O-phenylenediamine In Presence Research Articles

Electropolymerized InZnSe@PtAg quantum dots@molecularly imprinted polymer on screen-printed carbon electrodes for the ultrasensitive detection of NS1 dengue virus protein with smartphone-based sensing in saliva

According to the World Health Organization (WHO), an estimated 100–400 million cases of dengue virus (DENV) infections are recorded annually with half of the global population being at risk of infection. Currently, there is no known treatment for DENV; however, early, rapid and accurate (sensitive and selective) detection can help to alleviate fatality rates. This work reports on the novel development of a point-of-care electrochemical biosensor for DENV using nanostructured InZnSe@PtAg quantum dots (QDs)-molecularly imprinted polymer (MIP) with smartphone-based detection functionality. Highly conductive InZnSe@PtAg QDs were newly synthesized in the presence of metal precursors, organic surfactants and ligands and surface capped with glutathione (GSH) using a ligand exchange reaction. PtAg was used as an electroactive shell layer on the InZnSe QDs core surface to increase the QDs conductivity. The GSH-InZnSe@PtAg QDs were drop-casted onto screen-printed carbon electrodes (SPCEs) and electropolymerized using cyclic voltammetry (CV) in the presence of o-phenylenediamine and the template DENV. The robust electropolymerization process allowed the overcoating of the MIP layer on the QDs/SPCE, where specific DENV size and shape cavities were created. Under optimal experimental conditions, DENV was rapidly, selectively and ultra-sensitively detected. Using differential pulse voltammetry (DPV), quantitative rebinding of DENV on the MIP@QDs/SPCE surface led to a steady decrease of the anodic peak current and a limit of detection of 1.36 pg/mL was obtained for DENV detection. Using a hand-held smartphone-based potentiostat, DENV was successfully detected in human saliva with satisfactory analytic recoveries.

Optimization of the tandem enzyme activity of V-MOF and its derivatives for highly sensitive nonenzymatic detection of cholesterol in living cells

It remains a great challenge to properly design and synthesize single-component artificial tandem enzymes for specific substrates with high selectivity. Herein, V-MOF is synthesized by solvothermal method and its derivatives are constructed via pyrolyzing V-MOF in nitrogen atmosphere at different temperatures, which are denoted as V-MOF-y (y = 300, 400, 500, 700 and 800). V-MOF and V-MOF-y possess tandem enzyme-like activity, i.e. cholesterol oxidase-like and peroxidase-like activity. Among them, V-MOF-700 shows the strongest tandem enzyme activity for V-N bonds. Based on the cascade enzyme activity of V-MOF-700, the nonenzymatic detection platform for cholesterol by fluorescent assay can be established in the presence of o-phenylenediamine (OPD) for the first time. The detection mechanism is that V-MOF-700 catalyzes cholesterol to generate hydrogen peroxide and further form hydroxyl radical (•OH), which can oxidize OPD to obtain oxidized OPD (oxOPD) with yellow fluorescence. The linear detection of cholesterol ranges of 2–70 μM and 70–160 μM with a lower detection limit of 0.38 μM (S/N = 3) are obtained. This method is used to detect cholesterol in human serum successfully. Especially, it can be applied to the rough quantification of membrane cholesterol in living tumor cells, indicating that it has the potential for clinical application.

Hybridization-driven fluorometric platform based on metal-organic frameworks for the identification of the highly homologous viruses

A novel fluorometric strategy for the simultaneous identification of SARS-CoV-2 and SARS-CoV was successfully established based on a hybridization-induced signal on–off-on mechanism. Here, one part of the probe (P1) of SARS-CoV-2 (P = P1/P2) is partially related to SARS-CoV, while the other part (P2) is completely irrelevant to SARS-CoV. They as smart gatekeepers were anchored on NH2-MIL-88(Fe) (MOF@P1/P2) to turn off its catalytic performance. Only the specific SARS-CoV-2 genetic target can strongly restore the peroxidase-like activity of MOF@P1/P2. In the presence of o-phenylenediamine, SARS-CoV-2 can be efficiently detected with high sensitivity, accuracy, and reliability. This strategy demonstrated excellent analytical characteristics with a linear range (10-9 M ∼ 10-6 M) under the limit of detection of 0.11 nM not only in buffer but also in 10 % serum, which partly shows its practicability. Most importantly, with the help of the auxiliary test of MOF@P1 and MOF@P2, SARS-CoV-2 and SARS-CoV can be efficiently quantified and distinguished. This novel strategy has provided a breakthrough in the development of such identification. In the whole process, only a simple one-step experiment was involved. This circumvents the trouble of pretreatment experiments in traditional methods, including complex enzymatic mixtures, specialized experimental equipment, many primers optimization as well as reverse transcriptase. Additionally, this novel strategy is rapid, low-cost, and easy-to-use tools.

Facile, One Pot Synthesis of Indoloquinoxaline and its Derivatives Using Aqueous Orange Peel Extract at Room Temperature

A current report expresses that Orange Peel Extract use as catalyticmedium for the synthesis of Indoloquinoxaline derivatives from commercially available starting materials. Isatin and O-phenylenediamine in presence of fresh orange peel extractresulted into desired product at room temperature in a given reaction condition. Advantages of this method include greener and cleaner conditions, shorter reaction time, and good to moderate yield of products. A simple one-pot procedure has been developed for the synthesis of Indoloquinoxaline derivatives from readily available starting materials.

Benzothiazines as Major Intermediates in Enzymatic Browning Reactions of Catechin and Cysteine.

The course of melanin formation is yet not thoroughly resolved on a mechanistic level. With the present study, incubations of catechin (CA)- and cysteine-derived dihydro-1,4-benzothiazine carboxylic acid derivatives were investigated for colored products during enzymatic browning. Analyses by high-performance liquid chromatography (HPLC)-mass spectrometry revealed the formation of two novel decarboxylated dihydro-1,4-benzothiazine derivatives [8-(3,5,7-trihydroxy-3,4-dihydro-2H-chromen-2-yl)-5-hydroxy-3,4-dihydro-2H-benzothiazine and 7-(3,5,7-trihydroxy-3,4-dihydro-2H-chromen-2-yl)-5-hydroxy-3,4-dihydro-2H-benzothiazine] preferentially under acidic conditions. Furthermore, in model reactions under neutral pH, a colored phenazine dimer intermediate was isolated by high-performance countercurrent chromatography and preparative HPLC when conducting the incubations in the presence of o-phenylenediamine (OPD). Mass spectrometry and nuclear magnetic resonance spectroscopy unequivocally verified the structure as (12E)-5,5'-dioxo-11a,11a'-bis(3,5,7-trihydroxy-3,4-dihydro-2H-chromen-2-yl)-3,3',4,4',5a,5a',6,6',11,11',11a,11a'-dodecahydro-2H,2'H,5H,5'H-12,12'-bi[1,4]thiazino[2,3-b]phenazine-3,3'-dicarboxylic acid. Enzymatically catalyzed incubations under aeration starting from the initial CA-cysteine adducts and their follow-up dihydro-1,4-benzothiazine carboxylic acids, respectively, proved that the unstable colored compound was a trichochrome-like reaction intermediate of the browning reaction cascade which can be trapped by postincubation with OPD, thus verifying their direct mechanistic relationship.

Universal Nanoplatform for Formaldehyde Detection Based on the Oxidase-Mimicking Activity of MnO2 Nanosheets and the In Situ Catalysis-Produced Fluorescence Species.

Formaldehyde (HCHO) pollution is a scientific problem of general concern and has aroused wide attention. In this work, a fluorometric method for sensitive detection of formaldehyde was developed based on the oxidase-mimicking activity of MnO2 nanosheets in the presence of o-phenylenediamine (OPD). The MnO2 nanosheets were prepared by the bottom-up approach using manganese salt as the precursor, followed by the exfoliation with bovine serum albumin. The as-prepared MnO2 nanosheets displayed excellent oxidase-mimicking activity, and can be used as the nanoplatform for sensing in fluorometric analysis. OPD was used as a typical substrate because MnO2 nanosheets can catalyze the oxidation of OPD to generate yellow 2,3-diaminophenazine (DAP), which can emit bright yellow fluorescence at the wavelength of 560 nm. While in the presence of formaldehyde, the fluorescence was greatly quenched because formaldehyde can react with OPD to form Schiff bases that decreased the oxidation reaction of OPD to DAP. The main mechanism and the selectivity of the platform were studied. As a result, formaldehyde can be sensitively detected in a wide linear range of 0.8-100 μM with the detection limit as low as 6.2 × 10-8 M. The platform can be used for the detection of formaldehyde in air, beer, and various food samples with good performance. This work not only expands the application of MnO2 nanosheets in fluorescence sensing, but also provides a sensitive and selective method for the detection of formaldehyde in various samples via a new mechanism.

Copper sulfide nanoclusters with multi-enzyme-like activities and its application in acid phosphatase sensing based on enzymatic cascade reaction

Nanozymes are artificial enzymes, which can substitute natural enzymes for wide range of catalysis-based applications. However, it is challenging to explore novel mimic enzymes or multi-enzyme mimics. Herein we report the facile preparation of uniform CuS nanoclusters (NCs), which possessed outstanding tetra-enzyme mimetic catalytic activities, including peroxidase (POD)-mimics, catalase (CAT)-mimics, ascorbic acid oxidase (AAO)-mimics and superoxide dismutase (SOD)-mimics. The catalytic mechanism of POD-like was coming from the oxygen vacancies of CuS. Furthermore, the steady-state kinetics of POD-, CAT- and AAO mimics of CuS NCs were systematically explored. On basis of the enzymatic cascade reaction that acid phosphatase (ACP) involved in a weak acidic environment, in the presence of O-phenylenediamine, quinoxaline fluorescent substance will be generated. Thus, a fluorescent biosensor platform was proposed for detection of ACP with the linear range of 0.05–25 U L−1 and limit of detection of 0.01 U L−1. The as-proposed method was applicable to real serum sample detection accurately and reproducibly. Considering the simple preparation, good stability, excellent multi-enzyme activities and controllable experimental operation, CuS NCs would provide a basis for expanding to other biocatalytic and biomedical applications.

Charge transfer complexes of lanthanide 3,5-dinitrobenzoates and 1,2-phenylenediamine

Crystallization of lanthanide 3,5-dinitrobenzoates from MeCN-DMSO media in the presence of o-phenylenediamine (PDA) brings about the complexes of two types, the binuclear complexes built of the single molecules [Ln2(O2CC6H3(NO2)2)6(PDA)2(DMSO)2] and the supramolecular polymers [Ln2(O2CC6H3(NO2)2)6DMSO4]·PDA·4MeCN. In both types of complexes, charge transfer (CT) between PDA molecules and 3,5-dinitrobenzoate fragments takes place; in the first case it is intramolecular, in the second case the binuclear fragments are united into supramolecular chains due to CT effect. Compounds of different types are often formed simultaneously; the complexes of the first type were isolated in pure form and studied for Gd, Tb, and Ho, while the complexes of the second type were obtained for Dy and Er. The charge transfer in the complexes was characterized by reflectance spectra; according to EPR study, it is too weak to make any paramagnetic contribution.

A novel signal amplification strategy based on the use of copper nanoclusters for ratiometric fluorimetric determination of o-phenylenediamine.

Copper nanoclusters (CuNCs) were synthesized starting from glutathione and copper(II) nitrate. They show blue fluorescence peaking at 432nm when excited at 334nm. In the presence of o-phenylenediamine (OPD), the blue fluorescence is decreased, but a yellow fluorescence appears with a peak at 557nm. UV-visible absorptiometry, fluorometry and fluorescence lifetime measurements were used to show that OPD is oxidized by the small fraction of copper(II) ions present in the CuNCs to form the oxidized form of o-phenylenediamine (oxOPD) which displays weak yellow fluorescence, while the blue fluorescence decreases. The ratio of fluorescences at 557 and 432nm increases linearly in the 0.15 to 110μg·L-1 OPD concentration range, and the detection limit is 93ng·L-1. Compared to the method based on the use of dissolved Cu(II), the employment of CuNCs reduces the detection limit by a factor of 40. The method was applied to the determination of OPD in spiked environmental water and industrial wastewater samples. Recoveries ranged from 96.8 to 100.3%. Graphical abstract Schematic presentation of a ratiometric fluorometric method for detection of o-phenylenediamine (OPD) based on copper nanoclusters (CuNCs). OPD is oxidized by Cu2+ present in CuNCs to form theoxidized form of o-phenylenediamine (oxOPD). FRET occurred between oxOPD and CuNCs, and the F557/F432 value is amplified.

Purified nitrogen-doped reduced graphene oxide hydrogels for high-performance supercapacitors

To further improve the capacitive performances of reduced graphene oxide-based materials is still crucial although N-doped reduced graphene oxide hydrogels (NrGOHs) exhibit fairly good performance. Here the purified NrGOHs (NrGOHs-SA) are obtained by treating the NrGOHs which are hydrothermally synthesized in the presence of o-phenylenediamine (oPDA) with concentrated sulfuric acid. The effect of preparation conditions on the hydrogels' electrochemical behavior has been systematically investigated. The results reveal that the capacitive performances of NrGOHs-SA are remarkably enhanced compared with the samples of NrGOHs. The optimal NrGOH-SA shows specific capacitance about 519.8Fg−1 at low scan rate, and excellent rate capability. The cells assembled by the optimal hydrogels exhibit the maximum energy density of 11.1Whkg−1 and power density of 14.1kWkg−1, and can retain 93.3% of its initial capacitance after 15,000cycles. This method can be developed to prepare high-performance NrGOHs materials for energy storage applications.

Hydrogen storage in hybrid of layered double hydroxides/reduced graphene oxide using spillover mechanism

New efficient hydrogen storage hybrids were fabricated based on hydrogen spillover mechanism, including chemisorptions and dissociation of H2 on the surface of LDH (layered double hydroxides) and diffusion of H to rGO (reduced graphene oxide). The structures and compositions of all of the hybrids (LDHs/rGO) have been verified using different methods including transmission electron microscopy, X ray diffraction spectroscopy, infrared spectroscopy and Brunauer–Emmett–Teller analysis. Then, the abilities of the LDHs/rGOs, as hydrogen spillover, were investigated by electrochemical methods. In addition, the LDHs/rGOs were decorated with palladium, using redox replacement process, and their hydrogen spillover properties were studied. The results showed that the hydrogen adsorption/desorption kinetics, hydrogen storage capacities and stabilities of Pd#LDH/rGOs are better than Pd/rGO. Finally presence of different polymers (synthesis with monomers, 4–aminophenol, 4–aminothiophenol, o-phenylenediamine and p-phenylenediamine) at the surface of the Pd#LDH/rGOs on hydrogen storage were studied. The results showed that presence of o-phenylenediamine and p-phenylenediamine improves the kinetics of the hydrogen adsorption/desorption and increase the capacity of the hydrogen storage.

Flow method based on cloud point extraction for fluorometric determination of epinephrine in human urine

A novel stepwise injection fluorometric method for the determination of epinephrine in human urine has been developed. In the current study, the stepwise injection analysis (SWIA) was successfully combined with on-line in-syringe cloud point extraction (CPE) and fluorometric detection. The procedure was based on the epinephrine derivatization in the presence of o-phenylenediamine followed by the preconcentration stage based on the CPE with the nonionic surfactant Triton X-114. After the phase separation into a syringe of the flow system, the micellar phase containing the epinephrine derivative was transported to a fluorometric detector. The excitation and emission wavelengths were set at 447 nm and 550 nm, respectively. The conditions of epinephrine derivatization and CPE have been studied. The calibration plot constructed using the developed procedure was linear in the range of 1·10−11–5·10−7 mol L−1. The limit of detection, calculated as 3 σ of a blank test (n = 10), was found to be 3·10−12 mol L−1. The proposed method was successfully applied for the determination of epinephrine in human urine samples.

Synthesis, characterization, structure and catalytic activity of (NNN) tridentate azo-imine nickel(II), palladium(II) and platinum(II) complexes

The newly designed tridentate ligand, 2,2′-(bisdiamino)azobenzene, H2L, 1 derived from the oxidative coupling of o-phenylenediamine in presence of NaOH base, upon reaction with Ni(II), Pd(II) and Pt(II) separately in methanol yielded [(HL)Ni(PPh3)]ClO4, 2, [(HL)Pd(PPh3)]ClO4, 3 and [(L)Pt(PPh3)], 4 which were characterized by spectral data and authenticated by single crystal X-ray diffraction of 1–4. The diffraction analysis revealed that the ligand binds the metals (Ni(II), Pd(II)) in monoanionic and Pt(II) in dianionic tridentate (N,N,N) fashion offering distorted square planar geometry where fourth position is occupied by one PPh3 group. One ClO4− ion satisfies the charge of the former aggregate [(HL)Ni(PPh3)]+ and [(HL)Pd(PPh3)]+. Suzuki and Heck coupling reactions were carried out, in presence of air and moisture, using [(HL)Pd(PPh3)]ClO4, 3 as catalysts for a variety of substrates.

A new simple and reliable Hg2+ detection system based on anti-aggregation of unmodified gold nanoparticles in the presence of O-phenylenediamine

A simple and reliable colorimetric detection system based on anti-aggregation of gold nanoparticles (AuNPs) is proposed for rapid detection of Hg2+ with high selectivity and sensitivity. O-phenylenediamine (OPD) can cause the aggregation of AuNPs due to formation of the strong covalent NHAu bond, and then induce color change of the AuNPs solution from red to blue. However, in the presence of Hg2+, OPD prefers to combine with Hg2+ rather than AuNPs resulting in inhibition of the color change. Based on the anti-aggregation mechanism, Hg2+ can be detected by observing the color change of AuNPs solution containing OPD. After optimization, the selectivity of this Hg2+ detection system by the naked eyes and UV–vis spectra is excellent comparing with other ions. The limit of the detection (LOD) is 0.1μM by the naked eyes and 5.0nM by UV–vis spectroscopy, which is lower than the mercury toxic level (10nM) defined by US Environmental Protection Agency. It's a good linear relationship between A520/A680 and Hg2+ concentration from 0.01μM to 2.0μM, which is used for the quantitative assay of Hg2+. The applicability of our detection system is also verified by analysis of Hg2+ in tap water and lake water.

In-Situ Preparation of Binary-Phase Silver Nanoparticles at a High Ag+ Concentration

Stable and monodisperse silver nanoparticles (NPs) have been synthesized using high metal salt concentration (up to 0.735 M) through a simple but novel technique. It is based on one-step procedure that uses glycerol for reducing Ag+ in the presence of o-phenylenediamine (o-PDA) resulting the nanoparticles are in two forms (one water-soluble, the other a precipitated). The water-soluble phase contains NPs that have a bimodal size distribution (2-3 and 5-6 nm); the other comprises precipitated NPs, having a unimodal size distribution (2-3 nm). The water-soluble NPs are covalently bonded to the aromatic amine molecules to form isolated units, while the precipitated nanoparticles are embedded in the networks formed by cross-linking between COOH groups of hydroxypyruvic acid (oxidized form of glycerol) and NH2 groups of o-PDA molecules. We used transmission electron microscopy (TEM), UV-Vis spectroscopy, X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS) to characterize the silver products obtained.

Studies on electrochemical copolymerization of aniline with o-phenylenediamine and degradation of the resultant copolymers via electrochemical quartz crystal microbalance and scanning electrochemical microscope

Electropolymerization of aniline in sulfuric acid solution in the presence of o-phenylenediamine ( oPD) of various concentrations was investigated via the electrochemical quartz crystal microbalance (EQCM) technique. It was found that the polymerization occurred more favorably at high aniline-to- oPD molar ratios ( F 1, 20 or above). The stabilities of the resultant copolymers against degradation were efficiently improved compared with that of polyaniline (PANI). The first-order kinetic constants for polymer degradation were estimated to be 2.07 × 10 −3 s −1 for polyaniline, and 3.91 × 10 −4 and 1.28 × 10 −4 s −1 for copolymers with F 1 values of 50 and 20, respectively. The degradation product, benzoquinone, was also detected at the tip electrode of a scanning electrochemical microscope (SECM).

O‐Phenylenediamine as a New Catalyst in the Highly Regioselective Conversion of Epoxides to Halohydrins with Elemental Halogens.

AbstractFor Abstract see ChemInform Abstract in Full Text.

O-Phenylenediamine as a New Catalyst in the Highly Regioselective Conversion of Epoxides to Halohydrins with Elemental Halogens

The regioselective ring opening of epoxides using elemental iodine and bromine in the presence of o-phenylenediamine as a new catalyst affords vicinal iodo alcohols and bromo alcohols in high yields. The major advantages of this method are versatility, high regioselectivity, a cheap and commercially available catalyst, mild and neutral reaction conditions, and short reaction times. Fourier transform Raman spectroscopy was used to study the reaction of iodine with o-phenylenediamine. The results indicate that the complex [(Diamine)I]+·I5− is formed, and we suggest that the major nucleophile is the pentaiodide ion. This bulky nucleophile has a fundamental role in the high regioselectivity observed attacking the less sterically hindered epoxide carbon.

Reductones participate in redox reactions during amine-catalyzed sugar degradation

The term Maillard reaction stands as a synonym for the complicated reaction pathways of reducing sugars with amines [1]. Within this context, redox reactions represent a relatively new and by far an unclarified aspect. α-Oxoenediol and α-oxoeneaminol structures are potential reaction partners with major influence on the final product spectrum. Only recently, we succeeded in synthesizing 1-deoxyglucosone (1-DG) as a major representative of these so-called reductones [2]. 1-DG formation during the degradation of hexoses is explained via enolization of the Amadori product and cleavage of the amine. If, alternatively, the hydroxy function at C-4 is eliminated, 1-amino-1,4-dideoxyglucosone (1-A-1,4-DG) will be formed.1-DG is reduced during the Strecker degradation of amino acids to result in 1-deoxyfructose/1-deoxypsicose (1-DF). These sugars are then degraded via enolization and dehydration to 1,4-dideoxyglucosone (1,4-DG). Alternatively, the formation of 1,4-DG can also be explained by an intermolecular redox reaction of two molecules of 1-DG to give 1-DF, degrading to 1,4-DG, and a tricarbonyl compound. After synthesis of all participating structures, monitoring of incubations of glucose, 1-DG, and 1-DF with various amines lead to confirmation of the proposed reaction pathways.1-A-1,4-DG is of special interest, as it still incorporates the amine in contrast to most other reactive Maillard intermediates so far elucidated. Second, as an aminoreductone, 1-A-1,4-DG boasts a highly electron-rich moiety and therefore has to be judged as extremely reactive. In spite of this potential importance, so far only very limited information has been published, based exclusively on sugar–alkylamine reaction systems [3]. To gain further insight into the importance of 1-A-1,4-DG, we synthesized the quinoxaline–lysine derivative in a 6-step procedure as an authentic reference material. The structure was unequivocally identified and quantitated in incubations of Nα-t-BOC-lysine with glucose and maltose, and during the degradation of the respective Amadori products in presence of o-phenylenediamine. In addition, for the first time the formation of protein-bound 1-A-1,4-DG was monitored after enzymatic hydrolysis. Above formation pathway suggests the parallel synthesis of both 1-DG and 1-A-1,4-DG. However, our results show that the ratio of both structures is highly dependent on the quality of respective substituents at C-1 and C-4 as leaving groups. In glucose incubations at 50 °C, only trace amounts of 1-A-1,4-DG were formed. In contrast, maltose reaction mixtures lead to formation of significant quantities [4].

Isolation and characterization of Glyoxal–Arginine modifications

Glyoxal is generated in foods and in vivo by autoxidation of unsaturated fatty acids and by the Maillard reaction of reducing sugars and amines. Due to its high reactivity, the α-dicarbonyl easily reacts with protein-bound lysine and arginine residues. The quantitatively most important modification of the ε-amino group of lysine is Nε-carboxymethyllysine [1]. Reaction with glyoxal also leads to cross-linking of proteins by formation of amides (glyoxal–amide cross-link [2]), imidazole (MODIC [3]) and imidazolium structures (GOLD [4]).Concerning the reaction of glyoxal with the guanidino group of arginine, inconsistent results have been published in the literature. We could now verify 1-(4-amino-4-carboxybutyl)-2-imino-4,5-dihydroxy-4,5-dihydroimidazolidine (dihydroxyimidazolidine) as the single primary product in incubations of Nα-t-BOC-arginine with glyoxal under physiological conditions [5]. The structure was identified as a cis/trans-isomer mixture of ca. 1:4. In a much slower reaction, dihydroxyimidazolidine is degraded to N7-carboxymethylarginine (CMA), representing a novel stable endproduct. Both structures were unequivocally established by 1H-, 13C-, HMBC-NMR and high-resolution mass spectra. Other structures could not be found under these reaction conditions. Synthesis of 1-(4-amino-4-carboxybutyl)-2-imino-5-oxo-imidazolidine (imidazolinone), which has been published earlier as the only modification so far , could not be verified [6]. However, both arginine modifications, dihydroxyimidazolidine and CMA can be transformed to the imidazolinone under acid conditions. Therefore, the detection of the imidazolinone in incubations under physiological conditions must be evaluated as an artifact of the acid sample workup procedures applied.The mechanistic relationship of all three structures was clarified in incubations at various temperatures, pH values and in the presence of o-phenylenediamine and aminoguanidine. The latter experiment using α-dicarbonyl trapping reagents proved that the reaction to the dihydroxyimidazolidine can be reversed to regenerate arginine and a glyoxal derivative. As trapping reagents are commonly used to measure ‘free’ glyoxal in foods and in vivo samples, the published data has to be evaluated very critically. In addition, it was possible to elucidate the mechanism leading from the dihydroxyimidazolidine to CMA and to exclude any participation of the imidazolinone.