Institute of Macromolecular Compounds

Abstract Polyaniline is one of the most important conducting and responsive polymers. A molecular mechanism for the oxidation of aniline is proposed. This mechanism explains the specific features of aniline oligomerization and polymerization in various acidity ranges. The formation of polyaniline precipitates, colloids and thin films is reviewed and discussed on the basis of the chemistry of aniline oxidation. The generation of nanostructures, i.e. granules, nanotubes, nanowires and microspheres, is also considered. Oligomers containing phenazine constitutional units play an important role in self‐assembly to form templates. Polyaniline chains then grow from these templates and produce the various individual morphologies. Copyright © 2008 Society of Chemical Industry

Hierarchical self-assembly offers elegant and energy-efficient bottom-up strategies for the structuring of complex materials. For block copolymers, the last decade witnessed great progress in diversifying the structural complexity of solution-based assemblies into multicompartment micelles. However, a general understanding of what governs multicompartment micelle morphologies and polydispersity, and how to manipulate their hierarchical superstructures using straightforward concepts and readily accessible polymers remains unreached. Here we demonstrate how to create homogeneous multicompartment micelles with unprecedented structural control via the intermediate pre-assembly of subunits. This directed self-assembly leads to a step-wise reduction of the degree of conformational freedom and dynamics and avoids undesirable kinetic obstacles during the structure build-up. It yields a general concept for homogeneous populations of well-defined multicompartment micelles with precisely tunable patchiness, while using simple linear ABC triblock terpolymers. We further demonstrate control over the hierarchical step-growth polymerization of multicompartment micelles into micron-scale segmented supracolloidal polymers as an example of programmable mesoscale colloidal hierarchies via well-defined patchy nanoobjects. Multicompartment micelles can be assembled from block copolymers but it is difficult to manipulate their hierarchical superstructures using straightforward concepts. Here, methods are developed that involve the pre-assembly of subunits for the structurally controlled production of micelles.

Abstract A short review of the works of the author and his co‐workers in the field of configurational statistics of macromolecules is given. Results are quoted of the calculations relating the dimensions, dipole moments, and optical anisotropies of the chains with the conditions of internal rotation and stereoisomerism. Isotactic and syndiotactic chains are examined. The fundamental ideas of the mathematical methods developed are quoted. The calculations are carried out in usual approximation assuming the independence of the rotations around neighbor bonds, and in the next approximations taking into account the correlation of internal rotations inside monomeric units and between them. Comparison of the theory with experiment, using the rotational‐isomeric approximation, has shown in particular that the dimensions and the optical anisotropy of the polyisobutylene molecules can be explained by the examination of their configurations in the crystalline state. The excluded volume effects in the branched chains and their influence on the asymmetry of light scattering are investigated. Some experimental results are explained with the help of this investigation.

Aniline was oxidized with ammonium peroxydisulfate in solutions of strong acid (0.1 M sulfuric acid), weak acid (0.4 M acetic acid), or alkali (0.2 M ammonium hydroxide). The properties of the oxidation products and their morphology are controlled by the initial acidity of the medium and the acidity profile during the oxidation; the acidity increases because sulfuric acid is a byproduct. Conducting polyaniline nanogranules, nanotubes, or nonconducting oligoaniline microspheres were obtained, respectively. FTIR spectra suggest that the oligomers produced by the oxidation of neutral aniline molecules at the beginning of oxidation are similar, regardless of the acidity of the medium. Neutral aniline molecules, prevailing under alkaline conditions, are easily oxidized to aniline oligomers composed of ortho- and para-coupled aniline constitutional units. Ortho-coupled units are further converted by oxidative intramolecular cyclization to phenazines. It is proposed that, in acidic media, N-phenylphenazine units constitute the initiation centers for the subsequent polymerization of aniline, which takes place at pH < 2 when the intermediate pernigraniline chains become protonated. Anilinium cations, which dominate in strongly acidic media, are difficult to oxidize to oligomers, but they easily participate in the formation of polymer chains once their growth has started. The self-organization of phenazine units is responsible for the generation of polyaniline nanotubes. Partial sulfonation of aromatic amines occurs at higher pH, especially in alkaline media. The sulfonated oligomers stabilize aniline emulsions and enable the formation of oligoaniline microspheres, when the miscibility of aniline with aqueous medium is limited. The final oxidation products obtained in alkaline conditions contain only low-molecular-weight oligomers; the polymeric component is the dominating product only in strongly acidic media. Both components are present in various proportions when the oxidation takes place at intermediate pH ranges.

We performed theoretical and experimental investigations of dilute solutions of micelles of neutral amorphous diblock copolymers in selective solvents. The ranges of thermodynamic stability of spherical, cylindrical, and lamellar morphologies along with the equilibrium sizes and aggregation numbers of micelles are calculated and measured. For high molecular weight copolymers it is shown that the sphere-to-cylinder transition as well as precipitation of the micelles associated with cylinder-to-lamella transition occurs when aggregates have a crew-cut structure with the thickness of the corona smaller than the radius of the core. Similar to starlike micelles with corona larger than the core, the equilibrium parameters of crew-cut micelles are determined by the balance between the free energy of the corona and the surface energy of the core. The elastic free energy of the core remains small compared to the corona and surface free energies; however, it determines the transitions between different morphologies. The theoretical predictions including the existence of crew-cut spherical micelles, the range of stability of cylindrical micelles, and the significance of the contributions of the logarithmic corrections to scaling are in good agreement with experiments on polystyrene−polyisoprene block copolymer micelles in heptane, a selective solvent for the polyisoprene block.

Abstract The courses of aniline oxidation with ammonium peroxydisulfate in aqueous solutions of strong (sulfuric) and in weak (acetic) acids, followed by temperature and acidity changes, are different. In solutions of sulfuric acid, granular polyaniline (PANI) was produced; in solutions of acetic acid, PANI nanotubes were obtained. The external diameter of the nanotubes was 100–300 nm, the internal cavity 20–100 nm, and the length extended to several micrometres. The morphology of PANI, granular or tubular, depends on the acidity conditions during the reaction rather than on the chemical nature of the acid. PANI nanotubes were also produced when aniline was oxidized in the absence of any acid. The bulk conductivity of PANI prepared in solutions of acetic acid was 0.08–0.27 S cm −1 , depending on the acid concentration. Protonated PANI prepared in sulfuric and acetic acids were deprotonated with ammonium hydroxide to obtain PANI bases and the ammonium salt of the protonating acid. FTIR spectroscopy showed the differences in the molecular structure of the PANI bases. Irrespective of whether the polymerization was performed in solutions of sulfuric or acetic acid, PANI had hydrogen sulfate counter‐ions only. The PANI morphology is thus not controlled by the nature of counter‐ions. The acidity of the reaction medium determines the protonation of monomer, oligomer and polymer species. The chemistry of aniline oxidation is likely to be affected especially by the protonation of an intermediate in the pernigraniline form. It is proposed that, in the course of aniline oxidation, pH‐dependent self‐assembly of aniline oligomers predetermines the final PANI morphology. Copyright © 2005 Society of Chemical Industry

Abstract Several workers from various institutions in six countries have prepared thin films and colloidal polyaniline dispersions. The films were produced in situ on glass supports during the oxidation of anilinium chloride with ammonium peroxydisulfate in water. The average thickness of the films, assessed by optical absorption, was 125 ± 9 nm, and the conductivity of films was 2.6 ± 0.7 S cm –1 . Films prepared in 1 mol l –1 HCl had a similar thickness, 109 ± 10 nm, but a higher conductivity, 18.8 ± 7.1 S cm –1 . Colloidal polyaniline particles stabilized with a water-soluble polymer, poly( N -vinylpyrrolidone) [poly(1-vinylpyrrolidin-2-one)], have been prepared by dispersion polymerization. The average particle size, 241 ± 50 nm, and polydispersity, 0.26 ± 0.12, have been determined by dynamic light scattering. The preparation of these two supramolecular polyaniline forms was found to be well reproducible.

We present an overview of existing theories of block polymer micelles. We focus here on the equilibrium structure of nanoaggregates formed by solvophobic/solvophilic diblock copolymers in a dilute solution and briefly address the association behavior of triblock terpolymer. We outline recent advances in the field and some challenging problems for theoretical developments.

The solubility of silk fibroin in aqueous-salt, aqueous-organic, and organic media is analyzed. Factors affecting the formation of the secondary structural organization of fibroin in solutions and in the solid state after the recovery from solutions are analyzed.

Arginine-rich peptides, penetratins, as part of a number of cellular and viral proteins, can penetrate across plasma membrane directly, without participation of endocytosis. We show that one of penetratins, the basic domain 47-57 of human immunodeficiency virus, type 1, transcription factor Tat (Tat peptide), is able to interact with plasmid DNA electrostatically. These interactions result in formation of polyelectrolytic complexes at various negative/positive charge ratios of plasmid DNA and Tat peptide. Plasmid DNA is capable of binding to Tat peptide up to 1.7-fold excess of the complex positive charge. The DNA-Tat complexes can be used for delivery of plasmid DNA into mammalian cells. Transfection efficacy of cultured cells by DNA-Tat complexes is stimulated by free Tat peptide, most likely because it protects DNA-Tat complexes from disruption by anionic proteoglycans of cellular surface. Our data strongly argue in favor of the endocytosis-dependent mechanism of DNA-Tat complex uptake by mammalian cells similarly to internalization of complexes of plasmid DNA with other polycationic carriers. Moreover, different cell lines use different endocytosis-mediated pathways for DNA-Tat complex internalization. Intravenous injections to mice of DNA-Tat complexes in comparison with injections of naked DNA showed an inhibitory effect of DNA-Tat complex positive charge on expression of transferred gene. A low level of foreign gene expression in the liver of mice injected intravenously with positively charged DNA-Tat complexes is accounted for by inactivation of DNA-Tat complexes in the bloodstream due to their interactions with serum albumin. These data should be taken into account in an attempt to develop versatile gene delivery systems based on penetratin application for human disease therapy.

A method for the fast measurement of the diffusion coefficients of both small and large molecules in thin capillaries is reported. The method relies on Taylor-Aris dispersion theory and uses standard instrumentation for capillary zone electrophoresis. With this equipment, which consists of thin capillaries (50 to 100 micrometers in inner diameter), an injection system, detector ports, and computer data acquisition, a sample plug is pumped through the capillary at known velocity and the peak dispersion coefficient (D(*)) is measured. With the experimentally measured values of D(*) and flow velocity, and knowledge of the inner diameter of the capillary, the molecular diffusion coefficient (D) can be rapidly derived. For example, for ovalbumin a D value of 0.759 x 10(-6) square centimeter per second is found versus a tabulated value of 0.776 x 10(-6) square centimeter per second (error, 2 percent). For hemoglobin a D value of 0.676 x 10(-6) square centimeter per second is obtained versus a literature value of 0.690 x 10(-6) square centimeter per second (error, 1.5 percent).

One of the most favored trends in modern agriculture is biological control. However, many reports show that survival of biocontrol bacteria is poor in host plants. Providing biocontrol agents with protection by encapsulation within external coatings has therefore become a popular idea. Various techniques, including extrusion, spray drying, and emulsion, have been introduced for encapsulation of biocontrol bacteria. One commonly used biopolymer for this type of microencapsulation is alginate, a biopolymer extracted from seaweed. Recent progress has resulted in the production of alginate-based microcapsules that meet key bacterial encapsulation requirements, including biocompatibility, biodegradability, and support of long-term survival and function. However, more studies are needed regarding the effect of encapsulation on protective bacteria and their targeted release in organic crop production systems. Most importantly, the efficacy of alginate use for the encapsulation of biocontrol bacteria in pest and disease management requires further verification. Achieving a new formulation based on biodegradable polymers can have significant effects on increasing the quantity and quality of agricultural products.

ADVERTISEMENT RETURN TO ISSUEPREVReviewNEXTDefect-Mediated Trafficking across Cell Membranes: Insights from in Silico ModelingAndrey A. Gurtovenko*†, Jamshed Anwar‡, and Ilpo Vattulainen§∥⊥View Author Information Institute of Macromolecular Compounds, Russian Academy of Sciences, Bolshoi Prospect 31, V.O., St. Petersburg, 199004 Russia, Computational Laboratory, Institute of Pharmaceutical Innovation, University of Bradford, Bradford, West Yorkshire BD7 1DP, U.K., Department of Physics, Tampere University of Technology, P.O. Box 692, FI-33101 Tampere, Finland, Aalto University, School of Science and Technology, Finland, and MEMPHYS—Center for Biomembrane Physics, University of Southern Denmark, Odense, Denmark* Corresponding author. E-mail: [email protected]. Web: biosimu.org.†Russian Academy of Sciences.‡University of Bradford.§Tampere University of Technology.∥Aalto University.⊥University of Southern Denmark.Cite this: Chem. Rev. 2010, 110, 10, 6077–6103Publication Date (Web):August 6, 2010Publication History Received4 March 2010Published online6 August 2010Published inissue 13 October 2010https://pubs.acs.org/doi/10.1021/cr1000783https://doi.org/10.1021/cr1000783review-articleACS PublicationsCopyright © 2010 American Chemical SocietyRequest reuse permissionsArticle Views3123Altmetric-Citations161LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose SUBJECTS:Ions,Lipids,Membranes,Molecules,Vesicles Get e-Alerts

Abstract Polyaniline (PANI) was prepared by the oxidation of aniline in the presence of various inorganic and organic acids at 20 °C and −50 °C. When strong acids were used, the conductivity of the protonated PANI was typically 1–10 S cm −1 . The results indicate that the protonation of PANI in media containing carboxylic acids was achieved with the help of sulfuric acid produced during the reaction with ammonium peroxydisulfate. The conductivity of PANI prepared under such conditions was reduced. Partial benzene‐ring sulfonation has been proposed to explain the wide range in conductivity of PANI bases, 10 −11 –10 −7 S cm −1 . The densities of the samples reflect the nature of the acid used. The densities of the corresponding PANI bases exhibit much less variation. Molecular weight and degree of crystallinity of PANI are higher when the polymerization is carried out at −50 °C. The conductivity of the PANI is determined mainly by way of protonation. The effects of molecular weight and of crystallinity on PANI conductivity are marginal. Copyright © 2004 Society of Chemical Industry

The development of advanced composite biomaterials combining the versatility and biodegradability of polymers and the unique characteristics of metal oxide nanoparticles unveils new horizons in emerging biomedical applications, including tissue regeneration, drug delivery and gene therapy, theranostics and medical imaging. Nanocrystalline cerium(IV) oxide, or nanoceria, stands out from a crowd of other metal oxides as being a truly unique material, showing great potential in biomedicine due to its low systemic toxicity and numerous beneficial effects on living systems. The combination of nanoceria with new generations of biomedical polymers, such as PolyHEMA (poly(2-hydroxyethyl methacrylate)-based hydrogels, electrospun nanofibrous polycaprolactone or natural-based chitosan or cellulose, helps to expand the prospective area of applications by facilitating their bioavailability and averting potential negative effects. This review describes recent advances in biomedical polymeric material practices, highlights up-to-the-minute cerium oxide nanoparticle applications, as well as polymer-nanoceria composites, and aims to address the question: how can nanoceria enhance the biomedical potential of modern polymeric materials?

Abstract The possibility of determining the free energy of stabilization Δ G 0 of native DNA structure with the help of calorimetric data on heats Δ H of transition from the native to denaturated state is considered. Results of microcalorimetric measurements of heats of denaturation of T 2 phage DNA at, different values of pH and ionic strength of solution are given. Values of free energy of stabilization of the DNA native structure Δ G 0 under various conditions have been obtained. It is shown that under conditions close to physiological Δ G 0 approaches 1200 cal/mole per base pair.

We have developed an analytical self-consistent-field (SCF) theory describing conformations of weakly charged polyelectrolyte chains tethered to the solid-liquid interface and immersed in a solution of low molecular weight salt. Depending on the density of grafting of the polyelectrolytes to the interface and on the salt concentration we distinguish three main asymptotic regimes of behavior of the grafted layer. These regimes are characterized by (i) unscreened Coulomb repulsion between polyions, (ii) screening of the interchain interactions predominantly by counterions, or (iii) screening ensured by co-ions and counterions of the salt, respectively. We have demonstrated that all the structural and thermodynamic properties of the brush are determined by two dimensionless parameters, i.e., the bare Gouy-Chapman length normalized by the characteristic brush thickness and the bulk Debye screening length, respectively. The theory describes contraction of the brush as a whole and its internal structural rearrangements with increasing salt concentration. In particular, we consider variation of the polymer density profile and distributions of the end segments and small ions with increasing salt concentration. The maximum sensitivity of the brush to the addition of salt is predicted in the intermediate range of grafting density while dense and sparse brushes are less affected by added salt.

Block copolymers self-assemble into a variety of nanostructures that are relevant for science and technology. While the assembly of diblock copolymers is largely understood, predicting the solution assembly of triblock terpolymers remains challenging due to complex interplay of block/block and block/solvent interactions. Here we provide guidelines for the self-assembly of linear ABC triblock terpolymers into a large variety of multicompartment nanostructures with C corona and A/B cores. The ratio of block lengths NC/NA thereby controls micelle geometry to spheres, cylinders, bilayer sheets and vesicles. The insoluble blocks then microphase separate to core A and surface patch B, where NB controls the patch morphology to spherical, cylindrical, bicontinuous and lamellar. The independent control over both parameters allows constructing combinatorial libraries of unprecedented solution nanostructures, including spheres-on-cylinders/sheets/vesicles, cylinders-on-sheets/vesicles, and sheets/vesicles with bicontinuous or lamellar membrane morphology (patchy polymersomes). The derived parameters provide a logical toolbox towards complex self-assemblies for soft matter nanotechnologies.

Rigid macroporous polymers developed in the early 1990s are widely used as efficient stationary phases for all types of chromatographic separations. The main advantages of so-called monolithic supports are their high hydraulic permeability and the dominance of the convection over the diffusion mechanism of mass-exchange under dynamic conditions that allow the separation to be carried out at extremely high flow rates and, consequently, during very short operation times. Among other types of macroporous polymers, the methacrylate-based monolithic materials represent the most popular and successfully explored class of sorbents. This review is an attempt to collect together the contributions of different groups working in the area of monolith preparation. Examples of different methcrylate monomers and crosslinkers, as well as porogenic solvents, including polymer ones, used in monolith preparation are discussed.

This article presents a contribution to better understanding of the processes which take place during the synthesis of polypyrrole nanotubes using a structure-guiding agent, methyl orange. Polypyrrole was prepared by oxidation of pyrrole monomer with iron(III) chloride. In the presence of methyl orange, the formation of nanotubes was observed instead of the globular morphology. Two reaction schemes with reversed additions of oxidant and monomer have been tested and they show remarkable influence on the produced morphology. Nanotubes with circular or rectangular profiles and diameters from tens to hundreds of nanometres have been obtained. FTIR and Raman spectra were used to assess the molecular structure of polypyrrole and detect residual methyl orange in the samples. The conductivity of nanotubes compressed into pellets was as high as 68 S cm−1. The mechanism of nanotubular formation starting at the nucleus produced with the participation of organic dye is proposed. The growth of a nanotube, however, proceeds in the absence of a template. An alternative mechanism for the formation of nanotubes, the coating of solid templates with a polypyrrole overlayer, is also discussed.