1,3-Dipolar cycloadditions of silicon and tin alkynes and alkenes. Regiospecific synthesis of silyl and stannylpyrazoles and pyrazolines

Silicon and tin 3-, 3,5-, and 3,4,5-metalated pyrazoles have been synthesized by 1,3-dipolar cycloadditions of silyl-, disilyl-, and silylstannylacetylenes with N-phenylsydnone or trimethylsilyldiazomethane. On the other hand, 1- and 2-pyrazolines monometalated and dimetalated in different positions of the heterocycle have been prepared by reaction of vinylsilanes and vinylstannanes with the same 1,3-dipolar reagents. Other interesting products resulting from homologation were obtained by cycloaddition of trimethylsilyldiazomethane with β-silyl enones and esters. Moreover, for the first time a 3-silylpyrazole has been converted into a 3-cyanopyrazole.     

Trennung von Strontium und Calcium mit Rhodizonsäure bei radiochemischen Untersuchungen

Zusammenfassung Mit alkoholischer Rhodizonsäurelösung kann Strontium von Calcium getrennt werden. Die Fällung muß bei Siedehitze durchgeführt werden; nachträglicher Zusatz von Alkohol ist erforderlich. Zur pM- und p_H-Kontrolle wird HEDTA verwendet. Bei größeren Calciummengen muß mehrmals gefällt werden, um das Strontium quantitativ zu erfassen.

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Summary Strontium can be separated from calcium by alcoholic rhodizonic acid solution. The precipitation must be conducted at boiling temperature; auxiliary addition of alcohol is necessary. HEDTA is employed for p_H- and pM-control. If large quantities of calcium are present the precipitation must be repeated several times to obtain the strontium quantitatively.

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Résumé On peut séparer le strontium d'avec le calcium au moyen d'une solution alcoolique d'acide rhodizonique. On doit effectuer la précipitation à la température de l'ebullition; une addition ultérieure d'alcool est nécessaire. On utilise l'HEDTA pour le contrôle du pM et du p_H-Pour de plus grandes quantités de calcium on doit précipiter plusieurs fois, afin de recueillir le strontium quantitativement.

     

A steroids QSAR approach based on approximate similarity measurements

A new QSAR method based on approximate similarity measurements is described in this paper. Approximate similarity is calculated using both the classical similarity based on the graph isomorphism and a distance computation between nonisomorphic subgraphs. The latter is carried out through a parametric function where different topological invariants can be considered. After optimizing the contribution of nonisomorphic distance to the new graph similarity, predictive models built with approximate similarity matrixes show higher predictive ability than those using traditional similarity matrixes. The new method has been applied to the prediction of steroids binding to the corticosteroid globulin receptor. The proposed model allows us to obtain valuable external predictions (r=0.82 and SEP=0.30) after training the model by cross-validation (Q2=0.84 and SECV=0.47). Slope and bias parameters are also given.     

Delay equation formulation of a cyclin-structured cell population model

The aim of this paper is to derive a system of two renewal equations from individual-level assumptions concerning a cyclin-structured cell population. Nonlinearity arises from the assumption that the rate at which quiescent cells become proliferating is determined by feedback. In fact, we assume that this rate is a nonlinear function of a weighted population size. We characterize steady states and establish the validity of the principle of linearized stability.     

Reactions of TiX4 and VOCl3 with P=S ligands

Summary The reactions of TiX₄ (X=Cl or Br) with the bidentate ligands, L, (Figure 1), yield hexacoordinate complexes TiX₄·L, whereas similar reactions with VOCl₃ lead to reduction of vanadium and give rise to vanadium(IV) pentacoordinate complexes, VOCl₂·L. All the compounds have been characterized by elemental analyses, i.r., visible and e.p.r. spectra. The occupation of the sixth coordination position in pentacoordinate complexes, VOCl₄·L, by different donor solvents, has been studied by means of visible and e.p.r. spectra.     

Alkyl and cyclic substituted thiuram disulphides as ligands. titanium(iv), vanadium(iv), and oxovanadium(iv) complexes

Summary Titanium(IV) hexacoordinate thiuram disulphide complexes of the type [TiX₄R₂NC(S)SSC(S)NR₂}] (X=Cl or Br; R=Me, Et, piperidinyl or morpholinyl) have been prepared by reaction between TiX₄ (X=Cl or Br) and the thiuram disulphide. Similar reactions with VOCl₃ lead to reduction of vanadium(V) and give rise to the oxovanadium(IV) pentacoordinate complexes [VOCl₂{R₂NC(S)SSC(S)NR₂}]. However, the reactions of these same thiuram disulphide ligands with [VCl₂(THF)₂] (THF=tetrahydrofuran) cause oxidation of vanadium and to the reduction of the disulphide to the corresponding dithiocarbamate [R₂NCS₂]^–, resulting in new dichlorobis (dithiocarbamate)vanadium(IV) complexes [VCl₂-(R₂NCS₂)₂]. All the compounds have been characterized by elemental analyses, i.r., visible and e.p.r. spectra. Both thiuram disulphides and dithiocarbamate ligands exhibit bidentate     

Liquid chromatographic study of two methoxypsoralen isomers with β-cyclodextrin

Abstract

The inclusion into β-cyclodextrin (β-Cyd) by the two methoxypsoralen isomers (5-methoxypsoralen (5-MOP) and 8-methoxypsoralen (8-MOP)) has been extensively studied by reverse phase liquid chromatography (RP-HPLC). Some important quantitative data concerning the complexation in a dynamic flow system have been drawn. The stoichiometry of the complex formation (1:1 in all instances), and the affinity constants with the β-Cyd cavity (K_f) of the two guest compounds, have been established. By taking into account the competitive effect of the organic modifier of the eluent (methanol), the K_fs of both compounds have been extrapolated to pure water (233 M^?1 and 106 M^?1 for 5-MOP and 8-MOP, respectively). On the other hand, the established stoichiometry and affinity constants have been interpreted in terms of enthalpy and entropy changes. Finally, the importance of the position of the methoxy substituent has been underlined and seems to rule the quality of the fit of each isomer within the inner cavity of β-cyclodextrin.