Demetallation of α,β,γ,δ-tetrakis(p-sulfophenyl) porphiniron(III) in mineral acid–alcohol–water media

Demetallation rates of α,β,γ,δ-tetrakis(p-sulfophenyl)porphiniron(III) in hydrochloric acid–ethanol–water, perchloric acid–ethanol–water, and sulfuric acid–alcohol–water media were determined. For a given acidity value H₀ the order of the rates for the three acids was HCl > H₂SO₄ > HClO₄. This is also the order for complex formation between acid anion and iron(III). Consequently ligands as well as protons are involved in the breaking of bonds between the metal and the porphyrin leading to the formation of the activated complex. The log k values for HCl and HClO₄ media were not linearly related to the Hammett acidity function as they were for sulfuric acid–ethanol–water media. The average ΔH? and ΔS?values for the HCl media were 18.4 ± 1.4 kcal/mol and ? 19 ± 3 cal K mol, respectively, in very close agreement with those for H₂SO₄ media despite the difference in H ₀ dependence. For H₂SO₄–alcohol–water media the order of the rates was butanol > propanol > ethanol with little difference between isomeric alcohols.     

Shear-induced β-form crystallization in isotactic polypropylene

Extruded, injection-molded, unoriented crystallized specimens and capillary rheometer efflux strands of commercially stabilized polypropylene without nucleating agents were examined by optical microscopy and x-ray diffraction to determine the conditions for β-form crystallization as a function of the distance from the surface and of the shear rate at commercial processing conditions. Results demonstrate that at all “cooling conditions” ΔT = T_m ? T_b (defined as the melt temperature T_m minus the bath temperature T_b) effects of strain flow initiate nucleation of β-form crystals. The shear rate is demonstrated to be important for β-form crystallization. A critical average threshold value for the shear rate of approximately 3 × 10² sec^?1 has to be exceeded. The β modification is mostly connected with type-III spherulites and partly to row structures, and it is observed at processing conditions in oriented structures only.     

Two phosphonodehydrotripeptides: Boc0–Gly1–Δ(Z)Phe2–α‐Abu3PO3Me2 and Boc0–Gly1–Δ(Z)Phe2–α‐Nva3PO3Et2

The present paper reports the crystal structures of two short phosphonotripeptides (one in two crystal forms) containing one ΔPhe (dehydrophenylalanine) residue, namely dimethyl (3‐{[tert‐butoxycarbonylglycyl‐α,β‐(Z)‐dehydrophenylalanyl]amino}propyl)phosphonate, Boc⁰–Gly¹–Δ(Z)Phe²–α‐Abu³PO₃Me₂, C₂₁H₃₂N₃O₇P, (I), and diethyl (4‐{[tert‐butoxycarbonylglycyl‐α,β‐(Z)‐dehydrophenylalanyl]amino}butyl)phosphonate, Boc⁰–Gly¹–Δ(Z)Phe²–α‐Nva³PO₃Et₂, as the propan‐2‐ol monosolvate 0.122‐hydrate, C₂₄H₃₈N₃O₇P·C₃H₈O·0.122H₂O, (II), and the ethanol monosolvate 0.076‐hydrate, C₂₄H₃₈N₃O₇P·C₂H₆O·0.076H₂O, (III). The crystals of (II) and (III) are isomorphous but differ in the type of solvent. The phosphono group is linked directly to the last C_α atom in the main chain for all three peptides. All the amino acids are trans linked in the main chains. The crystal structures exhibit no intramolecular hydrogen bonds and are stabilized by intermolecular hydrogen bonds only.     

Lipophilic Functionalized Cobyrinic-Acid Derivatives. Part 1. Cobester α-monoacids (α,α,α,β,β,β-hexamethyl α-hydrogen Coα, Coβ-dicyanocobyrinates)

The four α,α,α, β,β,β,-hexamethyl α-hydrogen Coα, Coβ-dicyanocobyrinates 2b, d–f , with a free b-, d-, e-, and f-propionic-acid function, respectively, were prepared by partial hydrolysis of heptamethyl Coα, Coβ-dicyanocobyrinate (cobester; 1 ) in aqueous sulfuric acid. The cobester monoacids 2b, d–f were obtained as a ca. 1:1:1:1 mixture which was separated. The monoacids were purified by chromatography and isolated in crystalline form. The position of the free propionic-acid function was determined by an extensive analysis of 2b, d–f using 2D-NMR techniques; an analysis of the C,H-coupling network topology resulted in an alternative assignment strategy for cobyrinic-acid derivatives, based on pattern recognition. Additional information on the structure of the most polar of the four hexamethyl cobyrinates, of the b-isomer 2b , was also obtained in the solid state from a single-crystal X-ray analysis. Earlier structural assignments based on 1D-NMR spectra of the corresponding regioisomeric monoamides 3b, d–f (obtained from crystalline samples of the monoacids 2b, d–f ) were confirmed by the present investigations.     

A new estra‐1,3,5(10)‐triene‐3,17β‐diol solvate: estradiol–methanol–water (3/2/1)

The title solvate of the steroid 17β‐estradiol (E₂) with methanol and water, C₁₈H₂₄O₂·0.67CH₄O·0.33H₂O, is the first E₂ derivative to contain three crystallographically independent mol­ecules in the asymmetric unit. The three steroid mol­ecules, along with two methanol mol­ecules and a water mol­ecule, create a three‐dimensional hydrogen‐bonded system. Three‐sided columns are formed, with the estradiol mol­ecules aligned lengthwise parallel to (101), and joined by solvent mol­ecules at both hydro­philic ends. The three estradiol mol­ecules differ slightly in their ring‐bowing angles, i.e. the angle between the mean plane of the A ring and that of the BCD ring; this angle ranges from 7.1 to 12.2°.     

Powder neutron diffraction of α-UB2C (α-UB2C-type)

The crystal structure of α-UB₂C (low temperature modification below T = 1675(25)°C) was determined from powder X-ray data (RT) and powder neutron diffraction data (at 29 K) employing the Rietveld-Young-Wiles profile analysis method. α-UB₂C crystallizes in the orthorhombic space group Pmma with a = 0.60338(3), B = 0.35177(2), C = 0.41067(2) nm, V = 0.0872 nm³, Z = 2. The residuals of the neutron refinement were R₁ = 0.032 and R_F = 0.043. The crystal structure of α-UB₂C is a new structure type where planar nonregular 6³-U-metal layers alternate with planar nonmetal layers of the type (B₆C₂)³. Boron atoms are in a typical triangular prismatic metal surrounding with a tetrakaidekahedral coordination B[U₆B₂C₁], whereas carbon atoms occupy the center points of rectangular bipyramids C[U₄B₂]. The crystal structure of α-UB₂C derives from the high temperature modification β-UB₂C (ThB₂C-type, ), which reveals a similar stacking of slightly puckered metal layers 6³, alternating with planar layers B₆ · (B₆C₃)². The phase transition from β-UB₂C to α-UB₂C is thus essentially generated by carbon diffusion within the B₆ · (B₆C₃)² layers to form (B₆C₂)³ layers.