Synthesis and photochemistry of binary and mixed ligand complexes of copper(II) containing 5-arylazo-8-hydroxyquinoline derivatives and alkyl xanthates

Summary Mixed ligand complexes of the type K[Cu(x-HQA)Rxan] [x-HQA = 5-arylazo-8-hydroxyquinoline derivatives; Rxan = methyl or ethylxanthate] have been prepared and characterised by elemental analysis, spectral measurements and conductivity. Upon irradiation, solutions of these complexes photoeliminate dinitrogen and a mechanism for this reaction is proposed. The photosensitivity of the oxine ligand was found to be responsible for the observed photolysis of the complexes.     

Development of a new dimeric cyclophane ligand: application to enhanced diastereo- and enantioselectivity in the catalytic synthesis of beta-lactams

We detail the synthesis of a new C(2)-symmetric bis(cyclophane) ligand system that can be thought of as electronically analogous to binol, but which possesses the added "third dimension" of cyclophane chirality. The ligand synthesis involves a spontaneous (but unexpected) atropisomerization to the desired product. We have employed this ligand to form a metal complex that is an effective cocatalyst for the highly enantio- and diastereoselective catalytic asymmetric synthesis of a beta-lactam.     

Voltammetric determination of mercury levels in tuna fish

Summary A reliable and rapid procedure for the determination of Hg in fish by differential pulse anodic-stripping voltammetry (DPASV) at the gold electrode has been developed for use in food control and marine ecotoxicology. Potentialities and performance are demonstrated by the investigation of tuna fish. Samples of 0.5–2.5 g are subjected to pressurized digestion with HNO₃/HClO₄ (71). The resulting analyte solution is irradiated in closed flasks with ultraviolet light in presence of H₂O₂ to decompose dissolved organic substances. This is followed by DPASV with two standard additions. The relative standard deviation for the lower g/g range is below 5%. Comparative determination by gas chromatography confirmed that in fish-muscle mercury exists almost completely in the form of toxic organomercurials, i. e. methyl- and dimethylmercury.

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Voltammetrische Bestimmung von Quecksilber in Thunfischen

Zusammenfassung Für die Lebensmittelkontrolle und marine Ökotoxikologie wurde eine neue spurenanalytische Alternative zur raschen und zuverlässigen Bestimmung des Quecksilbergehaltes in Fisch unter Einsatz der differentiellen Pulsinversvoltammetrie (DPIV) und Verwendung einer Goldscheibenelektrode entwickelt.Möglichkeiten und Leistungsfähigkeit der Methode werden durch die Untersuchung von Thunfisch demonstriert. Proben von 0,5 bis 2,5 g Frischgewicht werden zunächst einem Druckaufschluß mit HNO₃/HClO₄ (71) unterworfen. Die resultierende Analytlösung wird zum Abbau gelöster organischer Substanzen im geschlossenen Gefäß einer UV-Bestrahlung (70° C, 150 W Quecksilberlampe, 4 h) unter oxydierenden Bedingungen (H₂O₂) unterzogen. Anschließend erfolgt die voltammetrische Bestimmung mit DPIV unter Vornahme von zwei Eichzusätzen. Die relative Standardabweichung liegt im unteren mg/kg-Bereich unter 5%. Die Richtigkeit wurde durch Vergleichsbestimmung mit der Gaschromatographie getestet. Die Übereinstimmung der ermittelten Quecksilbergehalte bestätigt, daß im Muskelfleisch von Fisch das Quecksilber nahezu vollständig in toxischen organischen

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Taken in part from the Ph. D. Thesis of R. Ahmed. Presented at the 8th International Microchemical Symposium, Graz, August 25–30, 1980.     

Anti-HIV Active Naphthyl Analogues of HEPT and DABO

Summary.  5-Isopropyl-6-naphthyl uracil and 5-isopropyl-6-naphthyl-2-thiouracil were alkylated to give N-1-(ethoxymethyl and methylthiomethyl) uracil and S²-cyclohexyl-thiouracil, respectively. 5-Ethyl-6-naphthyl uracil and 5-ethyl-6-naphthyl-2-thiouracil afforded N-1-(ethoxymethyl, methoxy-methyl, methylthiomethyl, acetoxyethoxy methyl and hydroxyethoxy methyl) uracil and S²-((2,2- diethoxyethyl), methoxycarbonylmethyl, ethoxycarbonylpropyl, methylthiomethyl, ethoxymethyl, methyl and cyclohexyl)-thiouracil upon alkylation. Received September 25, 2001. Accepted (revised) December 3, 2001     

Solvent extraction of trivalent lanthanide Pr(III), Ho(III) and Er(III) with N-benzoyl-N-phenylhydroxylamine

Extraction of Pr(III), Ho(III) and Er(III) has been studied in the pH range of 1–10 with N-benzoyl-N-phenylhydroxylamine (BPHA) in benzene. The separation was found to be quantitative in borate media from pH 7 to 10, at an ionic strength of 0.1M (H⁺, BO₃ ^3–). The stoichiometric composition of the complexes under the optimal conditions of shaking time, pH and reagent concentration was formulated using slope analysis and found to be M(BPHA)₃, where M=Pr(III), Ho(III) and Er(III). The effect of various masking agents shows that citrate, ascorbate, EDTA, oxalate, fluoride and phosphate form stable complexes with these rare earths as compared to BPHA. The decontamination factors for different cations with respect to these rare earths under the optimum conditions have been evaluated.     

Ruthenium(II) dendrimers containing carbazole-based chromophores as branches

Three new luminescent and redox-active Ru(II) complexes containing novel dendritic polypyridine ligands have been synthesized, and their absorption spectra, luminescence properties (both at room temperature in fluid solution and at 77 K in rigid matrix), and redox behavior have been investigated. The dendritic ligands are made of 1,10-phenanthroline coordinating subunits and of carbazole groups as branching sites. The first and second generation species of this novel class of dendritic ligands (L1 and L2, respectively; see Figure 1 for their structural formulas) have been prepared and employed. The metal dendrimers investigated are [Ru(bpy)(2)(L1)](2+) (1; bpy = 2,2'-bipyridine), [Ru(bpy)(2)(L2)](2+) (2), and [Ru(L1)(3)](2+) (3; see Figure 2). For the sake of completeness and comparison purposes, also the absorption spectra, redox behavior, and luminescence properties of L1 and L2 have been studied, together with the properties of 3,6-di(tert-butyl)carbazole (L0) and [Ru(bpy)(2)(phen)](2+) (4, phen = 1,10-phenanthroline). The absorption spectra of the free dendritic ligands show features which can be assigned to the various subunits (i.e., carbazole and phenanthroline groups) and additional bands at lower energies (at lambda > 300 nm) which are assigned to carbazole-to-phenanthroline charge-transfer (CT) transitions. These latter bands are significantly red-shifted upon acid and/or zinc acetate addition. Both L1 and L2 exhibit relatively intense luminescence at room temperature in fluid solution (lifetimes in the nanosecond time scale, quantum yields of the order of 10(-2)-10(-1)) and at 77 K in rigid matrix (lifetimes in the millisecond time scale). Such a luminescence is assigned to CT states at room temperature and to phenanthroline-centered pi-pi triplet levels at 77 K. The room-temperature luminescence of L1 and L2 is totally quenched by acid or zinc acetate. The metal dendrimers exhibit the typical absorption and luminescence properties of Ru(II) polypyridine complexes. In particular, metal-to-ligand charge-transfer (MLCT) bands dominate the visible absorption spectra, and formally triplet MLCT levels govern the excited-state properties. Excitation spectroscopy evidences that all the light absorbed by the dendritic branches is transferred with unitary efficiency to the luminescent MLCT states in 1-3, showing that the new metal dendrimers can be regarded as efficient light-harvesting antenna systems. All the free ligands and metal dendrimers exhibit a rich redox behavior (except L2 and 3, whose redox behavior was not investigated because of solubility reasons), with clearly attributable reversible carbazole- and metal-centered oxidation and polypyridine-centered reduction processes. The electronic interaction between the carbazole redox-active sites of the dendritic ligands is affected by Ru(II) coordination.     

Unveiling Carbon Dioxide and Ethanol Diffusion in Carbonated Water-Ethanol Mixtures by Molecular Dynamics Simulations

The diffusion of carbon dioxide (CO2) and ethanol (EtOH) is a fundamental transport process behind the formation and growth of CO2 bubbles in sparkling beverages and the release of organoleptic compounds at the liquid free surface. In the present study, CO2 and EtOH diffusion coefficients are computed from molecular dynamics (MD) simulations and compared with experimental values derived from the Stokes-Einstein (SE) relation on the basis of viscometry experiments and hydrodynamic radii deduced from former nuclear magnetic resonance (NMR) measurements. These diffusion coefficients steadily increase with temperature and decrease as the concentration of ethanol rises. The agreement between theory and experiment is suitable for CO2. Theoretical EtOH diffusion coefficients tend to overestimate slightly experimental values, although the agreement can be improved by changing the hydrodynamic radius used to evaluate experimental diffusion coefficients. This apparent disagreement should not rely on limitations of the MD simulations nor on the approximations made to evaluate theoretical diffusion coefficients. Improvement of the molecular models, as well as additional NMR measurements on sparkling beverages at several temperatures and ethanol concentrations, would help solve this issue.     

Therapeutic Versus Preventative Use of Ginkgo biloba Extract (EGb 761) against Indomethacin-Induced Gastric Ulcer in Mice

The main bioactive constituents in the standardized Ginkgo biloba leaf extract (EGb 761) are the terpene lactones and flavonoid glycosides. EGb 761’s antioxidant and anti-inflammatory properties have previously been demonstrated. Indomethacin-induced gastric ulcers have a multifactorial etiology and represent a major restriction to its therapeutic utility. The underlying ulcerogenic process involves oxidative and inflammatory biomolecular insults. This study was performed to explore the curative and preventative benefits of EGb 761 in experimentally-induced ulcers. To develop gastric ulcers in mice, indomethacin (40 mg/kg) was administered orally. EGb 761 (200 mg/kg) was given by gavage for 7 days before (preventative) and after (therapeutic) indomethacin administration. The histological alterations and macroscopic mucosal lesions were assessed. In gastric tissue homogenates, malondialdehyde (MDA), reduced glutathione (GSH), nitric oxide (NO), and inflammatory cytokines were measured. The expressions of cyclooxygenase-2 (COX-2), cytokines, and proliferating cell nuclear antigen (PCNA) in the stomach mucosa were also investigated. The ulcer index, histological alterations, gastric oxidants, and inflammatory biomarkers were all significantly increased by indomethacin. In stomach specimens, it increased COX-2 and PCNA expression. EGb 761 treatments, both prophylactic and therapeutic, resulted in significant reductions in ulcer lesions, nitrosative and oxidative damage, and inflammatory markers, along with the lowering of COX-2 and PCNA expressions. Furthermore, in the fight against stomach ulcers, EGb 761 treatment was found to be more efficient than prevention.     

Synthesis of Potential Antiviral Agents for SARS-CoV-2 Using Molecular Hybridization Approach

We synthesized a set of small molecules using a molecular hybridization approach with good yields. The antiviral properties of the synthesized conjugates against the SAR-CoV-2 virus were investigated and their cytotoxicity was also determined. Among all the synthesized conjugates, compound 9f showed potential against SARS-CoV-2 and low cytotoxicity. The conjugates’ selectivity indexes (SIs) were determined to correlate the antiviral properties and cytotoxicity. The observed biological data were further validated using computational studies.