Oligomeric phthalonitriles and tetrakis(phenylethynyl)benzene blends with improved processing and thermal properties

Blended resins were prepared from the resorcinol-based PEEK-like oligomeric phthalonitrile resin (RES) and tetrakis(phenylethynyl)benzene (TPEB), a high char yield arylacetylene resin. Initial probing of curing properties using differential scanning calorimetry, indicated that TPEB and RES co-cure when heated. Characterization of thermal properties using thermogravimetric analysis indicated that a 1:1 TPEB-RES blend (by weight) exhibited a char yield of 80% which was 6% larger compared to pure RES (74%). According to FTIR characterization, the enhanced thermal properties of TPEB-RES were the result of increased crosslinking density. Rheological studies of TPEB, RES, and TPEB-RES blends indicated that blended systems exhibit similar processing characteristics as RES resin. For example, resins display ideal viscosities and relatively large processing windows when cured at 175 °C. Alternatively, pure TPEB resin exhibits low viscosities when melted, which are not suitable for preparing composite materials. This study indicates that preparing TPEB-RES blends is an effect strategy for improving thermal performance of potential RES composites while still maintaining the required processability for fabrication of dense polymer composites. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2630–2640     

Rhodium(I) catalyst supported on polymer crystal surfaces: Further hydrogenation studies

Catalysts bound to polymers in the form of crosslinked beads have been demonstrated to have a number of advantages over homogeneous catalysts. However, there are several problems that exist due to the polymer support being in the form of a bead. The rate of reaction depends on the presence of solvents that adequately swell the bead in order to allow access to the catalytic sites. Differences in polarity and reactant size can inhibit diffusion into the bead. Recently a new system has been developed whereby tris(triphenyl phosphine) chlororhodium (I) (Wilkinson's catalyst) is bound to the surface of polyethylene single crystals. Polyethylene single crystals have a very high surface to volume ratio allowing for greater ease of reaction compared to a bead system. In a previous paper we showed that there is a dramatic increase in catalytic activity and that the reaction rate increased as the polarity of solvent was increased, even in ethanol where the homogeneous catalyst is not soluble and the polystyrene bead support would not swell. In this letter we are describing the activity of hydrogenation of olefins contained in both large and/or polar molecules. The results demonstrate the advantages of supported catalysts on polyethylene single crystals rather than on polymer beads.     

Electron paramagnetic resonance study of the reactions of tetrathiomolybdate with roussin salts and esters, and with some related iron nitrosyls

The tetrathiomolybdate ion [MoS₄]²⁻ reacts in DMF solution with Roussin esters Fe₂(SR)₂(NO)₄ (R = Me, Et, n-Pr, i-Pr, n-Bu,t-Bu, n-C₅H₁₁) to yield the paramagnetic iron nitrosyls [Fe(NO)₂(SR)₂]⁻ (1), [Fe(NO)₂(S₂MoS₂]⁻ (2) and [Fe(NO)(S₂MOS₂)₂]⁻ (3). The new complexes (2) and (3) have been characterized by EPR spectroscopy and the assignment to them of constitutions based respectively upon tetrahedral and square pyramidal iron is supported by EHMO calculations. Fe₂(SPh)₂(NO)₄ with [MoS₄]²⁻ yields only [Fe(NO)₂(SPh)₂]⁻, and preformed (3) reacts with PhS⁻ to give firstly EPR-silent species, and then [Fe(NO)₂(SPh)₂]⁻. The mononitrosyl (3) can also be formed by reaction of [MoS₄]²⁻ with [Fe₄S₃(NO)₇]⁻, Fe₄S₄(NO)₄, or Fe₂I₂(NO)₄.     

Regioselective Reduction of 1H-1,2,3-Triazole Diesters

Regioselective reactions can play pivotal roles in synthetic organic chemistry. The reduction of several 1-substituted 1,2,3-triazole 4,5-diesters by sodium borohydride has been found to be regioselective, with the C(5) ester groups being more reactive towards reduction than the C(4) ester groups. The amount of sodium borohydride and reaction time required for reduction varied greatly depending on the N(1)-substituent. The presence of a β-hydroxyl group on the N(1)-substituent was seen to have a rate enhancing effect on the reduction of the C(5) ester group. The regioselective reduction was attributed to the lower electron densities of the C(5) and the C(5) ester carbonyl carbon of the 1,2,3-triazole, which were further lowered in cases involving intramolecular hydrogen bonding.     

Rack-mounted chemistry IV: the thermal rearrangement of 7-oxabenzonorbornadienes into benzo[b]oxepines on and off the polycyclic rack

The thermal rearrangement of [3]polynorbornane bis-imide rack-mounted 7-oxabenzonorbornadienes has been conducted using flash vacuum pyrolysis (FVP) at 520 °C and is compared with the FVP of similar 7-oxabenzonorbornadienes off the rack. The isomerisation is considered to involve (a) C–O bond cleavage to a vinylogous 1,5-dipole, (b) formation of a benzene epoxide by nucleophilic ring-closure and (c) valence-isomerisation of the benzene epoxide to the oxepine. Competing fragmentation to the isobenzofuran by ejection of acetylene and other rearrangements become prominent pathways off the rack, whereas isomerisation to the oxepine is highly favored on the rack.     

The role of vanadium bromoperoxidase in the biosynthesis of halogenated marine natural products

Halogenated natural products are frequently reported metabolites in marine seaweeds. These compounds span a range from halogenated indoles, terpenes, acetogenins, phenols, etc., to volatile halogenated hydrocarbons that are produced on a very large scale. In many cases these halogenated marine metabolites possess biological activities of pharmacological interest. Given the abundance of halogenated marine natural products found in marine organisms and their potentially important biological activities, the biogenesis of these compounds has intrigued marine natural product chemists for decades. Over a quarter of a century ago, a possible role for haloperoxidase enzymes was first suggested in the biogenesis of certain halogenated marine natural products, although this was long before haloperoxidases were discovered in marine organisms. Since that time, FeHeme- and Vanadium-haloperoxidases (V-HPO) have been discovered in many marine organisms. The structure and catalytic activity of vanadium haloperoxidases is reviewed herein, including the importance of V-HPO-catalyzed bromination and cyclization of terpene substrates.     

Raman, FTIR, photoacoustic-infrared, and inelastic neutron scattering spectra of ternary metal hydride salts A2MH5, (A = Ca, Sr, Eu; M = Ir, Rh) and their deuterides

The vibrational spectra of the ternary metal hydride (deuteride) salts, A(2)MH(5) and A(2)MD(5), where A = calcium, strontium and europium and M = iridium(I) and rhodium(I), have been assigned using Raman, Fourier transform infrared, photoacoustic infrared, and inelastic neutron scattering spectroscopies and density functional theory (DFT) calculations. The wavenumbers of the infrared-active stretching vibrations depend upon the ionization energies of the central metal atom and the cation. The phase transition in calcium pentahydridoiridate(I) was studied as a function of temperature and pressure.     

Palladium on Carbon-Catalyzed Cross-Coupling of Aryl Halides with Potassium p-Tolyltrifluoroborate in Air

Palladium supported on carbon (Pd/C) has been shown to be an effective catalyst for the cross-coupling of potassium p-tolyltrifluoroborate with a variety of aryl bromides and iodides. Yields ranging from moderate to good were obtained using Pd/C in ethanol/water mixtures with potassium carbonate as base at 50 °C under an air atmosphere.     

The synthesis,structural characterization and biological evaluation of N‐(ferrocenylmethyl amino acid) fluorinated benzene‐carboxamide derivatives as potential anticancer agents

A series of N‐(ferrocenylmethyl amino acid) fluorinated benzene‐carboxamide derivatives 4b , 4c , 4d , 4e , 4f , 4g , 4h , 4i and 5b , 5c , 5d , 5e , 5f , 5g , 5h , 5i have been synthesized by coupling ferrocenylmethyl amine 3 with various substituted N‐(fluorobenzoyl) amino acid derivatives using the standard N‐(3‐dimethylaminopropyl)‐N′‐ethylcarbodiimide hydrochloride, 1‐hydroxybenzotriazole protocol. The amino acids employed in this study were glycine and L‐alanine. All of the compounds were fully characterized using a combination of ¹H NMR, ¹³C NMR, ¹⁹F NMR, distortionless enhancement by polarization transfer (DEPT)‐135, ¹H–¹H correlation spectroscopy (COSY) and ¹H–¹³C COSY (heteronuclear multiple‐quantum correlation) spectroscopy. The compounds were biologically evaluated on the oestrogen‐positive MCF‐7 breast cancer cell line. Compounds 4g , 4i , 5h and 5i exhibited cytotoxic effects on the MCF‐7 breast cancer cell line. N‐(Ferrocenylmethyl‐L‐alanine)‐3,4,5‐trifluorobenzene‐carboxamide ( 5h ) was the most active compound, with an IC₅₀ value of 2.84 μm . Compounds 4i , 5h and 5i had lower IC₅₀ values than that found for the clinically employed anticancer drug cisplatin (IC₅₀ = 16.3 μm against MCF‐7). Guanine oxidation studies confirmed that 5h was capable of generating oxidative damage via a reactive oxygen species‐mediated mechanism. Copyright © 2013 John Wiley & Sons, Ltd.     

Atomistic simulation of lipid and DiI dynamics in membrane bilayers under tension

Membrane tension modulates cellular processes by initiating changes in the dynamics of its molecular constituents. To quantify the precise relationship between tension, structural properties of the membrane, and the dynamics of lipids and a lipophilic reporter dye, we performed atomistic molecular dynamics (MD) simulations of DiI-labeled dipalmitoylphosphatidylcholine (DPPC) lipid bilayers under physiological lateral tensions ranging from -2.6 mN m(-1) to 15.9 mN m(-1). Simulations showed that the bilayer thickness decreased linearly with tension consistent with volume-incompressibility, and this thinning was facilitated by a significant increase in acyl chain interdigitation at the bilayer midplane and spreading of the acyl chains. Tension caused a significant drop in the bilayer's peak electrostatic potential, which correlated with the strong reordering of water and lipid dipoles. For the low tension regime, the DPPC lateral diffusion coefficient increased with increasing tension in accordance with free-area theory. For larger tensions, free area theory broke down due to tension-induced changes in molecular shape and friction. Simulated DiI rotational and lateral diffusion coefficients were lower than those of DPPC but increased with tension in a manner similar to DPPC. Direct correlation of membrane order and viscosity near the DiI chromophore, which was just under the DPPC headgroup, indicated that measured DiI fluorescence lifetime, which is reported to decrease with decreasing lipid order, is likely to be a good reporter of tension-induced decreases in lipid headgroup viscosity. Together, these results offer new molecular-level insights into membrane tension-related mechanotransduction and into the utility of DiI in characterizing tension-induced changes in lipid packing.