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Other Monomer (other + monomer)

Distribution by Scientific Domains
Polymers and Materials Science50%
Chemistry50%

Selected Abstracts

Synthesis and Characterization of Styrene/Butyl Acrylate Linear and Star Block Copolymers via Atom Transfer Radical Polymerization

MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 9 2006
Jinyu Huang
Abstract Summary: Well-defined styrene (S) and butyl acrylate (BA) linear and star-like block copolymers are synthesized via atom transfer radical polymerization (ATRP) using di- and trifunctional alkyl halide initiators employing the Cu/PMDETA (N,N,N,,N,,N,-pentamethyldiethylenetriamine) catalyst system. Initial addition of CuII deactivator and utilization of halogen exchange techniques suppresses the coupling of radicals and improves cross-propagation to a large extent, which results in better control over the polymerization. Two types of star-like PBA/PS block copolymers are prepared by using core-first techniques: a trifunctional PBA or PS macroinitiator extended with the other monomer. Block copolymers with a well-defined structure and low polydispersity (PDI,=,) are obtained in both cases. A trifunctional PBA3 macroinitiator with ,=,136,000 g,·,mol,1 and PDI,=,1.15 is extended to (PBA-PS)3 star-like block copolymer with ,=,171,100 g,·,mol,1 and PDI,=,1.15. A trifunctional PS3 macroinitiator with ,=,27,000 g,·,mol,1 and PDI,=,1.16 g,·,mol,1 is extended to (PS-PBA)3 with ,=,91,500 g,·,mol,1 and PDI,=,1.40. The individual star-like macromolecules as well as their aggregates are visualized by atomic force microscopy (AFM) where the PS and PBA adopt the globular and extended conformation, respectively. For the PBA core star block copolymers, PS segments tend to aggregate either intramolecularly or intermolecularly. PS core star block copolymers form aggregates with a PS core and emanating PBA chains. Most aggregates have ,n,×,3' arms but minor amounts of ,defective' stars with 4, 5, 8, or 11 arms are also observed. The AFM analysis shows that PS core star block copolymers contain about 92% three-arm block copolymers, and the efficiency of cross-propagation is 97.3%. Schematic representation of the synthesis of BA/S star-like block copolymers by ATRP, and their resultant AFM images. [source]

Structure of the T109S mutant of Escherichia coli dihydroorotase complexed with the inhibitor 5-­fluoroorotate: catalytic activity is reflected by the crystal form

ACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 3 2007
Mihwa Lee
Crystals of a single-point mutant (T109S) of Escherichia coli dihydroorotase (DHOase) with diminished activity grown in the presence of l -dihydroorotate (l -DHO) are tetragonal, with a monomer in the asymmetric unit. These crystals are extremely unstable and disintegrate shortly after formation, which is followed by the growth of orthorhombic crystals from the remnants of the tetragonal crystals or at new nucleation sites. Orthorhombic crystals, for which a structure has previously been reported [Thoden et al. (2001), Biochemistry, 40, 6989,6997; Lee et al. (2005), J. Mol. Biol.348, 523,533], contain a dimer of DHOase in the asymmetric unit; the active site of one monomer contains the substrate N -carbamyl- l -aspartate (l -CA-asp) and the active site of the other monomer contains the product of the reaction, l -DHO. In the subunit with l -­DHO in the active site, a surface loop (residues 105,115) is `open'. In the other subunit, with l -CA-asp in the active site, the loop folds inwards, forming specific hydrogen bonds from the loop to the l -CA-asp. The tetragonal crystal form can be stabilized by crystallization in the presence of the inhibitor 5-fluoroorotate (FOA), a product (l -DHO) mimic. Crystals of the complex of T109S DHOase with FOA are tetragonal, space group P41212, with unit-cell parameters a = b = 72.6, c = 176.1,Å. The structure has been refined to R and Rfree values of 0.218 and 0.257, despite severe anisotropy of the diffraction. In this structure, the flexible loops are both in the `open' conformation, which is consistent with FOA, like l -­DHO, binding at both sites. The behaviour of the T109S mutant crystals of DHOase in the presence of l -DHO is explained by initial binding of l -DHO to both subunits, followed by slow conversion to l -CA-asp, with consequent movement of the flexible loop and dissolution of the crystals. Orthorhombic crystals are then able to grow in the presence of l -DHO and l -CA-asp. [source]

Gelatin-based photopolymers for bone replacement materials

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 24 2009
Monika Schuster
Abstract Gelatin-based monomers were considered as suitable base component for the 3D structuring of potential bone replacement materials by stereolithographic techniques. Different methacrylate-based gelatin derivatives were prepared, whereas a polyethylene glycol modified derivative GP4M turned out to have the highest tolerance toward other monomers. These are essential as they allow the tuning of the photoreactivity and the mechanical properties. Cell culture experiments with osteoblast- and endothelial-like cells confirmed negligible cytotoxicity of these monomers. Finally, we were able to show the possibility of producing arbitrary cellular structures with these gelatin-containing formulations using stereolithography. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2009 [source]

Molecular replacement: the probabilistic approach of the program REMO09 and its applications

ACTA CRYSTALLOGRAPHICA SECTION A, Issue 6 2009
Rocco Caliandro
The method of joint probability distribution functions has been applied to molecular replacement techniques. The rotational search is performed by rotating the reciprocal lattice of the protein with respect to the calculated transform of the model structure; the translation search is performed by fast Fourier transform. Several cases of prior information are studied, both for the rotation and for the translation step: e.g. the conditional probability density for the rotation or the translation of a monomer is found both for ab initio and when the rotation and/or the translation values of other monomers are given. The new approach has been implemented in the program REMO09, which is part of the package for global phasing IL MILIONE [Burla, Caliandro, Camalli, Cascarano, De Caro, Giacovazzo, Polidori, Siliqi & Spagna (2007). J. Appl. Cryst.40, 609,613]. A large set of test structures has been used for checking the efficiency of the new algorithms, which proved to be significantly robust in finding the correct solutions and in discriminating them from noise. An important design concept is the high degree of automatism: REMO09 is often capable of providing a reliable model of the target structure without any user intervention. [source]