Voltammetric behavior and square-wave voltammetric determination of trepibutone at a pencil graphite electrode

The photocatalytic degradation of ketoprofen ( KP ), 2-(3-benzoylphenyl)-propionic acid, was studied under UV–vis irradiation using synthesized TiO 2 (anatase), composites of multi-walled carbon nanotubes with TiO 2 anatase (20-MWCNT–TiO 2 ), and commercial anatase. Different factors that affect this process are compared: irradiation source, load of catalyst, initial concentration of KP , pH, concentration of dissolved oxygen, addition of co-oxidants, and the presence of tert -butanol as HO scavenger. The fastest degradation of KP , with a rate constant (42 ± 3) × 10 −4  s −1 , was obtained under UV irradiation in air atmosphere, using 1.2 g L −1 of 20-MWCNT–TiO 2 . Composites of 20-MWCNT–TiO 2 also afforded the fastest degradation with UVA–vis irradiation, in the absence of oxygen, with a rate constant (13.6 ± 0.7) × 10 −4  s −1 . In this case, 60% mineralization of KP was observed after 30 min. Gibbs free energies, p K a values, and the standard reduction potential of KP and related species, calculated by DFT (6-311G(d,p)), are in agreement with the observed behavior. A feasible degradation mechanism is proposed, both for the photolysis and photocatalyzed processes. Similar transient species are involved, both routes leading to similar photoproducts, the main is (3-ethylphenyl)(phenyl)methanone ( m / z  = 211 g/mol), resulting from decarboxylation of KP .

Mechanism of degradation of ketoprofen by heterogeneous photocatalysis in aqueous solution

Ketoprofen (KP) and fenofibrate, respectively, anti-inflammatory and hypolipidemiant agents, promote anormal photosensitivity in patients and may induce photoallergic cross-reactions correlated to their benzophenone-like structure. Here, their ability to photosensitize the degradation of biological targets was particularly investigated in DNA. The photosensitization of DNA damage by KP and fenofibric acid (FB), the main metabolite of fenofibrate, and their parent compound, benzophenone (BZ), was examined on a 32P-end-labeled synthetic oligonucleotide in phosphate-buffered solution using gel sequencing experiments. Upon irradiation at lambda > 320 nm, piperidine-sensitive lesions were induced in single-stranded oligonucleotides by KP, FB and BZ at all G sites to the same extent. This pattern of damage, enhanced in D2O is characteristic of a Type-II mechanism. Spin trapping experiments using 2,2,6,6-tetramethyl-4-piperidone have confirmed the production of singlet oxygen during drug photolysis. On double-stranded oligonucleotides, highly specific DNA break occurred selectively at 5'-G of a 5'-GG-3' sequence, after alkali treatment. Prolonged irradiation led to the degradation of all G residues, with efficiency decreasing in the order 5'-GG > 5'-GA > 5'-GC > 5'-GT, in good agreement with the calculated lowest ionization potentials of stacked nucleobase models supporting the assumption of a Type-I mechanism involving electron transfer, also observed to a lesser extent with adenine. Cytosine sites were also affected but the action of mannitol which selectively inhibited cytosine lesions suggests, in this case, the involvement of hydroxyl radical, also detected by electronic paramagnetic resonance using 5,5-dimethyl-1-pyrrolidine-1-oxide as spin trap. On a double-stranded 32P-end-labeled 25-mer oligonucleotide containing TT and TTT sequences, the three compounds were found to photosensitize by triplet-triplet energy transfer the formation of cyclobutane thymine dimers detected using T4 endonuclease V.

Comparison of DNA Damage Photoinduced by Ketoprofen, Fenofibric Acid and Benzophenone via Electron and Energy Transfer¶

Computational design and development of a novel voltammetric sensor for minoxidil detection based on electropolymerized molecularly imprinted polymer

PET cat. While the copper(II) tren ketoprofenate precatalyst 1 (see picture) is inactive at room temperature in methanol, it is quantitatively and rapidly reduced to its cuprous state upon light irradiation to provide a highly reactive click catalyst. By simply introducing air into the reaction medium the catalysis can be switched off and then switched on again by bubbling argon followed by irradiation.

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Copper Catalyst Activation Driven by Photoinduced Electron Transfer: A Prototype Photolatent Click Catalyst†

A simple differential-pulse polarographic method has been developed for the determination of minoxidil in pharmaceutical dosage forms. The extracting solvent was methanol and the supporting electrolyte was 1.0 N sulphuric acid. An excellent linear relationship was obtained between the concentration and current peak height with a correlation coefficient of 0.9999. Good agreement was obtained between results with the differential-pulse polarography method and those by the manufacturer's method of assay. There was no interference by the tablet excipients. In acid solution, a mechanism for reduction at –1.2 V is proposed, which involves the transfer of four electrons as well as dehydration and deamination steps.

Electrochemical Studies on Minoxidil and Its Determination in Tablets by Differential-Pulse Polarography.

A simple differential-pulse polarographic method has been developed for the determination of ketoprofen in dosage forms. Methanol was employed as the solvent for extracting the drug from the formulations, and Britton-Robinson buffer (pH 6.0) containing 5%V/V methanol was used as the supporting electrolyte. The EP occurs at – 1.15 V. Results obtained by the proposed method are in excellent agreement with those provided by the manufacturer's laboratory. Commonly used tablet excipients and suppository bases were found not to interfere. A mechanism for the electrochemical reduction of ketoprofen at – 1.25 V is proposed that involves the transfer of two electrons.

Electrochemical reduction of ketoprofen and its determination in pharmaceutical dosage forms by differential-pulse polarography

A simple differential-pulse polarographic method has been developed for the determination of zomepirac sodium in tablets. Britton - Robinson buffer of pH 11.0, containing 5% V/V of methanol, was employed as the supporting electrolyte. The peak potential occurs at – 1.50 V. Results obtained by the proposed method are in excellent agreement with those provided by both the official and the manufacturer's methods of assay. It was found that commonly used tablet excipients did not interfere in the analyses.

Voltammetric studies of zomepirac sodium and its determination in tablets by differential-pulse polarography.

The electrochemical activities of (E)-5-(2-bromovinyl)-2′-deoxyuridine (BVDU) and 5-iodo-2′-deoxyuridine (idoxuridine) were investigated and a simple diffential-pulse polarographic method was developed for the determination of idoxuridine in ophthalmic solutions and ointments. Both compounds were reduced at the dropping-mercury electrode (D.M.E.). In phosphate buffer (pH 7.0), idoxuridine exhibits a well developed d.c. and differential-pulse polarographic wave with an E1/2 value of –0.97 V vs. S.C.E. The electroreduction mechanism for this substance involves a two-electron carbon–halogen bond fission. On the other hand, BVDU is reduced in tetraethylammonium bromide solution (pH 5.85) at an applied potential of –1.8 V. The mechanism of reduction for BVDU involves the transfer of four electrons, which has been attributed to the fission of the bromine–carbon bond followed by reduction of the vinyl double bond.The height of the differential-pulse polarographic peaks for idoxuridine and BVDU varies linearly with the concentration of the depolarisers over the range 1 × 10–4 to 5 × 10–4M and each substance exhibits a correlation coefficient of 0.9996. The assay method developed for idoxuridine is simple and has a detection limit of about 2.0 µg ml–1.

Lawrence Amankwa

Papers

Electrochemical Studies on Minoxidil and Its Determination in Tablets by Differential-Pulse Polarography.

Electrochemical reduction of ketoprofen and its determination in pharmaceutical dosage forms by differential-pulse polarography

Voltammetric studies of zomepirac sodium and its determination in tablets by differential-pulse polarography.

Studies on the electrochemical behaviour of two anti-herpes uridines