bluuebunny/crossref_metadata_2025_split huggingface dataset:
A statistical theory of polydisperse block copolymer systems under weak supercrystallization
Authors: Erukhimovioh Igor , Dobrynin Andrej V. 
Published: March 2011

AbstractA statistical theory of conjugated macro‐ and microphase separation in flexile polydisperse block copolymer systems with a given arbitrary molecular structural distribution is developed in the mean field approximation. A special attention is paid to recognizing and calculating all terms having the least order of magnitude to be taken into account. To this end a special procedure is elaborated enabling to distinguish between strongly and weakly fluctuating order parameters characterizing polydisperse systems and to construct explicitly a one‐field parametrization of the free energy of the systems under investigation. The contribution of so‐called higher harmonics and effect of a redistribution of macromolecules among coexisting phases are taken into account therewith by a proper renormalization of the fourth vertex of the corresponding effective hamiltonian. In order to compare the presented approach and other existing theories phase diagrams of molten polydisperse diblock copolymer are built numerically in approximations corresponding to different theories. It is shown that our rigorous approach results in phase diagrams qualitatively different from the conventional ones. In particular, we predict the existence of one‐phase region having a quasicrystal symmetry and regions of coexistence of this phase with disordered phase and one having the symmetry of the body‐centered‐oubic lattice as well as a considerable shrinking of the region of the existence of the lamellar phase.
A simple lennard‐jones model for computer simulation of conformational disordering in polymers
Authors: Hahn Jutta , Grossmann Hans Peter , Pertsin Alexander J. 
Published: March 2011

AbstractA simple generalized model is proposed to describe the phenomenon of conformational disordering in polymers. The model represents a two‐dimensional system of flexible particles interacting through a modified Lennard‐Jones potential. Monte Carlo simulation of the phase behavior of the model system shows that the model is quite adequate to describe all essential features inherent in the transition to the conformationally disordered state.
Copolymerization of fluorinated monomers with nonfluorinated monomers. Reactivity and mechanisms
Authors: Boutevin Bernard , Ameduri Bruno 
Published: March 2011

AbstractThe copolymerization of two monomers usually leads to random copolymers except when one of both bears an electron‐acceptor group and the other one has an electron‐donor group. Many copolymers are commercially available, mainly in the series of hydrogenated monomers (S.M.A., GANTREZ, MALIALIM resins). The field of fluorinated copolymers is very interesting because of the strong electron‐acceptor behaviour of the fluorine atoms and more generally of halogenated atoms. Thus, after HALAR (CTFEa)‐ethylene), TEFZEL (TFE‐ethylene) and AFLAS (TFEb)‐propylene) resins, a new series of resins have been produced (copolymers of CTFE and vinyl ethers commercialized by ASAHI Corp.). So it can be considered that ACCEPTOR‐DONOR copolymerization with fluorinated monomers is one of the most important applications of that kind of research. After reminding the main mechanisms of that reaction (homopolymerization of charge transfer complex and copolymerization of free monomers), it will be discussed about the mechanism in some examples (CTFE‐vinyl ethers and other pairs of monomers). Then it will be explained how cotelomerization has provided new data to prefer a copolymerization mechanism by free monomers.
Model compounds and monomers derived from 1,1‐difluoroethene
Authors: Chambers R. D. , Apsey G. C. , Odello P. , Moggi G. , Navarrini W. 
Published: March 2011

AbstractSaturated model compounds, related to elastomers that are derived from copolymers of CH2=CF2/CF2=CFCF3, have been synthesised and studied. Unsaturated compounds were obtained by both base‐ and Lewis‐acid induced processes. Some reactions with antimony pentafluoride lead to remarkably stable carbocations, and even di‐cations, and the nmr data for these systems is revealing about structure. Polyconjugated polymers may be obtained by this procedure. Preliminary studies are described, relating to the incorporation of crowded monomers into fluorocarbon polymers, ultimately, as a means of initiating cross‐linking processes for curing elastomers.
Fluorinated fullerenes: Synthesis and characterization
Authors: Selig H. , Kniaz K. , Vaughan G.B.M. , Fischer J. E. , Smith A. B. 
Published: March 2011

AbstractThe existence of the fully fluorinated fullerene, C60F60, is still subject to controversy. Mass spectrometric evidence shows that it exists, albeit in trace amounts five orders of magnitude in concentration below the most abundant C60F40‐42. Generally, mixtures of C60Fn are obtained where n ranges from 30 to 52, depending on fluorinating conditions. The species with n = 36 is particularly stable. Attempts to increase n by use of the strongly fluorinating halogen fluorides, ClF3 or BrF5, have led to products C60FXXyOz (X = Br or Cl), where the origin of the oxygen is probably hydrolysis during analysis. Fluorinated C60 crystallizes as a mixture of hexagonal close packed (40%) and face‐centered cubic (60%) phases. X‐ray analysis yields an average C‐F bond length of 1.49A. Fluorination of C70 leads to mixtures with maximum average stoichiometries of C70F52.
Perfluorinated ion exchange polymers and their use in research and industry
Authors: Grot Walther G. 
Published: March 2011

AbstractTetrafluoroethylene is copolymerized with a perfluorovinyl ether, containing a functional end group (‐SO2F or ‐CO2CH3) to yield a melt fabricable precursor polymer. After fabrication into the desired shape, the polymer is treated with a solution of potassium hydroxide to convert the functional group to an ion exchange site.The fundamental incompatibility of the ionic group with the perfluorinated polymer backbone results in a unique morphology, particularly in the presence of water or polar organic solvents. This has been the subject of extensive investigations by various research institutions.The most important industrial use for these polymers is in the electrolysis of sodium chloride solutions. Initially introduced in order to eliminate the environmental problems of the amalgam process, their performance has now improved to the point where they offer substantial savings, particularly in terms of energy costs, over the two older processes.An emerging, potentially very important use for perfluorinated ion exchange polymers is as an ionic conductor in fuel cells. Recent advances in this area will be discussed.
Ordered structures of poly(1H,1H,2H,2H‐perfluorodecyl α‐substituted acrylate)S
Authors: Shimizu Tetsuo , Tanaka Yoshito , Kutsumizu Shoichi , Yano Shinichi 
Published: March 2011

AbstractOrdered structures of poly(1H,1H,2H,2H‐perfluorodecyl α‐fluoroacrylate) (P17FF), poly(α‐chloroacrylate) (P17FC), poly(methacrylate) (P17FM) and poly(acrylate) (P17FA) were investigated by X‐ray diffraction, DSC and polarizing microscopic observations. At room temperature, both P17FF and P17FC prefer the layered structure of single‐layer packing of the fluoroalkyl side chains, while P17FM contains both single‐layer and double‐layer packing, and P17FA forms double‐layer packing. As temperature increases, particularly in P17FF and P17FC, there was observed a structural rearrangement of the single‐layer packing to double‐layer one accompanied by melting of the side chain crystallites, which may come from an intermolecular interaction between the main chains caused by polar effect of the α‐substituents.
Binary and ternary poly(lactic acid)/poly(ϵ‐caprolactone) blends: The effects of oligo‐ϵ‐caprolactones upon mechanical properties
Authors: Lostocco Michael R. , Borzacchiello Assunta , Huang Samuel J. 
Published: March 2011

AbstractOligo‐ε‐caprolactones(o‐CL) have been utilized as principle secondary components within poly(lactic acid)[PLA]‐based blends as well as additives within larger‐sized PCL/PLA blends in an effort to fully complement the mechanical attributes of the respective polyesters. Dynamic mechanical thermal analysis(DMTA) shows that the presence of o‐CL plasticizes the PLA non‐crystalline phase with a more pronounced effect seen as the size of o‐CL is reduced. Moreover, it appears that the size of o‐CL could also affect the static mechanical properties of the ternary systems as material stiffness and strength reside between those properties measured for high molecular weight PCL/PLA binary blends and the PLA homopolyester. Future work will examine the ability of these blends to sustain these properties during hydrolytic exposure.
Polymeric materials as biomaterials under particular consideration of biodegradable polymers
Authors: Höcker Hartwig 
Published: March 2011

AbstractBiomaterials may be defined as artificial materials which fulfill the mechanical requirements and interact with the biosystem they are in contact with in same way as a natural material would react in the same place. While the requirements of mechanical properties can be reached by suitable organo‐polymeric and inorganic materials the interfacial biocompatiblity is neither understood in all its complexity nor can be fulfilled by any of the applied materials. Surface modification and characterization with greatest scrutiny and the observation of the answer of selected parameters of the biosystem are a subject of utmost interest. A few examples will be presented. In the long range, however, it has to be considered that any material is degraded and hence should present continuously a renewable biocompatible surface. On the other hand, materials are desired which deliberately are biodegradable. Presently available materials are polylactides and copolymers. An alternative could be presented by polydepsipeptides because of two reasons, (i) the local concentration of acid formed upon degradation would be reduced as compared to polylactides which in certain cases might be advantageous and (ii) the aminoacid units could carry side groups with bioactive molecules attached. Therefore, a new method of acylation of an aminoacid with a hydroxyacid is presented as well as the cyclisation to result in the cyclic depsipeptide and the polymerisation to yield the polydepsipeptide. The microstructure of the polymers, the thermal properties and the degradation behaviour is presented.
Preparation of rapidly curable hydrogels from gelatin and poly (carboxylic acid) and their adhesion to skin
Authors: Otani Yuto , Tabata Yasuhiko , Ikada Yoshito 
Published: March 2011

AbstractPapidly curable hydrogels were prepared through chemical crosslinking of gelatin with poly(carboxylic acid)s including poly (L‐glutamic acid) (PLGA), hyaluronic acid (HA), and poly (acrylic acid) (PAA) by use of water‐soluble carbodiimide (WSC). The effects of the nature of added poly (carboxylic acid)s on gelation of mixed gelatinpoly (carboxylic acid) aqueous solutions and adhesion of the resulting hydrogels to the mouse skin were evaluated. The addition of poly (carboxylic acid) s reduced the gelation time of gelatin aqueous solutions except for HA. Mixed gelatin‐PLGA solutions were cured more rapidly than other mixed solutions and the gelation time was shortened with the increasing PLGA molecular weight. The resulting gelatin‐PLGA hydrogels exhibited stronger adhesion to the mouse skin than gelatin‐HA and gelatin‐PAA hydrogels. The bonding strength increased with the increase in PLGA molecular weight up to 83,000 and thereafter decreased. The longer gelation time and lower adhesion of the gelatin‐PAA hydrogels than the gelatin‐PLGA hydrogels seem to be due to poorer compatibility of gelatin with PAA than with PLGA. The mixed gelatin‐PLGA solution underwent phase separation when the concentration and molecular weight of PLGA became higher than a threshold. The insignificant or suppressive effect of HA addition might be ascribed to the HA‐WSC reaction which was the least effective in hydrogel formation.
Microscopy in the studies of polymer biodegradation
Authors: Janik Helena 
Published: March 2011

AbstractThe goal of the paper is to overview different possibilities of microscopy, which can be helpful in estimating some of the changes undergoing in the materials exposed to the action of micro‐organisms. The types of microscopic techniques and methods discussed in the paper are; optical transmission microscopy (OTM), optical transmission microscopy with polarised light (OPTM), optical reflected microscopy (ORM), optical reflected microscopy with polarised light (OPRM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The above methods allow to follow the changes of the surface view, the changes inside the polymer and the changes in birefringence (in the case of semi‐crystalline polymers). The results can be compared with other techniques used for monitoring of polymer biodegradation or biostability. The examples from author's studies on different types of polyurethanes and the blends of polyethylene with starch are also described in the paper.
Synthesis, recovery and possible application of medium‐chain‐length polyhydroxyalkanoates: A short overview
Authors: Kessler Birgit , Witholt Bernard 
Published: March 2011

AbstractBacterial polyhydroxyalkanoates (PHAs) are polyesters of 3‐hydroxyacids produced as intracellular granules by a large variety of bacteria, currently receiving much attention because of their potential as renewable and biodegradable plastics. The monomer units in these microbial polyesters are all in the R‐configuration due to the stereospecificity of biosynthetic enzymes. Pseudomonads synthesise mainly medium‐chain‐lenght PHAs, formed of monomers of 6 to 14 carbons. The PHA monomer composition is influenced by the substrate added to the growth media and determines the physical properties of the plastic material. The capability of Pseudomonads to incorporate many different functional groups into the PHAs does extend their physical properties and potential applications, and suggests various possibilities to produce tailor‐made polymers. The mcl‐PHAs are of major interest for specific uses, where chirality and elastomeric property of the polymers are important. In this report we will focus on the biotechnological production, recovery and possible applications of mcl‐PHAs.
Interactions between a biodegradable polymer, poly(hydroxybutyrate‐hydroxyvalerate), proteins and macrophages
Authors: Rouxhet L. , Legras R. , Schneider Y.‐J. 
Published: March 2011

AbstractThe effect of the chemical and morphological modifications of the surface of poly(hydroxybutyrate‐hydroxyvalerate) (92/8) (PHB/HV) films induced by an alkaline hydrolysis on the adsorption of three proteins known to modify cell behavior, namely albumin, collagen and fibronectin and on the adhesion and proliferation of monocytes‐macrophages of the J774 cell line, has been studied. Before treatment, the water contact angle θ of the face that went through a corona pre‐treatment was higher than the other one. It increases with hydrolysis to equal the value of θ angle of the other face after 2 hours. The XPS analysis revealed that all the impurities present on the native material have been eliminated after hydrolysis leading to a similar chemical composition on both faces. The surface concentrations of ‐COOH functions accessible to [3H]‐lysine increases sharply with the duration of hydrolysis. The sharpest increase is observed at the very beginning of hydrolysis. The surface morphology of the polymer is also modified by hydrolysis.The adsorption of the three proteins increases when the polymer is hydrolyzed as well as the adhesion and proliferation of the monocytes‐macrophages, no matter which protein was adsorbed. There are some evidence suggesting that the protein conformation is different on both substrates. Collagen has a drastic repulsive effect on the cells on the native polymer but this repulsive effect disappeared on the hydrolysed one. Accordingly, it clearly appears that it is possible to modulate the biocompatibility of PHB/HV by either chemical hydrolysis or protein adsorption.
PKCδ regulates Mdm2 independently of p53 in the apoptotic response to DNA damage
Authors: Hew Hoi Chin , Liu Hanshao , Miki Yoshio , Yoshida Kiyotsugu 
Published: March 2011

AbstractApoptosis is the key process in which cells with defective genome can be eliminated. Dys‐regulation of apoptosis causes accumulation of irreparable mutation arisen from DNA damage and is the underlying cause of carcinogenesis. PKCδ is a multifunctional kinase involved in signal transduction of genotoxic‐induced apoptosis. Previous studies have demonstrated that PKCδ transactivates p53 in response to DNA damage. These findings led us to determine if Mdm2, a nuclear phospho‐protein and negative regulator of p53, could also be a PKCδ‐modulated substrate. We discovered that inhibition of PKCδ down‐regulates Mdm2 protein expression regardless of p53 status. Given that Mdm2 mRNA change was detected in p53‐proficient, but not deficient cells, PKCδ affected Mdm2 on the post‐translational level. Interestingly, treatment of MG132 restored Mdm2 expression to the steady‐state level. Further investigation showed that PKCδ inhibited Mdm2 ubiquitination in p53‐deficient cells and loss of PKCδ resulted in an increase in Mdm2 proteosomal degradation. Moreover, P300/CBP‐associated factor (PCAF), an ubiquitin ligase 3 for Mdm2, was observed to participate in Mdm2 ubiquitination by PKCδ inhibition and knock‐down of PCAF rescued Mdm2 diminution. Finally, as shown for PKCδ, Mdm2 was also required to exert pro‐apoptotic response caused by genotoxic agents in p53‐null cells. In addition, overexpression of Mdm2 restored inhibitory effect of apoptosis in cells silenced for PKCδ. Taken together, we conclude that PKCδ regulates Mdm2 expression distinctively of p53 pathway by affecting Mdm2 ubiquitination and maintenance of Mdm2 expression by PKCδ is important to ensure normal genotoxic cell death response in human cancer cells. Mol. Carcinog. © 2011 Wiley‐Liss, Inc.
Possible involvement of lysophosphatidic acid receptor‐5 gene in the acquisition of growth advantage of rat tumor cells
Authors: Okabe Kyoko , Hayashi Mai , Yamawaki Yasuna , Teranishi Miki , Honoki Kanya , Mori Toshio , Fukushima Nobuyuki , Tsujiuchi Toshifumi 
Published: March 2011

AbstractAberrant expressions of lysophosphatidic acid (LPA) receptor genes have been reported in tumor cells. Here, we measured the expression levels of the Lpa5 gene and its DNA methylation status in rat tumor cells, and investigated cell growth effects of LPA in Lpa5 expressed cells. Real‐time reverse transcription (RT)‐polymerase chain reaction (PCR) analysis revealed that increased expressions of the Lpa5 gene were detected in rat liver‐derived hepatoma RH7777 and lung‐derived adenocarcinoma RLCNR cells. For the analysis of methylation status, bisulfite sequencing was performed with RH7777 and RLCNR cells and compared with other tumor cells and liver epithelial cells. The Lpa5 gene in Lpa5 unexpressed cells and liver epithelial cells were highly methylated in the 5′ upstream region. In contrast, the Lpa5 gene in RH7777 and RLCNR cells was unmethylated, correlating with increased expressions of Lpa5. In the assays for cell growth effects of LPA, LPA enhanced cell proliferation and motility in RH7777 and RLCNR cells. LPA also stimulated cell invasion in RLCNR, but not in RH7777 cells. In rat liver and lung tumors induced by nitroso‐compounds, 4 out of 6 hepatocellular carcinomas and 5 out of 6 lung adenocarcinomas indicated increased expressions of Lpa5 with unmethylated status. These results suggest that increased Lpa5 expressions due to aberrant DNA methylation may be involved in the acquisition of growth advantage of rat tumor cells. © 2011 Wiley‐Liss, Inc.
Nifedipine synergizes with calcium in activating the calcium sensing receptor, suppressing the expression of thymidylate synthase and survivin and promoting sensitivity to fluorouracil in human colon carcinoma cells
Authors: Liu Guangming , Hu Xin , Premkumar Louis , Chakrabarty Subhas 
Published: March 2011

AbstractWe have previously reported that activation of the G protein coupled calcium‐sensing receptor (CaSR) by extracellular Ca2+ down‐modulates the expression of thymidylate synthase (TS) and survivin and promotes sensitivity to fluorouracil in human colon carcinoma cells. Here, we report for the first time that the cardiac drug nifedipine acted synergistically with Ca2+ in CaSR activation and in the induction of intracellular Ca2+. Nifedipine in combination with Ca2+ significantly down‐modulated the expression of TS and survivin and promoted sensitivity to 5‐FU above and beyond the level achievable with Ca2+ alone. Nifedipine by itself, however, had no effect on the suppression of TS or survivin or sensitivity to 5‐FU. The action of Ca2+ or in combination with nifedipine was entirely CaSR dependent as the aforementioned effects did not occur in CaSR knocked down cells. siRNAs targeting TS or survivin or both could mimic the effect of CaSR activation in promoting sensitivity to 5‐FU. We conclude that nifedipine acts in synergy with Ca2+ in activating CaSR and in promoting sensitivity to 5‐FU by down modulating the expression of TS and survivin. G‐protein coupled CaSR has the potential of serving as a target for improving therapeutic outcome in colon cancer. © 2011 Wiley Periodicals, Inc.
Analysis of HP1α regulation in human breast cancer cells
Authors: Thomsen Rune , Christensen Dennis B. , Rosborg Sanne , Linnet Toke E. , Blechingberg Jenny , Nielsen Anders L. 
Published: March 2011

AbstractThe three mammalian HP1 proteins, HP1α/CBX5, HP1β/CBX1, and HPγ/CBX3, are involved in chromatin packing and gene regulation. The HP1α protein is down‐regulated in invasive compared to non‐invasive breast cancer cells and HP1α is a suppressor of cell migration and invasion. In this report, we examined the background for HP1α protein down‐regulation in invasive breast cancer cells. We identified a strict correlation between HP1α down‐regulation at the protein level and the mRNA level. The HP1α mRNA down‐regulation in invasive cancer cells was not caused by mRNA destabilization. Chromatin immunoprecipitation analysis of the HP1α gene showed a decrease in the histone mark for transcriptional activity H3‐K36 tri‐methylation and RNA polymerase II in invasive breast cancer cells which correlated with a decreased abundance of basal transcription factors at the HP1α promoter. E2F transcription factors regulate HP1α transcription and we identified that E2F5 depletion increased HP1α expression in invasive breast cancer cells. Finally, we have characterized two HP1α mRNA isoforms and both HP1α mRNA isoforms were down‐regulated to a similar extend at the transcriptional level in invasive breast cancer cells. Collectively the presented results show that HP1α down‐regulation in invasive breast cancer cells is primary a transcriptional effect and demonstrates a novel set of mechanisms involved in HP1α transcriptional regulation. The finding that HP1α is down‐regulated primarily at the transcriptional level provides a new insight for the further elucidation of the detailed molecular mechanisms causing the HP1α down‐regulation in invasive breast cancer cells. © 2011 Wiley‐Liss, Inc.