Rolf Norrestam

Three-dimensional structure of oligomycin B

The antibiotic oligomycin has been demonstrated by Lardy et al. [ 1] .to act as a potent inhibitor of oxidative phosphorylation. As the first specific inhibitor acting at the site of coupling between respiration and phosphorylation, oligomycin has become a most valuable tool for investigating the mechanism of this process, and has as such been widely used over the past years in studies with mitochondria [2], submitochondrial particles [3] and purified enzymes [4] . Its precise mode of action, however, has not yet been understood, and progress to this end has been seriously limited by the lack of knowledge of the structure of oligomycin. Preparations of oligomycin contain 3 molecular species, denoted A, B and C, which all inhibit oxidative phosphorylation with equal efficiencies [5] . By chemical studies of degradation products of purified oligomycin B, parts of its structure have been determined by Prouty et al, [6]. These studies have indicated that the molecule, with an observed chemical composition C4sHn 01*, consists of a large, 25or 26-membered, heterocyclic ring containing 3 double-bonds. The ring also contains keto, hydroxy and methyl substituents, and is linked to 2 saturated, hetero-atomic, 6-membered rings. The present paper reports the three-dimensional structure of oligomycin B, as determined from singlecrystal X-ray diffraction data.

5-Acetyl-3,7,8,10-tetramethyl-1,5-dihydroalloxazine: crystal structure and extended Hückel calculations for different molecular geometries

Structure determination and extended Huckel calculations have confirmed the angular form of the reduced state of flavin derivatives.

Percleveite-(Ce) — a new lanthanide disilicate mineral from Bastnäs, Skinnskatteberg, Sweden

Percleveite-(Ce), (Ce, La, Nd) 2 Si 2 O 7 , is a new mineral species from the Bastnas Fe-Cu-REE deposit, Skinnskatteberg, Vastmanland, Sweden. It occurs closely associated with mainly cerite-(Ce), bastnasite-(Ce) and quartz. The colour is greyish and the luster greasy to resinous. The anhedral crystals, up to 0.5 mm in size, are colourless in thin section and optically uniaxial (+). H ∼ 6. Cleavage is imperfect parallel to {001}. Electron-microprobe analyses give: La 2 O 3 14.66, Ce 2 O 3 31.36, Pr 2 O 3 3.41, Nd 2 O 3 12.97, Sm 2 O 3 2.69, Gd 2 O 3 2.26, Dy 2 O 3 0.53, Ho 2 O 3 0.07, Er 2 O 3 0.21, Yb 2 O 3 0.04, Y 2 O 3 2.93, CaO 0.10, FeO 0.01, SiO 2 26.55, sum 97.79, yielding the empirical formula (Ce 0.87 La 0.41 Nd 0.35 Y 0.12 Pr 0.09 Sm 0.07 Gd 0.06 Dy 0.01 Ca 0.01 ) Σ=1.99 Si 2.01 O 7 based on 7 O atoms. The mineral is shown to be isostructural with the synthetic, low-temperature lanthanide disilicates (general formula Ln 2 Si 2 O 7 ) with tetragonal symmetry (space group P 4 1 ). Unit-cell parameters are a = 6.7805(8) and c = 24.689(4) A (refined from powder data) with Z = 8. The structure has been refined from single crystal data to a weighted Rw value of 0.036. All four symmetry independent Ln positions are slightly differently occupied by the lanthanide ions. Percleveite is formed at conditions with slightly higher SiO 2 activities, and lower concentrations of Ca and Mg, than conditions favourable for the crystallization of cerite-(Ce).

A study of the hydrolysis-condensation pathways of a hetero bimetallic alkoxide, Ni2Sb4(OEt)16

The hydrolysis-condensation pathways of Ni-Sb-ethoxides in different toluene-ethanol solvents have been studied. The hydrolysis was performed by slow addition of controlled amounts of water, diluted in toluene-ethanol solvents. Characterization of the hydrolysis products was performed with single crystal X-ray determinations, IR-spectroscopy, UV-Vis spectroscopy and TGA. In this way, a number of different Ni-Sb-(oxo)-ethoxides have been isolated and characterized. It was thereby shown that the Ni∶Sb ratio of the hetero bimetallic oxoalkoxides varied much depending on the degree of hydrolysis and that the species formed vary with the solvent used and the speed at which the water is added.

Two transition-metal antimony ethoxides : M2Sb4(OEt)16;M = Ni or Mn

Two new metal alkoxides, nickel antimony ethoxide, Ni 2 Sb 4 (OEt) 16 , and manganese antimony ethoxide, Mn 2 Sb 4 (OEt) 16 , have been investigated by means of single-crystal X-ray diffraction. These two transition-metal ethoxides are isostructural with Mg 2 Sb 4 (OEt) 16 . The major structural differences between the three compounds result mainly from the different sizes of the nickel, manganese and magnesium ions. The fourfold coordination around the Sb atoms and the sixfold coordination around the other metal ions, as well as the conformations of the ethoxide groups, are similar in all three compounds.

Sr0.735Ba0.265Cu2(BO3)2 and Sr0.661Ca0.339Cu2(BO3)2

The crystal structures of Sr 0.735 Ba 0.265 Cu 2 (BO 3 ) 2 and Sr 0.661 Ca 0.339 Cu 2 (BO 3 ) 2 , which are isostructural with SrCu 2 (BO 3 ) 2 , have been refined from single-crystal X-ray diffraction data. The structures consist of slightly puckered layers with the composition [CuBO 3 ] − stacked along the c axes, with Sr, Ba or Ca atoms eight-coordinated between the layers. The interlayer separation is directly affected by the substitution of smaller Ca or larger Ba atoms in place of Sr. In both structures, each Cu atom is coordinated by four O atoms with Cu-O distances ranging from 1.91 to 1.94 A. The borate groups are distorted from D 3h to C 2v symmetry

STRUCTURAL STUDIES ON FLAVIN DERIVATIVES IN DIFFERENT STATES OF OXIDATION

Publisher Summary This chapter elaborates about structural studies on flavin derivatives in different states of oxidation. The object of the present X-ray diffraction studies has been to provide detailed structural information about flavins of biological interest. The structure investigations of the compounds confirm the planar diketo form of the oxidized neutral state of flavins as deduced on spectroscopic grounds. The primary aim of the determination of the structure of di-lumazine trihydrate, 2C6H4N4O2–3H2O, has been to examine the conformation and bonding system in a compound related to flavin derivatives but containing the pyrimidine and pyrazine rings. The structure was refined to an R-value of 4.6% and the molecule is planar within the standard deviations. The bond distances indicate that the π-electrons are delocalized in the pyrazine ring.