Potentiometric and spectroscopic studies on aluminium(III) complexes of some catechol derivatives

The interactions of aluminium(III) ion with the triprotic catechol derivatives (H3L), 2,3-dihydroxybenzoic acid (2,3-DHBA), 3,4-dihydroxyphenylacetic acid (3,4-DHPA), 3,4-dihydroxybenzoic acid (3,4-DHBA), and 3,4-dihydroxyhydrocinnamic acid (3,4-DHHCA) were investigated in aqueous solution at 25.0 degrees C. The Calvin-Bjerrum titration method was adopted for the determination of formation constants of proton-ligand and aluminium(III)-ligand complexes. Potentiometric and spectroscopic results indicated that these catechol derivatives exhibit a true bidentate character. The chelation occurs via their catecholate sites, with the exception of 2,3-DHBA. In the case of 2,3-DHBA complexes, the dominant species are either the salicylate type (COO-, O-) or catecholate type (O-, O-) complex. The protonation constants of ligands and their formation constants of Al(III) complexes were also correlated. The order of decreasing stabilities of complexes is: 3,4-DHPA>3,4-DHBA>3,4-DHHCA>2,3-DHBA.     

Electrochemical oxidation of some catechol derivatives in the presence of some betadicetone derivatives: mechanistic and thermodynamic study

Electrochemical oxidations of 4-methylcatechol (1), 4-tert-butylcatechol (5) and catechol (7) in the presence of different nucleophiles have been investigated both experimentally and theoretically. Experimental results have been obtained by means of cyclic voltammetry and controlled-potential coulometry. Also the theoretical results were calculated at DFT (B3LYP) level of theory and 6–311+G (p, d) basis set. The calculated results indicate that oxidation potential of catechols (1, 5, 7) and their substituted species are directly dependent on the ?G _tot, and continuance of reactions during electrolysis is dependent on ?G _tot of produced species on the surface of electrode. The current study indicates that theoretical studies along with empirical research can be useful in displaying electrochemical reaction mechanisms.     

Determination of some catechol derivatives by a flow injection electrochemiluminescent inhibition method

A flow injection electrochemiluminescent inhibition method has been developed for the determination of some catechol derivatives based on studying the inhibition phenomena of these compounds to the electrochemiluminescence of luminol. The linear calibration range of 5x10(-8) to 1x10(-5), 5x10(-8) to 1x10(-5) and 1x10(-8) to 5x10(-5) mol l(-1(,)) the detection limit of 1.2x10(-8), 2.1x10(-8) and 5.2x10(-9) mol l(-1)were obtained for catechol, 3,4-dihydroxybenzoic acid and chlorogenic acid, respectively. The method has higher sensitivity and wider dynamic range than conventional spectrophotometric method or chemiluminescent method. The method has been successfully applied to determine chlorogenic acid in cigarettes. The mechanism of the inhibition effect was proposed. Catechol derivatives mostly react with the freshly electrogenerated oxygen species on the electrode surface and lead to the inhibition of electrochemiluminescence.     

Polymeric catechol derivatives. IV. Polymerization behavior of 4-vinylcatechols and some properties of their polymeric derivatives

The polymerization and copolymerization of 4-vinylcatechols, such as 2-(0-methyl)-4-vinylcatechol (I), 3,4-dimethoxystyrene (II), and 3,4-methylenedioxystyrene (III), were investigated in cyclohexanone at 30°C, using tri-n-butylborane as an initiator. The reactions yielded vinyl polymers and copolymers. The copolymerization parameters of I–III were determined; their Q and e values were found to be similar to those of styrene and vinylhydroquinone. The copolymerization of I–III gave copolymers of a highly alternating character. The thermal stability of the polymers and copolymers so obtained was also studied. The redox potentials of hydroloyzed poly(I) were examined; the reverse “polymer effect” was observed.     

NMR study of catechol and some catecholamines

The proton magnetic resonance spectra of catechol, epinephrine, dopamine, synephrine, tyramine and amphetamine have been analysed by computer simulation. The chemical shifts and coupling constants are discussed, with their molecular implications. Convenient parameters are introduced for the additivity of substituent effects on chemical shifts of aromatic protons. The additivity rule of coupling constants is extended to these compounds.     

Contributions to group IV organometallic chemistry: VI. Preparation and properties of some organosilicon derivatives of catechol

The preparation and properties of some organosilicon derivatives of catechol are reported and their mass spectra and ¹H, ¹³C and ²⁹Si NMR spectra discussed in detail.     

IR and Raman investigations of structures and phase changes in scandium fluorides

Crystallographic data and IR Raman spectra are presented for a new series of compounds, M₃ScF₆ (M Na, K, Rb, Cs, T1). Spectral assignments are proposed and effects of the cation on vibrational modes is discussed. Preliminary temperature-dependant Raman spectra are presented and correlated with DSC and crystallographic data.     

Potentiometric microdetermination of ammonium salts of some nitroheterocycles

Summary Ammonium salts of nitroheterocyclic compounds containing from 2 to 4 heterocyclic nitrogen atoms can be determined by titration with silver nitrate or cetylpyridinium chloride. If a 5-H atom is present, the titration is feasible only with silver nitrate. If the molecule does not contain a hydrogen atom then the titration is feasible only vs. cetylpyridinium chloride. If there is a hydrogen atom inany position on the ring then the compound will yield a precipitate with silver nitrate, although the titration curves may not always be analytically useful. Titration with silver nitrate were monitored with a silver/sulfide ion-selective electrode and a double-junction reference electrode. Titrations with cetylpyridinium chloride were monitored either with a fluoroborate or cyanide ion-selective electrode and a double-junction reference electrode. Sodium-1,2,4-triazole can also be determined argentimetrically. However, we have not found a satisfactory argentimetric method for 1,2,4-triazole.

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Potentiometrische Mikrobestimmung von Ammoniumsalzen einiger Stickstoff-Heterocyklen

Zusammenfassung Ammoniumsalze von Stickstoffheterocyklen mit 2 bis 4 Stickstoffatomen im Ring können mit Silbernitrat oder mit Cetylpyridiniumchlorid titriert werden. Liegt ein 5-H-Atom vor, so läßt sich nur mit Silbernitrat titrieren. Enthält das Molekül kein H-Atom, so ist die Titration nur mit Cetyl-pyridiniumchlorid durchführbar. Ist ein H-Atom an irgendeiner Stelle des Ringes gebunden, so gibt die Verbindung mit Silbernitrat einen Niederschlag und die Titrationskurven sind nicht immer analytisch auswertbar. Die Titration mit Silbernitrat wird mit Hilfe einer Silber/Sulfidionen-spezifischen Elektrode und einer double-junction-Bezugselektrode durchgeführt. Titrationen mit Cetylpyridiniumchlorid werden mit einer Fluoroborat- oder mit einer Cyanidionen-spezifischen Elektrode und einer double-junction-Bezugselektrode durchgeführt. Natrium-1,2,4-triazol kann ebenfalls argento-metrisch titriert werden, für 1,2,4-Triazol haben wir jedoch keine befriedigende argentometrische Methode gefunden.

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Work performed under the auspices of the U. S. Department of Energy by the Lawrence Livermore National Laboratory under contract number W-7405-ENG-48.     

Potentiometric microdetermination of catechol in the presence of its isomers using a lead-ion selective electrode

Summary Catechol was determined on the microscale by potentiometric titration with lead nitrate. Solutions were buffered to pH 9.5 with borate buffer. Emf's were monitored with a lead ion-selective electrode and a single junction reference electrode. Up to an eightfold excess of hydroquinone or resorcinol can be tolerated.

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Potentiometrische Mikrobestimmung von Brenzcatechin in Gegenwart seiner Isomeren mit Hilfe einer blei-spezifischen Elektrode

Zusammenfassung Mikromengen Brenzcatechin wurden mit Bleinitrat potentiometrisch titriert. Die Lösungen wurden mit Borat auf pH 9,5 gepuffert. Die EMK wurde mit einer blei-spezifischen Elektrode gemessen. Hydrochinon und Resorcin stören bis zum achtfachen Überschuß nicht.

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Work performed under the auspices of the U. S. Department of Energy by the Lawrence Livermore Laboratory under Contract W-7405-Eng-48.     

Quantitative structure-activity relationship of catechol derivatives inhibiting 5-lipoxygenase.

Various catechol derivatives (beta-substituted 3,4-dihydroxystyrenes, 1-substituted 3,4-dihydroxybenzenes, and 6-substituted 2,3-dihydroxynaphthalenes) were synthesized and their inhibition of 5-lipoxygenase was assayed. Their structure-activity relationships were examined quantitatively with substituent and structural parameters and regression analysis. The variations in the inhibitory activity were explained in bilinear hydrophobic parameter (log P) terms, and steric (molecular thickness) and electronic (proton nuclear magnetic resonance (1H-NMR) chemical shift of the proton adjacent to the catechol group) parameter terms. The hydrophobicity of the inhibitor molecule was important, and the optimum value of logP was about 4.3-4.6, beyond which inhibition did not increase further. A lower electron density of the aromatic ring containing the catechol group and the greater thickness of the lipophilic side chains were unfavorable to the activity. The results added a physicochemical basis for the selection of candidate compounds for developmental studies.     

Potentiometric semimicrodetermination of some anions with 1,2,4,6-tetraphenylpyridinium acetate

Summary A new titrant, 1,2,4,6-tetraphenylpyridinium acetate, has been evaluated for the potentiometric precipitation titration of semimicro amounts of some large inorganic anions. Emf's were monitored with a perchlorate ion-selective electrode and a double-junction reference electrode. Satisfactory results were obtained for perchlorate, perrhenate, periodate, dichromate, permanganate, hexafluorophosphate, and hexachloroplatinate. Fluoroborate yielded a smaller endpoint break and poor precision. Thiocyanate, iodide, molybdate, tungstate, and tetrachloropalladate yielded partial or complete precipitation, but no analytically useful titration curves. We consider it likely that large anions such as pertechnetate, hexafluoro anions such as hexafluoroarsenate, and some complex metal chlorides such as those of mercury and tin (IV) can be determined in a similar fashion.

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Zusammenfassung Das neue Titrationsmittel 1,2,4,6-Tetraphenylpyridiniumacetat wurde zur potentiometrischen Fällungstitration von Semimikromengen einiger großer anorganischer Anionen herangezogen. Das Potential wurde mit einer selektiven Perchloratelektrode und einer doppeltverbundenen Bezugselektrode gemessen. Befriedigende Ergebnisse wurden mit Perchlorat, Perrhenat, Perjodat, Dichromat, Permanganat, Hexafluorophosphat und Hexachloroplatinat erhalten. Mit Fluoborat ergab sich ein schwächerer Endpunkt-Knick und geringere Genauigkeit. Thiocyanat, Jodid, Molybdat, Wolframat und Tetrachloropalladat ergaben teilweise oder vollständige Fällung, aber keine analytisch auswertbaren Titrationskurven. Wir nehmen an, daß sich große Anionen wie Pertechnetat, Hexafluoroarsenat u. dgl. sowie komplexe Metallchloride wie die des Quecksilbers und des Zinn(IV) in gleicher Weise bestimmen lassen.

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This work was performed under the auspices of the U. S. Energy Research and Development Administration, contract No. W-7405-Eng 48.     

Potentiometric investigations of carbonate ion stability in molten cesium and sodium iodides

The reaction of carbonate ion dissociation in molten CsI and NaI was studied in the temperature range from the melting point to 800 (CsI) and 830 degrees C (NaI) by a potentiometric method with the use of a membrane oxygen electrode as an indicator one. The dissociation constant of CO(3)(2-) in the molten iodides was found to increase with the temperature. pK values for CsI are 4.47 (650 degrees C), 4.23 (700 degrees C), 3.89 (750 degrees C), 3.44 (800 degrees C); those for NaI are 4.68 (700 degrees C), 4.39 (750 degrees C), 4.17 (800 degrees C), 3.92 (830 degrees C). The plots of pK vs reverse temperature are linear. Carbonate stability in molten CsI is lower than that in the NaI due to lower stability of Cs(2)CO(3) compared with Na(2)CO(3).     

Potentiometric semimicro determination of some tetrazoles with silver nitrate

Summary Tetrazoles possessing an hydrogen atom in the 1 H position can be assayed in aqueous solution by potentiometric titration with silver nitrate. Emf's were monitored with a sulfide ion-selective indicator electrode, and a double-junction reference electrode. These compounds can also be determined as acids in aqueous solution vs standard sodium hydroxide solution. If the 1H hydrogen atom is replaced by another group the acidic character of the molecule is lost and it cannot be analyzed by either of the two methods.

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Zusammenfassung Tetrazole mit einem Wasserstoffatom in 1H-Stellung können in wäßriger Lösung potentiometrisch mit Silbernitrat titriert werden. Die EMK wird mit einer sulfidionen-selektiven Indikatorelektrode und einer doppelt verbundenen Bezugselektrode gemessen. Diese Verbindungen können in wäßriger Lösung auch als Säuren gegen eine Standard-Natronlauge titriert werden. Wird aber das 1H-Wasserstoffatom substituiert, so geht der saure Charakter verloren und keine der beiden Methoden ist verwendbar.

     

Synthesis,characterization and pharmacological investigations of some novel heterocyclic derivatives incorporating pyrene and sugar moieties

A series of substituted pyrene derivatives 2–15 incorporated heterocyclic and sugar moieties were synthesized and evaluated as antiviral activities using 1-acetylpyrene as a starting material. The structure assignment of the new compounds was based on chemical and spectroscopic evidence. The detailed synthesis, spectroscopic data and pharmacological activities of the synthesized compounds were reported.     

Catalytic synthesis of 1,4-dihydropyridine derivatives using scandium(III) triflate

Scandium(III) triflate smoothly catalyzed the reaction of imines with ethyl propiolate (2.5 equiv) to produce the corresponding N-substituted 1,4-dihydropyridines in good yields in toluene or BTF under reflux conditions. It also catalyzed the reaction of aniline and ethyl propiolate (3.2 equiv) to give another 1,4-dihydropyridine bearing three ester groups in moderate yield under the same conditions.     

Spectroscopic investigations on phthalazino 2,3-b phthalazine-5,12-dione and some of its mono- and di-substituted derivatives

The spectroscopic properties of phthalazino 2,3-b phthalazine-5,12-dione (diphthalazindione) and of some of its mono- and di-substituted derivatives are investigated by means of XPS, UPS, i.r. Raman and NMR techniques. The main results deduced from the spectroscopic data are: the existence of two not interacting types of π systems, one delocalized on the aromatic rings, and the other on OCNNCO group; the substitutions involve geometric and electronic changes not only in the positions close to the attacked points but in the whole molecule; the presence of different geometric conformations at room temperature for the diphthalazindione.