Separation of organoselenium compounds and their electrochemical detection

A simplified procedure based on ion-exchange separation of selenourea (Se-U) and selenocystamine (Se-CM), which have very close half-wave potential when they are simultaneously analyzed by voltammetric techniques, has been developed and optimized. Thus, selenocystamine remains in the cation exchanger Purolite C 100 H, whereas selenourea is found in the effluent and is determined by square wave cathodic stripping voltammetry using Na₂CO₃ as electrolyte. Selenocystamine is then eluted from the cation exchanger using 4 M HCl and analyzed by square wave cathodic stripping voltammetry in the HCl solution. For each voltammetric determination the corresponding parameters were investigated and optimized; the obtained detection limits were 0.3 ng Se mL^–1 for Se-CM and 2 ng Se mL^–1 for Se-U. A flow sheet for the separation of inorganic (Se(IV) and Se(VI)) and organoselenium compounds (Se-U, Se-CM, (CH₃)₂Se₂, and (CH₃)₂Se) developed for their electrochemical detection is presented and it was successfully applied to a certified reference material, an environmental soil sample, and a urine sample.     

Highly stereoselective addition of stannylcuprates to alkynones

The addition of stannylcuprate reagents such as (Bu3Sn)(PhS)CuLi to alkynones has been found to proceed in high yield and with excellent stereoselectivity for the Z isomer of the product (>95%). The behavior of the stannylcuprates is thus very different from that of their "carbocuprate" counterparts such as Me2CuLi or Me2Cu(CN)Li2 which are nonstereoselective. Furthermore, in contrast to the reactions of (R3Sn)(PhS)CuLi with the corresponding alkynoates, the presence of a proton source in the reaction medium has no effect on the stereoselectivity of the reaction of alkynones.     

3′-Methylsulfinyl-3,4′-diquinolinyl sulfides

Reactions of 4-methoxy- or 1,4-dihydro-4-oxo-3′-methylthio-3,4′-diquinolinyl sulfides 1 and 7 with a nitrating mixture ran as the 3′-methylthio group 5-mono-oxidation followed by C₆- and C₈-nitration and led to the mixture composed of products 3, 4, 5 and 6 (in the case of substrate 1 ) or compounds 5 and 6 (for substrate 7 ). In the reaction with hydrochloric acid 4-methoxy-3′-methylsulfinyl-3,4′-diquinolinyl sulfides 3 and 4 could be hydrolysed to 3′-methylsulfinyl-4(1H)-quinolinones 5 or 6 respectively, the methylsulfinyl group remaining unaffected.     

Use of U-shaped donor-bridge-acceptor molecules to study electron tunneling through nonbonded contacts

A systematic determination of electronic coupling matrix elements in U-shaped molecules is demonstrated. The unique architecture of these systems allows for the determination of the electronic coupling through a pendant molecular moiety that resides between the donor and acceptor groups; this moiety quantifies the efficiency of electron tunneling through nonbonded contacts. Experimental electron-transfer rate constants and reaction free energies are used to calibrate a molecular-based model that describes the solvation energy. This approach makes it possible to experimentally determine electronic couplings and compare them with computational values.     

Skin Necrosis due to Photodynamic Action of Benzoporphyrin Depends on Circulating Rather than Tissue Drug Levels: Implications for Control of Photodynamic Therapy

In an ideal world, photodynamic therapy (PDT) of abnormal tissue would reliably spare the surrounding normal tissue. Normal tissue responses set the limits for light and drug dosimetry. The threshold fluence for necrosis (TFN) was measured in normal skin following intravenous infusion with a photosensitizer, benzoporphyrin derivative monoacid ring A (BPD-MA) Verteporfin as a function of drug dose (0.25-2.0 mg/kg), wavelength of irradiation (458 and 690 nm) and time interval (0–5h) between drug administration and irradiation. The BPD-MA levels were measured in plasma and skin tissue to elucidate the relationship between TFN, drug kinetics and biodistribution. The PDT response of normal skin was highly reproducible. The TFN for 458 and 690 nm wavelengths was nearly identical and the estimated quantum efficiency for skin response was equal at these two wavelengths. Skin phototoxicity, quantified in terms of 1/ TFN, closely correlated with the plasma pharmacokinetics rather than the tissue pharmacokinetics and was quadratically dependent on the plasma drug concentration regardless of the administered drug dose or time interval between drug and light exposure. This study strongly suggests that noninvasive measurements of the circulating drug level at the time of light treatment will be important for setting optimal light dosimetry for PDT with liposomal BPD-MA, a vascular photosensitizer.     

Determination of lithium in pharmaceutical formulations used in the treatment of bipolar disorder by flow injection analysis with spectrophotometric detection

In this work, a flow injection system with spectrophotometric detection was developed for the determination of lithium in pharmaceutical formulations used in the treatment of bipolar disorder. Reaction between Quinizarine (1,4-dihydroxyanthraquinone) and Li(I) ion in alkaline medium containing dimethylsulfoxide (DMSO) was explored for this purpose. The flow system was optimized regarding to its chemical (DMSO, Quinizarine and NaOH concentrations and sample pH) and physical parameters (sample loop volume, carrier flow rate and reactor length) in order to establish better conditions in terms of sensitivity and sampling frequency. The results obtained showed that the concentration of DMSO in the reagent solution presents remarkable influence on the magnitude of analytical signal. Chemical species that could be found in the formulations such as Na(I), K(I), Mg(II), Ca(II), Ti(IV), Cl⁻, CO₃²⁻ e sodium dodecylsulfate were tested as possible interfering ions. Among them, only non-monovalent cations presented noticeable interference on lithium signal. However, they were not found in concentrations high enough to cause interference in the determination of lithium in the samples. Sample preparation was performed by sonicating a slurry prepared by dispersing 100 mg of powdered sample in 15 mL of 0.10 mol L⁻¹ HCl solution. Results obtained by developed methodology were not statistically different from those obtained by flame emission spectrometry. In the optimized conditions the method presented a linear range of 5-40 mg L⁻¹ and a relative standard deviation of 3.6% at 5 mg L⁻¹ Li concentration. Detection and quantification limits were 0.54 and 1.8 mg L⁻¹, respectively. Sampling frequency, calculated as the time interval passed between two consecutive injections, was 60 samples per hour. The methodology was successfully applied in the determination of lithium in three commercial samples.     

Derivate des Methylendioxybenzols, 7. Mitt.: Über die Einwirkung nucleophiler Reagenzien auf Myristicinabkömmlinge

Zusammenfassung In dieser Arbeit wird über die alkalische Verseifung des 2,6-Dinitro-myristicinsäuremethylesters berichtet, die zur Spaltung der Methylendioxygruppierung unter, Bildung von neuen Phenoläthern führt. Weiterhin werden Amino-myristicinsäuremethylester mit Alkyl-, Aryl- und heterocyclischen Säurechloriden acyliert und die entstehenden Acylaminoderivate durch Behandlung mit Hydrazinhydrat in die entsprechenden Aminochinazolone übergeführt. Additions-, Substitutions- und Abspaltungsreaktionen der N-ständigen Aminogruppe des 2-Methyl-3-amino-6,7-methylendioxy-8-methoxy-chinazolons-(4) waren schließlich Gegenstand unserer Untersuchungen.     

Comparison of silanization/hydrosilation and organosilanization modification procedures on etched capillaries for electrokinetic chromatography

Etched capillaries for use in open tubular electrochromatography are modified by silanization/hydrosilation and organosilanization. The migration behavior of both types of capillaries is evaluated with small basic molecules, peptides and proteins. Comparisons of peak symmetry and efficiency are used to measure the effectiveness of the two methods for modifying the etched surface. From this information, the suitability of each method for use with etched capillaries can be determined.     

Thermal and Some other Properties of 2,4′-Bipyridyl Complexes with Various Salts of Lead(II)

New complexes of lead(II) with 2,4′-bipyridyl (L), with the general formulae PbL₂X₂ (where X ^?1=Cl, Br, I, NCS) and PbL₃X₂ (where (X]^?1=NO₃, ClO₄), have been prepared. Analysis of the IR spectra indicates that the 2,4′-bipyridyl is bonded to the Pb(II) ion through the least hindering N(4′). The thermal decompositions of the complexes were studied under non-isothermal conditions in air. The intermediates of decomposition at different temperatures were characterized by thermal analysis (TG and DTG), chemical analysis and X-ray diffraction. Upon heating, the complexes undergo full or partial deamination. The complexes PbL₂Cl₂ and PbL₂Br₂ decompose to volatile lead(II) halide. PbO is the final product of decomposition for the other complexes.     

Synthesis and structural characterization of integrally oxidized, metal-free phthalocyanine compounds: [H(2)(pc)][IBr(2)] and [H(2)(pc)](2)[IBr(2)]Br.C(10)H(7)Br

The first integrally oxidized metal-free phthalocyanine compounds have been synthesized by chemical oxidation. Phthalocyanine (H(2)(pc), pc = phthalocyaninato) was oxidized with IBr to afford the compounds [H(2)(pc)][IBr(2)] (1) and [H(2)(pc)](2)[IBr(2)]BrAC(10)H(7)Br (2), whose structures were determined by means of single-crystal X-ray diffraction methods: [H(2)(pc)][IBr(2)], P2(1)/c, a = 8.0272(9) A, b = 21.258(2) A, c = 18.1439(2) A, beta = 113.975(2) degrees, V = 2828.8(5) A(3), T = 153 K, Z = 4; [H(2)(pc)](2)[IBr(2)]Br.C(10)H(7)Br, P, a = 8.4724(6) A, b = 13.5794(10) A, c = 13.8403(10) A, alpha = 90.854(1) degrees, beta = 103.417(1) degrees, gamma = 97.049(1)E degrees, V = 1535.61(19) A(3), T = 153 K, Z = 1. The extended structure of [H(2)(pc)][IBr(2)] comprises slipped columns of pc rings stacked along the a axis in adjacent columns at approximately 70 degrees to one another. IBr(2-) ions occupy the interstitial columns. The extended structure of [H(2)(pc)](2)[IBr(2)]Br.C(10)H(7)Br comprises slant stacks of pc rings along the crystallographic a axis with IBr(2-) ions, Br(-) ions, and disordered 1-bromonaphthalene molecules in the adjacent, parallel columns. The overall reaction for the formation of 1 is 2H(2)(pc) + 4IBr --> 2[H(2)(pc)][IBr(2)] + I(2), and the overall reaction for the formation of 2 (not including solvent) is 2H(2)(pc) + 3IBr --> [H(2)(pc)](2)Br[IBr(2)] + I(2).