bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ab initio determination of the flexibility of 2′‐aminoribonucleosides and 2′‐aminoarabinonucleosides inserted in duplexes
Authors: Barbe Sophie , Le Bret Marc 
Published: January 2008

AbstractThe sugar puckering of adenosine and uridine nucleosides with an amino group at 2′ in the ribo or arabino orientations are determined using high‐level quantum mechanical calculations Only the conformations that have dihedrals compatible with their insertion into a duplex are retained. The amino group has always been found to be pyramidal and its orientation governs the conformation of the sugar. The energetically most favorable conformation of the 2′‐aminoribonucleosides has the south puckering but must be discarded. For another orientation of the 2′‐amino group, the conformation is energetically less favorable but has the north puckering. Calculations performed in the presence of a water molecule give similar results but with a smaller energy gap. The model then explains why the insertion of a 2′‐aminoribonucleotide destabilizes double‐stranded RNAs and also double‐stranded DNAs. In the arabino orientation, an NH2 substituent at 2′ favors north puckering. In contrast to 2′‐aminoribonucleosides, deoxynucleosides inserted into a duplex remain in the most energetically favorable conformation compatible with the canonical values of the torsion angles. The whole relaxed potential map, in the amplitude/pseudorotation space, shows that for natural deoxyadenosine there is only one valley in the east running from south to north puckering. © 2008 Wiley Periodicals, Inc. J Comput Chem 2008
Soft energy function and generic evolutionary method for discriminating native from nonnative protein conformations
Authors: Chiu Yi‐yuan , Hwang Jenn‐kang , Yang Jinn‐moon 
Published: January 2008

AbstractWe have developed a soft energy function, termed GEMSCORE, for the protein structure prediction, which is one of emergent issues in the computational biology. The GEMSORE consists of the van der Waals, the hydrogen‐bonding potential and the solvent potential with 12 parameters which are optimized by using a generic evolutionary method. The GEMSCORE is able to successfully identify 86 native proteins among 96 target proteins on six decoy sets from more 70,000 near‐native structures. For these six benchmark datasets, the predictive performance of the GEMSCORE, based on native structure ranking andZ‐scores, was superior to eight other energy functions. Our method is based solely on a simple and linear function and thus is considerably faster than other methods that rely on the additional complex calculations. In addition, the GEMSCORE recognized 17 and 2 native structures as the first and the second rank, respectively, among 21 targets in CASP6 (Critical Assessment of Techniques for Protein Structure Prediction). These results suggest that the GEMSCORE is fast and performs well to discriminate between native and nonnative structures from thousands of protein structure candidates. We believe that GEMSCORE is robust and should be a useful energy function for the protein structure prediction. © 2008 Wiley Periodicals, Inc. J Comput Chem 2008
Latin squares with no small odd plexes
Authors: Egan Judith , Wanless Ian M. 
Published: January 2008

AbstractAk‐plex in a Latin square of ordernis a selection ofknentries in which each row, column, and symbol is represented preciselyktimes. A transversal of a Latin square corresponds to the casek = 1. We show that for all evenn > 2 there exists a Latin square of ordernwhich has nok‐plex for any odd$k < \lfloor {n\over 4} \rfloor$but does have ak‐plex for every other$k \le {1\over 2} n$. © 2008 Wiley Periodicals, Inc. J Combin Designs 16: 477–492, 2008
Suppression of human tumor cell proliferation by Smurf2‐induced senescence
Authors: Zhang Hong , Teng Yuchin , Kong Yahui , Kowalski Paul E. , Cohen Stanley N. 
Published: January 2008

AbstractThe limitation of proliferative potential in human somatic cells imposed by replicative senescence has been proposed as a mechanism of tumor suppression. The E3 ubiquitin ligase Smurf2 is up‐regulated during replicative senescence in response to telomere shortening, and induces senescence when expressed adventitiously in early passage or telomerase‐immortalized human fibroblasts. To investigate the generality of Smurf2's control of cell proliferation, we have studied the effects of Smurf2 up‐regulation on cell proliferation in early passage human mammary epithelial cells which normally do not show elevated expression of Smurf2 during senescence, and in 16 human cancer cell lines derived from both sarcomas and carcinomas. Here we report that Smurf2 up‐regulation induced senescence in a wide variety of human cell types, including highly neoplastic cell lines. Consistent with our previous findings, the ability of Smurf2 to arrest cell proliferation did not require its ubiquitin ligase activity. Furthermore, expression of the cyclin‐dependent kinase inhibitor p21 was increased in tumor cells undergoing Smurf2‐induced senescence, and such increase occurred independently of the transactivation function of p53. Our results, which reveal a previously unsuspected tumor suppression function for Smurf2‐induced senescence, suggest that modulation of Smurf2 action may be a useful strategy for inhibition of cancer cell growth. J. Cell. Physiol. 215: 613–620, 2008. © 2008 Wiley‐Liss, Inc.
Cytochrome P450 (CYP) 2J2 gene transfection attenuates MMP‐9 via inhibition of NF‐κβ in hyperhomocysteinemia
Authors: Moshal Karni S. , Zeldin Darryl C. , Sithu Srinivas D. , Sen Utpal , Tyagi Neetu , Kumar Munish , Hughes William M. , Metreveli Naira , Rosenberger Dorothea S.E. , Singh Mahavir , Vacek Thomas P. , Rodriguez Walter E. , Ayotunde Adeagbo , Tyagi Suresh C. 
Published: January 2008

AbstractHyperhomocysteinemia (HHcy) is associated with atherosclerotic events involving the modulation of arachidonic acid (AA) metabolism and the activation of matrix metalloproteinase‐9 (MMP‐9). Cytochrome P450 (CYP) epoxygenase‐2J2 (CYP2J2) is abundant in the heart endothelium, and its AA metabolites epoxyeicosatrienoic acids (EETs) mitigates inflammation through NF‐κβ. However, the underlying molecular mechanisms for MMP‐9 regulation by CYP2J2 in HHcy remain obscure. We sought to determine the molecular mechanisms by which P450 epoxygenase gene transfection or EETs supplementation attenuate homocysteine (Hcy)‐induced MMP‐9 activation. CYP2J2 was over‐expressed in mouse aortic endothelial cells (MAECs) by transfection with the pcDNA3.1/CYP2J2 vector. The effects of P450 epoxygenase transfection or exogenous supplementation of EETs on NF‐κβ‐mediated MMP‐9 regulation were evaluated using Western blot, in‐gel gelatin zymography, electromobility shift assay, immunocytochemistry. The result suggested that Hcy downregulated CYP2J2 protein expression and dephosphorylated PI3K‐dependent AKT signal. Hcy induced the nuclear translocation of NF‐κβ via downregulation of IKβα (endogenous cytoplasmic inhibitor of NF‐κβ). Hcy induced MMP‐9 activation by increasing NF‐κβ–DNA binding. Moreover, P450 epoxygenase transfection or exogenous addition of 8,9‐EET phosphorylated the AKT and attenuated Hcy‐induced MMP‐9 activation. This occurred, in part, by the inhibition of NF‐κβ nuclear translocation, NF‐κβ–DNA binding and activation of IKβα. The study unequivocally suggested the pivotal role of EETs in the modulation of Hcy/MMP‐9 signal. J. Cell. Physiol. 215: 771–781, 2008. © 2008 Wiley‐Liss, Inc.
Adenosine A1 and A2A receptor regulation of protein phosphatase 2A in the murine heart
Authors: Tikh Eugene I. , Fenton Richard A. , Chen Jiang‐Fan , Schwarzschild Michael A. , Dobson James G. 
Published: January 2008

AbstractAdenosine plays a role in regulating the contractile function of the heart. This includes a positive ionotropic action via the adenosine A2A receptor (A2AR) and an inhibition of β1‐adrenergic receptor‐induced ionotropy (antiadrenergic action) via the adenosine A1 receptor (A1R). Phosphatase activity has also been shown to influence contractile function by affecting the level of protein phosphorylation. Protein phosphatase 2A (PP2A) plays a significant role in mediating the A1R antiadrenergic effect. The purpose of this study was to investigate the effects of A2AR and A1R on the activities of PP2A in hearts obtained from wild‐type (WT) and A2AR knockout (A2AR‐KO) mice. PP2A activities were examined in myocardial particulate and cytoplasmic extract fractions. Treatment of wild‐type hearts with the A1R agonist CCPA increased the total PP2A activity and increased the particulate:cytoplasmic PP2A activity ratio. Treatment with the A2AR agonist CGS‐21680 (CGS) decreased the total PP2A activity and decreased the particulate:cytoplasmic PP2A activity ratio. This indicated a movement of PP2A activity between cell fractions. The effect of CCPA was inhibited by CGS. In A2AR‐KO hearts the response to A1R activation was markedly enhanced whereas the response to A2AR activation was absent. These data show that A2AR and A1R regulate PP2A activity, thus suggesting an important mechanism for modulating myocardial contractility. J. Cell. Physiol. 216: 83–90, 2008. © 2008 Wiley‐Liss, Inc.
Purification of α‐toxin from Clostridium perfringens type A in PEG‐phosphate aqueous two‐phase systems: a factorial study
Authors: Cavalcanti Maria TH , Porto Tatiana S , Neto Benicio B , Lima‐Filho José L , Porto Ana L F , Pessoa Adalberto 
Published: January 2008

AbstractBACKGROUND: Purification of α‐toxin produced by Clostridium perfringens type A in aqueous two‐phase systems (ATPS) was studied with a full two‐level factorial design on two factors (concentrations of 8000 g mol−1 PEG and phosphate salt at pH 8.0), to estimate the influence of these factors on the purification results.RESULTS: The partition coefficient (K), purification factor (PF) and activity yield (Y) were strongly influenced by the PEG and phosphate concentrations. Raising the levels of the two factors increased these responses. The highest purification factor (5.7) was obtained with PEG and phosphate concentrations of 17.5% and 15%, respectively.CONCLUSION: These results support the proposal that polymer excluded volume and hydrophobic interactions are the factors that drive the α‐toxin in PEG/phosphate aqueous two‐phase systems. Copyright © 2008 Society of Chemical Industry
Colloid deposition experiments as a diagnostic tool for biomass attachment onto bioproduct adsorbent surfaces
Authors: Tari Canan , Vennapusa RamiReddy , Cabrera Rosa B , Fernández‐Lahore Marcelo 
Published: January 2008

AbstractBACKGROUND: Detrimental processing conditions can be expected in any downstream operation where direct contacting between a crude feedstock and a reactive solid phase is supposed to occur. In this paper we have investigated the factors influencing intact yeast cells deposition onto anion and cation exchangers currently utilized for expanded‐bed adsorption of biotechnological products. The aim of this study was twofold: (a) to confirm previous findings relating biomass deposition with surface energetics according to the extended Derjaguin, Landau, Verwey and Overbeek theory (XDLVO) theory; and (b) to provide a simple experimental tool to evaluate biomass deposition onto process surfaces.RESULTS:Biomass deposition experiments were performed on an automated workstation utilizing a packed‐bed format. Two commercial ion exchangers intended for the direct capture of bioproducts in the presence of suspended biological particles were employed. Intact yeast cells in the late exponential phase of growth were selected as model bio‐colloids. Cell deposition was systematically evaluated as a function of fluid‐phase conductivity and quantitatively expressed as a biomass deposition parameter (α).CONCLUSION: α ≤0.15 was established as a criterion to reflect negligible biomass adhesion to the process support(s). Biomass deposition experiments further confirmed predictions made on the basis of free interfacial energy calculations as per the extended DLVO approach. Copyright © 2008 Society of Chemical Industry
Some remarks about factors of graphs
Authors: Correa José R. , Matamala Martín 
Published: January 2008

AbstractA (g, f)‐factor of a graph is a subset F of E such that for all $v \in V$, $g(v)\le {\rm deg}_{F}(v)\le f(v)$. Lovasz gave a necessary and sufficient condition for the existence of a (g, f)‐factor. We extend, to the case of edge‐weighted graphs, a result of Kano and Saito who showed that if $g(v)< \lambda {\rm deg}_{E}(v) < f (v)$ for any $\lambda\in [0,1]$, then a (g, f)‐factor always exist. In addition, we use results of Anstee to provide new necessary and sufficient conditions for the existence of a (g, f)‐factor. © 2008 Wiley Periodicals, Inc. J Graph Theory 57: 265–274, 2008
Quality of life in the long‐term survivors after total gastrectomy for gastric carcinoma
Authors: Tyrväinen Tuula , Sand Juhani , Sintonen Harri , Nordback Isto 
Published: January 2008

AbstractBackground and ObjectivesSeveral studies report the health‐related quality of life (HRQoL) after total gastrectomy in short term but long‐term results have been less published.MethodsOne hundred and seventy two patients underwent total gastrectomy between years 1987–1999 for gastric carcinoma. In 2005, 30% of them were still alive. The final study population consisted of 25 patients less than 80 years of age, for whom validated control population data were available. The SF‐36 and 15D questionnaires were used as QoL instruments. The median follow‐up time from surgery was 9.ResultsThe study group did not differ significantly in any of the SF‐36 sub scores from the normal population controls. There was no significant difference in the total score in 15D but the patients did statistically significantly worse than the normal population controls in sleeping, elimination and distress. There was significant weight loss during the follow up, but this was not associated with any of HRQoL changes.ConclusionsThis study shows that patients who survived for long‐term after total gastrectomy for gastric carcinoma do generally as well as the normal population controls, but depending on the QoL instrument used, may have lower QoL in some sub dimensions. J. Surg. Oncol. 2008;97:121–124. © 2008 Wiley‐Liss, Inc.
Thermohydrodynamic analysis of infinitely wide cycloidal profiled pad thrust bearing with rough surface and a comparison to plane profiled pad
Authors: Sharma R. K. , Pandey R. K. 
Published: January 2008

AbstractThis work reports the thermal analysis of hydrodynamically lubricated cycloidal profiled pad thrust bearing (CPPTB) using an efficient numerical method based on Lobatto quadrature technique. The performance parameters with smooth and rough surfaces of cycloidal and plane profiled pads are presented for various operating inputs. Significant increase in magnitude of pressure and substantial reduction in coefficient of friction are observed in the presence of relatively large amplitude of roughness over the surface of stationary pads. Comparisons are made for performance parameters achieved with plane profiled pad thrust bearing (PPPTB) and CPPTB. The load carrying capacity of CPPTB is found significantly high than the PPPTB for the provided set of operating parameters. Copyright © 2008 John Wiley & Sons, Ltd.
In Situ Polymerization of Olefins with Nanoparticles by Metallocene‐Catalysis
Authors: Kaminsky Walter , Funck Andreas 
Published: January 2008

AbstractExceptionally strong materials could be synthesized by filled polyolefins with nanosized, regid particles or fibers. Metallocene catalysts are excellent tools in the production of tailored microstructures as well as tacticities of polypropylenes. They are soluble in hydrocarbons and therefore can cover perfectly the surface of nano particles. Here multi‐walled carbon nanotubes (MWCNT) (diameter 15–25 nm, length up to 50 µm) were used as fillers. Before polymerization, the fillers were separated by ultra sound and then treated with methylaluminoxane (MAO). MAO reacts partially with defects and functional groups of oxidized MWCNT. Catalytically active centers are formed after adding the zirconocenes or other transition metal complexes directly on the CNT surface. The thickness of the polymer layer can be controlled by the monomer pressure and polymerization time. We obtained coatings of 5 to 100 nm. By this method carbon nanotubes can be covered also with isotactic or syndiotactic polypropylene, but also with polyethylene with any molecular mass. The nanocomposites obtained were especially investigated in regard to their crystallization behavior, which depended significantly on the matrix used.
Macromolecular Non‐Releasing Additives for Commercial Polyolefins
Authors: Sacchi Maria Carmela , Cogliati Clelia , Losio Simona , Costa Giovanna , Stagnaro Paola , Menichetti Stefano , Viglianisi Caterina 
Published: January 2008

AbstractFour comonomers bearing a highly efficient phenolic antioxidant unit and different distance between the antioxidant moiety and the double bond have been prepared and tested in co‐polymerization with ethylene by means of three selected metallocene based catalysts. The possibility to obtain a masterbach suitable for melt blending with commercial polyolefins has been evaluated by modifying: i) the structure of the functionalized comonomer, ii) the kind of catalyst, iii) the polymerization conditions. The pair rac‐[Me2Si‐(2‐Me‐4,5‐BenzInd)2]ZrCl2 catalyst and comonomer with the longest spacer (8 methylene units) allowed the highest comonomer incorporation, while with rac‐(EBTHI)ZrCl2 catalyst the highest polymerization activity was observed. TGA analysis has been carried out on some of the copolymers in order to investigate the influence of type and amount of the comonomer on their thermal stability and to test the efficiency of the antioxidant group both in nitrogen and oxygen atmosphere.
Ethylene/Norbornene Copolymerization with iPr(Cp)(Flu)ZrCl2 Catalyst: Effect of MAO Cocatalyst and 3rd Monomer
Authors: Yoon Keun‐byoung , Choi Yeon Seok , Noh Seok Kyun , Lee Dong‐ho 
Published: January 2008

AbstractThe copolymerization of ethylene and norbornene (N) was carried out with iPr(Cp)(Flu)ZrCl2 catalyst and modified methylaluminoxane (MMAO) cocatalyst. The catalytic activity was dependent on the structure of MMAO, i.e., MMAO‐4 exhibited higher catalyst activity than MMAO‐3A containing more i‐butyl groups. The glass transition temperature (Tg) and the composition of the produced copolymer were not affected by MMAO type. With styrene derivatives as 3rd monomer, Tg of copolymer increased while the catalytic activity decreased. With the addition of 3rd monomer, not only the content of 3rd monomer but also the content of N increased.
One‐pot Synthesis of Long Chain Branch PP (LCBPP) Using Ziegler‐Natta Catalyst and Branching Reagents
Authors: Langston Justin A. , Colby Ralph H. , Shimizu Fumihiko , Suzuki Toru , Aoki Masaru , Chung T. C. Mike 
Published: January 2008

AbstractA new class of long chain branched isotactic polypropylene (LCBPP) polymers with high molecular weights and well‐controlled structures are prepared via a combination of rac‐Me2Si(2‐Me‐4‐Ph‐Ind)ZrCl2/MAO catalyst and a T‐reagent, such as p‐(3‐butenyl)styrene. The T‐reagent can simultaneously serve two functions (comonomer and chain transfer agent) during metallocene‐mediated propylene polymerization in the presence of a small amount of hydrogen. 1H NMR and SEC equipped with triple detectors revealed most of polymer chain containing LCB structure. LCBPPs displayed a systematic increase in zero‐shear viscosity and Arrhenius flow activation energy as branch density increased. LCBPPs with high branch point density displayed thermorheologically complex behavior, and strain hardening was observed in extensional flow.
Polyethylene‐Montmorillonite Nanocomposites: Preparation, Characterization and Properties
Authors: Cui Liqiang , Cho Hyun Yong , Shin Joong‐Won , Tarte Naresh Hiralal , Woo Seong Ihl 
Published: January 2008

AbstractPolyethylene(PE)/clay nanocomposites have been successfully prepared by in situ polymerization with an intercalation catalyst titanium‐montmorillonite (Ti‐MMT) and analyzed by X‐ray diffraction analysis (XRD), Fourier transform infrared analysis (FT‐IR), Transmission electron microscopy (TEM), differentail scanning calorimetry (DSC), thermal gravimetric analysis (TGA) and tensile testing. XRD and TEM indicate that the clay is exfoliated into nanometer size and disorderedly dispersed in the PE matrix, and the PE crystallinity of PE/clay nanocomposite declines to 15∼30%. Compared with pure PE, PE/clay nanocomposites behave higher thermal, physical and mechanical properties; the layer structure of the clay decreases the polymerization activity and produce polymer with a high molecular weight. For PE/clay nanocomposites, the highest tensile strength of 33.4 MPa and Young's modulus of 477.4 MPa has been achieved when clay content is 7.7 wt %. The maximum thermal decomposition temperature is up to 110 °C higher, but the thermal decomposition temperature of the PE/clay nanocomposites decreases with the increases of the clay contents in the PE matrix.
Growth and Evolution of Particle Morphology: An Experimental & Modelling Study
Authors: McKenna Timothy F. L. 
Published: January 2008

AbstractIn order to fully understand the crucial issues of how particles grow during olefin polymerisation, how the morphology evolves, how fines are formed, as well as related key issues it is necessary to develop more sophisticated single particle models than those currently available. Such models should ideally allow us to calculate how force, or stress, develops and is released in the growing polymer particles. However, it is shown that before such models can be developed with confidence, it is necessary to develop experimental techniques that allow us to study particle growth under precise conditions. Parallel development of well‐adapted experimental techniques and well‐conceived models is proving to be a useful means of achieving the above‐mentioned goals.
The Advantages of Metal Complexes as Catalysts toward Polyolefins ‐ The Vinyl Polymerization of Norbornene
Authors: Shi Qisong , Jie Suyun , Zhang Shu , Yang Haijian , Sun Wen‐Hua 
Published: January 2008

AbstractVarious nickel complexes bearing [N,O], [P,N] ligands as well as the supported nickel complexes were prepared and showed moderate to high catalytic activities for vinyl polymerization of norbornene. The formed polynorbornenes (PNBs) are soluble for measuring both the molecular weights and the molecular weight distributions. Comparing the results in homogeneous catalysis, the PNBs produced by supported catalysts possessed higher molecular weights and slightly broader molecular weight distributions. The reactor fouling generally happens in homogeneous catalytic systems, while spherical polymer particle morphology could be obtained without reactor fouling by using MgCl2‐supported nickel catalysts.
Development of an Unsteady‐State Model for Control of Polymer Grade Transitions in Ziegler‐Natta Catalyzed Reactor Systems
Authors: Rawatlal Randhir , Tincul Ioan 
Published: January 2008

AbstractThe dynamics of the activity and polymer growth in Ziegler‐Natta catalysts has been well established in the literature.1,2 The corresponding dynamic behaviour of the reactor system is predicted using a segregation model approach and the unsteady state model of residence time distribution previously developed.3 The model is therefore able to predict reactor performance for a time‐varying catalyst flow rate through the reactor, as well as time‐varying concentrations of monomer, co‐catalyst and chain termination agent. A method of determining grade transition policies by the use of the developed reactor models is then presented. It is demonstrated that the reactor productivity, catalyst efficiency, average chain length and polydispersity can be controlled by the catalyst flow rate and reactor monomer and hydrogen concentrations. The relationship between the required polymer product properties and the system flow rates is determined. Case studies are presented that evaluate various transition strategies for a specific polymer grades.