Home About us Contact
|
Home About us Contact | ||
|
|
||
Polymer Segments (polymer + segment)
Selected AbstractsNew environmentally responsive fluorescent N -isopropylacrylamide copolymer and its application to DNA sensingJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 19 2006Chang-Chung Yang Abstract We report two novel multifunctional copolymers consisting of a temperature-responsive poly(N -isopropylacrylamide) (PNIPAA) segment and a fluorescent fluorene-containing acrylic polymer segment with pH responsiveness and/or DNA-sensing ability. The functional acrylic monomer with a fluorene dimer side group substituted with amino units was synthesized first. Then, it was copolymerized with N -isopropylacrylamide to result in a new water-soluble, fluorescent PNIPAA copolymer (P1). The fluorescent properties of P1 under neutral and acidic conditions did not change with the temperature. However, significant variation was observed under basic conditions. The protonation of the amino moiety at a low pH improved the solubility and prevented aggregation for fluorescence quenching, but not under the basic conditions. Although aggregation of the fluorene units was significant at room temperature under basic conditions, the aggregation was resolved at a temperature above the lower critical solution temperature. These findings indicated the pH- and temperature-responsive characteristics of P1. Moreover, after the amino groups were quaternized, the obtained polymer could be used as a biosensor because the fluorescence intensity was quenched with the addition of DNA. This study demonstrates that multifunctional materials with pH- and temperature-sensing characteristics and biological molecules could be realized by the incorporation of a functional fluorene-containing moiety with PNIPAA. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5495,5504, 2006 [source] Annealing effect of perfluorosulfonated ionomer membranes on proton conductivity and methanol permeabilityJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2008Yinghao Luan Abstract Perfluorosulfonated ionomer (PFSI) was synthesized and PFSI membranes were prepared via a solution-cast method and annealed at different temperatures from 150 to 230°C. The annealing effect on water content, proton conductivity, and methanol permeability were reported and discussed. X-ray diffraction and small angle X-ray scattering were used to test the structure of the membranes. It was found that annealing increased the proton conductivity of the membranes because heat-treatment helped to free the sulfonic groups that were buried in the polymer segments and form more organized ionic clusters. Water content and methanol permeability of the annealed membranes decreased with increasing annealing temperature. Simultaneously, annealing induced more compact chain packing structure, which eventually affected the transport of the proton and methanol through these ionomer membranes. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Matrix formalism for site-specific binding of unstructured proteins to multicomponent lipid membranes,JOURNAL OF PEPTIDE SCIENCE, Issue 4 2008Vladimir B. Teif Abstract We describe a new approach to calculate the binding of flexible peptides and unfolded proteins to multicomponent lipid membranes. The method is based on the transfer matrix formalism of statistical mechanics recently described as a systematic tool to study DNA,protein,drug binding in gene regulation. Using the energies of interaction of the individual polymer segments with different membrane lipid species and the scaling corrections due to polymer looping, we calculate polymer adsorption characteristics and the degree of sequestration of specific membrane lipids. The method is applied to the effector domain of the MARCKS (myristoylated alanine rich C kinase substrate) protein known to be involved in signal transduction through membrane binding. The calculated binding constants of the MARCKS(151,175) peptide and a series of related peptides to mixed PC/PS/PIP2 membranes are in satisfactory agreement with in vitro experiments. Copyright © 2008 European Peptide Society and John Wiley & Sons, Ltd. [source] Chain Connectivity and Conformational Variability of Polymers: Clues to an Adequate Thermodynamic Description of Their Solutions, 1MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 11 2003Maria Bercea Abstract This is the first of two parts investigating the Flory-Huggins interaction parameter, ,, as a function of composition and chain length. Part 1 encompasses experimental and theoretical work. The former comprises the synthesis of poly(dimethylsiloxane)s with different molar mass and the measurements of their second osmotic virial coefficients, A2, in solvents of diverse quality as a function of M via light scattering and osmotic pressures. The theoretical analysis is performed by subdividing the dilution process into two clearly separable steps. It yields the following expression for ,o, the , value in range of pair interaction: ,o,=,,,,,,,,. The parameter , measures the effect of contact formation between solvent molecules and polymer segments at fixed chain conformation, whereas the parameter , quantifies the contributions of the conformational changes taking place in response to dilution; , becomes zero for theta conditions. The influences of M are exclusively contained in the parameter , The new relation is capable of describing hitherto incomprehensible experimental findings, like a diminution of ,o with rising M. The evaluation of experimental information for different systems according to the established equation displays the existence of a linear interrelation between , and ,. Part 2 of this investigation presents the generalization of the present approach to solutions of arbitrary composition and discusses the physical meaning of the parameters in more detail. Conformational response, ,, as a function of ,, the interaction parameter for fixed conformation. [source] Conformational Relaxation of p -Phenylenevinylene Trimers in Solution Studied by Picosecond Time-Resolved FluorescenceCHEMPHYSCHEM, Issue 18 2007Roberto E. Di Paolo Dr. Abstract Two p -phenylenevinylene (PV) trimers, containing 3,-methylbutyloxyl (in MBOPV3) and 2,-ethylhexyloxyl (in EHOPV3) side chains, are used as model compounds of PV-based conjugated polymers (PPV) with the purpose of clarifying the origin of fast (picosecond time) components observed in the fluorescence decays of poly[2-methoxy-5-(2,-ethylhexyloxy)- p -phenylenevinylene] (MEH-PPV). The fluorescence decays of MBOPV3 and EHOPV3 reveal the presence of similar fast components, which are assigned to excited-state conformational relaxation of the initial population of non-planar trimer conformers to lower-energy, more planar conformers. The rate constant of conformational relaxation kCR is dependent on solvent viscosity and temperature, according to the empirical relationship kCR=a,o,,,exp(,,E,/RT), where a,o,, is the frequency factor, ,o is the pre-exponential coefficient of viscosity, E, is the activation energy of viscous flow. The empirical parameter ,, relating the solvent microscopic friction involved in the conformational change to the macroscopic solvent friction (,=1), depends on the side chain. The fast component in the fluorescence decays of MEH-PPV polymers (PPVs), is assigned to resonance energy transfer from short to longer polymer segments. The present results call for revising this assignment/interpretation to account for the occurrence of conformational relaxation, concurrently with energy transfer, in PPVs. [source] | |||||||||||||