Mullite-derivative Bi2Mn(x)Al(7-x)O14 (x~1): structure determination by powder X-ray diffraction from a multi-phase sample

As a supplementary method to single crystal X-ray diffraction (XRD), nowadays crystal structure determination by powder XRD has become popular, especially for those areas with difficulties getting high quality single crystals. Here we observed an intermediate phase Bi(2)Mn(x)Al(7-x)O(14) (x~1) during the decomposition of mullite-Bi(2)Mn(x)Al(4-x)O(9+δ) (solid solution of Bi(2)Mn(4)O(10)-Bi(2)Al(4)O(9)). As a metastable phase, it started to decompose while forming, thus no single-phase sample can be obtained. We successfully determined its structure by powder XRD from a multi-phase sample. A modified Le Bail fitting using the atomic structure information of known impurities showed a more reliable intensity extraction from a multi-phase powder XRD than that without using atomic structures for the known impurities. The charge-flipping algorithm and Monte-Carlo based simulated annealing technique were then applied to obtain the full structural model. In principle, this strategy is applicable to more complex problems, and not limited to the oxide materials. Bi(2)Mn(x)Al(7-x)O(14) possesses a mullite-related structure. There are one tetrahedral and two octahedral sites for Mn and Al, where disordering with substantial site preferences is observed. Specifically, M1O(6) and M3O(6) octahedra share edges along the c-direction with the periodicity of 1 : 2. These octahedral chains are further connected into a 3D structure through M2O(4) dimmers and Bi.     

Selective transport of ATP across a phospholipid bilayer by a molecular umbrella

Acylation of each primary group of spermidine with cholic acid, followed by acylation of the secondary amino group using an activated form of Nalpha,Ndelta,Nomega-tri-CBZ-l-arginine, and subsequent hydrogenolysis, afforded a conjugate (i.e., 1) which readily transports adenosine 5-triphosphate, but not glutathione, across phospholipid bilayers made from 1-palmitoyl-2-oleyol-sn-glycero-3-phosphocholine and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylglycerol.     

Silver-ion reversed-phase comprehensive two-dimensional liquid chromatography combined with mass spectrometric detection in lipidic food analysis

The triacylglycerol (TAG) profiles present in real world lipidic samples are usually quite complex and, as such, monodimensional high-performance liquid chromatographic (HPLC) techniques are inadequate when challenged with such matrices. In this respect, the complementary use of silver-ion (Ag) and non-aqueous (NA) reversed-phase (RP) HPLC can be exploited if thorough TAG separations are required. The present investigation reports the employment of a newly developed comprehensive LC (LC x LC) system, based on the different separation mechanisms of the aforementioned techniques, and applied to a rice oil sample. The approach was successful in the separation of a high number of solutes, otherwise unachievable through monodimensional LC. Furthermore, the use of atmospheric pressure chemical ionization mass spectrometry (APCI-MS), as detection system, provided a third analytical dimension boosting the identification power of the comprehensive chromatographic method.     

Molecular umbrella-assisted transport of an oligonucleotide across cholesterol-rich phospholipid bilayers

A series of molecular umbrella conjugates, derived from cholic acid, deoxycholic acid, spermidine, lysine, and 5-mercapto-2-nitrobenzoic acid, have been synthesized and found capable of transporting an attached 16-mer oligonucleotide (S-dT16) across liposomal membranes made from 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidyldglycerol (POPG), and cholesterol [POPC/POPG/cholesterol (65/5/30; mol/mol/mol, v/v/v)] at 37 degrees C. Those molecular umbrellas containing four choloyl (or deoxycholoyl) groups resulted in significantly faster rates of transport as compared to those containing only two such moieties. A model that accounts for these membrane transport processes is proposed.     

Games with multiple payoffs

The traditional theories of decision making and games are based on an assumption that prevents their broader practical utilization:a single dimensional payoff. In reality, any alternative is likely to imply more than one payoff, e.g. not only costs but also time, price, quality, safety, maintainability, productivity, etc. Similarly, the Theory of Games faces difficulties as we attempt to apply it to the conflict situations of the social and business environment. The assumption that a single dimensional payoff, like money, points or chips, is a realistic consequence of individual moves or strategies, is difficult to sustain. In this short paper, concepts of nondominated solutions and a decomposition of parametric spaces are used to formulate and resolvedecision problems with vector payoffs. Both Games against Nature and Two-Person, Zero-Sum frameworks are considered. A concept of compromise solutions is introduced to help the decision maker with further reduction of the nondominated set. Some numerical examples are given.     

The possibility of a simple transformation of thermogravimetric curves

A simple method is suggested for the Arrhenius-like representation of the thermal decomposition of a wide variety of materials. It consists in the transformation of the TG and the corresponding DTG curves, obtained as a single measurement by a derivative thermobalance. The method consists mainly in the division of the momentary DTG ordinates by the corresponding momentary TG values, the transformation of this value into logarithmic form, and the plotting of the logarithmic expression as a 1/T function. In many cases a straight line results testifying to a first-order reaction or a tolerable approximation of it.

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Zusammenfassung Eine einfache Methode zur Arrheniusanalogen Darstellung der thermischen Zersetzung vieler Arten von Substanzen wird vorgeschlagen. Sie besteht in der Transformierung der TG- und der entsprechenden DTG-Kurven, welche mit Hilfe einer derivierenden Thermowaage durch eine einzige Messung erhalten worden sind. Die Methode besteht hauptsächlich in der Teilung der bestehenden DTG-Ordinaten durch die entsprechenden TG-Werte, dann in der Transformierung dieses Symbols in die logarithmische Form und schließlich in der Darstellung dieses logarithmischen Ausdruckes als Funktion von 1/T, wobei in vielen Fällen eine Gerade oder eine annehmbare Näherung einer Geraden erhalten wird, die für eine Reaktion erster Ordnung spricht.

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Résumé On propose une méthode simple pour représenter la décomposition thermique d'un grand nombre de substances par une loi analogue à celle d'Arrhenius. La méthode consiste à transformer les courbes TG et TGD obtenues par une mesure unique à l'aide d'une thermobalance comportant un dispositif de dérivation. En premier lieu, on divise les ordonnées de la courbe TGD par les valeurs TG correspondantes puis on exprime ce symbole sous forme logarithmique et finalement on représente cette expression logarithmique en fonction de 1/T, ce qui donne dans de nombreux cas une droite et prouve ainsi qu'il s'agit d'une réaction du premier ordre ou d'une approximation qui peut Être tolérée comme telle.

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Uncertainties of mercury determinations in biological materials using an atomic absorption spectrometer – AMA 254

 The method is based on catalysed ignition of a sample portion in a flow of oxygen, capture of mercury by an amalgamator and measurement of the mercury vapour's absorbance after thermic release from the amalgamator. Three powdered food samples, a certified reference material (CRM) human hair and a reference material (RM) urine (liquid) were measured in the first range of the instrument (the possible contents determined according to our measurement procedure were 0.0003–0.5 ppm). The calibration function used was a line passing through the origin. The combined standard uncertainties of the mercury determinations were computed from uncertainty components of five quantities: absorbance of the sample, absorbance of the sample blank, slope of the calibration line, correction factor of the abscissa axis, and mass or volume of the sample. The most important uncertainty component is the uncertainty of the sample absorbance measurement which amounts to 52% of the determination uncertainty at the minimum (RM urine) and about 90% at the maximum (in our laboratory homogenized powdered food samples; analysis of variance showed their homogeneity to be insufficient). The results of the CRM and RM analyses do not indicate a significant systematic error for this determination. The relative expanded uncertainty (coefficient was 2) of the determination increases from 9 to 13% for the insufficiently homogenized samples with decreasing mercury content (range of 0.004–0.03 ppm); higher homogeneity of samples results in a decrease of the expanded uncertainty, e.g. 4.6% for the liquid sample (RM urine). Received: 26 April 1999 / Accepted: 30 August 1999