A trial‐and‐error method is described for facilitating the indexing of X‐ray powder patterns with the help of a computer. It is based on the variation of parameters by dichotomy, i.e. successive division of available phase space. The observational errors are rigorously treated. The program, written in Fortran IV, presupposes orthorhombic or higher symmetry. The principles used are illustrated with several X‐ray powder patterns.
The theoretical structural study of the hydroxynitrates xM(OH)2 .yM(NOa)2.zH20 (M = Ni, Zn) based on the only hypothesis that their structure proceeds from that of the related hydroxides M(OH)2, leads to two main structural types. These basic nitrates can be characterized by a stacking of sheet sequences of formula MX2+m with m=z/(x+y) and X=OH-, H20, NO~'. The first structural type occurs when m is a positive integer (hydrated salts) or zero (anhydrous salts). There is, therefore, for hydrated salts a deficiency of cations with respect to the sheets MX2 characteristic of hydroxides M(OH)2.Each sheet consists of (2+m) hexagonal close packed layers, and the cations M occupy some of the octahedral holes. The second structural type occurs when m is not an integer; this produces the formation of layers not close packed. Then, each sheet comprises two hexagonal close packed layers and two layers not close packed, the cations M occurring at both octahedral and tetrahedral holes. The characteristics of each structural type are described together with x, y and z values consistent with the proposed models. The conclusions of this study are in excellent agreement with known structures. The systematic classification proposed enables one to predict, a priori, the formulae and structures of hydroxynitrates which are structurally derived from M(OH)2.
As an integral part of the development of a new technique using organometallic markers for the detection of hormone receptors by FT-IR spectroscopy, a series of estradiol derivatives labeled with Cr(CO)3 or Cr(CO)2CS fragments on the A ring has been synthesized. The stereochemistry of one of these steroids, alpha-[3-(dimethyl-tert-butylsiloxy)-17 beta-estradiol]dicarbonyl(thiocarbonyl)chromium(0), has been established by X-ray diffraction. The organochromium-labeled steroids are stable in aqueous methanol solution, and their relative binding affinities to estrogen receptor have been determined; these values vary from 0.4 to 28%. The complex exhibiting the strongest affinity, [3-O-(3-hydroxypropyl)-17 beta-estradiol]-chromium tricarbonyl complex, has been prepared in a tritiated form with a high specific activity (4.1 Ci/mmol). This tritiated hormone binds reversibly to the estradiol receptor in lamb uterine cytosol with an affinity (Kd = 0.85 nM) and number of binding sites (n = 770 fmol/mg of protein) close to the values observed for estradiol itself. The level of nonspecific binding is low, and the hormone is not bound significantly to other nontarget tissues. The observation that the binding affinity of the steroid depends on which side of the steroidal A ring the organometallic label is bound demonstrates the nonequivalence of the two sides of the A ring with respect to the receptor site. The FT-IR spectra of the organochromium markers in the v(CO) region can be used for the detection of the estradiol receptor in lamb uterine cytosol.
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