Microscopic study of a lattice defect trapped at in impurities in plastically deformed Al

¹¹¹In doped Al specimes (c _In1 ppm) were cold worked by extension at 77 K to several amounts of strain. The PAC method was applied to study the trapping of lattice defects at the indium impurities between 77 K and 293 K. From electron irradiation experiments it is known that the In probes are suitable traps for self-interstitials in Al. Since in the present experiment no such effect is observed, it is concluded that by extension at 77 K in Al essentially no freely migrating interstitials are created. Between 110 K and 210 K an increasing fraction of the indium impurities traps a well defined defect. The symmetry axis of the resulting indium-defect-complex is found to point along 111 crystallographic directions. It is proposed that the In impurity traps a divacancy at nearest neighbour sites and relaxes into the open space, thus forming an equilateral triangle of three vacancies in a {111} plane with the In atom in its centre. Reasons for the formation of this complex at rather low annealing temperatures are discussed.     

Cyclic Heptapeptides Axinastatin 2, 3, and 4: Conformational analysis and evaluation of the biological potential

The conformational analysis of naturally occurring cytostatic cyclic heptapeptides axinastatin 2, 3, and 4 was carried out by two-dimensional NMR spectroscopy in combination with distance-geometry (DG) and molecular-dynamics (MD) calculations in explicit solvents. The synthesized secondary metabolites were examined in (D₆)DMSO. Axinastatin 2 was also investigated in CD₃OH. In all structures, Pro² is in the i + 1 position of a βI turn and Pro⁶ occupies the i + 2 position of a βVIa turn about the cis amide bond between residue 5 and Pro^6. In all peptides, a bifurcated H-bond occurs between residue 4 CO and the amide protons of residue 1 and 7. For axinastatin 2 and 3, an Asn I_g turn was found about Asn¹ and Pro^2. We compared these structures with conformations of cyclic heptapeptides obtained by X-ray and NMR studies. A β-bulge motif with two β turns and one bifurcated H-bond is found as the dominating backbone conformation of cyclic all-L-heptapeptides. Axinastatin 2, 3, and 4 can be characterized by six trans and one cis amide bond resulting in a β/βVI(a)-turn motif, a conformation found for many cyclic heptapeptides. Detailed biological tests of the synthetic compounds in different human cancer cell lines indicates these axinastatins to be inactive or of low activity.     

Zur deprotonierung von chloromethyleniminiumchloriden

Deprotonation of chloromethyleniminium chlorides ($\text{1}$, $\text{13}$) leads to cis-trans-isomeres 1,2-diamino-1,2-dichloro-ethenes ($\text{3a}$, $\text{3b}$ resp. $\text{14a}$, $\text{14b}$); their reactivity is described.     

Untersuchungen über die Adsorption von Gasgemischen

Zusammenfassung Es werden Mischadsorptionsmessungen am SystemAceton-Chloroform mit einem Dampfdrukminimum an homogenen Oberflächen an Mikroglaskügelchen (2 bis 12 ) in einem rel. Druckbereich zwischen 0,1 und 0,9 ausgeführt. Dabei ist der Sättigungsdruck jeweils der Dampfdruck der mit der Gasphase im Adsorptionsgleichgewicht korrespondierenden flüssigen Phase imp _o , -Diagramm. Zugleich wurde die Zusammensetzung der adsorbierten Mischphase bestimmt und daraus die partielle Adsorption der Komponenten als Funktion des rel. Druckes bei verschiedener Zusammensetzungen der Gasphase.Für partielle Adsorption wurde auf der Grundlage eines vonHill entwickelten Ansatzes in Verbindung mit einer Gl. vonTheimer eine Formel aufgestellt, die die experimentellen Ergebnisse gut wiedergibt.Es werden Adsorptionswärmen für die verschiedenen Belegungsdichten in Abhängigkeit von der Zusammensetzung der Gasphase bestimmt.Mit 18 AbbildungenHerrn Prof.L. Ebert zum 60. Geburtstag gewidmet.     

Self-assembly of tetrahedral and trigonal antiprismatic clusters [Fe4(L4)4] and [Fe6(L5)6] on the basis of trigonal tris-bidentate chelators

In a one-pot reaction, the tetranuclear iron chelate complex [Fe4(L4)4] 6 was generated from benzene-1,3,5-tricarboxylic acid trichloride (4), bis-tert-butyl malonate (5a), methyllithium, and iron(II) dichloride under aerobic conditions. Alternatively, hexanuclear iron chelate complex [Fe(L5)6] 7 was formed starting from bis-para-tolyl malonate (5b) by employing identical reaction conditions to those applied for the synthesis of 6. The clusters 6 and 7 are present as racemic mixtures of homoconfigurational (delta,delta,delta,delta)/(lambda,lambda,lambda,lambda)-fac or (delta,delta,delta,delta,delta,delta)/(lambda,lambda,lambda,lambda,lambda,lambda)-fac stereoisomers. The structures of 6 and 7 were unequivocally resolved by single-crystal X-ray analyses. The all-iron(III) character of 6 and 7 was determined by M?ssbauer spectroscopy.     

On a class of Hammerstein integral equations

By a monotone representation of the nonlinearity we derive sufficient (and partly necessary) conditions for the unique existence of positive solutions of the Hammerstein integral equation $$\begin{array}{*{20}c} {u(x) = \int\limits_D {f(y,u(y)) k(x,y) dy ,} } & {x \in D,} \\ \end{array} $$ and for the convergence of successive approximations towards the solution. Further we study the corresponding nonlinear eigenvalue problem. Essentially we assume that the integral kernel k satisfies appropriate positivity conditions and that, for the nonlinearity f and any y ∈ D, rf(y,r) strictly monotone increases and f(y,r)/r strictly monotone decreases as r>0 increases.     

On the self-perimeter of pentagonal gauges

We give a sharp lower estimate on the self-perimeter of pentagonal gauges, thus solving the last respective case for polygonal unit circles with respect to convex distance functions.     

Liquid-Liquid Equilibrium of Copolymer Solutions with Broad and Asymmetric Chemical Distributions

ABSTRACT

A solution of a random copolymer showing polydispersity only with respect to chemical composition is considered. A model distribution very flexible in its breadth and in its asymmetry is used to describe the polydispersity. Based on continuous thermodynamics, equations for the cloud-point curve, the shadow curve, the spinodal, the critical point, and the heterogeneous double critical point are derived. the activity coefficients are calculated with the aid of Huggins' χ-parameter concept assuming χ to depend linearly on the average chemical composition of the copolymer. the influence of the breadth and the asymmetry of the distribution on the liquid-liquid equilibrium of the copolymer solution is discussed.