Reaction of early transition metal complexes with macrocycles. II. Synthesis and structure of TiCl3(H2O) · 18-crown-6, a compound with a unique bidentate bonding mode for the 18-crown-6 molecule

18-crown-6 reacts with TiCl₃ in CH₂Cl₂ to form a complex in which the crown ether functions as a tridentate ligand. Addition of moist hexane affords a molecular complex in which the crown ether functions as a bidentate ligand. A water molecule is bonded directly to the titanium atom and is further hydrogen bonded to three of the oxygen atoms of the crown. The deep blue crystals of the CH₂Cl₂ adduct belong to the monoclinic space groupP2₁/n witha=13.481(8),b=8.021(5),c=21.425(9) Å, =97.32(5)°, and _calc = 1.51 g cm^–3 forZ=4. Refinement led to a conventionalR value of 0.040 based on 873 observed reflections. The Ti–O bond distances for the crown oxygen atoms are 2.123(8) and 2.154(9) Å, while the oxygen atom of the water molecule is bonded at 2.072(8) Å. The octahedral coordination sphere of the titanium atom is completed by the three chlorine atoms at distances of 2.340(5), 2.352(4), and 2.373(4) Å. Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82034 (10 pages).     

(PPh4)2[WO2Cl3]2 · 2 CH2Cl2: Synthese,Schwingungsspektrum und Kristallstruktur

(PPh₄)₂[WO₂Cl₃]₂ · 2 CH₂Cl₂. Synthesis, Vibrational Spectrum, and Crystal Structure Depending on the stoichiometry and the solvent, dichloromethane or 1.2-dichloroethane, WO₂Cl₂ reacts with tetraphenylphosphonium chloride affording (PPh₄)₂[WO₂Cl₄] or (PPh₄)₂[WO₂Cl₃]₂, respectively. Both compounds are easily soluble in dichloromethane, from which they can be crystallized under incorporation of two molecules CH₂Cl₂ per formula unit. The crystalline compounds have been characterized by their IR and Raman spectra. According to the X-ray crystal structure analysis, (PPh₄)₂[WO₂Cl₃]₂ · 2 CH₂Cl₂ crystallizes in the triclinic space group P1 with one formula unit per unit cell (986 independent observed reflexions, R = 0.061). Lattice constants: a = 1100.2, b = 1116.9, c = 1238.4 pm, = 69.40, = 80.46 and = 85.62°. The crystals consist of PPh₄^⊕ ions, centrosymmetric [WO₂Cl₃]₂^2? anions and CH₂Cl₂ molecules. In the anions, the tungsten atoms are linked via two oxo bridges with WO distances of 184 and 252 pm. The distorted octahedral coordination around each tungsten atom is completed by three terminal chloro and one terminal oxo ligand (WO bond length 166 pm), the latter being in trans position to the longer WO bridging bond. (PPh₄)₂[WO₂Cl₄] · 2 CH₂Cl₂ also forms triclinic crystals that are isotypic with (PPh₄)₂[WOCl₅] · 2 CH₂Cl₂ and in which the anions must have orientational disorder.     

Identification of HcgC as a SAM‐Dependent Pyridinol Methyltransferase in [Fe]‐Hydrogenase Cofactor Biosynthesis

Previous retrosynthetic and isotope‐labeling studies have indicated that biosynthesis of the iron guanylylpyridinol (FeGP) cofactor of [Fe]‐hydrogenase requires a methyltransferase. This hypothetical enzyme covalently attaches the methyl group at the 3‐position of the pyridinol ring. We describe the identification of HcgC, a gene product of the hcgA‐G cluster responsible for FeGP cofactor biosynthesis. It acts as an S‐adenosylmethionine (SAM)‐dependent methyltransferase, based on the crystal structures of HcgC and the HcgC/SAM and HcgC/S‐adenosylhomocysteine (SAH) complexes. The pyridinol substrate, 6‐carboxymethyl‐5‐methyl‐4‐hydroxy‐2‐pyridinol, was predicted based on properties of the conserved binding pocket and substrate docking simulations. For verification, the assumed substrate was synthesized and used in a kinetic assay. Mass spectrometry and NMR analysis revealed 6‐carboxymethyl‐3,5‐dimethyl‐4‐hydroxy‐2‐pyridinol as the reaction product, which confirmed the function of HcgC.     

A Hexameric Cationic Copper(II) Metallacrown as a Pertechnetate and Perrhenate Scavenger

Materials based on the cationic copper(II) hexanuclear 18‐membered metallacrown [18‐MC ‐6]⁶⁺ (2phH=2‐piconyl hydrazide) and tetrafluoroborate, perchlorate, nitrate, sulfate, and perrhenate anions were prepared by an easy method in aqueous medium. Single‐crystal X‐ray characterization of six members of this new family of complexes showed that the anions are attached to the metallacrown by direct coordination to a copper cation or by hydrogen‐bonding interaction with the center of the hexamer. The stable cationic nature of the complexes and their ability to bind different anions allows them to adsorb and immobilize environmentally relevant anions such as MO₄^? (M=Tc, Re). The MO₄^? trapping capacities suggest that these materials would be useful in the treatment of oxoanionic contaminants in water.     

Delivering Structural Information on the Polar Face of Membrane‐Active Peptides: 19F‐NMR Labels with a Cationic Side Chain

Conformationally constrained non‐racemizing trifluoromethyl‐substituted lysine isosteres [(E)‐ and (Z)‐TCBLys] with charged side chains are presented as a new type of ¹⁹F‐NMR labels for peptide studies. Design of the labels, their synthesis, incorporation into peptides and experimental demonstration of their application for solid state NMR studies of membrane‐active peptides are described. A series of fluorine‐labeled analogues of the helical amphipathic antimicrobial peptide PGLa(Nle) was obtained, in which different lysine residues in the original peptide sequence were replaced, one at a time, by either (E)‐ or (Z)‐TCBLys. Antimicrobial activities of the synthesized analogues were practically the same as those of the parent peptide. The structural and orientational parameters of the helical PGLa(Nle) peptide in model bilayers, as determined using the novel labels confirmed and refined the previously known structure. (E)‐ and (Z)‐TCBLys, as a set of cationic ¹⁹F‐NMR labels, were shown to deliver structural information about the charged face of amphipathic peptides by solid state ¹⁹F‐NMR, previously inaccessible by this method.     

Intra‐ and inter‐supramolecular complexation of poly(butyl methacrylate)‐co‐2‐(1,2,3‐triazol‐4‐yl)pyridine copolymers induced by CoII,FeII, and EuIII ions monitored by molecular hydrodynamics methods

Poly(butyl methacrylate) copolymers embedding bidentate 2‐(1,2,3‐triazol‐4‐yl)pyridine (trzpy) chelating units as comonomer in the side chains were synthesized by controlled radical addition‐fragmentation transfer (RAFT) polymerization. Intracomplexation and intercomplexation of the macromolecules of the poly(butyl methacrylate) copolymers containing 20 % mol of trzpy units induced by Co^II, Fe^II, and Eu^III ions were studied in the solutions by macromolecular hydrodynamics methods. The sedimentation velocity of extremely diluted copolymer solutions and the dynamic viscosity of moderately diluted solutions were studied in a wide range of the salts concentrations. Differences were observed with respect to the copolymer behavior in the presence of the Co²⁺, Fe²⁺, Eu³⁺ ions. These differences are namely due to the differences in the number of coordination bonds required for complex formation and not explicitly to the nature of the corresponding anions. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2632–2639