Tadeusz Ossowski

Electrochemical and UV-spectrophotometric study of oxygen and superoxide anion radical interaction with anthraquinone derivatives and their radical anions

Abstract One-electron reduction of dihydroxyanthraquinone derivatives was studied in dimethylsulfoxide solution by means of electrochemical and spectrophotometric methods. It was found that dihydroxyanthraquinone reduction in the presence of oxygen occurs according to an EC mechanism, the second step being oxygen reaction with semiquinone anion radical. This mechanism was confirmed by the dependence of CV curves on dihydroxyanthraquinone and oxygen concentration. Supplementary spectrophotometric and electrochemical studies of the dihydroxyanthraquinone-potassium superoxide system have shown that no covalent compound is formed between seminquinone anion radical and molecular oxygen and therefore the reaction following dihydroxyanthraquinone reduction involves electron and proton transfer from semiquinone anion radical to molecular oxygen to form hydroperoxyl radical and deprotonated dihydroxyanthraquinone. The rate constants of the electron-transfer reactions from semiquinone anion radical to moleculax oxygen were determined from the dependence of anthraquinone cathodic reduction peak potential and the corresponding anodic peak current on oxygen concentration. It was found that the rate constants increase with decreasing p K a of the hydroxyanthraquinones, which confirms the postulated mechanism.

Electrochemical study of oxygen interaction with lapachol and its radical anions

Cyclovoltammetric studies were performed with lapachol [2-hydroxy-3-(3-methyl-2-butenyl)-1,4-naphthoquinone], in the absence and presence of oxygen, which aimed to investigate possible oxygen interaction with lapachol and its radical anion. The obtained results clearly indicate the consumption of the semiquinone anion-radicals by oxygen in an EC type reaction, generating the deprotonated form of lapachol and HOO*. The observed generation of reactive oxygen species (ROS) after electron transfer can be related to the mechanism of biological action of lapachol.

Synthesis and fluorescence behaviour of crown and azacrown ethers carrying the dansyl fluorophore as a pendant in acetonitrile solution

The influence of Li+, Na+, K+, Cs+, Mg2+, Ca2+, Sr2+, Ba2+, Co2+, Ni2+, Cu2+, Zn2+, Pb2+ and Al3+ ions on the spectroscopic properties of the dansyl group covalently linked to crown ether or diazacrown ethers was investigated by means of absorption and emission spectrophotometry. Interaction of the alkali metal ions with all fluoroionophores studied is weak, while alkaline earth metal ions interact strongly causing about 50% quenching of dansyl fluorescence of A21C5-Dns and A218C6-Dns. The Cu2+, Pb2+ and Al3+ cations interact very strongly with dansyl chromophore regardless the crown ether type, causing a major change in absorption spectrum of the chromophore and forming non-fluorescent complexes. The Co2+, Ni2+, Zn2, Mg2+ and Ag+ cations interact moderately with all fluoroionophores studied causing about 20% of fluorescence quenching of dansyl, except for a strong dansyl fluorescence quenching of 15C5-Dns by Co2+ ion. The quenching efficiency of didansylated fluoroionophores by the alkali metal ions and alkaline earth metal ions is weaker than monodansylated ones.

Interactions of metal ions with monoaza crown ethers A15C5 and A18C6 carrying dansyl fluorophore as pendant in acetonitrile solution

The influence of metal cations Li(+), Na(+), K(+), Cs(+), Mg(2+), Ca(2+), Sr(2+), Ba(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+), Pb(2+) and Al(3+) on the spectroscopic properties of the dansyl (1-dimethylaminonaphthalene-5-sulfonyl) group covalently linked to monoaza crown ethers 1-aza-15-crown-5 (1,4,7,10,-tetraoxa-13-azacyclopentadecane) (A15C5) and 1-aza-crown-6 (1,4,7,10,13-pentaoxa-16-azacyclooctadecane) (A18C6) was investigated by means of absorption and emission spectrophotometry. Interaction of the alkali metal ions with both fluoroionophores is weak, while alkaline earth metal ions interact strongly causing 50 and 85% quenching of dansyl fluorescence of N-(5-dimethylamine-1-naphthalenesulfonylo)-1,4,7,10,-tetraoxa-13-azacyclopentadecane (A15C5-Dns) and N-(5-dimethylamine-1-naphthalenesulfonylo)-1,4,7,10,13-pentaoxa-16-azacyclooctadecane (A18C6-Dns), respectively. The Cu(2+), Pb(2+) and Al(3+) cations interact very strongly with dansyl chromophore, causing a major change in absorption spectrum of the chromophore and forming non-fluorescent complexes. The Co(2+), Ni(2+), Zn(2+), Mg(2+) cations interact moderately with both fluoroionophores causing quenching of dansyl fluorescence by several percent only.

Synthesis, redox properties, and basicity of substituted 1-aminoanthraquinones: spectroscopic, electrochemical, and computational studies in acetonitrile solutions

Abstract1-Amino-, 1-ethylamino-, and 1-(diethylamino)-anthraquinone were characterized by UV–Vis spectroscopy, acid–base titration, electrochemical methods, and quantum-chemical (QM) calculations at the B3LYP/6-31 ++G** level. Acid–base titration and the relative differences between the free energies of the basic and acidic forms of the studied species show that 1-(diethylamino)anthraquinone is the strongest base in an acetonitrile solution. Moreover, the structural differences between the B3LYP-optimized neutral and protonated anthraquinones, notably the presence or the absence of internal hydrogen bonds, account well for the sequence of the measured/calculated basicity. The basicity of the investigated compounds strongly influences their electrochemical properties in acetonitrile. Indeed, the cyclic voltammograms of 1-aminoanthraquinone and 1-(ethylamino)anthraquinone display two well-resolved reduction waves that indicate a two-step reduction process (EE mechanism). On the other hand, the electroreduction of 1-(diethylamino)anthraquinone becomes complicated by the interaction of its reduced forms with traces of water present in an acetonitrile solution (ECE mechanism). The mechanism of this reaction is proposed, and its possibility to occur is examined based on QM calculations.

Single-crystal X-ray diffraction analysis of designer drugs: hydrochlorides of metaphedrone and pentedrone.

This article, written as a result of cooperation between a police forensic laboratory and an academic institution, outlines the possibility of applying single-crystal X-ray diffraction analysis as an effective method of identifying designer drugs in forensic analysis. This technique allows crystalline samples to be determined with full assurance about their identity, even in the case of new substances for which no reference standards yet exist. Here, single-crystal X-ray diffraction measurements of single-crystal specimens obtained from two samples were performed. Solution and refinement of the structures demonstrated that the target compounds were metaphedrone and pentedrone hydrochlorides - synthetic cathinone derivatives used as recreational stimulants. In addition to the identification of the title compounds, this paper gives a first report on their crystal structures. Once the CIF-files containing the crystal structure data of the title compounds have been deposited in the Cambridge Structural Database - the world repository of small molecule crystal structures - it will be possible to identify single crystals of the title compounds quickly on the basis of simple parameters (lattice parameters a, b, c, α, β, γ and unit cell volume). This description of the relationship between the geometrical parameters of moieties and the analysis of intermolecular interactions occurring in crystals of the title compounds extends knowledge about the synthetic derivatives of cathinone and may play a role in future studies, leading to a better understanding of their characteristic properties.

Application of BDD thin film electrode for electrochemical decomposition of heterogeneous aromatic compounds

The aim of the presented study is to investigate the applicability of electrochemical oxidation of aromatic compounds containing heteroatoms, e.g. waste from production of pesticides or pharmaceutics, at a borondoped diamond (BDD) electrode. The BDD electrodes were synthesized by microwave plasma enhanced chemical vapour deposition (MW PE CVD). Investigation of the electrode surface by optical microscopy and scanning electron microscopy (SEM) confirmed that the synthesized layer was continuous and formed a densely packed grain structure with an average roughness of less than 0:5 μm. The influence of important electrochemical parameters: current density, kind of reactor, pH or mixing operation, on the efficiency of the oxidation was investigated. The fouling of electrode’s surface caused by the deposition of organic material was observed during CV and galvanostatic experiments. At low current density the oxidation rate constant k was low, but the current efficiency was relatively high. The BDD can be used successfully to remove heterogeneous aromatic compounds existing either as molecules or cations. During 4 h of electrolysis 95% of aromatic compounds were electrochemically decomposed to mineral forms. It was observed that the influence of the initial pH on mineralization was marginal.

Determination of the pKa values of some biologically active and inactive hydroxyquinones

The apparent dissociation constants (pKa) of four 2-hydroxynaphthoquinones, differently substituted at C-3, were determined in water:ethanol (1:1, v/v) solutions by pH-metric and hybrid pH-metric/UV titration methods. Isolapachol (pKa 6). Two pKa values were determined for each of the methylamino-derivatives investigated, the first relating to the enol function and the second to the ammonium salt. It was determined that under physiological pH, these derivatives would be to a large extension, zwitterionic. The possible effects of the measured parameters on the biological activities of the studied compounds are discussed.

Cytostatic and Antiviral Activity Evaluations of Hydroxamic Derivatives of Some Non-steroidal Anti-inflammatory Drugs

Non‐steroidal anti‐inflammatory drugs (NSAID) pharmacophores are interesting in designing potential anticancer drugs. Indeed, numerous experimental, epidemiologic and clinical studies suggest that NSAIDs are promising anticancer drugs. Herein, NSAID hydroxamic acids 3a‐i were prepared by a new synthetic procedure and evaluated for their antiviral and cytostatic activity against malignant tumor cell lines and normal human fibroblasts (WI38). Antiviral activity evaluation results indicated that 3f had only a minor activity against the influenza virus A/H1N1 subtype with a selectivity index of 7–10. On the other hand, the results of the in vitro cytostatic activity evaluations revealed that the majority of NSAID hydroxamic acid derivatives 3a–i exhibited a strong non‐specific antiproliferative effect at the highest concentration (100 μm) on the tested cell line panel. Only compounds 3b, 3e and 3i exerted a differential dose‐dependent inhibitory activity against the growth of HeLa cells (p < 0.05) at concentration 10 μm. Among those three compounds, only compound 3b showed a selective cytostatic effect on HeLa in comparison with normal fibroblasts.

Copper(II) and nickel(II) complexes of a neutral pentadentate Schiff base

Abstract A new pentadentate Schiff base 2,6,10-triaza-1,11-bis(2′-aminophenyl)-undeca-1,10-diene, abaDPT , and its complexes of general formula M( abaDPT )X 2 where M = Cu(II), Ni(II), X = Cl, Br, I, NO 3 and ClO 4 , have been prepared. The complexes have been characterized by electronic and IR spectra, EPR, magnetic moments, molar conductances, and elemental analysis. IR data show an interaction between halide anion of the outer coordination sphere and the complexed amino group. EPR and spectrophotometric data of most of the copper compounds are consistent with a distorted square pyramidal geometry. Single crystal EPR studies of Cu( abaDPT )(NO 3 ) 2 and Cu( abaDPT )Br 2 revealed that copper atoms in the former compound occupy two magnetically inequivalent places in the lattice while copper atoms in the latter compound take identical sites. Principal g tensor axes of the two compounds have been determined.