naphthoquinones and hydroxide-ion

We developed a method to graft a tripeptide (glutathione) onto 5-hydroxy-1,4-naphthoquinone, an electropolymerizable molecule. The resulting thin conducting polymer presents a well-defined and stable electroactivity in neutral buffered solution, due to the embedded quinone group, and is able to covalently graft amino-modified DNA probe strands. It is shown that the bioelectrode presents positive current change following DNA hybridization. This makes a "signal-on" direct electrochemical DNA sensor. The results were obtained with low target concentration (50nM) and the selectivity is excellent as a single-mismatch sequence can be discriminated from the full-complementary target.

Topics: Amines; Base Sequence; Biosensing Techniques; DNA; DNA Probes; Electric Conductivity; Electrochemistry; Glutathione; Hydroxides; Naphthoquinones; Nucleic Acid Hybridization; Oxidation-Reduction; Photoelectron Spectroscopy; Polymers; Spectrometry, Fluorescence

A novel and simple spectrophotometric method for the determination of tiopronin with sodium 1,2-naphthoquinone-4-sulfonate (NQS) is established in this paper. The detailed mechanism is proposed and discussed. It is based on the fact that tiopronin can catalyze the reaction between sodium 1,2-naphthoquinone-4-sulfonate and hydroxyl ion to form 2-hydroxy-1,4-naphthoquinone in a buffer solution of pH 13.00 at the maximal absorption wavelength of 445 nm. When tetradecyl benzyl dimethyl ammonium chloride (Zeph) is added to the solution, the sensitivity of the reaction is improved. Beer's law is obeyed in a range of 0.39 - 15.67 microg mL(-1). The equation of linear regression is A = 0.11749 + 0.05914C (microg mL(-1)), with a linear correlation coefficient of 0.9973. The detection limit is 0.2 microg mL(-1), RSD is 0.88% and the recovery rate is in the range of 96.6 - 103.9%. Furthermore, the method has been validated and successfully applied to the determination of tiopronin in pharmaceutical samples.

Topics: Catalysis; Hydroxides; Naphthoquinones; Pharmaceutical Preparations; Spectrum Analysis; Tiopronin

A novel and simple spectrophotometric method for the determination of Captopril with sodium 1,2-naphthoquinone-4-sulfonate is established in this paper. The detailed reaction mechanism is proposed and discussed. It is based on the fact that captopril can catalyze the reaction between sodium 1,2-naphthoquinone-4-sulfonate and hydroxyl ion to form 2-hydroxy-1,4-naphthoquinone in buffer solution of pH 13.00. Beer's law is obeyed in a range of 0.64-80 mugmL(-1) at the maximal absorption wavelength of 442 nm. The equation of linear regression is A=0.05815+0.00589C (mugmL(-1)), with a linear regression correlation coefficient of 0.9981. The detection limit is 0.3 mugmL(-1), R.S.D. is 0.77% and the recovery rate is in range of 96.0-103.8%. Furthermore, the method has been validated and successfully applied to the determination of captopril in pharmaceutical samples.

Topics: Angiotensin-Converting Enzyme Inhibitors; Captopril; Catalysis; Hydrogen-Ion Concentration; Hydroxides; Mass Spectrometry; Naphthoquinones; Spectrophotometry; Spectrophotometry, Infrared

A novel and simple spectrophotometric method for the direct determination of methanol with 1,2-naphthoquinone-4-sulfonate (NQS) is developed in this paper. It is based on the fact that methanol can catalyze the reaction between 1,2-naphthoquinone-4-sulfonate and hydroxyl ion to form 2-hydroxy-1,4-naphthoquinone in buffer solution of pH 13.00. Beer's law is obeyed in a range of 0.26-15.8 mg/ml at the maximal absorption wavelength of 454 nm. The equation of linear regression is A = 0.01998 + 0.05944C (mg/ml), with a linear regression correlation coefficient of 0.9977. The detection limit is 0.25mg/ml (3sigma/k), while R.S.D. is 2.0% and the recovery rate is in a range of 96.5-103%. The detailed mechanism for the formation of the products is proposed and discussed.

Topics: Buffers; Catalysis; Hydrogen-Ion Concentration; Hydroxides; Ions; Magnetic Resonance Spectroscopy; Mass Spectrometry; Methanol; Models, Chemical; Naphthoquinones; Regression Analysis; Spectrophotometry; Spectrophotometry, Infrared; Sulfonic Acids; Temperature