Intramolecular Chains Research Articles

Structure of trans-bis(2,3-butanedione dioximato-N,N')(imidazole-N3)methylcobalt(III), C12H21CoN6O4

M r = 372.28, monoclinic, P21/n, a = 8.075 (2), b= 13.969 (3), c= 14.892 (4) A, fl= 97.98 (2) ° , V=1664/k 3, Z=4, D x=l.48Mgm -3, Mo Kal, 2 = 0.70932 A, g = 1.05 mm -~, F(000) = 776, T = 295 K, final R(F) = 0-043 for 2765 significant reflections (I.et > 2a(Inet)). The two butanedione dioxi- mato units and the Co atom lie in a plane with the planar imidazole group perpendicular to the butanedione plane. The Co coordination is a slightly distorted octahedron. The structure has two O-H...O intramolecular hydrogen bonds and chains of hydrogen-bonded molecules are formed almost perpen- dicular to the bc plane. lntroduetlon. The title compound is a model compound for the more complex cobalamines like vitamin B~2 coenzyme. The structure has been determined as a further aid to understanding the action of the cobalamines. Experimental. Brown prismatic crystals from a 1:9 water--ethanol mixture. Crystal 0.3 x 0.2 × 0.15 mm, 0/20 scan with line profile analysis (Grant & Gabe, 1978), 20max = 60 °, Picker four-circle automatic dif- fractometer, graphite-monochr omated Mo Ka ra- diation, no absorption correction, data corrected for direct-beam polarization (Le Page, Gabe & Calvert, 1979) and Lorentz effects, unit-cell parameters from least-squares refinement of measured angle values for 37 reflections with 45 2a(I.et); 3 standard reflec- tions measured every 100 reflections showed no significant variation; structure solution by Patterson and heavy-atom techniques; full-matrix least-squares refinement on IF I, isotropic temperature factors, gave R(F) = 0.090, Rw(F)= 0.078; hydrogen positions, from AF synthesis and geometry, refined with isotropic temperature factors; anisotropic refinement for all

The fine structure of Purkinje fiber glycogen. A comparative study of negatively stained and cytochemically stained particles

The fine structure of Purkinje fiber glycogen isolated and negatively stained and PA-TSC-SP stained in sections was revealed by high resolution electron microscopy and analyzed with an optical diffractometer. Irrespective of the preparative procedure, the glycogen seemed to be composed of subunits of the same order of magnitude (diameter approximately 3 nm) which were arranged in a regular pattern. These observations are discussed in relation to the preparative techniques used and are compared with models of glycogen proposed on the basis of chemical data. A gap still seems to exist between the ultrastructural and chemical data. However, the fine structure revealed for Purkinje fiber glycogen treated in two different ways suggests that the glycogen molecules partly contain a regular arrangement of the intramolecular chains.