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Molecular Distribution (molecular + distribution)
Selected AbstractsA physiologically based pharmacokinetic model of vascular,extravascular exchanges during liver carcinogenesis: application to MRI contrast agentsCONTRAST MEDIA & MOLECULAR IMAGING, Issue 5 2007Muriel Mescam Abstract The extraction of physiological parameters by non-invasive imaging techniques such as dynamic magnetic resonance imaging (MRI) or positron emission tomography requires a knowledge of molecular distribution and exchange between microvascularization and extravascular tissues. These phenomena not only depend on the physicochemical characteristics of the injected molecules but also the pathophysiological state of the targeted organ. We developed a five-compartment physiologically based pharmacokinetic model focused on hepatic carcinogenesis and MRI contrast agents. This model includes physical characteristics of the contrast agent, dual specific liver supply, microvessel wall properties and transport parameters that are compatible with hepatocarcinoma development. The evolution of concentrations in the five compartments showed significant differences in the distribution of three molecules (differentiated by their diameters and diffusion coefficients ranging, respectively, from 0.9 to 62,nm and from 68.10,9 to 47.10,7,cm2,s,1) in simulated regeneration nodules and dysplastic nodules, as well as in medium- and poorly differentiated hepatocarcinoma. These results are in agreement with known vascular modifications such as arterialization that occur during hepatocarcinogenesis. This model can be used to study the pharmacokinetics of contrast agents and consequently to extract parameters that are characteristic of the tumor development (like permeability), after fitting simulated to in vivo data. Copyright © 2007 John Wiley & Sons, Ltd. [source] Solar Cell Blends: High-Resolution Spectroscopic Mapping of the Chemical Contrast from Nanometer Domains in P3HT:PCBM Organic Blend Films for Solar-Cell Applications (Adv. Funct.ADVANCED FUNCTIONAL MATERIALS, Issue 3 2010Mater. The inside cover image presents a near-field spectroscopic map of a P3HT:PCBM solar cell blend film obtaining using a parabolic-mirror-assisted optical microscope. This technique allows for simultaneous recording of both morphological and spectroscopic information, and on page 492 Xiao Wang et al. use it to investigate local molecular distribution, photoluminescence quenching efficiency, and other key properties of the P3HT:PCBM blend film. [source] High-Resolution Spectroscopic Mapping of the Chemical Contrast from Nanometer Domains in P3HT:PCBM Organic Blend Films for Solar-Cell ApplicationsADVANCED FUNCTIONAL MATERIALS, Issue 3 2010Xiao Wang Abstract A high-resolution near-field spectroscopic mapping technique is successfully applied to investigate the influence of thermal annealing on the morphology of a poly(3-hexylthiophene) and [6,6]-penyl-C61 butyric acid methyl ester (P3HT:PCBM) blend film. Based on the simultaneously recorded morphological and spectroscopic information, the interplay among the blend film morphology, the local P3HT:PCBM molecular distribution, and the P3HT photoluminescence (PL) quenching efficiency are systematically discussed. The PL and Raman signals of the electron donor (P3HT) and acceptor (PCBM) are probed at an optical resolution of approximately 10,nm, which allows the chemical nature of the different domains to be identified directly. In addition, the local PL quenching efficiency, which is related to the electron transfer from P3HT to PCBM, is quantitatively revealed. From these experimental results, it is proposed that high-resolution near-field spectroscopic imaging is capable of mapping the local chemical composition and photophysics of the P3HT:PCBM blends on a scale of a few nanometers. [source] Synthesis of self-healing supramolecular rubbers from fatty acid derivatives, diethylene triamine, and ureaJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 24 2008Damien Montarnal Abstract We describe the synthesis of supramolecular self-healing elastomers from vegetable oil fatty acid derivatives, diethylene triamine, and urea. Our strategy to obtain materials that are self-healing but do not flow relies on the use of a wide molecular distribution of randomly branched oligomers equipped with self-complementary and complementary hydrogen bonding groups. We prepared such oligomers with a two steps procedure. In the first step, diethylene triamine was condensed with dimer acids. In the second step, the oligomers obtained were allowed to react with urea. The molecules were characterized by NMR and IR spectroscopies and Monte-Carlo simulations were used to analyze the molecular size distribution. The sensitivity to small variations of the experimental conditions has been examined and the robustness of the synthetic procedure optimized. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7925,7936, 2008 [source] Stereoselective polymerization of rac -lactide with a bulky aluminum/Schiff base complexJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 23 2004Zhaohui Tang Abstract An aluminum/Schiff base complex {[2,2-dimethyl-1,3-propylenebis(3,5-di- tert -butylsalicylideneiminato)](isopropanolato)aluminum(III) (2)} based on a bulky ligand and aluminum isopropoxide was prepared and employed for the stereoselective ring-opening polymerization (ROP) of rac -lactide (rac -LA). The initiator was characterized with nuclear magnetic resonance (NMR), crystal structure measurements, and elemental analysis. It contained a five-coordinate aluminum atom that was trigonal bipyramidal in the solid state according to the crystal structure measurements. The two conformational stereoisomers of 2 exchanged quickly on the NMR scale. Compound 2 polymerized rac -LA into a crystalline polymer that was characterized with 1H NMR, wide-angle X-ray diffraction, electrospray ionization mass spectrometry, and gel permeation chromatography. The kinetics of the polymerization were first-order in both the monomer and initiator, and there was a linear relationship between the rac -LA conversion and the number-average molecular weight of poly(rac -LA) with a narrow molecular distribution (1.04,1.08). These features showed that the polymerization was well controlled. The high melting temperature (196,201 °C) and isotacticity of poly(rac -LA) indicated that complex 2 was a highly stereoselective initiator for the ROP of rac -LA. The stereoselectivity was as high as 90%, and the stereoblocks of poly(rac -LA) by complex 2 contained an average of 20 units (average block length = 20) of enantiomerically pure lactic acid. The activation energy (23.6 kJ mol,1) was obtained according to an Arrhenius equation. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5974,5982, 2004 [source] A Study of the Use of Oscillatory Flow to Characterize Isotactic and Syndiotactic Poly(propylene)sMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 19 2006Elena Rojo Abstract Summary: A rheological characterization of poly(propylene)s (PP) of different tacticity, monomodal and bimodal molecular distribution and long chain branching (LCB), is presented. Loss factor , plotted as a function of the complex modulus G* allows to discriminate syndiotactic from isotactic PPs, as well as syndiotactic monomodal from bimodal samples. However, using such rheological plots is not effective to investigate the broadness of the molecular weight distribution and other rheological techniques are proposed. Isotactic and syndiotactic PPs submitted to electro beam irradiation give rise to thermorheological complexity, associated to LCB. The degree of LCB is estimated using complex viscosity results. Syndiotactic poly(propylene)s are more prone to give long branches than isotactic samples. A symptom of long chain branching is detected in irradiated syndiotactic PPs. [source] Comprehensive 2-D chromatography of random and block methacrylate copolymersJOURNAL OF SEPARATION SCIENCE, JSS, Issue 10 2010Monique van Hulst Abstract A comprehensive 2-D separation method was developed for the characterization of methacrylate copolymers. In both dimensions conditions were employed that give a critical separation for the homopolymer of one of the monomers in the copolymer, and exclusion behaviour for the other. The 2-D separation was realized by using a normal-phase column in one dimension and a reversed phase column in the other, and by precisely tuning the compositions of the two mobile phases employed. In the normal-phase dimension mixtures of THF and n -hexane or n -heptane were used as mobile phase, and in the reversed-phase dimension mixtures of ACN and THF. Moreover, stationary phase particles had to be selected for both columns that gave an exclusion window appropriate for the molecular size of the sample polymers to be characterized. The 2-D critical chromatography principle was tested with a polystyrene (PS)-polymethylmethacrylate (PMMA) block copolymer and with block and random polybutylmethacrylate (PBMA)-PMMA copolymers. Ideally, the retention time for a copolymer in both dimensions of this system would depend on the size of only one of the blocks, or on the contribution of only one of the monomers to the size of a random copolymer. However, it was found that the elution of the PS-PMMA block copolymer depended on the size of both blocks, even when the corresponding homopolymer of one of the monomers showed critical elution behaviour. Therefore, the method could not be calibrated for block sizes by using homopolymer standards alone. Still, it was shown that the method can be used to determine differences between samples (PS-PMMA and PBMA-PMMA) with respect to total molecular size or block sizes separately, or to average size and chemical composition for random copolymers. Block and random PBMA-PMMA copolymers showed a distinctly different pattern in the 2-D plots obtained with 2-D critical chromatography. This difference was shown to be related to the different procedures followed in the polymerization process, and the different molecular distributions resulting from these. [source] Synthesis of 2-(N -arylimino)pyrrolide nickel complexes and polymerization of methyl methacrylateAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 2 2010Jianfeng Li Abstract The synthesis, characterization and methyl methacrylate polymerization behaviors of 2-(N -arylimino)pyrrolide nickel complexes are described. The nickel complex [NN]2Ni (1, [NN] = [2-C(H)NAr-5- tBu-C4H2N],, Ar = 2,6- iPr2C6H3) was prepared in good yield by the reaction of [NN]Li with trans -[Ni(Cl)(Ph)(PPh3)2] in THF. Reaction of [NN]Li with NiBr2(DME) yielded the nickel bromide [NN]Ni(Br)[NNH] (2). Complexes 1 and 2 were characterized by 1H NMR and IR spectroscopy and elemental analysis, and by X-ray single crystal analysis. Both complexes, upon activation with methylaluminoxane, are highly active for the polymerization of methyl methacrylate to give high molecular weight polymethylmethacrylate with narrow molecular distributions. Copyright © 2009 John Wiley & Sons, Ltd. [source] | |||||||||||||