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Junction Point (junction + point)
Selected AbstractsTwisted Intercalating Nucleic Acids , Intercalator Influence on Parallel Triplex StabilitiesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 17 2006Vyacheslav V. Filichev Abstract Phosphoramidites of several new twisted intercalating nucleic acid (TINA) monomers and the previously discovered (R)-1- O -[4-(1-pyrenylethynyl)phenylmethyl]glycerol (1) were synthesized and used in DNA synthesis. Stabilization of Hoogsteen-type triplexes was observed in cases of insertion of the novel (R)-1- O -[3-(naphthalen-1-ylethynyl)phenylmethyl]glycerol (2) as a bulge into homopyrimidine oligodeoxynucleotides (ONs), whereas phenylethynyl and 4-(biphenylylethynyl) derivatives of TINAs resulted in destabilization of parallel triplexes relative to the wild-type triplex. It was concluded that TINA monomers should possess at least two fused phenyl rings attached through the triple bond at the 4-position of bulged (R)-1- O -(phenylmethyl)glycerol in homopyrimidine ONs in order to stabilize parallel triplexes. Slight destabilization of DNA/DNA Watson,Crick type duplexes (,Tm = 1.0,4.5 °C) was detected for 2 inserted as a bulge, while RNA/DNA duplexes and duplexes with other TINA analogues were considerably destabilized (,Tm > 6.0 °C). In cases of double insertion of 1 opposite to base inversions in dsDNA, the thermal stabilities of the triplexes were higher than that of the wild-type triplex, which is a new solution to overcome the problem of targeting homopurine stretches with single base pair inversions. A DNA three-way junction was considerably stabilized (,Tm in a range of 10.0,15.5 °C) upon insertion of TINA monomers in the junction point as a bulge. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Synthesis of amphiphilic and thermoresponsive ABC miktoarm star terpolymer via a combination of consecutive click reactions and atom transfer radical polymerizationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 16 2009Changhua Li Abstract Well-defined amphiphilic and thermoresponsive ABC miktoarm star terpolymer consisting of poly(ethylene glycol), poly(tert -butyl methacrylate), and poly(N -isopropylacrylamide) arms, PEG(- b -PtBMA)- b -PNIPAM, was synthesized via a combination of consecutive click reactions and atom transfer radical polymerization (ATRP). Click reaction of monoalkynyl-terminated PEG with a trifunctional core molecule bis(2-azidoethyl)amine, (N3)2NH, afforded difunctional PEG possessing an azido and a secondary amine moiety at the chain end, PEG- NHN3. Next, the amidation of PEG- NHN3 with 2-chloropropionyl chloride led to PEG-based ATRP macroinitiator, PEG(N3)Cl. The subsequent ATRP of N -isopropylacrylamide (NIPAM) using PEG(N3)Cl as the macroinitiator led to PEG(N3)- b -PNIPAM bearing an azido moiety at the diblock junction point. Finally, well-defined ABC miktoarm star terpolymer, PEG(- b -PtBMA)- b -PNIPAM, was prepared via the click reaction of PEG(N3)- b -PNIPAM with monoalkynyl-terminated PtBMA. In aqueous solution, the obtained ABC miktoarm star terpolymer self-assembles into micelles consisting of PtBMA cores and hybrid PEG/PNIPAM coronas, which are characterized by dynamic and static laser light scattering, and transmission electron microscopy. On heating above the phase transition temperature of PNIPAM in the hybrid corona, micelles initially formed at lower temperatures undergo further structural rearrangement and fuse into much larger aggregates solely stabilized by PEG coronas. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4001,4013, 2009 [source] ROMP-NMP-ATRP combination for the preparation of 3-miktoarm star terpolymer via click chemistryJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 2 2009Aziz Gozgen Abstract A combination of ring opening metathesis polymerization (ROMP) and click chemistry approach is first time utilized in the preparation of 3-miktoarm star terpolymer. The bromide end-functionality of monotelechelic poly(N -butyl oxanorbornene imide) (PNBONI-Br) is first transformed to azide and then reacted with polystyrene- b -poly(methyl methacrylate) copolymer with alkyne at the junction point (PS- b -PMMA-alkyne) via click chemistry strategy, producing PS-PMMA-PNBONI 3-miktoarm star terpolymer. PNBONI-Br was prepared by ROMP of N -butyl oxanorbornene imide (NBONI) 1 in the presence of (Z)-but-2-ene-1,4-diyl bis(2-bromopropanoate) 2 as terminating agent. PS- b -PMMA-alkyne copolymer was prepared successively via nitroxide-mediated radical polymerization (NMP) of St and atom transfer radical polymerization (ATRP) of MMA. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 497,504, 2009 [source] Preparation of H-shaped ABCAB terpolymers by atom transfer radical couplingJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 1 2009Xiaolan Luo Abstract H-shaped ABCAB terpolymers composed of polystyrene (PS) (A), poly(ethylene oxide) (PEO) (B), and poly(tert -butyl acrylate) (PtBA) (C) were prepared by atom transfer radical coupling reaction using ABC star terpolymers as precursors, CuBr and N,N,N,,N,,N,-pentamethyldiethylenetriamine (PMDETA) as catalysts, and nanosize copper as the reducing agent. The synthesis of 3-miktoarm star terpolymer PS-PEO-(PtBA-Br) involved following steps: (1) the preparation of PS with an active and an ethoxyethyl-ptotected hydroxyl group at the same end; (2) the preparation of diblock copolymer PS- b -PEO with ethoxyethyl-protected group at the junction point through the ring-opening polymerization (ROP) of EO; (3) after de-protection of ethoxyethyl group and further modification of hydroxyl group, tBA was polymerized by atom transfer radical polymerization using PS- b -PEO with 2-bromoisobutyryl functional group as macroinitiator. The H-shaped terpolymer could be successfully formed by atom transfer radical coupling reaction in the presence of small quantity of styrene, CuBr/PMDETA, and Cu at 90 °C. The copolymers were characterized by SEC, 1H NMR, and FTIR in detail. The optimized coupling temperature is 90 °C. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 59,68, 2009 [source] Self-Assembled Shape-Memory Fibers of Triblock Liquid-Crystal Polymers,ADVANCED FUNCTIONAL MATERIALS, Issue 4 2006V. Ahir Abstract New thermoplastic liquid-crystalline elastomers have been synthesized using the telechelic principle of microphase separation in triblock copolymers. The large central block is made of a main-chain nematic polymer renowned for its large spontaneous elongation along the nematic director. The effective crosslinking is established by small terminal blocks formed of terphenyl moieties, which phase separate into semicrystalline micelles acting as multifunctional junction points of the network. The resulting transient network retains the director alignment and shows a significant shape-memory effect, characteristic and exceeding that of covalently bonded nematic elastomers. Its plasticity at temperatures above the nematic,isotropic transition allows drawing thin well-aligned fibers from the melt. The fibers have been characterized and their thermal actuator behavior,reversible contraction of heating and elongation on cooling,has been investigated. [source] Numerical computation of a singular-state subarc in an economic optimal control modelOPTIMAL CONTROL APPLICATIONS AND METHODS, Issue 4 2006H. J. Oberle Abstract In this paper, optimal control problems (OCP) are considered which are characterized by a nonsmooth-state differential equation. More precisely, it is assumed that the right-hand side of the state equation is piecewise smooth and that the junction points between smooth subarcs are determined as roots of a state-dependent switching function. For this kind of OCP necessary conditions are developed. Special attention is paid to the situation that the switching function vanishes identically along a nontrivial subarc. Such subarcs, which are called singular-state subarcs, are investigated with respect to the necessary conditions and to the junction conditions. In this paper, we assume that the switching function is of first order with respect to the control. The theory is applied to an economic optimal control model due to Pohmer (Mikroökonomische Theorie der personellen Einkommens- und Vermögensverteilung. Studies in Contemporary Economics, vol. 16. Springer: Berlin, 1985), which describes the personal income distribution of a typical consumer, who wants to maximize the total utility of his lifetime by controlling the consumption, the rate of the total time used for working, and the rate of working time used for education and extended professional training. The state variables are the human capital and the capital itself. The utility function contains different parts which represent the influence of consumption, time of recreation, and human capital. Into this problem a parameter enters which describes the interest rate of capital. It is obvious that this parameter in general will differ for positive and negative values of the capital. Thus, the resulting OCP in a natural way becomes a nonsmooth one. For this problem, the necessary conditions are derived and numerical solutions are presented which are obtained by an indirect optimal control method. It turns out that for a certain distance of the positive and negative interest rate, the optimal solution contains a singular-state subarc. Copyright © 2006 John Wiley & Sons, Ltd. [source] Microcellular model evaluation for the deformation of dynamically vulcanized EPDM/iPP blendsPOLYMER ENGINEERING & SCIENCE, Issue 3 2003Kathryn J. Wright The origins of elasticity in thermoplastic vulcanizates have been debated for the past decade. Previous modeling attempts provide numerical solutions that make assessment of constituent concentration and interaction unclear. A microcellular modeling approach is proposed and evaluated herein to describe the steady-state behavior of dynamically vulcanized blends of ethylene-propylene-diene monomer (EPDM) and isotactic polypropylene (iPP). This approach provides an analytic result including terms for composition and cure state. Three types of deformation are accounted for: elastic and plastic deformation of iPP, elastic deformation of EPDM, and localized elastic and plastic rotation about iPP junction points. The viability of the constitutive model is evaluated in terms of iPP concentration and EPDM cure state. [source] | ||||||||||