Oxidation Chemistry of 3,7-Dimethylxanthine - a Central Behavioural Stimulant at Solid Electrodes

The electrochemical oxidation of 3,7-dimethylxanthine has been studied in the pH range 2.1-10.7 at pyrolytic graphite, platinum and glassy carbon electrodes. The electrooxidation of 3,7-dimethylxanthine at solid electrodes proceeds in a single 4e, 4H+ pH dependent step to give a diimine species which decomposes in Chemical followup steps. The UV absorbing intermediate generated during electrooxidation of 3,7-dimethylxanthine decayed approximately at the same rate as that of xanthine and followed the first order kinetics. The products of electrooxidation of 3,7-dimethylxanthine were characterized and a reaction scheme is suggested to explain their formation. The effect of introducing methyl groups into the electrooxidation of xanthine is also presented

Electrochemical Reduction of 2-(2-Thiazolylazo)-p-cresol at a Pyrolytic Graphite Electrode

The electrochemical reduction of 2-(2-thiazolylazo)-p-cresol has been studied in phosphate buffers of different pH at a pyrolytic graphite electrode. The reduction of the dye occurred in a single well-defined 4e, 4H+ step and the electrode reaction was found as ECE. The reduction products were separated and characterized by m.p., 1H-NMR and mass spectra. The hydrazo intermediate was found to be unstable and undergoes further reaction, the rate of which obeys the equation rate = r° + k}j [H+] + &QH [OH-]

Voltammetric Investigations of the Reduction of Direct Orange-31 a Bisazo Dye

The electrochemical reduction of bisazo dye Direct Orange–31 has been studied at Pyrolytic graphite electrode (PGE) in the pH range 2.0–10.3. Two well-defined 4e–, 4H+ pH dependent reduction peaks (Ic & IIc ) have been observed in linear and cyclic sweep voltammetry. It has been observed that reduction of azo groups in the dye does not stop at hydrazo stage but further reduction leads to the cleavage of –NH–NH– linkage to give amino compounds as the final products. At pH 3.0 and 7.0, 4-aminosalicylic acid and 3,3\u27-dimethylbenzidine have been characterized as the major products of reduction. A tentative mechanism for the reduction has also been suggested

Comparative studies of neodymium (III)-selective PVC membrane sensors

Sensors based on two neutral ionophores, N,N�-bis((1H-pyrrol-2-yl)methylene)cyclohexane-1,2-diamine (L1) and 3,3�-(cyclohexane-1,2-diylbis(azan-1-yl-1-ylidene)bis(methan-1-yl-1-ylidene)bis(5-hydroxymethyl)pyridine-2-ol) (L2) are described for quantification of neodymium (III). Effect of various plasticizers; 2-nitrophenyloctylether (o-NPOE), dibutyl butylphosphonate (DBBP), tri-n-butyl phosphates (TBP), dioctylpthalate (DOP) and chloronapthalen (CN) and anion excluder, sodiumtetraphenylborate (NaTPB) has been studied. The membrane composition of PVC:o-NPOE:ionophore (L1):NaTPB (w/w;mg) of 150:300:5:5 exhibited best performance. The sensor with ionophore (L1) exhibits significantly enhanced selectivity towards neodymium (III) in the concentration range 5.0×10−7 to 1.0×10−2M with a detection limit of 1.0×10−7M and a Nernstian compliance (19.8±0.3mVdecade−1 of activity) within pH range 4.0–8.0. The response time of sensorwas found as 10 s. The influence of the membrane composition and possible interfering ions has also been investigated on the response properties of the electrode. The fast and stable response, good reproducibility and long-term stability of the sensor are observed. The sensor has been found to work satisfactorily in partially non-aqueous media up to 20% (v/v) content of methanol, ethanol or acetonitrile and could be used for a period of 3 months. The selectivity coeffi-cients determined by using fixed interference method (FIM) indicate high selectivity for neodymium. The proposed electrode shows fairly good discrimination of neodymium (III) from other cations. The application of prepared sensor has been demonstrated in the determination of neodymium (III) in spiked water samples

Comparative studies of praseodymium(III) selective sensors based on newly synthesized Schiff’s bases

Praseodymium ion selective polyvinyl chloride (PVC) membrane sensors, based on two new Schiff’s bases 1,3-diphenylpropane-1,3-diylidenebis(azan-1-ylidene)diphenol (M1) and N,N�-bis(pyridoxylideneiminato) ethylene (M2) have been developed and studied. The sensor having membrane composition of PVC: o-NPOE: ionophore (M1): NaTPB (w/w; mg) of 150: 300: 8: 5 showed best performances in comparison to M2 based membranes. The sensor based on (M1) exhibits the working concentration range 1.0×10−8 to 1.0×10−2M with a detection limit of 5.0×10−9M and a Nernstian slope 20.0±0.3mVdecade−1 of activity. It exhibited a quick response time as <8 s and its potential responses were pH independent across the range of 3.5–8.5.The influence of the membrane composition and possible interfering ions have also been investigated on the response properties of the electrode. The sensor has been found to work satisfactorily in partially non-aqueous media up to 15% (v/v) content of methanol, ethanol or acetonitrile and could be used for a period of 3 months. The selectivity coefficients determined by using fixed interference method (FIM) indicate high selectivity for praseodymium(III) ions over wide variety of other cations. To asses its analytical applicability the prepared sensor was successfully applied for determination of praseodymium(III) in spiked water samples

Comparative studies of praseodymium(III) selective sensors based on newly synthesized Schiff’s bases

Praseodymium ion selective polyvinyl chloride (PVC) membrane sensors, based on two new Schiff’s bases 1,3-diphenylpropane-1,3-diylidenebis(azan-1-ylidene)diphenol (M1) and N,N�-bis(pyridoxylideneiminato) ethylene (M2) have been developed and studied. The sensor having membrane composition of PVC: o-NPOE: ionophore (M1): NaTPB (w/w; mg) of 150: 300: 8: 5 showed best performances in comparison to M2 based membranes. The sensor based on (M1) exhibits the working concentration range 1.0×10−8 to 1.0×10−2M with a detection limit of 5.0×10−9M and a Nernstian slope 20.0±0.3mVdecade−1 of activity. It exhibited a quick response time as <8 s and its potential responses were pH independent across the range of 3.5–8.5.The influence of the membrane composition and possible interfering ions have also been investigated on the response properties of the electrode. The sensor has been found to work satisfactorily in partially non-aqueous media up to 15% (v/v) content of methanol, ethanol or acetonitrile and could be used for a period of 3 months. The selectivity coefficients determined by using fixed interference method (FIM) indicate high selectivity for praseodymium(III) ions over wide variety of other cations. To asses its analytical applicability the prepared sensor was successfully applied for determination of praseodymium(III) in spiked water samples

Sinteza i farmakološka evaluacija 3-cikloheksil-2-supstituiranih hidrazino-3H-kinazolin-4-ona kao analgetika i antiinflamatorika

A series of novel 3-cyclohexyl-2-substituted hydrazino-quinazolin-4(3H)-ones were synthesized by reacting the amino group of 3-cyclohexyl-2-hydrazino quinazolin-4(3H)-one with a variety of aldehydes and ketones. The starting material, 3-cyclohexyl-2-hydrazino quinazolin-4(3H)-one, was synthesized from cyclohexyl amine. Title compounds were investigated for analgesic, anti-inflammatory and ulcerogenic behavior. The compound 3-cyclohexyl-2-(1-methylbutylidene-hydrazino)-3H-quinazolin-4-one (4c) emerged as the most active compound of the series and is moderately more potent in its analgesic and anti-inflammatory activities compared to the reference standard diclofenac sodium. Interestingly, test compounds showed only mild ulcerogenic potential when compared to acetylsalicylic acid.Reakcijom amino skupine 3-cikloheksil-2-hidrazino kinazolin-4(3H)-ona s različitim aldehidima i ketonima sintetizirani su novi 3-cikloheksil-2-supstituirani hidrazino-kinazolin-4(3H)-oni. Početni spoj 3-cikoheksil-2-hidrazino kinazolin-4(3H)-on pripravljen je iz cikloheksilamina. Sintetizirani spojevi testirani su na analgetsko i protuupalno djelovanje te ulcerogena svojstva. Spoj 3-cikloheksil-2-(1-metilbutiliden-hidrazino)-3H-kinazolin-4-on (4c) imao je najjače analgetsko i protuupalno djelovanje, nešto jače nego referentni spoj diklofenak natrij. Osim toga, testirani spojevi imaju samo blago ulcerogeno djelovanje u usporedbi s acetilsalicilnom kiselinom