X-ray elucidation of 17α-pregna-2,4-dien-20-yne-(2,3-d) isoxazole-17β-ol

Synthetic pregnen steroid 17-pregna-2,4-dien-20-yne-(2,3-d) isoxazole-17-ol crystallizes in the orthorhombic space group P2₁2₁2₁, with a = 6.601(4), b = 10.530(4), c = 26.177(9) Å, and Z = 4. The structure was solved from Enraf Nonius CAD4 diffractometer data by direct methods and refined to R = 0.0399 for 2041 observed reflections (I > 2(I)). The molecule contains five rings of which rings A, B, and C are cyclohexene; ring D is cyclopentene; and ring E is heterocyclic cyclopentene. Ring A acquires the conformation of a half-chair; ring B tends toward a half-chair conformation with a bias toward a chair conformation that contains a hydrogen at C8 and an hydrogen at C9. Ring C acquires a near chair conformation with an hydrogen at C14. Ring D is a 13, 14-half chair, and ring E is a O3-envelope. Both the ring junctions A/B and A/E are quasi-trans, whereas the ring junctions B/C and C/D are both trans. The molecule as a whole is slightly convex toward the -side, with an angle of 16.7(2)° between the C10–C19 and C13–C18 vectors. Structural association is due to hydrogen bonding and stacking interactions.     

Spectrophotometric determination of vanadium and niobium: Xylenol orange as a chromogenic reagent

Summary The formation of red coloured chelates of vanadium(V) and niobium(V) with xylenol orange (DCAC) having _max at 490 nm (at p_H 5.0) and 530 nm (at p_H 5.5) have been reported. The colour formation has been applied to the spectrophotometric determination of metal ions. The colour has been found to be stable between p_H 3.5–6.5 and 2.0–7.0 respectively. The sensitivity of the reagent is 0.051g/cm² of vanadium and 0.093g/cm² of niobium. Maximum colour intensity has been found for Nb-DCAC chelate at p_H 5.5 whereas no appreciable change has been found for V-DCAC chelate between p_H 4.5 and 6.5.

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Zusammenfassung Über die Bildung rot gefärbter Chelate von Vanadin und Niob mit Xylenolorange wurde berichtet. Deren Absorptionsmaxima liegen bei 490 nm (p_H 5,0) bzw. bei 530 nm (p_H 5,5). Die Farbreaktion wurde für die Bestimmung der beiden Metalle verwendet. Die Farbe ist zwischen p_H 3,5 und 6,5 bzw. zwischen p_H 2,0 und 7,0 stabil. Die Empfindlichkeit für Vanadin beträgt 0,051g/cm², für Niob 0,093g/cm². Die Farbe des Niobchelates erreicht bei p_H 5,5 ein Maximum, während die des Vanadinchelates zwischen p_H 4,5 und 6,5 keine wesentlichen Änderungen erkennen läßt.

     

Cation-exchange chromatography of some metal ions using aqueous NH4SCN-organic solvent mixtures

Summary Systematic cation-exchange studies of 19 metal ions have been made in various concentrations of NH₄SCN in 4060 organic solvent-water mixtures. The exchange behaviour of the ions depends on the solvent employed. Most of the metal ions show decreasing distribution coefficients with increasing concentration of ammonium thiocyanate in the solvent. Based on the variation of distribution coefficients as a function of NH₄SCN concentration, separations could be predicted and subsequently column chromatographic separations involving Zn, Hg(II), Mg, Mn(II), Co(II), Ni(II), Cd(II), Ce(III), Fe(III), La and Th(IV) were achieved.     

Ammonium aurin tricarboxylate as a reagent in inorganic analysis

Summary Ammonium aurin tricarboxylate produces characteristic colour with various metallic ions. The colour reactions are quite sensitive especially in the case of uranium and thorium besides aluminium and beryllium. The use of the reagent in analysis is suggested.     

On counting triangulations in d dimensions

Given a set of n labeled points on S^d, how many combinatorially different geometric triangulations for this point set are there? We show that the logarithm of this number is at most some positive constant times n^d/2+1. Evidence is provided that for even dimensions d the bound can be improved to some constant times n^d/2.     

Protonated,hydroxo, and mixed protonated - hydroxo species in metal - ligand equilibria: Complexes of thorium(IV) with xylenol orange in aqueous solution solution

Summary The equilibrium constants of chelate formation of thorium(IV) with 3,3-bis[N,N-di(carboxymethyl)-amino-methyll-o-cresolsulphonphthalein (xylenol orange, dcac) at 25° in aqueous solution have been evaluated. The values have been obtained both while considering and ignoring the presence of metal hydroxo species, using the method described earlier. The change in equilibrium constant values obtained in both these situations has been explained by introducing some possible equations, and it has been concluded that the consideration of metal hydroxo species, does not lead to any marked changes in the valules of the formation constants of complex formed, even at higherpH.Presented at the National Symposium on Coordination Chemistry, I.A.C.S., Calcutta, January 1977.