A reductometric determination of Os(VIII) with a standard solution of a ferrous salt in alkaline mannitol or triethanolamine media

Summary It is possible to titrate Os(VIII) potentiometrically [Os(VIII) Os(VI)] with iron(II) in potassium hydroxide medium in the presence of mannitol or triethanolamine as complexing agents. The method is suitable for the determination of 0.5–20 mg of Os; the titration error does not exceed ±1.8%.

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Zusammenfassung Osmium(VIII) läßt sich in Gegenwart von Mannit oder Triäthanolamin als Komplexbildnern in kaliumhydroxidhältigem Milieu mit Eisen(II) titrieren. Das Verfahren eignet sich zur Bestimmung von 0,5–20 mg Os; der Fehler beträgt höchstens ±1,8%.

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On leave from: Analytical Chemistry and Instrumentation Division, PCSIR Laboratories, Lahore, Pakistan.

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On leave from: Dept. of Chemistry, University of Rajasthan, Jaipur, India.     

A contribution to the volumetric electrometric determination of some organic peroxides in alkaline media

Conditions for the determination of DBP, CHP, MEKP, and MCHP, as well as m-chloroperbenzoic acid, with a standard solution of SnII-glyc or SnII-sorb by the potentiometric, bipotentiometric, and biamperometric method were found. Quite good results were obtained in comparison with individual modifications of the iodometric method. Large positive errors were found only for the determination of m-chloroperbenzoic acid with SnII-glyc. The reductometric procedure is an advantage in the determination of organic peroxides by this procedure.     

Electrometric titrations of Bi(III), Cu(II), Pt(IV), Te(VI) and Te(IV) with standard iron(II) solution in alkaline medla containing hexitols

Potentiometric, bipotentiometric and biamperometric titrations with an iron(II) salt in alkaline solutions containing sorbitol are reported. Suitable conditions are discussed for determinations based on the Bi(III) → Bi°, Cu(II) → Cu(I) → Cu°, Pt(IV) → Pt(II) → Pt° and Te(VI) → Te(IV) → Te° → telluride systems.     

Determination of Hypericin in Hypericum perforatum (St. John’s Wort) Using Classical C18 and Pentafluorophenyl Stationary Phases: Contribution of Pi–Pi Interactions to High-Performance Liquid Chromatography (HPLC)

Hypericin is one of the most important bioactive substances present in Hypericum perforatum (Saint John’s Wort), which exhibits various biological activities such as inhibition of neuronal processes coupled with transmission of serotonin, dopamine, gamma-amino butyric acid and L-glutamine. This red-colored derivative of anthraquinone contains six benzene cycles and four hydroxy groups that polarize electron density in the conjugated double bond system and enable the molecule to act as a Lewis base in charge-transfer complexes. In this study, four stationary phases modified by the pentafluorophenyl group were selected to investigate the contribution of π-π interactions to the improvement of hypericin separation in comparison to the separation provided with a classical C18 based chromatographic column. In order to develop a suitable gradient chromatographic method for the quantification of hypericin, normal, polar organic and reverse elution modes were evaluated using high-performance liquid chromatography with ultraviolet-visible and mass spectrometry detection. It was disclosed in the analyses that the pentafluorophenyl stationary phase can separate hypericin from hyperforin, which was not possible to achieve with the C18 based stationary phase. The best analytical method found, employing the pentafluorophenyl stationary phase, showed sufficient linearity, accuracy and precision and was used for the determination of hypericin in Saint John’s Wort.     

Preparation and cytotoxic activity of nickel(II) complexes with 6-benzylaminopurine derivatives

Nickel(II) complexes with 6-benzylaminopurine (BAP) derivatives, namely 6-(3-chlorobenzylamino)purine (HL₁), 6-(4-chlorobenzylamino)purine (HL₂) and 6-(4-fluorobenzylamino)purine (HL₃), have been prepared and characterized by elemental analyses, i.r., u.v.–v.i.s., ES+ and FAB+ mass spectroscopy, magnetic susceptibility and conductivity measurements, and by thermal analysis. The complexes are: [Ni(L₁(H₂O)₂Cl] · H₂O, [Ni(L₁)(H₂O)-(NO₃)] · H₂O, [Ni(L₂)(H₂O)₂Cl], [Ni(L₂)(H₂O)₂(NO₃)] · H₂O, [Ni(HL₂)(H₂O)Cl₂] · EtOH and [Ni(L₃)(H₂O)₂Cl]. They have been tested in vitro for their possible cytotoxic activity against G-361 (human malignant melanoma), HOS (human osteogenic sarcoma), K-562 (human chronic myelogenous leukemia) and MCF-7 (human breast adenocarcinoma) cell lines.     

Quantitative analysis of cytokinins in plants by liquid chromatography–single-quadrupole mass spectrometry

A sensitive method for the quantitative analysis of all natural isoprenoid cytokinins in plant material by electrospray single-quadrupole mass spectrometry is presented. A baseline chromatographic separation of 20 non-derivatised naturally occurring cytokinins has been developed. Precise analyses of O-glucoside and ribonucleotide fractions were also performed by the high-performance liquid chromatography–mass spectrometry (HPLC–MS) but run separately from the basic cytokinin metabolites. Using post-column splitting, the flux from narrow-bore (2.1 mm i.d.) reversed-phase liquid chromatography column was simultaneously introduced into the diode array and mass detector. Optimal conditions, including final flow rate, desolvation temperature, desolvation gas flow, capillary and cone voltage for effective ionisation in the electrospray ion source were found. When low cone voltage (20 V) was applied, all studied cytokinins were determined in aqueous methanol as dominant quasi-molecular ions of [M+H]⁺ with limits of detection ranging between 10 and 50 fmol. For routine analysis a linearity range between 25 (75) fmol and 100 pmol was obtained. Developed liquid chromatography–mass spectrometry (LC–MS) method in selective ion monitoring mode was employed to quantify cytokinin species in tobacco BY-2 suspension culture and poplar leaves (Populus×canadensis Moench, cv Robusta).

Purified plant cell (BY-2) and plant tissue (poplar leaves) extracts were obtained by using two different ion-exchange chromatography steps, in combination with immunoaffinity purification using a broad-spectrum monoclonal anti-cytokinin antibody. The antibody strongly recognises the presence of N⁶-substituent on purine skeleton and thus does not bind adenine and related compounds. The presence of authentic cytokinins in the extracts quantified by LC–MS was further verified by enzyme-linked immunosorbent assays (ELISAs) with prior LC preparation. The combination of liquid chromatography–single-quadrupole mass spectrometry with immunoaffinity chromatography offers an efficient and elegant method for detection and quantification of cytokinin metabolites.     

Distributional chaos and factors

We show the existence of a dynamical system without any distributionally scrambled pair which is semiconjugated to a distributionally chaotic factor.     

Synthesis and anthelmintic activity of benzopyrano[2,3-c]pyrazol-4(2H)-one derivatives

Molecular Diversity - A series of benzopyrano[2,3-c]pyrazol-4(2H)-one derivatives were synthesized from readily available 1-phenyl- and 1-methyl-1H-pyrazol-3-ols by sequentially employing...     

Comparative Lipophilicity of Morphine Derivatives

JPC – Journal of Planar Chromatography – Modern TLC - Lipophilicity is an important physicochemical characteristic of compounds having potential use in the treatment of humans and...