Ultrathin polymer coatings by complexation of polyelectrolytes at interfaces: suitable materials,structure and properties

The article presents the state‐of‐the‐art of alternating physisorption of oppositely charged polyelectrolytes, the so‐called “layer‐by‐layer” method or “electrostatic self‐assembly” (ESA), for the preparation of thin polymer coatings. In comparison to other, more established self‐organization techniques, this recent method is distinguished by its simplicity, versatility, and speed. In particular, the tendency for self‐healing is unique. Emphasis is given to the role of the molecular structure of the polyelectrolytes, and to the nature of the support. Also, various parameters for the preparation of multilayer films are highlighted, which are very important due to the kinetic control of the build‐up process. The structure of the resulting coatings, their quality and stability, chemical reactions in the films, and potential applications are discussed.     

Biosynthesis of hydroxydiphenylacetylene by regiospecific monooxygenation

Bacterial monooxygenase enzymes catalyze a regiospecific single-step hydroxylation of diphenylacetylene to yield meta- and para-hydroxydiphenylacetylene.     

Supramolecular polymer formation by metal-ligand complexation: Monte Carlo simulations and analytical modeling

Equilibrium metal-ligand complexation leading to formation of linear or ringlike supramolecular polymers is studied by means of Monte Carlo (MC) simulations and theoretical analysis. We found that in most of the cases high-molecular-weight polymers are formed over a rather narrow composition range (near the 2:1 ligand-metal ratio). Besides the imbalance in the number of metals and ligands, the molecular weight decrease in the metal-rich area is caused by an increase in 1:1 ligand-metal complex formation. The results of simulations and theoretical modeling show that the fraction of 1:1 complexes considerably decreases for metal-ligand pairs with a high cooperativity of complexation. On the basis of our analytical model, we suggest a simple criterion for choosing the metal/ligand pair to achieve high molecular weight complexes in a broad range of metal-rich compositions. Dilution of a solution of metallosupramolecular polymers is found to decrease the average molecular weight and to enhance ring formation, which otherwise is very limited.     

Tuning the thermochromism of water-soluble poly(3-thiopheneacetic acid) conjugated polymer by complexation with zwitterionic polymer

The spectral properties and phase behavior of the complexes of the water-soluble poly(3-thiopheneacetic acid) (P3TAA) conjugated polymer with zwitterionic 3-dimethyl(methacryloyloxyethyl) ammonium propane sulfone (PDMAPS) polymer were explored. A dramatic change in both electronic spectra and upper critical solution temperature (UCST) of P3TAA-PDMAPS complex solution was observed depending on the molar ratio of P3TAA and PDMAPS, suggesting that a conformational transition due to complexation occurred. The UV–vis λ_max of P3TAA-PDMAPS complex solutions was changed dramatically in a narrow temperature range around a UCST and found to be varied over approximately a 40 nm range by the temperature change of about 20 °C.     

Improvement of some pharmaceutical properties of carmoful by cycrodextrin complexation

Inclusion complexation of carmoful (1-hexylcarbamoyl-5-fluorouracil, HCFU) with three cyclodextrins (-, - and -CyDs) were studied by solubility method and X-ray diffractometry. On the basis of the phase solubility diagrams, solid complexes of HCFU with -, - and -CyDs were obtained in the molar ratios (host:guest) of 21, 11 and 11, respectively. The dissolution rate of HCFU from the solid complexes was much greater than that of HCFU itself (-CyD > complex > -CyD complex > -CyD complex > HCFU alone). The hydrolysis of HCFU was suppressed by -CyD, while no appreciable inhibition was observed by - and -CyDs. The rapid dissolving form of HCFU-CyD complexes was found to increase significantly the serum levels of the drug after oral administration to rabbits.     

Foaming properties of potato proteins recovered by complexation with carboxymethylcellulose

A protein isolate, with a 74.4% (w/w) protein content, was recovered from a simulated potato processing plant waste effluent by complexation with carboxymethylcellulose. The protein solubility of the isolate was satisfactory, it decreased in the presence of NaCl, but was not markedly affected by heat treatment. The isolate exhibited remarkable foaming and foam stabilizing properties, compared with lyophilized egg white, which are attributed to the very high surface activity of the potato protein molecules, which following adsorption at a/w interfaces, result in a much higher surface pressure development compared with egg albumen. A significant part of the foaming ability and the high surface activity of the isolate should be connected with the presence in the isolate of a small fraction of proteins with a relatively low molecular weight. The sulfhydryl groups of these proteins, following adsorption at the a/w interface, during the process of foam formation and denaturation are oxidized leading to the possible formation of intermolecular disulfide linkages.     

The mechanisms of porphyrin complexation in solvents and polymer matrices

Experimental data for the reactions of porphyrins with metal salts in various media are analyzed; possible mechanisms of the reactions are discussed. The experimental findings as well as quantum chemical calculations suggest that the most probable reaction mechanism should involve the formation of a SAT complex and a substantial deformation of the macrocycle.     

Manipulating interfacial polymer structures through mixed surfactant adsorption and complexation

The effects of a nonionic alcohol ethoxylate surfactant, C(13)E(7), on the interactions between PVP and SDS both in the bulk and at the silica nanoparticle interface are studied by photon correlation spectroscopy, solvent relaxation NMR, SANS, and optical reflectometry. Our results confirmed that, in the absence of SDS, C(13)E(7) and PVP are noninteracting, while SDS interacts strongly both with PVP and C(13)E(7) . Studying interfacial interactions showed that the interfacial interactions of PVP with silica can be manipulated by varying the amounts of SDS and C(13)E(7) present. Upon SDS addition, the adsorbed layer thickness of PVP on silica increases due to Coulombic repulsion between micelles in the polymer layer. When C(13)E(7) is progressively added to the system, it forms mixed micelles with the complexed SDS, reducing the total charge per micelle and thus reducing the repulsion between micelle and the silica surface that would otherwise cause the PVP to desorb. This causes the amount of adsorbed polymer to increase with C(13)E(7) addition for the systems containing SDS, demonstrating that addition of C(13)E(7) hinders the SDS-mediated desorption of an adsorbed PVP layer.     

Hydrothermal contraction–dilation of polymer networks by reversible complexation with a complementary macromolecule

A mechanochemical system which works by complexation between a poly(methacrylic acid) (PMAA) network and poly(ethylene glycol) (PEG) was studied. A PMAA membrane swollen with an aqueous PEG solution, to which a load 100 times the weight of the membrane was attached, contracts by over 90% of its length when heated from 10°C to 60°C. The work per contraction was 5 × 10^?3 cal/g of membrane. The temperature at which the mechanochemical system undergoes a specified contraction can be regulated by the PEG concentration of the swelling fluid. The sign of the temperature coefficient of the membrane dimension can be reversed by addition of a small amount of ethanol to the swelling solution of PEG. A simple method for calculating the stability constant and thermodynamic parameters for the complexation is outlined.     

Azidocryptands-synthesis, structure, and complexation properties

Cryptands bearing an intraannular azido substituent have been synthesized and characterized spectroscopically. Their complexation properties were investigated by picrate extraction analysis. The oxygen-containing cryptands were found to be good ligands for alkali cations, with a preference for Li(+) and Na(+). The molecular structure of the complex with KBr was determined by X-ray crystallography. In this, the first structurally characterized complex of an aryl azide bound to a metal cation, the potassium cation was found to show ninefold coordination to four oxygen atoms and two nitrogen atoms of the crown ether moiety, to the bromide anion and to N1 of the azido group, as well as C1 of the benzene ring.     

Photoresponsive crown ethers. 10. Metal complexation by light-switched crown ethers immobilized in polymer matrices

The crosslinked polystyrene beads which immobilized two terminal azophenoxide groups of an azobenzene-crown(24-crown-8)-azobenzene unit were synthesized. The polymer beads adsorbed Cs⁺ in the dark while they rapidly released Cs⁺ into the solution under UV-light irradiation, and the photoresponsive complexation occurred reversibly. On the other hand, the crosslinked polystyrene beads which immobilized one terminal azophenoxide group of an azobenzene-crown (24-crown-8) unit scarcely (or only to a smaller extent) exhibited such a photoresponsive behavior. Similarly, the polymer beads which immobilized two terminal azophenoxide groups of an azobenzene-crown (18-crown-6) azobenzene unit reversibly adsorbed and desorbed K⁺ in response to UV-light irradiation. The novel photoresponsive behavior is ascribed to a conformational distortion of the crown rings which induced by the photoisomerization of the azobenzene moiety, although the photoinduced polarity change of the polymer beads is not completely ruled out. The results suggest that the polymer support is useful as a “fixed point” to enforce the conformational changes of immobilized functional molecules.     

Synthesis and cation complexation properties of new macrolides

The cis-2-alkyl-3-oxy-tetrahydropyran unit as a novel structure for the design and synthesis of a new type of ionophores with C₂-symmetry is reported. The synthesis of seven different macrolides and a crown ether and their cation complexation properties were investigated. The X-ray crystal structure of some of the receptors provides valuable information on the preferred conformation of tetrahydropyrans in the solid state that can be related to the cation complexation properties in solution. The kinetic template effect has been proved to be a useful tool to improve the yield and selectivity in the synthesis of macrodiolide 3.     

A regiospecific double bond shift induced by titanocene catalysts

cis-Bicyclo(4.3.0)-3,7-nonadiene is isomerized by titanocene-derived catalysts to bicyclo(4.3.0)-2,9-nonadiene.     

Novel multidentate sulfur-nitrogen ligands with enhanced complexation properties

Di(tert-butyl)sulfur diimide and bis(trimethylsilyl)sulfur diimide were reacted with different metalated amines to form versatile novel multidentate ligand systems with side-arm donation. Their complexation properties in terms of ligand design, denticity and the cation size are discussed. We report herein the synthesis and structure elucidation of [(tBuN)(2)S{LiMe(2)N(C(6)H(4))S(NtBu)(2)}(2)] (1), [(Li{Me(2)N(C(6)H(4))S(NSiMe(3))(2)})(2)] (2), [(Li(thf){Me(2)N(C(6)H(4))S(NSiMe(3))(2)})(2)] (3), [(Li{2-PicS(NSiMe(3))(2)})(2)] (4), [(Li{Me(2)N(CH(2))(2)N(Me)S(NSiMe(3))(2)})(2)] (5), [(Na{Me(2)N(CH(2))(2)N(Me)S(NSiMe(3))(2)})(2)] (6) and [(K{Me(2)N(C(6)H(4))S(NSiMe(3))(2)})(2)] (7).     

Controlling the assembly of nanoparticle mixtures with two orthogonal polymer complexation reactions

Self-assembly from mixed dispersions of three sizes of monodisperse polystyrene nanoparticles, large (L), medium (M), and small (S), was controlled by coating each particle type with either a monofunctional or bifunctional polymer capable of participating in specific complexation reactions. The complexation reactions were (1) complexation between phenolic polymers and polyethylene glycol (PEG) containing polymers and (2) condensation of phenylboronic acid containing polymers with polyols. These complexation reactions function independently and can be "turned off" independently; phenylboronic acid complexation was reversed by lowering the pH, whereas the interactions of phenolic copolymers with PEG copolymers could be reversed by adding excess PEG homopolymer. The specificity and reversibility of the interactions was demonstrated by the formation of simple binary aggregates from mixtures. The bifunctional copolymers were poly(vinyl phenol-co-diallyldimethyl ammonium chloride), Ph-DADMAC, and poly(3-acrylamide phenylboronic acid-co-PEG methacrylate), PBA-PEG. The monofunctional polymer was polyvinylalcohol, PVA. Ph-DADMAC forms complexes with PBA-PEG (H-bonding) and with anionic surfaces or polymers (electrostatic/polyelectrolyte complexation). PBA-PEG complexes with Ph-DADMAC (H-bonding) and with PVA (boronate ester formation). PVA does not interact with Ph-DADMAC; therefore, PVA coated particles do not deposit onto Ph-DADMAC coated particles.     

A regiospecific benzoylation of alkyl vinyl ethers catalysed by palladium

A series of (E)-3-alkoxy-1-arylpropene-1-ones has been prepared by a regiospecific palladium-catalysed aroylation of alkylvinyl ethers.     

Controlling the thermomechanical properties of polymer nanocomposites by tailoring the polymer–particle interface

We show that the thermomechanical properties of polymer nanocomposites are critically affected by polymer-particle wetting behavior. Silica nanoparticles grafted with dense polystyrene brushes of degree of polymerization 1050 are blended with polystyrene melts to form nanocomposites. It was found that low molecular weight (MW) polystyrene melts with lengths <880 wet these particles. Concurrently, the glass transition temperature (T_g) of the nanocomposite increases. At higher MW, the matrix does not wet the particles and the T_g decreases. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2944–2950, 2006     

Nanomechanical properties of polymer brushes by colloidal AFM probes

Nanomechanical properties of end grafted polymer layers were studied by AFM based, colloidal probe compression measurements. Zwitterionic poly(sulfobetaine methacrylate) (PSBMA) brush was grafted from planar Si surface and poly(methyl methacrylate) (PMAA) brush was grown on colloidal probe by surface initiated atom transfer radical polymerization. PMAA brush was further modified with adhesion promoting arginyl-glycyl-aspartic acid (RGD) peptide sequences. Force–distance curves were obtained for systems where the polymer brushes were probed on unmodified surfaces or face to each other. For each systems the grafting density of the polymer brush was determined applying a ‘box’ like polymer brush model based on the theory by de Gennes. ‘Average’ grafting density was calculated in cases when two polymer brushes face each other: RGD functionalized PMAA or PMAA against PSBMA. For our systems the values for the grafting density was between 0.04 and 0.11 nm^?2. Furthermore the measured approach force–distance curves were fitted according to the Hertz model and the apparent Young’s modulus was determined for all measurements being in a range of around 250 kPa at physiological conditions.