DNA-directed assembly of polyanilines: modified cytosine nucleotides transfer sequence programmability to a conjoined polymer

A series of polyaniline (PANI) oligomers was constructed from monomer units covalently linked to duplex DNA through N-(2-aminoethyl) groups bonded through cytosines. DNA oligomers containing the aniline monomers were treated with horseradish peroxidase (HRP) and H2O2 under conditions known to cause polymerization of aniline. No change in the absorption spectrum of the DNA was observed for samples containing fewer than four contiguous aniline groups. However, for oligomers containing four, five, or six aniline units, treatment with HRP and H2O2 led to the appearance of absorption features characteristic of the conducting "proton doped" emeraldine oxidation state of PANI. Molecular modeling shows that the DNA is distorted in the region of the PANI, but flanking regions of the DNA maintain their B-form structure. These findings provide a method to exploit the self-recognition, self-assembly, and sequence programmability of DNA for the formation of conducting polymers.     

DNA-programmed modular assembly of cyclic and linear nanoarrays for the synthesis of two-dimensional conducting polymers

Nanometer-scale arrays of conducting polymers were prepared on scaffolds of self-assembling DNA modules. A series of DNA oligomers was prepared, each containing six 2,5-bis(2-thienyl)pyrrole (SNS) monomer units linked covalently to N4 atoms of alternating cytosines placed between leading and trailing 12-nucleobase recognition sequences. These DNA modules were encoded so the recognition sequences would uniquely associate through Watson-Crick assembly to form closed-cycle or linear arrays of aligned SNS monomers. The melting behavior and electrophoretic migration of these assemblies showed cooperative formation of multicomponent arrays containing two to five DNA modules (i.e., 12-30 SNS monomers). The treatment of these arrays with horseradish peroxidase and H(2)O(2) resulted in oxidative polymerization of the SNS monomers with concomitant ligation of the DNA modules. The resulting cyclic and linear arrays exhibited chemical and optical properties typical of conducting thiophene-like polymers, with a red-end absorption beyond 1250 nm. AFM images of the cyclic array containing 18 SNS units revealed highly regular 10 nm diameter objects.     

Synthesis,structure, and properties of aromatic polysulfides

Polycondensation of haloaromatics and sodium sulfide has been studied. An increase in reactivity of functional groups, a change of the composition of the elementary polymeric unit with a change of the relative amounts of the monomers, and a key role of side-reactions, i.e. intra(molecular) and macrocyclisation, have been revealed. Low-melting isomeric poly(phenylene sulfides), as well as their derivatives, reactive telechelic oligomers, have been prepared. New methods of preparation of poly(arene sulfides) by transarylation of diphenyl sulfide, polymerisation of cyclic aromatic sulfides, or by direct polycondensation of arenes with sulfur under the action of AlCl₃, as well as by polycondensation of aniline with sulfur in the absence of catalysts have been suggested. Structures and properties of newly prepared polymers have been studied.     

Sonochemical synthetic methods to produce functionalized conducting copolymers

Polyaniline (PANI) is one of the most investigated intrinsically conducting polymers. Copolymerization of aniline with aniline derivatives was considered one of the most effective and promising ways of improving the properties of PANI. In this work, firstly ethyl 3‐aminobenzoate and butyl 3‐aminobenzoate were synthesized from 3‐aminobenzoic acid by direct esterification. Then the copolymerization of 3‐amino benzoic acid, ethyl 3‐aminobenzoate, and butyl 3‐aminobenzoate with aniline was carried out by sonochemical polymerization in aqueous hydrochloric acid using ammonium persulfate (APS) as an initiator. The effects of variation in the molar ratio of the two monomers on chain structure, conductivity, and the redox properties of the copolymer are discussed. The prepared polymers are characterized by ¹H NMR spectroscopy, X‐ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT‐IR). Thermal behavior of the prepared copolymers was studied by differential scanning calorimetry. The copolymers were doped with HCl and their conductivity was measured. Copyright © 2009 John Wiley & Sons, Ltd.     

Theoretical study of the influence of monomer excess on the structure and properties of polyaniline oligomers

Polyaniline is among the most intensely investigated polymers because of its exceptional properties affording its current and potential applications. The structure and energy spectra of isolated oligomers and infinite chains in different oxidation states and degrees of protonation have been discussed at length from experimental and theoretical perspectives. The reaction environment effect, however, has received less attention and, particularly, the influence of monomer excess has been completely neglected in theoretical studies. Experimental measurements show that residual aniline is always detected in emeraldine samples obtained at low pH. Upon addition of oxidant to emeraldine PANI samples, post-polymerization due to the presence of excess monomers occurs. This is an indication of the formation of aniline-PANI complexes in the reaction medium. The presence of aniline monomers should affect the PANI chain arrangement and optical/conducting characteristics. Therefore, model clusters of aniline with neutral or singly protonated emeraldine tetramers in explicit water medium and periodic boundary conditions are addressed in this paper using a Monte Carlo/AMBER96/AM1 computational protocol to simulate the absorption spectra. The monomer impact on the structure, energy characteristics, and UV/vis spectra of the polymer are discussed.     

Electrochemically synthesized polymers in molecular imprinting for chemical sensing

This critical review describes a class of polymers prepared by electrochemical polymerization that employs the concept of molecular imprinting for chemical sensing. The principal focus is on both conducting and nonconducting polymers prepared by electropolymerization of electroactive functional monomers, such as pristine and derivatized pyrrole, aminophenylboronic acid, thiophene, porphyrin, aniline, phenylenediamine, phenol, and thiophenol. A critical evaluation of the literature on electrosynthesized molecularly imprinted polymers (MIPs) applied as recognition elements of chemical sensors is presented. The aim of this review is to highlight recent achievements in analytical applications of these MIPs, including present strategies of determination of different analytes as well as identification and solutions for problems encountered.     

Mixed-sequence pyrrolidine-amide oligonucleotide mimics: Boc(Z) synthesis and DNA/RNA binding properties

Pyrrolidine-amide oligonucleotide mimics (POMs) exhibit promising properties for potential applications, including in vivo DNA and RNA targeting, diagnostics and bioanalysis. Before POMs can be evaluated in these applications it is first necessary to synthesise and establish the properties of fully modified oligomers, with biologically relevant mixed sequences. Accordingly, Boc-Z-protected thyminyl, adeninyl and cytosinyl POM monomers were prepared and used in the first successful solid phase synthesis of a mixed sequence POM, Lys-TCACAACTT-NH2. UV thermal denaturation studies revealed that the POM oligomer is capable of hybridising with sequence selectivity to both complementary parallel and antiparallel RNA and DNA strands. Whilst the duplex melting temperatures (Tm) were higher than the corresponding duplexes formed with isosequential PNA, DNA and RNA oligomers the rates of association/dissociation of the mixed sequence POM with DNA/RNA targets were noticeably slower.     

原位核磁共振技术考察L-缬氨酸导引下合成花状纳米结构聚苯胺形成机理的研究

利用~1H-NMR原位追踪在L-缬氨酸存在下合成花状纳米聚苯胺的形成过程中发现此结构的形成经历3个阶段:首先在苯胺与缬氨酸构成的类胶束结构内聚合成吩嗪类寡聚物;其次通过p-p重叠作用及胶束融合过程成为片状聚集体;最终通过与缬氨酸形成氢键组装成花瓣状纳米聚苯胺.通过改变反应条件,对比形成过程中核磁共振图谱及产物形貌的变化发现花状纳米聚苯胺的形成有如下特征:反应初期L-缬氨酸作为缓冲试剂可以避免苯胺的骤然质子化,有利于生成具有吩嗪结构的寡聚物;反应前苯胺单体与缬氨酸形成稳定的反应环境保证寡聚物始终在其内聚集生长,有效避免了外部环境的影响.     

On the origin of the so-called nucleation loop during electropolymerization of conducting polymers

During the potentiodynamic preparation of conducting polymers, cyclic voltammograms of many pi-conjugated monomers and oligomers often show a marked crossing or loop effect. The so-called "nucleation loop" of the first cycle has been ascribed to the nucleation process requiring an activation energy provided by an overpotential. This paper presents cyclic voltammograms of pi-systems with trace crossing as well as loop effects that suggest that the homogeneous formation of oligomeric redoxactive follow-up products from the starting species is responsible for this occurrence. As the investigated species are typical starting components of resulting oligomers or polymers, all these findings are evidence that similar mechanisms also hold for the formation of many other classical polymers with a "nucleation loop" like polypyrrole, and that the true reason for the nucleation loop is the comproportionation reaction between an oligomeric follow-up product and the starting "monomer".     

The preparation of novel silica modified polyimide membranes: synthesis,characterization, and gas separation properties

In this study, new monomers having siloxane groups were synthesized as an intermediate for preparation of siloxane modified polyimide polymers. Then with these monomers, the synthesis of uncrosslinked and crosslinked polyimide–siloxane hybrid polymer membranes were achieved. The purposes of the preparation of modified polyimides were to modify the thermal and chemical stability, and mechanical strength of polyimides, and to improve the gas separation properties of polymers. The new diamine monomer having siloxane groups was prepared from 3,5‐diaminobenzoic acid (3,5‐DABA) and 3‐aminopropyltrimethoxysilane (3‐APTMS) in N‐methyl‐2‐pyrollidone (NMP) at 180°C. The modified polyimide membranes having different amount of siloxane groups were synthesized from pyromellitic dianhydride (PMDA), 4,4‐oxydianiline (ODA), and 3,5‐diaminobenzamido‐N‐propyltrimethoxy silane (DABA/PTMS) in NMP using a two‐step thermal imidization process. The synthesis of modified polyimide membranes were characterized by Fourier transform infrared spectroscopy (FTIR). The thermal analysis of the polyimides were carried out by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Water absorption and swelling experiments were also carried out for the investigation of structural properties of polymers. FTIR observations confirmed that the polyimide membranes with new diamine intermediate were successfully obtained. Thermal analysis showed that the uncrosslinked copolyimides exhibited two glass transition temperatures, indicating that they were separated microphases and it was found that all the modified copolyimides had showed higher glass transition temperature (T_g) than unmodified polyimides. The separation properties of the prepared polyimide membranes were also characterized by permeability for O₂ and N₂ gases and ideal selectivity values were calculated. Copyright © 2009 John Wiley & Sons, Ltd.     

Benzocyclobutenes: A New Class of High Performance Polymers

Benzocyclobutenes are a family of thermally polymerizable monomers which can be classified into two groups: 1) monomers which contain only benzocyclobutene moieties and 2) monomers which contain sites of unsaturation in addition to benzocyclobutene moieties. The monomers can be partially polymerized (B-staged) by heating to form oligomers having processing advantages for various composite fabrication techniques. The polymerization proceeds through the thermally initiated cyclobutene ring opening to yield an o-quinodimethane intermediate (calculated to be a ground state singlet). Preliminary characterization of the network structures indicates that monomers which contained multiple benzocyclobutene moieties, optionally with sites of unsaturation, were transformed into multifunctional network junctions when the thermosets were fully cured. The 3-maleimidobenzocyclobutenes thermally polymerize to yield substantially linear, high glass transition temperature (T_g) polymers. Thus benzocyclobutene polymers encompass materials which have properties ranging from high T_g, thermosets to those of substantially linear thermoplastics. Some polymers exhibit an excellent retention of their room temperature mechanical properties to at least 200-250°C, making them useful as high performance polymers for applications in the aerospace industry. Other polymers have outstanding electrical properties including very low dielectric constant and water pickup, making them useful in electronic applications.     

Synthesis and polymerization reactions of cyclic imino ethers. VI. Polymers with biphenyl structure

A monomer of the AB‐type and a bifunctional comonomer of the AA‐type containing two 2‐oxazoline rings and a biphenyl structural unit were prepared from the corresponding carboxylic acids via their esterification and subsequent amidation with an aminoalcohol. The cyclization of an amide to 2‐oxazoline structure was achieved by treatment with thionyl chloride followed by liberation of the free base with sodium hydrocarbonate in an aqueous solution. The prepared monomers were used for the polyaddition polymerization of the AB‐type monomer having a 2‐oxazoline and phenol group bound on adjacent rings of the biphenyl structure in solution. The monomer of the AA‐type was used for AA+BB‐type polyaddition reactions with aliphatic dicarboxylic acids. Both types of polymerizations have been performed in melt and in solution. The structures of the polymers were determined, and the thermal properties of the polymers were evaluated. Liquid‐crystalline (LC) structures of the prepared polymers were observed by DSC measurements and optical microscopy. The polyaddition reactions of the monomers containing a 2‐oxazoline ring and a biphenyl unit represent a new efficient way for the preparation of a biphenyl unit containing poly(ether amide)s and poly(ester amide)s. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Synthesis of polyaryloxysilanes by melt-polymerizing dianilino- and diphenoxysilanes with aromatic diols

A series of polyaryloxysilanes was prepared from aromatic diols and dianilino- and diphenoxysilanes. High molecular weight polymers were obtained at temperatures of 200°C. or higher by using melt-polymerization procedures. The polymers, which combine the structures of silicones and polyaromatics, possessed high thermal stabilities and were obtained as materials which (1) failed to melt or soften at 350°C., (2) were gumlike at elevated temperatures, or (3) were soluble, film- and fiber-forming polymers capable of being processed as conventional thermoplastics and having potentially useful mechanical properties. The preparation of monomers, general polymerization procedures, and certain structure-property relationships for the thermoplastic polyaryloxysilanes are considered.     

Coating of zinc ferrite particles with a conducting polymer, polyaniline

Particles of zinc ferrite, ZnOFe2O3, were coated with polyaniline (PANI) phosphate during the in situ polymerization of aniline in an aqueous solution of phosphoric acid. The PANI-ferrite composites were characterized by FTIR spectroscopy. X-ray photoelectron spectroscopy was used to determine the degree of coating with a conducting polymer. Even a low content of PANI, 1.4 wt%, resulted in the 45% coating of the particles' surface. On the other hand, even at high PANI content, the coating of ferrite surface did not exceeded 90%. This is explained by the clustering of hydrophobic aniline oligomers at the hydrophilic ferrite surface and the consequent irregular PANI coating. The conductivity increased from 2 x 10(-9) to 6.5 S cm(-1) with increasing fraction of PANI phosphate in the composite. The percolation threshold was located at 3-4 vol% of the conducting component. In the absence of any acid, a conducting product, 1.4 x 10(-2) Scm(-1), was also obtained. As the concentration of phosphoric acid increased to 3 M, the conductivity of the composites reached 1.8 S cm(-1) at 10-14 wt% of PANI. The ferrite alone can act as an oxidant for aniline; a product having a conductivity 0.11 S cm(-1) was obtained after a one-month immersion of ferrite in an acidic solution of aniline.     

Anodic behaviour of mono- and bisdithiafulvenyl-9,9′-spirobifluorene: insertion of vinylogous TTF into the spirobifluorenyle framework

New three-dimensional copolymers containing 9,9′-spirobifluorenyl-ethylene units were prepared by anodic oxidation of 9,9′-spirobifluorenes 2-mono- or 2,7′-disubstituted by a dithiafulvenyl unit. The synthesis, physicochemical properties and electrochemistry of both monomers and derived oligomers and polymers are reported.     

Synthesis of vinyl polymers with pendant phenoxazinyl group

Vinyl monomers bearing phenoxazine units, were synthesized: 2-vinyl-phenoxazine starting with phenoxazine in a five-step synthesis; 3-acrylamido- or 3-methacrylamido-phenoxazines with or without 10-PhCH₂ or 10-Me-substituent starting with o-benzylideneaminophenol or o-anisidine via 3-aminophenoxazines; and 3-(p-styrenesulfonamido)phenoxazines with or without 10-PhCH₂- or 10-Me-substituent, also via 3-aminophenoxazines. Polymerizations of these noval monomers proceeded smoothly, except those having no 10-substituent. Changes of the visible absorption spectrum of iodine in THF with addition of the polymers and oligomers thus prepared were considerable, with the appearance of new absorption peaks for polymers with 10-Me-substituent.     

Intrachain electron transfer in conducting oligomers and polymers: the mixed valence approach

Organic mixed valence compounds consisting of bisdiarylamino charge-bearing units with an oligothiophene bridge and oligothiophene radical cations have been compared using molecular modeling. The study has been performed with oligomers of 1 to 22 thiophene units. These two series of molecules have several properties in common, and intramolecular Single Electron Transfer (SET) in both series can be described within the same theoretical framework. Conducting oligomer radical cations and slightly doped conducting polymers appear as special cases of the vast ensemble of organic mixed valence compounds. Short oligomers are class III, whereas longer oligomers and conducting polymers are class II. Therefore, doped conducting polymers cannot be correctly modeled using oligomers with a short conjugation length. Experimental evidence extracted from the literature confirms these findings. Single electron transfer theories can thus be used when studying interchain and intrachain electron transfer in slightly doped conducting polymers and in materials consisting of short oligomers. This makes it possible to extract from the UV-vis-near-IR spectra the electron-transfer constant rate along or between the pi-conjugated chain. The main differences among inorganic, organic, and conducting oligomer or polymer mixed valence compounds lies in the H(ab) and lambda values associated with these different series. Inorganic mixed valence compounds have small H(ab) and lambda values; organic mixed valence compounds have large H(ab) and lambda values, whereas conducting oligomers and polymers have large H(ab) but small lambda values. This induces charge delocalization to occur for systems larger than those of inorganic and nitrogen-centered organic mixed valence compounds.     

聚苯胺/贵金属复合纳米材料的可控合成及催化应用

导电高分子/贵金属复合纳米材料因其在催化、传感、表面增强拉曼、光热治疗等诸多领域的应用前景而受到广泛关注.本文主要介绍我们课题组近年来利用可控合成策略制备的负载型和包埋型两种结构聚苯胺/贵金属复合纳米材料,以及利用复合纳米材料的结构和功能特性,对其在多相催化领域的应用、结构与催化性能之间构效关系的探索.     

Synthesis of phenylquinoxaline oligomers containing pendant electron‐donating and electron‐withdrawing groups

A series of extended 6‐substituted quinoxaline AB monomer mixtures, 2‐(4‐fluorophenyl)‐3‐[4‐(4‐hydroxyphenoxy)phenyl]‐6‐substituted quinoxaline and 3‐(4‐fluorophenyl)‐2‐[4‐(4‐hydroxyphenoxy)phenyl]‐6‐substituted quinoxaline, were prepared and polymerized to afford phenylquinoxaline oligomers. High‐molecular‐weight polymers could not be obtained because of the formation of cyclic oligomers. On the basis of matrix‐assisted laser desorption/ionization time‐of‐flight analysis and molecular modeling results, the formation of a cyclic dimer could be a favorable process resulting in low‐molecular‐weight oligomers. They were completely soluble and amorphous, with glass‐transition temperatures varying from 165 to 266 °C, and they had thermooxidative stability, with samples displaying 5% weight loss temperatures of 419–511 °C in nitrogen. The thermal properties of the monomers and resultant polymers dramatically depended on the polarity of the substituents. The monomers and resultant oligomers displayed high fluorescence in tetrahydrofuran solutions and N‐methyl‐2‐pyrrolidinone solutions, respectively. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6465–6479, 2005     

The study of electroactive block copolymer containing aniline pentamer isolated from different solvents

For the films and powder of polymers containing conductive oligomer are usually obtained from solution, the choice of better solvents for the regular arrangement of oligomers is very important for the higher conductivity. Because of the poor solubility of the oligomers, it is difficult to study the arrangement directly in most common solvents, so, we synthesized a triblock copolymer, mPEG2k‐aniline pentamer‐mPEG2k, as the model to investigate the arrangement–solvent relationship. For the poor solubility of the AP block in common solvents, the copolymer self‐assembled into spheric micelles in toluene and into lamellar crystals in water and THF. The crystallinity (X_c) and crystallization temperature (T_c) values of mPEG blocks in powders prepared from different solvents differed obviously, which may be the effect of different self‐assembled structures. From the two‐phase model of one‐dimensional electron density correlation function of SAXS, the long period of copolymer prepared from THF was presumably equal to the long period of pure mPEG plus the chain length of AP, which demonstrates that the AP blocks arrange regularly in the noncrystalline regions. In the selected solvents, the ones with higher polarity and better solubility induced more regular arrangement of AP blocks, which may be useful for choosing solvents for preparation of higher conductivity polymers' films containing aniline oligomers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1298–1307, 2009