Ag-doping on ZnO support mediated by bio-analytes rich in ascorbic acid for photocatalytic degradation of dipyrone drug

The analytes such as ascorbic acid (AA) present in Sechium edule were extracted (294 mg AA kg^-1 fruit) in an aqueous media for its potential application for Ag-doping onto wurtzite ZnO. The bandgap of ZnO was decreased to 2.85 eV at the optimal Ag-loading of 1.18% (w/w) against 3.13 eV for the control catalyst without using the analytes and, the commercial AA only could reduce the bandgap to 2.91 eV. The saturation photo-electrochemical current density (46.68 mA cm^-2) at E_anode ≥ 0.31 V vs. Ag/AgCl was almost double than pristine ZnO under visible light illumination (λ_mean = 525 nm, 18 K lux) and, the current density was insignificant in the dark. The doped catalyst exhibited the maximum 79.5% degradation (71% COD removal) of an anti-analgesic drug, dipyrone (100 μg L^-1 dipyrone, catalyst 100 mg L^-1) resulted from the formation of O₂^•- radical (g-factor of 2.002-2.008) and paramagnetic oxygen vacancies (g-factor of 2.020) and, no effect of dye-sensitization was noted. The highest quantum yield was found to be 34.7%. The catalyst loss was 6% after the fourth cycle and the dipyrone degradation was reduced to 70.8%.

Influence of dissolution-modifying excipients in various pharmaceutical formulations on electronic tongue results

The overall performance of a potentiometric electronic tongue (ET) as well as the sensitivity and selectivity pattern of particular ion-selective electrodes forming the array towards exemplary APIs (metamizole sodium, pseudoephedrine sulphate) and excipients (hypromellose, carmellose, Eudragit E) was determined. Simultaneous sensing of both API and the encapsulating excipient in their physical mixture was noticed using potentiometric sensors. Usually, such altering of chemical image is treated as an evidence of taste masking/modified release effect (linked with chemical entrapment of API in polymer matrix), while the observed "mixture effect" can also take place which may complicate the interpretation of ET results. Moreover, the influence of the same excipients on chemical images of various APIs was compared and related to sensor array performance. The presented considerations should be taken into account in the case of ET assessment of drug dissolution profiles and detection of modified release effect, especially when novel drug delivery systems are considered.

Importance of MS selectivity and chromatographic separation in LC-MS/MS-based methods when investigating pharmaceutical metabolites in water. Dipyrone as a case of study

Pharmaceuticals are emerging contaminants of increasing concern because of their presence in the aquatic environment and potential to reach drinking-water sources. After human and/or veterinary consumption, pharmaceuticals can be excreted in unchanged form, as the parent compound, and/or as free or conjugated metabolites. Determination of most pharmaceuticals and metabolites in the environment is commonly made by liquid chromatography (LC) coupled to mass spectrometry (MS). LC coupled to tandem MS is the technique of choice nowadays in this field. The acquisition of two selected reaction monitoring (SRM) transitions together with the retention time is the most widely accepted criterion for a safe quantification and confirmation assay. However, scarce attention is normally paid to the selectivity of the selected transitions as well as to the chromatographic separation. In this work, the importance of full spectrum acquisition high-resolution MS data using a hybrid quadrupole time-of-flight analyser and/or a suitable chromatographic separation (to reduce the possibility of co-eluting interferences) is highlighted when investigating pharmaceutical metabolites that share common fragment ions. For this purpose, the analytical challenge associated to the determination of metabolites of the widely used analgesic dipyrone (also known as metamizol) in urban wastewater is discussed. Examples are given on the possibilities of reporting false positives of dypirone metabolites by LC-MS/MS under SRM mode due to a wrong assignment of identity of the compounds detected.

Investigation of the microbial degradation of phenazone-type drugs and their metabolites by natural biofilms derived from river water using liquid chromatography/tandem mass spectrometry (LC-MS/MS)

The degradation of the pharmaceuticals phenazone and metamizole, two pyrazolone-derivates in widespread use, using biofilms created by natural organisms from the national park Unteres Odertal, Germany, were investigated. An analytical method based on LC-MS/MS was optimised to determine the substances phenazone and methylaminoantipyrine (MAA), the hydrolysis product of metamizole (also known as dipyrone), as well as their metabolites 1,5-dimethyl-1,2-dehydro-3-pyrazolone (DP), acetaminoantipyrine (AAA), formylaminoantipyrine (FAA) and 4-aminoantipyrine (AA). Performance characteristics of the method were evaluated in terms of recovery, standard deviation, coefficient of variation, method detection limits (MDL) and method quantification limits (MQL). Degradation studies of phenazone and MAA were conducted using a laboratory-scale continuous flow biofilm reactor fed with different nutrient media and with variable hydraulic retention times of 24 and 32 h. MAA was degraded rapidly to FAA and AA, while phenazone was not degraded under the prevailing conditions even after 32 h. By operating the bioreactor in batch mode to study the phenazone degradation potential of the biofilm under limiting nutrient conditions, an elimination rate of 85% phenazone was observed, but because of the slow elimination rate and aerobic conditions, the metabolite DP was not detected. In additional batch experiments using bacterial isolates from the natural biofilm to decompose phenazone, some bacterial strains were able to form DP from phenazone in marginal concentrations over the sampling period of eight weeks. Obviously, the microorganisms need a reasonably long time to adapt their metabolisms to enable the removal of phenazone from water samples.

Photodegradation study of three dipyrone metabolites in various water systems: identification and toxicity of their photodegradation products

The photochemical behaviour of three relevant metabolites of the analgesic and antipyretic drug dipyrone, 4-methylaminoantipyrine (4-MAA), 4-formylaminoantipyrine (4-FAA) and 4-acetylaminoantipyrine (4-AAA), was evaluated under simulated solar irradiation (Suntest system). For 4-MAA, different aqueous solutions (synthetic seawater, freshwater and Milli-Q water) as well as different operational conditions were compared. According to the experimental results, 4-MAA resulted as being an easily degraded molecule by direct photolysis, with half-life times (t1/2) ranging from 0.12 to 0.58 h, depending on the irradiation conditions. Faster degradation was observed in synthetic waters, suggesting that the photolysis was influenced by the salt composition of the waters. However, no effect on the degradation rate was observed by the presence of natural photosensitizers (dissolved organic matter, nitrate ions). 4-FAA and 4-AAA showed slower photodegradation kinetics, with t1/2 of 24 and 28 h, respectively. A study of photoproduct identification was carried out by gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-time-of-flight mass spectrometry (LC-TOF-MS) (ESI positive mode), which allowed us to propose a tentative photodegradation pathway for 4-MAA and the identification of persistent by-products in all the cases. Finally, the application of an acute toxicity test (Daphnia magna) showed an increase in toxicity during the photolytic process, a consequence of the formation of toxic photoproducts.

[Analysis of three metabolite residues of dipyrone in bovine muscle and pork muscle using high performance liquid chromatography]

A method for the determination of metabolite residues of dipyrone, 4-formylaminoantipyrine (FAA), 4-aminoantipyrine (AA) and 4-methylaminoantipyrine (MAA) in bovine muscle and pork muscle has been developed. Homogenized muscle sample was extracted with Na2SO4-Na2SO3 solution. After filtration, the extract was cleaned-up by a C18 solid phase extraction cartridge. Prepared sample was determined using high performance liquid chromatography under the following conditions: Inertsil ODS-3 column, methanol and water as mobile phase with gradient elution, detection wavelength of 265 nm. FAA was quantified by external standard method, while AA and MAA were quantified by internal standard method using isopropylaminoantipyrine as internal standard. Limits of detection of FAA was 12.5 microg/L, while those of AA and MAA were 15.0 microg/L and 20.0 microg/L, respectively. The limit of detection of this method was 50 microg/L for all the three metabolites. The recoveries of FAA, AA and MAA were 81.3% - 92.5%, 82.0% - 96.0%, and 80.4% - 90.6%, respectively, at the spiked levels of 50 - 400 microg/kg. The relative standard deviations of the method were less than 7%.

Considerations about the theoretically expected crushing strength of tablets from binary powder mixtures: Double layer tablets versus arithmetic additivity rule

The theoretically expected breaking strength of tablets from powder mixtures is often calculated by the weighted arithmetic mean from the breaking strength of the single components, which corresponds to a linear interpolation. The validity of this additivity of fracture strength shall be evaluated by the underlying model of parallel couplings. It assumes the components linked in parallel with respect to the direction of loading during diametrical strength testing. Parallel couplings were experimentally realised by the preparation of double layer tablets from crystalline and spray-dried lactose on the one hand and from maltitol and metamizol-sodium on the other. Constant total true volumes of the single substances and of layered powders in varying ratios of true volume were compressed on an eccentric tabletting machine to constant geometric mean punch force. Simulated crushing profiles of parallel couplings were derived from force-displacement profiles measured during diametrical compression of the one-component tablets. At given finely graded deformation levels, the forces exerted by the components during loading were added in the proportion of the true volume fractions of the components in the coupling. The results from the experiments and from the simulations are in good accordance. They demonstrate that a linear change of the crushing strength in dependence on the true volume fraction of the components can only be assumed if the single components deform to the same extent up to the point of fracture. This behaviour was approximately found with the parallel lactose system. In all other cases it must be expected that the crushing strength of parallel systems will be lowered beneath the weighted arithmetic mean values or even below the crushing strength of the single components. The latter was observed with the maltitol-metamizol combinations. Thus, if tablets from binary powder mixtures exhibit a crushing strength depression, this is not necessarily an indication of weak bonding between the components or of structural defects.

Prediction of Tablet Hardness Based on Near Infrared Spectra of Raw Mixed Powders by Chemometrics

The purpose of this research is to elucidate the effect of lubricant mixing on tablet hardness by near-infrared (NIR) chemometrics as a basic study of process analytical technology. Formulation cellulose (F-C) consisted of sulpyrine (SP), microcrystalline cellulose (MC), and magnesium stearate (MgSt). Formulation lactose/starch (F-L) consisted of SP bulk drug powder, spray-dried lactose (SL), corn starch (CS), and MgSt. First, F-L and F-C without MgSt were mixed in a twin-shell mixer for 60 min. MgSt was added to the mixed powder, and was mixed for various mixing times, after which the mixed powders were compressed by 8-mm diameter punch and die. NIR spectra of raw mixed powders of F-L and F-C were taken using a reflection type of Fourier transform NIR spectra spectrometer, and chemometric analysis was performed using principal component regression (PCR). The tablet hardnesses of F-L and F-C decreased with increasing mixing time. All NIR spectra of the mixed powders of F-L and F-C fluctuated depending on mixing time. In order to predict tablet hardness before tablet compression, NIR spectra of F-L and F-C mixed powders were analyzed and evaluated for hardness by PCR. The minimum standard error of cross-validation values could be realized by using five- and six-principal component models, respectively. In the cases of F-L and F-C, the relationships between the actual and predicted tablet hardnesses showed straight lines, respectively. In the regression vectors of F-L and FC, the peaks related to hydrogen groups of SP, CS, and MC appeared as positive peaks. In contrast, the peaks related to hydrocarbon due to MgSt appeared as negative peaks in the regression vectors. The calibration models to evaluate the tablet hardness were obtained based on NIR spectra of raw mixed powders by PCR. This approach to predicting tablet hardness prior to compression could be used as a routine test to indicate the quality of the final product without spending time and energy to produce samples of questionable quality.

Characterization of the role of physicochemical factors on the hydrolysis of dipyrone

Dipyrone is a prodrug which is used mainly for its analgesic and antipyretic effects. After oral intake, dipyrone is rapidly hydrolyzed to its main metabolite, 4-methylaminoantipyrine (4-MAA), from which many other metabolites are produced by enzymatic reactions. Even though it is well known that dipyrone is a prodrug and hydrolyzed non-enzymatically, in most of the studies of dipyrone the prodrug form is tested using in vitro methodologies, which do not represent or predict the actual in vivo activity of dipyrone. In this study, we characterize the hydrolysis kinetics of dipyrone as functions of concentration, temperature, and pH using a HPLC assay. Concentration is an important factor in the hydrolysis of dipyrone. Low concentrations of dipyrone are hydrolyzed more rapidly than are solutions of higher concentrations. At a concentration of 0.1M, which is 140 times, the concentration of the marketed pharmaceutical form, dipyrone is only minimally (10%) hydrolyzed to 4-MAA at 5h. Temperature, as expected, affects the hydrolysis reaction dramatically. We tested three temperatures (4, 21, and 37 degrees C) and found that at body temperature the hydrolysis is significantly faster than at room or at refrigerator temperatures. Compared with more alkaline solutions, the hydrolysis rate of dipyrone increases dramatically in acidic solutions. At low pH (2.5) and at a 0.01 mM concentration, the hydrolysis of dipyrone is completed within almost 30 min, which is the highest rate we observed. Experiments which involve in vitro and/or local application of dipyrone should consider these physicochemical factors and interpret the results accordingly.

[Selective quantitation of analgin by flow injection chemiluminescence method]

A new chemiluminescence-based method was proposed for selective quantitation of analgin in pharmaceutical preparation. The CL emission was generated by mixing analgin, polyethylene glycol-400 and rhodamine 6G in acidic medium. The analgin content could be determined by the CL intensity. No oxidants were used in the system, so it was difficult to explain why the CL emission was produced. The mechanism of CL emission remains under investigation. One of the advantages of this method is highly selective. No other pharmaceutical compounds and chemicals could produce CL emission whether they contain sulfuric group or not in the experiment. There was no disturbance in this method, which was different from others. Another advantage is high sensitivity. The quantitation range is from 0.01 to 10 microg x mL(-1) with a detection limit of 0.003 microg x mL(-1) for analgin. This is the lowest detection limit of any CL methods currently available for analgin determination. The proposed method was applied to the selective quantitation of analgin in pharmaceutical preparation.

Multi-pumping flow system for the spectrophotometric determination of dipyrone in pharmaceutical preparations

A novel flow system for the spectrophotometric determination of dipyrone with p-dimethylaminobenzaldehyde exploiting the multi-pumping approach was developed. The proposed methodology utilises several micro-pumps for propelling the involved fluids under improved mixing conditions, introducing sample/reagent aliquots and providing commuting facilities. As a consequence the multi-pumping system presents high versatility and manifold simplicity, as well as a straightforward operational control and enhanced analytical capabilities. Linearity of the analytical curve was observed within 10 and 400 mg l(-1) dipyrone (r=0.9997; n=6), results were precise (r.s.d.<0.12%; n=20) and sampling rate was 50 h(-1). Detection limit was estimated as 1 mg l(-1) dipyrone. The method was applied to pharmaceutical preparations and the results were in agreement with those obtained by the reference procedure with relative deviations within -1.7 and +2.2%.

Hypothermic and antipyretic effects of 3-methyl- and 3-phenyl-5-hydroxy-5-trichloromethyl-4,5-dihydro-1H-pyrazole-1-carboxyamides in mice

The effect of novel pyrazolines, 3-methyl-5-hydroxy-5-trichloromethyl-4,5-dihydro-1H-pyrazole-1-carboxyamide (MPCA) and 3-phenyl-5-hydroxy-5-trichloromethyl-4,5-dihydro-1H-pyrazole-1-carboxyamide (PPCA) on body temperature and endotoxin-induced fever was investigated in mice. The subcutaneous (s.c.) administration of 1.5 mmol/kg dipyrone, MPCA or PPCA and the intracerebroventricular (i.c.v.) administration of 225 nmol dipyrone reduced basal rectal temperature. Intracerebroventricular administration of 225 nmol MPCA or PPCA did not alter basal rectal temperature. The administration of 0.15 mmol/kg (s.c.) or 25 nmol (5 microl) dipyrone (i.c.v.), MPCA or PPCA had no effect on basal rectal temperature, but reversed lipopolysaccharide-induced fever. These results suggest that MPCA and PPCA cause antipyresis, which is similar to that caused by dipyrone, and may be useful antipyretic agents.

Amperometric determination of dipyrone in pharmaceutical formulations with a flow cell containing gold electrodes from recordable compact discs

A simple, rapid, and precise amperometric method for quantification of dipyrone in pharmaceutical formulations is presented. The proposed method permits determinations in the 10(-7) mol L(-1) of the analyte and enables 90 determinations h(-1), employing only 100 microL of sample per determination. This method is based on the direct quantification of dipyrone in many pharmaceutical products, avoiding cumbersome processes such as previous separations, solvent extraction, or sample filtration. This new procedure was applied to commercial pharmaceutical tablets, and the results obtained were in excellent agreement with the ones obtained by the classical iodometric method.

Impairment of the metabolism of dipyrone in asymptomatic carriers of the hepatitis-B virus does not occur in rapid acetylators

OBJECTIVE

We previously found that, compared with healthy subjects. asymptomatic hepatitis-B virus (HBV) carriers displaying slow acetylator phenotype demonstrate a significant prolongation of the elimination half-life of 4-methylaminoantipyrine (MAA) and a decrease in the clearance of formation of 4-aminoantipyrine (AA) and 4-formylaminoantipyrine (FAA). However, the formation of 4-acetylaminoantipyrine (AAA) was unchanged. The present study was designed to examine the effect of the asymptomatic HBV carrier state on the metabolism of dipyrone. as a model drug, in rapid acetylators.

METHODS

The plasma and urine concentrations of the metabolites of dipyrone were measured in eight asymptomatic HBV carriers and eight healthy subjects who had normal liver function tests, all displaying the rapid acetylation phenotype and genotype, after the administration of a 1.0-g oral dose of dipyrone.

RESULTS

The following pharmacokinetic parameters were evaluated: peak plasma concentration, time to peak plasma concentration, elimination rate constant, area under the plasma concentration-time curve (0-->infinity), amount excreted (0-->infinity), renal and non-renal clearances for MAA and the clearances of formation for AA, FAA and AAA. No significant differences were found between the two subject groups.

CONCLUSION

The effect of hepatic viral carrier state on drug metabolism may vary according to metabolic pathways and genetic polymorphism.

Tune compounds for electrospray ionisation/in-source collision-induced dissociation with mass spectral library searching

Haloperidol, paracetamol, metronidazole and metamizole have been tested as tune compounds for electrospray ionisation in-source collision-induced dissociation MS (ESI-CID-MS) with two different mass spectrometers (Sciex API 365 and Agilent 1100 MSD SL). The different electrospray sources of API 365 and MSD 1100 SL consist of an orifice with nitrogen curtain gas and a capillary interface, respectively. In-source CID occurs in both interfaces in front of the skimmers, which separate a region with a vacuum of approximately 300 Pa and the high vacuum (<10(-3) Pa). Comparison of the breakdown curves of selected tune compounds, depending on collision energy (orifice or fragmentor voltage), showed, that very similar fragmentation can be obtained with both instruments, when adjusting the fragmentor voltage of the MSD 1100 SL to higher values than the orifice voltage of the API 365. For three energy levels--low, medium and high--the corresponding voltages were 20, 50 and 80 V for the API 365 and 110, 190, 230 V for the MSD 1100 SL. These voltages resulted in the most similar spectra for haloperidol and paracetamol with both instruments. The comparison of ESI-CID-MS of all tune compounds at three energy levels showed, that - despite variations in relative ion abundances - all significant ions were present in one of the three CID spectra. Therefore, mass spectral library searching of an ESI-CID-MS library set-up with one of the two instruments should be possible with the other instrument after adjusting the CID energies by means of at least two tune compounds such as haloperidol and paracetamol, metronidazole or metamizole.

Study of load capacity of Avicel PH-200 and Cellactose, two direct compression excipients, using experimental design

The load capacity of two excipients, a large particle size grade of microcrystalline cellulose (Avicel PH-200) and a coprocessed material composed of lactose and pulverized cellulose (Cellactose) was determined using a model mix with Dipyrone (metamizol sodium) and experiments planned by design of experiments. A multiple-regression model was proposed, and as a result, a new parameter, called specific load capacity SLC was obtained. This constant can be determined for other excipients and drugs; it depends only on the excipient and the drug used.

Study on the charge-transfer reaction between 7,7,8,8-tetracyanoquinodimethane and drugs

The charge-transfer (CT) reaction between 7,7,8,8-tetracyanoquinodimethane (TCNQ) as a pi-electron acceptor and cinnarizine, analgin, norfloxacin as electron donors have been studied by spectrophotometric method. The charge transfer complexes between TCNQ and these drugs have stable blue color, therefore a simple, rapid, accurate and sensitive method for determination of these drugs has been developed. The optimization of the experimental conditions is described. Beer's law is obeyed in the ranges 2-18, 2-18 and 4-32 microg/ml for cinnarizine, analgin and norfloxacin, respectively. The apparent molar absorptivity of CT complexes at 743 nm is 1.58x10(4), 1.71x10(4) and 8.91x10(3) l/mol per cm, respectively. The composition of all these CT complexes are found to be 1:1 by different methods. The relative SDs are less than 3% (n = 10). The proposed method has been applied to the determination of these drugs in their each pharmaceutical dosage forms with satisfactory results.

[Determination of analginum in medicine by ironic rhodanate spectrophotometry]

Analginum in preparations was determined by the ironic rhodanate fading spectrophotometric method, based on Fe3+ reduced into Fe2+ by analginum and reacting on potassium rhodanate. The obtained results were in agreement with those of the iodine titration method and the ultraviolet photometric method.

[Chromatographic determination of novamidazofen in pharmaceutical preparations]

Novamidazofen (metamizol) has been used again as antipyretic and antirheumatic also in abroad recently. In aqueous solutions, such as injections, hydrolysis takes place in its formaldehyde sulfoxylate side chain resulting in an equilibrium mixture of novamidazofen and nor-amidazofen. A high-performance liquid chromatographic method was developed to study the hydrolysis and for the selective and accurate determination of the two components. UV detection at 242 nm wavelength, where the absorbance of novamidazofen and nor-amidazofen were identical, was applied. The rate constants k1 and k3 of the opposite direction reactions as well as K = k1 k3(-1), the hydrolytic equilibrium constant were determined. In aqueous solution, at I-->0 ionic strength and 25 degrees C pK = 3.52 +/- 0.12; 10(4) k1 = 1.74 (+/- 0.25) min-1, P = 0.95. Addition of methanol to the system decreased both the rate and equilibrium constants of the hydrolysis. For the quantitation of novamidazofen Nucleosil C18 column and 20 mmol dm-3 natrium sulphate in methanol-water 40 + 60 V + V eluent were used. The calibration curve was linear in the 20 to 1000 ng range. This method is suitable also for the detection of other, mostly oxidised impurities. A thin-layer chromatographic procedure was also developed on silica GF254 applying acetone-water-ether 30 + 40 + 5 V + V + V eluent. After extraction with chloroform, the oxidised decomposition products can be detected also in injections allowed to stand for a few minutes in an open vessel. The densitometric version of the TLC method was also developed but its precision was lower than that of the HPLC.

[Determination of content of chlorpromazine hydrochloride in compound metamizole sodium microenema by acid-dye colorimetric method]

An acid-dye colormetric method was described for the determination of chlorpromazine hydrochloride in the compound preparation. The method was based on the reaction of chlorpromazine hydrochloride with methyl orange, to form a yellow complex, which then was extracted by chloroform and exhibited a maximum absorption at 424 nm. The optimal conditions for determination were selected by orthogonal design test. The linear range of this method was 20-120 micrograms/ml (r = 0.9997). The average recovery of the three sample solutions of different concentrations was 99.72% +/- 0.46% (n = 6). The other ingredients of preparation do not interfere with chlorpromazine determination. This method is more sensitive and accurate and can be used for quality control of this compound preparation.

[Effect of immobilization of analgin in polyvinyl alcohol on its mutagenicity in mice]

Mutagenicity of analgin in the tests for sperm head anomalies (SHA) and chromosome aberrations (CA) in bone marrow cells was studied in male mice Mus musculus. Analgin (40 micrograms) was injected intraperitoneally in 0.2 ml of aqueous solution or 0.01-5% solution of polyvinyl alcohol (PVA). Analgin was found to increase both SHA and CA frequencies. The drug immobilized in PVA also increased SHA and CA frequencies, though in less degree than non-immobilized one.

[Aminopyrazolone free radicals in the hydrogen peroxide oxidation reaction]

Oxidation of amidopyrine, analgin and 4-aminoantipyrine by means of H2O2 was studied in presence of peroxidase and hemoglobin. As shown by NMR, EPR and spectrophotometry the oxidation was of single electron type accompanied by free radical formation. The radicals of amidopyrine and analgin were stable, colored, participated in chemical exchange with initial molecules and disproportionated as demonstrated by stoichiometry. Radicals of 4-aminoantipyrine were unstable and dimerized to antipyrine red. Aminopyrazolone radicals were also formed after direct oxidation by Fe3+ in acidified water containing no complexes. The Fe-complexes developed shifted the equilibrium towards reduction of radicals with formation of the initial molecules. Presence of 4-amino groups was responsible for oxidation of pyrazolones under mild conditions. Alkyl derivatives of 4-amino group protons stabilized the radicals and altered their subsequent transformation form dimerization to disproportionation. Proton catalysis of aminopyrazolone oxidation occurred.