An approach to the tricyclic core of madangamines based upon a biogenetic scheme

[reaction: see text] A short synthesis of intermediates possessing the tricyclic core of natural madangamines, bioactive alkaloids found in marine sponges, is described. The key reaction entails the condensation of the sodium salt of diethylacetonedicarboxylate with a dihydropyridinium salt derivative. This new approach is modeled on a biogenetic proposal linking madangamines to ircinals, related alkaloids occurring in sponges of the same order.     

Ag(I) complexes with alkylidene-bis(2-aminopyrimidines) as building units for discrete metallomacrocyclic frames. A structural and solution study

Alkylidene-bis(2-aminopyrimidines) (pyr2Cx, x = 2-5) are useful ligands to interact with Ag(I) yielding discrete metallocycles. Crystal structures of the [(pyr2C2)Ag(NO3)]2 and [(H-pyr2C4)Ag(NO3)2]2 have been isolated where each macrocyclic moiety interacts with their surroundings through weak interactions, yielding 3D discrete structures, On the other hand, the solution study shows that the equilibrium constants for the formation of Ag(pyr2Cx)+ complexes are higher than the literature values for Ag(I) complexes with single pyrimidines, although the differences could be explained by invoking the solid-state structures of the Ag(I)-pyr2Cx complexes.     

Vanadium determination in rat tissues and biological reference materials by neutron activation analysis

Vanadium was determined in adrenal gland, brain, ileum, kidney, liver, lung, muscle, myocard, skin, spleen, gonads, thyroid, and tibia of rats fed with normal diet and exposed to high vanadium doses in drinking water. Both radiochemical neutron activation analysis (RNAA) and instrumental neutron activation analysis (INAA) were employed. The RNAA procedure consisted in dry ashing samples prior to irradiation and vanadium separation from the irradiated samples by extraction with N-benzoyl-N-phenylhydroxylamine (BPHA) in toluene from 5 mol·l^–1 HCl. Vanadium accumulation as a function of a type of the tissue, exposure time, sex of rats, and administration of V(IV) or V(V) was studied. For quality assurance purposes, the biological (standard) reference materials NBS SRM 1571 Orchard Leaves, NBS SRM 1577a Bovine Liver, IAEA H-4 Animal muscle, and Bowen's Kale were analyzed.Presented at the 2nd Balkan Conference on Activation Analysis and Nuclear-Related Analytical Techniques, Bled, 4–6 October, 1989.     

Analytical applications of the o-dianisidine-persulfate reaction: Kinetic determination of silver and cobalt

A kinetic method for the silver determination based on the catalytic effect of Ag(I) on the oxidation of o-dianisidine by persulfate at pH = 4.5 in the presence of 1,10-phenanthroline is proposed. Ag(I) can be determined by measuring the absorbance of the reaction product at 450 nm, using the fixed time method. Co(II) does not have a catalytic effect in the reaction, but in the simultaneous presence of silver and cobalt the reaction shows an induction period the length of which is related to the Ag/Co molar ratio. As a consequence, two new methods for the determination of cobalt and silver using the induction period method are proposed. The two methods for silver are applied to the determination of silver in lead.     

Determination of iron and calcium impurities in magnesium oxide by atomic absorption

Summary An atomic absorption method has been developed for the determination of iron and calcium impurities in magnesium oxide. The effect of the magnesium matrix has been eliminated by the addition of hydroiodic acid and hydrogen peroxide to generate iodinein situ. The relative standard deviations were 0.5% for iron and between 0.5 and 1.5% for calcium.

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Die Bestimmung von Eisen- und Calcium-Verunreinigungen in Magnesiumoxid mit Hilfe der Atomabsorption

Zusammenfassung Zur Bestimmung der Eisen- und Calcium-Verunreinigungen in Magnesiumoxid wurde die Atomabsorptionsspektroskopie herangezogen. Der Einfluß der Magnesiummatrix wurde durch Zugabe von Jodwasserstoffsäure und Wasserstoffperoxid, d. h. durch Freisetzung von Jod in situ beseitigt. Die rel. Standardabweichung für Eisen betrug 0,5%, für Calcium 0,5–1,5%.

     

Exchange of halogen bonded on aromatic core. Heterogeneous catalysis—I : Reaction mechanism of iodine exchange in o-iodobenzoic acid

Reaction mechanism of halogen exchange between arylhalogenide and halogenide anion is studied in a case when the aromatic core is inactivated with respect to the S_NAr substitution by other substituents. The exchange of iodine between o-iodobenzoic acid and ¹³¹I labelled NaI serves as a modelling reaction. The reaction was found to proceed heterogeneously on a glass surface. In the case of a rapid course of the surface reaction the reaction mechanism is more complicated and the equation derived by McKay cannot be applied for expressing the time dependence of the degree of isotopic exchange. Reaction mechanism was proposed for this reaction and compared with experimental data.     

Palladium-catalyzed electrophilic allylation reactions via bis(allyl)palladium complexes and related intermediates

The synthetic scope of the allyl-palladium chemistry can be extended to involve electrophilic reagents. The greatest challenge in these reactions is the catalytic generation of an allyl-palladium intermediate incorporating a nucleophilic allyl moiety. A vast majority of the published reactions that involve palladium-catalyzed allylation of electrophiles proceed via bis(allyl)palladium intermediates. The eta(1)-moiety of the bis(allyl)palladium intermediates reacts with electrophiles, including aldehydes, imines, or Michael acceptors. Recently, catalytic electrophilic allylations via mono-allylpalladium complexes were also presented by employment of so-called "pincer complex" catalysts.     

Di-2-pyridylmethylamine-based palladium complexes as new catalysts for Heck,Suzuki, and Sonogashira reactions in organic and aqueous solvents

A new palladium-dipyridylmethylamine complex is an excellent catalyst for C-C bond-forming processes such as the Heck, Suzuki, and Sonogashira reactions in organic and aqueous solvents under homogeneous conditions. [reaction: see text]     

Reactions of substituted furo[3,2-<Emphasis Type="Italic">b</Emphasis>]pyrrole-5-carboxhydrazides and their biological activity

The reactions of substituted furo[3,2-b]pyrrole-5-carboxhydrazides 1 with 5-arylfuran-2-carboxaldehydes 2, 4,5-disubstituted furan-2-carboxaldehydes 3 and thiophene-2-carboxaldehyde 4 has been studied. The advantage of microwave irradiation on some of these reactions was reflected in the reduced reaction time and increased yields. Reactions of 1 with 4-substituted 1,3-oxazol-5(4H)-ones 11 led to diacylhydrazines 13 or to imidazole derivatives 14 depending on the temperature. 1,2,4-Triazole-3-thione 17 was synthesized by two-step reaction of 1 with phenylisothiocyanate and subsequent base-catalyzed cyclization of thiosemicarbazide 16. The effects of hydrazones 5–10 on inhibition of photosynthetic electron transport in spinach chloroplasts and chlorophyll content in the antialgal suspensions of Chlorella vulgaris were investigated.     

Fluoroapatite - material for medicine,Growth, morphology and thermoanalytical properties

Fluoroapatite containing glass-ceramics were prepared from Li₂O-CaO-CaF₂-P₂O₅-SiO₂ system. The glass was melted at 1480°C for 1 h. The object of observation was the preparing crystal phase of fluoroapatite in amorphous glass matrix. The morphology of lithium disilicate glass-ceramics was studied by SEM. The crystal growth and thermal properties of fluoroapatite were studied by X-ray diffraction and DTA. The more the content of P₂O₅, the more the presence of fluoroapatite particles. SEM investigation clearly indicated the phase separation and formation of a primary crystalline phase of fluoroapatite in the studied glass-ceramics. DTA curves of the fluoroapatite samples exhibit exothermic effects in the temperature range 337-694°C depending on the composition of the materials. The position of exothermic peak for lithium disilicate on DTA curves moves with increasing specific surfacetowards lower temperatures which points on its preferential surface crystallization. As far as physical qualities are concerned, mainly color and gloss, the best qualities of all observed materials belong to glass-ceramics with 10% P₂O₅. This revised version was published online in July 2006 with corrections to the Cover Date.