Azo–hydrazone tautomerism in 4-carboxyl-2,6-dinitrophenylazohydroxynaphthalenes
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► Behavior of resident azo–hydrazone tautomers on solvation is studied. ► Predominance of azo or ...hydrazone tautomer found in these closely related azo dyes. ► Despite presence of common OH in the dyes, differences exist in their behaviors. ► Predominance was a function of dye structure, solvent type and solvent properties.
Azo–hydrazone tautomerism is a phenomenon that occurs in azo dyes possessing substituents conjugated to the azo linkage which has labile proton that can be exchanged intramolecularly. Thus the predominance of one tautomer over another is a function of many factors among which are solvent polarity, solvent type, solute–solvent interactions and the structure of the dye molecule itself. The 4-carboxyl-2,6-dinitrophenylazohydroxynaphthalenes, previously shown to exhibit azo–hydrazone tautomerism, were studied for the relative predominance of one form over another based on interaction at the microenvironment of binary solvent mixtures containing DMF and non-hydrogen bonding (CCl
4), hydrogen bond donor (toluene, chloroform), hydrogen bond acceptor (acetonitrile, acetone) and the alcohols; ethanol and methanol as solvent pairs.
The three dyes gave two main bands in the 50:50 mixture of DMF with these solvents consisting of a high energy band at 250–382
nm while the low energy bands for the dyes occurred at 415–485
nm. Spectral shifts in the binary solvent mixtures were related to the solvent dipolarity, basicity of the less polar component relative to DMF, substituent type, molar transition energy, formation constant for the hydrogen-bonding solvated complexes and the standard free energy change for hydrogen bonding with DMF.
The relative predominance of the hydrazone tautomer bears a direct relationship to the basicity of the solvent, presence of hydrogen bond donor substituent and was associated with high molar transition energies and low formation constant. The microenvironment surrounding the dye molecules played a major role in the stability of one tautomer relative to the other.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
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•Azo-hydrazone tautomeric switch detected CN.•Bathochromic shift produced.•CN detected at low levels.•Simple methods developed.
The monoazo dyes, 4-carboxyl-2, ...6-dinitrophenylazohydroxynaphthalenes dyes (AZ-01, AZ-03 and AZ-04), were evaluated as a highly selective colorimetric chemosensor for cyanide ion. The recognition of cyanide ion gave an obvious colour change from light yellow to brownish red and upon dilution with acetone produced a purple to lilac colour.
Optimum conditions for the reaction between the azo dyes and cyanide ion were established at 30°C for 5min, and different variables affecting the reaction were carefully studied and optimised. Under the optimum conditions, linear relationships between the CN− concentrations and light absorption were established. Using these azo-hydrazone molecular switch entities, excellent selectivity towards the detection of CN− in aqueous solution over miscellaneous competitive anions was observed. Such selectivity mainly results from the possibility of nucleophilic attack on the azo-hydrazone chemosensors by cyanide anions in aqueous system, which is not afforded by other competing anions.
The cyanide chemosensor method described here should have potential application as a new family probes for detecting cyanide in aqueous solution.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The need for green synthesis of emerging industrial materials has led to the biosynthesis of nanoparticles from plants to circumvent the adverse by-products of chemical synthesis. In this study, the ...leaf extract of Detarium mirocarpum Guill & Perr, a small tree belonging to the family Fabaceae (Legume), was used to synthesize silver nanoparticles (DAgNPs). DAgNPs were characterized using spectroscopic techniques (Ultraviolet-Visible spectroscopy and Fourier Transform Infrared spectroscopy) which showed hydroxyl and carbonyl functional groups to be responsible for their synthesis. DAgNPs were observed to be crystalline and spherical. The average size, determined by transmission electron microscopy (TEM) was 17.05nm. The antioxidant activity of DAgNPs ranked from moderate to good. The ability of DAgNPs to sense Hg2+ and Fe3+ ions in aqueous medium was also investigated. The quenching of the SPR peak at 430nm was used to monitor the toxic and heavy metal ions with linear ranges of 20–70µgmL−1 and 10–40µgmL−1 for Hg2+ and Fe3+, respectively. The limit of detection (LOD) and limit of quantification (LOQ) obtained for Hg2+ was 2.05µgmL−1 and 6.21µgmL−1, respectively and for Fe3+ was 5.01µgmL−1 and 15.21µgmL−1, respectively. The intra- and inter-day assessments of accuracy and repeatability gave relative errors less than 1% in all instances. DAgNPs can therefore provide a convenient method of sensing the toxic metals easily.
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•Green synthesis of silver nanoparticles carried out.•Indigenous Detarium mirocarpum leave extract gave good yield of AgNPs.•Spectroscopic characterizations of DAgNPs carried out.•DAgNPs produced excellent antioxidant properties.•DAgNPs sensitively determined Hg2+ and Fe3+.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
A mechanism-based spectrophotometric titration of nano-alumina powder with calf thymus ds-DNA was carried out at two temperature levels with a view to generating possible mode of interaction between ...this industrially useful nanopowder and DNA. Varying molar ratio combinations of DNA with the nano-alumina powder were studied at 37 °C and 45 °C after 30 min incubation period. The UV–Vis spectral data were acquired from 200 to 650 nm. The effect of the nanopowder on the most prominent wavelength maximum of DNA at 280 nm was studied. Stoichiometric ratio determination was determined using Job’s method of continuous variation. The formation constants between the ds-DNA and alumina nanopowder were calculated from a modified Benesi–Hildebrand equation for complex formation. In order to understand the spectral changes observed, thermodynamic parameters were evaluated such as the Gibbs free energy, enthalpy and entropy changes. The alumina nanopowder produced a pronounced hypochromic effects on the spectra of ds-DNA at all mole ratios relative to 100% DNA. There was enhanced effect at the elevated temperature of 45 °C with slight hypsochromic shift. These suggest some level of interaction with ds-DNA. The plot of absorbance of complexes at the respective
λ
max
produced two points of inflection which suggest that the two atoms of aluminum in Al
2
O
3
were interacting with DNA molecule. The formation constant varied directly with increase in temperature exhibiting an endothermic reaction. Evaluation of the thermodynamic parameters showed a large free energy change with positive enthalpy and small positive entropy. This confirms a dative covalent bonding interaction. The simple method presented in this research can be used to screen suspected genotoxins especially following occupational exposures.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Due to their enhanced photochromic effects, hydrazone forms of tautomeric azo compounds are commercially preferred as photoreceptors and binary switches. While ortho-hydroxyazo compounds readily ...exhibit an intramolecular hydrazone re-arrangement, the predominance of hydrazone tautomers of para-hydroxyazo compounds is less frequently observed. The objective of this study was to design and synthesize sulphonated 4-naphthylazo naphth-1-ols with preferential hydrazone shift.
PM6 calculations were used to quantify contributions of selected structural features to hydrazone stability in a set of model compounds. Synthesis of five computationally-optimized compounds (3a-e) was subsequently carried out via diazo coupling of 5‑hydroxy-7-sulphonaphthalene-2-diazonium ion with naphthol derivatives. The azo-hydrazone equilibria of 3a-e were further characterized using spectroscopic techniques and density functional theory (DFT).
Computational design revealed that sulphonic acid substitution on the coupling components of the dyes and, solvation effect of the substituents were the highest contributors to hydrazone shift of the compounds. The ring position and electron withdrawing resonance effect of substituents were less contributory. Increasing substitution with sulphonic acid or another hydrophilic group (amino) also resulted in higher hydrazone stability. Mass spectral, IR and NMR data confirmed computational results with mono sulphonated 3a and poly substituted 3c-e existing predominantly as azo and hydrazone forms respectively. UV–Visible spectral analysis revealed that azo and hydrazone forms of 3a predominated in hydrogen bond acceptor and donor solvents respectively. In contrast, absorption spectra of 3b-e showed lone hydrazone bands in all solvents investigated. The DFT/M06-2X/6-31G(dp) characterization of the azo-hydrazone equilibrium of the compounds confirmed experimental results and showed that hydrazone tautomers of 3b, 3c and 3d were more stable than corresponding azo forms by 1.536, 0.289 and 1.359 kcal/mol respectively. DFT also confirmed involvement of sulphonic acid and imino groups in the transition of the dyes’ structures to the keto form.
Three novel p-hydroxyazo dyes with increased hydrazone stability have been synthesized.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
A new approach to the spectrophotometric determination of metronidazole (MZ) and tinidazole (TZ) has been developed. The procedure involves coupling of diazotized nitroimidazoles with ...p-dimethylaminobenzaldehyde (DMAB) to form a greenish-yellow solution. Optimal temperature and time were 0 °C (iced) and 3 minutes for diazotization and 30 °C and 2 minutes for coupling for both MZ and TZ. Coloured adducts of MZ and TZ showed shoulders at 406 nm and 404 nm, respectively, which were selected as analytical wavelengths. The reaction with p-DMAB occurred in a 1:1 mole ratio. Beer's law was obeyed within the 4.8-76.8 μg mL-1 concentration range with low limits of detection. The azo adducts were stable for over a week. Molar absorptivities were 1.10 × 103 (MZ) and 1.30 × 103 L mol-1 cm-1 (TZ). Overall recoveries of MZ and TZ from quality control samples were 103.2 ± 1.3 and 101.9 ± 1.3% over three days. There was no interference from commonly utilized tablet excipients. No significant difference was obtained between the results of the new method and the BP titrimetric procedures. The azo approach using the p-dimethylaminobenzaldehyde procedure described in this paper is simple, fast, accurate and precise. It is the first application of DMAB as a coupling component in the diazo coupling reaction.
U radu je opisan novi način spektrofotometrijskog određivanja metronidazola (MZ) i tinidazola (TZ). Postupak uključuje reakciju diazotiranog nitroimidazola s p-dimetilaminobenzaldehidom (DMAB), pri čemu nastaje zelenkasto-žuta otopina. Optimalna temperatura i vrijeme za diazotaciju su 0 °C (ledena kupelj) i 3 minute, a za reakciju kondenzacije 30 °C i 2 minute. Obojeni adukti imaju maksimum apsorpcije pri 406, odnosno 404 nm pa su te valne duljine izabrane za analitički postupak. Reakcija s p-DMAB zbiva se u množinskom omjeru 1:1. Reakcija slijedi Beerov zakon u koncentracijskom rasponu 4,8-76,8 μg mL-1 s niskim granicama detekcije. Azo adukti su stabilni preko tjedan dana. Molarna apsorptivnost bila je 1,10 × 103 (MZ), odnosno 1,30 × 103 L mol1 cm1 (TZ). Ukupni povrat MZ i TZ iz kontrolnih uzoraka bio je 103,2 ± 1,3, odnosno 101,9 ± 1,3 % tijekom tri dana. Nije zamijećena nikakva interferencija uobičajenih pomoćnih tvari koje se koriste za tabletiranje. Ne postoji značajna razlika između rezultata dobivenih novom metodom i rezultata dobivenih BP titrimetrijskim postupkom. Metoda određivanja opisana u ovom radu je jednostavna, brza, pogodna, točna i precizna i po prvi puta uključuje DMAB u reakciji diazo kopulacije.
A series of five tetracyclic mono azo dyes based on the diazotization of 1-amino-8-hydroxynaphthalene-3,6-disulphonic acid and subsequent coupling with substituted (un)sulphonated naphthalene ...derivatives have been synthesized. The chemical structures of the dyes were established using UV-visible, IR, NMR as well as mass spectrometry. Based on the number of sulphonic acid and other hydrophilic groups they contain, the compounds showed varying extent of water solubility. Spectroscopic characterization revealed the existence of azo-hydrazone tautomerism and the influence of the structures of solvating solvents on the equilibrium. Statistical analysis of single, dual and multiparametric equations of Kamlet Abboud and Taft parameters showed that solvent polarity was the most significant contributor to the observed spectral patterns of the dyes in pure solvents. The compounds could find useful applications as solvatochromic probes, food and drug colour additives.
► The genotoxicity of new dye series were evaluated using human lymphocytes. ► Two congeners having hydroxyl ortho and para to the azo linkage gave toxicity. ► Substituents at the C-7 position ...eliminated the genotoxicity. ► The genotoxicity of dyes bears a direct relationship to their chemical structure.
The genotoxicity of a new monoazo dye series, 4-carboxyl-2,6-dinitrophenylazohydroxynaphthalenes has been evaluated using human lymphocytes by alkaline comet assay. Freshly isolated human lymphocytes were exposed to the dyes (AZ-01, -02, -03 and -04) at concentrations ranging from 0 to 500μM for 3h at 37°C. Appropriate negative (culture medium) and positive (100μM methyl methane sulfonate) controls were set up alongside with the dye-treated cells. Comet assay was performed to assess the extent of DNA damage. The four dyes gave varying results with respect to the parameters of DNA damage studied. AZ-01 showed concentration-dependent DNA damage (% Tail DNA) while lower concentrations (31.25–62.5μM) did not produce any significant difference in the tail extent moment. AZ-02, the positional isomer of AZ-01, gave non-genotoxic effects at lower concentrations for the two DNA parameters. AZ-03 and AZ-04 (possessing additional C-7 substituents) did not produce significant genotoxic effect at all concentrations relative to the negative control. Two of these monoazo dyes show the potential of being used as edible colorants. The results revealed that genotoxicity of congeneric dyes bear a direct relationship to their chemical structure.
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► Dyes–BSA complex formation studied at various temperatures. ► BSA as donor binds dyes based on their structure. ► Two congeners gave 1:1mol ratio in binding to BSA. ► Thermodynamic ...considerations established mode of binding. ► One congener utilized electrostatic interactions in binding.
The intermolecular interaction occurring between bovine serum albumin and 4-carboxyl-2,6-dinitrophenylazohydroxynaphthalene in aqueous media has been studied spectrophotometrically at different temperatures including body temperature. Evidence for the formation of new molecular complexes was established by hypsochromic and hypochromic shifts of the spectra of dye–BSA complexes compared to the spectra of unbound dyes. One congener (AZ-02) gave a minor peak characteristic of charge-transfer complexation. The binding constants of the four monoazo dyes were investigated and found to vary according to the dye structure and temperature of investigation. AZ-01 and -04 combined with BSA at approximately 1:1mol ratio while the other two congeners with additional proton donors gave greater than this mole ratio. Thermodynamic considerations established that the dyes utilized the various forms of binding modes; hydrogen bonding, hydrophobic bonding, van der Waals and AZ-03 was particularly involved in electrostatic interactions giving positive entropy change for a small enthalpy change. The observed properties were correlated with the genotoxicity potentials of the monoazo dyes. The results obtained should prove beneficial in designing other molecules in this category of chemical class.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Comprehensive electronic absorption spectra of a new dye series, 4-carboxyl-2,6-dinitrophenylazohydroxynaphthalenes have been investigated in solvents of varying polarities. The solvent dependent ...UV–vis spectral shifts were analysed using some solvent physical parameters such as refractive index, dielectric function, hydrogen bonding acceptor ability, orientation of polarization and others. The observed spectral shifts were correlated with different solute–solvent interaction mechanisms using simple and multiple linear regression analyses. The results of the curve fitting coefficients enabled us to classify the various interactions of solvents with the dyes and relate the solvatochromic behaviours to the substituent effects on the dye molecules. Charge-transfer complexation occurring between one of the congeners and N,N′-dimethylformamide was extensively studied and discovered to be both concentration- and temperature-dependent.
The electronic character and the chemical nature of the solvents as well as the chemical nature of the other substituents, apart from the common hydroxyl group, are important factors for the observed solvatochromic properties of the 4-carboxyl-2, 6-dinitrophenylazohydroxynaphthalenes.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
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