Sudan I Research Articles

Contact sensitization to disperse dyes in children.

From January 1996 to December 2000, 1098 children, including 667 subjects with suspected allergic contact dermatitis and 431 patients with atopic dermatitis (AD), were patch tested with seven disperse dyes: disperse blue 124 (DB124), disperse blue 106 (DB106), disperse red 1 (DR1), disperse yellow 3 (DY3), disperse orange 3 (DO3), p-aminoazobenzene (PAAB), and p-dimethylaminoazobenzene (PDAAB). Of these, 51 patients (4.6%; 34 girls and 17 boys) proved sensitized to disperse dyes. AD or history of AD was present in 30 patients (59%). The most common sensitizer was DY3 (17 patients), followed by DO3 (15 patients), and DB124 (14 patients). Among dye-positive patients, about 12% were sensitized to disperse dyes alone and only 14% reacted to para-phenylenediamine. In disperse dye-sensitive children not affected by AD, the feet, axillae, and groin appeared to be the most common localizations, whereas in those with AD, involvement of the face and the flexural areas of the limbs was more common. In conclusion, our study showed that in children with suspected contact sensitization, disperse dyes should be regarded as potential triggering allergens.

Evaluation of Surface Acidity of Aluminum Oxide Film by Inelastic Electron Tunneling Spectroscopy

The surface acidity of aluminum oxide (AlOx) films was evaluated for the first time by inelastic electron tunneling (IET) spectroscopy using the Hammett indicators as probe molecules. The AlOx films were formed by oxidation of the aluminum films by DC glow discharge in oxygen atmosphere, and the indicators with pKa values ranging from -8.2 to +4.8 were used. The indicators, methyl red (MR) with pKa=+4.8 and methyl yellow (MY) with pKa=+3.3 contain the N=N bond and do not have the N–H bond. The IET spectrum of MR showed the peak related to the N–H stretching vibration at 3295 cm-1, while the spectrum of MY did not show the peak. These results indicate that the MR molecule chemisorbs at the N atom on the hydroxyl group acting as the Brønsted acid site and the MY molecule does not chemisorb on the site. Thus, the acid strength of the Brønsted site was determined to be approximately +3.3≦H0(B)≦+4.8.

Resonance Raman study of the solvent dynamics for ultrafast charge transfer transition in 4-nitro-4′-dimethylamino-azobenzene

Contribution of solvent reorganization energy is known to be significant for ultrafast charge transfer processes, when the solvent relaxation times are slower than the rate of charge transfer. In this paper, we show that from resonance Raman intensities of a charge transfer transition in combination with Heller’s time-dependent wave packet approach and Brownian oscillator model, one can have a reasonable estimate for the different types of solvent (inertial as well as diffusive) and vibrational reorganization energies. Resonance Raman spectra have been recorded for 4-nitro-4′-dimethylamino-azobenzene (DA) that undergoes photoinduced charge transfer transition, in acetonitrile and benzonitrile. In the two solvents, the total solvent reorganization energy is partitioned into its inertial and diffusive components from the available information on their relaxation time scales. Thus, partitioning of the solvent reorganization energy reveals the importance of the extent of contribution of the two components to the charge transfer rates. The short time dynamics of DA in the two solvents is then examined from a priori knowledge of the ground state normal modes in order to convert the wave packet motion in dimensionless displacements to internal coordinates. The dynamics in DA infers that within 20 fs after photoexcitation from the ground to the charge transfer state, the excited state evolution occurs along N–O, N=N, C–N, and C–C stretching vibrations.

Activation of the aryl hydrocarbon receptor by methyl yellow and related congeners: structure-activity relationships in halogenated derivatives.

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that mediates the biological action of many environmental compounds. Methyl yellow (4-dimethylaminoazobenzene; MY) is a principal azo-dye, and structurally related compounds were subjected to analysis of structure-activity relationships as AhR ligands by using a yeast AhR signaling assay. The effects of halogen-substitution among 23 halogenated MYs on the AhR ligand activity can be summarized as follows: enhancement by halogen-substitution at the ortho-position (2'- and 6'-position), and reduction by substitution at the para-position (4'-position). The greatest enhancement of the ligand activity was observed in 2',6'-dichlorinated MY (13.5-fold of MY), and its AhR ligand activity was very close to that of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in the present assay system. In the study of compounds structurally related to MY, benzanilide (BA) showed almost the same AhR ligand activity as azobenzene and trans-stilbene. Furthermore, 4'-chlorobenzanilide, in which the length of the molecule is similar to that of MY, enhanced the AhR ligand activity by ortho(2')-chlorine-substitution, and the AhR ligand activity of 2',4'-dichlorobenzanilide was similar to that of 2'-chloro-MY. These results suggest that the amide bond is equivalent to the -N=N- or -CH=CH- double bond for recognition as the ligand by AhR in 1,2-diphenyl-1,2-ene derivatives.

The synthesis and properties of some carboxy-substituted analogs of butter yellow

A seven step synthesis of 3,3′-bis(carbomethoxy)-4,4′-bis-(dimethylamino)-azobenzene from anthranilic acid is described. It has been found that the carbomethoxy groups affect the required oxidative azo coupling and methylation steps. Perborate coupling of 2-carbomethoxy- N-acetyl- p-phenylenediamine gives the corresponding azo compound in good yield, but the reaction also produces variable amounts of an azoxy compound. Tetramethylation of 3,3′-bis(carbomethoxy)-4,4′-diaminoazobenzene requires forcing conditions [(CH 3O) 2SO 2 at 160 °C]. Protonation of 3,3′-bis(carbomethoxy)-4,4′-bis-(dimethylamino)azobenzene gives the ammonium ion tautomer because the carbomethoxy groups force the adjacent dimethylamino groups out-of-plane. In contrast, protonation of 3,3′-bis(carbomethoxy)-4,4′-diamino-azobenzene and 4,4′-bis(dimethylamino)azobenzene-3,3′-dicarboxylic acid gives the azonium ion tautomer.

Study of solvent effects on the molecular structure and the reorganization energies of 4‐nitro‐4′‐dimethylaminoazobenzene using resonance Raman intensities

AbstractResonance Raman spectroscopy was used to probe the effect of solvent polarity on the molecular structure and isomerization dynamics of 4‐nitro‐4′‐dimethylaminoazobenzene (DA). In addition, the influence of the polarity and the relaxation behavior of the solvent on the mode‐specific vibrational and solvent reorganization energies was investigated. Raman spectra were recorded in solvents with different polarity parameters, n‐hexane and benzene, using 11 excitation wavelengths in the range 450–550 nm, scanning every 10 nm using the tunable laser pulse output of an optical parametric oscillator. It was observed that the solvent polarity plays a major role in influencing the excited‐state potential energy surfaces of DA. The plot of resonance Raman intensities versus excitation wavelength (Raman excitation profiles) of the Franck–Condon‐active fundamentals of DA shows that in n‐hexane, the locally excited state is more favorable than that in benzene where the charge‐transfer state is more stable. The distortions along the N N and C–N stretching vibrations of DA in n‐hexane and benzene infer isomerization via rotation in n‐hexane and inversion in benzene. The increase in solvent and vibrational reorganization energies with increasing solvent polarity parameter suggests greater distortion in the Franck–Condon excited state following photoexcitation. Copyright © 2001 John Wiley & Sons, Ltd.

Ab initio GB study of the acid-catalyzed cis– trans isomerization of methyl yellow and methyl orange in aqueous solution

Ab initio GB calculation that includes solvent effects by the generalized Born formula (GB) was applied to methyl yellow (4-dimethylaminophenylazobenzene, MY) and methyl orange (4-[4′-dimethylaminophenylazo]-benzenesulfonate, MO) and their protonated species, and the acid-catalyzed cis– trans isomerization of MY and MO was analyzed. The HF/3-21G (∗)/GB calculations determined the structures and relative energies of MY and MO, their ammonium and azonium ions, and the transitions state for the cis– trans isomerization of the azonium ions in aqueous solution. The calculations indicated that (i) the energy difference between the cis and trans forms of the azonium ion is much smaller than those of the ammonium ion and the unprotonated species, (ii) the cis-azonium ion is much more stable than the cis-ammonium ion, and (iii) the cis– trans isomerization occurs easily in the azonium ion which is produced by the protonation of the azo compound or by the acid-catalyzed proton transfer from the cis-ammonium ion.

Studies on the Physicochemical Properties of 3-Alkoxyl-2-hydroxypropyl Trimethylammonium Chloride-Sodium Dodecyl Sulfonate Binary-Surfactant Aqueous Systems

Surface tension, micelle formation, surface adsorption, and solubilization of dimethylaminoazobenzene (DMAB) are studied in aqueous solutions of 3-alkoxyl-2-hydroxypropyl trimethylammonium chloride (alkoxyl = CnH2n+1O, n = 8, 12, 14, 16), of sodium dodecyl sulfonate, and of mixtures of these cationic surfactants and the anionic surfactant at 40°C. Synergistic effects on micelle formation, surface tension reduction, and solubilization enhancement of DMAB are observed in the cationic–anionic mixed surfactant systems. The experimental results are discussed in the light of the interactions between the two kinds of surfactant ions.

Self-assembly of small molecules: An approach combining electrostatic self-assembly technology with host–guest chemistry

A fluorescence probe study, surface tension and dye solubilization tests indicate that the water-soluble calixarene, 5,11,17,23,29,35,41,47-octosulfonato-49,50,51,52,53,54,55,56-octododecyloxycalix[8]arene (18-C12) acts as a “unimolecular” micelle in water. By forming guest–host-type complexes with 18-C12, lipophilic dyes, such as methyl yellow (MY), p-hydroxyazobenzene (HAB) and 1-(p-phenylazophenylazo)-2-naphthol (Sudan III), dissolve in aqueous solution. By dipping a charged substrate in the 18-C12–dye solution and a cationic polyelectrolyte solution alternately, these small molecular dyes were successfully self-assembled into multilayer films.

Diffusion of small probe molecule in oligomers

Diffusion of methyl yellow (MY) in the oligomeric host of n-alkanes and n-alcohols was studied by forced Rayleigh scattering as a function of the molecular weight and the viscosity of the medium. We observe that the diffusivity of the probe molecule follows a power law dependence on the molecular weight of the oligomers, DMY∼M−α well. As the molecular weight of the oligomers increases, the exponent α shows a sharp transition from 1.88 to 0.91 near docosane (C22) in n-alkanes and from 1.31 to 0.60 near 1-hexadecanol (C16OH) in n-alcohols at 45 °C. A similar transition is also found in the molecular-dynamics simulation for the diffusion of a Lennard-Jones particle of a size similar to MY in n-alkanes. This transition deems to reflect a change of the dynamics of oligomeric chain molecules that the motion of the segments, not the entire molecules, becomes responsible for the transport of the probe molecule as the molecular weight of the oligomer increases. However, a weak but finite molecular weight dependence is observed above the transition point. Since it is well established that this molecular weight dependence disappears at high molecular weight medium, this indicates that the molecular weight of the oligomers is not high enough and the motion of the entire chain molecule is still correlated with the probe motion to some extent. The transition points in n-alkane and n-alcohol are in good agreement with the molecular weight at which the diffusional activation energy of MY reaches the asymptotic value, ∼20 kJ/mol near n-docosane and ∼30 kJ/mol near 1-hexadecanol.

Review: Hepatic Oval Cells: "Knocking on Forbidden Doors"

Hepatic oval “stem” cells were first described in 1956 by E. Farber (1), and are considered to be a cell capable of developing into hepatocytes or bile duct epithelial cells. Other investigators suggest that they are the progeny of a hepatic stem cell. Numerous in vivo and in vitro studies have documented a central role of oval cells in liver biology and carcinogenesis (2–4). In addition to the effects seen in the liver, oval cells (or cells very similar to oval cells) have been implicated in the architecture of the regenerating pancreas after injury (5–6) and they may be involved in the regeneration of other organs as well. While there is a precise purpose for this cell population in the liver, the mechanism(s) by which oval cells activate, proliferate and differentiate are poorly understood. Despite forty years of research and 300 publications on hepatic oval “stem” cells their ontogeny remains a mystery. “Oval cell proliferation” describes the occurrence of nonparenchymal cells detected in large numbers at early stages of carcinogenesis. The population is heterogeneous and contains cells that differ in their differentiation state and potential in their lineage commitment. “Oval cell compartment” is also used to describe the cells invading the parenchyma after the administration of certain carcinogens (7–8). Farber (1991) argued that although oval cells might be the progenitors of hepatocelluar carcinomas (HCC) induced by 3 9 methyl-4 9 -dimethyl-amino-azo-benzene (DMAB), this conclusion can not be generalized to other models of hepatocarcinogenesis (3). It is his view that cell lineage analyses cannot be achieved in a culture system(s) and that the markers used in studies of hepatocarcinogenesis can be considered reliable lineage markers for work done in vivo (3). Farber also reported that in each oval cell compartment model the oval cells will express different isoenzyme profiles, however, certain hepatic alpha-fetoprotien (AFP) and biliary cytokeratin-19 (CK-19) markers will always be expressed (3). In the DMAB model, the single most important conclusion provided by this data is that hepatocytes could be generated from nonparenchymal progenitor cells (3,9). This model establishes the key principle that some type of progenitor cell exists even if it turns out that precursor cell differentiation occurs only infrequently. Evarts et al. (1987 and 1989) show that the oval cell compartment is activated extensively in a 2-Acetylaminofluorene/two thirds partial-hepatecomy (2-AAF/PHx) model. This model is a variation of the SoltFarber protocol (2,10) and has become the industry standard. Figure 1 represents a timeline for this type of protocol. Under these conditions hepatocyte proliferation is heavily suppressed, and it was possible to label oval cells with [3H]-thymidine. This procedure allowed them the ability to follow the fate of the labeled cells. Four to five days after [3H]-thymidine injection, the label was found in basophilic hepatocytes expressing AFP and albumin (2). The authors concluded that there was a precursor-product relationship between the labeled cells of the oval cell compartment and the basophilic hepatocytes. Further studies, presented by the same investigators , show that proliferation of the oval cells and hepatocyte differentiation at early stages of carcinogenesis are associated with the activation of the stellate or Ito cells, which may reg-

Structures, Vibrational Frequencies, and Normal Modes of Substituted Azo Dyes: Infrared, Raman, and Density Functional Calculations

The vibrational structures of 4-nitro-azobenzene (NAB), 4-(dimethylamino)-azobenzene (DAB), and 4-nitro,4‘-(dimethylamino)-azobenzene (NDAB) are of interest due to their importance in optoelectronic applications as well as the unique isomerization mechanism involving the inversion process (at the nitrogen site). In this paper, we present the Fourier transform infrared (FTIR) and Raman spectral studies of NAB, DAB, and NDAB and also report their equilibrium structures, harmonic frequencies, and normal mode assignments, employing the hybrid Hartree−Fock/density functional (HF/DF) method with the 6-31G basis set. The results of the optimized molecular structure obtained on the basis of B3LYP with 6-31G basis set suggest a greater conjugation and π-electron delocalization for the substituted azo dyes in comparison to the parent azo molecule, viz. trans-azobenzene (TAB). It is found that the B3LYP/6-31G method is very accurate in predicting harmonic vibrational frequencies and the normal modes for the substituted azo dyes and their isotopic analogues. On the basis of the B3LYP/6-31G force field, the infrared intensities for NAB, DAB, and NDAB, and their isotopomers, are calculated and then compared with those observed experimentally. Finally, the main differences in the vibrational spectra of the substituted azobenzene derivatives are discussed from an analysis of the normal modes.

The solvent-dependent isomerization dynamics of 4-(dimethylamino)azobenzene (DMAAB) studied by subpicosecond pump–probe spectroscopy

The photoisomerization dynamics of 4-(dimethylamino)azobenzene (DMAAB) are studied using subpicosecond pump–probe spectroscopy. Following photoexcitation at 400 nm, resonant with the lowest-lying π–π * transition, excited-state internal conversion occurs with a time-constant of ∼0.8 ps in acetone and ethanol, and ∼1.4 ps in fluorotrichloromethane. Internal conversion is followed by ground-state vibrational relaxation on the ∼10 ps timescale. It is proposed that the solvent dependence of the excited-state decay reflects the solvent-polarity dependence of the excited-to-ground-state energy gap. The results presented here, in combination with earlier work, suggest that rapid isomerization following photoexcitation into the lowest-energy electronic state is a general feature of azobenzene photochemistry.

Spectrophotometric determination of the dissociation constants of methyl yellow in mixed protic solvents

The concentration dissociation constants (p K a) of methyl yellow, MY (H +In) in mixed aqueous solvents of methanol, ethanol, iso-propanol, tert-butanol have been accurately determined from spectrophotometric measurements at 25°C and a constant ionic strength of 0.1 mol l −1. It has been shown that in these solvents, the p K a values decrease with increasing composition of the organic co-solvent. A linear relationship between p K a and the mole fraction ( x 2) of the co-solvent was observed in a limited range of the compositions for each of the solvent systems. The results have been discussed in the light of transfer thermodynamic properties of the species existing in the dissociation equilibrium, solvent basicity and solute–solvent interactions. Furthermore, it was also observed that with the change of the solvents, the absorption spectra of MY shifted apparently and the color transition changed accordingly. The solvent effect on the spectra has been attributed to the isomerization equilibria of MY. A simple application of MY was also shown to the sodium acetate-hydrochloric acid titrations in the mixed solvents.

SERRS spectra of azo dyes from deposited Ag colloid-azo dye films: investigating the mechanism of film formation

The role of interphase transfer of azodye adsorbates in the mechanism of interfacial Ag colloid-azodye films formation was investigated. Ag colloid - azodye [azodye=methyl yellow (MY) or methyl red (MR)] were prepared by vigorous shaking of a two phase system consisting of an acidified Ag hydrosol of pH=3 [Ag colloid (ac)] and a solution of the azodye in dichloromethane. SERRS spectra of the glass deposited films were measured and compared to RR spectra of the azo-form in the dichloromethane solution and to RR spectra of the hydrazo-form present in an acidified aqueous solution of the dye. The presence of the characteristic bands of the hydrazo–form of the dyes both in Ag colloid (ac)–MY and Ag colloid (ac)–MR films provides evidence for the contact of the azodyes with the acidified aqueous phase in the course of the film formation.

Ag colloid–ethanethiol films: spacer-modified substrates for surface-enhanced resonance Raman scattering spectroscopy of chromophoric molecules

Interfacial Ag colloid–ethanethiol films were prepared by vigorous shaking of a two-phase system consisting of an aqueous Ag colloid and a solution of ethanethiol in dichloromethane. Surface-enhanced Raman scattering (SERS) spectra of the glass-deposited films confirm modification of Ag colloidal particles by the chemisorbed thiol. The deposited films were then used as substrates for adsorption of hydrophobic, water insoluble species: free-base 5, 10, 15, 20-tetraphenylporphine (H 2TPP) and β-carotene from their dichloromethane solutions. Good quality surface-enhanced resonance Raman scattering (SERRS) spectra of chemically unperturbed H 2TPP and β-carotene obtained from the Ag colloid–ethanethiol-adsorbate films indicate that Ag colloid–ethanethiol films can be employed as spacer-modified substrates for SERRS of water insoluble chromophoric species. However, further testing of the films by adsorption of azodyes methyl yellow and methyl red shows that the spacer efficiency of ethanethiol may be limited by the size and/or by the chemical nature of the adsorbate.

Aggregation of Azo Dyes with Cationic Amphiphiles at Low Concentrations in Aqueous Solution

The aggregation of a series of n-alkyltrimethylammonium bromide (CnTAB, n = 10, 12, 14, 16, and 18) and 4-n-alkyl-1-methylpyridinium iodide amphiphiles (CmpyI, m = 8, 10, 12, and 14) induced by low concentrations of azo dyes in aqueous solution has been investigated by means of ultraviolet (UV) spectroscopy. It was observed that aggregation takes place at surfactant concentrations far below the cmc of C12TAB, C14TAB, C16TAB, and C18TAB with methyl orange (MO), ethyl orange (EO), and para-methyl red (pMR). Aggregation below the cmc of C10TAB was also induced by EO. In the case of MO and pMR, however, higher dye concentrations were necessary to induce aggregation. Interactions at low surfactant concentrations have also been observed in aqueous solutions of C10pyI, C12pyI, and C14pyI with MO. Binding of methyl red (MR), methyl yellow (MY), and azobenzene sulfonate (ABS) with cationic surfactants below their cmc did not occur. Aggregation was reflected by the appearance of a blue-shifted absorption band in the spectra of the dyes. Precipitates formed in aqueous solutions from the cationic surfactants and MO and pMR are CnTA−MO, CnTA−pMR, and Cmpy−MO salts and consist of an equimolar ratio of surfactant and dye. In similar experiments with EO, MR, MY, or ABS as the solvatochromic dye molecules, no precipitation occurred, although surfactant−EO salts precipitated at high EO concentration. Dye−surfactant salts formed from CnTAB and MO were found to form myelins in phase penetration experiments. Temperatures at which myelins start to form increase upon increasing alkyl chain length of the surfactant as revealed by optical microscopy. The formation of vesicles from C10TA−MO and from C12TA−MO crystals was indicated by electron microscopy. The presence and position of the ionic group in the dye molecule is important in determining the association. The importance of hydrophobic interactions is revealed by the chain length dependence on the aggregation process and the observation that interactions are absent in ethanol. Electrostatic interactions also play an important role, as shown by the effect of NaCl on the binding process.

Partitioning of the total reorganization energy into its vibrational and solvent (inertial and reorientational) contributions using resonance Raman intensities

The concept and determination of inertial solvent reorganization energy for an intramolecular charge-transfer process are presented in this Letter. Resonance Raman (RR) spectra have been recorded for 4-nitro,4′-dimethylamino-azobenzene (DA) within the charge-transfer transition, in acetonitrile and benzonitrile. Mode-specific and solvent reorganization energies are determined by simulating the absorption and RR spectra. The results indicate that the vibrational reorganization energy for DA is comparable in the two solvents and the difference is observed mainly in the solvent reorganization energy that has been partitioned into inertial and reorientational components. The inertial response has greater contribution than its reorientational counterpart in acetonitrile, as expected, whereas the reverse trend is observed in benzonitrile.

Determination of Ultra Trace Amounts of Selenium(IV) by Means of a New Reaction System —Methyl Yellow and Hydrogen Peroxide

A spectrophotometric method for the determination of selenium is described, based on the selenium(IV)-catalyzed oxidation of methyl yellow with hydrogen peroxide in a nitric acid medium. As the redox reaction proceeds, the red color of methyl yellow is decolorized. The values of logA0/A show a good linear relationship with the amounts of selenium (A0: absorbance of uncatalyzed reaction solution; A: absorbance of catalyzed reaction solution.). The new method is extremely sensitive, as little as 2 × 10−10 g ml−1 can be easily measured. The detection range is from 5 × 10−7 to 2 × 10−10 g ml−1. In addition, the system possesses extremely high selectivity, most of ions including copper and tellurium can be tolerated during the determination of selenium. The method has been used to determine selenium in egg and wheat, and satisfactory results were obtained.

Low-temperature flash photolysis of 4-amino azobenzene and 4-dimethylamino azobenzene

Using laser flash photolysis, the photoisomerization and cis-trans equilibrium relaxation of 4-amino azobenzene and 4-dimethylamino azobenzene was studied. At low temperature, cis conformers on photoexcitation produced trans cont'ormers along with a fast-decaying intermediate absorbing in 450–490 nm region. These short-lived intermediates were assigned as their zwitterions.