Solvatochromic behaviours and structure-spectra relationships of 4-carboxyl-2,6-dinitrophenylazohydroxynaphthalenes

Synthesis and photophysical properties of deuteration of pirfenidone

In order to improve the metabolism of pirfenidone (5-methyl-1-phenylpyridin-2-one, PFD), the methyl-deuterated version of pirfenidone via the substitution of hydrogen (H) at C-5 by its isotope deuterium (D, 5D-PFD) was synthesized and its photophysical properties were investigated. The negative solvatochrom was observed in absorption and fluorescence spectra with increasing solvent polarity, which implied that intermolecular charge transfer (ICT) involved n → π* transition for both of PFD and 5D-PFD. The ground state and excited state dipole moment was calculated as 5.30 D and 3.30 D for PFD, and 3.70 D and 2.18 D for 5D-PFD, respectively, which suggested the more polar nature of PFD in the ground state than that of excited state compared with 5D-PFD. Density functional theory (DFT) results demonstrated a significant propensity of ICT from the electron-donor, methyl and carbonyl group to the amine group as an electron donor. The binding of metal ions with PFD or 5D-PFD induced a red-shift of π → π* transition and blue-shift of n → π* transition, respectively, indicating that the pyridone ring showed more stability upon binding of unoccupied orbital of metal ions with lone-pair electron of oxygen atom and thus prompted the electronic distribution on phenyl unit. Upon addition of metal ions, the aromatic region presented the characteristic upfield shifts, and the resonance contributed by 3-H showed a significant downfield chemical shift/deshielding effect, indicating the deduced resonance of 3-H and the improved electron distribution of phenyl unit. The binding and docking of human serum albumin showed that the affinity of 5D-PFD with HSA was lower than that of PFD, and also 5D-PFD might prefer to present free forms in the blood with better efficacy comparing with PFD. The pharmacokinetic of half-time (T_1/2) for oral and i.v. administration of 5D-PFD was found around 19 and 30 min, higher than that of i.v. administration of PFD, 8.6 min, reported by Giri et al. The results of this work suggest that the deuteration enhances the metabolism of PFD significantly with little change of physical-chemical property.

Spectroscopic studies of keto–enol tautomeric equilibrium of azo dyes

Keto–enol tautomeric equilibrium of an azo dye is shifted to the keto form as the solvent polarity is increased.

UV-Vis spectroscopic study and DFT calculation on the solvent effect of trimethoprim in neat solvents and aqueous mixtures

The solvatochromic behavior of trimethoprim (TMP) was analyzed using UV-Vis spectroscopy and DFT methods in neat and binary aqueous solvent mixtures. The effects of solvent dipolarity/polarizability and solvent-solute hydrogen bonding interactions on the absorption maxima were evaluated by means of the linear solvation energy relationship concept of Kamlet and Taft. This analysis indicated that both interactions play an important role in the position of the absorption maxima in neat solvents. The simulated absorption spectra of TMP and TMP:(solvent)n complexes in ACN and H2O using TD-DFT methods were in agreement with the experimental ones. Binary aqueous mixtures containing as co-solvents DMSO, ACN and EtOH were studied. Preferential solvation was detected as a nonideal behavior of the wavenumber curve respective to the analytical mole fraction of co-solvent in all binary systems. TMP molecules were preferentially solvated by the organic solvent over the whole composition range. Index of preferential solvation, as well as the influence of solvent parameters were calculated as a function of solvent composition.

Novel colorimetric sensors for cyanide based on azo-hydrazone tautomeric skeletons

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 5 min, 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.

Spectrophotometric and thermodynamic studies of the interactions of 4-carboxyl-2,6-dinitrophenylazohydroxynaphthalenes with bovine serum albumin

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 1:1 mol 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.

Genotoxicity evaluation of 4-carboxyl- 2,6-dinitrophenylazohydroxynaphthalenes in mice

A short-term in vivo genotoxicity evaluation of 4-carboxyl-2,6-dinitrophenylazohydronaphthalenes (AZ-01 to AZ-04) has been carried out in mice. Aqueous colloidal solutions of the dyes were administered to mice on each day for 5 successive days using gastric gavages. Two end point assessments of the genotoxicity potentials of the dyes were assessed using comet assay and chromosomal aberration studies using the mice bone marrow cells. The dyes were well tolerated at the doses investigated, as there were no deaths or any adverse pharmacotoxic events. Dose-dependent DNA damage (in terms of percentage of tail DNA and Olive tail moment) occurred with AZ-01 and AZ-02, although the effects were significant only with the highest doses. AZ-03 gave similar patterns with those of AZ-01 and AZ-02, while replacement with butanone in AZ-04 altered the observed pattern. Minimal chromosomal damages were obtained for the four dyes, with AZ-01 and AZ-02 giving nonsignificant damages, while the highest dose of AZ-03 produced significant aberrations in terms of breaks. Some minor isochromatid breaks and gaps were also noticed in the dye-treated mice. Mitotic indices in all cases were not significantly different from concomitantly administered vehicle control showing lack of cytotoxicity of the monoazo dyes at these doses. The monoazo dyes show the potential of being utilized as colorants, pending further required tests.

Spectroscopic study of solvent effects on the electronic absorption spectra of flavone and 7-hydroxyflavone in neat and binary solvent mixtures

The solvatochromic characteristics of flavone and 7-hydroxyflavone were investigated in neat and binary solvent mixtures. The spectral shifts of these solutes were correlated with the Kamlet and Taft parameters (α, β and π*) using linear solvation energy relationships. The multiparametric analysis indicates that both specific hydrogen bond donor ability and non-specific dipolar interactions of the solvents play an important role in absorption maxima of flavone in pure solvents. The hydrogen bond acceptor ability of the solvent was the main parameter affecting the absorption maxima of 7-hydroxyflavone. The simulated absorption spectra using a TD-DFT method were in good agreement with the experimental ones for both flavones. Index of preferential solvation was calculated as a function of solvent composition. Preferential solvation by ethanol was detected in cyclohexane-ethanol and acetonitrile-ethanol mixtures for flavone and in acetonitrile-ethanol mixtures for 7-hydroxyflavone. These results indicate that intermolecular hydrogen bonds between solute and solvent are responsible for the non-linear variation of the solvatochromic shifts on the mole fraction of ethanol in the analyzed binary mixtures.

Relative predominance of azo and hydrazone tautomers of 4-carboxyl-2,6-dinitrophenylazohydroxynaphthalenes in binary solvent mixtures

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.

In vitro genotoxicity evaluation of 4-carboxyl-2,6-dinitrophenylazohydroxynaphthalenes using human lymphocytes

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 500 μM for 3h at 37 °C. Appropriate negative (culture medium) and positive (100 μM 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 (31.25-62.5 μM) 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.

Ground state and excited state dipole moments of 6,8-diphenylimidazo[1,2-α]pyrazine determined from solvatochromic shifts of absorption and fluorescence spectra

Electronic absorption and dual fluorescence spectra of 6,8-diphenylimidazo[1,2-α]pyrazine (68DIP) was recorded in various solvents with different polarity at room temperature. The ground state (μg) and the excited state (μg) dipole moments of 68DIP were estimated from solvatochromic shifts of absorption and fluorescence spectra as a function of the dielectric constant (ɛ) and refractive index (n). The results show that the value of excited state dipole moment in SE: μeSE=2.8772 D and twisted intramolecular charge transfer (TICT) excited equilibrated state dipole moment value of μeLE=2.9744 D was found. The solvent dependent spectral shifts in absorption and fluorescence spectra were analyzed by the polarizability-polarity and Kamlet-Taft parameters.

Studies on the electronic absorption spectra of some monoazo derivatives

The electronic absorption spectra of a series of azo dye compounds containing -Cl, -SO3H and -OH groups were recorded in twenty one solvents with different polarities. The solvents were selected to cover a wide range of parameters (refractive index, dielectric constant and hydrogen bonding ability). Solvent-induced effect on the maximum absorption band frequencies of azo dye compounds are described in terms of solute-solvent interactions. Multiple linear regression equation for νmax was performed using polarizability-polarity parameters and Kamlet-Taft solvatochromic parameters. The results help to assign the solvent-solute interactions and the solvatochromic potential of the investigated compounds. It is concluded that the electronic of the substituent and hydrogen bonding acceptor ability of the solvents are the major factors to the interaction in solutions.