Ethane Units Research Articles

Crystal structure of the coordination polymer catena-poly[[bis-[hy-droxy(phen-yl)acetato-κ2 O 1,O 2]zinc(II)]-μ2-1,2-bis-(pyridin-4-yl)ethane-κ2 N:N'

In the title polymeric ZnII compound, [Zn(C8H7O3)2(C12H12N2)] n , the Zn cation is coordinated by two N atoms from 1,2-bis-(pyridin-4-yl)ethane unit and four O atoms from two mandelate [or hy-droxy(phen-yl)acetate] anions in a slightly distorted octa-hedral coordination geometry. The 1,2-bis-(pyridin-4-yl)ethane unit bridges two ZnII cations, related by an inversion centre, to form a polymeric chain along [110]. The crystal structure features extensive O-H⋯O and weak C-H ⋯O hydrogen bonds, with C-H ⋯ π inter-actions and π-π inter-actions also being present. The centroid-centroid distance between the phenyl ring of the mandelate group and the 1,2-bis-(pyridine-4-yl)ethane moiety is 4.951 (2) Å. The 1,2-bis-(pyridin-4-yl)ethane ligand is disordered over two positions, with a refined occupancy of 0.578 (14) for the major component.

Pyridine-Directed Asymmetric Hydrogenation of 1,1-Diarylalkenes.

Highly enantioselective pyridine-directed rhodium-catalyzed asymmetric hydrogenation of challenging 1,1-diarylalkenes is achieved by using [Rh(NBD)DuanPhos]BF4 as a precatalyst. Various types of 2-pyridine substituted 1,1-diarylalkenes could be hydrogenated with good to excellent enantioselectivities, which provide an efficient route to the synthesis of pharmaceutically and biologically active compounds containing a 2-pyridyl ethane unit.

A non-canonical peptide synthetase adenylates 3-methyl-2-oxovaleric acid for auriculamide biosynthesis.

Auriculamide is the first natural product known from the predatory bacterium Herpetosiphon aurantiacus. It is composed of three unusual building blocks, including the non-proteinogenic amino acid 3-chloro-L-tyrosine, the α-hydroxy acid L-isoleucic acid, and a methylmalonyl-CoA-derived ethane unit. A candidate genetic locus for auriculamide biosynthesis was identified and encodes four enzymes. Among them, the non-canonical 199 kDa four-domain nonribosomal peptide synthetase, AulA, is extraordinary in that it features two consecutive adenylation domains. Here, we describe the functional characterization of the recombinantly produced AulA. The observed activation of 3-methyl-2-oxovaleric acid by the enzyme supports the hypothesis that it participates in the biosynthesis of auriculamide. An artificially truncated version of AulA that lacks the first adenylation domain activated this substrate like the full-length enzyme which shows that the first adenylation domain is dispensable. Additionally, we provide evidence that the enzyme tolerates structural variation of the substrate. α-Carbon substituents significantly affected the substrate turnover. While all tested aliphatic α-keto acids were accepted by the enzyme and minor differences in chain size and branches did not interfere with the enzymatic activity, molecules with methylene α-carbons led to low turnover. Such enzymatic plasticity is an important attribute to help in the perpetual search for novel molecules and to access a greater structural diversity by mutasynthesis.

Rotaxanes and pseudorotaxanes with threads containing pyridinium units

In this review, a continuation of an earlier one concerning rotaxanes with threads containing viologen units, the syntheses and properties of rotaxanes with threads bearing quaternary pyridinium units are described, along with their possible applications. In the first part rotaxanes containing bis(dipyridiniumyl)ethane unit in the thread are presented; they include species with stoppers incorporating metal complexes. The second part concerns rotaxanes formed by anion templation, they are divided into those involving the Grubbs RCM procedure for construction of a ring, and those employing rings built by condensation reactions. Then rotaxanes synthesized with the use of previously prepared rings are described. The third part deals with rotaxane molecular machines, especially those bearing mannosyl moieties. In the last part pseudorotaxanes containing crown ether based cryptands as rings, are shown.

1,2-Bis[2-(2-nitro-1H-imidazol-1-yl)ethoxy]ethane

In the crystal structure, the title compound, C12H16N6O6, lies on an inversion centre. The mol­ecule has an anti­periplanar conformation with respect to the C—C bond of the central ethane unit and the two imidazole rings are parallel to each other. The dihedral angle between the imidazole ring and the mean plane of the C and O atoms of the bis­(eth­oxy)ethane group is 76.04 (6)°. The mol­ecules are stacked along the c axis through a weak C—H⋯O inter­action and a π⋯π inter­action between the imidazole rings with a centroid–centroid distance of 3.5162 (6) Å. An intramolecular C—H⋯O hydrogen bond is also present.

Towards a new type of step growth polymerization: Synthesis of dehydro-oligomers of 2,6- and 2,7-dimethylanthraquinone

Treatment of 2,6-dimethylanthraquinone and/or 2,7-dimethylanthraquinone with strong base affords, in good yields, oligomers consisting of anthraquinone units linked by ethylene or ethane units. These are formed by a new type of step growth oligomerization that can be summarized conveniently as the linking together of diradical–dianions, followed by air oxidation of the products.

Properties of modified cyclo-olefin copolymers predicted by ab initio and molecular simulation techniques

Mechanical, thermal and optical properties of modified cyclo-olefin copolymers COC were studied by molecular dynamics simulations and ab initio calculations. The COC chains were modified by substituting the norbornane rings with methyl groups and replacing ethane units with propane. A modified Dreiding 2.21 force field was developed for the molecular dynamics simulations. The bulk and Young’s moduli increased when the norbornane rings of COC were substituted with methyl groups and when the ethane units were replaced with propane. The highest glass transition temperature was obtained when the norbornane rings were substituted with methyl groups. Ab initio calculations of isotropic polarizability and refractive index were sensitive to the applied basis set and level of theory. Good agreement with available experimental data was obtained with the B3LYP/6-311G** method. Replacement of ethane units with propane lowered the refractive index significantly, whereas other structural modifications had practically no effect.

Characterization of the water-insoluble fraction from fast pyrolysis liquids (pyrolytic lignin): Part II. GPC, carbonyl goups, and 13C-NMR

Fast pyrolysis has become an interesting technology for the conversion of solid biomass into a liquid (bio-oil) that can easily be stored and transported. The structural features of pyrolytic lignin is of paramount interest in order to explain reaction mechanisms during pyrolysis and aging processes. In addition, a well-characterized pyrolytic lignin can be of interest for commercial applications such as adhesives in wood based panel industry. This paper describes methods to elucidate the structural configuration of pyrolytic lignin. Using gel permeation chromatography (GPC) the average molecular weight of pyrolytic lignin was determined to be between 650 and 1300 g mol −1. Ratios of hydroxyphenyl-, guaiacyl-, and syringyl- units (H, G, S-units) were obtained from pyrolysis gas chromatography-mass spectrometry (Pyroprobe-GC/MS) and were compared with milled wood lignin (MWL) data. Carbonyl groups were determined by oximation. Based on analytical data, a C 8-formula was established assuming a principal structure of phenyl ethane units. Combined with GPC results an average DP between 4 and 9 was calculated. Evaluation of 13C-NMR spectra shows some small signals indicating residual lignin moiëties with ether structures. However, most of the ether bonds in the native lignin were split. As a consequence pyrolytic lignin seems to consist of oligomeric alkylated aromatic units linked by newly formed bonds, probably CC bonds.

1,2-Diaminoethane-containing epoxy resins for separation of aldehydes

Epoxy-amine resin obtained by inverse suspension polycondensation of epichlorohydrin with ethylenediamine has been demonstrated to be very useful for selective separation of aldehydes from the mixtures. 1,2-Diamino ethane units in the crosslinked structure can be regard as polymeric analog of Wanzlick reagent (1,2-dianilo ethane) which readily condenses with aldehydes to form five-membered cyclic structures, imidazolines. In the presence of mineral acids the imidazoline ring decomposes into its components. This reverse reaction serves a means of regenerability of the aldehyde loaded polymer. The method described in the present study is especially suitable for extraction and recovery of aromatic aldehydes from organic mixtures, even in small quantities. The method works also for aliphatic aldehydes. However, in that case, aldol condensation products form in the solution and the insoluble polymer sorbs these by-products together with the aldehyde itself. Aldehyde sorptions are rapid in water-miscible solvents such as dioxane and methanol. Whereas in cyclohexane aldehyde sorption is very slow, due to hydrophilicity of the polymer.

Phase Transfer Catalysis in Polycondensation Processes: XVIII. Thermal properties and molecular simulation of some polyethers containing oxetane rings in the main chain

A study was made of the influence of the chemical structure of the chains on the thermal stability of a series of copolyethers obtained from 3,3-bis(chloromethyl)oxetane and various bisphenols: 4,4'-dihydroxyazobenzene, 4,4'-dihydroxydiphenyl, 4,4'-thiodiphenol, 1,1-bis(4-hydroxy-phenyl)ethane and 4,4'-dihydroxydiphenylsulfone. For a better correlation between chemical structure and thermal stability, molecular simulations were performed, using the HYPERCHEM (version 4.5) program. The lowest thermal stability was exhibited by the polymers that contain azobenzene units. The best thermal stability was that of the polyethers containing thiodiphenyl and 1,1-bis(phenyl)ethane units.

Stereoisomerism of 4a,4b-dihydrophenanthrenes

We reported previously that sterically hindered photochromic 4a,4b-dihydrophenanthrenes can exist in two modifications. These labile intermediates are designated as L (long) or S (short) according to the position of their visible absorption band. W e presently suggest that these are two conformers ap (L) and ac (S) of the central C(4a)-C(4b) ethane unit. ap is the more planar while ac is decidedly distorted. Spectral characteristics—the position and intensity of the visible absorption band-provide the basis for the conformation assignment. The relative stabilities of L and S depend on the type and magnitude of the steric interaction X(4)-X(5) vs. X(4)-H(4b) /X(5)-H(4a)

Synthesis and characterization of liquid crystalline polyacrylates and polymethacrylates containing benzyl ether and diphenyl ethane based mesogens

AbstractThe synthesis and radical polymerization of a novel series of acrylates and methacrylates containing p‐cyanophenyl‐p‐hydroxybenzyl ether, p‐methoxyphenyl‐p‐hydroxybenzyl ether, and 1‐(p‐cyanophenyl)‐2‐(p‐hydroxyphenyl) ethane groups attached to the polymerizable group through aliphatic spacers containing 11 and 6 methylenic units is described. The resulting polymers were characterized by differential scanning calorimetry and optical polarization microscopy. All polymers exhibited enantiotropic mesomorphism. Low molar mass compounds based on benzyl ether or diphenyl ethane units exhibit only monotropic or virtual transitions. This demonstrates that the “polymer effect” stabilizes mesophases obtained from “mesogenic units” which do not contain rigid interconnecting groups.