Phenylenediamine Isomers Research Articles

Carbon-dot-aerogel sensor for aromatic volatile organic compounds

Detection of aromatic volatile organic compounds (VOCs) is important for monitoring occupational hazards, industrial safety, and environmental applications. Here, we present a new in-situ-synthesized carbon dot – aerogel matrix and demonstrate its application for sensing aromatic VOCs. The composite aerogel exhibited high specific surface area and pore diameter, enabling efficient adsorption of the organic vapors. In particular, the excitation-dependent luminescence emission properties of the carbon dots were retained upon embedding within the aerogel host, and provided a sensitive transduction mechanism through both shifts and quenching of the fluorescence emissions. We show that distinct fluorescence shifts and degrees of quenching were induced by different aromatic VOCs. In particular, the C-dot-aerogel sensor could distinguish between isomers of phenylenediamine, an important achievement which has not been previously demonstrated in VOC sensing platforms.

Structure of functionalized nitrogen-doped graphene hydrogels derived from isomers of phenylenediamine and graphene oxide based on their high electrochemical performance

Three functionalized N-doped graphene hydrogels were prepared from graphene oxide (GO) and isomers of phenylenediamine through hydrothermal process, which were (1) FONGH prepared with o-phenylenediamine (OPD); (2) FMNGH prepared with m-phenylenediamine (MPD) and (3) FPNGH prepared with p-phenylenediamine (PPD). As-prepared FONGH, FMNGH and FPNGH possessed different microstructures and exhibited different specific surface area: 107.8, 24.3 and 145.2m2g−1. The prepared graphene hydrogels were found with different N contents: FONGH (11.1 at.%)>FPNGH (9.8 at.%)>FMNGH (7.2 at.%). High resolution N 1s spectra of as-prepared hydrogels revealed that OPD facilitated the preparation of graphene with high doping level of nitrogen; while PPD was favorable to preparing N-doped graphene hydrogel with high moieties of amine including -NH2 or N covalent bonded with sp3-C of graphene. As-prepared FONGH, FMNGH and FPNGH exhibited excellent electrochemical performance with high specific capacitance (645, 365.7 and 467Fg−1 at 1Ag−1) and superior cycling stability (97.6%, 83.1% and 91% retention at 20Ag−1 after 1000 cycles). The different microstructures and electrochemical performance of FONGH, FMNGH and FPNGH were caused by different positions of -NH2 groups on the benzene rings of OPD, MPD and PPD. The present work proposes a novel idea to prepare functionalized N-doped graphene with high electrochemical performance.

Facilely prepared Fe3O4/nitrogen-doped graphene quantum dot hybrids as a robust nonenzymatic catalyst for visual discrimination of phenylenediamine isomers

In this work, we report a reducing agent-free strategy for the synthesis of Fe3O4 nanoparticle/nitrogen-doped graphene quantum dot (Fe3O4/N-GQD) hybrids, and constructed a sensing platform based on Fe3O4/N-GQDs for the visual discrimination of phenylenediamine isomers. Fe3O4/N-GQDs were facilely prepared by hydrothermal treatment of Fe(3+)/N-GQD solutions under alkaline conditions without other reagents. The prepared Fe3O4/N-GQDs exhibited outstanding peroxidase-like activity and were stable under a wide range of pH values and temperatures. The phenylenediamine isomers (o-phenylenediamine, m-phenylenediamine, and p-phenylenediamine) were discriminated through the H2O2-mediated oxidation reaction using Fe3O4/N-GQDs as novel peroxidase mimics, which resulted in appreciable color changes. The proposed method is simple, economical, and effective for discrimination of isomers, and can be used for sensitive and selective quantitative analysis of o-phenylenediamine and p-phenylenediamine. A good linear relationship from 1 to 90 μM and a detection limit of 230 nM for o-phenylenediamine were achieved, and the linear relationship for p-phenylenediamine was from 2 to 70 μM with a detection limit of 530 nM. The proposed method may open new applications of Fe3O4/N-GQDs in biomedicine and environmental chemistry.

Electrochemical amination. synthesis of aniline in aqueous–acetonitrile solutions of sulfuric acid

The process of indirect cathodic amination of benzene is studied in aqueous media containing 4-10 M H2SO4 and, accordingly, 13.8–7.1 M CH3CN. At 50°C, electrolysis in the system of Ti(IV)–NH2OH–C6H6 results in formation of aniline and also small amounts of isomeric phenylenediamines and diphenyl. The current efficiency of aniline is maximum in the catholyte containing 8 M H2SO4 and 9.4 M CH3CN. Under these conditions, full conversion of hydroxylamine is observed; the 80% current efficiency of aniline corresponds to the efficiency of the amino radical source and its mass fraction among the products of electrolysis exceeds 97%.

Diffusion Studies of Phenylenediamine Isomers in Water-Monohydric-Alcohol Systems

The study of isomer diffusion provides useful information regarding solvent effects for mixture analysis. Isomers, particularly those with similar hydrodynamic radii, provide a mechanism for probing solute–solvent interactions. Here nuclear magnetic resonance was used to measure the self-diffusion of phenylenediamine isomers in various water–monohydric-alcohol (i.e. methanol, ethanol, 1-propanol, and tert-butanol) solvents. These systems allowed the effect of solvent modulation on isomer diffusion to be examined. It was found that the resonances of phenylenediamine isomers in a mixture were separable via diffusion, with the separation becoming greater at higher concentration of monohydric-alcohols. Unlike previously shown for dihydroxybenzene isomers, all three phenylenediamine isomers were differentiable via diffusion.

A comparative study of a label-free DNA capacitive sensor using a pyrrolidinyl peptide nucleic acid probe immobilized through polyphenylenediamine and polytyramine non-conducting polymers

This work has, for the first time, reported a comparative study on the performances of a label-free capacitive DNA sensor based on an immobilized pyrrolidinyl peptide nucleic acid with a d-prolyl-2-aminocyclopentanecarboxylic acid backbone (acpcPNA) attached to three easy to prepare non-conducting polymers. Two phenylenediamine (PD) isomers (ortho- and para-) and one tyramine monomer were electropolymerized to form polymer films. The hybridization between the acpcPNA probes, immobilized on the polymer layer, and the target DNA was detected directly by measuring the capacitance change. Using the optimal electropolymerized conditions, the highest sensitivity of 20.9 ± 0.6-nF cm−2 (log M)−1 was obtained from poly-para-PD (PpPD) with a lowest detection limit of 0.2 pM. A wide linear range, 1.0 × 10−12 to 1.0 × 10−8 M, was obtained for both the PpPD and polytyramine (Pty). A narrower linear range of 1.0 × 10−11 to 1.0 × 10−8 M was obtained from the poly-ortho-PD (PoPD). The surface morphology was observed using scanning electron microscopy and atomic force microscopy. The polymer with the better surface morphology, i.e., smoother, denser and more homogeneous was the one with more immobilized probes and a better overall performance. All modified polymers gave a high % signal suppression (%SS) for both the single and double mismatched target DNAs, and indicated its high specificity. The electrodes can be reused for at least 68 analytical cycles. The effects of the target length and probe concentrations were also investigated. Under the operating conditions of this work the system would be very useful for the cost-effective analysis of ultra-trace levels of DNA in samples.

An electrochemical study of corrosion protection by in situ oxidative polymerization in phenylenediamine crosslinked sol–gel hybrid coatings

The three isomers of phenylenediamine have been used as crosslinking agents for epoxide decorated silica colloids generated by high water content sol–gel chemistry techniques. The resulting materials were used as corrosion protection thin films for aluminum alloys in corrosive environments. These hybrid epoxy-amine crosslinked sol–gel materials have demonstrated an order of magnitude improvement over similar materials crosslinked with aliphatic diamines along with novel electrochemical and coloration behavior. The processes behind these performance improvements are explored and two possibly complementary mechanisms are identified, namely exposure-triggered toughening of the materials through oxidative polymerization of the phenylenediamines and an increase in corrosion inhibition via the formation of electroactive phenylenediamine oligomers.

Determination of phenylenediamine isomers in hair dyes by coal cinders micro-column extraction and MEKC

A new micellar electrokinetic chromatography (MEKC) method using beta-cyclodextrins (β-CDs) and 1-butyl-3-methylimidazolium hexafluorophosphates (ionic liquids) as additives was successfully developed for determination of para-, meta-, and ortho-phenylenediamines isomers (p-P, m-P, and o-P) in hair dyes. To improve the sensitivity of the MEKC-UV, a simple and cheap flow injection (FI) technique using a micro-column packed with coal cinders (the by-products from combustion in a boiler) as solid-phase extractant was also investigated. In the presence of 20 mmol L(-1) phosphates at pH 5.5, addition of 12 mmol L(-1) ionic liquids and 8 mmol L(-1) β-CDs greatly improved the separation efficiency. The three analytes could be quantitatively adsorbed by coal cinders, and desorbed readily with 0.15 mL of 0.01 mol L(-1) NaOH. Under the optimum conditions, an enrichment factor (EF) of 33.3 was obtained, and determination limits of p-P, m-P, and o-P were 1.97 × 10(-7), 0.99 × 10(-7), and 0.61 × 10(-7) mol L(-1), respectively. The adsorption capacities of the coal cinders micro-column for p-P, m-P, and o-P were all 1.20 mg g(-1). The presented procedure was successfully applied to the determination of p-P, m-P, and o-P in hair dyes with satisfactory results.

Poly(phenylenediamine) film for the construction of glucose biosensors based on platinized glassy carbon electrode

Three phenylenediamine isomers (including ortho-, meta- and para-derivatives) were electrochemically polymerized to give polyphenylenediamine (PPD) films on platinized glassy carbon electrodes. Amperometric glucose sensors were developed by immobilizing glucose oxidase (GOx) into these polymer matrices during polymerization. Effects of the polymerization potential, polymerization charge, monomer concentration, GOx concentration and Pt deposition charge on the performance of the enzyme electrode to glucose were investigated. These resulting GC/Pt/PPD-GOx electrodes showed rapid electrochemical responses to hydrogen peroxide and glucose, and very good anti-interference ability to ascorbic acid. Correlation between the electroanalytical behaviors of the enzyme electrodes and the polymer structures was examined.

One Ring to Bind Them All: Shape-Selective Complexation of Phenylenediamine Isomers with Cucurbit[6]uril in the Gas Phase

We examined complexes between cucurbit[6]uril and each of ortho-, meta-, and para-phenylenediamine using computational methods, Fourier transform ion cyclotron resonance mass spectrometry, and ion mobility spectrometry. These fundamental gas phase studies show that the lowest energy binding sites for ortho- and meta-phenylenediamine are on the exterior of cucurbit[6]uril, whereas para-phenylenediamine preferentially binds in the interior, in a pseudorotaxane fashion. This conclusion is based on reactivity of each of the complexes with tert-butylamine, where the ortho- and meta-phenylenediamine complexes exchange with tert-butylamine, whereas the para-phenylenediamine complex undergoes two slow additions without displacement. Further, under sustained off-resonance irradiation conditions, the ortho- and meta-phenylenediamine complexes fragment easily via losses of neutral phenylenediamine, whereas the para-phenylenediamine complex fragments at higher energies primarily via cleavage of covalent bonds in the cucurbituril. Finally, ion mobility studies show ion populations for the ortho- and meta-phenylenediamine complexes that primarily have collision cross sections consistent with external complexation, whereas the para-phenylenediamine complex has a collision cross section that is smaller, the same as that of protonated cucurbit[6]uril within experimental error. In agreement with experiment, computational studies indicate that at the HF/6-31G* and B3LYP/6-31G*//HF/6-31G* levels of theory external complexation is favored for ortho- and meta-phenylenediamine, whereas internal complexation is lower in energy for para-phenylenediamine. In contrast, MP2/6-31G*//HF-6-31G* calculations predict internal complexation for all three isomers.

Calculation of henry constants for the adsorption of isomeric phenylenediamines on graphitized thermal carbon black

Henry constants for the adsorption of o- and p-phenylenediamines on the surface of graphitized thermal carbon black within the temperature range 433–479 K were calculated by the molecular statistical method. The parameters of the atom-atom potential function of intermolecular interaction between the nitrogen atom in aniline and isomeric phenylenediamines and the carbon atom of the basal face of graphite were determined. It was shown that an intramolecular H bond influenced the geometry and adsorption properties of o-phenylenediamine.

Simultaneous determination of phenylenediamine isomers and dihydroxybenzene isomers in hair dyes by capillary zone electrophoresis coupled with amperometric detection

The simultaneous determination of three isomers of phenylenediamines (o, m, and p-phenylenediamine) and two isomers of dihydroxybenzenes (catechol and resorcinol) in hair dyes was performed by capillary zone electrophoresis coupled with amperometric detection (CZE-AD). The effects of working electrode potential, pH and concentration of running buffer, separation voltage, and injection time on CZE-AD were investigated. Under the optimum conditions the five analytes could be perfectly separated in 0.30mol L(-1) borate-0.40mol L(-1) phosphate buffer (pH 5.8) within 15min. A 300μm diameter platinum electrode had good responses at +0.85V (versus SCE) for the five analytes. Their linear ranges were from 1.0 × 10(-6) to 1.0 × 10(-4)mol L(-1) and the detection limits were as low as 10(-7)mol L(-1) (S/N = 3). This working electrode was successfully used to analyze eight kinds of hair dye sample with recoveries in the range 91.0-108.0% and RSDs less than 5.0%. These results demonstrated that capillary zone electrophoresis coupled with electrochemical detection using a platinum working electrode as detector was convenient, highly sensitive, highly repeatable and could be used in the rapid determination of practical samples.

Characterization of permselective coatings electrosynthesized on Pt–Ir from the three phenylenediamine isomers for biosensor applications

The permeability of polymers, electrosynthesized at neutral pH on Pt–Ir cylinders from each of the three isomers of phenylenediamine ( oPD, mPD and pPD), to H 2O 2 (signal transduction molecule in many oxidase-based biosensors) and ascorbic acid (AA, archetypal interference species in biological applications of biosensors) was measured, and used to determine the permselectivity of the three polymers. P mPD was the coating with the greatest permselectivity for H 2O 2 over AA, for low concentrations of AA. For AA levels greater than 200 μM, however, poly- ortho-phenylenediamine (P oPD) was superior. Furthermore, stability studies indicated that the permselectivity of P mPD degraded rapidly, even after 1 day, supporting the choice of P oPD as the permselective membrane for biosensor implantation where AA levels are high, such as in brain monitoring. A variety of techniques were used to gain further insight into the PPD layers, specifically electrochemical quartz crystal microbalance, mass spectrometry and scanning electron microscopy. Together these studies indicate that P mPD forms the thickest layer (∼15 nm) and is the least soluble of the polymers, that the P oPD layer is ∼4 nm thick and may consist mostly of tetramers, while P pPD is the thinnest (∼3 nm) and appears to consist of trimers.

Ultraviolet stimulation of hydrogen peroxide production using aminoindazole, diaminopyridine, and phenylenediamine solid polymer complexes of Zn(II)

Hydrogen peroxide (H 2O 2) is a valuable chemical commodity whose production relies on expensive and energy intensive methods. If an efficient, sustainable, and inexpensive solar-mediated production method could be developed from the reaction between dioxygen and water then the use of H 2O 2 as a fuel may be possible and gain acceptance. When concentrated at greater than 10 M, H 2O 2 possesses a high specific energy, is environmentally clean, and is easily stored. However, the current method of manufacturing H 2O 2 via the anthraquinone process is environmentally unfriendly making the unexplored nature of its photochemical production at high concentration from solar irradiation of interest. Towards this end, we studied the concentration and quantum yield of hydrogen peroxide produced in an ultraviolet (UV-B) irradiated environment using solid, Zn(II)-centered, complexes of amino-substituted isomers of indazole, pyridine, and phenylenediamine to catalyze the reaction. Aqueous suspensions in contact with air were exposed to 280–360-nm light from a low-power lamp. Of the ten complexes studied, Zn-5-aminoindazole had the greatest first-day production of 63 mM/day with a 37% quantum yield and p-phenylenediamine (PPAM) showed the greatest long-term stability. Isomeric forms of the catalysts’ organic components (e.g., amino groups) affected H 2O 2 production. For example, irradiation of diaminopyridine isomers indicated 2,3-diamino and 3,4-diamino structures were the most productive, each generating 32 mM/day H 2O 2, whereas the 2,5-diamino isomer generated no H 2O 2. A significant decrease in H 2O 2 production with time was observed for all but PPAM, suggesting the possibility of a catalyst-poisoning mechanism. We propose a reaction mechanism for H 2O 2 production based on the stability of the resonance structures of the different isomers.

Cationic double-chained surfactant as pseudostationary phase in micellar electrokinetic capillary chromatography for drug separations

The cationic double-chained surfactant didodecyldimethylammonium bromide (DDAB) was used as pseudostationary phase (PSP) in micellar electrokinetic capillary chromatography (MEKC). Its performance on the three kinds of drugs, i.e., basic, acidic, and neutral drugs, was systematically investigated. Nicotine, cotinine, caffeine, lidocaine, and procaine were selected as the model basic drugs. Good baseline separation and high efficiency were obtained under the optimal separation condition that consisted of 50 mM phosphate (pH 4.0) and 0.08 mM DDAB. Three basic phenylenediamine isomers can also be well separated with DDAB in buffer. In addition, DDAB can form cationic bilayer on the capillary wall, thus the wall adsorption of basic analytes was greatly suppressed. Compared with commonly used CTAB, the separation of basic drugs was significantly improved with a much lower amount of DDAB present in the buffer. The DDAB-involved MEKC also showed superiority to CTAB upon the separation of acidic drugs, amoxicillin and ampicillin. In the case of neutral compounds, a good separation of resorcinol, 1-naphthol and 2-naphthol was achieved with 0.1 mM DDAB and 30% (v/v) acetonitrile (ACN) present in buffer. Hence, it was concluded that the double-chained cationic surfactant DDAB can be a good substitute for traditional single-chained surfactant CTAB in MEKC.

Permeability and permselectivity of polyphenylenediamine films synthesized at a palladium disk electrode

Three phenylenediamine isomers (including ortho-, meta- and para-derivatives) were electrochemically polymerized on palladium disk electrodes. The permeability and permselectivity of polyphenylenediamine films for hydrogen peroxide, ascorbic acid, uric acid, acetaminophen, and cysteine were compared. The resulting polyphenylenediamine electrodes showed rapid electrochemical responses to hydrogen peroxide and good anti-fouling ability to possible interferences. Experimental results provide useful information for the fabrication of membrane-based enzyme electrodes.

The effect of isomers of some organic compounds as inhibitors for the corrosion of carbon steel in sulfuric acid

PurposeTo study the effects of isomers of organic compounds such as phenylenediamine, toluidine and nitroaniline as inhibitors for the corrosion of carbon steel in sulfuric acid.Design/methodology/approachStandard methods have been adopted in this study such as weight loss, polarization tests, impedance measurements and hydrogen permeation studies to find out the corrosion behavior of carbon steel in sulfuric acid with and without inhibitors.FindingsAll the selected isomers inhibited the corrosion. The best performance was found in ortho‐phenylenediamine when compared with other inhibitors under study.Originality/valueIt clearly shows the effect of isomers of phenylenediamine, toluidine and nitroaniline. The method of study may be applicable to find out the performance of other isomers of organic compounds. As these isomers behave as good inhibitors in sulfuric acid, these may be tried as inhibitors in other acids. Hence, this study is useful to academics and researchers in the field of corrosion science and engineering.

Electrochemical Amination: Efficiency of a Radical Substitution

Electrochemical amination of benzene in sulfuric acid electrolytes is studied and experimental conditions for highly efficient synthesis of primary aromatic amino compounds are determined. In the electrolysis of Ti(IV)–NH2OH–C6H6 in 11 M H2SO4 solutions containing acetic acid or acetonitrile as organic solvents, aniline and isomeric phenylenediamines are obtained with the total yields by hydroxylamine of 95.6 and 99.6%, respectively. A monoamino compound is the main product of radical substitution in acidic organo-aqueous media. It is found that the use of acetonitrile in electrochemical process is limited to certain sulfuric acid concentrations and temperatures.

Guest Selectivity in Complexation of β-Chitin

Guest selectivity in complexation of β-chitin with small molecules was studied. Since amines are strong agents for β-chitin complexation, selectivity for various amines was studied first. Of three isomers of phenylenediamine, the para isomer formed a complex, while ortho and meta isomers did not. The selectivity for linear aliphatic amines was examined for equimolar mixtures of various combinations, i.e., primary−secondary−tertiary amines of C6 main chain; C5 diamine and C6 monoamine; and C6 monoamine and C8 monoamine. The results showed a clear selectivity for primary amine over secondary and tertiary, diamine over monoamine, and longer alkyl chain over a shorter one. On the basis of such selectivity, complexation by guest incorporation from solution was established. This procedure allowed β-chitin complexation with high melting point compounds, to which pure liquid treatment was not applicable. By the solution treatment, complexes with acrylamide, p-aminobenzoic acid, and d-glucose were successfully prepared. In this method, even low-solubility combinations such as acrylamide/benzene (0.3% (w/w)) were found effective, presumably because of high chemical potential of solutes in the solution. The wide variety of guest species thus attained is expected to be useful in applications such as drug delivery or composite material preparation.

Reductive desorption of 11-mercaptoundecanoic acid monolayers modified by covalent attachment of 1,3- and 1,4-phenylenediamine

1,3- and 1,4-phenylenediamine were covalently attached to a self-assembled monolayer of 11-mercaptoundecanoic acid by formation of an amide bond. Bonding of the phenylenediamine isomers was confirmed by the presence of infrared features attributable to ring vibrational modes, the amide I vibration, and the amide II vibration in the reflection–absorption infrared spectrum of the modified interface. Reductive desorption peak potentials were shifted by 120 mV for the monolayer modified by 1,4-phenylenediamine and by 90 mV for the monolayer modified by 1,3-phenylenediamine relative to the desorption potential of the unmodified 11-mercaptoundecanoic acid monolayer. These potential shifts represent 23 and 17 kJ/mol stabilization of the monolayers modified by 1,4- and 1,3-phenylenediamine, respectively. Some of the additional stabilization energy is attributed to lateral hydrogen bonding between the amide groups and unreacted carboxylic acid groups in the monolayer. The difference between the stabilization energies for the interfaces modified with the different phenylenediamine isomers is attributed to structural differences between the isomeric monolayers influencing the molecular packing of the modified interface.