nitrophenols and 4-cyanophenol

Analysis of 4-cyanophenol and 3-nitrophenol was carried out using multi-walled carbon nanotubes-based solid-phase extraction (SPE) and capillary electrophoresis (CE) methods. Capillary electrophoresis was carried out with 18 kV voltage, 214 nm detection, and phosphate buffer (pH 7.0, 15 mM) as background electrolyte at 25 ± 1 °C temperature with 15.05 and 16.5 min migration times of 4-cyanophenol and 3-nitrophenol. The separation and resolution factors were 1.10 and 2.90. The optimized experimental conditions were 40 mg/L concentration, 1.0 g multi-walled carbon nanotubes (MWCNTs) per SPE cartridge, 5.0 mL/min flow rate of water, 0.1 mL flow rate of eluting solvent. The maximum recoveries were 91% and 98% at 0.1 mL/min flow rate of 4-cyanophenol and 3-nitrophenol. These methods were applied successfully for extraction and estimation of 4-cyanophenol and 3-nitrophenol in the municipal wastewater. The reported methods are reproducible, efficient, and practical for the estimation of these phenols in water.

Topics: Electrophoresis, Capillary; Nanotubes, Carbon; Nitrophenols; Phenols; Solid Phase Extraction; Water

Competitive inhibition by phenolic compounds of the ascorbic acid oxidation reaction catalyzed by ascorbate oxidase was investigated at pH 7.0 and 23.0 degrees C. Inhibition of p-nitrophenol is pH dependent over the range 5.0-8.0, with inhibitor binding favored at higher pH. Bulky substituents on the phenol nucleus reduce or prevent the inhibitory effect. The presence of phenol affects the binding characteristics of azide to the trinuclear cluster of the enzyme. In particular, binding of azide to type 2 copper is prevented, and the affinity of azide to type 3 copper is reduced. In addition, reduction of type 1 copper is observed upon prolonged incubation of ascorbate oxidase with excess phenol and azide, but not with phenol alone. It is proposed that binding of phenolic inhibitors occurs at or near the site where the substrate (ascorbate) binds. NMR relaxation measurements of the protons of phenols in the presence of ascorbate oxidase show paramagnetic effects due to the proximity of the bound inhibitor to a copper center, likely type 1 copper. Copper-proton distance estimates between this paramagnetic center and p-cresol or p-nitrophenol bound to ascorbate oxidase are between 4.4 and 5.9 A.

Topics: Ascorbate Oxidase; Binding, Competitive; Chlorophenols; Cresols; Electron Spin Resonance Spectroscopy; Enzyme Inhibitors; Hydrogen-Ion Concentration; Nitrophenols; Phenol; Phenols; Spectrophotometry, Ultraviolet