrodes (CA/MWCNT/GC, PEI/MWCNT/GC, and pristine MWCNT/GC) can discriminate ~μM of DA from 1mM AA using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) due to the inherent electrocatalytic effect of MWCNTs. Compared to positively charged PEI/MWCNT/GC and pristine MWCNT/GC electrodes, negatively charged CA/MWCNT/GC electrode remarkably enhanced the electrochemical sensitivity and selectivity of DA, showing the linear relationship between DPV signal and DA concentration in the range of 10–1000nM even in the presence of ~105 times concentrated AA, which is attributed to the synergistic effect of the electrostatic interaction between cationic DA molecules and negatively charged MWCNTs and the inherent electrocatalytic property of MWCNT. As a result, the limit of detection (LOD) of DA for CA/MWCNT/GC electrode was 4.2nM, which is 5.2 and 16.5 times better than those for MWCNT/GC electrode and PEI/MWCNT/GC electrode even in the presence of 1mM AA. This LOD value for DA at CA/MWCNT/GC electrode is one of the lowest values compared to the previous reports and is low enough for the early diagnosis of neurological disorder in the presence of physiological AA concentration (~0.5mM). In addition, the high selectivity and sensitivity of DA at CA/MWCNT/GC electrode were well kept even in the presence of both 1mM AA and 10μM uric acid (UA) as similar as neurophysiological concentration.

Clay Composite Modified Electrodes I: Voltammetric Method for Selective Analysis of Dopamine and Ascorbic Acid

Clay Composite Modified Electrodes I: Voltammetric Method for Selective Analysis of Dopamine and Ascorbic Acid

Micelle-encapsulated multi-wall carbon nanotubes with photosensitive copolymer and its application in the detection of dopamine

Photosensitive copolymer P(St-alt-MAn)-co-P(VM-alt-MAn) was synthesized and employed to disperse multi-wall carbon nanotubes (MWCNTs). It was found that copolymer could form micelles in aqueous solution and adsorb onto the surface of MWCNTs to produce micelle-encapsulated MWCNTs (e-MWCNTs) by in situ photo crosslinking after irradiation with ultraviolet light and a stable suspension of e-MWCNTs in aqueous solution was obtained. When deposited onto polyaniline (PANI)-modified glassy carbon electrodes, a thin film of e-MWCNTs composite was obtained and the performance of the e-MWCNTs/PANI electrode toward dopamine was then evaluated. The experimental results suggest that the hybrid film modified electrode exhibits a dramatic electrocatalytic effect on the oxidation of dopamine (DA), as evidenced by a marked enhancement of the current response. A series of CVs was obtained by modified glassy-carbon electrodes with different size of micelles was also researched. The result shows that the peak current increased with the increasing size of micelles. A linear calibration plot was obtained in a wide range of 1.0 × 10−7–1.0 × 10−3 M and the detection limit was 5.0 × 10−8 M. In addition, the interference from ascorbic acid (AA) was effectively suppressed due to the presence of the negatively charged carboxylate groups of copolymer on the outside of MWCNTs which repels AA anions and provides a transport channel only for DA cations.

Simultaneous/Selective Detection of Dopamine and Ascorbic Acid at Synthetic Zeolite-Modified/Graphite-Epoxy Composite Macro/Quasi-Microelectrodes

The present paper aims to miniaturize a graphite-epoxy and synthetic zeolite-modified graphite-epoxy composite macroelectrode as a quasi-microelectrode aiming in vitro and also, envisaging in vivo simultaneous electrochemical detection of dopamine (DA) and ascorbic acid (AA) neurotransmitters, or DA detection in the presence of AA. The electrochemical behavior and the response of the designed materials to the presence of dopamine and ascorbic acid without any protective membranes were studied by cyclic voltammetry and constant-potential amperometry techniques. The catalytic effect towards dopamine detection was proved for the synthetic zeolite-modified graphite-epoxy composite quasi-microelectrode, allowing increasing the sensitivity and selectivity for this analyte detection, besides a possible electrostatic attraction between dopamine cation and the negative surface of the synthetic zeolite and electrostatic repulsion with ascorbic acid anion. Also, the synthetic zeolite-modified graphite-epoxy composite quasi-microelectrode gave the best electroanalytical parameters for dopamine detection using constant-potential amperometry, the most useful technique for practical applications.

Design, Synthesis and Brain Uptake of LAT1-Targeted Amino Acid Prodrugs of Dopamine

Drug delivery to the brain is impeded by the blood-brain barrier (BBB). Here, we attempted to enhance the brain uptake of cationic dopamine by utilizing the large amino acid transporter 1 (LAT1) at the BBB by prodrug approach. Three amino acid prodrugs of dopamine were synthesized and their prodrug properties were examined in vitro. Their LAT1-binding and BBB-permeation were studied using the in situ rat brain perfusion technique. The brain uptake after intravenous administration and the dopamine-releasing ability in the rat striatum after intraperitoneal administration were also determined for the most promising prodrug. All prodrugs underwent adequate cleavage in rat tissue homogenates. The prodrug with phenylalanine derivative as the promoiety had both higher affinity for LAT1 and better brain uptake properties than those with an alkyl amino acid - mimicking promoiety. The phenylalanine prodrug was taken up into the brain after intravenous injection but after intraperitoneal injection the prodrug did not elevate striatal dopamine concentrations above those achieved by corresponding L-dopa treatment. These results indicate that attachment of phenylalanine to a cationic drug via an amide bond from the meta-position of its aromatic ring could be highly applicable in prodrug design for LAT1-mediated CNS-delivery of not only anionic but also cationic polar drugs.

Sodium dodecyl sulfate-modified electrochemical paper-based analytical device for determination of dopamine levels in biological samples

We report the development of an electrochemical paper-based analytical device (ePAD) for the selective determination of dopamine (DA) in model serum sample. The ePAD device consists of three layers. In the top layer, SU-8 photoresist defines a hydrophilic sample application spot on the filter paper. The middle layer was made from transparency film and contained two holes, one for sample preconcentration and the other for the surfactant to allow transfer to the third layer. A screen-printed carbon electrode formed the bottom layer and was used for electrochemical measurements. In the absence of the anionic surfactant, sodium dodecyl sulfate (SDS), the oxidation peaks of DA, ascorbic acid (AA) and uric acid (UA) overlapped. With the addition of SDS, the DA oxidation peak shifted to more negative values and was clearly distinguishable from AA and UA. The oxidation potential shift was presumably due to preferential electrostatic interactions between the cationic DA and the anionic SDS. Indeed, whilst the SDS-modified paper improved the DA current five-fold, the non-ionic Tween-20 and cationic tetradecyltrimethylammonium bromide surfactants had no effect or reduced the current, respectively. Furthermore, only the SDS-modified paper showed the selective shift in oxidation potential for DA. DA determination was carried out using square-wave voltammetry between −0.2 and 0.8V vs. Ag/AgCl, and this ePAD was able to detect DA over a linear range of 1–100μM with a detection limit (S/N=3) of 0.37μM. The ePAD seems suitable as a low cost, easy-to-use, portable device for the selective quantitation of DA in human serum samples.

Preparation of thiolated polymeric nanocomposite for sensitive electroanalysis of dopamine

We report on the thiol-ene chemistry guided preparation of novel thiolated polymeric nanocomposite films of abundant anionic carboxylic groups for electrostatic enrichment and sensitive electroanalysis of cationic dopamine (DA) in neutral solution. Briefly, the thiol-ene nucleophilic reaction of a carboxylated thiol with oxidized polypyrrole (PPy), which was electrosynthesized on an Au electrode in the presence of solution-dispersed acidified multiwalled carbon nanotubes (MWCNTs), produced an a PPy–thiol–MWCNTs/Au electrode, and the PPy can be electrochemically overoxidized (OPPy) to form an OPPy–thiol–MWCNTs/Au electrode. The carboxylic groups of the polymeric nanocomposite film originate from the acidified MWCNTs, PPy-tethered carboxylated thiol, and OPPy. The carboxylated thiols examined are mercaptosuccinic acid (MSA) and thioglycolic acid, with β-mercaptoethanol as a control. Electrochemical quartz crystal microbalance, scanning electron microscopy, Fourier transform infrared spectroscopy and ultraviolet–visible spectroscopy were used for film characterization and process monitoring. Under the optimized condition, the differential pulse voltammetry peak current of DA oxidation at OPPy–MSA–MWCNTs/Au electrode is linear with DA concentration from 1.00×10–9 to 2.87×10–6molL−1, with a limit of detection of 0.4nmolL−1, good anti-interferent ability and stability.

VUV Photoionization and Dissociation of Tyramine and Dopamine: the Joint Experimental and Theoretical Studies

Photon induced dissociation investigations of neutral tyramine and dopamine are carried out with synchrotron vacuum ultraviolet photoionization mass spectrometry and theoretical calculations. At low photon energy only molecular ions are measured by virtue of nearthreshold photoionization. While increasing photon energy to 11.7 eV or more, four distinct fragment ions are obtained for tyramine and dopamine, respectively. Besides, the ionization energies of tyramine and dopamine are determined to be 7.98±0.05 and 7.67±0.05 eV by measuring the photoionization efficiency curves of corresponding molecular ions. With help of density function theory calculations, the detailed fragmentation pathways are established as well. These two molecular cations have similar aminoethyl group elimination pathways, C7H8O2+· (m/z=124) and C7H8O+· (m/z=108) are supposed to be generated by the McLafferty rearrangement via γ-hydrogen (γ-H) shift inducing β-fission. And CH2NH2+ is proposed to derive from the direct fission of C7-C8 bond. Besides, the McLafferty rearrangement and the C7-C8 bond fission are validated to be dominant dissociation pathways for tyramine and dopamine cations.

Selective determination of dopamine using quantum-sized gold nanoparticles protected with charge selective ligands

We report here the selective determination of dopamine (DA) using quantum-sized gold nanoparticles coated with charge selective ligands. Glutathione protected gold nanoparticles (GS-Au(25)) were synthesized and immobilized into a sol-gel matrix via thiol linkers. The GS-Au(25) modified sol-gel electrode was found to show excellent electrocatalytic activity towards the oxidation of DA but no activity towards the oxidation of ascorbic acid. The role of electrostatic charge in the selective electrocatalytic activity of GS-Au(25) was verified by voltammetry of redox markers carrying opposite charges. The pH dependent sensitivity for the determination of DA further confirmed the charge screening effect of GS-Au(25). Mechanistic investigation revealed that the selectivity is attained by the selective formation of an electrostatic complex between the negatively charged GS-Au(25) and DA cation. The GS-Au(25) modified sol-gel electrode also showed excellent selectivity for DA in the presence of an interferent, ascorbic acid.

Enhanced sensing of dopamine in the present of ascorbic acid based on graphene/poly(p-aminobenzoic acid) composite film

Graphene/p-aminobenzoic acid composite film modified glassy carbon electrode (Gr/p-ABA/GCE) was first employed for the sensitive determination of dopamine (DA). The electrochemical behavior of DA at the modified electrode was investigated by cyclic voltametry (CV), differential pulse voltametry (DPV) and amperometric curve. The oxidation peak currents of DA increased dramatically at Gr/p-ABA/GCE. The modified electrode was used to electrochemically detect dopamine (DA) in the presence of ascorbic acid (AA). The Gr/p-ABA composite film showed excellent electrocatalytic activity for the oxidation of DA in phosphate buffer solution (pH 6.5). The peak separation between DA and AA was large up to 220 mV. Using DPV technique, the calibration curve for DA determination was obtained in the range of 0.05-10 μM. The detection limit for DA was 20 nM. AA did not interfere with the determination of DA because of the very distinct attractive interaction between DA cations and the negatively Gr/p-ABA composite film. The proposed method exhibited good stability and reproducibility.

Selective detection of dopamine with poly(diphenylamine sulfonic acid) modified electrode in the presence of ascorbic acid

A glassy carbon electrode was modified with electropolymerized film of diphenylamine sulfonic acid (DPASA). Electropolymerization was performed by cyclic voltammetry in 0.1 M KCl solution. The modified electrode showed an excellent electrocatalytic effect towards oxidation of dopamine (DA) and ascorbic acid (AA). Electrostatic interaction between the negatively charged poly(DPASA) film and either cationic DA species or anionic AA species favorably contributed to the redox response of DA and AA. Anodic peaks of DA and AA in their mixture were well separated by ca 168 and −11.8 mV. The proposed modified electrode was utilized for selective determination of dopamine in the concentration range of 5.0 × 10t7–2.0 × 10−5 M in the presence of high concentration of ascorbic acid. Detection limit was 6.5 × 10−9 M.