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PubMed2004

Spectroscopic studies on some azo compounds and their cobalt, copper and nickel complexes.

Synthesis and characterization of [o-carboxy phenylazo] moiety of barbituric acid, thiobarbituric acid, thiouracil, citrazinic acid, and disodium chromotropate and their complexes derived from cobalt (II), nickel (II), and copper (II) salts were done. The stereochemistry and the mode of bonding of the complexes were achieved based on elemental analysis, NMR, UV-Vis, IR and ESR. The dissociation constants of the free azo ligands are evaluated by spectrophotometric methods.

Azo Compounds↗
PubMedDate not supplied

Determination of tin (IV) in alloys and in canned food by visible spectrophotometric technique using pyrimidine azo compounds in presence of mixed surfactants.

The complex of tin (IV) with 5-(4'-nitro-2',6'-dichlorophenylazo) (I) and 5-(4'-chlorophenylazo)-6-hydroxypyrimidine-2,4-dione (II) in the presence of nonyl phenoxy polyethoxyethanol (NPE) and cetyltrimethylammonium bromide (CTAB) has a sensitive absorption band with lambda max 517 and 488 nm, respectively. Under the optimal conditions, Beer-Lambert law is obeyed over the range 0.05-1.50 and 0.05-1.30 micrograms ml-1 Sn(IV) with molar absorptivity being 9.50 x 10(4) and 1.05 x 10(5) L mol-1 using ligand I and II, respectively. As compared with the visible methods which uses bromopyrogallol red (BPR) as the chromogenic reagent (lambda max = 550 nm) and that using phenylfluorone (lambda max = 360 nm), our method is highly sensitive and selective because the complexes have a high and sharp absorption band. In addition, the present method is simple and rapid, no heating or standing time is needed. By means of the mixed surfactants, the precipitation caused by the ion association of cetyltrimethyl-ammonium cation and I3- anion is avoided if iodide is used for separating micro amounts of tin(IV) from a sample matrix. An application of the proposed method to the determination of tin(IV) in a variety of alloys and in a canned food was made with satisfactory results.

Alloys↗
PubMed2004

Photochemical and electronic properties of conjugated bis(azo) compounds: an experimental and computational study.

We have investigated the photophysical, photochemical and electrochemical properties of two bis(azo) derivatives, (E,E)-m-1 and (E,E)-p-1. The two compounds, which can be viewed as being composed of a pair of azobenzene units sharing one of their phenyl rings, differ only for the relative position of the two azo groups on the central phenyl ring-meta and para for m-1 and p-1, respectively. The UV-visible absorption spectra and photoisomerisation properties are noticeably different for the two structural isomers; (E,E)-m-1 behaves similarly to (E)-azobenzene, while (E,E)-p-1 exhibits a substantial red shift in the absorption bands and a decreased photoreactivity. The three geometric isomers of m-1, namely the E,E, E,Z and Z,Z isomers, cannot be resolved in a mixture by absorption spectroscopy, while the presence of three distinct species can be revealed by analysis of the absorption changes observed upon photoisomerisation of (E,E)-p-1. Quantum chemical ZINDO/1 calculations of vertical excitation energies nicely reproduce the observed absorption changes and support the idea that, while the absorption spectra of the geometrical isomers of m-1 are approximately given by the sum of the spectra of the constituting azobenzene units in their relevant isomeric form, this is not the case for p-1. From a detailed study on the E-->Z photoisomerisation reaction it was observed that the photoreactivity of an azo unit in m-1 is influenced by the isomeric state of the other one. Such observations indicate a different degree of electronic coupling and communication between the two azo units in m-1 and p-1, as confirmed by electrochemical experiments and quantum chemical calculations. The decreased photoisomerisation efficiency of (E,E)-p-1 compared to (E,E)-m-1 is rationalised by modelling the geometry relaxation of the lowest pi-pi* state. These results are expected to be important for the design of novel oligomers and polymers, based on the azobenzene unit, with predetermined photoreactivity.

Journal Article↗
PubMed2005

Light-induced changes of optical and electrical properties in bent-core azo compounds.

We have studied the optical and electrical properties of two bent-core substances with an azo linkage in their cores. Pump-probe laser studies, direct textural observations, and spectrophotometric recordings show an initial decrease of light transmission, which at larger light intensities (approximately 1 mW/mm2) is followed by a bleaching. Simultaneously the electrical properties (electric conductivity, antiferroelectric polarization, switching threshold, and switching time) decreased monotonically with increasing light intensities. The monotonic decrease of electrical properties indicates that the darkening and bleaching have the same origin, namely, the photochemical isomerization of the azo linkage from the trans to the cis isomer. The material with cis isomer has a lower clearing point and phase separates from the trans-rich domains. Initially the size of the separated isotropic domains is below the visible range, which causes increased scattering. As the size of the isotropic domains increase the scattering disappears and the transmittance becomes the average of the transmittances in the polar tilted smectic and isotropic phases.

Journal Article↗
PubMed2001

Electrochemical methods for monitoring of environmental carcinogens.

The use of modern electroanalytical techniques, namely differential pulse polarography, differential pulse voltammetry on hanging mercury drop electrode or carbon paste electrode, adsorptive stripping voltammetry and high performance liquid chromatography with electrochemical detection for the determination of trace amounts of carcinogenic N-nitroso compounds, azo compounds, heterocyclic compounds, nitrated polycyclic aromatic hydrocarbons and aromatic and heterocyclic amines is discussed. Scope and limitations of these methods are described and some practical applications based on their combination with liquid-liquid or solid phase extraction are given.

Azo Compounds↗
PubMed2004

[Azoic color reaction of flavonoids and their analytical application].

In NH4Cl-NH3 H2O buffer solution of pH 10.4, diazo salt of p-sulfodiazoben-zene chloride reacts with rutin, morin, genistin, quercetin, hesperidin, baicalin and daidzin to form color azo-compounds. These azo-compounds have an absorption maximum at 430 nm except for baicalin azo-compound, which has an absorption maximum at 380 nm. The sensitivity of azoic color reaction is reductive in the order of above flavonoids and the molar absorptivity is maximum for rutin and is minimal for daidzin among these azo-compounds, i. e. 3.28 x 10(4) and 8.3 x 10(2) L x mol(-1) x cm(-1) respectively. The proposed spectrophotometry has been applied to th determination of flavonoids in sophora seed and soybean cake. The RSDs of the method were found to be in the range of 0.75-4.48%, and the recoveries were in the range of 99.3%-105.0%.

Azo Compounds↗
PubMed1971

Separation and structural analysis of vinyl- and isovinyl-azobilirubin derivatives.

The coupling reaction of bilirubin with the diazonium salts of ethyl anthranilate or of aniline yields two isomeric azopigments. These can be separated by t.l.c. as their methyl esters. The mass spectra of each pair of azopigments are very similar, showing that they are isomers. Proton-magnetic-resonance spectrometric studies show that they differ in the positions of the substituents on the pyrrolenone end ring; in one compound the methyl and vinyl groups are interposed compared with the other compound. These azo compounds were used as reference standards for determination of the site of conjugation in bilirubin monoglucuronide prepared enzymically. Analysis showed that conjugation occurs at the carboxyethyl side chain of both sides of the bilirubin molecule. During the preparation of the ethyl anthranilate reference compounds a series of minor azopigments were isolated by t.l.c. Analysis of the mass spectra of many of these showed that three side reactions can occur: (1) methylation of the imide carbonyl group; (2) addition of methanol or water to the vinyl substituent; (3) transmethylation of the ethoxycarbonyl group.

Alkenes↗
PubMedDate not supplied

Determination of nitrite in foods by single-sweep polarography.

In an acid medium, nitrite diazotized with p-rosaniline and then coupled with 8-hydroxyquinoline in a weak alkaline medium produces azo compounds. The azo compounds produce a very sensitive polarographic wave at -0.70 V (versus the saturated calomel electrode). The height of the peak is linear with the concentration of nitrite in the range of 5 x 10(-9) to 5 x 10(-7) g/mL. The detection limit is 3 x 10(-9) g/mL. The electrochemical characteristics of the polarographic wave are also discussed. The method was used to determine nitrite in sausage. The results agree well with those obtained by spectrophotometry.

Food Analysis↗
PubMed1998

Characterization of metabolites in the biotransformation of 2,4,6-trinitrotoluene with anaerobic sludge: role of triaminotoluene.

The present study describes the biotransformation of 2,4,6-trinitrotoluene (TNT) (220 microM) by using anaerobic sludge (10%, vol/vol) supplemented with molasses (3.3 g/liter). Despite the disappearance of TNT in less than 15 h, roughly 0.1% of TNT was attributed to mineralization (14CO2). A combination of solid-phase microextraction-gas chromatography-mass spectrometry and liquid chromatography-mass spectrometry identified two distinctive cycles in the degradation of TNT. One cycle was responsible for the stepwise reduction of TNT to eventually produce triaminotoluene (TAT) in relatively high yield (160 microM). The other cycle involved TAT and was responsible for the production of azo derivatives, e.g., 2,2',4,4'-tetraamino-6,6'-azotoluene (2,2',4, 4'-TA-6,6'-azoT) and 2,2',6,6'-tetraamino-4,4'-azotoluene (2,2',6, 6'-TA-4,4'-azoT) at pH 7.2. These azo compounds were also detected when TAT was treated with the anaerobic sludge but not with an autoclaved sludge, suggesting the biotic nature of their formation. When the anaerobic conditions in the TAT-containing culture medium were removed by aeration and/or acidification (pH 3), the corresponding phenolic compounds, e.g., hydroxy-diaminotoluenes and dihydroxy-aminotoluenes, were observed at room temperature. Trihydroxytoluene was detected only after heating TAT in water at 100 degrees C. When 13CH3-labeled TNT was used as the N source in the above microcosms, we were unable to detect 13C-labeled p-cresol or [13CH3]toluene, indicating the absence of denitration or deamination in the biodegradation process. The formation and disappearance of TAT were not accompanied by mineralization, suggesting that TAT acted as a dead-end metabolite.

Anaerobiosis↗
PubMed1999

Resveratrol inhibits copper ion-induced and azo compound-initiated oxidative modification of human low density lipoprotein.

To investigate whether resveratrol, a polyphenolic compound in red wine, affects the oxidation of human low density lipoprotein (LDL), LDL purified from normolipidemic subjects was subjected to Cu(2+)-induce and azo compound-initiated oxidative modification, with and without the addition of varying concentrations of resveratrol. Modification of LDL was assessed by the formation of thiobarbituric acid reactive substances (TBARS) and changes in the relative electrophoretic mobility (REM) of LDL on agarose gels. Resveratrol (50 microM) reduced TBARS and REM of LDL during Cu(2+)-induced oxidation by 70.5% and 42.3%, respectively (p < 0.01), and prolonged the lag phase associated with the oxidative modification of LDL by copper ion or azo compound. These in vitro results suggest that resveratrol may afford protection of LDL against oxidative damage resulting from exposure to various environmental challenges, possibly by acting as a free radical scavenger.

Amidines↗
PubMed2004

Electronic spectra, solvatochromic behavior and acid-base properties of some azo cinnoline compounds.

The electronic spectra of three azo cinnoline derivatives have been studied in pure and mixed organic solvents of different characteristics as well as the effect of concentration of the compounds in the different solvents. The different bands observed have been assigned to the proper electronic transition. The longer wavelength band displayed by the para nitro cinnoline derivative in dimethylformamide (DMF) solution is assigned to an intermolecular CT transition. The solvated H-bonding complexes formed between DMF and the para nitro derivative were investigated. DeltaG and K(f) values of these complexes have been determined. The acidity constants of the para nitro compound were determined from the spectra in aquous-methanolic solution of varying pH values. The effect of temperature on the longer wavelength visible band of p-NO(2) has been investigated.

Acids↗