On precipitation effects of aluminum,lanthanum, iron (III), and thorium phosphates

Summary Typical precipitation curves of various metal phosphates have been obtained using the turbidimetric technique. The following systems have been investigated: Al(NO₃)₃-K₃PO₄, Al(NO₃)₃-KH₂PO₄, Al(NO₃)₃NaH₂PO₄, FeCl₃-K₃PO₄, FeCl₃-(NH₄)₂HPO₄, FeCl₃K₂HPO₄, FeCl₃-KH₂PO₄, FeCl₃-NaH₂PO₄, La(NO₃)₃K₃PO₄,La(NO₃)₃-K₂HPO₄,La(NO₃)₃-KH₂PO₄,La(NO₃)₃NaH₂PO₄ and Th(NO₃)₄-K₂HPO₄. Typical precipitation curves indicated concentration ranges of phosphate precipitation and of complex solubility.

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Zusammenfassung Typische F?llungskurven verschiedener Metallphosphate, die mittels Trübungsmessungen erhalten wurden, wurden graphisch dargestellt. Die folgenden Systeme wurden untersucht: Al(NO₃)₃-K₃PO₄,Al(NO₃)₃KH₂PO₄, Al(NO₃)₃-NaH₂PO₄, FeCl₃-K₃PO₄, FeCl₃(NH₄)₂HPO₄, FeCl₃-K₂HPO₄, FeCl₃-KH₂PO₄, FeCl₃NaH₂PO₄, La(NO₃)₃-K₃PO₄, La(NO₃)₃-K₂HPO₄, La(NO₃)₃-KH₂PO₄, La(NO₃)₃-NaH₂PO₄ und Th(NO₃)₄K₂HPO₄. Typische F?llungskurven zeigten Konzentrationsgebiete, in welchen die Metallphosphate gef?llt werden, sowie Konzentrationen, die zur Komplexbildung führten.

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Supported in part by the U.S. Army Research Office, Contract No. DA-ORD-10.     

Graph theory and molecular orbitals. The loop rule

Graph theory is applied to the study of the dependence of total π-electron energy, π-electron charge distribution and free valency indices of conjugated hydrocarbons on molecular topology. It is shown that the number of loops in the molecular graph determines these quantities.     

Global Forcing Number of Benzenoid Graphs

A global forcing set in a simple connected graph G with a perfect matching is any subset S of E(G) such that the restriction of the characteristic function of perfect matchings of G on S is an injection. The number of edges in a global forcing set of the smallest cardinality is called the global forcing number of G. In this paper we prove several results concerning global forcing sets and numbers of benzenoid graphs. In particular, we prove that all catacondensed benzenoids and catafused coronoids with n hexagons have the global forcing number equal to n, and that for pericondensed benzenoids the global forcing number is always strictly smaller than the number of hexagons.     

Can multivalency be expressed kinetically? The answer is yes

Inspired by the concept of multivalency and in pursuit of ever more intricate artificial molecular machines, we investigated the strict self-assembly of a triply threaded two-component superbundle, starting from a tritopic receptor in which three benzo[24]crown-8 macrorings are fused onto a triphenylene core and a trifurcated trication wherein three bipyridinium units are linked 1,3,5 to a central benzenoid core. The result of the investigation was quite unexpected and surprising. It transpired that the rapid formation of a doubly threaded two-component complex was followed by an extremely slow conversion (a week at 253 K in CD3COCD3 to reach equilibrium) of this kinetically controlled product into a thermodynamically controlled one, namely a triply threaded two-component superbundle. This intriguing observation begs the question: are there instances in nature where multivalency is expressed as a kinetically controlled process, prior to an equilibrium state being reached, and if so, what are the biological implications, if any?     

Metal contents in tench otoliths: relationships to the aquatic environment

A monitoring of the quality of waters was attempted determining metal accumulation in target organs as otoliths of freshwater fish. Tenchs of age ranging between 2 and 10 years were sampled in three different canals receiving wastewater from industrial, agricultural and urban activities. Metal contents were determined in both lapilli and asterisci otoliths, using inductively coupled plasma-atomic emission spectroscopy (ICP-AES). Analytical data are reported for minor metals and for some trace metals. Al, Fe and Zn have contents depending on the environment where the fish has lived, while Na, K, Ca and Sr contents are insensitive to the different aquatic habitat. Considering the two types of otolith separately, lapilli display a different affinity for trace metals (Al, Fe and Zn), while in asterisci this affinity is matched only for zinc. The high affinity of zinc for both types of otoliths suggests using this metal for discriminating the fresh waters by checking its accumulation in otoliths, as well as correlating this accumulation with age of the fish: a negative power curve equation is proposed. Since highest concentrations are found in individuals of 2-3 yr., it is advisable to use this fish for such environmental studies.     

Investigation of the Declared Value of Selenium in Food Supplements by HG-AFS

The method of hydride generation atomic fluorescence spectrometry (HG-AFS) was optimised for determination of selenium in food supplements. Due to the high and varied content of Cu, Mg and Zn in the samples, the standard addition method was found to be the most appropriate. The reliability of the method was checked by the independent method of radiochemical neutron activation analysis, and good agreement was found between the two methods. HG-AFS is simple and rapid for Se determination in food supplements based on minerals. Agreement between the selenium values found and declared was worse than 10% in 9 out of 13 supplements. Furthermore, 2 of the 14 supplements did not comply with the recommendations stated in the 27^th edition of the U.S. Pharmacopoeia, which states that minerals and vitamins in food supplements should be in the range of 90 and 200% of the declared value.     

Synthesis and fluorescent properties of some new unsymmetricbis-benzothiazolyl furans and thiophenes

Summary Some newmono- andbis-benzothiazolyl compounds with furan or thiophene nuclei were synthesized by multistep reactions from the corresponding furan and thiophene aldehydes. The data obtained from emission spectra show a large influence of the benzothiazole rings on the relative quantum efficiency of the compounds under investigation.

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Synthese und Fluoreszenzeigenschaften von neuen unsymmetrischenbis-Benzothiazolylfuranen und thiophenen

Zusammenfassung Einige neuebis-Benzothiazolylverbindungen mit einem Furan- bzw. Thiophenenring wurden in einer mehrstufigen Reaktion dargestellt. Die Fluoreszenzdaten der untersuchten Verbindungen zeigen einen großen Einfluß der Benzothiazolringe auf die relative Fluoreszenzquantenausbeute.

     

Coulometrische Wismutometrie

Zusammenfassung Durch elektrolytische Oxydation einer Bi-Anode in gesättigter NaCl-Lösung können Bi³⁺-Ionen in Lösung gebracht werden. Dieser Prozeß ermöglicht die coulometrische Bestimmung anwesender Anionen, die schwerlösliche Bi-Verbindungen bilden.Es wurden Semimikro- und Mikrobestimmungen von Phosphationen durch elektrolytisch erzeugte Bi³⁺-Ionen bei konstanter Stromstärke ausgeführt. Die Endpunktbestimmung erfolgte amperometrisch bei konstantem Potential mit einer Indikatorelektrode — tropfende Quecksilberelektrode — und mit einer gesättigten Kalomelelektrode als Bezugselektrode. Die coulometrische Wismutometrie bietet eine weitere Möglichkeit der coulometrischen Eichung volumetrischer Lösungen im Sinne des seinerzeitigen Vorschlags vonTutundi.

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Summary Bi³⁺ ions can be brought into solution through electrolytic oxidation of a Bi-anode in saturated NaCl solution. This process makes possible the coulometric determination of the anions present that yield difficulty soluble bismuth compounds.Semimicro- and micro-determinations of phosphate ions were made via Bi³⁺-ions produced electrolytically at constant current strength. The endpoint was determined amperometrically at constant potential with an indicator electrode-dropping mercury electrode-and with a saturated calomel electrode as reference electrode. The coulometric bismuthometry affords a further possibility of the coulometric standardization of volumetric solutions in the sense of the proposal previously advanced byTutundi.

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Résumé On peut utiliser les ions Bi³⁺ en solution par oxydation électrolytique d'une anode en bismuth, en solution de chlorure de sodium saturée. Ce procédé permet le dosage coulométrique des anions présents qui forment des composés peu solubles avec le bismuth.On a mis au point le dosage semimicro et micro des ions phosphates par les ions Bi³⁺ formés électrolytiquement sous intensité constante. On détermine par ampérométrie le point équivalent à potentiel constant à l'aide d'une électrode indicatrice — électrode de mercure à goutte pendante —et avec une électrode au calomel saturée comme électrode de référence. La «bismuthométrie» coulométrique offre de grandes possibilités pour l'étalonnage coulométrique de solutions volumétriques, suivant l'idée queTutundi a émise en son temps.

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Vorgetragen beim Symposium für analytische Chemie in Graz, 29. September bis 1. Oktober 1965.

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Wir danken Herrn Dipl.-Ing.Vladimir Pantovi für seine Hilfe bei unserer experimentellen Arbeit.     

The Staudinger ligation-a gift to chemical biology

Although the reaction between an azide and a phosphane to form an aza-ylide was discovered by Hermann Staudinger more than 80 years ago and has found widespread application in organic synthesis, its potential as a highly chemoselective ligation method for the preparation of bioconjugates has been recognized only recently. As the two reaction partners are bioorthogonal to almost all functionalities that exist in biological systems and react at room temperature in an aqueous environment, the Staudinger ligation has even found application in the complex environment of living cells. Herein we describe the current state of knowledge on this reaction and its application both for the preparation of bioconjugates and as a ligation method in chemical biology.