Dissolution of copper foil in aqueous solution ofpH=2

The specific dissolution rate, expressed in mol cm^–2s^–1, and time-variation of the rest potential of copper foil in an aerated aqueous solution ofpH = 2.0 were measured.

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Die Auflösbarkeit von Kupfer-Folie in wäriger Lösung von pH 2 (Kurze Mitteilung)

Zusammenfassung Es wurde die spezifische Auflösungsgeschwindigkeit (in mol cm^–2s^–1) und die zeitliche Veränderung des Restpotentials von Kupfer-Folie in einer belüfteten wäßrigen Lösung von pH 2,0 gemessen.

     

Quantitative determination of acetylsalicylic acid and acetaminophen in tablets by FT-Raman spectroscopy

A procedure for quantitative determination of acetylsalicylic acid and acetaminophen in pharmaceuticals by PLS (partial least squares) and PCR (principal component regression) treatment of FT (Fourier transform)-Raman spectroscopic data is proposed. The proposed method was tested on powdered samples. Three chemometric models were built: the first, for samples consisting of an active substance diluted by lactose, starch and talc; the second, in which a simple inorganic salt was applied as an internal standard and additions were not taken into account; and the third, in which a model was constructed for a commercial pharmaceutical, where all constituents of the tablet were known. By utilising selected spectral ranges and by changing the chemometric conditions it is possible to carry out fast and precise analysis of the active component content in medicines on the basis of the simplified chemometric models. The proposed method was tested on five commercial tablets. The results were compared with data obtained by intensity ratio and pharmacopoeial methods. To appraise the quality of the models, the relative standard error of predictions (RSEPs) were calculated for calibration and prediction data sets. These were 0.7-2.0% and 0.8-2.3%, respectively, for the different PLS models. Application of these models to the Raman spectra of commercial tablets containing acetylsalicylic acid gave RSEP values of 1.3-2.0% and a mean accuracy of 1.2-1.7% with a standard deviation of 0.6-1.2%.     

Increased structural complexity leads to higher activity: peptides as efficient and versatile catalysts for asymmetric aldol reactions

[reaction: see text] Peptides containing a secondary amine and a carboxylic acid in a specific orientation to each other are presented as highly efficient catalysts for asymmetric aldol reactions: (1) their activity is considerably higher compared to that of proline, and (2) the enantioselectivity of the peptidic catalysts can be changed from (R)- to (S)-selectivity by simple modifications of the secondary structure.     

The Inverse Scattering Method and Systems of Equations qxy = F(q,qy)

Consider equations of the form where q is in general a complex vector and the function F depends nontrivially both on q and on q_y. We show that a family S of such equations can be investigated by the inverse scattering method. If an equation (*) belongs to S, the function F depends linearly on q and algebraically on q_y. We show that the family S contains a subfamily in which each equation can be obtained from the two dimensional Toda lattice equations by a Bäcklund transformation.     

The stability of the exponential equation

We generalize the well-known Baker's superstability result for exponential mappings with values in the field of complex numbers to the case of an arbitrary commutative complex semisimple Banach algebra. It was shown by Ger that the superstability phenomenon disappears if we formulate the stability question for exponential complex-valued functions in a more natural way. We improve his result by showing that the maximal possible distance of an -approximately exponential function to the set of all exponential functions tends to zero as tends to zero. In order to get this result we have to prove a stability theorem for real-valued functions additive modulo the set of all integers .

     

Separation techniques for biotechnology in the 1990s.

Scientists are constantly looking for better and cheaper separation techniques to replace or complement the current technology. Over the past few decades, and in particular the last 10 years, new separation techniques or modifications of existing techniques have become available for separating compounds from complex sample matrices. There are many areas, however, where the separation technology is not sufficient to achieve high purity and yield while remaining cost effective. In the area of biotechnology, separation techniques are urgently needed to meet demands for ultra-high purity and yield. Thus, a variety of techniques are being developed to address these needs. Generally, biological compounds for the pharmaceutical and biotechnology industries must be obtained at greater than 99.9% purity (sometimes greater than 99.99%) while maintaining high yield. In any area of chemistry this degree of purity would cause problems; in biotechnology it is even more difficult to achieve because of the complex sample matrices. In addition, the compounds of interest may be very similar to impurities or contaminants in the sample matrix, and the compounds could be denatured (or even destroyed) by certain solvents and/or high temperature. In particular, three areas of biotechnology have presented scientists with problems in separations: cell separations, DNA-RNA separations, and protein-peptide separations. The current technology available and possible future trends in these areas are discussed, and also problems to be solved in the future.     

Calculs de complexité relatifs à une méthode de dissection emboîtée

Résumé Nous présentons une numérotation de type Nested Dissection des inconnues d'un système linéaireAX=B pour des ensembles de matricescreuses symétriques définies positives correspondant à des famille de graphes non orientés,à degré borné, et admettant un -thérème de séparation. Comparativement aux méthodes et résultats de Rose [9], l'algorithme présenté est plus simple, mais les théorèmes de complexité moins généraux, en raison de l'hypothèse restrictive de degré borné. En outre, les démonstrations font appel en permanence à la structure d'arbre sur la famille des séparateurs qui constitue, par ailleurs, une partition de l'ensemble des sommets du graphe initial. Nous présentons ensuite le schéma général d'implémentation dans le cadre du code d'éléments finis MODULEF pourdes problèmes plans d'éléments finis, et nous donnons quelques mesures comparatives avec la numérotation plus classique qui tend à minimiser le profil de la matrice.

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Complexity bounds for a nested dissection method

Summary A nested dissection ordering is given for solving any system of linear equationsAX=B, for the family ofsparse symmetric positive definite matrices corresponding to the class of undirected graphs withbounded degree, and satisfyinga -separator theorem. If we compare the methods and results presented by Rose [9], our algorithm is more simple, but the complexity results are less general because of the restriction of bounded degree. Besides, our proofs use continually the arborescent structure on the family of separators, which is, by another way, a partition of the set of vertices for the initial graph. Then, the general implementation scheme in the finite element package MODULEF, fortwo-dimensional finite element problems, is presented, and numerical comparisons between our ordering and the standard envelope method are given.

     

Arylselenenation of conjugated dienes by arylselenenamides in the presence of phosphorus(V) oxyhalides

Arylselenenation of conjugated and non-conjugated dienes by arylselenenamides in the presence of phosphorus(V) oxyhalides has been studied. Reactions with conjugated dienes lead to 1,4-adducts whilst only addition to double bonds takes place in reactions with non-conjugated dienes.     

Neue Macrolide und einige Sesquiterpen-Derivate aus dem Galbanum-Harz

New Macrolides and Some Sesquiterpenoid Derivatives Occurring in Galbanum Absolute Analytical investigations of a Galbanum absolute have revealed for the first time the presence of four macrolides 1 – 4 derived from the corresponding hydroxylated C₁₃–C₁₆ fatty acids by lactonization of a secondary alcoholic group with the carboxylic group. The musky odor strengthens with increasing number of members in the macrocycle, whereas the woody note is predominant in the smaller rings. Isolation, identification and synthesis of the new naturally occurring substances are described. Shyobunol ( 24 ) epishyobunol ( 25 ) as well as their acetates 26 and 27 were identified - together with 10-epijunenyl acetate ( 28 ) - in the same substrate, thus indicating 25 and 26 to be natural products. The corresponding known and already naturally occurring ketones 23 and 24 are trace components in the investigated material derived from the so-called Galbanum oleo-gum-resin.     

Hierarchical structure of the energy landscape of proteins revisited by time series analysis. I. Mimicking protein dynamics in different time scales

Time series models, which are constructed from the projections of the molecular-dynamics (MD) runs on principal components (modes), are used to mimic the dynamics of two proteins: tendamistat and immunity protein of colicin E7 (ImmE7). Four independent MD runs of tendamistat and three independent runs of ImmE7 protein in vacuum are used to investigate the energy landscapes of these proteins. It is found that mean-square displacements of residues along the modes in different time scales can be mimicked by time series models, which are utilized in dividing protein dynamics into different regimes with respect to the dominating motion type. The first two regimes constitute the dominance of intraminimum motions during the first 5 ps and the random walk motion in a hierarchically higher-level energy minimum, which comprise the initial time period of the trajectories up to 20-40 ps for tendamistat and 80-120 ps for ImmE7. These are also the time ranges within which the linear nonstationary time series are completely satisfactory in explaining protein dynamics. Encountering energy barriers enclosing higher-level energy minima constrains the random walk motion of the proteins, and pseudorelaxation processes at different levels of minima are detected in tendamistat, depending on the sampling window size. Correlation (relaxation) times of 30-40 ps and 150-200 ps are detected for two energy envelopes of successive levels for tendamistat, which gives an overall idea about the hierarchical structure of the energy landscape. However, it should be stressed that correlation times of the modes are highly variable with respect to conformational subspaces and sampling window sizes, indicating the absence of an actual relaxation. The random-walk step sizes and the time length of the second regime are used to illuminate an important difference between the dynamics of the two proteins, which cannot be clarified by the investigation of relaxation times alone: ImmE7 has lower-energy barriers enclosing the higher-level energy minimum, preventing the protein to relax and letting it move in a random-walk fashion for a longer period of time.