Endothermic quasicrystalline-to-crystalline phase transition in Al6CuMg4

Electron microscopic and differential scanning calorimetric (DSC) studies have been performed to investigate the phase transitions in the rapidly solidified Al₆CuMg₄ alloy system. We present evidence, for the first time, that anendothermic quasicrystalline to crystalline transition occurs in this system around 340°C. This is an unexpected feature—for conventional wisdom would lead one to expect exothermic behaviour as was seen in Al₈₆Mn₁₄—and points to the fact that stability of certain quasicrystalline phases may be much larger than hitherto expected. Some comments on the recently reported large quasicrystal for the Al₆CuLi₃ system are also made in the light of our observation.     

A new technique to compute polygonal schema for 2-manifolds with application to null-homotopy detection

We provide a new technique for deriving optimal-sized polygonal schema for triangulated compact 2-manifolds without boundary inO(n) time, wheren is the size of the given triangulationT. We first derive a polygonal schemaP embedded inT using Seifert-Van Kampen's theorem. A reduced polygonal schemaQ of optimal size is computed fromP, where a surjective map from the vertices ofP is retained to the vertices ofQ. This helps detecting null-homotopic (contractible to a point) cycles. Given a cycle of lengthk, we determine if it is null-homotopic inO(n+k logg) time and in θ(n+k) space, whereg is the genus of the given 2-manifold. The actual contraction for a null-homotopic cycle can be computed in θ(nk) time and space. This is a considerable improvement over the previous best-known algorithm for this problem.     

Perturbed iterative solution of nonlinear equations with applications to fluid dynamics

In this work a technique has been developed to solve a set of nonlinear equations with the assumption that a solution exists. The algorithm involves nonlinear Gauss-Seidel iteractions and at each iteration the value of the iterate is added to a predetermined perturbation parameter which is computed in terms of quantities already known. This perturbation parameter has two properties: (i) it determines the mode of convergence, that means it shows how many more computations are required so that convergence may be achieved, and (ii) it accelerates the rate of convergence. The algorithm is computationally simple. Several nonlinear equations have been studied. The results seem to be encouraging.     

OH radical reactions with ethanolamines: formation of reducing as well as oxidizing radicals

OH radical reactions with ethanolamine, diethanolamine and triethanolamine were studied at pH values below and above the pK_a values of these compounds. The rate constants were found to be lower for the protonated amines than those for their neutral forms. The OH radical reaction led to the formation of both oxidizing, as well as reducing species, as observed by their reactions with methyl viologen and ascorbic acid. The oxidizing species formed by OH radical reaction at the amine site was not found to react with the parent molecules and thereby no secondary yield of reducing species was obtained, as in the case of glycine (except in the case of triethanolamine at pH 9.2).     

Micro-determination of Uranium using ammonium aurintricarboxylate as a colorimetric reagent

Summary The formation of a colored chelate between UO₂ ²⁺ and ammonium aurintricarboxylate has been used for the colorimetric determination of uranium on a microscale. The chelate has a maximum of absorbance at 540 nm (m). The stability of the color with time, temperature, and p_H has been studied. The interferences by a large number of cations and anions have been investigated, and the tolerance limit has been determined for each ion. It is recommended that a 50-fold molar excess of the reagent should be added, the p_H maintained at 5.5 ± 0.5, and the temperature held between 20° to 30° C.

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Zusammenfassung Die Bildung eines gefärbten Chelatkomplexes aus Uranylion und Ammoniumaurintricarboxylat (Aluminon) läßt sich mit Vorteil für die Mikrobestimmung von Uran verwenden. Dieser Komplex hat ein Absorptionsmaximum bei 540 nm. Die Beständigkeit der Farbe gegenüber Zeit, Temperatur und p_H wurde untersucht. Die störende Wirkung einer großen Zahl von Kationen und Anionen und deren Toleranzgrenze wurde quantitativ bestimmt. Es wird empfohlen, bei der Durchführung der Reaktion einen 50fachen Überschuß des Reagens zu verwenden, ein P_H von 5,5 ± 0,5 und eine Temperatur von 20 bis 30° einzuhalten.

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Résumé Il est possible d'utiliser avantageusement la formation d'un complexe chélaté coloré de l'ion uranyle et du tricarboxylate d'aurinammonium (Aluminon) pour le microdosage de l'uranium. Ce complexe présente un maximum d'absorption à 540 nm. On a étudié la stabilité de la couleur en fonction du temps, de la température et du P_H. L'action perturbatrice d'un grand nombre de cations et d'anions et les limites de tolérance correspondantes ont été déterminées quantitativement. Il est recommandé d'effectuer la réaction avec un excès de réactif 50 fois supérieur à la quantité nécessaire, à un Ph de 5,5 ± 0,5 et de maintenir une température de 20 à 30°.

     

Weitere Untersuchungen über Zinkoxydhydrat

Zusammenfassung Die Bildung l?slicher Zinkate wurde durch Dialysieren von L?sungen aus Zinkhydroxyd in Natronlauge untersucht. In einem solchen System existiert ein Gleichgewicht zwischen der Natriumzinkat- und der kolloidalen Zinkhydroxydkonzentration. Die Menge und Stabilit?t des ersten w?chst mit der Alkalikonzentration. Mit fortschreitender Dialyse verschiebt sich das Gleichgewicht. Schlie?lich entsteht auf Grund der Hydrolyse der Zinkat-Ionen eine kolloide L?sung.

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Summary The formation of soluble zincates has been investigated by dialysing a solution of zinc hydroxide in sodium hydroxide solution. It has been concluded that the system contains an equilibrium mixture of sodium zincate and colloidal zinc hydroxide and the proportion and stability of the former increase with the increase in the concentration of alkali. The equilibrium shifts with progressive dialysis and ultimately the system passes to a colloidal solution as a result of the hydrolysis of zincate ions.

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übersetzt von Dr. K. J?ckel, Marburg.

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Die Experimente für diese Arbeit wurden in den Chemical Laboratories of Meerut College ausgeführt. Die Verfasser danken dem Leiter dieses Institutes, Herrn Prof. Dr. S. S. Joshi, für seine Unterstützung.     

Differentiation of human serum samples by surface plasmon resonance monitoring of the integral glycoprotein interaction with a lectin panel

Bacterial infection and inflammation result in massive changes in serum glycoproteins. These changes were investigated by the interaction of the saccharide glycoprotein moiety with lectins. A panel of eight lectins (Canavalia ensiformis, Bandeiraea simplicifolia BS-I, Arachis hypogaea, Phytolacca americana, Phaseolus vulgaris, Artocarpus integrifolia, Triticum vulgaris and Pisum sativum) was used to differentiate human serum glycoproteins obtained from patients with various bacterial infections. Lectin functionalised sensing layers were created on gold-coated wafers and lectin-glycoprotein interactions were monitored by surface plasmon resonance. The interaction of the lectin panel with serum glycoproteins produces unique patterns. Principal component analysis (PCA) was used to analyse the patterns. The actual panel of eight lectins enabled discrimination between sera obtained from patients sick with bacterial infection and healthy patients. Extended lectin panels have the potential to distinguish between types of bacterial infection and identify specific disease state.     

Dual binding mode of methylmethanetriacetic Acid to tripodal amidopyridine receptors

A series of tripodal amidopyridine receptors capable of selective recognition of methylmethanetriacetic acid (MMTA) in organic solvents is described. Intramolecular hydrogen-bonding groups, built into some of the receptors, were designed as preorganization devices. Binding was studied by NMR titration, variable temperature NMR experiments, 2D-NMR, isothermal titration calorimetry, and single-crystal X-ray crystallography. The results reveal that a balancing act between inter- and intramolecular hydrogen-bonding interactions in the complexes governs both the dynamics and the geometry of binding. Receptor 1b (without intramolecular hydrogen-bonding groups) features a simple symmetric MMTA binding geometry with optimal enthalpic interactions. In sharp contrast, receptor 1a (with intramolecular hydrogen-bonding groups) reveals a temperature-dependent dual binding mode where MMTA can bind in two completely different geometries. The two solution binding geometries of 1a.MMTA were unraveled by NMR experiments and correlated to the X-ray structures.     

Chromatographic study of anionic complexes

Summary In this paper the variation of diffusion, through filter paper strips by the ascending method, of citrate complexes of Cu²⁺, Ni²⁺, Co²⁺ and Fe³⁺ has been studied using 50%, 55% and 60% ethanol as solvents. The R_f value is found to be less with higher concentrations of ethanol used. It has been noted that with 50% ethanol the R_f value increases with the addition of citrate and finally tends to become constant with high concentrations of citrate ions. In 55% ethanol the R_f value becomes constant at a later stage. In 60% ethanol it is noted that the R_f value does not change with small additions of citrate, but on increasing its concentration the R_f value begins to diminish.Part II see Z. analyt. Chem. 165, 81 (1959).     

Reactions of platinum(II) dipicolinate complex with amino acids—chelation and isomerization

The kinetic course of the reactions of [Pt(dipic_tr)Cl]^? (where H₂dipic = pyridine‐2,6‐dicarboxylic acid; bonded in tridentate mode) with glycine, β‐alanine, and L‐histidine was followed at 25°C in aqueous medium at pH 3.00–10.73 at I = 0.5 mol dm^?3 (LiClO₄) spectrophotometrically and through ¹H NMR spectral analysis. The selectivity of platinum(II) toward the amino acids with regard to chelation and isomerization is controlled by donor atoms and steric properties. The aquation equilibrium of the designated platinum(II) complex also affects the binding rate in the case of glycine and β‐alanine. The reaction products have been isolated and characterized through ¹H NMR spectra. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 262–270, 2002