Facile Synthesis of Catechol Azo Dyes

Graphene oxide supported MnO2 nanorods: an efficient heterogeneous catalyst for oxidation of aromatic amines to azo-compounds

Graphene oxide supported MnO₂ nanorods (GOnc), a composite material, has been synthesized and characterized by XRD, FE-SEM, EDX, BET surface area measurement, FTIR and Raman Spectroscopy.

Oxidative dimerization of (hetero)aromatic amines utilizing t-BuOI leading to (hetero)aromatic azo compounds: scope and mechanistic studies

A straightforward synthetic method of both symmetric and unsymmetric aromatic azo compounds through an efficient and cross-selective oxidative dimerization of aromatic amines using tert-butyl hypoiodite (t-BuOI) under metal-free and mild conditions has been developed. This method was also found applicable to the synthesis of heteroaromatic azo compounds. The spectroscopic study indicates the involvement of N,N-diiodoanilines in the oxidative reaction as the key intermediate.

Pentakis(trifluoromethyl)benzenediazonium Cation: A Useful Building Block for the Syntheis of Trifluoromethyl-Substituted Derivatives

The sterically crowded, highly electron-deficient diazonium salt C₆ (CF₃ )₅ N₂ ⁺ BF₄ ^- has been synthesized and sample dediazotization reactions were carried out. New compounds, C₆ (CF₃ )₅ I, C₆ (CF₃ )₅ NO₂ , and C₆ (CF₃ )₅ NO were isolated and identified. Also, a more convenient route to C₆ (CF₃ )₅ NH₂ that gave good yield was achieved.

Highly efficient synthesis of aromatic azos catalyzed by unsupported ultra-thin Pt nanowires

Aromatic azos were synthesized using unsupported ultra-thin platinum nanowires as catalysts under mild reaction conditions and the reaction mechanism was proposed.

Spectrophotometric determination of aqueous acidity constants of three azo dyes

The two successive steps acidity constants of three azo dye derivatives D1–D3, were determined by a spectrophotometric method using 0.10 M KNO3 as supporting electrolyte in water solvent. The electronic spectra of the compounds were recorded in the course of their pH-metric titration with a standard base solution. The protolytic equilibrium constants can be solved very satisfactorily from absorbance data, by combining the data obtained in the spectrometric determinations with graphic methods as the absorbance diagrams. An A-diagram shows the relative absorbance changes at two wavelengths as a function of the pH. For a one-step system, the absorbance at any wavelength must be proportional to the absorbance at any other wavelength, so an A-diagram for all wavelength combinations for such a system must be linear (rank, s=1). However, if a system is governed by two or more equilibria, the A-diagrams corresponding to multi-step titrations will change direction every time a new equilibrium becomes dominant in the system. Analysis of the each uniform sub-region can then be used in evaluating of the corresponding equilibrium. A-diagrams for all wavelength combinations suggest that these systems have the rank two(s=2). The results revealed that the Ka(1) and Ka(2) values of different azo dyes follow the order D3>D2>D1.

Solvatochromism and temperature effects on the electronic absorption spectra of some azo dyes

The UV-visible electronic spectra of some azo dyes have been studied. The different bands observed in the electronic spectra of the compounds in various organic solvents have been assigned to the proper electronic transitions. The solvatochromic behaviour of these compounds was investigated by studying their visible spectra in several pure and mixed organic solvents. The longer wavelength band displayed by para-nitro azo dyes is assigned to an intermolecular charge-transfer transition. The solvated H-bonding complexes formed between N,N-dimethylformamide and the para-nitro azo dyes were investigated. DeltaG and formation constant, the values of K(f) of the molecular complexes formed in solution have been determined. The effects of increase of temperature and concentration dependent spectroscopic changes on the longer wavelength visible band of para-nitro azo dyes were also investigated.

Langmuir monolayer and Langmuir-Blodgett films formed by a melamine-headed azobenzene-derived amphiphile: interfacial assembly affected by host-guest interaction

A novel azobenzene-derived amphiphile with a melamine head, 2Azo-2C12H2-melamine, has been synthesized. pi-A isotherm measurements displayed that this amphiphile is able to form a stable Langmuir monolayer on both pure water and barbituric acid (BA)- or thymine (T)-containing subphases. The collapse surface pressure and limiting molecular area of its Langmuir monolayer on pure water are 40 mN/m and 0.56 nm2, respectively. However, when barbituric acid or thymine was introduced into the subphase, the corresponding pi-A isotherms of the monolayers exhibited a lower collapse surface pressure (22 mN/m for BA, 21 mN/m for T) and smaller limiting molecular area (0.54 nm2 for BA and 0.52 nm2 for T). UV-vis and FT-IR studies of the LB films formed by 2Azo-2C12H25-melamine have also been carried out. The results indicated that the LB films of 2Azo-2C12H25-melamine deposited from pure water undergo distinct collapse of the H-aggregate upon UV irradiation, while the LB films deposited from a BA- or T-containing subphase retain the H-aggregate. The host-guest-interaction-induced blockage of azobenzene photoisomerization should be responsible for the stabilized H-aggregate. A 1:1 host/guest binding mode to form a linear supramolecular polymeric chain has been proposed in the Langmuir monolayers formed on a BA- or T-containing subphase. The current results suggest that the host-guest interaction should be an effective means to manipulate the interfacial assembly of azobenzene-derived amphiphiles.

The inhibitory effect of some new synthesized xanthates on mushroom tyrosinase activities

Three iso-alkyldithiocarbonates (xanthates), as sodium salts, C3H7OCS2Na (I), C4H9OCS2Na (II) and C5H11OCS2Na (III), were synthesized, by the reaction between CS2 with the corresponding iso-alcohol in the presence of NaOH, and examined for inhibition of both cresolase and catecholase activities of mushroom tyrosinase (MT) from a commercial source of Agricus bisporus. 4-[(4-methylbenzo)azo]-1,2-benzendiol (MeBACat) and 4-[(4-methylphenyl)azo]-phenol (MePAPh) were used as synthetic substrates for the enzyme for the catecholase and cresolase reactions, respectively. Lineweaver-Burk plots showed different patterns of mixed and competitive inhibition for the three xanthates and also for cresolase and catecholase activities of MT. For cresolase activity, I and II showed a mixed inhibition pattern but III showed a competitive inhibition pattern. For catecholase activity, I showed mixed inhibition but II and III showed competitive inhibition. These new synthesized compounds are potent inhibitors of MT with K(i) values of 9.8, 7.2 and 6.1 microM for cresolase inhibitory activity, and also 12.9, 21.8 and 42.2 microM for catecholase inhibitory activity for I, II and III, respectively. They showed a greater inhibitory potency towards the cresolase activity of MT. Both substrate and inhibitor can be bound to the enzyme with negative cooperativity between the binding sites (alpha > 1) and this negative cooperativity increases with increasing length of the aliphatic tail in these compounds in both cresolase and catecholase activities. The cresolase inhibition is related to the chelating of the copper ions at the active site by a negative head group (S-) of the anion xanthate, which leads to similar values of K(i) for all three xanthates. Different K(i) values for catecholase inhibition are related to different interactions of the aliphatic chains of I, II and III with hydrophobic pockets in the active site of the enzyme.

Multiwavelength spectrophotometric determination of acidity constants of some azo dyes

A multiwavelength spectrophotometric titration method was applied to study the acidity constants of some azo dyes in water. The UV-vis absorption spectra of azo dye solutions were recorded in the course of their pH-metric titration with a standard base solution. The protolytic equilibrium constants, spectral profiles, concentration diagrams and also the number of components have been calculated. The quantitative effects of the substituents on the acidity of the studied azo dyes were investigated by the linear free energy relationship (LFER) using Hammet sigma constant (sigma) and field and resonance effects of Kamlet and Taft (f and Re, respectively).

Selective COX-2 inhibitors. Part 1: synthesis and biological evaluation of phenylazobenzenesulfonamides

A series of phenylazobenzenesulfonamide derivatives were designed and synthesized for the evaluation as selective cyclooxygenase-2 (COX-2) inhibitors in a cellular assay using human whole blood (HWB) and an enzymatic assay using purified ovine enzymes. Extensive structure-activity relationships (SAR) were studied within this series, and several of selective COX-2 inhibitors have been identified. Among them, compound 8, 4-(4-amino-2-methylsulfanyl-phenylazo)benzenesulfonamide, showed a potent inhibitory activity to the cyclooxygenase enzymes (IC(50)'s for COX-1: 23.28 microM; COX-2: 2.04 microM), being active but less COX-2 selective than celecoxib.

Phthalocyanine-modulated isomerization behaviour of an azo-based photoswitch

A photoswitchable azobenzene-phthalocyanine-azobenzene triad has been synthesized and its electrochemical properties determined. Energy transfer among the subunits allows for modification of the E-Z ratio by selective excitation of the phthalocyanine moiety.

Mushroom tyrosinase inhibition by two potent uncompetitive inhibitors

Two new bi-pyridine compounds, [1,4'] Bipiperidinyl-1'-yl-naphthan-2-yl-methanone (I) and [1,4'] Bipiperidinyl-1'-yl-4-methylphenyl-methane (II) were synthesized and examined for inhibition of the catecholase activity of mushroom tyrosinase in 10 mM phosphate buffer pH 6.8, at 293 K using UV spectrophotometry. Inhibition kinetics indicated that they were uncompetitive inhibitors and the value of the inhibition constants were 5.87 and 1.31 microM for I and II, respectively, which showed high potency. Fluorescent studies confirmed the uncompetitive type of inhibition for these two inhibitors. The inhibition mechanism presumably comes from the presence of a particular hydrophobe site which can accommodate these inhibitors. This site could be formed due to a probable conformational change that was induced by binding of substrate with the enzyme.

Substrate share in the suicide inactivation of mushroom tyrosinase

To address the real cause of the suicide inactivation of mushroom tyrosinase (MT), under in vitro conditions, cresolase and catecholase reactions of this enzyme were investigated in the presence of three different pairs of substrates, which had been selected for their structural specifications. It was showed that the cresolase activity is more vulnerable to the inactivation. Acetylation of the free tyrosyl residues of MT did not cure susceptibility of the cresolase activity, but clearly decreased the inactivation rate of MT in the presence of 4-[(4-methylbenzo)azo]-1,2-benzenediol (MeBACat) as a catecholase substrate. Considering the results of the previous works and this research, some different possible reasons for the suicide inactivation of MT have been discussed. Accordingly, it was proposed that the interruption in the conformational changes in the tertiary and quaternary structures of MT, triggered by the substrate then mediated by the solvent molecules, might be the real reason for the suicide inactivation of the enzyme. However, minor causes like the toxic effect of the ortho-quinones on the protein body of the enzyme or the oxidation of some free tyrosyl residues on the surface of the enzyme by itself, which could boost the inactivation rate, should not be ignored.

A colormetric assay for catechol-O-methyltransferase

A series of catechol diazo dyes were synthesized and tested as substrates for the enzyme catechol-O-methyltransferase (COMT) with the aim of developing a sensitive HPLC assay method using visible wavelength light detection. A method was developed which allowed for the determination of the two regioisomeric methylated products of the COMT catalyzed reaction of 4-[(3,4-dihydroxyphenyl)azo]benzenesulfonate with S-adenosylmethionine (AdoMet). Separation of the assay components was achieved by reverse phase chromatography using an isocratic mobile phase. No pre-preparation of the assay samples was required.

Stability, structural and suicide inactivation changes of Mushroom tyrosinase after acetylation by N-acetylimidazole

Modification (acetylation) of Tyr residues with N-acetylimidazole protects outstandingly mushroom tyrosinase (MT) from the suicide inactivation in the presence of its catecholic substrate, 4-[(4-methylbenzo) azo]-1,2-benzenediol. UV spectrophotometric experiments and differential scanning calorimetry (DSC) studies indicated a decrease in kinetic stability of the enzyme alongside with increase in its thermal stability as well as its stability against n-dodecyl trimethylammonium bromide as a denaturizing agent. Pace analysis resulted in standard Gibbs free energy values of 46.54 and 52.09 kJ/mol in the absence of denaturant for native and modified enzyme, respectively. Structural studies by circular dichroism (CD) spectrophotometry showed that modification did not have major impact on the secondary structure of MT; however, induced some changes in its tertiary structure. The near-UV CD results revealed that the modification had enhanced intramolecular van der Waals interactions in the enzyme structure, which was in coincidence with its thermodynamic stability.