Molecular structure of 6-methyleneoxytetracycline hydrobromide

The structure of 4(dimethylamino)-1, 4, 4a, 5, 5a, 6, 11, 12a-octahydro-3, 5, 10, 12, 12a-pentahydroxy-6-methylene-1, 11-dioxo-2-naphthacenecarboxamide hydrobromide salt was determined by an X-ray analysis. One methacycline cation and one bromide anion were found in the asymmetric unit of an orthorhombic cell, space group P2₁2₁2₁,a 9.580(1),b 12.147(2),c 18.735(3) å,V2180.0(5) å³, Z4,D _c 1.59 g cm^–3, (MoK) 19.15 cm^–1. The structure was solved and refined toR(F) 0.062 andR _w(F) 0.064 by a full matrix least-squares procedure. The conformation of the methacycline cation is found to be similar to that reported for 6-demethyl-7-chlorotetracycline hydrochloride trihydrate.     

Radical cyclization of sugar-derived beta-(alkynyloxy)acrylates: synthesis of novel fused ethers

[formula: see text] Tributyltin radical mediated cyclization of carbohydrate-derived beta-(alkynyloxy)acrylates leading to highly functionalized cis- and trans-fused bicyclic ethers of various ring sizes is described. The efficacy of the radical cyclization is nicely illustrated in the iterative construction of a trans-fused tricyclic tetrahydropyran.     

The polarographic determination of aluminium in zinc-base die-casting alloys

A procedure for the direct polarographic determination of aluminium is described, with particular reference to zinc-base die-casting alloys. Interfering elements are removed by electrolysis of a solution of the alloy in a mercury-cathode cell. The solution is polarographed at a carefully controlled pH in a supporting electrolyte of magnesium chloride and sodium sulfate of appropriate concentration. The precision and accuracy of the method are shown to be satisfactory by the analysis of standard samples from three different laboratories.     

Self-gravitating radiation in anti-de sitter space

Equilibrium configurations of self-gravitating massless thermal radiation inside spherical boxes of radiusR in asymptotically anti-de Sitter space (A = -3/b ₂) are constructed numerically for a range of central densities. For each box radius considered (R/b = 0, 1/2, 1, 2, 4, ), there is a unique configuration with maximal total mass and entropy, and another (at a lower central density) with maximum asymptotic red-shifted temperature. With the box removed toR=, the maximum total mass and entropy of self-gravitating thermal radiation areM _max 0.4598b0.7964(–A)^–1/2 andS _max1.3560a ^1/4 b ^3/2 3.0910a ^1/4(–A)^–3/4, and the maximum red-shifted temperature is