Easy α- to β-migration of an enol moiety on a pyrrole ring

Functionalized pyrrolic enols, 2-(2,2-dicyano-1-hydroxyethenyl)-1-methylpyrroles, synthesized from 2-ethenylpyrroles by a nucleophilic SEt-OH exchange, upon heating (75-142 °C) are readily rearranged to their 3-isomers in near to quantitative yield. The inter or intramolecular auto-protonation of a pyrrole ring by the acidic enol hydroxyl to form a mesomeric pyrrolium cation or zwitterion is suggested to be a key step in the rearrangement.     

Chiral induction in self-assembled helicates: CHIRAGEN type ligands with ferrocene bridging units

The aim of this work was the preparation of enantiomerically pure bis(pinene-bipyridine) ligands containing the ferrocenyl moiety. Several such ligands (1-3) were synthesized and completely characterized. These molecules can be diastereoselectively deprotonated at the acidic methylene group of the pinene moiety using a strong and sterically hindered base such as LDA. Subsequent reaction of the formed anion with alkyl halides yield the family of C(2)-symmetric enantiopure compounds (1a-c). Copper(I), silver(I), or zinc(II) complexes with several ligands (C1-C8) were prepared and structurally characterized in the solid state and in solution. Self-assembled helical species are formed in several cases. It became evident that the chiral groups present in the ligand do not completely determined the helical configuration of the assemblages. Diastereoselectivity is thus not complete with this type of ligands, contrary to other, similar ligands studied before.     

Certification of total mercury and methylmercury concentrations in mussel homogenate (Mytilus edulis) reference material, IAEA-142

Due to the increased demand for new reference materials certified for total and methylmercury (MeHg) a sample of mussel homogenate (IAEA-142) has been prepared. Thirteen experienced laboratories reported results for total Hg of which 9 laboratories also reported results for MeHg content. Laboratories reporting MeHg results used various isolation techniques (solvent extraction, saponification, acid leaching, ion-exchange separation, and distillation) and detection systems (cold vapour atomic absorption spectrometry (CV AAS), cold vapour atomic fluorescence spectrometry (CV AFS), gas chromatography with electron capture detector (GC/ECD) and HPLC with CV AAS detector). In the case of total Hg, most of the laboratories used acid digestion, only two used alkaline dissolution, followed either by CV AAS or CV AFS. One laboratory used neutron activation analyses with radiochemical separation. The data received were in good agreement. The value for total Hg was certified to be 126 ng/g, with a 95% confidence interval from 119 to 132 ng/g. For MeHg the certified value of 47 ng/g expressed as Hg was assigned, with a 95% confidence interval from 43 to 51 ng/g. Stability testing has shown that both total and MeHg are stable if samples are stored in a dry and dark place at room temperature. The sample is now available as a certified reference material and is, in particular, useful for quality control measurements of Hg and MeHg in mussel samples at low concentration levels.     

Epoxy-amine multimethacrylic prepolymers,kinetic and structural studies

Epoxy-amine methacrylated prepolymers are prepared in a 1-step synthesis by the reaction of Bisphenol A diglycidyl ether, glycidyl methacrylate, and different diamines. The adaptation of these reactions to production processes with a reduced reaction time requires a kinetic control and the use of efficient catalysts. The comparative kinetic treatment of the epoxy-amine reaction in the frame of Horie's and Rozenberg's kinetic schemes have been made. Cases where an efficient acid catalyst is used are also examined. Structural studies of these reactions established the occurrence of a Michael amine/double bond addition, when some amines are used. © 1995 John Wiley & Sons, Inc.     

Photometrische Kationenbestimmung mit Gelatinefolien

Zusammenfassung Eine einfache und schnelle Methode zur photometrischen Kationenbestimmung mittels Gelatinefolien wurde ausgearbeitet. Eine reine Filmfolie als Träger der Farbreaktion wird in die Kationenlösung und danach in die Reagenslösung eingetaucht, wobei sich in der Gelatineschicht ein gefärbter Niederschlag bildet, dessen Farbintensität proportional der Metallkonzentration ist.Die Folie wird photometriert und mittels einer Eichkurve die Metallkonzentration bestimmt. Das Verfahren wurde an Hand der Cu-Bestimmung mit Diäthyldithiocarbamidat erprobt. Die Färbung befolgt in diesem Fall das Beersche Gesetz. Eine Bestimmung erfordert etwa 20 min. Der relative Fehler beträgt ±5 % bei einer Konzentration von 3–30 g Cu²⁺/ml.

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Photometric determination of cations by means of gelatin filmDetermination of copper with diethyldithiocarbamidate

A simple and rapid method for the photometric determination of cations using a strip of gelatin film has been developed. The strip is immersed in the sample solution and afterwards in a reagent solution. The intensity of a the coloured precipitate formed in the strip is proportional to the metal ion concentration, which is determined photometrically using a calibration curve. The determination of Cu with diethyldithiocarbamidate has been selected for testing the technique. The colour intensity in this case follows Beer's law. The determination can be performed within 20 min. The relative error amounts to ±5 % for a concentration range of 3–30 g of Cu²⁺/ml.

     

NEW PHTHALOCYANINE PHOTOSENSITIZERS FOR PHOTODYNAMIC THERAPY

Six new aluminum and silicon phthalocyanines have been synthesized and their photocytotoxicity toward V79 cells has been studied. The compounds that have been prepared are: AIPcOSi(CH₃)₂(CH₂),N(CH₃)₂, I; AIPcOSi(CH₃)₂(CH₂)₃N(CH₃)₃⁺I^?, II; CH₃SiPcOSi(CH₃)₂(CH₂)₃N(CH₃)₂, III; HOSiPcOSi(CH₃)₂(CH₂)₃N(CH₃)₂, IV; HOSiPcOSi(CH₃)₂(CH₂)₃)₃(CH₃)₃⁺I^?, V; and SiPc[OSi(CH₃)₂(CH₂)₃N(CH₃)₃⁺I^?]₂, VI. Relative growth delay values for compounds I-VI and relative cytotoxicity values for compounds I, II, IV, V and VI have been determined. Compounds I and II have been shown to be comparable in photocytotoxicity to what is presumed to be AIPcOH.xH₂O, and compound IV has been shown to have greater activity. The classes of compounds to which these six compounds belong appear to have potential for photodynamic therapy.     

Cluster ions of diquat and paraquat in electrospray ionization mass spectra and their collision-induced dissociation spectra

Cluster ions such as [Cat+X+nM](+) (n = 0-4); [Cat-H+nM](+) (n = 1-3); and [2(Cat-H)+X+nM](+) (n = 0-2), where Cat, X, and M are the dication, anion, and neutral salt (CatX(2)), respectively, are observed in electrospray ionization (ESI) mass spectrometry of relatively concentrated solutions of diquat and paraquat. Collision-induced dissociation (CID) reactions of the clusters were observed by tandem mass spectrometry (MS/MS), including deprotonation to form [Cat-H](+), one-electron reduction of the dication to form Cat(+.), demethylation of the paraquat cation to form [Cat-CH(3)](+), and loss of neutral salt to produce smaller clusters. The difference in acidity and reduction power between diquat and paraquat, evaluated by thermodynamical estimates, can rationalize the different fractional yields of even-electron ([Cat-H](+) and its clusters) and odd-electron (mostly Cat(+)) ions in ESI mass spectra of these pesticides. The [Cat+n. Solv](2+) doubly charged cluster ions, where n 相似文献   

Synthesis of macrocycles incorporating azo‐bis(azofurazan) framework

A series of macrocycles containing four furazan rings bonded by three azo bonds 2, 5 and 7 have been synthesized from the common precursor, 3‐amino‐3′‐nitro(azofurazan) 3 . The macrocycles closure is a result of N?N bond formation at oxidative cyclization of corresponding bis(3‐aminofurazan‐4‐yl) precursors. X‐Ray crystal structures of macrocycles 2, 2 ?AcOH, 11 and 13 are reported.     

Fine structure of the (S(1)<--S(0)) band origins of phthalocyanine molecules in helium droplets

The laser-induced fluorescence (LIF) excitation spectra of free base phthalocyanine (Pc), Mg-Pc, and Zn-Pc molecules in superfluid helium droplets at T=0.38 K have been studied. The spectra reveal the rich vibronic structure of the S(1)<--S(0) electronic transitions. The band origins of the transitions consist of zero phonon lines accompanied by phonon wings, which originate from simultaneous electronic excitation of the molecule and excitation of the collective modes of the helium surrounding it. The phonon wings have discrete structures suggesting localization of some helium atoms in the neighborhood of the molecules. Zero phonon lines of Mg-Pc and Zn-Pc molecules are split into three components, which are separated by 0.2-0.4 cm(-1). Possible mechanism of splitting involves static or dynamic Jahn-Teller interaction of metal-phthalocyanine molecules in the twofold degenerate S(1)((1)E(u)) state with the helium shell.     

Direct vinylation of glucose derivatives with acetylene

Vinyl ethers, promising chiral carbohydrate synthons, have been synthesized by the addition of glucose acetals (1,2:5,6-di-O-isopropylidene-α-d-glucofuranose, methyl 4,6-O-benzylidene-α-d-glucopyranoside, 1,2-O-cyclohexylidene-α-d-glucofuranose, methyl α-d-glucopyranoside) to acetylene under atmospheric and elevated pressures in an autoclave in the presence of superbase catalytic systems (KOH-DMSO, t-BuOK-DMSO). The complete vinylation of 1,2:5,6-di-O-isopropylidene-α-d-glucofuranose and methyl α-d-glucopyranoside has been realized under elevated pressure of acetylene in the system KOH-THF as well.