Biphasic Aqueous Organometallic Catalysis Promoted by Cyclodextrins: How to Design the Water‐Soluble Phenylphosphane to Avoid Interaction with Cyclodextrin

The ability of cyclodextrin to interact with meta‐trisulfonated triphenylphosphane derivatives bearing one or two methyl (or methoxy) groups on the aromatic ring has been investigated by NMR and UV‐vis spectroscopy. In the case of native β‐cyclodextrin (β‐CD), the presence of one methyl or methoxy group in the ortho‐position on each aromatic ring is necessary to hamper the formation of an inclusion complex between the β‐CD and meta‐trisulfonated triphenylphosphane derivatives. In the case of methylated β‐CD, the formation of an inclusion complex is only observed when the meta‐trisulfonated triphenylphosphane contains a methyl group in the para‐position. The poor affinity of methylated β‐CD towards modified trisulfonated triphenylphosphanes was attributed to the steric hindrance generated by the methyl groups on the CD secondary face. The absence or presence of an interaction between phosphanes and methylated β‐CD was also confirmed by catalytic experiments. Thus, the phosphanes that do not interact with the methylated CD were the most efficient mass‐transfer promoters in an aqueous biphasic palladium‐catalyzed Tsuji–Trost reaction.     

Effect of a natural magnesium silicate treated with a new coupling agent on the properties of ethylene–propylene–diene rubber compounds

The behavior of sepiolite (magnesium silicate with a microfibrillar morphology) as a filler in ethylene–propylene–diene compounds was studied. A new coupling agent, meta‐isopropenyl dimethyl benzyl isocyanate, was used. The effect of the filler modified by meta‐isopropenyl dimethyl benzyl isocyanate on the physical properties was improved with respect to other fillers and commercial silane coupling agents under the same conditions. In addition to a smoother surface, the flow behavior of compounds filled with sepiolite, on account of its fibrous morphology, was better than that obtained with other fillers. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1489–1493, 2004     

Isomeric Detergent Comparison for Membrane Protein Stability: Importance of Inter‐Alkyl‐Chain Distance and Alkyl Chain Length

Membrane proteins encapsulated by detergent micelles are widely used for structural study. Because of their amphipathic property, detergents have the ability to maintain protein solubility and stability in an aqueous medium. However, conventional detergents have serious limitations in their scope and utility, particularly for eukaryotic membrane proteins and membrane protein complexes. Thus, a number of new agents have been devised; some have made significant contributions to membrane protein structural studies. However, few detergent design principles are available. In this study, we prepared meta and ortho isomers of the previously reported para‐substituted xylene‐linked maltoside amphiphiles (XMAs), along with alkyl chain‐length variation. The isomeric XMAs were assessed with three membrane proteins, and the meta isomer with a C₁₂ alkyl chain was most effective at maintaining solubility/stability of the membrane proteins. We propose that interplay between the hydrophile–lipophile balance (HLB) and alkyl chain length is of central importance for high detergent efficacy. In addition, differences in inter‐alkyl‐chain distance between the isomers influence the ability of the detergents to stabilise membrane proteins.     

Carborane‐Derived Local Anesthetics are Isomer Dependent

Clinically there is a need for local anesthetics with a greater specificity of action on target cells and longer duration. We have synthesized a series of local anesthetic derivatives we call boronicaines in which the aromatic phenyl ring of lidocaine was replaced with ortho‐, meta‐, C,C’‐dimethyl meta‐ and para‐carborane clusters. The boronicaine derivatives were tested for their analgesic activity and compared with lidocaine using standard procedures in mice following a plantar injection. The compounds differed in their analgesic activity in the following order: ortho‐carborane = C,C’‐dimethyl meta‐carborane > para‐carborane > lidocaine > meta‐carborane derivative. Both ortho‐boronicaine and C,C’‐dimethyl meta‐boronicaine had longer durations of analgesia than lidocaine. Differences in analgesic efficacies are rationalized by variations in chemical structure and protein binding characteristics.     

Photophysical properties of fluorene‐based copolymers synthesized by connecting twisted biphenyl units with fluorene via para‐ and meta‐linkages

BACKGROUND: Wide bandgap semiconducting polymers are of great interest in the development of organic and polymeric emissive materials for display purposes since they can be used to generate light of all colors either by irradiation of luminescent dyes or by energy transfer to emissive dopants. The aim of the present work is to construct new fluorene‐based semiconducting polymers with a wide bandgap. RESULTS: A novel polyfluorene derivative, poly[(9,9‐dihexyl‐2,7‐fluorene)‐alt‐(5,7‐dihydrodibenz[c,e]oxepin)], with a wide bandgap, was synthesized by connecting rigidly twisted biphenyl monomers with dihexylfluorene via para‐linkages and it was compared with poly[(9,9‐dihexyl‐2,7‐fluorene)‐alt‐(spirocyclohexane‐1,6′‐dibenzo[d,f][1,3]dioxepin)], which has meta‐linkages. Both polymers emit in the ultraviolet and blue regions. Electronic spectral absorption data and electrochemical measurements demonstrate that ca 40° torsion angle of the biphenyl units induces an increase in the HOMO–LUMO gap of 0.18 eV, and that meta‐linkage of the twisted segment in the polymer induces another increase of 0.24 eV compared to polydihexylfluorene. CONCLUSION: The new twisted biphenyl compounds are efficient segments to tune the bandgaps of conjugated polymers. The two fluorene‐based copolymers have wide bandgaps and exhibit potential as host materials. Copyright © 2008 Society of Chemical Industry     

Polyimides containing 4,4′‐bipyridinium units

New polyimides containing 4,4′‐bipyridinium units were synthesized by the reaction of bis(dichloromaleimide)arylene derivatives with 4,4′‐bipyridine in meta‐cresol. IR and ¹H‐NMR spectroscopy and elemental analysis as well confirmed their structures. The polymers were characterized by viscometric measurements, softening points, and thermogravimetric data. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 2091–2100, 2004     

Benzene‐di‐N‐substituted carbamates as conformationally constrained analogs of Pseudomonas lipase substrates

Benzene‐1,2‐, ‐1,3‐, and ‐1,4‐di‐N‐substituted carbamates ( 1 – 15 ) are synthesized as the constrained analogs of gauche, eclipsed, and anti conformations of diesters of ethylene glycol, respectively. Carbamates 1 – 15 are characterized as the pseudo‐substrate inhibitors of Pseudomonas species lipase. Long‐chain carbamates are more potent inhibitors than short‐chain ones. Different geometries of benzene‐di‐substituted carbamates, such as benzene‐1,2‐di‐N‐octylcarbamate ( 3 ) (ortho compound), benzene‐1,3‐di‐N‐octylcarbamate ( 8 ) (meta compound), and benzene‐1,4‐di‐N‐octylcarbamate ( 13 ) (para compound), show similar inhibitory potencies for the enzyme. In other words, kinetic data suggest that the enzyme does not discriminate ortho, meta, and para geometries of these constrained analogs.     

Effect of methyl position on the dynamic mechanical and shape‐memory properties of cresol‐based polybenzoxazines

Three difunctional benzoxazines were synthesized from cresol isomers (o‐, m‐, and p‐methylphenols), 1,3‐bis(3‐aminopropyl)‐1,1,3,3‐tetramethyldisiloxane, and formaldehyde. The ring‐opening polymerization temperature decreases in the order of ortho‐, para‐, and meta‐positions of methyl group for the benzoxazine monomers, whereas the glass transition temperature increases in the order of ortho‐, para‐, and meta‐positions of methyl group for the resultant polybenzoxazines. In addition, the polybenzoxazines exhibit one‐way dual‐shape‐memory behavior in response to changes in temperature, and the shape‐memory effects are evaluated by tensile and bending tests with a temperature program based on glass transition temperature. The o‐ and p‐cresol‐based polybenzoxazines exhibit higher shape‐memory performance than their m‐cresol‐based analogue/counterpart. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45443.     

2‐Carbaborane‐3‐phenyl‐1H‐indoles—Synthesis via McMurry Reaction and Cyclooxygenase (COX) Inhibition Activity

Cyclooxygenase‐2 (COX‐2) inhibitors have been the focus of medicinal chemistry efforts for years, and many compounds that exhibit high selectivity and affinity have been developed. As carbaboranes represent interesting pharmacophores as phenyl mimetics in drug development, this paper presents the synthesis of carbaboranyl derivatives of COX‐2‐selective 2,3‐disubstituted indoles. Despite the lability of carbaboranes under reducing conditions, 2‐carbaborane‐3‐phenyl‐1H‐indoles could be synthesized by McMurry cyclization of the corresponding amides. Whereas the meta‐carbaboranyl‐substituted derivatives lacked COX inhibitory activity, an ortho‐carbaboranyl analogue was active, but showed a selectivity shift toward COX‐1.     

Kinetic Resolution of 1‐Biaryl‐ and 1‐(Pyridylphenyl)alkan‐1‐ols Catalysed by the Lipase B from Candida antarctica

Lipase B from Candida antarctica (CAL‐B) catalyses the highly enantioselective (E>200) transesterification of some 1‐biaryl‐2‐yl‐, ‐3‐yl‐, and ‐4‐ylethanols and ‐propan‐1‐ols, as well as 1‐(o‐, m‐, and p‐pyridylphenyl)ethanols, 6 , with vinyl acetate, Kazlauskas' rule being obeyed in all cases. meta and para‐Substituted substrates were transformed within several hours (conversion degree ranging from 23–50%), reaction rates for propan‐1‐ol derivatives being slower than those for ethanol derivatives. Transesterifications of ortho‐substituted alcohols took several days and were accompanied by a chemoenzymatic side reaction: the formation of another acetate derived from the hemiacetal between 6 and acetaldehyde coming from vinyl acetate. This side reaction was suppressed in the presence of isopropenyl acetate as acyl donor, conversion degrees for transesterification ranging from 20–40% after ten days (E>200). The usefulness of (R)‐ 6p as ligand in the asymmetric addition of diethylzinc to benzaldehyde was also demonstrated.     

Synthesis and properties of poly(amide–imide)s based on N,N′‐bis(4‐carboxyphenyl)‐4,4′‐oxydiphthalimide,p‐aminobenzoic acid and various aromatic diamines

A new diimide–diacid monomer, N,N′‐bis(4‐carboxyphenyl)‐4,4′‐oxydiphthalimide (I), was prepared by azeotropic condensation of 4,4′‐oxydiphthalic anhydride (ODPA) and p‐aminobenzoic acid (p‐ABA) at a 1:2 molar ratio in a polar solvent mixed with toluene. A series of poly(amide–imide)s (PAI, III_a–m) was synthesized from the diimide–diacid I (or I′, diacid chloride of I) and various aromatic diamines by direct polycondensation (or low temperature polycondensation) using triphenyl phosphite and pyridine as condensing agents. It was found that only III_k–m having a meta‐structure at two terminals of the diamine could afford good quality, creasable films by solution‐casting; other PAIs III using diamine with para‐linkage at terminals were insoluble and crystalline; though III_g–i contained the soluble group of the diamine moieties, their solvent‐cast films were brittle. In order to improve their to solubility and film quality, copoly(amide–imide)s (Co‐PAIs) based on I and mixtures of p‐ABA and aromatic diamines were synthesized. When on equimolar of p‐ABA (m = 1) was mixed, most of Co‐PAIs IV had improved solubility and high inherent viscosities in the range 0.9–1.5 dl g^?1; however, their films were still brittle. With m = 3, series V was obtained, and all members exhibited high toughness. The solubility, film‐forming ability, crystallinity, and thermal properties of the resultant poly(amide–imide)s were investigated. © 2002 Society of Chemical Industry     

Effect of steric constraints on the physico‐electrochemical properties of sulfonated polyaromatic copolymers

The impact of incorporating additional steric restrictions into highly sterically encumbered sulfonated polyaromatic polymers was investigated. Copolymers possessing between 0 and 10% nonlinear ortho or meta biphenyl units in an otherwise linear para biphenyl‐containing sulfo‐phenylated poly(phenylene) were synthesized in yields >80% and evaluated on the basis of their physical and electrochemical properties. When incorporated into sulfonated copolymers in ≤5 mol%, ortho and meta linked biphenyl moieties reduced membrane swelling in water by up to 23 and 19 vol%, respectively, compared to strictly para biphenyl‐linked copolymers. Despite this, copolymers possessing nonlinear, biphenyl‐linked monomers displayed a decrease in proton conductivity and mechanical strength. This study reinforces the importance of considering restricted rotation, backbone flexibility, and chain entanglement in the design of polymers aimed at improving their physical and electrochemical properties. © 2020 Society of Industrial Chemistry     

Influence of Cleavage Site on Global Folding of an RNA‐Cleaving DNAzyme

8–17 is a DNAzyme with metal‐dependent endoribonuclease activity. Recently, a variant termed 8–17NG was reported as the first nucleic acid enzyme capable of cleaving all 16 dinucleotide junctions of RNA with rate enhancements ranging from 1000‐ to 1 000 000 000‐fold over background activity. We attributed this broad‐ranging cleavage efficiency to global folding of the DNAzyme. We sought to examine the influence of dinucleotides at the cleavage site of 8–17NG on global folding by using three‐color (3c) FRET. By comparing the folding of 8–17NG with all 16 possible dinucleotide junctions, we found all examined DNAzyme–substrate constructs adopted a two‐step folding process in the presence of Mn²⁺, which was consistent with previous metal‐induced folding studies of 8–17. Interestingly, Mn²⁺ titration experiments also suggest that the second folding step is dependent on dinucleotide identity: purine–purine junctions allowed 8–17NG to fold at lower concentrations than pyrimidine–pyrimidine linkages. This finding was corroborated by RNA cleavage assays, in which the largest improvement in cleavage yield was observed in pyrimidine–pyrimidine junctions when [Mn²⁺] was increased. Taken together, these results support the previously observed hierarchy of 8–17 activity for different cleavage sites. Complemented by earlier sequence and structure–function studies, this investigation allowed for the first detailed examination of crucial relationships between the structural influence and junction preferences of nucleic acid‐catalyzed RNA cleavage reactions.     

Reactivity of Electrogenerated N‐Heterocyclic Carbenes in Room‐Temperature Ionic Liquids. Cyclization to 2‐Azetidinone Ring via C‐3/C‐4 Bond Formation

The intrinsic chemistry of imidazolium‐based room‐temperature ionic liquids, related to the acidity of the C‐2 imidazolium cation, can be modified via cathodic cleavage of the C‐2/hydrogen bond. N‐Heterocyclic carbenes, electrogenerated by electrolysis of imidazolium‐based room‐temperature ionic liquids, are stable bases that are strong enough to deprotonate bromoamides 1a–k yielding the azetidin‐2‐one ring via C‐3/C 4 bond formation. The electrosynthesis of β‐lactams 2a–k has been achieved under mild conditions, elevated yields and avoiding the use of toxic, volatile, molecular solvents.     

C?C Hydrolases for Biocatalysis

Although C C bond hydrolases are distributed widely in Nature, they has as yet have received only limited attention in the area of biocatalysis compared to their counterpart the C‐heteroatom hydrolases, such as lipases and proteases. However, the substrate range of C C hydrolases, and their non‐dependence on cofactors, suggest that these enzymes may have considerable potential for applications in synthesis. In addition, hydrolases such as the β‐diketone hydrolase from Rhodococcus (OCH) are known, that catalyse the formation of interesting chiral intermediates. Further enzymes, such as kynureninase and a meta‐cleavage product hydrolase (MhpC), are able to catalyse carbon‐carbon bond formation, suggesting wider applications in biocatalysis than previously envisaged. In this review, the distribution, catalytic characteristics and applications of C C hydrolases are described, with a view to assessing their potentialfor use in biocatalytic processes in the future.     

High Polymer Content 3,5‐Pyridine‐Polybenzimidazole Copolymer Membranes with Improved Compressive Properties

Three series of polybenzimidazole (PBI) copolymers (3,5‐pyridine‐r‐2OH‐PBI, 3,5‐pyridine‐r‐para‐PBI, and 3,5‐pyridine‐r‐meta‐PBI) were polymerized and cast into membranes by the polyphosphoric acid (PPA) process. Monomer pairs with high and low solubility characteristics were used to define phase stability‐processing windows for preparing membranes with high temperature membrane gel stability. Creep compliance of these membranes (measured in compression at 180 °C) generally decreased with increasing polymer content. Membrane proton conductivities decreased linearly with increasing membrane polymer content. Fuel cell performances of some high‐solids 3,5‐pyridine‐based copolymer membranes (up to 0.66 V at 0.2 A cm^–2 following break‐in) were comparable to para‐PBI (0.68 V at 0.2 A cm^–2) despite lower phosphoric acid (PA) loadings in the high solids membranes. Long‐term steady‐state fuel cell studies showed 3,5‐pyridine‐r‐para‐PBI copolymers maintained a consistent fuel cell voltage of >0.6 V at 0.2 A cm^–2 for over 2,300 h. Phosphoric acid that was continuously collected from the long‐term study demonstrated that acid loss is not a significant mode of degradation for these membranes. The PBI copolymer membranes' reduced high‐temperature creep and long‐term operational stability suggests that they are excellent candidates for use in extended lifetime electrochemical applications.     

3‐Heterocycle‐Phenyl N‐Alkylcarbamates as FAAH Inhibitors: Design,Synthesis and 3D‐QSAR Studies

Carbamates are a well‐established class of fatty acid amide hydrolase (FAAH) inhibitors. Here we describe the synthesis of meta‐substituted phenolic N‐alkyl/aryl carbamates and their in vitro FAAH inhibitory activities. The most potent compound, 3‐(oxazol‐2yl)phenyl cyclohexylcarbamate ( 2 a ), inhibited FAAH with a sub‐nanomolar IC₅₀ value (IC₅₀=0.74 nM ). Additionally, we developed and validated three‐dimensional quantitative structure–activity relationships (QSAR) models of FAAH inhibition combining the newly disclosed carbamates with our previously published inhibitors to give a total set of 99 compounds. Prior to 3D‐QSAR modeling, the degree of correlation between FAAH inhibition and in silico reactivity was also established. Both 3D‐QSAR methods used, CoMSIA and GRID/GOLPE, produced statistically significant models with coefficient of correlation for external prediction (R²_PRED) values of 0.732 and 0.760, respectively. These models could be of high value in further FAAH inhibitor design.     

Construction of Efficient Solid Emitters with Tetraphenylethene Trimers for Non-doped Blue OLEDs

Three TPE trimers with meta or para linkage modes have been successfully synthesized. When fabricated as emissive layers in non-doped OLEDs, they all exhibit blue or deep-blue emissions with maximum current efficiency up to 4.03 cd A⁻¹, further verifying the facile but ingenious approach by utilizing meta-linkage mode in longer conjugated systems.     

Gas‐sorption properties of 6FDA–durene/1,4‐phenylenediamine (pPDA) and 6FDA–durene/1,3‐phenylenediamine (mPDA) copolyimides

We investigated the sorption isotherms of O₂, N₂, CH₄, and CO₂ gases in 6FDA–durene, 6FDA–1,4‐phenylenediamine (6FDA–pPDA), and 6FDA–1,3‐phenylenediamine (6FDA–mPDA) homopolymers and 6FDA–durene/pPDA and 6FDA–durene/mPDA copolyimides. The solubilities decrease in the order of the inherent condensabilities of the penetrant gases, namely, CO₂, CH₄, O₂, and N₂. The chemical structures of the polymer, as well as the chain packing, determine the sorption properties of these homopolymers and copolymers. The FDA–durene homopolymer has the highest solubility for all gases because of its high specific free volume and fractional free volume. The solubilities of the copolymers increase with an increasing 6FDA–durene content, while the solubility selectivities of the copolymers only vary slightly. The values of K_D (Henry's law constant) and C_H′ (Langmuir site capacity) of these copolyimides decrease with a decreasing 6FDA–durene content. To our surprise, contradictory to the previous known fact that the meta‐connected materials tend to have denser molecular packing than that of the para‐linked materials for homopolymers, the 6FDA–durene/mPDA 80/20 copolymer has higher gas solubilities than those of the 6FDA–durene/pPDA 80/20 copolymer. The random moiety sequence within the copolymer may be the main cause for the abnormal phenomenon. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2187–2193, 2003     

Catalytic Hydrocracking of a Bitumen‐Derived Asphaltene over NiMo/γ‐Al2O3 at Various Temperatures

Hydrocracking of a bitumen‐derived asphaltene over NiMo/γ‐Al₂O₃ was investigated in a microbatch reactor at varying temperatures. The molar kinetics of asphaltene cracking reaction was examined by fitting the experimental data. Below a defined temperature, the molar reaction showed the first‐order kinetic feature while at higher temperatures secondary reactions such as coke formation became significant, causing deviation of the reaction behavior from the proposed first‐order kinetic model. Selectivity analysis proved that dominant products varied from gases to liquids to gases with increasing temperature, shifting the dominant reaction from C–S bonds cleavage to C–C bonds cleavage.