Synthesis of thiophene/phenylene co‐oligomers. V. Functionalization at molecular terminals toward optoelectronic device applications

We report the synthesis of various thiophene/phenylene co‐oligomers with a total number of thiophene and benzene (phenylene) rings of 5 and 6 with various terminal groups. Those terminal groups have been chosen from among alkyl groups, methoxy groups, trifluoromethyl groups, and cyano groups. The molecular backbone of these compounds comprises phenyl‐ or biphenylyl‐capped thiophene (or oligothiophene) or an alternating co‐oligomer. The synthesis is based on either the Suzuki coupling reaction or the Negishi coupling reaction. These reaction schemes enabled us to obtain the target compounds in high quality. In particular, the latter coupling method turned out to produce the compounds at a high yield. The terminal groups are expected to produce various functionalities based upon their electron donating character (alkyl groups and methoxy groups) or electron withdrawing character (trifluoromethyl groups and cyano groups). Additionally some of these groups bring about enhanced solubility. This will lead to the production of a diversity of modified compounds of thiophene/phenylene co‐oligomers. To give an example that demonstrates usefulness of the target compounds, we present optoelectronic data that are associated with their device applications.     

Protecting groups in carbohydrate chemistry: influence on stereoselectivity of glycosylations

Saccharides are polyhydroxy compounds, and their synthesis requires complex protecting group manipulations. Protecting groups are usually used to temporarily mask a functional group which may interfere with a certain reaction, but protecting groups in carbohydrate chemistry do more than protecting groups usually do. Particularly, protecting groups can participate in reactions directly or indirectly, thus affecting the stereochemical outcomes, which is important for synthesis of oligosaccharides. Herein we present an overview of recent advances in protecting groups influencing stereoselectivity in glycosylation reactions, including participating protecting groups, and conformation-constraining protecting groups in general.     

Protecting and Leaving Functions of Trimethylsilyl Groups in Trimethylsilylated Silicates for the Synthesis of Alkoxysiloxane Oligomers

The concept of protecting groups and leaving groups in organic synthesis was applied to the synthesis of siloxane‐based molecules. Alkoxy‐functionalized siloxane oligomers composed of SiO₄, RSiO₃, or R₂SiO₂ units were chosen as targets (R: functional groups, such as Me and Ph). Herein we describe a novel synthesis of alkoxysiloxane oligomers based on the substitution reaction of trimethylsilyl (TMS) groups with alkoxysilyl groups. Oligosiloxanes possessing TMS groups were reacted with alkoxychlorosilane in the presence of BiCl₃ as a catalyst. TMS groups were substituted with alkoxysilyl groups, leading to the synthesis of alkoxysiloxane oligomers. Siloxane oligomers composed of RSiO₃ and R₂SiO₂ units were synthesized more efficiently than those composed of SiO₄ units, suggesting that the steric hindrance around the TMS groups of the oligosiloxanes makes a difference in the degree of substitution. This reaction uses TMS groups as both protecting and leaving groups for SiOH/SiO⁻ groups.     

Tuning the Properties of Graphdiyne by Introducing Electron‐Withdrawing/Donating Groups

The properties of graphdiyne (GDY), such as energy gap, morphology, and affinity to alkali metals, can be adjusted by including electron‐withdrawing/donating groups. The push–pull electron ability and size differences of groups play a key role on the partial property adjusting of GDY derivatives MeGDY, HGDY, and CNGDY. Cyano groups (electron‐withdrawing) and methyl groups (electron‐donating) decrease the band gap and increase the conductivity of the GDY network. The cyano and methyl groups affects the aggregation of GDY, providing a higher number of micropores and specific surface area. These groups also endow the original GDY additional advantages: the stronger electronegativity of cyano groups increase the affinity of GDY frameworks to lithium atoms, and the larger atomic volume of methyl groups increases the interlayer distance and provides more storage space and diffusion tunnels.     

Surface-grafting of phosphates onto a polymer for potential biomimetic functionalization of biomaterials

In the human body, phosphate groups play important roles in signaling and the biological functions of proteins and peptides. Despite the importance of phosphate groups, polymer surfaces have not been directly grafted with phosphate groups by chemical reactions because the usual organic solvents used to graft phosphate groups can dissolve or swell polymers. We focused this study on grafting phosphate groups onto a poly(ethylene-co-acrylic acid) (PEAA) surface in an aqueous solution. O-phospho L-serine and O-phosphoethanolamine were grafted on PEAA surfaces to introduce phosphate groups by activating carboxylic acid groups of PEAA using N-hydroxysuccinimide (NHS) and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) in an aqueous environment. X-ray photoelectron spectroscopy (XPS) was used to elucidate the process by which surface grafting occurs and the process that the phosphate group is cleaved into a phosphate ion and a hydrolyzed molecule at high pH. It was found that under appropriate reaction conditions the phosphate groups could be successfully grafted on the polymer surfaces. The phosphate-grafted polymer surfaces showed lower water contact angles than the initial polymer surfaces likely due to their highly mobile and hydrophilic phosphate side groups. This work demonstrates a technique to successfully graft phosphate groups onto organic polymer surfaces in a biocompatible aqueous environment, which may open new avenues to functionalizing synthetic polymeric and natural macromolecule derived biomaterials.     

Tuning the Properties of Graphdiyne by Introducing Electron-Withdrawing/Donating Groups

The properties of graphdiyne (GDY), such as energy gap, morphology, and affinity to alkali metals, can be adjusted by including electron-withdrawing/donating groups. The push–pull electron ability and size differences of groups play a key role on the partial property adjusting of GDY derivatives MeGDY, HGDY, and CNGDY. Cyano groups (electron-withdrawing) and methyl groups (electron-donating) decrease the band gap and increase the conductivity of the GDY network. The cyano and methyl groups affects the aggregation of GDY, providing a higher number of micropores and specific surface area. These groups also endow the original GDY additional advantages: the stronger electronegativity of cyano groups increase the affinity of GDY frameworks to lithium atoms, and the larger atomic volume of methyl groups increases the interlayer distance and provides more storage space and diffusion tunnels.     

Synthesis and photochemical properties of novel multifunctional photopolymers with both pendant epoxy groups and phenacyl ester groups

Novel multifunctional photopolymers with both pendant epoxy groups and phenacyl ester groups were synthesized by the one‐pot method for the reaction of poly(methacrylic acid) with epibromohydrin; this was followed by a reaction with phenacylbromide with 1,8‐diazabicyclo‐[5.4.0]undecene‐7 as a condensation reagent. These esterification reactions proceeded smoothly and quantitatively under mild conditions. Moreover, the photochemical reactions of the resulting polymers were evaluated by UV and IR spectroscopy. The pendant phenacyl ester groups were photocleaved to give corresponding carboxyl groups, and then the produced carboxyl groups reacted with pendant epoxy groups. Furthermore, the baking process promoted a crosslinking reaction because of the addition reaction of epoxy groups with carboxyl groups after irradiation. It was also proven that the photochemical reactivity of the resulting polymers was affected by the structure of the phenacyl ester group. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 530–538, 2001     

Estimation of the dissociation constants for functional groups on modified and unmodified silica gel supports from the relationship between electroosmotic flow velocity and pH

Electroosmotic volume flow was directly observed in a simple instrument consisting of 1 cm long a home-made support, packed between two polyethylene frits in the polypropylene tube. Equations relating electroosmotic flow (EOF) velocity and pH for two functional groups on the surface of the solid materials were developed. With these equations, we can estimate the dissociation constants of two different kinds of functional groups on modified silica gel materials simultaneously. The dissociation constants of silanol groups, benzene sulfonic acid groups, and alkyl quaternary ammonium groups on the modified and unmodified silica gel supports were estimated. The estimated pK values of the silanol groups on the silica gel and modified silica gel surfaces are between 4.0 and 4.3. The estimated pK values of the benzene sulfonic acid groups and alkyl quaternary ammonium groups on the surface of the modified silica gel are 2.6 and 8.6, respectively.     

The hydration of glucose: the local configurations in sugar-water hydrogen bonds

The hydration of a simple sugar is an essential model for understanding interactions between hydrophilic groups and interfacial water molecules. Here I perform first-principles molecular dynamics simulations on a glucose-water system and investigate how individual hydroxyl groups are locally hydrated. I demonstrate that the hydroxyl groups are less hydrated and more incompatible with a locally tetrahedral network of hydrogen bonds than previously thought. The results suggest that the hydroxyl groups form roughly two hydrogen bonds. Further, I find that the local hydration of the hydroxyl groups is sensitively affected by seemingly small variations in the local electronic structure and bond polarity of the groups. My findings offer insight into an atomic-level understanding of sugar-water interactions.     

Transformations of polymers and copolymers of acrylonitrile during heterogeneous saponification

The kinetic and thermodynamic specific features of the process of heterogeneous alkaline saponification of the copolymer of acrylonitrile (92.2%), methyl acrylate (6.3%), and sodium monoithaconate (1.5%) were investigated. Chemical and infrared spectroscopic methods reveal that the saponification of the nitrile groups of copolymer of acrylonitrile proceeds faster to yield amide groups and then slower to yield carboxylate groups. The order of both stages of the process with respect to the accumulation of the respective groups was evaluated. The dependence of the rate of saponification on the packing density of the structural units was demonstrated. With increasing conversion, the fiber structure becomes looser, as demonstrated by density and sorption investigations. If acrylonitrile copolymer is treated with alkali, the carboxylate groups in the polymer substrate accumulate as a result of saponification of the ester groups of the copolymer, while the nitrile groups are predominantly transformed into the amide groups. If the degree of conversion (with respect to the CN groups) is higher than 62.7%, the copolymer abruptly suffers a marked change in its mechanical properties and gradually dissolves. The products of partial saponification of copolymer were investigated by thermomechanical methods and DTA. The polycyclization of the polymer substrate was found to proceed at a temperatures which decreases as the content of the amide groups increases.     

季铵盐、季膦盐类高分子抗菌剂的研究进展

综述了季铵盐、季膦盐类高分子抗菌剂的研究进展,包括该类抗菌剂的合成、性能及抗菌机理。现有的研究结果表明,含有多种杀菌基团高分子抗菌剂的抗菌作用可能与杀菌基团的种类、杀菌基团的固载量、载体与杀菌基的结合位置、杀菌基团的分布、载体的表面亲水性能、聚合物的交联度、链结构等有关。若能在分子结构中同时有序引入季铵盐或季膦盐、海因类杀菌基团,有可能存在杀菌基团的协同效应,并且可能形成一个新的高分子抗菌材料的研究分支。     

Crosslinking of oligomers bearing carbamoyloxyimino groups with their photochemical and thermal reactions

Carbamoyloxyimino (COI) groups are precursors of photochemically base‐generating groups as well as those of thermally isocyanate‐generating groups. In this study, photochemical and thermal reactions of COI groups in oligomers were investigated by spectral analyses and solubility changes. Oligomers bearing three types of COI groups were prepared. COI groups in all oligomer films were photolyzed on irradiation with 254 nm of light and were deblocked to form isocyanato groups on heating. From the IR spectral analyses, the formation of urea linkage was confirmed by the decrease in isocyanato groups and peak generation because of urea groups on postexposure bake (PEB) treatment. For all oligomer films, PEB was effective for the enhancement of insolubilization of the films in tetrahydrofuran. Heating followed by irradiation was also effective for the insolubilization. These results indicated that photochemical and thermal treatments of COI groups afforded highly sensitive crosslinking systems because of photochemically generated basic groups and thermally generated isocyanato groups. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2612–2620, 2004     

Adsorption of epoxy and hydroxyl groups on zigzag graphene nanoribbons: Insights from density functional calculations

Density functional theory calculations have been used to investigate the adsorption of epoxy and hydroxyl groups on zigzag graphene nanoribbons. Our calculations show that the adsorbed epoxy groups and both the epoxy and hydroxyl groups on a ribbon surface can be transformed to a carbonyl pair and a carbonyl-hydroxyl pair. The energy barriers of these processes are 1.13 and 0.37 eV, respectively. In contrast to the reduced GO sheets, the stabilities of the carbonyl-hydroxyl pair and the carbonyl pair, with respect to the corresponding initial configuration, strongly depend on the adsorbed sites of groups. The vacancy defect improves the adsorptions of oxygen-containing groups on the surface. Because of the adsorption of new hydroxyl groups, the O-H bond belonging to the carbonyl-hydroxyl pair was highly dissociative and led to the formation of a highly stable carbonyl group with the release of water. The magnetic and electronic properties of the zigzag graphene nanoribbons were well tuned by different oxidized groups.     

Molecular design and synthesis of novel side-chain liquid crystalline polymers

Novel side-chain liquid crystalline polymers were synthesized based on the molecular design of the chemical structures of main-chain, spacer, and mesogenic groups. The main-chain structures are polyether, by the cationic ring-opening polymerization of oxetane derivatives, and polydiene, by the radical polymerization of diene derivatives. Some of the polymers from oxetanes with various mesogen and spacer groups show smectic liquid crystalline phase. Both cyano- and fluorine-substituted biphenyls are good mesogenic groups in these liquid crystalline polymers. Polydiene also acts as a novel main-chain to give smectic liquid crystalline state with cyanobiphenyl or fluorobiphenyl as a mesogen. Not only oligomethylene groups but also siloxane and oligo(oxyethylene) groups act as a component of the spacer groups to give liquid crystalline state.     

Determination of Epoxy and Isocyanate Groups in the Presence of Each Other

Analytical reactions for the determination of epoxy and isocyanate groups in the presence of each other in epoxy–isocyanate compositions were studied. For the determination of epoxy groups in the presence of isocyanate groups, a test with HBr in glacial acetic acid was proposed; acetic acid reacts with isocyanate groups and, hence, masks them. Isocyanate groups in the presence of epoxy groups were determined by potentiometric titration with a solution of piperidine in ethyl methyl ketone. The addition of toluene to the test solution decreases the fraction of the enol form of ethyl methyl ketone, which interferes with the determination.     

Syntheses of functional condensation polymer. I. Polyesters having pendant functional groups such as hydroxyl,formyl, aldoxime,aminomethyl and hydroxymethyl

Unsaturated polyesters having pendant functional groups such as hydroxyl, formyl, aldoxime, aminomethyl and hydroxymethyl, have been prepared and characterized, and some of their properties were investigated. Reaction conditions for the epoxidation of unsaturated polyesters and hydrolysis of the epoxy groups in the polyesters were established to control the amount of pendant diol groups. It was possible to incorporate up to 90 mole-% of formyl side groups into the unsaturated polyester by the hydroformylation with the rhodium catalyst. In addition, the formyl side groups of the modified polyester were converted into hydroxymethyl or aldoxime groups and were then converted to amino groups. The melting points of the modified polyesters decreased with increasing the pendant group content of the polyesters, as expected. Aliphatic polyesters having pendant hydroxyl or amino groups had a high affinity for moisture, which might be ascribed to the participation of the hydrophilic pendant groups in the modified polyesters.     

Reduction of dielectric loss in radiation-polymerized polyethylene

Low dielectric loss polyethylenes have been produced by γ-radiation polymerization of oxygen-free ethylene monomers. Dielectric measurements were made at 500 MHz and 20°C. The lowest dielectric loss tangent of the polyethylene was 3.3 × 10^?5. Polar groups contributing to the dielectric loss have been found to be carbonyl groups, terminal vinyl groups, methyl groups, and hydroxyl groups contained in the polyethylene. The contribution of each group to the loss tangent has been calculated from a comparison of the variation of the loss tangent with the content of each group as determined by infrared analysis. It has been found that the reduction of the loss tangent is mainly due to the decrease in the concentrations of the carbonyl groups and the terminal vinyl groups and that the presence of a considerable amount of the hydroxyl groups prevents a further reduction of the loss in the polyethylenes. The results obtained from the analysis of the radiation-polymerized polyethylenes were applied to commercially available polyethylenes.     

Advances in Protecting Groups for Oligosaccharide Synthesis

Carbohydrates contain numerous hydroxyl groups and sometimes amine functionalities which lead to a variety of complex structures. In order to discriminate each hydroxyl group for the synthesis of complex oligosaccharides, protecting group manipulations are essential. Although the primary role of a protecting group is to temporarily mask a particular hydroxyl/amino group, it plays a greater role in tuning the reactivity of coupling partners as well as regioselectivity and stereoselectivity of glycosylations. Several protecting groups offer anchimeric assistance in glycosylation. They also alter the solubility of substrates and thereby influence the reaction outcome. Since oligosaccharides comprise branched structures, the glycosyl donors and acceptors need to be protected with orthogonal protected groups that can be selectively removed one at a time without affecting other groups. This minireview is therefore intended to provide a discussion on new protecting groups for amino and hydroxyl groups, which have been introduced over last ten years in the field of carbohydrate synthesis. These protecting groups are also useful for synthesizing non‐carbohydrate target molecules as well.     

Colorimetric determination of reactive amino groups of a solid support using Traut’s and Ellman’s reagents

A simple colorimetric method has been developed for the quantitative determination of reactive amino groups of a solid support. The method calls for the use of a reagent that reacts specifically and facilely with amino groups and concurrently introduces free sulfhydryl groups. The latter can then be titrated colorimetrically by using the well-known Ellman’s reagent. Thus, an excess of 2-iminothiolane (Traut’s reagent) was reacted with amine-carrying solid supports. After removing unreacted 2-iminothiolane and keeping the resultant solid-phase sulfhydryl groups in a reduced state by using dithiothreitol, the solid supports, after being thoroughly washed, were then reacted with 5,5′-dithiobis-(2-nitrobenzoic acid) to quantify the sulfhydryl groups that were generated from reacting solid-phase amino groups with Traut’s reagents.